A Spectroscopic Binary at the M/L Transition

We report the discovery of a single-lined spectroscopic binary with an Ultra Cool Dwarf (UCD) primary with a spectral type between M8 and L0.5. This system was discovered during the course of an ongoing survey to monitor L dwarfs for radial velocity variations and is the first known small separation (a<1 AU) spectroscopic binary among dwarfs at the M/L transition. Based on radial-velocity measurements with a typical precision of 300 m/s we estimate the orbital parameters of this system to be P=246.73+/-0.49 d, a1 sin(i)=0.159+/-0.003 AU, M2 sin(i)=0.2062 (M1+M2)^(2/3)+/-0.0034 M_{\sun}. Assuming a primary mass of M1=0.08M_{\sun} (based on spectral type), we estimate the secondary minimum mass to be M2 sin(i)=0.054 M_{\sun}. With future photometric, spectroscopic, and interferometric observations it may be possible to determine the dynamical masses of both components directly, making this system one of the best characterized UCD binaries known.Comment: 11 pages, 2 figures. Accepted for publication in ApJ Letter

The Evolution of L and T Dwarfs in Color-Magnitude Diagrams

We present new evolution sequences for very low mass stars, brown dwarfs and giant planets and use them to explore a variety of influences on the evolution of these objects. We compare our results with previous work and discuss the causes of the differences and argue for the importance of the surface boundary condition provided by atmosphere models including clouds. The L- to T-type ultracool dwarf transition can be accommodated within the Ackerman & Marley (2001) cloud model by varying the cloud sedimentation parameter. We develop a simple model for the evolution across the L/T transition. By combining the evolution calculation and our atmosphere models, we generate colors and magnitudes of synthetic populations of ultracool dwarfs in the field and in galactic clusters. We focus on near infrared color- magnitude diagrams (CMDs) and on the nature of the ``second parameter'' that is responsible for the scatter of colors along the Teff sequence. Variations in metallicity and cloud parameters, unresolved binaries and possibly a relatively young population all play a role in defining the spread of brown dwarfs along the cooling sequence. We find that the transition from cloudy L dwarfs to cloudless T dwarfs slows down the evolution and causes a pile up of substellar objects in the transition region, in contradiction with previous studies. We apply the same model to the Pleiades brown dwarf sequence. Taken at face value, the Pleiades data suggest that the L/T transition occurs at lower Teff for lower gravity objects. The simulated populations of brown dwarfs also reveal that the phase of deuterium burning produces a distinctive feature in CMDs that should be detectable in ~50-100 Myr old clusters.Comment: Accepted for publication in the ApJ. 52 pages including 20 figure

Comparing key compositional indicators in Jupiter with those in extra-solar giant planets

Spectroscopic transiting observations of the atmospheres of hot Jupiters around other stars, first with Hubble Space Telescope and then Spitzer, opened the door to compositional studies of exoplanets. The James Webb Space Telescope will provide such a profound improvement in signal-to-noise ratio that it will enable detailed analysis of molecular abundances, including but not limited to determining abundances of all the major carbon- and oxygen-bearing species in hot Jupiter atmospheres. This will allow determination of the carbon-to-oxygen ratio, an essential number for planet formation models and a motivating goal of the Juno mission currently around JupiterComment: Submitted to the Astro2020 Decadal Survey as a white paper; thematic areas "Planetary Systems" and "Star and Planet Formation

Multiepoch Radial Velocity Observations of L Dwarfs

We report on the development of a technique for precise radial-velocity measurements of cool stars and brown dwarfs in the near infrared. Our technique is analogous to the Iodine (I2) absorption cell method that has proven so successful in the optical regime. We rely on telluric CH4 absorption features to serve as a wavelength reference, relative to which we measure Doppler shifts of the CO and H2O features in the spectra of our targets. We apply this technique to high-resolution (R~50,000) spectra near 2.3 micron of nine L dwarfs taken with the Phoenix instrument on Gemini-South and demonstrate a typical precision of 300 m/s. We conduct simulations to estimate our expected precision and show our performance is currently limited by the signal-to-noise of our data. We present estimates of the rotational velocities and systemic velocities of our targets. With our current data, we are sensitive to companions with M sin i > 2MJ in orbits with periods less than three days. We identify no companions in our current data set. Future observations with improved signal-to-noise should result in radial-velocity precision of 100 m/s for L dwarfs.Comment: Accepted for publication in ApJ, 24 pages, 7 figure

A Comparison of the Efficacy of an Ultra-Low Volume Applicator for Liquid-Applied Silage Inoculants with That of a Conventional Applicator

Liquid-applied silage inoculants are normally sprayed onto forages cut for ensiling at application rates from 1 to 3 l/t. Applicator tanks can require frequent re-filling, especially with large self-propelled forage harvesters having harvest rates in excess of 1000 t/d. This can be an issue for fields remote from the farm, for areas with restricted water availability and for contractors paid by the area harvested. This study was conducted to assess the efficacy of inoculant distribution on the crop using a simple, ultra-low volume (ULV) applicator compared with a conventional liquid-applied silage inoculant applicator

Comparison of the Goryachkin Theory to Soil Flow on a Sweep

The Goryachkin trihedral wedge theories describe soil flow over a surface resembling the wing of a sweep. The current study tested the Goryachkin crushing and lifting theories’ prediction of soil flow across a sweep by comparing with measurements from observed soil flow. Treatments included sweeps with three different rake angles (13.5, 16, and 44°) operated at three speeds (5, 7, and 9 km/h) and at two depths (50 and 100 mm). Flow direction was determined from scratch marks on the sweep surface

Methods for measuring soil velocities caused by a sweep

A field experiment was conducted to measure surface soil velocity and to determine the relation between soil aggregate velocities at the tool surface and at the soil surface. A technique incorporating use of both a video camcorder and wood blocks was developed to measure surface soil velocity. Soil velocity direction at the tool surface was measured from scratch marks on the tool. Velocity measurements were made for three sweeps with different rake angles operated at three speeds and two depths. Surface soil moved in either of two modes: V-flow (upward and laterally in the shape of one leg of the letter V) or snowplow (initially moving upward and subsequently being buried in a wave of soil). Surface soil velocities were uncorrelated with velocities on the tool surface, indicating that soil flow paths over the sweep were not parallel. The ratio of vertical to lateral soil flow at the tool surface increased with larger rake angle and was greater than the ratio at the soil surface. At the soil surface, vertical velocity was greater near the nose than near the wing tip and velocity parallel to the travel direction increased with increased speed and rake angle