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 language | English (US) |
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Pages (from-to) | 90-101 |
Number of pages | 12 |
Journal | Publications of the Astronomical Society of the Pacific |
Volume | 119 |
Issue number | 851 |
DOIs | |
State | Published - Jan 2007 |
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science