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Travis Barman

Publications and source records attributed to Travis Barman.

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

Modeling the Chromosphere and Transition Region of Planet-hosting Star GJ 436

Ahead of upcoming space missions intending to conduct observations of low-mass stars in the ultraviolet (UV) spectral region it becomes imperative to simultaneously conduct atmospheric modeling from the UV to the visible (VIS) and near-infrared (NIR). Investigations on extended spectral regions will help to improve the overall understanding of the diversity of spectral lines arising from very different atmospheric temperature regions. Here we investigate atmosphere models with a chromosphere and transition region for the M2.5V star GJ 436, which hosts a close-in Hot Neptune. The atmosphere models are guided by observed spectral features from the UV to the VIS/NIR originating in the chromosphere and transition region of GJ 436. High-resolution observations from the Hubble Space Telescope and Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs (CARMENES) are used to obtain an appropriate model spectrum for the investigated M dwarf. We use a large set of atomic species considered in nonlocal thermodynamic equilibrium conditions within our PHOENIX model computations to approximate the physics within the low-density atmospheric regions. In order to obtain an overall match for the nonsimultaneous observations, it is necessary to apply a linear combination of two model spectra, where one of them better reproduces the UV lines while the other better represents the lines from the VIS/NIR range. This is needed to adequately handle different activity states across the observations.

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NASA NTRS2023

HAZMAT. IX. An Analysis of the UV and X-Ray Evolution of Low-mass Stars in the Era of Gaia

Low-mass stars (≤1 M⊙) are some of the best candidates for hosting planets with detectable life because of these stars' long lifetimes and relative ratios of planet to star mass and radius. An important aspect of these stars to consider is the amount of ultraviolet (UV) and X-ray radiation incident on planets in the habitable zones due to the ability of UV and X-ray radiation to alter the chemistry and evolution of planetary atmospheres. In this work, we build on the results of the HAZMAT I and HAZMAT III M-star studies to determine the intrinsic UV and X-ray flux evolution with age for M stars using Gaia parallactic distances. We then compare these results to the intrinsic fluxes of K stars adapted from HAZMAT V. We find that although the intrinsic M-star UV flux is 10–100 times lower than that of K stars, the UV fluxes in their respective habitable zone are similar. However, the habitable zone X-ray flux evolutions are slightly more distinguishable with a factor of 3–15 times larger X-ray flux for late M stars than for K stars. These results suggest that there may not be a K-dwarf advantage compared to M stars in the UV, but one may still exist in the X-ray.

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NASA NTRS2022

SPARCS Payload Assembly, Integration, and Test Update

The Star-Planet Activity Research CubeSat (SPARCS) is a 6U CubeSat under construction that is devoted to the photometric monitoring of M stars in the far-UV (FUV) and near-UV (NUV), to measure the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation. We report on the progress made in the assembly, integration and test of the instrument payload at Arizona State University using a custom TVAC chamber and optical stimulus that provides calibration light sources and the custom contamination control environment that the FUV demands. The payload consists of a custom 90mm clear aperture telescope developed by Hexagon/Sigma Space, combined with a dichroic plate to separate the FUV and NUV beams developed by Teledyne Acton and Materion, married with twin focal plane array cameras separately optimized for their band passes as developed by JPL.

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