1,915 research outputs found
Light Curve Solutions of Eclipsing Binaries in SMC
We propose a procedure for light-curve solution of eclipsing binary stars in
the Small Magellanic Cloud for which photometric data have been obtained in the
framework of the OGLE project as well as way of determination of the global
stellar parameters on the basis of the obtained solutions, some empirical
relations as well as the distance to the SMC. Several examples illustrate this
procedure.Comment: 10 pages, 2 figures, accepte
Near-infrared spectroscopy of candidate red supergiant stars in clusters
Clear identifications of Galactic young stellar clusters farther than a few
kpc from the Sun are rare, despite the large number of candidate clusters. We
aim to improve the selection of candidate clusters rich in massive stars with a
multiwavelength analysis of photometric Galactic data that range from optical
to mid-infrared wavelengths. We present a photometric and spectroscopic
analysis of five candidate stellar clusters, which were selected as
overdensities with bright stars (Ks < 7 mag) in GLIMPSE and 2MASS images. A
total of 48 infrared spectra were obtained. The combination of photometry and
spectroscopy yielded six new red supergiant stars with masses from 10 Msun to
15 Msun. Two red supergiants are located at Galactic coordinates
(l,b)=(16.7deg,-0.63deg) and at a distance of about ~3.9 kpc; four other red
supergiants are members of a cluster at Galactic coordinates
(l,b)=(49.3deg,+0.72deg) and at a distance of ~7.0 kpc. Spectroscopic analysis
of the brightest stars of detected overdensities and studies of interstellar
extinction along their line of sights are fundamental to distinguish regions of
low extinction from actual stellar clusters. The census of young star clusters
containing red supergiants is incomplete; in the existing all-sky near-infrared
surveys, they can be identified as overdensities of bright stars with infrared
color-magnitude diagrams characterized by gaps.Comment: 16 pages, 10 figures, accepted to A&A 201
On the Relation Between Peak Luminosity and Parent Population of Type Ia Supernovae: A New Tool for Probing the Ages of Distant Galaxies
We study the properties of Type Ia Supernovae (SNe Ia) as functions of the
radial distance from their host galaxy centers. Using a sample of 62 SNe Ia
with reliable luminosity, reddening, and decline rate determinations, we find
no significant radial gradients of SNe Ia peak absolute magnitudes or decline
rates in elliptical+S0 galaxies, suggesting that the diversity of SN properties
is not related to the metallicity of their progenitors. We do find that the
range in brightness and light curve width of supernovae in spiral galaxies
extends to brighter, broader values. These results are interpreted as support
for an age, but not metallicity, related origin of the diversity in SNe Ia. If
confirmed with a larger and more accurate sample of data, the age-luminosity
relation would offer a new and powerful tool to probe the ages and age
gradients of stellar populations in galaxies at redshift as high as .
The absence of significant radial gradients in the peak and colors of SNe Ia supports the redding correction method of Phillips et
al (1999). We find no radial gradient in residuals from the SN Ia
luminosity-width relation, suggesting that the relation is not affected by
properties of the progenitor populations and supporting the reliability of
cosmological results based upon the use of SNe Ia as distance indicators.Comment: 19 pages, incl. 3 tables & 3 figures; to appear in Nov 2000 issue of
Ap
The VMC survey - XIV : First results on the look-back time star formation rate tomography of the Small Magellanic Cloud
Date of Acceptance: 20/01/2015We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJKs filters, covering 14 deg2 (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour-magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68 per cent confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39°, although deviations of up to ±3 kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age-metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2 Gyr and the peak of star formation in the SMC Bar at ~40 Myr. We clearly detect periods of enhanced star formation at 1.5 and 5 Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1 Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages.Peer reviewe
A Medium-Resolution Near-Infrared Spectral Library of Late Type Stars: I
We present an empirical infrared spectral library of medium resolution
(R~2000-3000) H (1.6 micron) and K (2.2 micron) band spectra of 218 red stars,
spanning a range of [Fe/H] from ~-2.2 to ~+0.3. The sample includes Galactic
disk stars, bulge stars from Baade's window, and red giants from Galactic
globular clusters. We report the values of 19 indices covering 12 spectral
features measured from the spectra in the library. Finally, we derive
calibrations to estimate the effective temperature, and diagnostic
relationships to determine the luminosity classes of individual stars from
near-infrared spectra.
This paper is part of a larger effort aimed at building a near-IR spectral
library to be incorporated in population synthesis models, as well as, at
testing synthetic stellar spectra.Comment: 34 pages, 12 figures; accepted for publication at ApJS; the spectra
are available from the authors upon reques
The VMC Survey -- XXXIV. Morphology of Stellar Populations in the Magellanic Clouds
The Magellanic Clouds are nearby dwarf irregular galaxies whose morphologies
show different properties when traced by different stellar populations, making
them an important laboratory for studying galaxy morphologies. We study the
morphology of the Magellanic Clouds using data from the VISTA survey of the
Magellanic Clouds system (VMC). We used about and million sources
across an area of deg and deg towards the Large and
Small Magellanic Cloud (LMC and SMC), respectively. We estimated median ages of
stellar populations occupying different regions of the near-infrared
() colour-magnitude diagram. Morphological maps
were produced and detailed features in the central regions were characterised
for the first time with bins corresponding to a spatial resolution of
kpc (LMC) and kpc (SMC). In the LMC, we find that main sequence stars
show coherent structures that grow with age and trace the multiple spiral arms
of the galaxy, star forming regions become dimmer as we progress in age, while
supergiant stars are centrally concentrated. Intermediate-age stars, despite
tracing a regular and symmetrical morphology, show central clumps and hints of
spiral arms. In the SMC, young main sequence stars depict a broken bar.
Intermediate-age populations show signatures of elongation towards the
Magellanic Bridge that can be attributed to the LMC-SMC interaction
Myr ago. They also show irregular central features suggesting that the inner
SMC has also been influenced by tidal interactions.Comment: Accepted for publication in MNRAS, 20 pages, 12 figures and 2 table
Common Proper Motion Search for Faint Companions Around Early-Type Field Stars - Progress Report
The multiplicity of early-type stars is still not well established. The
derived binary fraction is different for individual star forming regions,
suggesting a connection with the age and the environment conditions. The few
studies that have investigated this connection do not provide conclusive
results. To fill in this gap, we started the first detailed
adaptive-optic-assisted imaging survey of early-type field stars to derive
their multiplicity in a homogeneous way. The sample has been extracted from the
Hipparcos Catalog and consists of 341 BA-type stars within ~300 pc from the
Sun. We report the current status of the survey and describe a Monte-Carlo
simulation that estimates the completeness of our companion detection.Comment: 4 pages, 1 figure, conference proc. Syros 200
Massive Stars In The W33 Giant Molecular Complex
Rich in H II regions, giant molecular clouds are natural laboratories to study massive stars and sequential star formation. The Galactic star-forming complex W33 is located at = ⌠⊠l 12.8 and at a distance of 2.4 kpc and has a size of â10 pc and a total mass of â(0.8â8.0) Ă 105 Mâ. The integrated radio and IR luminosity of W33âwhen combined with the direct detection of methanol masers, the protostellar object W33A, and the protocluster embedded within the radio source W33 mainâmark the region as a site of vigorous ongoing star formation. In order to assess the long-term star formation history, we performed an infrared spectroscopic search for massive stars, detecting for the first time 14 early-type stars, including one WN6 star and four O4â7 stars. The distribution of spectral types suggests that this population formed during the past âŒ2â4 Myr, while the absence of red supergiants precludes extensive star formation at ages 6â30 Myr. This activity appears distributed throughout the region and does not appear to
have yielded the dense stellar clusters that characterize other star-forming complexes such as Carina and G305. Instead, we anticipate that W33 will eventually evolve into a loose stellar aggregate, with Cyg OB2 serving as a useful, albeit richer and more massive, comparator. Given recent distance estimates, and despite a remarkably similar stellar population, the rich cluster Cl 1813â178 located on the northwest edge of W33 does not appear to be physically associated with W33
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