The triple star system LTT 1445, at a distance of 22.5 light-years, hosts some of the nearest rocky planets.
This Chandra image shows the LTT 1445 system: LTT 1445A is the fainter source at the center of the image with the brighter resolved binary LTT 1445 BC. Image credit: NASA / Chandra / Brown et al., arXiv: 2209.11314.
“Understanding what happens to rocky planets and their atmospheres in the habitable zones of low mass stars is currently one of the greatest astronomical challenges,” said University of Colorado’s Dr. Alexander Brown and colleagues.
“The nearest Earth-mass planets in the habitable zones orbit red dwarf stars (M dwarfs), and these are prime targets for spectroscopic atmospheric characterization in the next decade.”
“M dwarfs are the most common type of star in the Milky Way, and over 25% of them have planets orbiting in their habitable zones.”
“Theoretical work shows that planets around M dwarfs could be habitable despite their phase-locked orbits and dynamic modeling of transiting systems reveals that most systems permit stable orbits of Earth-mass planets long enough for the development of life, i.e. over 1.7 billion years.”
“Over the past several years, the exoplanet community has recognized the importance of obtaining ultraviolet and X-ray spectroscopy and time-series monitoring of M dwarfs to provide a comprehensive picture of their energetic radiation environments.”
In their study, Dr. Brown and co-authors focused on LTT 1445, a hierarchical trio of M dwarfs.
Also known as TIC 98796344, TOI 455, L 730-18 or BD-17 588, the system consists of the brighter star LTT 1445A and the fainter visual binary LTT 1445BC.
LTT 1445A hosts two terrestrial exoplanets with Earth-like compositions: LTT 1445Ab and LTT 1445Ac.
First discovered in 2018, LTT 1445Ab is about 1.3 times bigger than Earth, 2.9 times more massive, and has an orbital period of 5.36 days.
LTT 1445Ac, spotted earlier this year, has a mass of 1.54 Earth masses, a radius of 1.15 Earth radii, and an orbital period of 3.12 days.
“These planets lie interior to the habitable zone around the star with the cooler LTT 1445Ab having an equilibrium temperature of 424 K, which is intermediate to other rocky planets such as Gliese 1132b and TRAPPIST-1b,” the astronomers said.
“Although LTT 1445Ab and LTT 1445Ac are likely not habitable, they remain excellent targets for detailed atmospheric studies with Webb.”
Using NASA’s Chandra X-ray Observatory, they detected the coronal X-ray emission from all three stars in the LTT 1445 system, including from the exoplanet-hosting star LTT 1445A.
They also found that the lowest mass star LTT 1445C is the dominant X-ray emitter in the system.
“Chandra observations of LTT 1445A provide further evidence that the coronal emission of older, slowly-rotating M dwarfs can be highly variable and the coronal emission already seen from LTT 1445A suggests that this star may have interesting influences on the atmospheres of its exoplanets,” they said.
“During the observed flare the X-ray luminosity is only a factor of 10 below the saturated activity level expected from young, very active stars, even though LTT 1445A is thought to be slowly rotating.”
“More extensive studies of its X-ray activity should provide a clearer picture of the range of coronal emission from all three mid-M dwarfs in the LTT 1445 system.”
The team’s work will appear in the Astronomical Journal.
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Alexander Brown et al. 2022. X-ray Emission from the Exoplanet Hosting LTT 1445 Triple Star System. AJ, in press; arXiv: 2209.11314
Source link: https://www.sci.news/astronomy/x-ray-emission-exoplanet-hosting-triple-star-system-11282.html
