55 research outputs found
A ROSAT Survey of Contact Binary Stars
Contact binary stars are common variable stars which are all believed to emit
relatively large fluxes of x-rays. In this work we combine a large new sample
of contact binary stars derived from the ROTSE-I telescope with x-ray data from
the ROSAT All-Sky Survey (RASS) to estimate the x-ray volume emissivity of
contact binary stars in the galaxy. We obtained x-ray fluxes for 140 contact
binaries from the RASS, as well as 2 additional stars observed by the
XMM-Newton observatory. From these data we confirm the emission of x-rays from
all contact binary systems, with typical luminosities of approximately 1.0 x
10^30 erg s^-1. Combining calculated luminosities with an estimated contact
binary space density, we find that contact binaries do not have strong enough
x-ray emission to account for a significant portion of the galactic x-ray
background.Comment: 19 pages, 5 figures, accepted by A
A Catalog of 1022 Bright Contact Binary Stars
In this work we describe a large new sample of contact binary stars extracted
in a uniform manner from sky patrol data taken by the ROTSE-I telescope.
Extensive ROTSE-I light curve data is combined with J, H, and K band
near-infrared data taken from the Two Micron All-Sky Survey (2MASS) to add
color information. Contact binaries candidates are selected using the observed
period-color relation. Candidates are confirmed by visual examination of the
light curves. To enhance the utility of this catalog, we derive a new J-H
period-color-luminosity relation and use this to estimate distances for the
entire catalog. From these distance estimates we derive an estimated contact
binary space density of (1.7 +/- 0.6) x 10^-5 pcs^-3.Comment: 26 pages, 12 figures, accepted for publication in A
High Fill-Out, Extreme Mass Ratio Overcontact Binary Systems. X. The new discovered binary XY Leonis Minoris
The new discovered short-period close binary star, XY LMi, was monitored
photometrically since 2006. It is shown that the light curves are typical
EW-type and show complete eclipses with an eclipse duration of about 80
minutes. By analyzing the complete B, V, R, and I light curves with the 2003
version of the W-D code, photometric solutions were determined. It is
discovered that XY LMi is a high fill-out, extreme mass ratio overcontact
binary system with a mass ratio of q=0.148 and a fill-out factor of f=74.1%,
suggesting that it is on the late evolutionary stage of late-type tidal-locked
binary stars. As observed in other overcontact binary stars, evidence for the
presence of two dark spots on both components are given. Based on our 19
epoches of eclipse times, it is found that the orbital period of the
overcontact binary is decreasing continuously at a rate of
dP/dt=-1.67\times10^{-7}\,days/year, which may be caused by the mass transfer
from the primary to the secondary or/and angular momentum loss via magnetic
stellar wind. The decrease of the orbital period may result in the increase of
the fill-out, and finally, it will evolve into a single rapid-rotation star
when the fluid surface reaching the outer critical Roche Lobe.Comment: 19 pages, 4 figures, 9 table
Precision Astrometry of the Exoplanet Host Candidate GD 66
The potential existence of a giant planet orbiting within a few AU of a
stellar remnant has profound implications for both the survival and possible
regeneration of planets during post-main sequence stellar evolution. This paper
reports Hubble Space Telescope Fine Guidance Sensor and U.S. Naval Observatory
relative astrometry of GD 66, a white dwarf thought to harbor a giant planet
between 2 and 3 AU based on stellar pulsation arrival times. Combined with
existing infrared data, the precision measurements here rule out all
stellar-mass and brown dwarf companions, implying that only a planet remains
plausible, if orbital motion is indeed the cause of the variations in pulsation
timing.Comment: 6 pages, 3 figures, 1 table, accepted to MNRA
Solubility of Rock in Steam Atmospheres of Planets
Extensive experimental studies show that all major rock-forming elements (e.g., Si, Mg, Fe, Ca, Al, Na, K) dissolve in steam to a greater or lesser extent. We use these results to compute chemical equilibrium abundances of rocky-element-bearing gases in steam atmospheres equilibrated with silicate magma oceans. Rocky elements partition into steam atmospheres as volatile hydroxide gases (e.g., Si(OH)4, Mg(OH)2, Fe(OH)2, Ni(OH)2, Al(OH)3, Ca(OH)2, NaOH, KOH) and via reaction with HF and HCl as volatile halide gases (e.g., NaCl, KCl, CaFOH, CaClOH, FAl(OH)2) in much larger amounts than expected from their vapor pressures over volatile-free solid or molten rock at high temperatures expected for steam atmospheres on the early Earth and hot rocky exoplanets. We quantitatively compute the extent of fractional vaporization by defining gas/magma distribution coefficients and show that Earth's subsolar Si/Mg ratio may be due to loss of a primordial steam atmosphere. We conclude that hot rocky exoplanets that are undergoing or have undergone escape of steam-bearing atmospheres may experience fractional vaporization and loss of Si, Mg, Fe, Ni, Al, Ca, Na, and K. This loss can modify their bulk composition, density, heat balance, and interior structure
An Accurate Mass Determination for Kepler-1655b, a Moderately Irradiated World with a Significant Volatile Envelope
Funding: A.C.C. acknowledges support from STFC consolidated grant number ST/M001296/1. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant Agreement No. 313014 (ETAEARTH).We present the confirmation of a small, moderately-irradiated (F= 155±7 F⊕) Neptune with a substantial gas envelope in a P=11.8728787±0.0000085-day orbit about a quiet, Sun-like G0V star Kepler-1655. Based on our analysis of the Kepler light curve, we determined Kepler-1655b’s radius to be 2.213±0.082 R⊕. We acquired 95 high-resolution spectra with TNG/HARPS-N, enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0±^3.1_2.8 M⊕ via Gaussian-process regression. Our mass determination excludes an Earth-like composition with 98% confidence. Kepler-1655b falls on the upper edge of the evaporation valley, in the relatively sparsely occupied transition region between rocky and gas-rich planets. It is therefore part of a population of planets that we should actively seek to characterize further.PostprintPeer reviewe
A 1.9 Earth Radius Rocky Planet and the Discovery of a Non-Transiting Planet in the Kepler-20 System*
Kepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own Solar System. A transition from rocky to gaseous planets with a planetary transition radius of ∼ 1.6 R⊕ has recently been proposed by several publications in the literature (Rogers 2015; Weiss& Marcy 2014). Kepler-20b (Rp ∼ 1.9 R⊕) has a size beyond this transition radius, however previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of Kepler-20 three of the planets in the Kepler-20 system facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (M* = 0.948 ± 0.051 M☉ and R* = 0.964 ± 0.018 R☉).Kepler-20b is a 1.868+0.066 −0.034 R⊕ planet in a 3.7 day period with amass of 9.70+1.41 −1.44 M⊕ resulting in a mean density of 8.2 +1.5 −1.3 g cm−3 indicating a rocky composition with an iron to silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of 19.96+3.08 −3.61 M⊕ and an orbital period of ∼ 34 days in the gap between Kepler-20f (P ∼ 11 days) and Kepler-20d (P ∼78 days).PostprintPeer reviewe
VizieR Online Data Catalog: A transiting rocky planet at 6.5pc from the Sun (Motalebi+ 2015)
We obtained 98 spectra of HD219134 using the HARPS-N spectrograph. Our RV data are provided online. spitzer.dat contains the photometric time-series presented in the paper for HD219134 and gathered by the IRAC instrument aboard the Spitzer telescope in its channel 2 (4.5 microns) on 2015-04-14
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