The Detection of M Dwarf UV Flare Events in the
                    <i>GALEX</i>
                    Data Archives

Welsh, Barry Y.; Wheatley, Jonathan; Seibert, Mark; Browne, S. E.; West, Andrew A.; Siegmund, Oswald H. W.; Barlow, Tom A.; Forster, Karl; Friedman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Small, Todd; Wyder, Ted K.; Schiminovich, David; Neff, Susan G.; Rich, R. Michael

doi:10.1086/516640

Cited by 60 publications

(64 citation statements)

References 32 publications

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“…While this strategy does not provide continuous coverage due to Earth occultation, it is optimized for constraining the types and frequency of flare behavior on low-mass exoplanet host stars. Since the characteristic timescale for UV/optical flare activity on M dwarfs is thought to be minutes to hours (Welsh et al 2007;Kowalski et al 2009;), our observations are ideal for quantifying the importance of flare activity to the local UV radiation field in these systems. With the above considerations in mind, we arranged the UV -visible observations for each target into campaigns comprising three HST visits: (1) COS G130M, (2) COS G160M +G230L, and (3) STIS G/E140M+G230L+G430L, all executed within a day of each other to mitigate uncertainties introduced by month or year timescale variations in the stellar flux.…”

Section: Muscles Observing Strategymentioning

confidence: 99%

The Muscles Treasury Survey. I. Motivation and Overview*

Loyd

Youngblood

Brown

et al. 2016

ApJ

390

381

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Ground-and space-based planet searches employing radial velocity techniques and transit photometry have detected thousands of planet-hosting stars in the Milky Way. With so many planets discovered, the next step toward identifying potentially habitable planets is atmospheric characterization. While the Sun-Earth system provides a good framework for understanding the atmospheric chemistry of Earth-like planets around solar-type stars, the observational and theoretical constraints on the atmospheres of rocky planets in the habitable zones (HZs) around low-mass stars (K and M dwarfs) are relatively few. The chemistry of these atmospheres is controlled by the shape and absolute flux of the stellar spectral energy distribution (SED), however, flux distributions of relatively inactive low-mass stars are poorly understood at present. To address this issue, we have executed a panchromatic (X-ray to mid-IR) study of the SEDs of 11 nearby planet-hosting stars, the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury Survey. The MUSCLES program consists visible observations from Hubble and ground-based observatories. Infrared and astrophysically inaccessible wavelengths (EUV and Lyα) are reconstructed using stellar model spectra to fill in gaps in the observational data. In this overview and the companion papers describing the MUSCLES survey, we show that energetic radiation (X-ray and ultraviolet) is present from magnetically active stellar atmospheres at all times for stars as late as M6. The emission line luminosities of C IV and Mg II are strongly correlated with band-integrated luminosities and we present empirical relations that can be used to estimate broadband FUV and XUV (≡X-ray + EUV) fluxes from individual stellar emission line measurements. We find that while the slope of the SED, FUV/NUV, increases by approximately two orders of magnitude form early K to late M dwarfs (≈0.01-1), the absolute FUV and XUV flux levels at their corresponding HZ distances are constant to within factors of a few, spanning the range 10-70 erg cm −2 s −1 in the HZ. Despite the lack of strong stellar activity indicators in their optical spectra, several of the M dwarfs in our sample show spectacular UV flare emission in their light curves. We present an example with flare/quiescent ultraviolet flux ratios of the order of 100:1 where the transition region energy output during the flare is comparable to the total quiescent luminosity of the star E flare (UV) ∼ 0.3 L * Δt (Δt = 1 s). Finally, we interpret enhanced L(line)/L Bol ratios for C IV and N V as tentative observational evidence for the interaction of planets with large planetary mass-to-orbital distance ratios (M plan /a plan ) with the transition regions of their host stars.

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Section: Muscles Observing Strategymentioning

confidence: 99%

The Muscles Treasury Survey. I. Motivation and Overview*

Loyd

Youngblood

Brown

et al. 2016

ApJ

390

381

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“…Previous studies in the far and extreme UV are scarcer. Welsh et al (2007) leveraged data from the Galaxy Evolution Explorer in the broadband near and far-ultraviolet to find 49 variable sources exhibiting 52 flares. The Galaxy Evolution Explorer FUV band data contain the Si iv line we analyzed for variability.…”

Section: A Selection Of Relevant Flare and Variability Studiesmentioning

confidence: 99%

Fluctuations and Flares in the Ultraviolet Line Emission of Cool Stars: Implications for Exoplanet Transit Observations

Loyd¹,

France²

2014

ApJS

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Variations in stellar flux can potentially overwhelm the photometric signal of a transiting planet. Such variability has not previously been well-characterized in the ultraviolet lines used to probe the inflated atmospheres surrounding hot Jupiters. Therefore, we surveyed 38 F-M stars for intensity variations in four narrow spectroscopic bands: two enclosing strong lines from species known to inhabit hot Jupiter atmospheres, C ii λλ1334, 1335 and Si iii λ1206; one enclosing Si iv λλ1393, 1402; and 36.5 Å of interspersed continuum. For each star/band combination, we generated 60 s cadence lightcurves from archival Hubble Space Telescope Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph time-tagged photon data. Within these lightcurves, we characterized flares and stochastic fluctuations as separate forms of variability. Flares: we used a cross-correlation approach to detect 116 flares. These events occur in the time-series an average of once per 2.5 hr, over 50% last 4 minutes or less, and most produce the strongest response in Si iv. If the flare occurred during a transit measurement integrated for 60 minutes, 90/116 would destroy the signal of an Earth, 27/116 Neptune, and 7/116 Jupiter, with the upward bias in flux ranging from 1% to 109% of quiescent levels. Fluctuations: photon noise and underlying stellar fluctuations produce scatter in the quiescent data. We model the stellar fluctuations as Gaussian white noise with standard deviation σ x . Maximum likelihood values of σ x range from 1% to 41% for 60 s measurements. These values suggest that many cool stars will only permit a transit detection to high confidence in ultraviolet resonance lines if the radius of the occulting disk is 1 R J . However, for some M dwarfs this limit can be as low as several R ⊕ .

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“…Although the primary purpose of GALEX was to examine the UV properties of extragalactic objects, several Galactic studies have used it to measure stellar UV emission. Welsh et al (2007) used GALEX data in order to examine the characteristics of M dwarf flares at UV wavelengths. Shkolnik et al (2011) and Rodriguez et al (2011) used GALEX to show that ultraviolet activity is an indication of youth in low-mass stars and can be used to search for members of young moving groups in the solar neighborhood.…”

Section: Introductionmentioning

confidence: 99%

A Catalog of Galex Ultraviolet Emission From Spectroscopically Confirmed M Dwarfs*

Jones¹,

West²

2016

ApJ

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We present a catalog of Galaxy Evolution Explorer Near-UV (NUV) and Far-UV (FUV) photometry for the Palomar/MSU and SDSS DR7 spectroscopic M dwarf catalogs. The catalog contains NUV measurements matched to 577 spectroscopically confirmed M dwarfs and FUV measurements matched to 150 spectroscopically confirmed M dwarfs. Using these data, we find that NUV and FUV luminosities strongly correlate with Hα emission, a typical indicator of magnetic activity in M dwarfs. We also examine the fraction of M dwarfs with varying degrees of strong line emission at NUV wavelengths. Our results indicate that the frequency of M dwarf NUV emission peaks at intermediate spectral types, with at least ∼30% of young M4-M5 dwarfs having some level of activity. For mid-type M dwarfs, we show that NUV emission decreases with distance from the Galactic plane, a proxy for stellar age. Our complete matched source catalog is available online.

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The Detection of M Dwarf UV Flare Events in the GALEX Data Archives

Cited by 60 publications

References 32 publications

The Muscles Treasury Survey. I. Motivation and Overview*

The Muscles Treasury Survey. I. Motivation and Overview*

Fluctuations and Flares in the Ultraviolet Line Emission of Cool Stars: Implications for Exoplanet Transit Observations

A Catalog of Galex Ultraviolet Emission From Spectroscopically Confirmed M Dwarfs*

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