arXiv subjects

Michael Bottom

Publications and source records attributed to Michael Bottom.

57 records · Page 4Linked to original sources

arXiv2013

Using High-Resolution Optical Spectra to Measure Intrinsic Properties of Low-Mass Stars: New Properties for KOI-314 and GJ 3470

We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby dwarfs spanning K7 to M4, taken with Keck/HIRES as part of the California Planet Search. We identify several spectral regions in the visible (370 - 800 nm) that are sensitive to the stellar luminosity and metallicity. We use these regions to develop a spectral calibration method to measure the mass, metallicity, and distance of low-mass stars, without the requirement of geometric parallaxes. Testing our method on a sample of nearby M dwarfs we show that we can reproduce stellar masses to about 8 - 10%, metallicity to ~0.15 dex and distance to 11%. We were able to make use of HIRES spectra obtained as part of the radial velocity monitoring of the star KOI-314 to derive a new mass estimate of 0.57 +/- 0.05 Msun, a radius of 0.54 +/- 0.05 Rsun, a metallicity, [Fe/H], of -0.28 +/- 0.10 and a distance of 66.5 +/- 7.3 pc. Using HARPS archival data and combining our spectral method with constraints from transit observations, we are also able to derive the stellar properties of GJ3470, a transiting planet hosting M dwarf. We estimate a mass of 0.53 +/- 0.05 Msun, a radius of 0.50 +/- 0.05 Rsun, a metallicity, [Fe/H] = 0.12 +/- 0.12 and a distance of 29.9_{-3.4}^{+3.7} pc.

astro-ph.SR↗

arXiv2013

Optimizing Doppler Surveys for Planet Yield

One of the most promising methods of discovering nearby, low-mass planets in the habitable zones of stars is the precision radial velocity technique. However, there are many challenges that must be overcome to efficiently detect low-amplitude Doppler signals. This is both due to the required instrumental sensitivity and the limited amount of observing time. In this paper, we examine statistical and instrumental effects on precision radial velocity detection of extrasolar planets, an approach by which we maximize the planet yield in a fixed amount of observing time available on a given telescope. From this perspective, we show that G and K dwarfs observed at 400-600 nm are the best targets for surveys complete down to a given planet mass and out to a specified orbital period. Overall we find that M dwarfs observed at 700-800 nm are the best targets for habitable-zone planets, particularly when including the effects of systematic noise floors. Also, we give quantitative specifications of the instrumental stability necessary to achieve the required velocity precision.

astro-ph.EP↗

arXiv2012

Characterizing the Cool KOIs III. KOI-961: A Small Star with Large Proper Motion and Three Small Planets

We present the characterization of the star KOI 961, an M dwarf with transit signals indicative of three short-period exoplanets, originally discovered by the Kepler Mission. We proceed by comparing KOI 961 to Barnard's Star, a nearby, well-characterized mid-M dwarf. By comparing colors, optical and near-infrared spectra, we find remarkable agreement between the two, implying similar effective temperatures and metallicities. Both are metal-poor compared to the Solar neighborhood, have low projected rotational velocity, high absolute radial velocity, large proper motion and no quiescent H-alpha emission--all of which is consistent with being old M dwarfs. We combine empirical measurements of Barnard's Star and expectations from evolutionary isochrones to estimate KOI 961's mass (0.13 +/- 0.05 Msun), radius (0.17 +/- 0.04 Rsun) and luminosity (2.40 x 10^(-3.0 +/- 0.3) Lsun). We calculate KOI 961's distance (38.7 +/- 6.3 pc) and space motions, which, like Barnard's Star, are consistent with a high scale-height population in the Milky Way. We perform an independent multi-transit fit to the public Kepler light curve and significantly revise the transit parameters for the three planets. We calculate the false-positive probability for each planet-candidate, and find a less than 1% chance that any one of the transiting signals is due to a background or hierarchical eclipsing binary, validating the planetary nature of the transits. The best-fitting radii for all three planets are less than 1 Rearth, with KOI 961.03 being Mars-sized (Rp = 0.57 +/- 0.18 Rearth), and they represent some of the smallest exoplanets detected to date.

astro-ph.SR↗