National Astronomical Research Institute of Thailand

Chiang Mai, Thailand

National Astronomical Research Institute of Thailand

Chiang Mai, Thailand

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Richichi A.,National Astronomical Research Institute of Thailand | Fors O.,University of Barcelona | Fors O.,Qatar Environment and Energy Research Institute | Cusano F.,National institute for astrophysics | Ivanov V.D.,European Southern Observatory
Astronomical Journal | Year: 2014

We report on 13 subarcsecond binaries, detected by means of lunar occultations in the near-infrared at the ESO Very Large Telescope (VLT). They are all first-time detections except for the visual binary HD 158122, which we resolved for the first time in the near-infrared. The primaries have magnitudes in the range K = 4.5-10.0, and companions in the range K = 6.8-11.1. The magnitude differences have a median value of 2.4, with the largest being 4.6. The projected separations are in the range of 4-168 mas, with a median of 13 mas. We discuss and compare our results with the available literature. With this paper, we conclude the mining for binary star detections in the 1226 occultations recorded at the VLT with the ISAAC instrument. We expect that the majority of these binaries may be unresolvable by adaptive optics on current telescopes, and they might be challenging for long-baseline interferometry. However, they constitute an interesting sample for future larger telescopes and for astrometric missions such as GAIA. © 2014. 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.


Nikoloudakis N.,Durham University | Shanks T.,Durham University | Sawangwit U.,Durham University | Sawangwit U.,National Astronomical Research Institute of Thailand
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present a clustering analysis of luminous red galaxies (LRGs) in Stripe 82 from the Sloan Digital Sky Survey (SDSS). We study the angular two-point autocorrelation function, ω(Θ), of a selected sample of over 130 000 LRG candidates via colour-cut selections in izK with the K-band coverage coming from UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). We have used the crosscorrelation technique of Newman to establish the redshift distribution of the LRGs. Crosscorrelating them with SDSS quasi-stellar objects (QSOs),MegaZ-LRGs andDEEPExtragalactic Evolutionary Probe 2 (DEEP2) galaxies, implies an average redshift of the LRGs to be z ≈ 1 with space density, ng ≈ 3.20 ± 0.16 × 10-4 h3 Mpc-3. For Θ ≤ 10 arcmin (corresponding to ≈10 h-1 Mpc), the LRG w(Θ) significantly deviates from a conventional single power law as noted by previous clustering studies of highly biased and luminous galaxies. A double power law with a break at rb ≈ 2.4 h-1 Mpc fits the data better, with best-fitting scale length, r0, 1 = 7.63 ± 0.27 h-1 Mpc and slope γ1 = 2.01 ± 0.02 at small scales and r0, 2 = 9.92 ± 0.40 h-1 Mpc and γ2 = 1.64 ± 0.04 at large scales. Due to the flat slope at large scales, we find that a standard Λ cold dark matter (ΛCDM) linear model is accepted only at 2-3σ, with the best-fitting bias factor, b = 2.74 ± 0.07.We also fitted the halo occupation distribution (HOD) models to compare our measurements with the predictions of the dark matter clustering. The effective halo mass of Stripe 82 LRGs is estimated as Meff = 3.3 ± 0.6 × 1013 h-1M⊙. But at large scales, the current HOD models did not help explain the power excess in the clustering signal. We then compare the w(Θ) results to the results of Sawangwit et al. from three samples of photometrically selected LRGs at lower redshifts to measure clustering evolution. We find that a long-lived model may be a poorer fit than at lower redshifts, although this assumes that the Stripe 82 LRGs are luminosity-matched to the AAΩLRGs.We find stronger evidence for evolution in the form of the z ≈ 1 LRG correlation function with the above flat two-halo slope maintaining to s 50 h -1 Mpc. Applying the cross-correlation test of Ross et al., we find little evidence that the result is due to systematics. Otherwise, it may represent evidence for primordial non-Gaussianity in the density perturbations at early times, with flocalNL = 90 ± 30. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Richichi A.,National Astronomical Research Institute of Thailand | Fors O.,University of Barcelona | Cusano F.,National institute for astrophysics | Moerchen M.,European Southern Observatory | Moerchen M.,Leiden 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..


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.


Surcis G.,University of Bonn | Vlemmings W.H.T.,University of Bonn | Curiel S.,Institute Astronomia UNA | Hutawarakorn Kramer B.,Max Planck Institute for Radio Astronomy | And 3 more authors.
Astronomy and Astrophysics | Year: 2011

Context. A debated topic in star formation theory is the role of magnetic fields during the protostellar phase of high-mass stars. It is still unclear how magnetic fields influence the formation and dynamics of massive disks and outflows. Most current information on magnetic fields close to high-mass protostars comes from polarized maser emissions, which allows us to investigate the magnetic field on small scales by using very long-baseline interferometry. Aims. The massive star-forming region W75N contains three radio continuum sources (VLA 1, VLA 2, and VLA 3), at three different evolutionary stages, and associated masers, while a large-scale molecular bipolar outflow is also present. Very recently, polarization observations of the 6.7 GHz methanol masers at milliarsecond resolution have been able to probe the strength and structure of the magnetic field over more than 2000 AU around VLA 1. The magnetic field is parallel to the outflow, suggesting that VLA 1 is its powering source. The observations of H2O masers at 22 GHz can give more information about the gas dynamics and the magnetic fields around VLA 1 and VLA 2. Methods. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman-splitting of the 22 GHz water masers in the star-forming region W75N. Results. We detected 124 water masers, 36 around VLA 1 and 88 around VLA 2 of W75N, which indicate two different physical environments around the two sources, where VLA 1 is in a more evolved state. The linear polarization of the masers confirms the tightly ordered magnetic field around VLA 1, which is aligned with the large-scale molecular outflow, and also reveals an ordered magnetic field around VLA 2, which is not parallel to the outflow. The Zeeman-splitting measured on 20 of the masers indicates strong magnetic fields around both sources (the averaged values are |BVLA1| ~ 700 mG and |B VLA2| ~ 1700 mG). The high values of the magnetic field strengths, which come from the shock compression of the gas, are consistent with the methanol and OH magnetic field strengths. Moreover, by studying the maser properties we were also able to determine that the water masers are pumped in C-shocks in both sources. © 2011 ESO.


Caswell J.L.,CSIRO | Kramer B.H.,Max Planck Institute for Radio Astronomy | Kramer B.H.,National Astronomical Research Institute of Thailand | Reynolds J.E.,CSIRO
Monthly Notices of the Royal Astronomical Society | Year: 2011

New high resolution studies of the Galactic maser site 337.705-0.053 reveal its magnetic field and velocity morphology. The long baseline array of the Australia Telescope National Facility provided simultaneous observations of both the 1665- and 1667-MHz OH transitions which yielded a sequence of maps at velocity spacing 0.09 kms-1, in both senses of circular polarization, with tenth-arcsec spatial resolution. 38 small diameter maser spots were detected, spread over an ellipse with largest dimension of 1.5arcsec. Pairs of spots with the same position, but with right and left circular polarization at different frequency, reveal Zeeman splitting. Five pairs at 1665 MHz and four at 1667 MHz are seen; at one position, pairs at both transitions indicate a comparable magnetic field and similar (central) velocity. All estimates of magnetic field are in the same sense, with a median value of -2.5 mG (pointing towards the earth), confirming an interpretation from single-dish observations. The morphology and kinematics have been compared with that of maser emission from the excited state of OH at 6035 MHz, with methanol at 6668 MHz and 12 GHz, and with water at 22 GHz. All species are intermingled, and associated with an ultracompact Hii region. The site most likely lies near the tangent point of the Galactic 3-kpc ring, at a distance of 7.9kpc. The maser spot distribution over 1.5arcsec then corresponds to a diameter of 60 mpc, amongst the largest known, and likely to be approaching the end of the maser emitting phase. 337.705-0.053 adds to the maser sites studied in sufficient detail to explore ordered patterns in the global Galactic magnetic field. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Caswell J.L.,CSIRO | Kramer B.H.,Max Planck Institute for Radio Astronomy | Kramer B.H.,National Astronomical Research Institute of Thailand | Reynolds J.E.,CSIRO
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.


Richichi A.,National Astronomical Research Institute of Thailand | Fors O.,University of Barcelona | Cusano F.,National institute for astrophysics | Moerchen M.,European Southern Observatory | Moerchen M.,US Space Telescope Science Institute
Astronomical Journal | Year: 2013

We report on 25 subarcsecond binaries, detected for the first time by means of lunar occultations in the near-infrared (near-IR) as part of a long-term program using the ISAAC instrument at the ESO Very Large Telescope. The primaries have magnitudes in the range K = 3.8-10.4, and the companions in the range K = 6.4-12.1. The magnitude differences have a median value of 2.8, with the largest being 5.4. The projected separations are in the range 6-748 mas and with a median of 18 mas, or about three times less than the diffraction limit of the telescope. Among our binary detections are a pre-main-sequence star and an enigmatic Mira-like variable previously suspected to have a companion. Additionally, we quote an accurate first-time near-IR detection of a previously known wider binary. We discuss our findings on an individual basis as far as made possible by the available literature, and we examine them from a statistical point of view. We derive a typical frequency of binarity among field stars of ≈10%, in the resolution and sensitivity range afforded by the technique (≈0.″003 to ≈0.″5, and K ≈ 12 mag, respectively). This is in line with previous results using the same technique but we point out interesting differences that we can trace up to sensitivity, time sampling, and average distance of the targets. Finally, we discuss the prospects for further follow-up studies. © 2013. The American Astronomical Society. All rights reserved.


Richichi A.,National Astronomical Research Institute of Thailand | Richichi A.,European Southern Observatory | Glindemann A.,European Southern Observatory
Astronomy and Astrophysics | Year: 2012

Context. The introduction of fast 2D detectors and the use of very large telescopes have significantly advanced the sensitivity and accuracy of the lunar occultation technique. Recent routine observations at the ESO Very Large Telescope have yielded hundreds of events with results, especially in the area of binary stars, which are often beyond the capabilities of any other techniques. Aims. With the increase in the quality and in the number of the events, subtle features in the light curve patterns have occasionally been detected which challenge the standard analytical definition of the lunar occultation phenomenon as diffraction from an infinite straight edge. We investigate the possible causes for the observed peculiarities. Methods. We have evaluated the available statistics of distortions in occultation light curves observed at the ESO VLT, and compared it to data from other facilities. We have developed an alternative approach to model and interpret lunar occultation light curves, based on 2D diffraction integrals describing the light curves in the presence of an arbitrary lunar limb profile. We distinguish between large limb irregularities requiring the Fresnel diffraction formalism, and small irregularities described by Fraunhofer diffraction. We have used this to generate light curves representative of several limb geometries, and attempted to relate them to some of the peculiar data observed. Results. We conclude that the majority of the observed peculiarities is due to limb irregularities, which can give origin both to anomalies in the amplitude of the diffraction fringes and to varying limb slopes. We investigate also other possible effects, such as detector response and atmospheric perturbations, finding them negligible. We have developed methods and procedures that for the first time allow us to analyze data affected by limb irregularities, with large ones bending the fringe pattern along the shape of the irregularity, and small ones creating fringe amplitude perturbations in comparison to the ideal fringe pattern. Conclusions. The effects of a variable limb slope can be satisfactorily corrected. More complex limb irregularities could be fitted in principle with a grid search based on the standard analytical model, however this method is time consuming and does not lead to unique solutions. The incidence of the limb perturbations is relatively small, but its significance is increased with the use of very large telescopes due both to the footprint at the lunar limb and to the increased sensitivity. In general, we recommend to observe occultations using sub-pupils. This will be a necessary requirement with the next generation of extremely large telescopes. © 2012 ESO.

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