6 research outputs found
Faint High Latitude Carbon Stars Discovered by the Sloan Digital Sky Survey: Methods and Initial Results
We report the discovery of 39 Faint High Latitude Carbon Stars (FHLCs) from
Sloan Digital Sky Survey commissioning data. The objects, each selected
photometrically and verified spectroscopically, range over 16.6 < r* < 20.0,
and show a diversity of temperatures as judged by both colors and NaD line
strengths. At the completion of the Sloan Survey, there will be many hundred
homogeneously selected and observed FHLCs in this sample. We present proper
motion measures for each object, indicating that the sample is a mixture of
extremely distant (>100 kpc) halo giant stars, useful for constraining halo
dynamics, plus members of the recently-recognized exotic class of very nearby
dwarf carbon (dC) stars. Motions, and thus dC classification, are inferred for
40-50 percent of the sample, depending on the level of statistical significance
invoked. The new list of dC stars presented here, although selected from only a
small fraction of the final SDSS, doubles the number of such objects found by
all previous methods. (Abstract abridged).Comment: Accepted for publication in The Astronomical Journal, Vol. 124, Sep.
2002, 40 pages, 7 figures, AASTeX v5.
New insights on the Draco dwarf spheroidal galaxy from SDSS: a larger radius and no tidal tails
We have investigated the spatial extent and structure of the Draco dwarf
spheroidal galaxy using deep wide-field multicolor CCD photometry from the
Sloan Digital Sky Survey (SDSS). Our study covers an area of 27 square degrees
around the center of the Draco dwarf. We show that the spatial distribution of
Draco's red giants, red horizontal branch stars and subgiants down to i=21.7
mag does not provide evidence for the existence of tidally induced tails or a
halo of unbound stars. The radial profile can be fit by King models as well as
by a generalized exponential. The core radius and the limiting (or tidal)
radius along the major axis are 7.7' and 40.1', respectively, making Draco 40%
larger than previously measured. Down to our magnitude limit tidal effects can
only exist at a level of 10^-3 of the central surface density of Draco or
below. The regular structure of Draco found from the new data argues against it
being a portion of an unbound tidal stream and lends support to the assumption
of dynamical equilibrium. We estimate Draco's total mass to be 2.2 - 3.5 times
10^7 solar masses. We obtain an overall mass-to-light ratio of 146+-42 or
92+-28 solar masses depending on the details of the mass and luminosity
estimates. In summary, our results strengthen the case for a strongly dark
matter dominated, bound stellar system. (Abstract strongly abridged).Comment: 30 pages, 11 figures (in part with degraded resolution). Accepted for
publication in the Astronomical Journa
The 2.5 m Telescope of the Sloan Digital Sky Survey
We describe the design, construction, and performance of the Sloan Digital
Sky Survey Telescope located at Apache Point Observatory. The telescope is a
modified two-corrector Ritchey-Chretien design which has a 2.5-m, f/2.25
primary, a 1.08-m secondary, a Gascoigne astigmatism corrector, and one of a
pair of interchangeable highly aspheric correctors near the focal focal plane,
one for imaging and the other for spectroscopy. The final focal ratio is f/5.
The telescope is instrumented by a wide-area, multiband CCD camera and a pair
of fiber-fed double spectrographs. Novel features of the telescope include: (1)
A 3 degree diameter (0.65 m) focal plane that has excellent image quality and
small geometrical distortions over a wide wavelength range (3000 to 10,600
Angstroms) in the imaging mode, and good image quality combined with very small
lateral and longitudinal color errors in the spectroscopic mode. The unusual
requirement of very low distortion is set by the demands of
time-delay-and-integrate (TDI) imaging; (2) Very high precision motion to
support open loop TDI observations; and (3) A unique wind baffle/enclosure
construction to maximize image quality and minimize construction costs. The
telescope had first light in May 1998 and began regular survey operations in
2000.Comment: 87 pages, 27 figures. AJ (in press, April 2006
Instrument Science Report STIS 95-011 STIS Slit Wheel Repeatability
This report outlines the results of the STIS Slit Wheel Repeatability Test. The slit wheel repeatability was found to be +/- 7.5 milli-arcseconds in the direction of rotation and +/-2.5 milli-arcseconds in the radial direction, as projected onto the sky. This is well below the performance requirement of +/- 20 milli-arcseconds