Predicting the UV Emission of M dwarfs with Exoplanets from Ca II and H-α
Abstract
Given the current capabilities of exoplanet detection methods, M dwarf stars are excellent candidates around which to search for temperate, Earth-sized planets. The UV wavelength regime is important to evaluate the photochemistry of the planetary atmosphere because many molecules have highly wavelength dependent absorption cross sections that peak in the UV (900-3200 Å). M dwarfs are highly active stars with unique spectra that can drive the abiotic production of key planetary biosignatures. We seek to provide a broadly applicable method of estimating the UV emission of an M dwarf, without direct UV data, by identifying a relationship between non-simultaneous optical and UV observations. Our work uses the largest sample of low-mass star UV observations yet assembled, including data from the MUSCLES and Mega-MUSCLES Treasury Surveys (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems), the FUMES survey (Far Ultraviolet M-dwarf Evolution Survey), and the HAZMAT survey (HAbitable Zones and M dwarf Activity across Time). We measure Hα equivalent widths and the Mount Wilson CaII H&K S and R'HK indices using ground-based optical spectra from the HARPS, UVES, and HIRES archives and new HIRES spectra. Archival and new Hubble Space Telescope COS and STIS spectra are used to measure line fluxes for the brightest chromospheric and transition region emission lines between 1200-2800 Å. Our results show a correlation between UV line luminosity and CaII R'HK with standard deviations in the range of 0.25-0.54 dex about the best-fit lines. Correlations between UV luminosity and Hα or the S index are weak. The results presented in this talk will be important for near-future allocations of competitive Hubble time as well as the post-Hubble era. We demonstrate that with a precise R'HK measurement obtained from the ground (e.g., 5-10% precision), the estimate of the intrinsic Lyα luminosity is 12-20%, which is typically better than what can be achieved with direct, low-to-medium S/N Hubble spectra. After we gather more data this summer, we will also be able to detail dependencies on age and spectral type.
- Publication:
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AAS/Division for Extreme Solar Systems Abstracts
- Pub Date:
- August 2019
- Bibcode:
- 2019ESS.....433103M