11:00 〜 13:00
[PAE17-P05] Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf
キーワード：サブネプチューン、系外惑星発見確認、透過光分光法
Small planets with a radius between 1 - 4 Earth radii, are extremely common in the Milky Way but do not exist in our solar system. NASA's Kepler space telescope revealed that this population has a bimodal distribution which presumably separated the planets into super-Earths (1 - 2 Earth radii) and sub-Neptunes (2 - 4 Earth radii) populations (Fulton et al. 2017). This radius valley is thought to be consistent with the transition from rocky to non-rocky planets and predicted by photoevaporation (e.g. Owen & Wu 2013), core-powered mass-loss model (e.g. Ginzburg et al. 2016), and gas-poor formation model (Cloutier & Menou 2020). Recent studies also revealed that the location of the radius valley is dependent on the planetary period, insolation, and stellar type. To confirm and improve these predictions, it is important to measure the radius and mass with high precision to investigate the existence of the H2-He envelop from the mass-radius relationship.
In addition, sub-Neptune-size planets get attention because they are likely to have large oceans with habitable conditions under H2-rich atmospheres (Madhusudhan et al. 2021) in addition to a rocky core enveloped in a H2-He gaseous envelope and H2O-dominated ices/fluids (e.g. Zeng et al. 2019). It is however difficult to constrain the bulk composition of a planet from the mass and radius alone. To break the degeneracy, it is important to increase the number of known planets around bright stars close to our solar system and to observe their atmospheres directly.
The infrared helium triplet is a good indicator to investigate the existence of a primary atmosphere. Previous studies have detected the He I triplet lines in the atmosphere of some Jupiter and Neptune-sized planets (e.g. Nortmann et al. 2018) but only in two sub-Neptunes (Palle et al 2020, Orell-Miquel et al. 2022). Other studies on sub-Neptunes planets have been able to place only upper limits on He I absorption, but they still can help to constrain the mass-loss rate (e.g. Krishnamurthy et al. 2021).
We have validated a new sub-Neptune-sized planet around a nearby M3 dwarf (TOI-2136) with an orbital period of 7.852 days. Using TESS photometry, ground-based multi-color photometry, and high-precision RV measurements, we derived a planetary radius of 2.2 ± 0.07 Earth Radii and a mass of 4.7 +3.1 -2.6 Earth Mass. We also observed a transit event with high-resolution spectroscopy in an attempt to detect the helium in its atmosphere with InfraRed Doppler (IRD) instrument on the Subaru telescope. There is no significant planetary absorption detection, but we can place an upper limit on the equivalent width of < 7.8 mÅ (95% confidence) and on the absorption signal of < 1.44 % (95% confidence) around helium triplet lines. In this presentation, we will report on these results and discuss the physical property of TOI-2136b.
In addition, sub-Neptune-size planets get attention because they are likely to have large oceans with habitable conditions under H2-rich atmospheres (Madhusudhan et al. 2021) in addition to a rocky core enveloped in a H2-He gaseous envelope and H2O-dominated ices/fluids (e.g. Zeng et al. 2019). It is however difficult to constrain the bulk composition of a planet from the mass and radius alone. To break the degeneracy, it is important to increase the number of known planets around bright stars close to our solar system and to observe their atmospheres directly.
The infrared helium triplet is a good indicator to investigate the existence of a primary atmosphere. Previous studies have detected the He I triplet lines in the atmosphere of some Jupiter and Neptune-sized planets (e.g. Nortmann et al. 2018) but only in two sub-Neptunes (Palle et al 2020, Orell-Miquel et al. 2022). Other studies on sub-Neptunes planets have been able to place only upper limits on He I absorption, but they still can help to constrain the mass-loss rate (e.g. Krishnamurthy et al. 2021).
We have validated a new sub-Neptune-sized planet around a nearby M3 dwarf (TOI-2136) with an orbital period of 7.852 days. Using TESS photometry, ground-based multi-color photometry, and high-precision RV measurements, we derived a planetary radius of 2.2 ± 0.07 Earth Radii and a mass of 4.7 +3.1 -2.6 Earth Mass. We also observed a transit event with high-resolution spectroscopy in an attempt to detect the helium in its atmosphere with InfraRed Doppler (IRD) instrument on the Subaru telescope. There is no significant planetary absorption detection, but we can place an upper limit on the equivalent width of < 7.8 mÅ (95% confidence) and on the absorption signal of < 1.44 % (95% confidence) around helium triplet lines. In this presentation, we will report on these results and discuss the physical property of TOI-2136b.