Friday, May 31, 2013

1305.6985 (Norio Narita et al.)

Multi-Color Transit Photometry of GJ 1214b through BJHKs-Bands and a Long-Term Monitoring of the Stellar Variability of GJ 1214    [PDF]

Norio Narita, Akihiko Fukui, Masahiro Ikoma, Yasunori Hori, Kenji Kurosaki, Yui Kawashima, Takahiro Nagayama, Masahiro Onitsuka, Amnart Sukom, Yasushi Nakajima, Motohide Tamura, Daisuke Kuroda, Kenshi Yanagisawa, Teruyuki Hirano, Kiyoe Kawauchi, Masayuki Kuzuhara, Hiroshi Ohnuki, Takuya Suenaga, Yasuhiro H. Takahashi, Hideyuki Izumiura, Nobuyuki Kawai, Michitoshi Yoshida
We present 5 new transit light curves of GJ 1214b taken in BJHKs-bands. Two transits were observed in B-band using the Suprime-Cam and the FOCAS instruments onboard the Subaru 8.2m telescope, and one transit was done in JHKs-bands simultaneously with the SIRIUS camera on the IRSF 1.4m telescope. MCMC analyses show that the planet-to-star radius ratios are, Rp/Rs = 0.11651 \pm 0.00065 (B-band, Subaru/Suprime-Cam), Rp/Rs = 0.11601 \pm 0.00117 (B-band, Subaru/FOCAS), Rp/Rs = 0.11654 \pm 0.00080 (J-band, IRSF/SIRIUS), Rp/Rs = 0.11550 ^{+0.00142}_{-0.00153} (H-band, IRSF/SIRIUS), and Rp/Rs = 0.11547 \pm 0.00127 (Ks-band, IRSF/SIRIUS). The Subaru Suprime-Cam transit photometry shows a possible spot-crossing feature. Provided that this is truly a spot-crossing and if the feature is removed, the radius ratio rises to Rp/Rs = 0.11882 \pm 0.00070. Comparisons of the new transit depths and those from previous studies with the theoretical models by Howe & Burrows (2012) suggest that the high molecular weight atmosphere (e.g., 1% H$_2$O + 99% N$_2$) models are most likely, however, the low molecular weight (hydrogen dominated) atmospheres with extensive clouds are still not excluded. We also report a long-term monitoring of the stellar brightness variability of GJ 1214 observed with the MITSuME 50cm telescope in g'-, Rc-, and Ic-bands simultaneously. The monitoring was conducted for 32 nights spanning 78 nights in 2012, and we find a periodic brightness variation with a period of Ps = 44.3 \pm 1.2 days and semi-amplitudes of 2.1% \pm 0.4% in g'-band, 0.56% \pm 0.08% in Rc-band, and 0.32% \pm 0.04% in Ic-band.
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