The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of %10 6 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg 2 of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux-and wavelength-calibrated, with 4096 pixels from 3800 to 9200 Å at R % 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.

We identify new structures in the halo of the Milky Way Galaxy from positions, colors and magnitudes of five million stars detected in the Sloan Digital Sky Survey. Most of these stars are within 1.26 degrees of the celestial equator. We present color-magnitude diagrams (CMDs) for stars in two previously discovered, tidally disrupted structures. The CMDs and turnoff colors are consistent with those of the Sagittarius dwarf galaxy, as had been predicted. In one direction, we are even able to detect a clump of red stars, similar to that of the Sagittarius dwarf, from stars spread across 110 square degrees of sky. Focusing on stars with the colors of F turnoff objects, we identify at least five additional overdensities of stars. Four of these may be pieces of the same halo structure, which would cover a region of the sky at least 40 degrees in diameter, at a distance of 11 kpc from the Sun (18 kpc from the center of the Galaxy). The turnoff is significantly bluer than that of thick disk stars, and closer to the Galactic plane than a power-law spheroid. We suggest two models to explain this new structure. One possibility is that this new structure could be a new dwarf satellite of the Milky Way, hidden in the Galactic plane, and in the process of being tidally disrupted. The other possibility is that it could be part of a disk-like distribution of stars which is metal-poor, with a scale height of approximately 2 kpc and a scale length of approximately 10 kpc. The fifth overdensity, which is 20 kpc away, is some distance from the Sagittarius dwarf streamer orbit and is not associated with any known structure in the Galactic plane. It is likely that there are many smaller streams of stars in the Galactic halo.Comment: ApJ, in press; 26 figures including several in colo

The Sloan Digital Sky Survey has validated and made publicly available its First Data Release. This consists of 2099 square degrees of five-band (u, g, r, i, z) imaging data, 186,240 spectra of galaxies, quasars, stars and calibrating blank sky patches selected over 1360 square degrees of this area, and tables of measured parameters from these data. The imaging data go to a depth of r ~ 22.6 and are photometrically and astrometrically calibrated to 2% rms and 100 milli-arcsec rms per coordinate, respectively. The spectra cover the range 3800--9200 A, with a resolution of 1800--2100. Further characteristics of the data are described, as are the data products themselves.Comment: Submitted to The Astronomical Journal. 16 pages. For associated documentation, see http://www.sdss.org/dr

Using wide-field photometric data from the Sloan Digital Sky Survey (SDSS) we recently showed that the Galactic globular cluster Palomar 5 is in the process of being tidally disrupted. Its tidal tails were initially detected in a 2.5 degree wide band along the celestial equator. A new analysis of SDSS data for a larger field now reveals that the tails of Pal 5 have a much larger spatial extent and can be traced over an arc of 10 • on the sky, corresponding to a projected length of 4 kpc at the distance of the cluster. The tail that trails behind the Galactic motion of the cluster fades into the field at an angular distance of 6. • 5 from the cluster center but shows a pronounced density maximum between 2 • and 4 • from the center. The leading tail of length 3. • 5 extends down to the border of the available field and thus presumably continues beyond it. The projected width of these tails is small and almost constant (FWHM ∼ 120 pc), which implies that they form a dynamically cold and hence long-lived structure. The number of former cluster stars found in the tails adds up to about 1.2 times the number of stars in the cluster, i.e. the tails are more massive than the cluster in its present state. The radial profile of stellar surface density in the tails follows approximately a power law r γ with −1.5 ≤ γ ≤ −1.2.The stream of debris from Pal 5 is significantly curved, which demonstrates its acceleration by the Galactic potential. The stream sets tight constraints on the geometry of the cluster's Galactic orbit. We conclude that the cluster is presently near the apocenter but has repeatedly undergone disk crossings in the inner part of the Galaxy leading to strong tidal shocks. Using the spatial offset between the tails and the cluster's orbit we estimate the mean drift rate of the tidal debris and thus the mean mass loss rate of the cluster. Our results suggest that the observed debris originates mostly from mass loss within the last 2 Gyrs. The cluster is likely to be destroyed after the next disk crossing, which will happen in about 100 Myr. There is strong evidence against the suggestion that Pal 5 might be associated with the Sgr dwarf galaxy.

We present evidence for a ring of stars in the plane of the Milky Way, extending at least from l ¼ 180 to 227 with turnoff magnitude g $ 19:5; the ring could encircle the Galaxy. We infer that the low Galactic latitude structure is at a fairly constant distance of R ¼ 18 AE 2 kpc from the Galactic center above the Galactic plane and has R ¼ 20 AE 2 kpc in the region sampled below the Galactic plane. The evidence includes 500 Sloan Digital Sky Survey spectroscopic radial velocities of stars within 30 of the plane. The velocity dispersion of the stars associated with this structure is found to be 27 km s À1 at ðl; bÞ ¼ ð198 ; À27 Þ, 22 km s À1 at ðl; bÞ ¼ ð225 ; 28 Þ, 30 km s À1 at ðl; bÞ ¼ ð188 ; 24 Þ, and 30 km s À1 at ðl; bÞ ¼ ð182 ; 27 Þ. The structure rotates in the same prograde direction as the Galactic disk stars but with a circular velocity of 110 AE 25 km s À1 . The narrow measured velocity dispersion is inconsistent with power-law spheroid or thick-disk populations. We compare the velocity dispersion in this structure with the velocity dispersion of stars in the Sagittarius dwarf galaxy tidal stream, for which we measure a velocity dispersion of 20 km s À1 at ðl; bÞ ¼ ð165 ; À55 Þ. We estimate a preliminary metallicity from the Ca ii (K) line and color of the turnoff stars of ½Fe=H ¼ À1:6 with a dispersion of 0.3 dex and note that the turnoff color is consistent with that of the spheroid population. We interpret our measurements as evidence for a tidally disrupted satellite of 2 Â 10 7 to 5 Â 10 8 M that rings the Galaxy.