1,105 research outputs found
M Dwarf Metallicities and Giant Planet Occurrence: Ironing Out Uncertainties and Systematics
Comparisons between the planet populations around solar-type stars and those
orbiting M dwarfs shed light on the possible dependence of planet formation and
evolution on stellar mass. However, such analyses must control for other
factors, i.e. metallicity, a stellar parameter which strongly influences the
occurrence of gas giant planets. We obtained infrared spectra of 121 M dwarfs
stars monitored by the California Planet Search (CPS) and determined
metallicities with an accuracy of 0.08 dex. The mean and standard deviation of
the sample is -0.05 and 0.20 dex, respectively. We parameterized the
metallicity dependence of the occurrence of giant planets on orbits with period
less than 2 yr around solar-type stars and applied this to our M dwarf sample
to estimate the expected number of giant planets. The number of detected
planets (3) is lower than the predicted number (6.4) but the difference is not
very significant (12% probability of finding as many or fewer planets). The
three M dwarf planet hosts are not especially metal rich and the most likely
value of the power-law index relating planet occurrence to metallicity is 1.06
dex per dex for M dwarfs compared to 1.80 for solar-type stars; this
difference, however, is comparable to uncertainties. Giant planet occurrence
around both types of stars allows, but does not necessarily require, mass
dependence of dex per dex. The actual planet-mass-metallicity relation
may be complex and elucidating it will require larger surveys like those to be
conducted by ground-based infrared spectrographs and the Gaia space astrometry
mission.Comment: Accepted to The Astrophysical Journa
A Survey of 10-Micron Silicate Emission from Dust around Young Sun-Like Stars
We obtained low resolution (R = 100) mid-infrared (8-13 micron wavelengths)
spectra of 8 nearby young main sequence stars with the Keck 1 telescope and
Long-Wavelength Spectrometer (LWS) to search for 10 micron silicate (Si-O
stretch) emission from circumstellar dust. No stars exhibited readily apparent
emission: Spectra were then analyzed by least-squares fitting of a template
based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to
constrain the level of silicate emission to a threshold ten times below what
was previously possible from space. We found one star, HD 17925, with a
spectrum statistically different from its calibrator and consistent with a
silicate emission peak of 7% of the photosphere at a wavelength of 10 microns.
Excess emission at 60 microns from this star has already been reported.Comment: 19 total pages, 5 Postscript figures, 2 tables, Late
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