CaltechAUTHORS
Published May 10, 2013 | Version Published
Journal Article Open

Spitzer Observations of GJ 3470 b: A Very Low-density Neptune-size Planet Orbiting a Metal-rich M Dwarf

Creators

  • 1. ROR icon Massachusetts Institute of Technology
  • 2. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 3. ROR icon University of Porto
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon University of Liège
  • 6. ROR icon Southern Connecticut State University
  • 7. ROR icon Kitt Peak National Observatory
  • 8. ROR icon University of Geneva
  • 9. ROR icon Keele University

Abstract

We present Spitzer/IRAC 4.5 μm 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 be metal-rich, with a metallicity of [Fe/H] = +0.20 ± 0.10 and an effective temperature of T_(eff) = 3600 ± 100 K. The revised stellar parameters yield a planetary radius R_p = 4.83_(-0.21)^(+0.22)R_⊕ that is 13% larger than the value previously reported in the literature. We find a planetary mass M_p = 13.9^(+1.5)_(-1.4)M_⊕ that translates to a very low planetary density, P_p= 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.

Additional Information

© 2013 American Astronomical Society. Received 2013 January 28; accepted 2013 March 4; published 2013 April 25. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. We thank Zach Berta and Elisabeth Newton for helpful discussions regarding near-IR M-dwarf spectral characterization. We are grateful to Rob Simcoe, Paul Schechter, Elisabeth Adams, and David Ciardi for their help in obtaining the ground-based observations presented in this paper. We thank the anonymous referee for a report that improved the paper. We thank the Spitzer Science Center staff, and especially Nancy Silbermann, for the efficient scheduling of our observations. We also wish to thank the staff of the Magellan Telescopes and Las Campanas Observatory for their assistance in obtaining the FIRE observations. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatory. Support for LAR was provided by NASA through Hubble Fellowship grant HF-51313.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. This work was supported by the European Research Council/European Community under the FP7 through Starting Grant agreement number 239953 and by Fundação para a Ciência e a Tecnologia (FCT) in the form of grants PTDC/CTE-AST/098528/2008 and PTDC/CTE-AST/ 120251/2010. The financial support from the "Programme National de Planétologie" (PNP) of CNRS/INSU, France, is gratefully acknowledged. G.T. acknowledges partial support for this work through NSF grant AST-1007992. V.N. also acknowledges the support from the FCT in the form of the fellowship SFRH/BD/60688/2009. M.G. is Research Associate at the Belgian Fonds National de la Recherche Scientifique (FNRS). Facilities: Spitzer, Magellan:Baade, WIYN

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Additional details

Identifiers

Eprint ID
38793
Resolver ID
CaltechAUTHORS:20130604-154141597

Funding

NASA/JPL/Caltech
NASA Hubble Fellowship
HF-51313.01-A
NASA
NAS 5-26555
European Research Council (ERC)
239953
Fundação para a Ciência e a Tecnologia (FCT)
PTDC/CTE-AST/098528/2008
Fundação para a Ciência e a Tecnologia (FCT)
PTDC/CTE-AST/ 120251/2010
Programme National de Planétologie (PNP)
NSF
AST-1007992
Fundação para a Ciência e a Tecnologia (FCT)
SFRH/BD/60688/2009
Fonds National de la Recherche Scientifique (FNRS)
Centre National de la Recherche Scientifique (CNRS)
Institut National de Physique Nucléaire et de Physique des Particules (IN2P3)

Dates

Created
2013-06-05
Created from EPrint's datestamp field
Updated
2021-11-09
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