15:00 〜 15:15
[PAE17-12] Atmospheres of low-mass star planets: Atmospheric escape and beyond
キーワード：Exoplanet atmosphere, radius-gap, NIR spectroscopy, secondary atmosphere, habitability
Understanding the formation and evolution of rocky planets becomes a key in our quest to finding a habitable planet. And planets around low-mass stars (<0.8 M_Sun) are in general rocky and are easier to detect and characterize using the transit technique. The atmospheric characterization of such planets provides a window in understanding the evolution of the planets. In general, small planets (<3 R_Earth) are expected to be accreted with 1-2% of H/He primordial atmosphere by the end of their protoplanetary disc dissipation (Owen & Wu 2017). This primordial atmosphere can be evaporated by the high-energy X-ray and EUV flux from their host star in the initial few million years. This photoevaporation process is dominant when the star is young and active (Owen & Wu 2013, 2017). Or the planet could dissipate the primordial atmosphere by its own internal heating of the cooling core. This core-powered mass-loss does not depend on the stellar environment, but just on the heat dissipating from the planet (Ginzburg et al. 2016, 2018; Gupta & Schlichting 2019, 2020). Finally, another class of models predict that the low-mass star planets essentially do not accrete enough gas during its formation (Lee et al. 2014; Lee & Chiang 2016; Lopez & Rice 2018). It is essential to distinguish between these models to have a robust prediction on the evolution of small planets.
The distinction between these models can be achieved by observing planets in and around the transition region between rocky and non-rocky planets (a.k.a radius-gap; 1.5-2 R_Earth). Unfortunately, the origin of radius-gap is not clearly understood in low-mass star planets due to poor sample size in this region (Cloutier & Menou 2020). Here we present near infrared (NIR) high-resolution transit observations of TRAPPIST-1b, TRAPPIST-1e, TRAPPIST-1f, GJ 9827b, GJ 9827d and TOI-1235b, small planets around cool stars. We target the He I triplet lines at 1083 nm as a marker for detecting any evaporating atmospheres (Oklopčić & Hirata 2018). The observations were carried out on several open use programs on the Subaru telescope infrared Doppler (IRD) instrument (R~70,000; Tamura et al. 2012; Kotani et al. 2018).
Evaporation of primordial atmosphere pave way for the formation and evolution of secondary heavier atmosphere. This heavier atmosphere is the key in habitability studies as they might host water, oxygen etc. But probing them with ground-based telescopes have been difficult due to telluric contamination and low signal strengths when probing the features from an 8-10 m class telescope. We overcome one of these difficulties by implementing a novel two-step telluric correction to remove the Earth’s atmospheric signatures from our spectra (Krishnamurthy et al. in prep.). We demonstrate this capability by probing the lower atmospheres of few terrestrial planets.
In the next generation 30 m class of telescopes, probing the lower atmosphere of terrestrial planets can be feasible with a high-resolution spectrograph (R~100,000). We performed a feasibility study on the detection of feature like Oxygen on terrestrial planet for various atmospheric compositions (Krishnamurthy et al. in prep.). Our study on probing both primary and secondary atmospheres can provide useful insights on the atmospheric evolution of low-mass star planets.
The distinction between these models can be achieved by observing planets in and around the transition region between rocky and non-rocky planets (a.k.a radius-gap; 1.5-2 R_Earth). Unfortunately, the origin of radius-gap is not clearly understood in low-mass star planets due to poor sample size in this region (Cloutier & Menou 2020). Here we present near infrared (NIR) high-resolution transit observations of TRAPPIST-1b, TRAPPIST-1e, TRAPPIST-1f, GJ 9827b, GJ 9827d and TOI-1235b, small planets around cool stars. We target the He I triplet lines at 1083 nm as a marker for detecting any evaporating atmospheres (Oklopčić & Hirata 2018). The observations were carried out on several open use programs on the Subaru telescope infrared Doppler (IRD) instrument (R~70,000; Tamura et al. 2012; Kotani et al. 2018).
Evaporation of primordial atmosphere pave way for the formation and evolution of secondary heavier atmosphere. This heavier atmosphere is the key in habitability studies as they might host water, oxygen etc. But probing them with ground-based telescopes have been difficult due to telluric contamination and low signal strengths when probing the features from an 8-10 m class telescope. We overcome one of these difficulties by implementing a novel two-step telluric correction to remove the Earth’s atmospheric signatures from our spectra (Krishnamurthy et al. in prep.). We demonstrate this capability by probing the lower atmospheres of few terrestrial planets.
In the next generation 30 m class of telescopes, probing the lower atmosphere of terrestrial planets can be feasible with a high-resolution spectrograph (R~100,000). We performed a feasibility study on the detection of feature like Oxygen on terrestrial planet for various atmospheric compositions (Krishnamurthy et al. in prep.). Our study on probing both primary and secondary atmospheres can provide useful insights on the atmospheric evolution of low-mass star planets.