MSTARPANSPEC

The team presents a panchromatic spectrum, from 1 Angstrom to 10 microns, of the nearby, planet-hosting M dwarf LHS 3844. This data product is motivated by high-energy measurements of LHS 3844 in the ultraviolet with the Cosmic Origins Spectrograph on board the Hubble Space Telescope (HST/COS), and an upper limit on the soft X-ray flux from Swift's X-ray Telescope (Swift-XRT). Ten orbits of HST and 31.8ks of Swift-XRT were used to obtain these data. The HST/COS data cover the far and near ultraviolet (FUV and NUV) with the G130M, G160M, and G230L gratings. During one of the FUV (G130M) observations the team observed a flare with an absolute energy of 8.96 +/- 0.77 x 10²⁸ erg in the FUV and an equivalent duration of 355 +/- 31 seconds. The team excises this flare from the UV spectral data and produce panchromatic spectra for both the quiescent and flare cases of the star. Due to the large aperture of COS the prominent Lyman-alpha line is obscured by geocoronal emission. The team employs the UV-UV line correlations developed by the MUSCLES program to estimate the Lyman-α flux using measured UV emission lines in the rest of the COS data. For the rest of the high-energy spectrum, which is not measured directly, the team employs a differential emission measure (DEM) to fill in the gaps. Redward of the NUV the team uses a PHOENIX model and a blackbody curve to fill out the spectrum. 

To summarize, in constructing the quiescent LHS 3844 panchromatic spectrum the team uses:

• X-ray: Swift-XRT (upper limit)
• Unmeasured regions of X-ray and EUV: Differential emission measure (this method is described in detail in Duvvuri et al, arXiv:2102.08493)
• Ly-α: UV-UV correlations with measured emission lines (correlations from Youngblood et al. 2017, ApJ, 843, 31)
• UV: HST/COS
• Optical, infrared: PHOENIX models out to 5.5 microns (Husser et al. 2013, A&A, 553, 6) and a blackbody function out to 10 microns

The flare spectrum is constructed in a similar manner with the following exceptions:

• X-ray: Estimated from the quiescent soft X-ray upper limit using a multiplicative factor
• Unmeasured regions of UV (spectral data only exists for the G130M FUV grating): Differential emission measure (Duvvuri et al, arXiv:2102.08493)

The data products presented here are designed to be similar to those provided by the MUSCLES survey, such that users of MUSCLES data can easily access the spectrum of LHS 3844 and vice versa.