An intriguing correlation between the masses and periods of the transiting planets

We point out an intriguing relation between the masses of the transiting planets and their orbital periods. For the six currently known transiting planets, the data are consistent with a decreasing linear relation. The other known short-period planets, discovered through radial-velocity techniques, seem to agree with this relation. We briefly speculate about a tentative physical model to explain such a dependence.Comment: 4 pages, 2 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Spectroscopic Binary Mass Determination using Relativity

High-precision radial-velocity techniques, which enabled the detection of extrasolar planets are now sensitive to relativistic effects in the data of spectroscopic binary stars (SBs). We show how these effects can be used to derive the absolute masses of the components of eclipsing single-lined SBs and double-lined SBs from Doppler measurements alone. High-precision stellar spectroscopy can thus substantially increase the number of measured stellar masses, thereby improving the mass-radius and mass-luminosity calibrations.Comment: 10 pages, 1 figure, accepted for publication by the Astrophysical Journal Letter

Interstellar medium oxygen abundances of dwarf irregular galaxies in Centaurus A and nearby groups

We present results of optical spectroscopy of 35 H ii regions from eight dwarf galaxies in the Centaurus A (Cen A) group. [O iii]λ4363 is detected in ESO272−G025 and ESO324−G024, and direct oxygen abundances of 12 + log (O/H) = 7.76 ± 0.09 and 7.94 ± 0.11 are derived, respectively. For the remaining galaxies, abundances are derived using common bright-line methods. To compare the influence of group environments on dwarf galaxies, we have also gathered data for additional dwarf irregular galaxies from the Cen A and the Sculptor groups from the literature. We have examined possible relationships between oxygen abundance, gas fraction, effective chemical yield and tidal indices. Despite large positive tidal indices for a number of Cen A dwarfs in the present sample, there is no clear separation between galaxies with positive tidal indices and galaxies with negative tidal indices in the luminosity-metallicity, metallicity-gas fraction and metallicity-tidal index diagrams. The H i surface mass density decreases with increasing positive tidal index, which is expected in strong tidal encounters. There are no strong trends between oxygen abundances or yields and projected distances of galaxies within their respective groups. We also present spectra for 13 H ii regions in three nearby dwarf irregular galaxies: DDO 47, NGC 3109 and Sextans B. For DDO 47, the [O iii]λ4363 oxygen abundance (7.92 ± 0.06) for the H ii region SHK91 No. 18 agrees with recently published values. For Sextans B, the [O iii]λ4363 oxygen abundance (7.80 ± 0.13) for H ii region SHK91 No. 5 agrees with published work in which O+ abundances were determined entirely from [O ii]λλ7320, 7330 fluxe

Studies of multiple stellar systems - IV. The triple-lined spectroscopic system Gliese 644

We present a radial-velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.9655 and 627 days. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M_A = 0.410 +/- 0.028 (6.9%), M_Ba = 0.336 +/- 0.016 (4.7%), and $M_Bb = 0.304 +/- 0.014 (4.7%) M_solar. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass-luminosity relation near the bottom of the Main Sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common-proper-motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration.Comment: 17 pages, 9 figures, Accepted for publication in MNRA

Orbital migration and the frequency of giant planet formation

We present a statistical study of the post-formation migration of giant planets in a range of initial disk conditions. For given initial conditions we model the evolution of giant planet orbits under the influence of disk, stellar, and mass loss torques. We determine the mass and semi-major axis distribution of surviving planets after disk dissipation, for various disk masses, lifetimes, viscosities, and initial planet masses. The majority of planets migrate too fast and are destroyed via mass transfer onto the central star. Most surviving planets have relatively large orbital semi-major axes of several AU or larger. We conclude that the extrasolar planets observed to date, particularly those with small semi-major axes, represent only a small fraction (~25% to 33%) of a larger cohort of giant planets around solar-type stars, and many undetected giant planets must exist at large (>1-2 AU) distances from their parent stars. As sensitivity and completion of the observed sample increases with time, this distant majority population of giant planets should be revealed. We find that the current distribution of extrasolar giant planet masses implies that high mass (more than 1-2 Jupiter masses) giant planet formation must be relatively rare. Finally, our simulations imply that the efficiency of giant planet formation must be high: at least 10% and perhaps as many as 80% of solar-type stars possess giant planets during their pre-main sequence phase. These predictions, including those for pre-main sequence stars, are testable with the next generation of ground- and space-based planet detection techniquesComment: 25 pages, 5 figures. Double-space, single-column format to show long equations. Accepted for publication in A&

Statistical properties of exoplanets II. Metallicity, orbital parameters, and space velocities

In this article we present a detailed spectroscopic analysis of more than 50 extra-solar planet host stars. Stellar atmospheric parameters and metallicities are derived using high resolution and high S/N spectra. The spectroscopy results, added to the previous studies, imply that we have access to a large and uniform sample of metallicities for about 80 planet hosts stars. We make use of this sample to confirm the metal-rich nature of stars with planets, and to show that the planetary frequency is rising as a function of the [Fe/H]. Furthermore, the source of this high metallicity is shown to have most probably an ``primordial'' source, confirming previous results. The comparison of the orbital properties (period and eccentricity) and minimum masses of the planets with the stellar properties also reveal some emerging but still not significant trends. These are discussed and some explanations are proposed. Finally, we show that the planet host stars included in the CORALIE survey have similar kinematical properties as the whole CORALIE volume-limited planet search sample. Planet hosts simply seem to occupy the metal-rich envelope of this latter population.Comment: 15 pages, 10 (eps) figures, Astronomy & Astrophysics, in pres

Alcohol expectancies in childhood: Change with the onset of drinking and ability to predict adolescent drunkenness and binge drinking

Aims: Childhood expectancies about alcohol are present long before drinking begins. We examined the relationship between alcohol expectancies in childhood and onset of drinking, binge drinking, and drunkenness in adolescence and the influence of drinking onset on development of alcohol expectancies. Design: A prospective, longitudinal study of children assessed for alcohol expectancies and drinking at 4 time points between ages 6 and 17. Setting: Community study of families at high risk for alcoholism conducted in a 4-county area in the Midwest. Participants: The study involved 614 children; 460 were children of alcoholics and 70% were male. Measurements: Expectancies about effects of alcohol were measured using the Beverage Opinion Questionnaire and child’s drinking was measured using the Drinking and Drug History - Youth Form. Findings: Partial factor invariance was found for expectancy factors from age 6 to age 17. Survival analysis showed that social/relaxation expectancies in childhood predicted time to onset of binge drinking and first time drunk (Wald chi-square, 1 d.f. = 3.8, p < .05 and 5.1, p < .05, respectively). The reciprocal effect was also present; when adolescents began drinking, there was an increase in social/relaxation expectancy and a concomitant increase in slope of the expectancy change lasting throughout adolescence. Conclusions: A reciprocal relationship exists between childhood alcohol expectancies and involvement with alcohol. Higher expectancies for positive effects predict earlier onset of problem drinking. Onset of use, in turn, predicts an increase in rate of development of positive expectancies.NIH R37 AA07065 K01AA016591Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110697/1/Jester alcohol expectancies.pdfDescription of Jester alcohol expectancies.pdf : Main articl

A box-fitting algorithm in the search for periodic transits

We study the statistical characteristics of a box-fitting algorithm to analyze stellar photometric time series in the search for periodic transits by extrasolar planets. The algorithm searches for signals characterized by a periodic alternation between two discrete levels, with much less time spent at the lower level. We present numerical as well as analytical results to predict the possible detection significance at various signal parameters. It is shown that the crucial parameter is the effective signal-to-noise ratio -- the expected depth of the transit divided by the standard deviation of the measured photometric average within the transit. When this parameter exceeds the value of 6 we can expect a significant detection of the transit. We show that the box-fitting algorithm performs better than other methods available in the astronomical literature, especially for low signal-to-noise ratios.Comment: 9 pages, 12 figures and 1 table, to appear in Astronomy & Astrophysic

The CORALIE survey for southern extra-solar planets VIII. The very low-mass companions of HD141937, HD162020, HD168443, HD202206: brown dwarfs or superplanets?

Doppler CORALIE measurements of the solar-type stars HD141937, HD162020, HD168443 and HD202206 show Keplerian radial-velocity variations revealing the presence of 4 new companions with minimum masses close to the planet/brown-dwarf transition, namely with m_2sin(i) = 9.7, 14.4, 16.9, and 17.5 M_Jup, respectively. The orbits present fairly large eccentricities (0.22<e<0.43). Except for HD162020, the parent stars are metal rich compared to the Sun, as are most of the detected extra-solar planet hosts. Considerations of tidal dissipation in the short-period HD162020 system points towards a brown-dwarf nature for the low-mass companion. HD168443 is a multiple system with two low-mass companions being either brown dwarfs or formed simultaneously in the protoplanetary disks as superplanets. For HD202206, the radial velocities show an additional drift revealing a further outer companion, the nature of which is still unknown. Finally, the stellar-host and orbital properties of massive planets are examined in comparison to lighter exoplanets. Observed trends include the need of metal-rich stars to form massive exoplanets and the lack of short periods for massive planets. If confirmed with improved statistics, these features may provide constraints for the migration scenario.Comment: 14 pages including figures, accepted for publication in A&

The effects of viewing angle on the mass distribution of exoplanets

We present a mathematical method to statistically decouple the effects of unknown inclination angles on the mass distribution of exoplanets that have been discovered using radial-velocity techniques. The method is based on the distribution of the product of two random variables. Thus, if one assumes a true mass distribution, the method makes it possible to recover the observed distribution. We compare our prediction with available radial-velocity data. Assuming the true mass function is described by a power-law, the minimum mass function that we recover proves a good fit to the observed distribution at both mass ends. In particular, it provides an alternative explanation for the observed low-mass decline, usually explained as sample incompleteness. In addition, the peak observed near the the low-mass end arises naturally in the predicted distribution as a consequence of imposing a low-mass cutoff in the true-distribution. If the low-mass bins below 0.02 M_J are complete, then the mass distribution in this regime is heavily affected by the small fraction of lowly inclined interlopers that are actually more massive companions. Finally, we also present evidence that the exoplanet mass distribution changes form towards low-mass, implying that a single power law may not adequately describe the sample population.Comment: ApJ, accepte