408 research outputs found
Near-IR line-strengths in elliptical galaxies: evidence for IMF variations?
We present new relations between recently defined line-strength indices in
the near-IR (CaT*, CaT, PaT, MgI, and sTiO) and central velocity dispersion
(sigma_0) for a sample of 35 early-type galaxies, showing evidence for
significant anti-correlations between CaII triplet indices (CaT* and CaT) and
log(sigma_0). These relations are interpreted in the light of our recent
evolutionary synthesis model predictions, suggesting the existence of important
Ca underabundances with respect to Fe and/or an increase of the dwarf to giant
stars ratio along the mass sequence of elliptical galaxies.Comment: 5 pages, 3 figures, LaTeX. Accepted for publication in MNRAS Pink
Pages. See related information in
http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.htm
Empirical calibration of the near-IR Ca II triplet - I. The stellar library and index definition
A new stellar library at the near-IR spectral region developed for the
empirical calibration of the Ca II triplet and stellar population synthesis
modeling is presented. The library covers the range 8348-9020 Angstrom at 1.5
Angstrom (FWHM) spectral resolution, and consists of 706 stars spanning a wide
range in atmospheric parameters. We have defined a new set of near-IR indices,
CaT*, CaT and PaT, which mostly overcome the limitations of previous
definitions, the former being specially suited for the measurement of the Ca II
triplet strength corrected for the contamination from Paschen lines. We also
present a comparative study of the new and the previous calcium indices, as
well as the corresponding transformations between the different systems. A
thorough analysis of the sources of index errors and the procedure to calculate
them is given. Finally, index and error measurements for the whole stellar
library are provided together with the final spectra.Comment: 24 pages, 10 figures, LaTeX. For associated spectra, tables and
software, see http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.html or
http://www.nottingham.ac.uk/~ppzrfp/CATRIPLET.htm
MIUSCAT: extended MILES spectral coverage. I. Stellar populations synthesis models
We extend the spectral range of our stellar population synthesis models based
on the MILES and CaT empirical stellar spectral libraries. For this purpose we
combine these two libraries with the Indo-U.S. to construct composite stellar
spectra to feed our models. The spectral energy distributions (SEDs) computed
with these models and the originally published models are combined to construct
composite SEDs for single-age, single-metallicity stellar populations (SSPs)
covering the range 3465 - 9469\AA at moderately high, and uniform, resolution
(FWHM=2.51\AA). The colours derived from these SSP SEDs provide good fits to
Galactic globular cluster data. We find that the colours involving redder
filters are very sensitive to the IMF, as well as a number of features and
molecular bands throughout the spectra. To illustrate the potential use of
these models we focus on the NaI doublet at 8200 \AA and with the aid of the
newly synthesized SSP model SEDs we define a new IMF-sensitive index that is
based on this feature, which overcomes various limitations from previous index
definitions for low velocity dispersion stellar systems. We propose an
index-index diagram based on this feature and the neighboring CaII triplet at
8600 \AA, to constrain the IMF if the age and [Na/Fe] abundance are known.
Finally we also show a survey-oriented spectrophotometric application which
evidences the accurate flux calibration of these models for carrying out
reliable spectral fitting techniques. These models are available through our
user-friendly website.Comment: 16 pages, 17 figures, 2 tables; MNRAS in press. Model predictions
available at our website: http://miles.iac.e
Evidence for Blue Straggler Stars Rejuvenating the Integrated Spectra of Globular Clusters
Integrated spectroscopy is the method of choice for deriving the ages of
unresolved stellar systems. However, hot stellar evolutionary stages, such as
hot horizontal branch stars and blue straggler stars (BSSs), can affect the
integrated ages measured using Balmer lines. Such hot, "non-canonical" stars
may lead to overestimations of the temperature of the main sequence turn-off,
and therefore underestimations of the integrated age of a stellar population.
Using an optimized Hbeta index in conjunction with HST/WFPC2 color-magnitude
diagrams (CMDs), we show that Galactic globular clusters exhibit a large
scatter in their apparent "spectroscopic" ages, which does not correspond to
that in their CMD-derived ages. We find for the first time that the specific
frequency of BSSs, defined within the same aperture as the integrated spectra,
shows a clear correspondence with Hbeta in the sense that, at fixed
metallicity, higher BSS ratios lead to younger "apparent" spectroscopic ages.
Thus, the specific frequency of BSSs in globular clusters sets a fundamental
limit on the accuracy for which spectroscopic ages can be determined for
globular clusters, and maybe for other stellar systems like galaxies. The
observational implications of this result are discussed.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in ApJ
La falange es un modo de ser (mujer): Discursos e identidades de género en las publicaciones de la sección femenina (1938-1945)
Las publicaciones periódicas de la Sección Femenina de Falange en la posguerra, Medina e Y, contribuyeron a construir y a difundir los modelos de feminidad que se consideraron válidos en la primera etapa de la Dictadura de Franco. Frente a la tesis generalizada de que el referente de la domesticidad, que concebía a la mujer como esposa y madre, se reforzó y fue el único modelo para las mujeres españolas de la posguerra, el análisis de estas revistas confirma que la construcción de los ideales de género fue un proceso atravesado por tensiones y contradicciones. Estas fueron el resultado de la herencia de los cambios socioculturales que habían tenido lugar durante las décadas anteriores, así como de la experiencia de la Guerra Civil, que, por la participación activa de miles de mujeres en el trabajo de retaguardia, alteró los modelos dominantes de género incluso en la zona sublevada. Asimismo, las publicaciones reflejaron los intentos de las mujeres falangistas por negociar su lugar en la España de Franco así como visibilizar su contribución a la Nueva España. El artículo, en definitiva, propone que la construcción de la feminidad en la posguerra española estuvo marcada por la inestabilidad, y no tanto por la imposición de un modelo rígido o e inmutable. The Women Section of the Falange''s periodicals in the forties, Medina and Y, contributed to the construction and dissemination of ideals for womanhood accepted in the early period of Franco Dictatorship. Contrary to the thesis that the domesticity model, by virtue of which women were exclusively conceived as spouses and mothers, was reinforced and it emerged as the only referent for Spanish women in the postwar, the analysis of these periodicals confirms that the construction of gender models was a process permeated by tensions and contradictions. These were the legacy of social and cultural changes that had taken place in previous decades, as well as the experience of the Spanish Civil War that, by means of the active participation of thousands of women in the war effort, the dominant gender models in the Francoist side became redefined. Besides, altered these female publications reflected the fascist women''s efforts to negotiate their place in Franco Dictatorship, as well as their desire to make visible their contribution to the ''New Spain''. To sum up, the article explores the construction of femininity in the Spanish postwar as a process defined by the instability instead of the imposition of a rigid and immutable model
MIUSCAT: extended MILES spectral coverage. II. Constraints from optical photometry
In the present work we show a comprehensive comparison of our new stellar
population synthesis MIUSCAT models with photometric data of globular clusters
and early-type galaxies. The models compare remarkably well with the colours of
Milky Way globular clusters in the optical range. Likewise, the colours of M31
globular clusters can also be explained by the models by assuming younger ages
then their Galactic counterparts. When compared with quiescent galaxies we
reproduce the colour evolution at intermediate redshift. On the other hand we
find that the colour relations of nearby early-type galaxies are still a
challenge for present-day stellar population synthesis models. We investigate a
number of possible explanations and establish the importance of alpha-enhanced
models to bring down the discrepancy with observations.Comment: 20 pages, 17 figures; MNRAS in press. Model predictions available at
our website: http://miles.iac.e
The CaT strength in Seyfert nuclei revisited: analyzing young stars and non-stellar light contributions to the spectra
In a former paper (Garcia-Rissmann et al. 2005; hereafter Paper I), we have
presented spectra of 64 active, 9 normal and 5 Starburst galaxies in the region
around the near-IR Calcium triplet absorption lines and the [SIII]9069 line. In
the present paper we analyze the CaT strength (WCaT), and kinematical products
derived in that study, namely stellar and ionized gas velocity dispersions. Our
main results may be summarized as follows: (1) Seyfert 2s show no sign of
dilution in WCaT with respect to the values spanned by normal galaxies, even
when optical absorption lines such as the CaII K band at 3933 A are much weaker
than in old, bulge-like stellar populations. (2) The location of Seyfert 2s in
the WCaT-WCaK plane is consistent with evolutionary synthesis models. The
implication is that the source responsible for the dilution of optical lines in
these AGN is a young stellar population, rather than an AGN featureless
continuum, confirming the conclusion of the pioneer study of Terlevich, Diaz &
Terlevich. (3) In Seyfert 1s, both W[SIII] and WCaT tend to be diluted due to
the presence of a non-stellar component, in agreement with the unification
paradigm. (4) A comparison of stellar and gas velocity dispersions confirms the
existence of a correlation between the typical velocities of stars and clouds
of the Narrow Line Region. The strength and scatter around this correlation are
similar to those previously obtained from the [OIII]5007 line width.Comment: 14 pages, 15 figures. Paper accepted for publication in MNRA
Deriving Metallicities From the Integrated Spectra of Extragalactic Globular Clusters Using the Near-Infrared Calcium Triplet
The Ca triplet (CaT) feature in the near-infrared has been employed as a
metallicity indicator for individual stars as well as integrated light of
Galactic globular clusters (GCs) and galaxies with varying degrees of success,
and sometimes puzzling results. Using the DEIMOS multi-object spectrograph on
Keck we obtain a sample of 144 integrated light spectra of GCs around the
brightest group galaxy NGC 1407 to test whether the CaT index can be used as a
metallicity indicator for extragalactic GCs. Different sets of single stellar
population models make different predictions for the behavior of the CaT as a
function of metallicity. In this work, the metallicities of the GCs around NGC
1407 are obtained from CaT index values using an empirical conversion. The
measured CaT/metallicity distributions show unexpected features, the most
remarkable being that the brightest red and blue GCs have similar CaT values
despite their large difference in mean color. Suggested explanations for this
behavior in the NGC 1407 GC system are: 1) the CaT may be affected by a
population of hot blue stars, 2) the CaT may saturate earlier than predicted by
the models, and/or 3) color may not trace metallicity linearly. Until these
possibilities are understood, the use of the CaT as a metallicity indicator for
the integrated spectra of extragalactic GCs will remain problematic.Comment: 14 pages, 18 figures, accepted for publication in A
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