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The effect of activity on stellar temperatures and radii
Context: Recent analyses of low-mass eclipsing binary stars haveunveiled a significant disagreement between the observations andpredictions of stellar structure models. Results show that theoreticalmodels underestimate the radii and overestimate the effectivetemperatures of low-mass stars but yield luminosities that accord withobservations. A hypothesis based upon the effects of stellar activitywas put forward to explain the discrepancies. Aims: In this paper westudy the existence of the same trend in single active stars and providea consistent scenario to explain systematic differences between activeand inactive stars in the H-R diagram reported earlier. Methods: Theanalysis is done using single field stars of spectral types late-K and Mand computing their bolometric magnitudes and temperatures throughinfrared colours and spectral indices. The properties of the stars insamples of active and inactive stars are compared statistically toreveal systematic differences. Results: After accounting for a numberof possible bias effects, active stars are shown to be cooler thaninactive stars of similar luminosity therefore implying a larger radiusas well, in proportions that are in excellent agreement with those foundfrom eclipsing binaries. Conclusions: The present results generalisethe existence of strong radius and temperature dependences on stellaractivity to the entire population of low-mass stars, regardless of theirmembership in close binary systems.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/478/507
| 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.
| 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.
| The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&db_key=AST
| Preliminary Version of the Third Catalogue of Nearby Stars
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