MSTARPANSPEC

The team presents a panchromatic spectrum, from 1 Angstrom to 10 microns, of the planet-hosting M dwarfs LHS 3844 and K2-3. These data products are motivated by high-energy measurements of LHS 3844 and K2-3 in the ultraviolet with the Cosmic Origins Spectrograph on board the Hubble Space Telescope (HST/COS), and an upper limit on the X-ray flux from Swift's X-ray Telescope (Swift-XRT) and XMM-Newton. The HST/COS data cover the far and near ultraviolet (FUV and NUV) with the G130M, G160M, and G230L gratings. Due to the large aperture of COS the prominent Lyman-α 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 we use either a PHOENIX model plus a blackbody curve or a BT-Settl model to fill out the spectrum. 

To summarize, in constructing the LHS 3844 and K2-3 panchromatic spectra, the team uses:

• X-ray: Swift-XRT (upper limit) or XMM-Newton (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; ; or a BT-Settl model out to 10 microns (Allard, 2014, IAUS, 299, 271A)

In the case of LHS 3844, the team observed a flare with COS G130M. 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 K2-3, and vice versa.