The M dwarf GJ 436 and its Neptune-mass planet

H. L. Maness, G. W. Marcy, E. B. Ford, P. H. Hauschildt, A. T. Shreve, G. B. Basri, R. P. Butler, S. S. Vogt

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Abstract

We determine stellar parameters for the M dwarf GJ 436, which hosts a Neptune-mass planet. We employ primarily spectral modeling at low and high resolution, examining the agreement between model and observed optical spectra of five comparison stars of type M0-M3. The modeling of high-resolution optical spectra suffers from uncertainties in TiO transitions, affecting the predicted strengths of both atomic and molecular lines in M dwarfs. The determination of Teff, gravity, and metallicity from optical spectra remains at ∼10%. As molecules provide opacity both in lines and as an effective continuum, determining molecular transition parameters remains a challenge facing models such as the PHOENIX series, best verified with high resolution and spectro-photometric spectra. Our analysis of GJ 436 yields an effective temperature of Teff = 3350 ± 300 K and a mass of 0.44 M . New Doppler measurements of GJ 436 with a precision of 3 m s-1 taken during 6 years improve the Keplerian model of the planet, giving it a minimum mass M sin i = 0.0713MJup = 22.6 M , period P = 2.6439 days, and eccentricity e = 0.16 ±0.02. The noncircular orbit contrasts with the tidally circularized orbits of all close-in exoplanets, implying either ongoing pumping of eccentricity by a more distant companion, or a higher Q value for this low-mass planet. The velocities indeed reveal a long-term trend, indicating a possible distant companion.

Original languageEnglish (US)
Pages (from-to)90-101
Number of pages12
JournalPublications of the Astronomical Society of the Pacific
Volume119
Issue number851
DOIs
StatePublished - Jan 1 2007

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All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Maness, H. L., Marcy, G. W., Ford, E. B., Hauschildt, P. H., Shreve, A. T., Basri, G. B., Butler, R. P., & Vogt, S. S. (2007). The M dwarf GJ 436 and its Neptune-mass planet. Publications of the Astronomical Society of the Pacific, 119(851), 90-101. https://doi.org/10.1086/510689