Site Map
Contacts
Follow us on Facebook Follow us on Twitter YouTube channel
Centro de Astrofísica da Universidade do Porto

Spitzer observations of GJ 3470 b: A very low-density neptune-size planet orbiting a metal-rich m dwarf

B.-O. Demory, G. Torres, V. Neves, L. Rogers, M. Gillon, E. Horch, P. Sullivan, X. Bonfils, X. Delfosse, T. Forveille, C. Lovis, M. Mayor, N. C. Santos, S. Seager, B. Smalley, S. Udry

Abstract
We present Spitzer/IRAC 4.5µm transit photometry of GJ 3470 b, a Neptune-size planet orbiting an M1.5 dwarf star with a 3.3 day period recently discovered in the course of the HARPS M-dwarf survey. We refine the stellar parameters by employing purely empirical mass–luminosity and surface brightness relations constrained by our updated value for the mean stellar density, and additional information from new near-infrared spectroscopic observations.We derive a stellar mass of M* = 0.539+0.047-0.043 M and a radius of R* = 0.568+0.037-0.031 R. We determine the host star of GJ 3470 b to bemetal-rich, with ametallicity of [Fe/H] = +0.20±0.10 and an effective temperature of Teff = 3600±100 K. The revised stellar parameters yield a planetary radius Rp = 4.83+0.22-0.21 R that is 13% larger than the value previously reported in the literature. We find a planetary mass Mp = 13.9+1.5-1.4 M that translates to a very low planetary density, ρp = 0.72+0.13-0.12 g cm-3, which is 33% smaller than the original value. With a mean density half of that of GJ 436 b, GJ 3470 b is an example of a very low-density low-mass planet, similar to Kepler-11 d, Kepler-11 e, and Kepler-18 c, but orbiting a much brighter nearby star that is more conducive to follow-up studies.

Keywords
planetary systems – stars: individual (GJ 3470) – techniques: photometric – techniques: spectroscopic

The Astrophysical Journal
Volume 768, Page 154_1
May 2013

>> PDF>> ADS>> DOI

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website