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Keck DEIMOS Spectroscopy of a GALEX UV-Selected Sample from the Medium Imaging Survey
We report results from a pilot program to obtain spectroscopy forobjects detected in the Galaxy Evolution Explorer (GALEX) Medium ImagingSurvey (MIS). Our study examines the properties of galaxies detected byGALEX fainter than the Sloan Digital Sky Survey (SDSS) spectroscopicsurvey. This is the first study to extend the techniques of Salim andcoworkers to estimate stellar masses, star formation rates (SFRs), andthe b (star formation history) parameter for star-forming galaxies outto z~0.7. We obtain redshifts for 50 GALEX MIS sources reaching NUV=23.9(AB mag) having counterparts in the SDSS Data Release 4 (DR4). Of oursample, 43 are star-forming galaxies with z<0.7, 3 have emission-lineratios indicative of active galactic nuclei with z<0.7, and 4 objectswith z>1 are QSOs, 3 of which are not previously cataloged. Wecompare our sample to a much larger sample of ~50,000 matched GALEX/SDSSgalaxies with SDSS spectroscopy; while our survey is shallow, theoptical counterparts to our sources reach ~3 mag fainter in SDSS r thanthe SDSS spectroscopic sample. We use emission-line diagnostics for thegalaxies to determine that the sample contains mostly star-forminggalaxies. The galaxies in the sample populate the blue sequence in theNUV-r versus Mr color-magnitude diagram. The derived stellarmasses of the galaxies range from 108 to 1011Msolar, and derived SFRs are between 10-1 and102 Msolar yr-1. Our sample has SFRs,luminosities, and velocity dispersions that are similar to the samplesof faint compact blue galaxies studied previously in the same redshiftrange by Koo and collaborators, Guzmán and collaborators, andPhillips and collaborators. However, our sample is ~2 mag fainter insurface brightness than the compact blue galaxies. We find that the starformation histories for a majority of the galaxies are consistent with arecent starburst within the last 100 Myr.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHKphotometry for over 100 M stars selected from an earlier paper on thebasis of apparent photometric constancy. L photometry has been obtainedfor stars brighter than about L = 6. Most of the stars have asubstantial number of UBV(RI)C observations and, it is hoped,will prove useful as red supplementary standards. Additionally, we listJHK photometry for nearly 300 Hipparcos red stars not selected asstandards, as well as L photometry for the brightest stars.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
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