09:15 〜 09:30
[PEM11-02] Multi-color observations of a young M-dwarf K2-25 to assess the effect of starspots on planetary transits
キーワード：サブネプチューン、恒星活動、トランジット法
The rise of space telescopes such as the James Webb Space Telescope will allow more detailed investigations of the atmospheres of small planets. However, recent studies suggest such an atmospheric characterization by transmission spectroscopy needs careful consideration of the stellar surface inhomogeneity by starspots, as they obscure or mimic the atmospheric signals (e.g., Rackham et al., 2018). This effect is particularly problematic for planetary systems around M-dwarfs that tend to be magnetically active, but their spot properties (spot temperature, covering fractions, distributions) are not fully-studied. Therefore, it is essential to reveal their spot properties to interpret the obtained spectra appropriately.
In this context, we conducted multi-band photometric observations to investigate the stellar activity of the young M-dwarf K2-25 and its effect on transit observations of its sub-Neptune planet K2-25b.
We monitored the stellar brightness variation of the star by the LCO 1m telescopes in the g- and z- band simultaneously with the TESS observing period. By also using the archived g-band and r-band data from the ZTF survey, we have derived the monitoring light curves in five optical bands. From the difference in their modulation amplitude, we found the typical spot temperature of K2-25 to be ~ 100-200 K below or higher than the photosphere, and the spot covering fraction to be around < 20% if there are no always-visible spots.
We also investigated the effect of stellar activity by performing multiple transit observations with the ground-based multi-band photometric instrument MuSCAT series. Although the obtained transit depths had large uncertainties, they ruled out the cases with extremely high/low spot temperatures and large spot-covering fractions. The results suggest that the TLSE could distort the transmission spectrum of the target with >100 ppm amplitude, which is detectable with the JWST transmission spectroscopy.
Our study demonstrates that the spot properties of M-dwarfs can be constrained with good precision with current instruments by designing observation methods such as simultaneous observations with a space-based survey. The presentation will include the prospects for future research using this approach.
In this context, we conducted multi-band photometric observations to investigate the stellar activity of the young M-dwarf K2-25 and its effect on transit observations of its sub-Neptune planet K2-25b.
We monitored the stellar brightness variation of the star by the LCO 1m telescopes in the g- and z- band simultaneously with the TESS observing period. By also using the archived g-band and r-band data from the ZTF survey, we have derived the monitoring light curves in five optical bands. From the difference in their modulation amplitude, we found the typical spot temperature of K2-25 to be ~ 100-200 K below or higher than the photosphere, and the spot covering fraction to be around < 20% if there are no always-visible spots.
We also investigated the effect of stellar activity by performing multiple transit observations with the ground-based multi-band photometric instrument MuSCAT series. Although the obtained transit depths had large uncertainties, they ruled out the cases with extremely high/low spot temperatures and large spot-covering fractions. The results suggest that the TLSE could distort the transmission spectrum of the target with >100 ppm amplitude, which is detectable with the JWST transmission spectroscopy.
Our study demonstrates that the spot properties of M-dwarfs can be constrained with good precision with current instruments by designing observation methods such as simultaneous observations with a space-based survey. The presentation will include the prospects for future research using this approach.