Interesting Features in the Combined GALEX and Sloan Color Diagrams of Solar-like Galactic Populations

Abstract

We report on intriguing photometric properties of Galactic stars observed in the GALEX satellite's far-UV and near-UV bandbasses as well as from the SDSS survey and the Kepler Input Catalog. First, the FUV-NUV color distribution of stars in the Kepler field consists of 2 distinct peaks. Second, curiously, for stars with spectral types G or later the mean FUV-NUV color becomes much bluer, contrary to expectation. we have found in two samples of mid-F through K type stars that ~14-18% of them exhibit FUV-excesses relative to their NUV fluxes and spectral types. Nearly the same fractions are also discovered among members of the Kepler Eclipsing Binary Catalog and in the published list of Kepler Objects of Interest. These UV-excess ("UVe") colors are confirmed by the UV continuum slopes in GALEX spectra. The SDSS spectra of some UVe stars exhibit metallic line weakening especially in the blue. This suggests an enhanced contribution of UV flux relative to photospheric flux of a solar-type single star. We consider the possibility that the UV excesses originate from various types of hot stars, including binaries, and strong chromosphere stars that. Our model atmosphere-derived simulations of colors for binaries with main sequence pairs with a hot secondary demonstrate that the color loci conflict with the observed sequence. We are left with the active chromospheres explanation, whether in active binaries or young stars, as a still tentative explanation for the UVe stars. We also address the presence of an island of "UV red" stars in the NUV-g, g-i color diagram. The subpopulation comprising this island are mainly horizontal branch stars. These objects do not exhibit UV excesses and therefore have UV colors typical for their spectral types. This subpopulation appears "red" in the UV because their colors are not pulled to the blue by the UVe stars.

arXiv comment17 pages, 12 figures, to be published by Astronomical Journal

References in corpus (47)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Sloan Digital Sky Survey: Technical Summary
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• The Dartmouth Stellar Evolution Database
• SEGUE: A Spectroscopic Survey of 240,000 stars with g=14-20
• The false positive rate of Kepler and the occurrence of planets
• The Multi-Object, Fiber-Fed Spectrographs for SDSS and the Baryon Oscillation Spectroscopic Survey
• Evolution of the Solar Activity over Time and Effects on Planetary Atmospheres: I. High-energy Irradiances (1-1700 A)
• Kepler Input Catalog: Photometric Calibration and Stellar Classification
• The origin of sdB stars (II)
• The Ages of Stars
• Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7
• Revised Stellar Properties of Kepler Targets for the Quarter 1-16 Transit Detection Run
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• Selection, Prioritization, and Characteristics of Kepler Target Stars
• A Revised Effective Temperature Scale for the Kepler Input Catalog
• The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
• A uniform asteroseismic analysis of 22 solar-type stars observed by Kepler
• Prospecting in late-type dwarfs: a calibration of infrared and visible spectroscopic metallicities of late-K and M dwarfs spanning 1.5 dex
• White-light flares on cool stars in the Kepler Quarter 1 Data
• Kepler Eclipsing Binary Stars. III. Classification of Kepler Eclipsing Binary Light Curves with Locally Linear Embedding
• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• Characterizing the Variability of Stars with Early-Release Kepler Data
• Photometric Variability in Kepler Target Stars: The Sun Among Stars -- A First Look
• DA white dwarfs in SDSS DR7 and a search for infrared excess emission
• They might be giants: luminosity class, planet frequency, and planet-metallicity relation of the coolest Kepler target stars
• The Age-Activity-Rotation Relationship in Solar-Type Stars
• Post-common envelope binaries from SDSS - VII: A catalogue of white dwarf-main sequence binaries
• An observational correlation between stellar brightness variations and surface gravity
• The chemical diversity of exo-terrestrial planetary debris around white dwarfs
• The Stellar Metallicity Distribution Function of the Galactic Halo from SDSS Photometry
• Catalogs of Hot White Dwarfs in the Milky Way from GALEX's Ultraviolet Sky Surveys. Constraining Stellar Evolution
• Post-common envelope binaries from SDSS - XIV. The DR7 white dwarf-main sequence binary catalogue
• Stellar Activity in the Broad-Band Ultraviolet
• Initial data release of the Kepler-INT Survey
• Statistical Properties of the GALEX/SDSS matched source catalogs, and classification of the UV sources
• The UV-Excess Survey of the Northern Galactic Plane (UVEX)
• The age of the Galactic thin disk from Th/Eu nucleocosmochronology III. Extended sample
• Population synthesis of Galactic subdwarf B stars
• Far Ultraviolet Continuum Emission: Applying this Diagnostic to the Chromospheres of Solar-Mass Stars
• A Radial Velocity Study of Composite-Spectra Hot Subdwarf Stars with the Hobby-Eberly Telescope
• Extreme UV QSOs
• The Unseen Population of F to K-type Companions to Hot Subdwarf Stars
• A first catalogue of automatically selected UV-excess sources from the UVEX survey
• Spectroscopic follow-up of UV-excess objects selected from the UVEX survey
• Statistical properties of the GALEX spectroscopic stellar sample

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• Revised Catalog of GALEX Ultraviolet Sources. I. The All-sky Survey: GUVcat_AIS
• Blue Lurkers: Hidden Blue Stragglers on the M67 Main Sequence Identified from their Kepler/K2 Rotation Periods
• The White Dwarf Binary Pathways Survey I: A sample of FGK stars with white dwarf companions
• The white dwarf binary pathways survey - II. Radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR4
• The UV Emission of Stars in LAMOST Survey I. Catalogs
• Matched photometric catalogs of GALEX UV sources with Gaia DR2 and SDSS DR14 databases (GUVmatch)
• Where are the missing symbiotic stars? Uncovering hidden Symbiotic Stars in public catalogues
• The Identification of RR Lyrae and Delta Scuti Stars from Variable GALEX Ultraviolet Sources
• Young Blue Straggler Stars in the Galactic Field
• UV bright red-sequence galaxies: a comparative study between UV upturn and UV weak systems