88 research outputs found
The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment
We present the results of a spectroscopic analysis of rotational velocities
in 714 M dwarf stars observed by the SDSS III Apache Point Galactic Evolution
Experiment (APOGEE) survey. We use a template fitting technique to estimate
while simultaneously estimating , ,
and . We conservatively estimate that our detection limit is 8
km s. We compare our results to M dwarf rotation studies in the
literature based on both spectroscopic and photometric measurements. Like other
authors, we find an increase in the fraction of rapid rotators with decreasing
stellar temperature, exemplified by a sharp increase in rotation near the M
transition to fully convective stellar interiors, which is consistent with the
hypothesis that fully convective stars are unable to shed angular momentum as
efficiently as those with radiative cores. We compare a sample of targets
observed both by APOGEE and the MEarth transiting planet survey and find no
cases were the measured and rotation period are physically
inconsistent, requiring . We compare our spectroscopic results to
the fraction of rotators inferred from photometric surveys and find that while
the results are broadly consistent, the photometric surveys exhibit a smaller
fraction of rotators beyond the M transition by a factor of . We
discuss possible reasons for this discrepancy. Given our detection limit, our
results are consistent with a bi-modal distribution in rotation that is seen in
photometric surveys.Comment: 31 pages, 11 figures, 4 tables. Accepted for publication by A
The Metallicity of the CM Draconis System
The CM Draconis system comprises two eclipsing mid-M dwarfs of nearly equal mass in a 1.27-day orbit. This well-studied eclipsing binary has often been used for benchmark tests of stellar models, since its components are amongst the lowest mass stars with well-measured masses and radii (~ 1% relative precision). However, as with many other low-mass stars, non-magnetic models have been unable to match the observed radii and effective temperatures for CM Dra at the 5-10% level. To date, the uncertain metallicity of the system has complicated comparison of theoretical isochrones with observations. In this Letter, we use data from the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) to measure the metallicity of the system during primary and secondary eclipses, as well as out of eclipse, based on an empirical metallicity calibration in the H and K near-infrared (NIR) bands. We derive a [Fe/H] = -0.30 +- 0.12 that is consistent across all orbital phases. The determination of [Fe/H] for this system constrains a key dimension of parameter space when attempting to reconcile model isochrone predictions and observations
The APOGEE Spectroscopic Survey of Kepler Planet Hosts: Feasibility, Efficiency, and First Results
The Kepler mission has yielded a large number of planet candidates from among the Kepler Objects of Interest (KOIs), but spectroscopic follow-up of these relatively faint stars is a serious bottleneck in confirming and characterizing these systems. We present motivation and survey design for an ongoing project with the Sloan Digital Sky Survey III multiplexed Apache Point Observatory Galactic Evolution Experiment (APOGEE) near-infrared spectrograph to monitor hundreds of KOI host stars. We report some of our first results using representative targets from our sample, which include current planet candidates that we find to be false positives, as well as candidates listed as false positives that we do not find to be spectroscopic binaries. With this survey, KOI hosts are observed over ~20 epochs at a radial velocity (RV) precision of 100--200 m s-1. These observations can easily identify a majority of false positives caused by physically associated stellar or substellar binaries, and in many cases, fully characterize their orbits. We demonstrate that APOGEE is capable of achieving RV precision at the 100--200 m s-1 level over long time baselines, and that APOGEE's multiplexing capability makes it substantially more efficient at identifying false positives due to binaries than other single-object spectrographs working to confirm KOIs as planets. These APOGEE RVs enable ancillary science projects, such as studies of fundamental stellar astrophysics or intrinsically rare substellar companions. The coadded APOGEE spectra can be used to derive stellar properties (Teff, log g) and chemical abundances of over a dozen elements to probe correlations of planet properties with individual elemental abundances
The Epoch of Giant Planet Migration Planet Search Program. I. Near-Infrared Radial Velocity Jitter of Young Sun-like Stars
We present early results from the Epoch of Giant Planet Migration program, a
precise RV survey of over one hundred intermediate-age (20200 Myr) G
and K dwarfs with the Habitable-Zone Planet Finder spectrograph (HPF) at
McDonald Observatory's Hobby-Eberly Telescope (HET). The goals of this program
are to determine the timescale and dominant physical mechanism of giant planet
migration interior to the water ice line of Sun-like stars. Here, we summarize
results from the first 14 months of this program, with a focus on our custom RV
pipeline for HPF, a measurement of the intrinsic near-infrared RV activity of
young Solar analogs, and modeling the underlying population-level distribution
of stellar jitter. We demonstrate on-sky stability at the sub-2 m s
level for the K2 standard HD 3765 using a least-squares matching method to
extract precise RVs. Based on a subsample of 29 stars with at least three RV
measurements from our program, we find a median RMS level of 34 m s.
This is nearly a factor of 2 lower than the median RMS level in the optical of
60 m s for a comparison sample with similar ages and spectral types as
our targets. The observed near-infrared jitter measurements for this subsample
are well reproduced with a log-normal parent distribution with and
. Finally, by compiling RMS values from previous planet search
programs, we show that near-infrared jitter for G and K dwarfs generally decays
with age in a similar fashion to optical wavelengths, albeit with a shallower
slope and lower overall values for ages 1 Gyr
Long-term operation of a laser frequency comb with the Habitable Zone Planet Finder
Laser frequency combs are an ideal calibration source for precision astronomical spectrographs. We report on the demonstrated long term operation of a laser frequency comb that we designed and built as the primary calibrator for the Habitable Zone Planet Finder (HPF). The core technology of the comb is based on robust, polarization maintaining fiber coupled electro-optic modulators and broadband supercontinuum generation spanning 700-1600 nm in an efficient silicon nitride waveguide. The comb is continuously maintained on and ready to use, and since May 2018 the laser frequency comb has had a total uptime of 97%
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