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Heidi Jo Newberg

Publications and source records attributed to Heidi Jo Newberg.

79 records · Page 5Linked to original sources
arXiv2003

SDSS Catalog of Stars in the Draco Dwarf Spheroidal Galaxy

The Sloan Digital Sky Survey (SDSS) has scanned the entire region containing the Draco dwarf spheroidal galaxy to 23rd magnitude in g*. We present a catalog of stars found in a 453 square arcminute, elliptical region centered on the Draco dwarf spheroidal galaxy. Objects in the catalog are matched with five previously published catalogs. The catalog contains SDSS photometry for 5634 individual objects, and also the photometry from matches to any of the other catalogs. A comparison of the photometry between catalogs allows us to identify 142 candidate variable objects. One hundred and twelve of the suspected variables have colors consistent with RR Lyrae variables.

astro-ph↗
arXiv2002

Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample

We describe the algorithm for selecting quasar candidates for optical spectroscopy in the Sloan Digital Sky Survey. Quasar candidates are selected via their non-stellar colors in "ugriz" broad-band photometry, and by matching unresolved sources to the FIRST radio catalogs. The automated algorithm is sensitive to quasars at all redshifts lower than z=5.8. Extended sources are also targeted as low-redshift quasar candidates in order to investigate the evolution of Active Galactic Nuclei (AGN) at the faint end of the luminosity function. Nearly 95% of previously known quasars are recovered (based on 1540 quasars in 446 square degrees). The overall completeness, estimated from simulated quasars, is expected to be over 90%, whereas the overall efficiency (quasars:quasar candidates) is better than 65%. The selection algorithm targets ultraviolet excess quasars to i^*=19.1 and higher-redshift (z>3) quasars to i^*=20.2, yielding approximately 18 candidates per square degree. In addition to selecting ``normal'' quasars, the design of the algorithm makes it sensitive to atypical AGN such as Broad Absorption Line quasars and heavily reddened quasars.

astro-ph↗
arXiv2001

The Ghost of Sagittarius and Lumps in the Halo of the Milky Way

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.

astro-ph↗
arXiv2001

The Sloan Digital Sky Survey Quasar Catalog I. Early Data Release

We present the first edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 3814 objects (3000 discovered by the SDSS) in the initial SDSS public data release that have at least one emission line with a full width at half maximum larger than 1000 km/s, luminosities brighter than M_i^* = -23, and highly reliable redshifts. The area covered by the catalog is 494 square degrees; the majority of the objects were found in SDSS commissioning data using a multicolor selection technique. The quasar redshifts range from 0.15 to 5.03. For each object the catalog presents positions accurate to better than 0.2" rms per coordinate, five band (ugriz) CCD-based photometry with typical accuracy of 0.05 mag, radio and X-ray emission properties, and information on the morphology and selection method. Calibrated spectra of all objects in the catalog, covering the wavelength region 3800 to 9200 Angstroms at a spectral resolution of 1800-2100, are also available. Since the quasars were selected during the commissioning period, a time when the quasar selection algorithm was undergoing frequent revisions, the sample is not homogeneous and is not intended for statistical analysis.

astro-ph↗
arXiv2001

Sloan Digital Sky Survey Multicolor Observations of GRB010222

The discovery of an optical counterpart to GRB010222 (detected by BeppoSAX; Piro 2001) was announced 4.4 hrs after the burst by Henden (2001a). The Sloan Digital Sky Survey's 0.5m photometric telescope (PT) and 2.5m survey telescope were used to observe the afterglow of GRB010222 starting 4.8 hours after the GRB. The 0.5m PT observed the afterglow in five, 300 sec g' band exposures over the course of half an hour, measuring a temporal decay rate in this short period of F_nu \propto t^{-1.0+/-0.5}. The 2.5m camera imaged the counterpart nearly simultaneously in five filters (u' g' r' i' z'), with r' = 18.74+/-0.02 at 12:10 UT. These multicolor observations, corrected for reddening and the afterglow's temporal decay, are well fit by the power-law F_nu \propto nu^{-0.90+/-0.03} with the exception of the u' band UV flux which is 20% below this slope. We examine possible interpretations of this spectral shape, including source extinction in a star forming region.

astro-ph↗
arXiv1998

An Absence of Gaps in the Main Sequence Population of Field Stars

Using high precision parallaxes from the Hipparcos catalog, we construct H-R diagrams for two samples of bright stars. The first is a magnitude-limited sample that is over 90% complete and uses uniform photometry from the Catalog of WBVR Magnitudes of Northern Sky Bright Stars (declination above -14 deg). This sample shows a smooth distribution of stars along the main sequence, with no detectable gaps. The second contains all of the stars closer than 100 parsecs in the Hipparcos catalog with declination less than -12 deg. Uniform spectroscopy from the Michigan Spectral Survey shows that some stars which appear on the main sequence in the H-R diagram, particularly those in the 0.2 < B-V < 0.3 region that has been labeled the Bohm-Vitense gap, are classified as giants by the MK system of spectral classification. Other gaps that have been identified in the main sequence are also affected by such classification criteria. This analysis casts doubt on the existence of the Bohm-Vitense gap, which is thought to result from the sudden onset of convection in stars. The standard identification of main sequence stars with luminosity class V, and giants with luminosity class III, must be reconsidered for some spectral types. The true nature of the stars that lie on the main sequence in the H-R diagram, but which do not have luminosity class V designations, remains to be investigated.

astro-ph↗