Range Extension of the Paleback Darter

Surveys from 1990 through 1992 resulted in a significant range extension of the paleback darter, Etheostoma pallididorsum, which is endemic to the Ouachita Mountains. Prior to 1990, it had only been collected in the upper Caddo River drainage and a tributary to the Ouachita River below Lake Ouachita. The collections that extended this darter\u27s range occurred in tributaries of the Ouachita River above Lake Ouachita

Spitzer observations of the Hyades: Circumstellar debris disks at 625 Myr of age

We use the Spitzer Space Telescope to search for infrared excess at 24, 70, and 160 micron due to debris disks around a sample of 45 FGK-type members of the Hyades cluster. We supplement our observations with archival 24 and 70 micron Spitzer data of an additional 22 FGK-type and 11 A-type Hyades members in order to provide robust statistics on the incidence of debris disks at 625 Myr of age an era corresponding to the late heavy bombardment in the Solar System. We find that none of the 67 FGK-type stars in our sample show evidence for a debris disk, while 2 out of the 11 A-type stars do so. This difference in debris disk detection rate is likely to be due to a sensitivity bias in favor of early-type stars. The fractional disk luminosity, L_dust/L*, of the disks around the two A-type stars is ~4.0E-5, a level that is below the sensitivity of our observations toward the FGK-type stars. However, our sensitivity limits for FGK-type stars are able to exclude, at the 2-sigma level, frequencies higher than 12% and 5% of disks with L_dust/L* > 1.0E-4 and L_dust/L* > 5.0E-4, respectively. We also use our sensitivity limits and debris disk models to constrain the maximum mass of dust, as a function of distance from the stars, that could remain undetected around our targets.Comment: 33 pages, 11 figures, accepted by Ap

A Dedicated M-Dwarf Planet Search Using The Hobby-Eberly Telescope

We present first results of our planet search program using the 9.2 meter Hobby-Eberly Telescope (HET) at McDonald Observatory to detect planets around M-type dwarf stars via high-precision radial velocity (RV) measurements. Although more than 100 extrasolar planets have been found around solar-type stars of spectral type F to K, there is only a single M-dwarf (GJ 876, Delfosse et al. 1998; Marcy et al. 1998; Marcy et al. 2001) known to harbor a planetary system. With the current incompleteness of Doppler surveys with respect to M-dwarfs, it is not yet possible to decide whether this is due to a fundamental difference in the formation history and overall frequency of planetary systems in the low-mass regime of the Hertzsprung-Russell diagram, or simply an observational bias. Our HET M-dwarf survey plans to survey 100 M-dwarfs in the next 3 to 4 years with the primary goal to answer this question. Here we present the results from the first year of the survey which show that our routine RV-precision for M-dwarfs is 6 m/s. We found that GJ 864 and GJ 913 are binary systems with yet undetermined periods, while 5 out of 39 M-dwarfs reveal a high RV-scatter and represent candidates for having short-periodic planetary companions. For one of them, GJ 436 (rms = 20.6 m/s), we have already obtained follow-up observations but no periodic signal is present in the RV-data.Comment: 12 pages, 14 figures, accepted for publication in the Astronomical Journa

The Kepler Follow-up Observation Program

The Kepler Mission was launched on March 6, 2009 to perform a photometric survey of more than 100,000 dwarf stars to search for terrestrial-size planets with the transit technique. Follow-up observations of planetary candidates identified by detection of transit-like events are needed both for identification of astrophysical phenomena that mimic planetary transits and for characterization of the true planets and planetary systems found by Kepler. We have developed techniques and protocols for detection of false planetary transits and are currently conducting observations on 177 Kepler targets that have been selected for follow-up. A preliminary estimate indicates that between 24% and 62% of planetary candidates selected for follow-up will turn out to be true planets.Comment: 12 pages, submitted to the Astrophysical Journal Letter

Kepler Observations of Transiting Hot Compact Objects

Kepler photometry has revealed two unusual transiting companions orbiting an early A-star and a late B-star. In both cases the occultation of the companion is deeper than the transit. The occultation and transit with follow-up optical spectroscopy reveal a 9400 K early A-star, KOI-74 (KIC 6889235), with a companion in a 5.2 day orbit with a radius of 0.08 Rsun and a 10000 K late B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with a radius of 0.2 Rsun. We infer a temperature of 12250 K for KOI-74b and 13500 K for KOI-81b. We present 43 days of high duty cycle, 30 minute cadence photometry, with models demonstrating the intriguing properties of these object, and speculate on their nature.Comment: 12 pages, 3 figures, submitted to ApJL (updated to correct KOI74 lightcurve

Searching for Planets in the Hyades. I. The Keck Radial Velocity Survey

We describe a high-precision radial velocity search for jovian-mass companions to main sequence stars in the Hyades star cluster. The Hyades provides an extremely well controlled sample of stars of the same age, the same metallicity, and a common birth and early dynamical environment. This sample allows us to explore the dependence of the process of planet formation on only a single independent variable: the stellar mass. In this paper we describe the survey and summarize results for the first five years.Comment: 8 pages, 3 figures; To appear in the July 2002 issue of The Astronomical Journa

The Extrasolar Planet epsilon Eridani b - Orbit and Mass

Hubble Space Telescope observations of the nearby (3.22 pc), K2 V star epsilon Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, \eps b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the \HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8 -- 2006.3. We obtain a perturbation period, P = 6.85 +/- 0.03 yr, semi-major axis, alpha =1.88 +/- 0.20 mas, and inclination i = 30.1 +/- 3.8 degrees. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M_* = 0.83 M_{\sun}, we obtain a companion mass M = 1.55 +/- 0.24 M_{Jup}. Given the relatively young age of epsilon Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct imaging attempts. We predict the next periastron at 2007.3 with a total separation, rho = 0.3 arcsec at position angle, p.a. = -27 degrees. Orbit orientation and geometry dictate that epsilon Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly responsible for one feature of the dust morphology, the inner cavity