A New Form of Estimating Stellar Parameters Using an Optimization Approach
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Arxiv:1809.07342V1 [Astro-Ph.SR] 19 Sep 2018
Draft version September 21, 2018 Preprint typeset using LATEX style emulateapj v. 11/10/09 FAR-ULTRAVIOLET ACTIVITY LEVELS OF F, G, K, AND M DWARF EXOPLANET HOST STARS* Kevin France1, Nicole Arulanantham1, Luca Fossati2, Antonino F. Lanza3, R. O. Parke Loyd4, Seth Redfield5, P. Christian Schneider6 Draft version September 21, 2018 ABSTRACT We present a survey of far-ultraviolet (FUV; 1150 { 1450 A)˚ emission line spectra from 71 planet- hosting and 33 non-planet-hosting F, G, K, and M dwarfs with the goals of characterizing their range of FUV activity levels, calibrating the FUV activity level to the 90 { 360 A˚ extreme-ultraviolet (EUV) stellar flux, and investigating the potential for FUV emission lines to probe star-planet interactions (SPIs). We build this emission line sample from a combination of new and archival observations with the Hubble Space Telescope-COS and -STIS instruments, targeting the chromospheric and transition region emission lines of Si III,N V,C II, and Si IV. We find that the exoplanet host stars, on average, display factors of 5 { 10 lower UV activity levels compared with the non-planet hosting sample; this is explained by a combination of observational and astrophysical biases in the selection of stars for radial-velocity planet searches. We demonstrate that UV activity-rotation relation in the full F { M star sample is characterized by a power-law decline (with index α ≈ −1.1), starting at rotation periods & 3.5 days. Using N V or Si IV spectra and a knowledge of the star's bolometric flux, we present a new analytic relationship to estimate the intrinsic stellar EUV irradiance in the 90 { 360 A˚ band with an accuracy of roughly a factor of ≈ 2. -