Gliese 581g as a scaled-up version of Earth: atmospheric circulation simulations

We use 3D simulations to study the atmospheric circulation on the first Earth-sized exoplanet discovered in the habitable zone of an M star. We treat Gliese 581g as a scaled-up version of Earth by considering increased values for the exoplanetary radius and surface gravity, while retaining terrestrial values for parameters which are unconstrained by current observations. We examine the long-term, global temperature and wind maps near the surface of the exoplanet - the climate. The specific locations for habitability on Gliese 581g depend on whether the exoplanet is tidally locked and how fast radiative cooling occurs on a global scale. Independent of whether the existence of Gliese 581g is confirmed, our study highlights the use of general circulation models to quantify the atmospheric circulation on potentially habitable, Earth-sized exoplanets, which will be the prime targets of exoplanet discovery and characterization campaigns in the next decad

The Physical Conditions of Intermediate Redshift MgII Absorbing Clouds from Voigt Profile Analysis

[Slightly Abridged] We present a detailed statistical analysis of the column densities, N, and Doppler parameters, b, of MgII absorbing clouds at redshifts 0.4<z<1.2. We use the HIRES/Keck data and Voigt profile (VP) fitting results presented by Churchill & Vogt (Paper I). The sample is comprised of 175 clouds from 23 systems along 18 quasar lines of sight. In order to understand whether inferred conditions could be "false", we performed extensive simulations of our VP analyses. In brief, we find: (1) N(FeII) and N(MgII) are correlated at the 9-sigma level. There is a 5-sigma anti-correlation between N(MgI)/N(MgII) and N(MgII). (2) Power-law fits to the distributions of N(MgII), N(FeII), and N(MgI) yielded power-law slopes of -1.6, -1.7, and -2.0. (3) The modes of the Doppler parameter distributions were ~5 km/s for MgII and FeII and ~7 km/s for MgI. The clouds are consistent with being thermally broadened, with temperatures in the 30-40,000K range. (4) A two-component Gaussian model to the velocity two-point correlation function yielded velocity dispersions of 54 km/s and 166 km/s. The narrow component has roughly twice the amplitude of the broader component. The width and amplitude of the broader component decreases as equivalent width increases. (5) From photoionization models we find that the column density ratios are most consistent with photoionization by the extragalactic background, as opposed to stars. Based upon N(MgI)/N(MgII), it appears that at least two-phase ionization models are required to explain the data.Comment: Accepted to the Astronomical Journal (January 2003

Sub-Saturn Planet Candidates to HD 16141 and HD 46375

Precision Doppler measurements from the Keck/HIRES spectrometer reveal periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD 16141 (G5 IV) has a period of 75.8 d and a velocity amplitude of 11 m/s, yielding a companion having Msini = 0.22 Mjup and a semimajor axis, a = 0.35 AU. HD 46375 (K1 IV/V) has a period of 3.024 d and a velocity amplitude of 35 m/s, yielding a companion with Msini=0.25 Mjup, a semimajor axis of a = 0.041 AU, and an eccentricity of 0.04 (consistent with zero). These companions contribute to the rising planet mass function toward lower masses.Comment: 4 Figure

The Lick-Carnegie Exoplanet Survey: A Saturn-Mass Planet in the Habitable Zone of the Nearby M4V Star HIP 57050

Precision radial velocities from Keck/HIRES reveal a Saturn-mass planet orbiting the nearby M4V star HIP 57050. The planet has a minimum mass of 0.3 Jupiter-mass, an orbital period of 41.4 days, and an orbital eccentricity of 0.31. V-band photometry reveals a clear stellar rotation signature of the host star with a period of 98 days, well separated from the period of the radial velocity variations and reinforcing a Keplerian origin for the observed velocity variations. The orbital period of this planet corresponds to an orbit in the habitable zone of HIP 57050, with an expected planetary temperature of approximately 230 K. The star has a metallicity of [Fe/H] = 0.32+/-0.06 dex, of order twice solar and among the highest metallicity stars in the immediate solar neighborhood. This newly discovered planet provides further support that the well-known planet-metallicity correlation for F, G, and K stars also extends down into the M-dwarf regime. The a priori geometric probability for transits of this planet is only about 1%. However, the expected eclipse depth is ~7%, considerably larger than that yet observed for any transiting planet. Though long on the odds, such a transit is worth pursuing as it would allow for high quality studies of the atmosphere via transmission spectroscopy with HST. At the expected planetary effective temperature, the atmosphere may contain water clouds.Comment: 20 pages, 5 figures, 3 tables, to appear in the May 20 issue of ApJ

On the Spatial and Kinematic Distributions of Mg II Absorbing Gas in <z>=0.7 Galaxies

(Abridged) We present HIRES/Keck spectra having resolution 6 km/s of Mg II 2796 absorption profiles which arise in the gas associated with 15 identified galaxies over the redshift range 0.5 < z < 0.9. Using non-parametric rank correlation tests, we searched for correlations of the absorption strengths, saturation, and line-of-sight kinematics with the galaxy redshifts, rest frame B and K luminosities, rest colors, and impact parameters D. We found no correlations at the 2.5-sigma level between these properties. Of primary significance is the fact that the QSO-galaxy impact parameter apparently does not provide the primary distinguishing factor by which absorption properties can be characterized. The galaxy absorption properties exhibit a large scatter, which, we argue, is suggestive of a picture in which the gas arises from a variety of on-going dynamical events. Inferences from our study include: (1) The spatial distribution of absorbing gas in galaxies does not appear to follow a simple galactocentric functional dependence. (2) A single systematic kinematic model apparently cannot describe the observed velocity spreads in the absorbing gas. It is more that a heterogeneous population of sub-galaxy scale structures are giving rise to the observed cloud velocities. (3) The absorbing gas spatial distribution and kinematics may depend upon gas producing events and mechanisms that are recent to the epoch at which the absorption is observed. These distributions likely change over a few Gyr timescale. Based upon these inferences, we note that any evolution in the absorption gas properties over a larger redshift range should be directly quantifiable from a larger dataset of high-resolution absorption profiles.Comment: uuencoded: 22 pages, AASTeX file, 5 encapsulated PostScript figures; Accepted for publication in The Astrophysical Journal; Also available for pick-up at http://www.ucolick.org/~cwc/qso/abstract.htm

The Lick-Carnegie Survey: A New Two-Planet System Around the Star HD 207832

Keck/HIRES precision radial velocities of HD 207832 indicate the presence of two Jovian-type planetary companions in Keplerian orbits around this G star. The planets have minimum masses of 0.56 and 0.73 Jupiter-masses with orbital periods of ~162 and ~1156 days, and eccentricities of 0.13 and 0.27, respectively. Stromgren b and y photometry reveals a clear stellar rotation signature of the host star with a period of 17.8 days, well separated from the period of the radial velocity variations, reinforcing their Keplerian origin. The values of the semimajor axes of the planets suggest that these objects have migrated from the region of giant planet formation to closer orbits. In order to examine the possibility of the existence of additional (small) planets in the system, we studied the orbital stability of hypothetical terrestrial-sized objects in the region between the two planets and interior to the orbit of the inner body. Results indicated that stable orbits exist only in a small region interior to planet b. However, the current observational data offer no evidence for the existence of additional objects in this system.Comment: 23 pages, 4 figures, 5 tables, accepted for publication in Ap