Author name code: meunier
ADS astronomy entries on 2022-09-14
author:"Meunier, N."
------------------------------------------------------------------------
Title: Direct Discovery of the Inner Exoplanet in the HD206893 System
Authors: Hinkley, S.; Lacour, S.; Marleau, G. D.; Lagrange, A. M.;
Wang, J. J.; Kammerer, J.; Cumming, A.; Nowak, M.; Rodet, L.; Stolker,
T.; Balmer, W. -O.; Ray, S.; Bonnefoy, M.; Mollière, P.; Lazzoni,
C.; Kennedy, G.; Mordasini, C.; Abuter, R.; Aigrain, S.; Amorim, A.;
Asensio-Torres, R.; Babusiaux, C.; Benisty, M.; Berger, J. -P.; Beust,
H.; Blunt, S.; Boccaletti, A.; Bohn, A.; Bonnet, H.; Bourdarot, G.;
Brandner, W.; Cantalloube, F.; Caselli, P.; Charnay, B.; Chauvin,
G.; Chomez, A.; Choquet, E.; Christiaens, V.; Clénet, Y.; Coudé du
Foresto, V.; Cridland, A.; Delorme, P.; Dembet, R.; de Zeeuw, P. T.;
Drescher, A.; Duvert, G.; Eckart, A.; Eisenhauer, F.; Feuchtgruber,
H.; Galland, F.; Garcia, P.; Garcia Lopez, R.; Gardner, T.; Gendron,
E.; Genzel, R.; Gillessen, S.; Girard, J. H.; Grandjean, A.; Haubois,
X.; Heißel, G.; Henning, Th.; Hippler, S.; Horrobin, M.; Houllé,
M.; Hubert, Z.; Jocou, L.; Keppler, M.; Kervella, P.; Kreidberg, L.;
Lapeyrère, V.; Le Bouquin, J. -B.; Léna, P.; Lutz, D.; Maire, A. -L.;
Mang, F.; Mérand, A.; Meunier, N.; Monnier, J. D.; Mordasini, C.;
Mouillet, D.; Nasedkin, E.; Ott, T.; Otten, G. P. P. L.; Paladini, C.;
Paumard, T.; Perraut, K.; Perrin, G.; Philipot, F.; Pfuhl, O.; Pourré,
N.; Pueyo, L.; Rameau, J.; Rickman, E.; Rubini, P.; Rustamkulov, Z.;
Samland, M.; Shangguan, J.; Shimizu, T.; Sing, D.; Straubmeier, C.;
Sturm, E.; Tacconi, L. J.; van Dishoeck, E. F.; Vigan, A.; Vincent,
F.; Ward-Duong, K.; Widmann, F.; Wieprecht, E.; Wiezorrek, E.; Woillez,
J.; Yazici, S.; Young, A.; Zicher, N.; the GRAVITY Collaboration
Bibcode: 2022arXiv220804867H
Altcode:
Long term precise radial velocity (RV) monitoring of HD206893, as well
as anomalies in the system proper motion, have suggested the presence of
an additional, inner companion in the system. In this work we describe
the results of a search for the companion responsible for this RV drift
and proper motion anomaly. Utilizing information from ongoing precision
RV measurements with the HARPS spectrograph, as well as Gaia host star
astrometry, we have undertaken a multi-epoch search for the purported
additional planet using the VLTI/GRAVITY instrument. We report a high
significance detection of the purported companion HD206893c over three
epochs, with clear evidence for Keplerian orbital motion. Our astrometry
with $\sim$50-100 $\mu$arcsec precision afforded by GRAVITY allows us
to derive a dynamical mass of 12.3$^{+1.1}_{-1.2}$ M$_{\rm Jup}$ and
an orbital separation of 3.53$^{+0.80}_{-0.70}$ au for HD206893c. Our
fits to the orbits of both companions in the system utilize both Gaia
astrometry and RVs to also provide a precise dynamical estimate of the
previously uncertain mass of the B component, and therefore derive an
age of 170 Myr. Importantly, we find that the bolometric luminosity of
the newly discovered HD206893c is anomalously high, and that standard
cooling curves are unable to simultaneously account for the brightness
of both members of the system at a common age of 170 Myr. However, we
find that incorporating an elevated helium abundance into our cooling
models in turn results in an enhanced level of deuterium burning in
the "c" companion, bringing the predicted luminosity in line with our
measured value. In addition to utilizing long-term RV information,
this effort is an early example of a direct imaging discovery of a
bona fide exoplanet that was guided in part with Gaia astrometry.
Title: Unsigned Magnetic Flux as a Proxy for Radial-velocity
Variations in Sun-like Stars
Authors: Haywood, R. D.; Milbourne, T. W.; Saar, S. H.; Mortier, A.;
Phillips, D.; Charbonneau, D.; Cameron, A. Collier; Cegla, H. M.;
Meunier, N.; , M. L. Palumbo, III
Bibcode: 2022ApJ...935....6H
Altcode: 2020arXiv200513386H
A major obstacle to detecting and characterizing long-period, low-mass
exoplanets is the intrinsic radial-velocity (RV) variability of host
stars. To better understand RV variability, we estimate disk-averaged
RV variations of the Sun over its magnetic cycle, from the Fe I line
observed by SDO/HMI, using a physical model for rotationally modulated
magnetic activity that was previously validated against HARPS-N solar
observations. We estimate the unsigned magnetic flux and show that
a linear fit to it reduces the RMS of RV variations by 62%, i.e., a
factor of 2.6. We additionally apply the FF' method, which predicts
RV variations based on a star's photometric variations. At cycle
maximum, we find that additional processes must be at play beyond
suppression of convective blueshift and velocity imbalances resulting
from brightness inhomogeneities, in agreement with recent studies
of RV variations. By modeling RV variations over the magnetic cycle
using a linear fit to the unsigned magnetic flux, we recover injected
planets at a period of ≍300 days with RV semi-amplitudes down to
0.3 m s-1. To reach 0.1 m s-1, we will need to
identify and model additional phenomena that are not well traced by
$| {\hat{B}}_{\mathrm{obs}}| $ or FF'. This study motivates ongoing
and future efforts to develop observation and analysis techniques
to measure the unsigned magnetic flux at high precision in slowly
rotating, relatively inactive stars like the Sun. We conclude that
the unsigned magnetic flux is an excellent proxy for rotationally
modulated, activity-induced RV variations, and could become key to
confirming and characterizing Earth analogs.
Title: Exocomets size distribution in the β ? Pictoris planetary
system
Authors: Lecavelier des Etangs, Alain; Cros, Lucie; Hébrard,
Guillaume; Martioli, Eder; Duquesnoy, Marc; Kenworthy, Matthew A.;
Kiefer, Flavien; Lacour, Sylvestre; Lagrange, Anne-Marie; Meunier,
Nadège; Vidal-Madjar, Alfred
Bibcode: 2022NatSR..12.5855L
Altcode: 2022arXiv220413618L
The star β ? Pictoris harbors a young planetary system of about
20 million years old, which is characterized by the presence of a
gaseous and dusty debris disk, at least two massive planets and many
minor bodies. For more than thirty years, exocomets transiting the
star have been detected using spectroscopy, probing the gaseous part
of the cometary comas and tails. The detection of the dusty component
of the tails can be performed through photometric observations of the
transits. Since 2018, the Transiting Exoplanet Survey Satellite has
observed β ? Pic for a total of 156 days. Here we report an analysis
of the TESS photometric data set with the identification of a total
of 30 transits of exocomets. Our statistical analysis shows that
the number of transiting exocomet events (N) as a function of the
absorption depth (AD) in the light curve follows a power law in the
form d N (A D ) ∝A D-α ?, where α =2.3 ±0.4 ?. This
distribution of absorption depth leads to a differential comet size
distribution proportional to R-γ?, where γ =3.6 ±0.8 ?,
showing a striking similarity to the size distribution of comets in the
Solar system and the distribution of a collisionally relaxed population
(γD=3.5 ?).
Title: A new estimation of astrometric exoplanet detection limits
in the habitable zone around nearby stars
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2022A&A...659A.104M
Altcode: 2022arXiv220206301M
Context. Astrometry is less sensitive to stellar activity than the
radial velocity technique when attempting to detect Earth mass planets
in the habitable zone of solar-type stars. This is due to a smaller
number of physical processes affecting the signal, and a larger ratio
of the amplitude of the planetary signal to the stellar signal than
with radial velocities. A few high-precision astrometric missions have
therefore been proposed over the past two decades.
Aims: We
aim to re-estimate the detection limits in astrometry for the nearby
stars which are the main targets proposed for the THEIA astrometric
mission, which is the most elaborate mission to search for planets,
and to characterise its performance on the fitted parameters. This
analysis is performed for the 55 F-G-K stars in the THEIA sample.
Methods: We used realistic simulations of stellar activity and selected
those that correspond best to each star in terms of spectral type and
average activity level. Then, we performed blind tests to estimate the
performance.
Results: We find worse detection limits compared to
those previously obtained for that sample based on a careful analysis
of the false positive rate, with values typically in the Earth-mass
regime for most stars of the sample. The difference is attributed to
the fact that we analysed full time series, adapted to each star in
the sample, rather than using the expected solar jitter only. Although
these detection limits have a relatively low signal-to-noise ratio,
the fitted parameters have small uncertainties.
Conclusions: We
confirm the low impact of stellar activity on exoplanet detectability
for solar-type stars, although it plays a significant role for the
closest stars such as α Cen A and B. We identify the best targets to
be the stars with a close habitable zone. However, for the few stars
in the sample with a habitable zone corresponding to long periods,
namely subgiants, the THEIA observational strategy is not well adapted
and should prevent the detection of planets in the habitable zone,
unless a longer mission can be proposed.
Title: Relationship between Ca and Hα chromospheric emission in
F-G-K stars: Indication of stellar filaments?
Authors: Meunier, N.; Kretzschmar, M.; Gravet, R.; Mignon, L.;
Delfosse, X.
Bibcode: 2022A&A...658A..57M
Altcode: 2022arXiv220105492M
Context. Different relationships between the Hα and Ca II
chromospheric emissions have been reported in solar-type stars. In
particular, the time-series of emissions in these two lines are clearly
anti-correlated for a few percent of the stars, contrary to what is
observed on the Sun.
Aims: Our objective is to characterise
these relationships in more detail using complementary criteria, and
to constrain the properties of filaments and plages that are necessary
to explain the observations.
Methods: We analysed the average
level and variability of the Hα and Ca II emission for 441 F-G-K
stars, paying particular attention to their (anti-)correlations on
both short and long timescales. We also computed synthetic Hα and
Ca II time-series for different assumptions of plage and filament
properties and compared them with the observations.
Results: We
were not able to find plage properties that, alone, are sufficient to
reproduce the observations at all timescales simultaneously, even when
allowing different Hα and Ca II emission relationships for different
stars. We also specified the complex and surprising relationship
between the average activity levels of both indexes, in particular for
low-activity stars.
Conclusions: We conclude that plages alone
are unlikely to explain the observed variety of relationships between
Ca II and Hα emission, and that the presence of other phenomena like
filaments may help to reconcile the models with observations. Full Table A.1 is only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/658/A57
Title: The impact of surface flows at different scales: exoplanet
detectability in radial velocity and high-precision astrometry
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2021sf2a.conf..371M
Altcode:
It is now well accepted that stellar activity prevents the detection
of Earth-like planets around solar type stars when using the radial
velocity technique. Although the impact of dark spots and bright
plages, through various processes, is now well modelled, surface flows
at different time scales (granulation, supergranulation, meridional
circulation) also lead to important radial velocity signatures due to
their temporal variability but have been less studied. Those signatures
are larger than an Earth-like signal. In this talk, we will focus on
those flows, which we have studied based on our knowledge of the Sun and
extended towards other stars. We will also show that a high-precision
astrometric mission would not be strongly impacted by stellar activity
for such planets.
Title: VizieR Online Data Catalog: SHINE II (Langlois+, 2021)
Authors: Langlois, M.; Gratton, R.; Lagrange, A. -M.; Delorme, P.;
Boccaletti, A.; Bonnefoy, M.; Maire, A. -L.; Mesa, D.; Chauvin, G.;
Desidera, S.; Vigan, A.; Cheetham, A.; Hagelberg, J.; Feldt, M.;
Meyer, M.; Rubini, P.; Le Coroller, H.; Cantalloube, F.; Biller, B.;
Bonavita, M.; Bhowmik, T.; Brandner, W.; Daemgen, S.; D'Orazi, V.;
Flasseur, O.; Fontanive, C.; Galicher, R.; Girard, J.; Janin-Potiron,
P.; Janson, M.; Keppler, M.; Kopytova, T.; Lagadec, E.; Lannier,
J.; Lazzoni, C.; Ligi, R.; Meunier, N.; Perreti, A.; Perrot, C.;
Rodet, L.; Romero, C.; Rouan, D.; Samland, M.; Salter, G.; Sissa,
E.; Schmidt, T.; Zurlo, A.; Mouillet, D.; Denis, L.; Thiebaut, E.;
Milli, J.; Wahhaj, Z.; Beuzit, J. -L.; Dominik, C.; Henning, Th.;
Menard, F.; Mueller, A.; Schmid, H. M.; Turatto, M.; Udry, S.; Abe,
L.; Antichi, J.; Allard A. Baruolo, F.; Baudoz, P.; Baudrand, J.;
Bazzon, A.; Blanchard, P.; Carbillet, M.; Carle, M.; Cascone, E.;
Charton, J.; Claudi, R.; Costille, A.; de Caprio, V.; Delboulbe, A.;
Dohlen, K.; Fantinel, D.; Feautrier, P.; Fusco, T.; Gigan, P.; Giro,
E.; Gisler, D.; Gluck, L.; Gry, C.; Hubin, N.; Hugot, E.; Jaquet,
M.; Kasper, M.; Le Mignant, D.; Llored, M.; Madec, F.; Magnard, Y.;
Martinez, P.; Maurel, D.; Messina, S.; Moeller-Nilsson, O.; Mugnier,
L.; Moulin, T.; Origne, A.; Pavlov, A.; Perret, D.; Petit, C.; Pragt,
J.; Puget, P.; Rabou, P.; Ramos, J.; Rigal, F.; Rochat, S.; Roelfsema,
R.; Rousset, G.; Roux, A.; Salasnich, B.; Sauvage, J. -F.; Sevin, A.;
Soenke, C.; Stadler, E.; Suarez, M.; Weber, L.; Wildi, F.; Rickman, E.
Bibcode: 2021yCat..36510071L
Altcode:
We process, in a uniform manner, more than 300 datasets from the
SPHERE/SHINE Survey obtained at the VLT/ESO in visitor mode and assess
the SHINE survey's typical sensitivity as a function of the host star
and observing conditions. (1 data file).
Title: The SPHERE infrared survey for exoplanets
(SHINE). II. Observations, data reduction and analysis, detection
performances, and initial results
Authors: Langlois, M.; Gratton, R.; Lagrange, A. -M.; Delorme, P.;
Boccaletti, A.; Bonnefoy, M.; Maire, A. -L.; Mesa, D.; Chauvin, G.;
Desidera, S.; Vigan, A.; Cheetham, A.; Hagelberg, J.; Feldt, M.;
Meyer, M.; Rubini, P.; Le Coroller, H.; Cantalloube, F.; Biller, B.;
Bonavita, M.; Bhowmik, T.; Brandner, W.; Daemgen, S.; D'Orazi, V.;
Flasseur, O.; Fontanive, C.; Galicher, R.; Girard, J.; Janin-Potiron,
P.; Janson, M.; Keppler, M.; Kopytova, T.; Lagadec, E.; Lannier, J.;
Lazzoni, C.; Ligi, R.; Meunier, N.; Perreti, A.; Perrot, C.; Rodet, L.;
Romero, C.; Rouan, D.; Samland, M.; Salter, G.; Sissa, E.; Schmidt,
T.; Zurlo, A.; Mouillet, D.; Denis, L.; Thiébaut, E.; Milli, J.;
Wahhaj, Z.; Beuzit, J. -L.; Dominik, C.; Henning, Th.; Ménard, F.;
Müller, A.; Schmid, H. M.; Turatto, M.; Udry, S.; Abe, L.; Antichi,
J.; Allard, F.; Baruffolo, A.; Baudoz, P.; Baudrand, J.; Bazzon, A.;
Blanchard, P.; Carbillet, M.; Carle, M.; Cascone, E.; Charton, J.;
Claudi, R.; Costille, A.; De Caprio, V.; Delboulbé, A.; Dohlen, K.;
Fantinel, D.; Feautrier, P.; Fusco, T.; Gigan, P.; Giro, E.; Gisler,
D.; Gluck, L.; Gry, C.; Hubin, N.; Hugot, E.; Jaquet, M.; Kasper,
M.; Le Mignant, D.; Llored, M.; Madec, F.; Magnard, Y.; Martinez, P.;
Maurel, D.; Messina, S.; Möller-Nilsson, O.; Mugnier, L.; Moulin, T.;
Origné, A.; Pavlov, A.; Perret, D.; Petit, C.; Pragt, J.; Puget, P.;
Rabou, P.; Ramos, J.; Rigal, F.; Rochat, S.; Roelfsema, R.; Rousset,
G.; Roux, A.; Salasnich, B.; Sauvage, J. -F.; Sevin, A.; Soenke, C.;
Stadler, E.; Suarez, M.; Weber, L.; Wildi, F.; Rickman, E.
Bibcode: 2021A&A...651A..71L
Altcode: 2021arXiv210303976L
Context. In recent decades, direct imaging has confirmed the existence
of substellar companions (exoplanets or brown dwarfs) on wide orbits
(>10 au) around their host stars. In striving to understand their
formation and evolution mechanisms, in 2015 we initiated the SPHERE
infrared survey for exoplanets (SHINE), a systematic direct imaging
survey of young, nearby stars that is targeted at exploring their
demographics.
Aims: We aim to detect and characterize the
population of giant planets and brown dwarfs beyond the snow line
around young, nearby stars. Combined with the survey completeness,
our observations offer the opportunity to constrain the statistical
properties (occurrence, mass and orbital distributions, dependency
on the stellar mass) of these young giant planets.
Methods:
In this study, we present the observing and data analysis strategy,
the ranking process of the detected candidates, and the survey
performances for a subsample of 150 stars that are representative of
the full SHINE sample. Observations were conducted in a homogeneous way
between February 2015 and February 2017 with the dedicated ground-based
VLT/SPHERE instrument equipped with the IFS integral field spectrograph
and the IRDIS dual-band imager, covering a spectral range between 0.9
and 2.3 μm. We used coronographic, angular, and spectral differential
imaging techniques to achieve the best detection performances for this
study, down to the planetary mass regime.
Results: We processed,
in a uniform manner, more than 300 SHINE observations and datasets to
assess the survey typical sensitivity as a function of the host star and
of the observing conditions. The median detection performance reached
5σ-contrasts of 13 mag at 200 mas and 14.2 mag at 800 mas with the IFS
(YJ and YJH bands), and of 11.8 mag at 200 mas, 13.1 mag at 800 mas,
and 15.8 mag at 3 as with IRDIS in H band, delivering one of the deepest
sensitivity surveys thus far for young, nearby stars. A total of sixteen
substellar companions were imaged in this first part of SHINE: seven
brown dwarf companions and ten planetary-mass companions.These include
two new discoveries, HIP 65426 b and HIP 64892 B, but not the planets
around PDS70 that had not been originally selected for the SHINE core
sample. A total of 1483 candidates were detected, mainly in the large
field of view that characterizes IRDIS. The color-magnitude diagrams,
low-resolution spectrum (when available with IFS), and follow-up
observations enabled us to identify the nature (background contaminant
or comoving companion) of about 86% of our subsample. The remaining
cases are often connected to crowded-field follow-up observations that
were missing. Finally, even though SHINE was not initially designed
for disk searches, we imaged twelve circumstellar disks, including
three new detections around the HIP 73145, HIP 86598, and HD 106906
systems.
Conclusions: Nowadays, direct imaging provides a
unique opportunity to probe the outer part of exoplanetary systems
beyond 10 au to explore planetary architectures, as highlighted by
the discoveries of: one new exoplanet, one new brown dwarf companion,
and three new debris disks during this early phase of SHINE. It also
offers the opportunity to explore and revisit the physical and orbital
properties of these young, giant planets and brown dwarf companions
(relative position, photometry, and low-resolution spectrum in
near-infrared, predicted masses, and contrast in order to search
for additional companions). Finally, these results highlight the
importance of finalizing the SHINE systematic observation of about
500 young, nearby stars for a full exploration of their outer part
to explore the demographics of young giant planets beyond 10 au and
to identify the most interesting systems for the next generation of
high-contrast imagers on very large and extremely large telescopes. Full Table A.1 is only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/651/A71
Title: A SOPHIE RV search for giant planets around young nearby stars
(YNS). A combination with the HARPS YNS survey
Authors: Grandjean, A.; Lagrange, A. -M.; Meunier, N.; Rubini, P.;
Desidera, S.; Galland, F.; Borgniet, S.; Zicher, N.; Messina, S.;
Chauvin, G.; Sterzik, M.; Pantoja, B.
Bibcode: 2021arXiv210610754G
Altcode:
The search of close (a<=5 au) giant planet(GP) companions with radial
velocity(RV) around young stars and the estimate of their occurrence
rates is important to constrain the migration timescales. Furthermore,
this search will allow the giant planet occurrence rates to be
computed at all separations via the combination with direct imaging
techniques. The RV search around young stars is a challenge as they are
generally faster rotators than older stars of similar spectral types
and they exhibit signatures of spots or pulsation in their RV time
series. Specific analyses are necessary to characterize, and possibly
correct for, this activity. Our aim is to search for planets around
young nearby stars and to estimate the GP occurrence rates for periods
up to 1000 days. We used the SOPHIE spectrograph to observe 63 A-M
young (<400 Myr) stars. We used our SAFIR software to compute the
RVs and other spectroscopic observables. We then combined this survey
with the HARPS YNS survey to compute the companion occurrence rates
on a total of 120 young A-M stars. We report one new trend compatible
with a planetary companion on HD109647. We also report HD105693 and
HD112097 as binaries, and we confirm the binarity of HD2454, HD13531,
HD17250A, HD28945, HD39587, HD131156, HD 142229, HD186704A, and HD
195943. We constrained for the first time the orbital parameters of
HD195943B. We refute the HD13507 single brown dwarf (BD) companion
solution and propose a double BD companion solution. Based on our sample
of 120 young stars, we obtain a GP occurrence rate of 1_{-0.3}^{+2.2}%
for periods lower than 1000 days, and we obtain an upper limit on BD
occurrence rateof 0.9_{-0.9}^{+2}% in the same period range. We report
a possible lack of close (1<P<1000 days) GPs around young FK stars
compared to their older counterparts, with a confidence level of 90%.
Title: A SOPHIE RV search for giant planets around young nearby stars
(YNS). A combination with the HARPS YNS survey
Authors: Grandjean, A.; Lagrange, A. -M.; Meunier, N.; Rubini, P.;
Desidera, S.; Galland, F.; Borgniet, S.; Zicher, N.; Messina, S.;
Chauvin, G.; Sterzik, M.; Pantoja, B.
Bibcode: 2021A&A...650A..39G
Altcode:
Context. The search of close (a ≲ 5 au) giant planet (GP) companions
with radial velocity (RV) around young stars and the estimate of
their occurrence rates is important to constrain the migration
timescales. Furthermore, this search will allow the giant planet
occurrence rates to be computed at all separations via the combination
with direct imaging techniques. The RV search around young stars is
a challenge as they are generally faster rotators than older stars of
similar spectral types and they exhibit signatures of magnetic activity
(spots) or pulsation in their RV time series. Specific analyses are
necessary to characterize, and possibly correct for, this activity.
Aims: Our aim is to search for planets around young nearby stars and
to estimate the GP occurrence rates for periods up to 1000 days.
Methods: We used the SOPHIE spectrograph on the 1.93 m telescope at
the Haute-Provence Observatory to observe 63 A − M young (<400
Myr) stars. We used our Spectroscopic data via Analysis of the Fourier
Interspectrum Radial velocities software to compute the RVs and other
spectroscopic observables. We then combined this survey with the
HARPS YNS survey to compute the companion occurrence rates on a total
of 120 young A − M stars.
Results: We report one new trend
compatible with a planetary companion on HD 109647. We also report
HD 105693 and HD 112097 as binaries, and we confirm the binarity
of HD 2454, HD 13531, HD 17250 A, HD 28945, HD 39587, HD 131156, HD
142229, HD 186704 A, and HD 195943. We constrained for the first time
the orbital parameters of HD 195943 B. We refute the HD 13507 single
brown dwarf (BD) companion solution and propose a double BD companion
solution. Two GPs were previously reported from this survey in the HD
113337 system. Based on our sample of 120 young stars, we obtain a GP
occurrence rate of 1−0.3+2.2% for periods lower
than 1000 days, and we obtain an upper limit on BD occurrence rate of
0.9−0.9+2% in the same period range. We report
a possible lack of close (P ∈ [1;1000] days) GPs around young FK stars
compared to their older counterparts, with a confidence level of 90%. Tables A.1-A.4 are only available at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/650/A39
Title: Stellar variability in radial velocity
Authors: Meunier, Nadège
Bibcode: 2021arXiv210406072M
Altcode:
Stellar activity due to different processes (magnetic activity,
photospheric flows) affects the measurement of radial velocities
(RV). Radial velocities have been widely used to detect exoplanets,
although the stellar signal significantly impacts the detection and
characterisation performance, especially for low mass planets. On the
other hand, RV time series are also very rich in information on stellar
processes. In this lecture, I review the context of RV observations,
describe how radial velocities are measured, and the properties
of typical observations. I present the challenges represented by
stellar activity for exoplanet studies, and describe the processes
at play. Finally, I review the approaches which have been developed,
including observations and simulations, as well as solar and stellar
comparisons.
Title: VizieR Online Data Catalog: SOPHIE and HARPS Young Nearby
Stars - YNS (Grandjean+ 2021)
Authors: Grandjean, A.; Larange, A. -M.; Meunier, N.; Rubini, P.;
Desidera, S.; Galland, F.; Borgniet, S.; Zicher, N.; Messina, S.;
Chauvin, G.; Sterzik, M.; Pantoja, B.
Bibcode: 2021yCat..36500039G
Altcode:
The SOPHIE Young Nearby Stars catalogue (SOPHIE YNS) is based on
a survey of CNRS SOPHIE on young stars and contains 54 A to M type
stars. The HARPS Young Nearby Stars catalogue (HARPS YNS, Grandjean et
al., 2020A&A...633A..44G, Cat. J/A+A/633/A44) is based on a survey
of ESO HARPS on young stars and contains 89 A to M type stars. Here
is presented an updated version of the HARPS YNS results, including
Radial velocity (RV) results and activity indicator results. (4
data files).
Title: Activity time series of old stars from late F to early
K. V. Effect on exoplanet detectability with high-precision astrometry
Authors: Meunier, N.; Lagrange, A. -M.; Borgniet, S.
Bibcode: 2020A&A...644A..77M
Altcode: 2020arXiv201102158M
Context. Stellar activity strongly affects and may prevent the
detection of Earth-mass planets in the habitable zone of solar-type
stars with radial velocity technics. Astrometry is in principle less
sensitive to stellar activity because the situation is more favourable:
the stellar astrometric signal is expected to be fainter than the
planetary astrometric signal compared to radial velocities.
Aims: We quantify the effect of stellar activity on high-precision
astrometry when Earth-mass planets are searched for in the habitable
zone around old main-sequence solar-type stars.
Methods: We
used a very large set of magnetic activity synthetic time series to
characterise the properties of the stellar astrometric signal. We then
studied the detectability of exoplanets based on different approaches:
first based on the theoretical level of false positives derived from the
synthetic time series, and then with blind tests for old main-sequence
F6-K4 stars.
Results: The amplitude of the signal can be up
to a few times the solar value depending on the assumptions made
for activity level, spectral type, and spot contrast. The detection
rates for 1 MEarth planets are very good, however, with
extremely low false-positive rates in the habitable zone for stars in
the F6-K4 range at 10 pc. The standard false-alarm probability using
classical bootstrapping on the time series strongly overestimates
the false-positive level. This affects the detection rates.
Conclusions: We conclude that if technological challenges can be
overcome and very high precision is reached, astrometry is much more
suitable for detecting Earth-mass planets in the habitable zone around
nearby solar-type stars than radial velocity, and detection rates
are much higher for this range of planetary masses and periods when
astrometric techniques are used than with radial velocity techniques.
Title: The effects of granulation and supergranulation on Earth-mass
planet detectability in the habitable zone around F6-K4 stars
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2020A&A...642A.157M
Altcode: 2020arXiv200811952M
Context. The detectability of exoplanets and the determination of
their projected mass in radial velocity are affected by stellar
magnetic activity and photospheric dynamics. Among those processes,
the effect of granulation, and even more so of supergranulation, has
been shown to be significant in the solar case. The impact for other
spectral types has not yet been characterised.
Aims: Our study
is aimed at quantifying the impact of these flows for other stars and
estimating how such contributions affect their performance.
Methods: We analysed a broad array of extended synthetic time series
that model these processes to characterise the impact of these flows on
exoplanet detection for main sequence stars with spectral types from F6
to K4. We focussed on Earth-mass planets orbiting within the habitable
zone around those stars. We estimated the expected detection rates
and detection limits, tested the tools that are typically applied to
such observations, and performed blind tests.
Results: We find
that both granulation and supergranulation on these stars significantly
affect planet mass characterisation in radial velocity when performing a
follow-up of a transit detection: the uncertainties on these masses are
sometimes below 20% for a 1 MEarth (for granulation alone or
for low-mass stars), but they are much larger in other configurations
(supergranulation, high-mass stars). For granulation and low levels
of supergranulation, the detection rates are good for K and late G
stars (if the number of points is large enough), but poor for more
massive stars. The highest level of supergranulation leads to a very
poor performance, even for K stars; this is both due to low detection
rates and to high levels of false positives, even for a very dense
temporal sampling over 10 yr. False positive levels estimated from
standard false alarm probabilities sometimes significantly overestimate
or underestimate the true level, depending on the number of points: it
is, therefore, crucial to take this effect into account when analysing
observations.
Conclusions: We conclude that granulation and
supergranulation significantly affect the performance of exoplanet
detectability. Future works will focus on improving the following
three aspects: decreasing the number of false positives, increasing
detection rates, and improving the false alarm probability estimations
from observations.
Title: Unveiling the β Pictoris system, coupling high contrast
imaging, interferometric, and radial velocity data
Authors: Lagrange, A. M.; Rubini, P.; Nowak, M.; Lacour, S.; Grandjean,
A.; Boccaletti, A.; Langlois, M.; Delorme, P.; Gratton, R.; Wang,
J.; Flasseur, O.; Galicher, R.; Kral, Q.; Meunier, N.; Beust, H.;
Babusiaux, C.; Le Coroller, H.; Thebault, P.; Kervella, P.; Zurlo, A.;
Maire, A. -L.; Wahhaj, Z.; Amorim, A.; Asensio-Torres, R.; Benisty, M.;
Berger, J. P.; Bonnefoy, M.; Brandner, W.; Cantalloube, F.; Charnay,
B.; Chauvin, G.; Choquet, E.; Clénet, Y.; Christiaens, V.; Coudé
Du Foresto, V.; de Zeeuw, P. T.; Desidera, S.; Duvert, G.; Eckart,
A.; Eisenhauer, F.; Galland, F.; Gao, F.; Garcia, P.; Garcia Lopez,
R.; Gendron, E.; Genzel, R.; Gillessen, S.; Girard, J.; Hagelberg,
J.; Haubois, X.; Henning, T.; Heissel, G.; Hippler, S.; Horrobin, M.;
Janson, M.; Kammerer, J.; Kenworthy, M.; Keppler, M.; Kreidberg, L.;
Lapeyrère, V.; Le Bouquin, J. -B.; Léna, P.; Mérand, A.; Messina,
S.; Mollière, P.; Monnier, J. D.; Ott, T.; Otten, G.; Paumard, T.;
Paladini, C.; Perraut, K.; Perrin, G.; Pueyo, L.; Pfuhl, O.; Rodet,
L.; Rodriguez-Coira, G.; Rousset, G.; Samland, M.; Shangguan, J.;
Schmidt, T.; Straub, O.; Straubmeier, C.; Stolker, T.; Vigan, A.;
Vincent, F.; Widmann, F.; Woillez, J.; GRAVITY Collaboration
Bibcode: 2020A&A...642A..18L
Altcode:
Context. The nearby and young β Pictoris system hosts a well
resolved disk, a directly imaged massive giant planet orbiting at
≃9 au, as well as an inner planet orbiting at ≃2.7 au, which was
recently detected through radial velocity (RV). As such, it offers
several unique opportunities for detailed studies of planetary system
formation and early evolution.
Aims: We aim to further constrain
the orbital and physical properties of β Pictoris b and c using a
combination of high contrast imaging, long base-line interferometry,
and RV data. We also predict the closest approaches or the transit
times of both planets, and we constrain the presence of additional
planets in the system.
Methods: We obtained six additional
epochs of SPHERE data, six additional epochs of GRAVITY data, and five
additional epochs of RV data. We combined these various types of data
in a single Markov-chain Monte Carlo analysis to constrain the orbital
parameters and masses of the two planets simultaneously. The analysis
takes into account the gravitational influence of both planets on the
star and hence their relative astrometry. Secondly, we used the RV and
high contrast imaging data to derive the probabilities of presence of
additional planets throughout the disk, and we tested the impact of
absolute astrometry.
Results: The orbital properties of both
planets are constrained with a semi-major axis of 9.8 ± 0.4 au and
2.7 ± 0.02 au for b and c, respectively, and eccentricities of 0.09
± 0.1 and 0.27 ± 0.07, assuming the HIPPARCOS distance. We note that
despite these low fitting error bars, the eccentricity of β Pictoris
c might still be over-estimated. If no prior is provided on the mass
of β Pictoris b, we obtain a very low value that is inconsistent
with what is derived from brightness-mass models. When we set an
evolutionary model motivated prior to the mass of β Pictoris b, we
find a solution in the 10-11 MJup range. Conversely, β
Pictoris c's mass is well constrained, at 7.8 ± 0.4 MJup,
assuming both planets are on coplanar orbits. These values depend
on the assumptions on the distance of the β Pictoris system. The
absolute astrometry HIPPARCOS-Gaia data are consistent with the
solutions presented here at the 2σ level, but these solutions are
fully driven by the relative astrometry plus RV data. Finally, we
derive unprecedented limits on the presence of additional planets in
the disk. We can now exclude the presence of planets that are more
massive than about 2.5 MJup closer than 3 au, and more
massive than 3.5 MJup between 3 and 7.5 au. Beyond 7.5 au,
we exclude the presence of planets that are more massive than 1-2
MJup.
Conclusions: Combining relative astrometry
and RVs allows one to precisely constrain the orbital parameters of
both planets and to give lower limits to potential additional planets
throughout the disk. The mass of β Pictoris c is also well constrained,
while additional RV data with appropriate observing strategies are
required to properly constrain the mass of β Pictoris b.
Title: VizieR Online Data Catalog: RV jitter and photometric
var. correlation (Hojjatpanah+, 2020)
Authors: Hojjatpanah, S.; Oshagh, M.; Figueira, P.; Santos, N. C.;
Amazo-Gomez, E. M.; Sousa, S. G.; Adibekyan, V.; Akinsanmi, B.;
Demangeon, O.; Faria, J.; Gomes da Silva, J.; Meunier, N.
Bibcode: 2020yCat..36390035H
Altcode:
We present a study on the correlation between RV jitter and photometric
variability. We used a sample of 171 starts that have been observed
by both the HARPS spectrograph and TESS space telescope. We derived
the RV-RMS and peak-to-peak of light curve variability as well as the
stellar parameters. (2 data files).
Title: The correlation between photometric variability and radial
velocity jitter. Based on TESS and HARPS observations
Authors: Hojjatpanah, S.; Oshagh, M.; Figueira, P.; Santos, N. C.;
Amazo-Gómez, E. M.; Sousa, S. G.; Adibekyan, V.; Akinsanmi, B.;
Demangeon, O.; Faria, J.; Gomes da Silva, J.; Meunier, N.
Bibcode: 2020A&A...639A..35H
Altcode: 2020arXiv200510105H
Context. Characterizing the relation between stellar photometric
variability and radial velocity (RV) jitter can help us to better
understand the physics behind these phenomena. The current and
upcoming high precision photometric surveys such as TESS, CHEOPS,
and PLATO will provide the community with thousands of new exoplanet
candidates. As a consequence, the presence of such a correlation
is crucial in selecting the targets with the lowest RV jitter for
efficient RV follow-up of exoplanetary candidates. Studies of this
type are also crucial to design optimized observational strategies to
mitigate RV jitter when searching for Earth-mass exoplanets.
Aims: Our goal is to assess the correlation between high-precision
photometric variability measurements and high-precision RV jitter over
different time scales.
Methods: We analyze 171 G, K, and M stars
with available TESS high precision photometric time-series and HARPS
precise RVs. We derived the stellar parameters for the stars in our
sample and measured the RV jitter and photometric variability. We
also estimated chromospheric Ca II H & K activity indicator
log(RHK'), v sin i, and the stellar rotational
period. Finally, we evaluate how different stellar parameters and an RV
sampling subset can have an impact on the potential correlations.
Results: We find a varying correlation between the photometric
variability and RV jitter as function of time intervals between the
TESS photometric observation and HARPS RV. As the time intervals of the
observations considered for the analysis increases, the correlation
value and significance becomes smaller and weaker, to the point that
it becomes negligible. We also find that for stars with a photometric
variability above 6.5 ppt the correlation is significantly stronger. We
show that such a result can be due to the transition between the
spot-dominated and the faculae-dominated regime. We quantified the
correlations and updated the relationship between chromospheric
Ca II H & K activity indicator log(RHK')
and RV jitter. Based on observations collected at the La Silla
Observatory, ESO(Chile), with the HARPS spectrograph at the 3.6-m
telescope. See the acknowledgements for the list of specific programs.
Title: Radial-velocity variations due to meridional flows in the
Sun and solar-type stars: impact on exoplanet detectability
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2020A&A...638A..54M
Altcode: 2020arXiv200410611M
Context. Stellar variability due to magnetic activity and flows at
different spatial scales strongly impacts radial velocities. This
variability is seen as oscillations, granulation, supergranulation,
and meridional flows. The effect of this latter process is currently
poorly known but could affect exoplanet detectability.
Aims:
We aim to quantify the amplitude of the meridional flow integrated over
the disc and its temporal variability, first for the Sun, as seen with
different inclinations, and then for other solar-type stars. We then
want to compare these amplitudes with low-mass exoplanetary amplitudes
in radial velocity.
Methods: We used long time series (covering
two 11-yr cycles) of solar latitudinal meridional circulation to
reconstruct its integrated contribution and study its properties. We
then used scaling laws from hydrodynamical simulations relating the
amplitude of the meridional flow variability with stellar mass and
rotation rate to estimate the typical amplitude expected for other
solar-type stars.
Results: We find typical rms of the order
of 0.5-0.7 m s-1 (edge-on) and 1.2-1.7 m s-1
(pole-on) for the Sun (peak-to-peak amplitudes are typically 1-1.4 m
s-1 and 2.3-3.3 m s-1 resp.), with a minimal
jitter for an inclination of 45-55°. This signal is significant
compared to other stellar activity contributions and is much larger
than the radial-velocity signal of the Earth. The variability is
strongly related to the activity cycle, with maximum flows during the
descending phase of the cycle, and possible variability on timescales
lower than the cycle period. Extension to other solar-type stars
shows that the variability due to meridional flows is dominated by
the amplitude of the cycle of those stars (compared with mass and
rotation rate), and that the peak-to-peak amplitudes can reach 4 m
s-1 for the most variable stars when seen pole-on. The
meridional flow contribution sometimes represents a high fraction
of the convective blueshift inhibition signal, especially for quiet,
low-mass stars. For fast-rotating stars, the presence of multi-cellular
patterns should significantly decrease the meridional flow contribution
to the radial-velocity signal.
Conclusions: Our study shows that
these meridional flows could be critical for exoplanet detection. Low
inclinations are more impacted than edge-on configurations, but these
latter still exhibit significant variability. Meridional flows also
degrade the correlation between radial velocities due to convective
blueshift inhibition and chromospheric activity indicators. This will
make the correction from this signal challenging for stars with no
multi-cellular patterns, such as the Sun for example, although there
may be some configurations for which the line shape variations may be
used if the precision is sufficient.
Title: SPHERE+: Imaging young Jupiters down to the snowline
Authors: Boccaletti, A.; Chauvin, G.; Mouillet, D.; Absil, O.;
Allard, F.; Antoniucci, S.; Augereau, J. -C.; Barge, P.; Baruffolo,
A.; Baudino, J. -L.; Baudoz, P.; Beaulieu, M.; Benisty, M.; Beuzit,
J. -L.; Bianco, A.; Biller, B.; Bonavita, B.; Bonnefoy, M.; Bos, S.;
Bouret, J. -C.; Brandner, W.; Buchschache, N.; Carry, B.; Cantalloube,
F.; Cascone, E.; Carlotti, A.; Charnay, B.; Chiavassa, A.; Choquet,
E.; Clenet, Y.; Crida, A.; De Boer, J.; De Caprio, V.; Desidera, S.;
Desert, J. -M.; Delisle, J. -B.; Delorme, P.; Dohlen, K.; Doelman,
D.; Dominik, C.; Orazi, V. D; Dougados, C.; Doute, S.; Fedele, D.;
Feldt, M.; Ferreira, F.; Fontanive, C.; Fusco, T.; Galicher, R.;
Garufi, A.; Gendron, E.; Ghedina, A.; Ginski, C.; Gonzalez, J. -F.;
Gratadour, D.; Gratton, R.; Guillot, T.; Haffert, S.; Hagelberg, J.;
Henning, T.; Huby, E.; Janson, M.; Kamp, I.; Keller, C.; Kenworthy,
M.; Kervella, P.; Kral, Q.; Kuhn, J.; Lagadec, E.; Laibe, G.; Langlois,
M.; Lagrange, A. -M.; Launhardt, R.; Leboulleux, L.; Le Coroller, H.;
Li Causi, G.; Loupias, M.; Maire, A. L.; Marleau, G.; Martinache,
F.; Martinez, P.; Mary, D.; Mattioli, M.; Mazoyer, J.; Meheut, H.;
Menard, F.; Mesa, D.; Meunier, N.; Miguel, Y.; Milli, J.; Min, M.;
Molliere, P.; Mordasini, C.; Moretto, G.; Mugnier, L.; Muro Arena,
G.; Nardetto, N.; Diaye, M. N; Nesvadba, N.; Pedichini, F.; Pinilla,
P.; Por, E.; Potier, A.; Quanz, S.; Rameau, J.; Roelfsema, R.; Rouan,
D.; Rigliaco, E.; Salasnich, B.; Samland, M.; Sauvage, J. -F.; Schmid,
H. -M.; Segransan, D.; Snellen, I.; Snik, F.; Soulez, F.; Stadler, E.;
Stam, D.; Tallon, M.; Thebault, P.; Thiebaut, E.; Tschudi, C.; Udry,
S.; van Holstein, R.; Vernazza, P.; Vidal, F.; Vigan, A.; Waters,
R.; Wildi, F.; Willson, M.; Zanutta, A.; Zavagno, A.; Zurlo, A.
Bibcode: 2020arXiv200305714B
Altcode:
SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for
more than 5 years, demonstrating a high level of performance. SPHERE
has produced outstanding results using a variety of operating modes,
primarily in the field of direct imaging of exoplanetary systems,
focusing on exoplanets as point sources and circumstellar disks as
extended objects. The achievements obtained thus far with SPHERE
(~200 refereed publications) in different areas (exoplanets, disks,
solar system, stellar physics...) have motivated a large consortium
to propose an even more ambitious set of science cases, and its
corresponding technical implementation in the form of an upgrade. The
SPHERE+ project capitalizes on the expertise and lessons learned
from SPHERE to push high contrast imaging performance to its limits
on the VLT 8m-telescope. The scientific program of SPHERE+ described
in this document will open a new and compelling scientific window for
the upcoming decade in strong synergy with ground-based facilities
(VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and
WFIRST). While SPHERE has sampled the outer parts of planetary systems
beyond a few tens of AU, SPHERE+ will dig into the inner regions
around stars to reveal and characterize by mean of spectroscopy the
giant planet population down to the snow line. Building on SPHERE's
scientific heritage and resounding success, SPHERE+ will be a dedicated
survey instrument which will strengthen the leadership of ESO and the
European community in the very competitive field of direct imaging
of exoplanetary systems. With enhanced capabilities, it will enable
an even broader diversity of science cases including the study of the
solar system, the birth and death of stars and the exploration of the
inner regions of active galactic nuclei.
Title: Testing the Spectroscopic Extraction of Suppression of
Convective Blueshift
Authors: Miklos, M.; Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.;
Saar, S. H.; Meunier, N.; Cegla, H. M.; Dumusque, X.; Langellier, N.;
Maldonado, J.; Malavolta, L.; Mortier, A.; Thompson, S.; Watson, C. A.;
Cecconi, M.; Cosentino, R.; Ghedina, A.; Li, C. -H.; López-Morales,
M.; Molinari, E.; Poretti, Ennio; Sasselov, D.; Sozzetti, A.;
Walsworth, R. L.
Bibcode: 2020ApJ...888..117M
Altcode: 2019arXiv191009038M
Efforts to detect low-mass exoplanets using stellar radial
velocities (RVs) are currently limited by magnetic photospheric
activity. Suppression of convective blueshift is the dominant magnetic
contribution to RV variability in low-activity Sun-like stars. Due to
convective plasma motion, the magnitude of RV contributions from the
suppression of convective blueshift is related to the depth of formation
of photospheric spectral lines for a given species used to compute
the RV time series. Meunier et al. used this relation to demonstrate
a method for spectroscopic extraction of the suppression of convective
blueshift in order to isolate RV contributions, including planetary RVs,
that contribute equally to the time series for each spectral line. Here,
we extract disk-integrated solar RVs from observations over a 2.5 yr
time span made with the solar telescope integrated with the HARPS-N
spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary
Islands, Spain). We apply the methods outlined by Meunier et al. We
are not, however, able to isolate physically meaningful contributions
due to the suppression of convective blueshift from this solar data
set, potentially because our data set is taken during solar minimum
when the suppression of convective blueshift may not sufficiently
dominate activity contributions to RVs. This result indicates that,
for low-activity Sun-like stars, one must include additional RV
contributions from activity sources not considered in the Meunier et
al. model at different timescales, as well as instrumental variation,
in order to reach the submeter per second RV sensitivity necessary to
detect low-mass planets in orbit around Sun-like stars.
Title: A HARPS RV search for planets around young nearby stars
Authors: Grandjean, A.; Lagrange, A. -M.; Keppler, M.; Meunier, N.;
Mignon, L.; Borgniet, S.; Chauvin, G.; Desidera, S.; Galland, F.;
Messina, S.; Sterzik, M.; Pantoja, B.; Rodet, L.; Zicher, N.
Bibcode: 2020A&A...633A..44G
Altcode: 2019arXiv191202741G
Context. Young nearby stars are good candidates in the search
for planets with both radial velocity (RV) and direct imaging
techniques. This, in turn, allows for the computation of the giant
planet occurrence rates at all separations. The RV search around young
stars is a challenge as they are generally faster rotators than older
stars of similar spectral types and they exhibit signatures of magnetic
activity (spots) or pulsation in their RV time series. Specific
analyses are necessary to characterize, and possibly correct for,
this activity.
Aims: Our aim is to search for planets around
young nearby stars and to estimate the giant planet (GP) occurrence
rates for periods up to 1000 days.
Methods: We used the HARPS
spectrograph on the 3.6 m telescope at La Silla Observatory to observe
89 A-M young (<600 Myr) stars. We used our SAFIR (Spectroscopic
data via Analysis of the Fourier Interspectrum Radial velocities)
software to compute the RV and other spectroscopic observables. Then,
we computed the companion occurrence rates on this sample.
Results: We confirm the binary nature of HD 177171, HD 181321
and HD 186704. We report the detection of a close low mass stellar
companion for HIP 36985. No planetary companion was detected. We obtain
upper limits on the GP (<13 MJup) and BD (∈ [13;80]
MJup) occurrence rates based on 83 young stars for periods
less than 1000 days, which are set, 2-2+3
and 1-1+3%. A table of the radial
velocities 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/cat/J/A+A/633/A44
Title: From the Sun to solar-type stars: radial velocity, photometry,
astrometry and logR'HK time series for late-F to early-K
old stars
Authors: Meunier, Nadège; Lagrange, Anne-Marie
Bibcode: 2020IAUS..354..286M
Altcode:
Solar simulations and observations showed that the detection of Earth
twins around Sun-like stars is difficult in radial velocities with
current methods techniques. The Sun has proved to be very useful to
test processes, models, and analysis methods. The convective blueshift
effect, dominating for the Sun, decreases towards lower mass stars,
providing more suitable conditions to detect low mass planets. We
describe the basic processes at work and how we extended a realistic
solar model of radial velocity, photometry, astrometry and LogR'HK
variability, using a coherent grid of stellar parameters covering a
large range in mass and average activity levels. We present selected
results concerning the impact of magnetic activity on Earth-mass planet
detectability as a function of stellar type. We show how such realistic
simulations can help characterizing the effect of stellar activity on
RV and astrometric exoplanet detection.
Title: Activity time series of old stars from late F to early
K. IV. Limits of the correction of radial velocities using
chromospheric emission
Authors: Meunier, N.; Lagrange, A. -M.; Cuzacq, S.
Bibcode: 2019A&A...632A..81M
Altcode: 2019arXiv191105319M
Context. Inhibition of the convective blueshift in active regions is
a major contribution to the radial velocity (RV) variations, at least
for solar-like stars. A common technique to correct for this component
is to model the RV as a linear function of chromospheric emission,
because both are strongly correlated with the coverage by plages.
Aims: This correction, although efficient, is not perfect: the aim
of the present study is to understand the limits of this correction
and to improve it.
Methods: We investigate these questions
by analysing a large set of synthetic time series corresponding to
old main sequence F6-K4 stars modelled using a consistent set of
parameters. We focus here on the analysis of the correlation between
time series, in particular between RV (variability due to different
processes) and chromospheric emission on different timescales. We also
study the temporal variation for each time series.
Results:
We find that inclination strongly impacts these correlations, as well
as the presence of additional signals (in particular granulation and
supergranulation). Although RV and log R'HK are often well
correlated, a combination of geometrical effects (butterfly diagrams
related to dynamo processes and inclination) and activity level
variations over time create an hysteresis pattern during the cycle,
which produces a departure from an excellent correlation: for a given
activity level, the RV is higher or lower during the ascending phase
compared to the descending phase of the cycle depending on inclination,
with a reversal for inclinations about 60° from pole-on. We find
that this hysteresis is also observed for the Sun, as well as for
other stars. This property is due to the spatio-temporal distribution
of the activity pattern (and therefore to the dynamo processes) and
to the difference in projection effects of the RV and chromospheric
emission.
Conclusions: These results allow us to propose a new
method which significantly improves the correction for long timescales
(fraction of the cycle), and could be crucial to improving detection
rates of planets in the habitable zone around F6-K4 stars.
Title: VLT/SPHERE exploration of the young multiplanetary system PDS70
Authors: Mesa, D.; Keppler, M.; Cantalloube, F.; Rodet, L.; Charnay,
B.; Gratton, R.; Langlois, M.; Boccaletti, A.; Bonnefoy, M.; Vigan,
A.; Flasseur, O.; Bae, J.; Benisty, M.; Chauvin, G.; de Boer, J.;
Desidera, S.; Henning, T.; Lagrange, A. -M.; Meyer, M.; Milli, J.;
Müller, A.; Pairet, B.; Zurlo, A.; Antoniucci, S.; Baudino, J. -L.;
Brown Sevilla, S.; Cascone, E.; Cheetham, A.; Claudi, R. U.; Delorme,
P.; D'Orazi, V.; Feldt, M.; Hagelberg, J.; Janson, M.; Kral, Q.;
Lagadec, E.; Lazzoni, C.; Ligi, R.; Maire, A. -L.; Martinez, P.;
Menard, F.; Meunier, N.; Perrot, C.; Petrus, S.; Pinte, C.; Rickman,
E. L.; Rochat, S.; Rouan, D.; Samland, M.; Sauvage, J. -F.; Schmidt,
T.; Udry, S.; Weber, L.; Wildi, F.
Bibcode: 2019A&A...632A..25M
Altcode: 2019arXiv191011169M
Context. PDS 70 is a young (5.4 Myr), nearby ( 113 pc) star hosting
a known transition disk with a large gap. Recent observations with
SPHERE and NACO in the near-infrared (NIR) allowed us to detect a
planetary mass companion, PDS 70 b, within the disk cavity. Moreover,
observations in Hα with MagAO and MUSE revealed emission
associated to PDS 70 b and to another new companion candidate, PDS 70
c, at a larger separation from the star. PDS 70 is the only multiple
planetary system at its formation stage detected so far through direct
imaging.
Aims: Our aim is to confirm the discovery of the
second planet PDS 70 c using SPHERE at VLT, to further characterize its
physical properties, and search for additional point sources in this
young planetary system.
Methods: We re-analyzed archival SPHERE
NIR observations and obtained new data in Y, J, H and K spectral bands
for a total of four different epochs. The data were reduced using the
data reduction and handling pipeline and the SPHERE data center. We
then applied custom routines (e.g., ANDROMEDA and PACO) to subtract
the starlight.
Results: We re-detect both PDS 70 b and c and
confirm that PDS 70 c is gravitationally bound to the star. We estimate
this second planet to be less massive than 5 MJup and with
a Teff around 900 K. Also, it has a low gravity with logg
between 3.0 and 3.5 dex. In addition, a third object has been identified
at short separation ( 0.12'') from the star and gravitationally bound
to the star. Its spectrum is however very blue, meaning that we are
probably seeing stellar light reflected by dust and our analysis seems
to demonstrate that it is a feature of the inner disk. We cannot however
completely exclude the possibility that it is a planetary mass object
enshrouded by a dust envelope. In this latter case, its mass should be
of the order of a few tens of M⊕. Moreover, we propose
a possible structure for the planetary system based on our data, and
find that this structure cannot be stable on a long timescale. The
reduced images are also 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/cat/J/A+A/632/A25
Based on observation made with European Southern Observatory
(ESO) telescopes at Paranal Observatory in Chile, under programs ID
095.C-0298(B), 1100.C-0481(D), 1100.C-0481(L) and 1100.C-0481(M).
Title: VizieR Online Data Catalog: PDS70 VLT/SPHERE images (Mesa+,
2019)
Authors: Mesa, D.; Keppler, M.; Cantalloube, F.; Rodet, L.; Charnay,
B.; Gratton, R.; Langlois, M.; Boccaletti, A.; Bonnefoy, M.; Vigan,
A.; Flasseur, O.; Bae, J.; Benisty, M.; Chauvin, G.; de Boer, J.;
Desidera, S.; Henning, T.; Lagrange, A. -M.; Meyer, M.; Milli, J.;
Mueller, A.; Pairet, B.; Zurlo, A.; Antoniucci, S.; Baudino, J. -L.;
Brown Sevilla, S.; Cascone, E.; Cheetham, A.; Claudi, R. U.; Delorme,
P.; D'Orazi, V.; Feldt, M.; Hagelberg, J.; Janson, M.; Kral, Q.;
Lagadec, E.; Lazzoni, C.; Ligi, R.; Maire, A. -L.; Martinez, P.;
Menard, F.; Meunier, N.; Perrot, C.; Petrus, S.; Pinte, C.; Rickman,
E. L.; Rochat, S.; Rouan, D.; Samland, M.; Sauvage, J. -F.; Schmidt,
T.; Udry, S.; Weber, L.; Wildi, F.
Bibcode: 2019yCat..36320025M
Altcode:
For the present work we used both archival and new observations
taken with SPHERE (Beuzit et al., 2019A&A...631A.155B). The
archival observations were obtained on the nights of 2015-05-31
and 2018-02-24 and were previously used for the works presented
in Keppler et al. (2018A&A...617A..44K) and in Mueller et
al. (2018A&A...617L...2M). In addition to these data we also
acquired new data on the nights of 2019-03-06 and 2019-04-13. The
first of these observations was carried out in the IRDIFS mode, that is
with IFS operating in Y and J spectral bands (between 0.95 and 1.35um)
and IRDIS operating in the H band with the H23 filter pair (wavelength
H2=1.593um; wavelength H3=1.66 um) The remaining observations were
performed using the IRDIFS_EXT mode that uses IFS in Y, J, and H
spectral band (between 0.95 and 1.65um) and IRDIS exploiting the K
band with the K12 filter pair (K1=2.110um and K2=2.251um). (2
data files).
Title: VizieR Online Data Catalog: HARPS Young Nearby Stars - YNS
(Grandjean+, 2020)
Authors: Grandjean, A.; Larange, A. -M.; Kepler, M.; Meunier, N.;
Mignon, L.; Borgniet, S.; Chauvin, G.; Desidera, S.; Galland, F.;
Messina, S.; Sterzik, M.; Pantoja, B.; Rodet, L.; Zicher, N.
Bibcode: 2019yCat..36330044G
Altcode:
The HARPS Young Nearby Stars catalogue (YNS) is based on a survey of
ESO HARPS on young stars and contains 89 A to M type stars. The catalog
presents Radial velocity (RV) and activity indicator results. The
89 stars were observed mainly between 2013 and 2016. Some stars were
part of previous surveys by Borgniet et al. (2019A&A...621A..87B)
and Lagrange et al. (2009A&A...495..335L), which allowed to reach a
time base- line up to 10yr. Some stars had already been observed with
HARPS before, some since the HARPS commissioning in 2003. Additional
observations were also obtained in October 2017, December 2017, and
March 2018. The observing strategy is the one described in Borgniet et
al. (2017A&A...599A..57B), which consist of recording two spectra
per visit and to observe each target on several consecutive nights to
have a good sampling of the short-term jitter. The median time baseline
is 1639 days (mean time baseline of 2324 days), with a median number
of spectra per target of 25 (52 on average) spaced on a median number
of 12 nights (17 on average). Details can be found in Table A.1. (3 data files).
Title: Extreme Precision Radial Velocity Working Group
Authors: Gaudi, Scott; Blackwood, Gary; Howard, Andrew; Latham,
David; Fischer, Debra; Ford, Eric; Cegla, Heather; Plavchan, Peter;
Quirrenbach, Andreas; Burt, Jennifer; Mamajek, Eric; Beichman, Chas;
Bender, Chad; Crass, Jonathan; Diddams, Scott; Dumusque, Xavier;
Eastman, Jason; Fulton, BJ; Halverson, Sam; Haywood, Raphaelle;
Hearty, Fred; Leifer, Stephanie; Loehner-Boettcher, Johannes;
Mortier, Annelies; Reiners, Ansgar; Robertson, Paul; Roy, Arpita;
Schwab, Christian; Seifahrt, Andreas; Szentgyorgyi, Andrew; Terrien,
Ryan; Teske, Johanna; Thompson, Samantha; Vasisht, Gautam; Aigrain,
Suzanne; Bedell, Megan; Bernstein, Rebecca; Blackman, Ryan; Blake,
Cullen; Buchhave, Lars; Callas, John; Ciardi, David; Chaplain, William;
Cisewski-Kehe, Jessi; Collier-Cameron, Andrew; Cornachione, Matthew;
Meunier, Nadege; Ninan, Joe; O'Meara, John; Ong, Joel; Wang, Sharon;
Wedemeyer-Boehm, Sven; Zhao, Lily; Boss, Alan; Oppenheimer, Rebecca;
Pitman, Joe; Poyneer, Lisa; Ridgeway, Stephen
Bibcode: 2019BAAS...51g.232G
Altcode: 2019astro2020U.232G
NASA and NSF are jointly commissioning a community-based “Extreme
Precision Radial Velocity (EPRV) working Group” to develop a blueprint
for a strategy for an EPRV initiative. The purpose of this white paper
is to describe the (EPRV) Working Group, whose primary responsibility
is to lay out the blueprint mentioned above.
Title: Constraining the properties of HD 206893 B. A combination of
radial velocity, direct imaging, and astrometry data (Corrigendum)
Authors: Grandjean, A.; Lagrange, A. -M.; Beust, H.; Rodet, L.; Milli,
J.; Rubini, P.; Babusiaux, C.; Meunier, N.; Delorme, P.; Aigrain, S.;
Zicher, N.; Bonnefoy, M.; Biller, B. A.; Baudino, J. -L.; Bonavita,
M.; Boccaletti, A.; Cheetham, A.; Girard, J. H.; Hagelberg, J.;
Janson, M.; Lannier, J.; Lazzoni, C.; Ligi, R.; Maire, A. -L.; Mesa,
D.; Perrot, C.; Rouan, D.; Zurlo, A.
Bibcode: 2019A&A...629C...1G
Altcode:
HARPS run 089.C-0739(A), 192.C-0224(C), 099.C-0205(A), 098.C-0739(A) and
1101.C-0557(A); SPHERE run 096.C-0388, 097.C-0865(D) and 099.C-0708(A);
Gaia DR2.
Title: Activity time series of old stars from late F to early
K. III. Diagnosis from photometry
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2019A&A...629A..42M
Altcode: 2019arXiv190906566M
Context. A number of high-precision time series have recently
become available for many stars as a result of data from CoRoT,
Kepler, and TESS. These data have been widely used to study stellar
activity. Photometry provides information that is integrated over the
stellar disk. Therefore, there are many degeneracies between spots
and plages or sizes and contrasts. In addition, it is important to
relate activity indicators, derived from photometric light curves, to
other indicators (Log R'HK and radial velocities).
Aims: Our aim is to understand how to relate photometric variability
to physical parameters in order to help the interpretation of these
observations.
Methods: We used a large number of synthetic
time series of brightness variations for old main sequence stars
within the F6-K4 range. Simultaneously, we computed using consistent
modeling for radial velocity, astrometry, and chromospheric
emission. We analyzed these time series to study the effect of
the star spectral type on brightness variability, the relationship
between brightness variability and chromospheric emission, and the
interpretation of brightness variability as a function of spot and
plage properties. We then studied spot-dominated or plage-dominated
regimes.
Results: We find that within our range of activity
levels, the brightness variability increases toward low-mass stars,
as suggested by Kepler results. However, many elements can create an
interpretation bias. Brightness variability roughly correlates to Log
R'HK level. There is, however, a large dispersion in this
relationship, mostly caused by spot contrast and inclination. It is
also directly related to the number of structures, and we show that
it can not be interpreted solely in terms of spot sizes. Finally,
a detailed analysis of its relation with Log R'HK shows
that in the activity range of old main-sequence stars, we can obtain
both spot or plage dominated regimes, as was shown by observations
in previous works. The same star can also be observed in both regimes
depending on inclination. Furthermore, only strong correlations between
chromospheric emission and brightness variability are significant.
Conclusions: Our realistic time series proves to be extremely useful
when interpreting observations and understanding their limitations, most
notably in terms of activity interpretation. Inclination is crucial
and affects many properties, such as amplitudes and the respective
role of spots and plages.
Title: Search for Earth analogues in the habitable zone around solar
type stars: radial velocity or astrometry?
Authors: Meunier, Nadege
Bibcode: 2019ESS.....430301M
Altcode:
Stellar activity is currently a major limitation to the detection of
very low mass planets around solar type stars using radial velocity
techniques. Various techniques have been implemented to mitigate this
problem, without allowing to reach one Mearth planets for
stars similar to the Sun yet. It is therefore crucial to estimate
precisely the effect of activity on exoplanet detectability using
realistic time series for various types of stars to overcome this
problem. I will describe the basic processes at work and how we
extended a realistic solar model to build representative time series
of radial velocity, photometry, astrometry and chromospheric emission
variability. We built coherent sets of stellar parameters covering
a large range in effective temperature (K4-F6) and average activity
levels. Such simulations are extremely useful to better understand
the relationship between RV, astrometry and activity indicators and
the limitations of correction techniques. I will present the impact
of activity on the detectability of Earth mass planet in the habitable
zones of those stars using radial velocity and high precision astrometry
and discuss their respective performance.
Title: Activity time series of old stars from late F to early
K. II. Radial velocity jitter and exoplanet detectability
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2019A&A...628A.125M
Altcode: 2019arXiv190902969M
Context. The effect of stellar activity on radial velocity (RV)
measurements appears to be a limiting factor in detecting Earth-mass
planets in the habitable zone of a star that is similar to the
Sun in spectral type and activity level. It is crucial to estimate
whether this conclusion remain true for other stars with current
correction methods.
Aims: We built realistic time series in
radial velocity and chromospheric emission for old main-sequence F6-K4
stars. We studied the effect of the stellar parameters we investigate
on exoplanet detectability. The stellar parameters are spectral type,
activity level, rotation period, cycle period and amplitude, latitude
coverage, and spot constrast, which we chose to be in ranges that
are compatible with our current knowledge of stellar activity.
Methods: This very large set of synthetic time series allowed us
to study the effect of the parameters on the RV jitter and how the
different contributions to the RV are affected in this first analysis of
the data set. The RV jitter was used to provide a first-order detection
limit for each time series and different temporal samplings.
Results: We find that the coverage in latitude of the activity pattern
and the cycle amplitudes have a strong effect on the RV jitter, as has
stellar inclination. RV jitter trends with B-V and Log R'HK
are similar to observations, but activity cannot be responsible for
RV jitter larger than 2-3 m s-1 for very quiet stars:
this observed jitter is therefore likely to be due to other causes
(instrumental noise or stellar or planetary companions, e.g.). Finally,
we show that based on the RV jitter that is associated with each
time series and using a simple criterion, a planet with one Earth
mass and a period of one to two years probably cannot be detected
with current analysis techniques, except for the lower mass stars in
our sample, but very many observations would be required. The effect
of inclination is critical.
Conclusions: The results are very
important in the context of future RV follow-ups of transit detections
of such planets. We conclude that a significant improvement of analysis
techniques and/or observing strategies must be made to reach such low
detection limits.
Title: Evidence for an additional planet in the β Pictoris system
Authors: Lagrange, A. -M.; Meunier, Nadège; Rubini, Pascal; Keppler,
Miriam; Galland, Franck; Chapellier, Eric; Michel, Eric; Balona, Luis;
Beust, Hervé; Guillot, Tristan; Grandjean, Antoine; Borgniet, Simon;
Mékarnia, Djamel; Wilson, Paul Anthony; Kiefer, Flavien; Bonnefoy,
Mickael; Lillo-Box, Jorge; Pantoja, Blake; Jones, Matias; Iglesias,
Daniela Paz; Rodet, Laetitia; Diaz, Matias; Zapata, Abner; Abe, Lyu;
Schmider, François-Xavier
Bibcode: 2019NatAs...3.1135L
Altcode: 2019NatAs.tmp..421L
With its imaged debris disk of dust, its evaporating exocomets, and
an imaged giant planet, the young ( 23 Myr) β Pictoris system is a
unique proxy for detailed studies of planet formation processes as
well as planet-disk interactions. Here, we study ten years of European
Southern Observatory/High Accuracy Radial Velocity Planet Searcher
(HARPS) high-resolution spectroscopic data of β Pictoris. After
removing the radial velocity (RV) signals arising from the δ Scuti
pulsations of the star, a 1,200-d periodic signal remains, which, within
our current knowledge, we can only attribute to a second planet in the
system. The β Pic c mass is about nine times the mass of Jupiter; it
orbits at 2.7 uc(au) on an eccentric (e 0.24) orbit. More RV data are
needed to obtain more precise estimates of the properties of β Pic
c. The current modelling of the planet's properties and the dynamic
of the whole system has to be reinvestigated in light of this detection.
Title: Constraining the properties of HD 206893 B. A combination of
radial velocity, direct imaging, and astrometry data
Authors: Grandjean, A.; Lagrange, A. -M.; Beust, H.; Rodet, L.; Milli,
J.; Rubini, P.; Babusiaux, C.; Meunier, N.; Delorme, P.; Aigrain, S.;
Zicher, N.; Bonnefoy, M.; Biller, B. A.; Baudino, J. -L.; Bonavita,
M.; Boccaletti, A.; Cheetham, A.; Girard, J. H.; Hagelberg, J.;
Janson, M.; Lannier, J.; Lazzoni, C.; Ligi, R.; Maire, A. -L.; Mesa,
D.; Perrot, C.; Rouan, D.; Zurlo, A.
Bibcode: 2019A&A...627L...9G
Altcode: 2019arXiv190602058G
Context. High contrast imaging enables the determination of
orbital parameters for substellar companions (planets, brown
dwarfs) from the observed relative astrometry and the estimation
of model and age-dependent masses from their observed magnitudes
or spectra. Combining astrometric positions with radial velocity
gives direct constraints on the orbit and on the dynamical masses
of companions. A brown dwarf was discovered with the VLT/SPHERE
instrument at the Very Large Telescope (VLT) in 2017, which orbits at
∼11 au around HD 206893. Its mass was estimated between 12 and 50
MJ from evolutionary models and its photometry. However,
given the significant uncertainty on the age of the system and the
peculiar spectrophotometric properties of the companion, this mass is
not well constrained.
Aims: We aim at constraining the orbit
and dynamical mass of HD 206893 B.
Methods: We combined radial
velocity data obtained with HARPS spectra and astrometric data obtained
with the high contrast imaging VLT/SPHERE and VLT/NaCo instruments,
with a time baseline less than three years. We then combined those
data with astrometry data obtained by HIPPARCOS and Gaia with a time
baseline of 24 yr. We used a Markov chain Monte Carlo approach to
estimate the orbital parameters and dynamical mass of the brown dwarf
from those data.
Results: We infer a period between 21 and
33 yr and an inclination in the range 20-41° from pole-on from HD
206893 B relative astrometry. The RV data show a significant RV drift
over 1.6 yr. We show that HD 206893 B cannot be the source of this
observed RV drift as it would lead to a dynamical mass inconsistent
with its photometry and spectra and with HIPPARCOS and Gaia data. An
additional inner (semimajor axis in the range 1.4-2.6 au) and massive
(∼15 MJ) companion is needed to explain the RV drift,
which is compatible with the available astrometric data of the star,
as well as with the VLT/SPHERE and VLT/NaCo nondetection. HARPS
run 089.C-0739(A), 192.C-0224(C), 099.C-0205(A), 098.C-0739(A) and
1101.C-0557(A); SPHERE run 096.C-0388, 097.C-0865(D) and 099.C-0708(A);
Gaia DR2.
Title: Activity time series of old stars from late F to early
K. I. Simulating radial velocity, astrometry, photometry, and
chromospheric emission
Authors: Meunier, N.; Lagrange, A. -M.; Boulet, T.; Borgniet, S.
Bibcode: 2019A&A...627A..56M
Altcode: 2019arXiv190401437M
Context. Solar simulations and observations show that the detection of
long-period Earth-like planets is expected to be very difficult with
radial velocity techniques in the solar case because of activity. The
inhibition of the convective blueshift in active regions (which is then
dominating the signal) is expected to decrease toward lower mass stars,
which would provide more suitable conditions.
Aims: In this paper
we build synthetic time series to be able to precisely estimate the
effects of activity on exoplanet detectability for stars with a wide
range of spectral type (F6-K4) and activity levels (old main-sequence
stars).
Methods: We simulated a very large number of realistic
time series of radial velocity, chromospheric emission, photometry, and
astrometry. We built a coherent grid of stellar parameters that covers a
wide range in the (B-V, Log R'HK) space based on
our current knowledge of stellar activity, to be able to produce these
time series. We describe the model and assumptions in detail.
Results: We present first results on chromospheric emission. We find
the average Log R'HK to correspond well to the
target values that are expected from the model, and observe a strong
effect of inclination on the average Log R'HK
(over time) and its long-term amplitude.
Conclusions: This very
large set of synthetic time series offers many possibilities for future
analysis, for example, for the parameter effect, correction method,
and detection limits of exoplanets.
Title: Constraints on HD 113337 fundamental parameters and planetary
system. Combining long-base visible interferometry, disc imaging,
and high-contrast imaging
Authors: Borgniet, S.; Perraut, K.; Su, K.; Bonnefoy, M.; Delorme,
P.; Lagrange, A. -M.; Bailey, V.; Buenzli, E.; Defrère, D.; Henning,
T.; Hinz, P.; Leisenring, J.; Meunier, N.; Mourard, D.; Nardetto,
N.; Skemer, A.; Spalding, E.
Bibcode: 2019A&A...627A..44B
Altcode: 2019arXiv190511156B
Context. HD 113337 is a main-sequence F6V field star more massive
than the Sun. This star hosts one confirmed giant planet and possibly
a second candidate, detected by radial velocities (RVs). The star
also hosts a cold debris disc detected through the presence of an
infrared excess, making it an interesting system to explore.
Aims: We aim to bring new constraints on the star's fundamental
parameters, debris disc properties, and planetary companion(s) by
combining complementary techniques.
Methods: We used the VEGA
interferometer on the CHARA array to measure the angular diameter of
HD 113337. We derived its linear radius using the parallax from the
Gaia Second Data Release. We computed the bolometric flux to derive
its effective temperature and luminosity, and we estimated its mass
and age using evolutionary tracks. Then, we used Herschel images to
partially resolve the outer debris disc and estimate its extension
and inclination. Next, we acquired high-contrast images of HD 113337
with the LBTI to probe the ~10-80 au separation range. Finally, we
combined the deduced contrast maps with previous RVs of the star using
the MESS2 software to bring upper mass limits on possible companions at
all separations up to 80 au. We took advantage of the constraints on the
age and inclination brought by fundamental parameter analysis and disc
imaging, respectively, for this analysis.
Results: We derive
a limb-darkened angular diameter of 0.386 ± 0.009 mas that converts
into a linear radius of 1.50 ± 0.04 R⊙ for HD 113337. The
fundamental parameter analysis leads to an effective temperature of 6774
± 125 K and to two possible age solutions: one young within 14-21 Myr
and one old within 0.8-1.7 Gyr. We partially resolve the known outer
debris disc and model its emission. Our best solution corresponds to a
radius of 85 ± 20 au, an extension of 30 ± 20 au, and an inclination
within 10-30° for the outer disc. The combination of imaging contrast
limits, published RV, and age and inclination solutions allows us to
derive a first possible estimation of the true masses of the planetary
companions: ~7-2+4 MJup for HD 113337 b
(confirmed companion) and ~16-3+10 MJup
for HD 113337 c (candidate companion). We also constrain possible
additional companions at larger separations. Partly based on
observations made with the VEGA/CHARA spectro-interferometer.
Title: Unexpectedly strong effect of supergranulation on the
detectability of Earth twins orbiting Sun-like stars with radial
velocities
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2019A&A...625L...6M
Altcode: 2019arXiv190409089M
Context. Magnetic activity and surface flows at different scales
pertub radial velocity measurements. This affects the detectability
of low-mass exoplanets.
Aims: In these flows, the effect of
supergranulation is not as well characterized as the other flows,
and we wish to estimate its effect on the detection of Earth-like
planets in the habitable zone of Sun-like stars.
Methods:
We produced time series of radial velocities due to oscillations,
granulation, and supergranulation, and estimated the detection limit
for a G2 star and a period of 300 days. We also studied in detail
the behavior of the power when the signal of a 1 MEarth
planet was superposed on the signal from the stellar flows.
Results: We find that the detection rate does not reach 100% except
for the supergranulation level we assume, which is still optimistic,
and for an excellent sampling.
Conclusions: We conclude that
with current knowledge, it is a very challenging task to find Earth
twins around Sun-like stars with our current capabilities.
Title: Extrasolar planets and brown dwarfs around AF-type
stars. X. The SOPHIE sample: combining the SOPHIE and HARPS surveys
to compute the close giant planet mass-period distribution around
AF-type stars
Authors: Borgniet, S.; Lagrange, A. -M.; Meunier, N.; Galland, F.;
Arnold, L.; Astudillo-Defru, N.; Beuzit, J. -L.; Boisse, I.; Bonfils,
X.; Bouchy, F.; Debondt, K.; Deleuil, M.; Delfosse, X.; Desort, M.;
Díaz, R. F.; Eggenberger, A.; Ehrenreich, D.; Forveille, T.; Hébrard,
G.; Loeillet, B.; Lovis, C.; Montagnier, G.; Moutou, C.; Pepe, F.;
Perrier, C.; Pont, F.; Queloz, D.; Santerne, A.; Santos, N. C.;
Ségransan, D.; da Silva, R.; Sivan, J. P.; Udry, S.; Vidal-Madjar, A.
Bibcode: 2019A&A...621A..87B
Altcode: 2018arXiv180909914B
Context. The impact of stellar mass on the properties of giant
planets is still not fully understood. Main-sequence (MS) stars more
massive than the Sun remain relatively unexplored in radial velocity
(RV) surveys, due to their characteristics which hinder classical RV
measurements.
Aims: Our aim is to characterize the close (up to
~2 au) giant planet (GP) and brown dwarf (BD) population around AF MS
stars and compare this population to stars with different masses.
Methods: We used the SOPHIE spectrograph located on the 1.93 m
telescope at Observatoire de Haute-Provence to observe 125 northern,
MS AF dwarfs. We used our dedicated SAFIR software to compute the RV
and other spectroscopic observables. We characterized the detected
substellar companions and computed the GP and BD occurrence rates
combining the present SOPHIE survey and a similar HARPS survey.
Results: We present new data on two known planetary systems around
the F5-6V dwarfs HD 16232 and HD 113337. For the latter, we report
an additional RV variation that might be induced by a second GP on a
wider orbit. We also report the detection of 15 binaries or massive
substellar companions with high-amplitude RV variations or long-term
RV trends. Based on 225 targets observed with SOPHIE and/or HARPS, we
constrain the BD frequency within 2-3 au around AF stars to be below 4%
(1σ). For Jupiter-mass GPs within 2-3 au (periods ≤103
days), we find the occurrence rate to be 3.7-1+3%
around AF stars with masses <1.5 M⊙, and to be ≤6%
(1σ) around AF stars with masses >1.5 M⊙. For
periods shorter than 10 days, we find the GP occurrence rate to be
below 3 and 4.5% (1σ), respectively. Our results are compatible
with the GP frequency reported around FGK dwarfs and are compatible
with a possible increase in GP orbital periods with stellar mass as
predicted by formation models. Based in part on observations made
at Observatoire de Haute Provence (CNRS), France. RV time series of
the full sample 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/621/A87
Title: The GJ 504 system revisited. Combining interferometric,
radial velocity, and high contrast imaging data
Authors: Bonnefoy, M.; Perraut, K.; Lagrange, A. -M.; Delorme, P.;
Vigan, A.; Line, M.; Rodet, L.; Ginski, C.; Mourard, D.; Marleau,
G. -D.; Samland, M.; Tremblin, P.; Ligi, R.; Cantalloube, F.;
Mollière, P.; Charnay, B.; Kuzuhara, M.; Janson, M.; Morley, C.;
Homeier, D.; D'Orazi, V.; Klahr, H.; Mordasini, C.; Lavie, B.; Baudino,
J. -L.; Beust, H.; Peretti, S.; Musso Bartucci, A.; Mesa, D.; Bézard,
B.; Boccaletti, A.; Galicher, R.; Hagelberg, J.; Desidera, S.; Biller,
B.; Maire, A. -L.; Allard, F.; Borgniet, S.; Lannier, J.; Meunier,
N.; Desort, M.; Alecian, E.; Chauvin, G.; Langlois, M.; Henning,
T.; Mugnier, L.; Mouillet, D.; Gratton, R.; Brandt, T.; Mc Elwain,
M.; Beuzit, J. -L.; Tamura, M.; Hori, Y.; Brandner, W.; Buenzli,
E.; Cheetham, A.; Cudel, M.; Feldt, M.; Kasper, M.; Keppler, M.;
Kopytova, T.; Meyer, M.; Perrot, C.; Rouan, D.; Salter, G.; Schmidt,
T.; Sissa, E.; Zurlo, A.; Wildi, F.; Blanchard, P.; De Caprio, V.;
Delboulbé, A.; Maurel, D.; Moulin, T.; Pavlov, A.; Rabou, P.; Ramos,
J.; Roelfsema, R.; Rousset, G.; Stadler, E.; Rigal, F.; Weber, L.
Bibcode: 2018A&A...618A..63B
Altcode: 2018arXiv180700657B
Context. The G-type star GJ504A is known to host a 3-35 MJup
companion whose temperature, mass, and projected separation all
contribute to making it a test case for planet formation theories
and atmospheric models of giant planets and light brown dwarfs.
Aims: We aim at revisiting the system age, architecture, and
companion physical and chemical properties using new complementary
interferometric, radial-velocity, and high-contrast imaging data.
Methods: We used the CHARA interferometer to measure GJ504A's angular
diameter and obtained an estimation of its radius in combinationwith
the HIPPARCOS parallax. The radius was compared to evolutionary
tracks to infer a new independent age range for the system. We
collected dual imaging data with IRDIS on VLT/SPHERE to sample the
near-infrared (1.02-2.25 μm) spectral energy distribution (SED)
of the companion. The SED was compared to five independent grids
of atmospheric models (petitCODE,Exo-REM, BT-SETTL, Morley et al.,
and ATMO) to infer the atmospheric parameters of GJ 504b and evaluate
model-to-model systematic errors. In addition, we used a specific model
grid exploring the effect of different C/O ratios. Contrast limits
from 2011 to 2017 were combined with radial velocity data of the
host star through the MESS2 tool to define upper limits on the mass
of additional companions in the system from 0.01 to 100 au. We used
an MCMC fitting tool to constrain the companion'sorbital parameters
based on the measured astrometry, and dedicated formation models to
investigate its origin.
Results: We report a radius of 1.35 ±
0.04 R⊙ for GJ504A. The radius yields isochronal ages
of 21 ± 2 Myr or 4.0 ± 1.8 Gyr for the system and line-of-sight
stellar rotation axis inclination of 162.4-4.3+3.8
degrees or 186.6-3.8+4.3 degrees. We re-detect the
companion in the Y2, Y3, J3, H2, and K1 dual-band images. The complete
1-4 μm SED shape of GJ504b is best reproduced by T8-T9.5 objects with
intermediate ages (≤ 1.5Gyr), and/or unusual dusty atmospheres and/or
super-solar metallicities. All atmospheric models yield Teff
= 550 ± 50 K for GJ504b and point toward a low surface gravity
(3.5-4.0 dex). The accuracy on the metallicity value is limited by
model-to-model systematics; it is not degenerate with the C/O ratio. We
derive log L/L⊙ = -6.15 ± 0.15 dex for the companion
from the empirical analysis and spectral synthesis. The luminosity and
Teff yield masses of M = 1.3-0.3+0.6
MJup and M = 23-9+10 MJup
for the young and old age ranges, respectively. The semi-major axis
(sma) is above 27.8 au and the eccentricity is lower than 0.55. The
posterior on GJ 504b's orbital inclination suggests a misalignment
with the rotation axis of GJ 504A. We exclude additional objects (90%
prob.) more massive than 2.5 and 30 MJup with semi-major
axes in the range 0.01-80 au for the young and old isochronal ages,
respectively.
Conclusions: The mass and semi-major axis of GJ
504b are marginally compatible with a formation by disk-instability
if the system is 4 Gyr old. The companion is in the envelope of
the population of planets synthesized with our core-accretion
model. Additional deep imaging and spectroscopic data with SPHERE
and JWST should help to confirm the possible spin-orbit misalignment
and refine the estimates on the companion temperature, luminosity,
and atmospheric composition. Based on observations collected at
the European Organisation for Astronomical Research in the Southern
Hemisphere under ESO programs 093.C-0500, 095.C-0298, 096.C-0241,
and 198.C-0209, and on interferometric observations obtained with the
VEGA instrument on the CHARA Array.
Title: Investigating the young solar system analog HD 95086. A
combined HARPS and SPHERE exploration
Authors: Chauvin, G.; Gratton, R.; Bonnefoy, M.; Lagrange, A. -M.; de
Boer, J.; Vigan, A.; Beust, H.; Lazzoni, C.; Boccaletti, A.; Galicher,
R.; Desidera, S.; Delorme, P.; Keppler, M.; Lannier, J.; Maire, A. -L.;
Mesa, D.; Meunier, N.; Kral, Q.; Henning, T.; Menard, F.; Moor, A.;
Avenhaus, H.; Bazzon, A.; Janson, M.; Beuzit, J. -L.; Bhowmik, T.;
Bonavita, M.; Borgniet, S.; Brandner, W.; Cheetham, A.; Cudel, M.;
Feldt, M.; Fontanive, C.; Ginski, C.; Hagelberg, J.; Janin-Potiron,
P.; Lagadec, E.; Langlois, M.; Le Coroller, H.; Messina, S.; Meyer,
M.; Mouillet, D.; Peretti, S.; Perrot, C.; Rodet, L.; Samland, M.;
Sissa, E.; Olofsson, J.; Salter, G.; Schmidt, T.; Zurlo, A.; Milli,
J.; van Boekel, R.; Quanz, S.; Feautrier, P.; Le Mignant, D.; Perret,
D.; Ramos, J.; Rochat, S.
Bibcode: 2018A&A...617A..76C
Altcode:
Context. HD 95086 (A8V, 17 Myr) hosts a rare planetary system for which
a multi-belt debris disk and a giant planet of 4-5 MJup have
been directly imaged.
Aims: Our study aims to characterize the
global architecture of this young system using the combination of radial
velocity and direct imaging observations. We want to characterize the
physical and orbital properties of HD 95086 b, search for additional
planets at short and wide orbits and image the cold outer debris
belt in scattered light.
Methods: We used HARPS at the ESO
3.6 m telescope to monitor the radial velocity of HD 95086 over two
years and investigate the existence of giant planets at less than 3 au
orbital distance. With the IRDIS dual-band imager and the IFS integral
field spectrograph of SPHERE at VLT, we imaged the faint circumstellar
environment beyond 10 au at six epochs between 2015 and 2017.
Results: We do not detect additional giant planets around HD 95086. We
identify the nature (bound companion or background contaminant) of
all point-like sources detected in the IRDIS field of view. None of
them correspond to the ones recently discovered near the edge of the
cold outer belt by ALMA. HD 95086 b is resolved for the first time in
J-band with IFS. Its near-infrared spectral energy distribution is well
fitted by a few dusty and/or young L7-L9 dwarf spectral templates. The
extremely red 1-4 μm spectral distribution is typical of low-gravity
objects at the L/T spectral type transition. The planet's orbital
motion is resolved between January 2015 and May 2017. Together with
past NaCo measurements properly re-calibrated, our orbital fitting
solutions favor a retrograde low to moderate-eccentricity orbit e
= 0.2+0.3-0.2, with a semi-major axis 52 au
corresponding to orbital periods of 288 yr and an inclination that
peaks at i = 141°, which is compatible with a planet-disk coplanar
configuration. Finally, we report the detection in polarimetric
differential imaging of the cold outer debris belt between 100 and
300 au, consistent in radial extent with recent ALMA 1.3 mm resolved
observations. Based on observations collected at the European
Southern Observatory, Chile (ESO SPHERE Guaranteed Time Observation
Program 095.C-0273, 095.C-0298, 096.C-0241, 097.C-0865, 198.C-0209)
and ESO HARPS Open Time Observation Program 099.C-0205, 192. C-0224.
Title: Statistical analysis and lessons learned of SPHERE adaptive
optics performance
Authors: Mouillet, D.; Milli, J.; Sauvage, J. -F.; Fusco, T.;
Beuzit, J. -L.; Vigan, A.; Albert, D.; Boccaletti, A.; Cantalloube,
F.; Chauvin, G.; Correia, C.; Delorme, P.; Dohlen, K.; Kasper, M.;
Lagrange, A. -M.; Meunier, N.; Pannetier, C.
Bibcode: 2018SPIE10703E..1QM
Altcode:
The SPHERE instrument, dedicated to high contrast imaging on VLT, has
been routinely operated for more than 3 years, over a large range of
conditions and producing observations from visible to NIR. A central
part of the instrument is the high order adaptive optics system,
named SAXO, designed to deliver high Strehl image quality with a
balanced performance budget for bright stars up to magnitude R=9. We
take benefit now from the very large set of observations to revisit
the assumptions and analysis made at the time of the design phase:
we compare the actual AO behavior as a function of expectations. The
data set consists of the science detector data, for both coronagraphic
images and non-coronagraphic PSF calibrations, but also of AO internal
data from the high frequency sensors and statistics computations from
the real-time computer which are systematically archived, and finally
of environmental data, monitored at VLT level. This work is supported
and made possible by the SPHERE « Data Center » infrastructure hosted
at Grenoble which provides an efficient access and the capability for
the homogeneous analysis of this large and statistically-relevant data
set. We review in a statistical manner the actual AO performance as a
function of external conditions for different regimes and we discuss
the possible performance metrics, either derived from AO internal data
or directly from the high contrast images. We quantify the dependency of
the actual performance on the most relevant environmental parameters. By
comparison to earlier expectations, we conclude on the reliability of
the usual AO modeling. We propose some practical criteria to optimize
the queue scheduling and the expression of observer requirements ;
finally, we revisit what could be the most important AO specifications
for future high contrast imagers as a function of the primary science
goals, the targets and the turbulence properties.
Title: Solar chromospheric emission and magnetic structures from
plages to intranetwork: Contribution of the very quiet Sun
Authors: Meunier, N.
Bibcode: 2018A&A...615A..87M
Altcode: 2018arXiv180400869M
Context. We need to establish a correspondence between the magnetic
structures generated by models and usual stellar activity indexes to
simulate radial velocity time series for stars less active than the
Sun. This is necessary to compare the outputs of such models with
observed radial velocity jitters and is critical to better understand
the impact of stellar activity on exoplanet detectability.
Aims: We propose a coherent picture to describe the relationship
between magnetic activity, including the so-called quiet Sun regions,
and the chromospheric emission using the Sun as a test-bench and a
reference.
Methods: We analyzed a long time series of Michelson
Doppler imaging (MDI) magnetograms jointly with chromospheric
emission time series obtained at Sacramento Peak and Kitt Peak
observatories. This has allowed us to study the variability in the
quiet Sun over the solar cycle, and then, based on available relations
between magnetic fields in active structures and chromospheric emission,
to propose an empirical reconstruction of the solar chromospheric
emission based on all contributions.
Results: We show that
the magnetic flux covering the solar surface, including in the
quieted regions, varies in phase with the solar cycle, suggesting a
long-term relationship between the global dynamo and the contribution
of all components of solar activity. We have been able to propose a
reconstruction of the solar S-index, including a relationship between
the weak field component and its chomospheric emission, which is in
good agreement with the literature. This allows us to explain that
stars with a low average chromospheric emission level exhibit a low
variability.
Conclusions: We conclude that weak flux regions
significantly contribute to the chromospheric emission; these regions
should be critical in explaining the lower variability associated
with the lower average activity level in other stars as compared to
the Sun and estimated from their chromospheric emission.
Title: Astrometric and photometric accuracies in high contrast
imaging: The SPHERE speckle calibration tool (SpeCal)
Authors: Galicher, R.; Boccaletti, A.; Mesa, D.; Delorme, P.; Gratton,
R.; Langlois, M.; Lagrange, A. -M.; Maire, A. -L.; Le Coroller, H.;
Chauvin, G.; Biller, B.; Cantalloube, F.; Janson, M.; Lagadec, E.;
Meunier, N.; Vigan, A.; Hagelberg, J.; Bonnefoy, M.; Zurlo, A.; Rocha,
S.; Maurel, D.; Jaquet, M.; Buey, T.; Weber, L.
Bibcode: 2018A&A...615A..92G
Altcode: 2018arXiv180504854G
Context. The consortium of the Spectro-Polarimetric High-contrast
Exoplanet REsearch installed at the Very Large Telescope (SPHERE/VLT)
has been operating its guaranteed observation time (260 nights over five
years) since February 2015. The main part of this time (200 nights)
is dedicated to the detection and characterization of young and giant
exoplanets on wide orbits.
Aims: The large amount of data must
be uniformly processed so that accurate and homogeneous measurements
of photometry and astrometry can be obtained for any source in the
field.
Methods: To complement the European Southern Observatory
pipeline, the SPHERE consortium developed a dedicated piece of software
to process the data. First, the software corrects for instrumental
artifacts. Then, it uses the speckle calibration tool (SpeCal) to
minimize the stellar light halo that prevents us from detecting
faint sources like exoplanets or circumstellar disks. SpeCal is
meant to extract the astrometry and photometry of detected point-like
sources (exoplanets, brown dwarfs, or background sources). SpeCal was
intensively tested to ensure the consistency of all reduced images
(cADI, Loci, TLoci, PCA, and others) for any SPHERE observing strategy
(ADI, SDI, ASDI as well as the accuracy of the astrometry and photometry
of detected point-like sources.
Results: SpeCal is robust,
user friendly, and efficient at detecting and characterizing point-like
sources in high contrast images. It is used to process all SPHERE data
systematically, and its outputs have been used for most of the SPHERE
consortium papers to date. SpeCal is also a useful framework to compare
different algorithms using various sets of data (different observing
modes and conditions). Finally, our tests show that the extracted
astrometry and photometry are accurate and not biased. Based on
observations collected at the European Organisation for Astronomical
Research in the Southern Hemisphere under ESO programme 097.C-0865.
Title: Full exploration of the giant planet population around
β Pictoris
Authors: Lagrange, A. -M.; Keppler, M.; Meunier, N.; Lannier, J.;
Beust, H.; Milli, J.; Bonnavita, M.; Bonnefoy, M.; Borgniet, S.;
Chauvin, G.; Delorme, P.; Galland, F.; Iglesias, D.; Kiefer, F.;
Messina, S.; Vidal-Madjar, A.; Wilson, P. A.
Bibcode: 2018A&A...612A.108L
Altcode:
Context. The search for extrasolar planets has been limited so far to
close orbit (typ. ≤5 au) planets around mature solar-type stars on
the one hand, and to planets on wide orbits (≥10 au) around young
stars on the other hand. To get a better view of the full giant planet
population, we have started a survey to search for giant planets
around a sample of carefully selected young stars.
Aims: This
paper aims at exploring the giant planet population around one of our
targets, β Pictoris, over a wide range of separations. With a disk
and a planet already known, the β Pictoris system is indeed a very
precious system for studies of planetary formation and evolution,
as well as of planet-disk interactions.
Methods: We analyse
more than 2000 HARPS high-resolution spectra taken over 13 years as
well as NaCo images recorded between 2003 and 2016. We combine these
data to compute the detection probabilities of planets throughout
the disk, from a fraction of au to a few dozen au.
Results:
We exclude the presence of planets more massive than 3 MJup
closer than 1 au and further than 10 au, with a 90% probability. 15+
MJup companions are excluded throughout the disk except
between 3 and 5 au with a 90% probability. In this region, we exclude
companions with masses larger than 18 (resp. 30) MJup
with probabilities of 60 (resp. 90) %. Based on data obtained
with the ESO3.6 m/HARPS spectrograph at La Silla, and with NaCO on the
VLT.The RV 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/612/A108
Title: Investigating the young Solar System analog HD95086
Authors: Chauvin, G.; Gratton, R.; Bonnefoy, M.; Lagrange, A. -M.; de
Boer, J.; Vigan, A.; Beust, H.; Lazzoni, C.; Boccaletti, A.; Galicher,
R.; Desidera, S.; Delorme, P.; Keppler, M.; Lannier, J.; Maire, A. -L.;
Mesa, D.; Meunier, N.; Kral, Q.; Henning, T.; Menard, F.; Moor, A.;
Avenhaus, H.; Bazzon, A.; Janson, M.; Beuzit, J. -L.; Bhowmik, T.;
Bonavita, M.; Borgniet, S.; Brandner, W.; Cheetham, A.; Cudel, M.;
Feldt, M.; Fontanive, C.; Ginski, C.; Hagelberg, J.; Janin-Potiron,
P.; Lagadec, E.; Langlois, M.; Le Coroller, H.; Messina, S.; Meyer,
M.; Mouillet, D.; Peretti, S.; Perrot, C.; Rodet, L.; Samland, M.;
Sissa, E.; Olofsson, J.; Salter, G.; Schmidt, T.; Zurlo, A.; Milli, J.;
van Boekel, R.; Quanz, S.; Wilson, P. A.; Feautrier, P.; Le Mignant,
D.; Perret, D.; Ramos, J.; Rochat, S.
Bibcode: 2018arXiv180105850C
Altcode:
HD95086 (A8V, 17Myr) hosts a rare planetary system for which a
multi-belt debris disk and a giant planet of 4-5MJup have been directly
imaged. Our study aims to characterize the physical and orbital
properties of HD95086b, search for additional planets at short and
wide orbits and image the cold outer debris belt in scattered light. We
used HARPS at the ESO 3.6m telescope to monitor the radial velocity of
HD95086 over 2 years and investigate the existence of giant planets at
less than 3au orbital distance. With the IRDIS dual-band imager and
the IFS integral field spectrograph of SPHERE at VLT, we imaged the
faint circumstellar environment beyond 10au at six epochs between 2015
and 2017. We do not detect additional giant planets around HD95086. We
identified the nature (bound companion or background contaminant) of
all point-like sources detected in the IRDIS field of view. None of
them correspond to the ones recently discovered near the edge of the
cold outer belt by ALMA. HD95086b is resolved for the first time in
J-band with IFS. Its near-infrared spectral energy distribution is well
fitted by a few dusty and/or young L7-L9 dwarf spectral templates. The
extremely red 1-4um spectral distribution is typical of low-gravity
objects at the L/T spectral type transition. The planet's orbital
motion is resolved between January 2015 and May 2017. Together with
past NaCo measurements properly re-calibrated, our orbital fitting
solutions favor a retrograde low to moderate-eccentricity orbit e=0.2
(0.0 to 0.5), with a semi-major axis 52au corresponding to orbital
periods of 288$ yrs and an inclination that peaks at i = 141deg, which
is compatible with a planet-disk coplanar configuration. Finally,
we report the detection in polarimetric differential imaging of the
cold outer debris belt between 100 and 300au, consistent in radial
extent with recent ALMA 1.3mm resolved observations.
Title: Discovery of a stellar companion to HD 131399A
Authors: Lagrange, A. -M.; Keppler, M.; Beust, H.; Rodet, L.; Meunier,
N.; Lillo-Box, J.; Bonnefoy, M.; Galland, F.
Bibcode: 2017A&A...608L...9L
Altcode:
Context. The giant exoplanets imaged on wide orbits (≥10 au) around
young stars challenge the classical theories of planet formation. The
presence of perturbing bodies could have played a role in the dynamical
evolution of the planets once formed.
Aims: We aim to search for
close companions to HD 131399, a star around which a giant planet has
been discovered, at a projected separation of about 80 au. The star also
appears to be a member of a wide (320 au) binary system.
Methods:
We recorded HARPS high resolution spectra in January 2017.
Results: We find that HD 131399A is probably seen close to pole-on. We
discover a low mass star companion that orbits with a period of about
10 days on a misaligned orbit. Even though the companion does not have
an impact on the current dynamical evolution of the planet, it could
have played a role in its setting and in clearing the circumstellar
disk from which the planet may originate. Based on data obtained
with the ESO3.6 m/HARPS spectrograph at La Silla.
Title: The SPHERE Data Center: a reference for high contrast imaging
processing
Authors: Delorme, P.; Meunier, N.; Albert, D.; Lagadec, E.; Le
Coroller, H.; Galicher, R.; Mouillet, D.; Boccaletti, A.; Mesa, D.;
Meunier, J. -C.; Beuzit, J. -L.; Lagrange, A. -M.; Chauvin, G.; Sapone,
A.; Langlois, M.; Maire, A. -L.; Montargès, M.; Gratton, R.; Vigan,
A.; Surace, C.
Bibcode: 2017sf2a.conf..347D
Altcode: 2017arXiv171206948D
The objective of the SPHERE Data Center is to optimize the scientific
return of SPHERE at the VLT, by providing optimized reduction
procedures, services to users and publicly available reduced data. This
paper describes our motivation, the implementation of the service
(partners, infrastructure and developments), services, description
of the on-line data, and future developments. The SPHERE Data Center
is operational and has already provided reduced data with a good
reactivity to many observers. The first public reduced data have been
made available in 2017. The SPHERE Data Center is gathering a strong
expertise on SPHERE data and is in a very good position to propose new
reduced data in the future, as well as improved reduction procedures.
Title: Variability in stellar granulation and convective blueshift
with spectral type and magnetic activity . II. From young to old
main-sequence K-G-F stars
Authors: Meunier, N.; Mignon, L.; Lagrange, A. -M.
Bibcode: 2017A&A...607A.124M
Altcode: 2017arXiv171102331M
Context. The inhibition of small-scale convection in the Sun dominates
the long-term radial velocity (RV) variability: it therefore
has a critical effect on light exoplanet detectability using RV
techniques.
Aims: We here extend our previous analysis of stellar
convective blueshift and its dependence on magnetic activity to a larger
sample of stars in order to extend the Teff range, to study
the impact of other stellar properties, and finally to improve the
comparison between observed RV jitter and expected RV variations.
Methods: We estimate a differential velocity shift for Fe and Ti
lines of different depths and derive an absolute convective blueshift
using the Sun as a reference for a sample of 360 F7-K4 stars with
different properties (age, Teff, metallicity).
Results: We confirm the strong variation in convective blueshift
with Teff and its dependence on (as shown in the line list
in Paper I) activity level. Although we do not observe a significant
effect of age or cyclic activity, stars with a higher metallicity tend
to have a lower convective blueshift, with a larger effect than expected
from numerical simulations. Finally, we estimate that for 71% of the
stars in our sample the RV and Log R' _HK variations are compatible
with the effect of activity on convection, as observed in the solar
case, while for the other stars, other sources (such as binarity or
companions) must be invoked to explain the large RV variations. We also
confirm a relationship between Log R' _HK and metallicity, which may
affect discussions of the possible relationship between metallicity and
exoplanets, as RV surveys are biased toward low Log R' _HK and possibly
toward high-metallicity stars.
Conclusions: We conclude that
activity and metallicity strongly affect the small-scale convection
levels in stars in the F7-K4 range, with a lower amplitude for the
lower mass stars and a larger amplitude for low-metallicity stars. 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/607/A124
Title: A new method of correcting radial velocity time series for
inhomogeneous convection
Authors: Meunier, N.; Lagrange, A. -M.; Borgniet, S.
Bibcode: 2017A&A...607A...6M
Altcode: 2017arXiv170803458M
Context. Magnetic activity strongly impacts stellar radial velocities
(RVs) and therefore the search for small planets. We showed previously
that in the solar case it induces RV variations with an amplitude
over the cycle on the order of 8 m/s, with signals on both short
and long timescales. The major component is the inhibition of the
convective blueshift due to plages.
Aims: In this paper we
explore a new approach used to correct for this major component of
stellar radial velocities in the case of solar-type stars.
Methods: The convective blueshift depends on line depths; we use this
property to develop a method that will characterize the amplitude of
this effect and to correct for this RV component. We build realistic
RV time series corresponding to RVs computed using different sets
of lines, including lines in different depth ranges. We characterize
the performance of the method used to reconstruct the signal without
the convective component and the detection limits derived from the
residuals.
Results: We identified a set of lines which, combined
with a global set of lines, allows us to reconstruct the convective
component with a good precision and to correct for it. For the full
temporal sampling, the power in the range 100-500 d significantly
decreased, by a factor of 100 for a RV noise below 30 cm/s. We also
studied the impact of noise contributions other than the photon noise,
which lead to uncertainties on the RV computation, as well as the
impact of the temporal sampling. We found that these other sources of
noise do not greatly alter the quality of the correction, although they
need a better noise level to reach a similar performance level.
Conclusions: A very good correction of the convective component can
be achieved providing very good RV noise levels combined with a very
good instrumental stability and realistic granulation noise. Under the
conditions considered in this paper, detection limits at 480 d lower
than 1 MEarth could be achieved for RV noise below 15 cm/s.
Title: VizieR Online Data Catalog: K-G-F dwarfs stellar granulation
variability (Meunier+, 2017)
Authors: Meunier, N.; Mignon, L.; Lagrange, A. -M.
Bibcode: 2017yCat..36070124M
Altcode:
List of stars studied in the paper (HARPS data from the ESO archive),
together with informations from various sources and outputs from our
analysis. The number of stars is 360. (1 data file).
Title: Combining direct imaging and radial velocity data towards
a full exploration of the giant planet population. I. Method and
first results
Authors: Lannier, J.; Lagrange, A. M.; Bonavita, M.; Borgniet, S.;
Delorme, P.; Meunier, N.; Desidera, S.; Messina, S.; Chauvin, G.;
Keppler, M.
Bibcode: 2017A&A...603A..54L
Altcode: 2017arXiv170407432L
Context. Thanks to the detections of more than 3000 exoplanets
these last 20 yr, statistical studies have already highlighted some
properties of the distribution of the planet parameters. Nevertheless,
few studies have yet investigated the planet populations from short
to large separations around the same star since this requires the
use of different detection techniques that usually target different
types of stars.
Aims: We wish to develop a tool that combines
direct and indirect methods so as to correctly investigate the giant
planet populations at all separations.
Methods: We developed
the MESS2 code, a Monte Carlo simulation code combining radial velocity
and direct imaging data obtained at different epochs for a given star
to estimate the detection probability of giant planets spanning a
wide range of physical separations. It is based on the generation of
synthetic planet populations.
Results: We apply MESS2 on a young
M1-type, the nearby star AU Mic observed with HARPS and NACO/ESO. We
show that giant planet detection limits are significantly improved at
intermediate separations (≈20 au in the case of AU Mic). We show that
the traditional approach of analyzing the RV and DI detection limits
independently systematically overestimates the planet detection limits
and hence planet occurrence rates. The use of MESS2 allows us to obtain
correct planet occurrence rates in statistical studies, making use of
multi-epoch DI data and/or RV measurements. We also show that MESS2
can optimize the schedule of future DI observations.
Title: Extrasolar planets and brown dwarfs around AF-type
stars. IX. The HARPS southern sample
Authors: Borgniet, S.; Lagrange, A. -M.; Meunier, N.; Galland, F.
Bibcode: 2017A&A...599A..57B
Altcode: 2016arXiv160808257B
Context. Massive, main-sequence (MS) AF-type stars have so far remained
unexplored in past radial velocities (RV) surveys due to their small
number of spectral lines and high rotational velocities that prevent
the classic RV computation method.
Aims: Our aim is to search
for giant planets (GPs) around AF MS stars, to get primary statistical
information on their occurrence rate and to compare the results with
evolved stars and lower-mass MS stars.
Methods: We used the
HARPS spectrograph located on the 3.6 m telescope at ESO La Silla
Observatory to observe 108 AF MS stars with B-V in the range -0.04 to
0.58 and masses in the range 1.1 to 3.6 M⊙. We used our
SAFIR software developed to compute the RV and other spectroscopic
observables of these early-type stars. We characterized the detected
companions as well as the intrinsic stellar variability. We computed
the detection limits and used them as well as the detected companions
to derive the first estimates of the close-in brown dwarf (BD) and GP
frequencies around AF stars.
Results: We report the detection
of a mpsini = 4.51MJup planetary companion with
an 826-day period to the F6V dwarf HD 111998. We
also present new data on the two-planet system around the F6IV-V
dwarf HD 60532. We also report the detections of 14
binaries with long-term RV trends and/or high-amplitude RV variations
combined to a flat RV-bisector span diagram. We constrain the minimal
masses and semi-major axes of these companions and check that these
constraints are compatible with the stellar companions previously
detected by direct imaging or astrometry for six of these targets. We
get detection limits deep into the planetary domain with 70% of our
targets showing detection limits between 0.1 and 10 MJup at
all orbital periods in the 1- to 103-day range. We derive BD
(13 ≤mpsini ≤ 80 MJup) occurrence rates in the
1- to 103-day period range of 2-2+5%
and 2.6-2.6+6.7% for stars with M⋆ in
the ranges 1.1 to 1.5 and 1.5 to 3 M⊙, respectively. As for
Jupiter-mass companions (1 ≤ mpsini≤ 13 MJup),
we get occurrence rates in the 1- to 103-day period range of
4-0.9+5.9% and 6.3-6.3+15.9%
respectively for the same M⋆ ranges. When considering
the same Jupiter-mass companions but periods in the 1- to 100-day
range only, we get occurrence rates of 2-2+5.2%
and 3.9-3.9+9.9%. Given the present error
bars, these results do not show a significant difference from
companion frequencies derived in the same domains for solar-like
MS stars. Based on observations collected at the European
southern Observatory, Chile, ESO 072.C-0636, 073.C-0733, 075.C-0689,
076.C-0279, 077.C-0295, 078.C-0209, 080.C-0664, 080.C-0712., 081.C-0774,
082.C-0412, 083.C-0794, 084.C-1039, 184.C-0815, 192.C-0224.RV and other
observable data 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/599/A57
Title: Variability of stellar granulation and convective blueshift
with spectral type and magnetic activity. I. K and G main sequence
stars
Authors: Meunier, N.; Lagrange, A. -M.; Mbemba Kabuiku, L.; Alex,
M.; Mignon, L.; Borgniet, S.
Bibcode: 2017A&A...597A..52M
Altcode: 2016arXiv161002168M; 2016A&A...597A..52M
Context. In solar-type stars, the attenuation of convective blueshift by
stellar magnetic activity dominates the RV (radial velocity) variations
over the low amplitude signal induced by low mass planets. Models of
stars that differ from the Sun will require a good knowledge of the
attenuation of the convective blueshift to estimate its impact on
the variations.
Aims: It is therefore crucial to precisely
determine not only the amplitude of the convective blueshift for
different types of stars, but also the dependence of this convective
blueshift on magnetic activity, as these are key factors in our model
producing the RV.
Methods: We studied a sample of main sequence
stars with spectral types from G0 to K2 and focused on their temporally
averaged properties: the activity level and a criterion allowing to
characterise the amplitude of the convective blueshift. This criterion
is derived from the dependence of the convective blueshift with the
intensity at the bottom of a large set of selected spectral lines.
Results: We find the differential velocity shifts of spectral lines
due to convection to depend on the spectral type, the wavelength (this
dependence is correlated with the Teff and activity level),
and on the activity level. This allows us to quantify the dependence
of granulation properties on magnetic activity for stars other than
the Sun. We are indeed able to derive a significant dependence of the
convective blueshift on activity level for all types of stars. The
attenuation factor of the convective blueshift appears to be constant
over the considered range of spectral types. We derive a convective
blueshift which decreases towards lower temperatures, with a trend in
close agreement with models for Teff lower than 5800 K, but
with a significantly larger global amplitude. Differences also remain to
be examined in detail for larger Teff. We finally compare the
observed RV variation amplitudes with those that could be derived from
our convective blueshift using a simple law and find a general agreement
on the amplitude. We also show that inclination (viewing angle relative
to the stellar equator) plays a major role in the dispersion in RV
amplitudes.
Conclusions: Our results are consistent with previous
results and provide, for the first time, an estimation of the convective
blueshift as a function of Teff, magnetic activity, and
wavelength, over a large sample of G and K main sequence stars. Tables 3 and 4 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/597/A52
Title: National Observation Services at OSUG and construction of a
Data Center and of a mutualized information system
Authors: Meunier, N.
Bibcode: 2016sf2a.conf..483M
Altcode:
OSUG (Observatoire des Sciences de l'Univers de Grenoble) is strongly
involved in more than 20 national observation services (hereafter
SNO) covering the different INSU (Institut National des Sciences
de l'Univers) sections, and is the PI for ten of them. This strong
involvement led us to implement a data center (OSUG-DC), in order to
provide the SNO and many other projects an infrastructure and common
tools (software development, data monitoring, ...): the objective
is to allow them to make their data available to the community in
the best conditions. The OSUG-DC has been recognized as a Regional
Expertise Center for the astronomy-astrophysics component in 2003
(3 SNO are concerned). This construction is also part of a larger
reflexion concerning the mutualization of certain services of the
information system at OSUG and at University Grenoble Alpes, some
already in place for some time such as a high performance computation
regional center. This paper presents the management organisation of
these projects, strong points and issues.
Title: Disentangling planetary and stellar activity features in the
CoRoT-2 light curve
Authors: Bruno, G.; Deleuil, M.; Almenara, J. -M.; Barros, S. C. C.;
Lanza, A. F.; Montalto, M.; Boisse, I.; Santerne, A.; Lagrange,
A. -M.; Meunier, N.
Bibcode: 2016A&A...595A..89B
Altcode: 2016arXiv160801855B
Aims: Stellar activity is an important source of systematic
errors and uncertainties in the characterization of exoplanets. Most
of the techniques used to correct for this activity focus on an ad
hoc data reduction.
Methods: We have developed a software
for the combined fit of transits and stellar activity features in
high-precision long-duration photometry. Our aim is to take advantage
of the modelling to derive correct stellar and planetary parameters,
even in the case of strong stellar activity.
Results: We use an
analytic approach to model the light curve. The code KSint, modified
by adding the evolution of active regions, is implemented into our
Bayesian modelling package PASTIS. The code is then applied to the
light curve of CoRoT-2. The light curve is divided in segments to
reduce the number of free parameters needed by the fit. We perform
a Markov chain Monte Carlo analysis in two ways. In the first, we
perform a global and independent modelling of each segment of the
light curve, transits are not normalized and are fitted together with
the activity features, and occulted features are taken into account
during the transit fit. In the second, we normalize the transits with
a model of the non-occulted activity features, and then we apply a
standard transit fit, which does not take the occulted features into
account.
Conclusions: Our model recovers the activity features
coverage of the stellar surface and different rotation periods for
different features. We find variations in the transit parameters of
different segments and show that they are likely due to the division
applied to the light curve. Neglecting stellar activity or even only
bright spots while normalizing the transits yields a 1.2σ larger
and 2.3σ smaller transit depth, respectively. The stellar density
also presents up to 2.5σ differences depending on the normalization
technique. Our analysis confirms the inflated radius of the planet
(1.475 ± 0.031RJ) found by other authors. We show that
bright spots should be taken into account when fitting the transits. If
a dominance of dark spots over bright ones is assumed, and a fit on a
lower envelope of the deepest transits is carried out, overestimating
the planet-to-star radius ratio of CoRoT-2 b by almost 3% is likely.
Title: VizieR Online Data Catalog: K and G dwarfs stellar granulation
variability (Meunier+, 2017)
Authors: Meunier, N.; Lagrange, A. -M.; Mbemba Kabuiku, L.; Alex,
M.; Mignon, L.; Borgniet, S.
Bibcode: 2016yCat..35970052M
Altcode:
Table 3 lists stars studied in the paper (HARPS data from the ESO
archive), together with informations from various sources and outputs
from our analysis. The number of stars is 167. Table 4 lists
spectral lines used in the papers. It gives their laboratory wavelength,
elements, and number of data sets in which the line is used. The number
of lines is 196. (2 data files).
Title: Variability Of Stellar Granulation And Convective Blueshift
With Spectral Type And Magnetic Activity
Authors: Meunier, Nadege; Lagrange, Anne-Marie; Mbemba Kabuiku, Lydie;
Alex, Maxime; Mignon, Lucile; Borgniet, Simon
Bibcode: 2016csss.confE.104M
Altcode:
In solar type stars, the attenuation of convective blueshift by stellar
magnetic activity dominates the radial velocity variations over small
mass planets. Models of stars different from the Sun request a good
knowledge of these properties to allow a realistic extrapolation. It
is therefore crucial to precisely determine not only the amplitude
of the convective blueshift for different types of stars, but also
the variability of this convective blueshift with magnetic activity,
as they are key factors in models producing the radial velocity
variations. We study a large sample of G and K stars and focus on
their temporally averaged properties, i.e. the activity level and a
criterion allowing to characterize the amplitude of the convective
blueshift using the variation of the velocity versus the intensity
at the bottom of spectral lines. We find this criteria to depend on
spectral type, on wavelength and on the activity level. We derive a
convective blueshift decreasing towards lower temperature, with a good
agreement with models. Smaller differences remain to be examined in
details. We quantify the variability of granulation properties in stars
other than the Sun due to magnetic field. The relative variation (with
respect to the average convective blueshift for a given stellar type)
seems to be constant over the considered range of spectral types. We
finally compare the observed radial velocity variation amplitudes
with those derived from our convective blueshift estimations using
a simple law and find a general agreement on the amplitude, and show
that inclination plays a major role.
Title: Using the Sun to estimate Earth-like planet detection
capabilities. VI. Simulation of granulation and supergranulation
radial velocity and photometric time series
Authors: Meunier, N.; Lagrange, A. -M.; Borgniet, S.; Rieutord, M.
Bibcode: 2015A&A...583A.118M
Altcode:
Context. Stellar variability, at a variety of timescales, can strongly
affect the ability to detect exoplanets, in particular when using radial
velocity (RV) techniques. Accurately characterized solar variations are
precious in this context to study the impact of stellar variations on
planet detectability. Here we focus on the impact of small timescale
variability.
Aims: The objective of this paper is to model
realistic RV time series due to granulation and supergranulation and to
study in greater detail the impact of granulation and supergranulation
on RV times series in the solar case.
Methods: We have simulated
a collection of granules and supergranules evolving in time to reproduce
solar photometric and RV time series. Synthetic time series are built
over the full hemisphere over one solar cycle.
Results: We
obtain intensity and RV rms due to solar granulation of respectively
0.8 m/s and 67 ppm, with a strong variability at timescales up to more
than 1 h. The rms RV due to supergranulation is between 0.28 and 1.12
m/s.
Conclusions: To minimize the effect of granulation, the best
strategy is to split the observing time during the night into several
periods instead of observing over a consecutive duration. However,
the best strategy depends on the precise nature of the signal. The
granulation RV remains large after even an hour of smoothing (about
0.4 m/s) while the supergranulation signal cannot be significantly
reduced on such timescales: a reduction of a factor 2 in rms RV can for
example be obtained over 7 nights (with 26 min/night). The activity
RV variability dominates at larger timescales. Detection limits can
easily be as high as 1 MEarth or above for periods of
tens or hundreds of days. The impact on detection limits is therefore
important and may prevent the detection of 1 MEarth planets
for long orbital periods, while the impact is much smaller at small
orbital periods. These results do not take the presence of pulsations
into account.
Title: Disentangling planetary and starspots features in the CoRoT-2
light curve
Authors: Bruno, G.; Deleuil, M.; Almenara, J. -M.; Barros, S. C. C.;
Lanza, A. F.; Montalto, M.; Boisse, I.; Santerne, A.; Lagrange,
A. -M.; Meunier, N.
Bibcode: 2015tyge.conf...46B
Altcode:
We develop a software for the combined fit of transits and stellar
activity features in high-precision long-duration photometry. We take
advantage of the modeling to derive correct stellar and planetary
parameters, even in the case of strong stellar activity. The light
curve is modeled analytically. The code KSint, modified by adding
the evolution of active regions, is implemented into our transit
modeling package PASTIS. The code is then applied to the light curve
of CoRoT-2. The light curve is divided in segments, to reduce the
number of free parameters needed by the fit. We find variations in
the transit parameters of different segments, and show that these are
mostly due to the cut applied to the light curve. We show that faculae
should be taken into account when fitting the transits. Our fit yields
an inflated radius for the planet (1.475±0.031 R_J), as other authors
found while neglecting stellar activity.
Title: Using the Sun to estimate Earth-like planets detection
capabilities. V. Parameterizing the impact of solar activity
components on radial velocities
Authors: Borgniet, S.; Meunier, N.; Lagrange, A. -M.
Bibcode: 2015A&A...581A.133B
Altcode: 2015arXiv150507361B
Context. Stellar activity induced by active structures such as stellar
spots and faculae is known to have a strong impact on the radial
velocity (RV) time series. It is therefore a strong limitation to the
detection of small planetary RV signals, such as that of an Earth-mass
planet in the habitable zone of a solar-like star. In a series of
previous papers, we have studied the detectability of such planets
around the Sun observed as a star in an edge-on configuration. For this
purpose, we computed the RV, photometric and astrometric variations
induced by solar magnetic activity, using all active structures observed
over one entire cycle.
Aims: Our goal is to perform similar
studies on stars with different physical and geometrical properties. As
a first step, we focus on Sun-like stars seen with various inclinations,
and on estimating detection capabilities with future instruments.
Methods: To do so, we first parameterize the solar active structures
with the most realistic pattern so as to obtain results consistent
with the observed ones. We simulate the growth, evolution and decay of
solar magnetic features (spots, faculae and network), using parameters
and empiric laws derived from solar observations and literature. We
generate the corresponding structure lists over a full solar cycle. We
then build the resulting spectra and deduce the RV and photometric
variations, first in the case of a sun seen edge-on and then with
various inclinations. The produced RV signal takes into account
the photometric contribution of spots and faculae as well as the
attenuation of the convective blueshift in faculae. We then use these
patterns to study solar-like stars with various inclinations.
Results: The comparison between our simulated activity pattern and the
observed pattern validates our model. We show that the inclination of
the stellar rotation axis has a significant impact on the photometric
and RV time series. Radial velocity long-term amplitudes and short-term
jitters are significantly reduced when going from edge-on to pole-on
configurations. Assuming spin-orbit alignment, the best configuration
for planet detection is an inclined star (i ≃ 45°).
Title: Constraining the orbital properties of Beta Pictoris b with
Harps radial velocity data
Authors: Borgniet, S.; Lagrange, A. -M.; Meunier, N.; Beust, H.
Bibcode: 2014tybp.confE..26B
Altcode:
The Beta Pictoris system with its debris disk and a massive giant
planet orbiting at about 9 AU of the star represents an ideal case
study to test giant planet formation and evolution models on one hand,
and brightness-mass relations on another hand. We present here the
results of 11 years of intensive monitoring of Beta Pictoris with the
high-resolution spectrograph HARPS located on the 3.6 m telescope
in La Silla, leading to more than 1700 precise radial velocity
measurements. This study makes up an update of the study already
published in Lagrange et al. 2013. This study allowes for the first
time to directly constrain the mass of an imaged planet and test
the brightness-mass relations. Second, it improves the detection
limits over the complete range of separations, and helps to rule
out the presence of closer massive giant planets. Finally, beyond
the case of Beta Pictoris itself, this work underlines the interest
of precise radial velocity measurements of young, early-type stars,
and of combining radial velocity and direct imaging data.
Title: Physical and orbital properties of β Pictoris b
Authors: Bonnefoy, M.; Marleau, G. -D.; Galicher, R.; Beust, H.;
Lagrange, A. -M.; Baudino, J. -L.; Chauvin, G.; Borgniet, S.; Meunier,
N.; Rameau, J.; Boccaletti, A.; Cumming, A.; Helling, C.; Homeier,
D.; Allard, F.; Delorme, P.
Bibcode: 2014A&A...567L...9B
Altcode: 2014arXiv1407.4001B
The intermediate-mass star β Pictoris is known to be
surrounded by a structured edge-on debris disk within which a gas giant
planet was discovered orbiting at 8-10 AU. The physical properties of
β Pic b were previously inferred from broad- and
narrow-band 0.9-4.8 μm photometry. We used commissioning data of the
Gemini Planet Imager (GPI) to obtain new astrometry and a low-resolution
(R ~ 35-39) J-band (1.12-1.35 μm) spectrum of the planet. We find that
the planet has passed the quadrature. We constrain its semi-major axis
to ≤10 AU (90% prob.) with a peak at 8.9+0.4-0.6
AU. The joint fit of the planet astrometry and the most recent radial
velocity measurements of the star yields a planet dynamical mass lower
than 20 MJup (≥96% prob.). The extracted spectrum of β Pic
b is similar to those of young L1-1.5+1 dwarfs. We
used the spectral type estimate to revise the planet luminosity to
log (L/L⊙) = -3.90 ± 0.07. The 0.9-4.8 μm photometry
and spectrum are reproduced for Teff = 1650 ± 150 K and a
log g ≤ 4.7 dex by 12 grids of PHOENIX-based and LESIA atmospheric
models. For the most recent system age estimate (21 ± 4 Myr), the
bolometric luminosity and the constraints on the dynamical mass of β
Pic b are only reproduced by warm- and hot-start tracks with initial
entropies Si> 10.5 kB/baryon. These initial
conditions may result from an inefficient accretion shock and/or
a planetesimal density at formation higher than in the classical
core-accretion model. Considering a younger age for the system or
a conservative formation time for β Pic b does not change these
conclusions. Appendices are available in electronic form at http://www.aanda.org
Title: Planets around stars in young nearby associations. Radial
velocity searches: a feasibility study and first results
Authors: Lagrange, A. -M.; Meunier, N.; Chauvin, G.; Sterzik, M.;
Galland, F.; Lo Curto, G.; Rameau, J.; Sosnowska, D.
Bibcode: 2013A&A...559A..83L
Altcode: 2013arXiv1304.5505L
Context. Stars in young nearby associations are the only targets that
allow giant planet searches in the near future, at all separations by
coupling indirect techniques, such as radial velocity (RV) and deep
imaging. These stars are first priority targets for the forthcoming
planet imagers on eight- to ten-metre class telescopes. Young
stars rotate more rapidly and are more active than their older
counterparts. Both effects can limit the ability to detect planets using
RV.
Aims: We wish to explore the planet detection abilities
of a representative sample of stars in close and young associations
with RV data and to explore the complementarity between this technique
and direct imaging.
Methods: We observed 26 such targets with
spectral types from A to K and ages from 8 to 300 Myr with HARPS. We
computed the detection limits with two methods, in particular, a method
we have recently developed that takes the frequency distribution of the
RV variations into account. We also attempted to improve the detection
limits in a few cases by correcting for the stellar activity.
Results: Our A-type stars RV show high-frequency variations due to
pulsations, while our F-K stars clearly show activity with more or
less complex patterns. For F-K stars, the RV jitter and vsini rapidly
decrease with star age. The data allow us to search for planets with
periods typically ranging from 1 day to 100 days, and up to more
than 500 days in a few cases. Within the present detection limits,
no planet was found in our sample. For the bulk of our F-K stars, the
detection limits fall to sub-Jupiter masses. We show that these limits
can be significantly improved by correcting even partially for stellar
activity, down to a few Neptune masses for the least active stars. The
detection limits on A-type stars can be significantly improved, down
to a few Jupiter-mass planets, provided an appropriate observing
strategy. We finally show the tremendous potential of coupling RV
and adaptive-optics deep imaging results.
Conclusions: The RV
technique allows the detection of planets lighter than Jupiter, reaching
a few Neptune masses around young stars aged typically 30 Myr or
more. Detection limits increase at younger ages, but (sub-)Jupiter mass
planets are still detectable. In the next few years, using complementary
techniques will allow a full exploration of the Jupiter-mass planets'
content of many of these stars. Based on observations made with the
ESO3.6m/Harps spectrograph at La Silla.083.C-0794(ABCD); 084.C-1039(A);
084.C-1024(A).Appendices A and B are available in electronic form at http://www.aanda.orgTables of radial
velocities 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/559/A83
Title: Using the Sun to estimate Earth-like planets detection
capabilities. IV. Correcting for the convective component
Authors: Meunier, N.; Lagrange, A. -M.
Bibcode: 2013A&A...551A.101M
Altcode:
Context. Radial velocity (RV) time series are strongly impacted
by the presence of stellar activity. In a series of papers, we have
reconstructed solar RV variations over a full solar cycle from observed
solar structures (spots and plages) and studied their impact on the
detectability of an Earth-mass planet in the habitable zone of the Sun
as seen edge-on from a neighbour star in several typical cases. We found
that the convective contribution dominates the RV times series.
Aims: The objective of this paper is twofold: to determine detection
limits on a Sun-like star seen edge-on with different levels of
convection and to estimate the performance of the activity correction
using a Ca index.
Methods: We apply two methods to compute
the detection limits: a correlation-based method and a local power
analysis method, which both take into account the temporal structure
of the observations. Furthermore, we test two methods using a Ca index
to correct for the convective contribution to the RV: a sinusoidal
fit to the Ca variations and a linear fit to the RV-Ca relation. In
both cases, we use observed Ca and reconstructed Ca to study the
various effects and limitations of our estimations.
Results:
We confirm that an excellent sampling is necessary to have detection
limits below 1 MEarth (e.g. 0.2-0.3 MEarth)
when there is no convection and a low RV noise. With convection,
the detection limit is always above 7 MEarth. The two
correction methods perform similarly when the Ca time series are noisy,
leading to a significant improvement (down to a few MEarth),
which is above the 1 MEarth limit. With a very good Ca noise
(signal to noise ratio, S/N, around 130), the sinusoidal method does
not get significantly better because it is dominated by the fact
that the solar cycle is not sinusoidal, but the RV-Ca method can
reach the 1 MEarth for an excellent Ca noise level.
Conclusions: For Sun-like conditions and under the simplifying
assumptions considered, we first conclude that the detection limit of
a few MEarth planet can be reached providing good sampling
and Ca noise. The detection of a 1 MEarth may be possible,
but only with an excellent temporal sampling and an excellent Ca index
noise level: we estimate that a probability larger than 50% to detect
a 1 MEarth at 1.2 AU requires more than 1000 well-sampled
observations and a Ca S/N larger than 130.
Title: Using the Sun to study the impact of stellar activity on
exoplanet detectability
Authors: Meunier, N.; Lagrange, A. M.
Bibcode: 2013AN....334..141M
Altcode: 2013csss...17..141M
Stellar activity induced by spots and plages, even at a low level of
activity, affects the radial velocity signatures. It is therefore
crucial to determine how it impacts our ability to detect small
planetary signals such as those produced by Earth-mass planets in
the habitable zone of stars. We focus on the solar case: thanks to the
wealth of accurate data available, the Sun gives us a unique opportunity
to test the impact of stellar activity on such detections. We use the
Sun as a template and investigate in details the impact of spots and
plages as well as the role played by the attenuation of convection due
to the presence of magnetic activity. We present the detection limits
obtained in various conditions. We find that the plage contribution due
to the convective blueshift attenuation dominates the total signal,
with a peak-to-peak amplitude over the solar cycle of about 8 m
s-1, and show that this contribution would prevent the
detection of the Earth around the Sun, even with forthcoming high
precision radial velocity instruments, unless ways to correct the
signal are found. We therefore propose practical ways to correct for
the activity on various timescales from days to years, and use again
the Sun to estimate the ultimate detection limits achievable once
the signal is corrected from the Sun's activity. Estimations will be
briefly presented.
Title: High precision astrometry mission for the detection and
characterization of nearby habitable planetary systems with the
Nearby Earth Astrometric Telescope (NEAT)
Authors: Malbet, Fabien; Léger, Alain; Shao, Michael; Goullioud,
Renaud; Lagage, Pierre-Olivier; Brown, Anthony G. A.; Cara, Christophe;
Durand, Gilles; Eiroa, Carlos; Feautrier, Philippe; Jakobsson, Björn;
Hinglais, Emmanuel; Kaltenegger, Lisa; Labadie, Lucas; Lagrange,
Anne-Marie; Laskar, Jacques; Liseau, René; Lunine, Jonathan;
Maldonado, Jesús; Mercier, Manuel; Mordasini, Christoph; Queloz,
Didier; Quirrenbach, Andreas; Sozzetti, Alessandro; Traub, Wesley;
Absil, Olivier; Alibert, Yann; Andrei, Alexandre Humberto; Arenou,
Frédéric; Beichman, Charles; Chelli, Alain; Cockell, Charles S.;
Duvert, Gilles; Forveille, Thierry; Garcia, Paulo J. V.; Hobbs, David;
Krone-Martins, Alberto; Lammer, Helmut; Meunier, Nadège; Minardi,
Stefano; Moitinho de Almeida, André; Rambaux, Nicolas; Raymond,
Sean; Röttgering, Huub J. A.; Sahlmann, Johannes; Schuller, Peter
A.; Ségransan, Damien; Selsis, Franck; Surdej, Jean; Villaver, Eva;
White, Glenn J.; Zinnecker, Hans
Bibcode: 2012ExA....34..385M
Altcode: 2011ExA...tmp..153M; 2011ExA...tmp..109M; 2011ExA...tmp...87M;
2011arXiv1107.3643M
A complete census of planetary systems around a volume-limited sample
of solar-type stars (FGK dwarfs) in the Solar neighborhood ( d ≤
15 pc) with uniform sensitivity down to Earth-mass planets within
their Habitable Zones out to several AUs would be a major milestone
in extrasolar planets astrophysics. This fundamental goal can be
achieved with a mission concept such as NEAT—the Nearby Earth
Astrometric Telescope. NEAT is designed to carry out space-borne
extremely-high-precision astrometric measurements at the 0.05 μas
(1 σ) accuracy level, sufficient to detect dynamical effects due to
orbiting planets of mass even lower than Earth's around the nearest
stars. Such a survey mission would provide the actual planetary masses
and the full orbital geometry for all the components of the detected
planetary systems down to the Earth-mass limit. The NEAT performance
limits can be achieved by carrying out differential astrometry between
the targets and a set of suitable reference stars in the field. The
NEAT instrument design consists of an off-axis parabola single-mirror
telescope (D = 1 m), a detector with a large field of view located
40 m away from the telescope and made of 8 small movable CCDs located
around a fixed central CCD, and an interferometric calibration system
monitoring dynamical Young's fringes originating from metrology fibers
located at the primary mirror. The mission profile is driven by the
fact that the two main modules of the payload, the telescope and the
focal plane, must be located 40 m away leading to the choice of a
formation flying option as the reference mission, and of a deployable
boom option as an alternative choice. The proposed mission architecture
relies on the use of two satellites, of about 700 kg each, operating
at L2 for 5 years, flying in formation and offering a capability of
more than 20,000 reconfigurations. The two satellites will be launched
in a stacked configuration using a Soyuz ST launch vehicle. The NEAT
primary science program will encompass an astrometric survey of our
200 closest F-, G- and K-type stellar neighbors, with an average of
50 visits each distributed over the nominal mission duration. The
main survey operation will use approximately 70% of the mission
lifetime. The remaining 30% of NEAT observing time might be allocated,
for example, to improve the characterization of the architecture of
selected planetary systems around nearby targets of specific interest
(low-mass stars, young stars, etc.) discovered by Gaia, ground-based
high-precision radial-velocity surveys, and other programs. With its
exquisite, surgical astrometric precision, NEAT holds the promise to
provide the first thorough census for Earth-mass planets around stars
in the immediate vicinity of our Sun.
Title: Comparison of different exoplanet mass detection limit methods
using a sample of main-sequence intermediate-type stars
Authors: Meunier, N.; Lagrange, A. -M.; De Bondt, K.
Bibcode: 2012A&A...545A..87M
Altcode: 2012arXiv1207.4329M
Context. The radial velocity (RV) technique is a powerful tool for
detecting extrasolar planets and deriving mass detection limits that
are useful for constraining planet pulsations and formation models.
Aims: Detection limit methods must take into account the temporal
distribution of power of various origins in the stellar signal. These
methods must also be able to be applied to large samples of stellar
RV time series
Methods: We describe new methods for providing
detection limits. We compute the detection limits for a sample of ten
main-sequence stars, which are of G-F-A type, in general active, and/or
with detected planets and various properties. We use them to compare the
performances of these methods with those of two other methods used in
the litterature.
Results: We obtained detection limits in the
2-1000 day period range for ten stars. Two of the proposed methods,
based on the correlation between periodograms and the power in the
periodogram of the RV time series in specific period ranges, are
robust and represent a significant improvement compared to a method
based on the root mean square of the RV signal.
Conclusions:
We conclude that two of the new methods (correlation-based method and
local power analysis, i.e. LPA, method) provide robust detection limits,
which are better than those provided by methods that do not take into
account the temporal sampling.
Title: VizieR Online Data Catalog: βPic Harps radial velocity data
(Lagrange+, 2012)
Authors: Lagrange, A. -M.; de Bondt, K.; Meunier, N.; Sterzik, M.;
Beust, H.; Galland, F.
Bibcode: 2012yCat..35420018L
Altcode: 2012yCat..35429018L
We used high-precision Harps data collected over eight years since 2003
to measure and analyse β Pic radial velocities. (1 data file).
Title: Constraints on planets around β Pic with Harps radial
velocity data
Authors: Lagrange, A. -M.; De Bondt, K.; Meunier, N.; Sterzik, M.;
Beust, H.; Galland, F.
Bibcode: 2012A&A...542A..18L
Altcode: 2012arXiv1202.2579L
Context. The β Pictoris system with its debris disk and a massive
giant planet orbiting at ≃9 AU represents an ideal laboratory for
studying giant planet formation and evolution as well as planet-disk
interactions. β Pic b can also help in testing brightness-mass
relations at young ages. Other planets, yet undetected, may of
course be present in the system.
Aims: We aim at directly
constraining the mass of β Pic b and at searching for additional
jovian planets on orbits closer than typically 2 AU.
Methods:
We used high-precision Harps data collected over eight years since
2003 to measure and analyse β Pic radial velocities.
Results:
We show that the true mass of β Pic b is less than 10, 12, 15.5,
20, and 25 MJup if orbiting at 8, 9, 10, 11, and 12 AU,
respectively. This is the first direct constraint on the mass of an
imaged planet. The upper mass found is well in the range predicted by
brightness-mass relations provided by current "hot start" models. We
also exclude the presence of giant planets more massive than 2.5
MJup with periods less than 100 days (hot Jupiters),
more massive than 9 MJup for periods in the range 100-500
days. In the 500-1000 day range, the detection limit is in the brown
dwarf domain. Beyond the intrinsic interest for β Pic, these results
show the possibilities of precise RV measurements of early-type,
rapidly rotating stars. Based on observations collected at the
European Southern Observatory, Chile, ESO.RV data is 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/542/A18
Title: Detectability of Earth mass planets with RV techniques around
Sun-like stars. The example of the Sun
Authors: Lagrange, Anne-Marie; Meunier, Nadege; Desort, Morgan
Bibcode: 2011IAUS..276..537L
Altcode:
We present the results of detailed simulations of the RV and astrometric
signals expected from the Sun, when taking into account its activity
(spots, plages, convection). To do so, we considered all structures
(2,000,000) identified on the Sun surface over a full cycle. We show
that the Sun activity would prevent the detection of the Earth in
the Habitable Zone with RV technics with today or future forthcoming
instruments, mainly because of inhomogeneous convection. We also show
that the activity-induced signal would be comparatively easier for
the astrometric detection of the Earth of similar planets.
Title: Hot Jupiters in Young Open Clusters
Authors: Eggenberger, Anne; Bouvier, J.; Boisse, I.; Lagrange, A.;
Bonfils, X.; Moraux, E.; Randich, S.; Meunier, N.; Delfosse, X.
Bibcode: 2011ESS.....2.3902E
Altcode:
We are carrying out a Doppler search for short-period giant planets
around 100 solar-type stars in nearby open clusters aged 30-150
Myr. Finding planets around such young stars will provide unique
constraints on the formation and early dynamical evolution of planetary
systems. As the properties of our targets are precisely known, we
can subtract the large-amplitude radial velocity signal induced by
rotating spots to recover the lower-amplitude Doppler signal produced
by a close-in giant planet. We present here the results of a pilot
study conducted with ESO/HARPS and OHP/SOPHIE. These results
illustrate our methodology and demonstrate our ability to detect hot
Jupiters around a subsample of representative targets.
Title: Filaments and the magnetic configuration. I. Observation of
the solar case
Authors: Meunier, N.; Delfosse, X.
Bibcode: 2011A&A...532A..18M
Altcode:
Context. The emission of Ca and Hα is correlated for the Sun, but this
does not seem to be true for other stars. We previously demonstrated
that this lack of correlation could be due to the presence of
filaments.
Aims: We aim to establish a link between the activity
level, the magnetic configuration, and the number of filaments, and
therefore with observables of other stars that the Sun.
Methods:
We studied the relationship between the filaments and the magnetic
configuration using a large scale approach on MDI/SOHO magnetograms
and a large sample of filaments. We validated the reconstruction of
synthetic time series of filament surface coverage representative of
the magnetic configuration, and then apply it to observations over
a full solar cycle.
Results: We derived quantitative criteria
that relates the presence of filaments to the properties at polarity
inversion lines, hereafter PIL, magnetic field gradient, and unipolar
areas on the solar surface (size and distance to these areas). We
also observed that the number of PIL pixels is anti-correlated with
the activity level, and the increase in filament surface coverage is
due to the modification of the PIL pixel properties. We reconstructed
synthetic time series of filaments that are in good agreement with
observations.
Conclusions: This work validates our method,
which will later be applied to solar and stellar simulations.
Title: Using the Sun to estimate Earth-like planets detection
capabilities . III. Impact of spots and plages on astrometric
detection
Authors: Lagrange, A. -M.; Meunier, N.; Desort, M.; Malbet, F.
Bibcode: 2011A&A...528L...9L
Altcode: 2011arXiv1101.2512L
Aims: Stellar activity is a potentially important limitation
to the detection of low-mass extrasolar planets with indirect methods
(radial velocity, photometry, astrometry). In previous papers, using
the Sun as a proxy, we investigated the impact of stellar activity
(spots, plages, convection) on the detectability of an Earth-mass planet
in the habitable zone (HZ) of solar-type stars with radial velocity
techniques. We here extend the detectability study to astrometry.
Methods: We used the sunspot and plages properties recorded over
one solar cycle to infer the astrometric variations that a Sun-like
star seen edge-on, 10 pc away, would exhibit, if covered by such
spots/bright structures. We compare the signal to the one expected from
the astrometric wobble (0.3 μas) of such a star surrounded by a one
Earth-mass planet in the HZ. We also briefly investigate higher levels
of activity.
Results: The activity-induced astrometric signal
along the equatorial plane has an amplitude of typically less than 0.2
μas (rms = 0.07 μas), lower than the one expected from an Earth-mass
planet at 1 AU. Hence, for this level of activity, the detectability
is governed by the instrumental precision rather than the activity. We
show that for instance a one Earth-mass planet at 1 AU would be detected
with a monthly visit during less than five years and an instrumental
precision of 0.8 μas. A level of activity five times higher would
still allow this detection with a precision of 0.35 μas. We conclude
that astrometry is an attractive approach to search for such planets
around solar type stars with most levels of stellar activity.
Title: Reconstructing the solar integrated radial velocity using
MDI/SOHO
Authors: Meunier, N.; Lagrange, A. -M.; Desort, M.
Bibcode: 2010A&A...519A..66M
Altcode: 2010arXiv1005.4764M
Context. Searches for exoplanets with radial velocity techniques
are increasingly sensitive to stellar activity. It is therefore
crucial to characterize how this activity influences radial velocity
measurements in their study of the detectability of planets in these
conditions.
Aims: In a previous work we simulated the impact
of spots and plages on the radial velocity of the Sun. Our objective
is to compare this simulation with the observed radial velocity of
the Sun for the same period.
Methods: We use Dopplergrams and
magnetograms obtained by MDI/SOHO over one solar cycle to reconstruct
the solar integrated radial velocity in the Ni line 6768 Å. We
also characterize the relation between the velocity and the local
magnetic field to interpret our results.
Results: We obtain a
stronger redshift in places where the local magnetic field is larger
(and as a consequence for larger magnetic structures): hence we find
a higher attenuation of the convective blueshift in plages than in
the network. Our results are compatible with an attenuation of this
blueshift by about 50% when averaged over plages and network. We obtain
an integrated radial velocity with an amplitude over the solar cycle
of about 8 m s-1, with small-scale variations similar to the
results of the simulation, once they are scaled to the Ni line.
Conclusions: The observed solar integrated radial velocity agrees with
the result of the simulation made in our previous work within 30%,
which validates this simulation. The observed amplitude confirms that
the impact of the convective blueshift attenuation in magnetic regions
will be critical to detect Earth-mass planets in the habitable zone
around solar-like stars.
Title: Using the Sun to estimate Earth-like planets detection
capabilities . I. Impact of cold spots
Authors: Lagrange, A. -M.; Desort, M.; Meunier, N.
Bibcode: 2010A&A...512A..38L
Altcode: 2010arXiv1001.1449L
Aims: It is known that stellar spots may in some cases produce
radial velocity (RV) signatures similar to those of exoplanets. To date,
the most extensive set of data on spots, active regions, and activity
in general for any star is that obtained for the Sun. To investigate
the impact of these spots, we aim to study the detectability of
Earth-mass planets in the habitable zone (HZ) of solar-type stars,
if covered by spots similar to sunspots.
Methods: We used
the sunspot properties recorded over one solar cycle between 1993
and 2003 to infer the RV curve that a solar-type star seen edge-on
would exhibit, if covered by these spots. We also derive interesting
parameters such as bisector velocity span (BVS) and photometric curves,
commonly used in the analysis of RV data. We compare the obtained
data with archival solar data available for the same epoch (e.g.,
irradiance, Ca index). We also simulate the RV of such a spotted star
surrounded by an Earth-mass planet located in the HZ.
Results:
The RV of the spotted star appears to be very variable, in a complex
way, depending on the activity level, with amplitudes from a few
tens cm/s up to 5 m/s (assuming ΔTs = T⊙
- Tspot = 550 K). A correlation between the BVS and the
RV data is observed even when several spots are present with a slope
so small that only data of very high precision (better than 5 cm/s)
can enable its detection. Photometric variations of up to 0.5% are
predicted, depending on the level of activity, in agreement with
measured solar photometric variations. Based on present assumptions,
the detection of a 1 MEarth planet located between 0.8
and 1.2 AU requires intensive monitoring (weekly or more frequent),
over several years. The temporal sampling is more crucial than the
data precision (assuming precisions in the range [1-10] cm/s). Cooler
spots may become a problem for these detections. We also anticipate
that plages, not considered in this paper, could further complicate
or even compromise such detections.
Title: Using the Sun to estimate Earth-like planets detection
capabilities . II. Impact of plages
Authors: Meunier, N.; Desort, M.; Lagrange, A. -M.
Bibcode: 2010A&A...512A..39M
Altcode: 2010arXiv1001.1638M
Aims: Stellar activity produced by spots and plages affects
the radial velocity (RV) signatures. Because even low activity
stars would produce such a signal, it is crucial to determine how
it influences our ability to detect small planetary signals such as
those produced by Earth-mass planets in the habitable zone (HZ). In
a recent paper, we investigated the impact of sunlike spots. We aim
here to investigate the additional impact of plages.
Methods:
We used the spot and plage properties over a solar cycle to derive the
RV that would be observed if the Sun was seen edge-on. The RV signal
comes from the photometric contribution of spots and plages and from
the attenuation of the convective blueshift in plages. We analyzed
the properties of the RV signal at different activity levels and
compared it with commonly used activity indicators such as photometry
and the Ca index. We also compared it with the signal that would be
produced by an Earth-mass planet in the HZ.
Results: We find
that the photometric contributions of spots and plages to the RV
signal partially balance each other out, so that the residual signal
is comparable to the spot signal. However, the plage contribution due
to the convective blueshift attenuation dominates the total signal,
with an amplitude over the solar cycle of about 8-10 m/s. Short-term
variations are also significantly greater than the spot and plage
photometric contribution. This contribution is very strongly correlated
with the Ca index on the long term, which may be a way to distinguish
between stellar activity and a planet.
Conclusions: Providing a
very good temporal sampling and signal-to-noise ratio, the photometric
contribution of plages and spots should not prevent detection of
Earth-mass planets in the HZ. However, the convection contribution
makes such a direct detection impossible, unless its effect can be
corrected for by methods that still need to be found. We show that it
is possible to identify the convection contribution if the sensitivity
is good enough, for example, by using activity indicators.
Title: On the power spectrum of solar surface flows
Authors: Rieutord, M.; Roudier, T.; Rincon, F.; Malherbe, J. -M.;
Meunier, N.; Berger, T.; Frank, Z.
Bibcode: 2010A&A...512A...4R
Altcode: 2009arXiv0911.3319R
Context. The surface of the Sun provides us with a unique and
very detailed view of turbulent stellar convection. Studying its
dynamics can therefore help us make significant progress in stellar
convection modelling. Many features of solar surface turbulence like
the supergranulation are still poorly understood.
Aims: The aim
of this work is to give new observational constraints on these flows
by determining the horizontal scale dependence of the velocity and
intensity fields, as represented by their power spectra, and to offer
some theoretical guidelines to interpret these spectra.
Methods:
We use long time-series of images taken by the Solar Optical Telescope
(SOT) on board the Hinode satellite; we reconstruct both horizontal
(by granule tracking) and vertical (by Doppler effect) velocity
fields in a field-of-view of ~ 75 × 75 Mm2. The dynamics
in the subgranulation range can be investigated with unprecedented
precision thanks to the absence of seeing effects and the use of the
modulation transfer function of SOT for correcting the spectra.
Results: At small subgranulation scales down to 0.4 Mm the spectral
density of kinetic energy associated with vertical motions exhibits
a k-10/3-like power law, while the intensity fluctuation
spectrum follows either a k-17/3 or a k-3-like
power law at the two continuum levels investigated (525 and 450
nm respectively). We discuss the possible physical origin of these
scalings and interpret the combined presence of k-17/3 and
k-10/3 power laws for the intensity and vertical velocity
as a signature of buoyancy-driven turbulent dynamics in a strongly
thermally diffusive regime. In the mesogranulation range and up to a
scale of 25 Mm, we find that the amplitude of the vertical velocity
field decreases like λ-3/2 with the horizontal scale
λ. This behaviour corresponds to a k2 spectral power
law. Still in the 2.5-10 Mm mesoscale range, we find that intensity
fluctuations in the blue continuum also follow a k2
power law. In passing we show that granule tracking cannot sample
scales below 2.5 Mm. We finally further confirm the presence of a
significant supergranulation energy peak at 30 Mm in the horizontal
velocity power spectrum and show that the emergence of a pore erases
this spectral peak. We tentatively estimate the scale height of the
vertical velocity field in the supergranulation range and find 1 Mm;
this value suggests that supergranulation flows are shallow.
Title: Supergranulation, Network Formation, and TFGs Evolution from
Hinode Observations
Authors: Roudier, T.; Rincon, F.; Rieutord, M.; Brito, D.; Beigbeder,
F.; Parès, L.; Malherbe, J. -M.; Meunier, N.; Berger, T.; Frank, Z.
Bibcode: 2009ASPC..415..203R
Altcode:
In this paper, we analyse a a 48h high-resolution time sequence of the
quiet Sun photosphere obtained with the Solar Optical Telescope onboard
Hinode. Using floating corks advected by velocity fields inferred from
photometry measurements, we show that long-living Trees of Fragmenting
Granules play a crucial role in the advection of small-scale magnetic
fields and in the build-up of the magnetic network.
Title: Extrasolar planets and brown dwarfs around A-F type
stars. VII. θ Cygni radial velocity variations:
planets or stellar phenomenon?
Authors: Desort, M.; Lagrange, A. -M.; Galland, F.; Udry, S.;
Montagnier, G.; Beust, H.; Boisse, I.; Bonfils, X.; Bouchy, F.;
Delfosse, X.; Eggenberger, A.; Ehrenreich, D.; Forveille, T.; Hébrard,
G.; Loeillet, B.; Lovis, C.; Mayor, M.; Meunier, N.; Moutou, C.; Pepe,
F.; Perrier, C.; Pont, F.; Queloz, D.; Santos, N. C.; Ségransan,
D.; Vidal-Madjar, A.
Bibcode: 2009A&A...506.1469D
Altcode: 2009arXiv0908.4521D
Aims: In the framework of the search for extrasolar planets and brown
dwarfs around early-type main-sequence stars, we present the results
obtained on the early F-type star θ Cygni.
Methods: ELODIE
and SOPHIE at the Observatoire de Haute-Provence (OHP) were used to
obtain 91 and 162 spectra, respectively. Our dedicated radial-velocity
measurement method was used to monitor the star's radial velocities
over five years. We also used complementary, high angular resolution
and high-contrast images taken with PUEO at the CFHT.
Results:
We show that θ Cygni radial velocities are quasi-periodically
variable, with a ≃150-day period. These variations are not due to the
≃0.35-M⊙ stellar companion that we detected in imaging at
more than 46 AU from the star. The absence of correlation between the
bisector velocity span variations and the radial velocity variations
for this 7 km s^-1 v sin i star, as well as other criteria, indicate
that the observed radial velocity variations do not stem from stellar
spots. The observed amplitude of the bisector velocity span variations
also seems to rule out stellar pulsations. However, we observe a peak
in the bisector velocity span periodogram at the same period as the one
found in the radial velocity periodogram, which indicates a probable
link between these radial velocity variations and the low-amplitude
lineshape variations with a stellar origin. Long-period variations
are not expected from this type of star to our knowledge. If a stellar
origin (hence of new type) were to be confirmed for these long-period
radial velocity variations, this would have several consequences on
the search for planets around main-sequence stars, both in terms of
observational strategy and data analysis. An alternative explanation
for these variable radial velocities is the presence of at least one
planet of a few Jupiter masses orbiting at less than 1 AU; however,
this planet alone does not explain all observed features, and the θ
Cygni system is obviously more complex than a planetary system with 1
or 2 planets.
Conclusions: The available data do not allow us to
distinguish between these two possible origins. A vigourous follow-up
in spectroscopy and photometry is needed to get a comprehensive view
of the star intrinsic variability and/or its surrounding planetary
system. Based on observations made with the ELODIE and SOPHIE
spectrographs at the Observatoire de Haute-Provence (CNRS, France)
and with the PUEO adaptive optics system at the Canada-France-Hawaii
Telescope (CFHT), which is operated by the National Research Council of
Canada, the Institut National des Sciences de l'Univers of the Centre
National de la Recherche Scientifique of France, and the University of
Hawaii. Tables of radial velocities 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/506/1469
Title: VizieR Online Data Catalog: theta Cyg radial velocity
variations (Desort+, 2009)
Authors: Desort, M.; Lagrange, A. -M.; Galland, F.; Udry, S.;
Montagnier, G.; Beust, H.; Boisse, I.; Bonfils, X.; Bouchy, F.;
Delfosse, X.; Eggenberger, A.; Ehrenreich, D.; Forveille, T.; Hebrard,
G.; Loeillet, B.; Lovis, C.; Mayor, M.; Meunier, . N.; Moutou, C.;
Pepe, F.; Perrier, C.; Pont, F.; Queloz, D.; Santos, N. C.; Segransan,
D.; Vidal-Madjar, A.
Bibcode: 2009yCat..35061469D
Altcode:
In the frame of the search for extrasolar planets and brown dwarfs
around early-type main-sequence stars, we present the results obtained
on the early F-type star theta Cygni. ELODIE and SOPHIE at Observatoire
de Haute-Provence (OHP) were used to obtain 91 and 162 spectra,
respectively. Our dedicated radial-velocity measurement method was
used to monitor the star's radial velocities over five years. We also
use complementary, high angular resolution and high-contrast images
taken with PUEO at CFHT. We show that theta Cygni radial velocities are
quasi-periodically variable, with a ~150-day period. These variations
are not due to the ~0.35M{sun} stellar companion that
we detected in imaging at more than 46AU from the star. The absence
of correlation between the bisector velocity span variations and the
radial velocity variations for this 7km/s vsini star, as well as other
criteria indicate that the observed radial velocity variations are not
due to stellar spots. The observed amplitude of the bisector velocity
span variations also seems to rule out stellar pulsations. However,
we observe a peak in the bisector velocity span periodogram at the
same period as the one found in the radial velocity periodogram,
which indicates a probable link between these radial velocity
variations and the low amplitude lineshape variations which are of
stellar origin. Long-period variations are not expected from this
type of star to our knowledge. If a stellar origin (hence of new type)
was to be confirmed for these long-period radial velocity variations,
this would have several consequences on the search for planets around
main-sequence stars, both in terms of observational strategy and
data analysis. An alternative explanation for these variable radial
velocities is the presence of at least one planet of a few Jupiter
masses orbiting at less than 1AU; however this planet alone does not
explain all observed features, and the theta Cygni system is obviously
more complex than a planetary system with 1 or 2 planets. The available
data do not allow to distinguish between these two possible origins. A
vigourous follow-up in spectroscopy and photometry is needed to get
a comprehensive view of the star intrinsic variability and/or its
surrounding planetary system. (2 data files).
Title: On the correlation between Ca and Hα solar emission and
consequences for stellar activity observations
Authors: Meunier, N.; Delfosse, X.
Bibcode: 2009A&A...501.1103M
Altcode: 2009arXiv0905.4037M
Context: The correlation between Ca and Hα chromospheric emission,
known to be positive in the solar case, has been found to vary between
-1 and 1 for other stars.
Aims: Our objective is to understand
the factors influencing this correlation in the solar case, and then
to extrapolate our interpretation to other stars.
Methods: We
characterize the correlation between both types of emission in the solar
case for different time scales. Then we determine the filling factors
due to plages and filaments, and reconstruct the Ca and Hα emission
to test different physical conditions in terms of plage and filament
contrasts.
Results: We have been able to precisely determine
the correlation in the solar case as a function of the cycle phase. We
interpret the results as reflecting the balance between the emission
in plages and the absorption in filaments. We found that correlations
close to zero or slightly negative can be obtained when considering
the same spatio-temporal distribution of plages and filaments than
on the sun but with greater contrast. However, with that assumption,
correlations close to -1 cannot be obtained for example. Stars with
a very low Hα contrast in plages and filaments well correlated with
plages could produce a correlation close to -1.
Conclusions:
This study opens new ways to study stellar activity, and provides a
new diagnosis that will ultimately help to understand the magnetic
configuration of stars other than the sun.
Title: Observations of Photospheric Dynamics and Magnetic Fields:
From Large-Scale to Small-Scale Flows
Authors: Meunier, N.; Zhao, J.
Bibcode: 2009SSRv..144..127M
Altcode: 2008SSRv..tmp..190M
This paper reviews solar flows and magnetic fields observed at the
photospheric level. We first present the context in which these
observations are performed. We describe the various temporal and
spatial scales involved, and the coupling between them. Then we
present small-scale flows, mainly supergranulation and flows around
active regions. Flows at the global scale are then reviewed, again with
emphasis on the flows, i.e. differential rotation, torsional oscillation
and meridional circulation. In both small- and global-scale we discuss
the coupling between flow fields and magnetic field and give an overview
of observational techniques. Finally, the possible connection between
studies of solar activity and stellar activity is briefly discussed.
Title: Mesoscale dynamics on the Sun's surface from HINODE
observations
Authors: Roudier, Th.; Rieutord, M.; Brito, D.; Rincon, F.; Malherbe,
J. M.; Meunier, N.; Berger, T.; Frank, Z.
Bibcode: 2009A&A...495..945R
Altcode: 2009arXiv0902.2299R
Context:
Aims: The interactions of velocity scales on the Sun's
surface, from granulation to supergranulation are still not understood,
nor are their interaction with magnetic fields. We thus aim at giving
a better description of dynamics in the mesoscale range which lies
between the two scales mentioned above.
Methods: We analyse a
48 h high-resolution time sequence of the quiet Sun photosphere at
the disk center obtained with the Solar Optical Telescope onboard
Hinode. The observations, which have a field of view of 100´´ ×
100´´, typically contain four supergranules. We monitor in detail the
motion and evolution of granules as well as those of the radial magnetic
field.
Results: This analysis allows us to better characterize
Trees of Fragmenting Granules issued from repeated fragmentation of
granules, especially their lifetime statistics. Using floating corks
advected by measured velocity fields, we show their crucial role
in the advection of the magnetic field and in the build up of the
network. Finally, thanks to the long duration of the time series, we
estimate that the turbulent diffusion coefficient induced by horizontal
motion is approximately 430 km2 s-1.
Conclusions: These results demonstrate that the long living families
contribute to the formation of the magnetic network and suggest that
supergranulation could be an emergent length scale building up as small
magnetic elements are advected and concentrated by TFG flows. Our
estimate for the magnetic diffusion associated with this horizontal
motion might provide a useful input for mean-field dynamo models.
Title: Observations of Photospheric Dynamics and Magnetic Fields:
From Large-Scale to Small-Scale Flows
Authors: Meunier, N.; Zhao, J.
Bibcode: 2009odsm.book..127M
Altcode:
This paper reviews solar flows and magnetic fields observed at the
photospheric level. We first present the context in which these
observations are performed. We describe the various temporal and
spatial scales involved, and the coupling between them. Then we
present small-scale flows, mainly supergranulation and flows around
active regions. Flows at the global scale are then reviewed, again with
emphasis on the flows, i.e. differential rotation, torsional oscillation
and meridional circulation. In both small- and global-scale we discuss
the coupling between flow fields and magnetic field and give an overview
of observational techniques. Finally, the possible connection between
studies of solar activity and stellar activity is briefly discussed.
Title: Dynamo of the Sun and Solar-Type Stars
Authors: Meunier, N.
Bibcode: 2009EAS....39...83M
Altcode:
The objective of this paper is to give a review of solar and
stellar activity, from the observationnal constraints to dynamo
models. I first review solar observations and insist on the various
scales. Then I describe the photospheric magnetic structures (from
spots and plages to the magnetic network and internetwork magnetic
fields) and the energetic events in the chromosphere and corona,
such as prominences, flares and coronal mass ejections. It is mostly
photospheric observations (in addition to the results obtained with
helioseismolohy concerning the internal rotation) which are providing
the important constraints for dynamo models, that are reviewed. However
the energetic events can also be used as tracers of solar activity and
have a significant impact on earth. Stellar activity is then reviewed,
including results on differential rotation. I insist on the comparison
with solar properties. I then come back on the constraints these
stellar observations bring to dynamo models.
Title: Development of large and fast cmos aps cameras at latt
Authors: Beigbeder, F.; Bourrec, E.; Dupieux, M.; Delaigue, G.; Rondi,
S.; Rieutord, M.; Meunier, N.; Roudier, T.
Bibcode: 2009EAS....37..301B
Altcode:
Since 2004, at the Laboratoire d'Astrophysique de Toulouse Tarbes
(LATT), we work with CMOS APS detectors, firstly to develop a
large-field,high-resolution camera for the observation of the solar
supergranulation, secondly to develop a fast camera for an adaptive
optics test bench. In these two projects, we use detectors from
FillFactory, now continued by Cypress Semiconductor Corporation:
IBIS4-14000, IBIS-16000, LUPA-4000, 14 Mpixels, 16 Mpixels, 4 Mpixels
respectively. The last one just reads in a 240 × 240 pixels window to
obtain readout rate of 1000 Image/s. For these purposes we developed
dedicated controllers to follow the high pixel rate and multi-output
readout of this type of detectors. We also studied the characterization
methods and measured the main parameters of these CMOS detectors to
know their behaviour. Using these kinds of APS detectors in these
two particular projects proves that we can already find niches to
use CMOS detectors in astronomy taking advantage of their present
specificities. Recent improvements like back illumination, noise
reduction, should rapidly open news possibilities.
Title: Photospheric flows around a quiescent filament at Large and
small scale and their ffects on filament destabilization
Authors: Roudier, Th.; Malherbe, J. M.; Švanda, M.; Molodij, G.;
Keil, S.; Sütterlin, P.; Schmieder, B.; Bommier, V.; Aulanier, G.;
Meunier, N.; Rieutord, M.; Rondi, S.
Bibcode: 2008sf2a.conf..569R
Altcode:
We study the influence of large and small scales photospheric
motions on the destabilization of an eruptive filament, observed
on October 6, 7, and 8, 2004 as part of an international observing
campaign (JOP 178). Large-scale horizontal flows are invetigated
from a series of MDI/SOHO full-disc Dopplergrams and magnetograms
from THEMIS. Small-scale horizontal flows were derived using local
correlation tracking on TRACE satellite, Dutch Open Telescope (DOT)
and The Dunn Solar telescope (DST) data. The topology of the flow field
changed significantly during the filament eruptive phase, suggesting
a possible coupling between the surface flow field and the coronal
magnetic field. We measured an increase of the shear below the point
where the eruption starts and a decrease in shear after the eruption. We
conclude that there is probably a link between changes in surface flow
and the disappearance of the eruptive filament.
Title: Supergranules over the solar cycle
Authors: Meunier, N.; Roudier, T.; Rieutord, M.
Bibcode: 2008A&A...488.1109M
Altcode:
Context: The origin of supergranulation has not been understood
yet. Contradictory results have been obtained in the past concerning
the relation between supergranule properties (mostly cell size) and
the solar cycle.
Aims: We propose to study the variation in
supergranule cell sizes and velocity fields over the solar cycle, as
well as the intensity variation inside supergranules.
Methods:
We define supergranule cells from maps of horizontal velocity field
divergences. The flow fields are derived from MDI/SOHO intensity
maps. The intensity variation in supergranules are compared to the
variation inside granules resulting from a numerical simulation. The
variation in these profiles with the cell size and over the solar cycle
is also analysed.
Results: We find that cell sizes are smaller
on average at cycle maximum. We also find that the slope between Log
(V_rms) and Log (R) is weakly correlated with the spot number (i.e. the
global activity level) but anti-correlated with the local magnetic
field. We also confirm the decrease in the intensity variation from
cell centre to the boundary, which puts a lower limit on the temperature
variation of 0.57 ± 0.06 K. This temperature difference is of 1.03 ±
0.05 K when considering the areas of strongest divergence and strongest
convergence. We observe a strong similarity in the intensity variation
inside supergranules and granules. A significant variation with the
cell size is observed, also similar to that in granules, but the
variation over the solar cycle is not significant.
Conclusions:
The sign of the variation in supergranule cell sizes over the solar
cycle is in agreement with what can be expected from the influence
of the magnetic field. The observed intensity variations show that a
common process could be the origin of both granules and supergranules.
Title: Large-scale horizontal flows in the solar
photosphere. III. Effects on filament destabilization
Authors: Roudier, T.; Švanda, M.; Meunier, N.; Keil, S.; Rieutord,
M.; Malherbe, J. M.; Rondi, S.; Molodij, G.; Bommier, V.; Schmieder, B.
Bibcode: 2008A&A...480..255R
Altcode: 2007arXiv0711.3112R
Aims:We study the influence of large-scale photospheric motions on
the destabilization of an eruptive filament, observed on October 6,
7, and 8, 2004, as part of an international observing campaign (JOP
178).
Methods: Large-scale horizontal flows were investigated
from a series of MDI full-disc Dopplergrams and magnetograms. From
the Dopplergrams, we tracked supergranular flow patterns using the
local correlation tracking (LCT) technique. We used both LCT and manual
tracking of isolated magnetic elements to obtain horizontal velocities
from magnetograms.
Results: We find that the measured flow
fields obtained by the different methods are well-correlated on large
scales. The topology of the flow field changed significantly during
the filament eruptive phase, suggesting a possible coupling between
the surface flow field and the coronal magnetic field. We measured
an increase in the shear below the point where the eruption starts
and a decrease in shear after the eruption. We find a pattern in the
large-scale horizontal flows at the solar surface that interact with
differential rotation.
Conclusions: We conclude that there is
probably a link between changes in surface flow and the disappearance
of the eruptive filament.
Title: Solar supergranulation revealed by granule tracking
Authors: Rieutord, M.; Meunier, N.; Roudier, T.; Rondi, S.; Beigbeder,
F.; Parès, L.
Bibcode: 2008A&A...479L..17R
Altcode: 2008arXiv0801.1369R
Context: Supergranulation is a pattern of the velocity field at the
surface of the Sun, which has been known about for more than fifty
years, however, no satisfactory explanation of its origin has been
proposed.
Aims: New observational constraints are therefore
needed to guide theoretical approaches which hesitate between scenarios
that either invoke a large-scale instability of the surface turbulent
convection or a direct forcing by buoyancy.
Methods: Using the
14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained
a 7.5 h-long sequence of high resolution images with unprecedented
field size. Tracking granules, we have determined the velocity field
at the Sun's surface in great detail from a scale of 2.5 Mm up to
250 Mm.
Results: The kinetic energy density spectrum shows that
supergranulation peaks at 36 Mm and spans on scales ranging between 20
Mm and 75 Mm. The decrease of supergranular flows in the small scales
is close to a k-2-power law, steeper than the equipartition
Kolmogorov one. The probability distribution function of the divergence
field shows the signature of intermittency of the supergranulation
and thus its turbulent nature.
Conclusions:
Title: Tracking granules on the Sun's surface and reconstructing
velocity fields. II. Error analysis
Authors: Tkaczuk, R.; Rieutord, M.; Meunier, N.; Roudier, T.
Bibcode: 2007A&A...471..695T
Altcode: 2007arXiv0707.1994T
Context: The determination of horizontal velocity fields at the solar
surface is crucial to understanding the dynamics and magnetism of the
convection zone of the sun. These measurements can be done by tracking
granules.
Aims: Tracking granules from ground-based observations,
however, suffers from the Earth's atmospheric turbulence, which
induces image distortion. The focus of this paper is to evaluate the
influence of this noise on the maps of velocity fields.
Methods:
We use the coherent structure tracking algorithm developed recently
and apply it to two independent series of images that contain the same
solar signal.
Results: We first show that a k-ω filtering of
the times series of images is highly recommended as a pre-processing
to decrease the noise, while, in contrast, using destretching should
be avoided. We also demonstrate that the lifetime of granules has a
strong influence on the error bars of velocities and that a threshold
on the lifetime should be imposed to minimize errors. Finally, although
solar flow patterns are easily recognizable and image quality is very
good, it turns out that a time sampling of two images every 21 s is
not frequent enough, since image distortion still pollutes velocity
fields at a 30% level on the 2500 km scale, i.e. the scale on which
granules start to behave like passive scalars.
Conclusions:
The coherent structure tracking algorithm is a useful tool for noise
control on the measurement of surface horizontal solar velocity fields
when at least two independent series are available.
Title: Photospheric flows around a quiescent filament
Authors: Rondi, S.; Roudier, Th.; Molodij, G.; Bommier, V.; Keil,
S.; Sütterlin, P.; Malherbe, J. M.; Meunier, N.; Schmieder, B.;
Maloney, P.
Bibcode: 2007A&A...467.1289R
Altcode:
Context: The horizontal photospheric flows below and around a
filament are one of the components in the formation and evolution of
filaments. Few studies exist because they require multiwalength time
sequences at high spatial resolution.
Aims: Our objective
is to measure the horizontal photospheric flows associated
with the evolution and eruption of a filament.
Methods:
We present observations obtained in 2004 during the international
JOP 178 campaign which involved eleven instruments both in space
and at ground based observatories. We use TRACE WL, DOT and DST
observation to derive flow maps which are then coaligned with
intensity images and with the vector magnetic field map obtained with
THEMIS/MTR.
Results: Several supergranulation cells cross the
Polarity Inversion Line (PIL) and can transport magnetic flux through
the PIL, in particular parasitic polarities. We present a detailed
example of the formation of a secondary magnetic dip at the location
of a filament footpoint. Large-scale converging flows, which could
exist along the filament channel and contribute to its formation, are
not observed. Before the filament's eruptive phase, we observe both
parasitic and normal polarities being swept by a continuously diverging
horizontal flow located in the filament gap. The disappearance of the
filament initiates in this gap. Such purely horizontal motions could
lead to destabilization of the filament and could trigger the sudden
filament disappearance.
Title: Coronagraphic Broad-Band Hα Observations 1998 -- 2000
Authors: Meunier, N.; Noëns, J. -C.; Romeuf, D.; Koutchmy, S.;
Jimenez, R.; Wurmser, O.; Rochain, S.
Bibcode: 2007ASPC..368..351M
Altcode:
Broad-band full-limb Hα images of the inner corona were obtained
since the beginning of the solar cycle 23 using one of the Pic-du-Midi
coronagraph. We developed a tool to process the complete set of stored
images and to automatically extract the properties and evolutions of the
observed cold H I coronal structures over a large range of sizes and
light fluxes, from small jets and/or spikes to large prominences. The
paper describes the recognition techniques implemented in our
software and discusses its use. Then we present some new results
following a statistical analysis of the occurrence of structure
parameters applied to a large sample of observations. It illustrates
the capabilities of this software when applied to our database. Strong
activity-asymmetries over the solar poles are shown, confirming similar
results from elsewhere. We also discuss the distribution of relative
light fluxes of these structures over a wide range of sizes. See also
http://bass2000.bagn.obs-mip.fr.
Title: Are supergranule sizes anti-correlated with magnetic activity?
Authors: Meunier, N.; Roudier, T.; Tkaczuk, R.
Bibcode: 2007A&A...466.1123M
Altcode:
Context: The variation of supergranule cell sizes with the magnetic
environment is still controversial.
Aims: We study this relation
in detail to understand the discrepancies observed between previous
results.
Methods: We determine the cell size using divergence of
horizontal flows derived from local correlation tracking of intensity
maps (MDI/SOHO). We study the variation of the cell size as a function
of the magnetic field inside the cell. We also consider which component
of the magnetic field most influences the cell size.
Results: Our
main conclusion is that there are no large cells when the magnetic field
(in absolute value) averaged over the cell is large. This is mostly
due to the magnetic field inside the cell (intranetwork fields), while
strong network magnetic fields (at the cell boundary) are associated
with larger cells. Further studies of the evolution of the cells and of
the flux imbalance suggest that a high level of weak fields may prevent
the formation of large cells. This is compatible with the expectation
that strong magnetic fields should prevent large-scale flows.
Conclusions: The relation between the local activity level determined
by the average magnetic field inside the cells and the supergranule size
is not linear. Furthermore, it strongly depends on the definition of
the activity level (magnetic field inside the cell or magnetic network)
and on the magnetic sensitivity of the data. This last point probably
explains at least partially the conflicting results obtained up to now.
Title: The superrotation of solar supergranules
Authors: Meunier, N.; Roudier, T.
Bibcode: 2007A&A...466..691M
Altcode:
Context: Supergranules have long been believed to rotate faster
than plasma and than magnetic structures. However, it has recently
been shown that this could be due to a bias appearing when using
Dopplergrams, which are strongly affected by projection effets.
Aims: Our purpose is to perform new measurements of supergranule
angular velocities using a technique that would not be significantly
influenced by projection effets.
Methods: We are therefore
tracking horizontal divergence maps smoothed on the supergranular scale,
either globally or on the scale of cells. Tracking the magnetic field
using the same technique allows them to be used as a reference. Doppler
tracking is performed for a direct comparison.
Results: We
confirm that the tracking of Doppler features is not reliable when
computing the dynamics on the supergranular scale. However, we find
that divergence features are still rotating faster than the magnetic
field, when using two independent time series.
Conclusions: We
conclude that the long-standing puzzle of supergranular superrotation
persists, and that interpreting it in terms of anchorage depth inside
the convective zone may not be sufficient to explain it.
Title: Analysis of broad-band Hα coronagraphic observations
Authors: Romeuf, D.; Meunier, N.; Noëns, J. -C.; Koutchmy, S.;
Jimenez, R.; Wurmser, O.; Rochain, S.; "Observateurs Associés" Team
Bibcode: 2007A&A...462..731R
Altcode:
Context: Daily broad-band full-limb Hα images of the inner corona were
obtained during solar cycle 23 (1994-2005) using the 15 cm Pic-du-Midi
coronagraph.
Aims: We want to automatically extract the properties
and evolutions of the observed cool HI coronal structures over a wide
range of sizes and light fluxes, from small jets and/or spikes to
large prominences.
Methods: A tool was developed to process the
complete set of stored images. This paper describes the recognition
techniques implemented in our software and discusses its use. It
includes the removal of the parasitic diffraction ring produced by
the set of different occulting disks used throughout the year.
Results: We present and discuss selected results from a statistical
analysis of the occurrence of parameters characterizing the observed
structures applied to a large sample of observations. It illustrates
the capabilities of this software when applied to our database. Strong
asymmetries of the activity level over the solar poles become evident,
confirming similar results from previous works. We also discuss
the distribution of relative light fluxes of these structures over
a wide range of sizes.
Conclusions: The complete series of
FITS and calibrated images, the list of the detected structures,
and their geometric and luminosity evolutions are stored in the
BASS2000 solar database catalogue (http://bass2000.bagn.obs-mip.fr)
and are made publicly available. The Hα HI structures observed over
the limb of the sun present statistical properties of great interest
for understanding its eruptive activity.
Title: Intensity variations inside supergranules
Authors: Meunier, N.; Tkaczuk, R.; Roudier, Th.
Bibcode: 2007A&A...463..745M
Altcode:
Context: The convective origin of supergranulation is highly
controversial. Past measurements of intensity variations inside
supergranules have often been influenced by the brightness enhancement
at the cell boundaries due to the magnetic network.
Aims:
We conduct a precise determination of intensity variations inside
supergranules.
Methods: We determine the supergranule cell
boundary from smoothed divergence maps derived from horizontal flow
maps. We derive these flow maps from intensity maps obtained by MDI/SOHO
in high resolution mode. We discuss the different possible approaches
to take into account the influence of the magnetic field which can be
used to determine the intensity variations inside supergranules.
Results: We observe a significant decrease of the intensity from the
center to the boundary of supergranules. We also obtain additional clues
from the behavior of the maximum intensities and minimum intensities
around each pixel, which are related to granules and intergranules:
the maximum intensity decreases from center to boundary, while the
minimum intensity is constant or increases depending how restrictive
the selection is. The difference between intensity profiles versus
divergence and relative distance to cell center also provides
complementary information. The corresponding temperature differences
between cell center and boundary are in the range 0.8-2.8 K. The
intensity enhancement (for the magnetic network) or deficit (for
intranetwork fields) depends on the localisation inside the cell.
Conclusions: .It is the first time that such a detailed analysis
of intensity variations inside supergranulation is performed. Our
results are compatible with a convective origin of supergranulation,
as the intensity decreases toward the boundary of the cells. However,
new simulations of supergranulation are necessary to verify whether
the compared behavior of granule and intergranule intensity variations
is in close agreement with convection.
Title: Photospheric flows around a quiescent filament and CALAS
first results .
Authors: Rondi, S.; Roudier, Th.; Molodij, G.; Bommier, V.; Malherbe,
J. M.; Schmieder, B.; Meunier, N.; Rieutord, M.; Beigbeder., F.
Bibcode: 2007MmSAI..78..114R
Altcode:
The horizontal photospheric flows below and around a filament are one of
the components in the formation and evolution of filaments. Few studies
have been done so far because this requires multiwalength time sequences
with high spatial resolution. We present observations obtained in 2004
during the international JOP 178 campaign in which eleven instruments
were involved, from space and ground based observatories. Several
supergranulation cells are crossing the Polarity Inversion Line (PIL)
allowing the transport of magnetic flux through the PIL, in particular
the parasitic polarities. Before the filament eruptive phase, parasitic
and normal polarities are swept by a continuous diverging horizontal
flow located in the filament gap where the disappearance of the filament
starts. In the future, observations at high spatial resolution on a
large field-of-view would be very useful to study filaments, as they are
very large structures. We also present the first images obtained with
the use of our new 14 MPixel camera CALAS (CAmera for the LArge Scales
of the Solar Surface) (10 arcmin× 6.7 arcmin) . These are the first
large-scale and high-resolution images of the solar surface ever made.
Title: BASS2000-Tarbes: current status and THEMIS data processing .
Authors: Meunier, N.; Lafon, M.; Maeght, P.; Grimaud, F.; Roudier, Th.
Bibcode: 2007MmSAI..78..172M
Altcode:
I will review the history and status of the data archive BASS2000 and
will concentrate my presentation on the BASS2000-Tarbes data base, which
contains a very large volume of THEMIS data, i.e. spectropolarimetric
data. I will insist the implementation of the processing of MTR-THEMIS
(multi-line spectropolarimetry) data by the BASS2000 team, which has
been our main project in 2006. New data levels are Stokes profiles and
clean spectra, maps of continuum intensity and line-center intensity,
Dopplergrams, magnetograms and vector magnetic field maps. I will also
present the tools and services that we are providing.
Title: The granular magnetic field as observed with THEMIS
Authors: Bommier, V.; Molodij, G.; Meunier, N.
Bibcode: 2007MmSAI..78...65B
Altcode:
The search for correlation along the slit in THEMIS spectropolarimetric
observations of a quiet region shows a positive autocorrelation of the
magnetic field direction with a pixel size of 0.45 arcsec. Accordingly,
the magnetic field appears as partially resolved with such a pixel
size. Further spectropolarimetric observations have been performed by
scanning a quiet region with THEMIS tip-tilt ON, in order to investigate
a possible relationship between the granulation and the magnetic
field vector which is known in each pixel of this observation (pixel
size of 0.25 arcsec). As a result, we see a very clear correlation
between the granulation observed in the continuum and the longitudinal
velocity field observed via the Doppler effect, but the granulation
and the magnetic field vector (strength and direction) appear us as
uncorrelated, by looking at their respective maps. These quantities
(velocity and magnetic field) have been derived from spectropolarimetric
observations of the Fe I 6302.5 line, to which UNNOFIT inversion has
been applied to derive the magnetic field vector.
Title: Velocities and divergences as a function of supergranule size
Authors: Meunier, N.; Tkaczuk, R.; Roudier, Th.; Rieutord, M.
Bibcode: 2007A&A...461.1141M
Altcode:
Context: The origin of supergranulation is not understood yet and many
scenarios, which range from large-scale deep convection to large-scale
instabilities of surface granular flows, are possible.
Aims: We
characterize the velocities and divergences in supergranulation cells
as a function of their size.
Methods: Using local correlation
tracking, we determine the horizontal flow fields from MDI intensity
maps and derive the divergences. The smoothed divergences are used to
determine the cells for various spatial smoothings, in particular at the
supergranular scale.
Results: We find evidence of intermittency
in the supergranular range and a correlation between the size of
supergranules and the strength of the diverging flow. We also show
that the relation between rms velocities and scale (the supergranule
radius R) can be represented by a law V_rms∼ R0.66.
Conclusions: . The results issued from our data point towards a
scenario where supergranulation is a surface phenomenon of the sun,
probably the consequence of a large-scale instability triggered by
strong positive correlated rising flows.
Title: BASS2000: on-going projects and results
Authors: Meunier, N.; Lafon, M.; Maeght, P.; Grimaud, F.; Roudier, Th.
Bibcode: 2006sf2a.conf..553M
Altcode:
We review the current status of the services proposed by the database
BASS2000. Then we describe our main on-going project, i.e. the
implementation of the processing, by the BASS2000 team, of a large
data set (several Terabytes) of solar multi-line spectropolarimetric
data (MTR mode) obtained by many observers at the THEMIS telescope
in Tenerife. The implementation of this data processing and the data
products are described as well as the future services associated
to this processing: data sets of magnetograms, dopplergrams, vector
magnetic field maps, organization of workshops. The other projects we
are involved in are also briefly described, and concerns the Pic du
Midi Coronagraph (HACO, as well as the future new version CLIMSO),
the Lunette Jean Rösch of the Pic du Midi (mostly imagery data)
and the implications in the Virtual Observatory.
Title: Analysis of broad-band Hα coronagraphic observations
Authors: Noëns, J. -C.; Romeuf, D.; Meunier, N.; Koutchmy, S.;
Jimenez, R.; Wurmser, O.; Rochain, S.; "O. A. " Team
Bibcode: 2006sf2a.conf..557N
Altcode:
Broad-band full-limb H-alpha images of the inner corona were obtained
since the beginning of the solar cycle 23 using one of the Pic-du-Midi
coronagraph. We developed a tool to process the complete set of stored
images and to extract automatically the properties and evolutions of
the observed cold HI coronal structures over a large range of sizes and
light fluxes, from small jets and/or spikes to large prominences. The
paper describes the recognition techniques implemented in our
software and discusses its use. Then we present some new results
following a statistical analysis of the occurrence of structure
parameters applied to a large sample of observations. It illustrates
the capabilities of this software when applied to our database. Strong
activity-asymmetries over the solar poles are shown, confirming similar
results from elsewhere. We also discuss the distribution of relative
light fluxes of these structures over a wide range of sizes. See also:
http://bass2000.bagn.obs-mip.fr.
Title: A CMOS Sensor for Solar Observation
Authors: Beigbeder, Francis; Rondi, Sylvain; Meunier, Nadège;
Rieutord, Michel
Bibcode: 2006ASSL..336..123B
Altcode: 2006sda..conf..123B
No abstract at ADS
Title: Toward a Virtual Observatory for Solar System Plasmas: an
exceptional scientific opportunity
Authors: Jacquey, C.; Bocchialini, K.; Aboudarham, J.; Meunier, N.;
Andre, N.; Genot, V.; Harvey, C.; Budnik, E.; Hitier, R.; Gangloff,
M.; Bouchemit, M.
Bibcode: 2006epsc.conf..714J
Altcode:
During the coming years, the "Solar System Plasma" environment will
be explored by an exceptional set of observatories : RHESSI, SOHO,
STEREO, SOLAR-B and ground based observatories will all provide
continuous observations of the Sun and its corona. In situ plasma and
field measurements will be obtained at and near Mercury (MESSENGER),
Venus (VEX), Earth (ACE, WIND, GEOTAIL, CLUSTER, THEMIS), Mars (MEX,
MGS) and Saturn (CASSINI), and inside the heliosphere (STEREO, ULYSSES,
VOYAGER). These data will be complemented by UV and radio astronomical
observations of Jovian, Saturnian and terrestrial auroral activity. This
wealth of data will offer previously unequalled opportunities to study
(i) global and multi-scale phenomena of the inner heliosphere (ii)
the propagation of the solar perturbations and space meteorology,
(iii) local interplanetary conditions around planets and (iv) the
comparison of the ionised environments of various planets. However,
the exploitation of all these data is a major technical challenge, as it
requires accessing heterogeneous data from diverse origins to perform an
integrated study using software tools appropriate for analysis of the
phenomena observed. Moreover, the huge amount of data to manage coming
from future space and ground based instruments requires extraction
that could no more be done by hand, but automatically. This challenge
is unlikely to be met by instrument teams or laboratories working
individually ; it requires collaboration of the whole international
community through a Virtual Observatory. The Europlanet/IDIS prototype
will give a foretaste of what will be achievable by a Virtual
Observatory for planetology. The overlap in functionality between a
"Planetary VO" and a "Solar System Plasma VO" remains to be defined,
but both are undoubtedly essential and complimentary components of any
Solar System VO. In this paper, we present potential science cases
in Space Plasma, which we then use to identify requirements for the
access and analysis tools needed to exploit the promised exceptional
harvest of solar and in situ plasma data.
Title: Observations of the solar surface dynamics
Authors: Meunier, N.
Bibcode: 2006EAS....21..221M
Altcode:
The dynamics of solar and stellar surfaces is very important to
understand the dynamics of their interior as well as their activity
cycles. This paper describes the dynamics observed at the solar surface
from small scales (granulation) to the largest scales (differential
rotation and meridional circulation).
Title: BASS2000-Tarbes status: data, services and projects
Authors: Meunier, N.; Lafon, M.; Maeght, P.; Grimaud, F.; Roudier, Th.
Bibcode: 2005sf2a.conf..169M
Altcode:
The data base BASS2000 in Tarbes has archived THEMIS raw data in its
spectropolarimetric mode since 1999. Other data are also available
(Nancay Radioheliograph, Pic du Midi Coronagraph since 1994). We
first present the catalogue and our services. Then we present in
more details two of our projects. First, we plan to process as many
THEMIS data as possible in order to make them available to a wide
community. Spectropolarimetric data are indeed difficult to process,
and many users would be interested to have data such as ready-to-use
magnetic field maps. Second, we present our project to develop an
archive for stellar spectropolarimetric data from the Narval instrument
at the TBL (Pic du Midi), starting 2006, as these data should be
integrated in a catalogue in order to be used by as large a community
as possible. Such a catalogue should also contain data from the Musicos
instrument as well as from ESPaDOns (CFHT). This stellar data archive
would be complementary to the POLLUX data base of reference stellar
spectra, and its catalogue should be available from CDS in Strasbourg.
Title: CALAS, A Camera for the Large-scale of the Solar Surface
Authors: Meunier, N.; Rondi, S.; Tkaczuk, R.; Rieutord, M.;
Beigbeder, F.
Bibcode: 2005ASPC..346...53M
Altcode:
The origin of supergranulation (convective or not) is still
much debated. Among various possible approaches, one way to study
supergranulation is to observe the horizontal motions of granules. A
combination of a very large field-of-view (in order to see as
many supergranules as possible), a very high spatial resolution
(to sample granules with a high accuracy, even the small ones)
and a high cadence is necessary to study this pattern in detail. We
plan to implement a 4k×4k CMOS camera at the Lunette Jean Rösch
(previously Coupole Tourelle) at the Pic du Midi Observatory (a
50 cm diameter refractor). The main objective of the camera, CALAS
(Camera for the Large Scale of the Solar Surface), is the study of
supergranulation. This will allow to sample granules with a high spatial
resolution on a 10'×10' field-of-view (∼ 100 supergranules). We
present our objectives, the instrumental set-up and organization,
and the status of the instrument.
Title: Temporal variations in the magnetic network large-scale
dynamics
Authors: Meunier, N.
Bibcode: 2005A&A...442..693M
Altcode:
The variation in the magnetic network large-scale dynamics is
investigated using MDI magnetograms from 1996 to 2004. Cross-correlation
and feature tracking techniques are used on pairs of magnetograms in
order to derive the dynamics at the solar surface, including magnetic
network regions. The variations for both methods are very different,
the feature tracking technique leading to generally much less variable
dynamics over the cycle, except for the rotation versus latitude. At
cycle minimum, the increased differential rotation at high latitude
combined with a more rigid rotation at low latitude is indeed more
pronounced with the feature tracking. The rotation variations put a
strong constraint on the origin of these variations, as some strong
correlations between coefficients deduced from fits with Legendre
polynomials are observed. When using the cross-correlation technique,
the meridional circulation also tends to exhibit a more complex behavior
compared to rotation. This study provides the temporal variations in
the dependence of the dynamics on the magnetic field and feature size
as well as on polarities. The dispersions in velocity for the following
and leading polarities are studied over the cycle.
Title: Large-scale photospheric dynamics below coronal holes
Authors: Meunier, N.
Bibcode: 2005A&A...443..309M
Altcode:
A large data set of MDI magnetograms is studied to analyze the global
dynamics of magnetic structures from network to active regions inside
and outside coronal holes. We find a weaker meridional circulation
at almost all latitudes, as well as a more differential rotation
of the photospheric magnetic structures below high-latitude coronal
holes. Stronger asymmetries in the dynamics are observed in coronal
holes at high latitude compared to outside coronal holes. The variation
in the dynamics is also studied as a function of the coronal hole
size as well as its variation with time and with magnetic field. The
smaller velocity dispersion obtained in coronal holes when using a
cross-correlation technique shows that the large-scale circulation
may be inhibited inside coronal holes compared to outside. However,
there is an indication of a larger diffusion of magnetic features
within coronal holes than outside.
Title: Large-scale dynamics and polarities of magnetic structures
Authors: Meunier, N.
Bibcode: 2005A&A...437..303M
Altcode:
A large data set of MDI magnetograms is studied in order to analyse
the dependence of the global dynamics of magnetic structures on
their polarity. Two complementary techniques (feature tracking and
correlation tracking) are used to determine the differential rotation
and meridional circulation. A faster rotation of leading polarity
structures is found for active areas, while a faster rotation of
following polarity structures is found for weak field areas. However
the latter is found only when using correlation tracking: individual
small features do not seem to exhibit any difference between leading
and following polarities. From correlation tracking, the mixed polarity
areas (with a low activity level) do rotate as the following polarity
areas. Furthermore, the latter have a more poleward motion when the
correlation tracking is used.
Title: Magnetic network dynamics: Activity level, feature size and
anchoring depth
Authors: Meunier, N.
Bibcode: 2005A&A...436.1075M
Altcode:
A large data set of MDI magnetograms is studied in order to analyze
the global dynamics of magnetic structures from network to active
regions. Two complementary techniques are used: feature tracking and
correlation tracking. The very large data set allows the variation of
their dynamics (angular rotation velocity and meridional circulation)
to be studied in detail. Variation both in the dynamics as a function
of size and distance to active regions (for feature tracking) and as a
function of activity level in the correlation box are studied. These new
results allow the possible anchoring depth of these magnetic features
to be constrained. The observations of the magnetic network dynamics
are not consistent with the dynamics deduced from helioseismology. So,
some additional processes must be acting on the magnetic network in
order to explain their global dynamics.
Title: Complexity of magnetic structures: Flares and cycle phase
dependence
Authors: Meunier, N.
Bibcode: 2004A&A...420..333M
Altcode:
A long data set of MDI/SOHO full-disk magnetograms is analyzed
to provide a large sample of active regions. The objective is to
study the variations of the fractal dimension of these structures
on different time scales: in relation to their activity level
(spots, flares) and during the solar cycle. First, the variations
of the fractal dimension of the structure during solar flares are
studied using a very large sample. Variations are found to be of
very small amplitude. The complexity of the structures is slightly
larger after the flare when considering regions close to the flare
(2-3°), while a decrease seems to be observed at larger
scales (up to 10°), although this should be confirmed using
other approaches. The results obtained by Meunier (\cite{Meunier1999a})
concerning the fractal dimension versus the size of the structures for
various magnetic thresholds are confirmed on a much larger sample, with
a peculiar behavior seen around 550-800 Mm2. This scale is
observed to increase from cycle minimum to cycle maximum. In addition,
I observe that the fractal dimension of active regions reaches a plateau
above 3000 Mm2 and that structures of a given size are more
complex when they have spots. The fractal dimension is strongly variable
during the solar cycle, with the sign of the variation depending on
their size and on their flux content (spot or no spot) and with an
amplitude up to 0.17 between the ascending phase and cycle maximum.
Title: Fast photospheric flows and magnetic fields in a flaring
active region
Authors: Meunier, N.; Kosovichev, A.
Bibcode: 2003A&A...412..541M
Altcode:
We present new results from the coordinated observations between
the THEMIS telescope (in the multi-line spectropolarimetric mode)
and Michelson Doppler Imager (MDI) on SOHO obtained in November 2000
for active region NOAA 9236 which was the source of several X-class
flares. The goal of these observations was twofold: to verify MDI
measurements of the line-of-sight components of flow velocity and
magnetic field, and to obtain more information about the photospheric
flows and magnetic fields in flaring regions. Using the simultaneous
observational data in several lines we have analyzed the structure and
dynamics of this active region at the photospheric level before and
after a X4.0 flare of November 26, the last major flare produced by
this very active region. Vector magnetic field maps are computed from
the THEMIS data by full inversion of the Stokes line profiles. In
the Doppler velocity maps from THEMIS and MDI, we observe fast
photospheric flows which appear to be supersonic in two regions
located close to the region where the flare occurred. These flows
seem to be long-lived (several hours at least). In one position,
we observe a supersonic downflow strongly inclined with respect to
the vertical (by 51deg), while in another position, a flow
suggesting a strong shear with a supersonic component as well, although
almost horizontal upflows and downflows cannot be ruled out in that
case. These flows seem to be present at least 8 hours before the flare,
and the amplitude in the second case appeared to be modified during
the flare, especially, during the first minutes. In the MDI data, we
observed strong permanent changes of the longitudinal magnetic flux,
associated with the flare. The role of the strong flows and their
interaction with the magnetic field in the development of the active
region and the flare is not understood yet.
Title: Statistical properties of magnetic structures: Their dependence
on scale and solar activity
Authors: Meunier, N.
Bibcode: 2003A&A...405.1107M
Altcode:
A long data set of MDI/SOHO full-disk magnetograms is analyzed in
order to provide a large sample of network features as well as active
regions associated with their magnetic properties (magnetic flux and
magnetic flux density for example). The main objective of the paper
is to study the variations of these properties along the solar cycle,
and to compare the behavior of the magnetic features at various scales
(covering three orders of magnitude in size). I also investigate
the dependence of these properties on the activity level in their
neighborhood and in the context of their global configuration on
the solar disk. This study is important for a better understanding
of the emergence and decay of active regions, as well as of the
role of the network in the removal of the magnetic flux and in solar
irradiance variations. The main results are as follows. (i) I observe
a characteristic scale in the range 400-800 Mm2 (close
to the supergranular scale) below which the size and magnetic flux
distributions are power laws down to 40 Mm2 (corresponding
to the range 3*E19-1021 Mx). This scale increases
from solar minimum to solar maximum. The shape of the distributions
also suggests a strong similarity between small active regions (below
the supergranular scale) and network patches. (ii) The North-South
asymmetry in the number of structures, compatible with easier-to-detect
leading structures in most cases, surprisingly exhibits a sign reversal
for the weakest structures, suggesting a different origin, while
the East-West asymmetry is compatible with a predominantly eastward
inclination of magnetic flux tubes, including network structures and
not only for emerging active regions as suggested by models. (iii)
The dependence of the magnetic characterictics on the size of the
structures is found to be variable with the activity level, the magnetic
flux beeing more concentrated at solar maximum (especially for small
features). Small-scale properties are also dependent on the proximity
of an active region. (iv) Latitudinal distributions and flux variations
along the solar cycle suggests a significant role of the meridional
flows in the properties of the very small network features as well as
an influence of supergranulation properties. (v) The variations of the
magnetic properties of network elements and active regions with time are
strongly size-dependent. The results also show a correlation between
the number (or magnetic flux) of network structures and the sunspot
cycle, with an amplitude larger than expected from previous results.
Title: Magnetism and Activity of the Sun and Stars
Authors: Arnaud, J.; Meunier, N.
Bibcode: 2003EAS.....9.....A
Altcode:
No abstract at ADS
Title: CALAS: a CAmera for the LArge Scales of the solar surface
Authors: Meunier, N.; Rieutord, M.; Beigbeder, F.
Bibcode: 2003sf2a.conf...93M
Altcode: 2003sf2a.confE..29M
Supergranulation is constituted of cells of horizontal outflows with a
typical size of 30000 km at the surface of the Sun. The origin of this
pattern (convection or not) is still controversial. Usually observed
using Doppler shifts at the photospheric level, it can also be studied
using horizontal motions of solar granules. A combination of a large
field of view (containing as many supergranules as possible) and a
high spatial resolution (to sample granules with a high accuracy,
even the small ones) is then necessary to study this process in more
details. Our project is to implement a large scale CMOS camera, CALAS
(CAmera for the LArge Scales of the solar surface) at the Coupole
Tourelle at the Pic du Midi. The field of view will be 10'x10',
allowing to sample 100 hundred supergranules. We will present the
scientific objectives and the organisation of our project.
Title: The Advanced Technology Solar Telescope
Authors: Paletou, F.; López Ariste, A.; Meunier, N.; Molodij, G.
Bibcode: 2003sf2a.conf...97P
Altcode: 2003sf2a.confE..30L
The Advanced Technology Solar Telescope (ATST) is a 4-m aperture solar
telescope project lead by the NSO and supported by all major solar US
research institutes. Also a European initiative gathering 17 countries,
so far, is currently being prepared in support of the project. ATST,
intended for first light in 2010, will provide the high-angular
resolution required for nowadays photospheric studies; but its large
aperture and controlled scattered-light design makes it also a very
promising tool for high sensitivity spectropolarimetric observations
needed throughout the whole solar atmosphere up to the corona, and in
spectral windows ranging from the visible to the thermal infrared.
Title: Observation of solar photospheric magnetic fields and
differential rotation
Authors: Meunier, N.
Bibcode: 2003EAS.....9..159M
Altcode:
This review about solar photospheric magnetic fields will follow
the two traditionnal approaches to study these fields. I will first
review some recent results about magnetic fields observed at
small scales, from sunspots and active regions down to network and
intranetwork magnetic fields. The second part of the talk will be
devoted to the global approach, mostly concerning the solar cycle:
large spatial and temporal scales as well as global motions including
differential rotation. I will finish by a discussion about studies
attempting to link the two approaches.
Title: Fast photospheric flows in a flaring active region
Authors: Meunier, N.; Kosovichev, A.
Bibcode: 2002ESASP.505..505M
Altcode: 2002IAUCo.188..505M; 2002solm.conf..505M
We present new results from coordinated observations with THEMIS
(multi-line spectropolarimetric mode) and MDI/SOHO obtained in Nov
2000. We observed active region AR 9236 using several photospheric
lines before and after the last main flare produced by this very
active region. Vector magnetic fields are computed from THEMIS data
and a full inversion of the interesting profiles is performed. We
observe fast flows which are probably supersonic in two regions located
where this flare occurs. These flows seem to be long-lived structures
(several hours). One of them is related to a strong shear with flows
almost horizontal while the other is a downflow strongly inclined
with respect to the vertical. They are present 9 hours before the
flare, however their amplitude appears to be modified by the flare
(especially during the first minutes).
Title: Two-dimensional Modeling of the Solar Oscillation l-ν Power
Spectrum
Authors: Meunier, Nadège; Jefferies, Stuart M.
Bibcode: 2000ApJ...530.1016M
Altcode:
We describe an algorithm which can accurately model the spatial-temporal
l-ν solar oscillation power spectrum over large ranges in frequency
(ν) and degree (l). We show how modeling in two dimensions provides
a better representation of the observed spectrum than can be obtained
with traditional one-dimensional approaches. The gain comes from
using more of the observed signal to constrain the model and improved
descriptions of the solar background spectrum and the signal leakage
between different spatial scales. We discuss the level of systematic
error that can be expected in the solar oscillation mode frequency
data published to date.
Title: Solar Surface Magnetism and the Increase of Solar Irradiance
between Activity Minimum and Maximum
Authors: Fligge, M.; Solanki, Sami K.; Meunier, Nadege; Unruh,
Yvonne C.
Bibcode: 2000ESASP.463..117F
Altcode: 2000sctc.proc..117F
No abstract at ADS
Title: Large-Scale Dynamics of Active Regions and Small Photospheric
Magnetic Features
Authors: Meunier, N.
Bibcode: 1999ApJ...527..967M
Altcode:
This paper presents an analysis of the dynamics of magnetic features
within and outside active regions using full-disk magnetograms
obtained by the MDI (Michelson Doppler Imager) instrument on the SOHO
spacecraft. The absence of distortion and the short time interval
(96 minutes) between images allow us to calculate high-quality
cross-correlations between regions on each magnetogram. Therefore,
each cross-correlation can be studied individually, which provides
information with resolution in longitude as well as good temporal
resolution. Rotation rates and meridional motions are simultaneously
derived from an analysis of the cross-correlation functions. This
analysis shows that the meridional motions are very different during
the quiet period and the active period. In the former case, a poleward
meridional circulation is observed, which increases with latitude. In
the latter case, the meridional motions of magnetic features in active
regions are smaller by a factor of 2 than those exhibited by small
magnetic structures outside active regions. The rotation rate seems
slightly larger in active regions, while the rotation rate decreases as
the activity level rises. Some differences in the meridional circulation
of different polarities are found.
Title: Fractal Analysis of Michelson Doppler Imager Magnetograms:
A Contribution to the Study of the Formation of Solar Active Regions
Authors: Meunier, N.
Bibcode: 1999ApJ...515..801M
Altcode:
In this paper a fractal analysis of active regions observed by the
Michelson Doppler Imager (MDI) instrument on the SOHO spacecraft is
performed. The purpose of such an analysis is to study the shape of
these magnetic regions via their fractal dimension, which characterizes
their complexity, and to deduce some information on the processes
that led to their formation. Both full disk and high-resolution
MDI magnetograms are used and the fractal dimensions using the
perimeter/area relation (d1) and the linear size/area
relation (d2) are calculated. A statistical analysis of the
estimate of a fractal dimension is performed, as well as that of the
influence of noise on it. The fractal dimension for a range of sizes is
calculated. The fractal dimension d1 is found to increase
with the area of the active regions (from 1.48 for supergranular size
structures to 1.68 for the largest structures). The fractal dimension
d2 also increases with the area of the active regions
(from 1.78 to 1.94). The fractal dimension d1 decreases
with the magnetic threshold for moderate sizes and increases for the
largest structures. The high-resolution results match those of full
disk magnetograms when the images are degraded. This fractal analysis
is performed in relation to the size distribution properties: the two
analyses provide complementary information. Then some models of active
regions very similar to those of Wentzel & Seiden are introduced
to interpret the observations in terms of a percolation process at the
bottom of the convective zone and diffusion at the surface. These models
lead to structures that are more complex than the observed structures.
Title: Infrared lines as probes of solar magnetic features. XIII. The
relative flux in weak and strong quiet-sun magnetic fields
Authors: Meunier, N.; Solanki, S. K.; Livingston, W. C.
Bibcode: 1998A&A...331..771M
Altcode:
An estimate of the fraction of magnetic flux in intrinsically weak-field
form, i.e. fields with less than 1 kG intrinsic strength, in the
quiet Sun is presented. We find that on average approximately 2/3 of
the flux is in weak-field form, although our data allow a range of
values between 25%\ and 85%. These estimates have been derived with
the help of radiative transfer model calculations from low-noise
scans through the quiet Sun at fixed wavelengths within a Zeeman
sensitive spectral line at 1.56 mu m. They represent the first rapidly
modulated polarimetric observations of solar 1.56 mu m radiation. These
scans show that the polarimetric signature near the core of the line
exhibits a very different spatial structure than in the outer line
wings. Since the outer part of the line profile is only sensitive to
intrinsically strong magnetic fields, while the central part reacts
also to intrinsically weak fields, this implies that intrinsically weak
fields are distributed differently on the surface than strong fields
are (weak-field features lie closer together). The spatial distribution
suggests that the strong fields we are observing are network elements,
whereas the weak fields are intranetwork features. Further results,
such as the average distance between weak and strong field features,
flux distribution, spatial power spectra and the Stokes asymmetry
of intrinsically weak fields are also presented. In particular, we
find that the flux per magnetic feature is distributed lognormally,
in agreement with a similar finding for sunspot umbral areas by Bogdan
et al. (1988).
Title: Modeling the Solar Oscillation l-v Power Spectrum
Authors: Meunier, N.; Jefferies, S. M.
Bibcode: 1998ESASP.418..267M
Altcode: 1998soho....6..267M
We have developed a ``two-dimensional'' algorithm which simultaneously
models the ell- ν spectrum over several n-values and a wide
range of ell-values. In addition to the estimation of the line
profile parameters, the algorithm also allows a determination of the
spatial response function for the observations. This is an important
improvement over algorithms which either rely on theoretical leakage
matrix calculations, or use many extra free parameters to model the
features due to spatial leakage. Using intensity data obtained at
the South Pole, and velocity data from GONG and MDI, we show that 2-D
modeling allows significant increases in the precision of the measured
line profile parameters for peaks with low peak-to-background ratios.