438 research outputs found
Whiting 1: the youngest globular cluster associated with the Sgr dSph
Recently, Carraro (2005) drew attention to the remarkable star cluster
Whiting 1 by showing that it lies about 40 kpc from the Sun and is therefore
unquestionably a member of the Galactic halo (b=-60.6 deg.). Its CMD indicated
that Whiting 1 is very young (5 Gyrs) for a globular cluster. It is very likely
that Whiting 1 originated in a dwarf galaxy that has since been disrupted by
the Milky Way. Deep CCD photometry in the BVI pass-bands obtained with the VLT
is used to improve the quality of the CMD and to determine the cluster's
luminosity function and surface density profile. High-resolution spectrograms
obtained with Magellan are used to measure the cluster's radial velocity and to
place limits on its possible metallicity. The measurements of distance and
radial velocity are used to test the cluster's membership in the stellar
streams from the Sgr dSph. From our CMD of Whiting 1, we derive new estimates
for the cluster's age (6.5 Gyrs), metallicity ([Fe/H]=-0.65), and distance
(29.4 kpc). From echelle spectrograms of three stars, we obtain -130.6 km/s for
the cluster's radial velocity and show from measurements of two infra-red CaII
lines that the [Fe/H] of the cluster probably lies in the range -1.1 to -0.4.
We demonstrate that the position of Whiting 1 on the sky, its distance from the
Sun, and its radial velocity are identical to within the errors of both the
theoretical predictions of the trailing stream of stars from the Sgr dSph
galaxy and the previous observations of the M giant stars that delineate the
streams. With the addition of Whiting 1, there is now strong evidence that 6
globular clusters formed within the Sgr dSph.Comment: 9 pages, 9 eps figures (some degraded in resolution), in press in
Astronomy and Astrophysics. Abstract here below has been shortened to fit i
The QUEST RR Lyrae Survey: III. The Low Galactic Latitude Catalogue
We present results for the QUEST RR Lyrae Survey at low galactic latitude,
conducted entirely with observations obtained with the QUEST mosaic camera and
the 1.0/1.5m J\"urgen Stock Schmidt telescope at the National Observatory of
Venezuela. The survey spans an area of 476 sq. deg on the sky, with multi-epoch
observations in the V, R and I photometric bands for 6.5x10^6 stars in the
galactic latitude range 30<= b(deg) <=+25, in a direction close to the Galactic
Anticenter 190<= l(deg)<= 230. The variability survey has a typical number of
30 observations per object in V and I and ~25 in R, with up to ~120-150 epochs
in V and I and up to ~100 in R in the best sampled regions. The completeness
magnitudes of the survey are V=R=18.5 mag, and I=18.0 mag. We identified 211 RR
Lyrae stars, 160 bona fide stars of type ab and 51 candidates of type c, ours
being the first deep RR Lyrae survey conducted at low galactic latitude.The
completeness of the RR Lyrae survey was estimated in >95 per cent and ~85 per
cent for RRab and RRc stars respectively. Photometric metallicities were
computed based on the light curves and individual extinctions calculated from
minimum light colours for each RRab star. Distances were obtained with typical
errors ~7 per cent. The RR Lyrae survey simultaneously spans a large range of
heliocentric distances 0.5<= R_hel(kpc)<=40 and heights above the plane
-15<=z(kpc)<=+20, with well known completeness across the survey area, making
it an ideal set for studying the struc ture of the Galactic thick disk.Comment: 24 pages, 17 figures, 8 tables. Accepted for publication in MNRA
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