4:30 PM - 4:45 PM
[PAE17-17] Validation of TOI-1696 b: a temperate planet in the Neptunian desert around a nearby M dwarf
Keywords:Sub-Neptune, Validation, Planetary Atmosphere
Statistical studies of exoplanets have shown that there are few planets in the parameter space of Neptune's mass and radius (~3-4 RE) and orbital period of less than 2-4 days, which is the so-called "Neptunian desert" (Szabo et al. 2011, Mazeh et al. 2016). The photoevaporation theory explains this scarcity that planetary atmospheres from protoplanetary disks are blown off by high-energy stellar radiation from their host stars, resulting in smaller planetary radii (Owen et al. 2017). The planets in the Neptunian desert are thought to be either still retaining their atmospheres or just in the process of losing them, but the physical mechanisms behind this are not well understood.
We present the discovery and validation of a temperate sub-Neptune around the nearby (~65pc) M dwarf TIC 470381900 (TOI-1696), with a radius of 3.04±0.19 RE and an orbital period of 2.5days. We conducted follow-up observations of the system including ground-based transit photometry, high-resolution imaging, and high- and medium-resolution spectroscopy. Joint analysis of multi-band transit photometry from TESS, MuSCAT, MuSCAT3, Sinistro, and KeplerCam confirms the TESS signal is achromatic and on-target, and refining the orbital ephemeris. High-resolution imaging with Gemini/'Alopeke and spectroscopy with the Subaru Telescope/IRD confirmed that there are no stellar companions or background sources on the star. For the stellar parameters, we obtained the metallicity and effective temperature from the spectroscopic observations with IRD and IRTF/SpeX, and the remaining parameters such as stellar mass and radius were determined using several empirical relations or stellar models. The radial velocities measured from IRD are used to put the upper mass limit of the planet.
As the star is located near the Galactic plane, that is, in a crowded region of stars, a careful examination was required to rule out the possibility of false positive scenarios, such as diluted eclipsing binaries. With a combination of multi-band transit observations and imaging/spectroscopic observations, we were able to rule out those scenarios.
The target locates in the Neptunian desert, which makes future atmosphere research interesting. We computed the thermal evolution of TOI-1696 b with an H2/He atmosphere by calculating its interior structure in hydrostatic equilibrium for ∼8 Gyr, followed by the mass loss, and found that the planet is likely to retain the H2/He atmosphere. To statistically evaluate the feasibility of transmission spectroscopy on this planet, we have calculated and compared the transmission spectroscopy metric (TSM) defined in Kempton et al. (2018). We concluded that this target is one of the planets with the best prospects for atmospheric detection among the currently known Sub-Neptune-sized planets. In addition, future RV observations with high-resolution infrared spectrographs such as IRD will allow us to place more substantial limits on the planetary mass.
In this talk, I will explain the validation method, which combined various observations and analyses, and the interest of TOI-1696b with a view to future observations of planetary atmospheres.
We present the discovery and validation of a temperate sub-Neptune around the nearby (~65pc) M dwarf TIC 470381900 (TOI-1696), with a radius of 3.04±0.19 RE and an orbital period of 2.5days. We conducted follow-up observations of the system including ground-based transit photometry, high-resolution imaging, and high- and medium-resolution spectroscopy. Joint analysis of multi-band transit photometry from TESS, MuSCAT, MuSCAT3, Sinistro, and KeplerCam confirms the TESS signal is achromatic and on-target, and refining the orbital ephemeris. High-resolution imaging with Gemini/'Alopeke and spectroscopy with the Subaru Telescope/IRD confirmed that there are no stellar companions or background sources on the star. For the stellar parameters, we obtained the metallicity and effective temperature from the spectroscopic observations with IRD and IRTF/SpeX, and the remaining parameters such as stellar mass and radius were determined using several empirical relations or stellar models. The radial velocities measured from IRD are used to put the upper mass limit of the planet.
As the star is located near the Galactic plane, that is, in a crowded region of stars, a careful examination was required to rule out the possibility of false positive scenarios, such as diluted eclipsing binaries. With a combination of multi-band transit observations and imaging/spectroscopic observations, we were able to rule out those scenarios.
The target locates in the Neptunian desert, which makes future atmosphere research interesting. We computed the thermal evolution of TOI-1696 b with an H2/He atmosphere by calculating its interior structure in hydrostatic equilibrium for ∼8 Gyr, followed by the mass loss, and found that the planet is likely to retain the H2/He atmosphere. To statistically evaluate the feasibility of transmission spectroscopy on this planet, we have calculated and compared the transmission spectroscopy metric (TSM) defined in Kempton et al. (2018). We concluded that this target is one of the planets with the best prospects for atmospheric detection among the currently known Sub-Neptune-sized planets. In addition, future RV observations with high-resolution infrared spectrographs such as IRD will allow us to place more substantial limits on the planetary mass.
In this talk, I will explain the validation method, which combined various observations and analyses, and the interest of TOI-1696b with a view to future observations of planetary atmospheres.