Yang Y.-G.,Huaibei Normal University |
Yang Y.-G.,Chinese Academy of Sciences |
Qian S.-B.,Chinese Academy of Sciences |
Qian S.-B.,CAS National Astronomical Observatories |
Soonthornthum B.,National Astronomical Research Institute of Thailand
Astronomical Journal | Year: 2012
We present precision CCD photometry, a period study, and a two-color simultaneous Wilson code solution of the short-period contact binary CK Bootis. The asymmetric light curves were modeled by a dark spot on the primary component. The result identifies that CK Boo is an A-type W UMa binary with a high fillout of f = 71.7(± 4.4)%. From the O - C curve, it is found that the orbital period changes in a complicated mode, i.e., a long-term increase with two sinusoidal variations. One cyclic oscillation with a period of 10.67(± 0.20) yr may result from magnetic activity cycles, which are identified by the variability of Max. I-Max. II. Another sinusoidal variation (i.e., A = 0.0131 days(± 0.0009 days) and P 3 = 24.16(± 0.64) yr) may be attributed to the light-time effect due to a third body. This kind of additional companion can extract angular momentum from the central binary system. The orbital period secularly increases at a rate of dP/dt = +9.79 (0.80) × 10 -8 days yr -1, which may be interpreted by conservative mass transfer from the secondary to the primary. This kind of deep, low-mass ratio overcontact binaries may evolve into a rapid-rotating single star, only if the contact configuration do not break down at J spin > (1/3)J orb. © 2012. The American Astronomical Society. All rights reserved.
Lee B.-C.,Korea Astronomy and Space Science Institute |
Han I.,Korea Astronomy and Space Science Institute |
Park M.-G.,Kyungpook National University |
Mkrtichian D.E.,National Astronomical Research Institute of Thailand |
Kim K.-M.,Korea Astronomy and Space Science Institute
Astronomy and Astrophysics | Year: 2012
Aims. Our aim is to search for and study the origin of the low-amplitude and long-periodic radial velocity (RV) variations in K giants. Methods. We present high-resolution RV measurements of K2 giant ε CrB from February 2005 to January 2012 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at the Bohyunsan Optical Astronomy Observatory (BOAO). Results. We find that the RV measurements for ε CrB exhibit a periodic variation of 417.9 ± 0.5 days with a semi-amplitude of 129.4 ± 2.0 m s -1. There is no correlation between RV measurements and chromospheric activity in the Ca II H region, the Hipparcos photometry, or bisector velocity span. Conclusions. Keplerian motion is the most likely explanation, with the RV variations arising from an orbital motion. Assuming a possible stellar mass of 1.7 ± 0.1 M ȯ for ε CrB, we obtain a minimum mass for the planetary companion of 6.7 ± 0.3 M Jup with an orbital semi-major axis of 1.3 AU and eccentricity of 0.11. We also discuss the implications of our observations for stellar metallicity versus planet occurrence rate and stellar mass versus planetary mass relations. ©2012 ESO.
Richichi A.,National Astronomical Research Institute of Thailand |
Fors O.,University of Barcelona |
Cusano F.,National institute for astrophysics |
Moerchen M.,European Southern Observatory
Astrophysical Journal, Supplement Series | Year: 2012
Calibration is one of the long-standing problems in optical interferometric measurements, particularly with long baselines which demand stars with angular sizes on the milliarcsecond scale and no detectable companions. While systems of calibrators have been generally established for the near-infrared in the bright source regime (K ≲ 3mag), modern large interferometers are sensitive to significantly fainter magnitudes. We aim to provide a list of sources found to be unresolved from direct observations with high angular resolution and dynamic range, which can be used to choose interferometric calibrators. To this purpose, we have used a large number of lunar occultations recorded with the ISAAC instrument at the Very Large Telescope to select sources found to be unresolved and without close companions. An algorithm has been used to determine the limiting angular resolution achieved for each source, taking into account a noise model built from occulted and unocculted portions of the light curves. We have obtained upper limits on the angular sizes of 556 sources, with magnitudes ranging from K s 4 to 10, with a median of 7.2mag. The upper limits on possible undetected companions (within 0.″5) range from K s 8 to 13, with a median of 11.5mag. One-third of the sources have angular sizes ≤1 mas, and two-thirds have sizes ≤2 mas. This list of unresolved sources matches well the capabilities of current large interferometric facilities. We also provide available cross-identifications, magnitudes, spectral types, and other auxiliary information. A fraction of the sources are found to be potentially variable. The list covers parts of the Galactic Bulge and in particular the vicinity of the Galactic Center, where extinction is very significant and traditional lists of calibrators are often insufficient. © 2012. The American Astronomical Society. All rights reserved..
Kaeonikhom C.,Naresuan University |
Gumjudpai B.,Naresuan University |
Gumjudpai B.,National Astronomical Research Institute of Thailand |
Saridakis E.N.,Chongqing University of Posts and Telecommunications
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011
We investigate phantom cosmology in which the scale factor is a power law, and we use cosmological observations from Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations (BAO) and observational Hubble data, in order to impose complete constraints on the model parameters. We find that the power-law exponent is β≈-6.51-0.25 +0.24, while the Big Rip is realized at ts≈104.5-2.0 +1.9 Gyr, in 1 σ confidence level. Providing late-time asymptotic expressions, we find that the dark-energy equation-of-state parameter at the Big Rip remains finite and equal to wDE≈-1.153, with the dark-energy density and pressure diverging. Finally, we reconstruct the phantom potential. © 2010 Elsevier B.V.
Caswell J.L.,CSIRO |
Kramer B.H.,Max Planck Institute for Radio Astronomy |
Kramer B.H.,National Astronomical Research Institute of Thailand |
Monthly Notices of the Royal Astronomical Society | Year: 2011
Hydroxyl (OH) masers at two Galactic sites of massive star formation have been studied using the Long Baseline Array of the Australia Telescope National Facility. The 6035- and 6030-MHz OH excited-state transitions were observed, yielding a series of maps at velocity spacing 0.10kms-1, in both senses of circular polarization, with angular resolution of approximately 50 mas. Within a radius of several arcsec each site displays many maser spots. Pairs of spots with the same position, but with right and left circular polarization separated in frequency, reveal Zeeman splitting. Towards 351.417+0.645, positions and velocities were measured for 56 discrete maser spots. Remarkably, all of these are components of Zeeman pairs, with 6035-MHz pairs at 23 distinct locations, five of which show matching 6030-MHz pairs. Strikingly, at 14 southerly locations the magnetic field is typically -5mG (towards us), whereas seven of the northerly locations show a magnetic field of opposite sign, of up to +6.4mG. The velocity field spanning -11.2 to -5kms-1 shows no simple pattern. Maser emission towards 353.410-0.360 is confined to half an arcsecond total extent, comprising 24 maser spots, most of them members of nine Zeeman pairs. Derived magnetic fields are all negative, three between -4.8 and -10.6mG and three much weaker fields between 0 and -1.6mG. There is no simple pattern in the velocity field. OH masers at the 1665- and 1720-MHz transitions, and prominent ultracompact Hii regions, are present at both 351.417+0.645 and 353.410-0.360. They are accompanied by methanol maser emission at the 6668-MHz, 12-GHz, and 107-GHz transitions. Masers at the 1667-MHz transition of OH and at the 22-GHz transition of water are found towards 351.417+0.645, but not towards 353.410-0.360. The magnetic fields of both sites are in accord with tracing an ordered Galactic magnetic field. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.