2,186 research outputs found
Parking planets in circumbinary discs
The Kepler space mission has discovered about a dozen planets orbiting around binary stars systems. Most of these circumbinary planets lie near their instability boundaries, at about three to five binary separations. Past attempts to match these final locations through an inward migration process were only shown to be successful for the Kepler-16 system. Here, we study ten circumbinary systems and attempt to match the final parking locations and orbital parameters of the planets with a disc-driven migration scenario. We performed 2D locally isothermal hydrodynamical simulations of circumbinary discs with embedded planets and followed their migration evolution using different values for the disc viscosity and aspect ratio. We found that for the six systems with intermediate binary eccentricities (0.1 ≤ ebin ≤ 0.21), the final planetary orbits matched the observations closely for a single set of disc parameters, specifically, a disc viscosity of α = 10−4 and an aspect ratio of H∕r ~ 0.04. For these systems the planet masses are large enough to open at least a partial gap in their discs as they approach the binary, forcing the discs to become circularised and allowing for further migration towards the binary – ultimately leading to a good agreement with the observed planetary orbital parameters. For systems with very small or large binary eccentricities, the match was not as good as the very eccentric discs and the large inner cavities in these cases prevented close-in planet migration. In test simulations with higher than observed planet masses, a better agreement was found for those systems. The good agreement for six out of the ten modelled systems, where the relative difference between observed and simulated final planet orbit is ≤10% strongly supports the idea that planet migration in the disc brought the planets to their present locations
Speckle Interferometry of Metal-Poor Stars in the Solar Neighborhood. I
We report the results of speckle-interferometric observations of 109 high
proper-motion metal-poor stars made with the 6-m telescope of the Special
Astrophysical Observatory of the Russian Academy of Sciences. We resolve eight
objects -- G102-20, G191-55, BD+19~1185A, G89-14, G87-45, G87-47,
G111-38, and G114-25 -- into individual components and we are the first to
astrometrically resolve seven of these stars. New resolved systems included two
triple (G111-38, G87-47) and one quadruple (G89-14) star. The ratio of
single-to-binary-to-triple-to-quadruple systems among the stars of our sample
is equal to 71:28:6:1.Comment: 8 pages, 4 figures, accepted to Astrophysical Bulleti
Diffractive Meson Production and the Quark-Pomeron Coupling
Diffractive meson production at HERA offers interesting possibilities to
investigate diffractive processes and thus to learn something about the
properties of the pomeron. The most succesful phenomenological description of
the pomeron so far assumes it to couple like a isoscalar photon to
single quarks. This coupling leads, however, to problems for exclusive
diffractive reactions. We propose a new phenomenological pomeron vertex, which
leads to very good fits to the known data, but avoids the problems of the old
vertex.Comment: 20 pages, latex with uuencoded postscript, revised versio
Spectroscopic Orbits for 15 Late-Type Stars
Spectroscopic orbital elements are determined for 15 stars with periods from 8 to 6528 days with six orbits computed for the first time. Improved astrometric orbits are computed for two stars and one new orbit is derived. Visual orbits were previously determined for four stars, four stars are members of multiple systems, and five stars have Hipparcos G designations or have been resolved by speckle interferometry. For the nine binaries with previous spectroscopic orbits, we determine improved or comparable elements. For HD 28271 and HD 200790, our spectroscopic results support the conclusions of previous authors that the large values of their mass functions and lack of detectable secondary spectrum argue for the secondary in each case being a pair of low-mass dwarfs. The orbits given here may be useful in combination with future interferometric and Gaia satellite observations
Spectroscopic Orbits for 15 Late-Type Stars
Spectroscopic orbital elements are determined for 15 stars with periods from 8 to 6528 days with six orbits computed for the first time. Improved astrometric orbits are computed for two stars and one new orbit is derived. Visual orbits were previously determined for four stars, four stars are members of multiple systems, and five stars have Hipparcos G designations or have been resolved by speckle interferometry. For the nine binaries with previous spectroscopic orbits, we determine improved or comparable elements. For HD 28271 and HD 200790, our spectroscopic results support the conclusions of previous authors that the large values of their mass functions and lack of detectable secondary spectrum argue for the secondary in each case being a pair of low-mass dwarfs. The orbits given here may be useful in combination with future interferometric and Gaia satellite observations
Spectroscopic Orbits for Late-type Stars. II
We have determined spectroscopic orbital elements for 13 systems—10 single-lined binaries and three double-lined binaries. For the three binaries with previously published spectroscopic orbits, we have computed improved or comparable elements. While two systems have relatively short periods between 10 and 19 days, the remaining systems have much longer periods ranging from 604 to 9669 days. One of the single-lined systems, HD 142640, shows both short-period and long-period velocity variations and so is triple. For three systems—HD 59380, HD 160933, and HD 161163—we have combined our spectroscopic results with Hipparcos astrometric observations to obtain astrometric orbits. For HD 14802 we have determined a joint orbital solution from spectroscopic velocities and interferometric observations. The orbits given here will be useful in combination with future interferometric and Gaia satellite observations
Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355
We report the detection of a strong, organized magnetic field in the
helium-variable early B-type star HR 7355 using spectropolarimetric data
obtained with ESPaDOnS on the 3.6-m Canada-France-Hawaii Telescope within the
context of the Magnetism in Massive Stars (MiMeS) Large Program. HR 7355 is
both the most rapidly rotating known main-sequence magnetic star and the most
rapidly rotating helium-strong star, with = 300 15 km s
and a rotational period of 0.5214404 0.0000006 days. We have modeled our
eight longitudinal magnetic field measurements assuming an oblique dipole
magnetic field. Constraining the inclination of the rotation axis to be between
and , we find the magnetic obliquity angle to be
between and , and the polar strength of the magnetic
field at the stellar surface to be between 13-17 kG. The photometric light
curve constructed from HIPPARCOS archival data and new CTIO measurements shows
two minima separated by 0.5 in rotational phase and occurring 0.25 cycles
before/after the magnetic extrema. This photometric behavior coupled with
previously-reported variable emission of the H line (which we confirm)
strongly supports the proposal that HR 7355 harbors a structured magnetosphere
similar to that in the prototypical helium-strong star, Ori E.Comment: 6 pages, 3 figures. Accepted for publication in MNRAS Letter
The effect of rotation on the abundances of the chemical elements of the A-type stars in the Praesepe cluster
We study how chemical abundances of late B-, A- and early F-type stars evolve
with time, and we search for correlations between the abundance of chemical
elements and other stellar parameters, such as effective temperature and Vsini.
We have observed a large number of B-, A- and F-type stars belonging to open
clusters of different ages. In this paper we concentrate on the Praesepe
cluster (log t = 8.85), for which we have obtained high resolution, high
signal-to-noise ratio spectra of sixteen normal A- and F-type stars and one Am
star, using the SOPHIE spectrograph of the Observatoire de Haute-Provence. For
all the observed stars, we have derived fundamental parameters and chemical
abundances. In addition, we discuss another eight Am stars belonging to the
same cluster, for which the abundance analysis had been presented in a previous
paper. We find a strong correlation between peculiarity of Am stars and Vsini.
The abundance of the elements underabundant in Am stars increases with Vsini,
while it decreases for the overabundant elements. Chemical abundances of
various elements appear correlated with the iron abundance.Comment: Accepted for publication on A&
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