805 research outputs found
Carbon Stars and other Luminous Stellar Populations in M33
The M33 galaxy is a nearby, relatively metal-poor, late-type spiral. Its
proximity and almost face-on inclination means that it projects over a large
area on the sky, making it an ideal candidate for wide-field CCD mosaic
imaging. Photometry was obtained for more than 10^6 stars covering a 74' x 56'
field centered on M33. Main sequence (MS), supergiant branch (SGB), red giant
branch (RGB) and asymptotic giant branch (AGB) populations are identified and
classified based on broad-band V and I photometry. Narrow-band filters are used
to measure spectral features allowing the AGB population to be further divided
into C and M-star types. The galactic structure of M33 is examined using star
counts, colour-colour and colour-magnitude selected stellar populations. We use
the C to M-star ratio to investigate the metallicity gradient in the disk of
M33. The C/M-star ratio is found to increase and then flatten with increasing
galactocentric radius in agreement with viscous disk formation models. The
C-star luminosity function is found to be similar to M31 and the SMC,
suggesting that C-stars should be useful distance indicators. The ``spectacular
arcs of carbon stars'' in M33 postulated recently by Block et al. (2004) are
found in our work to be simply an extension of M33's disk.Comment: 20 pages, 20 figures. Accepted for publication in The Astronomical
Journa
Searching for tidal tails around Centauri using RR Lyrae Stars
We present a survey for RR Lyrae stars in an area of 50 deg around the
globular cluster Centauri, aimed to detect debris material from the
alleged progenitor galaxy of the cluster. We detected 48 RR Lyrae stars of
which only 11 have been previously reported. Ten among the eleven previously
known stars were found inside the tidal radius of the cluster. The rest were
located outside the tidal radius up to distances of degrees from the
center of the cluster. Several of those stars are located at distances similar
to that of Centauri. We investigated the probability that those stars
may have been stripped off the cluster by studying their properties (mean
periods), calculating the expected halo/thick disk population of RR Lyrae stars
in this part of the sky, analyzing the radial velocity of a sub-sample of the
RR Lyrae stars, and finally, studying the probable orbits of this sub-sample
around the Galaxy. None of these investigations support the scenario that there
is significant tidal debris around Centauri, confirming previous
studies in the region. It is puzzling that tidal debris have been found
elsewhere but not near the cluster itself.Comment: 11 pages, 11 figures, Accepte
A segmented period-luminosity relation for nearby extragalactic Scuti stars
The period-luminosity relations (PLR) of Milky Way Scuti (
Sct) stars have been described to the present day by a linear relation.
However, when studying extragalactic systems such as the Magellanic Clouds and
several dwarf galaxies, we notice for the first time a non-linear behaviour in
the PLR of Sct stars. Using the largest sample of
extragalactic Sct stars from data available in the literature
mainly based on OGLE and SuperMACHO survey in the Large Magellanic Cloud
(LMC) we obtain that the best fit to the period-luminosity () plane is
given by the following piecewise linear relation with a break at (or d) for shorter periods (sp) and longer
periods (lp) than the break-point:
Geometric or depth effects in the LMC, metallicity dependence, or different
pulsation modes are discarded as possible causes of this segmented PLR seen in
extragalactic Sct stars. The origin of the segmented relation at days remains unexplained based on the current data.Comment: 9 pages, 3 figures, 1 table. Accepted for publication into The
Astrophysical Journal Letter
The Virgo stellar over-density: Mapping the infall of the Sagittarius tidal stream onto the Milky Way disk
The recently discovered Virgo stellar over-density, which expands over
\~1000deg^2 perpendicularly to the Galactic disk plane (7< Z <15 kpc, R~7 kpc),
is the largest clump of tidal debris ever detected in the outer halo and is
likely related with the accretion of a nearby dwarf galaxy by the Milky Way. We
carry out N-body simulations of the Sagittarius stream to show that this giant
stellar over-density is a confirmation of theoretical model predictions for the
leading tail of the Sagittarius stream to cross the Milky Way plane in the
Solar neighborhood. Radial velocity measurements are needed to confirm this
association and to further constrain the shape of the Milky Way dark matter
halo through a new generation of theoretical models. If the identification of
Virgo over-density and the Sagittarius leading arm is correct, we predict
highly negative radial velocities for the stars of Virgo over-density. The
detection of this new portion of the Sagittarius tidal stream would represent
an excellent target for the on-going and future kinematic surveys and for dark
matter direct detection experiments in the proximity of the Sun.Comment: Accepted for publication in The Astrophysical Journal. Supplementary
movies to this paper are available at:
http://www.astro.princeton.edu/~mjuric/sgr-virgo
Proper Motions in Kapteyn Selected Area 103: A Preliminary Orbit for the Virgo Stellar Stream
We present absolute proper motions in Kapteyn Selected Area (SA) 103. This
field is located 7 degrees west of the center of the Virgo Stellar Stream (VSS,
Duffau et al. 2006), and has a well-defined main sequence representing the
stream. In SA 103 we identify one RR Lyrae star as a member of the VSS
according to its metallicity, radial velocity and distance. VSS candidate
turnoff stars and subgiant stars have proper motions consistent with that of
the RR Lyrae star. The 3D velocity data imply an orbit with a pericenter of 11
kpc and an apocenter of ~90 kpc. Thus, the VSS comprises tidal debris found
near the pericenter of a highly destructive orbit. Examining the six globular
clusters at distances larger than 50 kpc from the Galactic center, and the
proposed orbit of the VSS, we find one tentative association, NGC 2419. We
speculate that NGC 2419 is possibly the nucleus of a disrupted system of which
the VSS is a part.Comment: ApJL accepte
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