RR Lyrae Variables in the Ultraviolet: The View from GALEX

Wheatley, Jonathan; Welsh, Barry Y.; Browne, S. E.

doi:10.1086/666593

Cited by 16 publications

(20 citation statements)

References 17 publications

(19 reference statements)

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“…The NUV pulsation amplitude of RR Lyrae stars is roughly twice that of their V amplitude (as found earlier by Wheatley et al 2012). This allows us to detect low-amplitude variables such as J013642.0−062743.1 and J171251.8+185452.4 which have V amplitudes of 0.25 and 0.38 mag, respectively.…”

Section: Discussionsupporting

confidence: 78%

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THE IDENTIFICATION OF RR LYRAE AND δ SCUTTI STARS FROM VARIABLEGALAXY EVOLUTION EXPLORERULTRAVIOLET SOURCES

Kinman¹,

Brown²

2014

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We identify the RR Lyrae and δ Scuti stars in three catalogs of Galaxy Evolution Explorer (GALEX) variable sources. The NUV amplitude of RR Lyrae stars is about twice that in V, so we find a larger percentage of low-amplitude variables than catalogs such as Abbas et al. Interestingly, the (NUV − V ) 0 color is sensitive to metallicity and can be used to distinguish between variables of the same period but differing [Fe/H]. This color is also more sensitive to T eff than optical colors and can be used to identify the red edge of the instability gap. We find 8 δ Scuti stars, 17 RRc stars, 1 RRd star, and 84 RRab stars in the GALEX variable catalogs of Welsh et al. and Wheatley et al. We also classify 6 δ Scuti stars, 5 RRc stars, and 18 RRab stars among the 55 variable GALEX sources identified as "stars" or RR Lyrae stars in the catalog of Gezari et al. We provide ephemerides and light curves for the 26 variables that were not previously known.

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Section: Discussionsupporting

confidence: 78%

“…Wheatley et al (2012) fit model light curves to the FUV and NUV photometry of six well-observed bright RR Lyrae stars. They find that the FUV and NUV light curves, which primarily reflect temperature changes during the pulsation cycle, also depend on metallicity.…”

Section: Introductionmentioning

confidence: 99%

THE IDENTIFICATION OF RR LYRAE AND δ SCUTTI STARS FROM VARIABLEGALAXY EVOLUTION EXPLORERULTRAVIOLET SOURCES

Kinman¹,

Brown²

2014

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“…The intrinsic variability declines with the increase of T eff , implying that late-type stars tend to have strong variabilities. The σ int values in the FUV are generally larger than those in the NUV, probably due to the higher amplitudes of light curves in the shorter wavelength (Wheatley et al 2012). Another parameter to characterize the variability is the structure function (see di Clemente et al 1996 for details),…”

Section: Variability Statisticsmentioning

confidence: 99%

“…However, the color of the (NUV − J) can separate M giants from M dwarfs in Figure 15. Here we use a robust linear separation, the lowest density of the stars in the diagram of molecular-band indices in Figure 16 of 2−5 mag (Wheatley et al 2012), making them more likely to be detected in the UV. They are thus popular tracers of Galactic structures, the halo and streams (Drake et al 2013).…”

Section: Colors Of Giant and Dwarf Starsmentioning

confidence: 99%

The UV Emission of Stars in the LAMOST Survey. I. Catalogs

Bai

Liu

Wicker

et al. 2018

ApJS

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We present the ultraviolet magnitudes for over three million stars in the LAMOST survey, in which 2,202,116 stars are detected by GALEX. For 889,235 undetected stars, we develop a method to estimate their upper limit magnitudes. The distribution of (FUV − NUV) shows that the color declines with increasing effective temperature for stars hotter than 7000 K in our sample, while the trend disappears for the cooler stars due to upper atmosphere emission from the regions higher than their photospheres. For stars with valid stellar parameters, we calculate the UV excesses with synthetic model spectra, and find that the (FUV − NUV) vs. R FUV can be fitted with a linear relation and late-type dwarfs tend to have high UV excesses. There are 87,178 and 1,498,103 stars detected more than once in the visit exposures of GALEX in the FUV and NUV, respectively. We make use of the quantified photometric errors to determine statistical properties of the UV variation, including intrinsic variability and the structure function on the timescale of days. The overall occurrence of possible false positives is below 1.3% in our sample. UV absolute magnitudes are calculated for stars with valid parallaxes, which could serve as a possible reference frame in the NUV. We conclude that the colors related to UV provide good criteria to distinguish between M giants and M dwarfs, and the variability of RR Lyrae stars in our sample is stronger than that of other A and F stars.

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“…M dwarf flare stars have strong magnetic activity that manifests itself in flares of thermal UV emission on the timescale of minutes (Kowalski et al 2009). RR Lyrae stars have periodic pulsations which drive temperature fluctuations from ∼ 6000 to 8000 K that cause periodic variability in the UV on a timescale of ∼ 0.5 d (Wheatley et al 2012). Core-collapse supernovae (SNe) remain bright in the UV for hours up to several days following shock breakout, depending on the radius of the progenitor star (Nakar & Sari 2010;Rabinak & Waxman 2011), and the presence of a dense wind (Ofek et al 2010;Chevalier & Irwin 2011;Svirski et al 2012).…”

Section: Introductionmentioning

confidence: 99%

THEGALEXTIME DOMAIN SURVEY. I. SELECTION AND CLASSIFICATION OF OVER A THOUSAND ULTRAVIOLET VARIABLE SOURCES

Gezari

Martin

Forster

et al. 2013

ApJ

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We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ∼ 40 deg 2 of GALEX Time Domain Survey (TDS) N U V images observed with a cadence of 2 days and a baseline of observations of ∼ 3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5σ level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). We detect a largeamplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |∆m| = 4.6 mag and 2.9 mag, respectively. The mean amplitude of the structure function for quasars on year timescales is 5 times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with N U V < 23 mag and |∆m| > 0.2 mag of ∼ 8.0, 7.7, and 1.8 deg −2 for quasars, AGNs, and RR Lyrae stars, respectively. We also calculate a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of ∼ 15 and 52 deg −2 yr −1 for M dwarfs and extragalactic transients, respectively.

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RR Lyrae Variables in the Ultraviolet: The View from GALEX

Cited by 16 publications

References 17 publications

THE IDENTIFICATION OF RR LYRAE AND δ SCUTTI STARS FROM VARIABLEGALAXY EVOLUTION EXPLORERULTRAVIOLET SOURCES

THE IDENTIFICATION OF RR LYRAE AND δ SCUTTI STARS FROM VARIABLEGALAXY EVOLUTION EXPLORERULTRAVIOLET SOURCES

The UV Emission of Stars in the LAMOST Survey. I. Catalogs

THEGALEXTIME DOMAIN SURVEY. I. SELECTION AND CLASSIFICATION OF OVER A THOUSAND ULTRAVIOLET VARIABLE SOURCES

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