Optical-to-Near-Infrared Simultaneous Observations for the Hot Uranus GJ3470b: A Hint for Cloud-free Atmosphere

Дата и время публикации : 2013-02-28T16:59:54Z

Авторы публикации и институты :
Akihiko Fukui
Norio Narita
Kenji Kurosaki
Masahiro Ikoma
Kenshi Yanagisawa
Daisuke Kuroda
Yasuhiro Shimizu
Yasuhiro H. Takahashi
Hiroshi Ohnuki
Masahiro Onitsuka
Teruyuki Hirano
Takuya Suenaga
Kiyoe Kawauchi
Shogo Nagayama
Kouji Ohta
Michitoshi Yoshida
Nobuyuki Kawai
Hideyuki Izumiura

Ссылка на журнал-издание: 2013, ApJ, 770, 95
Коментарии к cтатье: 14 pages, 8 figures, published in ApJ
Первичная категория: astro-ph.EP

Все категории : astro-ph.EP, astro-ph.SR

Краткий обзор статьи: We present optical (g’, R_c, and I_c) to near-infrared (J) simultaneous photometric observations for a primary transit of GJ3470b, a Uranus-mass transiting planet around a nearby M dwarf, by using the 50-cm MITSuME telescope and the 188-cm telescope, both at Okayama Astrophysical Observatory. From these data, we derive the planetary mass, radius, and density as 14.1 pm 1.3 M_earth, 4.32^{+0.21}_{-0.10} R_earth, and 0.94 pm 0.12 g cm^{-3}, respectively, thus confirming the low density that was reported by Demory et al. based on the Spitzer/IRAC 4.5-micron photometry (0.72^{+0.13}_{-0.12} g cm^{-3}). Although the planetary radius is about 10% smaller than that reported by Demory et al., this difference does not alter their conclusion that the planet possesses a hydrogen-rich envelope whose mass is approximately 10% of the planetary total mass. On the other hand, we find that the planet-to-star radius ratio (R_p/R_s) in the J band (0.07577^{+0.00072}_{-0.00075}) is smaller than that in the I_c (0.0802 pm 0.0013) and 4.5-micron (0.07806^{+0.00052}_{-0.00054}) bands by 5.9% pm 2.0% and 3.0% pm 1.2%, respectively. A plausible explanation for the differences is that the planetary atmospheric opacity varies with wavelength due to absorption and/or scattering by atmospheric molecules. Although the significance of the observed R_p/R_s variations is low, if confirmed, this fact would suggest that GJ3470b does not have a thick cloud layer in the atmosphere. This property would offer a wealth of opportunity for future transmission-spectroscopic observations of this planet to search for certain molecular features, such as H2O, CH4, and CO, without being prevented by clouds.

Category: Physics