Author name code: eriksson
ADS astronomy entries on 2022-09-14
author:"Eriksson, Kjell"
------------------------------------------------------------------------
Title: Dynamic atmospheres and winds of cool luminous
giants. II. Gradual Fe enrichment of wind-driving silicate grains
Authors: Höfner, S.; Bladh, S.; Aringer, B.; Eriksson, K.
Bibcode: 2022A&A...657A.109H
Altcode: 2021arXiv211015899H
Context. The winds observed around asymptotic giant branch (AGB)
stars are generally attributed to radiation pressure on dust
formed in the extended dynamical atmospheres of these long-period
variables. The composition of wind-driving grains is affected by a
feedback between their optical properties and the resulting heating
due to stellar radiation.
Aims: We explore the gradual Fe
enrichment of wind-driving silicate grains in M-type AGB stars to
derive typical values for Fe/Mg and to test the effects on wind
properties and synthetic spectra.
Methods: We present new
radiation-hydrodynamical DARWIN models that allow for the growth of
silicate grains with a variable Fe/Mg ratio and predict mass-loss
rates, wind velocities, and grain properties. Synthetic spectra and
other observables are computed a posteriori with the COMA code.
Results: The self-regulating feedback between grain composition
and radiative heating, in combination with quickly falling densities
in the stellar wind, leads to low values of Fe/Mg, typically a few
percent. Nevertheless, the new models show distinct silicate features
around 10 and 18 microns. Fe enrichment affects visual and near-IR
photometry moderately, and the new DARWIN models agree well with
observations in (J − K) versus (V − K) and Spitzer color-color
diagrams. The enrichment of the silicate dust with Fe is a secondary
process, taking place in the stellar wind on the surface of large
Fe-free grains that have initiated the outflow. Therefore, the mass-loss
rates are basically unaffected, while the wind velocities tend to be
slightly higher than in corresponding models with Fe-free silicate
dust.
Conclusions: The gradual Fe enrichment of silicate grains
in the inner wind region should produce signatures observable in mid-IR
spectro-interferometrical measurements. Mass-loss rates derived from
existing DARWIN models, based on Fe-free silicates, can be applied to
stellar evolution models since the mass-loss rates are not significantly
affected by the inclusion of Fe in the silicate grains.
Title: Gaia Data Release 2. The kinematics of globular clusters and
dwarf galaxies around the Milky Way (Corrigendum)
Authors: Gaia Collaboration; Helmi, A.; van Leeuwen, F.; McMillan,
P. J.; Massari, D.; Antoja, T.; Robin, A. C.; Lindegren, L.;
Bastian, U.; Arenou, F.; Babusiaux, C.; Biermann, M.; Breddels,
M. A.; Hobbs, D.; Jordi, C.; Pancino, E.; Reylé, C.; Veljanoski,
J.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne,
J. H. J.; Bailer-Jones, C. A. L.; Evans, D. W.; Eyer, L.; Jansen,
F.; Klioner, S. A.; Lammers, U.; Luri, X.; Mignard, F.; Panem,
C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.;
Soubiran, C.; Walton, N. A.; Cropper, M.; Drimmel, R.; Katz, D.;
Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castañeda, J.; Chaoul,
L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra, R.; Holl, B.;
Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Panuzzo,
P.; Portell, J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thévenin,
F.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Teyssier,
D.; Altmann, M.; Andrae, R.; Audard, M.; Bellas-Velidis, I.; Benson,
K.; Berthier, J.; Blomme, R.; Burgess, P.; Busso, G.; Carry, B.;
Cellino, A.; Clementini, G.; Clotet, M.; Creevey, O.; Davidson,
M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.;
Fernández-Hernández, J.; Fouesneau, M.; Frémat, Y.; Galluccio, L.;
García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hernández, J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.;
Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.;
Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Löffler, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Muinonen, K.; Osinde, J.; Pauwels, T.; Petit, J. -M.;
Recio-Blanco, A.; Richards, P. J.; Rimoldini, L.; Sarro, L. M.;
Siopis, C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.; van
Reeven, W.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.;
Altavilla, G.; Álvarez, M. A.; Alvarez, R.; Alves, J.; Anderson,
R. I.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.; Arcay, B.;
Astraatmadja, T. L.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.;
Balm, P.; Barache, C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem,
P. S.; Barrado, D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz,
S.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.;
Bertone, S.; Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch,
T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon,
S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Bressan, A.; Brouillet,
N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli, B.; Burlacu, A.;
Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau, E.; Cancelliere,
R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo, R.; Carlucci, T.;
Carrasco, J. M.; Casamiquela, L.; Castellani, M.; Castro-Ginard, A.;
Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan, G.;
Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers, J.; Dafonte,
C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; de Laverny,
P.; De Luise, F.; De March, R.; de Martino, D.; de Souza, R.; de
Torres, A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.;
Delgado, H. E.; Di Matteo, P.; Diakite, S.; Diener, C.; Distefano,
E.; Dolding, C.; Drazinos, P.; Durán, J.; Edvardsson, B.; Enke, H.;
Eriksson, K.; Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio,
M.; Faigler, S.; Falcão, A. J.; Farràs Casas, M.; Federici, L.;
Fedorets, G.; Fernique, P.; Figueras, F.; Filippi, F.; Findeisen, K.;
Fonti, A.; Fraile, E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti,
S.; Garabato, D.; García-Sedano, F.; Garofalo, A.; Garralda, N.;
Gavel, A.; Gavras, P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore,
G.; Girona, S.; Giuffrida, G.; Glass, F.; Gomes, M.; Granvik, M.;
Gueguen, A.; Guerrier, A.; Guiraud, J.; Gutiérrez-Sánchez, R.;
Haigron, R.; Hatzidimitriou, D.; Hauser, M.; Haywood, M.; Heiter,
U.; Heu, J.; Hilger, T.; Hofmann, W.; Holland, G.; Huckle, H. E.;
Hypki, A.; Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.; Jonker,
P. G.; Juhász, Á. L.; Julbe, F.; Karampelas, A.; Kewley, A.; Klar,
J.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.; Kontizas,
E.; Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.; Koubsky,
P.; Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; López,
M.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant,
J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall, D. J.;
Martino, M.; Marton, G.; Mary, N.; Matijevič, G.; Mazeh, T.; Messina,
S.; Michalik, D.; Millar, N. R.; Molina, D.; Molinaro, R.; Molnár,
L.; Montegriffo, P.; Mor, R.; Morbidelli, R.; Morel, T.; Morris, D.;
Mulone, A. F.; Muraveva, T.; Musella, I.; Nelemans, G.; Nicastro,
L.; Noval, L.; O'Mullane, W.; Ordénovic, C.; Ordóñez-Blanco,
D.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler, F.; Palacin, H.;
Palaversa, L.; Panahi, A.; Pawlak, M.; Piersimoni, A. M.; Pineau,
F. -X.; Plachy, E.; Plum, G.; Poggio, E.; Poujoulet, E.; Prša, A.;
Pulone, L.; Racero, E.; Ragaini, S.; Rambaux, N.; Ramos-Lerate, M.;
Regibo, S.; Riclet, F.; Ripepi, V.; Riva, A.; Rivard, A.; Rixon, G.;
Roegiers, T.; Roelens, M.; Romero-Gómez, M.; Rowell, N.; Royer,
F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann,
J.; Salgado, J.; Salguero, E.; Sanna, N.; Santana-Ros, T.; Sarasso,
M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol, M.; Segovia,
J. C.; Ségransan, D.; Shih, I. -C.; Siltala, L.; Silva, A. F.; Smart,
R. L.; Smith, K. W.; Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto,
S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.;
Steidelmüller, H.; Stephenson, C. A.; Stoev, H.; Suess, F. F.; Surdej,
J.; Szabados, L.; Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran,
G.; Taylor, M. B.; Teixeira, R.; Terrett, D.; Teyssandier, P.;
Thuillot, W.; Titarenko, A.; Torra Clotet, F.; Turon, C.; Ulla, A.;
Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini, G.; Valette, V.;
van Elteren, A.; Van Hemelryck, E.; van Leeuwen, M.; Vaschetto, M.;
Vecchiato, A.; Viala, Y.; Vicente, D.; Vogt, S.; von Essen, C.; Voss,
H.; Votruba, V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Wertz, O.;
Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Ziaeepour,
H.; Zorec, J.; Zschocke, S.; Zucker, S.; Zurbach, C.; Zwitter, T.
Bibcode: 2020A&A...642C...1G
Altcode:
No abstract at ADS
Title: Gaia Data Release 2. Kinematics of globular clusters and
dwarf galaxies around the Milky Way (Corrigendum)
Authors: Gaia Collaboration; Helmi, A.; van Leeuwen, F.; McMillan,
P. J.; Massari, D.; Antoja, T.; Robin, A. C.; Lindegren, L.;
Bastian, U.; Arenou, F.; Babusiaux, C.; Biermann, M.; Breddels,
M. A.; Hobbs, D.; Jordi, C.; Pancino, E.; Reylé, C.; Veljanoski,
J.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne,
J. H. J.; Bailer-Jones, C. A. L.; Evans, D. W.; Eyer, L.; Jansen,
F.; Klioner, S. A.; Lammers, U.; Luri, X.; Mignard, F.; Panem,
C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.;
Soubiran, C.; Walton, N. A.; Cropper, M.; Drimmel, R.; Katz, D.;
Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castañeda, J.; Chaoul,
L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra, R.; Holl, B.;
Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Panuzzo,
P.; Portell, J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thévenin,
F.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Teyssier,
D.; Altmann, M.; Andrae, R.; Audard, M.; Bellas-Velidis, I.; Benson,
K.; Berthier, J.; Blomme, R.; Burgess, P.; Busso, G.; Carry, B.;
Cellino, A.; Clementini, G.; Clotet, M.; Creevey, O.; Davidson,
M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.;
Fernández-Hernández, J.; Fouesneau, M.; Frémat, Y.; Galluccio, L.;
García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hernández, J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.;
Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.;
Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Löffler, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Muinonen, K.; Osinde, J.; Pauwels, T.; Petit, J. -M.;
Recio-Blanco, A.; Richards, P. J.; Rimoldini, L.; Sarro, L. M.;
Siopis, C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.; van
Reeven, W.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.;
Altavilla, G.; Álvarez, M. A.; Alvarez, R.; Alves, J.; Anderson,
R. I.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.; Arcay, B.;
Astraatmadja, T. L.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.;
Balm, P.; Barache, C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem,
P. S.; Barrado, D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz,
S.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.;
Bertone, S.; Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch,
T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon,
S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Bressan, A.; Brouillet,
N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli, B.; Burlacu, A.;
Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau, E.; Cancelliere,
R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo, R.; Carlucci, T.;
Carrasco, J. M.; Casamiquela, L.; Castellani, M.; Castro-Ginard, A.;
Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan, G.;
Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers, J.; Dafonte,
C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; de Laverny,
P.; De Luise, F.; De March, R.; de Martino, D.; de Souza, R.; de
Torres, A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.;
Delgado, H. E.; Di Matteo, P.; Diakite, S.; Diener, C.; Distefano,
E.; Dolding, C.; Drazinos, P.; Durán, J.; Edvardsson, B.; Enke, H.;
Eriksson, K.; Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio,
M.; Faigler, S.; Falcão, A. J.; Farràs Casas, M.; Federici, L.;
Fedorets, G.; Fernique, P.; Figueras, F.; Filippi, F.; Findeisen, K.;
Fonti, A.; Fraile, E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti,
S.; Garabato, D.; García-Sedano, F.; Garofalo, A.; Garralda, N.;
Gavel, A.; Gavras, P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore,
G.; Girona, S.; Giuffrida, G.; Glass, F.; Gomes, M.; Granvik, M.;
Gueguen, A.; Guerrier, A.; Guiraud, J.; Gutiérrez-Sánchez, R.;
Haigron, R.; Hatzidimitriou, D.; Hauser, M.; Haywood, M.; Heiter,
U.; Heu, J.; Hilger, T.; Hofmann, W.; Holland, G.; Huckle, H. E.;
Hypki, A.; Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.; Jonker,
P. G.; Juhász, Á. L.; Julbe, F.; Karampelas, A.; Kewley, A.; Klar,
J.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.; Kontizas,
E.; Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.; Koubsky,
P.; Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; López,
M.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant,
J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall, D. J.;
Martino, M.; Marton, G.; Mary, N.; Matijevič, G.; Mazeh, T.; Messina,
S.; Michalik, D.; Millar, N. R.; Molina, D.; Molinaro, R.; Molnár,
L.; Montegriffo, P.; Mor, R.; Morbidelli, R.; Morel, T.; Morris, D.;
Mulone, A. F.; Muraveva, T.; Musella, I.; Nelemans, G.; Nicastro,
L.; Noval, L.; O'Mullane, W.; Ordénovic, C.; Ordóñez-Blanco,
D.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler, F.; Palacin, H.;
Palaversa, L.; Panahi, A.; Pawlak, M.; Piersimoni, A. M.; Pineau,
F. -X.; Plachy, E.; Plum, G.; Poggio, E.; Poujoulet, E.; Prša, A.;
Pulone, L.; Racero, E.; Ragaini, S.; Rambaux, N.; Ramos-Lerate, M.;
Regibo, S.; Riclet, F.; Ripepi, V.; Riva, A.; Rivard, A.; Rixon, G.;
Roegiers, T.; Roelens, M.; Romero-Gómez, M.; Rowell, N.; Royer,
F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann,
J.; Salgado, J.; Salguero, E.; Sanna, N.; Santana-Ros, T.; Sarasso,
M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol, M.; Segovia,
J. C.; Ségransan, D.; Shih, I. -C.; Siltala, L.; Silva, A. F.; Smart,
R. L.; Smith, K. W.; Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto,
S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.;
Steidelmüller, H.; Stephenson, C. A.; Stoev, H.; Suess, F. F.; Surdej,
J.; Szabados, L.; Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran,
G.; Taylor, M. B.; Teixeira, R.; Terrett, D.; Teyssandier, P.;
Thuillot, W.; Titarenko, A.; Torra Clotet, F.; Turon, C.; Ulla, A.;
Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini, G.; Valette, V.;
van Elteren, A.; Van Hemelryck, E.; van Leeuwen, M.; Vaschetto, M.;
Vecchiato, A.; Viala, Y.; Vicente, D.; Vogt, S.; von Essen, C.; Voss,
H.; Votruba, V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Wertz, O.;
Wevems, T.; Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Ziaeepour,
H.; Zorec, J.; Zschocke, S.; Zucker, S.; Zurbach, C.; Zwitter, T.
Bibcode: 2020A&A...637C...3G
Altcode:
No abstract at ADS
Title: Precision Monitoring of Cool Evolved Stars: Constraining
Effects of Convection and Pulsation
Authors: Wittkowski, M.; Bladh, S.; Chiavassa, A.; de Wit, W. -J.;
Eriksson, K.; Freytag, B.; Haubois, X.; Höfner, S.; Kravchenko, K.;
Paladini, C.; Paumard, T.; Rau, G.; Wood, P. R.
Bibcode: 2019Msngr.178...34W
Altcode:
Mass loss from cool evolved stars is an important ingredient of
the cosmic matter cycle, enriching the Universe with newly formed
elements and dust. However, physical processes that are not considered
in current models represent uncertainties in our general understanding
of mass loss. Time-series of interferometric data provide the strongest
tests of dynamical processes in the atmospheres of these stars. Here,
we present a pilot study of such measurements obtained with the GRAVITY
instrument on the Very Large Telescope Interferometer.
Title: A DARWIN C-star model grid with new dust opacities
Authors: Eriksson, Kjell; Höfner, Susanne; Aringer, Bernhard
Bibcode: 2019IAUS..343..391E
Altcode:
We have improved the treatment of dust opacity from the small-particle
limit approximation to size-dependent which leads to models with
smaller grains, lower dust-to-gas ratios, but about the same mass-loss
rates and outflow velocities. The K-magnitudes get brighter, whereas
the V-magnitudes can be either brighter or dimmer depending on the
wind properties.
Title: Constraining the thermally pulsing asymptotic giant branch
phase with resolved stellar populations in the Small Magellanic Cloud
Authors: Pastorelli, Giada; Marigo, Paola; Girardi, Léo; Chen,
Yang; Rubele, Stefano; Trabucchi, Michele; Aringer, Bernhard; Bladh,
Sara; Bressan, Alessandro; Montalbán, Josefina; Boyer, Martha L.;
Dalcanton, Julianne J.; Eriksson, Kjell; Groenewegen, Martin A. T.;
Höfner, Susanne; Lebzelter, Thomas; Nanni, Ambra; Rosenfield, Philip;
Wood, Peter R.; Cioni, Maria-Rosa L.
Bibcode: 2019MNRAS.485.5666P
Altcode: 2019MNRAS.tmp..738P; 2019arXiv190304499P
The thermally pulsing asymptotic giant branch (TP-AGB) experienced by
low- and intermediate-mass stars is one of the most uncertain phases
of stellar evolution and the models need to be calibrated with the aid
of observations. To this purpose, we couple high-quality observations
of resolved stars in the Small Magellanic Cloud (SMC) with detailed
stellar population synthesis simulations computed with the TRILEGAL
code. The strength of our approach relies on the detailed spatially
resolved star formation history of the SMC, derived from the deep
near-infrared photometry of the VISTA survey of the Magellanic Clouds,
as well as on the capability to quickly and accurately explore a
wide variety of parameters and effects with the COLIBRI code for the
TP-AGB evolution. Adopting a well-characterized set of observations -
star counts and luminosity functions - we set up a calibration cycle
along which we iteratively change a few key parameters of the TP-AGB
models until we eventually reach a good fit to the observations. Our
work leads to identify two best-fitting models that mainly differ in
the efficiencies of the third dredge-up and mass-loss in TP-AGB stars
with initial masses larger than about 3 M⊙. On the basis
of these calibrated models, we provide a full characterization of the
TP-AGB stellar population in the SMC in terms of stellar parameters
(initial masses, C/O ratios, carbon excess, mass-loss rates). Extensive
tables of isochrones including these improved models are publicly
available.
Title: VizieR Online Data Catalog: Gaia DR2. Variable stars in CMD
(Gaia Collaboration+, 2019)
Authors: Gaia Collaboration; Eyer, L.; Rimoldini, L.; Audard, M.;
Anderson, R. I.; Nienartowicz, K.; Glass, F.; Marchal, O.; Grenon, M.;
Mowlavi, N.; Holl, B.; Clementini, G.; Aerts, C.; Mazeh, T.; Evans,
D. W.; Szabados, L.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de
Bruijne, J. H. J.; Babusiaux, C.; Bailer-Jones, C. A. L.; Biermann,
M.; Jansen, F.; Jordi, C.; Klioner, S. A.; Lammers, U.; Lindegren,
L.; Luri, X.; Mignard, F.; Panem, C.; Pourbaix, D.; Randich, S.;
Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; van Leeuwen, F.;
Walton, N. A.; Arenou, F.; Bastian, U.; Cropper, M.; Drimmel, R.;
Katz, D.; Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castaneda,
J.; Chaoul, L.; Cheek, N.; de Angeli, F.; Fabricius, C.; Guerra,
R.; Masana, E.; Messineo, R.; Panuzzo, P.; Portell, J.; Riello, M.;
Seabroke, G. M.; Tanga, P.; Thevenin, F.; Gracia-Abril, G.; Comoretto,
G.; Garcia-Reinaldos, M.; Teyssier, D.; Altmann, M.; Andrae, R.;
Bellas-Velidis, I.; Benson, K.; Berthier, J.; Blomme, R.; Burgess,
P.; Busso, G.; Carry, B.; Cellino, A.; Clotet, M.; Creevey, O.;
Davidson, M.; de Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant,
C.; Fernandez-Hernandez, J.; Fouesneau, M.; Fremat, Y.; Galluccio, L.;
Garcia-Torres, M.; Gonzalez-Nunez, J.; Gonzalez-Vidal, J. J.; Gosset,
E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison, D. L.;
Hernandez, J.; Hestroer, D.; Hodgkin, S. T.; Hutton, A.; Jasniewicz,
G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.; Krone-Martins,
A.; Lanzafame, A. C.; Lebzelter, T.; Loeer, W.; Manteiga, M.; Marrese,
P. M.; Martin-Fleitas, J. M.; Moitinho, A.; Mora, A.; Muinonen, K.;
Osinde, J.; Pancino, E.; Pauwels, T.; Petit, J. -M.; Recio-Blanco,
A.; Richards, P. J.; Robin, A. C.; Sarro, L. M.; Siopis, C.; Smith,
M.; Sozzetti, A.; Sueveges, M.; Torra, J.; van Reeven, W.; Abbas,
U.; Abreu Aramburu, A.; Accart, S.; Altavilla, G.; Alvarez, M. A.;
Alvarez, R.; Alves, J.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.;
Antoja, T.; Arcay, B.; Astraatmadja, T. L.; Bach, N.; Baker, S. G.;
Balaguer-Nunez, L.; Balm, P.; Barache, C.; Barata, C.; Barbato, D.;
Barblan, F.; Barklem, P. S.; Barrado, D.; Barros, M.; Barstow, M. A.;
Bartholome Munoz, S.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.;
Berihuete, A.; Bertone, S.; Bianchi, L.; Bienayme, O.; Blanco-Cuaresma,
S.; Boch, T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bossini, D.;
Bouquillon, S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Breddels,
M. A.; Bressan, A.; Brouillet, N.; Bruesemeister, T.; Brugaletta,
E.; Bucciarelli, B.; Burlacu, A.; Busonero, D.; Butkevich, A. G.;
Buzzi, R.; Caau, E.; Cancelliere, R.; Cannizzaro, G.; Cantat-Gaudin,
T.; Carballo, R.; Carlucci, T.; Carrasco, J. M.; Casamiquela, L.;
Castellani, M.; Castro-Ginard, A.; Charlot, P.; Chemin, L.; Chiavassa,
A.; Cocozza, G.; Costigan, G.; Cowell, S.; Crifo, F.; Crosta, M.;
Crowley, C.; Cuypersy, J.; Dafonte, C.; Damerdji, Y.; Dapergolas,
A.; David, P.; David, M.; de Laverny, P.; de Luise, F.; de March,
R.; de Martino, D.; de Souza, R.; de Torres, A.; Debosscher, J.;
Del Pozo, E.; Delbo, M.; Delgado, A.; Delgado, H. E.; Diakite, S.;
Diener, C.; Distefano, E.; Dolding, C.; Drazinos, P.; Duran, J.;
Edvardsson, B.; Enke, H.; Eriksson, K.; Esquej, P.; Eynard Bontemps,
G.; Fabre, C.; Fabrizio, M.; Faigler, S.; Falcao, A. J.; Farras Casas,
M.; Federici, L.; Fedorets, G.; Fernique, P.; Figueras, F.; Filippi,
F.; Findeisen, K.; Fonti, A.; Fraile, E.; Fraser, M.; Frezouls, B.;
Gai, M.; Galleti, S.; Garabato, D.; Garcia-Sedano, F.; Garofalo, A.;
Garralda, N.; Gavel, A.; Gavras, P.; Gerssen, J.; Geyer, R.; Giacobbe,
P.; Gilmore, G.; Girona, S.; Giurida, G.; Gomes, M.; Granvik, M.;
Gueguen, A.; Guerrier, A.; Guiraud, J.; Gutierrez-Sanchez, R.; Haigron,
R.; Hatzidimitriou, D.; Hauser, M.; Haywood, M.; Heiter, U.; Helmi,
A.; Heu, J.; Hilger, T.; Hobbs, D.; Hofmann, W.; Holland, G.; Huckle,
H. E.; Hypki, A.; Icardi, V.; Janssen, K.; Jevardat de Fombelle,
G.; Jonker, P. G.; Juhasz, A. L.; Julbe, F.; Karampelas, A.; Kewley,
A.; Klar, J.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.;
Kontizas, E.; Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.;
Koubsky, P.; Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.;
Le Fustec, Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.;
Leclerc, N.; Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.;
Licata, E.; Lindstrom, H. E. P.; Lister, T. A.; Livanou, E.; Lobel,
A.; Lopez, M.; Lorenz, D.; Managau, S.; Mann, R. G.; Mantelet, G.;
Marchant, J. M.; Marconi, M.; Marinoni, S.; Marschalko, G.; Marshall,
D. J.; Martino, M.; Marton, G.; Mary, N.; Massari, D.; Matijevic, G.;
McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Molina,
D.; Molinaro, R.; Molnar, L.; Montegrio, P.; Mor, R.; Morbidelli, R.;
Morel, T.; Morgenthaler, S.; Morris, D.; Mulone, A. F.; Muraveva, T.;
Musella, I.; Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane, W.;
Ordenovic, C.; Ordonez-Blanco, D.; Osborne, P.; Pagani, C.; Pagano,
I.; Pailler, F.; Palacin, H.; Palaversa, L.; Panahi, A.; Pawlak, M.;
Piersimoni, A. M.; Pineau, F. -X.; Plachy, E.; Plum, G.; Poggio,
E.; Poujoulet, E.; Prsa, A.; Pulone, L.; Racero, E.; Ragaini, S.;
Rambaux, N.; Ramos-Lerate, M.; Regibo, S.; Reyle, C.; Riclet, F.;
Ripepi, V.; Riva, A.; Rivard, A.; Rixon, G.; Roegiers, T.; Roelens,
M.; Romero-Gomez, M.; Rowell, N.; Royer, F.; Ruiz-Dern, L.; Sadowski,
G.; Sagrista Selles, T.; Sahlmann, J.; Salgado, J.; Salguero, E.;
Sanna, N.; Santana-Ros, T.; Sarasso, M.; Savietto, H.; Schultheis, M.;
Sciacca, E.; Segol, M.; Segovia, J. C.; Segransan, D.; Shih, I. -C.;
Siltala, L.; Silva, A. F.; Smart, R. L.; Smith, K. W.; Solano, E.;
Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay, J.; Spagna, A.;
Spoto, F.; Stampa, U.; Steele, I. A.; Steidelmueller, H.; Stephenson,
C. A.; Stoev, H.; Suess, F. F.; Surdej, J.; Szegedi-Elek, E.; Tapiador,
D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.; Terrett, D.;
Teyssandier, P.; Thuillot, W.; Titarenko, A.; Torra Clotet, F.; Turon,
C.; Ulla, A.; Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini, G.;
Valette, V.; van Elteren, A.; van Hemelryck, E.; van Leeuwen, M.;
Vaschetto, M.; Vecchiato, A.; Veljanoski, J.; Viala, Y.; Vicente,
D.; Vogt, S.; von Essen, C.; Voss, H.; Votruba, V.; Voutsinas, S.;
Walmsley, G.; Weiler, M.; Wertz, O.; Wevers, T.; Wyrzykowski, L.;
Yoldas, A.; Zerjal, M.; Ziaeepour, H.; Zorec, J.; Zschocke, S.;
Zucker, S.; Zurbach, C.; Zwitter, T.
Bibcode: 2019yCat..36230110G
Altcode:
Time series in the G, BP, and RP bands of the selected field-of-view
transits for 224 sources that are not published in Gaia DR2, but
are plotted in Fig. 11. An animated version of Fig. 11 is provided
online and at https://www.cosmos.esa.int/web/gaia/gaiadr2_cu7. (2
data files).
Title: Gaia Data Release 2. Variable stars in the colour-absolute
magnitude diagram
Authors: Gaia Collaboration; Eyer, L.; Rimoldini, L.; Audard, M.;
Anderson, R. I.; Nienartowicz, K.; Glass, F.; Marchal, O.; Grenon,
M.; Mowlavi, N.; Holl, B.; Clementini, G.; Aerts, C.; Mazeh, T.;
Evans, D. W.; Szabados, L.; Brown, A. G. A.; Vallenari, A.; Prusti,
T.; de Bruijne, J. H. J.; Babusiaux, C.; Bailer-Jones, C. A. L.;
Biermann, M.; Jansen, F.; Jordi, C.; Klioner, S. A.; Lammers, U.;
Lindegren, L.; Luri, X.; Mignard, F.; Panem, C.; Pourbaix, D.; Randich,
S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; van Leeuwen, F.;
Walton, N. A.; Arenou, F.; Bastian, U.; Cropper, M.; Drimmel, R.;
Katz, D.; Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castañeda,
J.; Chaoul, L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra,
R.; Masana, E.; Messineo, R.; Panuzzo, P.; Portell, J.; Riello, M.;
Seabroke, G. M.; Tanga, P.; Thévenin, F.; Gracia-Abril, G.; Comoretto,
G.; Garcia-Reinaldos, M.; Teyssier, D.; Altmann, M.; Andrae, R.;
Bellas-Velidis, I.; Benson, K.; Berthier, J.; Blomme, R.; Burgess,
P.; Busso, G.; Carry, B.; Cellino, A.; Clotet, M.; Creevey, O.;
Davidson, M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant,
C.; Fernández-Hernández, J.; Fouesneau, M.; Frémat, Y.; Galluccio,
L.; García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hernández, J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.;
Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.;
Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Löffler, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Muinonen, K.; Osinde, J.; Pancino, E.; Pauwels, T.; Petit,
J. -M.; Recio-Blanco, A.; Richards, P. J.; Robin, A. C.; Sarro,
L. M.; Siopis, C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.;
van Reeven, W.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Altavilla,
G.; Álvarez, M. A.; Alvarez, R.; Alves, J.; Andrei, A. H.; Anglada
Varela, E.; Antiche, E.; Antoja, T.; Arcay, B.; Astraatmadja, T. L.;
Bach, N.; Baker, S. G.; Balaguer-Núñez, L.; Balm, P.; Barache,
C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem, P. S.; Barrado,
D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz, S.; Bassilana,
J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.; Bertone, S.;
Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch, T.; Boeche, C.;
Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon, S.; Bourda, G.;
Bragaglia, A.; Bramante, L.; Breddels, M. A.; Bressan, A.; Brouillet,
N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli, B.; Burlacu, A.;
Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau, E.; Cancelliere,
R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo, R.; Carlucci, T.;
Carrasco, J. M.; Casamiquela, L.; Castellani, M.; Castro-Ginard, A.;
Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan, G.;
Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers, J.; Dafonte,
C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; de Laverny, P.;
De Luise, F.; De March, R.; de Martino, D.; de Souza, R.; de Torres,
A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.; Delgado,
H. E.; Diakite, S.; Diener, C.; Distefano, E.; Dolding, C.; Drazinos,
P.; Durán, J.; Edvardsson, B.; Enke, H.; Eriksson, K.; Esquej, P.;
Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Faigler, S.; Falcão,
A. J.; Farràs Casas, M.; Federici, L.; Fedorets, G.; Fernique,
P.; Figueras, F.; Filippi, F.; Findeisen, K.; Fonti, A.; Fraile,
E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti, S.; Garabato, D.;
García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel, A.; Gavras,
P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.; Girona, S.;
Giuffrida, G.; Gomes, M.; Granvik, M.; Gueguen, A.; Guerrier, A.;
Guiraud, J.; Gutiérrez-Sánchez, R.; Haigron, R.; Hatzidimitriou,
D.; Hauser, M.; Haywood, M.; Heiter, U.; Helmi, A.; Heu, J.; Hilger,
T.; Hobbs, D.; Hofmann, W.; Holland, G.; Huckle, H. E.; Hypki, A.;
Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.; Jonker, P. G.;
Juhász, Á. L.; Julbe, F.; Karampelas, A.; Kewley, A.; Klar, J.;
Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.; Kontizas, E.;
Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.; Koubsky, P.;
Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; López,
M.; Lorenz, D.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchant,
J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall, D. J.;
Martino, M.; Marton, G.; Mary, N.; Massari, D.; Matijevič, G.;
McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Molina,
D.; Molinaro, R.; Molnár, L.; Montegriffo, P.; Mor, R.; Morbidelli,
R.; Morel, T.; Morgenthaler, S.; Morris, D.; Mulone, A. F.; Muraveva,
T.; Musella, I.; Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane,
W.; Ordénovic, C.; Ordóñez-Blanco, D.; Osborne, P.; Pagani, C.;
Pagano, I.; Pailler, F.; Palacin, H.; Palaversa, L.; Panahi, A.;
Pawlak, M.; Piersimoni, A. M.; Pineau, F. -X.; Plachy, E.; Plum,
G.; Poggio, E.; Poujoulet, E.; Prša, A.; Pulone, L.; Racero, E.;
Ragaini, S.; Rambaux, N.; Ramos-Lerate, M.; Regibo, S.; Reylé, C.;
Riclet, F.; Ripepi, V.; Riva, A.; Rivard, A.; Rixon, G.; Roegiers,
T.; Roelens, M.; Romero-Gómez, M.; Rowell, N.; Royer, F.; Ruiz-Dern,
L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann, J.; Salgado, J.;
Salguero, E.; Sanna, N.; Santana-Ros, T.; Sarasso, M.; Savietto, H.;
Schultheis, M.; Sciacca, E.; Segol, M.; Segovia, J. C.; Ségransan, D.;
Shih, I. -C.; Siltala, L.; Silva, A. F.; Smart, R. L.; Smith, K. W.;
Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay, J.;
Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.; Steidelmüller, H.;
Stephenson, C. A.; Stoev, H.; Suess, F. F.; Surdej, J.; Szegedi-Elek,
E.; Tapiador, D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira,
R.; Terrett, D.; Teyssandier, P.; Thuillot, W.; Titarenko, A.; Torra
Clotet, F.; Turon, C.; Ulla, A.; Utrilla, E.; Uzzi, S.; Vaillant,
M.; Valentini, G.; Valette, V.; van Elteren, A.; Van Hemelryck,
E.; van Leeuwen, M.; Vaschetto, M.; Vecchiato, A.; Veljanoski, J.;
Viala, Y.; Vicente, D.; Vogt, S.; von Essen, C.; Voss, H.; Votruba,
V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Wertz, O.; Wevers, T.;
Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Ziaeepour, H.; Zorec, J.;
Zschocke, S.; Zucker, S.; Zurbach, C.; Zwitter, T.
Bibcode: 2019A&A...623A.110G
Altcode: 2018arXiv180409382G
Context. The ESA Gaia mission provides a unique time-domain survey
for more than 1.6 billion sources with G ≲ 21 mag.
Aims:
We showcase stellar variability in the Galactic colour-absolute
magnitude diagram (CaMD). We focus on pulsating, eruptive, and
cataclysmic variables, as well as on stars that exhibit variability
that is due to rotation and eclipses.
Methods: We describe
the locations of variable star classes, variable object fractions,
and typical variability amplitudes throughout the CaMD and show
how variability-related changes in colour and brightness induce
"motions". To do this, we use 22 months of calibrated photometric,
spectro-photometric, and astrometric Gaia data of stars with a
significant parallax. To ensure that a large variety of variable
star classes populate the CaMD, we crossmatched Gaia sources with
known variable stars. We also used the statistics and variability
detection modules of the Gaia variability pipeline. Corrections for
interstellar extinction are not implemented in this article.
Results: Gaia enables the first investigation of Galactic variable
star populations in the CaMD on a similar, if not larger, scale as
was previously done in the Magellanic Clouds. Although the observed
colours are not corrected for reddening, distinct regions are visible
in which variable stars occur. We determine variable star fractions
to within the current detection thresholds of Gaia. Finally,
we report the most complete description of variability-induced
motion within the CaMD to date.
Conclusions: Gaia enables
novel insights into variability phenomena for an unprecedented
number of stars, which will benefit the understanding of stellar
astrophysics. The CaMD of Galactic variable stars provides crucial
information on physical origins of variability in a way that
has previously only been accessible for Galactic star clusters or
external galaxies. Future Gaia data releases will enable significant
improvements over this preview by providing longer time series, more
accurate astrometry, and additional data types (time series BP and
RP spectra, RVS spectra, and radial velocities), all for much larger
samples of stars. A movie associated to Fig. 11 is available at https://www.aanda.org.Data
are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A110.
Title: Carbon star wind models at solar and sub-solar metallicities:
a comparative study. I. Mass loss and the properties of dust-driven
winds
Authors: Bladh, S.; Eriksson, K.; Marigo, P.; Liljegren, S.;
Aringer, B.
Bibcode: 2019A&A...623A.119B
Altcode: 2019arXiv190205352B
Context. The heavy mass loss observed in evolved stars on the
asymptotic giant branch (AGB) is usually attributed to dust-driven
winds, but it is still an open question how much AGB stars contribute
to the dust production in the interstellar medium, especially at
lower metallicities. In the case of C-type AGB stars, where the
wind is thought to be driven by radiation pressure on amorphous
carbon grains, there should be significant dust production even in
metal-poor environments. Carbon stars can manufacture the building
blocks needed to form the wind-driving dust species themselves,
irrespective of the chemical composition they have, by dredging
up carbon from the stellar interior during thermal pulses.
Aims: We investigate how the mass loss in carbon stars is affected
by a low-metallicity environment, similar to the Large and Small
Magellanic Clouds (LMC and SMC).
Methods: The atmospheres and
winds of C-type AGB stars are modeled with the 1D spherically symmetric
radiation-hydrodynamical code Dynamic Atmosphere and Radiation-driven
Wind models based on Implicit Numerics (DARWIN). The models include a
time-dependent description for nucleation, growth, and evaporation of
amorphous carbon grains directly out of the gas phase. To explore the
metallicity-dependence of mass loss we calculate model grids at three
different chemical abundances (solar, LMC, and SMC). Since carbon may
be dredged up during the thermal pulses as AGB stars evolve, we keep
the carbon abundance as a free parameter. The models in these three
different grids all have a current mass of one solar mass; effective
temperatures of 2600, 2800, 3000, or 3200 K; and stellar luminosities
equal to logL*/L⊙ = 3.70, 3.85, or 4.00.
Results: The DARWIN models show that mass loss in carbon stars is
facilitated by high luminosities, low effective temperatures, and a high
carbon excess (C-O) at both solar and subsolar metallicities. Similar
combinations of effective temperature, luminosity, and carbon excess
produce outflows at both solar and subsolar metallicities. There
are no large systematic differences in the mass-loss rates and wind
velocities produced by these wind models with respect to metallicity,
nor any systematic difference concerning the distribution of grain sizes
or how much carbon is condensed into dust. DARWIN models at subsolar
metallicity have approximately 15% lower mass-loss rates compared to
DARWIN models at solar metallicity with the same stellar parameters and
carbon excess. For both solar and subsolar environments typical grain
sizes range between 0.1 and 0.5 μm, the degree of condensed carbon
varies between 5 and 40%, and the gas-to-dust ratios between 500 and
10 000.
Conclusions: C-type AGB stars can contribute to the
dust production at subsolar metallicities (down to at least [Fe/H] =
-1) as long as they dredge up sufficient amounts of carbon from the
stellar interior. Furthermore, stellar evolution models can use the
mass-loss rates calculated from DARWIN models at solar metallicity when
modeling the AGB phase at subsolar metallicities if carbon excess is
used as the critical abundance parameter instead of the C/O ratio.
Title: Gaia Data Release 2. Observations of solar system objects
Authors: Gaia Collaboration; Spoto, F.; Tanga, P.; Mignard, F.;
Berthier, J.; Carry, B.; Cellino, A.; Dell'Oro, A.; Hestroffer, D.;
Muinonen, K.; Pauwels, T.; Petit, J. -M.; David, P.; De Angeli, F.;
Delbo, M.; Frézouls, B.; Galluccio, L.; Granvik, M.; Guiraud, J.;
Hernández, J.; Ordénovic, C.; Portell, J.; Poujoulet, E.; Thuillot,
W.; Walmsley, G.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de
Bruijne, J. H. J.; Babusiaux, C.; Bailer-Jones, C. A. L.; Biermann,
M.; Evans, D. W.; Eyer, L.; Jansen, F.; Jordi, C.; Klioner, S. A.;
Lammers, U.; Lindegren, L.; Luri, X.; Panem, C.; Pourbaix, D.; Randich,
S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; van Leeuwen, F.;
Walton, N. A.; Arenou, F.; Bastian, U.; Cropper, M.; Drimmel, R.;
Katz, D.; Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castañeda, J.;
Chaoul, L.; Cheek, N.; Fabricius, C.; Guerra, R.; Holl, B.; Masana,
E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Panuzzo, P.; Riello,
M.; Seabroke, G. M.; Thévenin, F.; Gracia-Abril, G.; Comoretto,
G.; Garcia-Reinaldos, M.; Teyssier, D.; Altmann, M.; Andrae, R.;
Audard, M.; Bellas-Velidis, I.; Benson, K.; Blomme, R.; Burgess, P.;
Busso, G.; Clementini, G.; Clotet, M.; Creevey, O.; Davidson, M.; De
Ridder, J.; Delchambre, L.; Ducourant, C.; Fernández-Hernández, J.;
Fouesneau, M.; Frémat, Y.; García-Torres, M.; González-Núñez,
J.; González-Vidal, J. J.; Gosset, E.; Guy, L. P.; Halbwachs,
J. -L.; Hambly, N. C.; Harrison, D. L.; Hodgkin, S. T.; Hutton,
A.; Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn,
A. J.; Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Lö, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Osinde, J.; Pancino, E.; Recio-Blanco, A.; Richards, P. J.;
Rimoldini, L.; Robin, A. C.; Sarro, L. M.; Siopis, C.; Smith, M.;
Sozzetti, A.; Süveges, M.; Torra, J.; van Reeven, W.; Abbas, U.;
Abreu Aramburu, A.; Accart, S.; Aerts, C.; Altavilla, G.; Álvarez,
M. A.; Alvarez, R.; Alves, J.; Anderson, R. I.; Andrei, A. H.; Anglada
Varela, E.; Antiche, E.; Antoja, T.; Arcay, B.; Astraatmadja, T. L.;
Bach, N.; Baker, S. G.; Balaguer-Núñez, L.; Balm, P.; Barache,
C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem, P. S.; Barrado,
D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz, L.; Bassilana,
J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.; Bertone, S.;
Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch, T.; Boeche, C.;
Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon, S.; Bourda, G.;
Bragaglia, A.; Bramante, L.; Breddels, M. A.; Bressan, A.; Brouillet,
N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli, B.; Burlacu, A.;
Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau, E.; Cancelliere,
R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo, R.; Carlucci, T.;
Carrasco, J. M.; Casamiquela, L.; Castellani, M.; Castro-Ginard,
A.; Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan,
G.; Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers, J.;
Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, M.; de Laverny, P.;
De Luise, F.; De March, R.; de Souza, R.; de Torres, A.; Debosscher,
J.; del Pozo, E.; Delgado, A.; Delgado, H. E.; Diakite, S.; Diener,
C.; Distefano, E.; Dolding, C.; Drazinos, P.; Durán, J.; Edvardsson,
B.; Enke, H.; Eriksson, K.; Esquej, P.; Eynard Bontemps, G.; Fabre,
C.; Fabrizio, M.; Faigler, S.; Falcão, A. J.; Farràs Casas, M.;
Federici, L.; Fedorets, G.; Fernique, P.; Figueras, F.; Filippi, F.;
Findeisen, K.; Fonti, A.; Fraile, E.; Fraser, M.; Gai, M.; Galleti, S.;
Garabato, D.; García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel,
A.; Gavras, P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.;
Girona, S.; Giuffrida, G.; Glass, F.; Gomes, M.; Gueguen, A.; Guerrier,
A.; Gutié, R.; Haigron, R.; Hatzidimitriou, D.; Hauser, M.; Haywood,
M.; Heiter, U.; Helmi, A.; Heu, J.; Hilger, T.; Hobbs, D.; Hofmann,
W.; Holland, G.; Huckle, H. E.; Hypki, A.; Icardi, V.; Janßen, K.;
Jevardat de Fombelle, G.; Jonker, P. G.; Juhász, Á. L.; Julbe,
F.; Karampelas, A.; Kewley, A.; Klar, J.; Kochoska, A.; Kohley, R.;
Kolenberg, K.; Kontizas, M.; Kontizas, E.; Koposov, S. E.; Kordopatis,
G.; Kostrzewa-Rutkowska, Z.; Koubsky, P.; Lambert, S.; Lanza, A. F.;
Lasne, Y.; Lavigne, J. -B.; Le Fustec, Y.; Le Poncin-Lafitte, C.;
Lebreton, Y.; Leccia, S.; Leclerc, N.; Lecoeur-Taibi, I.; Lenhardt,
H.; Leroux, F.; Liao, S.; Licata, E.; Lindstrøm, H. E. P.; Lister,
T. A.; Livanou, E.; Lobel, A.; López, M.; Managau, S.; Mann, R. G.;
Mantelet, G.; Marchal, O.; Marchant, J. M.; Marconi, M.; Marinoni,
S.; Marschalkó, G.; Marshall, D. J.; Martino, M.; Marton, G.; Mary,
N.; Massari, D.; Matijevič, G.; Mazeh, T.; McMillan, P. J.; Messina,
S.; Michalik, D.; Millar, N. R.; Molina, D.; Molinaro, R.; Molnár,
L.; Montegriffo, P.; Mor, R.; Morbidelli, R.; Morel, T.; Morris, D.;
Mulone, A. F.; Muraveva, T.; Musella, I.; Nelemans, G.; Nicastro, L.;
Noval, L.; O'Mullane, W.; Ordóñez-Blanco, D.; Osborne, P.; Pagani,
C.; Pagano, I.; Pailler, F.; Palacin, H.; Palaversa, L.; Panahi, A.;
Pawlak, M.; Piersimoni, A. M.; Pineau, F. -X.; Plachy, E.; Plum, G.;
Poggio, E.; Prša, A.; Pulone, L.; Racero, E.; Ragaini, S.; Rambaux,
N.; Ramos-Lerate, M.; Regibo, S.; Reylé, C.; Riclet, F.; Ripepi,
V.; Riva, A.; Rivard, A.; Rixon, G.; Roegiers, T.; Roelens, M.;
Romero-Gómez, M.; Rowell, N.; Royer, F.; Ruiz-Dern, L.; Sadowski,
G.; Sagristà Sellés, T.; Sahlmann, J.; Salgado, J.; Salguero, E.;
Sanna, N.; Santana-Ros, T.; Sarasso, M.; Savietto, H.; Schultheis, M.;
Sciacca, E.; Segol, M.; Segovia, J. C.; Ségransan, D.; Shih, I. -C.;
Siltala, L.; Silva, A. F.; Smart, R. L.; Smith, K. W.; Solano, E.;
Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay, J.; Spagna, A.;
Stampa, U.; Steele, I. A.; Steidelmüller, H.; Stephenson, C. A.;
Stoev, H.; Suess, F. F.; Surdej, J.; Szabados, L.; Szegedi-Elek, E.;
Tapiador, D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.;
Terrett, D.; Teyssandier, P.; Titarenko, A.; Torra Clotet, F.; Turon,
C.; Ulla, A.; Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini, G.;
Valette, V.; van Elteren, A.; Van Hemelryck, E.; van Leeuwen, M.;
Vaschetto, M.; Vecchiato, A.; Veljanoski, J.; Viala, Y.; Vicente,
D.; Vogt, S.; von Essen, C.; Voss, H.; Votruba, V.; Voutsinas, S.;
Weiler, M.; Wertz, O.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.;
Žerjal, M.; Ziaeepour, H.; Zorec, J.; Zschocke, S.; Zucker, S.;
Zurbach, C.; Zwitter, T.
Bibcode: 2018A&A...616A..13G
Altcode: 2018arXiv180409379G
Context. The Gaia spacecraft of the European Space Agency (ESA)
has been securing observations of solar system objects (SSOs) since
the beginning of its operations. Data Release 2 (DR2) contains the
observations of a selected sample of 14,099 SSOs. These asteroids have
been already identified and have been numbered by the Minor Planet
Center repository. Positions are provided for each Gaia observation at
CCD level. As additional information, complementary to astrometry, the
apparent brightness of SSOs in the unfiltered G band is also provided
for selected observations.
Aims: We explain the processing of SSO
data, and describe the criteria we used to select the sample published
in Gaia DR2. We then explore the data set to assess its quality.
Methods: To exploit the main data product for the solar system in Gaia
DR2, which is the epoch astrometry of asteroids, it is necessary to take
into account the unusual properties of the uncertainty, as the position
information is nearly one-dimensional. When this aspect is handled
appropriately, an orbit fit can be obtained with post-fit residuals
that are overall consistent with the a-priori error model that was used
to define individual values of the astrometric uncertainty. The role
of both random and systematic errors is described. The distribution
of residuals allowed us to identify possible contaminants in the
data set (such as stars). Photometry in the G band was compared
to computed values from reference asteroid shapes and to the flux
registered at the corresponding epochs by the red and blue photometers
(RP and BP).
Results: The overall astrometric performance is
close to the expectations, with an optimal range of brightness G 12 -
17. In this range, the typical transit-level accuracy is well below
1 mas. For fainter asteroids, the growing photon noise deteriorates
the performance. Asteroids brighter than G 12 are affected by a lower
performance of the processing of their signals. The dramatic improvement
brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons
to the archive data and by preliminary tests on the detection of subtle
non-gravitational effects.
Title: Gaia Data Release 2. The celestial reference frame (Gaia-CRF2)
Authors: Gaia Collaboration; Mignard, F.; Klioner, S. A.; Lindegren,
L.; Hernández, J.; Bastian, U.; Bombrun, A.; Hobbs, D.; Lammers, U.;
Michalik, D.; Ramos-Lerate, M.; Biermann, M.; Fernández-Hernández,
J.; Geyer, R.; Hilger, T.; Siddiqui, H. I.; Steidelmüller, H.;
Babusiaux, C.; Barache, C.; Lambert, S.; Andrei, A. H.; Bourda, G.;
Charlot, P.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne,
J. H. J.; Bailer-Jones, C. A. L.; Evans, D. W.; Eyer, L.; Jansen, F.;
Jordi, C.; Luri, X.; Panem, C.; Pourbaix, D.; Randich, S.; Sartoretti,
P.; Soubiran, C.; van Leeuwen, F.; Walton, N. A.; Arenou, F.; Cropper,
M.; Drimmel, R.; Katz, D.; Lattanzi, M. G.; Bakker, J.; Cacciari,
C.; Castañeda, J.; Chaoul, L.; Cheek, N.; De Angeli, F.; Fabricius,
C.; Guerra, R.; Holl, B.; Masana, E.; Messineo, R.; Mowlavi, N.;
Nienartowicz, K.; Panuzzo, P.; Portell, J.; Riello, M.; Seabroke,
G. M.; Tanga, P.; Thévenin, F.; Gracia-Abril, G.; Comoretto,
G.; Garcia-Reinaldos, M.; Teyssier, D.; Altmann, M.; Andrae, R.;
Audard, M.; Bellas-Velidis, I.; Benson, K.; Berthier, J.; Blomme,
R.; Burgess, P.; Busso, G.; Carry, B.; Cellino, A.; Clementini, G.;
Clotet, M.; Creevey, O.; Davidson, M.; De Ridder, J.; Delchambre, L.;
Dell'Oro, A.; Ducourant, C.; Fouesneau, M.; Frémat, Y.; Galluccio,
L.; García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.; Jasniewicz, G.;
Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.; Krone-Martins, A.;
Lanzafame, A. C.; Lebzelter, T.; Löffler, W.; Manteiga, M.; Marrese,
P. M.; Martín-Fleitas, J. M.; Moitinho, A.; Mora, A.; Muinonen, K.;
Osinde, J.; Pancino, E.; Pauwels, T.; Petit, J. -M.; Recio-Blanco, A.;
Richards, P. J.; Rimoldini, L.; Robin, A. C.; Sarro, L. M.; Siopis,
C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.; van Reeven,
W.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.; Altavilla,
G.; Álvarez, M. A.; Alvarez, R.; Alves, J.; Anderson, R. I.; Anglada
Varela, E.; Antiche, E.; Antoja, T.; Arcay, B.; Astraatmadja, T. L.;
Bach, N.; Baker, S. G.; Balaguer-Núñez, L.; Balm, P.; Barata, C.;
Barbato, D.; Barblan, F.; Barklem, P. S.; Barrado, D.; Barros, M.;
Barstow, M. A.; Bartholomé Muñoz, L.; Bassilana, J. -L.; Becciani,
U.; Bellazzini, M.; Berihuete, A.; Bertone, S.; Bianchi, L.; Bienaymé,
O.; Blanco-Cuaresma, S.; Boch, T.; Boeche, C.; Borrachero, R.;
Bossini, D.; Bouquillon, S.; Bragaglia, A.; Bramante, L.; Breddels,
M. A.; Bressan, A.; Brouillet, N.; Brüsemeister, T.; Brugaletta, E.;
Bucciarelli, B.; Burlacu, A.; Busonero, D.; Butkevich, A. G.; Buzzi,
R.; Caffau, E.; Cancelliere, R.; Cannizzaro, G.; Cantat-Gaudin,
T.; Carballo, R.; Carlucci, T.; Carrasco, J. M.; Casamiquela, L.;
Castellani, M.; Castro-Ginard, A.; Chemin, L.; Chiavassa, A.; Cocozza,
G.; Costigan, G.; Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.;
Cuypers, J.; Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, P.;
David, M.; de Laverny, P.; De Luise, F.; De March, R.; de Souza, R.;
de Torres, A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.;
Delgado, H. E.; Diakite, S.; Diener, C.; Distefano, E.; Dolding, C.;
Drazinos, P.; Durán, J.; Edvardsson, B.; Enke, H.; Eriksson, K.;
Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Faigler,
S.; Falcão, A. J.; Farràs Casas, M.; Federici, L.; Fedorets, G.;
Fernique, P.; Figueras, F.; Filippi, F.; Findeisen, K.; Fonti, A.;
Fraile, E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti, S.; Garabato,
D.; García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel, A.; Gavras,
P.; Gerssen, J.; Giacobbe, P.; Gilmore, G.; Girona, S.; Giuffrida, G.;
Glass, F.; Gomes, M.; Granvik, M.; Gueguen, A.; Guerrier, A.; Guiraud,
J.; Gutié, R.; Haigron, R.; Hatzidimitriou, D.; Hauser, M.; Haywood,
M.; Heiter, U.; Helmi, A.; Heu, J.; Hofmann, W.; Holland, G.; Huckle,
H. E.; Hypki, A.; Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.;
Jonker, P. G.; Juhász, A. L.; Julbe, F.; Karampelas, A.; Kewley,
A.; Klar, J.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.;
Kontizas, E.; Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska,
Z.; Koubsky, P.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; López,
M.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant,
J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall, D. J.;
Martino, M.; Marton, G.; Mary, N.; Massari, D.; Matijevič, G.;
Mazeh, T.; McMillan, P. J.; Messina, S.; Millar, N. R.; Molina, D.;
Molinaro, R.; Molnár, L.; Montegriffo, P.; Mor, R.; Morbidelli,
R.; Morel, T.; Morris, D.; Mulone, A. F.; Muraveva, T.; Musella, I.;
Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane, W.; Ordénovic, C.;
Ordóñez-Blanco, D.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler,
F.; Palacin, H.; Palaversa, L.; Panahi, A.; Pawlak, M.; Piersimoni,
A. M.; Pineau, F. -X.; Plachy, E.; Plum, G.; Poggio, E.; Poujoulet,
E.; Prša, A.; Pulone, L.; Racero, E.; Ragaini, S.; Rambaux, N.;
Regibo, S.; Reylé, C.; Riclet, F.; Ripepi, V.; Riva, A.; Rivard,
A.; Rixon, G.; Roegiers, T.; Roelens, M.; Romero-Gómez, M.; Rowell,
N.; Royer, F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés, T.;
Sahlmann, J.; Salgado, J.; Salguero, E.; Sanna, N.; Santana-Ros, T.;
Sarasso, M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol, M.;
Segovia, J. C.; Ségransan, D.; Shih, I. -C.; Siltala, L.; Silva,
A. F.; Smart, R. L.; Smith, K. W.; Solano, E.; Solitro, F.; Sordo,
R.; Soria Nieto, S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa, U.;
Steele, I. A.; Stephenson, C. A.; Stoev, H.; Suess, F. F.; Surdej,
J.; Szabados, L.; Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran,
G.; Taylor, M. B.; Teixeira, R.; Terrett, D.; Teyssandier, P.;
Thuillot, W.; Titarenko, A.; Torra Clotet, F.; Turon, C.; Ulla,
A.; Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini, G.; Valette,
V.; van Elteren, A.; Van Hemelryck, E.; van Leeuwen, M.; Vaschetto,
M.; Vecchiato, A.; Veljanoski, J.; Viala, Y.; Vicente, D.; Vogt, S.;
von Essen, C.; Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.;
Weiler, M.; Wertz, O.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.;
Žerjal, M.; Ziaeepour, H.; Zorec, J.; Zschocke, S.; Zucker, S.;
Zurbach, C.; Zwitter, T.
Bibcode: 2018A&A...616A..14G
Altcode: 2018arXiv180409377M
Context. The second release of Gaia data (Gaia DR2) contains the
astrometric parameters for more than half a million quasars. This set
defines a kinematically non-rotating reference frame in the optical
domain. A subset of these quasars have accurate VLBI positions
that allow the axes of the reference frame to be aligned with the
International Celestial Reference System (ICRF) radio frame.
Aims: We describe the astrometric and photometric properties of
the quasars that were selected to represent the celestial reference
frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio
positions for sources with accurate VLBI positions.
Methods:
Descriptive statistics are used to characterise the overall properties
of the quasar sample. Residual rotation and orientation errors and
large-scale systematics are quantified by means of expansions in vector
spherical harmonics. Positional differences are calculated relative to
a prototype version of the forthcoming ICRF3.
Results: Gaia-CRF2
consists of the positions of a sample of 556 869 sources in Gaia DR2,
obtained from a positional cross-match with the ICRF3-prototype and
AllWISE AGN catalogues. The sample constitutes a clean, dense, and
homogeneous set of extragalactic point sources in the magnitude range
G ≃ 16 to 21 mag with accurately known optical positions. The median
positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at
G = mag. Large-scale systematics are estimated to be in the range 20
to 30 μas. The accuracy claims are supported by the parallaxes and
proper motions of the quasars in Gaia DR2. The optical positions for
a subset of 2820 sources in common with the ICRF3-prototype show very
good overall agreement with the radio positions, but several tens of
sources have significantly discrepant positions.
Conclusions:
Based on less than 40% of the data expected from the nominal Gaia
mission, Gaia-CRF2 is the first realisation of a non-rotating global
optical reference frame that meets the ICRS prescriptions, meaning
that it is built only on extragalactic sources. Its accuracy matches
the current radio frame of the ICRF, but the density of sources in
all parts of the sky is much higher, except along the Galactic equator.
Title: Gaia Data Release 2. Mapping the Milky Way disc kinematics
Authors: Gaia Collaboration; Katz, D.; Antoja, T.; Romero-Gómez, M.;
Drimmel, R.; Reylé, C.; Seabroke, G. M.; Soubiran, C.; Babusiaux,
C.; Di Matteo, P.; Figueras, F.; Poggio, E.; Robin, A. C.; Evans,
D. W.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne,
J. H. J.; Bailer-Jones, C. A. L.; Biermann, M.; Eyer, L.; Jansen,
F.; Jordi, C.; Klioner, S. A.; Lammers, U.; Lindegren, L.; Luri,
X.; Mignard, F.; Panem, C.; Pourbaix, D.; Randich, S.; Sartoretti,
P.; Siddiqui, H. I.; van Leeuwen, F.; Walton, N. A.; Arenou, F.;
Bastian, U.; Cropper, M.; Lattanzi, M. G.; Bakker, J.; Cacciari,
C.; Casta n, J.; Chaoul, L.; Cheek, N.; De Angeli, F.; Fabricius,
C.; Guerra, R.; Holl, B.; Masana, E.; Messineo, R.; Mowlavi, N.;
Nienartowicz, K.; Panuzzo, P.; Portell, J.; Riello, M.; Tanga, P.;
Thévenin, F.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.;
Teyssier, D.; Altmann, M.; Andrae, R.; Audard, M.; Bellas-Velidis,
I.; Benson, K.; Berthier, J.; Blomme, R.; Burgess, P.; Busso, G.;
Carry, B.; Cellino, A.; Clementini, G.; Clotet, M.; Creevey, O.;
Davidson, M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant,
C.; Fernández-Hernández, J.; Fouesneau, M.; Frémat, Y.; Galluccio,
L.; García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hernández, J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.;
Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.;
Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Löffler, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Muinonen, K.; Osinde, J.; Pancino, E.; Pauwels, T.; Petit,
J. -M.; Recio-Blanco, A.; Richards, P. J.; Rimoldini, L.; Sarro,
L. M.; Siopis, C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.;
van Reeven, W.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.;
Altavilla, G.; Álvarez, M. A.; Alvarez, R.; Alves, J.; Anderson,
R. I.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.; Arcay, B.;
Astraatmadja, T. L.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.;
Balm, P.; Barache, C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem,
P. S.; Barrado, D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz,
L.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.;
Bertone, S.; Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch,
T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon,
S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Breddels, M. A.; Bressan,
A.; Brouillet, N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli,
B.; Burlacu, A.; Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau,
E.; Cancelliere, R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo,
R.; Carlucci, T.; Carrasco, J. M.; Casamiquela, L.; Castellani, M.;
Castro-Ginard, A.; Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza,
G.; Costigan, G.; Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.;
Cuypers, J.; Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, P.;
David, M.; de Laverny, P.; De Luise, F.; De March, R.; de Souza, R.;
de Torres, A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.;
Delgado, H. E.; Diakite, S.; Diener, C.; Distefano, E.; Dolding, C.;
Drazinos, P.; Durán, J.; Edvardsson, B.; Enke, H.; Eriksson, K.;
Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Faigler,
S.; Falc a, A. J.; Farràs Casas, M.; Federici, L.; Fedorets, G.;
Fernique, P.; Filippi, F.; Findeisen, K.; Fonti, A.; Fraile, E.;
Fraser, M.; Frézouls, B.; Gai, M.; Galleti, S.; Garabato, D.;
García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel, A.; Gavras,
P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.; Girona,
S.; Giuffrida, G.; Glass, F.; Gomes, M.; Granvik, M.; Gueguen, A.;
Guerrier, A.; Guiraud, J.; Gutié, R.; Haigron, R.; Hatzidimitriou,
D.; Hauser, M.; Haywood, M.; Heiter, U.; Helmi, A.; Heu, J.; Hilger,
T.; Hobbs, D.; Hofmann, W.; Holland, G.; Huckle, H. E.; Hypki, A.;
Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.; Jonker, P. G.;
Juhász, Á. L.; Julbe, F.; Karampelas, A.; Kewley, A.; Klar, J.;
Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.; Kontizas, E.;
Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.; Koubsky, P.;
Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; López,
M.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant,
J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall, D. J.;
Martino, M.; Marton, G.; Mary, N.; Massari, D.; Matijevič, G.; Mazeh,
T.; McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Molina,
D.; Molinaro, R.; Molnár, L.; Montegriffo, P.; Mor, R.; Morbidelli,
R.; Morel, T.; Morris, D.; Mulone, A. F.; Muraveva, T.; Musella, I.;
Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane, W.; Ordénovic, C.;
Ordóñez-Blanco, D.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler,
F.; Palacin, H.; Palaversa, L.; Panahi, A.; Pawlak, M.; Piersimoni,
A. M.; Pineau, F. -X.; Plachy, E.; Plum, G.; Poujoulet, E.; Prša,
A.; Pulone, L.; Racero, E.; Ragaini, S.; Rambaux, N.; Ramos-Lerate,
M.; Regibo, S.; Riclet, F.; Ripepi, V.; Riva, A.; Rivard, A.; Rixon,
G.; Roegiers, T.; Roelens, M.; Rowell, N.; Royer, F.; Ruiz-Dern,
L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann, J.; Salgado, J.;
Salguero, E.; Sanna, N.; Santana-Ros, T.; Sarasso, M.; Savietto, H.;
Schultheis, M.; Sciacca, E.; Segol, M.; Segovia, J. C.; Ségransan,
D.; Shih, I. -C.; Siltala, L.; Silva, A. F.; Smart, R. L.; Smith,
K. W.; Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay,
J.; Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.; Steidelmüller,
H.; Stephenson, C. A.; Stoev, H.; Suess, F. F.; Surdej, J.; Szabados,
L.; Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran, G.; Taylor,
M. B.; Teixeira, R.; Terrett, D.; Teyssandier, P.; Thuillot, W.;
Titarenko, A.; Torra Clotet, F.; Turon, C.; Ulla, A.; Utrilla, E.;
Uzzi, S.; Vaillant, M.; Valentini, G.; Valette, V.; van Elteren,
A.; Van Hemelryck, E.; van Leeuwen, M.; Vaschetto, M.; Vecchiato,
A.; Veljanoski, J.; Viala, Y.; Vicente, D.; Vogt, S.; von Essen, C.;
Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Wertz,
O.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Ziaeepour,
H.; Zorec, J.; Zschocke, S.; Zucker, S.; Zurbach, C.; Zwitter, T.
Bibcode: 2018A&A...616A..11G
Altcode: 2018arXiv180409380G
Context. The second Gaia data release (Gaia DR2) contains high-precision
positions, parallaxes, and proper motions for 1.3 billion sources as
well as line-of-sight velocities for 7.2 million stars brighter than
GRVS = 12 mag. Both samples provide a full sky coverage.
Aims: To illustrate the potential of Gaia DR2, we provide a first
look at the kinematics of the Milky Way disc, within a radius of several
kiloparsecs around the Sun.
Methods: We benefit for the first
time from a sample of 6.4 million F-G-K stars with full 6D phase-space
coordinates, precise parallaxes (σϖ/ϖ ≤ 20%), and
precise Galactic cylindrical velocities (median uncertainties of 0.9-1.4
km s-1 and 20% of the stars with uncertainties smaller than
1 km s-1 on all three components). From this sample, we
extracted a sub-sample of 3.2 million giant stars to map the velocity
field of the Galactic disc from 5 kpc to 13 kpc from the Galactic
centre and up to 2 kpc above and below the plane. We also study the
distribution of 0.3 million solar neighbourhood stars (r < 200 pc),
with median velocity uncertainties of 0.4 km s-1, in velocity
space and use the full sample to examine how the over-densities evolve
in more distant regions.
Results: Gaia DR2 allows us to draw 3D
maps of the Galactocentric median velocities and velocity dispersions
with unprecedented accuracy, precision, and spatial resolution. The
maps show the complexity and richness of the velocity field of the
galactic disc. We observe streaming motions in all the components of
the velocities as well as patterns in the velocity dispersions. For
example, we confirm the previously reported negative and positive
galactocentric radial velocity gradients in the inner and outer disc,
respectively. Here, we see them as part of a non-axisymmetric kinematic
oscillation, and we map its azimuthal and vertical behaviour. We also
witness a new global arrangement of stars in the velocity plane of
the solar neighbourhood and in distant regions in which stars are
organised in thin substructures with the shape of circular arches
that are oriented approximately along the horizontal direction in the
U - V plane. Moreover, in distant regions, we see variations in the
velocity substructures more clearly than ever before, in particular,
variations in the velocity of the Hercules stream.
Conclusions:
Gaia DR2 provides the largest existing full 6D phase-space coordinates
catalogue. It also vastly increases the number of available distances
and transverse velocities with respect to Gaia DR1. Gaia DR2 offers
a great wealth of information on the Milky Way and reveals clear
non-axisymmetric kinematic signatures within the Galactic disc, for
instance. It is now up to the astronomical community to explore its
full potential.
Title: Gaia Data Release 2. Observational Hertzsprung-Russell diagrams
Authors: Gaia Collaboration; Babusiaux, C.; van Leeuwen, F.;
Barstow, M. A.; Jordi, C.; Vallenari, A.; Bossini, D.; Bressan,
A.; Cantat-Gaudin, T.; van Leeuwen, M.; Brown, A. G. A.; Prusti,
T.; de Bruijne, J. H. J.; Bailer-Jones, C. A. L.; Biermann, M.;
Evans, D. W.; Eyer, L.; Jansen, F.; Klioner, S. A.; Lammers, U.;
Lindegren, L.; Luri, X.; Mignard, F.; Panem, C.; Pourbaix, D.;
Randich, S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; Walton,
N. A.; Arenou, F.; Bastian, U.; Cropper, M.; Drimmel, R.; Katz, D.;
Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castañeda, J.; Chaoul,
L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra, R.; Holl, B.;
Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Panuzzo,
P.; Portell, J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thévenin,
F.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Teyssier,
D.; Altmann, M.; Andrae, R.; Audard, M.; Bellas-Velidis, I.; Benson,
K.; Berthier, J.; Blomme, R.; Burgess, P.; Busso, G.; Carry, B.;
Cellino, A.; Clementini, G.; Clotet, M.; Creevey, O.; Davidson,
M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.;
Fernández-Hernández, J.; Fouesneau, M.; Frémat, Y.; Galluccio, L.;
García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hernández, J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.;
Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.;
Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Löffler, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Muinonen, K.; Osinde, J.; Pancino, E.; Pauwels, T.; Petit,
J. -M.; Recio-Blanco, A.; Richards, P. J.; Rimoldini, L.; Robin,
A. C.; Sarro, L. M.; Siopis, C.; Smith, M.; Sozzetti, A.; Süveges,
M.; Torra, J.; van Reeven, W.; Abbas, U.; Abreu Aramburu, A.; Accart,
S.; Aerts, C.; Altavilla, G.; Álvarez, M. A.; Alvarez, R.; Alves,
J.; Anderson, R. I.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.;
Antoja, T.; Arcay, B.; Astraatmadja, T. L.; Bach, N.; Baker, S. G.;
Balaguer-Núñez, L.; Balm, P.; Barache, C.; Barata, C.; Barbato,
D.; Barblan, F.; Barklem, P. S.; Barrado, D.; Barros, M.; Bartholomé
Muñoz, L.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.; Berihuete,
A.; Bertone, S.; Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.;
Boch, T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bouquillon, S.;
Bourda, G.; Bragaglia, A.; Bramante, L.; Breddels, M. A.; Brouillet,
N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli, B.; Burlacu, A.;
Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau, E.; Cancelliere,
R.; Cannizzaro, G.; Carballo, R.; Carlucci, T.; Carrasco, J. M.;
Casamiquela, L.; Castellani, M.; Castro-Ginard, A.; Charlot, P.;
Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan, G.; Cowell,
S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers, J.; Dafonte, C.;
Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; de Laverny, P.;
De Luise, F.; De March, R.; de Martino, D.; de Souza, R.; de Torres,
A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.; Delgado,
H. E.; Diakite, S.; Diener, C.; Distefano, E.; Dolding, C.; Drazinos,
P.; Durán, J.; Edvardsson, B.; Enke, H.; Eriksson, K.; Esquej, P.;
Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Faigler, S.; Falcão,
A. J.; Farràs Casas, M.; Federici, L.; Fedorets, G.; Fernique,
P.; Figueras, F.; Filippi, F.; Findeisen, K.; Fonti, A.; Fraile,
E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti, S.; Garabato, D.;
García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel, A.; Gavras,
P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.; Girona,
S.; Giuffrida, G.; Glass, F.; Gomes, M.; Granvik, M.; Gueguen, A.;
Guerrier, A.; Guiraud, J.; Gutié, R.; Haigron, R.; Hatzidimitriou,
D.; Hauser, M.; Haywood, M.; Heiter, U.; Helmi, A.; Heu, J.; Hilger,
T.; Hobbs, D.; Hofmann, W.; Holland, G.; Huckle, H. E.; Hypki, A.;
Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.; Jonker, P. G.;
Juhász, Á. L.; Julbe, F.; Karampelas, A.; Kewley, A.; Klar, J.;
Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.; Kontizas, E.;
Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.; Koubsky, P.;
Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; López,
M.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant,
J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall, D. J.;
Martino, M.; Marton, G.; Mary, N.; Massari, D.; Matijevič, G.; Mazeh,
T.; McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Molina,
D.; Molinaro, R.; Molnár, L.; Montegriffo, P.; Mor, R.; Morbidelli,
R.; Morel, T.; Morris, D.; Mulone, A. F.; Muraveva, T.; Musella, I.;
Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane, W.; Ordénovic, C.;
Ordóñez-Blanco, D.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler, F.;
Palacin, H.; Palaversa, L.; Panahi, A.; Pawlak, M.; Piersimoni, A. M.;
Pineau, F. -X.; Plachy, E.; Plum, G.; Poggio, E.; Poujoulet, E.; Prša,
A.; Pulone, L.; Racero, E.; Ragaini, S.; Rambaux, N.; Ramos-Lerate,
M.; Regibo, S.; Reylé, C.; Riclet, F.; Ripepi, V.; Riva, A.; Rivard,
A.; Rixon, G.; Roegiers, T.; Roelens, M.; Romero-Gómez, M.; Rowell,
N.; Royer, F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés, T.;
Sahlmann, J.; Salgado, J.; Salguero, E.; Sanna, N.; Santana-Ros, T.;
Sarasso, M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol, M.;
Segovia, J. C.; Ségransan, D.; Shih, I. -C.; Siltala, L.; Silva,
A. F.; Smart, R. L.; Smith, K. W.; Solano, E.; Solitro, F.; Sordo,
R.; Soria Nieto, S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa,
U.; Steele, I. A.; Steidelmüller, H.; Stephenson, C. A.; Stoev, H.;
Suess, F. F.; Surdej, J.; Szabados, L.; Szegedi-Elek, E.; Tapiador,
D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.; Terrett,
D.; Teyssandier, P.; Thuillot, W.; Titarenko, A.; Torra Clotet, F.;
Turon, C.; Ulla, A.; Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini,
G.; Valette, V.; van Elteren, A.; Van Hemelryck, E.; Vaschetto, M.;
Vecchiato, A.; Veljanoski, J.; Viala, Y.; Vicente, D.; Vogt, S.;
von Essen, C.; Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.;
Weiler, M.; Wertz, O.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.;
Žerjal, M.; Ziaeepour, H.; Zorec, J.; Zschocke, S.; Zucker, S.;
Zurbach, C.; Zwitter, T.
Bibcode: 2018A&A...616A..10G
Altcode: 2018arXiv180409378G
Context. Gaia Data Release 2 provides high-precision astrometry and
three-band photometry for about 1.3 billion sources over the full
sky. The precision, accuracy, and homogeneity of both astrometry and
photometry are unprecedented.
Aims: We highlight the power of
the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell
diagram (HRD). Gaia allows us to present many different HRDs, depending
in particular on stellar population selections. We do not aim here
for completeness in terms of types of stars or stellar evolutionary
aspects. Instead, we have chosen several illustrative examples.
Methods: We describe some of the selections that can be made in Gaia
DR2 to highlight the main structures of the Gaia HRDs. We select both
field and cluster (open and globular) stars, compare the observations
with previous classifications and with stellar evolutionary tracks,
and we present variations of the Gaia HRD with age, metallicity, and
kinematics. Late stages of stellar evolution such as hot subdwarfs,
post-AGB stars, planetary nebulae, and white dwarfs are also analysed,
as well as low-mass brown dwarf objects.
Results: The Gaia HRDs
are unprecedented in both precision and coverage of the various Milky
Way stellar populations and stellar evolutionary phases. Many fine
structures of the HRDs are presented. The clear split of the white
dwarf sequence into hydrogen and helium white dwarfs is presented
for the first time in an HRD. The relation between kinematics and the
HRD is nicely illustrated. Two different populations in a classical
kinematic selection of the halo are unambiguously identified in the
HRD. Membership and mean parameters for a selected list of open
clusters are provided. They allow drawing very detailed cluster
sequences, highlighting fine structures, and providing extremely
precise empirical isochrones that will lead to more insight in
stellar physics.
Conclusions: Gaia DR2 demonstrates the
potential of combining precise astrometry and photometry for large
samples for studies in stellar evolution and stellar population
and opens an entire new area for HRD-based studies. The full
Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A10
Title: Gaia Data Release 2. Kinematics of globular clusters and
dwarf galaxies around the Milky Way
Authors: Gaia Collaboration; Helmi, A.; van Leeuwen, F.; McMillan,
P. J.; Massari, D.; Antoja, T.; Robin, A. C.; Lindegren, L.;
Bastian, U.; Arenou, F.; Babusiaux, C.; Biermann, M.; Breddels,
M. A.; Hobbs, D.; Jordi, C.; Pancino, E.; Reylé, C.; Veljanoski,
J.; Brown, A. G. A.; Vallenari, A.; Prusti, T.; de Bruijne,
J. H. J.; Bailer-Jones, C. A. L.; Evans, D. W.; Eyer, L.; Jansen,
F.; Klioner, S. A.; Lammers, U.; Luri, X.; Mignard, F.; Panem,
C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.;
Soubiran, C.; Walton, N. A.; Cropper, M.; Drimmel, R.; Katz, D.;
Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castañeda, J.; Chaoul,
L.; Cheek, N.; De Angeli, F.; Fabricius, C.; Guerra, R.; Holl, B.;
Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Panuzzo,
P.; Portell, J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thévenin,
F.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Teyssier,
D.; Altmann, M.; Andrae, R.; Audard, M.; Bellas-Velidis, I.; Benson,
K.; Berthier, J.; Blomme, R.; Burgess, P.; Busso, G.; Carry, B.;
Cellino, A.; Clementini, G.; Clotet, M.; Creevey, O.; Davidson,
M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.;
Fernández-Hernández, J.; Fouesneau, M.; Frémat, Y.; Galluccio, L.;
García-Torres, M.; González-Núñez, J.; González-Vidal, J. J.;
Gosset, E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison,
D. L.; Hernández, J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.;
Jasniewicz, G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.;
Krone-Martins, A.; Lanzafame, A. C.; Lebzelter, T.; Löffler, W.;
Manteiga, M.; Marrese, P. M.; Martín-Fleitas, J. M.; Moitinho, A.;
Mora, A.; Muinonen, K.; Osinde, J.; Pauwels, T.; Petit, J. -M.;
Recio-Blanco, A.; Richards, P. J.; Rimoldini, L.; Sarro, L. M.;
Siopis, C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.; van
Reeven, W.; Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.;
Altavilla, G.; Álvarez, M. A.; Alvarez, R.; Alves, J.; Anderson,
R. I.; Andrei, A. H.; Anglada Varela, E.; Antiche, E.; Arcay, B.;
Astraatmadja, T. L.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.;
Balm, P.; Barache, C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem,
P. S.; Barrado, D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz,
S.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.;
Bertone, S.; Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch,
T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon,
S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Bressan, A.; Brouillet,
N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli, B.; Burlacu, A.;
Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau, E.; Cancelliere,
R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo, R.; Carlucci, T.;
Carrasco, J. M.; Casamiquela, L.; Castellani, M.; Castro-Ginard, A.;
Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan, G.;
Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers, J.; Dafonte,
C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; de Laverny,
P.; De Luise, F.; De March, R.; de Martino, D.; de Souza, R.; de
Torres, A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado, A.;
Delgado, H. E.; Di Matteo, P.; Diakite, S.; Diener, C.; Distefano,
E.; Dolding, C.; Drazinos, P.; Durán, J.; Edvardsson, B.; Enke, H.;
Eriksson, K.; Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio,
M.; Faigler, S.; Falcão, A. J.; Farràs Casas, M.; Federici, L.;
Fedorets, G.; Fernique, P.; Figueras, F.; Filippi, F.; Findeisen, K.;
Fonti, A.; Fraile, E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti, S.;
Garabato, D.; García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel,
A.; Gavras, P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.;
Girona, S.; Giuffrida, G.; Glass, F.; Gomes, M.; Granvik, M.; Gueguen,
A.; Guerrier, A.; Guiraud, J.; Gutiérrez-Sánchez, R.; Hofmann,
W.; Holland, G.; Huckle, H. E.; Hypki, A.; Icardi, V.; Janßen, K.;
Jevardat de Fombelle, G.; Jonker, P. G.; Juhász, Á. L.; Julbe,
F.; Karampelas, A.; Kewley, A.; Klar, J.; Kochoska, A.; Kohley, R.;
Kolenberg, K.; Kontizas, M.; Kontizas, E.; Koposov, S. E.; Kordopatis,
G.; Kostrzewa-Rutkowska, Z.; Koubsky, P.; Lambert, S.; Lanza, A. F.;
Lasne, Y.; Lavigne, J. -B.; Le Fustec, Y.; Le Poncin-Lafitte, C.;
Lebreton, Y.; Leccia, S.; Leclerc, N.; Lecoeur-Taibi, I.; Lenhardt,
H.; Leroux, F.; Liao, S.; Licata, E.; Lindstrøm, H. E. P.; Lister,
T. A.; Livanou, E.; Lobel, A.; López, M.; Managau, S.; Mann, R. G.;
Mantelet, G.; Marchal, O.; Marchant, J. M.; Marconi, M.; Marinoni,
S.; Marschalkó, G.; Marshall, D. J.; Martino, M.; Marton, G.; Mary,
N.; Matijevič, G.; Mazeh, T.; Messina, S.; Michalik, D.; Millar,
N. R.; Molina, D.; Molinaro, R.; Molnár, L.; Montegriffo, P.; Mor,
R.; Morbidelli, R.; Morel, T.; Morris, D.; Mulone, A. F.; Muraveva,
T.; Musella, I.; Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane, W.;
Ordénovic, C.; Ordóñez-Blanco, D.; Osborne, P.; Pagani, C.; Pagano,
I.; Pailler, F.; Palacin, H.; Palaversa, L.; Panahi, A.; Pawlak, M.;
Piersimoni, A. M.; Pineau, F. -X.; Plachy, E.; Plum, G.; Poggio, E.;
Poujoulet, E.; Prša, A.; Pulone, L.; Racero, E.; Ragaini, S.; Rambaux,
N.; Ramos-Lerate, M.; Regibo, S.; Riclet, F.; Ripepi, V.; Riva, A.;
Rivard, A.; Rixon, G.; Roegiers, T.; Roelens, M.; Romero-Gómez, M.;
Rowell, N.; Royer, F.; Ruiz-Dern, L.; Sadowski, G.; Sagristà Sellés,
T.; Sahlmann, J.; Salgado, J.; Salguero, E.; Sanna, N.; Santana-Ros,
T.; Sarasso, M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol,
M.; Segovia, J. C.; Ségransan, D.; Shih, I. -C.; Siltala, L.; Silva,
A. F.; Smart, R. L.; Smith, K. W.; Solano, E.; Solitro, F.; Sordo,
R.; Soria Nieto, S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa,
U.; Steele, I. A.; Steidelmüller, H.; Stephenson, C. A.; Stoev, H.;
Suess, F. F.; Surdej, J.; Szabados, L.; Szegedi-Elek, E.; Tapiador,
D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.; Terrett, D.;
Teyssandier, P.; Thuillot, W.; Titarenko, A.; Torra Clotet, F.;
Turon, C.; Ulla, A.; Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini,
G.; Valette, V.; van Elteren, A.; Van Hemelryck, E.; van Leeuwen,
M.; Vaschetto, M.; Vecchiato, A.; Viala, Y.; Vicente, D.; Vogt, S.;
von Essen, C.; Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.;
Weiler, M.; Wertz, O.; Wevems, T.; Wyrzykowski, Ł.; Yoldas, A.;
Žerjal, M.; Ziaeepour, H.; Zorec, J.; Zschocke, S.; Zucker, S.;
Zurbach, C.; Zwitter, T.
Bibcode: 2018A&A...616A..12G
Altcode: 2018arXiv180409381G
Note to the Readers: Following the publication of the corrigendum,
the article was corrected on 15 May 2020. Context.
Aims:
The goal of this paper is to demonstrate the outstanding quality
of the second data release of the Gaia mission and its power for
constraining many different aspects of the dynamics of the satellites
of the Milky Way. We focus here on determining the proper motions of
75 Galactic globular clusters, nine dwarf spheroidal galaxies, one
ultra-faint system, and the Large and Small Magellanic Clouds.
Methods: Using data extracted from the Gaia archive, we derived
the proper motions and parallaxes for these systems, as well as
their uncertainties. We demonstrate that the errors, statistical
and systematic, are relatively well understood. We integrated the
orbits of these objects in three different Galactic potentials, and
characterised their properties. We present the derived proper motions,
space velocities, and characteristic orbital parameters in various
tables to facilitate their use by the astronomical community.
Results: Our limited and straightforward analyses have allowed us
for example to (i) determine absolute and very precise proper motions
for globular clusters; (ii) detect clear rotation signatures in the
proper motions of at least five globular clusters; (iii) show that
the satellites of the Milky Way are all on high-inclination orbits,
but that they do not share a single plane of motion; (iv) derive a lower
limit for the mass of the Milky Way of 9.1-2.6+6.2
× 1011 M⊙ based on the assumption that the Leo
I dwarf spheroidal is bound; (v) derive a rotation curve for the Large
Magellanic Cloud based solely on proper motions that is competitive
with line-of-sight velocity curves, now using many orders of magnitude
more sources; and (vi) unveil the dynamical effect of the bar on the
motions of stars in the Large Magellanic Cloud.
Conclusions: All
these results highlight the incredible power of the Gaia astrometric
mission, and in particular of its second data release. Full
Table D.3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A12
Title: Gaia Data Release 2. Summary of the contents and survey
properties
Authors: Gaia Collaboration; Brown, A. G. A.; Vallenari, A.; Prusti,
T.; de Bruijne, J. H. J.; Babusiaux, C.; Bailer-Jones, C. A. L.;
Biermann, M.; Evans, D. W.; Eyer, L.; Jansen, F.; Jordi, C.; Klioner,
S. A.; Lammers, U.; Lindegren, L.; Luri, X.; Mignard, F.; Panem,
C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.;
Soubiran, C.; van Leeuwen, F.; Walton, N. A.; Arenou, F.; Bastian,
U.; Cropper, M.; Drimmel, R.; Katz, D.; Lattanzi, M. G.; Bakker,
J.; Cacciari, C.; Castañeda, J.; Chaoul, L.; Cheek, N.; De Angeli,
F.; Fabricius, C.; Guerra, R.; Holl, B.; Masana, E.; Messineo, R.;
Mowlavi, N.; Nienartowicz, K.; Panuzzo, P.; Portell, J.; Riello,
M.; Seabroke, G. M.; Tanga, P.; Thévenin, F.; Gracia-Abril, G.;
Comoretto, G.; Garcia-Reinaldos, M.; Teyssier, D.; Altmann, M.;
Andrae, R.; Audard, M.; Bellas-Velidis, I.; Benson, K.; Berthier,
J.; Blomme, R.; Burgess, P.; Busso, G.; Carry, B.; Cellino, A.;
Clementini, G.; Clotet, M.; Creevey, O.; Davidson, M.; De Ridder, J.;
Delchambre, L.; Dell'Oro, A.; Ducourant, C.; Fernández-Hernández,
J.; Fouesneau, M.; Frémat, Y.; Galluccio, L.; García-Torres,
M.; González-Núñez, J.; González-Vidal, J. J.; Gosset, E.; Guy,
L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison, D. L.; Hernández,
J.; Hestroffer, D.; Hodgkin, S. T.; Hutton, A.; Jasniewicz, G.;
Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.; Krone-Martins, A.;
Lanzafame, A. C.; Lebzelter, T.; Löffler, W.; Manteiga, M.; Marrese,
P. M.; Martín-Fleitas, J. M.; Moitinho, A.; Mora, A.; Muinonen, K.;
Osinde, J.; Pancino, E.; Pauwels, T.; Petit, J. -M.; Recio-Blanco, A.;
Richards, P. J.; Rimoldini, L.; Robin, A. C.; Sarro, L. M.; Siopis,
C.; Smith, M.; Sozzetti, A.; Süveges, M.; Torra, J.; van Reeven, W.;
Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.; Altavilla, G.;
Álvarez, M. A.; Alvarez, R.; Alves, J.; Anderson, R. I.; Andrei,
A. H.; Anglada Varela, E.; Antiche, E.; Antoja, T.; Arcay, B.;
Astraatmadja, T. L.; Bach, N.; Baker, S. G.; Balaguer-Núñez, L.;
Balm, P.; Barache, C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem,
P. S.; Barrado, D.; Barros, M.; Barstow, M. A.; Bartholomé Muñoz,
S.; Bassilana, J. -L.; Becciani, U.; Bellazzini, M.; Berihuete, A.;
Bertone, S.; Bianchi, L.; Bienaymé, O.; Blanco-Cuaresma, S.; Boch,
T.; Boeche, C.; Bombrun, A.; Borrachero, R.; Bossini, D.; Bouquillon,
S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Breddels, M. A.; Bressan,
A.; Brouillet, N.; Brüsemeister, T.; Brugaletta, E.; Bucciarelli,
B.; Burlacu, A.; Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caffau,
E.; Cancelliere, R.; Cannizzaro, G.; Cantat-Gaudin, T.; Carballo,
R.; Carlucci, T.; Carrasco, J. M.; Casamiquela, L.; Castellani, M.;
Castro-Ginard, A.; Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.;
Costigan, G.; Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypers,
J.; Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.;
de Laverny, P.; De Luise, F.; De March, R.; de Martino, D.; de Souza,
R.; de Torres, A.; Debosscher, J.; del Pozo, E.; Delbo, M.; Delgado,
A.; Delgado, H. E.; Di Matteo, P.; Diakite, S.; Diener, C.; Distefano,
E.; Dolding, C.; Drazinos, P.; Durán, J.; Edvardsson, B.; Enke, H.;
Eriksson, K.; Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio,
M.; Faigler, S.; Falcão, A. J.; Farràs Casas, M.; Federici, L.;
Fedorets, G.; Fernique, P.; Figueras, F.; Filippi, F.; Findeisen, K.;
Fonti, A.; Fraile, E.; Fraser, M.; Frézouls, B.; Gai, M.; Galleti, S.;
Garabato, D.; García-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel,
A.; Gavras, P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.;
Girona, S.; Giuffrida, G.; Glass, F.; Gomes, M.; Granvik, M.; Gueguen,
A.; Guerrier, A.; Guiraud, J.; Gutiérrez-Sánchez, R.; Haigron, R.;
Hatzidimitriou, D.; Hauser, M.; Haywood, M.; Heiter, U.; Helmi, A.;
Heu, J.; Hilger, T.; Hobbs, D.; Hofmann, W.; Holland, G.; Huckle,
H. E.; Hypki, A.; Icardi, V.; Janßen, K.; Jevardat de Fombelle, G.;
Jonker, P. G.; Juhász, Á. L.; Julbe, F.; Karampelas, A.; Kewley,
A.; Klar, J.; Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.;
Kontizas, E.; Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.;
Koubsky, P.; Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.;
Le Fustec, Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.;
Leclerc, N.; Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.;
Licata, E.; Lindstrøm, H. E. P.; Lister, T. A.; Livanou, E.; Lobel,
A.; López, M.; Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.;
Marchant, J. M.; Marconi, M.; Marinoni, S.; Marschalkó, G.; Marshall,
D. J.; Martino, M.; Marton, G.; Mary, N.; Massari, D.; Matijevič,
G.; Mazeh, T.; McMillan, P. J.; Messina, S.; Michalik, D.; Millar,
N. R.; Molina, D.; Molinaro, R.; Molnár, L.; Montegriffo, P.; Mor,
R.; Morbidelli, R.; Morel, T.; Morris, D.; Mulone, A. F.; Muraveva,
T.; Musella, I.; Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane,
W.; Ordénovic, C.; Ordóñez-Blanco, D.; Osborne, P.; Pagani, C.;
Pagano, I.; Pailler, F.; Palacin, H.; Palaversa, L.; Panahi, A.;
Pawlak, M.; Piersimoni, A. M.; Pineau, F. -X.; Plachy, E.; Plum,
G.; Poggio, E.; Poujoulet, E.; Prša, A.; Pulone, L.; Racero, E.;
Ragaini, S.; Rambaux, N.; Ramos-Lerate, M.; Regibo, S.; Reylé, C.;
Riclet, F.; Ripepi, V.; Riva, A.; Rivard, A.; Rixon, G.; Roegiers,
T.; Roelens, M.; Romero-Gómez, M.; Rowell, N.; Royer, F.; Ruiz-Dern,
L.; Sadowski, G.; Sagristà Sellés, T.; Sahlmann, J.; Salgado, J.;
Salguero, E.; Sanna, N.; Santana-Ros, T.; Sarasso, M.; Savietto, H.;
Schultheis, M.; Sciacca, E.; Segol, M.; Segovia, J. C.; Ségransan, D.;
Shih, I. -C.; Siltala, L.; Silva, A. F.; Smart, R. L.; Smith, K. W.;
Solano, E.; Solitro, F.; Sordo, R.; Soria Nieto, S.; Souchay, J.;
Spagna, A.; Spoto, F.; Stampa, U.; Steele, I. A.; Steidelmüller, H.;
Stephenson, C. A.; Stoev, H.; Suess, F. F.; Surdej, J.; Szabados, L.;
Szegedi-Elek, E.; Tapiador, D.; Taris, F.; Tauran, G.; Taylor,
M. B.; Teixeira, R.; Terrett, D.; Teyssandier, P.; Thuillot, W.;
Titarenko, A.; Torra Clotet, F.; Turon, C.; Ulla, A.; Utrilla, E.;
Uzzi, S.; Vaillant, M.; Valentini, G.; Valette, V.; van Elteren,
A.; Van Hemelryck, E.; van Leeuwen, M.; Vaschetto, M.; Vecchiato,
A.; Veljanoski, J.; Viala, Y.; Vicente, D.; Vogt, S.; von Essen, C.;
Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.; Weiler, M.; Wertz,
O.; Wevers, T.; Wyrzykowski, Ł.; Yoldas, A.; Žerjal, M.; Ziaeepour,
H.; Zorec, J.; Zschocke, S.; Zucker, S.; Zurbach, C.; Zwitter, T.
Bibcode: 2018A&A...616A...1G
Altcode: 2018arXiv180409365G
Context. We present the second Gaia data release, Gaia DR2, consisting
of astrometry, photometry, radial velocities, and information on
astrophysical parameters and variability, for sources brighter than
magnitude 21. In addition epoch astrometry and photometry are provided
for a modest sample of minor planets in the solar system.
Aims: A summary of the contents of Gaia DR2 is presented, accompanied
by a discussion on the differences with respect to Gaia DR1 and
an overview of the main limitations which are still present in
the survey. Recommendations are made on the responsible use of
Gaia DR2 results.
Methods: The raw data collected with the
Gaia instruments during the first 22 months of the mission have
been processed by the Gaia Data Processing and Analysis Consortium
(DPAC) and turned into this second data release, which represents
a major advance with respect to Gaia DR1 in terms of completeness,
performance, and richness of the data products.
Results: Gaia
DR2 contains celestial positions and the apparent brightness in G for
approximately 1.7 billion sources. For 1.3 billion of those sources,
parallaxes and proper motions are in addition available. The sample
of sources for which variability information is provided is expanded
to 0.5 million stars. This data release contains four new elements:
broad-band colour information in the form of the apparent brightness
in the GBP (330-680 nm) and GRP (630-1050 nm)
bands is available for 1.4 billion sources; median radial velocities for
some 7 million sources are presented; for between 77 and 161 million
sources estimates are provided of the stellar effective temperature,
extinction, reddening, and radius and luminosity; and for a pre-selected
list of 14 000 minor planets in the solar system epoch astrometry
and photometry are presented. Finally, Gaia DR2 also represents a
new materialisation of the celestial reference frame in the optical,
the Gaia-CRF2, which is the first optical reference frame based solely
on extragalactic sources. There are notable changes in the photometric
system and the catalogue source list with respect to Gaia DR1, and we
stress the need to consider the two data releases as independent.
Conclusions: Gaia DR2 represents a major achievement for the Gaia
mission, delivering on the long standing promise to provide parallaxes
and proper motions for over 1 billion stars, and representing a first
step in the availability of complementary radial velocity and source
astrophysical information for a sample of stars in the Gaia survey
which covers a very substantial fraction of the volume of our galaxy.
Title: VizieR Online Data Catalog: 46 open clusters GaiaDR2 HR
diagrams (Gaia Collaboration, 2018)
Authors: Gaia Collaboration; Babusiaux, C.; van Leeuwen, F.;
Barstow; M., A.; Jordi, C.; Vallenari, A.; Bossini, A.; Bressan,
A.; Cantat-Gaudin, T.; van Leeuwen, M.; Brown, A. G. A.; Prusti,
T.; de Bruijne, J. H. J.; Bailer-Jones, C. A. L.; Biermann, M.;
Evans, D. W.; Eyer, L.; Jansen, F.; Klioner, S. A.; Lammers, U.;
Lindegren, L.; Luri, X.; Mignard, F.; Panem, C.; Pourbaix, D.;
Randich, S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; Walton,
N. A.; Arenou, F.; Bastian, U.; Cropper, M.; Drimmel, R.; Katz, D.;
Lattanzi, M. G.; Bakker, J.; Cacciari, C.; Castaneda, J.; Chaoul,
L.; Cheek, N.; de Angeli, F.; Fabricius, C.; Guerra, R.; Holl, B.;
Masana, E.; Messineo, R.; Mowlavi, N.; Nienartowicz, K.; Panuzzo,
P.; Portell, J.; Riello, M.; Seabroke, G. M.; Tanga, P.; Thevenin,
F.; Gracia-Abril, G.; Comoretto, G.; Garcia-Reinaldos, M.; Teyssier,
D.; Altmann, M.; Andrae, R.; Audard, M.; Bellas-Velidis, I.; Benson,
K.; Berthier, J.; Blomme, R.; Burgess, P.; Busso, G.; Carry, B.;
Cellino, A.; Clementini, G.; Clotet, M.; Creevey, O.; Davidson,
M.; De Ridder, J.; Delchambre, L.; Dell'Oro, A.; Ducourant, C.;
Fernandez-Hernandez, J.; Fouesneau, M.; Fremat, Y.; Galluccio, L.;
Garcia-Torres, M.; Gonzalez-Nunez, J.; Gonzalez-Vidal, J. J.; Gosset,
E.; Guy, L. P.; Halbwachs, J. -L.; Hambly, N. C.; Harrison, D. L.;
Hernandez, J.; Hestroer, D.; Hodgkin, S. T.; Hutton, A.; Jasniewicz,
G.; Jean-Antoine-Piccolo, A.; Jordan, S.; Korn, A. J.; Krone-Martins,
A.; Lanzafame, A. C.; Lebzelter, T.; Loeer, W.; Manteiga, M.; Marrese,
P. M.; Martin-Fleitas, J. M.; Moitinho, A.; Mora, A.; Muinonen, K.;
Osinde, J.; Pancino, E.; Pauwels, T.; Petit, J. -M.; Recio-Blanco, A.;
Richards, P. J.; Rimoldini, L.; Robin, A. C.; Sarro, L. M.; Siopis,
C.; Smith, M.; Sozzetti, A.; Sueveges, M.; Torra, J.; van Reeven, W.;
Abbas, U.; Abreu Aramburu, A.; Accart, S.; Aerts, C.; Altavilla, G.;
Alvarez, M. A.; Alvarez, R.; Alves, J.; Anderson, R. I.; Andrei, A. H.;
Anglada Varela, E.; Antiche, E.; Antoja, T.; Arcay, B.; Astraatmadja,
T. L.; Bach, N.; Baker, S. G.; Balaguer-Nunez, L.; Balm, P.; Barache,
C.; Barata, C.; Barbato, D.; Barblan, F.; Barklem, P. S.; Barrado,
D.; Barros, M.; Bartholome Munoz, S.; Bassilana, J. -L.; Becciani, U.;
Bellazzini, M.; Berihuete, A.; Bertone, S.; Bianchi, L.; Bienayme, O.;
Blanco-Cuaresma, S.; Boch, T.; Boeche, C.; Bombrun, A.; Borrachero,
R.; Bouquillon, S.; Bourda, G.; Bragaglia, A.; Bramante, L.; Breddels,
M. A.; Brouillet, N.; Bruesemeister, T.; Brugaletta, E.; Bucciarelli,
B.; Burlacu, A.; Busonero, D.; Butkevich, A. G.; Buzzi, R.; Caau,
E.; Cancelliere, R.; Cannizzaro, G.; Carballo, R.; Carlucci, T.;
Carrasco, J. M.; Casamiquela, L.; Castellani, M.; Castro-Ginard,
A.; Charlot, P.; Chemin, L.; Chiavassa, A.; Cocozza, G.; Costigan,
G.; Cowell, S.; Crifo, F.; Crosta, M.; Crowley, C.; Cuypersy, J.;
Dafonte, C.; Damerdji, Y.; Dapergolas, A.; David, P.; David, M.; de
Laverny, P.; de Luise, F.; de March, R.; de Martino, D.; de Souza,
R.; de Torres, A.; Debosscher, J.; Del Pozo, E.; Delbo, M.; Delgado,
A.; Delgado, H. E.; Diakite, S.; Diener, C.; Distefano, E.; Dolding,
C.; Drazinos, P.; Duran, J.; Edvardsson, B.; Enke, H.; Eriksson, K.;
Esquej, P.; Eynard Bontemps, G.; Fabre, C.; Fabrizio, M.; Faigler,
S.; Falcao, A. J.; Farras Casas, M.; Federici, L.; Fedorets, G.;
Fernique, P.; Figueras, F.; Filippi, F.; Findeisen, K.; Fonti, A.;
Fraile, E.; Fraser, M.; Frezouls, B.; Gai, M.; Galleti, S.; Garabato,
D.; Garcia-Sedano, F.; Garofalo, A.; Garralda, N.; Gavel, A.; Gavras,
P.; Gerssen, J.; Geyer, R.; Giacobbe, P.; Gilmore, G.; Girona, S.;
Giurida, G.; Glass, F.; Gomes, M.; Granvik, M.; Gueguen, A.; Guerrier,
A.; Guiraud, J.; Gutierrez-Sanchez, R.; Haigron, R.; Hatzidimitriou,
D.; Hauser, M.; Haywood, M.; Heiter, U.; Helmi, A.; Heu, J.; Hilger,
T.; Hobbs, D.; Hofmann, W.; Holland, G.; Huckle, H. E.; Hypki, A.;
Icardi, V.; Janssen, K.; Jevardat de Fombelle, G.; Jonker, P. G.;
Juhasz, A. L.; Julbe, F.; Karampelas, A.; Kewley, A.; Klar, J.;
Kochoska, A.; Kohley, R.; Kolenberg, K.; Kontizas, M.; Kontizas, E.;
Koposov, S. E.; Kordopatis, G.; Kostrzewa-Rutkowska, Z.; Koubsky, P.;
Lambert, S.; Lanza, A. F.; Lasne, Y.; Lavigne, J. -B.; Le Fustec,
Y.; Le Poncin-Lafitte, C.; Lebreton, Y.; Leccia, S.; Leclerc, N.;
Lecoeur-Taibi, I.; Lenhardt, H.; Leroux, F.; Liao, S.; Licata, E.;
Lindstrom, H. E. P.; Lister, T. A.; Livanou, E.; Lobel, A.; Lopez, M.;
Managau, S.; Mann, R. G.; Mantelet, G.; Marchal, O.; Marchant, J. M.;
Marconi, M.; Marinoni, S.; Marschalko, G.; Marshall, D. J.; Martino,
M.; Marton, G.; Mary, N.; Massari, D.; Matijevi?C, G.; Mazeh, T.;
McMillan, P. J.; Messina, S.; Michalik, D.; Millar, N. R.; Molina,
D.; Molinaro, R.; Molnar, L.; Montegrio, P.; Mor, R.; Morbidelli,
R.; Morel, T.; Morris, D.; Mulone, A. F.; Muraveva, T.; Musella, I.;
Nelemans, G.; Nicastro, L.; Noval, L.; O'Mullane, W.; Ordenovic, C.;
Ordonez-Blanco, D.; Osborne, P.; Pagani, C.; Pagano, I.; Pailler, F.;
Palacin, H.; Palaversa, L.; Panahi, A.; Pawlak, M.; Piersimoni, A. M.;
Pineau, F. -X.; Plachy, E.; Plum, G.; Poggio, E.; Poujoulet, E.; Prsa,
A.; Pulone, L.; Racero, E.; Ragaini, S.; Rambaux, N.; Ramos-Lerate,
M.; Regibo, S.; Reyle, C.; Riclet, F.; Ripepi, V.; Riva, A.; Rivard,
A.; Rixon, G.; Roegiers, T.; Roelens, M.; Romero-Gomez, M.; Rowell,
N.; Royer, F.; Ruiz-Dern, L.; Sadowski, G.; Sagrista Selles, T.;
Sahlmann, J.; Salgado, J.; Salguero, E.; Sanna, N.; Santana-Ros,
T.; Sarasso, M.; Savietto, H.; Schultheis, M.; Sciacca, E.; Segol,
M.; Segovia, J. C.; Segransan, D.; Shih, I. -C.; Siltala, L.; Silva,
A. F.; Smart, R. L.; Smith, K. W.; Solano, E.; Solitro, F.; Sordo,
R.; Soria Nieto, S.; Souchay, J.; Spagna, A.; Spoto, F.; Stampa,
U.; Steele, I. A.; Steidelmueller, H.; Stephenson, C. A.; Stoev, H.;
Suess, F. F.; Surdej, J.; Szabados, L.; Szegedi-Elek, E.; Tapiador,
D.; Taris, F.; Tauran, G.; Taylor, M. B.; Teixeira, R.; Terrett, D.;
Teyssandier, P.; Thuillot, W.; Titarenko, A.; Torra Clotet, F.; Turon,
C.; Ulla, A.; Utrilla, E.; Uzzi, S.; Vaillant, M.; Valentini, G.;
Valette, V.; van Elteren, A.; van Hemelryck, E.; Vaschetto, M.;
Vecchiato, A.; Veljanoski, J.; Viala, Y.; Vicente, D.; Vogt, S.;
von Essen, C.; Voss, H.; Votruba, V.; Voutsinas, S.; Walmsley, G.;
Weiler, M.; Wertz, O.; Wevers, T.; Wyrzykowski, L.; Yoldas, A.; Zerjal,
M.; Ziaeepour, H.; Zorec, J.; Zschocke, S.; Zucker, S.; Zurbach, C.;
Zwitter, T.
Bibcode: 2018yCat..36160010G
Altcode:
We have determined the membership of 46 open clusters. For the nine
clusters within 250pc we determined optimised parallaxes based on
the combined information extracted from the measured parallax and
proper motion values. These clusters are : in Tables A1a & A3:
alphaPer, Blanco1, ComaBer, Hyades, IC2391, IC2602, NGC2451A, Pleiades,
Praesepe. The remaining 37 clusters are in Table A1b & A4: Coll140,
IC4651, IC4665, IC4725, IC4756, NGC0188, NGC0752, NGC0869, NGC0884,
NGC1039, NGC1901, NGC2158, NGC2168, NGC2232, NGC2323, NGC2360, NGC2422,
NGC2423, NGC2437, NGC2447, NGC2516, NGC2547, NGC2548, NGC2682, NGC3228,
NGC3532, NGC6025, NGC6281, NGC6405, NGC6475, NGC6633, NGC6774, NGC6793,
NGC7092, Stock2, Trump02, Trump10. (4 data files).
Title: Pulsation-induced atmospheric dynamics in M-type AGB
stars. Effects on wind properties, photometric variations and near-IR
CO line profiles
Authors: Liljegren, S.; Höfner, S.; Eriksson, K.; Nowotny, W.
Bibcode: 2017A&A...606A...6L
Altcode: 2017arXiv170608332L
Context. Wind-driving in asymptotic giant branch (AGB) stars is
commonly attributed to a two-step process. First, matter in the stellar
atmosphere is levitated by shock waves, induced by stellar pulsation,
and second, this matter is accelerated by radiation pressure on dust,
resulting in a wind. In dynamical atmosphere and wind models the
effects of the stellar pulsation are often simulated by a simplistic
prescription at the inner boundary.
Aims: We test a sample of
dynamical models for M-type AGB stars, for which we kept the stellar
parameters fixed to values characteristic of a typical Mira variable
but varied the inner boundary condition. The aim was to evaluate the
effect on the resulting atmosphere structure and wind properties. The
results of the models are compared to observed mass-loss rates
and wind velocities, photometry, and radial velocity curves, and to
results from 1D radial pulsation models. The goal is to find boundary
conditions which give realistic atmosphere and wind properties.
Methods: Dynamical atmosphere models are calculated, using the
DARWIN code for different combinations of photospheric velocities and
luminosity variations. The inner boundary is changed by introducing
an offset between maximum expansion of the stellar surface and the
luminosity and/or by using an asymmetric shape for the luminosity
variation. Ninety-nine different combinations of theses two changes
are tested.
Results: The model atmospheres are very sensitive to
the inner boundary. Models that resulted in realistic wind velocities
and mass-loss rates, when compared to observations, also produced
realistic photometric variations. For the models to also reproduce the
characteristic radial velocity curve present in Mira stars (derived
from CO Δv = 3 lines), an overall phase shift of 0.2 between the maxima
of the luminosity and radial variation had to be introduced. This is a
larger phase shift than is found by 1D radial pulsation models.
Conclusions: We find that a group of models with different boundary
conditions (29 models, including the model with standard boundary
conditions) results in realistic velocities and mass-loss rates, and
in photometric variations. To achieve the correct line splitting time
variation a phase shift is needed.
Title: A grid of MARCS model atmospheres for late-type stars. II. S
stars and their properties
Authors: Van Eck, Sophie; Neyskens, Pieter; Jorissen, Alain; Plez,
Bertrand; Edvardsson, Bengt; Eriksson, Kjell; Gustafsson, Bengt;
Jørgensen, Uffe Gråe; Nordlund, Åke
Bibcode: 2017A&A...601A..10V
Altcode:
S-type stars are late-type giants whose atmospheres are enriched in
carbon and s-process elements because of either extrinsic pollution
by a binary companion or intrinsic nucleosynthesis and dredge-up on
the thermally-pulsing asymptotic giant branch. A grid of MARCS model
atmospheres has been computed for S stars, covering the range 2700 ≤
Teff(K) ≤ 4000, 0.50 ≤ C/O ≤ 0.99, 0 ≤ log g ≤ 5,
[Fe/H] = 0., -0.5 dex, and [s/Fe] = 0, 1, and 2 dex (where the latter
quantity refers to the global overabundance of s-process elements). The
MARCS models make use of a new ZrO line list. Synthetic spectra
computed from these models are used to derive photometric indices in
the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A
method is proposed to select the model best matching any given S star,
a non-trivial operation since the grid contains more than 3500 models
covering a five-dimensional parameter space. The method is based on
the comparison between observed and synthetic photometric indices and
spectral band strengths, and has been applied on a vast subsample of
the Henize sample of S stars. Our results confirm the old claim by
Piccirillo (1980, MNRAS, 190, 441) that ZrO bands in warm S stars
(Teff>3200 K) are not caused by the C/O ratio being
close to unity, as traditionally believed, but rather by some Zr
overabundance. The TiO and ZrO band strengths, combined with V-K and
J-K photometric indices, are used to select Teff, C/O, [Fe/H]
and [s/Fe]. The Geneva U-B1 and B2-V1
indices (or any equivalent) are good at selecting the gravity. The
defining spectral features of dwarf S stars are outlined, but none is
found among the Henize S stars. More generally, it is found that, at
Teff = 3200 K, a change of C/O from 0.5 to 0.99 has a strong
impact on V-K (2 mag). Conversely, a range of 2 mag in V-K corresponds
to a 200 K shift along the (Teff, V-K) relationship
(for a fixed C/O value). Hence, the use of a (Teff, V-K)
calibration established for M stars will yield large errors for S stars,
so that a specific calibration must be used, as provided in the present
paper. Using the atmospheric parameters derived by our method for the
sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy
among S stars reveals itself very clearly as a bimodal distribution in
the effective temperatures. Moreover, the increase of s-process element
abundances with increasing C/O ratios and decreasing temperatures is
apparent among intrinsic stars, confirming theoretical expectations. Based on observations carried out at the European Southern Observatory
(ESO, La Silla, Chile; program 58.E-0942), on the Swiss 70 cm telescope
(La Silla, Chile) and on the Mercator telescope (La Palma, Spain).The
MARCS S star model atmospheres will be archived on the MARCS website:
http://marcs.astro.uu.seFull
Tables 2 and 3 are only available at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A10
Title: Aperture synthesis imaging of the carbon AGB star R
Sculptoris. Detection of a complex structure and a dominating spot
on the stellar disk
Authors: Wittkowski, M.; Hofmann, K. -H.; Höfner, S.; Le Bouquin,
J. B.; Nowotny, W.; Paladini, C.; Young, J.; Berger, J. -P.; Brunner,
M.; de Gregorio-Monsalvo, I.; Eriksson, K.; Hron, J.; Humphreys,
E. M. L.; Lindqvist, M.; Maercker, M.; Mohamed, S.; Olofsson, H.;
Ramstedt, S.; Weigelt, G.
Bibcode: 2017A&A...601A...3W
Altcode: 2017arXiv170202574W
Aims: We present near-infrared interferometry of the carbon-rich
asymptotic giant branch (AGB) star R Sculptoris (R Scl).
Methods:
We employ medium spectral resolution K-band interferometry obtained with
the instrument AMBER at the Very Large Telescope Interferometer (VLTI)
and H-band low spectral resolution interferometric imaging observations
obtained with the VLTI instrument PIONIER. We compare our data to a
recent grid of dynamic atmosphere and wind models. We compare derived
fundamental parameters to stellar evolution models.
Results:
The visibility data indicate a broadly circular resolved stellar disk
with a complex substructure. The observed AMBER squared visibility
values show drops at the positions of CO and CN bands, indicating that
these lines form in extended layers above the photosphere. The AMBER
visibility values are best fit by a model without a wind. The PIONIER
data are consistent with the same model. We obtain a Rosseland angular
diameter of 8.9 ± 0.3 mas, corresponding to a Rosseland radius of 355
± 55 R⊙, an effective temperature of 2640 ± 80 K, and a
luminosity of log L/L⊙ = 3.74 ± 0.18. These parameters
match evolutionary tracks of initial mass 1.5 ± 0.5 M⊙
and current mass 1.3 ± 0.7 M⊙. The reconstructed PIONIER
images exhibit a complex structure within the stellar disk including
a dominant bright spot located at the western part of the stellar
disk. The spot has an H-band peak intensity of 40% to 60% above the
average intensity of the limb-darkening-corrected stellar disk. The
contrast between the minimum and maximum intensity on the stellar
disk is about 1:2.5.
Conclusions: Our observations are broadly
consistent with predictions by dynamic atmosphere and wind models,
although models with wind appear to have a circumstellar envelope
that is too extended compared to our observations. The detected
complex structure within the stellar disk is most likely caused by
giant convection cells, resulting in large-scale shock fronts, and
their effects on clumpy molecule and dust formation seen against
the photosphere at distances of 2-3 stellar radii. Based on
observations made with the VLT Interferometry (VLTI) at Paranal
Observatory under programme IDs 090.D-0136, 093.D-0015, 096.D-0720.
Title: The adventure of carbon stars. Observations and modeling of
a set of C-rich AGB stars
Authors: Rau, G.; Hron, J.; Paladini, C.; Aringer, B.; Eriksson, K.;
Marigo, P.; Nowotny, W.; Grellmann, R.
Bibcode: 2017A&A...600A..92R
Altcode: 2017arXiv170104331R
Context. Modeling stellar atmospheres is a complex and intriguing
task in modern astronomy. A systematic comparison of models with
multi-technique observations is the only efficient way to constrain
the models.
Aims: We intend to perform self-consistent
modeling of the atmospheres of six carbon-rich AGB stars (R
Lep, R Vol, Y Pav,
AQ Sgr, U Hya, and X
TrA) with the aim of enlarging the knowledge of the
dynamic processes occurring in their atmospheres.
Methods:
We used VLTI/MIDI interferometric observations, in combination with
spectro-photometric data, and compared them with self-consistent,
dynamic model atmospheres.
Results: We found that the models can
reproduce spectral energy distribution (SED) data well at wavelengths
longer than 1 μm, and the interferometric observations between 8 μm
and 10 μm. Discrepancies observed at wavelengths shorter than 1 μm in
the SED, and longer than 10 μm in the visibilities, could be due to a
combination of data- and model-related effects. The models best fitting
the Miras are significantly extended, and have a prominent shell-like
structure. On the contrary, the models best fitting the non-Miras are
more compact, showing lower average mass loss. The mass loss is of
episodic or multi-periodic nature but causes the visual amplitudes to
be notably larger than the observed ones. A number of stellar parameters
were derived from the model fitting: TRoss, LRoss,
M, C/O, and Ṁ. Our findings agree well with literature values within
the uncertainties. TRoss, and LRoss are also in
good agreement with the temperature derived from the angular diameter
T(θ(V-K)) and the bolometric luminosity from the SED fitting
Lbol, except for AQ Sgr. The possible reasons are discussed
in the text. Finally, θRoss and θ(V-K) agree
with one another better for the Miras than for the non-Miras targets,
which is probably connected to the episodic nature of the latter
models. We also located the stars in the H-R diagram, comparing them
with evolutionary tracks. We found that the main derived properties (L,
Teff, C/O ratios and stellar masses) from the model fitting
are in good agreement with TP-AGB evolutionary calculations for carbon
stars carried out with the COLIBRI code. Based on observations made
with ESO telescopes at La Silla Paranal Observatory under program IDs:
090.D-0410, 086.D-899, 187.D-0924, 081.D-0021, 086.D-0899.
Title: Abundances of disk and bulge giants from high-resolution
optical spectra. I. O, Mg, Ca, and Ti in the solar neighborhood and
Kepler field samples
Authors: Jönsson, H.; Ryde, N.; Nordlander, T.; Pehlivan Rhodin,
A.; Hartman, H.; Jönsson, P.; Eriksson, K.
Bibcode: 2017A&A...598A.100J
Altcode: 2016arXiv161105462J
Context. The Galactic bulge is an intriguing and significant part
of our Galaxy, but it is hard to observe because it is both distant
and covered by dust in the disk. Therefore, there are not many
high-resolution optical spectra of bulge stars with large wavelength
coverage, whose determined abundances can be compared with nearby,
similarly analyzed stellar samples.
Aims: We aim to determine
the diagnostically important alpha elements of a sample of bulge
giants using high-resolution optical spectra with large wavelength
coverage. The abundances found are compared to similarly derived
abundances from similar spectra of similar stars in the local thin and
thick disks. In this first paper we focus on the solar neighborhood
reference sample.
Methods: We used spectral synthesis to derive
the stellar parameters as well as the elemental abundances of both the
local and bulge samples of giants. We took special care to benchmark
our method of determining stellar parameters against independent
measurements of effective temperatures from angular diameter
measurements and surface gravities from asteroseismology.
Results: In this first paper we present the method used to determine
the stellar parameters and elemental abundances, evaluate them, and
present the results for our local disk sample of 291 giants.
Conclusions: When comparing our determined spectroscopic temperatures
to those derived from angular diameter measurements, we reproduce
these with a systematic difference of +10 K and a standard deviation
of 53 K. The spectroscopic gravities reproduce those determined from
asteroseismology with a systematic offset of +0.10 dex and a standard
deviation of 0.12 dex. When it comes to the abundance trends, our
sample of local disk giants closely follows trends found in other works
analyzing solar neighborhood dwarfs, showing that the much brighter
giant stars are as good abundance probes as the often used dwarfs. Based on observations made with the Nordic Optical Telescope (programs
51-018 and 53-002), operated by the Nordic Optical Telescope Scientific
Association at the Observatorio del Roque de los Muchachos, La Palma,
Spain, of the Instituto de Astrofisica de Canarias, and on spectral
data retrieved from PolarBase at Observatoire Midi Pyrénées.Full
Tables A.1 and A.3 are only available at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A100
Title: VizieR Online Data Catalog: A grid of MARCS model atmospheres
for S stars (Van Eck+, 2017)
Authors: van Eck, S.; Neyskens, P.; Jorissen, A.; Plez, B.; Edvardsson,
B.; Eriksson, K.; Gustafsson, B.; Jorgensen, U. G.; Nordlund, A.
Bibcode: 2017yCat..36010010V
Altcode:
Johnson and Geneva (G) photometric indices and band indices measured
on the observed Henize S stars. (3 data files).
Title: Observational constraints for C-rich AGB stars
Authors: Rau, G.; Hron, J.; Paladini, C.; Aringer, B.; Marigo, P.;
Eriksson, K.
Bibcode: 2017MmSAI..88..455R
Altcode:
We modeled the atmospheres of six carbon-rich Asymptotic Giant Branch
stars (R Lep, R Vol, Y
Pav, AQ Sgr, U Hya,
and X TrA) using VLTI/MIDI interferometric
observations, together with spectro-photometric data, we compared
them with self-consistent, dynamic model atmospheres. The results show
that the models can reproduce the Spectral Energy Distribution (SED)
data well at wavelengths longer than 1 mu m, and the interferometric
observations between 8 mu m and 10 mu m. We found differences at
wavelengths shorter than 1 mu m in the SED, and longer than 10 mu m
in the visibilities. The discrepancies observed can be explained in
terms of a combination of data- and model-related reasons. We derived
some stellar parameters, and our findings agree well with literature
values within the uncertainties. Also, when comparing the location of
the stars in the H-R diagram, with evolutionary tracks, the results
show that the main derived properties (L, Teff, C/O ratios
and stellar masses) from the model fitting are in good agreement with
TP-AGB evolutionary calculations.
Title: VizieR Online Data Catalog: Abundances of disk giants: O,
Mg, Ca and Ti (Jonsson+, 2017)
Authors: Jonsson, H.; Ryde, N.; Nordlander, T.; Pehlivan Rhodin, A.;
Hartman, H.; Jonsson, P.; Eriksson, K.
Bibcode: 2016yCat..35980100J
Altcode:
Spectroscopic stellar parameters and oxygen, magnesium, calcium, and
titanium abundances for 291 local disk giants are presented. Spectra
from observations with the spectrometer FIES at NOT, and from archives
(FIES and PolarBase) are used. The FIES spectra have R=67000 and the
ones from PolarBase have R=67000. In general most stars are very bright
and have S/N around 100. (2 data files).
Title: Future Directions In The Study Of Asymptotic Giant Branch
Stars With The James Webb Space Telescope
Authors: Hjort, Adam; Zackrisson, Erik; Eriksson, Kjell
Bibcode: 2016csss.confE..40H
Altcode:
In this study we present photometric predictions for C-type Asymptotic
Giant Branch Stars (AGB) stars from Eriks- son et al. (2014) for the
James Webb Space Telescope (JWST) and the Wide- eld Infrared Survey
Explorer (WISE) instruments. The photometric predictions we have done
are for JWST's general purpose wide-band lters on NIR- Cam and MIRI
covering wavelengths of 0.7 — 21 microns. AGB stars contribute
substantially to the integrated light of intermediate-age stellar
popula- tions and is a substantial source of the metals (especially
carbon) in galaxies. Studies of AGB stars are (among other reasons)
important for the understanding of the chemical evolution and dust cycle
of galaxies. Since the JWST is scheduled for launch in 2018 it should be
a high priority to prepare observing strategies. With these predictions
we hope it will be possible to optimize observing strategies of AGB
stars and max- imize the science return of JWST. By testing our method
on Whitelock et al. (2006) objects from the WISE catalog and comparing
them with our photometric results based on Eriksson et al. (2014)
we have been able to fit 20 objects with models. The photometric data
set can be accessed at: http://www.astro.uu.se/AGBmodels/ABmags/
Title: The Dynamic Atmospheres of Carbon Rich Giants: Constraining
Models Via Interferometry
Authors: Rau, Gioia; Hron, Josef; Paladini, Claudia; Aringer, Bernard;
Eriksson, Kjell; Marigo, Paola
Bibcode: 2016csss.confE.111R
Altcode:
Dynamic models for the atmospheres of C-rich Asymptotic Giant
Branch stars are quite advanced and have been overall successful in
reproducing spectroscopic and photometric observations. Interferometry
provides independent information and is thus an important technique
to study the atmospheric stratification and to further constrain the
dynamic models. We observed a sample of six C-rich AGBs with the mid
infrared interferometer VLTI/MIDI. These observations, combined with
photometric and spectroscopic data from the literature, are compared
with synthetic observables derived from dynamic model atmospheres (DMA,
Eriksson et al. 2014). The SEDs can be reasonably well modelled and the
interferometry supports the extended and multi-component structure of
the atmospheres, but some differences remain. We discuss the possible
reasons for these differences and we compare the stellar parameters
derived from this comparison with stellar evolution models. Finally,
we point out the high potential of MATISSE, the second generation VLTI
instrument allowing interferometric imaging in the L, M, and N bands,
for further progress in this field.
Title: Modelling a Set of Carbon-Rich AGB Stars at High-Angular
Resolution
Authors: Rau, Gioia; Hron, Josef; Paladini, Claudia; Aringer, Bernard;
Eriksson, Kjell; Marigo, Paola; Nowotny, Walter; Grellmann, Rebekka
Bibcode: 2016csss.confE.110R
Altcode:
We compared spectro-photometric and interferometric observations
of six carbon-rich AGB stars with a grid of self-consistentmodel
atmospheres. The targets are: R Lep, R Vol, Y Pav, AQ Sgr, U Hya and
X TrA. Please refer to the publication Rau et al. 2016(subm.) for
further details on those findings.
Title: Dust-driven winds of AGB stars: The critical interplay of
atmospheric shocks and luminosity variations
Authors: Liljegren, S.; Höfner, S.; Nowotny, W.; Eriksson, K.
Bibcode: 2016A&A...589A.130L
Altcode: 2016arXiv160306735L
Context. Winds of AGB stars are thought to be driven by a combination
of pulsation-induced shock waves and radiation pressure on dust. In
dynamic atmosphere and wind models, the stellar pulsation is often
simulated by prescribing a simple sinusoidal variation in velocity and
luminosity at the inner boundary of the model atmosphere.
Aims:
We experiment with different forms of the luminosity variation in order
to assess the effects on the wind velocity and mass-loss rate, when
progressing from the simple sinusoidal recipe towards more realistic
descriptions. This will also give an indication of how robust the
wind properties derived from the dynamic atmosphere models are.
Methods: Using state-of-the-art dynamical models of C-rich AGB stars,
a range of different asymmetric shapes of the luminosity variation
and a range of phase shifts of the luminosity variation relative to
the radial variation are tested. These tests are performed on two
stellar atmosphere models. The first model has dust condensation and,
as a consequence, a stellar wind is triggered, while the second model
lacks both dust and wind.
Results: The first model with dust and
stellar wind is very sensitive to moderate changes in the luminosity
variation. There is a complex relationship between the luminosity
minimum, and dust condensation: changing the phase corresponding to
minimum luminosity can either increase or decrease mass-loss rate and
wind velocity. The luminosity maximum dominates the radiative pressure
on the dust, which in turn, is important for driving the wind. An
earlier occurrence of the maximum, with respect to the propagation of
the pulsation-induced shock wave, then increases the wind velocity,
while a later occurrence leads to a decrease. These effects of changed
luminosity variation are coupled with the dust formation. In contrast
there is very little change to the structure of the model without
dust.
Conclusions: Changing the luminosity variation, both
by introducing a phase shift and by modifying the shape, influences
wind velocity and the mass-loss rate. To improve wind models it would
probably be desirable to extract boundary conditions from 3D dynamical
interior models or stellar pulsation models.
Title: The Carbon Stars Adventure
Authors: Rau, Gioia; Paladini, C.; Hron, J.; Aringer, B.; Eriksson,
K.; Groenewegen, M. A. T.; Nowotny, W.
Bibcode: 2016IAUFM..29B.160R
Altcode:
We compare in a systematic way spectrometric, photometric and
mid-infrared (VLTI/MIDI) interferometric measurements with different
types of model atmospheres. Self-consistent dynamic model atmospheres
in particular were used to interpret in a consistent way the dynamic
behavior of gas and dust. The results underline how the joint use
of different kind of observations, as photometry, spectroscopy and
interferometry, is essential to understand the atmospheres of pulsating
C-rich AGB stars. The sample of C-rich stars discussed in this work
provides crucial constraints for the atmospheric structure.
Title: A New Library of Synthetic Spectra and Photometry for Evolved
C Stars
Authors: Eriksson, K.; Nowotny, W.; Höfner, S.; Aringer, B.
Bibcode: 2015ASPC..497..111E
Altcode:
We present a library of synthetic spectra and photometry calculated
on the basis of a grid of atmosphere and wind models for carbon-rich,
pulsating AGB stars. The spectra cover the range between 0.35 and 25
μm with a spectral resolution of R = 200. The corresponding photometric
variations during several pulsation periods were computed for standard
broadband filters in the visual and near-infrared.
Title: Evolved Stars with Complex Atmospheres - the High Spectral
Resolution, mid-IR View
Authors: Ryde, N.; Lambert, J.; Richter, M. J.; Josselin, E.; Harper,
G. M.; Eriksson, K.; Boogert, A.; DeWitt, C.; Encrenaz, T.; Greathouse,
T.; Jaffe, D.; Kulas, K.; McKelvey, M.; Najita, J.; Vacca, W.
Bibcode: 2015ASPC..497...67R
Altcode: 2014arXiv1408.6055R
The physical structures of the outer atmospheres of red giants are not
known. They are certainly complex, and a range of recent observations
are showing that we need to embrace non-classical model atmospheres to
interpret these regions. This region's properties are of importance,
not the least for an understanding of the mass-loss mechanism for these
stars. Here we present observational constraints on the outer regions
of red giants, based on mid-IR, high spectral resolution spectra. We
also discuss possible non-LTE effects and highlight a new non-LTE
code that will be used to analyse the spectra of these atmospheric
layers. We conclude by mentioning our new SOFIA/EXES observations
of red giants at 6 μm, where the vibration-rotation lines of water
vapour can be detected and spectrally resolved for the first time.
Title: Into the Modelling of RU Vir
Authors: Rau, G.; Hron, J.; Paladini, C.; Eriksson, K.; Aringer, B.;
Groenewegen, M. A. T.; Mečina, M.
Bibcode: 2015ASPC..497..137R
Altcode:
We present an attempt to model the atmosphere of the carbon-rich Mira
star RU Vir, using different techniques including spectroscopy,
photometry, and interferometry. A radiative transfer code and
hydrostatic model atmospheres were used for a preliminary study. To
investigate the dynamic processes happening in RU Vir, dynamic model
atmospheres were compared to new MIDI/VLTI observations obtained in
April 2014, and SiC opacities were added.
Title: Winds of AGB Stars - The Role of Stellar Pulsation
Authors: Liljegren, S.; Höfner, S.; Eriksson, K.
Bibcode: 2015ASPC..497..127L
Altcode:
Changing the stellar pulsation properties has large impact on the
behavior of the atmosphere of C-type AGB stars. This relationship
is examined.
Title: Exploring Mass-Loss in M-type AGB Stars
Authors: Bladh, S.; Höfner, S.; Aringer, B.; Eriksson, K.
Bibcode: 2015ASPC..497..345B
Altcode:
Stellar winds observed in asymptotic giant branch (AGB) stars are
usually attributed to a combination of stellar pulsations and radiation
pressure on dust. Strong candidates for wind-driving dust species in
M-type AGB stars are magnesium silicates (Mg2SiO4
and MgSiO3). Such grains can form close to the stellar
surface; they consist of abundant materials and, if they grow to
sizes comparable to the wavelength of the stellar flux maximum,
they experience strong acceleration by photon scattering. Here we
present results from an extensive set of time-dependent wind models
for M-type AGB stars with a detailed description for the growth
of Mg2SiO4 grains. We show that these models
reproduce observed mass-loss rates and wind velocities, as well as
visual and near-IR photometry. However, the current models do not
show the characteristic silicate features at 10 and 18 μm, due to a
rapidly falling temperature of Mg2SiO4 grains
in the wind. Including a small amount of Fe in the grains further out
in the circumstellar envelope will increase the grain temperature and
result in pronounced silicate features, without significantly affecting
the photometry in the visual and near-IR.
Title: Exploring wind-driving dust species in cool luminous
giants. III. Wind models for M-type AGB stars: dynamic and photometric
properties
Authors: Bladh, S.; Höfner, S.; Aringer, B.; Eriksson, K.
Bibcode: 2015A&A...575A.105B
Altcode: 2015arXiv150200032B
Context. Stellar winds observed in asymptotic giant branch (AGB)
stars are usually attributed to a combination of stellar pulsations
and radiation pressure on dust. Shock waves triggered by pulsations
propagate through the atmosphere, compressing the gas and lifting
it to cooler regions which creates favourable conditions for
grain growth. If sufficient radiative acceleration is exerted
on the newly formed grains through absorption or scattering of
stellar photons, an outflow can be triggered. Strong candidates for
wind-driving dust species in M-type AGB stars are magnesium silicates
(Mg2SiO4 and MgSiO3). Such grains
can form close to the stellar surface, they consist of abundant
materials and, if they grow to sizes comparable to the wavelength of
the stellar flux maximum, they experience strong acceleration by photon
scattering.
Aims: The purpose of this study is to investigate
if photon scattering on Mg2SiO4 grains can
produce realistic outflows for a wide range of stellar parameters
in M-type AGB stars.
Methods: We use a frequency-dependent
radiation-hydrodynamics code with a detailed description for the
growth of Mg2SiO4 grains to calculate the
first extensive set of time-dependent wind models for M-type AGB
stars. This set includes 139 solar-mass models, with three different
luminosities (5000 L⊙, 7000 L⊙, and 10 000
L⊙) and effective temperatures ranging from 2600 K to
3200 K. The resulting wind properties, visual and near-IR photometry
and mid-IR spectra are compared with observations.
Results:
We show that the models can produce outflows for a wide range of
stellar parameters. We also demonstrate that they reproduce observed
mass-loss rates and wind velocities, as well as visual and near-IR
photometry. However, the current models do not show the characteristic
silicate features at 10 and 18 μm as a result of the cool temperature
of Mg2SiO4 grains in the wind. Including a small
amount of Fe in the grains further out in the circumstellar envelope
will increase the grain temperature and result in pronounced silicate
features, without significantly affecting the photometry in the visual
and near-IR wavelength regions.
Conclusions: Outflows driven by
photon scattering on Mg2SiO4 grains are a viable
wind scenario for M-type AGB stars, given the success of the current
models in reproducing observed mass-loss rates, wind velocities, and
photometry. Both synthetic and observed photometry suggest that the
dusty envelopes of M-type AGB stars are quite transparent at visual
and near-IR wavelengths, otherwise the variations in visual flux would
not be dominated by molecular features.
Title: Systematic trend of water vapour absorption in red giant
atmospheres revealed by high resolution TEXES 12 μm spectra
Authors: Ryde, N.; Lambert, J.; Farzone, M.; Richter, M. J.; Josselin,
E.; Harper, G. M.; Eriksson, K.; Greathouse, T. K.
Bibcode: 2015A&A...573A..28R
Altcode: 2014arXiv1410.3999R
Context. The structures of the outer atmospheres of red giants are very
complex. Recent interpretations of a range of different observations
have led to contradictory views of these regions. It is clear, however,
that classical model photospheres are inadequate to describe the
nature of the outer atmospheres. The notion of large optically thick
molecular spheres around the stars (MOLspheres) has been invoked in
order to explain spectro-interferometric observations and low- and
high-resolution spectra. On the other hand high-resolution spectra in
the mid-IR do not easily fit into this picture because they rule out
any large sphere of water vapour in LTE surrounding red giants.
Aims: In order to approach a unified scenario for these outer regions
of red giants, more empirical evidence from different diagnostics are
needed. Our aim here is to investigate high-resolution, mid-IR spectra
for a range of red giants, spanning spectral types from early K to mid
M. We want to study how the pure rotational lines of water vapour change
with effective temperature, and whether we can find common properties
that can put new constraints on the modelling of these regions,
so that we can gain new insights.
Methods: We have recorded
mid-IR spectra at 12.2 - 12.4 μm at high spectral resolution of ten
well-studied bright red giants, with TEXES mounted on the IRTF on Mauna
Kea. These stars span effective temperatures from 3450 K to 4850 K.
Results: We find that all red giants in our study cooler than 4300 K,
spanning a wide range of effective temperatures (down to 3450 K), show
water absorption lines stronger than expected and none are detected
in emission, in line with what has been previously observed for a few
stars. The strengths of the lines vary smoothly with spectral type. We
identify several spectral features in the wavelength region that are
undoubtedly formed in the photosphere. From a study of water-line
ratios of the stars, we find that the excitation temperatures, in the
line-forming regions, are several hundred Kelvin lower than expected
from a classical photospheric model.
Conclusions: All stars in
our sample show several photospheric features in their 12 μm spectra,
which can be modelled with a classical model photosphere. However, in
all stars showing water-vapour lines (stars cooler than ~4300 K), the
water lines are found to be much deeper than expected. The line ratios
of these pure-rotational lines reveal low excitation temperatures. This
could either be due to lower temperatures than expected in the outer
regions of the photospheres caused by for example extra cooling,
or due to non-LTE level populations, affecting the source function
and line opacities, but this needs further investigation. We have
demonstrated that these diagnostically interesting water lines are
a general feature of red giants across spectral types, and we argue
for a general explanation of their formation rather than explanations
requiring specific properties, such as dust. Since the water lines are
neither weak (filled in by emission) nor do they appear in emission,
as predicted by LTE MOLsphere models in their simplest forms, the
evidence of the existence of such large optically-thick, molecular
spheres enshrouding the stars is weakened. It is still a challenge
to find a unifying picture of the outer regions of the atmospheres
of red giants, but we have presented new empirical evidence that
needs to be taken into account and explained in any model of
these regions. Table 4 is available in electronic form at http://www.aanda.org
Title: The Hamburg/ESO R-process Enhanced Star survey (HERES). X. HE
2252-4225, one more r-process enhanced and actinide-boost halo star
Authors: Mashonkina, L.; Christlieb, N.; Eriksson, K.
Bibcode: 2014A&A...569A..43M
Altcode: 2014arXiv1407.5379M
Context. Studies of the r-process enhanced stars are important for
understanding the nature and origin of the r-process better.
Aims: We present a detailed abundance analysis of a very metal-poor
giant star discovered in the HERES project, HE 2252-4225, which
exhibits overabundances of the r-process elements with [r/Fe]
= +0.80.
Methods: We determined the stellar atmosphere
parameters, Teff = 4710 K, log g = 1.65, and [ Fe/H ] =
-2.63, and chemical abundances by analysing the high-quality VLT/UVES
spectra. The surface gravity was calculated from the non-local
thermodynamic equilibrium (NLTE) ionisation balance between Fe i
and Fe ii.
Results: Accurate abundances for a total of 38
elements, including 22 neutron-capture elements beyond Sr and up
to Th, were determined in HE 2252-4225. For every chemical species,
the dispersion in the single line measurements around the mean does
not exceed 0.12 dex. This object is deficient in carbon, as expected
for a giant star with Teff < 4800 K. The stellar Na-Zn
abundances are well fitted by the yields of a single supernova of
14.4 M⊙. For the neutron-capture elements in the Sr-Ru,
Ba-Yb, and Os-Ir regions, the abundance pattern of HE 2252-4225 is in
excellent agreement with the average abundance pattern of the strongly
r-process enhanced stars CS 22892-052, CS 31082-001, HE 1219-0312,
and HE 1523-091. This suggests a common origin of the first, second,
and third r-process peak elements in HE 2252-4225 in the classical
r-process. We tested the solar r-process pattern based on the most
recent s-process calculations of Bisterzo, Travaglio, Gallino, Wiescher,
and Käppeler and found that elements in the range from Ba to Ir match
it very well. No firm conclusion can be drawn about the relationship
between the first neutron-capture peak elements, Sr to Ru, in HE
2252-4225 and the solar r-process, owing to the uncertainty in the
solar r-process. The investigated star has an anomalously high Th/Eu
abundance ratio, so that radioactive dating results in a stellar age
of τ = 1.5 ± 1.5 Gyr that is not expected for a very metal-poor
halo star. Based on observations collected at the European
Southern Observatory, Paranal, Chile (Proposal numbers 170.D-0010, and
280.D-5011).Table 3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/569/A43
Title: VizieR Online Data Catalog: HE 2252-4225 abundance analysis
(Mashonkina+, 2014)
Authors: Mashonkina, L.; Christlieb, N.; Eriksson, K.
Bibcode: 2014yCat..35690043M
Altcode: 2014yCat..35699043M
HE 2252-4225 was identified as a candidate metal-poor star in the
Hamburg/ESO Survey (HES), and it was included in the target list of the
Hamburg/ESO R-process-Enhanced Star survey (HERES, Christlieb et al.,
Paper I, 2004A&A...428.1027C). Stellar parameters, Teff=4708+-100K,
logg=1.53+/-0.24, and [Fe/H]=-2.83+/-0.12, were first determined
by Barklem et al. (Paper II. Cat. J/A+A/439/129) based on automated
abundance analysis of high-resolution "snapshot" spectra. The photometry
was taken from Beers et al. (2007, Cat. J/ApJS/168/128). High-quality
spectra of this star was acquired during May-September 2005 with the
VLT and UVES in dichroic mode. The BLUE390+RED580 (9h total integration
time) and BLUE437+RED860 (10h) standard settings were employed to
ensure a wide wavelength coverage. (2 data files).
Title: Synthetic photometry for carbon-rich giants. IV. An extensive
grid of dynamic atmosphere and wind models
Authors: Eriksson, K.; Nowotny, W.; Höfner, S.; Aringer, B.;
Wachter, A.
Bibcode: 2014A&A...566A..95E
Altcode: 2014arXiv1404.7515E
Context. The evolution and spectral properties of stars on the
asymptotic giant branch (AGB) are significantly affected by mass
loss through dusty stellar winds. Dynamic atmosphere and wind
models are an essential tool for studying these evolved stars, both
individually and as members of stellar populations, to understand
their contribution to the integrated light and chemical evolution
of galaxies.
Aims: This paper is part of a series with the
purpose of testing state-of-the-art atmosphere and wind models of
C-type AGB stars against observations, and making them available
to the community for use in various theoretical and observational
studies.
Methods: We have computed low-resolution spectra and
photometry (in the wavelength range 0.35-25 μm) for a grid of 540
dynamic models with stellar parameters typical of solar-metallicity
C-rich AGB stars and with a range of pulsation amplitudes. The models
cover the dynamic atmosphere and dusty outflow (if present), assuming
spherical symmetry, and taking opacities of gas-phase species and dust
grains consistently into account. To characterize the time-dependent
dynamic and photometric behaviour of the models in a concise way we
defined a number of classes for models with and without winds.
Results: Comparisons with observed data in general show a quite
satisfactory agreement for example regarding mass-loss rates vs. (J -
K) colours or K magnitudes vs. (J - K) colours. Some exceptions from
the good overall agreement, however, are found and attributed to
the range of input parameters (e.g. relatively high carbon excesses)
or intrinsic model assumptions (e.g. small particle limit for grain
opacities).
Conclusions: While current results indicate
that some changes in model assumptions and parameter ranges should
be made in the future to bring certain synthetic observables into
better agreement with observations, it seems unlikely that these
pending improvements will significantly affect the mass-loss rates
of the models. Appendices are available in electronic form at http://www.aanda.orgTable
B.1, photometry, and spectra for all snapshots are available from http://www.astro.uu.se/AGBmodels
and also at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/566/A95
Title: Chemical evolution of fluorine in the bulge. High-resolution
K-band spectra of giants in three fields
Authors: Jönsson, H.; Ryde, N.; Harper, G. M.; Cunha, K.; Schultheis,
M.; Eriksson, K.; Kobayashi, C.; Smith, V. V.; Zoccali, M.
Bibcode: 2014A&A...564A.122J
Altcode: 2014arXiv1403.2594J
Context. Possible main formation sites of fluorine in the Universe
include asymptotic giant branch (AGB) stars, the ν-process in Type II
supernova, and/or Wolf-Rayet stars. The importance of the Wolf-Rayet
stars has theoretically been questioned and they are probably not
needed in modeling the chemical evolution of fluorine in the solar
neighborhood. It has, however, been suggested that Wolf-Rayet stars
are indeed needed to explain the chemical evolution of fluorine in the
bulge. The molecular spectral data, needed to determine the fluorine
abundance, of the often used HF-molecule has not been presented
in a complete and consistent way and has recently been debated in
the literature.
Aims: We intend to determine the trend of
the fluorine-oxygen abundance ratio as a function of a metallicity
indicator in the bulge to investigate the possible contribution from
Wolf-Rayet stars. Additionally, we present here a consistent HF line
list for the K- and L-bands including the often used 23 358.33 Å
line.
Methods: High-resolution near-infrared spectra of eight
K giants were recorded using the spectrograph CRIRES mounted at the
VLT. A standard setting was used that covered the HF molecular line at
23 358.33 Å. The fluorine abundances were determined using spectral
fitting. We also re-analyzed five previously published bulge giants
observed with the Phoenix spectrograph on Gemini using our new HF
molecular data.
Results: We find that the fluorine-oxygen
abundance in the bulge probably cannot be explained with chemical
evolution models that only include AGB stars and the ν-process
in supernovae Type II, that is a significant amount of fluorine
production in Wolf-Rayet stars is most likely needed to explain the
fluorine abundance in the bulge. For the HF line data, we find that a
possible reason for the inconsistencies in the literature, where two
different excitation energies were used, is two different definitions
of the zero-point energy for the HF molecule and therefore also two
accompanying different dissociation energies. Both line lists are
correct as long as the corresponding consistent partition function is
used in the spectral synthesis. However, we suspect this has not been
the case in several earlier works, which led to fluorine abundances
~0.3 dex too high. We present a line list for the K- and L-bands and an
accompanying partition function. Based on observations collected
at the European Southern Observatory, Chile (ESO programs 71.B-0617(A),
073.B0074(A), and 079.B-0338(A)) and observations obtained at the Gemini
Observatory, which is operated by the Association of Universities
for Research in Astronomy, Inc., under a cooperative agreement with
the NSF on behalf of the Gemini partnership: the National Science
Foundation (United States), the National Research Council (Canada),
CONICYT (Chile), the Australian Research Council (Australia), CNPq
(Brazil), and CONICRT (Argentina), as program GS-2004A-Q-20.Figure
4 and Tables 5 and 6 are available in electronic form at http://www.aanda.org
Title: VizieR Online Data Catalog: C-rich giants synthetic
spectrophotometry. IV (Eriksson+, 2014)
Authors: Eriksson, K.; Nowotny, W.; Hofner, S.; Aringer, B.;
Wachter, A.
Bibcode: 2014yCat..35660095E
Altcode: 2014yCat..35669095E
For each model there are a number of files with photometry data,
one for each epoch, and there are up to five different epochs per
model, typically two epochs. Each of these files contains photometry
data for at least two pulsation periods. The files are in the
following format: Byte-by-byte Description of file: DMAfilters/*/*
------------------------------------------------------------------------------
Bytes Format Units Label Explanations
------------------------------------------------------------------------------
3- 8 F6.3 mag Bmag Synthetic Johnson-Cousins B magnitude (1) 11-
16 F6.3 mag Vmag Synthetic Johnson-Cousins V magnitude (1) 19-
24 F6.3 mag Rmag Synthetic Johnson-Cousins Rc magnitude (1) 27-
32 F6.3 mag Imag Synthetic Johnson-Cousins I magnitude (1) 35-
40 F6.3 mag Jmag Synthetic Johnson-Glass J magnitude (1) 43- 48
F6.3 mag Hmag Synthetic Johnson-Glass H magnitude (1) 51- 56 F6.3
mag Kmag Synthetic Johnson-Glass K magnitude (1) 58- 64 F7.3 mag
Lmag Synthetic Johnson-Glass L magnitude (1) 66- 72 F7.3 mag L'mag
Synthetic Johnson-Glass L' magnitude (1) 74- 80 F7.3 mag Mmag Synthetic
Johnson-Glass M magnitude (1) 83- 88 F6.3 mag J2mag Synthetic 2MASS
J magnitude 91- 96 F6.3 mag H2mag Synthetic 2MASS H magnitude 99-104
F6.3 mag Ks2mag Synthetic 2MASS Ks magnitude 107-112 F6.3 --- Phase
Pulsational phase, with luminosity maxima at 0.0, 1.0 etc. 115-120
I6 --- Snapshot Snapshot identification number (timestep number)
------------------------------------------------------------------------------
Note (1): B,V,R,I; see Bessell 1990PASP..102.1181B),
and in the Johnson-Glass (J, H, K, L, L',
M; see Bessell and Brett 1988PASP..100.1134B)
------------------------------------------------------------------------------
(4 data files).
Title: Detailed near-IR stellar abundances of red giants in the Bulge
Authors: Ryde, N.; Jönsson, H.; Schultheis, M.; Matteucci, F.;
Harper, G. M.; Cunha, K.; Eriksson, K.; Kobayashi, C.; Smith, V. V.;
Zoccali, M.
Bibcode: 2014fegb.confE..12R
Altcode:
No abstract at ADS
Title: Fundamental parameters of 16 late-type stars derived from
their angular diameter measured with VLTI/AMBER
Authors: Cruzalèbes, P.; Jorissen, A.; Rabbia, Y.; Sacuto, S.;
Chiavassa, A.; Pasquato, E.; Plez, B.; Eriksson, K.; Spang, A.;
Chesneau, O.
Bibcode: 2013MNRAS.434..437C
Altcode: 2013arXiv1306.3288C; 2013MNRAS.tmp.1678C
Thanks to their large angular dimension and brightness, red giants
and supergiants are privileged targets for optical long-baseline
interferometers. 16 red giants and supergiants have been observed
with the VLTI/AMBER facility over a 2-year period, at medium spectral
resolution (R=1500) in the K band. The limb-darkened angular diameters
are derived from fits of stellar atmospheric models on the visibility
and the triple product data. The angular diameters do not show any
significant temporal variation, except for one target: TX Psc, which
shows a variation of 4 per cent using visibility data. For the eight
targets previously measured by long-baseline interferometry (LBI)
in the same spectral range, the difference between our diameters and
the literature values is less than 5 per cent, except for TX Psc,
which shows a difference of 11 per cent. For the eight other targets,
the present angular diameters are the first measured from LBI. Angular
diameters are then used to determine several fundamental stellar
parameters, and to locate these targets in the Hertzsprung-Russell
diagram (HRD). Except for the enigmatic Tc-poor low-mass carbon star W
Ori, the location of Tc-rich stars in the HRD matches remarkably well
the thermally-pulsating asymptotic giant branch, as it is predicted
by the stellar evolution models. For pulsating stars with periods
available, we compute the pulsation constant and locate the stars along
the various sequences in the period-luminosity diagram. We confirm
the increase in mass along the pulsation sequences, as predicted by
theory, except for W Ori which, despite being less massive, appears
to have a longer period than T Cet along the first-overtone sequence.
Title: Exploring wind-driving dust species in cool luminous
giants. II. Constraints from photometry of M-type AGB stars
Authors: Bladh, S.; Höfner, S.; Nowotny, W.; Aringer, B.; Eriksson, K.
Bibcode: 2013A&A...553A..20B
Altcode: 2013arXiv1302.6572B
Context. The heavy mass loss observed in evolved asymptotic giant
branch (AGB) stars is usually attributed to a two-stage process:
atmospheric levitation by pulsation-induced shock waves, followed
by radiative acceleration of newly formed dust grains. The dust
transfers momentum to the surrounding gas through collisions and
thereby triggers a general outflow. Radiation-hydrodynamical models
of M-type AGB stars suggest that these winds can be driven by photon
scattering - in contrast to absorption - on Fe-free silicate grains
of sizes 0.1-1 μm.
Aims: In this paper we study photometric
constraints for wind-driving dust species in M-type AGB stars, as part
of an ongoing effort to identify likely candidates among the grain
materials observed in circumstellar envelopes.
Methods: To
investigate the scenario of stellar winds driven by photon scattering
on dust, and to explore how different optical and chemical properties
of wind-driving dust species affect photometry we focus on two sets of
dynamical models atmospheres: (i) models using a detailed description
for the growth of Mg2SiO4 grains, taking into
account both scattering and absorption cross-sections when calculating
the radiative acceleration; and (ii) models using a parameterized dust
description, constructed to represent different chemical and optical
dust properties. By comparing synthetic photometry from these two
sets of models to observations of M-type AGB stars we can provide
constraints on the properties of wind-driving dust species.
Results: Photometry from wind models with a detailed description for
the growth of Mg2SiO4 grains reproduces well
both the values and the time-dependent behavior of observations of
M-type AGB stars, providing further support for the scenario of winds
driven by photon scattering on dust. The photometry from the models
with a parameterized dust description suggests that wind-drivers need
to have a low absorption cross-section in the visual and near-IR to
reproduce the time-dependent behavior, i.e. small variations in (J - K)
and spanning a larger range in (V - K). This places constraints on the
optical and chemical properties of the wind-driving dust species.
Conclusions: To reproduce the observed photometric variations in (V -
K) and (J - K) both detailed and parameterized models suggest that the
wind-driving dust materials have to be quite transparent in the visual
and near-IR. Consequently, strong candidates for outflows driven by
photon scattering on dust grains are Mg2SiO4,
MgSiO3, and potentially SiO2.
Title: What is the Origin of the Water Vapour Signatures in Red
Giant Stars?
Authors: Farzone, M.; Ryde, N.; Harper, G. M.; Lambert, J.; Josselin,
E.; Richter, M. J.; Eriksson, K.
Bibcode: 2013EAS....60..155F
Altcode:
We investigate the occurrence of water vapour signatures in a total of
10 red giants in the solar neighbourhood at mid-infrared wavelengths
(12 μm). With the use of high resolution spectra from TEXES and
synthesized spectra based on MARCS model atmospheres, we analyse the
differences and discuss plausible causes. These include abundance
adjustments, the addition of non-photospheric components (MOLspheres)
and a different temperature profile.
Title: Synthetic photometry for carbon-rich giants. III. Tracing
the sequence of mass-losing galactic C-type Miras
Authors: Nowotny, W.; Aringer, B.; Höfner, S.; Eriksson, K.
Bibcode: 2013A&A...552A..20N
Altcode: 2013arXiv1302.3715N
Late-type giant stars in the evolutionary stage of the asymptotic giant
branch increasingly lose mass via comparatively slow but dense stellar
winds. Not only do these evolved red giants contribute in this way to
the enrichment of the surrounding interstellar medium, but the outflows
also have a substantial influence on the spectro-photometric appearance
of such objects. In the case of carbon-rich atmospheric chemistries,
the developing cool circumstellar envelopes contain dust grains mainly
composed of amorphous carbon. With increasing mass-loss rates, this
leads to more and more pronounced circumstellar reddening. With the
help of model calculations we aim at reproducing the observational
photometric findings for a large sample of well-characterised galactic
C-type Mira variables losing mass at different rates. We used dynamic
model atmospheres, describing the outer layers of C-rich Miras,
which are severly affected by dynamic effects. Based on the resulting
structures and under the assumptions of chemical equilibrium as well as
LTE, we computed synthetic spectra and synthetic broad-band photometry
(Johnson-Cousins-Glass BVRIJHKL'M). A set of five representative models
with different stellar parameters describes a sequence from less to
more evolved objects with steadily increasing mass-loss rates. This
allowed us to study the significant influence of circumstellar dust on
the spectral energy distributions and the (amplitudes of) lightcurves
in different filters. We tested the photometric properties (mean
NIR magnitudes, colours, and amplitudes) and other characteristics
of the models (mass-loss rates, periods, and bolometric corrections)
by comparing these with the corresponding observational data adopted
from the literature. Using different kinds of diagrams we illustrate
where the models are located in a supposed evolutionary sequence
defined by observed C-type Mira samples. Based on comparisons of
galactic targets with empirical relations derived for C stars in the
Large Magellanic Cloud we discuss the relevance of metallicity and
excess carbon (C-O) for the development of dust-driven winds. Having
investigated the dynamic model atmospheres from different (mainly
photometric) perspectives, we conclude that our modelling approach
(meaning the combination of numerical method and a suitable choice of
model parameters) is able to describe C-rich long-period variables over
a wide range of mass-loss rates, i.e., from moderately pulsating objects
without any dusty wind to highly dust-enshrouded Carbon Miras. Thus,
we can trace the observed sequence of C-type Miras, which is mainly
determined by the mass loss. Appendices are available in electronic
form at http://www.aanda.org
Title: The wind of the M-type AGB star RT Virginis
probed by VLTI/MIDI
Authors: Sacuto, S.; Ramstedt, S.; Höfner, S.; Olofsson, H.; Bladh,
S.; Eriksson, K.; Aringer, B.; Klotz, D.; Maercker, M.
Bibcode: 2013A&A...551A..72S
Altcode: 2013arXiv1301.5872S
Aims: We study the circumstellar environment of the M-type
AGB star RT Vir using mid-infrared high spatial
resolution observations from the ESO-VLTI focal instrument MIDI. The
aim of this study is to provide observational constraints on
theoretical prediction that the winds of M-type AGB objects can be
driven by photon scattering on iron-free silicate grains located in
the close environment (about 2 to 3 stellar radii) of the star.
Methods: We interpreted spectro-interferometric data, first using
wavelength-dependent geometric models. We then used a self-consistent
dynamic model atmosphere containing a time-dependent description
of grain growth for pure forsterite dust particles to reproduce
the photometric, spectrometric, and interferometric measurements of
RT Vir. Since the hydrodynamic computation needs
stellar parameters as input, a considerable effort was first made to
determine these parameters.
Results: MIDI differential phases
reveal the presence of an asymmetry in the stellar vicinity. Results
from the geometrical modeling give us clues to the presence of aluminum
and silicate dust in the close circumstellar environment (<5
stellar radii). Comparison between spectro-interferometric data and a
self-consistent dust-driven wind model reveals that silicate dust has
to be present in the region between 2 to 3 stellar radii to reproduce
the 59 and 63 m baseline visibility measurements around 9.8 μm. This
gives additional observational evidence in favor of winds driven by
photon scattering on iron-free silicate grains located in the close
vicinity of an M-type star. However, other sources of opacity are
clearly missing to reproduce the 10-13 μm visibility measurements
for all baselines.
Conclusions: This study is a first attempt
to understand the wind mechanism of M-type AGB stars by comparing
photometric, spectrometric, and interferometric measurements with
state-of-the-art, self-consistent dust-driven wind models. The agreement
of the dynamic model atmosphere with interferometric measurements in
the 8-10 μm spectral region gives additional observational evidence
that the winds of M-type stars can be driven by photon scattering on
iron-free silicate grains. Finally, a larger statistical study and
progress in advanced self-consistent 3D modeling are still required
to solve the remaining problems. Based on observations made with
the Very Large Telescope Interferometer at Paranal Observatory under
programs 083.D-0234 and 086.D-0737 (Open Time Observations).
Title: Comparative modelling of the spectra of cool giants⋆⋆⋆
Authors: Lebzelter, T.; Heiter, U.; Abia, C.; Eriksson, K.; Ireland,
M.; Neilson, H.; Nowotny, W.; Maldonado, J.; Merle, T.; Peterson,
R.; Plez, B.; Short, C. I.; Wahlgren, G. M.; Worley, C.; Aringer,
B.; Bladh, S.; de Laverny, P.; Goswami, A.; Mora, A.; Norris, R. P.;
Recio-Blanco, A.; Scholz, M.; Thévenin, F.; Tsuji, T.; Kordopatis,
G.; Montesinos, B.; Wing, R. F.
Bibcode: 2012A&A...547A.108L
Altcode: 2012arXiv1209.2656L
Context. Our ability to extract information from the spectra of stars
depends on reliable models of stellar atmospheres and appropriate
techniques for spectral synthesis. Various model codes and strategies
for the analysis of stellar spectra are available today.
Aims:
We aim to compare the results of deriving stellar parameters using
different atmosphere models and different analysis strategies. The
focus is set on high-resolution spectroscopy of cool giant stars.
Methods: Spectra representing four cool giant stars were made
available to various groups and individuals working in the area
of spectral synthesis, asking them to derive stellar parameters
from the data provided. The results were discussed at a workshop
in Vienna in 2010. Most of the major codes currently used in the
astronomical community for analyses of stellar spectra were included
in this experiment.
Results: We present the results from
the different groups, as well as an additional experiment comparing
the synthetic spectra produced by various codes for a given set of
stellar parameters. Similarities and differences of the results are
discussed.
Conclusions: Several valid approaches to analyze a
given spectrum of a star result in quite a wide range of solutions. The
main causes for the differences in parameters derived by different
groups seem to lie in the physical input data and in the details of the
analysis method. This clearly shows how far from a definitive abundance
analysis we still are. Based on observations obtained at the
Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées
Observatory, which is operated by the Institut National des Sciences
de l'Univers of the Centre National de la Recherche Scientifique
of France.Tables 6-11 are only available in electronic form at http://www.aanda.orgThe spectra of stars
1 to 4 used in the experiment presented here are only availalbe at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/547/A108
Title: VizieR Online Data Catalog: Comparative modelling of cool
giants spectra (Lebzelter+, 2012)
Authors: Lebzelter, T.; Heiter, U.; Abia, C.; Eriksson, K.; Ireland,
M.; Neilson, H.; Nowotny, W.; Maldonado, J.; Merle, T.; Peterson,
R.; Plez, B.; Short, C. I.; Wahlgren, G. M.; Worley, C.; Aringer,
B.; Bladh, S.; de Laverny, P.; Goswami, A.; Mora, A.; Norris, R. P.;
Recio-Blanco, A.; Scholz, M.; Thevenin, F.; Tsuji, T.; Kordopatis,
G.; Montesinos, B.; Wing, R. F.
Bibcode: 2012yCat..35470108L
Altcode: 2012yCat..35479108L
Spectra representing four cool giant stars were made available
to various groups and individuals working in the area of spectral
synthesis, asking them to derive stellar parameters from the data
provided. The results were discussed at a workshop in Vienna in
2010. Most of the major codes currently used in the astronomical
community for analyses of stellar spectra were included in this
experiment. The files contain the spectra in the same form as
they were made available to the experiment participants. The
spectra for Star 1 and Star 2 are on the heliocentric wavelength
scale (i.e. corrected for Earth motion, but not for stellar radial
velocity). The spectra are normalized to the continuum by an
automatic pipeline, which first divides the spectrum by a flat
field response function and then removes the overall slope of
the whole spectrum. These optical spectra also contain a number
of telluric lines. The spectra for Star 3 and Star 4 are on
the laboratory wavelength scale and the flux is normalized to the
continuum. They do not contain telluric lines. Additional
information which was provided to the experiment participants:
----------------------------------------------------------------
FileName Spectral resolution Signal-to-noise ratio
----------------------------------------------------------------
star1.dat 80000 463 at 871 nm star2.dat 80000 517
at 871 nm star3.dat 70000 125 star4.dat 70000 125
----------------------------------------------------------------
(10 data files).
Title: The Oxygen Abundance of the Ultra-metal-poor Star HE 0557-4840
Authors: Norris, John E.; Christlieb, N.; Bessell, M. S.; Asplund,
M.; Eriksson, K.; Korn, A. J.
Bibcode: 2012ApJ...753..150N
Altcode:
We present a high-resolution ultraviolet (UV) spectrum of the
ultra-metal-poor (UMP) carbon-enhanced red giant HE 0557-4840 (T
eff/log g/[Fe/H] = 4900/2.2/-4.8). Combining these data
with earlier observations, the radial velocity is 212.0 ± 0.4 km
s-1, with no evidence of variability during 2006 February
to 2007 December. One-dimensional (1D) LTE model-atmosphere analysis
of UV Fe and CH lines confirms the iron and carbon abundances obtained
previously ([Fe/H] = -4.8 and [C/Fe]1D = +1.7), and places
a more stringent limit on nitrogen abundance of [N/Fe]1D
< +1.0. Analysis of the UV OH lines yields [O/Fe]1D
= +2.3 ± 0.4. When corrections are made for three-dimensional (3D)
effects we obtain [C/Fe]3D = +1.1, [N/Fe]3D <
+0.1, and [O/Fe]3D = +1.4. Comparison of the abundances
of HE 0557-4840 with those of supernova models of Nomoto et al. and
Joggerst et al. suggests that none is able to explain fully the observed
abundance pattern. For HE 0557-4840, the Frebel et al. transition
discriminant D trans(= log(10[C/H] + 0.3 ×
10[O/H]) = -3.4 ± 0.2, consistent with fine-structure
transitions of C II and O I being a major cooling mechanism of
star-forming regions at the earliest times. Of the four stars known
to have [Fe/H] <~ -4.3, three are strongly carbon and oxygen
enhanced. If the suggestion by Caffau et al. that SDSS J102915+172927
([Fe/H] = -4.7) does not belong to the class of C-rich, O-rich, UMP
stars is supported by future similar discoveries, one will need to
consider multiple channels for the production of stars having [Fe/H]
<~ -4.3. Based on observations collected at European Southern
Observatory, Paranal, Chile (proposal 380.D-0040).
Title: Determination of rotation periods in solar-like stars with
irregular sampling: the Gaia case
Authors: Distefano, E.; Lanzafame, A. C.; Lanza, A. F.; Messina, S.;
Korn, A. J.; Eriksson, K.; Cuypers, J.
Bibcode: 2012MNRAS.421.2774D
Altcode: 2012arXiv1202.0759D; 2012MNRAS.tmp.2452D
We present a study on the determination of rotation periods (P) of
solar-like stars from the photometric irregular time sampling of the
European Space Agency Gaia mission, currently scheduled for launch in
2013, taking into account its dependence on ecliptic coordinates. We
examine the case of solar twins as well as thousands of synthetic time
series of solar-like stars rotating faster than the Sun. In the case of
solar twins, we assume that the Gaia unfiltered photometric passband G
will mimic the variability of the total solar irradiance as measured by
the Variability of solar IRradiance and Gravity Oscillations (VIRGO)
experiment. For stars rotating faster than the Sun, light curves are
simulated using synthetic spectra for the quiet atmosphere, the spots
and the faculae combined by applying semi-empirical relationships
relating the level of photospheric magnetic activity to the stellar
rotation and the Gaia instrumental response. The capabilities of the
Deeming, Lomb-Scargle and phase dispersion minimization methods in
recovering the correct rotation periods are tested and compared. The
false alarm probability is computed using Monte Carlo simulations
and compared with analytical formulae. The Gaia scanning law makes
the rate of correct detection of rotation periods strongly dependent
on the ecliptic latitude (β). We find that for P≃ 1 d, the rate of
correct detection increases with β from 20-30 per cent at β≃ 0 to
a peak of 70 per cent at β= 45°; then it abruptly falls below 10 per
cent at β > 45°. For P > 5 d, the rate of correct detection
is quite low and for solar twins is only 5 per cent on average.
Title: The Gaia-ESO Public Spectroscopic Survey
Authors: Gilmore, G.; Randich, S.; Asplund, M.; Binney, J.; Bonifacio,
P.; Drew, J.; Feltzing, S.; Ferguson, A.; Jeffries, R.; Micela, G.;
Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Alfaro, E.;
Allende-Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia,
A.; Flaccomio, E.; François, P.; Irwin, M.; Koposov, S.; Korn, A.;
Lanzafame, A.; Pancino, E.; Paunzen, E.; Recio-Blanco, A.; Sacco,
G.; Smiljanic, R.; Van Eck, S.; Walton, N.; Aden, D.; Aerts, C.;
Affer, L.; Alcala, J. -M.; Altavilla, G.; Alves, J.; Antoja, T.;
Arenou, F.; Argiroffi, C.; Asensio Ramos, A.; Bailer-Jones, C.;
Balaguer-Nunez, L.; Bayo, A.; Barbuy, B.; Barisevicius, G.; Barrado
y Navascues, D.; Battistini, C.; Bellas Velidis, I.; Bellazzini, M.;
Belokurov, V.; Bergemann, M.; Bertelli, G.; Biazzo, K.; Bienayme, O.;
Bland-Hawthorn, J.; Boeche, C.; Bonito, S.; Boudreault, S.; Bouvier,
J.; Brandao, I.; Brown, A.; de Bruijne, J.; Burleigh, M.; Caballero,
J.; Caffau, E.; Calura, F.; Capuzzo-Dolcetta, R.; Caramazza, M.;
Carraro, G.; Casagrande, L.; Casewell, S.; Chapman, S.; Chiappini,
C.; Chorniy, Y.; Christlieb, N.; Cignoni, M.; Cocozza, G.; Colless,
M.; Collet, R.; Collins, M.; Correnti, M.; Covino, E.; Crnojevic,
D.; Cropper, M.; Cunha, M.; Damiani, F.; David, M.; Delgado, A.;
Duffau, S.; Edvardsson, B.; Eldridge, J.; Enke, H.; Eriksson, K.;
Evans, N. W.; Eyer, L.; Famaey, B.; Fellhauer, M.; Ferreras, I.;
Figueras, F.; Fiorentino, G.; Flynn, C.; Folha, D.; Franciosini,
E.; Frasca, A.; Freeman, K.; Fremat, Y.; Friel, E.; Gaensicke, B.;
Gameiro, J.; Garzon, F.; Geier, S.; Geisler, D.; Gerhard, O.; Gibson,
B.; Gomboc, A.; Gomez, A.; Gonzalez-Fernandez, C.; Gonzalez Hernandez,
J.; Gosset, E.; Grebel, E.; Greimel, R.; Groenewegen, M.; Grundahl,
F.; Guarcello, M.; Gustafsson, B.; Hadrava, P.; Hatzidimitriou, D.;
Hambly, N.; Hammersley, P.; Hansen, C.; Haywood, M.; Heber, U.; Heiter,
U.; Held, E.; Helmi, A.; Hensler, G.; Herrero, A.; Hill, V.; Hodgkin,
S.; Huelamo, N.; Huxor, A.; Ibata, R.; Jackson, R.; de Jong, R.;
Jonker, P.; Jordan, S.; Jordi, C.; Jorissen, A.; Katz, D.; Kawata,
D.; Keller, S.; Kharchenko, N.; Klement, R.; Klutsch, A.; Knude,
J.; Koch, A.; Kochukhov, O.; Kontizas, M.; Koubsky, P.; Lallement,
R.; de Laverny, P.; van Leeuwen, F.; Lemasle, B.; Lewis, G.; Lind,
K.; Lindstrom, H. P. E.; Lobel, A.; Lopez Santiago, J.; Lucas, P.;
Ludwig, H.; Lueftinger, T.; Magrini, L.; Maiz Apellaniz, J.; Maldonado,
J.; Marconi, G.; Marino, A.; Martayan, C.; Martinez-Valpuesta, I.;
Matijevic, G.; McMahon, R.; Messina, S.; Meyer, M.; Miglio, A.;
Mikolaitis, S.; Minchev, I.; Minniti, D.; Moitinho, A.; Momany, Y.;
Monaco, L.; Montalto, M.; Monteiro, M. J.; Monier, R.; Montes, D.;
Mora, A.; Moraux, E.; Morel, T.; Mowlavi, N.; Mucciarelli, A.; Munari,
U.; Napiwotzki, R.; Nardetto, N.; Naylor, T.; Naze, Y.; Nelemans, G.;
Okamoto, S.; Ortolani, S.; Pace, G.; Palla, F.; Palous, J.; Parker, R.;
Penarrubia, J.; Pillitteri, I.; Piotto, G.; Posbic, H.; Prisinzano,
L.; Puzeras, E.; Quirrenbach, A.; Ragaini, S.; Read, J.; Read, M.;
Reyle, C.; De Ridder, J.; Robichon, N.; Robin, A.; Roeser, S.; Romano,
D.; Royer, F.; Ruchti, G.; Ruzicka, A.; Ryan, S.; Ryde, N.; Santos,
N.; Sanz Forcada, J.; Sarro Baro, L. M.; Sbordone, L.; Schilbach, E.;
Schmeja, S.; Schnurr, O.; Schoenrich, R.; Scholz, R. -D.; Seabroke, G.;
Sharma, S.; De Silva, G.; Smith, M.; Solano, E.; Sordo, R.; Soubiran,
C.; Sousa, S.; Spagna, A.; Steffen, M.; Steinmetz, M.; Stelzer, B.;
Stempels, E.; Tabernero, H.; Tautvaisiene, G.; Thevenin, F.; Torra,
J.; Tosi, M.; Tolstoy, E.; Turon, C.; Walker, M.; Wambsganss, J.;
Worley, C.; Venn, K.; Vink, J.; Wyse, R.; Zaggia, S.; Zeilinger, W.;
Zoccali, M.; Zorec, J.; Zucker, D.; Zwitter, T.; Gaia-ESO Survey Team
Bibcode: 2012Msngr.147...25G
Altcode:
The Gaia-ESO Public Spectroscopic Survey has begun and will obtain high
quality spectroscopy of some 100000 Milky Way stars, in the field and
in open clusters, down to magnitude 19, systematically covering all the
major components of the Milky Way. This survey will provide the first
homogeneous overview of the distributions of kinematics and chemical
element abundances in the Galaxy. The motivation, organisation and
implementation of the Gaia-ESO Survey are described, emphasising the
complementarity with the ESA Gaia mission. Spectra from the very first
observing run of the survey are presented.
Title: Synthetic Spectra and Photometry of C-rich Hydrodynamical
Model Atmospheres
Authors: Wachter, A.; Eriksson, K.; Aringer, B.; Höfner, S.;
Nowotny, W.
Bibcode: 2011ASPC..448..969W
Altcode: 2011csss...16..969W
We have calculated synthetic spectra for a set of hydrodynamical
dust-driven wind models with carbon-rich chemistry to investigate their
optical and infrared appearance depending on model parameters. The
spectra were computed at various phases covering several pulsation
periods to examine cycle-to-cycle variations. Furthermore, we determined
photometric magnitudes in different broadband filters to present and
compare lightcurves. Relations between mass-loss rates and colour
indices are also dicussed.
Title: A grid of S stars MARCS model atmospheres
Authors: Van Eck, Sophie; Neyskens, Pieter; Plez, Bertrand; Jorissen,
Alain; Edvardsson, Bengt; Eriksson, Kjell; Gustafsson, Bengt; Gråe
Jørgensen, Uffe; Nordlund, Åke
Bibcode: 2011JPhCS.328a2009V
Altcode:
S stars are cool stars of temperatures similar to those of M giants,
but their atmospheres are enriched in carbon and s-process elements
because of either extrinsic pollution by a binary companion or intrinsic
nucleosynthesis and dredge-up on the thermally-pulsing AGB. Despite
numerous attempts to link phenomenological spectral classification
criteria to physical parameters (Teff, gravity, C/O, [s/Fe],
[Fe/H]), the parameter space of S stars is poorly known and this has
prevented accurate abundance analysis of S stars until now. Here we
present a large grid of S-star model atmospheres. ZrO and TiO band
strength indices as well as VJHKL photometry are needed to disentangle
the effective temperature, C/O and [s/Fe]. The stellar parameters
derived on the basis of low-resolution spectra and photometry are
shown to be fairly accurate when compared to high-resolution data
of the same stars. The C/O ratio of S stars is found to be between
the solar value (0.5) and 0.99, and not 1 as often claimed in the
literature. Consistently with stellar evolution expectations, the C/O
ratio increases as the effective temperature decreases.
Title: Analysis of old very metal rich stars in the solar
neighbourhood
Authors: Trevisan, M.; Barbuy, B.; Eriksson, K.; Gustafsson, B.;
Grenon, M.; Pompéia, L.
Bibcode: 2011A&A...535A..42T
Altcode: 2011arXiv1109.6304T
Context. A sample of mostly old metal-rich dwarf and turn-off stars with
high eccentricity and low maximum height above the Galactic plane has
been identified. From their kinematics, it was suggested that the inner
disk is their most probable birthplace. Their chemical imprints may
therefore reveal important information about the formation and evolution
of the still poorly understood inner disk.
Aims: To probe the
formation history of these stellar populations, a detailed analysis
of a sample of very metal-rich stars is carried out. We derive the
metallicities, abundances of α elements, ages, and Galactic orbits.
Methods: The analysis of 71 metal-rich stars is based on optical
high-resolution échelle spectra obtained with the FEROS spectrograph
at the ESO 1.52-m Telescope at La Silla, Chile. The metallicities
and abundances of C, O, Mg, Si, Ca, and Ti were derived based on LTE
detailed analysis, employing the MARCS model atmospheres.
Results: We confirm the high metallicity of these stars reaching
up to [Fe i/H] = 0.58, and the sample of metal-rich dwarfs can be
kinematically subclassified in samples of thick disk, thin disk, and
intermediate stellar populations. All sample stars show solar α-Fe
ratios, and most of them are old and still quite metal rich. The orbits
suggest that the thin disk, thick disk and intermediate populations
were formed at Galactocentric distances of ~8 kpc, ~6 kpc, and ~7 kpc,
respectively. The mean maximum height of the thick disk subsample of
Zmax ~ 380 pc, is lower than for typical thick disk stars. A
comparison of α-element abundances of the sample stars with bulge stars
shows that the oxygen is compatible with a bulge or inner thick disk
origin. Our results suggest that models of radial mixing and dynamical
effects of the bar and bar/spiral arms might explain the presence
of these old metal-rich dwarf stars in the solar neighbourhood. Observations collected at the European Southern Observatory, La
Silla, Chile.Full Tables A.1 to A.4 are only available at the CDS
via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/535/A42
Title: VizieR Online Data Catalog: Metal rich stars in solar
neighbourhood (Trevisan+, 2011)
Authors: Trevisan, M.; Barbuy, B.; Eriksson, K.; Gustafsson, B.;
Grenon, M.; Pompeia, L.
Bibcode: 2011yCat..35350042T
Altcode: 2011yCat..35359042T
Spectroscopic stellar parameters and abundances of C, O, Mg, Si, Ca, Ti
and Ni for 71 stars. U, V, W velocities and orbital parameters derived
using the GRINTON integrator (Carraro et al. 2002MNRAS.332..705C,
Bedin et al. 2006A&A...460L..27B). Atomic data for Fe I, Fe II,
Si I, Ca I, and Ti I lines. (7 data files).
Title: Structure of the outer layers of cool standard stars
Authors: Dehaes, S.; Bauwens, E.; Decin, L.; Eriksson, K.; Raskin,
G.; Butler, B.; Dowell, C. D.; Ali, B.; Blommaert, J. A. D. L.
Bibcode: 2011A&A...533A.107D
Altcode: 2009arXiv0905.1240D
Context. Among late-type red giants, an interesting change occurs in
the structure of the outer atmospheric layers as one moves to later
spectral types in the Hertzsprung-Russell diagram: a chromosphere
is always present, but the coronal emission diminishes and a cool
massive wind steps in.
Aims: Where most studies have focussed
on short-wavelength observations, this article explores the influence
of the chromosphere and the wind on long-wavelength photometric
measurements. The goal of this study is to assess wether a set of
standard near-infrared calibration sources are fiducial calibrators
in the far-infrared, beyond 50 μm.
Methods: The observational
spectral energy distributions were compared with the theoretical model
predictions for a sample of nine K- and M-giants. The discrepancies
found are explained using basic models for flux emission originating
in a chromosphere or an ionised wind.
Results: For seven out of
nine sample stars, a clear flux excess is detected at (sub)millimetre
and/or centimetre wavelengths, while only observational upper limits
are obtained for the other two. The precise start of the excess depends
upon the star under consideration. For six sources the flux excess
starts beyond 210 μm and they can be considered as fiducial calibrators
for Herschel/PACS (60-210 μm). Out of this sample, four sources show
no flux excess in the Herschel/SPIRE wavelength range (200-670 μm)
and are good calibration sources for this instrument as well. The
flux at wavelengths shorter than ~1 mm is most likely dominated by an
optically thick chromosphere, where an optically thick ionised wind is
the main flux contributor at longer wavelengths.
Conclusions:
Although the optical to mid-infrared spectrum of the studied K- and
M-type infrared standard stars is represented well by a radiative
equilibrium atmospheric model, a chromosphere and/or ionised stellar
wind at higher altitudes dominates the spectrum in the (sub)millimetre
and centimetre wavelength ranges. The presence of a flux excess has
implications on the role of the stars as fiducial spectrophotometric
calibrators in these wavelength ranges. Appendix A is available in
electronic form at http:www.aanda.org
Title: VizieR Online Data Catalog: SED for 7 stellar calibrators
(Dehaes+, 2011)
Authors: Dehaes, S.; Bauwens, E.; Decin, L.; Eriksson, K.; Raskin,
G.; Butler, B.; Dowell, C. D.; Ali, B.; Blommaert, J. A. D. L.
Bibcode: 2011yCat..35330107D
Altcode: 2011yCat..35339107D
This catalogue presents the theoretical spectral energy distributions
for 7 stellar calibrators of the ESA Herschel satellite in the
wavelength range from 2 to 200 micron. The stellar atmosphere model
and theoretical spectrum are generated using the MARCS theoretical
stellar atmosphere code (Gustafsson et al., 1975A&A....42..407G
and further updates; Gustafsson et al. 2003A&A...400..709D)
and the TURBOSPECTRUM synthetic spectrum code (Plez et al.,
1992A&A...256..551P). Stellar parameters (and uncertainties thereon)
have been derived by Decin et al. (2003A&A...400..709D) and are
described in the text files added to this catalogue. The line lists used
in the spectrum calculation are discussed in Decin (2000, PhD Thesis,
Leuven University) and Decin and Eriksson (2007A&A...472.1041D). The outermost depth point of the theoretical atmosphere model
was taken at log(taulambda)=-7.2 with lambda being 2.2
micron. The atmosphere model was calculated with a spherically
symmetric (parallel for Sirius) geometry, under the assumption of
radiative and hydrostatic equilibrium, local thermodynamic equilibrium
(LTE) and homogeneous layers. The original theoretical spectrum
was calculated at a resolution of Δλ=0.5Å, and then degraded to
a resolution of λ/Δλ=5000 applying a gaussian convolution. The
wavelength coverage is from 2 to 200 micron. Uncertainties on the
theoretical spectrum predictions are discussed in depth in Decin &
Eriksson (2007A&A...472.1041D). Absolute flux calibration
is based on Selby (1988A&AS...74..127S) K-band (TCS for Sirius)
photometry Zero-point is determined on the basis of an ideal
'Vega', i.e. the K-band photometry of Vega is corrected for a flux
excess of 1.29% (cf. Absil et al. 2006A&A...452..237A). The
determined Selby K-band zeropoint is 4.0517E-10 W/m2/um. The
determined TCS K-band zeropoint is 4.4506E-10W/m2/um (for Sirius)
The estimated absolute flux uncertainty is 1% These
theoretical spectra should be referenced as Decin & Eriksson
(2007A&A...472.1041D). (3 data files).
Title: A Grid of MARCS Model Atmospheres for S Stars
Authors: van Eck, S.; Neyskens, P.; Plez, B.; Jorissen, A.; Edvardsson,
B.; Eriksson, K.; Gustafsson, B.; Jørgensen, U. G.; Nordlund, Å.
Bibcode: 2011ASPC..445...71V
Altcode: 2010arXiv1011.2092V
S-type stars are late-type giants whose atmospheres are enriched in
carbon and s-process elements because of either extrinsic pollution by
a binary companion or intrinsic nucleosynthesis and dredge-up on the
thermally-pulsing AGB. A large grid of S-star model atmospheres has
been computed covering the range 2700 ≤ Teff(K) ≤ 4000
with 0.5 ≤ C/O ≤ 0.99. ZrO and TiO band strength indices as well
as VJHKL photometry are needed to disentangle Teff, C/O and
[s/Fe]. A “best-model finding tool” has been developed using a set
of well-chosen indices and checked against photometry as well as low-
and high-resolution spectroscopy. It is found that applying M-star
model atmospheres (i.e., with a solar C/O ratio) to S stars can lead
to errors in Teff up to 400 K. We constrain the parameter
space occupied by the S stars of the vast Henize sample in terms of
Teff, [C/O] and [s/Fe].
Title: Synthetic Colors for Dynamic C-Star Models
Authors: Eriksson, K.; Wachter, A.; Höfner, S.; Aringer, B.;
Nowotny, W.
Bibcode: 2011ASPC..445..325E
Altcode:
Dust is formed in the outer atmospheres and winds of AGB stars and
severely affects their observed spectra and colours. Synthetic JHK
colours from a grid of time-dependent C-star models are presented
and compared to observed colours. The combined effects of pulsation
and dust are significant, especially for the coolest and most luminous
models. We are now extending the calculations with respect to effective
temperature, luminosity, stellar mass, and pulsation amplitude, as
well as the carbon excess.
Title: Detached Shells of Dust and Gas around Carbon Stars
Authors: Maercker, M.; Olofsson, H.; Eriksson, K.; Gustafsson, B.;
Schöier, F. L.
Bibcode: 2011ASPC..445..345M
Altcode:
We present observations of dust-scattered light of the carbon stars
U Ant, R Scl, and U Cam taken with the EFOSC2 camera on the ESO 3.6-m
telescope and the ACS on the Hubble Space Telescope. The observations
show the detached shells around these stars in unprecedented detail,
revealing a distinctively clumpy structure in the HST images of R Scl,
and a separation of the dust and gas in the ground-based data for
U Ant. This allows us to investigate the detached shells and their
origin with exceptional precision.
Title: Sulphur abundances in halo giants from the [S I] line at 1082
nm and the [S I] triplet around 1045 nm
Authors: Jönsson, H.; Ryde, N.; Nissen, P. E.; Collet, R.; Eriksson,
K.; Asplund, M.; Gustafsson, B.
Bibcode: 2011A&A...530A.144J
Altcode: 2011arXiv1104.2148J
Context. It is still debated whether or not the Galactic chemical
evolution of sulphur in the halo follows the flat trend with [Fe/H]
that is ascribed to the result of explosive nucleosynthesis in type
II SNe. It has been suggested that the disagreement between different
investigations of sulphur abundances in halo stars might be owing
to problems with the diagnostics used, that a new production source
of sulphur might be needed in the early Universe, like hypernovae, or
that the deposition of supernova ejecta into the interstellar medium is
time-delayed.
Aims: The aim of this study is to try to clarify
this situation by measuring the sulphur abundance in a sample of halo
giants using two diagnostics: the S i triplet around 1045 nm and the
[S i] line at 1082 nm. The latter of the two is not believed to be
sensitive to non-LTE effects. We can thereby minimize the uncertainties
in the diagnostic used and estimate the usefulness of the triplet for
the sulphur determination in halo K giants. We will also be able to
compare our sulphur abundance differences from the two diagnostics
with the expected non-LTE effects in the 1045 nm triplet previously
calculated by others.
Methods: High-resolution near-infrared
spectra of ten K giants were recorded using the spectrometer CRIRES
mounted at VLT. Two standard settings were used, one covering the S i
triplet and one covering the [S i] line. The sulphur abundances were
individually determined with equivalent widths and synthetic spectra
for the two diagnostics using tailored 1D model atmospheres and relying
on non-LTE corrections from the litterature. Effects of convective
inhomogeneities in the stellar atmospheres are investigated.
Results: The sulphur abundances derived from both the [S i] line and the
non-LTE corrected 1045 nm triplet favor a flat trend for the evolution
of sulphur. In contrast to some previous studies, we saw no "high"
values of [S/Fe] in our sample.
Conclusions: We corroborate
the flat trend in the [S/Fe] vs. [Fe/H] plot for halo stars found in
some previous studies but do not find a scatter or a rise in [S/Fe]
as obtained in other works. We find the sulphur abundances deduced
from the non-LTE corrected triplet to be somewhat lower than the
abundances from the [S i] line, possibly indicating too large non-LTE
corrections. Considering 3D modeling, however, they might instead
be too small. Moreover, we show that the [S i] line can be used as
a sulphur diagnostic down to [Fe/H] ~ -2.3 in giants. Based on
observations collected at the European Southern Observatory, Chile
(ESO program 080.D-0675(A)).
Title: Ices in the Quiescent IC 5146 Dense Cloud
Authors: Chiar, J. E.; Pendleton, Y. J.; Allamandola, L. J.; Boogert,
A. C. A.; Ennico, K.; Greene, T. P.; Geballe, T. R.; Keane, J. V.;
Lada, C. J.; Mason, R. E.; Roellig, T. L.; Sandford, S. A.; Tielens,
A. G. G. M.; Werner, M. W.; Whittet, D. C. B.; Decin, L.; Eriksson, K.
Bibcode: 2011ApJ...731....9C
Altcode: 2011arXiv1102.2488C
This paper presents spectra in the 2 to 20 μm range of quiescent
cloud material located in the IC 5146 cloud complex. The spectra were
obtained with NASA's Infrared Telescope Facility SpeX instrument and
the Spitzer Space Telescope's Infrared Spectrometer. We use these
spectra to investigate dust and ice absorption features in pristine
regions of the cloud that are unaltered by embedded stars. We find that
the H2O-ice threshold extinction is 4.03 ± 0.05 mag. Once
foreground extinction is taken into account, however, the threshold
drops to 3.2 mag, equivalent to that found for the Taurus dark cloud,
generally assumed to be the touchstone quiescent cloud against which
all other dense cloud and embedded young stellar object observations
are compared. Substructure in the trough of the silicate band for
two sources is attributed to CH3OH and NH3 in
the ices, present at the ~2% and ~5% levels, respectively, relative
to H2O-ice. The correlation of the silicate feature with
the E(J - K) color excess is found to follow a much shallower slope
relative to lines of sight that probe diffuse clouds, supporting the
previous results by Chiar et al.
Title: An abundance study of red-giant-branch stars in the Hercules
dwarf spheroidal galaxy
Authors: Adén, D.; Eriksson, K.; Feltzing, S.; Grebel, E. K.; Koch,
A.; Wilkinson, M. I.
Bibcode: 2011A&A...525A.153A
Altcode: 2010arXiv1010.5683A
Context. Dwarf spheroidal galaxies are some of the most metal-poor,
and least luminous objects known. Detailed elemental abundance analysis
of stars in these faint objects is key to our understanding of star
formation and chemical enrichment in the early universe, and may provide
useful information on how larger galaxies form.
Aims: Our aim is
to provide a determination of [Fe/H] and [Ca/H] for confirmed red-giant
branch member stars of the Hercules dwarf spheroidal galaxy. Based
on this we explore the ages of the prevailing stellar populations in
Hercules, and the enrichment history from supernovae. Additionally,
we aim to provide a new simple metallicity calibration for Strömgren
photometry for metal-poor, red giant branch stars.
Methods:
High-resolution, multi-fibre spectroscopy and Strömgren photometry are
combined to provide as much information on the stars as possible. From
this we derive abundances by solving the radiative transfer equations
through marcs model atmospheres.
Results: We find that the
red-giant branch stars of the Hercules dSph galaxy are more metal-poor
than estimated in our previous study that was based on photometry
alone. From this, we derive a new metallicity calibration for the
Strömgren photometry. Additionally, we find an abundance trend such
that [Ca/Fe] is higher for more metal-poor stars, and lower for more
metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe] trend
suggests an early rapid chemical enrichment through supernovae of type
II, followed by a phase of slow star formation dominated by enrichment
through supernovae of type Ia. A comparison with isochrones indicates
that the red giants in Hercules are older than 10 Gyr.
Title: Fluorine Abundances in Galactic Asymptotic Giant Branch Stars
Authors: Abia, C.; Cunha, K.; Cristallo, S.; de Laverny, P.;
Domínguez, I.; Eriksson, K.; Gialanella, L.; Hinkle, K.; Imbriani,
G.; Recio-Blanco, A.; Smith, V. V.; Straniero, O.; Wahlin, R.
Bibcode: 2010ApJ...715L..94A
Altcode:
An analysis of the fluorine abundance in Galactic asymptotic giant
branch (AGB) carbon stars (24 N-type, 5 SC-type, and 5 J-type) is
presented. This study uses the state-of-the-art carbon-rich atmosphere
models and improved atomic and molecular line lists in the 2.3 μm
region. Significantly lower F abundances are obtained in comparison to
previous studies in the literature. This difference is mainly due to
molecular blends. In the case of carbon stars of SC-type, differences
in the model atmospheres are also relevant. The new F enhancements
are now in agreement with the most recent theoretical nucleosynthesis
models in low-mass AGB stars, solving the long-standing problem of F in
Galactic AGB stars. Nevertheless, some SC-type carbon stars still show
larger F abundances than predicted by stellar models. The possibility
that these stars are of larger mass is briefly discussed.
Title: High-resolution HST/ACS images of detached shells around
carbon stars
Authors: Olofsson, H.; Maercker, M.; Eriksson, K.; Gustafsson, B.;
Schöier, F.
Bibcode: 2010A&A...515A..27O
Altcode: 2010arXiv1003.0362O
Context. Overall spherically symmetric, geometrically thin gas and dust
shells have been found around a handful of asymptotic giant branch (AGB)
carbon stars. Their dynamical ages lie in the range of 103
to 104 years. A tentative explanation for their existence is
that they have formed as a consequence of mass-loss-rate modulations
during a He-shell flash.
Aims: The detached shells carry
information on their formation process, as well as on the small-scale
structure of the circumstellar medium around AGB stars due to the
absence of significant line-of-sight confusion.
Methods: The
youngest detached shells, those around the carbon stars R Scl and U
Cam, are studied here in great detail in scattered stellar light with
the Advanced Survey Camera on the Hubble Space Telescope. Quantitative
results are derived assuming optically thin dust scattering.
Results: The detached dust shells around R Scl and U Cam are found to
be consistent with an overall spherical symmetry. They have radii of
19.2 arcsec (corresponding to a linear size of 8 × 1016
cm) and 7.7 arcsec (5 × 1016 cm), widths of 1.2 arcsec
(5 × 1015 cm) and 0.6 arcsec (4 × 1015 cm),
and dust masses of 3 × 10-6 and 3 × 10-7 M_⊙,
respectively. The dynamical ages of the R Scl and U Cam shells are
estimated to be 1700 and 700 yr, respectively, and the shell widths
correspond to time scales of 100 and 50 yr, respectively. Small-scale
structure in the form of less than arcsec-sized clumps is clearly
seen in the images of the R Scl shell. Average clump dust masses are
estimated to be about 2 × 10-9 M_⊙. Comparisons with CO
line interferometer data show that the dust and gas shells coincide
spatially, within the errors (≤1´´ for U Cam and ≈2´´ for
R Scl).
Conclusions: The results are consistent with the
interpretation of geometrically thin gas and dust shells formed by
a mass-loss eruption during a He-shell flash, and where interaction
with a previous wind plays a role as well. The mass loss responsible
for the shells must have been remarkably isotropic, and, if wind
interaction plays a role, this also applies to the mass loss prior
to the eruption. Clumpy structure is present in the R Scl shell,
possibly as a consequence of the mass loss itself, but more likely
as a consequence of instabilities in the expanding shell. Based
on observations with the NASA/ESA Hubble Space Telescope, obtained at
the Space Telescope Science Insitute, which is operated by the AURA,
Inc., under NASA contract NAS5-26555.
Title: Oxygen Isotopic Ratios in Cool R Coronae Borealis Stars
Authors: García-Hernández, D. A.; Lambert, David L.; Kameswara Rao,
N.; Hinkle, Ken H.; Eriksson, Kjell
Bibcode: 2010ApJ...714..144G
Altcode: 2010arXiv1003.2901A
We investigate the relationship between R Coronae Borealis (RCB)
stars and hydrogen-deficient carbon (HdC) stars by measuring precise
16O/18O ratios for five cool RCB stars. The
16O/18O ratios are derived by spectrum synthesis
from high-resolution (R ~ 50, 000) K-band spectra. Lower limits to the
16O/17O and 14N/15N ratios
as well as Na and S abundances (when possible) are also given. RCB
stars in our sample generally display less 18O than HdC
stars—the derived 16O/18O ratios range from 3
to 20. The only exception is the RCB star WX CrA, which seems to be an
HdC-like star with 16O/18O = 0.3. Our result of
a higher 16O/18O ratio for the RCB stars must
be accounted for by a theory of the formation and evolution of HdC
and RCB stars. We speculate that a late dredge-up of products of He
burning, principally 12C and 16O, may convert an
18O-rich HdC star into an 18O-poor RCB star as
the H-deficient star begins its final evolution from a cool supergiant
to the top of the white dwarf cooling track.
Title: Lithium abundances in Bulge-like SMR stars
Authors: Barbuy, Beatriz; Trevisan, M.; Gustafsson, B.; Eriksson,
K.; Grenon, M.; Pompéia, L.
Bibcode: 2010IAUS..268..325B
Altcode:
We analyze a sample of 21 super-metal-rich (SMR) stars, using
high-resolution échelle spectra obtained with the FEROS Spectrograph
at the 1.5m ESO telescope. The metallicities are in the range 0.15 <
[Fe/H] < 0.5, 3 of them in common with Pompéia et al. (2002). Geneva
photometry, astrometric data from Hipparcos, and radial velocities
from CORAVEL are available for these stars. The peculiar kinematics
suggests the thin disk close to the bulge as the probable birthplace
of these stars (Grenon 1999). From Hipparcos data, it appears that
the turnoff of this population indicates an age of 10-11 Gyr (Grenon
1999). Detailed analysis of the sample stars is carried out. Lithium
abundances of these stars were derived, and their behaviour with
effective temperature is shown.
Title: Fluorine Abundances in Galactic AGB Stars
Authors: Abia, C.; Cunha, K.; Cristallo., S.; de Laverny, P.;
Dominguez, I.; Eriksson, K.; Gialanella, L.; Hinkle, K.; Imbriani,
G.; Recio-Blanco, A; Smith, V. V.; Straniero, O.; Wahlin, R.
Bibcode: 2010arXiv1004.4451A
Altcode:
An analysis of the fluorine abundance in Galactic AGB carbon stars
(24 N-type, 5 SC-type and 5 J-type) is presented. This study uses the
state- of-the-art carbon rich atmosphere models and improved atomic
and molecular line lists in the 2.3 {\mu}m region. F abundances
significantly lower are obtained in comparison to previous study in
the literature. The main reason of this difference is due to molecular
blends. In the case of carbon stars of SC-type, differences in the
model atmospheres are also relevant. The new F enhancements are now in
agreement with the most recent theoretical nucleosynthesis models in
low- mass AGB stars, solving the long standing problem of F in Galactic
AGB stars. Nevertheless, some SC-type carbon stars still show larger
F abundances than predicted by stellar models. The possibility that
these stars are of larger mass is briefly discussed.
Title: The detached dust and gas shells around the carbon star
U Antliae
Authors: Maercker, M.; Olofsson, H.; Eriksson, K.; Gustafsson, B.;
Schöier, F. L.
Bibcode: 2010A&A...511A..37M
Altcode: 2009arXiv0912.2673M
Context. Geometrically thin, detached shells of gas have been found
around a handful of carbon stars. The current knowledge on these shells
is mostly based on CO radio line data. However, imaging in scattered
stellar light adds important new information as well as allows studies
of the dust shells.
Aims: Previous observations of scattered
stellar light in the circumstellar medium around the carbon star U
Ant were taken through filters centred on the resonance lines of K
and Na. These observations could not separate the scattering by dust
and atoms. The aim of this paper is to remedy this situation.
Methods: We have obtained polarization data on stellar light scattered
in the circumstellar medium around U Ant through filters which contain
no strong lines, making it possible to differentiate between the two
scattering agents. Kinematic, as well as spatial, information on the
gas shells were obtained through high-resolution echelle spectrograph
observations of the KI and NaD lines.
Results: We confirm the
existence of two detached shells around U Ant. The inner shell (at a
radius of ≈43´´ and a width of ≈2´´) consists mainly of gas,
while the outer shell (at a radius of ≈50´´ and a width of ≈7´´)
appears to consist exclusively of dust. Both shells appear to have
an over-all spherical geometry. The gas shell mass is estimated to
be 2 × 10-3~M⊙, while the mass of the dust
shell is estimated to be 5 × 10-5~M⊙. The
derived expansion velocity, from the KI and NaD lines, of the gas
shell, 19.5 km s-1, agrees with that obtained from CO radio
line data. The inferred shell age is 2700 years. There is structure,
e.g. in the form of arcs, inside the gas shell, but it is not clear
whether these are due to additional shells.
Conclusions: Our
results support the hypothesis that the observed geometrically thin,
detached shells around carbon stars are the results of brief periods
of intense mass loss, probably associated with thermal pulses, and
subsequent wind-wind interactions. The separation into a gas and a dust
shell, with different widths, is most likely the effect of different
dynamical evolutions of the two media after their ejection.
Title: Is the fluorine abundance problem in AGB stars solved? .
Authors: Abia, C.; Cunha, K.; Cristallo, S.; de Laverny, P.;
Domínguez, I.; Eriksson, K.; Gialanella, L.; Hinkle, K.; Imbriani,
G.; Recio-Blanco, A.; Smith, V. V.; Straniero, O.; Wahlin, R.
Bibcode: 2010MmSAI..81..986A
Altcode:
A reanalysis of the fluorine abundance in Galactic AGB carbon stars
has been performed from several HF (1-0) molecular lines in the 2.3
mu m range. High-resolution and high signal to noise spectra from the
FTS spectrograph were obtained from the NOAO archive. Using spectral
synthesis in LTE we derive fluorine abundances that are systematically
lower by ∼ 0.7 dex on average with respect to previous estimates. We
conclude that the reason for this relies mainly on differences in the
molecular line list, which has been largely improved in this work. The
new F abundances are in much better agreement with the predictions
from full network stellar models of low mass AGB stars.
Title: Evidence of enrichment by individual SN from elemental
abundance ratios in the very metal-poor dSph galaxy Boötes I
Authors: Feltzing, S.; Eriksson, K.; Kleyna, J.; Wilkinson, M. I.
Bibcode: 2009A&A...508L...1F
Altcode: 2009arXiv0910.1557F
Aims. We establish the mean metallicity from high-resolution
spectroscopy for the recently found dwarf spheroidal galaxy Boötes
I and test whether it is a common feature for ultra-faint dwarf
spheroidal galaxies to show signs of inhomogeneous chemical evolution
(e.g. as found in the Hercules dwarf spheroidal galaxy).
Methods:
We analyse high-resolution, moderate signal-to-noise spectra for seven
red giant stars in the Boötes I dSph galaxy using standard abundance
analysis techniques. In particular, we assume local thermodynamic
equilibrium and employ spherical model atmospheres and codes that take
the sphericity of the star into account when calculating the elemental
abundances.
Results: We confirm previous determinations of the
mean metallicity of the Boötes I dwarf spheroidal galaxy to be -2.3
dex. Whilst five stars are clustered around this metallicity, one is
significantly more metal-poor, at -2.9 dex, and one is more metal-rich
at, -1.9 dex. Additionally, we find that one of the stars, Boo-127,
shows an atypically high [Mg/Ca] ratio, indicative of stochastic
enrichment processes within the dSph galaxy. Similar results have
previously only been found in the Hercules and Draco dSph galaxies and
appear, so far, to be unique to this type of galaxy.
The
data presented herein were obtained at the W.M. Keck Observatory,
which is operated as a scientific partnership among the California
Institute of Technology, the University of California and the National
Aeronautics and Space Administration. The Observatory was made possible
by the generous financial support of the W.M. Keck Foundation.
Title: The Hamburg/ESO R-process enhanced star survey
(HERES). IV. Detailed abundance analysis and age dating of the
strongly r-process enhanced stars CS 29491-069 and HE 1219-0312
Authors: Hayek, W.; Wiesendahl, U.; Christlieb, N.; Eriksson, K.;
Korn, A. J.; Barklem, P. S.; Hill, V.; Beers, T. C.; Farouqi, K.;
Pfeiffer, B.; Kratz, K. -L.
Bibcode: 2009A&A...504..511H
Altcode: 2009arXiv0910.0707H
We report on a detailed abundance analysis of two strongly
r-process enhanced, very metal-poor stars newly discovered in
the HERES project, CS 29491-069 ([Fe/H]=-2.51,
[r/Fe]=+1.1) and HE 1219-0312 ([Fe/H]=-2.96,
[r/Fe]=+1.5). The analysis is based on high-quality VLT/UVES spectra
and MARCS model atmospheres. We detect lines of 15 heavy elements in
the spectrum of CS 29491-069, and 18 in HE
1219-0312; in both cases including the Th II 4019 Å
line. The heavy-element abundance patterns of these two stars are
mostly well-matched to scaled solar residual abundances not formed
by the s-process. We also compare the observed pattern with recent
high-entropy wind (HEW) calculations, which assume core-collapse
supernovae of massive stars as the astrophysical environment for the
r-process, and find good agreement for most lanthanides. The abundance
ratios of the lighter elements strontium, yttrium, and zirconium, which
are presumably not formed by the main r-process, are reproduced well by
the model. Radioactive dating for CS 29491-069 with
the observed thorium and rare-earth element abundance pairs results in
an average age of 9.5 Gyr, when based on solar r-process residuals, and
17.6 Gyr, when using HEW model predictions. Chronometry seems to fail
in the case of HE 1219-0312, resulting in a negative
age due to its high thorium abundance. HE 1219-0312
could therefore exhibit an overabundance of the heaviest elements,
which is sometimes called an “actinide boost”. Based on
observations collected at the European Southern Observatory, Paranal,
Chile (Proposal Number 170.D-0010). Table 8 is only available in
electronic form at http://www.aanda.org
Title: CNO Abundances of Hydrogen-Deficient Carbon and R Coronae
Borealis Stars: A View of the Nucleosynthesis in a White Dwarf Merger
Authors: García-Hernández, D. A.; Hinkle, K. H.; Lambert, David. L.;
Eriksson, K.
Bibcode: 2009ApJ...696.1733G
Altcode: 2009arXiv0901.3667G
We present high-resolution (R ~ 50, 000) observations of near-IR
transitions of CO and CN of the five known hydrogen-deficient carbon
(HdC) stars and four R Coronae Borealis (RCB) stars. We perform an
abundance analysis of these stars by using spectrum synthesis and
state-of-the-art MARCS model atmospheres for cool hydrogen-deficient
stars. Our analysis confirms reports by Clayton and colleagues
that those HdC stars exhibiting CO lines in their spectrum and the
cool RCB star S Aps are strongly enriched in 18O (with
16O/18O ratios ranging from 0.3 to 16). Nitrogen
and carbon are in the form of 14N and 12C,
respectively. Elemental abundances for CNO are obtained from C I,
C2, CN, and CO lines. Difficulties in deriving the carbon
abundance are discussed. Abundances of Na from Na I lines and S from
S I lines are obtained. Elemental and isotopic CNO abundances suggest
that HdC and RCB stars may be related objects, and that they probably
formed from a merger of an He white dwarf with a C-O white dwarf.
Title: Calibration of Strömgren uvby-Hβ photometry for late-type
stars - a model atmosphere approach
Authors: Önehag, A.; Gustafsson, B.; Eriksson, K.; Edvardsson, B.
Bibcode: 2009A&A...498..527O
Altcode: 2009A&A...498..527A
Context: The use of model atmospheres for deriving stellar fundamental
parameters, such as T_eff, log g, and [Fe/H], will increase as we find
and explore extreme stellar populations where empirical calibrations
are not yet available. Moreover, calibrations for upcoming large
satellite missions of new spectrophotometric indices, similar to the
uvby-Hβ system, will be needed.
Aims: We aim to test the power
of theoretical calibrations based on a new generation of MARCS models
by comparisons with observational photomteric data.
Methods: We
calculated synthetic uvby-Hβ colour indices from synthetic spectra. A
sample of 367 field stars, as well as stars in globular clusters, is
used for a direct comparison of the synthetic indices versus empirical
data and for scrutinizing the possibilities of theoretical calibrations
for temperature, metallicity, and gravity.
Results: We show that
the temperature sensitivity of the synthetic (b-y) colour is very close
to its empirical counterpart, whereas the temperature scale based upon
Hβ shows a slight offset. The theoretical metallicity sensitivity of
the m1 index (and for G-type stars its combination with c_1)
is somewhat higher than the empirical one, based upon spectroscopic
determinations. The gravity sensitivity of the synthetic c1
index shows satisfactory behaviour when compared to obervations of F
stars. For stars cooler than the sun, a deviation is significant in the
c1-(b-y) diagram. The theoretical calibrations of (b-y),
(v-y), and c1 seem to work well for Pop II stars and lead
to effective temperatures for globular cluster stars supporting recent
claims that atomic diffusion occurs in stars near the turnoff point of
NGC 6397.
Conclusions: Synthetic colours of stellar atmospheres
can indeed be used, in many cases, to derive reliable fundamental
stellar parameters. The deviations seen when compared to observational
data could be due to incomplete linelists but are possibly also due
to the effects of assuming plane-parallell or spherical geometry and
LTE. Model colours are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/498/527
Title: The dust condensation sequence in red supergiant stars
Authors: Verhoelst, T.; van der Zypen, N.; Hony, S.; Decin, L.; Cami,
J.; Eriksson, K.
Bibcode: 2009A&A...498..127V
Altcode: 2009arXiv0901.1262V
Context: Red supergiant (RSG) stars exhibit significant mass loss by
means of a slow, dense wind. They are often considered to be the more
massive counterparts of Asymptotic Giant Branch (AGB) stars. While AGB
mass loss is related to their strong pulsations, the RSG are often only
weakly variable. This raises the question of whether their wind-driving
mechanism and the dust composition of the wind are the same.
Aims:
We study the conditions at the base of the wind by determining the
dust composition of a sample of RSG. The dust composition is assumed
to be sensitive to the density, temperature, and acceleration at the
base of the wind. We compare the derived dust composition with the
composition measured in AGB star winds.
Methods: We compile a
sample of 27 RSG infrared spectra (ISO-SWS) and supplement these with
photometric measurements to derive the full spectral energy distribution
(SED). These data are modelled using a dust radiative-transfer code,
taking into account the optical properties of the relevant candidate
materials to search for correlations between mass-loss rate, density
at the inner edge of the dust shell, and stellar parameters.
Results: We find strong correlations between the dust composition,
mass-loss rate, and the stellar luminosity, roughly in agreement with
the theoretical dust condensation sequence. We identify the need for
a continuous (near-)IR dust opacity and tentatively propose amorphous
carbon, and we note significant differences with AGB star winds in
terms of the presence of PAHs, absence of “the” 13 μm band, and a
lack of strong water bands.
Conclusions: Dust condensation in RSG
is found to experience a freeze-out process that is similar to that in
AGB stars. Together with the positive effect of the stellar luminosity
on the mass-loss rate, this suggests that radiation pressure on dust
grains is an important ingredient in the driving mechanism. Still,
differences with AGB stars are manifold and thus the winds of RSG
should be studied individually in further detail.
Title: VizieR Online Data Catalog: Calibration of Stromgren phot. for
late-type stars (Onehag+, 2009)
Authors: Onehag, A.; Gustafsson, B.; Eriksson, K.; Edvardsson, B.
Bibcode: 2009yCat..34980527O
Altcode:
The file "stellar.dat" contains coordinates (J2000) and identifiers
of the comparison stars. Furthermore the stellar parameters: effective
temperature (Teff), logarithmic surface gravity (logg), and metallicity
with respect to the sun ([Fe/H]) are listed. The reddening corrected
Stromgren indices c1 and m1 and the reddening corrected Stromgren
(b-y) colours are listed together with the Crawford/Mander H-beta
indices. The file "model.dat" contains data calculated from the
MARCS models. The following model parameters are listed: effective
temperature (Teff), logarithmic surface gravity (logg), and metallicity
with respect to the sun ([Fe/H]). Synthetic Stromgren indices c1 and
m1 and synthetic Stromgren (b-y) colours are listed together with the
synthetic Crawford/Mander H-beta indices. (2 data files).
Title: Abundances in bulge stars from high-resolution, near-IR
spectra. I. The CNO elements observed during the science verification
of CRIRES at VLT
Authors: Ryde, N.; Edvardsson, B.; Gustafsson, B.; Eriksson, K.;
Käufl, H. U.; Siebenmorgen, R.; Smette, A.
Bibcode: 2009A&A...496..701R
Altcode: 2009arXiv0902.2124R
Context: The formation and evolution of the Milky Way bulge is not yet
well understood and its classification is ambiguous. Constraints can,
however, be obtained by studying the abundances of key elements in
bulge stars.
Aims: The aim of this study is to determine the
chemical evolution of C, N, O, and a few other elements in stars in
the Galactic bulge, and to discuss the sensitivities of the derived
abundances from molecular lines.
Methods: High-resolution,
near-infrared spectra in the H band were recorded using the CRIRES
spectrometer on the Very Large Telescope. Due to the high and variable
visual extinction in the line-of-sight towards the bulge, an analysis
in the near-IR is preferred. The C, N, and O abundances can all be
determined simultaneously from the numerous molecular lines in the
wavelength range observed.
Results: The three giant stars in
Baade's window presented here are the first bulge stars observed
with CRIRES during its science verification observations. We have
especially determined the C, N, and O abundances, with uncertainties
of less than 0.20 dex, from CO, CN, and OH lines. Since the systematic
uncertainties in the derived C, N, and O abundances due to uncertainties
in the stellar fundamental parameters, notably T_eff, are significant,
a detailed discussion of the sensitivities of the derived abundances
is included. We find good agreement between near-IR and optically
determined O, Ti, Fe, and Si abundances. Two of our stars show a solar
[C+N/Fe], suggesting that these giants have experienced the first
dredge-up and that the oxygen abundance should reflect the original
abundance of the giants. The two giants fit into the picture, in which
there is no significant difference between the oxygen abundance in bulge
and thick-disk stars. Our determination of the sulphur abundances is the
first for bulge stars. The high [S/Fe] values for all the stars indicate
a high star-formation rate in an early phase of the bulge evolution. Based on observations collected at the European Southern Observatory,
Chile (ESO Programme 60.A-9058A). Table [see full text] is only
available in electronic from at http://www.aanda.org
Title: A new sample of extremely/ultra metal-poor stars
Authors: García Pérez, A. E.; Christlieb, N.; Ryan, S. G.; Beers,
T. C.; Aoki, W.; Asplund, M.; Barklem, P. S.; Bessell, M. S.; Eriksson,
K.; Frebel, A.; Gustafsson, B.; Korn, A. J.; Nordström, B.; Norris,
J. E.
Bibcode: 2008PhST..133a4036G
Altcode:
A sample of 30 very metal-poor stars from the Hamburg-European
Southern Observatory (ESO) objective-prism survey have been observed
at high spectral resolution at the Very Large Telescope (VLT) using the
Ultraviolet and Visual Echelle Spectrograph (UVES). Two of the observed
stars are very interesting not only because of their very low iron
content, approximately four orders of magnitude lower than the solar
value, but also because we detected the neutral lithium resonance line
at 670.8 nm. Hydrogen lines suggest that the two observed stars have
effective temperatures around 6000 6250 K and according to isochrones,
they are either on the main sequence or on the subgiant branch, in
which case they would probably be the most metal-poor dwarfs or warm
subgiants with lithium detections known. These detections would allow
to determine more accurately the slope of the trend of the lithium
abundance with [Fe/H] than was possible with samples of unevolved
stars restricted to higher metallicities.
Title: CNO abundances in carbon star atmospheres—a progress report
Authors: Eriksson, K.
Bibcode: 2008PhST..133a4029E
Altcode:
A brief progress report is given on an on-going project to estimate the
C, N and O abundances in carbon stars of the Magellanic Cloud clusters
NGC 1846 and NGC 419. The changes in these abundances as a function
of position along the asymptotic giant branch (AGB) are sought for.
Title: HE 1327-2326, an Unevolved Star with [Fe/H]<-5.0. II. New
3D-1D Corrected Abundances from a Very Large Telescope UVES Spectrum
Authors: Frebel, Anna; Collet, Remo; Eriksson, Kjell; Christlieb,
Norbert; Aoki, Wako
Bibcode: 2008ApJ...684..588F
Altcode: 2008arXiv0805.3341F
We present a new abundance analysis of HE 1327-2326, which is currently
the most iron-poor star, based on observational data obtained with the
VLT Ultraviolet and Visual Echelle Spectrograph (UVES). We correct the
one-dimensional (1D) LTE abundances for three-dimensional (3D) effects
to provide an abundance pattern that supersedes previous works and
should be used to observationally test current models of the chemical
yields of the first-generation supernovae (SNe). Apart from confirming
the 1D LTE abundances found in previous studies before accounting for 3D
effects, we make use of a novel technique to apply the 3D-1D corrections
for CNO which are a function of excitation potential and line strength
for the molecular lines that comprise the observable CH, NH, and OH
features. We find that the fit to the NH band at 3360 Å is greatly
improved due to the application of the 3D-1D corrections. This may
indicate that 3D effects are actually observable in this star. We also
report the first detection of several weak Ni lines. The cosmologically
important element Li is still not detected; the new Li upper limit is
extremely low, A(Li) < 0.62, and in stark contrast with results not
only from the Wilkinson Microwave Anisotropy Probe (WMAP) but also
from other metal-poor stars. We also discuss how the new corrected
abundance pattern of HE 1327-2326 is being reproduced by individual and
integrated yields of SNe. Based on observations collected at the
European Southern Observatory, Paranal, Chile (Proposal ID 075.D-0048).
Title: A grid of MARCS model atmospheres for late-type
stars. I. Methods and general properties
Authors: Gustafsson, B.; Edvardsson, B.; Eriksson, K.; Jørgensen,
U. G.; Nordlund, Å.; Plez, B.
Bibcode: 2008A&A...486..951G
Altcode: 2008arXiv0805.0554G
Context: In analyses of stellar spectra and colours, and for the
analysis of integrated light from galaxies, a homogeneous grid
of model atmospheres of late-type stars and corresponding flux
spectra is needed.
Aims: We construct an extensive grid of
spherically-symmetric models (supplemented with plane-parallel ones
for the highest surface gravities), built on up-to-date atomic and
molecular data, and make it available for public use.
Methods:
The most recent version of the MARCS program is used.
Results:
We present a grid of about 104 model atmospheres for stars
with 2500 K ≤ T_eff ≤ 8000 K, -1 ≤ log g = log (GM/R^2) ≤ 5
(cgs) with various masses and radii, -5 ≤ [Me/H] ≤ +1, with [
α/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This
includes “CN-cycled” models with C/N = 4.07 (solar), 1.5 and 0.5,
C/O ranging from 0.09 to (normally) 5.0 to also represent stars of
spectral types R, S and N, and with 1.0 ≤ ξt ≤ 5 km
s-1. We also list thermodynamic quantities (T, P_g, P_e, ρ,
partial pressures of molecules, etc.) and provide them on the World Wide
Web, as well as calculated fluxes in approximately 108 000 wavelength
points. Underlying assumptions in addition to 1D stratification
(spherical or plane-parallel) include hydrostatic equilibrium,
mixing-length convection and local thermodynamic equilibrium. We
discuss a number of general properties of the models, in particular
in relation to the effects of changing abundances, of blanketing, and
of sphericity. We illustrate positive and negative feedbacks between
sphericity and molecular blanketing. We compare the models with those of
other available grids and find excellent agreement with plane-parallel
models of Castelli & Kurucz (if convection is treated consistently)
within the overlapping parameter range. Although there are considerable
departures from the spherically-symmetric NextGen models, the agreement
with more recent PHOENIX models is gratifying.
Conclusions: The
models of the grid show considerable regularities, but some interesting
departures from general patterns occur for the coolest models due
to the molecular opacities. We have tested a number of approximate
“rules of thumb” concerning effects of blanketing and sphericity
and often found them to be astonishingly accurate. Some interesting
new phenomena have been discovered and explored, such as the intricate
coupling between blanketing and sphericity, and the strong effects of
carbon enhancement on metal-poor models. We give further details of
line absorption data for molecules, as well as details of models and
comparisons with observations in subsequent papers.
Title: The limb-darkened Arcturus: imaging with the IOTA/IONIC
interferometer
Authors: Lacour, S.; Meimon, S.; Thiébaut, E.; Perrin, G.; Verhoelst,
T.; Pedretti, E.; Schuller, P. A.; Mugnier, L.; Monnier, J.; Berger,
J. P.; Haubois, X.; Poncelet, A.; Le Besnerais, G.; Eriksson, K.;
Millan-Gabet, R.; Ragland, S.; Lacasse, M.; Traub, W.
Bibcode: 2008A&A...485..561L
Altcode: 2008arXiv0804.0192L
Aims: We undertook an H band interferometric examination of Arcturus,
a star frequently used as a spatial and spectral calibrator.
Methods: Using the IOTA 3 telescope interferometer, we performed
spectro-interferometric observations (R≈35) of Arcturus. Atmospheric
models and prescriptions were fitted to the data to derive the
brightness distribution of the photosphere. Image reconstruction was
performed using two software algorithms: Wisard and Mira.
Results:
An achromatic power law proved to be a good model of the brightness
distribution, with a limb darkening compatible with the one derived
from atmospheric model simulations using our marcs model. A Rosseland
diameter of 21.05±0.21 was derived, corresponding to an effective
temperature of Teff = 4295±26 K. No companion was detected
from the closure phases, with an upper limit on the brightness ratio
of 8×10-4 at 1 AU. The dynamic range at such distance from
the photosphere was established as 1.5×10-4 (1σ rms). An
upper limit of 1.7×10-3 was also derived for the level of
brightness asymmetries present in the photosphere.
Title: Intense mass loss from C-rich AGB stars at low metallicity?
Authors: Mattsson, L.; Wahlin, R.; Höfner, S.; Eriksson, K.
Bibcode: 2008A&A...484L...5M
Altcode: 2008arXiv0804.2482M
We argue that the energy injection of pulsations may be of greater
importance to the mass-loss rate of AGB stars than metallicity, and
that the mass-loss trend with metallicity is not as simple as sometimes
assumed. Using our detailed radiation hydrodynamical models that include
dust formation, we illustrate the effects of pulsation energy on wind
properties. We find that the mass-loss rate scales with the kinetic
energy input by pulsations as long as a dust-saturated wind does not
occur, and all other stellar parameters are kept constant. This includes
the absolute abundance of condensible carbon (not bound in CO), which
is more relevant than keeping the C/O-ratio constant when comparing
stars of different metallicity. The pressure and temperature gradients
in the atmospheres of stars, become steeper and flatter, respectively,
when the metallicity is reduced, while the radius where the atmosphere
becomes opaque is typically associated with a higher gas pressure. This
effect can be compensated for by adjusting the velocity amplitude of
the variable inner boundary (piston), which is used to simulate the
effects of pulsation, to obtain models with comparable kinetic-energy
input. Hence, it is more relevant to compare models with similar
energy-injections than of similar velocity amplitude. Since there
is no evidence for weaker pulsations in low-metallicity AGB stars,
we conclude that it is unlikely that low-metallicity C-stars have
lower mass-loss rates, than their more metal-rich counterparts with
similar stellar parameters, as long as they have a comparable amount
of condensible carbon.
Title: The Giants Stars HE 0107-5240 and HE 0557-4840 and New Searches
for Metal-Poor Stars
Authors: Christlieb, Norbert; Korn, Andreas J.; Eriksson, Kjell;
Bessell, Michael S.; Norris, John E.; Keller, Stefan C.; Zhao,
Yongheng; Zhang, Haotong; Beers, Timothy C.
Bibcode: 2008AIPC..990..109C
Altcode:
We report on a new determination of the iron abundance of HE 0107-5240,
based on the detection of two Fe II lines in an UV spectrum of the star,
which yields [Fe/H] = -5.7. Another interesting metal-poor star recently
discovered with Hamburg/ESO Survey (HES) is HE 0557-4840. With [Fe/H]
= -4.8, it is the first star located in the ``gap'' in the metallicity
distribution function of the galactic halo, in metallicity between the
two stars known at [Fe/H]>-4.0. HE 0557-4840 is carbon-enhanced
(i.e., [C/Fe] = +1.7). The abundance ratios of the heavier elements
are similar to those seen in the majority of the metal-poor stars at
[Fe/H]>-4.0. We also describe two upcoming wide-angle surveys
which will be used for searches for metal-poor stars: The Southern Sky
Survey (SSS), and a stellar survey to be conducted with the Chinese
LAMOST telescope. These efforts are expected to increase the number
of known extremely metal-poor stars, including stars below [Fe/H] =
-5.0, by about two orders of magnitude.
Title: On the Use of Blanketed Atmospheres as Boundary Conditions
for Stellar Evolutionary Models
Authors: VandenBerg, Don A.; Edvardsson, Bengt; Eriksson, Kjell;
Gustafsson, Bengt
Bibcode: 2008ApJ...675..746V
Altcode: 2007arXiv0708.1188V
Stellar models have been computed for stars having [ Fe/H ]
= 0.0 (assuming both the Grevesse & Sauval and Asplund et
al. heavy-element mixtures) and -2.0 to determine the effects on the
predicted Teff scale of using boundary conditions derived
from the latest MARCS model atmospheres. The latter were fitted in a
fully consistent way to the interior models at the photosphere and at
τ = 100: the resultant evolutionary sequences on the H-R diagram were
found to be nearly independent of the chosen fitting point. Tracks
were also computed in which the pressure at T = Teff was
obtained by integrating the hydrostatic equation together with either
the classical gray T(τ , Teff) relation or that derived by
Krishna Swamy from an empirical solar atmosphere. Due to the effects
of differences in the solar-calibrated values of the mixing-length
parameter, αMLT, very similar tracks were obtained for the
different treatments of the atmosphere, except at solar abundances,
where the models based on the Krishna Swamy T(τ , Teff)
relationship predicted ~150 K hotter giant branches than the others,
in good agreement with the inferred temperatures of giants in the open
cluster M67 from recent (V - K) -Teff relations. Tracks that
used new ``scaled solar, differentially corrected'' MARCS atmospheres
were found to agree well with those that employed the Krishna Swamy
T(τ , Teff) relationship, independently of the assumed
metal abundance. (Gray atmospheres are quite different from MARCS
models.) Fits of isochrones for [ Fe/H ] = - 2.0 to the CMD of the
globular cluster M68, as well as the possibility that αMLT
varies with stellar parameters, are also discussed.
Title: Do R Coronae Borealis stars evolve from white dwarf mergers?
Authors: Lambert, David L.; Kameswara Rao, N.; Hinkle, Kenneth H.;
Garcia-Hernandez, D. A.; Eriksson, Kjell
Bibcode: 2008noao.prop..316L
Altcode:
Phoenix spectra of C_2, CN and CO lines will provide oxygen isotopic
abundance ratios (^16O/^17O/^18O) and CNO abundances for cool R Coronae
Borealis (RCB) stars. The ratios, especially the ^16O/^18O ratio, will
be used to test the two leading scenarios for RCB production. These
observations were prompted by Clayton et al.'s striking discovery of
low ^16O/^18O (<1) ratios for H-deficient carbon (HdC) stars. This
ratio requires the formation of HdC stars by the merger of two white
dwarfs as some ^14N is burnt to ^18O. The HdC are possible immediate
relatives of the RCBs. Yet, our Phoenix observations of the cool RCB
S Aps give a higher ratio (^16O/^18O=16) than for the HdCs perhaps
questioning a direct evolutionary connection between HdC and RCB
stars. Also, our Phoenix CNO abundance analysis of HdCs shows the ^14N
to ^18O conversion is far from complete. In this proposal, we seek to
extend our CNO elemental and isotopic abundance analyses from one RCB
to several in order to explore the evolutionary connection between HdC
and RCB stars and to constrain the nucleosynthesis that occurs during
the cannibalism of a He white dwarf by a C-O white dwarf.
Title: M 67: a constraint on Z_⊙ and/or on diffusive processes in
stellar interiors.
Authors: VandenBerg, D. A.; Gustafsson, B.; Edvardsson, B.; Eriksson,
K.; Ferguson, J. W.
Bibcode: 2008MmSAI..79..759V
Altcode:
The mass of the lowest mass star that has a convective core throughout
the main-sequence phase is predicted to be a fairly sensitive function
of Z (especially the CNO abundances). The ∼ 4 Gyr open cluster M 67
thus provides a constraint on Z_⊙ (and the solar metals mix) because
(i) it has the same metallicity as the Sun according to high-resolution
spectroscopy, and (ii) its turnoff stars have masses just above this
lower mass limit. While isochrones computed for Z = 0.0165, assuming
the Grevesse & Sauval (1998) heavy-element mixture, are able to
reproduce the M 67 color-magnitude diagram satisfactorily, those for the
solar abundances derived by M. Asplund et al. (implying Z_⊙ = 0.0125)
do not predict a gap near the turnoff where one is observed. These
results suggest either that there is a problem with the solar metal
abundances derived by Asplund et al. or that the neglect of diffusive
processes in the present models is responsible for this difficulty. If
the latter is the correct explanation, then M 67 provides an important
constraint on the rates of diffusive processes in the deep interiors
of stars.
Title: HE 0557-4840: Ultra-Metal-Poor and Carbon-Rich
Authors: Norris, John E.; Christlieb, N.; Korn, A. J.; Eriksson, K.;
Bessell, M. S.; Beers, Timothy C.; Wisotzki, L.; Reimers, D.
Bibcode: 2007ApJ...670..774N
Altcode: 2007arXiv0707.2657N
We report the discovery and high-resolution, high-S/N spectroscopic
analysis of the ultra-metal-poor red giant HE 0557-4840, which is the
third most heavy-element-deficient star currently known. Its atmospheric
parameters are Teff=4900 K, logg=2.2, and [Fe/H]=-4.75. This
brings the number of stars with [Fe/H]<-4.0 to three, and the
discovery of HE 0557-4840 suggests that the metallicity distribution
function of the Galactic halo does not have a ``gap'' between
[Fe/H]=-4.0, where several stars are known, and the two most metal-poor
stars, at [Fe/H]~-5.3. HE 0557-4840 is carbon rich ([C/Fe]=+1.6), a
property shared by all three objects with [Fe/H]<-4.0, suggesting
that the well-known increase of carbon relative to iron with decreasing
[Fe/H] reaches its logical conclusion (ubiquitous carbon richness) at
lowest abundance. We also present abundances (nine) and limits (nine)
for a further 18 elements. For species having well-measured abundances
or strong upper limits, HE 0557-4840 is ``normal'' in comparison with
the bulk of the stellar population at [Fe/H]~-4.0, with the possible
exception of Co. We discuss the implications of these results for
chemical enrichment at the earliest times, in the context of single-
(``mixing and fallback'') and two-component enrichment models. While
neither offers a clear solution, the latter appears closer to the
mark. Further data are required to determine the oxygen abundance
and improve that of Co, and hence more strongly constrain the origin
of this object. Based on observations collected at ANU's 2.3 m
telescope on Siding Spring Mountain, Australia, and European Southern
Observatory, Paranal, Chile (proposal 276.D-5041).
Title: Carbon Stars in the Bulge -- or Beyond It?
Authors: Wahlin, R.; Eriksson, K.; Gustafsson, B. >; Ryde, N.;
Westerlund, B.; Lambert, D. L.
Bibcode: 2007ASPC..378..410W
Altcode:
The carbon stars in the direction of the Bulge were recently proposed
to belong to the Sagittarius system which, with its lower metallicity,
would more easily produce carbon stars. The compositions of the carbon
stars might be used to distinguish between true members of the Bulge and
members of the Sagittarius stream seen through the Bulge. We present
oxygen abundances for a sample of carbon stars in the Sagittarius
dwarf galaxy including its tidal stream, and towards the galactic
Bulge. The abundances were determined from infrared spectra obtained
with the ISAAC spectrometer on VLT (R=1500). We find that the oxygen
abundances of the Bulge carbon stars are compatible with membership
of the Sagittarius stream, but we also discuss possible scenarios that
might explain their abundances if they were true Bulge members.
Title: Theoretical model atmosphere spectra used for the calibration
of infrared instruments
Authors: Decin, L.; Eriksson, K.
Bibcode: 2007A&A...472.1041D
Altcode: 2007arXiv0708.4120D
Context: One of the key ingredients in establishing the relation
between input signal and output flux from a spectrometer is accurate
determination of the spectrophotometric calibration. In the case
of spectrometers onboard satellites, the accuracy of this part of
the calibration pedigree is ultimately linked to the accuracy of
the set of reference spectral energy distributions (SEDs) that the
spectrophotometric calibration is built on.
Aims: In this
paper, we deal with the spectrophotometric calibration of infrared
(IR) spectrometers onboard satellites in the 2 to 200 μm wavelength
range. We aim at comparing the different reference SEDs used for the IR
spectrophotometric calibration. The emphasis is on the reference SEDs
of stellar standards with spectral type later than A0, with special
focus on the theoretical model atmosphere spectra.
Methods:
Using the MARCS model atmosphere code, spectral reference SEDs were
constructed for a set of IR stellar standards (A dwarfs, solar analogs,
G9-M0 giants). A detailed error analysis was performed to estimate
proper uncertainties on the predicted flux values.
Results:
It is shown that the uncertainty on the predicted fluxes can be
as high as 10%, but in case high-resolution observational optical
or near-IR data are available, and IR excess can be excluded, the
uncertainty on medium-resolution SEDs can be reduced to 1-2% in the
near-IR, to ~3% in the mid-IR, and to ~5% in the far-IR. Moreover,
it is argued that theoretical stellar atmosphere spectra are at the
moment the best representations for the IR fluxes of cool stellar
standards.
Conclusions: When aiming at a determination of the
spectrophotometric calibration of IR spectrometers better than 3%,
effort should be put into constructing an appropriate set of stellar
reference SEDs based on theoretical atmosphere spectra for some 15
standard stars with spectral types between A0 V and M0 III.
Title: A Constraint on Zsolar from Fits of Isochrones to
the Color-Magnitude Diagram of M67
Authors: VandenBerg, Don A.; Gustafsson, Bengt; Edvardsson, Bengt;
Eriksson, Kjell; Ferguson, Jason
Bibcode: 2007ApJ...666L.105V
Altcode: 2007arXiv0708.1172V
The mass at which a transition is made between stars that have radiative
or convective cores throughout the core H burning phase is a fairly
sensitive function of Z (particularly, the CNO abundances). As a
consequence, the ~4 Gyr, open cluster M67 provides a constraint on
Zsolar (and the solar heavy-element mixture) because (1)
high-resolution spectroscopy indicates that this system has virtually
the same metal abundances as the Sun, and (2) its turnoff stars have
masses just above the lower limit for sustained core convection on
the main sequence. In this study, evolutionary tracks and isochrones
using the latest MARCS model atmospheres as boundary conditions have
been computed for 0.6-1.4 Msolar on the assumption of a
metals mix (implying Zsolar~0.0125) based on the solar
abundances derived by M. Asplund and collaborators using 3D model
atmospheres. These calculations do not predict a turnoff gap where one
is observed in M67. No such difficulty is found if the analysis uses
isochrones for Zsolar=0.0165, assuming the Grevesse and
Sauval mix of heavy elements. Our findings, like the inferences from
helioseismology, indicate a problem with the abundances of Asplund
and collaborators. However, it is possible that low-Z models with
diffusive processes taken into account will be less problematic.
Title: The Presence of Diffuse Interstellar Bands in the Spectra of
Cool Stars
Authors: Destree, Joshua D.; Snow, Theodore P.; Eriksson, Kjell
Bibcode: 2007ApJ...664..909D
Altcode:
Data from the Kitt Peak National Observatory (KPNO) coudé feed
telescope were used to analyze the strength of three well-known diffuse
interstellar bands (DIBs; 5780, 5797, and 6614 Å). Ten mid-A, mid-F,
and mid-G stars with moderate reddening (EB-V=0.2-1.2) were
observed, along with one reddened B0 dwarf for comparison. Synthetic
spectra were calculated to remove the interference of stellar
features. We report the detection of all three DIBs in A, F, and
G stars. We also find the correlation of DIB strengths with E(B-V),
in our sight lines, to be consistent with previous results from Herbig
(1993), demonstrating that DIB strength is not dependent on the spectral
type of the target star.
Title: On Stellar Models with Blanketed Atmospheres as Boundary
Conditions
Authors: Vandenberg, Don A.; Edvardsson, Bengt; Eriksson, Kjell;
Gustafsson, Bengt; Ferguson, Jason W.
Bibcode: 2007IAUS..241...23V
Altcode:
No abstract at ADS
Title: AGB nucleosynthesis in the Large Magellanic Cloud. Detailed
abundance analysis of the RV Tauri star MACHO 47.2496.8
Authors: Reyniers, M.; Abia, C.; van Winckel, H.; Lloyd Evans, T.;
Decin, L.; Eriksson, K.; Pollard, K. R.
Bibcode: 2007A&A...461..641R
Altcode: 2006astro.ph.10240R
Context: Abundance analysis of post-AGB objects as probes of AGB
nucleosynthesis.
Aims: A detailed photospheric abundance study
is performed on the carbon-rich post-AGB candidate MACHO 47.2496.8
in the LMC.
Methods: High-resolution, high signal-to-noise ESO
VLT-UVES spectra of MACHO 47.2496.8 are analysed by performing detailed
spectrum synthesis modelling using state-of-the-art carbon-rich MARCS
atmosphere models.
Results: The spectrum of MACHO 47.2496.8 is
not only dominated by bands of carbon bearing molecules, but also by
lines of atomic transitions of s-process elements. The metallicity of
[Fe/H] = -1.4 is surprisingly low for a field LMC star. The C/O ratio,
however difficult to quantify, is greater than 2, and the s-process
enrichment is large: the light s-process elements are enhanced by 1.2
dex compared to iron ([ls/Fe] = +1.2), while for the heavy s-process
elements an even stronger enrichment is measured: [hs/Fe] = +2.1. The
lead abundance is comparable to the [hs/Fe]. With its low intrinsic
metallicity and its luminosity at the low end of the carbon star
luminosity function, the star represents likely the final stage of
a low initial mass star.
Conclusions: .The LMC RV Tauri star
MACHO 47.2496.8 is highly carbon and s-process enriched, and is most
probable a genuine post-C(N-type) AGB star. This is the first detailed
abundance analysis of an extragalactic post-AGB star to date.
Title: An abundance study of the most iron-poor star HE1327-2326
with Subaru/HDS
Authors: Aoki, W.; Frebel, A.; Christlieb, N.; Norris, J. E.; Beers,
T. C.; Minezaki, T.; Barklem, P. S.; Honda, S.; Takada-Hidai, M.;
Asplund, M.; Ryan, S. G.; Tsangarides, S.; Eriksson, K.; Steinhauer,
A.; Deliyannis, C. P.; Nomoto, K.; Fujimoto, M. Y.; Ando, H.; Yoshii,
Y.; Kajino, T.
Bibcode: 2006AIPC..847...53A
Altcode:
We present an elemental abundance analysis of HE 1327-2326, the most
iron-deficient star known, based on a comprehensive investigation of
spectra obtained with the Subaru Telescope. HE 1327-2326 is either
in its main sequence or subgiant phase of evolution, hence it is
essentially unevolved. The chemical abundances of this star have
the following properties, which provide new constraints on models of
nucleosynthesis processes that occurred in first-generation objects: (1)The iron abundance (NLTE) is [Fe/H]= -5.45. This value is 0.2 dex
lower than that of HE 0107-5240, the previously most iron-poor object
known. No object having [Fe/H]= -5 ~ -4 is known to date. (2)This
star, as well as HE 0107-5240, exhibits extremely large overabundances
of carbon relative to solar ratios ([C/Fe]~ +4). (3)HE 1327-2326
exhibits remarkable overabundances of the light elements (N, Na, Mg
and Al), while HE 0107-5240 shows only relatively small excesses of N
and Na. (4)A large overabundance of Sr is found in HE 1327-2326
as compared to other extremely low metallicity stars. (5)The Li
I 6707 Å line, which is detected in the great majority of metal-poor
dwarfs and warm subgiants, is not found in HE 1327-2326. The upper
limit on the Li abundance we determine (log ɛ (Li) < 1.5) is
clearly lower than the expected value from the Spite plateau.
Title: Water Vapor on Supergiants: The 12 μm TEXES Spectra of
μ Cephei
Authors: Ryde, N.; Richter, M. J.; Harper, G. M.; Eriksson, K.;
Lambert, D. L.
Bibcode: 2006ApJ...645..652R
Altcode: 2006astro.ph..3384R
Several recent papers have argued for warm, semidetached, molecular
layers surrounding red giant and supergiant stars, a concept known as
a MOLsphere. Spectroscopic and interferometric analyses have often
corroborated this general picture. Here we present high-resolution
spectroscopic data of pure rotational lines of water vapor at 12 μm
for the supergiant μ Cep. This star has often been used to test the
concept of molecular layers around supergiants. Given the prediction of
an isothermal, optically thick water vapor layer in local thermodynamic
equilibrium around the star (MOLsphere), we expected the 12 μm lines
to be in emission or at least in absorption but filled in by emission
from the molecular layer around the star. Our data, however, show the
contrary; we find definite absorption. Thus, our data do not easily fit
into the suggested isothermal MOLsphere scenario. The 12 μm lines,
therefore, put new, strong constraints on the MOLsphere concept and
on the nature of water seen in signatures across the spectra of early
M supergiants. We also find that the absorption is even stronger
than that calculated from a standard, spherically symmetric model
photosphere without any surrounding layers. A cool model photosphere,
representing cool outer layers, is, however, able to reproduce the
lines, but this model does not account for water vapor emission at
6 μm. Thus, a unified model for water vapor on μ Cep appears to be
lacking. It does seem necessary to model the underlying photospheres
of these supergiants in their whole complexity. The strong water vapor
lines clearly reveal inadequacies of classical model atmospheres.
Title: Geometry of giant star model atmospheres: a consistency test
Authors: Heiter, U.; Eriksson, K.
Bibcode: 2006A&A...452.1039H
Altcode: 2006astro.ph..3273H
Aims.We investigate the effect of a geometric inconsistency in the
calculation of synthetic spectra of giant stars.
Methods: .Spectra
computed with model atmospheres calculated in spherical geometry while
using the plane-parallel approximation for line formation calculations
(s_p), as well as the fully plane-parallel case (p_p), are compared
to the consistently spherical case (s_s).
Results: .We present
abundance differences for solar metallicity models with T_eff ranging
from 4000 to 6500 K and log g from 0.5 to 3.0 [cgs]. The effects are
smaller for sp calculations (-0.1 dex in the worst case)
than for the pp case (up to +0.35 dex for minority species
and at most -0.04 dex for majority species), both with respect to the
ss case. In the sp case the differences increase
slightly with temperature, while in the pp case they show
a more complex behaviour. In both cases the effects decrease with
increasing log g and increase with equivalent width.
Conclusions:
.Within the parameter range of F, G and K giants, consistency seems
to be less important than using a spherical model atmosphere. The
abundance differences due to sphericity effects presented here can be
used for error estimation in abundance studies relying on plane-parallel
modelling.
Title: HE 1327-2326, an Unevolved Star with [Fe/H]<-5.0. I. A
Comprehensive Abundance Analysis
Authors: Aoki, W.; Frebel, A.; Christlieb, N.; Norris, J. E.; Beers,
T. C.; Minezaki, T.; Barklem, P. S.; Honda, S.; Takada-Hidai, M.;
Asplund, M.; Ryan, S. G.; Tsangarides, S.; Eriksson, K.; Steinhauer,
A.; Deliyannis, C. P.; Nomoto, K.; Fujimoto, M. Y.; Ando, H.; Yoshii,
Y.; Kajino, T.
Bibcode: 2006ApJ...639..897A
Altcode: 2005astro.ph..9206A
We present the elemental abundances of HE 1327-2326, the most
iron-deficient star known, determined from a comprehensive analysis
of spectra obtained with the Subaru Telescope High Dispersion
Spectrograph. HE 1327-2326 is either in its main-sequence or
subgiant phase of evolution. Its non-LTE-corrected iron abundance is
[Fe/H]=-5.45, 0.2 dex lower than that of HE 0107-5240, the previously
most iron-poor object known, and more than 1 dex lower than those
of all other metal-poor stars. Both HE 1327-2326 and HE 0107-5240
exhibit extremely large overabundances of carbon ([C/Fe]~+4). The
combination of extremely high carbon abundance with outstandingly
low iron abundance in these objects clearly distinguishes them from
other metal-poor stars. The large carbon excesses in these two stars
are not the result of a selection effect. There also exist important
differences between HE 1327-2326 and HE 0107-5240. While the former
shows remarkable overabundances of the light elements (N, Na, Mg,
and Al), the latter shows only relatively small excesses of N and
Na. The neutron-capture element Sr is detected in HE 1327-2326,
but not in HE 0107-5240 its Sr abundance is significantly higher
than the upper limit for HE 0107-5240. The Li I λ6707 line, which is
detected in most metal-poor dwarfs and warm subgiants having the same
temperature as HE 1327-2326, is not found in this object. The upper
limit of its Li abundance [logɛ(Li)<1.5] is clearly lower than the
Spite plateau value. These data provide new constraints on models of
nucleosynthesis processes in the first-generation objects that were
responsible for metal enrichment at the earliest times. We discuss
possible scenarios to explain the observed abundance patterns. Based on data collected with the Subaru Telescope, which is operated
by the National Astronomical Observatory of Japan.
Title: Amorphous alumina in the extended atmosphere of α Orionis
Authors: Verhoelst, T.; Decin, L.; van Malderen, R.; Hony, S.; Cami,
J.; Eriksson, K.; Perrin, G.; Deroo, P.; Vandenbussche, B.; Waters,
L. B. F. M.
Bibcode: 2006A&A...447..311V
Altcode: 2005astro.ph.10486V
In this paper we study the extended atmosphere of the late-type
supergiant α Orionis. Infrared spectroscopy of red supergiants
reveals strong molecular bands, some of which do not originate in
the photosphere but in a cooler layer of molecular material above
it. Lately, these layers have been spatially resolved by near and
mid-IR interferometry. In this paper, we try to reconcile the IR
interferometric and ISO-SWS spectroscopic results on α Orionis with
a thorough modelling of the photosphere, molecular layer(s) and dust
shell. From the ISO and near-IR interferometric observations, we find
that α Orionis has only a very low density water layer close above
the photosphere. However, mid-IR interferometric observations and a
narrow-slit N-band spectrum suggest much larger extra-photospheric
opacity close to the photosphere at those wavelengths, even when
taking into account the detached dust shell. We argue that this cannot
be due to the water layer, and that another source of mid-IR opacity
must be present. We show that this opacity source is probably neither
molecular nor chromospheric. Rather, we present amorphous alumina
(Al2O3) as the best candidate and discuss this hypothesis in the
framework of dust-condensation scenarios.
Title: Chemical analysis of carbon stars in the Local Group
Authors: de Laverny, P.; Abia, C.; Domínguez, I.; Plez, B.; Straniero,
O.; Wahlin, R.; Eriksson, K.; Jørgensen, U. G.
Bibcode: 2006A&A...446.1107D
Altcode: 2005astro.ph.10131D
We present the first results of our ongoing chemical study of carbon
stars in the Local Group of galaxies. We used spectra obtained with
UVES at the 8.2 m Kueyen-VLT telescope and a new grid of spherical
model atmospheres for cool carbon-rich stars which include polyatomic
opacities, to perform a full chemical analysis of one carbon star, BMB-B
30, in the Small Magellanic Cloud (SMC) and two, IGI95-C1 and IGI95-C3,
in the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. Our main goal
is to test the dependence on the stellar metallicity of the s-process
nucleosynthesis and mixing mechanism occurring in AGB stars. For these
three stars, we find important s-element enhancements with respect
to the mean metallicity ([M/H]), namely [s/M]≈+1.0, similar to
the figure found in galactic AGB stars of similar metallicity. The
abundance ratios derived between elements belonging to the first and
second s-process abundance peaks, corresponding to nuclei with a magic
number of neutrons N=50 (88Sr, 89Y, 90Zr) and N=82 (138Ba, 139La, 140Ce,
141Pr), agree remarkably well with the theoretical predictions of low
mass (M <3~M_⊙) metal-poor AGB nucleosynthesis models where the
main source of neutrons is the 13C(α,n)16O
reaction activated during the long interpulse phase, in a small
pocket located within the He-rich intershell. The derived C/O and
12C/13C ratios are, however, more difficult
to reconcile with theoretical expectations. Possible explanations,
like the extrinsic origin of the composition of these carbon stars or
the operation of a non-standard mixing process during the AGB phase
(such as the cool bottom process), are discussed on the basis of the
collected observational constraints.
Title: Carbon stars in local group dwarf galaxies: C and O abundances
Authors: Wahlin, R.; Eriksson, K.; Gustafsson, B.; Hinkle, K. H.;
Lambert, D. L.; Ryde, N.; Westerlund, B.
Bibcode: 2006MmSAI..77..955W
Altcode: 2006astro.ph..5244W
We present abundances of carbon and oxygen as well as abundance
ratios 12C/13C for a sample of carbon stars
in the LMC, SMC, Carina, Sculptor and Fornax dwarf galaxies. The
overall metallicities in these dwarf galaxies are lower than in the
galactic disc. The observations cover most of the AGB and we discuss
the abundance patterns in different regions along the AGB. The
abundances are determined from infrared spectra obtained with the
ISAAC spectrometer on VLT (R=1500) and the Phoenix Spectrometer on
Gemini South (R=50000). The synthetic spectra used in the analysis
were computed with MARCS model atmospheres. We find that the oxygen
abundance is decreasing with decreasing overall metallicity of the
system while the C/O ratio at a given evolutionary phase is increasing
with decreasing oxygen abundance. Based on observations collected
at the European Southern Observatory, Paranal, Chile (ESO Programme
70.D-0414 & 072.D-0501)
Title: Interferometric Detection of Amorphous Alumina Grains in
Betelgeuse
Authors: Verhoelst, T.; Decin, L.; Hony, S.; Cami, J.; Eriksson, K.;
Perrin, G.; Deroo, P.; Vandenbussche, B.; Waters, R.
Bibcode: 2006via..conf..361V
Altcode:
We present a study of the extended atmosphere of the late-type
supergiant Betelgeuse. From near-IR observations, we find that
Betelgeuse has only a very low density water layer just above the
photosphere. However, mid-IR observations suggest a much larger
opacity source close to the photosphere, which can not be due to the
water layer. We show that amorphous alumina grains are the most likely
source of this opacity and discuss this hypothesis in the context of
dust-condensation scenarios.
Title: A strongly s-process enriched RV Tauri star in the LMC.
Authors: Reyniers, M.; Abia, C.; Van Winckel, H.; Lloyd Evans, T.;
Decin, L.; Eriksson, K.
Bibcode: 2006MmSAI..77..949R
Altcode:
A detailed abundance analysis is presented of an intriguing object in
the Large Magellanic Cloud that links the class of RV Tauri stars to the
post-AGB phase of evolution: MACHO 47.2496.8. The spectrum, taken with
VLT-UVES, is dominated by molecular lines of carbon bearing molecules,
together with strong transitions of s-process species. Detailed
spectral syntheses were made using a state-of-the-art carbon rich
MARCS model. A surprisingly low metallicity ([Fe/H] = -1.4), together
with strong carbon (C/O>2) and s-process overabundances were found,
reaching values of [ls/Fe] = +1.2 for the light s-process elements,
and even [hs/Fe] = +2.1 for the heavy ones. The strong s-process
enhancements are in agreement with the theoretical expectations at
that metallicity. Only the combination of a low lead content and a
high [hs/ls] is not easily explained by the current nucleosynthetic
models. It is not clear whether this star is intrisically or
extrinsically enriched, but several arguments favour an intrisic
enrichment, implying the object to be a genuine post carbon (N-type)
AGB star. With the low metallicity and a luminosity at the very low
end of the carbon star luminosity function, MACHO 47.2496.8 represents
the final evolutionary state of a star of low initial mass. Based
on observations collected at ESO, Chile (programme 074.D-0619(A))
Title: Is Arcturus a well-understood K giant?. Test of model
atmospheres and potential companion detection by near-infrared
interferometry
Authors: Verhoelst, T.; Bordé, P. J.; Perrin, G.; Decin, L.; Eriksson,
K.; Ridgway, S. T.; Schuller, P. A.; Traub, W. A.; Millan-Gabet, R.;
Lacasse, M. G.; Waelkens, C.
Bibcode: 2005A&A...435..289V
Altcode: 2005astro.ph..1669V
We present near-IR interferometric measurements of the K1.5 giant
Arcturus (α Bootis), obtained at the IOTA interferometer with the FLUOR
instrument, in four narrow filters with central wavelengths ranging
from 2.03 μm to 2.39 μm. These observations were expected to allow
us to quantify the wavelength dependence of the diameter of a typical
K giant. They are compared to predictions from both plane-parallel and
spherical model atmospheres. Unexpectedly, neither can explain the
observed visibilities. We show that these data suggest the presence
of a companion, in accordance with the Hipparcos data on this star,
and discuss this solution with respect to Arcturus' single star status.
Title: Nucleosynthetic signatures of the first stars
Authors: Frebel, Anna; Aoki, Wako; Christlieb, Norbert; Ando, Hiroyasu;
Asplund, Martin; Barklem, Paul S.; Beers, Timothy C.; Eriksson,
Kjell; Fechner, Cora; Fujimoto, Masayuki Y.; Honda, Satoshi; Kajino,
Toshitaka; Minezaki, Takeo; Nomoto, Ken'ichi; Norris, John E.; Ryan,
Sean G.; Takada-Hidai, Masahide; Tsangarides, Stelios; Yoshii, Yuzuru
Bibcode: 2005Natur.434..871F
Altcode: 2005astro.ph..3021F
The chemically most primitive stars provide constraints on the nature
of the first stellar objects that formed in the Universe; elements
other than hydrogen, helium and traces of lithium present within
these objects were generated by nucleosynthesis in the very first
stars. The relative abundances of elements in the surviving primitive
stars reflect the masses of the first stars, because the pathways of
nucleosynthesis are quite sensitive to stellar masses. Several models
have been suggested to explain the origin of the abundance pattern
of the giant star HE0107-5240, which hitherto exhibited the highest
deficiency of heavy elements known. Here we report the discovery of
HE1327-2326, a subgiant or main-sequence star with an iron abundance
about a factor of two lower than that of HE0107-5240. Both stars
show extreme overabundances of carbon and nitrogen with respect to
iron, suggesting a similar origin of the abundance patterns. The
unexpectedly low Li and high Sr abundances of HE1327-2326, however,
challenge existing theoretical understanding: no model predicts the
high Sr abundance or provides a Li depletion mechanism consistent with
data available for the most metal-poor stars.
Title: Carbon stars in local group dwarf galaxies: C &
O abundances
Authors: Wahlin, R.; Eriksson, K.; Gustafsson, B.; Hinkle, K. H.;
Lambert, D. L.; Ryde, N.; Westerlund, B.
Bibcode: 2005ESASP.560.1017W
Altcode: 2005csss...13.1017W
No abstract at ADS
Title: Phoenix Spectra of Carbon Stars in the LMC
Authors: Wahlin, Rurik; Eriksson, Kjell; Gustafsson, Bengt; Hinkle,
Kenneth; Lambert, David; Ryde, Nils; Westerlund, Bengt
Bibcode: 2005hris.conf..439W
Altcode:
We present high-resolution, IR-spectra of Carbon stars in the LMC
obtained with the Phoenix spectrometer on the Gemini South 8-meter
telescope. This is part of an ongoing project where CNO abundances
and 12C/13C ratios of Carbon Stars are determined in Local-Group
dwarf galaxies of different metallicities. The spectra obtained so
far cover two 20 cm 1 wide spectral regions in the H and K bands. The
bands contain lines from CN, C2, and CO, with 12C and 13C isotopes, and
several atomic lines. The spectra are analyzed with synthetic spectra
of model atmospheres from the MARCS spherical-model-atmosphere code.
Title: The new record holder for the most iron-poor star: HE 1327
2326, a dwarf or subgiant with [Fe/H[=[minus sign]5.4
Authors: Frebel, A.; Aoki, W.; Christlieb, N.; Ando, H.; Asplund, M.;
Barklem, P. S.; Beers, T. C.; Eriksson, K.; Fechner, C.; Fujimoto,
M. Y.; Honda, S.; Kajino, T.; Minezaki, T.; Nomoto, K.; Norris, J. E.;
Ryan, S. G.; Takada-Hidai, M.; Tsangarides, S.; Yoshii, Y.
Bibcode: 2005IAUS..228..207F
Altcode: 2005astro.ph..9658F
We describe the discovery of HE 1327-2326, a dwarf or subgiant with
[Fe/H]=-5.4. The star was found in a sample of bright metal-poor
stars selected from the Hamburg/ESO survey. Its abundance pattern is
characterized by very high C and N abundances. The detection of Sr
which is overabundant by a factor of 10 as compared to iron and the
Sun, suggests that neutron-capture elements had already been produced
in the very early Galaxy. A puzzling Li depletion is observed in this
unevolved star which contradicts the value of the primordial Li derived
from WMAP and other Li studies. Possible scenarios for the origin of
the abundance pattern (Pop. II or Pop. III) are presented as well as
an outlook on future observations.
Title: The Abundance of Elements in Cool Stars, as Determined from
High-Resolution 1 5 μm Spectroscopy
Authors: Ryde, Nils; Gustafsson, Bengt; Eriksson, Kjell; Wahlin, Rurik
Bibcode: 2005hris.conf..365R
Altcode: 2004astro.ph..7340R
We review the field of abundance determinations of elements in cool
stars, with special interest paid to determinations based on analyses
of high-resolution, 1 5 μm spectra. We discuss the current status,
problems, and challenges of exploring high-resolution, near-infrared
spectra. In particular, advantages and drawbacks are pointed out. A few
examples of current, chemical-abundance determinations are highlighted
and, finally, we discuss the development and future prospects of
the field.
Title: Abundances of s-elements in Extragalactic Carbon Stars
Authors: de Laverny, P.; Abia, C.; Domínguez, I.; Plez, B.; Straniero,
O.; Wahlin, R.; Eriksson, K.; Jørgensen, U. G.
Bibcode: 2005IAUS..228..533D
Altcode:
Carbon stars found in the Small Magellanic Cloud and the Sagittarius
Dwarf Spheroidal galaxy have been chemically analysed. We found
that the abundance ratios derived between elements belonging to the
first and the second s-process abundance peaks agree remarkably
well with the theoretical predictions of low mass metal-poor AGB
nucleosynthesis models. Together with their estimated luminosities,
their derived abundances and their carbon isotopic ratio we speculate
on the evolutionary status of these carbon stars.
Title: ISO-SWS calibration and the accurate modelling of cool-star
atmospheres. IV. G9 to M2 stars
Authors: Decin, L.; Vandenbussche, B.; Waelkens, C.; Decin, G.;
Eriksson, K.; Gustafsson, B.; Plez, B.; Sauval, A. J.
Bibcode: 2003A&A...400..709D
Altcode: 2002astro.ph..7653D
A detailed spectroscopic study of 11 giants with spectral type
from G9 to M2 is presented. The 2.38-4.08 mu m wavelength-range of
band 1 of ISO-SWS (Short-Wavelength Spectrometers on board of the
Infrared Space Observatory) in which many different molecules -
with their own dependence on each of the stellar parameters - are
absorbing, enables us to estimate the effective temperature, the
gravity, the microturbulence, the metallicity, the CNO-abundances,
the 12C/13C-ratio and the angular diameter from
the ISO-SWS data. Using the Hipparcos' parallax, the radius, luminosity
and gravity-inferred mass are derived. The stellar parameters obtained
are in good agreement with other published values, though also some
discrepancies with values deduced by other authors are noted. For a
few stars (delta Dra, xi Dra, alpha Tuc, H Sco and alpha Cet) some
parameters - e.g. the CNO-abundances - are derived for the first
time. By examining the correspondence between different ISO-SWS
observations of the same object and between the ISO-SWS data and
the corresponding synthetic spectrum, it is shown that the relative
accuracy of ISO-SWS in band 1 (2.38-4.08 mu m) is better than 2%
for these high-flux sources. The high level of correspondence between
observations and theoretical predictions, together with a confrontation
of the estimated Teff (ISO) value with Teff values
derived from colours - which demonstrates the consistency between V-K,
BCK, Teff and thetad derived from
optical or IR data - proves that both the used MARCS models to derive
the stellar quantities and the flux calibration of the ISO-SWS detectors
have reached a high level of reliability. Based on observations
with ISO, an ESA project with instruments funded by ESA Member States
(especially the PI countries France, Germany, The Netherlands and the
UK) and with the participation of ISAS and NASA. Appendices A-D
are only available in electronic form at http://www.edpsciences.org
Title: ISO-SWS calibration and the accurate modelling of cool-star
atmospheres. II. General results
Authors: Decin, L.; Vandenbussche, B.; Waelkens, C.; Eriksson, K.;
Gustafsson, B.; Plez, B.; Sauval, A. J.; Hinkle, K.
Bibcode: 2003A&A...400..679D
Altcode: 2002astro.ph..7621D
The fine calibration of the ISO-SWS detectors (Infrared Space
Observatory - Short Wavelength Spectrometer) has proven to be a delicate
problem. We therefore present a detailed spectroscopic study in the
2.38-12 mu m wavelength range of a sample of 16 A0-M2 stars used for
the calibration of ISO-SWS. By investigating the discrepancies between
the ISO-SWS data of these sources, the theoretical predictions of their
spectra, the high-resolution FTS-KP (Kitt Peak) spectrum of alpha Boo
and the solar FTS-ATMOS (Atmospheric Trace Molecule Spectroscopy)
spectrum, both calibration problems and problems in computing the
theoretical models and the synthetic spectra are revealed. The
underlying reasons for these problems are sought for and the impact
on the further calibration of ISO-SWS and on the theoretical modelling
is discussed extensively. Based on observations with ISO, an ESA
project with instruments funded by ESA Member States (especially the
PI countries France, Germany, The Netherlands and the UK) and with
the participation of ISAS and NASA. Appendix is only available
in electronic form at http://www.edpsciences.org
Title: Imaging polarimetry of stellar light scattered in detached
shells around the carbon stars R Scl and U Ant
Authors: González Delgado, D.; Olofsson, H.; Schwarz, H. E.; Eriksson,
K.; Gustafsson, B.; Gledhill, T.
Bibcode: 2003A&A...399.1021G
Altcode:
Imaging polarimetry has been used to study the extended, detached
circumstellar shells around the bright carbon stars R
Scl and U Ant. The observations were
done in two narrow band filters centred on the resonance lines of
neutral K and Na, but much broader than the expected line widths. The
polarimetric data reveal brightness distributions, in both cases,
which are in perfect agreement with previous observations of scattered
light obtained through direct imaging techniques. The total intensity
images towards R Scl outline, in both filters,
circular disk-like distributions out to a radius of ~21arcsec , where
the intensity drops sharply. The polarised intensity images reveal,
however, that the scattering occurs in a geometrically thin shell. The
degree of polarisation reaches values of ~35% in both filters. The
imaging polarimetry observations of U Ant reveal a
somewhat more complex structure, where the existence of several shells
can be discerned. The polarised scattered light comes from a component,
at a radius of ~50arcsec from the star, which lies outside the region
where the bulk of the light is scattered. The latter comes from a
dominating shell at ~43arcsec , which coincides spatially with the
detached gas shell inferred from CO radio line data, and there may be
another two shells inside this. The polarisation degree reaches ~50%
in the outer component. We model, with a code based on the Monte Carlo
method, the scattered emission under the assumption of dust scattering,
using the observed polarised brightness distributions as constraints. In
the case of R Scl we found that the polarised, as
well as the total, light distributions can be explained by scattering
in a 2arcsec wide shell of radius 20arcsec containing a dust mass of
~2*E-6 Msun. This dust shell is also responsible
for the thermal dust emission measured by IRAS. There is room, up to 30%
of the total scattered flux, for other scattering agents. Comparison
with CO radio line data shows that this dust shell probably lies outside
the detached CO gas shell. In the case of U Ant the
modelling explains the outer component in terms of a 5arcsec wide shell
at a radius of about 52arcsec with a dust mass of ~4*E-6
Msun. This is also the dust shell responsible for the
emission measured by IRAS. However, the bulk of the scattered light
cannot in this case be due to scattering by dust. In accordance
with a discussion in a previous paper we attribute the remaining,
unpolarised, scattering to the KI and Na D resonance lines. In both
cases we found evidence that a dust shell has separated from the rest
of the circumstellar medium. This may be due to gas-grain drift,
or to hydrodynamical effects, which may also explain the complex
multiple-shell structure seen towards U Ant. The
model results are very dependent on the grain size distribution,
and the observational data can only be reconciled with a very steep
decline in grain size. Based on observations using the 3.6 m
telescope of the European Southern Observatory, La Silla, Chile.
Title: Carbon Stars in the Local Group -- Detailed Abundance Analysis
of Carbon Stars in the LMC
Authors: Lambert, David L.; Eriksson, Kjell; Gustafsson, Bengt;
Hinkle, Kenneth H.; Ryde, Nils; Wahlin, Rurik; Westerlund, Bengt
Bibcode: 2003noao.prop..265L
Altcode:
Using the Phoenix on Gemini we propose to observe a sample of carbon
stars in the LMC in four different wavelength regions at high spectral
resolution and with high S/N. The spectra will provide CO, CN, and
C_2 and atomic lines from which elemental and isotopic C, N, and O
abundances and metal abundances will be derived by an approach similar
to that previously used for Galactic field carbon stars (Lambert et
al. 1986). We will then be able to calibrate lower resolution spectra
of carbon stars in other Local Group galaxies. The observational study
of carbon stars is a key to understanding late evolutionary stages
and nucleosynthesis of low mass stars.
Title: The Infrared Spectrum of R Doradus
Authors: Ryde, N.; Eriksson, K.
Bibcode: 2003IAUS..210P.E53R
Altcode: 2002astro.ph.10188R
Here, we present our modelling (Ryde & Eriksson, 2002 A&A 386,
874) of the 2.6-3.7 micron spectrum of the red semiregular variable R
Doradus observed with the Short-Wavelength Spectrometer on board the
Infrared Space Observatory. We will also present the entire spectrum
of R Dor up to 5 microns based on our model photosphere in order to
show which molecules are important for the emergent spectrum.
Title: A Grid of Model Atmospheres for Cool Stars
Authors: Gustafsson, B.; Edvardsson, B.; Eriksson, K.; Mizuno-Wiedner,
M.; Jørgensen, U. G.; Plez, B.
Bibcode: 2003ASPC..288..331G
Altcode: 2003sam..conf..331G
An extensive grid of spherically symmetric model atmospheres of stars
with 1. 2500 K ≤ Teff ≤ 8000 K, 2. -1.0 ≤ log g
(= log GM/R2) ≤ 5.0 (cgs units), 3. different combinations
of M and R, 4. -5 ≤ [A/H] ≤ 1, and 5. a number of CNO abundance
combinations is being constructed with an updated version of the
MARCS program. Special efforts are made to reach accuracy and
completeness in opacity data. Opacity sampling is used with 10,000
and (for a minority of models) 90,000 wavelength points. Synthetic
spectra are also provided. We shall show how these classical
models may be used to illustrate important physical properties of cool
star atmospheres.
Title: A New MARCS Grid
Authors: Gustafsson, B.; Edvardsson, B.; Eriksson, K.; Jørgensen,
U. G.; Mizuno-Wiedner, M.; Plez, B.
Bibcode: 2003IAUS..210P..A4G
Altcode:
No abstract at ADS
Title: A MARCS Grid of S-Type Star Atmospheres
Authors: Plez, B.; van Eck, S.; Jorissen, A.; Edvardsson, B.; Eriksson,
K.; Gustafsson, B.
Bibcode: 2003IAUS..210P..A2P
Altcode:
No abstract at ADS
Title: The 3 mu m spectrum of R Doradus observed with the ISO-SWS
Authors: Ryde, N.; Eriksson, K.
Bibcode: 2002A&A...386..874R
Altcode: 2002astro.ph..2171R
We have modeled the 2.6-3.7 μm spectrum of the red semiregular
variable R Doradus observed with the Short-Wavelength Spectrometer on
board the Infrared Space Observatory. The wavelength resolution of
the observations varies between R ~ 2000-2500. We have calculated a
synthetic spectrum using a hydrostatic model photosphere in spherical
geometry. The agreement between the synthetic spectrum and the ISO
observations is encouraging, especially in the wavelength region
of 2.8-3.7 μm, suggesting that a hydrostatic model photosphere is
adequate for the calculation of synthetic spectra in the near infrared
for this moderately varying red giant star. However, an additional
absorption component is needed at 2.6-2.8 μm and this discrepancy is
discussed. The spectral signatures are dominated by water vapour in the
stellar photosphere, but several photospheric OH, CO, and SiO features
are also present. The effective temperature and surface gravity derived
for R Dor, based on the 2.6-3.7 μm ISO spectrum and the modeling of
it with a hydrostatic model photosphere, are 3000+/- 100 K and log g =
0 +/- 1 (cgs), respectively. The spectral region observed is found to be
temperature sensitive. The effective temperature given here is slightly
higher than those reported in the literature. We also discuss possible
reasons for this. Based on observations with ISO, an ESA project with
instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands and the UK) and with the participation
of ISAS and NASA. The SWS is a joint project of SRON and MPE.
Title: Imaging of detached shells around the carbon stars R
Scl and U Ant through scattered
stellar light
Authors: González Delgado, D.; Olofsson, H.; Schwarz, H. E.; Eriksson,
K.; Gustafsson, B.
Bibcode: 2001A&A...372..885G
Altcode: 2001astro.ph..4140G; 2001astro.ph..4140D
We present the first optical images of scattered light from large,
detached gas/dust shells around two carbon stars, R
Scl and U Ant, obtained in narrow band
filters centred on the resonance lines of neutral K and Na, and in
a Ström}gren b filter (only U Ant). They confirm
results obtained in CO radio line observations, but also reveal new
and interesting structures. Towards R Scl the
scattering appears optically thick in both the K and Na filters, and
both images outline almost perfectly circular disks with essentially
uniform intensity out to a sharp outer radius of ~21arcsec . These
disks are larger - by about a factor of two - than the radius of the
detached shell which has been marginally resolved in CO radio line
data. In U Ant the scattering in the K filter
appears to be, at least partially, optically thin, and the image is
consistent with scattering in a geometrically thin (~3arcsec ) shell
(radius ~43arcsec ) with an overall spherical symmetry. The size of
this shell agrees very well with that of the detached shell seen in
CO radio line emission. The scattering in the Na filter appears more
optically thick, and the image suggests the presence of at least one,
possibly two, shells inside the 43arcsec shell. There is no evidence
for such a multiple-shell structure in the CO data, but this can be due
to considerably lower masses for these inner shells. Weak scattering
appears also in a shell which is located outside the 43arcsec shell. The
present data do not allow us to conclusively identify the scattering
agent, but we argue that most of the emission in the K and Na filter
images is to due to resonance line scattering, and that there is
also a weaker contribution from dust scattering in the U
Ant data. Awaiting new observational data, our interpretation
must be regarded as tentative. Based on observations using the 3.6 m
telescope of the European Southern Observatory, La Silla, Chile.
Title: Images in Scattered Light of Two Carbon Stars (CD-ROM
Directory: contribs/gonzalez)
Authors: González Delgado, D.; Olofsson, H.; Schwarz, H.; Eriksson,
K.; Gustafsson, B.
Bibcode: 2001ASPC..223.1219G
Altcode: 2001csss...11.1219G
No abstract at ADS
Title: ISO-SWS calibration and the accurate modelling of cool-star
atmospheres. I. Method
Authors: Decin, L.; Waelkens, C.; Eriksson, K.; Gustafsson, B.; Plez,
B.; Sauval, A. J.; Van Assche, W.; Vandenbussche, B.
Bibcode: 2000A&A...364..137D
Altcode: 2000astro.ph..8316D
A detailed spectroscopic study of the ISO-SWS data of the red
giant alpha Tau is presented, which enables not only the accurate
determination of the stellar parameters of alpha Tau, but also serves
as a critical review of the ISO-SWS calibration. This study is situated
in a broader context of an iterative process in which both accurate
observations of stellar templates and cool star atmosphere models
are involved to improve the ISO-SWS calibration process as well as the
theoretical modelling of stellar atmospheres. Therefore a sample of cool
stars, covering the whole A0 - M8 spectral classification, has been
observed in order to disentangle calibration problems and problems
in generating the theoretical models and corresponding synthetic
spectrum. By using stellar parameters found in the literature large
discrepancies were seen between the ISO-SWS data and the generated
synthetic spectrum of alpha Tau. A study of the influence of various
stellar parameters on the theoretical models and synthetic spectra,
in conjunction with the Kolmogorov-Smirnov test to evaluate objectively
the goodness-of-fit, enables us to pin down the stellar parameters with
a high accuracy: Teff = 3850 +/- 70 K, log g = 1.50 +/- 0.15,
M = 2.3 +/- 0.8 Msun, z = -0.15 +/- 0.20 dex, xit
= 1.7 +/- 0.3 km s-1, 12C/13C = 10
+/- 1, varepsilon (C) = 8.35 +/- 0.20 dex, varepsilon (N) = 8.35 +/-
0.25 dex, varepsilon (O) = 8.83 +/- 0.15 dex and thetad =
20.77 +/- 0.83 mas. These atmospheric parameters were then compared
with the results provided by other authors using other methods
and/or spectra. Based on observations with ISO, an ESA project with
instruments funded by ESA Member States (especially the PI countries
France, Germany, the Netherlands and the United Kingdom) and with the
participation of ISAS and NASA.
Title: Mira's Wind Explored in Scattering Infrared CO Lines
Authors: Ryde, N.; Gustafsson, B.; Eriksson, K.; Hinkle, K. H.
Bibcode: 2000ApJ...545..945R
Altcode: 2000astro.ph..8235R
We have observed the intermediate regions of the circumstellar
envelope of Mira (ο Ceti) in photospheric light scattered by three
vibration-rotation transitions of the fundamental band of CO, from
low-excited rotational levels of the ground vibrational state, at an
angular distance of β~2''-7" away from the star. The data
were obtained with the Phoenix spectrometer mounted on the 4 m Mayall
telescope at Kitt Peak. The spatial resolution is approximately 0.5"
and seeing limited. Our observations provide absolute fluxes, leading
to an independent new estimate of the mass-loss rate of approximately
3×10-7 Msolar yr-1, as derived from
a simple analytic wind model. We find that the scattered intensity
from the wind of Mira for 2''<~β<~7''
decreases as β-3, which suggests a time constant mass-loss
rate, when averaged over 100 yr, over the past 1200 yr.
Title: ISO Impact on Stellar Models and Viceversa
Authors: Decin, L.; Waelkens, C.; Eriksson, K.; Gustafsson, B.; Plez,
B.; Sauval, A. J.; van Assche, W.; Vandenbussche, B.
Bibcode: 2000ESASP.456..289D
Altcode: 2000astro.ph..8362D; 2000ibp..conf..289D
We present a detailed spectroscopic study of a sample of bright,
mostly cool, stars observed with the Short-Wavelength Spectrometer
(SWS) on board ISO, which enables the accurate determination of the
stellar parameters of the cool giants, but also serves as a critical
review of the ISO-SWS calibration.
Title: Gasdynamics of Detached Shells Around Carbon Stars With
Variable Mass Loss
Authors: Myasnikov, A. V.; Belov, N. A.; Gustafsson, B.; Eriksson, K.
Bibcode: 2000Ap&SS.274..231M
Altcode:
Gasdynamic features of detached shells around carbon stars with
variable mass loss rate are investigated in detail numerically. It
is shown that a shell is unstable and also, 2D perturbations are less
developed that 3D ones. The structure of perturbed flows corresponding
to different evolution scenarios is compared. The results obtained
seem to be promising for interpretation of observations, in particular,
the recently obtained detailed data of TT Cyg.
Title: CO Imaging of Late-Type Circumstellar Shells
Authors: Gustafsson, Bengt; Eriksson, Kjell; Lambert, David L.;
Olofsson, Hans; Ryde, Nils; Schoier, Fredrik L.
Bibcode: 2000noao.prop..293G
Altcode:
Microwave emission lines and optical resonance lines have been used
to image circumstellar shells on the sky. Now it is possible to
image resonance scattering from infrared vibration-rotational carbon
monoxide lines (see Ryde et al. A& A 347, L35, 1999). Infrared CO is
formed closer to the star than microwave CO and provides complementary
information. Infrared CO mapping is especially powerful because many
CO lines of differing excitation are present, allowing the extraction
of excitation temperature and abundance from the measured column
densities. Previous on-star observations have led to the detection
of multiple velocity components in the CO lines, formed in different
parts of the circumstellar shell. We have found in an earlier observing
run with this method that the shell of CO gas around Mira (4 arcsec-10
arcsec from the star) is spherically symmetric and homogeneous. But we
also trace from the data a region close to the star devoid of gas or
at least of CO (Ryde et al. ApJ, soon to be submitted). Each CO line
can be used to image the circumstellar outflow at different stellar
radii. Information on the velocity structure and the development of
clumps in the flow will be extracted. The present proposal focuses on
the study of shells around carbon stars for which we have complementary
mm and optical data. We will furthermore for the first time map detached
shells with this method.
Title: Interferometric Molecular Line observations of RW LMi
Authors: Lindqvist, Michael; Lucas, Robert; Olofsson, Hans; Larsen,
Fredrick; Omont, Alain; Eriksson, Kjell; Gustafsson, Bengt
Bibcode: 2000IAUS..177..557L
Altcode:
No abstract at ADS
Title: VizieR Online Data Catalog: Atmospheric parameters in
metal-poor stars. II (Gratton+, 1999)
Authors: Gratton, R. G.; Carretta, E.; Eriksson, K.; Gustafsson, B.
Bibcode: 2000yCat..33500955G
Altcode:
We present non-LTE corrections to abundances of Fe, O, Na, and Mg
derived from LTE analyses of F-K stars over a broad range of gravities
and metal abundances; they were obtained using statistical equilibrium
calculations and new model atoms. Line opacity was considered by
means of an empirical procedure where it was attributed to a veil
of weak Fe I lines; in the case of solar-type dwarfs, results were
compared with those obtained using (LTE) mean intensities computed
from OSMARCS models. We think that the empirical procedure produces
better results for metal-poor stars, while mean intensities should
perhaps be preferred for the Sun (where departures from LTE are
anyway not very large). Collisions with both electrons and H I atoms
were considered. Since cross sections for this second mechanism
are very poorly known, we calibrated them empirically by matching
observations of RR Lyrae variables at minimum light (discussed in
Clementini et al., 1995, Cat. ). These stars were selected because
non-LTE effects are expected to be larger in these stars than in
those usually considered in the study of the chemical evolution of the
Galaxy (cool main sequence and red giant branch stars). We found that
different non-LTE mechanisms are important for the different species
and transitions considered; on the whole, our calculations yielded
moderate corrections to LTE abundances for high excitation O lines
in warm dwarfs and giants, Na and Mg lines in giants and supergiants,
and Fe I lines in F-supergiants (where corrections becomes very large
for IR O lines). Non-LTE corrections were found to be negligible in
the other cases studied. (3 data files).
Title: A high-resolution study of episodic mass loss from the carbon
star TT Cygni
Authors: Olofsson, H.; Bergman, P.; Lucas, R.; Eriksson, K.;
Gustafsson, B.; Bieging, J. H.
Bibcode: 2000A&A...353..583O
Altcode:
CO radio line observations with the IRAM Plateau de Bure interferometer
show that the carbon star TT Cyg is surrounded by a large (radius
~ 35arcsec or 2.7x1017 cm), geometrically thin (average
width ~ 2farcs 5 or 1.9x1016 cm) shell of gas, which has a
remarkable overall spherical symmetry (e.g., its radius varies by less
than +/-3%). It expands with a velocity of ~ 12.6 km s-1. The
emitting gas is very evenly distributed in the shell when averaged
over a solid angle of about 0.2 steradians. We estimate a molecular
hydrogen density of ~ 250 cm-3, a gas kinetic temperature
of ~ 100 K, and a mass of ~ 0.007 M_sun for the shell if the medium
is homogeneous. There is no evidence for matter immediately inside
or outside the shell, nor is there any evidence for structure in the
radial direction of the shell brightness distribution (it is essentialy
perfectly fitted with Gaussians). The shell centre is displaced ~
1farcs 7 (position angle ~ -20degr ) with respect to the star. We
favour an interpretation of this displacement in terms of TT Cyg being
a member of a binary system. We put forward several arguments for a
shell medium that consists almost entirely of a large number of small
(la 1arcsec ) clumps (in which case the density required to fit the
observational data is much higher, ~ 104 cm-3,
and the kinetic temperature is considerably lower, la 20 K). TT Cyg is
presently losing mass at a modest rate, ~ 3x10-8 M_sunpyr,
and with a low expansion velocity, ~ 3.8 km s-1. This is
inferred from CO line emission from a region centred on the present
position of the star. The systemic velocity is estimated, from both
the centre and the shell emission, to be -27.3+/-0.1 km s-1
in the LSR system. All quantitative results are obtained assuming
the Hipparcos distance of 510 pc. These data strongly support that TT
Cyg has recently ( ~ 7x103 yr ago) gone through a period
of drastically varying mass loss properties. We discuss briefly two
scenarios: a short period (a few hundred years) of very intense mass
loss (a rate in excess of 10-5 M_sunpyr), and a related
scenario with a more modest mass ejection and where most of the shell
gas is swept-up from a previous, slower stellar wind. It is presently
not possible to favour any of these two scenarios, but we suggest that
in either case it is a coordinated mass ejection that caused the shell
formation. The He-shell flash phenomenon in AGB-stars can provide this
coordination, and it also fits the time scales involved.
Title: Scattered Light from Envelopes around N-type Stars
Authors: Gustafsson, Bengt; Eriksson, Kjell; Kiselman, Dan; Olander,
Nils; Olofsson, Hans; Schwarz, Hugo E.
Bibcode: 2000IAUS..177..409G
Altcode:
No abstract at ADS
Title: Abundances of light elements in metal-poor stars. II. Non-LTE
abundance corrections
Authors: Gratton, R. G.; Carretta, E.; Eriksson, K.; Gustafsson, B.
Bibcode: 1999A&A...350..955G
Altcode:
We present non-LTE corrections to abundances of Fe, O, Na, and Mg
derived from LTE analyses of F-K stars over a broad range of gravities
and metal abundances; they were obtained using statistical equilibrium
calculations and new model atoms. Line opacity was considered by
means of an empirical procedure where it was attributed to a veil
of weak Fe I lines; in the case of solar-type dwarfs, results were
compared with those obtained using (LTE) mean intensities computed
from OSMARCS models. We think that the empirical procedure produces
better results for metal-poor stars, while mean intensities should
perhaps be preferred for the Sun (where departures from LTE are
anyway not very large). Collisions with both electrons and H I atoms
were considered. Since cross sections for this second mechanism
are very poorly known, we calibrated them empirically by matching
observations of RR Lyrae variables at minimum light (discussed in
Clementini et al. 1995). These stars were selected because non-LTE
effects are expected to be larger in these stars than in those
usually considered in the study of the chemical evolution of the
Galaxy (cool main sequence and red giant branch stars). We found that
different non-LTE mechanisms are important for the different species
and transitions considered; on the whole, our calculations yielded
moderate corrections to LTE abundances for high excitation O lines
in warm dwarfs and giants, Na and Mg lines in giants and supergiants,
and Fe I lines in F-supergiants (where corrections becomes very large
for IR O lines). Non-LTE corrections were found to be negligible in
the other cases studied. The Tables~1 to 12 are available only in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
Title: Preliminary results on the circumstellar envelopes of alpha
ORI and R Leo from CO 4.6 micron line emission
Authors: Ryde, N.; Gustafsson, B.; Hinkle, K. H.; Eriksson, K.;
Lambert, D. L.; Olofsson, H.
Bibcode: 1999A&A...347L..35R
Altcode:
CO 4.6 mu m vibration-rotational lines are detected in fluorescent
emission from the inner regions of the Betelgeuse (alpha
Orionis) and R Leonis stellar winds. The
spatially and spectrally resolved 1-0 R(1), R(2), and R(3) line profiles
are found to be highly useful probes of circumstellar shells. The
current data sample only a few regions of the circumstellar shells of
the program stars. However, now it should be possible to obtain envelope
maps and absolute flux estimates, allowing new independent estimates
of mass loss rates. This will open up new possibilities in the study
of the structure and dynamics of stellar winds around red giants. The
temperature 4arcsec away from alpha Ori is found to be 38(+6}_{-5} {K)
. For R Leo the temperature 4arcsec North is derived to be 24(+3}_{-2}
{K) and 4arcsec South 35(+7}_{-4} {K) .
Title: The nature of the circumstellar CO_2 emission from M giants
Authors: Ryde, N.; Eriksson, K.; Gustafsson, B.
Bibcode: 1999A&A...341..579R
Altcode: 1998astro.ph.11330R
The 13-16mu m region observed by the Infrared Space Observatory (ISO)
of several ABG stars are discussed. We present and analyse spectra
of seven M giants which show carbon dioxide features. To explain the
features of the bands, we suggest they originate from two different
circumstellar layers, one being a warm and high density layer close
to the star, possibly making the 15mbox {\mum} band optically thick,
and the other being a large, cold and optically thin layer extending
far out in the wind. This could explain the difference in temperatures
of the different bands found in the analysis of the spectra and the
number of molecules needed for the emission. It is demonstrated that
in spite of the bands probably not being formed in vibrational LTE,
the temperatures can be estimated from the widths of the bands. Based
on observations with ISO, an ESA project with instruments funded by
ESA Member States (especially the PI countries: France, Germany, the
Netherlands and the United Kingdom) and with the participation of ISAS
and NASA. The SWS is a joint project of SRON and MPE.
Title: A thin molecular shell around the carbon star TT CYG
Authors: Olofsson, H.; Bergman, P.; Lucas, R.; Eriksson, K.;
Gustafsson, B.; Bieging, J. H.
Bibcode: 1998A&A...330L...1O
Altcode:
Interferometric CO({\jtra10} and {\tra21}) observations reveal a
remarkably thin shell of molecular gas around the carbon star TT Cyg,
width/radius la 1farcs 3/34arcsec ~ 0.04. It expands at ~13{km s(-1) ,
and contains ~ 0.02M_sun of gas provided the CO abundance with respect
to H_2 is 10(-3) and the distance is 1kpc. Only about a quarter of the
shell has been mapped, but we infer an overall spherical shell with
only small, but clear, deviations at the per cent level. The radial
structure of the shell is barely resolved at the arc second level,
but there exists weak emission extending a few arc seconds inwards
from the peak. A drastic change in mass loss properties, possibly
combined with the effects of interacting winds, provides the most
likely explanation to the origin of the shell. %
Title: Tentative Detection of Circumstellar CO2 from the AGB Star
R Crateris
Authors: Ryde, N.; Eriksson, K.; Gustafsson, B.; Lindqvist, M.;
Olofsson, H.
Bibcode: 1998Ap&SS.255..301R
Altcode: 1997Ap&SS.255..301R
We report on and discuss the detection of an emission feature at 14.98
µm from the oxygen-rich, semi-regularly pulsating Asymptotic Giant
Branch star R Crateris, a feature which we suggest to be due to the
<Stack> 0 1 </Stack> Q-branch of
circumstellar CO2. We also suggest a reasonable excitation mechanism,
which could explain the height, the width and the asymmetry of the
feature.
Title: Modelling of molecular bands of oxygen-rich AGB stars
Authors: Ryde, N.; Eriksson, K.; Gustafsson, B.; Olofsson, H.; Plez, B.
Bibcode: 1998IAUS..191P.118R
Altcode:
ISO observations of infrared molecular bands of oxygen-rich AGB stars
are compared with synthetic spectra generated using model atmospheres
from the new large grid of model atmospheres that we are currently
calculating with the newest MARCS code in spherical geometry. Seven
molecular bands of eight M-giants, observed by ISO in medium resolution
mode (SWS06), are analysed in this way.
Title: Modelling of ISO-SWS spectra of red giants
Authors: Decin, L.; Cohen, M.; Eriksson, K.; Gustafsson, B.; Huygen,
E.; Morris, P.; Plez, B.; Sauval, J.; Vandenbussche, B.; Waelkens, C.
Bibcode: 1998IAUS..191P.120D
Altcode:
The modelling and interpretation of the ISO-SWS (Infrared Space
Observatory - Short Wavelength Spectrometer) data require accurately
calibrated spectrometers. In the SWS spectral region (2.38-45.2 microns)
the primary standard calibration candles are bright, mostly cool,
stars. The better these calibration sources are known in the infrared,
the more accurate the spectrometers can be calibrated. Since ISO offers
the first opportunity to observe in the infrared with a resolving power
of ~1500, our knowledge on stellar sources -and more specifically on
stellar atmospheres- is not so refined. A full exploitation of the ISO
data will therefore result from an iterative process in which both
accurate observations and new modelling are involved. A comparison
between the observed SWS spectra and the predicted ones based on the
Opacity Sampling spherical models of B. Plez (Plez et al., 1992; 1993)
is performed. This reveals not only calibration problems, but also
shortcomings in generating the synthetic spectra. Our results will not
only contribute to a better calibration of the ISO-SWS data, but also to
a better understanding and modelling of the atmosphere of cool giants.
Title: Mid and far-infrared spectra of the third brightest carbon
star IRAS 15194-5115
Authors: Ryde, N.; Eriksson, K.; Gustafsson, B.; Jorgensen, U. G.;
Nyman, L. -Aa.; Olofsson, H.; Plez, B.; Wolstencroft, R.
Bibcode: 1998IAUS..191P.312R
Altcode:
ISO observations from 2 to 197 microns of the recently discovered,
third brightest (at 12 microns) carbon star IRAS 15194-5115, are
analysed. Eighty spectra, covering the entire range from 2.3 microns
to 45 microns, were observed in the ISO medium-high resolution mode
(SWS06). Also, observations were made with the ISO long wavelength
spectrometer (LWS) from 42 to 197 microns. The evolutionary stage and
chemistry are discussed and a comparison to the similar carbon star
IRC+10216 is made.
Title: Episodic mass loss of the carbon star TT CYG
Authors: Olofsson, H.; Bergman, P.; Lucas, R.; Eriksson, K.;
Gustafsson, B.; Bieging, J. H.
Bibcode: 1998IAUS..191P.415O
Altcode:
There exists now seven carbon stars for which there is good evidence
that the mass loss has been highly episodic. Detached gas shells were
first imaged in circumstellar CO emission, R Scl, U Ant, S Sct, and TT
Cyg (see Olofsson et al. 1996), or in other molecular line emissions,
U Cam. Detached dust shells have been observed towards U Hya, Y CVn, and
U Ant (probably two shells). So far there is only one M-star for which a
similar detached shell has been found, R Hya. It has been suggested that
these shells are due to episodic high mass loss rate events connected
with the thermal pulses of the central star. In this poster we present
high resolution (~2 arcsecond) CO(J = 1-0) observations of the carbon
star TT Cyg performed with the IRAM interferometer on Plateau de Bure,
France (a minor part of the data have been presented in Olofsson et
al. 1998). To cover the entire shell we have observed eight primary
fields. We have used four configurations to be sensitive to extended
as well as sharply peaked emission. The data reveal an overall close
to spherically symmetric, very narrow (width/radius approximately less
than 0.04, except to the north) shell. Yet, there are clear deviations
from perfect spherical symmetry, e.g., the star does not lie exactly
at the centre of the shell, which appears to break up in the north. The
brightness distribution is very patchy. If the shell is due to a phase
of substantially increased mass loss, the time scale for this phase is
at most a few hundred years and the mass loss rate must have approached
10^{-4} Modot yr^{-1} ~5000 years ago (adopting the HIPPARCOS
distance of ~500 pc). The present mass loss of the star is very low.
Title: Images in scattered light of detached circumstellar shells
Authors: Delgado, D. G.; Olofsson, H.; Schwarz, H.; Eriksson, K.;
Gustafsson, B.
Bibcode: 1998IAUS..191P.404D
Altcode:
The temporal variations of the mass loss rate of an AGB-star as it
evolves is to a large extent unknown. This applies to all time scales
from the pulsation period to the full time scale for the AGB-phase. For
the shortest time scales we are limited by the spatial resolution of
the observations, while for the longest time scales we lack suitable
observational probes. On the intermediate time scales (10^2-10^4
yr) there is now growing evidence for substantial variations in the
mass loss rate, perhaps due to the effects of thermal pulses. Some
of the best examples are provided by CO radio line observations of
detached gas shells, and at least in one case the shell is extremely
narrow compared to its radius (width/radius approximately less than
0.04, see P4-15). The interpretation of the CO data are hampered by
the fact that the emission depends on the excitation as well as the
photodissociation of the CO-molecules, and hence the relation between
the density distribution (and consequently the mass loss history)
and the brightness distribution is uncertain. Here we present images
obtained in 50 AA narrow filters (centered on the KI and Na D lines)
with the ESO 3.6m telescope of three carbon stars with detached CO
shells: R Scl, U Ant, and S Sct. In the two former we detect light
scattered in extended envelopes. The brightness is relatively constant
out to a relatively sharp outer radius, R Scl (~19 arcsecond) and U
Ant (~41 arcsecond). For U Ant this radius coincides exactly with the
observed peak radius of the CO shell. For R Scl this radius coincides
with the outer radius of the CO distribution (as estimated from a
model fit to the CO data; the CO shell is only marginally resolved
and hence its radius is not well determined). [In the case of S Sct,
with the largest CO shell radius (~70 arcsecond), no scattered light
is detected.] This strongly supports the conclusion that the density
distribution has a sharp outer edge. The shell distribution of the CO
emission can only be reasonably explained by a sharp inner edge of the
density distribution. Hence, these stars have gone through a period of
significant change in the mass loss rate. Whether the shells are formed
by a brief period of very enhanced mass loss, or are due to a faster
wind sweeping up material from a slower wind remains to be determined.
Title: Hubble Space Telescope Spectroscopy of the Carbon Star
TX Piscium
Authors: Carpenter, Kenneth G.; Robinson, Richard D.; Johnson, Hollis
R.; Eriksson, Kjell; Gustafsson, Bengt; Pijpers, Frank P.; Querci,
Francois; Querci, Monique
Bibcode: 1997ApJ...486..457C
Altcode:
Ultraviolet spectra obtained with the Hubble Space Telescope of the
carbon star TX Piscium (HR 9004) are presented, along with analysis
providing information on its outer atmosphere, including flow and
turbulent velocities, line formation mechanisms, and variations with
time. Both thermal (collisionally excited) and fluorescent emission
from the chromosphere of the star appear to be formed near the stellar
rest velocity, i.e., in a region below that in which the stellar wind is
accelerated. Absorption self-reversals in the Mg II emission confirm the
presence of an outflowing stellar wind at a mean velocity of about 9-10
km s-1. Circumstellar absorption features (Mn I and Fe I)
overlying the Mg II emission indicate a cool shell expanding at about
5-6 km s-1 relative to the photosphere. The widths (FWHM)
of various emission lines indicate that the chromospheric turbulence is
at least 16 km s-1, but that it may increase with altitude
to as much as 34 km s-1. Three hours of integration on
the C II] lines are examined for any signs of variability that might
indicate the presence of shocks, but no statistically significant
variations are seen. A previous identification (in spectra of UU Aur)
of an emission line at 2807 Å, seen only in spectra of carbon stars,
as belonging to Fe I multiplet UV45 pumped by the C II] line at 2325 Å
is confirmed by the discovery of an absorption feature corresponding
exactly to the wavelength of the pumped transition (Fe I UV13) near
2325 Å. Lines from Fe II UV165, previously seen in solar off-limb
spectra and in Goddard High-Resolution Spectrograph spectra of α Tau,
are clearly present. The normally much stronger Fe II UV32, 62, and
63 multiplets are seen but are weaker relative to both the UV165 lines
and the intercombination lines of C II] and Si II] than in α Tau. The
weakness of these Fe II lines is indicated both by their absolute flux
levels and by their narrow, single-peaked profiles, which are in sharp
contrast to the broad, double-peaked profiles seen in oxygen-rich cool
giant and supergiant stars. The weakness of the Fe II lines and the
presence of the Fe I 2807 Å line suggest that the ionization fraction
of iron (Fe II/Fe I) is significantly lower in the outer atmospheres of
carbon stars. Fluxes in emission lines of Fe II and Mg II are >=2-3
times lower than in a 1984 IUE spectrum of TX Psc, confirming that
the latter was obtained at an epoch of unusual UV brightness for the
star. The Mg II profiles are heavily mutilated by overlying absorption,
even more so than in 1984. The TX Psc profiles are very similar to
those seen in the carbon star TW Hor but are dramatically different
than those in another carbon star, UU Aur, whose lines show violet
wing emission out to much shorter wavelengths than in the other two
stars. Based on observations with the NASA/ESA Hubble Space
Telescope, which is operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS 5-26555 and on
observations at the Haute-Provence Observatory.
Title: (Erratum) Line-blanketed model atmospheres for R Coronae
Borealis stars and hydrogen-deficient carbon stars.
Authors: Asplund, M.; Gustafsson, B.; Kiselman, D.; Eriksson, K.
Bibcode: 1997A&A...323..286A
Altcode:
Erratum to Astron. Astrophys. 318, 521-534 (1997)
Title: Molecules in Circumstellar Envelopes of Carbon Stars
Authors: Larsen, F.; Olofsson, H.; Eriksson, K.; Gustafsson, B.
Bibcode: 1997Ap&SS.251..235L
Altcode:
We have searched for line emission from various transitions of
a number of molecules, including CO, HCN, CN, CS and SiO, as
well as some of their isotopic variants, towards a sample of 68
bright carbon stars. Part of the data has already been published
in Olofsson et al. (1993a,b). The aim of the project is to obtain a
better understanding of the carbon star phenomenon and the processes
involved. In particular, we would like to obtain reliable mass loss
rates and molecular abundances for these objects. This requires careful
and detailed modelling, which is currently underway. Our hope is that
the study of these bright carbon stars will serve as a guide to the
study of higher mass loss rate objects. Some preliminary observational
results are presented here.
Title: KI emission from envelopes around N-type stars. Spectroscopic
observations and interpretations.
Authors: Gustafsson, B.; Eriksson, K.; Kiselman, D.; Olander, N.;
Olofsson, H.
Bibcode: 1997A&A...318..535G
Altcode:
Circumstellar envelopes around three bright N-type stars, R Scl,
X TrA, and V Aql have been detected in emission in resonance lines
from KI. This radiation, which is most probably scattered photospheric
radiation, was first found spectroscopically, but has later been imaged
with coronographic and polarimetric techniques. In the present paper,
which is the first in a series, the spectroscopic KI observations are
discussed. From the observations of the KI 769.9nm emission we find
systemic and expansion velocities in fair agreement with those obtained
from the CO millimetre lines. We find a decline of the emission with
distance from the star, in rough agreement with the assumption of a
constant expansion velocity, mass-loss rate and KI abundance. Our mass
loss rate estimates from the KI line observations agree rather well with
those obtained from CO (ranging from 1/4 to 1/1 of the CO mass loss),
which suggests that a considerable fraction of the potassium stays
neutral through the envelope. This puts strong upper limits on the
photoionizing chromospheric UV emission from the stars. Some indirect
indications that the envelopes have inhomogeneous structures, clumps,
are discussed.
Title: Line-blanketed model atmospheres for R Coronae Borealis stars
and hydrogen-deficient carbon stars.
Authors: Asplund, M.; Gustafsson, B.; Kiselman, D.; Eriksson, K.
Bibcode: 1997A&A...318..521A
Altcode:
We have constructed line-blanketed model atmospheres for the
hydrogen-deficient and carbon-rich R Coronae Borealis (RCrB) stars,
as well as for the similar hydrogen-deficient carbon (HdC) stars and
the cool extreme helium (EHe) stars. Improved continuum opacities have
been used together with realistic line absorption data for atomic
and molecular transitions. The observed dereddened fluxes of R CrB
are compared with the calculated model fluxes and found to agree best
with a model effective temperature of 6900K, while the infrared flux
method gives between 6600 and 6900K, depending on the nature of the
flux excess in the J and H bands compared to the model fluxes. The
excess may correspond to a recently formed dust cloud close to the
star, with a typical temperature around 2000K and a dust mass of
~10^-11^Msun_. The agreement for the ultraviolet flux
distribution is also very satisfactory as seen from IUE spectra of
RCrB. Theoretical broad band photometry is presented and effective
temperatures of RCrB and HdC stars estimated. The constructed
models show a significantly steeper temperature gradient compared
to previously existing models as a result of the line opacity. Due
to the cool surface and high abundance of carbon, molecular bands of
e.g. C_2_ and CO are visible in the spectra even at as high effective
temperatures as 7000K. Furthermore, the high temperatures encountered
at depth explain the observed Hei and CII lines for T_eff_ down to
~7000K. In the inner layers (τ_Ross_ > 3) the models show density
inversions related to the ionization zone of helium. For certain low
gravity models the luminosity exceeds the local Eddington limit and
hence gas pressure inversions occur as well, which could be related
to the decline events of RCrB stars.
Title: The ISO-SWS flux standard stars: synthetic spectra and
observations.
Authors: der Bliek, N. S.; Morris, P. W.; Vandenbussche, B.; Waters,
L. B. F. M.; Zaal, P.; Bell, R. A.; Gustafsson, B.; Eriksson, K.;
de Graauw, T.
Bibcode: 1997IAUS..189...89D
Altcode: 1998IAUS..189...89D
The authors present flux-calibrated, synthetic spectra for the
calibration stars of the Short Wavelength Spectrometer of the Infrared
Space Observatory ISO-SWS.
Title: H band spectra of cool dwarfs and giants
Authors: van der Bliek, N. S.; Gustafsson, B.; Eriksson, K.
Bibcode: 1997IAUS..189P..32V
Altcode: 1998IAUS..189P..32V
No abstract at ADS
Title: Accuracy of synthetic far IR fluxes of stars
Authors: van der Bliek, N. S.; Gustafsson, B.; Eriksson, K.
Bibcode: 1997IAUS..189P..28V
Altcode: 1998IAUS..189P..28V
No abstract at ADS
Title: Comparison Bertween ISO-SWS Observations and Synthetic Spectra
of K Giants and M Giants α Boo and β Peg (Invited Paper)
Authors: Decin, L.; Cohen, M.; Eriksson, K.; Gustafsson, B.; Huygen,
E.; Morris, P.; Plez, B.; Sauval, J.; Vandenbussche, B.; Waelkens, C.
Bibcode: 1997ESASP.419..185D
Altcode: 1997fiso.work..185D
The accurate flux calibration of SWS requires the observation of spectra
of stellar templates (Schaeidt et al., 1996). On the other hand, our
knowledge of stellar spectra in the broad spectral domain that ISO has
opened for the first time is still incomplete, and must be improved
with these same ISO data. Clearly, the final flux calibration of SWS
data will result from an iterative process, that should benefit to
both our understanding of the instrument and of the atmo- spheres of
cool stars. We report on the progress of a project which confronts SWS
observations of cool stars with state-of-the-art synthetic spectra. The
ISO observations enable us to discriminate between various sources of
molecular data and put tight constraints on the atmospheric parameters
of the stellar templates. Preliminary results suggest that a 2% relative
flux accuracy may be attainable in bands 1 and 2 of the SWS range.
Title: Carbon stars with episodic mass loss: observations and models
of molecular emission from detached circumstellar shells.
Authors: Olofsson, H.; Bergman, P.; Eriksson, K.; Gustafsson, B.
Bibcode: 1996A&A...311..587O
Altcode:
We have obtained detailed CO radio line maps of the circumstellar
medium around the bright carbon stars R Scl, U Ant, S Sct, and TT
Cyg. They provide direct evidence for the existence of large [radii
between 10-70", or (1-5)x10^17^cm], geometrically thin (we estimate
that the shell widths are <~10"), over-all spherically symmetric
shells of CO line-emitting gas around these stars. The shells expand
with velocities in the range 13-20km/s, i.e., their ages lie in
the range (1-10)x10^3^years. Less extensive CO observations of
the carbon star V644 Sco suggest that also it is surrounded by a
detached shell. The expansion velocities of the present mass loss
winds, as evidenced by weak CO emission from regions close to the
stars, are considerably lower, of the order 5km/s. We conclude that
the mass loss characteristics of these, otherwise apparently normal,
carbon stars have changed significantly over the last 10^4^years. For
such a shell structure, the most reasonable cause is a short period
of very intense mass loss (i.e., a mass loss eruption), although
an interacting-wind scenario cannot be excluded. The CO brightness
distributions are very patchy, suggesting an inhomogeneous circumstellar
medium. Using a model where the shell consists of a large number of
small, homogeneous clumps, we estimate that the H_2_-masses of the
four, spatially resolved shells are all around 0.01Msun_
(for an adopted CO abundance with respect to H_2_ of =~10^-3^), and
that in the mass loss eruption -scenario the H_2_-mass loss rates
of the stars were =~10^-5^x(10"/{DELTA}R)Msun_/yr during
the formation of the shells ({DELTA}R being the unresolved shell
width in arc seconds). The present mass loss rates are very low,
<~10^-7^Msun_/yr. These results suggest that the four
stars have all gone through a type of event that led to a dramatic
change in the mass loss characteristics. The adopted model is an
initial, relatively crude, attempt to provide a more realistic base
for the interpretation of line emission from a circumstellar medium
in which, in general, the physical conditions are very likely quite
inhomogeneous. It is the accidental overlap along the line-of-sight
and in velocity space of the many small clumps that in the model
produces a clumpy appearance of the brightness distribution, at the
larger scale set by the observational resolution, that resembles the
observed ones. In the mass loss eruption -scenario the estimated life
time of a CO line-emitting shell of the type discussed in this paper
is =~10^4^years, and it is determined by the photodissociation of the
CO molecules. Only shells younger than =~10^3^years are expected to
be observable in molecular radio lines other than those of CO. There
is a period after formation when such shells should be characterized
by very anomalous line intensity ratios. For instance, in our model
the line intensity ratio between the photodissociation product CN
and the parent molecule HCN increases drastically on a time scale of
hundreds of years as the shell recedes from the star. We suggest that
the shell around R Scl is in this phase, since this is the only object,
among the five observed, in which we have clearly detected also lines
of HCN and CN, albeit with anomalous line intensity ratios.
Title: Stellar far-IR fluxes: how accurate are model predictions?
Authors: van der Bliek, N. S.; Gustafsson, B.; Eriksson, K.
Bibcode: 1996A&A...309..849V
Altcode:
We present the results of an analysis of the accuracy of predicted
far infrared (FIR) fluxes of stars. Sources of errors are a) the input
parameters for the model atmospheres; b) assumptions in the modelling,
resulting in errors in the structure of the model atmospheres; c) the
adopted IR continuous opacity, dominated by the H^-^_ff_ opacity; d)
the possible presence of circumstellar (CS) dust. Stellar effective
temperatures are typically determined with an accuracy of about
100K. This leads to an uncertainty in the predicted far infrared
(FIR) flux of 1 to 4%, depending on the spectral type. Errors in the
other two fundamental parameters of a star, the surface gravity and
the metallicity, have a minor effect on the prediction of stellar FIR
fluxes, less than 1%. The various assumptions made in the modelling
result in errors in the temperature structure T(τ) of model
atmospheres. By using the depth and shape of spectral lines, T(τ)
in the outer layers of the atmosphere, where the lines are formed,
can be pinned down to about 100K, resulting in uncertainties of about
1 to 2% in the FIR. Errors in the H^-^_ff_ opacity are small and as a
result uncertainties in the FIR fluxes due to the continuous opacity are
less than 0.1%. CS dust can have a large impact on the IR fluxes. We
find that the uncertainties due to the possible presence of CS dust
can be more than an order of magnitude larger than the uncertainties
resulting from modelling the stellar atmosphere. Unfortunately with
the present day accuracies of IR data no further constraints can be
set to limit these uncertainties.
Title: Interferometric molecular line observations of the
circumstellar envelope(s) around U Camelopardalis.
Authors: Lindqvist, M.; Lucas, R.; Olofsson, H.; Omont, A.; Eriksson,
K.; Gustafsson, B.
Bibcode: 1996A&A...305L..57L
Altcode:
We have observed the circumstellar envelope of the carbon star U
Cam in the HCN(J=1->0) and CN(N=1->0) lines using the IRAM
Plateau de Bure interferometer. There is evidence of a two-envelope
structure: an outer extended envelope, possibly a shell, with a radius
of ~7x10^16^cm, that expands with a velocity of ~25km/s, surrounding an
inner envelope with a radius of ~6x10^15^cm and an expansion velocity
of only ~13km/s. Mass loss rate estimates based on these data alone
are uncertain, but they suggest that the mass loss rate during the
formation of the outer envelope was higher than during the present
mass loss epoch. Thus, we have evidence for a significant variation
in the mass loss characteristics of U Cam within the last 10^3^years.
Title: Outer Layers of a Carbon Star: The View from the Hubble
Space Telescope
Authors: Johnson, Hollis R.; Ensman, Lisa M.; Alexander, David R.;
Avrett, Eugene H.; Brown, Alexander; Carpenter, Kenneth G.; Eriksson,
Kjell; Gustafsson, Bengt; Jorgensen, Uffe G.; Judge, Philip D.; Linsky,
Jeffrey L.; Luttermoser, Donald G.; Querci, Francois; Querci, Monique;
Robinson, Richard D.; Wing, Robert F.
Bibcode: 1995ApJ...443..281J
Altcode:
To advance our understanding of the relationship between stellar
chromospheres and mass loss, which is a common property of carbon stars
and other asymptotic giant branch stars, we have obtained ultraviolet
spectra of the nearby N-type carbon star UU Aur using the Hubble
Space Telescope (HST). In this paper we describe the HST observations,
identify spectral features in both absorption and emission, and attempt
to infer the velocity field in the chromosphere, upper troposphere,
and circumstellar envelope from spectral line shifts. A mechanism
for producing fluoresced emission to explain a previously unobserved
emission line is proposed. Some related ground-based observations are
also described.
Title: Early Proterozoic crustal evolution: Geochemical and NdPb
isotopic evidence from metasedimentary rocks, southwestern North
America
Authors: McLennan, S. M.; Hemming, S. R.; Taylor, S. R.; Eriksson,
K. A.
Bibcode: 1995GeCoA..59.1153M
Altcode:
Early Proterozoic (1.8-1.7 Ga) metasedimentary rocks in northern New
Mexico and southern Colorado, USA, can be divided into turbidite
successions (commonly volcanogenic) associated with mafic/felsic
metavolcanic successions (e.g., Irving Fm.) and stable shelf
quartzite-pelite successions of shallow marine origin (e.g., Hondo
Gp.). Metapelites from the turbidite successions reported here
have low K2O/Na2O, low Th/U (<3.0), low to
moderate Th/Sc (0.1-0.6), and slight negative Eu-anomalies, although
regionally, negative Eu-anomalies in such rocks are common. At the
time of sedimentation (ca. 1.7-1.8 Ga), ɛNd values were
in the range +3 to +7, indistinguishable from associated metavolcanic
and plutonic rocks. Similarly, lead isotopic data scatter about a
1.7 Ga reference isochron. Low κ (232Th/238U)
values for the Irving Formation are consistent with derivation from
crustal sources similar to the southern Colorado/northern New Mexico
lead isotope crustal province. These data are further consistent with a
volcanic arc related origin. In contrast, stable shelf metapelites have
high K2O/Na2O, variable but commonly high Th/U
(2.0-7.0), moderate to high Th/Sc (0.5-1.4), and substantial negative
Eu-anomalies. Although compositions are rather variable, they are
typical of post-Archean shales. Neodymium isotopes are surprisingly
radiogenic with ɛNd(1.7 Ga) in the range -0.2 to +4. Lead
isotopic data for the least radiogenic samples also are consistent with
a dominantly juvenile source and on a 207Pb/204Pb
vs. 206Pb/204Pb diagram, data scatter slightly
above the 1.7 Ga reference isochron, suggesting minor components of
significantly older material. Lead isotopic systematics suggest that
a major component of the provenance was derived from the immediately
associated metavolcanic-plutonic terranes, consistent with suggestions
of a first-cycle origin, but with an Archean component. Isotopic
data restrict the Archean component to about 10%, on average, and
no more than 25% in any sample. This older crustal component may be
derived either by direct erosion of Archean rocks, such as the Wyoming
Province, or indirectly through assimilation into Early Proterozoic
igneous rocks. Although the stable shelf sedimentary rocks are derived
from a provenance with similar ages as the volcanogenic turbidites,
the geochemical characteristics of the provenance are significantly
different. Accordingly, these data are consistent with especially
rapid and widespread crustal growth and evolution in southwestern North
America during the period 1.9-1.7 Ga. Several samples from the Hondo
Group and Uncompahgre Formation have REE patterns that are rotated
to LREE depletion and perhaps HREE enrichment. The change in REEs
correlate with Mo, U, and V abundances and Pb isotopic characteristics
suggesting sedimentary processes similar to those operating in black
shales affected these REE patterns. REE patterns and Th/U ratios of
Early Proterozoic volcanogenic turbidites examined in this and other
studies differ on average from turbidites found in Archean greenstone
belts. Negative Eu-anomalies are common, HREE-depletion is seen but
comparatively rare, and Th/U ratios are commonly below 3.0. Accordingly,
these data are consistent with models suggesting that the upper crust
had a different composition in the Archean.
Title: Interferometric Observations of HCN and CN towards Carbon Stars
Authors: Lindqvist, M.; Lucas, R.; Olofsson, H.; Omont, A.; Eriksson,
K.; Gustafsson, B.
Bibcode: 1995Ap&SS.224..501L
Altcode:
Using the IRAM interferometer we have observed four carbon stars (U
Cam, CIT6, Y CVn, IRC+40540) in the HCN(J=1 → 0) and CN(N=1 → 0)
lines. Here we present some results for CIT6 and U Cam.
Title: Sedimentology of archean greenstone belts: Signatures of
tectonic evolution
Authors: Eriksson, K. A.; Krapez, B.; Fralick, P. W.
Bibcode: 1994ESRv...37....1E
Altcode:
Stratigraphic styles in Archean greenstone belts are compared to
those of modern and Phanerozoic depositional basins in order to
test the conformity of tectonic style through time. Six lithological
associations in greenstone belts are recognized: (1) mafic-ultramafic
volcanic, (2) calc-alkaline volcanic, (3) bimodal volcanic, (4)
quartz arenite-iron-formation or carbonate, (5) conglomerate-wacke
and (6) conglomerate-arenite. Examples of the associations are
described from the Kaapvaal, Superior and Zimbabwe Provinces and
the Pilbara Block. Each association differs only slightly between
the four regions, thereby emphasizing a common tectonostratigraphic
theme. Sedimentary rocks are a minor component of the mafic-ultramafic
volcanic association. They were deposited in two types of volcanic-basin
environments: one similar to barred lagoons and bays around oceanic
volcanic islands, and the other similar to sediment-starved platforms
adjacent to coalesced volcanoes in inter-arc, intra-arc and back-are
basins. In contrast, sedimentary rocks in the calc-alkaline volcanic
association comprise thick wedges of epiclastic and volcaniclastic
detritus deposited in elongate sedimentary basins, and thick wedges
of pyroclastic and volcaniclastic detritus deposited adjacent to
volcanic centers. Sedimentary facies were identical to those of
forearc-trench and marine volcanoplutonic-arc settings. Chemogenic
lithofacies in both volcanic associations were deposited in shallow to
deep-marine waters, although shallow-water profiles were selectively
preserved in some terrains. Sedimentary rocks of the bimodal volcanic
association are thick wedges of siliciclastic and volcaniclastic
deposits interbedded with subaerial to submarine erupted flows of
komatiite, basalt, and rhyolite. Depositional environments ranged
from braid-plain and braid-delta to coastal marine and submarine
fan. Starved-basin deposits include banded iron-formation and
sulfidic black shale. The association is identical to that of
cratonic extensional basins in arc-continent and intracontinental
rifts. Sedimentary rocks of the quartz arenite-iron-formation or
carbonate association onlap weathered basement or bimodal-volcanic
association rocks. Depositional environments were either transitional
from fluvial to siliciclastic and carbonate marginal-marine to
offshore pelagic-hemipelagic, or from inshore intrabasinal-clastic and
volcaniclastic to offshore pelagic-hemipelagic. Siliciclastic deposits
are supermature. Two tectonic sites are represented: those with
siliciclastic facies represent continent-adjacent syn- to post-rift
stable shelves and those dominated by banded iron-formation, with
volcaniclastic deposits, represent arc-adjacent post-rift stable
shelves. Sedimentary rocks of the conglomerate-wacke association
are represented by thick wedges of siliciclastic or volcaniclastic
sandstone, with minor volcanic components. These were deposited in
braid-plain, braid-delta and submarine-fan environments within elongate
sedimentary basins. Coastal-plain and pelagic basin facies are also
present. Siliciclastic detritus was derived from syndepositional,
magmatic and metasedimentary thrust-belts. Two stratigraphic styles
are preserved: one that records a flysch-like stage of deep-
to marginal-marine environments, and the other that records a
molasse-like stage of marginal-marine to fluvial environments. The
association is identical to that of compressional-foreland basins of
arc-continent collisional and compressional-arc tectonic affinities. The
conglomerate-arenite association is preserved in elongate structural
basins that transgress crustal components and all other supracrustal
units. It is dominated by thick wedges of siliciclastic sandstone,
although bimodal volcanic and volcaniclastic rocks can also be
present. Depositional environments ranged from talus and alluvial fan,
and braid-plain to either lacustrine or coastal marine. Local basin
margins often show lateral offsets from source terrains and vertically
skewed facies patterns. Longitudinal facies geometries are typical. The
association is similar to that of strike-slip collisional graben in
hinterland tectonic-escape and terrane-accretion orogens. The examples
show that, despite all the ramifications of secular geophysical,
geothermal and geochemical global change, the stratigraphic style of
sedimentary rocks in Archean greenstone belts can be matched with modern
tectonic analogues, thereby emphasizing the conformity of stratigraphic
style through time. The inseparable link between stratigraphic and
tectonic styles implies that the tectonic style of greenstone belts
was not temporally unique. Major differences exist with regards to
the chemical composition of certain magmatic and sedimentary products,
but these are compensated for by their constant stratigraphic function
in terms of depositional processes, depositional environments and
tectonic sites.
Title: A Study of Circumstellar Envelopes around Bright Carbon
Stars. I. Structure, Kinematics, and Mass-Loss Rate
Authors: Olofsson, H.; Eriksson, K.; Gustafsson, B.; Carlstrom, U.
Bibcode: 1993ApJS...87..267O
Altcode:
Results are presented of a survey of circumstellar CO emission on a
sample of bright carbon stars, which is relatively complete out to
about 900 pc from the sun. A total of 68 detections were made. All
objects within 600 pc of the sun were detected. It is suggested that the
large majority of all carbon stars have circumstellar envelopes. The
CO-emitting parts of these envelopes have angular sizes less than
about 15 arcsec. The median gas expansion velocity is 12.5 km/s, and
the expansion velocities for the majority of the objects fall in the
range 9-15 km/s. The median mass-loss rate is 1.5 x 10 exp -7 solar
mass/yr, and the mass loss rate for the majority of stars lies within
the narrow range (0.8-2.5) x 10 exp -7 solar mass/yr. Circumstellar
and photospheric HCN, CN, and CS abundances are estimated and compared
for a sample for bright carbon stars. The chemistry in the envelope
around R Scl is determined.
Title: A Study of Circumstellar Envelopes around Bright Carbon
Stars. II. Molecular Abundances
Authors: Olofsson, H.; Eriksson, K.; Gustafsson, B.; Carlstroem, U.
Bibcode: 1993ApJS...87..305O
Altcode:
We have estimated and compared circumstellar and photospheric HCN, CN,
and CS abundances for a sample of bright carbon stars. The circumstellar
HCN and CS abundances roughly correlate with the photospheric ones,
but the former appear to be systematically overestimated by a factor
of 5-10. Although we cannot exclude the presence of a circumstellar
chemistry that efficiently produces HCN and CS in the inner parts
of these relatively hot circumstellar envelopes, we attribute this
difference between photospheric and circumstellar abundances to
errors in the circumstellar envelope model used. In particular,
for the low mass-loss rate objects a systematic underestimate of
the mass-loss rate may be suspected. In addition to this general
trend, stars that are in some sense peculiar also show circumstellar
abundances that deviate significantly from the expected. There is
evidence for the presence of maser features in the HCN (J = 1-0)
emission toward some of the stars. The estimated circumstellar CN
abundances suggest that this species is a photodissociation product of
HCN. A search for circumstellar HNC, SiS, and HC3N shows
that molecular emission from species other than CO, HCN, CN, and CS
is very weak in these low mass-loss rate objects. An attempt has been
made to determine the chemistry in the (probably detached) envelope
around R Scl. The data suggest a carbon-rich chemistry. Finally, it
is shown that the circumstellar 12CO/13CO and
H12CN/H13CN intensity ratios roughly correlate
with the photospheric 12C/13C isotope ratios
for a small number of low mass-loss rate objects, although the former
ratios are systematically lower than the latter by a factor of about 2.
Title: Detailed modelling of the shell around S Scuti.
Authors: Eriksson, K.; Stenholm, L.
Bibcode: 1993A&A...271..508E
Altcode:
We have calculated a large number of models of the circumstellar
material around the carbon star S Sct and compared the results with
detailed maps in the CO J=1-O and J=2-1 lines. The radiative transfer
calculations were performed in non-LTE using a nine-level CO model
atom and using the geometrical assumption of spherical symmetry. The
best fit to the main part of the emission was obtained for a thin
shell far from the star.
Title: A Complete Sample of Carbon Stars
Authors: Eriksson, K.
Bibcode: 1993iue..prop.4732E
Altcode:
No abstract at ADS
Title: Geochemistry of 1.8-1.67 Ga mudstones and siltstones from
the Mount Isa Inlier, Queensland Australia: Provenance and tectonic
implications
Authors: Eriksson, K. A.; Taylor, S. R.; Korsch, R. J.
Bibcode: 1992GeCoA..56..899E
Altcode:
Sedimentary and volcanic rocks overlying basement in the Mount Isa
Inlier, Australia, are subdivided into three cover sequences. The upper
two sequences range in age from 1800 to 1670 Ma and each consist of rift
and overlying sag phases of sedimentation. Fine-grained siliciclastic
sedimentary rocks in the upper two sequences define two distinct
geochemical groups. Samples from Groups I and II are mainly from the
lower and upper rift and upper thermal phases, respectively. One sample
from the lower rift phase has affinities with Group II, whereas samples
from the lower thermal phase belong to both Groups I and II. Eu/Eu∗
values are 0.70 to 0.85 for Group Iand 0.55 to 0.70 for Group II. Group
I samples are characterized by lower La/Sc and Th/Sc ratios and higher
Cr/Th ratios than Group II. Cr, Niand Co concentrations are greater
in Group I than Group II. Groups I and II also are distinguished on
plots of Eu/Eu∗ vs. La N/Sm N and Eu/Eu∗
vs. Gd N/Yb N. Two samples from Group I have
elevated LREE/HREE and La N/Yb N ratios that are
attributed to intense weathering as revealed by their high Chemical
Index of Weathering values. The geochemical data reflect a combination
of local and more distant regional provenances and can be related to
the tectonic evolution of the Mount Isa Inlier. Group I samples are
attributed to dilution of a mature, post-Archean source by addition of
recycled mafic volcanics. Group II samples are typical post-Archean
sediments derived from differentiated upper continental crust with
no dilution by local sources. The lower rift phase displays great
geochemical variability (samples from both groups) that is typical of
active tectonic settings such as rifts. The great variability of samples
from the lower sag phase (both groups) is surprising but probably
reflects the diverse rock types beneath this basin. Stable tectonic
conditions during this phase of sedimentation are indicated instead by
major element geochemistry that records severe weathering. Similarity
of the upper rift phase sample with some samples from the lower sag
phase reflects recycling of the latter. Samples from the upper sag
phase are remarkably uniform in composition (Group II) and reflect
the stable tectonic conditions under which this basin developed.
Title: The large-scale atmospheric motion field of Alpha Orionis
Authors: de Jager, C.; Eriksson, K.
Bibcode: 1992iesh.conf..117D
Altcode:
No abstract at ADS
Title: The circumstellar envelope of the carbon star S Scuti.
Authors: Olofsson, H.; Carlstrom, U.; Eriksson, K.; Gustafsson, B.
Bibcode: 1992A&A...253L..17O
Altcode:
CO(J = 1-0) observations of the bright carbon star S Sct show that
the star is surrounded by a large (about 5.3 x 10 exp 17 cm) shell
of gas expanding at a velocity of 16.5 km/s. It was produced during a
brief period (about 1200 years) of high mass loss (about 4 x 10 exp-5
solar mass/yr) about 10 exp 4 years ago. The current mass losss rate
and gas expansion velocity are only about 3 x 10 exp -8 solar mass/yr
and about 5 km/s, respectively. This indicates that the star has gone
through a very eruptive phase, possibly induced by a thermal pulse. The
simple kinematics of the shell makes it possible to infer an overall
spherical symmetry of the otherwise definitely clumpy CO brightness
distribution. Thus, the mass loss must have been globally spherically
symmetric, and the material was probably ejected in the form of lumps.
Title: S Persei : optical and water maser variability - 1984 to 1990.
Authors: Little-Marenin, I. R.; Benson, P. J.; McConahay, M. M.;
Cadmus, R. R., Jr.; Stencel, R. E.; Eriksson, K.
Bibcode: 1991A&A...249..465L
Altcode:
The M supergiant S Persei was monitored since 1984 optically and
since 1987 for water maser emission at 22 GHz. The dozen H2O maser
features show complex variations in intensity with many of the features
varying independently of one another. Some of the water maser features
brightened dramatically at the time of the bright optical maximum
observed in 1988 August and again 10 weeks later. It is possible the
increase in water maser intensity is related to the ejection of a dust
shell near the time of the preceding optical minimum. The intensity
variations of the maser spectrum as being produced by an asymmetric
distribution of maser spots are interpreted. A double shell of maser
spots may be present on the near side of the shell, but appears to be
lacking or be occulted on the far side. No chromospheric activity was
detected about 10 weeks after optical maximum. A well developed shock
is seen in a near-infrared spectrum obtained in 1988 October.
Title: A comparison of photospheric and circumstellar HCN / CO
-ratios for bright carbon stars.
Authors: Olofsson, H.; Eriksson, K.; Gustafsson, B.
Bibcode: 1990A&A...230..405O
Altcode:
Measures of circumstellar HCN/CO abundance ratios for carbon stars are
compared with corresponding ratios estimated from photospheric abundance
analysis. A satisfactory agreement is found for most stars. However, V
Hya and two 60 μm-excess sources have significantly lower circumstellar
ratios than expected, and for the 13C-rich stars the ratios
are somewhat higher.
Title: Bright carbon stars with detached circumstellar envelopes -
A naturalconsequence of helium shell flashes ?
Authors: Olofsson, H.; Carlstrom, U.; Eriksson, K.; Gustafsson, B.;
Willson, L. A.
Bibcode: 1990A&A...230L..13O
Altcode:
CO radio map data are presented for the bright carbon stars R Scl, U
Ant, S Sct, and TT Cyg. The stars are found to have large circumstellar
envelopes which, at least in the last three cases, are geometrically
thin and clearly detached from the stars, indicating that the mass
loss has occurred episodically. The possibility that these episodes
are triggered by helium shell flashes is discussed and found consistent
with existing data.
Title: Book Review: Cool stars, stellar systems and the sun. /
Springer-Verlag, 1987
Authors: Eriksson, K.
Bibcode: 1990SSRv...52..195E
Altcode: 1990SSRv...52..195L
No abstract at ADS
Title: Modeling of shells around carbon stars.
Authors: Carlström, U.; Eriksson, K.; Gustafsson, B.; Olofsson, H.;
Stenholm, L.; Willson, L. A.
Bibcode: 1990apsu.conf...13C
Altcode:
No abstract at ADS
Title: A Study of Bright Carbon Stars
Authors: Olofsson, H.; Carlstrom, U.; Eriksson, K.; Gustafsson, B.;
Willson, L. A.
Bibcode: 1990fmpn.coll..341O
Altcode:
No abstract at ADS
Title: Chromospheres of Naked Carbon Stars
Authors: Eriksson, K.
Bibcode: 1990iue..prop.3878E
Altcode:
No abstract at ADS
Title: Observations of envelopes around carbon stars.
Authors: Eriksson, K.; Gustafsson, B.; Selhammar, M.
Bibcode: 1990apsu.conf...26E
Altcode:
No abstract at ADS
Title: A comparison of photospheric and circumstellar
(HCN)/(CO)-ratios for bright carbon stars
Authors: Olofsson, H.; Eriksson, K.; Gustafsson, B.
Bibcode: 1989STIN...9022477O
Altcode:
Measures of circumstellar HCN/CO abundance ratios for carbon stars are
compared with corresponding ratios estimated from photospheric abundance
analysis. A satisfactory agreement is found for most stars. However,
V Hya and two 60 micrometer-excess sources have significantly lower
circumstellar ratios than expected, and for the (13)C-rich stars the
ratios are somewhat higher.
Title: SEST CO (J=1-0) observations of carbon-rich circumstellar
envelopes.
Authors: Olofsson, H.; Eriksson, K.; Gustafsson, B.
Bibcode: 1988A&A...196L...1O
Altcode:
The authors have used the Swedish ESO Submillimetre Telescope (SEST)
to search for circumstellar CO (J = 1-0) emission towards bright carbon
stars in the southern hemisphere. A correlation between the estimated
mass loss rate and a far-IR excess measure is discussed. The CO (1-0)
line profiles indicate a diversity in the characteristics of the
circumstellar envelopes. In particular, two stars with distinctly
double-peaked line shapes have been detected. One of them, S Sct,
is interpreted in terms of an extended, cold, detached shell, with no
hot gas/dust close to the star.
Title: Accurate wavelengths in O II.
Authors: Eriksson, K. B. S.
Bibcode: 1987JOSAB...4.1369E
Altcode: 1987OSAJB...4.1369E
The wavelengths of 71 strong O II lines between 4676 and 525 Å have
been measured. Improved energy levels have been derived. Smoothed
wavelengths have been recalculated from these. The uncertainty is
about 1 mÅ.
Title: CO (J=1-0) observations of bright carbon stars.
Authors: Olofsson, H.; Eriksson, K.; Gustafsson, B.
Bibcode: 1987A&A...183L..13O
Altcode:
The authors have surveyed a sample of bright N-type stars, with recent
estimates of chemical composition, in the CO(J = 1-0) line. Almost
all stars were detected. The mass loss rate is well correlated with
a far-IR excess measure, and the gas-to-dust mass ratio, estimated to
be 350±200, seems relatively constant for this sample of stars. The
mass loss rate appears to be dependent on the effective temperature,
the carbon excess, and the 12C/13C-ratio of the
central star. In particular, the peculiar 13C-rich stars have
comparatively low mass loss rates. A weak dependence of gas expansion
velocity of the circumstellar envelope on the carbon excess may exist.
Title: Oxygen Isotopic Abundances in Evolved Stars. III. 26 Carbon
Stars
Authors: Harris, Michael J.; Lambert, David L.; Hinkle, Kenneth H.;
Gustafsson, Bengt; Eriksson, Kjell
Bibcode: 1987ApJ...316..294H
Altcode:
Oxygen isotope ratios have been measured in 21 ordinary N-type carbon
stars and in five 13C-rich J-type stars. The ratios in
the ordinary N-type stars are 550 ≤ 16O/17O
≤ 4100 and 700 ≤ 16O/18O ≤ 2400. These
ratios are much higher than expected and are extremely difficult to
explain in terms of present theories of stellar evolution. The J-type
stars exhibit ratios 350 ≤ 16O/17O ≤ 850,
16O/18O ratios being very uncertain. Together with
nitrogen abundances measured by Lambert et al., these ratios preclude
the envelope burning (hot-bottom convection) hypothesis which has been
proposed for these stars.
Title: Chemical composition and circumstellar shells of carbon stars -
any obvious relations?
Authors: Eriksson, K.; Gustafsson, B.; Olofsson, H.
Bibcode: 1987IAUS..122..381E
Altcode:
The authors detectd CO emission from 8 of 12 bright, galactic N-type
stars with different chemical profiles.
Title: Line blanketing in model atmospheres of carbon stars.
Authors: Ekberg, U.; Eriksson, K.; Gustafsson, B.
Bibcode: 1986A&A...167..304E
Altcode:
A comparison of opacity sampling (OS) and opacity distribution function
(ODF) methods for the calculation of the model atmospheres of carbon
stars is presented. In order to determine the structure of OS model
atmospheres to an accuracy of about 30 K or better, at least 5000
frequency points with a near optimum distribution are found to be
necessary. The ODF approximation is shown to cause significant errors,
particularly where polyatomic opacity dominates in the surface layers,
and the diatomic molecules at larger depths. The noncorrelation
assumption is not found to lead to significant errors, even for very
cool and carbon rich stars. Good agreement is found between multiple
component ODF models and ODF models calculated using the ODF-summation
procedure of Saxner and Gustafsson (1984) for single component ODFs.
Title: The Chemical Composition of Carbon Stars. I. Carbon, Nitrogen,
and Oxygen in 30 Cool Carbon Stars in the Galactic Disk
Authors: Lambert, David L.; Gustafsson, Bengt; Eriksson, Kjell;
Hinkle, Kenneth H.
Bibcode: 1986ApJS...62..373L
Altcode:
Chemical compositions of 30 Galactic carbon stars are determined from
high-resolution infrared spectra and new model atmospheres. Elemental C,
N, and O abundances are quite similar to those seen in planetary nebulae
and are consistent with those reported for G to M giants. Carbon stars
show only modest carbon enrichments: C/O is less than 1.6, and half the
sample have C/O less than 1.1. The 12C/13C ratio
is between 20 and 90 except for a few 13C-rich stars. When
line blanketing by HCN and C2H2 is included,
models predict the observed intensity of the H2 quadrupole
lines. This and other evidence shows that the carbon stars are not
hydrogen-deficient.
Title: Tz-Fornacis - an Eclipsing Capella-Like System Observed
with IUE
Authors: Eriksson, K.; Saxner, M.; Gustafsson, B.; Ayres, T. R.;
Linsky, J. L.; Anderson, J.
Bibcode: 1986ESASP.263..225E
Altcode: 1986niia.conf..225E; 1986NIA86......225E
The IUE observed TZ Fornacis at orbital phases 0.0, 0.25 and 0.79 in
1986. Most of the exposures were LWP-HI or SWP-LO. Results show that:
the surface fluxes for transition region emission lines are similar
to those for the Capella system while that of the Mg II emission is
smaller; the total flux in the Mg II emission lines is constant with
phase, whereas the flux in the C IV emission lines decreases by 1/3
during primary eclipse, indicating that most of the activity is due
to the hotter giant (F7 III), which is also the case for Capella.
Title: The outer atmosphere of the carbon star TX Piscium.
Authors: Eriksson, K.; Gustafsson, B.; Johnson, H. R.; Querci, F.;
Querci, M.; Baumert, J. H.; Carlsson, M.; Olofsson, H.
Bibcode: 1986A&A...161..305E
Altcode:
A high-resolution LWP IUE spectrum of the bright N-type carbon star TX
Psc demonstrates that the Mg II h and k emission profiles are strongly
affected by absorption from Mg II, Mn I, probably Fe I, and possibly
from molecules. The indication that the absorbing matter has a column
density of not less than 10 to the 20th H atoms or molecules per sq
cm is consistent with absorption in a slowly expanding envelope. The
integrated Mg II line flux is found to be much greater than in 1981,
and the radio CO (J = 1 - 0) line from the circumstellar shell is
detected. Results for a column density of not larger than 10 to the 22nd
H2 molecules/sq cm, and a radial velocity close to that of the star,
are in agreement with those obtained from UV data. Some dust emission
from carbon grains is suggested by the far infrared flux distribution,
and a mass-loss rate estimation for the star of 10 to the -6th to 10
to the -8th solar masses is obtained.
Title: Carbon and oxygen abundances of field RR Lyrae
stars. II. Oxygen abundances.
Authors: Butler, D.; Laird, J. B.; Eriksson, K.; Manduca, A.
Bibcode: 1986AJ.....91..570B
Altcode:
From non-LTE analysis of the neutral oxygen triplet (7771-7775 Å)
absorption-line strengths on KPNO 4 m echelle plates, we have determined
oxygen abundances and oxygen-to-iron ratios for a large number of field
RR Lyrae stars covering the range in iron abundance +0.1> [Fe/H]>
- 2.2. We have found that (1) RR Lyrae stars at the metal-poor end of
the range have [O/Fe] values near zero. This is somewhat surprising
since previous studies of metal-poor field stars have found oxygen
to be enhanced relative to iron. (2) RR Lyrae stars at the metal-rich
end of the range have [O/Fe] values between + 0.25 and + 0.95. Again,
this result is in disagreement with expectations based on studies of
other field stars in the disk. (3) The abundance sum C + N + O, or its
possible range, has been determined. For most stars, including those
at the metal-rich end of the range, the ratio (C + N + O)/Fe is high
relative to the solar value. Possible explanations for these results
are discussed.
Title: The Unique Eclipsing Binary System TZ Fornacis
Authors: Eriksson, K.
Bibcode: 1986iue..prop.2697E
Altcode:
No abstract at ADS
Title: CNO abundances and 12C/13C ratios in
30 galactic N stars.
Authors: Gustafsson, B.; Lambert, D. L.; Hinkle, K. H.; Eriksson, K.
Bibcode: 1985ESOC...21..151G
Altcode: 1985pdce.work..151G; 1985pdcn.conf..151G
CNO abundances and C-12/C-13 ratios have been determined for 30 bright
galactic N stars by means of high-resolution FTS spectra, obtained with
the Kitt Peak 4 m Mayall reflector and covering the spectral region
from 4000/cm to 6600/cm. The spectra were analyzed with a new grid of
model atmospheres. Weak second-overtone vibration-rotation lines of CO
were used for determining the oxygen abundances, while C2 lines of the
Phillips system were used in the carbon determinations. Lines of the
Ballik-Ramsay system give similar results. The nitrogen abundances
were obtained from weak CN lines of the red system, and such lines
were also used for the determination of C-12/C-13 ratios. Consistent
isotopic ratios were obtained from the C-13O lines.
Title: The temperatures of G and K stars.
Authors: Wing, R. F.; Gustafsson, B.; Eriksson, K.
Bibcode: 1985IAUS..111..571W
Altcode:
Effective temperatures have been determined for G and K stars by
comparing synthetic colors computed from model atmospheres to observed
colors measured at near-infrared continuum points. Results are presented
for giant stars in the range K0 III - K4 III.
Title: The Unique Eclipsing Binary System TZ Fornacis
Authors: Eriksson, K.
Bibcode: 1985iue..prop.2278E
Altcode:
No abstract at ADS
Title: The outer atmosphere of the carbon star TX Piscium.
Authors: Eriksson, K.; Gustafsson, B.; Johnson, H. R.; Querci, F.;
Querci, M.; Baumert, J. H.; Carlsson, M.; Olofsson, H.
Bibcode: 1985BETSP...2....5E
Altcode:
No abstract at ADS
Title: A progress report on the analysis of long exposure SWP high
resolution spectra of cool stars.
Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Carpenter, K.;
Jordan, C.; Judge, P.; Gustafsson, B.; Eriksson, K.; Saxner, M.;
Engvold, O.; Jensen, E.; Moe, O. K.; Simon, T.
Bibcode: 1984NASCP2349..445L
Altcode: 1984fiue.rept..445L; 1984IUE84......445L
The IUE is the first experiment with sufficient sensitivity to obtain
high resolution spectra (lambda/delta lambda is approximately 10,000)
of many cool stars in the vitally important 1200 to 2000 A spectral
region. These data provide qualitatively new information with
which to understand the properties of and structures in the outer
atmospheres of these stars. Also, these cool star spectra will be
extremely useful in planning for the Space Telescope High Resolution
Spectrograph, which will be 1000 times more sensitive than IUE but will
be hampered by limited observing time and limited spectral bandwidth
in each exposure. Very long exposure, high disperson SWP spectra of
many stars located throughout the cool half of the HR diagram were
obtained. These 12 to 21 hour exposures were obtained by combining
NASA and Vilspa shifts so as to obtain the longest possible exposures
at times of low background. Included are dwarf stars of spectral type
G0 V to M2 V, G9.5 III to M5 II giants, G2 Ib to M2 Iab supergiants,
a number of RS CVn-type systems, and Barium stars.
Title: Effects of HCN molecules in carbon star atmospheres.
Authors: Eriksson, K.; Gustafsson, B.; Jorgensen, U. G.; Nordlund, A.
Bibcode: 1984A&A...132...37E
Altcode:
Existing model atmospheres for carbon stars as well as observations
indicate that some polyatomic molecules may be important opacity
sources in at least the cooler carbon stars. In order to investigate
the importance of the absorption from HCN, which seems to be one
of the most important polyatomic opacity sources, monochromatic
absorption cross sections have been calculated at a great number of
wavelengths for this molecule. These calculations have been based on
the assumption that the ratios between the transition probabilities
of the combination transitions relative to the fundamentals follow
rules, deduced empirically for other molecules. Opacity distribution
functions were calculated and model atmospheres including the HCN
opacity were constructed. The effects of HCN on the models turned out
to be remarkably great.
Title: A model for the cosmic creation of nuclear energy-a
reassessment
Authors: Eriksson, K. -E.; Islam, S.; Skagerstam, B. -S.
Bibcode: 1984Natur.308..210E
Altcode:
No abstract at ADS
Title: HCN and C2H2 in Carbon Stars
Authors: Eriksson, K.; Gustafsson, B.; Jorgensen, U. G.; Nordlund, A.
Bibcode: 1984IAUS..105..199E
Altcode:
HCN and C2H2 have numerous bands at wavelengths
where a major part of the stellar flux is transported. This opacity
could therefore be of great importance when constructing models
for cool carbon star atmospheres, but has not been included in
earlier models. Models without the HCN and C2H2
opacity show a strange transition to "thin", high-pressure atmospheric
structures when Teff is decreased below about 2900K. When
HCN (and C2H2) opacity was added in the model
atmosphere calculations, great effects on the structure were found
for the lower temperatures.
Title: Outer atmospheres of cool stars. XIV. A model for the
chromosphere and transition region of beta Ceti (G9.5 III).
Authors: Eriksson, K.; Linsky, J. L.; Simon, T.
Bibcode: 1983ApJ...272..665E
Altcode:
In the present chromospheric and transition region model for Beta
Ceti, which is consistent with IUE spectra of the Mg II, C II,
and C IV resonance lines, the Mg II h and k lines are treated
in partial redistribution and the C II and C IV lines in complete
redistribution. Computed line fluxes are presented for a range of models
to show the range of permitted temperature structures. A comparison
of the Beta Ceti model to models previously computed in a similar way
for other stars shows a trend of decreasing chromospheric pressures
and increasing geometric scales as single stars evolve across the
transition region boundary. The present analysis also suggests that
transition region pressures drastically decrease and geometric scales
rapidly increase as single giant stars evolve to the right, toward
the boudnary. Beta Ceti's exceptional X-ray brightness is discussed.
Title: The Temperatures of G and K Stars
Authors: Wing, R. F.; Gustafsson, B.; Eriksson, K.
Bibcode: 1983BAAS...15..969W
Altcode:
No abstract at ADS
Title: The narrow ultraviolet emission lines of the red dwarf AU
Microscopii(dM1.6e).
Authors: Ayres, T. R.; Eriksson, K.; Linsky, J. L.; Stencel, R. E.
Bibcode: 1983ApJ...270L..17A
Altcode:
It is pointed out that the red dwarfs are the smallest, coolest,
faintest, least massive, but most common of normal main-sequence
stars. The dMe (H-alpha emission) subclass of the red dwarfs
exhibits the largest median soft X-ray to bolometric luminosity
ratio of any group of late-type stars. In connection with the present
investigation, attention is given to the first high-dispersion spectra
of the chromospheric (6000 K) and higher temperature (up to 100,000
K) emissions of a dMe star, AU Microscopii in the far-ultraviolet
(1150-2000 A) and middle-ultraviolet (2000-3000 A) bands accessible to
the International Ultraviolet Explorer (IUE). AU Mic is one of the most
luminous of lower main-sequence stars in C IV and soft X-ray emission.
Title: Geochemistry of Archean shales from the Pilbara Supergroup,
Western Australia
Authors: McLennan, Scott M.; Taylor, S. R.; Eriksson, K. A.
Bibcode: 1983GeCoA..47.1211M
Altcode:
Archean clastic sedimentary rocks are well exposed in the Pilbara
Block of Western Australia. Shales from turbidites in the Gorge
Creek Group ( ca. 3.4 Ae) and shales from the Whim Creek Group
( ca. 2.7 Ae) have been examined. The Gorge Creek Group samples,
characterized by muscovite-quartzchlorite mineralogy, are enriched in
incompatible elements (K, Th, U, LREE) by factors of about two, when
compared to younger Archean shales from the Yilgarn Block. Alkali
and alkaline earth elements are depleted in a systematic fashion,
according to size, when compared with an estimate of Archean upper
crust abundances. This depletion is less notable in the Whim Creek
Group. Such a pattern indicates the source of these rocks underwent
a rather severe episode of weathering. The Gorge Creek Group also
has fairly high B content (85 ± 29 ppm) which may indicate normal
marine conditions during deposition. Rare earth element (REE) patterns
for the Pilbara samples are characterized by light REE enrichment (
La N/Yb N ≥ 7.5 ) and no or very slight Eu
depletion ( Eu/Eu ∗ = 0.82 - 0.99 ). A source comprised
of about 80% felsic igneous rocks without large negative Eu-anomalies
(felsic volcanics, tonalites, trondhjemites) and 20% mafic-ultramafic
volcanics is indicated by the trace element data. Very high abundances
of Cr and Ni cannot be explained by any reasonable provenance model
and a secondary enrichment process is called for.
Title: Stellar atmospheres projects.
Authors: Eriksson, K.
Bibcode: 1983ITABO..60...37E
Altcode:
No abstract at ADS
Title: The Narrow Ultraviolet Emission Lines of the Red Dwarf AU
Microscopii (dM1.6e)
Authors: Ayres, T. R.; Eriksson, K.; Gustafsson, B.; Linsky, J. L.;
Saxner, M.; Stencel, R. E.
Bibcode: 1982BAAS...14Q.865A
Altcode:
No abstract at ADS
Title: A model for the cosmic creation of nuclear exergy
Authors: Eriksson, K. -E.; Islam, S.; Skagerstam, B. -S.
Bibcode: 1982Natur.296..540E
Altcode:
The exergy1 of a physical system is the maximum amount of
mechanical work that can be extracted from that system so that a system
in thermodynamic equilibrium has zero exergy. An old theme in cosmic
thermodynamics is that the second law implies that the Universe is
running down (running out of exergy) and approaching thermodynamic
equilibrium, `heat death'. However, in the standard model of the
early Universe2, at 0.01 s after the big bang the Universe
consisted of ordinary matter (nucleons), electrons and positrons,
neutrinos, photons and gravitons. The gravitons were decoupled, but the
others were in thermodyamic equilibrium. Thus the Universe had already
reached the state of heat death, and its exergy was zero. The main
problem is, therefore, not to describe the running-down of the Universe,
but to understand its revival. When and how was exergy created, in
particular the nuclear exergy, which is transformed into life-supporting
light in our Sun? We have studied a model which should represent the
nucleon gas of the early Universe quite well. We find that the main
creation of nuclear exergy started around 10 s after the big bang,
and most of the exergy was created during the first few minutes, 85%
during the first hour, and that the process was essentially completed
during the first 24 h. The final value of the exergy was 7.72 MeV per
nucleon. The consumption of this exergy started much later and takes
place in the stars over a time scale of hundreds and thousands of
millions of years.
Title: Outer atmospheres of cool stars. VIII. IUE observations
and chromospheric models for the supergiant stars beta Draconis,
epsilon Geminorum and alpha Orionis.
Authors: Basri, G. S.; Linsky, J. L.; Eriksson, K.
Bibcode: 1981ApJ...251..162B
Altcode:
A semiempirical modeling of stellar chromospheres is extended to
late-type supergiants, where computations match high-resolution,
absolute-flux profiles of the Ca II K and Mg II h and k lines. IUE
UV spectra of Epsilon Gem and Alpha Ori show no evidence of emission
lines formed at temperatures greater than 10,000 K, leading to the
computation of chromospheric models extending to 10 to the -6th g/sq cm
at temperatures that rise to 6500 K for the former star and 7000 K for
the latter. By contrast, the C II-IV, Si IV, and He II and N V strong
emission lines of Beta Dra lead to a tentative chromospheric model
extension to 16,000 K at 0.012 dynes/sq cm. It is pointed out that
the Ca II and Mg II line analyses presented, which assume hydrostatic
equilibrium with only thermal and turbulent components to the pressure,
imply nearly plane-parallel chromospheres even in the case of Alpha Ori.
Title: A model of the outer atmosphere of beta Ceti.
Authors: Eriksson, K.; Simon, T.; Linsky, J. L.
Bibcode: 1981BAAS...13..547E
Altcode:
No abstract at ADS
Title: F Dwarfs
Authors: Eriksson, K.
Bibcode: 1979iue..prop..367E
Altcode:
No abstract at ADS
Title: The O I triplet lambda 7773 Å in late-type giant stars.
Authors: Eriksson, K.; Toft, S. C.
Bibcode: 1979A&A....71..178E
Altcode:
Observations of the 7773-A triplet of O I in about 20 G and K giants are
presented which were performed with either an echelle photoelectric
spectrophotometer or a high-dispersion spectrograph. Theoretical
indices proportional to the difference in equivalent width between
the lines in the line and continuum regions are obtained via non-LTE
calculations of the 7773-A triplet lines, LTE computations of other
lines in the two narrow bands observed, and use of the continuum slope
in the framework of constant-flux line-blanketed model atmospheres
with effective temperatures of 4000 to 5000 K, log g of 1.5 to 3.0,
A/H in the range from -0.5 to 0.5, and a microturbulent velocity of
1.7 km/s. The strengths of the 7773-A triplet lines and the 6300-A
forbidden line of O I (computed in LTE) in different model atmospheres
are examined, and it is found that the non-LTE effect for the 7773-A
lines is to increase the equivalent widths by 10% to 30%. The behavior
of the triplet lines in a model atmosphere with an effective temperature
of 7600 K is briefly considered.
Title: Observed transitions between the levels of the ground
configuration in S I.
Authors: Eriksson, K. B. S.
Bibcode: 1978ApJ...222..398E
Altcode:
Accurate wavelengths of three transitions in the S I ground
configuration are obtained, and the intensities are discussed in view
of the theoretical transition probabilities. The level values are
revised. The solar-line identifications are strengthened.
Title: Soft gravitation radiation.
Authors: Alvegard, C.; Eriksson, K. -E.; Hogfors, C.
Bibcode: 1978PhyS...17...95A
Altcode:
The methods of soft photon radiation are applied to the linearized
theory of gravitation in a radiation gauge similar to the radiation
gauge in quantum electrodynamics. The time evolution of soft graviton
emission following any scattering process is studied in detail. Results
obtained by Weinberg in a different way are reproduced.
Title: The oxygen triplet lambda 7773 Å in late-type giant stars.
Authors: Eriksson, K.
Bibcode: 1978sss..meet..C15E
Altcode:
No abstract at ADS
Title: A grid of model atmospheres for metal-deficient giant
stars. II.
Authors: Bell, R. A.; Eriksson, K.; Gustafsson, B.; Nordlund, A.
Bibcode: 1976A&AS...23...37B
Altcode:
Details are presented for a previously calculated grid of LTE model
atmospheres for yellow and red giant stars. The grid covers the general
range of effective temperatures from 3750 K to 6000 K, log g from 0.75
to 3.0, and (A/H) from -3.0 to 0.0. For each model, numerical values
are given for the optical depth, the Rosseland mean, the corresponding
optical depth, the geometric depth and temperature, the electron
pressure, gas pressure, radiative pressure, density, specific heat,
and flux fraction. A model with typical solar parameters is included.
Title: A grid of model atmospheres for metal-deficient giant stars. I.
Authors: Gustafsson, B.; Bell, R. A.; Eriksson, K.; Nordlund, A.
Bibcode: 1975A&A....42..407G
Altcode: 2009A&A...500...67G
A grid of flux-constant model atmospheres for stars with effective
temperatures between 3750 and 6000 K, log g between 0.75 and 3.0, and
(A/H) between -3.0 and 0.0 has been constructed. The line absorption
is approximated by opacity distribution functions. Metal lines and
molecular lines, including those from the infrared bands of CO and CN,
are taken into account. The variation of the structure of the models
with metal abundance and microturbulence parameter is found to be
quite regular and not very drastic. The surface cooling produced
by CO is important for all the models with a maximum temperature
of 5000 K, while CN mainly causes a backwarming effect but is not
very important for solar CNO abundances. The effects of convection,
estimated by using the mixing-length approximation, are important only
for the coldest models. The models compare very well with models from
overlapping regions of other grids. A solar model consistent with the
grid models is found to agree satisfactorily with empirical solar model
atmospheres. The careful use of scaled solar models for stars with
(A/H) approximately equal to zero is justified.
Title: Forbidden transitions in S I.
Authors: Eriksson, K. B. S.
Bibcode: 1973JOSA...63..632E
Altcode:
No abstract at ADS