343 research outputs found
Stellar Associations and their Field East of LMC 4 in the Large Magellanic Cloud
We report about the stellar content and the luminosity and mass functions of
three stellar associations and their field located on the north-east edge of
the super-bubble LMC 4 in the Large Magellanic Cloud.Comment: To be appeared in the meeting Proceedings of ``Modes of Star
Formation and the Origin of Field Populations'', Heidelberg, Germany, October
2000; to be published in the ASP Conference Series, edited by E. K. Grebel
and W. Brandne
Spatial distribution of stellar populations in the Magellanic Clouds: Implementation to Gaia
The main goal of our project is to investigate the spatial distribution of
different stellar populations in the Magellanic Clouds. The results from
modelling the Magellanic Clouds can be useful, among others, for simulations
during the Gaia mission preparation. Isodensity contour maps have been used in
order to trace the morphology of the different stellar populations and estimate
the size of these structures. Moreover, star density maps are constructed
through star counts and projected radial density profiles are obtained. Fitting
exponential disk and King law curves to the spatial distribution allows us to
derive the structural parameters that describe these profiles. The
morphological structure and spatial distributions of various stellar components
in the Magellanic Clouds (young and intermediate age stars, carbon stars) along
with the overall spatial distribution in both Clouds are provided.Comment: 12 pages, 9 figures, to be published in Astronomy & Astrophysics;
typos and language correcte
Photographic photometry of star clusters in the small magellanic cloud
Photographic photometry of 20 star clusters and their
adjoining fields has been carried out to determine the
colour magnitude diagram for stellar systems in the Small
Magellanic Cloud, using plates from the U.K. 1.2m Schmidt
telescope. The W-N-E periphery of the Cloud has been
examined.The main difficulty of the SMC star clusters is the
contamination of cluster members by stars in the surrounding
field.The evolutionary history of the star clusters seems to
be similar to that of the surrounding field, implying that
the background halo of the SMC is not well mixed.Old clusters have been found over the whole Cloud
exhibiting differences in the morphology of the H-B which
in most cases is very well populated at the red side of
the RR Lyrae stars strip.Two more characteristics are i) the existence of very
red stars (in three cases they are proved carbon stars) and
ii) the large number of blue faint stars.The metallicity has been shown to be low in the SMC
but the characteristics found in the old clusters are
those normally found in intermediate age clusters of our
Galaxy. Thus the age of the western halo clusters is
~10âč - 5 x 10âč yrs, whereas the northern halo clusters
are even younger.The second group of clusters comprises young clusters
which occupy the north part of the SMC or the north-east
arm, since no young objects have been detected at the
western part of this galaxy.The colour magnitude diagrams of the clusters and
the adjoining field of the north-west arm give an age
estimate of this feature of about 5 x 10â· yrs.The other small young clusters in the northern side
of the Cloud are objects of the SMC disc and their ages
are 10ⶠ- 10ⷠyears
HST WFPC2 Observations of the Peculiar Main Sequence of the Double Star Cluster NGC 2011 in the Large Magellanic Cloud
We report the serendipitous discovery of a peculiar main sequence in archived
Hubble Space Telescope WFPC2 observations of the young star cluster NGC 2011 in
the Large Magellanic Cloud. The bright part of this main sequence exhibits a
prominent double, fork-like feature, as if it consists of twin main sequences,
one of them being redder. The color-magnitude diagram, constructed from the
stars found in the only available WFPC2 field of the cluster, is used to
distinguish the stars according to their membership to each of these sequences
and to study their spatial distribution. We find that there are two well
distinguished populations in the sense that the redder main sequence is
dominated by stars that belong to the main body of the cluster, while the stars
of the bluer main sequence belong to the surrounding region. Providing that NGC
2011 is a verified binary cluster, with the second companion unfortunately not
observed, and taking into account the general region where this cluster is
located, we discuss the possible scenarios from both star formation, and early
dynamical evolution point-of-view that might explain this unique discovery.Comment: Astrophysical Journal Letters, in press. Figures in higher resolution
available upon request to D. Gouliermis ([email protected]
J-type Carbon Stars in the Large Magellanic Cloud
A sample of 1497 carbon stars in the Large Magellanic Cloud has been observed
in the red part of the spectrum with the 2dF facility on the AAT. Of these, 156
have been identified as J-type (i.e. 13C-rich) carbon stars using a technique
which provides a clear distinction between J stars and the normal N-type carbon
stars that comprise the bulk of the sample, and yields few borderline cases. A
simple 2-D classification of the spectra, based on their spectral slopes in
different wavelength regions, has been constructed and found to be related to
the more conventional c- and j-indices, modified to suit the spectral regions
observed. Most of the J stars form a photometric sequence in the K - (J-K)
colour magnitude diagram, parallel to and 0.6 mag fainter than the N star
sequence. A subset of the J stars (about 13 per cent) are brighter than this J
star sequence; most of these are spectroscopically different from the other J
stars. The bright J stars have stronger CN bands than the other J stars and are
found strongly concentrated in the central regions of the LMC. Most of the
rather few stars in common with Hartwick and Cowley's sample of suspected CH
stars are J stars. Overall, the proportion of carbon stars identified as J
stars is somewhat lower than has been found in the Galaxy. The Na D lines are
weaker in the LMC J stars than in either the Galactic J stars or the LMC N
stars, and do not seem to depend on temperature.Comment: 19 pages, 21 figures, Latex; in press, MNRA
Luminous AGB stars in nearby galaxies. A study using Virtual Observatory tools
Aims. This study focuses on very luminous Mbol<-6.0 mag AGB stars with
J-Ks>1.5 mag and H-Ks>0.4 mag in the LMC, SMC, M31, and M33 from 2MASS data.
Methods.The data were taken from the 2MASS All-Sky Point Source catalogue
archive. We used Virtual Observatory tools and took advantage of its
capabilities at various stages in the analysis.
Results. It is well known that stars with the colors we selected correspond
mainly to carbon stars. Although the most luminous AGBs detected here contain a
large number of carbon stars,they are not included in existing catalogues
produced from data in the optical domain, where they are not visible since they
are dust-enshrouded. A comparison of the AGB stars detected with combined near
and mid-infrared data from MSX and 2MASS in the LMC shows that 10% of the
bright AGB stars are bright carbon stars never detected before and that the
other 50% are OH/IR oxygen rich stars, whereas the 40% that remain were not
cross-matched.
Conclusions. The catalogues of the most luminous AGB stars compiled here are
an important complement to existing data. In the LMC, these bright AGB stars
are centrally located, whereas they are concentrated in an active
star-formation ring in M31. In the SMC and M33, there are not enough of them to
draw definite conclusions, although they tend to be centrally located. Their
luminosity functions are similar for the four galaxies we studied.Comment: 16 pages, 12 figures, 4 tables (Appendix A), accepted in A&
Structure of the SMC - Stellar component distribution from 2MASS data
The spatial distribution of the SMC stellar component is investigated from
2MASS data. The morphology of the different age populations is presented. The
center of the distribution is calculated and compared with previous
estimations. The rotation of the stellar content and possible consequence of
dark matter presence are discussed. The different stellar populations are
identified through a CMD diagram of the 2MASS data. Isopleth contour maps are
produced in every case, to reveal the spatial distribution. The derived density
profiles are discussed. The older stellar population follows an exponential
profile at projected diameters of about 5 kpc (~5 deg) for the major axis and
~4 kpc for the minor axis, centred at RA: 0h:51min, Dec: -73deg 7' (J2000.0).
The centre coordinates are found the same for all the different age population
maps and are in good accordance with the kinematical centre of the SMC. However
they are found considerably different from the coordinates of the centre of the
gas distribution. The fact that the older population found on an exponential
disk, gives evidence that the stellar content is rotating, with a possible
consequence of dark matter presence. The strong interactions between the MCs
and the MilkyWay might explain the difference in the distributions of the
stellar and gas components. The lack in the observed velocity element, that
implies absence of rotation, and contradicts with the consequences of
exponential profile of the stellar component, may also be a result of the
gravitational interactions.Comment: 7 Pages, 6 figures, accepted for publication in A&
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