THE NIRSPEC ULTRACOOL DWARF RADIAL VELOCITY SURVEY

By C. Blake, D. Charbonneau, Russel J. White. 2010

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We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs. Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity (RV) measurements over a period of six years of a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets has been observed on three or more epochs. We rely on telluric CH4 absorption features in Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure RVs and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate an RV precision of 50 m s−1 and for slowly rotating L dwarfs we achieve a typical RV precision of approximately 200 m s−1. This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a < 2 AU). We present an orbital solution for the subdwarf binary LSR1610 − 0040 as well as an improved solution for the M/T binary 2M0320 − 04. We compare the distribution of our observed values for the projected rotational velocities, Vsin i, to those in the literature and find that our sample contains examples of slowly rotating mid-L dwarfs, which have not been seen in other surveys. We also combine our RV measurements with distance estimates and proper motions from the literature and estimate the dispersion of the space velocities of the objects in our sample. Using a kinematic age estimate, we conclude that our UCDs have an age of 5.0+0.7−0.6 Gyr, similar to that of nearby sun-like stars. We simulate the efficiency with which we detect spectroscopic binaries and find that the rate of tight (a < 1 AU) binaries in our sample is 2.5+8.6−1.6%, consistent with recent estimates in the literature of a tight binary fraction of 3%–4%.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/186182e82be4a9c7b5ce71420af594ac00071a99

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WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS (2014, background): “The 10 h upper limit was partly motivated by the lack of v sin i < 10 km s−1 measurements among L and T dwarfs (e.g., Bailer-Jones 2004; Blake et al. 2010), which imply spin periods of <12 h for one Jupiter-radius objects.”
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, methodology): “Based on a parallax-free analysis using an radial velocity of 9.8 ± 0.8 km s−1 (Blake et al. 2010; Kirkpatrick et al. 2010) and an assumption of low gravity, Gagné et al. (2014b) assign this young field membership (>99.9”
BANYAN. VII. A NEW POPULATION OF YOUNG SUBSTELLAR CANDIDATE MEMBERS OF NEARBY MOVING GROUPS FROM THE BASS SURVEY (2015, methodology): “The RV of −9.8±0.1 km s−1 measured by Blake et al. (2010) does not match the predicted RV of −18.9± 1.5 km s−1 for membership to ABDMG.”
THE EXTREMELY RED, YOUNG L DWARF PSO J318.5338−22.8603: A FREE-FLOATING PLANETARY-MASS ANALOG TO DIRECTLY IMAGED YOUNG GAS-GIANT PLANETS (2013, background): “Published RVs (Blake et al. 2010; Seifahrt et al. 2010; Rice et al. 2010; Shkolnik et al. 2012) find that low-gravity late-M and L dwarfs reside in the range of [−20, +25] km s−1, with the smaller RV range compared to field objects being expected given the young ages.”
Observations of Cool-Star Magnetic Fields (2012, background): “Evidence for the latter is found in observations of high rotation velocities interpreted as very weak angular momentum loss in very-low mass stars and brown dwarfs (Reiners and Basri, 2008; Blake et al., 2010).”
State of the Field: Extreme Precision Radial Velocities (2016, background): “Poorly fitted lines are masked out or rejected (Bean et al. 2010; Seifahrt et al. 2010; Blake et al. 2010).”
NEAR-INFRARED METALLICITIES, RADIAL VELOCITIES, AND SPECTRAL TYPES FOR 447 NEARBY M DWARFS (2013, methodology): “Blake et al. (2010) were able to find a single linear scaling between airmass andτ using a large sample of A0V stars.”
BANYAN. II. VERY LOW MASS AND SUBSTELLAR CANDIDATE MEMBERS TO NEARBY, YOUNG KINEMATIC GROUPS WITH PREVIOUSLY KNOWN SIGNS OF YOUTH (2013, background): “Blake et al. (2010) measured a radial velocity of 11.9± 0.2 km s−1 for this object.”