sanchez-almeida

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Author name code: sanchez-almeida
ADS astronomy entries on 2022-09-14
author:"Sanchez Almeida, Jorge"

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Title: Discovery of Faint Double-peak Hα Emission in the Halo of
Low Redshift Galaxies
Authors: Sánchez Almeida, J.; Calhau, J.; Muñoz-Tuñón, C.;
González-Morán, A. L.; Rodríguez-Espinosa, J. M.
2022ApJ...934..100S Altcode: 2022arXiv220512782S
Aimed at the detection of cosmological gas being accreted onto
galaxies in the local universe, we examined the Hα emission in
the halo of 164 galaxies in the field of view of the Multi-Unit
Spectroscopic Explorer Wide survey (MUSE-Wide) with observable Hα
(redshift &lt;0.42). An exhaustive screening of the corresponding Hα
images led us to select 118 reliable Hα emitting gas clouds. The
signals are faint, with a surface brightness of ${10}^{-17.3\pm
0.3}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$
. Through statistical tests and other arguments, we ruled out that
they are created by instrumental artifacts, telluric line residuals,
or high-redshift interlopers. Around 38% of the time, the Hα line
profile shows a double peak with the drop in intensity at the rest frame
of the central galaxy, and with a typical peak-to-peak separation of
the order of ±200 km s-1. Most line emission clumps are
spatially unresolved. The mass of emitting gas is estimated to be
between 1 and 10-3 times the stellar mass of the central
galaxy. The signals are not isotropically distributed; their azimuth
tends to be aligned with the major axis of the corresponding galaxy. The
distances to the central galaxies are not random either. The counts
drop at a distance &gt;50 galaxy radii, which roughly corresponds to
the virial radius of the central galaxy. We explore several physical
scenarios to explain this Hα emission, among which accretion disks
around rogue intermediate-mass black holes fit the observations best.

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Title: The Principle of Maximum Entropy and the Distribution of Mass
in Galaxies
Authors: Sánchez Almeida, Jorge
2022Univ....8..214S Altcode: 2022arXiv220304150S
We do not have a final answer to the question of why galaxies choose
a particular internal mass distribution. Here we examine whether the
distribution is set by thermodynamic equilibrium (TE). Traditionally,
TE is discarded for a number of reasons including the inefficiency
of two-body collisions to thermalize the mass distribution in a
Hubble time, and the fact that the mass distribution maximizing the
classical Boltzmann–Gibbs entropy is unphysical. These arguments are
questionable. In particular, when the Tsallis entropy that describes
self-gravitating systems is used to define TE, the mass distributions
that result (i.e., the polytropes) are physically sensible. This work
spells out this and other arguments for TE and presents the polytropes
and their properties. It puts forward empirical evidence for the mass
distribution observed in galaxies to be consistent with polytropes. It
compares polytropes with Sérsic functions and it shows how the
DM halos resulting from cosmological numerical simulations become
polytropes when efficient collisions are allowed. It also discusses
pathways to thermalization bypassing two-body collisions. It finally
outlines future developments including deciphering whether or not DM
particles collide efficiently.

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Title: Polarity-reversal subduction zone initiation triggered by
buoyant plateau obstruction
Authors: Almeida, J.; Riel, N.; Rosas, F. M.; Duarte, J. C.; Schellart,
W. P.
2022E&PSL.57717195A Altcode:
Oceanic lithosphere worldwide is younger than ca. 200 Myr, suggesting
that it must have been globally recycled by the recurrent formation
of new subduction zones since the existence of subduction on
Earth. However, postulated subduction zone initiation processes
remain difficult to explain in many cases, and the specific geodynamic
conditions under which these might occur are still largely unknown. We
here use numerical models driven by the internal force balance of a
subduction system to better understand the (geo)dynamics governing
(intra-oceanic) polarity-reversal subduction zone initiation. This
initiation mode assumes that the birth of a new subduction zone could be
triggered by buoyant plateau-obstruction of a pre-existent one dipping
in the opposite direction. Our work provides a new insight on the key
geodynamic conditions governing this type of subduction zone initiation
and discusses their general compliance with known natural examples.

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Title: VizieR Online Data Catalog: MaNGA; parameters of 668 galaxies
(Sanchez-Menguiano+, 2020)
Authors: Sanchez-Menguiano, L.; Almeida, J. S.; Munoz-Tunon, C.;
Sanchez, S. F.
2022yCat..19030052S Altcode:
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is
an ongoing part of the fourth-generation Sloan Digital Sky Survey
(SDSS-IV). The data were collected using the BOSS spectrographs mounted
on the Sloan 2.5m telescope at Apache Point Observatory. The field of
view (FoV) of the instrument varies from 125 to 325 in diameter for the
five different hexagonal configurations displayed by the 17 simultaneous
bundles of fibers. The covered wavelength range spans 3600-10300Å,
with a nominal resolution of R~2100 at 6000Å. (1 data file).

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Title: Physically Motivated Fit to Mass Surface Density Profiles
Observed in Galaxies
Authors: Sánchez Almeida, Jorge; Trujillo, Ignacio; Plastino, Angel R.
2021ApJ...921..125S Altcode: 2021arXiv210902615S
Polytropes have gained renewed interest because they account for several
seemingly disconnected observational properties of galaxies. Here
we study whether polytropes are also able to explain the stellar
mass distribution within galaxies. We develop a code to fit surface
density profiles using polytropes projected in the plane of the sky
(propols). Sérsic profiles are known to be good proxies for the global
shapes of galaxies and we find that, ignoring central cores, propols,
and Sérsic profiles are indistinguishable within observational errors
(within 5% over five orders of magnitude in surface density). The
range of physically meaningful polytropes yields Sérsic indexes
between 0.4 and 6. The code has been systematically applied to ~750
galaxies with carefully measured mass density profiles and including all
morphological types and stellar masses ( $7\lt {\rm{log}}[{M}_{\star
}/{{\rm{M}}}_{\odot }]\lt 12$ ). The propol fits are systematically
better than Sérsic profiles when ${\rm{log}}({M}_{\star
}/{{\rm{M}}}_{\odot })\lesssim 9$ and systematically worse when
${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\gtrsim 10$ . Although
with large scatter, the observed polytropic indexes increase with
increasing mass and tend to cluster around m = 5. For the most massive
galaxies, propols are very good at reproducing their central parts,
but they do not handle well cores and outskirts overall. Polytropes
are self-gravitating systems in thermal meta-equilibrium as defined by
the Tsallis entropy. Thus, the above results are compatible with the
principle of maximum Tsallis entropy dictating the internal structure
in dwarf galaxies and in the central region of massive galaxies.

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Title: The Mass-Metallicity Relation at z 1-2 and Its Dependence
on the Star Formation Rate
Authors: Henry, Alaina; Rafelski, Marc; Sunnquist, Ben; Pirzkal,
Norbert; Pacifici, Camilla; Atek, Hakim; Bagley, Micaela; Baronchelli,
Ivano; Barro, Guillermo; Bunker, Andrew J.; Colbert, James; Dai,
Y. Sophia; Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Finkelstein,
Steven; Kocevski, Dale; Koekemoer, Anton; Malkan, Matthew; Martin,
Crystal L.; Mehta, Vihang; Pahl, Anthony; Papovich, Casey; Rutkowski,
Michael; Sánchez Almeida, Jorge; Scarlata, Claudia; Snyder, Gregory;
Teplitz, Harry
2021ApJ...919..143H Altcode: 2021arXiv210700672H
We present a new measurement of the gas-phase mass-metallicity relation
(MZR) and its dependence on star formation rates (SFRs) at 1.3 &lt; z
&lt; 2.3. Our sample comprises 1056 galaxies with a mean redshift of z
= 1.9, identified from the Hubble Space Telescope Wide Field Camera 3
(WFC3) grism spectroscopy in the Cosmic Assembly Near-infrared Deep
Extragalactic Survey and the WFC3 Infrared Spectroscopic Parallel
Survey. This sample is four times larger than previous metallicity
surveys at z ~ 2 and reaches an order of magnitude lower in stellar
mass (108 M⊙). Using stacked spectra, we find
that the MZR evolves by 0.3 dex relative to z ~ 0.1. Additionally,
we identify a subset of 49 galaxies with high signal-to-noise (S/N)
spectra and redshifts between 1.3 &lt; z &lt; 1.5, where Hα emission
is observed along with [O III] and [O II]. With accurate measurements of
SFR in these objects, we confirm the existence of a mass-metallicity-SFR
(M-Z-SFR) relation at high redshifts. These galaxies show systematic
differences from the local M-Z-SFR relation, which vary depending on
the adopted measurement of the local relation. However, it remains
difficult to ascertain whether these differences could be due to
redshift evolution, as the local M-Z-SFR relation is poorly constrained
at the masses and SFRs of our sample. Lastly, we reproduced our sample
selection in the IllustrisTNG hydrodynamical simulation, demonstrating
that our line flux limit lowers the normalization of the simulated MZR
by 0.2 dex. We show that the M-Z-SFR relation in IllustrisTNG has an
SFR dependence that is too steep by a factor of around 3.

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Title: History of the gas fuelling star formation in EAGLE galaxies
Authors: Scholz-Díaz, Laura; Sánchez Almeida, Jorge; Dalla Vecchia,
Claudio
2021MNRAS.505.4655S Altcode: 2021arXiv210602478S
Theory predicts that cosmological gas accretion plays a fundamental role
fuelling star formation in galaxies. However, a detailed description
of the accretion process to be used when interpreting observations is
still lacking. Using the state-of-the-art cosmological hydrodynamical
simulation EAGLE, we work out the chemical inhomogeneities arising in
the disc of galaxies due to the randomness of the accretion process. In
low-mass systems and outskirts of massive galaxies, low metallicity
regions are associated with enhanced star-formation, a trend that
reverses in the centres of massive galaxies. These predictions agree
with the relation between surface density of star formation rate
and metallicity observed in the local spiral galaxies from the MaNGA
survey. Then, we analyse the origin of the gas that produce stars at
two key epochs, z ≃ 0 and z ≃ 2. The main contribution comes from
gas already in the galaxy about 1 Gyr before stars are formed, with a
share from external gas that is larger at high redshift. The accreted
gas may come from major and minor mergers, but also as gravitationally
unbound gas and from mergers with dark galaxies (i.e. haloes where more
than 95 per cent of the baryon mass is in gas). We give the relative
contribution of these sources of gas as a function of stellar mass
(8 ≤ log [M⋆/M⊙] ≤ 11). Even at z =
0, some low-mass galaxies form a significant fraction of their total
stellar mass during the last Gyr from mergers with dark galaxies.

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Title: Extreme emission-line galaxies in SDSS - I. Empirical and
model-based calibrations of chemical abundances
Authors: Pérez-Montero, E.; Amorín, R.; Sánchez Almeida, J.;
Vílchez, J. M.; García-Benito, R.; Kehrig, C.
2021MNRAS.504.1237P Altcode: 2021arXiv210310464P; 2021MNRAS.tmp..891P
Local star-forming galaxies show properties that are thought to differ
from galaxies in the early Universe. Among them, the ionizing stellar
populations and the gas geometry make the recipes designed to derive
chemical abundances from nebular emission lines to differ from those
calibrated in the Local Universe. A sample of 1969 extreme emission-line
galaxies (EELGs) at a redshift 0 ≲ z ≲ 0.49, selected from the
Sloan Digital Sky Survey (SDSS) to be local analogues of high-redshift
galaxies, was used to analyse their most prominent emission lines
and to derive total oxygen abundances and nitrogen-to-oxygen ratios
following the direct method in the ranges 7.7 &lt; 12 + log(O/H)
&lt; 8.6 and -1.8 &lt; log(N/O) &lt; -0.8. They allow us to obtain
new empirically calibrated strong-line methods and to evaluate other
recipes based on photoionization models that can be later used for
a chemical analysis of actively star-forming galaxies in very early
stages of galaxy evolution. Our new relations are in agreement with
others found for smaller samples of objects at higher redshifts. When
compared with other relations calibrated in the local Universe, they
differ when the employed strong-line ratio depends on the hardness of
the ionizing radiation, such as O32 or Ne3O2, but they do not when the
main dependence is on the ionization parameter, such as S23. In the
case of strong-line ratios depending on [N II] lines, the derivation
of O/H becomes very uncertain due to the very high N/O values derived
in this sample, above all in the low-metallicity regime. Finally, we
adapt the Bayesian-like code H II-CHI-MISTRY for the conditions found
in this kind of galaxies and we prove that it can be used to derive
within errors both O/H and N/O, in consistency with the direct method.

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Title: Numerical simulations of dark matter haloes produce polytropic
central cores when reaching thermodynamic equilibrium
Authors: Sánchez Almeida, Jorge; Trujillo, Ignacio
2021MNRAS.504.2832S Altcode: 2021arXiv210408055S; 2021MNRAS.tmp.1088S; 2021MNRAS.tmp.1088A
Self-gravitating astronomical objects often show a central plateau in
the density profile (core) whose physical origin is hotly debated. Cores
are theoretically expected in N-body systems of maximum entropy,
however, they are not present in the canonical N-body numerical
simulations of cold dark matter (CDM). Our work shows that despite
this apparent contradiction between theory and numerical simulations,
they are fully consistent. Simply put, cores are characteristic of
systems in thermodynamic equilibrium, but thermalizing collisions
are purposely suppressed in CDM simulations. When collisions are
allowed, N-body numerical simulations develop cored density profiles,
in perfect agreement with the theoretical expectation. We compare
theory and two types of numerical simulations: (1) when DM particles
are self-interacting (SIDM) with enough cross-section, then the
effective two-body relaxation time-scale becomes shorter than the
Hubble time resulting in cored DM haloes. The haloes thus obtained,
with masses from dwarf galaxies to galaxy clusters, collapse to a
single shape after normalization, and this shape agrees with the
polytropic density profile theoretically expected. (2) The inner
radii in canonical N-body numerical simulations are always discarded
because the use of finite-mass DM particles artificially increases
the two-body collision rate. We show that the discarded radii develop
cores which are larger than the employed numerical softening and have
polytropic shape independently of halo mass. Our work suggests that
the presence of cores in simulated (or observed) density profiles can
used as evidence for systems in thermodynamic equilibrium.

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Title: Models source code: CE-QUAL-W2 v3.6, FLake (windows version
1.0), Hostetler and ANN (momentum alg.) - Modeling reservoir surface
temperatures for regional and global climate models
Authors: Almeida
2021zndo...4803480A Altcode:
The source code of the following models: CE-QUAL-W2 V3.6 (Cole
and Wells, 2008); FLake model - windows pre-compiled version 1.0
(Mironov et al., 2010); Artificial neural network (Momentum algorithm)
and Hostetler model (Hostetler and Bartlein, 1990), was used during
the development of the study titled “Modeling reservoir surface
temperatures for regional and global climate models: a multi-model
study on the inflow and level variation effects”.

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Title: Evidence for the Accretion of Gas in Star-forming Galaxies:
High N/O Abundances in Regions of Anomalously Low Metallicity
Authors: Luo, Yuanze; Heckman, Timothy; Hwang, Hsiang-Chih;
Rowlands, Kate; Sánchez-Menguiano, Laura; Riffel, Rogério; Bizyaev,
Dmitry; Andrews, Brett H.; Fernández-Trincado, José G.; Drory,
Niv; Sánchez Almeida, Jorge; Maiolino, Roberto; Lane, Richard R.;
Argudo-Fernández, Maria
2021ApJ...908..183L Altcode: 2020arXiv201204073L
While all models for the evolution of galaxies require the accretion
of gas to sustain their growth via on-going star formation, it has
proven difficult to directly detect this inflowing material. In this
paper we use data of nearby star-forming galaxies in the SDSS IV
Mapping Nearby Galaxies at Apache Point Observatory survey to search
for evidence of accretion imprinted in the chemical composition of
the interstellar medium. We measure both the O/H and N/O abundance
ratios in regions previously identified as having anomalously low
values of O/H. We show that the unusual locations of these regions in
the N/O versus O/H plane indicate that they have been created through
the mixing of disk gas having higher metallicity with accreted gas
having lower metallicity. Taken together with previous analysis on
these anomalously low-metallicity regions, these results imply that
accretion of metal-poor gas can probably sustain star formation in
present-day late-type galaxies.

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Title: VizieR Online Data Catalog: SFR &amp; gas-phase metallicity
in MaNGA gal. (Sanchez-Menguiano+, 2019)
Authors: Sanchez-Menguiano, L.; Sanchez Almeida, J.; Munoz-Tunon,
C.; Sanchez, S. F.; Filho, M.; Hwang, H. -C.; Drory, N.
2021yCat..18820009S Altcode:
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA; Bundy+
2015ApJ...798....7B) is an ongoing survey developed as part of the
SDSS-IV project. The observations are conducted on the basis of an
integral field unit (IFU) fiber system feeding the BOSS spectrographs on
the Sloan 2.5m telescope at Apache Point Observatory, New Mexico. The
field of view (FoV) of the instrument varies from 12.5" to 32.5" in
diameter. The spectrographs provide wavelength coverage from 3600 to
10300Å, with a nominal resolution of R~2100 at 6000Å. In this
study, the analyzed sample is extracted from the internal release MaNGA
Product Launches 7 (MPL-7) comprising 4688 galaxies. (1 data file).

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Title: VizieR Online Data Catalog: 3D shapes of extremely metal-poor
galaxies (Putko+, 2019)
Authors: Putko, J.; Sanchez Almeida, J.; Munoz-Tunon, C.; Asensio
Ramos, A.; Elmegreen, B. G.; Elmegreen, D. M.
2021yCat..18830010P Altcode:
The galaxies used in our inference of 3D shape are from Sanchez Almeida+
(2016, J/ApJ/819/110), who mined the spectroscopic catalog of the Sloan
Digital Sky Survey (SDSS) in producing the largest published sample
(195) of extremely metal-poor galaxies (XMPs) from a single survey. (1 data file).

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Title: Direct multielement determination of Cd, Pb, Fe, and Mn in
ground coffee samples using energy dispersive X-ray fluorescence
spectrometry
Authors: Almeida, Jorge S.; Meira, Lucilia A.; Oliveira, Maiara S.;
Teixeira, Leonardo S. G.
2021XRS....50....2A Altcode:
No abstract at ADS

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Title: Local and Global Gas Metallicity versus Stellar Age Relation
in MaNGA Galaxies
Authors: Sánchez-Menguiano, Laura; Sánchez Almeida, Jorge;
Muñoz-Tuñón, Casiana; Sánchez, Sebastián F.
2020ApJ...903...52S Altcode: 2020arXiv200914211S
The search for new global scaling relations linking the physical
properties of galaxies has a fundamental interest. Furthermore, their
recovery from spatially resolved relations has been in the spotlight
of integral field spectroscopy (IFS). In this study, we investigate
the existence of global and local relations between stellar age
(Age⋆) and gas-phase metallicity (Zg). To
this aim, we analyze IFS data for a sample of 736 star-forming disk
galaxies from the MaNGA survey. We report a positive correlation between
the global Zg and D(4000) (an indicator of stellar age),
with a slope that decreases with increasing galaxy mass. Locally, a
similar trend is found when analyzing the Zg and D(4000)
of the star-forming regions, as well as the residuals resulting
from removing the radial gradients of both parameters. The local
laws have systematically smaller slopes than the global one. We
ascribe this difference to random errors that cause the true slope
of the Age⋆-Zg relation to be systematically
underestimated when performing a least-squares fitting. The explored
relation is intimately linked with the already known relation between
gas metallicity and star formation rate at fixed mass, both presenting
a common physical origin.

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Title: The principle of maximum entropy explains the cores observed
in the mass distribution of dwarf galaxies
Authors: Sánchez Almeida, Jorge; Trujillo, Ignacio; Plastino,
Angel Ricardo
2020A&A...642L..14S Altcode: 2020arXiv200908994S
Cold dark matter (CDM) simulations predict a central cusp in the
mass distribution of galaxies. This prediction is in stark contrast
with observations of dwarf galaxies that show a central plateau or
"core" in their density distribution. The proposed solutions to
this core-cusp problem can be classified into two types. One invokes
feedback mechanisms produced by the baryonic component of the galaxies
and the other assumes that the properties of the dark matter particle
depart from the CDM hypothesis. Here we propose an alternative yet
complementary explanation. We argue that cores are unavoidable in
the self-gravitating systems of maximum entropy that result from
non-extensive statistical mechanics. Their structure follows from
the Tsallis entropy, which is attributed to systems with long-range
interactions. Strikingly, the mass density profiles predicted by
such thermodynamic equilibrium match the observed cores without any
adjustment or tuning. Thus, the principle of maximum Tsallis entropy
explains the presence of cores in dwarf galaxies.

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Title: White Paper on MAAT@GTC
Authors: Prada, Francisco; Content, Robert; Goobar, Ariel; Izzo,
Luca; Pérez, Enrique; Agnello, Adriano; del Burgo, Carlos; Dhillon,
Vik; Diego, José M.; Galbany, Lluis; García-Rojas, Jorge; Jones,
David; Lawrence, Jon; Martín, Eduardo; Mediavilla, Evencio; Ángeles
Pérez García, M.; Sánchez Almeida, Jorge; Acosta Pulido, José A.;
López-Sánchez, Angel R.; Arribas, Santiago; Carrera, Francisco J.;
Corral, Amalia; Domínguez, Inmaculada; Mateos, Silvia; Martínez
Nuñez, Silvia; Villaver, Eva; Rosa Zapatero Osorio, María; Albertus,
Conrado; Arrigoni Battaia, Fabrizio; Barrado, David; Bejar, Víctor
J. S.; Boffin, Henri M. J.; Bouy, Herve; Burgasser, Adam; Esteban,
Cesar; Lodieu, Nicolas; Morales Calderón, María; Pérez Garrido,
Antonio; Rodríguez Gil, Pablo; Sagués Carracedo, Ana; Santander
García, Miguel; Solano, Enrique; Torres, Manuel A. P.; Wesson, Roger
2020arXiv200701603P Altcode:
MAAT is proposed as a visitor mirror-slicer optical system that
will allow the OSIRIS spectrograph on the 10.4-m Gran telescopio
CANARIAS (GTC) the capability to perform Integral Field Spectroscopy
(IFS) over a seeing-limited FoV 14.20”x10” with a slice width of
0.303”. MAAT@GTC will enhance the resolution power of OSIRIS by 1.6
times as compared to its 0.6” wide long-slit. All the eleven OSIRIS
grisms and volume-phase holographic gratings will be available to
provide broad spectral coverage with moderate resolution (R=600 up to
4100) in the 3600 - 10000 Å wavelength range. MAAT unique observing
capabilities will broaden its use to the needs of the GTC community
to unveil the nature of most striking phenomena in the universe well
beyond time-domain astronomy. The GTC equipped with OSIRIS+MAAT will
also play a fundamental role in synergy with other facilities, some
of them operating on the northern ORM at La Palma. This White Paper
presents the different aspects of MAAT@GTC - including scientific and
technical specifications, outstanding science cases, and an outline
of the instrument concept.

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Title: Analysis of the galaxy size versus stellar mass relation
Authors: Sánchez Almeida, J.
2020MNRAS.495...78S Altcode: 2020arXiv200409433S; 2020MNRAS.tmp.1268S
The scatter in the galaxy size versus stellar mass (M⋆)
relation gets largely reduced when, rather than the half-mass radius
Re, the size at a fixed surface density is used. Here, we
address why this happens. We show how a reduction is to be expected
because any two galaxies with the same M⋆ have at least
one radius with identical surface density, where the galaxies have
identical size. However, the reason why the scatter is reduced to
the observed level is not trivial, and we pin it down to the galaxy
surface density profiles approximately following Sersic profiles
with their Re and Sersic index (n) anticorrelated
(I.e. given M⋆, n increases when Re
decreases). Our analytical results describe very well the behaviour
of the observed galaxies as portrayed in the NASA Sloan Atlas (NSA),
which contains more than half a million local objects with 7 &lt;
log (M⋆/M⊙) &lt; 11.5. The comparison with
NSA galaxies also allows us to find the optimal values for the mass
surface density ( $2.4_{-0.9}^{+1.3}\, M_\odot \, {\rm pc}^{-2}$ ) and
surface brightness (r band $24.7\pm 0.5\, {\rm mag\, arcsec^{-2}}$ )
that minimize the scatter, although the actual values depend somehow
on the subset of NSA galaxies used for optimization. The physical
reason for the existence of optimal values is unknown but, as Trujillo,
Chamba &amp; Knapen (2020) point out, they are close to the gas surface
density threshold to form stars and thus may trace the physical end of
a galaxy. Our NSA-based size-mass relation agrees with theirs on the
slope as well as on the magnitude of the scatter. As a by-product of
the narrowness of the size-mass relation (only 0.06 dex), we propose
to use the size of a galaxy to measure its stellar mass. In terms of
observing time, it is not more demanding than the usual photometric
techniques and may present practical advantages in particular cases.

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Title: Triaxiality can Explain the Alleged Dark Matter Deficiency
in some Dwarf Galaxies
Authors: Sánchez Almeida, J.; Filho, M.
2019RNAAS...3..191S Altcode: 2019arXiv191205268S
Dark Matter (DM) is an ingredient essential to the current cosmological
concordance model. It provides the gravitational pull needed for the
baryons to form galaxies. Therefore, the existence of galaxies without
DM is both disquieting and extremely interesting. Guo et al. recently
presented "further evidence for a population of DM-deficient dwarf
galaxies", however, their analysis bypasses the triaxiality of the dwarf
galaxies. We carry out a Monte Carlo simulation showing how triaxiality
must be considered to measure dynamical masses from projected axial
ratios, calling into question the evidence for a population of
DM-deficient dwarf galaxies. Such a population may consist of normal
almost face-on HI disks with their inclination overestimated.

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Title: A contribution of star-forming clumps and accreting satellites
to the mass assembly of z ∼ 2 galaxies
Authors: Zanella, A.; Le Floc'h, E.; Harrison, C. M.; Daddi, E.;
Bernhard, E.; Gobat, R.; Strazzullo, V.; Valentino, F.; Cibinel, A.;
Sánchez Almeida, J.; Kohandel, M.; Fensch, J.; Behrendt, M.; Burkert,
A.; Onodera, M.; Bournaud, F.; Scholtz, J.
2019MNRAS.489.2792Z Altcode: 2019arXiv190712136Z; 2019MNRAS.tmp.2058Z
We investigate the contribution of clumps and satellites to the
galaxy mass assembly. We analysed spatially resolved HubbleSpace
Telescope observations (imaging and slitless spectroscopy) of 53
star-forming galaxies at z ∼ 1-3. We created continuum and emission
line maps and pinpointed residual `blobs' detected after subtracting
the galaxy disc. Those were separated into compact (unresolved)
and extended (resolved) components. Extended components have sizes
∼2 kpc and comparable stellar mass and age as the galaxy discs,
whereas the compact components are 1.5 dex less massive and 0.4
dex younger than the discs. Furthermore, the extended blobs are
typically found at larger distances from the galaxy barycentre than
the compact ones. Prompted by these observations and by the comparison
with simulations, we suggest that compact blobs are in situ formed
clumps, whereas the extended ones are accreting satellites. Clumps and
satellites enclose, respectively, ∼20 per cent and ≲80 per cent
of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its
star formation rate. Considering the compact blobs, we statistically
estimated that massive clumps (M⋆ ≳ 109
M⊙) have lifetimes of ∼650 Myr, and the less massive
ones (108 &lt; M⋆ &lt; 109
M⊙) of ∼145 Myr. This supports simulations predicting
long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent
(13 per cent) of our sample galaxies are undergoing single (multiple)
merger(s), they have a projected separation ≲10 kpc, and the typical
mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1),
in agreement with literature results for close pair galaxies.

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Title: Inferring the 3D Shapes of Extremely Metal-poor Galaxies from
Sets of Projected Shapes
Authors: Putko, J.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Asensio
Ramos, A.; Elmegreen, B. G.; Elmegreen, D. M.
2019ApJ...883...10P Altcode: 2019arXiv190710496P
The three-dimensional (3D) shape of a galaxy inevitably is tied to how
it has formed and evolved and to its dark matter halo. Local extremely
metal-poor galaxies (XMPs; defined as having an average gas-phase
metallicity &lt;0.1 solar) are important objects for understanding
galaxy evolution largely because they appear to be caught in the act
of accreting gas from the cosmic web, and their 3D shape may reflect
this. Here, we report on the 3D shape of XMPs as inferred from their
observed projected minor-to-major axial ratios using a hierarchical
Bayesian inference model, which determines the likely shape and
orientation of each galaxy, while simultaneously inferring the average
shape and dispersion. We selected a sample of 149 XMPs and divided
it into three subsamples according to physical size and found that
(1) the stellar component of XMPs of all sizes tends to be triaxial,
with an intermediate axis ≈0.7 times the longest axis and that (2)
smaller XMPs tend to be relatively thicker, with the shortest axis going
from ≈0.15 times the longest axis for the large galaxies to ≈0.4 for
the small galaxies. We provide the inferred 3D shape and inclination of
the individual XMPs in electronic format. We show that our results for
the intermediate axis are not clouded by a selection effect against
face-on XMPs. We discuss how an intermediate axis significantly
smaller than the longest axis may be produced by several mechanisms,
including lopsided gas accretion, non-axisymmetric star formation, or
coupling with an elongated dark matter halo. Large relative thickness
may reflect slow rotation, stellar feedback, or recent gas accretion.

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Title: Characterizing the Local Relation between Star Formation Rate
and Gas-phase Metallicity in MaNGA Spiral Galaxies
Authors: Sánchez-Menguiano, Laura; Sánchez Almeida, Jorge;
Muñoz-Tuñón, Casiana; Sánchez, Sebastián F.; Filho, Mercedes;
Hwang, Hsiang-Chih; Drory, Niv
2019ApJ...882....9S Altcode: 2019arXiv190403930S
The role of gas accretion in galaxy evolution is still a matter of
debate. The presence of inflows of metal-poor gas that trigger star
formation bursts of low metallicity has been proposed as an explanation
for the local anticorrelation between star formation rate (SFR) and
gas-phase metallicity (Z g ) found in the literature. In
the present study, we show how the anticorrelation is also present
as part of a diversified range of behaviors for a sample of more
than 700 nearby spiral galaxies from the SDSS-IV MaNGA survey. We
have characterized the local relation between SFR and Z g
 after subtracting the azimuthally averaged radial profiles
of both quantities. Of the analyzed galaxies, 60% display an SFR-Z
 g anticorrelation, with the remaining 40% showing no
correlation (19%) or positive correlation (21%). Applying a random
forest machine-learning algorithm, we find that the slope of the
correlation is mainly determined by the average gas-phase metallicity of
the galaxy. Galaxy mass, g - r colors, stellar age, and mass density
seem to play a less significant role. This result is supported by
the performed second-order polynomial regression analysis. Thus, the
local SFR-Z g slope varies with the average metallicity,
with the more metal-poor galaxies presenting the lowest slopes (i.e.,
the strongest SFR-Z g anticorrelations), and reversing the
relation for more metal-rich systems. Our results suggest that external
gas accretion fuels star formation in metal-poor galaxies, whereas in
metal-rich systems, the gas comes from previous star formation episodes.

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Title: Machine learning in APOGEE. Identification of stellar
populations through chemical abundances
Authors: Garcia-Dias, Rafael; Allende Prieto, Carlos; Sánchez Almeida,
Jorge; Alonso Palicio, Pedro
2019A&A...629A..34G Altcode: 2019arXiv190712796G
Context. The vast volume of data generated by modern astronomical
surveys offers test beds for the application of machine-learning. In
these exploratory applications, it is important to evaluate potential
existing tools and determine those that are optimal for extracting
scientific knowledge from the available observations. Aims: We
explore the possibility of using unsupervised clustering algorithms to
separate stellar populations with distinct chemical patterns. 
Methods: Star clusters are likely the most chemically homogeneous
populations in the Galaxy, and therefore any practical approach
to identifying distinct stellar populations should at least be
able to separate clusters from each other. We have applied eight
clustering algorithms combined with four dimensionality reduction
strategies to automatically distinguish stellar clusters using
chemical abundances of 13 elements. Our test-bed sample includes
18 stellar clusters with a total of 453 stars. Results: We
have applied statistical tests showing that some pairs of clusters
(e.g., NGC 2458-NGC 2420) are indistinguishable from each other
when chemical abundances from the Apache Point Galactic Evolution
Experiment (APOGEE) are used. However, for most clusters we are able
to automatically assign membership with metric scores similar to
previous works. The confusion level of the automatically selected
clusters is consistent with statistical tests that demonstrate the
impossibility of perfectly distinguishing all the clusters from each
other. These statistical tests and confusion levels establish a limit
for the prospect of blindly identifying stars born in the same cluster
based solely on chemical abundances. Conclusion. We find that some
of the algorithms we explored are capable of blindly identify stellar
populations with similar ages and chemical distributions in the APOGEE
data. Even though we are not able to fully separate the clusters
from each other, the main confusion arises from clusters with similar
ages. Because some stellar clusters are chemically indistinguishable,
our study supports the notion of extending weak chemical tagging that
involves families of clusters instead of individual clusters. The
list of stars is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/629/A34">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/629/A34</A>

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Title: Stellar content, planetary nebulae, and globular clusters of
[KKS2000]04 (NGC 1052-DF2)
Authors: Ruiz-Lara, T.; Trujillo, I.; Beasley, M. A.; Falcón-Barroso,
J.; Vazdekis, A.; Filho, M.; Monelli, M.; Román, J.; Sánchez
Almeida, J.
2019MNRAS.486.5670R Altcode: 2019MNRAS.tmp.1193R; 2019arXiv190309163R
[KKS2000]04 (NGC 1052-DF2) has become a controversial and well-studied
galaxy after the claims suggesting a lack of dark matter and the
presence of an anomalously bright globular cluster (GC) system around
it. A precise determination of its overall star formation history
(SFH) and a better characterization of its GC or planetary nebulae
(PNe) systems are crucial aspects to (i) understand its real nature, in
particular placing it within the family of ultra diffuse galaxies and
(ii) shed light on its possible formation, evolution, and survival in
the absence of dark matter. With this purpose we expand on the knowledge
of [KKS2000]04 from the analysis of OSIRIS@GTC spectroscopic data. On
the one hand, we claim the possible detection of two new PNe and confirm
membership of 5 GCs. On the other hand, we find that the stars shaping
[KKS2000]04 are intermediate-age to old (90 per cent of its stellar mass
older than 5 Gyr, average age of 8.7 ± 0.7 Gyr) and metal-poor ([M/H]
∼ -1.18 ± 0.05), in general agreement with previous results. We do
not find any clear hints of significant changes in its stellar content
with radius. In addition, the possibility of [KKS2000]04 being a tidal
dwarf galaxy with no dark matter is highly disfavoured.

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Title: VizieR Online Data Catalog: APOGEE stars members of 35 star
clusters (Garcia-Dias+, 2019)
Authors: Garcia-Dias, R.; Allende Prieto, C.; Sanchez Almeida, J.;
Alonso Palicio, P.
2019yCat..36290034G Altcode:
Initial list of stars used in the article. (1 data file).

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Title: The Fundamental Metallicity Relation Emerges from the Local
Anti-correlation between Star Formation Rate and Gas-phase Metallicity
that Exists in Disk Galaxies
Authors: Sánchez Almeida, J.; Sánchez-Menguiano, L.
2019ApJ...878L...6S Altcode: 2019arXiv190505826S
The fundamental metallicity relation (FMR) states that galaxies of
the same stellar mass but larger star formation rate (SFR) tend
to have smaller gas-phase metallicity (&lt; {Z}g&gt;
). It is thought to be fundamental because it naturally arises from
the stochastic feeding of star formation from external metal-poor
gas accretion, a process extremely elusive to observe but essential
according the cosmological simulations of galaxy formation. In this
Letter, we show how the FMR emerges from the local anti-correlation
between SFR surface density and Z g recently observed to
exist in disk galaxies. We analytically derive the global FMR from the
local law, and then show that both relations agree quantitatively when
considering the star-forming galaxies of the Mapping Nearby Galaxies
at APO (MaNGA) survey. Thus, understanding the FMR becomes equivalent
to understanding the origin of the anti-correlation between SFR and
metallicity followed by the set of star-forming regions of any typical
galaxy. The correspondence between local and global laws is not specific
to the FMR, so that a number of local relations should exist that are
associated with known global relations.

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Title: Accretion-Triggered Starbursts in Tadpole Galaxies
Authors: Elmegreen, Bruce; Elmegreen, Debra M.; Andersen, Morten;
Gallagher, John S.; Kotulla, Ralf; Munoz-Tunon, Casiana; Rafelski,
Marc; Sanchez Almeida, Jorge
2019hst..prop15860E Altcode:
Gas accretion onto galaxies is believed to drive the average star
formation rate. However, there are few observations of this accretion
for late-type galaxies, especially impacting the disk or triggering
a starburst in the disk. Here we propose optical and Halpha imaging
of four metal-poor tadpole galaxies that have local metallicity drops
by a factor of 5 in relatively large off-center starburst clumps. The
bursts and the unusual metallicities suggest recent accretion of large
gas masses. Photometry plus SED modeling will determine the ages,
masses, and luminosity distributions of the star clusters and star
complexes in the bursts. Halpha will reveal ionization rates along
with feedback and possible accretion structures. The sample represents
the nearest low-mass galaxies that have high-resolution metallicity
variations and single dominant starburst clumps. The results have
broad implications for understanding the mass-metallicity relation for
galaxies, the formation and feedback of stars and massive clusters in
accretion-induced starbursts, and the origin of metal-poor globular
clusters in the early universe. Only HST has the combination of angular
resolution and sensitivity to carry out this program.

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Title: A distance of 13 Mpc resolves the claimed anomalies of the
galaxy lacking dark matter
Authors: Trujillo, Ignacio; Beasley, Michael A.; Borlaff, Alejandro;
Carrasco, Eleazar R.; Di Cintio, Arianna; Filho, Mercedes; Monelli,
Matteo; Montes, Mireia; Román, Javier; Ruiz-Lara, Tomás; Sánchez
Almeida, Jorge; Valls-Gabaud, David; Vazdekis, Alexandre
2019MNRAS.486.1192T Altcode: 2019MNRAS.tmp..733T; 2018arXiv180610141T
The claimed detection of a diffuse galaxy lacking dark matter represents
a possible challenge to our understanding of the properties of these
galaxies and galaxy formation in general. The galaxy, already identified
in photographic plates taken in the summer of 1976 at the UK 48-in
Schmidt telescope, presents normal distance-independent properties
(e.g. colour, velocity dispersion of its globular clusters). However,
distance-dependent quantities are at odds with those of other similar
galaxies, namely the luminosity function and sizes of its globular
clusters, mass-to-light ratio, and dark matter content. Here we
carry out a careful analysis of all extant data and show that they
consistently indicate a much shorter distance (13 Mpc) than previously
indicated (20 Mpc). With this revised distance, the galaxy appears
to be a rather ordinary low surface brightness galaxy (Re
= 1.4 ± 0.1 kpc; M⋆ = 6.0 ± 3.6 × 107
M⊙) with plenty of room for dark matter (the fraction
of dark matter inside the half-mass radius is &gt;75 per cent and
Mhalo/M⋆&gt;20) corresponding to a minimum halo
mass &gt;109 M⊙. At 13 Mpc, the luminosity
and structural properties of the globular clusters around the object
are the same as those found in other galaxies.

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Title: Global correlations between the radio continuum, infrared,
and CO emissions in dwarf galaxies
Authors: Filho, Mercedes E.; Tabatabaei, Fatemeh S.; Sánchez Almeida,
Jorge; Muñoz-Tuñón, Casiana; Elmegreen, Bruce G.
2019MNRAS.484..543F Altcode: 2018arXiv181106577F; 2018MNRAS.tmp.3083F
Correlations between the radio continuum, infrared, and CO emissions are
known to exist for several types of galaxies and across several orders
of magnitude. However, the low-mass, low-luminosity, and low-metallicity
regime of these correlations is not well known. A sample of metal-rich
and metal-poor dwarf galaxies from the literature has been assembled to
explore this extreme regime. The results demonstrate that the properties
of dwarf galaxies are not simple extensions of those of more massive
galaxies; the different correlations reflect different star-forming
conditions and different coupling between the star formation and the
various quantities. It is found that dwarfs show increasingly weaker CO
and infrared emissions for their luminosity, as expected for galaxies
with a low dust content, slower reaction rates, and a hard ionizing
radiation field. In the higher-luminosity dwarf regime [L_{1.4 GHz}
≳ 10^{27} W, where L_{1.4 GHz} ∼eq 10^{29} W for a Milky Way star
formation rate (SFR) of ≃1 M⊙ yr-1], the total
and non-thermal radio continuum emissions appear to adequately trace
the SFR. A breakdown of the dependence of the (H α-based) thermal,
non-thermal, and, hence, total radio continuum emission on SFR occurs
below L_{1.4 GHz} ∼eq 10^{27} W, resulting in a steepening or downturn
of the relations at extreme low luminosity. Below LFIR ≃
1036 W ≃ 3 × 109 L⊙, the infrared
emission ceases to adequately trace the SFR. A lack of a correlation
between the magnetic field strength and the SFR in low SFR dwarfs
suggests a breakdown of the equipartition assumption. As extremely
metal-poor dwarfs mostly populate the low SFR and low-luminosity regime,
they stand out in their infrared, radio continuum, and CO properties.

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Title: Anomalously Low-metallicity Regions in MaNGA Star-forming
Galaxies: Accretion Caught in Action?
Authors: Hwang, Hsiang-Chih; Barrera-Ballesteros, Jorge K.; Heckman,
Timothy M.; Rowlands, Kate; Lin, Lihwai; Rodriguez-Gomez, Vicente;
Pan, Hsi-An; Hsieh, Bau-Ching; Sánchez, Sebastian; Bizyaev, Dmitry;
Sánchez Almeida, Jorge; Thilker, David A.; Lotz, Jennifer M.; Jones,
Amy; Nair, Preethi; Andrews, Brett H.; Drory, Niv
2019ApJ...872..144H Altcode: 2018arXiv181204614H
We use data from 1222 late-type star-forming galaxies in the SDSS IV
Mapping Nearby Galaxies at Apache Point Observatory survey to identify
regions in which the gas-phase metallicity is anomalously low compared
to expectations from the tight empirical relation between metallicity
and stellar surface mass density at a given stellar mass. We find
anomalously low-metallicity (ALM) gas in 10% of the star-forming
spaxels and in 25% of the galaxies in the sample. The incidence rate
of ALM gas increases strongly with both global and local measures
of the specific star formation rate and is higher in lower mass
galaxies and in the outer regions of galaxies. The incidence rate is
also significantly higher in morphologically disturbed galaxies. We
estimate that the lifetimes of the ALM regions are a few hundred Myr. We
argue that the ALM gas has been delivered to its present location by
a combination of interactions, mergers, and accretion from the halo,
and that this infusion of gas stimulates star formation. Given the
estimated lifetime and duty cycle of such events, we estimate that
the time-averaged accretion rate of ALM gas is similar to the star
formation rate in late-type galaxies over the mass range {M}*
∼ {10}9-1010 M ⊙.

---------------------------------------------------------
Title: A Headless Tadpole Galaxy: The High Gas-phase Metallicity of
the Ultra-diffuse Galaxy UGC 2162
Authors: Sánchez Almeida, J.; Olmo-García, A.; Elmegreen, B. G.;
Elmegreen, D. M.; Filho, M.; Muñoz-Tuñón, C.; Pérez-Montero, E.;
Román, J.
2018ApJ...869...40S Altcode: 2018arXiv181008453S
The cosmological numerical simulations tell us that accretion
of external metal-poor gas drives star formation (SF) in galaxy
disks. One the best pieces of observational evidence supporting this
prediction is the existence of low-metallicity star-forming regions
in relatively high-metallicity host galaxies. The SF is thought to
be fed by metal-poor gas recently accreted. Since the gas accretion
is stochastic, there should be galaxies with all the properties of a
host but without the low-metallicity starburst. These galaxies have
not been identified yet. The exception may be UGC 2162, a nearby
ultra-diffuse galaxy (UDG) that combines low surface brightness and
relatively high metallicity. We confirm the high metallicity of UGC
2162 (12+{log}({{O}}/{{H}})={8.52}-0.24+0.27)
using spectra taken with the 10 m GTC telescope. UGC 2162 has the
stellar mass, metallicity, and star formation rate surface density
expected for a host galaxy in between outbursts. This fact suggests a
physical connection between some UDGs and metal-poor galaxies, which may
be the same type of object in a different phase of the SF cycle. UGC
2162 is a high-metallicity outlier of the mass-metallicity relation,
a property shared by the few UDGs with known gas-phase metallicity.

---------------------------------------------------------
Title: An unusual transient in the extremely metal-poor Galaxy SDSS
J094332.35+332657.6 (Leoncino Dwarf)
Authors: Filho, Mercedes E.; Sánchez Almeida, J.
2018MNRAS.478.2541F Altcode: 2018arXiv180411166F; 2018MNRAS.tmp.1073F
We have serendipitously discovered that Leoncino Dwarf, an ultrafaint,
low-metallicity record-holder dwarf galaxy, may have hosted a transient
source, and possibly exhibited a change in morphology, a shift in the
centre of brightness, and peak variability of the main (host) source
in images taken approximately 40 yr apart; it is highly likely that
these phenomena are related. Scenarios involving a Solar System object,
a stellar cluster, dust enshrouding, and accretion variability have been
considered, and discarded, as the origin of the transient. Although a
combination of time-varying strong and weak lensing effects, induced
by an intermediate-mass black hole (104-5 × 105
M⊙) moving within the Milky Way halo ( 0.1-4 kpc), can
conceivably explain all of the observed variable galaxy properties,
it is statistically highly unlikely according to current theoretical
predictions, and, therefore, also discarded. A cataclysmic event such
as a supernova/hypernova could have occurred, as long as the event was
observed towards the later/late-stage descent of the light curve, but
this scenario fails to explain the absence of a post-explosion source
and/or host H II region in recent optical images. An episode related
to the giant eruption of a luminous blue variable star, a stellar
merger or a nova, observed at, or near, peak magnitude may explain
the transient source and possibly the change in morphology/centre
of brightness, but cannot justify the main source peak variability,
unless stellar variability is evoked.

---------------------------------------------------------
Title: Extremely metal-poor galaxies: Chemical laboratories of the
Early Universe
Authors: Pérez-Montero, E.; Sánchez-Almeida, J.; Amorín,
R.; Vílchez, J. M.; Morales-Luis, A. B.; Muñoz-Tuñón, C.;
García-Benito, R.
2018cagn.conf...49P Altcode:
Extremely metal-poor galaxies (XMPs) are objects whose gas-phase
metallicity is smaller than one tenth than the solar value, so they
are thought to be un-evolved objects and hence to be analogs to the
primeval galaxies when they are found in the Local Universe. In this
contribution, we review results from several studies of our group to
search for XMPs at low- (SDSS) and mid-redshift (zCOSMOS), focused
on improving the methods to identify them. Our analysis of the metal
content of these objects includes the derivation of abundances of
elements with both primary and secondary nucleosynthetic origin. The
chemical analysis combined with the use of spatially resolved
observations allow us to discriminate true primitive galaxies from other
objects rejuvenated by the fall of pristine gas, helping to perform a
better analysis of the analogs to the objects in the primitive Universe.

---------------------------------------------------------
Title: First scientific observations with MEGARA at GTC
Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Iglesias-Páramo,
J.; Cedazo, R.; García-Vargas, M. L.; Arrillaga, X.; Avilés,
J. L.; Bouquin, A.; Carbajo, J.; Cardiel, N.; Carrera, M. A.;
Castillo-Morales, A.; Castillo-Domínguez, E.; Esteban San Román,
S.; Ferrusca, D.; Gómez-Álvarez, P.; Izazaga-Pérez, R.; Lefort,
B.; López-Orozco, J. A.; Maldonado, M.; Martínez-Delgado,
I.; Morales-Durán, I.; Mujica, E.; Páez, G.; Pascual, S.;
Pérez-Calpena, A.; Picazo, P.; Sánchez-Penim, A.; Sánchez-Blanco,
E.; Tulloch, S.; Velázquez, M.; Vílchez, J. M.; Zamorano, J.;
Aguerri, A. L.; Barrado y Navascues, D.; Berlanas, S. R.; Bertone,
E.; Cava, A.; Catalán-Torrecilla, C.; Cenarro, J.; Chávez,
M.; Dullo, B. T.; García, M.; García-Rojas, J.; Guichard, J.;
González-Delgado, R.; Guzmán, R.; Herrero, A.; Huélamo, N.;
Hughes, D. H.; Jiménez-Vicente, J.; Kehrig, C.; Marino, R. A.;
Márquez, I.; Masegosa, J.; Mayya, D.; Méndez-Abreu, J.; Mollá,
M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.;
Pérez-Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.;
Rodríguez Merino, L.; Rodríguez-Muñoz, L.; Rosa-González, D.;
Sánchez-Almeida, J.; Sánchez-Contreras, C.; Sánchez-Blázquez,
P.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón-Díaz, S.;
Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert,
S.; Trujillo, I.; Tsamis, Y.; Vega, O.
2018SPIE10702E..17G Altcode:
On June 25th 2017, the new intermediate-resolution optical IFU and MOS
of the 10.4-m GTC had its first light. As part of the tests carried out
to verify the performance of the instrument in its two modes (IFU and
MOS) and 18 spectral setups (identical number of VPHs with resolutions
R=6000-20000 from 0.36 to 1 micron) a number of astronomical objects
were observed. These observations show that MEGARA@GTC is called
to fill a niche of high-throughput, intermediateresolution IFU and
MOS observations of extremely-faint narrow-lined objects. Lyman-α
absorbers, star-forming dwarfs or even weak absorptions in stellar
spectra in our Galaxy or in the Local Group can now be explored to
a new level. Thus, the versatility of MEGARA in terms of observing
modes and spectral resolution and coverage will allow GTC to go beyond
current observational limits in either depth or precision for all these
objects. The results to be presented in this talk clearly demonstrate
the potential of MEGARA in this regard.

---------------------------------------------------------
Title: MEGARA, the R=6000-20000 IFU and MOS of GTC
Authors: Carrasco, E.; Gil de Paz, A.; Gallego, J.; Iglesias-Páramo,
J.; Cedazo, R.; García Vargas, M. L.; Arrillaga, X.; Avilés,
J. L.; Bouquin, A.; Carbajo, J.; Cardiel, N.; Carrera, M. A.; Castillo
Morales, A.; Castillo-Domínguez, E.; Esteban San Román, S.; Ferrusca,
D.; Gómez-Álvarez, P.; Izazaga-Pérez, R.; Lefort, B.; López
Orozco, J. A.; Maldonado, M.; Martínez Delgado, I.; Morales Durán,
I.; Mújica, E.; Ortiz, R.; Páez, G.; Pascual, S.; Pérez-Calpena,
A.; Picazo, P.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch,
S.; Velázquez, M.; Vílchez, J. M.; Zamorano, J.; Aguerri, A. L.;
Barrado, D.; Bertone, E.; Cava, A.; Catalán-Torrecilla, C.;
Cenarro, J.; Chávez, M.; Dullo, B. T.; Eliche, C.; García, Mi.;
García-Rojas, J.; Guichard, J.; González-Delgado, R.; Guzmán,
R.; Herrero, A.; Huélamo, N.; Hughes, D. H.; Jiménez-Vicente,
J.; Kehrig, C.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mayya,
D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert,
M.; Pérez-González, P. G.; Pérez-Montero, E.; Roca-Fàbrega, S.;
Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.;
Rodríguez-Muñoz, L.; Rosa-González, D.; Sánchez-Almeida, J.;
Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S. F.;
Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.;
Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.;
Tsamis, Y.; Vega, O.
2018SPIE10702E..16C Altcode:
MEGARA is the new generation IFU and MOS optical spectrograph built
for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed
by a consortium led by UCM (Spain) that also includes INAOE (Mexico),
IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on
March 28th 2017 and was successfully integrated and commissioned at
the telescope from May to August 2017. During the on-sky commissioning
we demonstrated that MEGARA is a powerful and robust instrument that
provides on-sky intermediate-to-high spectral resolutions RFWHM 6,000,
12,000 and 20,000 at an unprecedented efficiency for these resolving
powers in both its IFU and MOS modes. The IFU covers 12.5 x 11.3
arcsec2 while the MOS mode allows observing up to 92 objects
in a region of 3.5 x 3.5 arcmin2. In this paper we describe
the instrument main subsystems, including the Folded-Cassegrain unit,
the fiber link, the spectrograph, the cryostat, the detector and
the control subsystems, and its performance numbers obtained during
commissioning where the fulfillment of the instrument requirements
is demonstrated.

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Title: The Origin of the Relation between Metallicity and Size in
Star-forming Galaxies
Authors: Sánchez Almeida, J.; Dalla Vecchia, C.
2018ApJ...859..109S Altcode: 2018arXiv180409406S
For the same stellar mass, physically smaller star-forming galaxies are
also metal richer. What causes the relation remains unclear. The central
star-forming galaxies in the EAGLE cosmological numerical simulation
reproduce the observed trend. We use them to explore the origin of
the relation assuming that the physical mechanism responsible for the
anticorrelation between size and gas-phase metallicity is the same in
the simulated and the observed galaxies. We consider the three most
likely causes: (1) metal-poor gas inflows feeding the star formation
(SF) process, (2) metal-rich gas outflows particularly efficient in
shallow gravitational potentials, and (3) enhanced efficiency of the
SF process in compact galaxies. Outflows (cause 2) and enhanced SF
efficiency (cause 3) can be discarded. Metal-poor gas inflows (cause
1) produce the correlation in the simulated galaxies. Galaxies grow
in size with time, so those that receive gas later are both metal
poorer and larger, giving rise to the observed anticorrelation. As
expected within this explanation, larger galaxies have younger stellar
populations. We explore the variation with redshift of the relation,
which is maintained up to, at least, redshift 8.

---------------------------------------------------------
Title: Local anticorrelation between star formation rate and gas-phase
metallicity in disc galaxies
Authors: Sánchez Almeida, J.; Caon, N.; Muñoz-Tuñón, C.; Filho,
M.; Cerviño, M.
2018MNRAS.476.4765S Altcode: 2018arXiv180208111S; 2018MNRAS.tmp..488S
Using a representative sample of 14 star-forming dwarf galaxies
in the local Universe, we show the existence of a spaxel-to-spaxel
anticorrelation between the index N2 ≡ log ([N II]λ 6583/H α )
and the H α flux. These two quantities are commonly employed as
proxies for gas-phase metallicity and star formation rate (SFR),
respectively. Thus, the observed N2 to H α relation may reflect the
existence of an anticorrelation between the metallicity of the gas
forming stars and the SFR it induces. Such an anticorrelation is to be
expected if variable external metal-poor gas fuels the star-formation
process. Alternatively, it can result from the contamination of the
star-forming gas by stellar winds and SNe, provided that intense
outflows drive most of the metals out of the star-forming regions. We
also explore the possibility that the observed anticorrelation is due
to variations in the physical conditions of the emitting gas, other
than metallicity. Using alternative methods to compute metallicity,
as well as previous observations of H II regions and photoionization
models, we conclude that this possibility is unlikely. The radial
gradient of metallicity characterizing disc galaxies does not produce
the correlation either.

---------------------------------------------------------
Title: NOEMA Observations of a Molecular Cloud in the Low-metallicity
Galaxy Kiso 5639
Authors: Elmegreen, Bruce G.; Herrera, Cinthya; Rubio, Monica;
Elmegreen, Debra Meloy; Sánchez Almeida, Jorge; Muñoz-Tuñón,
Casiana; Olmo-García, Amanda
2018ApJ...859L..22E Altcode: 2018arXiv180508253E
A giant star-forming region in a metal-poor dwarf galaxy has been
observed in optical lines with the 10 m Gran Telescopio Canarias
(GTC) and in the emission line of CO(1-0) with the Northern Extended
Millimeter Array (NOEMA) mm-wave interferometer. The metallicity
was determined to be 12+{log}({{O}}/{{H}})=7.83+/- 0.09, from
which we estimate a conversion factor of α CO ∼ 100 M
⊙ pc-2(K km s-1)-1 and a
molecular cloud mass of ∼2.9 × 107 M ⊙. This
is an enormous concentration of molecular mass at one end of a
small galaxy, suggesting a recent accretion. The molecular cloud
properties seem normal: the surface density, 120 M ⊙
pc-2, is comparable to that of a standard giant molecular
cloud; the cloud’s virial ratio of ∼1.8 is in the star formation
range; and the gas consumption time, 0.5 Gyr, at the present star
formation rate is typical for molecular regions. The low metallicity
implies that the cloud has an average visual extinction of only 0.8
mag, which is close to the threshold for molecule formation. With
such an extinction threshold, molecular clouds in metal-poor regions
should have high surface densities and high internal pressures. If
high pressure is associated with the formation of massive clusters,
then metal-poor galaxies such as dwarfs in the early universe could
have been the hosts of metal-poor globular clusters.

---------------------------------------------------------
Title: Cosmic Magnetic Fields
Authors: Sánchez Almeida, J.; Martínez González, M. J.
2018cmf..book.....S Altcode:
Magnetic fields play an important role in many astrophysical
processes. They are difficult to detect and characterize since
often their properties have to be inferred through interpreting the
polarization of the light. Magnetic fields are also challenging to
model and understand. Magnetized plasmas behave following highly
non-linear differential equations having no general solution, so that
every astrophysical problem represents a special case to be studied
independently. Hence, magnetic fields are often an inconvenient subject
which is overlooked or simply neglected (the elephant in the room,
as they are dubbed in poster of the school). Such difficulty burdens
the research on magnetic fields, which has evolved to become a very
technical subject, with many small disconnected communities studying
specific aspects and details. The school tried to amend the situation
by providing a unifying view of the subject. The students had a chance
to understand the behavior of magnetic fields in all astrophysical
contexts, from cosmology to the Sun, and from starbursts to AGNs. The
school was planed to present a balanced yet complete review of our
knowledge, with excursions into the unknown to point out present and
future lines of research. The subject of Cosmic Magnetic Fields was
split into seven different topics: cosmic magnetic field essentials,
solar magnetic fields, stellar magnetic fields, the role of magnetic
fields on AGN feedback, magnetic fields in galaxies, magnetic fields in
galaxy clusters and at larger scales, and primordial magnetic fields
and magnetic fields in the early Universe. The corresponding lectures
were delivered by seven well known and experienced scientists that
have played key roles in the major advances of the field during the
last years: F. Cattaneo, P. Judge, O. Kochukhov, R. Keppens, R. Beck,
K. Dolag, and F. Finelli. Their lectures were recorded and are freely
available at the IAC website: http://iactalks.iac.es/talks/serie/19.

---------------------------------------------------------
Title: Machine learning in APOGEE. Unsupervised spectral
classification with K-means
Authors: Garcia-Dias, Rafael; Allende Prieto, Carlos; Sánchez Almeida,
Jorge; Ordovás-Pascual, Ignacio
2018A&A...612A..98G Altcode: 2018arXiv180107912G
Context. The volume of data generated by astronomical surveys is
growing rapidly. Traditional analysis techniques in spectroscopy
either demand intensive human interaction or are computationally
expensive. In this scenario, machine learning, and unsupervised
clustering algorithms in particular, offer interesting alternatives. The
Apache Point Observatory Galactic Evolution Experiment (APOGEE)
offers a vast data set of near-infrared stellar spectra, which is
perfect for testing such alternatives. Aims: Our research
applies an unsupervised classification scheme based on K-means
to the massive APOGEE data set. We explore whether the data are
amenable to classification into discrete classes. Methods:
We apply the K-means algorithm to 153 847 high resolution spectra
(R ≈ 22 500). We discuss the main virtues and weaknesses of the
algorithm, as well as our choice of parameters. Results: We
show that a classification based on normalised spectra captures the
variations in stellar atmospheric parameters, chemical abundances,
and rotational velocity, among other factors. The algorithm is able
to separate the bulge and halo populations, and distinguish dwarfs,
sub-giants, RC, and RGB stars. However, a discrete classification in
flux space does not result in a neat organisation in the parameters'
space. Furthermore, the lack of obvious groups in flux space
causes the results to be fairly sensitive to the initialisation,
and disrupts the efficiency of commonly-used methods to select
the optimal number of clusters. Our classification is publicly
available, including extensive online material associated with the
APOGEE Data Release 12 (DR12). Conclusions: Our description
of the APOGEE database can help greatly with the identification
of specific types of targets for various applications. We find a
lack of obvious groups in flux space, and identify limitations of
the K-means algorithm in dealing with this kind of data. Full
Tables B.1-B.4 are only available at the CDS via anonymous ftp to
<A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/612/A98">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/612/A98</A>

---------------------------------------------------------
Title: The Fourteenth Data Release of the Sloan Digital Sky Survey:
First Spectroscopic Data from the Extended Baryon Oscillation
Spectroscopic Survey and from the Second Phase of the Apache Point
Observatory Galactic Evolution Experiment
Authors: Abolfathi, Bela; Aguado, D. S.; Aguilar, Gabriela; Allende
Prieto, Carlos; Almeida, Andres; Ananna, Tonima Tasnim; Anders,
Friedrich; Anderson, Scott F.; Andrews, Brett H.; Anguiano, Borja;
Aragón-Salamanca, Alfonso; Argudo-Fernández, Maria; Armengaud,
Eric; Ata, Metin; Aubourg, Eric; Avila-Reese, Vladimir; Badenes,
Carles; Bailey, Stephen; Balland, Christophe; Barger, Kathleen A.;
Barrera-Ballesteros, Jorge; Bartosz, Curtis; Bastien, Fabienne;
Bates, Dominic; Baumgarten, Falk; Bautista, Julian; Beaton, Rachael;
Beers, Timothy C.; Belfiore, Francesco; Bender, Chad F.; Bernardi,
Mariangela; Bershady, Matthew A.; Beutler, Florian; Bird, Jonathan C.;
Bizyaev, Dmitry; Blanc, Guillermo A.; Blanton, Michael R.; Blomqvist,
Michael; Bolton, Adam S.; Boquien, Médéric; Borissova, Jura;
Bovy, Jo; Bradna Diaz, Christian Andres; Brandt, William Nielsen;
Brinkmann, Jonathan; Brownstein, Joel R.; Bundy, Kevin; Burgasser,
Adam J.; Burtin, Etienne; Busca, Nicolás G.; Cañas, Caleb I.;
Cano-Díaz, Mariana; Cappellari, Michele; Carrera, Ricardo; Casey,
Andrew R.; Cervantes Sodi, Bernardo; Chen, Yanping; Cherinka, Brian;
Chiappini, Cristina; Choi, Peter Doohyun; Chojnowski, Drew; Chuang,
Chia-Hsun; Chung, Haeun; Clerc, Nicolas; Cohen, Roger E.; Comerford,
Julia M.; Comparat, Johan; Correa do Nascimento, Janaina; da Costa,
Luiz; Cousinou, Marie-Claude; Covey, Kevin; Crane, Jeffrey D.;
Cruz-Gonzalez, Irene; Cunha, Katia; da Silva Ilha, Gabriele; Damke,
Guillermo J.; Darling, Jeremy; Davidson, James W., Jr.; Dawson, Kyle;
de Icaza Lizaola, Miguel Angel C.; de la Macorra, Axel; de la Torre,
Sylvain; De Lee, Nathan; de Sainte Agathe, Victoria; Deconto Machado,
Alice; Dell'Agli, Flavia; Delubac, Timothée; Diamond-Stanic,
Aleksandar M.; Donor, John; Downes, Juan José; Drory, Niv; du
Mas des Bourboux, Hélion; Duckworth, Christopher J.; Dwelly, Tom;
Dyer, Jamie; Ebelke, Garrett; Davis Eigenbrot, Arthur; Eisenstein,
Daniel J.; Elsworth, Yvonne P.; Emsellem, Eric; Eracleous, Michael;
Erfanianfar, Ghazaleh; Escoffier, Stephanie; Fan, Xiaohui; Fernández
Alvar, Emma; Fernandez-Trincado, J. G.; Fernando Cirolini, Rafael;
Feuillet, Diane; Finoguenov, Alexis; Fleming, Scott W.; Font-Ribera,
Andreu; Freischlad, Gordon; Frinchaboy, Peter; Fu, Hai; Gómez Maqueo
Chew, Yilen; Galbany, Lluís; García Pérez, Ana E.; Garcia-Dias,
R.; García-Hernández, D. A.; Garma Oehmichen, Luis Alberto; Gaulme,
Patrick; Gelfand, Joseph; Gil-Marín, Héctor; Gillespie, Bruce A.;
Goddard, Daniel; González Hernández, Jonay I.; Gonzalez-Perez,
Violeta; Grabowski, Kathleen; Green, Paul J.; Grier, Catherine J.;
Gueguen, Alain; Guo, Hong; Guy, Julien; Hagen, Alex; Hall, Patrick;
Harding, Paul; Hasselquist, Sten; Hawley, Suzanne; Hayes, Christian
R.; Hearty, Fred; Hekker, Saskia; Hernandez, Jesus; Hernandez Toledo,
Hector; Hogg, David W.; Holley-Bockelmann, Kelly; Holtzman, Jon A.;
Hou, Jiamin; Hsieh, Bau-Ching; Hunt, Jason A. S.; Hutchinson, Timothy
A.; Hwang, Ho Seong; Jimenez Angel, Camilo Eduardo; Johnson, Jennifer
A.; Jones, Amy; Jönsson, Henrik; Jullo, Eric; Khan, Fahim Sakil;
Kinemuchi, Karen; Kirkby, David; Kirkpatrick, Charles C., IV; Kitaura,
Francisco-Shu; Knapp, Gillian R.; Kneib, Jean-Paul; Kollmeier, Juna A.;
Lacerna, Ivan; Lane, Richard R.; Lang, Dustin; Law, David R.; Le Goff,
Jean-Marc; Lee, Young-Bae; Li, Hongyu; Li, Cheng; Lian, Jianhui;
Liang, Yu; Lima, Marcos; Lin, Lihwai; Long, Dan; Lucatello, Sara;
Lundgren, Britt; Mackereth, J. Ted; MacLeod, Chelsea L.; Mahadevan,
Suvrath; Maia, Marcio Antonio Geimba; Majewski, Steven; Manchado,
Arturo; Maraston, Claudia; Mariappan, Vivek; Marques-Chaves, Rui;
Masseron, Thomas; Masters, Karen L.; McDermid, Richard M.; McGreer,
Ian D.; Melendez, Matthew; Meneses-Goytia, Sofia; Merloni, Andrea;
Merrifield, Michael R.; Meszaros, Szabolcs; Meza, Andres; Minchev,
Ivan; Minniti, Dante; Mueller, Eva-Maria; Muller-Sanchez, Francisco;
Muna, Demitri; Muñoz, Ricardo R.; Myers, Adam D.; Nair, Preethi;
Nandra, Kirpal; Ness, Melissa; Newman, Jeffrey A.; Nichol, Robert
C.; Nidever, David L.; Nitschelm, Christian; Noterdaeme, Pasquier;
O'Connell, Julia; Oelkers, Ryan James; Oravetz, Audrey; Oravetz,
Daniel; Ortíz, Erik Aquino; Osorio, Yeisson; Pace, Zach; Padilla,
Nelson; Palanque-Delabrouille, Nathalie; Palicio, Pedro Alonso; Pan,
Hsi-An; Pan, Kaike; Parikh, Taniya; Pâris, Isabelle; Park, Changbom;
Peirani, Sebastien; Pellejero-Ibanez, Marcos; Penny, Samantha;
Percival, Will J.; Perez-Fournon, Ismael; Petitjean, Patrick; Pieri,
Matthew M.; Pinsonneault, Marc; Pisani, Alice; Prada, Francisco;
Prakash, Abhishek; Queiroz, Anna Bárbara de Andrade; Raddick,
M. Jordan; Raichoor, Anand; Barboza Rembold, Sandro; Richstein,
Hannah; Riffel, Rogemar A.; Riffel, Rogério; Rix, Hans-Walter; Robin,
Annie C.; Rodríguez Torres, Sergio; Román-Zúñiga, Carlos; Ross,
Ashley J.; Rossi, Graziano; Ruan, John; Ruggeri, Rossana; Ruiz, Jose;
Salvato, Mara; Sánchez, Ariel G.; Sánchez, Sebastián F.; Sanchez
Almeida, Jorge; Sánchez-Gallego, José R.; Santana Rojas, Felipe
Antonio; Santiago, Basílio Xavier; Schiavon, Ricardo P.; Schimoia,
Jaderson S.; Schlafly, Edward; Schlegel, David; Schneider, Donald P.;
Schuster, William J.; Schwope, Axel; Seo, Hee-Jong; Serenelli, Aldo;
Shen, Shiyin; Shen, Yue; Shetrone, Matthew; Shull, Michael; Silva
Aguirre, Víctor; Simon, Joshua D.; Skrutskie, Mike; Slosar, Anže;
Smethurst, Rebecca; Smith, Verne; Sobeck, Jennifer; Somers, Garrett;
Souter, Barbara J.; Souto, Diogo; Spindler, Ashley; Stark, David V.;
Stassun, Keivan; Steinmetz, Matthias; Stello, Dennis; Storchi-Bergmann,
Thaisa; Streblyanska, Alina; Stringfellow, Guy S.; Suárez, Genaro;
Sun, Jing; Szigeti, Laszlo; Taghizadeh-Popp, Manuchehr; Talbot,
Michael S.; Tang, Baitian; Tao, Charling; Tayar, Jamie; Tembe,
Mita; Teske, Johanna; Thakar, Aniruddha R.; Thomas, Daniel; Tissera,
Patricia; Tojeiro, Rita; Tremonti, Christy; Troup, Nicholas W.; Urry,
Meg; Valenzuela, O.; van den Bosch, Remco; Vargas-González, Jaime;
Vargas-Magaña, Mariana; Vazquez, Jose Alberto; Villanova, Sandro;
Vogt, Nicole; Wake, David; Wang, Yuting; Weaver, Benjamin Alan;
Weijmans, Anne-Marie; Weinberg, David H.; Westfall, Kyle B.; Whelan,
David G.; Wilcots, Eric; Wild, Vivienne; Williams, Rob A.; Wilson,
John; Wood-Vasey, W. M.; Wylezalek, Dominika; Xiao, Ting; Yan, Renbin;
Yang, Meng; Ybarra, Jason E.; Yèche, Christophe; Zakamska, Nadia;
Zamora, Olga; Zarrouk, Pauline; Zasowski, Gail; Zhang, Kai; Zhao,
Cheng; Zhao, Gong-Bo; Zheng, Zheng; Zheng, Zheng; Zhou, Zhi-Min; Zhu,
Guangtun; Zinn, Joel C.; Zou, Hu
2018ApJS..235...42A Altcode: 2017arXiv170709322A
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV)
has been in operation since 2014 July. This paper describes the
second data release from this phase, and the 14th from SDSS overall
(making this Data Release Fourteen or DR14). This release makes the
data taken by SDSS-IV in its first two years of operation (2014-2016
July) public. Like all previous SDSS releases, DR14 is cumulative,
including the most recent reductions and calibrations of all data
taken by SDSS since the first phase began operations in 2000. New
in DR14 is the first public release of data from the extended Baryon
Oscillation Spectroscopic Survey; the first data from the second phase
of the Apache Point Observatory (APO) Galactic Evolution Experiment
(APOGEE-2), including stellar parameter estimates from an innovative
data-driven machine-learning algorithm known as “The Cannon”
and almost twice as many data cubes from the Mapping Nearby Galaxies
at APO (MaNGA) survey as were in the previous release (N = 2812 in
total). This paper describes the location and format of the publicly
available data from the SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken
(both targeting and observation details) and processed for scientific
use. The SDSS web site (<A href="http://www.sdss.org">www.sdss.org</A>)
has been updated for this release and provides links to data downloads,
as well as tutorials and examples of data use. SDSS-IV is planning to
continue to collect astronomical data until 2020 and will be followed
by SDSS-V.

---------------------------------------------------------
Title: VizieR Online Data Catalog: APOGEE full information on classes
(Garcia-Dias+, 2018)
Authors: Garcia-Dias, R.; Allende Prieto, C.; Sanchez Almeida, J.;
Ordovas-Pascual, I.
2018yCat..36120098G Altcode:
Data for the classes derived on the paper. The tables provide the star
labels, the mean spectra of the classes and the within class standard
deviation. (3 data files).

---------------------------------------------------------
Title: The Shape of Extremely Metal-Poor Galaxies
Authors: Putko, Joseph; Sánchez Almeida, Jorge; Muñoz-Tuñón,
Casiana; Elmegreen, Bruce; Elmegreen, Debra
2018AAS...23134002P Altcode:
This work is the first study on the 3D shape of starbursting extremely
metal-poor galaxies (XMPs; a galaxy is said to be an XMP if its
ionized gas-phase metallicity is less than 1/10 the solar value). A
few hundred XMPs have been identified in the local universe primarily
through mining the spectroscopic catalog of the Sloan Digital Sky Survey
(SDSS), and follow-up observations have shown that metallicity drops
significantly at the starburst (compared to the quiescent component of
the galaxy). As the timescale for gas mixing is short, the metal-poor
gas triggering the starburst must have been accreted recently. This is
strong observational evidence for the cold flow accretion predicted
by cosmological models of galaxy formation, and, in this respect,
XMPs seem to be the best local analogs of the very first galaxies.The
ellipsoidal shape of a class of galaxies can be inferred from the
observed axial ratio (q) distribution (q = minor axis/major axis)
of a large sample of randomly-oriented galaxies. Fitting ellipses to
200 XMPs using r-band SDSS images, we observe that the axial ratio
distribution falls off at q &lt; ~0.4 and q &gt; ~0.8, and we determine
that these falloffs are not due to biases in the data. The falloff at
low axial ratio indicates that the XMPs are thick for their size, and
the falloff at high axial ratio suggests the vast majority of XMPs are
triaxial. We also observe that smaller XMPs are thicker in proportion
to their size, and it is expected that for decreasing galaxy size
the ratio of random to rotational motions increases, which correlates
with increasing relative thickness. The XMPs are low-redshift dwarf
galaxies dominated by dark matter, and our results are compatible
with simulations that have shown dark matter halos to be triaxial,
with triaxial stellar distributions for low-mass galaxies and with
triaxiality increasing over time. We will offer precise constraints on
the 3D shape of XMPs via Bayesian analysis of our observed axial ratio
distribution.This work has been supported by the La Caixa Foundation
and the Estallidos Spanish Ministry of Science and Innovation grant.

---------------------------------------------------------
Title: Gas accretion from the cosmic web feeding disk galaxies
Authors: Sánchez Almeida, J.; Olmo-García, A.; Elmegreen, B. G.;
Muñoz-Tuñón, C.; Elmegreen, D. M.; Filho, M. E.; Pérez-Montero,
E.; Amorín, R.
2017IAUS..321..208S Altcode:
Disk galaxies in cosmological numerical simulations grow by accreting
gas from the cosmic web. This gas reaches the external disk, and then
spirals in dragged along by tidal forces and/or disk instabilities. The
importance of gas infall is as clear from numerical simulations as
it is obscure to observations. Extremely metal poor (XMP) galaxies
seem to be the best example we have of the gas accretion process at
work. They have large off-center starbursts which show significant
metallicity drop compared with the host galaxy. This observation is
naturally explained as a gas accretion event caught in the act. We
present preliminary results of the kinematical properties of the
metal poor starbursts in XMPs, which suggest that the starbursts are
kinematically decoupled entities within the host galaxy.

---------------------------------------------------------
Title: Circumgalactic gas absorption in extremely metal-poor dwarf
dalaxies
Authors: Filho, M. E.; Sánchez Almeida, J.; Muñoz Tuñón, C.
2017IAUS..321..287F Altcode:
Accretion of metal-poor gas via cold accretion flows has been
recently proposed as a means to trigger/sustain star formation in
extremely metal-poor dwarf galaxies (XMPs), a scenario in agreement
with theoretical predictions. We report on the tentative detection of
CaII absorption used to trace the conditions of the gas clouds in the
halo of the XMP UGCA 20.

---------------------------------------------------------
Title: On the Dearth of Ultra-faint Extremely Metal-poor Galaxies
Authors: Sánchez Almeida, J.; Filho, M. E.; Dalla Vecchia, C.;
Skillman, E. D.
2017ApJ...835..159S Altcode: 2016arXiv161200273S
Local extremely metal-poor galaxies (XMPs) are of particular
astrophysical interest since they allow us to look into physical
processes characteristic of the early universe, from the assembly
of galaxy disks to the formation of stars in conditions of low
metallicity. Given the luminosity-metallicity relationship, all galaxies
fainter than Mr ≃ -13 are expected to be XMPs. Therefore,
XMPs should be common in galaxy surveys. However, they are not common,
because several observational biases hamper their detection. This work
compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey
with the expected number, given the known biases and the observed
galaxy luminosity function (LF). The faint end of the LF is poorly
constrained observationally, but it determines the expected number
of XMPs. Surprisingly, the number of observed faint XMPs (∼10)
is overpredicted by our calculation, unless the upturn in the faint
end of the LF is not present in the model. The lack of an upturn can
be naturally understood if most XMPs are central galaxies in their
low-mass dark matter halos, which are highly depleted in baryons due
to interaction with the cosmic ultraviolet background and to other
physical processes. Our result also suggests that the upturn toward
low luminosity of the observed galaxy LF is due to satellite galaxies.

---------------------------------------------------------
Title: The Nearest Ultra Diffuse Galaxy: UGC 2162
Authors: Trujillo, Ignacio; Roman, Javier; Filho, Mercedes; Sánchez
Almeida, Jorge
2017ApJ...836..191T Altcode: 2017arXiv170103804T
We describe the structural, stellar population and gas properties of the
nearest ultra diffuse galaxy discovered so far: UGC 2162 (z = 0.00392
{R}e,g=1.7(+/- 0.2) kpc; {μ }g(0) = 24.4 ±
0.1 mag arcsec-2 g-I = 0.33 ± 0.02). This galaxy, located
at a distance of 12.3(±1.7) Mpc, is a member of the M77 group. UGC
2162 has a stellar mass of ∼ 2{(}-1+2) ×
107 {M}⊙ and is embedded within a cloud of
HI gas ∼10 times more massive: ∼1.9(±0.6) × 108
{M}⊙ . Using the width of its HI line as a dynamical
proxy, the enclosed mass within the inner R ∼ 5 kpc is ∼4.6(±0.8)
× 109 {M}⊙ (I.e., M/L ∼ 200). The estimated
virial mass from the cumulative mass curve is ∼8(±2)×1010
M ⊙. Ultra-deep imaging from the IAC Stripe82 Legacy
Project show that the galaxy is irregular and has many star-forming
knots, with a gas-phase metallicity around one-third of the solar
value. Its estimated star-formation rate is ∼0.01 {M}⊙ 
yr-1. This SFR would double the stellar mass of the object
in ∼2 Gyr. If the object were to stop forming stars at this moment,
after a passive evolution, its surface brightness would become extremely
faint: {μ }g(0) ∼ 27 mag arcsec-2 and its
size would remain large {R}e,g ∼ 1.8 kpc. Such faintness
would make it almost undetectable to most present-day surveys. This
suggests that there could be an important population of {M}\star
 ∼ 107 {M}⊙ “dark galaxies” in
rich environments (depleted of HI gas) waiting to be discovered by
current and future ultra-deep surveys.

---------------------------------------------------------
Title: Evidence of a White-Light Flare on 10 September 1886
Authors: Vaquero, J. M.; Vázquez, M.; Sánchez Almeida, J.
2017SoPh..292...33V Altcode: 2017arXiv170105910V
We present evidence of the occurrence of a white-light flare on 10
September 1886. It represents the third such rare event reported
in the history of astronomy. The flare was mentioned by Valderrama
(L'Astronomie5, 388, 1886). In this article we have used the original
logbook of the observer, J. Valderrama y Aguilar, an amateur astronomer
who lived in Madrid and Santa Cruz de Tenerife at that time.

---------------------------------------------------------
Title: Gas Accretion and Star Formation Rates
Authors: Sánchez Almeida, Jorge
2017ASSL..430...67S Altcode: 2016arXiv161200776S
Cosmological numerical simulations of galaxy evolution show that
accretion of metal-poor gas from the cosmic web drives the star
formation in galaxy disks. Unfortunately, the observational support for
this theoretical prediction is still indirect, and modeling and analysis
are required to identify hints as actual signs of star formation feeding
from metal-poor gas accretion. Thus, a meticulous interpretation of
the observations is crucial, and this observational review begins with
a simple theoretical description of the physical process and the key
ingredients it involves, including the properties of the accreted gas
and of the star formation that it induces. A number of observations
pointing out the connection between metal-poor gas accretion and
star formation are analyzed, specifically, the short gas-consumption
time-scale compared to the age of the stellar populations, the
fundamental metallicity relationship, the relationship between disk
morphology and gas metallicity, the existence of metallicity drops in
starbursts of star-forming galaxies, the so-called G dwarf problem,
the existence of a minimum metallicity for the star-forming gas in the
local universe, the origin of the α-enhanced gas forming stars in the
local universe, the metallicity of the quiescent BCDs, and the direct
measurements of gas accretion onto galaxies. A final section discusses
intrinsic difficulties to obtain direct observational evidence, and
points out alternative observational pathways to further consolidate
the current ideas.

---------------------------------------------------------
Title: Kinematics of Extremely Metal-poor Galaxies: Evidence for
Stellar Feedback
Authors: Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.;
Filho, M. E.; Elmegreen, B. G.; Elmegreen, D. M.; Pérez-Montero,
E.; Méndez-Abreu, J.
2017ApJ...834..181O Altcode: 2016arXiv161107426O
The extremely metal-poor (XMP) galaxies analyzed in a previous paper
have large star-forming regions with a metallicity lower than the rest
of the galaxy. Such a chemical inhomogeneity reveals the external
origin of the metal-poor gas fueling star formation, possibly
indicating accretion from the cosmic web. This paper studies the
kinematic properties of the ionized gas in these galaxies. Most XMPs
have a rotation velocity around a few tens of km s-1. The
star-forming regions appear to move coherently. The velocity is
constant within each region, and the velocity dispersion sometimes
increases within the star-forming clump toward the galaxy midpoint,
suggesting inspiral motion toward the galaxy center. Other regions
present a local maximum in velocity dispersion at their center,
suggesting a moderate global expansion. The Hα line wings show a
number of faint emission features with amplitudes around a few per
cent of the main Hα component, and wavelength shifts between 100
and 400 km s-1. The components are often paired, so that
red and blue emission features with similar amplitudes and shifts
appear simultaneously. Assuming the faint emission to be produced
by expanding shell-like structures, the inferred mass loading factor
(mass loss rate divided by star formation rate) exceeds 10. Since the
expansion velocity far exceeds the rotational and turbulent velocities,
the gas may eventually escape from the galaxy disk. The observed
motions involve energies consistent with the kinetic energy released
by individual core-collapse supernovae. Alternative explanations for
the faint emission have been considered and discarded.

---------------------------------------------------------
Title: MEGARA, the Next Generation Optical MOS and IFU for GTC
Authors: Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias, J.;
Sánchez, F.; Vílchez, J.; García Vargas, M.; Andrés, P.; Arrillaga,
X.; Avilés, J.; Bonache, J.; Carrera, M.; Castillo, A.; Castillo,
E.; Cedazo, R.; Dormido, J.; Eliche Moral, C.; Esteban, S.; Ferrusca,
D.; González, E.; Lefort, B.; López, J.; Maldonado, M.; Marino, R.;
Martínez, I.; Morales, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez,
A.; Sánchez, A.; Sánchez, E.; Tolloch, S.; Velázquez, M.; Zamorano,
J.; Aguerri, A.; Barrado, D.; Bertone, E.; Cardiel, N.; Cava, A.;
Cenarro, A.; Chávez, M.; García, M.; González Delgado, R.; Guichard,
J.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D.; Jiménez,
J.; Kehrig, C.; Márquez, I.; Masegosa, J.; Mayya, D.; Méndez Abreu,
J.; Mollá, M.; Muñoz Tuñón, C.; Peimbert, M.; Pérez González,
P.; Pérez Montero, E.; Rodríguez, M.; Rodríguez Espinosa, J. M.;
Rodríguez, L.; Rosa, D.; Sánchez Almeida, J.; Sánchez Contreras,
C.; Sánchez Blázquez, P.; Sánchez, S. F.; Sarajedini, A.; Silich,
S.; Simón Díaz; S.; Tenorio Tagle, G.; Terlevich, E.; Terlevich,
R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O.; Villar, V.
2016ASPC..507..103G Altcode:
MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para
Astronomía) is the new optical spectrograph for the 10.4 m Gran
Telescopio CANARIAS (GTC). Once installed at GTC by the end of
2016, MEGARA will provide both Integral Field Unit and Multi-Object
Spectroscopy capabilities covering a field-of-view of 12.5×11.3
arcsec2 and 3.5×3.5 arcmin2, respectively. The
MEGARA spectrograph will yield spectral resolutions in the range
R=6,000-18,700 across the entire optical window with superb image
quality and throughput, thanks to the use of state-of-the-art optical
fibers, pupil elements (VPHs) and CCD detector. In this contribution
we provide a brief description of the status of the instrument
construction and of the science that our Science Team is aiming to
pursue with MEGARA, with special emphasis on potential synergies with
the future Multi-Object Spectrograph for the William Herschel Telescope
(WHT), WEAVE.

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Title: Gas accretion from the cosmic web in the local Universe
Authors: Sánchez Almeida, J.; Elmegreen, B. G.; Muñoz-Tuñón, C.;
Elmegreen, D. M.
2016IAUS..308..390S Altcode:
Numerical simulations predict that gas accretion from the cosmic web
drives star formation in disks galaxies. The process is important in low
mass haloes (&lt; 1012 M⊙), therefore, in the
early universe when galaxies were low mass, but also in dwarf galaxies
of the local universe. The gas that falls in is predicted to be tenuous,
patchy, partly ionized, multi-temperature, and large-scale; therefore,
hard to show in a single observation. One of the most compelling cases
for gas accretion at work in the local universe comes from the extremely
metal poor (XMP) galaxies. They show metallicity inhomogeneities
associated with star-forming regions, so that large starbursts have
lower metallicity than the underlying galaxy. Here we put forward
the case for gas accretion from the web posed by XMP galaxies. Two
other observational results are discussed too, namely, the fact that
the gas consumption time-scale is shorter than most stellar ages,
and the systematic morphological distortions of the HI around galaxies.

---------------------------------------------------------
Title: MEGARA, the new intermediate-resolution optical IFU and MOS
for GTC: getting ready for the telescope
Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Iglesias-Páramo,
J.; Cedazo, R.; García Vargas, M. L.; Arrillaga, X.; Avilés, J. L.;
Cardiel, N.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez,
E.; de la Cruz García, J. M.; Esteban San Román, S.; Ferrusca, D.;
Gómez-Álvarez, P.; Izazaga-Pérez, R.; Lefort, B.; López-Orozco,
J. A.; Maldonado, M.; Martínez-Delgado, I.; Morales Durán, I.;
Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Picazo, P.;
Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.;
Vílchez, J. M.; Zamorano, J.; Aguerri, A. L.; Barrado y Naváscues,
D.; Bertone, E.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.;
García-Rojas, J.; Guichard, J.; González-Delgado, R.; Guzmán,
R.; Herrero, A.; Huélamo, N.; Hughes, D. H.; Jiménez-Vicente,
J.; Kehrig, C.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mayya,
Y. D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert,
M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.;
Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rodríguez-Muñoz,
L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez Contreras,
C.; Sánchez-Blázquez, P.; Sánchez Moreno, F. M.; Sánchez, S. F.;
Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.;
Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.;
Tsamis, Y.; Vega, O.
2016SPIE.9908E..1KG Altcode:
MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para
Astronomía) is an optical Integral-Field Unit (IFU) and Multi-Object
Spectrograph (MOS) designed for the GTC 10.4m telescope in La Palma that
is being built by a Consortium led by UCM (Spain) that also includes
INAOE (Mexico), IAA-CSIC (Spain), and UPM (Spain). The instrument
is currently finishing AIV and will be sent to GTC on November 2016
for its on-sky commissioning on April 2017. The MEGARA IFU fiber
bundle (LCB) covers 12.5x11.3 arcsec2 with a spaxel size of 0.62
arcsec while the MEGARA MOS mode allows observing up to 92 objects
in a region of 3.5x3.5 arcmin2 around the IFU. The IFU
and MOS modes of MEGARA will provide identical intermediate-to-high
spectral resolutions (RFWHM 6,000, 12,000 and 18,700, respectively
for the low-, mid- and high-resolution Volume Phase Holographic
gratings) in the range 3700-9800ÅÅ. An x-y mechanism placed at the
pseudo-slit position allows (1) exchanging between the two observing
modes and (2) focusing the spectrograph for each VPH setup. The
spectrograph is a collimator-camera system that has a total of
11 VPHs simultaneously available (out of the 18 VPHs designed and
being built) that are placed in the pupil by means of a wheel and an
insertion mechanism. The custom-made cryostat hosts a 4kx4k 15-μm
CCD. The unique characteristics of MEGARA in terms of throughput and
versatility and the unsurpassed collecting are of GTC make of this
instrument the most efficient tool to date to analyze astrophysical
objects at intermediate spectral resolutions. In these proceedings we
present a summary of the instrument characteristics and the results
from the AIV phase. All subsystems have been successfully integrated
and the system-level AIV phase is progressing as expected.

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Title: Hubble Space Telescope Observations of Accretion-Induced Star
Formation in the Tadpole Galaxy Kiso 5639
Authors: Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida,
Jorge; Muñoz-Tuñón, Casiana; Mendez-Abreu, Jairo; Gallagher,
John S.; Rafelski, Marc; Filho, Mercedes; Ceverino, Daniel
2016ApJ...825..145E Altcode: 2016arXiv160502822E
The tadpole galaxy Kiso 5639 has a slowly rotating disk with a
drop in metallicity at its star-forming head, suggesting that star
formation was triggered by the accretion of metal-poor gas. We
present multi-wavelength Hubble Space Telescope Wide Field Camera
3 images of UV through I band plus Hα to search for peripheral
emission and determine the properties of various regions. The head
has a mass in young stars of ∼ {10}6 {M}⊙ 
and an ionization rate of 6.4× {10}51 s-1,
equivalent to ∼2100 O9-type stars. There are four older star-forming
regions in the tail, and an underlying disk with a photometric age
of ∼1 Gyr. The mass distribution function of 61 star clusters is a
power law with a slope of -1.73 ± 0.51. Fourteen young clusters in
the head are more massive than {10}4 {M}⊙ ,
suggesting a clustering fraction of 30%-45%. Wispy filaments of Hα
emission and young stars extend away from the galaxy. Shells and holes
in the head H II region could be from winds and supernovae. Gravity
from the disk should limit the expansion of the H II region, although
hot gas might escape through the holes. The star formation surface
density determined from Hα in the head is compared to that expected
from likely pre-existing and accreted gas. Unless the surface density
of the accreted gas is a factor of ∼3 or more larger than what was
in the galaxy before, the star formation rate has to exceed the usual
Kennicutt-Schmidt rate by a factor of ≥slant 5.

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Title: Starbursts and Galaxy Evolution: results from COSMOS survey.
Authors: Muñoz-Tuñón, C.; Hinojosa Goñi, R.; Jairo Méndez Abreu,
J.; Sánchez Alméida, J.
2016ilgp.confE..64M Altcode:
The search for starbursts galaxies in COSMOS database by a tailored
procedure that uses the photometry from SUBARU, results in 220
targets at z&lt;0.5. The typical mass of the starburst is 10^8 and its
distribution is similar to that of the quiescent galaxies in the survey
at the same redshift range. From the detailed analysis of the galaxies
images using the HST, the star forming clumps are characterized. The
galaxies are of three different kinds, Snot, Snot and diffuse light
and multiple knots. The mass of the knots are typically one order of
magnitude below that of the host galaxy and the clumps in multiple
knot galaxies are bigger the closer they are to the center. The sSFR
however does not change with the particular position of the burst in
their host galaxy, which suggests a similar process independently
of their location. This result applies also to the galaxies at the
largest z range (0.9). Our interpretation is that the star formation
is happening at all possible locations on the galaxy discs, possibly
from gas accreted from the halo or the IGM, with clumps which grow as
they spiral and get to the centermost regions. Our previous work on
nearby SF -tadpole galaxies of similar mass reported metallicity drops
coinciding with the location of the burst what we have interpreted
as SF driven by cold flows. Our results in COSMOS would be consistent
with a similar interpretation and a scenario in which medium mass disks
are growing by gas accretion that show up as scattered starbursts knots.

---------------------------------------------------------
Title: The Role of Galaxy Morphology in the Mass-Metallicity-SFR
Relation
Authors: Rafelski, Marc; Elmegreen, Bruce; Elmegreen, Debra M.;
Gardner, Jonathan P.; Henry, Alaina L.; Munoz-Tunon, Casiana; Sanchez
Almeida, Jorge; Straughn, Amber
2016hst..prop14580R Altcode:
The mass-metallicity-SFR (M-Z-SFR) relation for galaxies gives
insight into the accretion and outflow of gas. Heightened accretion
should increase disk turbulence and the corresponding Jeans mass
for gravitational instabilities, making star-formation clumpy, and
it should also trigger star formation directly in large clumps where
infalling clouds impact the disk. It follows that if the most irregular
and clumpy galaxies are the most actively accreting, then they should
be low-Z outliers in the M-Z-SFR relation. We propose to investigate
for the first time whether any relationship exists between position
on the M-Z-SFR relation and clumpy morphology. We will use WFC3/IR
grism observations from several large surveys in the CANDELS fields
to measure metallicities of intermediate redshift (1.3

---------------------------------------------------------
Title: VizieR Online Data Catalog: Extremely metal-poor galaxies in
SDSS. II. (Sanchez Almeida+ 2016)
Authors: Sanchez Almeida, J.; Perez-Montero, E.; Morales-Luis, A. B.;
Munoz-Tunon, C.; Garcia-Benito, R.; Nuza, S. E.; Kitaura, F. S.
2016yCat..18190110S Altcode:
First, we search for XMP candidates using the algorithm k-means (Sanchez
Almeida et al. 2010ApJ...714..487S; Ordovas-Pascual &amp; Sanchez
Almeida 2014A&amp;A...565A..53O). It leads to 1281 candidates. Then, we
use the SDSS-DR7 spectra of the candidates to measure their integrated
metallicity, which narrows down the list to 196 XMPs. We also include a
second list (Table 2) with 332 potential XMPs that are selected under
less restrictive noise constraints. (2 data files).

---------------------------------------------------------
Title: Gas inflow and metallicity drops in star-forming galaxies
Authors: Ceverino, Daniel; Sánchez Almeida, Jorge; Muñoz Tuñón,
Casiana; Dekel, Avishai; Elmegreen, Bruce G.; Elmegreen, Debra M.;
Primack, Joel
2016MNRAS.457.2605C Altcode: 2015arXiv150902051C
Gas inflow feeds galaxies with low-metallicity gas from the cosmic web,
sustaining star formation across the Hubble time. We make a connection
between these inflows and metallicity inhomogeneities in star-forming
galaxies, by using synthetic narrow-band images of the Hα emission
line from zoom-in AMR cosmological simulations of galaxies with stellar
masses of M* ≃ 109 M⊙ at redshifts
z = 2-7. In ∼50 per cent of the cases at redshifts lower than 4,
the gas inflow gives rise to star-forming, Hα-bright, off-centre
clumps. Most of these clumps have gas metallicities, weighted by Hα
luminosity, lower than the metallicity in the surrounding interstellar
medium by ∼0.3 dex, consistent with observations of chemical
inhomogeneities at high and low redshifts. Due to metal mixing by
shear and turbulence, these metallicity drops are dissolved in a few
disc dynamical times. Therefore, they can be considered as evidence
for rapid gas accretion coming from cosmological inflow of pristine gas.

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Title: The fate of high-redshift massive compact galaxies
Authors: de la Rosa, Ignacio G.; La Barbera, Francesco; Ferreras,
Ignacio; Sánchez Almeida, Jorge; Dalla Vecchia, Claudio;
Martínez-Valpuesta, Inma; Stringer, Martin
2016MNRAS.457.1916D Altcode: 2016arXiv160103920D
Massive high-redshift quiescent compact galaxies (nicknamed red nuggets)
have been traditionally connected to present-day elliptical galaxies,
often overlooking the relationships that they may have with other
galaxy types. We use large bulge-disc decomposition catalogues based on
the Sloan Digital Sky Survey to check the hypothesis that red nuggets
have survived as compact cores embedded inside the haloes or discs of
present-day massive galaxies. In this study, we designate a compact
core as the bulge component that satisfies a prescribed compactness
criterion. Photometric and dynamic mass-size and mass-density relations
are used to show that, in the inner regions of galaxies at z ∼ 0.1,
there are abundant compact cores matching the peculiar properties of
the red nuggets, an abundance comparable to that of red nuggets at z
∼ 1.5. Furthermore, the morphology distribution of the present-day
galaxies hosting compact cores is used to demonstrate that, in addition
to the standard channel connecting red nuggets with elliptical galaxies,
a comparable fraction of red nuggets might have ended up embedded in
discs. This result generalizes the inside-out formation scenario;
present-day massive galaxies can begin as dense spheroidal cores
(red nuggets), around which either a spheroidal halo or a disc is
formed later.

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Title: The Kennicutt-Schmidt Relation in Extremely Metal-Poor Dwarf
Galaxies
Authors: Filho, M. E.; Sánchez Almeida, J.; Amorín, R.;
Muñoz-Tuñón, C.; Elmegreen, B. G.; Elmegreen, D. M.
2016ApJ...820..109F Altcode: 2016arXiv160204772F
The Kennicutt-Schmidt (KS) relation between the gas mass and star
formation rate (SFR) describes the star formation regulation in disk
galaxies. It is a function of gas metallicity, but the low-metallicity
regime of the KS diagram is poorly sampled. We have analyzed data for
a representative set of extremely metal-poor galaxies (XMPs), as well
as auxiliary data, and compared these to empirical and theoretical
predictions. The majority of the XMPs possess high specific SFRs,
similar to high-redshift star-forming galaxies. On the KS plot,
the XMP H I data occupy the same region as dwarfs and extend the
relation for low surface brightness galaxies. Considering the H I gas
alone, a considerable fraction of the XMPs already fall off the KS
law. Significant quantities of “dark” H2 mass (I.e.,
not traced by CO) would imply that XMPs possess low star formation
efficiencies (SFEgas). Low SFEgas in XMPs may
be the result of the metal-poor nature of the H I gas. Alternatively,
the H I reservoir may be largely inert, the star formation being
dominated by cosmological accretion. Time lags between gas accretion
and star formation may also reduce the apparent SFEgas,
as may galaxy winds, which can expel most of the gas into the
intergalactic medium. Hence, on global scales, XMPs could be H
I-dominated, high-specific-SFR (≳10-10 yr-1),
low-SFEgas (≲10-9 yr-1) systems,
in which the total H I mass is likely not a good predictor of the
total H2 mass, nor of the SFR.

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Title: Search for Extremely Metal-poor Galaxies in the Sloan Digital
Sky Survey. (II). High Electron Temperature Objects
Authors: Sánchez Almeida, J.; Pérez-Montero, E.; Morales-Luis, A. B.;
Muñoz-Tuñón, C.; García-Benito, R.; Nuza, S. E.; Kitaura, F. S.
2016ApJ...819..110S Altcode: 2016arXiv160101631S
Extremely metal-poor (XMP) galaxies are defined to have a
gas-phase metallicity smaller than a tenth of the solar value
(12+{log}[{{O/H}}]&lt; 7.69). They are uncommon, chemically and possibly
dynamically primitive, with physical conditions characteristic of
earlier phases of the universe. We search for new XMPs in the Sloan
Digital Sky Survey (SDSS) in a work that complements Paper I. This time,
high electron temperature objects are selected; metals are a main
coolant of the gas, so metal-poor objects contain high-temperature
gas. Using the algorithm k-means, we classify 788,677 spectra to
select 1281 galaxies that have particularly intense [O III]λ4363
with respect to [O III]λ5007, which is a proxy for high electron
temperature. The metallicity of these candidates was computed using
a hybrid technique consistent with the direct method, rendering 196
XMPs. A less restrictive noise constraint provides a larger set with 332
candidates. Both lists are provided in electronic format. The selected
XMP sample has a mean stellar mass around {10}8 {M}⊙
, with the dust mass ∼ {10}3{M}⊙ 
for typical star-forming regions. In agreement with previous findings,
XMPs show a tendency to be tadpole-like or cometary. Their underlying
stellar continuum corresponds to a fairly young stellar population (&lt;
1 {{Gyr}}), although young and aged stellar populations coexist at the
low-metallicity starbursts. About 10% of the XMPs show large N/O. Based
on their location in constrained cosmological numerical simulations,
XMPs have a strong tendency to appear in voids and to avoid galaxy
clusters. The puzzling 2%-solar low-metallicity threshold exhibited
by XMPs remains.

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Title: Evidence of Cosmic Accretion in Local Tadpole Galaxies
Authors: Elmegreen, Debra M.; Elmegreen, Bruce; Sanchez Almeida,
Jorge; Munoz-Tunon, Casiana; Rafelski, Marc; Gallagher, John S.;
Mendez-Abreu, Jairo; Amorin, R.; Filho, M.; Ascasibar, Y.; Papaderos,
P.; Vilchez, J.; Perez-Montero, E.
2016AAS...22711101E Altcode:
Star formation in galaxies over cosmic time may be driven by gas
accretion from the cosmic web. Spectra of local extremely metal-poor
galaxies (XMPs), obtained using the Gran Telescopio Canarias, show
oxygen abundances that decrease by a factor of 5 to 10 in the main
star-forming regions compared with the disks in 9 of 10 observed
galaxies. The results suggest that the galaxies have accreted metal-poor
gas in the starburst regions. Tadpole galaxies, which have a main
star-forming head and a tail, are common at high redshift but rare
locally. Local tadpoles tend to be XMPs. We present multiband HST
WFC3 observations of Kiso 5639, one of the tadpole XMPs in our GTC
sample. There are faint extended H alpha filaments, and dense star
clusters in the midst of a powerful starburst. The clusters, with
log masses of 4 to 5, are reminiscent of those found in other dwarf
irregular galaxies where impacting gas streams have been suggested.

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Title: Localized Starbursts in Dwarf Galaxies Produced by the Impact
of Low-metallicity Cosmic Gas Clouds
Authors: Sánchez Almeida, J.; Elmegreen, B. G.; Muñoz-Tuñón,
C.; Elmegreen, D. M.; Pérez-Montero, E.; Amorín, R.; Filho, M. E.;
Ascasibar, Y.; Papaderos, P.; Vílchez, J. M.
2015ApJ...810L..15S Altcode: 2015arXiv150900180S
Models of galaxy formation predict that gas accretion from the cosmic
web is a primary driver of star formation over cosmic history. Except
in very dense environments where galaxy mergers are also important,
model galaxies feed from cold streams of gas from the web that penetrate
their dark matter halos. Although these predictions are unambiguous,
the observational support has been indirect so far. Here, we report
spectroscopic evidence for this process in extremely metal-poor galaxies
(XMPs) of the local universe, taking the form of localized starbursts
associated with gas having low metallicity. Detailed abundance analyses
based on Gran Telescopio Canarias optical spectra of 10 XMPs show that
the galaxy hosts have metallicities around 60% solar, on average,
while the large star-forming regions that dominate their integrated
light have low metallicities of some 6% solar. Because gas mixes
azimuthally in a rotation timescale (a few hundred Myr), the observed
metallicity inhomogeneities are only possible if the metal-poor gas
fell onto the disk recently. We analyze several possibilities for
the origin of the metal-poor gas, favoring the metal-poor gas infall
predicted by numerical models. If this interpretation is correct, XMPs
trace the cosmic web gas in their surroundings, making them probes to
examine its properties.

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Title: Gas accretion from halos to disks: observations, curiosities,
and problems
Authors: Elmegreen, Bruce G.; Hunter, Deidre A.; Ashley, Trisha;
Nidever, David; Johnson, Megan; Simpson, Caroline; Pokrel, Nau Raj;
Sanchez Almeida, Jorge; Munoz-Tunon, Casiana; Elmegreen, Debra;
Mendez-Abreu, Jairo; Belen Morales-Luis, Ana
2015IAUGA..2251098E Altcode:
Accretion of gas from the cosmic web to galaxy halos and ultimately
their disks is a prediction of modern cosmological models but is rarely
observed directly or at the full rate expected from star formation. Here
we illustrate possible large-scale cosmic HI accretion onto the nearby
dwarf starburst galaxy IC10, observed with the VLA and GBT. We also
suggest that cosmic accretion is the origin of sharp metallicity drops
in the starburst regions of other dwarf galaxies, as observed with the
10-m GCT. Finally, we question the importance of cosmic accretion in
normal dwarf irregulars, for which a recent study of their far-outer
regions sees no need for, or evidence of, continuing gas buildup.

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Title: Gas accretion from the cosmic web in the local Universe
Authors: Sánchez Almeida, J.; Elmegreen, B. G.; Muñoz-Tuñón, C.;
Elmegreen, D. M.
2015hsa8.conf..335S Altcode:
Numerical simulations predict that gas accretion from the cosmic web
drives star formation in disks galaxies. The process is more important
in low mass haloes, therefore, when galaxies were low mass in the early
universe, but also in dwarf galaxies of the local universe. The central
role played by cosmic gas infall is as clear from numerical simulations
as it is obscure to observations. The gas that falls in is predicted to
be tenuous, patchy, partly ionized, multi-temperature, low-metallicity,
and large-scale; thus, hard to show in a single observation. One of
the most compelling cases for gas accretion at work in the local
universe comes from the extremely metal poor (XMP) galaxies. They
show metallicity inhomogeneities associated with star-forming regions,
so that large starbursts have lower metallicity that then underlying
galaxy. This and other evidence suggest that local XMP are primitive
disks sustained by cosmic web gas accretion. In the contribution we
described the case posed by XMP galaxies to support the existence of
cosmological gas accretion.

---------------------------------------------------------
Title: MEGARA, the new IFU and MOS for the GTC
Authors: Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias-Páramo,
J.; Sánchez Moreno, F. M.; Vílchez, J. M.; García Vargas,
M. L.; Arrillaga, X.; Carrera, M. A.; Castillo-Morales, A.;
Castillo-Domínguez, E.; Cedazo, R.; Eliche-Moral, M. C.; Ferrusca,
D.; González-Guardia, E.; Lefort, B.; Maldonado, M.; Marino, R. A.;
Martínez-Delgado, I.; Morales Durán, I.; Mujica, E.; Páez, G.;
Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.; Sánchez-Blanco,
E.; Tulloch, S.; Velázquez, M.; Zamorano, J.; Aguerri, A. L.;
Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.;
Cenarro, J.; Chávez, M.; García, M.; Guichard, J.; Guzmán, R.;
Herrero, A.; Huélamo, N., Hughes, D.; Jiménez-Vicente, J.; Kehrig,
C.; Márquez, I.; Masegosa, J.; Mayya, Y. D.; Méndez-Abreu, J.;
Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González,
P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa,
J. M.; Rodríguez-Merino, L.; Rosa-González, D.; Sánchez-Almeida,
J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S. F.;
Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.;
Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.;
Tsamis, Y.; Vega, O.; Villar, V.
2015hsa8.conf..804G Altcode:
MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para
Astronomía) is the future intermediate-resolution optical
Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) of the
10.4m GTC telescope. The instrument can be used to observe either
a contiguous (100% filling factor) field-of-view of 12.5×11.3
arcsec^{2} or 92 objects anywhere in a 3.5×3.5 arcmin^{2} field
patrolled by robotic actuactors attached to optical-fiber minibundles,
respectively in its IFU and MOS modes. The MEGARA Consortium is led by
the Universidad Complutense de Madrid (UCM, Spain) and also includes
the Instituto Nacional de Astrofísica, óptica y Electrónica (INAOE,
Mexico), the Instituto de Astrofísica de Andalucía (IAA-CSIC, Spain)
and the Universidad Politécnica de Madrid (UPM, Spain). The instrument
passed its Critical Design Review (CDR) on late 2014 and is currently in
construction phase with a planned date for the start of operations at
GTC on early 2017. In this paper we summarize the main characteristics
of the instrument and the status of the project.

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Title: Extremely Metal-poor Galaxies: The Environment
Authors: Filho, M. E.; Sánchez Almeida, J.; Muñoz-Tuñón, C.;
Nuza, S. E.; Kitaura, F.; Heß, S.
2015ApJ...802...82F Altcode: 2015arXiv150106709F
We have analyzed bibliographical observational data and theoretical
predictions, in order to probe the environment in which extremely
metal-poor dwarf galaxies (XMPs) reside. We have assessed the H i
component and its relation to the optical galaxy, the cosmic web type
(voids, sheets, filaments and knots), the overdensity parameter and
analyzed the nearest galaxy neighbors. The aim is to understand the
role of interactions and cosmological accretion flows in the XMP
observational properties, particularly the triggering and feeding of
the star formation. We find that XMPs behave similarly to Blue Compact
Dwarfs; they preferably populate low-density environments in the local
universe: ∼60% occupy underdense regions, and ∼75% reside in voids
and sheets. This is more extreme than the distribution of irregular
galaxies, and in contrast to those regions preferred by elliptical
galaxies (knots and filaments). We further find results consistent
with previous observations; while the environment does determine the
fraction of a certain galaxy type, it does not determine the overall
observational properties. With the exception of five documented cases
(four sources with companions and one recent merger), XMPs do not
generally show signatures of major mergers and interactions; we find
only one XMP with a companion galaxy within a distance of 100 kpc,
and the H i gas in XMPs is typically well-behaved, demonstrating
asymmetries mostly in the outskirts. We conclude that metal-poor
accretion flows may be driving the XMP evolution. Such cosmological
accretion could explain all the major XMP observational properties:
isolation, lack of interaction/merger signatures, asymmetric optical
morphology, large amounts of unsettled, metal-poor H i gas, metallicity
inhomogeneities, and large specific star formation.

---------------------------------------------------------
Title: On the Use of the Index N2 to Derive the Metallicity in
Metal-poor Galaxies
Authors: Morales-Luis, A. B.; Pérez-Montero, E.; Sánchez Almeida,
J.; Muñoz-Tuñón, C.
2014ApJ...797...81M Altcode: 2014arXiv1410.2850M
The N2 index ([N II] λ6584/Hα) is used to determine emission line
galaxy metallicities at all redshifts, including high redshift,
where galaxies tend to be metal-poor. The initial aim of this work
was to improve the calibrations used to infer oxygen abundance from
N2 by employing updated low-metallicity galaxy databases. We compare
N2 and the metallicity determined using the direct method for the set
of extremely metal-poor galaxies compiled by Morales-Luis et al. To
our surprise, the oxygen abundance presents a tendency to be constant
with N2, with a very large scatter. Consequently, we find that the
existing N2 calibrators overestimate the oxygen abundance for most
low-metallicity galaxies, and can therefore only be used to set upper
limits to the true metallicity in low-metallicity galaxies. An explicit
expression for this limit is given. In addition, we try to explain the
observed scatter using photoionization models. It is mostly due to the
different evolutionary state of the H II regions producing the emission
lines, but it also arises due to differences in N/O among the galaxies.

---------------------------------------------------------
Title: Star Formation in Tadpole Galaxies
Authors: Muñoz-Tuñon, Casiana; Sanchez Almeida, Jorge; Elmegreen,
Debra M.; Elmegreen, Bruce G.
2014mbhe.conf...96M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Does Cold-Flow Accretion Drive Star-Formation in the Local
Universe?
Authors: Sánchez Almeida, J.; Muñoz, C.; Elmegreen, D.; Elmegreen,
B. G.; Méndez-Abreu, J.
2014mysc.conf...99S Altcode:
Numerical simulations of galaxy formation predict direct gas
accretion from the cosmic web to be the main mode of disk galaxy
formation. However, observational evidence of the process are so far
scarce and indirect. This write up should be regarded as a progress
report listing several of our works which, in the long term, aim at
finding evidence for or against pristine gas accretion as a driver of
star formation in the local Universe. Here we motivate the interest
of the study, and then refer the reader to the actual papers for
further details.

---------------------------------------------------------
Title: Chemical Evolution of Super Star Clusters in a Positive Star
Formation Feedback Scenario
Authors: Mollá, M.; Sánchez Almeida, J.; Terlevich, R.;
Tenorio-Tagle, G.; Silich, S.; Muñoz-Tuñón, C.
2014mysc.conf...79M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Star formation sustained by gas accretion
Authors: Sánchez Almeida, Jorge; Elmegreen, Bruce G.; Muñoz-Tuñón,
Casiana; Elmegreen, Debra Meloy
2014A&ARv..22...71S Altcode: 2014arXiv1405.3178S
Numerical simulations predict that metal-poor gas accretion from the
cosmic web fuels the formation of disk galaxies. This paper discusses
how cosmic gas accretion controls star formation, and summarizes
the physical properties expected for the cosmic gas accreted by
galaxies. The paper also collects observational evidence for gas
accretion sustaining star formation. It reviews evidence inferred
from neutral and ionized hydrogen, as well as from stars. A number
of properties characterizing large samples of star-forming galaxies
can be explained by metal-poor gas accretion, in particular, the
relationship among stellar mass, metallicity, and star-formation rate
(the so-called fundamental metallicity relationship). They are put
forward and analyzed. Theory predicts gas accretion to be particularly
important at high redshift, so indications based on distant objects are
reviewed, including the global star-formation history of the universe,
and the gas around galaxies as inferred from absorption features in
the spectra of background sources.

---------------------------------------------------------
Title: MEGARA: a new generation optical spectrograph for GTC
Authors: Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias-Páramo,
J.; Cedazo, R.; Vílchez, J. M.; García-Vargas, M. L.; Arrillaga,
X.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.;
Eliche-Moral, M. C.; Ferrusca, D.; González-Guardia, E.; Lefort,
B.; Maldonado, M.; Marino, R. A.; Martínez-Delgado, I.; Morales
Durán, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.;
Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez,
M.; Zamorano, J.; Aguerri, A. L.; Barrado y Naváscues, D.; Bertone,
E.; Cardiel, N.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.;
Guichard, J.; Gúzman, R.; Herrero, A.; Huélamo, N.; Hughes, D.;
Jiménez-Vicente, J.; Kehrig, C.; Márquez, I.; Masegosa, J.; Mayya,
Y. D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert,
M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.;
Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rosa-González,
D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez,
P.; Sánchez Moreno, F. M.; Sánchez, S. F.; Sarajedini, A.; Serena,
F.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.;
Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega,
O.; Villar, V.
2014SPIE.9147E..0OG Altcode:
MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para
Astronomía) is an optical Integral-Field Unit (IFU) and Multi-Object
Spectrograph (MOS) designed for the GTC 10.4m telescope in La
Palma. MEGARA offers two IFU fiber bundles, one covering 12.5x11.3
arcsec2 with a spaxel size of 0.62 arcsec (Large Compact
Bundle; LCB) and another one covering 8.5x6.7 arcsec2 with
a spaxel size of 0.42 arcsec (Small Compact Bundle; SCB). The MEGARA
MOS mode will allow observing up to 100 objects in a region of 3.5x3.5
arcmin2 around the two IFU bundles. Both the LCB IFU and
MOS capabilities of MEGARA will provide intermediate-to-high spectral
resolutions (RFWHM~6,000, 12,000 and 18,700, respectively for
the low-, mid- and high-resolution Volume Phase Holographic gratings)
in the range 3650-9700ÅÅ. These values become RFWHM~7,000,
13,500, and 21,500 when the SCB is used. A mechanism placed at the
pseudo-slit position allows exchanging the three observing modes and
also acts as focusing mechanism. The spectrograph is a collimator-camera
system that has a total of 11 VPHs simultaneously available (out of the
18 VPHs designed and being built) that are placed in the pupil by means
of a wheel and an insertion mechanism. The custom-made cryostat hosts
an E2V231-84 4kx4k CCD. The UCM (Spain) leads the MEGARA Consortium that
also includes INAOE (Mexico), IAA-CSIC (Spain), and UPM (Spain). MEGARA
is being developed under a contract between GRANTECAN and UCM. The
detailed design, construction and AIV phases are now funded and the
instrument should be delivered to GTC before the end of 2016.

---------------------------------------------------------
Title: A fast version of the k-means classification algorithm for
astronomical applications
Authors: Ordovás-Pascual, I.; Sánchez Almeida, J.
2014A&A...565A..53O Altcode: 2014arXiv1404.3097O
Context. K-means is a clustering algorithm that has been used to
classify large datasets in astronomical databases. It is an unsupervised
method, able to cope very different types of problems. Aims:
We check whether a variant of the algorithm called single pass k-means
can be used as a fast alternative to the traditional k-means. Methods: The execution time of the two algorithms are compared
when classifying subsets drawn from the SDSS-DR7 catalog of galaxy
spectra. Results: Single-pass k-means turn out to be between
20% and 40% faster than k-means and provide statistically equivalent
classifications. This conclusion can be scaled up to other larger
databases because the execution time of both algorithms increases
linearly with the number of objects. Conclusions: Single-pass
k-means can be safely used as a fast alternative to k-means.

---------------------------------------------------------
Title: Star Formation in Tadpole Galaxies
Authors: Munoz-Tunon, Casiana; Sanchez Almeida, Jorge; Elmegreen,
Debra M.; Elmegreen, Bruce G.
2014arXiv1404.5170M Altcode:
Tadpole Galaxies look like a star forming head with a tail structure
to the side. They are also named cometaries. In a series of recent
works we have discovered a number of issues that lead us to consider
them extremely interesting targets. First, from images, they are disks
with a lopsided starburst. This result is firmly established with long
slit spectroscopy in a nearby representative sample. They rotate with
the head following the rotation pattern but displaced from the rotation
center. Moreover, in a search for extremely metal poor (XMP) galaxies,
we identified tadpoles as the dominant shapes in the sample- nearly 80%
of the local XMP galaxies have a tadpole morphology. In addition, the
spatially resolved analysis of the metallicity shows the remarkable
result that there is a metallicity drop right at the position of
the head. This is contrary to what intuition would say and difficult
to explain if star formation has happened from gas processed in the
disk. The result could however be understood if the star formation is
driven by pristine gas falling into the galaxy disk. If confirmed,
we could be unveiling, for the first time, cool flows in action in
our nearby world. The tadpole class is relatively frequent at high
redshift - 10% of resolvable galaxies in the Hubble UDF but less than
1% in the local Universe. They are systems that could track cool flows
and test models of galaxy formation.

---------------------------------------------------------
Title: Metallicity Inhomogeneities in Local Star-forming Galaxies
as a Sign of Recent Metal-poor Gas Accretion
Authors: Sánchez Almeida, J.; Morales-Luis, A. B.; Muñoz-Tuñón,
C.; Elmegreen, D. M.; Elmegreen, B. G.; Méndez-Abreu, J.
2014ApJ...783...45S Altcode: 2014arXiv1401.1985S
We measure the oxygen metallicity of the ionized gas along the major
axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and
SDSSJ2238+14, show sime0.5 dex metallicity decrements in inner regions
with enhanced star formation activity. This behavior is similar to
the metallicity drop observed in a number of local tadpole galaxies by
Sánchez Almeida et al., and was interpreted as showing early stages
of assembling in disk galaxies, with the star formation sustained
by external metal-poor gas accretion. The agreement with tadpoles
has several implications. (1) It proves that galaxies other than the
local tadpoles present the same unusual metallicity pattern. (2) Our
metallicity inhomogeneities were inferred using the direct method, thus
discarding systematic errors usually attributed to other methods. (3)
Taken together with the tadpole data, our findings suggest a threshold
around one-tenth the solar value for the metallicity drops to show
up. Although galaxies with clear metallicity drops are rare, the
physical mechanism responsible for them may sustain a significant part
of the star formation activity in the local universe. We argue that
the star formation dependence of the mass-metallicity relationship,
as well as other general properties followed by most local disk
galaxies, is naturally interpreted as side effects of pristine gas
infall. Alternatives to the metal-poor gas accretion are examined
as well.

---------------------------------------------------------
Title: Extremely metal-poor galaxies: The H I content
Authors: Filho, M. E.; Winkel, B.; Sánchez Almeida, J.; Aguerri,
J. A.; Amorín, R.; Ascasibar, Y.; Elmegreen, B. G.; Elmegreen,
D. M.; Gomes, J. M.; Humphrey, A.; Lagos, P.; Morales-Luis, A. B.;
Muñoz-Tuñón, C.; Papaderos, P.; Vílchez, J. M.
2013A&A...558A..18F Altcode: 2013arXiv1307.4899F
Context. Extremely metal-poor (XMP) galaxies are chemically, and
possibly dynamically, primordial objects in the local Universe. Aims: Our objective is to characterize the H i content of the XMP
galaxies as a class, using as a reference the list of 140 known local
XMPs compiled by Morales-Luis et al. (2011). Methods: We have
observed 29 XMPs, which had not been observed before at 21 cm, using
the Effelsberg radio telescope. This information was complemented with
H i data published in literature for a further 53 XMPs. In addition,
optical data from the literature provided morphologies, stellar masses,
star-formation rates and metallicities. Results: Effelsberg H i
integrated flux densities are between 1 and 15 Jy km s-1,
while line widths are between 20 and 120 km s-1. H i
integrated flux densities and line widths from literature are in
the range 0.1-200 Jy km s-1 and 15-150 km s-1,
respectively. Of the 10 new Effelsberg detections, two sources show an
asymmetric double-horn profile, while the remaining sources show either
asymmetric (seven sources) or symmetric (one source) single-peak 21 cm
line profiles. An asymmetry in the H i line profile is systematically
accompanied by an asymmetry in the optical morphology. Typically,
the g-band stellar mass-to-light ratios are ~0.1, whereas the H
i gas mass-to-light ratios may be up to two orders of magnitude
larger. Moreover, H i gas-to-stellar mass ratios fall typically
between 10 and 20, denoting that XMPs are extremely gas-rich. We find
an anti-correlation between the H i gas mass-to-light ratio and the
luminosity, whereby fainter XMPs are more gas-rich than brighter XMPs,
suggesting that brighter sources have converted a larger fraction of
their H i gas into stars. The dynamical masses inferred from the H
i line widths imply that the stellar mass does not exceed 5% of the
dynamical mass, while the H i mass constitutes between 20 and 60%
of the dynamical mass. Furthermore, the dark matter mass fraction
spans a wide range, but can account, in some cases, for over 65%
of the dynamical mass. XMPs are found to be outliers of the mass -
and luminosity - metallicity relation, whereby they lack metals for
their estimated dynamical mass and luminosity, suggesting the presence
of pristine gas. However, they generally follow the luminosity - and
baryonic mass Tully-Fisher relation, indicating that the H i gas is
partly virialized and contains some rotational support. 60% of the
XMP sources show a small velocity offset (10-40 km s-1)
between the H i gas and the stellar/nebular component, implying that,
in these sources, the H i gas is not tightly coupled to the stars and
ionized gas. The effective yields provided by oxygen are often larger
than the standard theoretical yields, suggesting that the observed
H i gas is relatively metal-free. 80% of the XMP sources present
asymmetric optical morphology - 60 XMPs show cometary structure, 11
show two bright star-forming knots and 18 show multiple star-forming
regions. Star-formation rates are found to be similar to those typically
found in BCDs. However, specific star-formation rates are high,
with timescales to double their stellar mass, at the current rate,
of typically less than 1 Gyr. Conclusions: XMP galaxies are
among the most gas-rich objects in the local Universe. The observed H
i component suggests kinematical disruption and hints at a primordial
composition. Full Fig. 1, Tables 3-5 are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>Reduced
spectra are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A18">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A18</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: HI spectra of extremely metal-poor
(XMP) galaxies (Filho+, 2013)
Authors: Filho, M. E.; Winkel, B.; Sanchez Almeida, J.; Aguerri, J. A.;
Amorin, R.; Ascasibar, Y.; Elmegreen, B. G.; Elmegreen, D. M.; Gomes,
J. M.; Humphrey, A.; Lagos, P.; Morales-Luis, A. B.; Munoz-Tunon,
C.; Papaderos, P.; Vilchez, J. M.
2013yCat..35580018F Altcode: 2013yCat..35589018F
The HI spectra, in FITS format, of the XMP galaxies observed with
Effelsberg. (5 data files).

---------------------------------------------------------
Title: Massive Clumps in Local Galaxies: Comparisons with
High-redshift Clumps
Authors: Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Sánchez
Almeida, J.; Muñoz-Tuñón, C.; Dewberry, J.; Putko, J.; Teich, Y.;
Popinchalk, M.
2013ApJ...774...86E Altcode: 2013arXiv1308.0306E
Local UV-bright galaxies in the Kiso survey include clumpy systems with
kiloparsec-size star complexes that resemble clumpy young galaxies
in surveys at high redshift. We compare clump masses and underlying
disks in several dozen galaxies from each of these surveys to the star
complexes and disks of normal spirals. Photometry and spectroscopy for
the Kiso and spiral sample come from the Sloan Digital Sky Survey. We
find that the largest Kiso clumpy galaxies resemble Ultra Deep Field
(UDF) clumpies in terms of the star formation rates, clump masses,
and clump surface densities. Clump masses and surface densities in
normal spirals are smaller. If the clump masses are proportional
to the turbulent Jeans mass in the interstellar medium, then for
the most luminous galaxies in the sequence of normal:Kiso:UDF, the
turbulent speeds and surface densities increase in the proportions
1.0:4.7:5.0 and 1.0:4.0:5.1, respectively, for fixed restframe B-band
absolute magnitude. For the least luminous galaxies in the overlapping
magnitude range, the turbulent speed and surface density trends are
1.0:2.7:7.4 and 1.0:1.4:3.0, respectively. We also find that while all
three types have radially decreasing disk intensities when measured
with ellipse-fit azimuthal averages, the average profiles are more
irregular for UDF clumpies (which are viewed in their restframe UV)
than for Kiso galaxies (viewed at g-band), and major axis intensity
scans are even more irregular for the UDF than Kiso galaxies. Local
clumpy galaxies in the Kiso survey appear to be intermediate between
UDF clumpies and normal spirals.

---------------------------------------------------------
Title: A Virtual Observatory Census to Address Dwarfs Origins
(AVOCADO). I. Science goals, sample selection, and analysis tools
Authors: Sánchez-Janssen, R.; Amorín, R.; García-Vargas, M.;
Gomes, J. M.; Huertas-Company, M.; Jiménez-Esteban, F.; Mollá, M.;
Papaderos, P.; Pérez-Montero, E.; Rodrigo, C.; Sánchez Almeida,
J.; Solano, E.
2013A&A...554A..20S Altcode: 2013arXiv1301.5320S
Context. Even though they are by far the most abundant of all
galaxy types, the detailed properties of dwarf galaxies are still
only poorly characterised - especially because of the observational
challenge that their intrinsic faintness and weak clustering properties
represent. Aims: AVOCADO aims at establishing firm conclusions
on the formation and evolution of dwarf galaxies by constructing and
analysing a homogeneous, multiwavelength dataset for a statistically
significant sample of approximately 6500 nearby dwarfs (Mi
- 5 log h100 &gt; - 18 mag). The sample is selected to
lie within the 20 &lt; D &lt; 60 h100-1 Mpc
volume covered by the SDSS-DR7 footprint, and is thus volume-limited
for Mi - 5 log h100 &lt; -16 mag dwarfs - but
includes ≈1500 fainter systems. We will investigate the roles of mass
and environment in determining the current properties of the different
dwarf morphological types - including their structure, their star
formation activity, their chemical enrichment history, and a breakdown
of their stellar, dust, and gas content. Methods: We present
the sample selection criteria and describe the suite of analysis tools,
some of them developed in the framework of the Virtual Observatory. We
use optical spectra and UV-to-NIR imaging of the dwarf sample to derive
star formation rates, stellar masses, ages, and metallicities - which
are supplemented with structural parameters that are used to classify
them morphologically. This unique dataset, coupled with a detailed
characterisation of each dwarf's environment, allows for a fully
comprehensive investigation of their origins and enables us to track the
(potential) evolutionary paths between the different dwarf types. Results: We characterise the local environment of all dwarfs in our
sample, paying special attention to trends with current star formation
activity. We find that virtually all quiescent dwarfs are located in the
vicinity (projected distances ≲ 1.5 h100-1 Mpc)
of ≳ L∗ companions, consistent with recent results. While
star-forming dwarfs are preferentially found at separations of the
order of 1 h100-1 Mpc, there appears to be a
tail towards low separations (≲ 100 h100-1 kpc)
in the distribution of projected distances. We speculate that, modulo
projection effects, this probably represents a genuine population of
late-type dwarfs caught upon first infall about their host and before
environmental quenching has fully operated. In this context, these
results suggest that internal mechanisms - such as gas exhaustion via
star formation or feedback effects - are not sufficient to completely
cease the star formation activity in dwarf galaxies, and that becoming
the satellite of a massive central galaxy appears to be a necessary
condition to create a quiescent dwarf.

---------------------------------------------------------
Title: Outliers of the ASK classification as targets for GTC
serendipity
Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C.
2013RMxAC..42..111S Altcode:
We classified the ∼10^6 galaxy spectra in SDSS/DR7 (Abazajian
et al. 2009) into only 17 major classes (ASK classification;
Sánchez Almeida et al. 2010). The algorithm provides the goodness
of the classification for each individual spectrum and, therefore,
a straightforward way to identify those targets which do not fit in
the ASK classes. A significant part of these outliers turn out to be
failures of the automatic reduction pipelines. However, a fraction
of them represents genuine unusual objects which deserve detailed
follow up work to assess their nature. These targets provide a unique
opportunity for GTC to carry out serendipitous discoveries. This
contribution summarizes the main properties of the outliers.

---------------------------------------------------------
Title: MEGARA: The future IFU and MOS of the 10.4 m GTC
Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Vílchez, J. M.;
Sánchez, F. M.; García-Vargas, M. L.; Arrillaga, X.; Carrera, M. A.;
Castillo-Morales, A.; Castillo, E.; Cedazo, R.; Eliche-Moral, M. C.;
Ferrusca, D.; González, E.; Maldonado, M.; Marino, R. A.; Martínez,
I.; Morales Durán, I.; Mújica, E.; Pascual, S.; Pérez-Calpena,
A.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Serena, F.; Tulloch,
S. M.; Villar, V.; Zamorano, J.; Barrado y Naváscues, D.; Bertone,
E.; Cardiel, N.; Cava, A.; Cenarro, A. J.; Chávez, M.; García, M.;
Guichard, J.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D.;
Iglesias, J.; Jiménez-Vicente, J.; Aguerri, J. A. L.; Mayya, Y. D.;
Méndez-Abreu, J. M.; Mollá, M.; Muñoz-Tuñón, C.; Torres-Peimbert,
S.; Peimbert, M.; Pérez-González, P. G.; Pérez-Montero, E.;
Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.;
Rosa-González, D.; Sánchez Almeida, J.; Sánchez Contreras, C.;
Sánchez-Blázquez, P.; Sánchez, S.; Sarajedini, A.; Silich, S.;
Simón, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Trujillo,
I.; Tsamis, Y.; Vega, O.
2013RMxAC..42...90G Altcode:
In these proceedings we summarize the characteristics and current
status of MEGARA, the future optical IFU and MOS for the 10.4 m
GTC. MEGARA is being built by a Consortium led by the UCM (Spain)
that also includes the INAOE (Mexico), the IAA-CSIC (Spain) and the
UPM (Spain). The MEGARA IFU offers two different bundles, one called
LCB with a field-of-view of 14×12 arcsec^2 and a spaxel size of 0.685
arcsec yielding spectral resolutions between R=6000-19000 and another
one called SCB covering 10×8 arcsec^2 with 0.48 arcsec spaxels and
resolutions R=8000-25000. The MOS component allows observing up to 100
targets in 3.5×3.5 arcmin^2. In September 2010 MEGARA was selected
as the next optical spectrograph for GTC. Its PDR is scheduled for
March 2012 with First Light on 2015.

---------------------------------------------------------
Title: Oxygen abundance from strong-line methods at extremely low
metallicities
Authors: Morales-Luis, A. B.; Sánchez Almeida, J.; Pérez Montero,
E.; Muñoz-Tuñon, C.; Aguerri, J. A. L.; Vilchez, J. M.; Terlevich,
E.; Terlevich, R.
2013hsa7.conf..294M Altcode:
The determination of oxygen abundance in nebulae requires measuring a
significant number of emission lines distributed along a wide spectral
range. The required measurements are hard to obtain at high redshift,
where sources are very faint, and where the accessible spectral range
is limited. These difficulties are often overcome using empirical
relationships between the oxygen abundance and the fluxes in a small
number of strong lines. The so-called strong-line methods are often
the only practical alternative for metallicity estimate at high
redshift. In this sense, the low metallicities range is particularly
important since high redshift objects are primitive and so of low
metallic content. One of the most widely used relationships links the
oxygen with the ratio between [NII]6583 and Hα. This relationship
shows a large scatter at low metallicity. In an effort to bring
down the errors, we re-calibrated the relationship using a large
sample of extremely metal-poor galaxies. The SDSS spectra of the
galaxies were all analyzed in the same way to minimize systematic
errors. To our surprise, the decrease of scatter reveals that the
ratio [N{II}]6583 to Hα seems to be independent of metallicity at
low oxygen abundance (12+log[{O}/{H}] &lt; 7.6). This result casts
doubts on the metallicities of high-redshift objects based on the
relationship. We explain how the re-calibration was carried (including
the sample selection and the abundance determinations). In addition,
we try explain what produces the lack of correlation.

---------------------------------------------------------
Title: Study of the AGN population at intermediate redshifts in the
SHARDS survey
Authors: Hernán-Caballero, A.; Alonso-Herrero, A.,; Pérez-González,
P. G.; Cava, A.; Barro, G.; Balcells, M.; Cardiel, N.; Cenarro, J.;
Cepa, J.; Charlot, S.; Cimatti, A.; Conselice, C. J.; Daddi, E.;
Donley, J.; Elbaz, D.; Ferreras, I.; Gallego, J.; Gobat, R.; Guzmán,
R.; Renzini, A.; Rieke, G.; Rodríguez-Espinosa, J. M.; Tresse, L.;
Trujillo, I.; Villar, V.; Zamorano, J.; de Diego, J. A. López-Aguerri,
J. A.; Masegosa, J.; Muñoz Tuñon, C.; Prieto, M.; Sánchez Almeida,
J.
2013hsa7.conf..442H Altcode:
We present the first results of a program aimed to study the stellar
populations of moderate luminosity X-ray selected Active Galactic Nuclei
(AGN) at intermediate redshifts. We use observations taken as part of
the Survey for High-z Absorption Red and Dead Sources (SHARDS) with
the optical instrument OSIRIS on the 10.4m Gran Telescopio Canarias
(GTC). SHARDS is an on-going ESO/GTC Large Programme that is observing
the GOODS-North cosmological field with 24 medium-band filters (22
of 17nm and 3 of 25nm) in the spectral range 500-950nm. Although
SHARDS was originally designed to select and study the properties of
high-z massive and passively evolving galaxies, it can also provide
very valuable information about AGN at intermediate redshifts. We
show that the SHARDS observations provide sufficiently high spectral
resolution (R∼50) to detect broad absorption stellar features (e.g.,
the 4000Å{} break) as well as emission lines and to estimate accurate
photometric redshifts. Together with the SHARDS observations we use
the wealth of multi-wavelength data from the UV to radio available
for this cosmological field to study the stellar populations and star
formation histories of AGN at z∼0.5-1.2.

---------------------------------------------------------
Title: Local Tadpole Galaxies: Dynamics and Metallicity
Authors: Sánchez Almeida, J.; Muñoz-Tuñón, C.; Elmegreen, D. M.;
Elmegreen, B. G.; Méndez-Abreu, J.
2013ApJ...767...74S Altcode: 2013arXiv1302.4352S
Tadpole galaxies, with a bright peripheral clump on a faint tail, are
morphological types unusual in the nearby universe but very common early
on. Low mass local tadpoles were identified and studied photometrically
in a previous work, which we complete here analyzing their chemical and
dynamical properties. We measure Hα velocity curves of seven local
tadpoles, representing 50% of the initial sample. Five of them show
evidence for rotation (~70%), and a sixth target hints at it. Often
the center of rotation is spatially offset with respect to the tadpole
head (three out of five cases). The size and velocity dispersion
of the heads are typical of giant H II regions, and three of them
yield dynamical masses in fair agreement with their stellar masses as
inferred from photometry. In four cases the velocity dispersion at the
head is reduced with respect to its immediate surroundings. The oxygen
metallicity estimated from [N II] λ6583/Hα often shows significant
spatial variations across the galaxies (~0.5 dex), being smallest
at the head and larger elsewhere. The resulting chemical abundance
gradients are opposite to the ones observed in local spirals, but agrees
with disk galaxies at high redshift. We interpret the metallicity
variation as a sign of external gas accretion (cold-flows) onto the
head of the tadpole. The galaxies are low-metallicity outliers of the
mass-metallicity relationship. In particular, two of the tadpole heads
are extremely metal poor, with a metallicity smaller than a tenth of
the solar value. These two targets are also very young (ages smaller
than 5 Myr). All these results combined are consistent with the local
tadpole galaxies being disks in early stages of assembling, with their
star formation sustained by accretion of external metal-poor gas.

---------------------------------------------------------
Title: Automated Unsupervised Classification of the Sloan Digital
Sky Survey Stellar Spectra using k-means Clustering
Authors: Sánchez Almeida, J.; Allende Prieto, C.
2013ApJ...763...50S Altcode: 2012arXiv1211.5321S
Large spectroscopic surveys require automated methods of analysis. This
paper explores the use of k-means clustering as a tool for automated
unsupervised classification of massive stellar spectral catalogs. The
classification criteria are defined by the data and the algorithm,
with no prior physical framework. We work with a representative set
of stellar spectra associated with the Sloan Digital Sky Survey (SDSS)
SEGUE and SEGUE-2 programs, which consists of 173,390 spectra from 3800
to 9200 Å sampled on 3849 wavelengths. We classify the original spectra
as well as the spectra with the continuum removed. The second set only
contains spectral lines, and it is less dependent on uncertainties of
the flux calibration. The classification of the spectra with continuum
renders 16 major classes. Roughly speaking, stars are split according
to their colors, with enough finesse to distinguish dwarfs from giants
of the same effective temperature, but with difficulties to separate
stars with different metallicities. There are classes corresponding
to particular MK types, intrinsically blue stars, dust-reddened,
stellar systems, and also classes collecting faulty spectra. Overall,
there is no one-to-one correspondence between the classes we derive
and the MK types. The classification of spectra without continuum
renders 13 classes, the color separation is not so sharp, but it
distinguishes stars of the same effective temperature and different
metallicities. Some classes thus obtained present a fairly small
range of physical parameters (200 K in effective temperature, 0.25
dex in surface gravity, and 0.35 dex in metallicity), so that the
classification can be used to estimate the main physical parameters
of some stars at a minimum computational cost. We also analyze the
outliers of the classification. Most of them turn out to be failures
of the reduction pipeline, but there are also high redshift QSOs,
multiple stellar systems, dust-reddened stars, galaxies, and, finally,
odd spectra whose nature we have not deciphered. The template spectra
representative of the classes are publicly available in the online
journal and at ftp://stars:kmeans@ftp.iac.es.

---------------------------------------------------------
Title: The Ninth Data Release of the Sloan Digital Sky Survey:
First Spectroscopic Data from the SDSS-III Baryon Oscillation
Spectroscopic Survey
Authors: Ahn, Christopher P.; Alexandroff, Rachael; Allende Prieto,
Carlos; Anderson, Scott F.; Anderton, Timothy; Andrews, Brett H.;
Aubourg, Éric; Bailey, Stephen; Balbinot, Eduardo; Barnes, Rory;
Bautista, Julian; Beers, Timothy C.; Beifiori, Alessandra; Berlind,
Andreas A.; Bhardwaj, Vaishali; Bizyaev, Dmitry; Blake, Cullen H.;
Blanton, Michael R.; Blomqvist, Michael; Bochanski, John J.; Bolton,
Adam S.; Borde, Arnaud; Bovy, Jo; Brandt, W. N.; Brinkmann, J.; Brown,
Peter J.; Brownstein, Joel R.; Bundy, Kevin; Busca, N. G.; Carithers,
William; Carnero, Aurelio R.; Carr, Michael A.; Casetti-Dinescu,
Dana I.; Chen, Yanmei; Chiappini, Cristina; Comparat, Johan;
Connolly, Natalia; Crepp, Justin R.; Cristiani, Stefano; Croft,
Rupert A. C.; Cuesta, Antonio J.; da Costa, Luiz N.; Davenport,
James R. A.; Dawson, Kyle S.; de Putter, Roland; De Lee, Nathan;
Delubac, Timothée; Dhital, Saurav; Ealet, Anne; Ebelke, Garrett L.;
Edmondson, Edward M.; Eisenstein, Daniel J.; Escoffier, S.; Esposito,
Massimiliano; Evans, Michael L.; Fan, Xiaohui; Femenía Castellá,
Bruno; Fernández Alvar, Emma; Ferreira, Leticia D.; Filiz Ak, N.;
Finley, Hayley; Fleming, Scott W.; Font-Ribera, Andreu; Frinchaboy,
Peter M.; García-Hernández, D. A.; García Pérez, A. E.; Ge,
Jian; Génova-Santos, R.; Gillespie, Bruce A.; Girardi, Léo;
González Hernández, Jonay I.; Grebel, Eva K.; Gunn, James E.; Guo,
Hong; Haggard, Daryl; Hamilton, Jean-Christophe; Harris, David W.;
Hawley, Suzanne L.; Hearty, Frederick R.; Ho, Shirley; Hogg, David W.;
Holtzman, Jon A.; Honscheid, Klaus; Huehnerhoff, J.; Ivans, Inese I.;
Ivezić, Željko; Jacobson, Heather R.; Jiang, Linhua; Johansson,
Jonas; Johnson, Jennifer A.; Kauffmann, Guinevere; Kirkby, David;
Kirkpatrick, Jessica A.; Klaene, Mark A.; Knapp, Gillian R.; Kneib,
Jean-Paul; Le Goff, Jean-Marc; Leauthaud, Alexie; Lee, Khee-Gan;
Lee, Young Sun; Long, Daniel C.; Loomis, Craig P.; Lucatello, Sara;
Lundgren, Britt; Lupton, Robert H.; Ma, Bo; Ma, Zhibo; MacDonald,
Nicholas; Mack, Claude E.; Mahadevan, Suvrath; Maia, Marcio A. G.;
Majewski, Steven R.; Makler, Martin; Malanushenko, Elena; Malanushenko,
Viktor; Manchado, A.; Mandelbaum, Rachel; Manera, Marc; Maraston,
Claudia; Margala, Daniel; Martell, Sarah L.; McBride, Cameron K.;
McGreer, Ian D.; McMahon, Richard G.; Ménard, Brice; Meszaros,
Sz.; Miralda-Escudé, Jordi; Montero-Dorta, Antonio D.; Montesano,
Francesco; Morrison, Heather L.; Muna, Demitri; Munn, Jeffrey A.;
Murayama, Hitoshi; Myers, Adam D.; Neto, A. F.; Nguyen, Duy Cuong;
Nichol, Robert C.; Nidever, David L.; Noterdaeme, Pasquier; Nuza,
Sebastián E.; Ogando, Ricardo L. C.; Olmstead, Matthew D.; Oravetz,
Daniel J.; Owen, Russell; Padmanabhan, Nikhil; Palanque-Delabrouille,
Nathalie; Pan, Kaike; Parejko, John K.; Parihar, Prachi; Pâris,
Isabelle; Pattarakijwanich, Petchara; Pepper, Joshua; Percival,
Will J.; Pérez-Fournon, Ismael; Pérez-Ràfols, Ignasi; Petitjean,
Patrick; Pforr, Janine; Pieri, Matthew M.; Pinsonneault, Marc H.;
Porto de Mello, G. F.; Prada, Francisco; Price-Whelan, Adrian M.;
Raddick, M. Jordan; Rebolo, Rafael; Rich, James; Richards, Gordon
T.; Robin, Annie C.; Rocha-Pinto, Helio J.; Rockosi, Constance M.;
Roe, Natalie A.; Ross, Ashley J.; Ross, Nicholas P.; Rossi, Graziano;
Rubiño-Martin, J. A.; Samushia, Lado; Sanchez Almeida, J.; Sánchez,
Ariel G.; Santiago, Basílio; Sayres, Conor; Schlegel, David J.;
Schlesinger, Katharine J.; Schmidt, Sarah J.; Schneider, Donald P.;
Schultheis, Mathias; Schwope, Axel D.; Scóccola, C. G.; Seljak,
Uros; Sheldon, Erin; Shen, Yue; Shu, Yiping; Simmerer, Jennifer;
Simmons, Audrey E.; Skibba, Ramin A.; Skrutskie, M. F.; Slosar, A.;
Sobreira, Flavia; Sobeck, Jennifer S.; Stassun, Keivan G.; Steele,
Oliver; Steinmetz, Matthias; Strauss, Michael A.; Streblyanska, Alina;
Suzuki, Nao; Swanson, Molly E. C.; Tal, Tomer; Thakar, Aniruddha R.;
Thomas, Daniel; Thompson, Benjamin A.; Tinker, Jeremy L.; Tojeiro,
Rita; Tremonti, Christy A.; Vargas Magaña, M.; Verde, Licia; Viel,
Matteo; Vikas, Shailendra K.; Vogt, Nicole P.; Wake, David A.; Wang,
Ji; Weaver, Benjamin A.; Weinberg, David H.; Weiner, Benjamin J.;
West, Andrew A.; White, Martin; Wilson, John C.; Wisniewski, John P.;
Wood-Vasey, W. M.; Yanny, Brian; Yèche, Christophe; York, Donald G.;
Zamora, O.; Zasowski, Gail; Zehavi, Idit; Zhao, Gong-Bo; Zheng, Zheng;
Zhu, Guangtun; Zinn, Joel C.
2012ApJS..203...21A Altcode: 2012arXiv1207.7137S
The Sloan Digital Sky Survey III (SDSS-III) presents the first
spectroscopic data from the Baryon Oscillation Spectroscopic Survey
(BOSS). This ninth data release (DR9) of the SDSS project includes
535,995 new galaxy spectra (median z ~ 0.52), 102,100 new quasar
spectra (median z ~ 2.32), and 90,897 new stellar spectra, along
with the data presented in previous data releases. These spectra were
obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline,
which determines radial velocities, surface temperatures, surface
gravities, and metallicities of stars, has been updated and refined with
improvements in temperature estimates for stars with T eff
&lt; 5000 K and in metallicity estimates for stars with [Fe/H] &gt;
-0.5. DR9 includes new stellar parameters for all stars presented in
DR8, including stars from SDSS-I and II, as well as those observed as
part of the SEGUE-2. The astrometry error introduced in the DR8 imaging
catalogs has been corrected in the DR9 data products. The next data
release for SDSS-III will be in Summer 2013, which will present the
first data from the APOGEE along with another year of data from BOSS,
followed by the final SDSS-III data release in 2014 December.

---------------------------------------------------------
Title: MEGARA: the future optical IFU and multi-object spectrograph
for the 10.4m GTC telescope
Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Sánchez,
F. M.; Vílchez Medina, J. M.; García-Vargas, M. L.; Arrillaga,
X.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.;
Cedazo, R.; Eliche-Moral, C.; Ferrusca, D.; González-Guardia, E.;
Maldonado, M.; Marino, R. A.; Martínez-Delgado, I.; Morales Durán,
I.; Mújica, E.; Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.;
Sánchez-Blanco, E.; Serena, F.; Tulloch, S.; Villar, V.; Zamorano,
J.; Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.;
Cenarro, J.; Chávez, M.; García, M.; Guichard, J.; Gúzman, R.;
Herrero, A.; Huélamo, N.; Hughes, D.; Iglesias, J.; Jiménez-Vicente,
J.; Aguerri, A. L.; Mayya, D.; Méndez-Abreu, J. M.; Mollá, M.;
Muñoz-Tuñón, C.; Peimbert, S.; Peimbert, M.; Pérez-González,
P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa,
J. M.; Rodríguez-Merino, L.; Rosa, D.; Sánchez-Almeida, J.;
Sánchez Contreras, C.; Sánchez-Blázquez, Patricia; Sánchez, S.;
Sarajedini, A.; Silich, S.; Simón, S.; Tenorio-Tagle, G.; Terlevich,
E.; Terlevich, R.; Trujillo, I.; Tsamis, Y.; Vega, O.
2012SPIE.8446E..4QG Altcode:
In these proceedings we give a summary of the characteristics and
current status of the MEGARA instrument, the future optical IFU and
MOS for the 10.4-m Gran Telescopio Canarias (GTC). MEGARA is being
built by a Consortium of public research institutions led by the
Universidad Complutense de Madrid (UCM, Spain) that also includes INAOE
(Mexico), IAA-CSIC (Spain) and UPM (Spain). The MEGARA IFU includes
two different fiber bundles, one called LCB (Large Compact Bundle)
with a field-of-view of 12.5×11.3 arcsec2 and a spaxel size
of 0.62 arcsec yielding spectral resolutions between R=6,800-17,000
and another one called SCB (Small Compact Bundle) covering 8.5×6.7
arcsec2 with hexagonally-shaped and packed 0.42-arcsec
spaxels and resolutions R=8,000-20,000. The MOS component allows
observing up to 100 targets in 3.5×3.5 arcmin2. Both the
IFU bundles and the set of 100 robotic positioners of the MOS will
be placed at one of the GTC Folded-Cass foci while the spectrographs
(one in the case of the MEGARA-Basic concept) will be placed at the
Nasmyth platform. On March 2012 MEGARA passed the Preliminary Design
Review and its first light is expected to take place at the end of 2015.

---------------------------------------------------------
Title: Qualitative Interpretation of Galaxy Spectra
Authors: Sánchez Almeida, J.; Terlevich, R.; Terlevich, E.; Cid
Fernandes, R.; Morales-Luis, A. B.
2012ApJ...756..163S Altcode: 2012arXiv1207.3928S
We describe a simple step-by-step guide to qualitative interpretation
of galaxy spectra. Rather than an alternative to existing automated
tools, it is put forward as an instrument for quick-look analysis
and for gaining physical insight when interpreting the outputs
provided by automated tools. Though the recipe is for general
application, it was developed for understanding the nature of the
Automatic Spectroscopic K-means-based (ASK) template spectra. They
resulted from the classification of all the galaxy spectra in the
Sloan Digital Sky Survey data release 7, thus being a comprehensive
representation of the galaxy spectra in the local universe. Using the
recipe, we give a description of the properties of the gas and the
stars that characterize the ASK classes, from those corresponding to
passively evolving galaxies, to H II galaxies undergoing a galaxy-wide
starburst. The qualitative analysis is found to be in excellent
agreement with quantitative analyses of the same spectra. We compare
the mean ages of the stellar populations with those inferred using the
code STARLIGHT. We also examine the estimated gas-phase metallicity
with the metallicities obtained using electron-temperature-based
methods. A number of byproducts follow from the analysis. There is a
tight correlation between the age of the stellar population and the
metallicity of the gas, which is stronger than the correlations between
galaxy mass and stellar age, and galaxy mass and gas metallicity. The
galaxy spectra are known to follow a one-dimensional sequence, and
we identify the luminosity-weighted mean stellar age as the affine
parameter that describes the sequence. All ASK classes happen to have
a significant fraction of old stars, although spectrum-wise they are
outshined by the youngest populations. Old stars are metal-rich or
metal-poor depending on whether they reside in passive galaxies or in
star-forming galaxies.

---------------------------------------------------------
Title: Flux-Calibrated Emission-Line Imaging of Extended Sources
Using GTC/OSIRIS Tunable Filters
Authors: Mayya, Y. D.; Rosa González, D.; Vega, O.; Méndez-Abreu, J.;
Terlevich, R.; Terlevich, E.; Bertone, E.; Rodríguez-Merino, L. H.;
Muñoz-Tuñón, C.; Rodríguez-Espinosa, J. M.; Sánchez Almeida,
J.; Aguerri, J. A. L.
2012PASP..124..895M Altcode: 2012arXiv1203.1842M
We investigate the utility of the tunable filters (TFs) for obtaining
flux-calibrated emission-line maps of extended objects such as galactic
nebulae and nearby galaxies using the Optical System for Imaging and
low Resolution Integrated Spectroscopy (OSIRIS) at the 10.4-m Gran
Telescopio Canarias (GTC). Despite the relatively large field of view
(FoV) of OSIRIS (8‧ × 8‧), the change
in wavelength across the field (∼80 Å) and the long tail of the
TF spectral response function are hindrances for obtaining accurate
flux-calibrated emission-line maps of extended sources. The purpose
of this article is to demonstrate that emission-line maps useful for
diagnostics of nebulae can be generated over the entire FoV of OSIRIS
if we make use of theoretically well-understood characteristics of
TFs. We have successfully generated the flux-calibrated images of the
nearby large late-type spiral galaxy M101 in the emission lines of Hα,
[N II]λ6583, [S II]λ6716 and [S II]λ6731. We find that the present
uncertainty in setting the central wavelength of TFs (∼1 Å) is the
biggest source of error in the emission-line fluxes. By comparing the
Hα fluxes of H II regions in our images with the fluxes derived from
Hα images obtained using narrow-band filters, we estimate an error of
∼11% in our fluxes. The flux-calibration of the images was carried
out by fitting the Sloan Digital Sky Survey (SDSS) griz magnitudes
of in-frame stars with the stellar spectra from the SDSS spectral
database. This method resulted in an accuracy of 3% in flux-calibration
of any narrow-band image, which is as good as, if not better than,
what has been feasible using the observations of spectrophotometric
standard stars. Thus time-consuming calibration images need not be
taken. A user-friendly script under the IRAF environment was developed
and is available on request. Based on observations made with the
Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio
del Roque de los Muchachos of the Instituto de Astrofísica de Canarias,
in the island of La Palma.

---------------------------------------------------------
Title: Stokes V Asymmetries in the Quiet Sun
Authors: Viticchié, B.; Sanchez Almeida, J.; Moro, D. D.; Berrilli, F.
2012ASPC..455..271V Altcode:
Stokes profiles emerging from the magnetized quiet photosphere and
observed by the Solar Optical Telescope (SOT) spectropolarimeter
(SP) aboard the Hinode satellite present a large variety of complex
shapes. These are indicative of unresolved magnetic structures and/or
gradients along the line of sight that have been overlooked in the
inversion analyses performed so far. The interpretation of the complex
shapes of SOT/SP Stokes V profiles for the understanding of the quiet
Sun magnetism must be seriously considered in the near future. In fact,
Stokes V profiles significantly deviating from an antisymmetric shape
are rather common in the quiet Sun and, in particular, in intranetwork
(IN) regions. Here we present the results of the analysis of the
shapes of SOT/SP Stokes V profiles performed through a k-means
classification. Such an analysis aims at defining different profile
classes representative of SOT/SP polarization measurements. We found
that about 35 classes can be defined from quiet Sun measurements. Among
these, two main subsets can be recognized: network profiles and IN
profiles. Approximately 34% of quiet Sun profiles present important
asymmetries. From such results, it follows that new inversion
techniques able to reproduce line asymmetries must be considered in
future analyses of Hinode SOT/SP measurements. The number of line
shapes to be reproduced by such analyses is finite and small.

---------------------------------------------------------
Title: Local Tadpole Galaxies
Authors: Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida,
Jorge; Muñoz-Tuñón, Casiana; Putko, Joseph; Dewberry, Janosz
2012ApJ...750...95E Altcode: 2012arXiv1203.2486E
Tadpole galaxies have a giant star-forming region at the end of
an elongated intensity distribution. Here we use Sloan Digital Sky
Survey data to determine the ages, masses, and surface densities of
the heads and tails in 14 local tadpoles selected from the Kiso and
Michigan surveys of UV-bright galaxies, and we compare them to tadpoles
previously studied in the Hubble Ultra Deep Field. The young stellar
mass in the head scales linearly with rest-frame galaxy luminosity,
ranging from ~105 M ⊙ at galaxy absolute
magnitude U = -13 mag to 109 M ⊙ at U = -20
mag. The corresponding head surface density increases from several
M ⊙ pc-2 locally to 10-100 M ⊙
pc-2 at high redshift, and the star formation rate (SFR)
per unit area in the head increases from ~0.01 M ⊙
yr-1 kpc-2 locally to ~1 M ⊙
yr-1 kpc-2 at high z. These local values are
normal for star-forming regions, and the increases with redshift
are consistent with other cosmological SFRs, most likely reflecting
an increase in gas abundance. The tails in the local sample look
like bulge-free galaxy disks. Their photometric ages decrease from
several Gyr to several hundred Myr with increasing z, and their
surface densities are more constant than the surface densities of
the heads. The far-outer intensity profiles in the local sample are
symmetric and exponential. We suggest that most local tadpoles are
bulge-free galaxy disks with lopsided star formation, perhaps from
environmental effects such as ram pressure or disk impacts, or from
a Jeans length comparable to half the disk size.

---------------------------------------------------------
Title: Dissecting the morphological and spectroscopic properties of
galaxies in the local Universe. I. Elliptical galaxies
Authors: Aguerri, J. A. L.; Huertas-Company, M.; Sánchez Almeida,
J.; Muñoz-Tuñón, C.
2012A&A...540A.136A Altcode: 2012arXiv1201.2409A
 Aims: We revisit the scaling relations and star-forming histories
of local elliptical galaxies using a novel selection method applied
to the Sloan Digital Sky Survey DR7. Methods: We combine
two probability-based automated spectroscopic and morphological
classifications of ~600 000 galaxies with z &lt; 0.25 to isolate true
elliptical galaxies. Our sample selection method does not introduce
artificial cuts into the parameters describing the galaxy but instead
associates every object with a weight measuring the probability of being
in a given spectro-morphological class. Thus, the sample minimizes
the selection biases. Results: We show that morphologically
defined ellipticals are basically distributed into three spectral
classes, which dominate at different stellar masses. The bulk of
the population (~50%) is formed by a well-defined class of galaxies
with old stellar populations that formed their stars at very early
epochs in a short episode of star formation. They dominate the
scaling relations of elliptical galaxies known from previous works
and represent the canonical elliptical class. At the low mass end,
we find a population of ellipticals with relatively large shapes and
smaller velocity dispersions at fixed stellar mass, which seem to have
experienced a more recent episode of star formation probably triggered
by gas-rich minor mergers. The high mass end tends to be dominated
by a third spectral class that is slightly more metal rich and hosts
more efficient stellar formation than the reference class. This third
class contributes to the curvature in the mass-size relation at high
masses reported in previous works. Our method is therefore able to
isolate the typical spectra of elliptical galaxies following different
evolutionary pathways. Appendix A is available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: ASK spectroscopic sequence of
galaxies (Ascasibar+, 2011)
Authors: Ascasibar, Y.; Sanchez Almeida, J.
2012yCat..74152417A Altcode:
We identify a spectroscopic sequence of galaxies, analogous to
the Hubble sequence of morphological types, based on the Automatic
Spectroscopic K-means-based (ASK) classification. Considering galaxy
spectra as multidimensional vectors, the majority of the spectral
classes are distributed along a well-defined curve going from the
earliest to the latest types, suggesting that the optical spectra
of normal galaxies can be described in terms of a single affine
parameter. Optically bright active galaxies, however, appear as
an independent, roughly orthogonal branch that intersects the main
sequence exactly at the transition between early and late types. (1 data file).

---------------------------------------------------------
Title: Center-to-limb variation of the area covered by magnetic
bright points in the quiet Sun
Authors: Bonet, J. A.; Cabello, I.; Sánchez Almeida, J.
2012A&A...539A...6B Altcode: 2011arXiv1112.2513B
Context. The quiet Sun magnetic fields produce ubiquitous bright points
(BPs) that cover a significant fraction of the solar surface. Their
contribution to the total solar irradiance (TSI) is so-far unknown. Aims: We aim at measuring the center-to-limb variation (CLV) of
the fraction of solar surface covered by quiet Sun magnetic bright
points. The fraction is referred to as the fraction of covered
surface (FCS). Methods: We count the area covered by BPs in
G-band images obtained at various heliocentric angles with the 1-m
Swedish Solar Telescope on La Palma. We restore the images to bring
them close to the diffraction limit of the instrument (~0'.1). 
Results: The FCS is largest at the disk center (≃1%), and then drops
down to become ≃0.2% at μ ≃ 0.3 (where μ is the cosine of the
heliocentric angle). The relationship has a large scatter, which we
evaluate by comparing different subfields within our FOVs. We develop
a toy-model to describe the observed CLV, which considers the BPs as
depressions in the mean solar photosphere characterized by a depth,
a width, and a spread in the inclinations. Although the model is
poorly constrained by observations, it shows the BPs to be shallow
structures (depth &lt; width) with a large range of inclinations. We
also estimate how different parts of the solar disk may contribute to
the TSI variations, finding that 90% is contributed by BPs with μ &gt;
0.5, and half of it is due to BPs with μ &gt; 0.8.

---------------------------------------------------------
Title: Local Tadpole Galaxies
Authors: Elmegreen, Debra M.; Elmegreen, B. G.; Sanchez Almeida, J.;
Muñoz-Tuñón, C.; Putko, J.; Dewberry, J.
2012AAS...21924409E Altcode:
Tadpole galaxies have a giant star-forming region at the end of
an elongated intensity distribution. The origin of this asymmetric
structure is not known, although suggestions range from ram pressure
to mergers. We use SDSS data to determine the ages, masses, surface
densities, and star formation rates of the heads and tails in 13 local
tadpoles identified from Kiso and Michigan surveys and compare them
to tadpoles previously surveyed in the Hubble Ultra Deep Field. The
young stellar mass in the head scales linearly with restframe galaxy
luminosity, ranging from 105 Mo at galaxy U =
-13 mag to 109 Mo at U = -20 mag. The young star
surface density in the head is relatively small for local tadpoles,
1 Mo pc-2, but much larger for high redshift
tadpoles, 10 - 100 Mo pc-2. The star formation
rate per unit area increases with increasing redshift by 2 orders of
magnitude from z=0 to 3. J. Putko was supported through NSF REU
grant AST-1005024, and J. Dewberry through the Vassar URSI program.

---------------------------------------------------------
Title: The Distribution of Galaxies in Spectral Space
Authors: Ascasibar, Y.; Sánchez Almeida, J.
2012adm..book...63A Altcode:
Considering Galaxy spectra as multidimensional vectors, we use the
k-means algorithm and the minimum spanning tree to show that the data
in the Sloan Digital Sky Survey do not fill the entire space but are
confined to a manifold with very low dimensionality. More precisely, all
the spectra can be described in terms of only two degrees of freedom:
one discrete parameter labelling the Galaxy as "normal" or "active,"
and one continuous affine parameter describing its position along the
corresponding sequence.

---------------------------------------------------------
Title: Systematic Search for Extremely Metal-poor Galaxies in the
Sloan Digital Sky Survey
Authors: Morales-Luis, A. B.; Sánchez Almeida, J.; Aguerri, J. A. L.;
Muñoz-Tuñón, C.
2011ApJ...743...77M Altcode: 2011arXiv1109.0235M
We carry out a systematic search for extremely metal-poor (XMP) galaxies
in the spectroscopic sample of Sloan Digital Sky Survey (SDSS) data
release 7 (DR7). The XMP candidates are found by classifying all the
galaxies according to the form of their spectra in a region 80 Å wide
around Hα. Due to the data size, the method requires an automatic
classification algorithm. We use k-means. Our systematic search
renders 32 galaxies having negligible [N II] lines, as expected in XMP
galaxy spectra. Twenty-one of them have been previously identified
as XMP galaxies in the literature—the remaining 11 are new. This
was established after a thorough bibliographic search that yielded
only some 130 galaxies known to have an oxygen metallicity 10 times
smaller than the Sun (explicitly, with 12 + log (O/H) &lt;= 7.65). XMP
galaxies are rare; they represent 0.01% of the galaxies with emission
lines in SDSS/DR7. Although the final metallicity estimate of all
candidates remains pending, strong-line empirical calibrations indicate
a metallicity about one-tenth solar, with the oxygen metallicity
of the 21 known targets being 12 + log (O/H) ~= 7.61 ± 0.19. Since
the SDSS catalog is limited in apparent magnitude, we have been able
to estimate the volume number density of XMP galaxies in the local
universe, which turns out to be (1.32 ± 0.23) × 10-4
Mpc-3. The XMP galaxies constitute 0.1% of the galaxies in
the local volume, or ~0.2% considering only emission-line galaxies. All
but four of our candidates are blue compact dwarf galaxies, and 24 of
them have either cometary shape or are formed by chained knots.

---------------------------------------------------------
Title: Wavelength Calibration for OSIRIS/GTC Tunable Filters
Authors: Méndez-Abreu, J.; Sánchez Almeida, J.; Muñoz-Tuñón,
C.; Rodríguez-Espinosa, J. M.; Aguerri, J. A. L.; Rosa González,
D.; Mayya, Y. D.; Vega, O.; Terlevich, R.; Terlevich, E.; Bertone,
E.; Rodríguez-Merino, L. H.
2011PASP..123.1107M Altcode: 2011arXiv1107.4000M
OSIRIS (Optical System for Imaging and low Resolution Integrated
Spectroscopy) is the first light instrument of the Gran Telescopio
Canarias (GTC). It provides a flexible and competitive tunable filter
(TF). Since it is based on a Fabry-Perot interferometer working in
a collimated beam, the TF transmission wavelength depends on the
position of the target with respect to the optical axis. This effect
is nonnegligible and must be accounted for in the data reduction. Our
article establishes a wavelength calibration for OSIRIS TF with the
accuracy required for spectrophotometric measurements using the
full field of view (FOV) of the instrument. The variation of the
transmission wavelength λ(R) across the FOV is well described by
, where λ(0) is the central wavelength, R represents the physical
distance from the optical axis, and f2 = 185.70 ± 0.17 mm
is the effective focal length of the camera lens. This new empirical
calibration yields an accuracy better than 1 Å across the entire
OSIRIS FOV (∼8‧ × 8‧), provided that the
position of the optical axis is known within 45 μm (≡1.5 binned
pixels). We suggest a calibration protocol to grant such precision
over long periods, upon realignment of OSIRIS optics, and in different
wavelength ranges. This calibration differs from the calibration in
the OSIRIS manual, which nonetheless provides an accuracy ≲1 Å for
R ≲ 2‧. This work is based on observations made
with the GTC operated on the island of La Palma by Grantecan in the
Spanish Observatorio del Roque de los Muchachos.

---------------------------------------------------------
Title: Do galaxies form a spectroscopic sequence?
Authors: Ascasibar, Y.; Sánchez Almeida, J.
2011MNRAS.415.2417A Altcode: 2011arXiv1104.1388A; 2011MNRAS.tmp..956A
We identify a spectroscopic sequence of galaxies, analogous to
the Hubble sequence of morphological types, based on the Automatic
Spectroscopic K-means-based (ASK) classification. Considering galaxy
spectra as multidimensional vectors, the majority of the spectral
classes are distributed along a well-defined curve going from the
earliest to the latest types, suggesting that the optical spectra
of normal galaxies can be described in terms of a single affine
parameter. Optically bright active galaxies, however, appear as
an independent, roughly orthogonal branch that intersects the main
sequence exactly at the transition between early and late types.

---------------------------------------------------------
Title: Relationship between Hubble Type and Spectroscopic Class in
Local Galaxies
Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón,
C.; Huertas-Company, M.
2011ApJ...735..125S Altcode: 2011arXiv1104.4864S
We compare the Hubble type and the spectroscopic class of the galaxies
with spectra in the Sloan Digital Sky Survey Data Release 7. As has
long been known, elliptical galaxies tend to be red whereas spiral
galaxies tend to be blue; however, this relationship presents a large
scatter, which we measure and quantify in detail for the first time. We
compare the Automatic Spectroscopic K-means-based classification (ASK)
with most of the commonly used morphological classifications. Despite
the degree of subjectivity involved in morphological classifications,
all of them provide consistent results. Given a spectral class, the
morphological type wavers with a standard deviation between 2 and 3 T
types, and the same large dispersion characterizes the variability of
spectral classes given a morphological type. The distributions of Hubble
types for each ASK class are very skewed—they present long tails that
extend to late morphological types in the red galaxies and to early
morphological types in the blue spectroscopic classes. The scatter
is not produced by problems with the classification and it remains
when particular subsets are considered—low and high galaxy masses,
low and high density environments, barred and non-barred galaxies,
edge-on galaxies, small and large galaxies, or when a volume-limited
sample is considered. A considerable fraction of red galaxies are
spirals (40%-60%), but they never present very late Hubble types (Sd or
later). Even though red spectra are not associated with ellipticals,
most ellipticals do have red spectra: 97% of the ellipticals in the
morphological catalog by Nair &amp; Abraham used here for reference
belong to ASK 0, 2, or 3; only 3% of the ellipticals are blue. The
galaxies in the green valley class (ASK 5) are mostly spirals, and the
active galactic nuclei class (ASK 6) presents a large scatter of Hubble
types from E to Sd. We investigate variations with redshift using a
volume-limited subsample mainly formed by luminous red galaxies. From
redshift 0.25 to the present, the galaxies redden from ASK 2 to ASK 0,
as expected from the passive evolution of their stellar populations. Two
of the ASK classes (1 and 4) gather edge-on spirals, and they may be
useful in studies requiring knowledge of the intrinsic shape of a galaxy
(e.g., weak-lensing calibration).

---------------------------------------------------------
Title: Asymmetries of the Stokes V profiles observed by HINODE SOT/SP
in the quiet Sun
Authors: Viticchié, B.; Sánchez Almeida, J.
2011A&A...530A..14V Altcode: 2011arXiv1103.1987V
 Aims: A recent analysis of polarization measurements of HINODE
SOT/SP in the quiet Sun pointed out very complex shapes of Stokes
V profiles. Here we present the first classification of the SOT/SP
circular polarization measurements with the aim of highlighting
exhaustively the whole variety of Stokes V shapes emerging from the
quiet Sun. Methods: k-means is used to classify HINODE SOT/SP
Stokes V profiles observed in the quiet Sun network and internetwork
(IN). We analyze a 302 × 162 arcsec2 field-of-view (FOV)
that can be considered a complete sample of quiet Sun measurements
performed at the disk center with 0.32 arcsec angular resolution and
10-3 polarimetric sensitivity. This classification allows us
to divide the whole dataset into classes, with each class represented by
a cluster profile, i.e., the average of the profiles in the class. Results: The set of 35 cluster profiles derived from the analysis
completely characterizes the SOT/SP quiet Sun measurements. The
separation between network and IN profile shapes is evident - classes
in the network are not present in the IN, and vice versa. Asymmetric
profiles are approximately 93% of the total number of profiles. Among
these, about 34% of the profiles are strongly asymmetric, and they
can be divided into three families: blue-lobe, red-lobe, and Q-like
profiles. The blue-lobe profiles tend to be associated with upflows
(granules), whereas the red-lobe and Q-like ones appear in downflows
(intergranular lanes). Conclusions: These profiles need to be
interpreted considering model atmospheres different from a uniformly
magnetized Milne-Eddington (ME) atmosphere, i.e., characterized by
gradients and/or discontinuities in the magnetic field and velocity
along the line-of-sight (LOS). We propose the use of cluster profiles
as a standard archive to test inversion codes, and to check the validity
and/or completeness of synthetic profiles produced by MHD simulations.

---------------------------------------------------------
Title: Relationship between Hubble type and spectroscopic class in
local galaxies
Authors: Sánchez Almeida, J.
2011iac..talk..282S Altcode: 2011iac..talk..218S
No abstract at ADS

---------------------------------------------------------
Title: The Magnetic Fields of the Quiet Sun
Authors: Sánchez Almeida, J.; Martínez González, M.
2011ASPC..437..451S Altcode: 2011arXiv1105.0387S
This work reviews our understanding of the magnetic fields observed
in the quiet Sun. The subject has undergone a major change during the
last decade (quiet revolution), and it will remain changing since the
techniques of diagnostic employed so far are known to be severely
biased. Keeping these caveats in mind, our work covers the main
observational properties of the quiet Sun magnetic fields: magnetic
field strengths, unsigned magnetic flux densities, magnetic field
inclinations, as well as the temporal evolution on short time-scales
(loop emergence), and long time-scales (solar cycle). We also summarize
the main theoretical ideas put forward to explain the origin of the
quiet Sun magnetism. A final prospective section points out various
areas of solar physics where the quiet Sun magnetism may have an
important physical role to play (chromospheric and coronal structure,
solar wind acceleration, and solar elemental abundances).

---------------------------------------------------------
Title: MISMA Interpretation of Stokes V Asymmetries Measured by
HINODE in Internetwork and Network Regions
Authors: Viticchiè, B.; Sánchez Almeida, J.; Del Moro, D.;
Berrilli, F.
2011ASPC..437..127V Altcode:
Stokes profiles observed in the quiet photosphere by HINODE SOT/SP
present very complex shapes. These are indicative of unresolved
magnetic structures and/or gradients along the line of sight in
HINODE's pixels which have linear dimension of ∼0.15". We present
the first interpretation of the Stokes profile asymmetries measured
in the 630 nm Fe I lines by SOT/SP in both quiet Sun internetwork
(IN) and network. The inversion is carried out under the hypothesis
of MIcro-Structured Magnetized Atmosphere (MISMA) which can account
for sub-pixel structuring of magnetic fields. The MISMA code is
able to reproduce the observed asymmetries in a very satisfactory
way. Moreover, 25% of inverted profiles present asymmetries that
are interpreted as produced by regions in which mixed polarities are
present. kG field strengths are found in both network and internetwork
regions. In the internetwork both kG fields and hG fields are found. Our
analysis constrains the magnetic field of only 4.5% of the analyzed
photosphere. The rest of the plasma can be thought to be filled by
weak fields not contributing to the detected polarization signals.

---------------------------------------------------------
Title: Interpretation of HINODE SOT/SP asymmetric Stokes profiles
observed in the quiet Sun network and internetwork
Authors: Viticchié, B.; Sánchez Almeida, J.; Del Moro, D.;
Berrilli, F.
2011A&A...526A..60V Altcode: 2010arXiv1009.6065V
Stokes profiles emerging from the magnetized solar photosphere and
observed by SOT/SP aboard the HINODE satellite exhibit a variety of
complex shapes. These are indicative of unresolved magnetic structures
that have been overlooked in the inversion analyses performed so
far. Here we present the first interpretation of the Stokes profile
asymmetries measured in the ion{Fe}{i} 630 nm lines by SOT/SP, in both
quiet Sun internetwork (IN) and network regions. The inversion is
carried out based on the hypothesis of MIcro-Structured Magnetized
Atmosphere (MISMA), where the unresolved structure is assumed
to be optically thin. We analyze a 29.52 arcsec × 31.70 arcsec
subfield carefully selected to be representative of the properties
of a 302 arcsec × 162 arcsec quiet Sun field-of-view (FOV) at the
disk center. The inversion code is able to reproduce the observed
asymmetries in a very satisfactory way, including 35% of the inverted
profiles with large asymmetries. The inversion code interprets 25%
of inverted profiles as emerging from pixels in which both positive
and negative polarities coexist. These pixels are located in either
frontiers between opposite polarity patches or very quiet regions. The
kG field strengths are found at the base of the photosphere in both
network and IN regions; in the case of the latter, both kG fields and
hG fields are admixed. When considering the magnetic properties of
the mid photosphere, most kG fields do not exist, and the statistics
is dominated by hG fields. According to the magnetic filling factors
derived from the inversion, we constrain the magnetic field of only
4.5% of the analyzed photosphere (and this percentage reduces to 1.3%
when considering all pixels, including those with low polarization
that have not been analyzed). The properties of the rest of the plasma
imply that weak fields do not contribute to the detected polarization
signals. The average flux densities derived in the full subfield and
IN regions are higher than those derived from the same dataset by
Milne-Eddington (ME) inversion. We detect large asymmetries in the
HINODE SOT/SP polarization profiles. These are not negligible in quiet
Sun data. The MISMA inversion code reproduces them in a satisfactory
way, and provides a statistical description of the magnetized IN and
network which partly differs and complements the results obtained so
far. The importance of having a complete interpretation of the line
profile shapes is therefore clearly evident.

---------------------------------------------------------
Title: Revisiting the Hubble sequence in the SDSS DR7 spectroscopic
sample: a publicly available Bayesian automated classification
Authors: Huertas-Company, M.; Aguerri, J. A. L.; Bernardi, M.; Mei,
S.; Sánchez Almeida, J.
2011A&A...525A.157H Altcode: 2010arXiv1010.3018H
We present an automated morphological classification in 4 types (E,
S0, Sab, Scd) of ~700 000 galaxies from the SDSS DR7 spectroscopic
sample based on support vector machines. The main new property
of the classification is that we associate a probability to each
galaxy of being in the four morphological classes instead of
assigning a single class. The classification is therefore better
adapted to nature where we expect a continuous transition between
different morphological types. The algorithm is trained with a
visual classification and then compared to several independent
visual classifications including the Galaxy Zoo first-release
catalog. We find a very good correlation between the automated
classification and classical visual ones. The compiled catalog is
intended for use in different applications and is therefore freely
available through a dedicated webpage* and soon from the CasJobs
database. Full catalog is only available in electronic form
at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A157">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A157</A>
or via <A
href="http://gepicom04.obspm.fr/sdss_morphology/Morphology_2010.html">http://gepicom04.obspm.fr/sdss_morphology/Morphology_2010.html</A>

---------------------------------------------------------
Title: The Sun, the Solar Wind, and the Heliosphere
Authors: Miralles, Mari Paz; Sánchez Almeida, Jorge
2011sswh.book.....M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sun, the Solar Wind, and the Heliosphere
Authors: Miralles, M. P.; Sánchez Almeida, J.
2011sswh.book....3M Altcode:
We describe the aims and contents of the book entitled "The Sun, the
Solar Wind, and the Heliosphere". This is a volume in the IAGA Special
Book Series dedicated to the science covered by IAGA Division IV,
Solar Wind and Interplanetary Field. The book features review articles
on topics from the interior of the Sun to the outermost regions of the
heliosphere. In addition, we highlight some of the results presented
during the Division IV symposia at the 11th Scientific Assembly of IAGA
in Sopron, Hungary, which was planned simultaneously with this book.

---------------------------------------------------------
Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
Knölker, M.
2010ApJ...723L.139B Altcode: 2010arXiv1009.1992B
We characterize the observational properties of the convectively driven
vortex flows recently discovered on the quiet Sun, using magnetograms,
Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
telescope. By visual inspection of time series, we find some 3.1
× 10-3 vortices Mm-2 minute-1,
which is a factor of ~1.7 larger than previous estimates. The mean
duration of the individual events turns out to be 7.9 minutes, with
a standard deviation of 3.2 minutes. In addition, we find several
events appearing at the same locations along the duration of the time
series (31.6 minutes). Such recurrent vortices show up in the proper
motion flow field map averaged over the time series. The typical
vertical vorticities are lsim6 × 10-3 s-1,
which corresponds to a period of rotation of some 35 minutes. The
vortices show a preferred counterclockwise sense of rotation, which
we conjecture may have to do with the preferred vorticity impinged by
the solar differential rotation.

---------------------------------------------------------
Title: VizieR Online Data Catalog: SDSS automated morphology
classification (Huertas-Company+, 2011)
Authors: Huertas-Company, M.; Aguerri, J. A. L.; Bernardi, M.; Mei,
S.; Sanchez Almeida, J.
2010yCat..35250157H Altcode: 2010yCat..35259157H
We used all the SDSS DR7 spectroscopic sample as the starting
base. Then, the selection of objects was based on Sanchez Almeida et
al. (2010ApJ...714..487A) who performed an unsupervised automated
classification of all the SDSS spectra. Basically, we chose galaxies
with redshift below 0.25, and with good photometric data and clean
spectra, meaning objects not too close to the edges, not saturated,
or not properly deblended. The final catalog contains 698420
objects for which we estimate the morphology (also available at
http://gepicom04.obspm.fr/sdssmorphology/Morphology2010.html
). (3 data files).

---------------------------------------------------------
Title: Automatic unsupervised spectral classification of all SDSS/DR7
galaxies
Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón,
C.; de Vicente, A.
2010ada..confE...3S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Safe and Secure Virtualization: Answers for IMA next Generation
and Beyond
Authors: Almeida, J.; Vatrinet, F.
2010ESASP.682E..56A Altcode:
This paper presents some of the challenges the aerospace industry
is facing for the future and explains why and how a safe and secured
virtualization technology can help solving these challenges Efforts
around the next generation of IMA have already started, like the
European FP7 funded project SCARLETT or the IDEE5 project and
many avionics players and working groupware focused on how the
new technologies like SMP capabilities introduced in latest CPU
architectures, can help increasing system performances in future
avionics system. We present PikeOS, a separation micro-kernel, which
applies the state-of-the-art techniques and widely recognized standards
such as ARINC 653 and MILS in order to guarantee safety and security
properties, and still improve overall performance.

---------------------------------------------------------
Title: Automatic unsupervised classification of all Sloan Digital
Sky Survey Data Release 7 galaxy spectra
Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón,
C.; de Vicente, A.
2010iac..talk...25S Altcode: 2010iac..talk..164S
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Bright Points in the Quiet Sun
Authors: Sánchez Almeida, J.; Bonet, J. A.; Viticchié, B.; Del
Moro, D.
2010ApJ...715L..26S Altcode: 2010arXiv1004.1885S
We present a visual determination of the number of bright points
(BPs) existing in the quiet Sun, which are structures though to trace
intense kG magnetic concentrations. The measurement is based on a
0farcs1 angular resolution G-band movie obtained with the Swedish Solar
Telescope at the solar disk center. We find 0.97 BPs Mm-2,
which is a factor 3 larger than any previous estimate. It corresponds to
1.2 BPs per solar granule. Depending on the details of the segmentation,
the BPs cover between 0.9% and 2.2% of the solar surface. Assuming their
field strength to be 1.5 kG, the detected BPs contribute to the solar
magnetic flux with an unsigned flux density between 13 G and 33 G. If
network and inter-network regions are counted separately, they contain
2.2 BPs Mm-2 and 0.85 BPs Mm-2, respectively.

---------------------------------------------------------
Title: Magnetic bright points in the quiet Sun
Authors: Sánchez Almeida, J.; Bonet, J. A.; Viticchie, B.; Del
Moro, D.
2010iac..talk...95S Altcode: 2010iac..talk..157S
No abstract at ADS

---------------------------------------------------------
Title: Automatic Unsupervised Classification of All Sloan Digital
Sky Survey Data Release 7 Galaxy Spectra
Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón,
C.; de Vicente, A.
2010ApJ...714..487S Altcode: 2010arXiv1003.3186S
Using the k-means cluster analysis algorithm, we carry out an
unsupervised classification of all galaxy spectra in the seventh
and final Sloan Digital Sky Survey data release (SDSS/DR7). Except
for the shift to rest-frame wavelengths and the normalization to the
g-band flux, no manipulation is applied to the original spectra. The
algorithm guarantees that galaxies with similar spectra belong to the
same class. We find that 99% of the galaxies can be assigned to only 17
major classes, with 11 additional minor classes including the remaining
1%. The classification is not unique since many galaxies appear in
between classes; however, our rendering of the algorithm overcomes
this weakness with a tool to identify borderline galaxies. Each class
is characterized by a template spectrum, which is the average of all
the spectra of the galaxies in the class. These low-noise template
spectra vary smoothly and continuously along a sequence labeled from
0 to 27, from the reddest class to the bluest class. Our Automatic
Spectroscopic K-means-based (ASK) classification separates galaxies
in colors, with classes characteristic of the red sequence, the blue
cloud, as well as the green valley. When red sequence galaxies and
green valley galaxies present emission lines, they are characteristic
of active galactic nucleus activity. Blue galaxy classes have emission
lines corresponding to star formation regions. We find the expected
correlation between spectroscopic class and Hubble type, but this
relationship exhibits a high intrinsic scatter. Several potential
uses of the ASK classification are identified and sketched, including
fast determination of physical properties by interpolation, classes as
templates in redshift determinations, and target selection in follow-up
works (we find classes of Seyfert galaxies, green valley galaxies,
as well as a significant number of outliers). The ASK classification
is publicly accessible through various Web sites.

---------------------------------------------------------
Title: A Topology for the Penumbral Magnetic Fields
Authors: Sánchez Almeida, J.
2010ASSP...19..210S Altcode: 2009arXiv0902.4532S; 2010mcia.conf..210S
We describe a scenario for the topology of the magnetic field in
penumbrae that accounts for recent observations showing upflows,
downflows, and reverse magnetic polarities. According to our conjecture,
short narrow magnetic loops fill the penumbral photosphere. Flows along
these arched field lines are responsible for both the Evershed effect
and the convective transport. This scenario seems to be qualitatively
consistent with most existing observations, including the dark cores in
penumbral filaments reported by Scharmer et al. Each bright filament
with dark core would be a system of two paired convective rolls with
the dark core tracing the common lane where the plasma sinks down. The
magnetic loops would have a hot footpoint in one of the bright filament
and a cold footpoint in the dark core. The scenario fits in most of
our theoretical prejudices (siphon flows along field lines, presence
of overturning convection, drag of field lines by downdrafts, etc). If
the conjecture turns out to be correct, the mild upward and downward
velocities observed in penumbrae must increase upon improving the
resolution. This and other observational tests to support or disprove
the scenario are put forward.

---------------------------------------------------------
Title: On the origin of reverse polarity patches found by Hinode in
sunspot penumbrae
Authors: Sánchez Almeida, J.; Ichimoto, K.
2009A&A...508..963S Altcode: 2009arXiv0909.3232S
Context: The topology of penumbral magnetic fields is poorly known. The
satellite Hinode has recently revealed penumbral structures of a
magnetic polarity that is opposite to the main sunspot polarity. They
may be direct confirmation that magnetic field lines and mass flows
return to the solar interior throughout the penumbra, a configuration
previously inferred from interpretation of observed Stokes profile
asymmetries. Aims: We try to point out the relationship
between the reverse polarity features found by Hinode, and the
model Micro-Structured Magnetic Atmospheres (MISMAs) proposed for
sunspots. Methods: The work is based on synthesis and inversion
of sunspot Stokes profiles. Results: Existing model MISMAs
produce strongly redshifted reverse polarity structures as found
by Hinode. Ad hoc model MISMAs also explain the asymmetric Stokes
profiles observed by Hinode. The same modeling may be consistent with
magnetograms of dark cored penumbral filaments if the dark cores are
associated with the reverse polarity. This hypothetical relationship
can only be identified in the far red wings of the spectral lines. Conclusions: The reverse polarity patches may result from aligned
magnetic field lines and mass flows that bend over and return to the
solar interior throughout the penumbra.

---------------------------------------------------------
Title: Mn I Lines with Hyperfine Structure Synthesized in Realistic
Quiet-Sun Atmospheres
Authors: Viticchié, B.; Sánchez Almeida, J.; Landi Degl'Innocenti,
E.; Berrilli, F.
2009ASPC..405..319V Altcode:
We present the first synthesis of Mn I lines in realistic
multi-component magnetized quiet Sun atmospheres, including variation
of magnetic field strength, magnetic field direction, plasma velocity,
and coupling between magnetic field and thermodynamics. All synthesized
Mn I lines weaken for strong magnetic fields. A detailed analysis of
the Mn I λ5538 line shows that the Weak Field Approximation (WFA)
breaks down at 400~G, and that kG magnetic fields produce Stokes V
profiles with amplitudes up to two orders of magnitude smaller than
those predicted by the WFA. Consequently, the polarization emerging
from an atmosphere in which weak (hG) and strong (kG) fields coexist
is biased towards the hG field polarization. When including velocity
gradients, profiles showing important asymmetries are produced, and
these profiles cannot be obtained using single-component magnetized
model atmospheres. We synthesize Mn I lines presenting very different
hyperfine structure (HFS) patterns, and all of them reproduce the
observed Stokes I profiles in a really satisfactory way.

---------------------------------------------------------
Title: Search for Blue Compact Dwarf Galaxies During
Quiescence. II. Metallicities of Gas and Stars, Ages, and Star
Formation Rates
Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón,
C.; Vazdekis, A.
2009ApJ...698.1497S Altcode: 2009arXiv0904.2150S
We examine the metallicity and age of a large set of Sloan Digital Sky
Survey/Data Release 6 galaxies that may be blue compact dwarf (BCD)
galaxies during quiescence (QBCDs). The individual spectra are first
classified and then averaged to reduce noise. The metallicity inferred
from emission lines (tracing ionized gas) exceeds by ~0.35 dex the
metallicity inferred from absorption lines (tracing stars). Such a small
difference is significant according to our error budget estimate. The
same procedure was applied to a reference sample of BCDs, and in this
case the two metallicities agree, being also consistent with the stellar
metallicity in QBCDs. Chemical evolution models indicate that the gas
metallicity of QBCDs is too high to be representative of the galaxy
as a whole, but it can represent a small fraction of the galactic gas,
self-enriched by previous starbursts. The luminosity-weighted stellar
age of QBCDs spans the whole range between 1 and 10 Gyr, whereas it is
always smaller than 1 Gyr for BCDs. Our stellar ages and metallicities
rely on a single stellar population spectrum fitting procedure,
which we have specifically developed for this work using the stellar
library MILES.

---------------------------------------------------------
Title: Safe and Secure Partitioning with Pikeos: Towards Integrated
Modular Avionics in Space
Authors: Almeida, J.; Prochazka, M.
2009ESASP.669E..27A Altcode:
This paper presents our approach to logical partitioning of spacecraft
onboard software. We present PikeOS, a separation micro-kernel which
applies the state-of-the- art techniques and widely recognised standards
such as ARINC 653 and MILS in order to guarantee safety and security
properties of partitions executing software with different criticality
and confidentiality. We provide an overview of our approach, also used
in the Securely Partitioning Spacecraft Computing Resources project, an
ESA TRP contract, which shifts spacecraft onboard software development
towards the Integrated Modular Avionics concept with relevance for
dual-use military and civil missions.

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Title: The dynamic magnetic quiet Sun: physical mechanisms and
UV signature
Authors: Sánchez Almeida, J.
2009Ap&SS.320..121S Altcode: 2008Ap&SS.tmp..156S
The changes in the Sun occurring at human time-scales can be pinned
down to the presence of magnetic fields. These fields determine
the structure of the outer solar atmosphere and, therefore, they
are responsible for all the energetic part of the solar spectrum,
including the UV. Our understanding of the magnetic fields existing
at the base of the atmosphere has changed during the last years. The
new spectro-polarimeters reveal an ubiquitous magnetic field, present
even in the quiet regions. They are widespread and of complex topology,
containing far more (unsigned) magnetic flux and magnetic energy that
all traditional manifestations of solar activity. These so-called quiet
Sun magnetic fields are the subject of the contribution. I summarize
their main observational properties, as well as the models put forward
to explain them. According to the common wisdom, they may be generated
by a turbulent dynamo driven by convective motions. Their true physical
role is not understood yet, but it may be consequential both for the Sun
(e.g., in determining the structure of the quiet corona), and for other
astronomical objects (e.g., if a turbulent dynamo operates in the Sun,
the same mechanism provides a very efficient mean of creating surface
magnetic fields in all stars with convective envelopes). I discuss the
impact of the quiet Sun fields on the transition region and corona,
trying to point out the UV signatures of those fields.

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Title: MISMA inversion of HINODE SOT/SP data. Preliminary results
Authors: Viticchiè, B.; Berrilli, F.; Sánchez Almeida, J.; Orozco
Suárez, D.
2009MmSAI..80..255V Altcode:
We analyze full Stokes observations of a quiet Sun region at disk
center taken with the spectropolarimeter of the Solar Optical Telescope
aboard the HINODE satellite. We present the preliminary results derived
from the MISMA inversion of the observed Stokes I and V profiles. The
complete analysis has as a final goal the definition of probability
density function for the statistical description of the quiet Sun
magnetic field vector for a direct comparison with recently published
results.

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Title: A topology for the penumbral magnetic fields
Authors: Sanchez Almeida, J.
2008arXiv0811.4319S Altcode:
We describe a scenario for the sunspot magnetic field topology
that may account for recent observations of upflows and downflows in
penumbrae. According to our conjecture, short narrow magnetic loops fill
the penumbral volume. Flows along these field lines are responsible for
both the Evershed effect and the convective transport. This scenario
seems to be qualitatively consistent with most existing observations,
including the dark cores in penumbral filaments reported by Scharmer
et al. Each bright filament with dark core would be a system of two
paired convective rolls with the dark core tracing the lane where the
plasma sinks down. The magnetic loops would have a hot footpoint in
one of the bright filament and a cold footpoint in the dark core. The
scenario also fits in most of our theoretical prejudices (siphon flows
along field lines, presence of overturning convection, drag of field
lines by downdrafts, etc). If the conjecture turns out to be correct,
the mild upward and downward velocities observed in penumbrae must
increase upon improvement of the current spatial resolution. This and
other observational tests to support or disprove the proposed scenario
are put forward.

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Title: Convectively Driven Vortex Flows in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello,
I.; Domingo, V.
2008ApJ...687L.131B Altcode: 2008arXiv0809.3885B
We have discovered small whirlpools in the Sun, with a size similar to
terrestrial hurricanes (lesssim0.5 Mm). The theory of solar convection
predicts them, but they had remained elusive so far. The vortex flows
are created at the downdrafts where the plasma returns to the solar
interior after cooling down, and we detect them because some magnetic
bright points (BPs) follow a logarithmic spiral on their way to being
engulfed by a downdraft. Our disk-center observations show 0.9 ×
10-2 vortexes per Mm2, with a lifetime of the
order of 5 minutes, and with no preferred sense of rotation. They are
not evenly spread out over the surface, but they seem to trace the
supergranulation and the mesogranulation. These observed properties are
strongly biased by our type of measurement, unable to detect vortexes
except when they are engulfing magnetic BPs.

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Title: Convectively driven vortex flows in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello,
I.; Domingo, V.
2008iac..talk..143B Altcode: 2008iac..talk...26B
No abstract at ADS

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Title: MISMA inversion of HINODE SOT/SP and IBIS data: Preliminary
Results
Authors: Viticchiè, B.; Berrilli, F.; Sanchez Almeida, J.; Del
Moro, D.
2008ESPM...12.2.33V Altcode:
We present the preliminary results derived from the MISMA inversion of
Stokes I and V profiles of FeI 630.1nm FeI 630.2nm lines observed with:
1. SOT/SP instrument aboard the HINODE satellite. 2. IBIS
in spectropolarimetric mode imaging, supported by simultaneous white
light and G-band images, for blind deconvolution reconstruction. The complete analysis has as a final goal the comparison of the
results obtained from the analysis of the two datasets for a reliable
statistical description of the quiet Sun through the definition of a
probability density function.

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Title: Search for Blue Compact Dwarf Galaxies During Quiescence
Authors: Sánchez Almeida, J.; Muñoz-Tuñón, C.; Amorín, R.;
Aguerri, J. A.; Sánchez-Janssen, R.; Tenorio-Tagle, G.
2008ApJ...685..194S Altcode: 2008arXiv0805.3298S
Blue compact dwarf (BCD) galaxies are metal-poor systems going
through a major starburst that cannot last for long. We have
identified galaxies which may be BCDs during quiescence (QBCD),
i.e., before the characteristic starburst sets in or when it has
faded away. These QBCD galaxies are assumed to be like the BCD host
galaxies. The SDSS DR6 database provides ~21,500 QBCD candidates. We
also select from SDSS DR6 a complete sample of BCD galaxies to serve as
reference. The properties of these two galaxy sets have been computed
and compared. The QBCD candidates are 30 times more abundant than the
BCDs, with their luminosity functions being very similar except for
the scaling factor and the expected luminosity dimming associated with
the end of the starburst. QBCDs are redder than BCDs, and they have
larger H II region-based oxygen abundance. QBCDs also have lower surface
brightness. The BCD candidates turn out to be the QBCD candidates with
the largest specific star formation rate (actually, with the largest
Hα equivalent width). One out of every three dwarf galaxies in the
local universe may be a QBCD. The properties of the selected BCDs and
QBCDs are consistent with a single sequence in galactic evolution,
which the quiescent phase lasting 30 times longer than the starburst
phase. The resulting time-averaged star formation rate is low enough
to allow this cadence of BCD-QBCD phases during the Hubble time.

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Title: Quiet-Sun Magnetic Field Measurements Based on Lines with
Hyperfine Structure
Authors: Sánchez Almeida, J.; Viticchié, B.; Landi Degl'Innocenti,
E.; Berrilli, F.
2008ApJ...675..906S Altcode: 2007arXiv0710.5393S
The Zeeman pattern of Mn I lines is sensitive to hyperfine structure
(HFS), and because of this, they respond to hectogauss magnetic
field strengths differently than the lines commonly used in solar
magnetometry. This peculiarity has been employed to measure magnetic
field strengths in quiet-Sun regions, assuming the magnetic field to
be constant over a resolution element. This assumption is clearly
insufficient, biasing the measurements. The diagnostic potential
of Mn I lines can be fully exploited only after one understands the
sense and magnitude of such bias. We present the first syntheses of
Mn I lines in realistic quiet-Sun model atmospheres. The Mn I lines
weaken with increasing field strength. In particular, kilogauss magnetic
concentrations produce Mn I λ5538 circular polarization signals (Stokes
V) that can be up to 2 orders of magnitude smaller than what the weak
magnetic field approximation predicts. The polarization emerging
from an atmosphere having weak and strong fields is biased toward
the weak fields, and HFS features characteristic of weak fields show
up even when the magnetic flux and energy are dominated by kilogauss
fields. For the HFS feature of Mn I λ5538 to disappear, the filling
factor of kilogauss fields has to be larger than the filling factor of
subkilogauss fields. Since the Mn I lines are usually weak, Stokes V
depends on magnetic field inclination according to the simple cosine
law. Atmospheres with unresolved velocities produce very asymmetric
line profiles, which cannot be reproduced by simple one-component model
atmospheres. Using the HFS constants available in the literature,
we reproduce the observed line profiles of nine lines with varied
HFS patterns.

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Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and
6302 Å
Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.;
Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez
González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez
Almeida, J.
2008ApJ...674..596S Altcode:
The reliability of quiet-Sun magnetic field diagnostics based on the
Fe I lines at 6302 Å has been questioned by recent work. Here we
present the results of a thorough study of high-resolution multiline
observations taken with the new spectropolarimeter SPINOR, comprising
the 5250 and 6302 Å spectral domains. The observations were analyzed
using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Å lines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magnetohydrodynamic constrains. When this is done, the 5250 Å lines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point toward a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic
field strengths. Instead, we advocate for a combined analysis of both
spectral ranges, which yields a better determination of the quiet-Sun
magnetic properties. Finally, we propose the use of two other Fe I
lines (at 4122 and 9000 Å) with identical line opacities that seem
to work much better than the others.

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Title: Small magnetic structures in the photosphere, radiative
properties
Authors: Palacios, Judith; Domingo, Vicente; Cabello, Iballa; Bonet,
José Antonio; Sánchez Almeida, Jorge
2008cosp...37.2331P Altcode: 2008cosp.meet.2331P
The three dimensional structure of small magnetic field features in the
photosphere, their dynamic behavior and their radiative properties are
studied. We analyze data obtained in simultaneous observations made on
Sept 29 and 30, 2007 with the HINODE spacecraft and the Swedish Solar
Telescope (SST) in La Palma in different wavelengths, such as CaII
(396.85 nm) and CN (388.35 nm) and other with Hinode data; and Gband
(430.56 nm) with SST. Tha analysis is completed with high resolution
Gband and Gcontinuum (436.39 nm) images from SST obtained on 2005 and
2006. Magnetograms have been obtained from both observatories. SST
images have been processed with MOMFB code. Ribbon-like structures and
"flowers" are studied in detail. Comparisons with solar atmospheric
models are presented.

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Title: de Sitter Relativity and Quantum Physics
Authors: Aldrovandi, R.; Almeida, J. P. Beltrán; Mayor, C. S. O.;
Pereira, J. G.
2007AIPC..962..175A Altcode: 2007arXiv0710.0610A
In the presence of a cosmological constant, interpreted as a purely
geometric entity, absence of matter is represented by a de Sitter
spacetime. As a consequence, ordinary Poincaré special relativity
is no longer valid and must be replaced by a de Sitter special
relativity. By considering the kinematics of a spinless particle
in a de Sitter spacetime, we study the geodesics of this spacetime,
the ensuing definitions of canonical momenta, and explore possible
implications for quantum mechanics.

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Title: Search for photospheric footpoints of quiet Sun transition
region loops
Authors: Sánchez Almeida, J.; Teriaca, L.; Sütterlin, P.; Spadaro,
D.; Schühle, U.; Rutten, R. J.
2007A&A...475.1101S Altcode: 2007arXiv0709.3451S
Context: The footpoints of quiet Sun Transition Region (TR) loops
do not seem to coincide with the photospheric magnetic structures
appearing in traditional low-sensitivity magnetograms. Aims: We
look for the so-far unidentified photospheric footpoints of TR loops
using G-band bright points (BPs) as proxies for photospheric magnetic
field concentrations. Methods: We compare TR measurements with
SoHO/SUMER and photospheric magnetic field observations obtained with
the Dutch Open Telescope. Results: Photospheric BPs are associated
with bright TR structures, but they seem to avoid the brightest parts
of the structure. BPs appear in regions that are globally redshifted,
but they avoid extreme velocities. TR explosive events are not clearly
associated with BPs. Conclusions: The observations are not
inconsistent with the BPs being footpoints of TR loops, although we
have not succeeded to uniquely identify particular BPs with specific
TR loops.

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Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å
Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados,
M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González,
M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J.
2007arXiv0710.1099S Altcode:
The reliability of quiet Sun magnetic field diagnostics based on the
\ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We
present here the results of a thorough study of high-resolution
multi-line observations taken with the new spectro-polarimeter SPINOR,
comprising the 5250 and 6302 Åspectral domains. The observations were
analyzed using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Ålines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magneto-hydrodynamical constrains. When this is done, the 5250 Ålines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point towards a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic field
strengths. Instead, we advocate for a combined analysis of both spectral
ranges, which yields a better determination of the quiet Sun magnetic
properties. Finally, we propose the use of two other \ion{Fe}{1} lines
(at 4122 and 9000 Å) with identical line opacities that seem to work
much better than the others.

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Title: The Evershed Effect Observed with 0.2" Angular Resolution
Authors: Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez
Cerdeña, I.
2007ApJ...658.1357S Altcode: 2006astro.ph.11523S
We present an analysis of the Evershed effect observed with a resolution
of 0.2". Using the new Swedish 1 m Solar Telescope and its Littrow
spectrograph, we scan a significant part of a sunspot penumbra. Spectra
of the nonmagnetic line Fe I λ7090.4 allows us to measure Doppler
shifts without magnetic contamination. The observed line profiles are
asymmetric. The Doppler shift depends on the part of the line used for
measuring, indicating that the velocity structure of penumbrae remains
unresolved, even with our angular resolution. The observed line profiles
are properly reproduced if two components with velocities between zero
and several km s-1 coexist in the resolution elements. Using
Doppler shifts at fixed line depths, we find a local correlation
between upflows and bright structures and between downflows and dark
structures. This association is not specific to the outer penumbra,
but it also occurs in the inner penumbra. The existence of such a
correlation was originally reported in 1969 by Beckers and Schröter,
and it is suggestive of energy transport by convection in penumbrae.

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Title: A Simple Model for the Distribution of Quiet-Sun Magnetic
Field Strengths
Authors: Sánchez Almeida, J.
2007ApJ...657.1150S Altcode: 2006astro.ph.11711S
We derive a first-order linear differential equation describing the
shape of the probability density function (PDF) of magnetic field
strengths in the quiet Sun. The modeling is very schematic. It considers
convective motions which continuously supply and withdraw magnetic
structures. In addition, a magnetic amplification mechanism increases
the field strength up to a threshold that cannot be exceeded. These
three basic ingredients provide PDFs in good agreement with the PDFs
produced by realistic numerical simulations of magnetoconvection, as
well as with quiet-Sun PDFs inferred from observations. In particular,
the distribution is approximately lognormal, and it produces an excess
of magnetic fields (i.e., a hump in the distribution) right before the
maximum field strength. The success of this simple model may indicate
that only a few basic ingredients shape the quiet-Sun PDF. Our approach
provides a concise parametric representation of the PDF, as required
to develop automatic methods of diagnostics.

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Title: The Micro-Structure of a Sunspot Penumbra
Authors: Sánchez Almeida, J.
2006ASPC..358...13S Altcode:
The spectral lines observed in penumbrae are asymmetrical, revealing
the existence of spatially unresolved structures. We infer their
physical properties by fitting Stokes spectra of Fe I 6301.5 Å and
Fe I 6302.5 Å with model atmospheres having two magnetic components
interleaved along the line-of-sight (LOS). Combining ten thousand fits,
we set up a semi-empirical model sunspot, whose two components present
very different magnetic-field inclinations. The major component,
which contains most of the mass, is more vertical than the minor
component, which is inclined below the horizontal plane throughout
the penumbra. Magnetic field lines and mass flows are parallel,
consequently both upflows and downflows are present everywhere in the
penumbra. Major and minor components have very different velocities
(several 102 m s-1 vs. 10 km s-1),
but they transport the same mass per unit time. The similarity between
the vertical mass flow and the magnetic flux of the two components
suggests that field lines emerging as major component may return to
the photosphere as minor component. If so, the observed magnetic field
strength difference between components leads to a siphon flow whose
magnitude and direction agree with the Evershed flow. Several
tests support the internal consistency of the retrieved model sunspot,
in particular, the magnetic field vector B does not violate the div B=0
condition. A detailed description of the techniques and results
presented in this meeting is given by tet{s1 SA05}.

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Title: Proper Motions in Sunspot Penumbrae: Signs of Convection
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.
2006ASPC..358...80B Altcode:
Proper motions in penumbra have been measured using local correlation
tracking techniques in a high spatial resolution series of images
(∼0.12 arcsec). Assuming these motions to trace true plasma motions,
we have detected converging flows that arrange the plasma in long
narrow filaments mostly placed along dark penumbral filaments. These
converging flows suggest downflows in the filaments of ∼ 200 m
s-1. We interpret the association between downflows and
dark features as a sign of convection that, once several observational
biases are considered, could transport enough energy to balance the
radiative losses of penumbra.

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Title: The Evershed Effect with 0.2 arcsec Angular Resolution
Authors: Márquez, I.; Bonet, J. A.; Sánchez Almeida, J.; Domínguez
Cerdeña, I.
2006ASPC..358...96M Altcode:
We present a preliminary analysis of penumbral spectra observed with
unprecedented angular resolution (0.2 arcsec) using the new Swedish 1-m
Solar Telescope. The use of a non-magnetic line allows us to measure
Doppler shifts without magnetic contamination. The observed
Doppler shifts depend on the part of the line used for measuring,
indicating that the velocity structure of penumbrae remains unresolved
even with our resolution. We find a correlation between upflows
and bright filaments. This association is not specific of the outer
penumbra but it also occurs in the inner penumbra. The existence
of such correlation was originally reported by tet{m1 BS69}, and
it is suggestive of energy transport by convection in penumbrae.

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Title: Magnetic Fields of the Quiet Sun: Distribution of Field
Strengths
Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F.
2006ASPC..358...48D Altcode:
The quiet Sun photospheric plasma has a variety of magnetic field
strengths going from zero to 1800 G. The empirical characterization of
these field strengths requires a probability density function (PDF),
i.e., a function P(B) describing the fraction of quiet Sun occupied by
each field strength B. We present a method to combine magnetic field
strength measurements based on the Zeeman effect and the Hanle effect
in order to estimate the true P(B). The application of the method
to real observations renders a set of possible PDFs, which outline
the general characteristics of the quiet Sun magnetic fields. Their
most probable field strength differs from zero. The magnetic energy
density is a significant fraction of the kinetic energy of the granular
motions at the base of the photosphere (larger than 15 or larger than
2×103 erg cm-3). The unsigned flux density
(or mean magnetic field strength) has to be between 130 G and 190
G. A significant part of the unsigned flux (between 10% and 40%) and
of the magnetic energy (between 40% and 80%) are provided by the field
strengths larger than 1 kG which, however, occupy only a small fraction
of the surface (between 1% and 4%). The quiet Sun photosphere has
far more unsigned magnetic flux and magnetic energy than the active
regions and the network together.

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Title: Quiet-Sun Magnetic Fields: Simultaneous Inversion of Visible
and IR Spectro-Polarimetric Observations
Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F.
2006ASPC..358...88D Altcode:
We studied the quiet-Sun magnetic fields interpreting
spectro-polarimetric observations of infrared and visible spectral
lines. Magnetic field strengths and filling factors were inferred by the
simultaneous inversion of Stokes profiles of the Fe I lines at 6301.5,
6302.5, 15648, and 15653 Å under the MISMA hypothesis. They cover a
solar intra-network region at disk center. We analyzed Stokes profiles
with signals above noise in both spectral ranges, which correspond
to 40% of the field of view. Most of these 2280 profiles could only
be inverted with a model including 3 magnetic components with very
different field strengths, which indicates the co-existence of kG and
sub-kG fields. We measured a total unsigned magnetic flux density
of 9.6 G over the whole field of view. For half of the pixels the
magnetic field has opposite polarities within the resolution element. We
computed the probability density function of finding each magnetic field
strength. It has an important contribution of kG field strengths, which
concentrates most of the magnetic flux and energy. This kG contribution
has a preferred magnetic polarity while the weak fields are balanced.

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Title: Quiet Sun Magnetic Fields from Simultaneous Inversions of
Visible and Infrared Spectropolarimetric Observations
Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F.
2006ApJ...646.1421D Altcode: 2006astro.ph..4381D
We study the quiet Sun magnetic fields using spectropolarimetric
observations of the infrared and visible Fe I lines at 6301.5, 6302.5,
15648, and 15653 Å. Magnetic field strengths and filling factors
are inferred by the simultaneous fit of the observed Stokes profiles
under the MISMA hypothesis. The observations cover an intranetwork
region at the solar disk center. We analyze 2280 Stokes profiles whose
polarization signals are above noise in the two spectral ranges, which
correspond to 40% of the field of view. Most of these profiles can
be reproduced only with a model atmosphere including three magnetic
components with very different field strengths, which indicates the
coexistence of kG and sub-kG fields in our 1.5" resolution elements. We
measure an unsigned magnetic flux density of 9.6 G considering the full
field of view. Half of the pixels present magnetic fields with mixed
polarities in the resolution element. The fraction of mixed polarities
increases as the polarization weakens. We compute the probability
density function of finding each magnetic field strength. It has a
significant contribution of kG field strengths, which concentrates
most of the observed magnetic flux and energy. This kG contribution
has a preferred magnetic polarity, while the polarity of the weak
fields is balanced.

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Title: Magnetic flux in the inter-network quiet Sun from comparison
with numerical simulations
Authors: Sánchez Almeida, J.
2006A&A...450.1199S Altcode: 2005astro.ph.12395S
Khomenko et al. estimate the mean magnetic field strength of the
quiet Sun to be 20 G. The figure is smaller than several existing
estimates, and it comes from the comparison between observed Zeeman
polarization signals and synthetic signals from numerical simulations of
magneto-convection. The numerical simulations require an artificially
large magnetic diffusivity, which smears out magnetic structures
smaller than the grid scale. Assuming a turbulent cascade for the
unresolved artificially smeared magnetic fields, we find that their
unsigned magnetic flux is at least as important as that explicitly
shown in the simulation. The unresolved fields do not produce Zeeman
polarization but contribute to the unsigned flux. Since they are not
considered by Khomenko et al., their mean magnetic field strength has
to be regarded as a lower limit. This kind of bias is not specific
of a particular numerical simulation or a spectral line. It is to
be expected when observed quiet Sun Zeeman signals are compared with
synthetic signals from simulations.

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Title: High-Resolution Proper Motions in a Sunspot Penumbra
Authors: Márquez, I.; Sánchez Almeida, J.; Bonet, J. A.
2006ApJ...638..553M Altcode: 2005astro.ph.10220M
Local correlation tracking techniques are used to measure proper
motions in a series of high angular resolution (~0.1") penumbra
images. If these motions trace true plasma motions, then we have
detected converging flows that arrange the plasma in long narrow
filaments cospatial with dark penumbral filaments. Assuming that these
flows are stationary, the vertical stratification of the atmosphere
and the conservation of mass suggest downflows in the filaments on
the order of 200 m s-1. The association between downflows
and dark features may be a sign of convection, as it happens with the
nonmagnetic granulation. Insufficient spatial resolution may explain
why the estimated vertical velocities are not fast enough to supply
the radiative losses of penumbrae.

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Title: The Distribution of Quiet Sun Magnetic Field Strengths from
0 to 1800 G
Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F.
2006ApJ...636..496D Altcode: 2005astro.ph..9243D; 2006ApJ...636..496C
The quiet-Sun photospheric plasma has a variety of magnetic field
strengths going from zero to 1800 G. The empirical characterization
of these field strengths requires a probability density function
(PDF), i.e., a function P(B) describing the fraction of quiet Sun
occupied by each field strength B. We show how to combine magnetic
field strength measurements based on the Zeeman effect and the Hanle
effect to estimate an unbiased P(B). The application of the method
to real observations renders a set of possible PDFs, which outline
the general characteristics of the quiet-Sun magnetic fields. Their
most probable field strength differs from zero. The magnetic energy
density is a significant fraction of the kinetic energy of the
granular motions at the base of the photosphere (larger than 15%
or larger than 2×103 ergs cm-3). The unsigned
flux density (or mean magnetic field strength) has to be between 130
and 190 G. A significant part of the unsigned flux (between 10% and
50%) and of the magnetic energy (between 45% and 85%) are provided by
the field strengths larger than 500 G, which, however, occupy only a
small fraction of the surface (between 1% and 10%). The fraction of kG
fields in the quiet Sun is even smaller, but they are important for a
number of reasons. The kG fields still trace a significant fraction of
the total magnetic energy, they reach the high photosphere, and they
appear in unpolarized light images. The quiet-Sun photosphere has
far more unsigned magnetic flux and magnetic energy than the active
regions and the network combined.

---------------------------------------------------------
Title: On the Sr I λ4607 Å Hanle depolarization signals in the
quiet Sun
Authors: Sánchez Almeida, J.
2005A&A...438..727S Altcode: 2005astro.ph..4339S
The Hanle depolarization signals of Sr i λ4607 Å have been used to
estimate the unsigned magnetic flux and magnetic energy existing in
the quiet Sun photosphere. However, the Sr i λ4607 Å Hanle signals
are not sensitive to the unsigned flux and energy. They only bear
information on the fraction of photosphere occupied by magnetic field
strengths smaller than the Hanle saturation, which do not contribute to
the unsigned flux and energy. We deduce an approximate expression for
the relationship between magnetic fill factor and Hanle signal. When
applied to existing Hanle depolarization measurements, it indicates
that only 40% of the quiet Sun is filled by magnetic fields with a
strength smaller than 60 G. The remaining 60% of the surface has field
strengths above this limit. Such constraint will be needed to determine
the distribution of magnetic field strengths existing in the quiet Sun.

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Title: Quiet sun magnetic fields vs. polar faculae - local vs. global
dynamo?
Authors: Okunev, O. V.; Domínguez Cerdeña, I.; Puschmann, K. G.;
Kneer, F.; Sánchez Almeida, J.
2005AN....326..205O Altcode:
Quiet Sun magnetic fields in the internetwork are almost
ubiquitous. Simultaneous observations in infra-red and visible lines
and high spatial resolution (&lt; 0.5”) data in visible
lines show that their field strengths range from below few hundred
Gauss to kilo-Gauss. Most of the flux is contained in small-scale,
strong-field features located mainly in intergranular lanes. The
average unsigned flux density exceeds 20 Gauss. The new detections
are confirmed by recent quiet Sun observations in the G band. The
generation of the strong fields in the internetwork, which may be due
to a local dynamo, poses a challenging problem. - Polar faculae (PFe)
are small-scale magnetic features at the polar caps of the Sun. They
take part in the solar cycle and are thus likely to be rooted deeply
in the solar interior. They are the result of the global dynamo at
the solar poles. PFe also possess kilo-Gauss magnetic fields which
have the same polarity as the global magnetic field. The rôle of
quiet Sun magnetic field structures and of PFe for the dynamics of
the corona and for the solar wind are addressed.

---------------------------------------------------------
Title: Physical Properties of the Solar Magnetic Photosphere under
the MISMA Hypothesis. III. Sunspot at Disk Center
Authors: Sánchez Almeida, J.
2005ApJ...622.1292S Altcode: 2004astro.ph.12217S; 2004astro.ph.12217A
Small-scale fluctuations of magnetic field and velocity may be
responsible for the Stokes asymmetries observed in all photospheric
magnetic structures (the microstructured magnetic atmosphere [MISMA]
hypothesis). We support the hypothesis by showing that atmospheres
with optically thin microstructure reproduce the polarization of
Fe I λλ6301.5 and 6302.5 observed in a sunspot. Ten thousand
spectra were fitted by model MISMAs with two magnetic components
interleaved along the line of sight. Combining all the fits, we set
up a semiempirical model sunspot characterized by two components with
very different magnetic field inclinations. The major component,
which contains most of the mass, is more vertical than the minor
component. The field lines of the minor component are inclined below
the horizontal plane throughout the penumbra. Magnetic field lines
and mass flows are parallel; consequently, both upflows and downflows
are present everywhere on the penumbra. Major and minor components
have very different velocities (several hundred meters per second
for the major component versus 10 km s-1 for the minor
component), but the mass transported per unit time is similar. The
similarity between the vertical mass flow and the magnetic flux of the
two components suggests that field lines emerging as major components
may return to the photosphere as minor components. If so, the observed
magnetic field strength difference between components leads to a siphon
flow whose magnitude and direction agree with the inferred Evershed
flow. Several tests support the internal consistency of the retrieved
model sunspot. The magnetic field vector B does not violate the ∇B=0
condition. The model sunspot reproduces the net circular polarization
of the observed lines plus the abnormal behavior of Fe I λ15648. The
use of only one magnetic component to interpret the spectra leads to
inferring upflows in the inner penumbra and downflows in the outer
penumbra, in agreement with previous findings.

---------------------------------------------------------
Title: Counting Publications in Astronomy
Authors: Corral, L. J.; Sanchez Almeida, J.
2005coas.conf...14C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Visible and IR spectropolarimetry of the quiet Sun
Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F.
2005ASSL..320..175D Altcode: 2005ASSL..320..175C; 2005smp..conf..175D
This work presents the first quiet Sun spectropolarimetric observations
carried out in the visible and the infrared (IR) simultaneously. The
Fe I lines at 6301.5, 6302.5, 15648, and 15652 Å were observed
co-spatially, and at the same time (with a time lag of only 1 minute),
with high sensitive spectropolarimeters operated in two different
telescopes (VTT and THEMIS at the Observatorio del Teide). We find
Stokes V profiles above noise in 30% of the observed area, showing
intrinsic magnetic fields of kG (traced by visible lines) co-existing
with sub-kG fields (traced by infrared lines). We also found V profiles
with opposite polarity in the visible and the IR in 25% of the pixels
under study (8% of the area).

---------------------------------------------------------
Title: The Magnetism of the Very Quiet Sun
Authors: Sánchez Almeida, J.
2004ASPC..325..115S Altcode: 2004astro.ph..4053S; 2004astro.ph..4053A
When the polarimetric sensitivity and the angular resolution
exceed a threshold, magnetic fields show up almost everywhere on
the solar surface. Here I revise the observational properties of
the weakest polarization signals, which appear in the InterNetwork
(IN) regions. We already have some information on the magnetic field
strengths and inclinations, mass motions, lifetimes, magnetic fluxes,
magnetic energies, etc. Since the IN covers a substantial faction of the
solar surface, it may account for most of the unsigned magnetic flux
and energy existing on the solar surface at any given time. This fact
makes IN fields potentially important to understand the global magnetic
properties of the Sun (e.g. the structure of the quiet solar corona,
an issue briefly addressed here). The spectropolarimeters on board of
SolarB have the resolution and sensitivity to routinely detect these
IN fields.

---------------------------------------------------------
Title: Bright Points in the Internetwork Quiet Sun
Authors: Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez
Cerdeña, I.; Muller, R.
2004ApJ...609L..91S Altcode: 2004astro.ph..5515S; 2004astro.ph..5515A
High-resolution G-band images of the interior of a supergranulation
cell show ubiquitous bright points (BPs; some 0.3 BPs per
Mm2). They are located in intergranular lanes and often
form chains of elongated blobs whose smallest dimension is at
the resolution limit (135 km on the Sun). Most of them live for a
few minutes, having peak intensities from 0.8 to 1.8 times the mean
photospheric intensity. These BPs are probably tracing intense magnetic
concentrations, whose existence has been inferred in spectropolarimetric
measurements. Our finding provides a new convenient tool for the study
of the internetwork magnetism, so far restricted to the interpretation
of weak polarimetric signals.

---------------------------------------------------------
Title: Analysis of simultaneous visible and infrared
spectropolarimetric observations of quiet Sun.
Authors: Dominguez Cerdena, I.; Sanchez Almeida, J.; Kneer, F.
2004ANS...325...94D Altcode: 2004ANS...325a..94D; 2004ANS...325..P23D
No abstract at ADS

---------------------------------------------------------
Title: Inter-Network magnetic fields observed during the minimum of
the solar cycle
Authors: Sánchez Almeida, J.
2003A&A...411..615S Altcode: 2003astro.ph.10164S; 2003astro.ph.10164A
We analyze a time series of high angular resolution magnetograms of
quiet Sun Inter-Network (IN) magnetic fields. These magnetograms have
a spatial resolution better than 0\farcs5, a noise of some 20 G, and
they have been obtained at the disk center during the minimum of the
solar cycle. The IN regions show a typical unsigned flux density of
the order of 15 G. Signals occur, preferentially, in the intergranular
lanes, and the strongest signals trace a network with a scale similar
to the mesogranulation. All these features are consistent with the IN
magnetograms by \citet{dom03a,dom03b}, obtained during the maximum
of the solar cycle. Consequently, the unsigned magnetic flux of the
structures that give rise to the IN polarization signals does not seem
to undergo large variations during the solar cycle.

---------------------------------------------------------
Title: Simultaneous Visible and Infrared Spectropolarimetry of a
Solar Internetwork Region
Authors: Sánchez Almeida, J.; Domínguez Cerdeña, I.; Kneer, F.
2003ApJ...597L.177S Altcode: 2003astro.ph..9727A; 2003astro.ph..9727S
We present the first simultaneous infrared (IR) and visible
spectropolarimetric observations of a solar internetwork region. The
Fe I lines at 6301.5, 6302.5, 15648, and 15652 Å were observed, with
a lag of only 1 minute, using highly sensitive spectropolarimeters
operated in two different telescopes (Vacuum Tower Telescope and THEMIS
at the Observatorio del Teide). Some 30% of the observed region shows
IR and visible Stokes V signals above noise. These polarization signals
indicate the presence of kilogauss (kG) magnetic field strengths (traced
by the visible lines) coexisting with sub-kG fields (traced by the
infrared lines). In addition, one-quarter of the pixels with signal have
visible and IR Stokes V profiles with opposite polarity. We estimate
the probability density function of finding each longitudinal magnetic
field strength in the region. It has a tail of kG field strengths that
accounts for most of the (unsigned) magnetic flux of the region.

---------------------------------------------------------
Title: Quiet Sun Magnetic Fields
Authors: Sánchez Almeida, J.
2003AIPC..679..293S Altcode:
The seemingly un-magnetized part of the solar surface is not really
un-magnetized. It is occupied by magnetic structures producing low
polarization which, therefore, escape detection in traditional
measurements. Since most of the solar surface belongs to this
category, the quiet Sun magnetic fields can easily carry most of the
magnetic flux and energy existing in the photosphere at any given
time. Consequently, they are a potentially important ingredient of
the solar magnetism. Most of the physical properties of the quiet Sun
are still uncertain (distribution of field strengths, area coverage,
influence on higher atmospheric layers, etc.).It is clear, however,
that the topology of the field is complex, with field lines of very
different properties coexisting in each resolution element. This fact
hampers the detection of the quiet Sun magnetic fields. I argue that
the best present measurements detect, at most, 30 % of the existing
magnetic flux. Then the quiet Sun contains at least as much magnetic
flux as all active regions and the network during the solar maximum.

---------------------------------------------------------
Title: Magnetic Fields in the Quiet Sun: Observational Discrepancies
and Unresolved Structure
Authors: Socas-Navarro, H.; Sánchez Almeida, J.
2003ApJ...593..581S Altcode:
Observations of magnetically sensitive lines in the visible and the
infrared yield apparently contradictory values for the intrinsic
field strength in the internetwork quiet Sun. It is shown that this
discrepancy can be understood if one assumes that the magnetic field
is not homogeneous over the resolution element. The difference between
visible and infrared measurements may be used to set constrains on
the subpixel distribution of field strengths. We suggest a specific
probability density function that seems to satisfy the existing
observational constraints.

---------------------------------------------------------
Title: Inter-network magnetic fields observed with sub-arcsec
resolution
Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F.
2003A&A...407..741D Altcode: 2003astro.ph..6329C; 2003astro.ph..6329D
We analyze a time sequence of Inter-Network (IN) magnetograms
observed at the solar disk center. Speckle reconstruction techniques
provide a good spatial resolution (0\farcs5 cutoff frequency) yet
maintaining a fair sensitivity (some 20 G). Patches with signal above
noise cover 60% of the observed area, most of which corresponds to
intergranular lanes. The large surface covered by signal renders a mean
unsigned magnetic flux density between 17 G and 21 G (1 G equiv 1 Mx
cm-2). The difference depends on the spectral line used to
generate the magnetograms (łinetwo or łineone ). Such systematic
difference can be understood if the magnetic structures producing
the polarization have intrinsic field strengths exceeding 1 kG, and
consequently, occupying only a very small fraction of the surface
(some 2%). We observe both, magnetic signals changing in time scales
smaller than 1 min, and a persistent pattern lasting longer than the
duration of the sequence (17 min). The pattern resembles a network
with a spatial scale between 5 and 10 arcsec, which we identify as the
mesogranulation. The strong dependence of the polarization signals
on spatial resolution and sensitivity suggests that much quiet Sun
magnetic flux still remains undetected.

---------------------------------------------------------
Title: Polarization of Photospheric Lines from Turbulent Dynamo
Simulations
Authors: Sánchez Almeida, J.; Emonet, T.; Cattaneo, F.
2003ApJ...585..536S Altcode: 2002astro.ph.11175S; 2002astro.ph.11175A
We employ the magnetic and velocity fields from turbulent dynamo
simulations to synthesize the polarization of a typical photospheric
line. The synthetic Stokes profiles have properties in common with
those observed in the quiet Sun. The simulated magnetograms present a
level of signal similar to that of the Inter-Network regions. Asymmetric
Stokes V profiles with two, three, and more lobes appear in a natural
way. The intensity profiles are broadened by the magnetic fields
in fair agreement with observational limits. Furthermore, the Hanle
depolarization signals of the Sr I λ4607 Å line turn out to be within
the solar values. Differences between synthetic and observed polarized
spectra can also be found. There is a shortage of Stokes V asymmetries,
which we attribute to a deficit of structuring in the magnetic and
velocity fields from the simulations as compared to the Sun. This
deficit may reflect the fact that the Reynolds numbers of the numerical
data are still far from solar values. We consider the possibility that
intense and tangled magnetic fields, like those in the simulations,
exist in the Sun. This scenario has several important consequences. For
example, less than 10% of the existing unsigned magnetic flux would
be detected in present magnetograms. The existing flux would exceed
by far that carried by active regions during the maximum of the solar
cycle. Detecting these magnetic fields would involve improving the
angular resolution, the techniques to interpret the polarization
signals, and to a lesser extent, the polarimetric sensitivity.

---------------------------------------------------------
Title: Quiet-Sun Magnetic Fields at High Spatial Resolution
Authors: Domínguez Cerdeña, I.; Kneer, F.; Sánchez Almeida, J.
2003ApJ...582L..55D Altcode: 2002astro.ph.11454C; 2002astro.ph.11454D
We present spectropolarimetric observations of internetwork magnetic
fields at the solar disk center. A Fabry-Pérot spectrometer was used to
scan the two Fe I lines at 6301.5 and 6302.5 Å. High spatial resolution
(0.5") magnetograms were obtained after speckle reconstruction. The
patches with magnetic fields above noise cover approximately 45%
of the observed area. Such large coverage renders a mean unsigned
magnetic flux density of some 20 G (or 20 Mx cm-2), which
exceeds all previous measurements. Magnetic signals occur predominantly
in intergranular spaces. The systematic difference between the flux
densities measured in the two iron lines leads to the conclusion that,
typically, we detect structures with intrinsic field strengths larger
than 1 kG occupying only 2% of the surface.

---------------------------------------------------------
Title: High Resolution 2D Spectro-polarimetric Observations of Polar
Faculae and Quiet Sun in Two Iron Lines
Authors: Domínguez Cerdeña, I.; Okunev, O.; Kneer, F.; Sánchez
Almeida, J.
2003ASPC..307..370D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Na I D1 Stokes V Asymmetries and Velocity Structure
Around Sunspots
Authors: Eibe, M. T.; Sánchez Almeida, J.; Mein, P.; Aulanier, G.;
Malherbe, J. M.
2003ASPC..307..374E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Polarized Spectrum Emerging from Fast Dynamo Simulations
Authors: Sánchez Almeida, J.; Emonet, T.; Cattaneo, F.
2003ASPC..307..293S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Polarization
Authors: Trujillo-Bueno, Javier; Sanchez Almeida, Jorge
2003ASPC..307.....T Altcode: 2003sopo.conf.....T
No abstract at ADS

---------------------------------------------------------
Title: High resolution 2D spectro-polarimetric observations of the
quiet Sun in two iron lines
Authors: Domínguez Cerdeña, I.; Kneer, F.; Sánchez Almeida, J.
2003AN....324..327D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Properties of Photospheric Regions with Very Low
Magnetic Flux
Authors: Socas-Navarro, H.; Sánchez Almeida, J.
2002ApJ...565.1323S Altcode: 2001astro.ph.10025S
The magnetic properties of the quiet Sun are investigated using a novel
inversion code, FATIMA, based on the Principal Component Analysis of
the observed Stokes profiles. The stability and relatively low noise
sensitivity of this inversion procedure allows for the systematic
inversion of large data sets with a very weak polarization signal. Its
application to quiet-Sun observations of network and internetwork
regions reveals that a significant fraction of the quiet-Sun contains
kilogauss fields (usually with very small filling factors) and confirms
that the pixels with weak polarization account for most of the magnetic
flux. Mixed polarities in the resolution element are also found to
occur more likely as the polarization weakens.

---------------------------------------------------------
Title: Results from the Thermal Vacuum Tests of the Chinese-Brazilian
Earth Resources Satellite - CBERS FM2
Authors: Almeida, J. S.; Garcia, E. C.; Santos, M. B.; Fu, P. Z.
2002iaf..confE.478A Altcode:
This paper details the approach adopted and applied on the thermal
vacuum tests campaign of the CBERS Flight Model #2 spacecraft,
successfully performed at the Integration and Tests Laboratory -
LIT, National Institute for Space Research - INPE, in São José dos
Campos, SP, from September 7th to 28th, 2001. Measuring approximately
1.8 x 2.0 x 2.2m, weighting 1,500kg and carrying three cameras as the
main payload, this spacecraft is scheduled to be launched in China
and it will be orbiting the Earth at 778km as part of its remote
sensing mission profile. Exploring the capabilities of LIT's 3m x
3m thermal vacuum chamber in terms of appropriately selecting and
adjusting its cold shroud temperatures and also some low cost heat
input/sink techniques, the spacecraft was adequately disjoined at its
service and payload model interface in such a way that each part could
physically fit inside the T/V chamber one at a time. Assuring all the
necessary functional and test cabling interconnection between the two
models through the chamber walls for the proper spacecraft electrical
operations as an integrated system, specific thermal test techniques
were applied in order to obtain the required hot and cold acceptance
levels of temperature at the spacecraft subsystems and structural
surfaces, as a consequence of the simulated thermal conditioning from
the distinct orbital configurations. These thermal simulation techniques
consisted of a combination of skin-heaters, the thermal vacuum chamber
main shrouds and dedicated LN2 cold plates, effectively leading to
reliable and very satisfactory testing methodology results. Taking
more than 350 hours and having 67 people directly involved, including
teams from both Brazil and China, this test can be considered as a very
important accomplishment in terms of distinct technique of spacecraft
testing and also in terms of the satisfactory working relationship
between two quite different cultures.

---------------------------------------------------------
Title: Thermal Relaxation of Very Small Solar Magnetic Structures
in Intergranules: A Process That Produces Kilogauss Magnetic Field
Strengths
Authors: Sánchez Almeida, J.
2001ApJ...556..928S Altcode: 2001astro.ph..3415A; 2001astro.ph..3415S
The equilibrium configuration of very small magnetic flux tubes in an
intergranular environment automatically produces kilogauss magnetic
field strengths. We argue that such a process takes place in the Sun
and complements the convective collapse (CC), which is traditionally
invoked to explain the formation of kilogauss magnetic concentrations in
the solar photosphere. In particular, it can concentrate the very weak
magnetic fluxes revealed by the new IR spectropolarimeters, for which
the operation of the CC may have difficulty. As part of the argument,
we show the existence of solar magnetic features of very weak fluxes yet
concentrated magnetic fields (some 3×1016 Mx and 1500 G).

---------------------------------------------------------
Title: G-Band Spectral Synthesis in Solar Magnetic Concentrations
Authors: Sánchez Almeida, J.; Asensio Ramos, A.; Trujillo Bueno,
J.; Cernicharo, J.
2001ApJ...555..978S Altcode: 2001astro.ph..3006A; 2001astro.ph..3006S
Narrowband imaging in the G band is commonly used to trace the small
magnetic field concentrations of the Sun, although the mechanism that
makes them bright has remained unclear. We carry out LTE syntheses
of the G band in an assorted set of semiempirical model magnetic
concentrations. The syntheses include all CH lines as well as the main
atomic lines within the bandpass. The model atmospheres produce bright
G-band spectra having many properties in common with the observed G-band
bright points. In particular, the contrast referring to the quiet Sun
is about twice the contrast in continuum wavelengths. The agreement
with observations does not depend on the specificities of the model
atmosphere; rather, it holds from single flux tubes to microstructured
magnetic atmospheres. However, the agreement requires that the real
G-band bright points are not spatially resolved, even in the best
observations. Since the predicted G-band intensities exceed by far
the observed values, we foresee a notable increase of contrast of the
G-band images upon improvement of the angular resolution. According
to the LTE modeling, the G-band spectrum emerges from the deep
photosphere that produces the continuum. Our syntheses also predict
solar magnetic concentrations showing up in continuum images but
not in the G band. Finally, we have examined the importance of the
CH photodissociation in setting the amount of G-band absorption. It
turns out to play a minor role.

---------------------------------------------------------
Title: Spectral signature of uncombed penumbral magnetic
fields. Comment
Authors: Sánchez Almeida, J.
2001A&A...369..643S Altcode:
The conservation of magnetic flux demands a magnetic field fine
structure as small as 15 km to explain the net circular polarization
observed in penumbrae (Sánchez Almeida \cite{san98a}). A recent work
by Martínez Pillet (\cite{mar00}) claims that modeling penumbrae as
a collection of fluxtubes 100 km wide suffices. We identify several
shortcomings of such modeling so that it is presently unclear whether
it really contradicts the former conclusion.

---------------------------------------------------------
Title: The Micro-Structure of the Solar Magnetic Fields
Authors: Sánchez Almeida, J.
2001ASPC..248...55S Altcode: 2001mfah.conf...55S
No abstract at ADS

---------------------------------------------------------
Title: Ghost Magnetic Structures in the Sun and Solar-type Stars
(CD-ROM Directory: contribs/sanchez)
Authors: Sánchez Almeida, J.
2001ASPC..223..145S Altcode: 2001csss...11..145S
No abstract at ADS

---------------------------------------------------------
Title: Elusive Magnetic Structures in the Sun and Solar-Type Stars
Authors: Sánchez Almeida, J.
2000ApJ...544.1135S Altcode:
The magnetic structures of the Sun are very inhomogeneous, with
irregularities smaller than the smallest sizes that we resolve
from Earth. Such irregularities are not properly accounted for by
standard magnetic field diagnostic techniques. We have identified
a quantitatively important bias that has remained unnoticed
hitherto. Intense magnetic fields embedded in inhomogeneous magnetic
structures produce little light and easily escape detection. These
elusive magnetic fields, which cheat standard observing techniques,
seem to be common. We estimate that they carry at least half of the
solar magnetic flux. Should the bias be so severe, it would cast doubts
on the present interpretation of many solar magnetic phenomena. Since
magnetic field measurements in solar-type stars reproduce solar methods,
they are liable to the same systematic errors.

---------------------------------------------------------
Title: Physical Properties of the Solar Magnetic Photosphere under
the MISMA Hypothesis. II. Network and Internetwork Fields at the
Disk Center
Authors: Sánchez Almeida, J.; Lites, B. W.
2000ApJ...532.1215S Altcode:
This paper is the second in a series that models photospheric magnetic
structures in terms of atmospheres having optically thin fluctuations
of magnetic field and thermodynamic state (the MISMA hypothesis). We
apply an inversion procedure to the polarization of Fe I λ6301.5 and
Fe I λ6302.5 observed in network and internetwork regions with the
Advanced Stokes Polarimeter. Some 5200 independent spectra, comprising
mildly asymmetric to very abnormal Stokes profiles, were reproduced
by a single type of model atmosphere. It has three components, two
that are magnetized and one that is not. A large fraction among the
field strengths we measure are in the kG regime, but simulations
suggest that the polarization of the observed Fe I lines weakens
below detectable levels for fields substantially smaller than the
observed ones. Synthesis of Stokes profiles of the IR Fe I λ15648.5
line in MISMAs reveals the opposite behavior, i.e., an increase of
polarization for sub-kG fields. The highly transparent MISMAs inferred
from observations are significantly brighter in the continuum than an
unmagnetized atmosphere. The mass of the magnetic structures tends to be
at rest, although a minor fraction undergoes strong downflows. Downflows
are also present in the nonmagnetic environment. A significant number
of fitted Stokes profiles require opposite magnetic polarities within
the same resolution element. The occurrence of mixed polarities
increases with weakening degree of polarization, such that 25% of
the weakest signals require mixed polarity. The weak polarization
signals account for most of the total (unsigned) magnetic flux of the
observed region. By extrapolation, this indicates that a significant
fraction of photospheric magnetic flux remains undetected. The MISMA
framework provides a unified and physically consistent scenario for
interpretation of quiet Sun magnetism. Moreover, it is the only one
available at present that is able to fit the abnormal Stokes profiles
as revealed by the new generation of sensitive Stokes polarimeters.

---------------------------------------------------------
Title: Radiative Transfer in Weakly Polarizing Media
Authors: Sánchez Almeida, J.; Trujillo Bueno, J.
1999ApJ...526.1013S Altcode:
We study radiative transfer through a weakly polarizing medium,
i.e., a medium in which the degree of polarization of the absorbed,
retarded, and emitted light is always weak. In this case, the general
radiative transfer equation for the Stokes parameters yields very simple
formal solutions. The intensity does not depend on the polarization,
and the other Stokes parameters are uncoupled from each other. It is
shown how this simplified radiative transfer equation holds in many
realistic cases relevant for solar and stellar magnetometry. It can be
applied whenever the weak magnetic field approximation works, i.e.,
for weakly split lines. In addition, it handles weak spectral lines,
structures with complex magnetic topology, chromospheric lines formed
under non-LTE conditions, etc. The merits of the approximation, which we
call the weakly polarizing medium (WPM) approximation, are illustrated
by means of several LTE and non-LTE line syntheses in realistic solar
model atmospheres. The WPM approximation should be useful in planning
and understanding measurements based on polarization. It simplifies
the relationship between the observed polarization and the physical
structure that one tries to retrieve. The approximation may also be
used in numerical problems requiring extensive polarized radiative
transfer (inversion codes, syntheses of stellar spectra, self-consistent
multilevel non-LTE Zeeman line transfer with atomic polarization, etc.).

---------------------------------------------------------
Title: The profuse optically-thin irregularities of the photospheric
magnetic fields
Authors: Sánchez Almeida, J.
1999AIPC..471...55S Altcode: 1999sowi.conf...55S
The highly irregular nature of most photospheric magnetic fields is
analyzed here, trying to emphasize the connection between photospheric
fluctuations and those existing in the solar wind. It is discussed
how the magnetic flux conservation in sunspots demands penumbrae
pervaded by kilometer-wide irregularities. The diagnosis of this
type of tiny scales requires special tools having degrees of freedom
for optically-thin magnetic irregularities. One of such tools is
introduced here, to be subsequently applied to the quiet Sun. It turns
out to reproduce the observed Zeeman induced polarization, despite
the fact that the polarization is frequently very abnormal. The kind
of irregular atmosphere that the inversion technique favors seems to
provide a consistent picture of the quiet Sun magnetism.

---------------------------------------------------------
Title: The Spectrum of Intensity Fluctuations Across Penumbral
Filaments
Authors: Sánchez Almeida, J.; Bonet, J.
1999ASPC..183...87S Altcode: 1999hrsp.conf...87S
No abstract at ADS

---------------------------------------------------------
Title: LPSP &amp; TIP: Full Stokes Polarimeters for the Canary
Islands Observatories
Authors: Mártinez Pillet, V.; Collados, M.; Sánchez Almeida, J.;
González, V.; Cruz-Lopez, A.; Manescau, A.; Joven, E.; Paez, E.;
Diaz, J.; Feeney, O.; Sánchez, V.; Scharmer, G.; Soltau, D.
1999ASPC..183..264M Altcode: 1999hrsp.conf..264M
No abstract at ADS

---------------------------------------------------------
Title: Influence of Unresolved Optically-Thin Irregularities on
Quiet Sun Magnetic Field Determinations
Authors: Sánchez Almeida, J.
1999AGAb...15Q..10S Altcode: 1999AGM....15..A10S
Observations and theory both point out that the magnetic photosphere
is not smooth but irregular at optically-thin scales. The relevance of
these irregularities for a proper magnetic field diagnostics depends
upon the not yet known structure of the magnetic field fluctuations
(and, of course, on the purpose of our determination). Sánchez
Almeida &amp; Lites (1999) analyze quiet Sun network and internetwork
Stokes profiles allowing for optically thin fluctuations (i.e.,
they use MIcro-Structured Magnetic Atmospheres). The retrieved
semi-empirical quiet Sun model atmospheres present several conspicuous
counter-intuitive properties. If these models contain the essentials
of the real Sun then standard quiet Sun magnetic field determinations
are seriously biased. This contribution presents and discusses some
of these unexpected properties: the IR Fe i 15648 Å line is rather
insensitive to strong kG fields; large magnetic field strengths can
easily escape detection; unresolved mixed polarities seems to be the
rule when dealing with most of the solar surface, that is to say,
when measuring the signals that may be carrying most of the solar
magnetic flux, etc. The conclusion to be drawn from these results
is that accounting for optically-thin fluctuations does matter for a
proper quiet Sun magnetic field diagnostics.

---------------------------------------------------------
Title: The current status of the MISMA hypothesis
Authors: Sánchez Almeida, J.
1999ASSL..243..251S Altcode: 1999sopo.conf..251S
No abstract at ADS

---------------------------------------------------------
Title: The Spectrum of Fluctuations across Penumbral Filaments
Authors: Sánchez Almeida, J.; Bonet, J. A.
1998ApJ...505.1010S Altcode:
We estimate the typical spectrum of spatial fluctuations of intensity
due to the penumbral filaments. High angular resolution continuum
images are used (cut-off frequencies equivalent to 0.28" wavelength
of about 5257 Å). The amplitude of the observed spectra follows the
modulation transfer function of our optical system. In other words,
the spectrum of real penumbral fluctuations seems to be flat up to the
higher observable spatial frequency. We expect it to continue far beyond
the artificial instrumental cutoff, which implies that the structure
of the penumbra remains unresolved to the present solar observations.

---------------------------------------------------------
Title: Optically Thin Irregularities in the Penumbrae of Sunspots
Authors: Sánchez Almeida, J.
1998ApJ...497..967S Altcode:
Different estimates of the vertical gradient of magnetic field
inclination in penumbrae disagree by 2 orders of magnitude. This
disagreement may be resolved if measuring with typical angular
resolutions implies averaging hundreds of independent fibrils whose
residual variation, upon spatial averaging, gives rise to the observed
large-scale structures. The small-scale gradients show up in estimates
based on the broadband circular polarization, whereas significant
bias affects other methods. From the comparison of these two types
of measurements, one can infer the typical sizes of the penumbral
irregularities. They turn out to be between 1 and 15 km wide, depending
on details of the calculation. This result supports the kind of highly
irregular atmosphere that Sánchez Almeida and coworkers proposed to
represent the solar magnetic photosphere.

---------------------------------------------------------
Title: The Unresolved Structure of Photospheric Magnetic Fields:
Truths, Troubles and Tricks (Invited review)
Authors: Sánchez Almeida, J.
1998ASPC..155...54S Altcode: 1998sasp.conf...54S
No abstract at ADS

---------------------------------------------------------
Title: Physical Properties of the Solar Magnetic Photosphere under
the MISMA Hypothesis. I. Description of the Inversion Procedure
Authors: Sánchez Almeida, J.
1997ApJ...491..993S Altcode:
The paper describes an automatic inversion code to recover
microstructured magnetic atmospheres (MISMAs) by fitting Stokes
profiles. These solar model atmospheres incorporate small-scale
fluctuations of the magnetic field vector, the velocity, the
temperature, etc., which seems to be an intrinsic property of the
magnetic photosphere. The model MISMAs considered for inversion
have several distinct components. Each one of them is made of
slender flux tubes, so that the whole vertical stratification of
the MISMA is reconstructed from a finite set of parameters. The
inversion code has been thoroughly tested using both synthetic and
real observations. In particular, it successfully reproduces line
profiles and model atmospheres corresponding to the quiet Sun and
plage regions. As a by-product, we introduce a new error estimate for
nonlinear least-squares minimizations.

---------------------------------------------------------
Title: Chromospheric polarity reversals on sunspots. Are they
consistent with weak line emission?
Authors: Sanchez Almeida, J.
1997A&A...324..763S Altcode:
Photospheric and chromospheric solar magnetograms sometimes show
opposite polarity. This intriguing phenomenon is associated with
the emergence of magnetic flux and with nearby, but not necessarily
superposed, flaring activity. Despite the fact that there may be
different explanations, it is shown here that the observed reversals
are consistent with weak flare-like line emission all over the reversed
polarity regions. Although this emission does not show up as a flare
in filtergrams, it exhibits itself as a polarity reversal of the
chromospheric magnetograms. If this interpretation were correct, the
reversal would not correspond to a real flip of the magnetic field
direction from the photosphere to the chromosphere. It would be an
artifact due to radiative transfer effects. Observations to support
or discard this hypothesis are briefly pointed out.

---------------------------------------------------------
Title: The IAC Solar Polarimeters: Goals and Review of Two Ongoing
Projects
Authors: Sanchez Almeida, J.; Collados, M.; Martinez Pillet, V.;
Gonzalez Escalera, V.; Scharmer, G. B.; Shand, M.; Moll, L.; Joven,
E.; Cruz, A.; Diaz, J. J.; Rodriguez, L. F.; Fuentes, J.; Jochum,
L.; Paez, E.; Ronquillo, B.; Carranza, J. M.; Escudero-Sanz, I.
1997ASPC..118..366S Altcode: 1997fasp.conf..366S
The IAC is currently developing two similar polarimeters, one for
optical wavelengths and one for near infra-red wavelengths (1.5
mu m). Both instruments will provide spectra of the four Stokes
parameters over 2D solar regions. The visible spectro-polarimeter will
be operated at the Swedish Tower (La Palma), and it is being developed
in collaboration with the Royal Swedish Academy of Sciences. We intend
to take advantage of the excellent seeing conditions at this telescope,
while maintaining high polarimetric precision. The IR polarimeter
is being designed for the German VTT (Tenerife) which has better
angular resolution in the near infra-red. This report describes the
goals and technical solutions. It also briefs on the current status
of the projects.

---------------------------------------------------------
Title: Heights of formation for measurements of atmospheric
parameters.
Authors: Sanchez Almeida, J.; Ruiz Cobo, B.; del Toro Iniesta, J. C.
1996A&A...314..295S Altcode:
We argue that heights of formation (HOFs) should not be assigned to
spectral lines since a single line my sample very different layers of
the atmosphere, depending on the physical parameter of interest and
the technique employed to determine it. HOFs should be assigned to
specific measurements. General expressions to compute these HOFs for
measurements are derived. The equations are subsequently used to show,
in representative solar measurements, the uncertainties produced by
assigning HOFs to lines. Only weak lines can probe a single height of
the atmosphere.

---------------------------------------------------------
Title: Line Asymmetries and the Microstructure of Photospheric
Magnetic Fields
Authors: Sanchez Almeida, J.; Landi Degl'Innocenti, E.; Martinez
Pillet, V.; Lites, B. W.
1996ApJ...466..537S Altcode:
A systematic structuring of magnetic fields over scales much smaller
than the mean free path of photospheric photons may be responsible for
the observed asymmetrical Stokes profiles. We explore this possibility
by deriving the radiative transfer equation for microstructured magnetic
atmospheres (the MISMA approximation). This equation is subsequently
employed to show that very schematic MISMA scenarios for the penumbrae
of sunspots, plage and network regions, and internetwork regions produce
Stokes profiles that have the observed asymmetries. The details of
these model atmospheres are of secondary importance, but the ease of
generating the type of observed asymmetries with MISMAs is significant,
so the existence of MISMAs deserves serious consideration. Should such
microstructures exist, the techniques currently employed to infer
properties of the solar photosphere need to be revised. MISMAs are
also of concern for the physics of the photosphere itself. These two
topics are briefly discussed.

---------------------------------------------------------
Title: Micro-structured magnetic atmospheres
Authors: Sánchez Almeida, J.; Landi Degl'innogenti, E.
1996SoPh..164..203S Altcode:
Asymmetrical Stokes profiles are produced if the photospheric
magnetic and velocity fields are structured on scales smaller than
the mean-free-path of the photons. Here we put forward a compact
analytical expression for the radiative transfer equation in this
case. Explicitly, micro-variations of the magnetic field strength
and the velocity are considered. The existence of micro-structures
might have serious implications on the techniques currently used to
measure solar magnetic fields. For example, we show the failure of
the relationship employed to calibrate magnetographs.

---------------------------------------------------------
Title: Two-dimensional, high spatial resolution, solar spectroscopy
using a Correlation Tracker. II. Maps of spectral quantities.
Authors: Collados, M.; Rodriguez Hidalgo, I.; Ballesteros, E.; Ruiz
Cobo, B.; Sanchez Almeida, J.; del Toro Iniesta, J. C.
1996A&AS..115..367C Altcode:
In this paper we illustrate some of the capabilities of the Correlation
Tracker prototype developed at the Instituto de Astrofisica de
Canarias used for two-dimensional, high spatial resolution, solar
spectroscopy. Slit spectra have been taken, using the Correlation
Tracker as a stabilizer (minimizing image motion during exposures) and
as an accurate positioning device (allowing to precisely locate the
entrance slit of the spectrograph at adjacent positions on the solar
disc). Spectral information is obtained from several solar regions
of different sizes. Granules (including some exploding ones) and
intergranules are clearly resolved. Several sub-arcsecond structures
are undoubtedly distinguished as well. The two-dimensional variation
of several spectral quantities in the solar atmosphere is shown,
demonstrating the power of this technique and its future possibilities.

---------------------------------------------------------
Title: Empirical granular/intergranular average model atmospheres.
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Del Toro Iniesta,
J. C.; Collados, M.; Sánchez Almeida, J.
1996joso.proc..162R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Empirical model of an average solar granule
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Rodriguez Hidalgo,
I.; Collados, M.; Sanchez Almeida, J.
1996ASPC..109..155R Altcode: 1996csss....9..155R
No abstract at ADS

---------------------------------------------------------
Title: A proposal for a low instrumental polarization coude
telescope. II. The German Gregory-Coude Telescope at the Observatorio
del Teide.
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Kneer, F.
1995A&AS..113..359S Altcode:
We have put into practice the technique to minimize the instrumental
polarization (IP) of coude telescopes proposed by Martinez Pillet &amp;
Sanchez Almeida (1991): a λ/2-plate inserted into the optical path,
with the proper orientation, cancels the IP. The compensation of the
Gregory-Coude Telescope at the Observatorio del Teide turns out to
fulfil theoretical expectations. Empirical tests at 630nm demonstrate
that its IP decreases by a factor ~4. We show that the residual IP is
not intrinsic to the method but it is due to the limited precision of
the retarder presently used. In addition, observations indicate that
the insertion of the λ/2-plate does not noticeably deteriorate the
optical quality of the whole telescope. In short, this work proves
the practical soundness of the λ/2-plate technique to reduce IP.

---------------------------------------------------------
Title: Uncertainties in the determination of the Stokes parameters
due to photon noise.
Authors: Sanchez Almeida, J.
1995A&AS..109..417S Altcode:
We derive inequalities which restrict the precision of the Stokes
parameters imposed by photon noise. The signal-to-noise ratio of the
measured Stokes parameters is never better than the square root of the
number of detected photons. In case of weakly polarized sources (i.e.,
most astronomical sources), such an inequality imposes no practical
limit and it should be replaced by the intensity-to-noise ratio,
which approximately follows the same square root law. Besides these
general results, we also find relationships between the errors of the
Stokes parameters which apply to particular (although fairly common)
analyzers. The equations are presented in a device-independent fashion,
so that they can be used to tell, in an absolute sense, whether photon
noise allows the measurement of small polarimetric signals.

---------------------------------------------------------
Title: Lithium at High Redshifts
Authors: Sánchez Almeida, J.; Rebolo, R.
1995lea..conf...85S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Li, Na, K and Hα in a Sunspot
Authors: Barrado Y Navascués, D.; de Castro, E.; García López,
R. J.; Sánchez Almeida, J.; Montesinos, B.
1995IAUS..176P.123B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Instrumental polarization in the focal plane of
telescopes. II. Effects induced by seeing.
Authors: Sanchez Almeida, J.
1994A&A...292..713S Altcode:
This work quantifies the influence of the terrestrial atmosphere on the
instrumental polarization (IP) of telescopes. Our numerical simulations
show that seeing mostly induces a random crosstalk between Stokes
parameters. The main contamination affects the linear polarization
signals and is due to mixing with intensity. In general, circular
polarization signals are less corrupted by atmospheric effects. We
have analyzed the IP considering the imaging mirrors and the entrance
window of a particular instrument, namely the Large Earth-based Solar
Telescope (LEST). Crosstalks up to 2x10^-2^ (window) and up to 2x10^-3^
(mirrors) occur in short-exposure images. This level of IP is largely
reduced by increasing the exposure time or the pixel size. Means for
extrapolating the IP of LEST to other instruments are provided. Using
them, the dependence of the seeing-induced IP on wavelength, telescope
size etc. is briefly examined.

---------------------------------------------------------
Title: The Inclination of Network Magnetic Fields
Authors: Sanchez Almeida, J.; Martinez Pillet, V.
1994ApJ...424.1014S Altcode:
We have observed the linear polarization of 21 bright grains of the
photospheric network close to the disk center. The linear polarization
of Fe I 6302.5 A was always lower than 1.9 x 10-3 (referred
to continuum intensity). This level of linear polarization implies a
very small magnetic field inclination with respect to the vertical,
which we estimate below 10 deg. Our finding is in apparent disagreement
with previous studies which claim large inclinations; however, it
fulfills theoretical expectations. Plage regions close to sunspots
might show inclination, but isolated network elements do not.

---------------------------------------------------------
Title: Spectral lines unaffected by instrumental
polarization. II. Selected lines of astrophysical interest
Authors: Vela Villahoz, E.; Sanchez Almeida, J.; Wittmann, A. D.
1994A&AS..103..293V Altcode:
Lines with no linear polarization induced by Zeeman effect
are unaffected by instrumental polarization. We compile 86 such
electric dipole lines with differing temperature and magnetic field
sensitivities. In addition, we list 420 spectral lines which produce
negligible linear polarization. In most cases, this second set can
also be regarded as lines unaffected by instrumental polarization.

---------------------------------------------------------
Title: Instrumental polarization.
Authors: Sánchez Almeida, J.
1994imfm.conf..106S Altcode:
The techniques employed to overcome the instrumental polarization
(IP) of solar observations are revised. Special attention is paid
to the method used by the new generation of IP-free telescopes (LEST
&amp; THEMIS). The specific polarimetric errors of spectrographs and
telescopes are discussed.

---------------------------------------------------------
Title: The inclination of magnetic fields in small-scale flux
concentrations
Authors: Sánchez Almeida, J.; Martínez Pillet, V.
1994smf..conf..316S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectral lines insensitive to instrumental polarization
Authors: Vela Villahoz, E.; Sánchez Almeida, J.
1994smf..conf..340V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Instrumental polarization of telescopes: a laboratory test
of the diffraction model
Authors: Sánchez Almeida, J.; Martínez Pillet, V.
1994smf..conf..343S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spectral lines unaffected by instrumental polarization. 1:
Theory
Authors: Sanchez Almeida, J.; Vela Villahoz, E.
1993A&A...280..688S Altcode:
We propose a new approach to minimize the instrumental polarization (IP)
of current polarimetric observations. It is shown how the instrumental
polarization can be deduced and removed, by using lines with no
intrinsic linear polarization. Notably, no specific understanding
of the polarizing properties of our optical setup is required. For
the technique to be of practical application, lines unaffected by IP
presenting various temperature, magnetic field, etc. sensitivities must
be identified. We work out the atomic levels involved in electric dipole
transitions which create no linear polarization, from the Zeeman effect.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Lines unaffected by polarization
(Vela Villahoz+ 1994)
Authors: Vela Villahoz, E.; Sanchez Almeida, J.; Wittmann, A. D.
1993yCat..41030293V Altcode:
Not Available (2 data files).

---------------------------------------------------------
Title: Polarizing properties of grazing-incidence X-ray mirrors
- Comment
Authors: Sanchez Almeida, J.; Martinez Pillet, V.
1993ApOpt..32.4231S Altcode:
We show that grazing-incidence telescopes, like those used for X-ray
imaging, present negligible instrumental polarization. This property
does not depend on the number of reflections the telescope employs
to lead light from the entrance pupil to the focal plane. The result
applies to the various mirrors of the advanced X-ray astrophysics
facility satellite. In this particular case we have quantified the
residual instrumental polarization to be between 10 exp -3 and 5 x 10
exp -5, depending on the size of the resolution elements.

---------------------------------------------------------
Title: A multiline method to determine stellar magnetic fields
Authors: Ripodas, P.; Collados, M.; Sanchez Almeida, J.; Garcia Lopez,
R. J.
1993ASPC...40..196R Altcode: 1993IAUCo.137..196R; 1993ist..proc..196R
No abstract at ADS

---------------------------------------------------------
Title: Asymmetric Stokes Q, U and V Line Profiles Observed in Sunspots
Authors: Sanchez Almeida, J.; Lites, B. W.
1993ASPC...46..177S Altcode: 1993mvfs.conf..177S; 1993IAUCo.141..177S
No abstract at ADS

---------------------------------------------------------
Title: Atomic orientation in chromospheric lines.
Authors: Trujillo Bueno, J.; Martínez Pillet, V.; Sánchez Almeida,
J.; Landi Degl'Innocenti, E.
1993ASPC...46..526T Altcode: 1993ASPC...46..526B; 1993mvfs.conf..526T; 1993IAUCo.141..526T
Observations of the Stokes I and V profiles of the Ca II H and K lines
in solar magnetic regions are presented. Least-squares fits of dI/dλ
to V are obtained and the wavelength variation of the residuals,
i.e. V-kdI/dλ, calculated. The authors find significant symmetric
residuals in umbrae, which are in agreement with the effect on the
V profiles due to atomic orientation, i.e. with the existence of an
unequal population of the Zeeman sublevels with M &gt; 0 with respect
to those with M &lt; 0.

---------------------------------------------------------
Title: High Angular Resolution Stokes V Spectra in Penumbrae
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Lites, J. T. Buenol
B. W.
1993ASPC...46..192S Altcode: 1993mvfs.conf..192S; 1993IAUCo.141..192S
No abstract at ADS

---------------------------------------------------------
Title: Observation and Interpretation of the Asymmetric Stokes Q,
U, and V Line Profiles in Sunspots
Authors: Sanchez Almeida, J.; Lites, B. W.
1992ApJ...398..359S Altcode:
We present a first approach to systematic characterization and
interpretation of observed asymmetries of Stokes profiles as a function
of spatial position within sunspots. Spatial maps of the full Stokes
profiles of Fe I 6302.5 A gathered in large sunspots using the HAO
Stokes II instrument reveal asymmetries that vary systematically across
large sunspots observed during 1980. We use the inversion technique
by Landolfi to extract the velocity gradients along the line of sight
(LOS) which give rise to these asymmetries. The gradients derived from
full Stokes profiles are in agreement with previous characterizations
of the Evershed flow derived from Stokes I profiles alone (i.e., a flow
increasing with depth in the atmosphere). By coupling this semiempirical
gradient of velocity with a magnetic field inclination varying along the
LOS, the synthesized profiles are able to mimic basic observed features
of the broad-band circular polarization present in our data and observed
previously by others. This characterization has magnetic field lines
which become progressively more horizontal with depth in the penumbra.

---------------------------------------------------------
Title: Observations of the microwave background on a scale of 8
deg. I - The observing system
Authors: Davies, R. D.; Watson, R. A.; Daintree, E. J.; Hopkins, J.;
Lasenby, A. N.; Sanchez Almeida, J.; Beckman, J. E.; Rebolo, R.
1992MNRAS.258..605D Altcode:
A sensitive observing system for observing the cosmic microwave
background on an angular scale of 8 deg is described. This angular
scale is appropriate for studies of intrinsic fluctuations in the CMB
generated by gravitational potential fluctuations (the Sachs-Wolfe
effect). The beam-switching system employs low-noise and broadband
cryogenically cooled receivers. A major improvement in the stability
of the system has resulted from triple-beam operation which removes
the effect of atmospheric water vapour and ambient temperature changes
to a level of several millikelvin on a single scan. The evaluation
and assessment of this system operating at an elevation of 2400 m on
Tenerife is described. Results for an RA circle at Dec. = 40 deg are
shown; these reach a sensitivity of better than 100 micro-K in an 8.4
deg beam.

---------------------------------------------------------
Title: Instrumental polarization in the focal plane of telescopes
Authors: Sanchez Almeida, J.; Martinez Pillet, V.
1992A&A...260..543S Altcode:
We present a technique to model the instrumental polarization in
the focal plane of a telescope. It takes into account that different
rays of an incoming beam suffer different variation of the original
polarization in their paths through the system. It also considers that
the net effect depends on the way in which the different rays interfere
with each other. We show that the Mueller matrix which describes this
instrumental polarization greatly simplifies if the polarimetric
measurements have poor spatial resolution. The Mueller matrices
corresponding to a pair of academic cases are worked out: a diffraction
limited telescope when the source lies on its axis and an axisymmetric
mirror with the source off the axis. We discuss the consequences of
these mathematical results on real telescopes (e.g. LEST). Finally,
we briefly consider the seeing-induced instrumental polarization.

---------------------------------------------------------
Title: Radiative transfer for polarized light: Equivalence between
Stokes parameters and coherency matrix formalisms
Authors: Sanchez Almeida, J.
1992SoPh..137....1S Altcode: 1992SoPh..137....1A
Two formal solutions of the radiative transfer equation for polarized
light have been proposed. One uses the Stokes parameters to describe
the polarization, while the other uses the coherency matrix. It is
shown in the present work that they are equivalent. Both can be used to
compute response and contribution functions for the Stokes parameters
and both require the solution of systems of differential equations with
similar numbers of independent variables. New equations to solve the
radiative transfer problem using the Stokes parameters formalism are
presented. In addition, a computer code which synthesizes the Stokes
profiles by means of these equations is described.

---------------------------------------------------------
Title: A proposal for a low instrumental polarization coude telescope
Authors: Martinez Pillet, V.; Sanchez Almeida, J.
1991A&A...252..861M Altcode: 1991A&A...252..861P
A technique for obtaining an ideal two-mirror coude system with no
instrumental polarization is described. A half-wave plate positioned
between the two mirrors with the proper orientation produces the
desired effect. The level of spurious polarization is limited by the
characteristics of the retarder and the similarity of the mirrors. The
telescope design and accuracy are discussed.

---------------------------------------------------------
Title: Spectrograph distortion in sunspot line profiles
Authors: Pillet, V. Martínez; Almeida, J. Sánchez
1991SoPh..134..403P Altcode:
We show empirically how the effect of the instrumental polarization
of the spectrograph can distort the shape of the intensity profiles
in sunspots. In order to avoid the problems an analysis of the
polarization of the light should be performed at the entrance slit of
the spectrograph.

---------------------------------------------------------
Title: Spectrograph distortion in sunspot line profiles
Authors: Martinez Pillet, V.; Sanchez Almeida, J.
1991SoPh..134..403M Altcode:
We show empirically how the effect of the instrumental polarization
of the spectrograph can distort the shape of the intensity profiles
in sunspots. In order to avoid the problems an analysis of the
polarization of the light should be performed at the entrance slit of
the spectrograph.

---------------------------------------------------------
Title: The instrumental polarization of a Gregory-Coudé telescope
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Wittmann, A. D.
1991SoPh..134....1A Altcode:
We calculate a theoretical model of the polarization properties of
a Gregory-Coudé telescope to predict the behaviour of the German
Gregory-Coudé Telescope installed at the Observatorio del Teide
(Spain). Measurements of the real effects produced by this telescope
acting upon light of known polarization are compared with the model. We
estimate an uncertainty in its predictions of about 10%, which is
produced by the uncertainties of the (complex) refractive index of the
metallic layers covering the mirrors. The paper concludes by briefly
considering the way in which the plain telescope changes the Stokes'
profiles.

---------------------------------------------------------
Title: Performance of the IAC Stokes I and V analyzer.
Authors: Sánchez Almeida, J.; Martínez Pillet, V.
1991sopo.work..191S Altcode:
The chromatic behaviour of the IAC analyzer, commonly used at the German
Vacuum Gregory-Coude telesope at the Spanish Observatorio del Teide
(Canary Islands), is investigated. It is shown that, through careful
alignment of the optical components, a nearly perfect circular analysis
can be obtained at wavelengths of 4000 Å and 6000 Å. For other visible
regions the crosstalk between linear and circular polarization can be
always made lower than 10%.

---------------------------------------------------------
Title: Magnetic Flux Determination in Late-Type Dwarfs
Authors: Rípodas, P.; Sánchez Almeida, J.; García López, R. J.;
Collados, M.
1991LNP...380..417R Altcode: 1991IAUCo.130..417R; 1991sacs.coll..417R
We present a very preliminary and simplified analysis designed to
measure photospheric magnetic fields in late-type stars, using the FeI
5247.06 Å and 5250.22 Å lines. We show how the use of the equivalent
widths of the lines and differences in their depth can give a rapid
estimation of the magnetic flux.

---------------------------------------------------------
Title: A New Technique to Measure Magnetic Field Strength in Active
Stars
Authors: Sánchez Almeida, J.; García López, R. J.
1991LNP...380..414S Altcode: 1991IAUCo.130..414S; 1991sacs.coll..414S
We explore the use of the flux difference between the lines Fe 15250 Å
and Fe 15247 Å as a technique to measure photospheric magnetic fields
in late-type stars. The technique developed takes into account all the
LTE physics of the problem, assuming a radial and homogeneous magnetic
field distribution over the stellar surface. Some test calculations,
in order to prove the feasibility of the method, are shown.

---------------------------------------------------------
Title: Numerical Test of a New V-Profile Inversion Technique
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Collados, M.;
Sanchez Almeida, J.
1990Ap&SS.170..113R Altcode:
The diagnostic method proposed by Landi Degl'Innocenti and Landolfi
(1982), based on the observation of circular polarization, has been
generalized to derive the thermodynamic properties of unresolved
magnetic elements in the solar atmosphere. The final aim is to derive
the height dependence of several parameters of the flux tube atmosphere
(such as temperature, magnetic field and velocity distributions,
macroturbulence and filling factor). We have used a perturbation
method based on the concept of response functions for the Stokes
profiles introduced by Landi Degl'Innocenti and Landi Degl'Innocenti
(1977). We present here the preliminary results of invertingV-profiles
by an iterative standard least-squares technique, which allows to find
the magnetic 1-D atmosphere consistent with simulated data.

---------------------------------------------------------
Title: Facular points and small-scale magnetic elements
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
1990Ap&SS.170....9D Altcode:
We present spectroscopic observations, with high spatial resolution, of
Ca ii K bright points very near the disc centre. Magnetic concentrations
have been detected in these network (facular) points by only using
intensity profiles of the well-known pair of lines Fe i5250.22 Å and
5247.06 Å. No brightening of these structures with respect to the quiet
photosphere can be ascertained within an accuracy threshold of 1.2%.

---------------------------------------------------------
Title: Velocity Fields Associated with the Magnetic Component of
Solar Faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
1990Ap&SS.170...31S Altcode:
The StokesV asymmetries observed in solar faculae can be interpreted
by invoking the presence of magnetic and velocity fields variations
along the line-of-sight. By means of a perturbative approach, we
develop the theoretical dependence on magnetic and velocity fields
of the StokesV profile around its zero-crossing point. We find that
the empirical curves of growth for theV zero-crossing point and the
slope, as well as the curve of growth for the integral (previously
derived by Sánchez Almeidaet al., 1989, through the same approach),
are reproduced quite well with a single atmosphere which assumes such
simultaneous variations. The depth dependence of the fields that give
the best fit in our model presents several striking properties which
cannot be released without totally compromising the goodness of the
fit. Namely, the magnetic field strength increases towards the observer
while the downflowing velocity field decreases. Both variations must
occur co-spatially, in the same atmospheric layers. This fact seems to
contradict theoretical models for the fanning out parts of magnetic
concentrations which foresee a sharp separation between a static
magnetic layer and a deep zone with velocity fields. We discuss a
possible solution of such contradiction in terms of a finite optical
thickness of the boundary layer between zones with and without magnetic
field in faculae.

---------------------------------------------------------
Title: Are small-scale magnetic concentrations spatially coincident
with bright facular points?
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
1990A&A...233..570D Altcode:
The usually assumed identification of small-scale magnetic
concentrations with bright facular or network points on the photosphere
is observationally checked by using high spatial resolution spectra
of Ca II K bright points very near the disk center. The detection of
spatially unresolved magnetic structures is made via a new differential
analysis of the well-known pair of Fe I lines 5247.06 A and 5250.22
A; these concentrations are present in the central part of a line
weakening zone, which is of some 2 arcsec wide. No continuum intensity
enhancement with respect to the quiet photosphere can be ascertained of
these structures, within an accuracy threshold of 1.2 percent. In spite
of this, magnetic concentrations brighter than the quiet photosphere
are compatible with the observations, but if so, they must be narrower
than 0.2 arcsec.

---------------------------------------------------------
Title: Spectropolarimetry of solar faculae - High spatial resolution
results
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Semel, M.
1990A&A...227..591D Altcode:
A new method to measure the magnetic field strength of small-scale
solar magnetic concentrations is presented. It is based on the center
of gravity method (Semel, 1967), is independent of radiative transfer
calculations and only observable parameters are needed. This method
also provides parameters like filling factor (area fraction occupied by
the tubes), continuum intensity contrast between flux tubes and their
surroundings, in a two-component model scheme. The method is applied
to spectropolarimetric high spatial resolution data. Local variations
of the above parameters inside single faculae are found. This result
suggests some indications about flux tube evolution. A comparison with
low spatial resolution results is also made.

---------------------------------------------------------
Title: On the generation of the net circular polarization observed
in solar faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
1989A&A...222..311S Altcode:
The net circular polarization observed in solar faculae (Stenflo et
al., 1984) follows a law expected from the combination of velocity
and magnetic field gradients in the photosphere. To show this, the
theoretical curve of growth (net circular polarization produced by
a single line versus its absorption coefficient) predicted by this
mechanism is developed. An empirical curve of growth with more than
80 Fe I lines is also constructed. The agreement between theory and
observation seems to point toward this mechanism as responsible for
circular polarization in faculae at the disk center.

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Title: Les facules solaires ou comment observer l'invisible.
Authors: Sanchez Almeida, J.; Collados, M.; Del Toro Iniesta, J. C.
1989Rech...20..810S Altcode: 1989Rech...20..810A
No abstract at ADS

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Title: An explanation for the Stokes V asymmetry in solar faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
1988A&A...201L..37S Altcode:
The asymmetry in the Stokes V profile observed in solar faculae
can be explained by assuming that the magnetic field increases with
height while downflow speed decreases. The MHD compatibility of such
solution is briefly discussed together with an observational test for
that possibility.

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Title: Magnetic field strength in solar flux tubes - A model
atmosphere independent determination
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
1988A&A...196..266S Altcode:
The "line ratio method" (Stenflo, 1973) has been extensively used in
the past to carry out measurements of the magnetic field strength in
spatially unresolved magnetic flux concentrations. The authors present
here a new variant of this technique, which is particularly simple as
it does not depend on any radiative transfer calculations and thus the
assumption of a model atmosphere is not required. General properties
of the transfer equation lead to a relationship between the circular
polarization generated by two lines which are identical except for
their Landé factors. This can be used to directly determine the field
strength from the measured line profiles. In order to test the method
the authors have applied it to experimental data. A comparison with
the traditional line ratio method is shown.

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Title: Estudio de la componente magnética de fáculas y red
fotosférica

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Title: Estudio de la componente magnética de fáculas
y red fotosférica

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Title: Study of the magnetic component of faculae
and the photospheric network;
Authors: Sánchez Almeida, Jorge
1988PhDT.......280S Altcode:
No abstract at ADS

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Title: Sensitive measurement of fluctuations in the cosmic microwave
background
Authors: Davies, R. D.; Lasenby, A. N.; Watson, R. A.; Daintree,
E. J.; Hopkins, J.; Beckman, J.; Sanchez Almeida, J.; Rebolo, R.
1987Natur.326..462D Altcode:
Extensive high sensitivity observations of the cosmic microwave
background have been made on an angular scale of 8° covering a
substantial fraction of the northern sky. An observed anisotropy in
the sky emission at a level of δT/T = 3.7×l0-5 has been
detected (T is temperature). This level should strictly be interpreted
as an upper limit to the cosmic microwave background fluctuations. It
is possibly the direct imprint of density perturbations in the early
Universe.

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Title: Continuum intensity and magnetic flux of solar fluxtubes.
Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.; Sánchez
Almeida, J.
1987PAICz..66..265D Altcode: 1987eram....1..265D
The continuum contrast between fluxtubes and their quiet background,
and the magnetic flux carried by these magnetic elements, have been
determined at different points of a solar facula, in the frame of a
two-component model from spectropolarimetric observations of 1arcsec
spatial resolution. Local spatial variations of these two parameters
have been obtained.

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Title: Isotopic neon cross sections for a study of neutron balance
and temperature during s-process nucleosynthesis
Authors: Almeida, J.; Kaeppeler, F.
1983ApJ...265..417A Altcode:
The neutron source of the s-process is believed to be the
22Ne(α, n) reaction, taking place in the He-burning shell
of a pulsating red giant. Such a periodic neutron irradiation leads to
an exponential distribution of neutron fluences for the seed nuclei,
which can be deduced from the observed solar system abundances. Using
this empirically determined distribution of neutron fluences and the
abundances and the experimental cross sections of the elements present
in the He shell, the number of neutrons captured by each nuclear species
during the s-process has been calculated. The authors have measured
the capture cross sections of the three stable neon isotopes in the
energy range 5-400 keV; the total cross sections were also measured,
between 5 and 800 keV. It is concluded that the traditional s-process
treatment of the neutron balance yields strong evidence in favor of
the 22Ne(α,n) reaction as the effective neutron source to
build most s-process abundances.

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Title: Neutron capture cross sections of 20,21,22Ne between
5 and 400 keV and the neutron balance in s-process nucleosynthesis.
Authors: Almeida, J.; Kappeler, F.
1983ndst.conf..948A Altcode:
No abstract at ADS