780 research outputs found
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
Hardy spaces for a class of singular domains
We set a framework for the study of Hardy spaces inherited by complements of analytic hypersurfaces in domains with a prior Hardy space structure. The inherited structure is a filtration, various aspects of which are studied in specific settings. For punctured planar domains, we prove a generalization of a famous rigidity lemma of Kerzman and Stein. A stabilization phenomenon is observed for egg domains. Finally, using proper holomorphic maps, we derive a filtration of Hardy spaces for certain power-generalized Hartogs triangles, although these domains fall outside the scope of the original framework
A Photometric Study of the Outer Halo Globular Cluster NGC 5824
Multi-wavelength CCD photometry over 21 years has been used to produce deep
color-magnitude diagrams together with light curves for the variables in the
Galactic globular cluster NGC 5824. Twenty-one new cluster RR Lyrae stars are
identified, bringing the total to 47, of which 42 have reliable periods
determined for the first time. The color-magnitude diagram is matched using
BaSTI isochrones with age of ~Gyr. and reddening is found to be ; using the period-Wesenheit relation in two colors the distance
modulus is corresponding to a distance of 30.9 Kpc.
The observations show no signs of populations that are significantly younger
than the ~Gyr stars. The width of the red giant branch does not allow for a
spread in [Fe/H] greater than dex, and there is no photometric
evidence for widened or parallel sequences. The pseudo-color
magnitude diagram shows a bifurcation of the red giant branch that by analogy
with other clusters is interpreted as being due to differing spectral
signatures of the first (75\%) and second (25\%) generations of stars whose age
difference is close enough that main sequence turnoffs in the color-magnitude
diagram are unresolved. The cluster main sequence is visible against the
background out to a radial distance of arcmin. We conclude that NGC
5824 appears to be a classical Oosterhoff Type II globular cluster, without
overt signs of being a remnant of a now-disrupted dwarf galaxy.Comment: 26 pages, 15 figures, 4 tables, accepted for publication in
Astronomical Journa
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
Spectroscopy of QUEST RR Lyrae Variables: the new Virgo Stellar Stream
Eighteen RR Lyrae variables (RRLs) that lie in the "12\fh 4 clump"
identified by the QUEST survey have been observed spectroscopically to measure
their radial velocities and metal abundances. Ten blue horizontal branch (BHB)
stars identified by the Sloan Digital Sky Survey (SDSS) were added to this
sample. Six of the 9 stars in the densest region of the clump have a mean
radial velocity in the galactic rest frame () of 99.8 and
= 17.3 , which is slightly smaller than the average error of
the measurements. The whole sample contains 8 RRLs and 5 BHB stars that have
values of suggesting membership in this stream. For 7 of these
RRLs, the measurements of [Fe/H], which have an internal precision of 0.08 dex,
yield and = 0.40. These values suggest that
the stream is a tidally disrupted dwarf spheroidal galaxy of low luminosity.
Photometry from the database of the SDSS indicates that this stream covers at
least 106 deg of the sky in the constellation Virgo. The name Virgo Stellar
Stream is suggested.Comment: Replaced with revised version accepted for publication in ApJ Letters
13 pages 4 figure
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