The Near-Ultraviolet Luminosity Function of Young, Early M-Type Dwarf Stars

Ansdell, Megan; Gaidos, Eric; Mann, Andrew W.; Lépine, Sébastien; James, D. J.; Buccino, A. P.; Baranec, Christoph; Law, Nicholas M.; Riddle, Reed; Mauas, P. J. D.; Petrucci, R.

doi:10.1088/0004-637x/798/1/41

Cited by 46 publications

(48 citation statements)

References 74 publications

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“…There is an increase of flux density with effective temperature in both GALEX bands with young (≤300 Myr) stars emitting more emission than older stars. These trends are consistent with the work of and Ansdell et al (2015), who used averaged GALEX flux densities. Despite later M stars showing more variability (in the NUV), they emit less excess UV emission in both GALEX bands.…”

Section: Galex Fuv and Nuv Correlations And Ratiossupporting

confidence: 91%

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

Miles

Shkolnik

2017

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The ultraviolet (UV) light from a host star influences a planet's atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope. These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer (GALEX ) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771 -2831Å) and far-ultraviolet (FUV; 1344 -1786Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.

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Section: Galex Fuv and Nuv Correlations And Ratiossupporting

confidence: 91%

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

Miles

Shkolnik

2017

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“…The fastest rotator of our example stars (P rot ∼ 1 d) falls into the saturated regime of the near-UV activity-age relation ( Fig. 13 of Ansdell et al 2015), which indicates an age < 160 Myr, while the other fast rotator (P rot ∼ 6 d) shows a near-UV excess emission consistent with a Hyades age (approximately the age of Praesepe). The flare data of Ilin et al (2019) of the Pleiades are therefore inconsistent with our FFD measurements.…”

Section: Discussionmentioning

confidence: 67%

“…Based on this, the two fast-rotating mid-M dwarfs that we show as examples might be young. For these two stars, Ansdell et al (2015) found significant near-UV excess emission. The fastest rotator of our example stars (P rot ∼ 1 d) falls into the saturated regime of the near-UV activity-age relation ( Fig.…”

Section: Discussionmentioning

confidence: 91%

Rotation-activity relations and flares of M dwarfs with K2 long- and short-cadence data

Raetz

Stelzer

Damasso

et al. 2020

A&A

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Using light curves obtained by the K2 mission, we study the relation between stellar rotation and magnetic activity with special focus on stellar flares. Our sample comprises 56 bright and nearby M dwarfs observed by K2 during campaigns C0-C18 in long-and short-cadence mode. We derive rotation periods for 46 M dwarfs and measure photometric activity indicators such as amplitude of the rotational signal, standard deviation of the light curves, and the basic flare properties (flare rate, flare energy, flare duration, and flare amplitude). We found 1662 short-cadence flares, 363 of which have a long-cadence counterpart with flare energies of up to 5.6 · 10 34 erg. The flare amplitude, duration, and frequency derived from the short-cadence light curves differ significantly from those derived from the long-cadence data. The analysis of the short-cadence light curves results in a flare rate that is 4.6 times higher than the long-cadence data. We confirm the abrupt change in activity level in the rotation-activity relation at a critical period of ∼10 d when photometric activity diagnostics are used. This change is most drastic in the flare duration and frequency for short-cadence data. Our flare studies revealed that the highest flare rates are not found among the fastest rotators and that stars with the highest flare rates do not show the most energetic flares. We found that the superflare frequency (E ≥ 5 · 10 34 erg) for the fast-rotating M stars is twice higher than for solar like stars in the same period range. By fitting the cumulative FFD, we derived a power-law index of α = 1.84 ± 0.14, consistent with previous M dwarf studies and the value found for the Sun.

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“…Here, we find that our object appears to lie between the active and inactive loci and that while it does not have a far-UV detection, it could have emission above Shkolnik et al (2009)'s F NUV /F J > 10 −5 and still remain undetected by GALEX. However, the near-UV emission is of little use as Ansdell et al (2014) noted that the fully convective transition in mid-M dwarfs makes it impossible to define a near-UV inactive locus of M dwarfs beyond M3. Hence, we do not consider 2MASS J0213+3648 AB's near-UV emission to be a reliable age diagnostic.…”

Section: The Age Of 2mass J0213+3648 Abmentioning

confidence: 99%

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

Deacon

Magnier

Liu

et al. 2017

Mon. Not. R. Astron. Soc.

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We present the discovery of a 360 AU separation T3 companion to the tight (3.1 AU) M4.5+M6.5 binary 2MASS J02132062+3648506. This companion was identified using Pan-STARRS 1 data and, despite its relative proximity to the Sun (22.2 +6.4 −4.0 pc; Pan-STARRS 1 parallax) and brightness (J=15.3), appears to have been missed by previous studies due to its position near a diffraction spike in 2MASS. The close M dwarf binary has active X-ray and Hα emission and shows evidence for UV flares. The binary's weak GALEX UV emission and strong Na I 8200 Å Na absorption leads us to an age range of ∼1-10 Gyr. Applying this age range to evolutionary models implies the wide companion has a mass of 0.063±0.009 M ⊙ . 2MASS J02132+3648 C provides a relatively old benchmark close to the L/T transition and acts as a key, older comparison to the much younger early-T companions HN Peg B and GU Psc b.

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The Near-Ultraviolet Luminosity Function of Young, Early M-Type Dwarf Stars

Cited by 46 publications

References 74 publications

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

Rotation-activity relations and flares of M dwarfs with K2 long- and short-cadence data

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

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