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Unraveling Variability and Estimating Mass Loss of Exoplanets in the Triplet Star System LTT 1445

S. RukdeeJ. BuchnerV. BurwitzK. Poppenh\"agerB. StelzerP. Predehl
Jan 2024
The high-energy environment of the host stars could be deleterious for their planets. It is crucial to ascertain this contextual information to fully characterize the atmospheres of terrestrial exoplanets. We aim to fully characterize a unique triple system, LTT 1445, with three known rocky exoplanets around LTT 1445A. The X-ray irradiation and flaring of this system are studied through a new 50 ks Chandra observation, which is divided into 10 ks, 10 ks, and 30 ks segments conducted two days apart, and two months apart, respectively. This is complemented by an archival Chandra observation approximately one year earlier and repeated observations with eROSITA (extended ROentgen Survey with an Imaging Telescope Array), the soft X-ray instrument on the Spectrum-Roentgen-Gamma (SRG) mission, enabling the investigation of X-ray flux behavior across multiple time scales. The flux data acquired from these observations serve as a basis for estimating the photo-evaporation mass loss of the individual exoplanets with their host stars. To gain deeper insights into the environmental context influenced by XUV flux and to better understand the anticipated atmospheric conditions of the planets orbiting the A component, we integrate the use of the planet modeling package, VPLanet. Our findings indicate that LTT 1445C is the primary contributor to X-ray emissions, with additional input from LTT 1445B. Moreover, our study confirms that LTT1445A, recognized as a slowly-rotating star, exhibits no significant flare activity in the observed dataset. The observed results also suggest that the X-ray emissions from the LTT 1445BC components do not pose a greater threat to the planets orbiting LTT 1445A than the emissions from A itself. According to simulation results, LTT 1445Ad might have the capacity to retain its water surface.
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