1,064 research outputs found
Carbon and nitrogen abundances of stellar populations in the globular cluster M 2
We present CH and CN index analysis and C and N abundance calculations based
on the low-resolution blue spectra of red giant branch (RGB) stars in the
Galactic globular cluster NGC 7089 (M 2). Our main goal is to investigate the
C-N anticorrelation for this intermediate metallicity cluster. The data were
collected with DOLORES, the multiobject, low-resolution facility at the
Telescopio Nazionale Galileo. Spectroscopic data were coupled with UV
photometry obtained during the spectroscopic run. We found a considerable
star-to-star variation in both A(C) and A(N) at all luminosities for our sample
of 35 targets. These abundances appear to be anticorrelated, with a hint of
bimodality in the C content for stars with luminosities below the RBG bump
(V~15.7), while the range of variations in N abundances is very large and spans
almost ~ 2 dex. We find additional C depletion as the stars evolve off the RGB
bump, in fairly good agreement with theoretical predictions for metal-poor
stars in the course of normal stellar evolution. We isolated two groups with
N-rich and N-poor stars and found that N abundance variations correlate with
the (U-V) color in the DOLORES color-magnitude diagram (CMD). The V, (U-V) CMD
for this cluster shows an additional RGB sequence, located at the red of the
main RGB and amounting to a small fraction of the total giant population. We
identified two CH stars detected in previous studies in our U, V images. These
stars, which are both cluster members, fall on this redder sequence, suggesting
that the anomalous RGB should have a peculiar chemical pattern. Unfortunately,
no additional spectra were obtained for stars in this previously unknown RGB
branch.Comment: 15 pages, 14 figures; accepted for publication in A&
Stellar population analysis of two ellipticals
The spatial distributions of the mean luminosity-weighted stellar age,
metallicity, and alpha/Fe ratio along both photometric axes of two nearby
elliptical galaxies have been obtained using Lick index measurements on long
slit spectra in order to reconstruct the star formation history in their
kinematically distinct subsystems. Lick indexes were compared with those of
single-aged stellar population (SSP) models. A population synthesis method was
also applied in order to help disentangling the age-metallicity degeneracy. The
stars characteristics are associated with their kinematics: they are older and
alpha-enhanced in the not rotating bulge of NGC 1052 and counter rotating core
of NGC 7796, while they show a strong spread of alpha/Fe and age along the
rotating disk of NGC 1052 and an outwards radial decreasing of them outside the
core of NGC 7796.Comment: 2 pages, to appear in the Proceedings of IAU Symposium 241 "Stellar
populations as building blocks of galaxies", A. Vazdekis & R. Peletier, ed
Homogeneous abundance analysis of dwarf, subgiant and giant FGK stars with and without giant planets
We have analyzed high-resolution and high signal-to-noise ratio optical
spectra of nearby FGK stars with and without detected giant planets in order to
homogeneously measure their photospheric parameters, mass, age, and the
abundances of volatile (C, N, and O) and refractory (Na, Mg, Si, Ca, Ti, V, Mn,
Fe, Ni, Cu, and Ba) elements. Our sample contains 309 stars from the solar
neighborhood (up to the distance of 100 pc), out of which 140 are dwarfs, 29
are subgiants, and 140 are giants. The photospheric parameters are derived from
the equivalent widths of Fe I and Fe II lines. Masses and ages come from the
interpolation in evolutionary tracks and isochrones on the HR diagram. The
abundance determination is based on the equivalent widths of selected atomic
lines of the refractory elements and on the spectral synthesis of C_2, CN, C I,
O I, and Na I features. We apply a set of statistical methods to analyze the
abundances derived for the three subsamples. Our results show that: i) giant
stars systematically exhibit underabundance in [C/Fe] and overabundance in
[N/Fe] and [Na/Fe] in comparison with dwarfs, a result that is normally
attributed to evolution-induced mixing processes in the envelope of evolved
stars; ii) for solar analogs only, the abundance trends with the condensation
temperature of the elements are correlated with age and anticorrelated with the
surface gravity, which is in agreement with recent studies; iii) as in the case
of [Fe/H], dwarf stars with giant planets are systematically enriched in [X/H]
for all the analyzed elements, except for O and Ba (the former due to
limitations of statistics), confirming previous findings in the literature that
not only iron has an important relation with the planetary formation; and iv)
giant planet hosts are also significantly overabundant for the same metallicity
when the elements from Mg to Cu are combined together.Comment: 20 pages, 16 figures, 8 table
The Near Infrared NaI Doublet Feature in M Stars
The NaI near-infrared doublet has been used to indicate the dwarf/giant
population in composite systems, but its interpretation is still a contentious
issue. In order to understand the behaviour of this controversial feature, we
study the observed and synthetic spectra of cool stars. We conclude that the
NaI infrared feature can be used as a dwarf/giant discriminator. We propose a
modified definition of the NaI index by locating the red continuum at 8234
angstrons and by measuring the equivalent width in the range 8172-8197
angstrons, avoiding the region at lambda > 8197 angstrons, which contains VI,
ZrI, FeI and TiO lines. We also study the dependence of this feature on stellar
atmospheric parameters.Comment: 9 pages, (TeX file) + 7 Figures in Postscript format. Accepted for
publication in The Astrophysical Journa
Evaluating GAIA performances on eclipsing binaries. III. Orbits and stellar parameters for UW LMi, V432 Aur and CN Lyn
The orbits and physical parameters of three detached F and G-type eclipsing
binaries have been derived combining Hipparcos H(P) photometry with 8480-8740
Ang ground-based spectroscopy, simulating the photometric+spectroscopic
observations that the GAIA mission will obtain. Tycho B(T) and V(T) light
curves are too noisy to be modeled for the three targets, and only mean Tycho
colors are retained to constrain the temperature. No previous combined
photometric+spectroscopic solution exists in literature for any of the three
targets. Quite remarkably, CN Lyn turned out to be an equal masses F5 triple
system. Distances from the orbital solutions agree within the astrometric error
with the Hipparcos parallaxes.Comment: A&A, accepted in pres
The discovery of an anomalous RGB in M 2
Using UV images taken with the Telescopio Nazionale Galileo, we discovered an anomalous sequence in the color-magnitude diagram of M 2. This feature appears as a narrow poor-populated red giant branch, which extends down to the sub giant branch region. We speculate that this new feature could be the extension of the faint component of the split sub giant branch recently discovered by Piotto et al. We identified in our UV images two CH stars detected in previous studies. These stars, which are both cluster members, fall on this redder sequence, suggesting indeed that the anomalous RGB should have a peculiar chemical pattern. Unfortunately, no additional spectra were obtained for stars in this previously unknown substructur
NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
High-resolution spectroscopic observations were taken of 29 extended main
sequence turn-off (eMSTO) stars in the young (200 Myr) LMC cluster, NGC
1866 using the Michigan/Magellan Fiber System and MSpec spectrograph on the
Magellan-Clay 6.5-m telescope. These spectra reveal the first direct detection
of rapidly rotating stars whose presence has only been inferred from
photometric studies. The eMSTO stars exhibit H-alpha emission (indicative of
Be-star decretion disks), others have shallow broad H-alpha absorption
(consistent with rotation 150 km s), or deep H-alpha core
absorption signaling lower rotation velocities (150 km s ).
The spectra appear consistent with two populations of stars - one rapidly
rotating, and the other, younger and slowly rotating.Comment: 9 pages, 4 figures, Accepted for publication in ApJ Letter
The Temperature Scale of Metal-Rich M Giants Based on TiO Bands: Population Synthesis in the Near Infrared
We have computed a grid of high resolution synthetic spectra for cool stars
(2500<Teff<6000 K) in the wavelength range 6000 -- 10200A, by employing an
updated line list of atomic and molecular lines, together with state-of-the-art
model atmospheres.
As a by-product, by fitting TiO bandheads in spectra of well-known M giants,
we have derived the electronic oscillator strengths of the TiO gamma prime,
delta, epsilon and phi systems. The derived oscillator strenghts for the gamma
prime, epsilon and phi systems differ from the laboratory and ab initio values
found in the literature, but are consistent with the model atmospheres and line
lists employed, resulting in a good match to the observed spectra of M giants
of known parameters.
The behavior of TiO bands as a function of the stellar parameters Teff, log g
and [Fe/H] is presented and the use of TiO spectral indices in stellar
population studies is discussed.Comment: ApJ accepted, 27 pages + 11 figures, AASLatex v4.
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