bluuebunny/crossref_metadata_2025_split huggingface dataset:
Occultation by (22) Kalliope and its satellite Linus
Authors: Sôma M. , Hayamizu T. , Miyashita K. , Setoguchi T. , Hirose T. 
Published: July 2008

AbstractThe occultation of a 9.1 magnitude star by asteroid (22) Kalliope and its satellite Linus was successfully observed in Japan in 2006 November 7.826 UT. This was the first definite observation of an occultation of a satellite of an asteroid that was discovered previously by other means. As a result the position of the satellite relative to Kalliope was obtained to be d = 0.246 ± 0.011 (arcsec), and P = 313.8 ± 2.7 (deg), where d is the angular distance and P is the position angle. The derived size for Kalliope is (209 ± 40)km × (136 ± 26)km (with the major axis in position angle of (8 ± 17) deg), and that for Linus is (33 ± 3) km. From the observations, the occulted star is also found to be a close double star whose separation is about 0.7 mas in position angle of about 300 deg, and the magnitudes of the components are found to be almost the same (~9.9 mag).
Astrometric observations of neutron stars
Authors: Chatterjee S. 
Published: July 2008

AbstractPrecision astrometry can yield model-independent distances and velocities for neutron stars. Such measurements can be exploited, for example, to locate neutron star birth sites, establish reference frame ties, model the Galactic electron density distribution, and constrain the astrophysics of supernova explosions. As a case study, I discuss recent some parallax and proper motion measurements, and their scientific implications for supernova core collapse and the velocities of ordinary pulsars versus magnetars. I also outline the calibration techniques that are enabling sub-milliarcsecond astrometry of neutron stars with VLBI. In the short term, systematic surveys and high sensitivity on very long baselines will produce ongoing science dividends from precision astrometry at radio wavelengths. In the longer term, new technology such as focal plane arrays, new telescopes such as the Square Kilometre Array, and synergy with new instruments such as Gaia, LSST, and GLAST, all hold great promise in an upcoming era of microarcsecond astrometry.
VLBA determinations of the distances to nearby star-forming regions
Authors: Loinard L. , Torres R. M. , Mioduszewski A. J. , Rodríguez L. F. 
Published: July 2008

AbstractUsing phase-referenced multi-epoch Very Long Baseline Array observations, we have measured the trigonometric parallax of several young stars in the Taurus and Ophiuchus star-forming regions with unprecedented accuracy. The mean distance to the Taurus complex was found to be about 140 pc, and its depth around 20 pc, comparable to the linear extent of Taurus on the sky. In Ophiuchus, 4 sources have been observed so far. Two of them were found to be at about 160 pc (the distance traditionally attributed to Ophiuchus), while the other 2 are at about 120 pc. Since the entire Ophiuchus complex is only a few parsecs across, this difference is unlikely to reflect the depth of the region. Instead, we argue that two physically unrelated sites of star-formation are located along the line of sight toward Ophiuchus.
VERA observation of the massive star forming region G34.4+0.23
Authors: Kurayama T. 
Published: July 2008

AbstractWe observed with VERA the massive star forming region G34.4+0.23, to obtain parallaxes and proper motions. Four infrared dark clouds were observed and water maser were found in two dark clouds, MM1 and MM4. In MM1, the distribution of maser spots shows a “V-shaped” structure and most features co-moving with this structure. Phase-referenced images have peaks and their motion is much larger than the expected parallax. Further analysis is needed to correctly interpret our measurement of parallax.
Milli-arcsecond binaries
Authors: Torres R. M. , Loinard L. , Mioduszewski A. J. , Rodríguez L. F. 
Published: July 2008

AbstractAs part of an astrometric program (see Loinard et al. in this volume), we have obtained an unprecedented sample of high-resolution (~ 1 mas) VLBA images of several nearby young stellar systems. As was to be expected, these images revealed interesting new characteristics of these objects. Perhaps the most interesting of these characteristics is the detection of a high rate of very tight binary stars (separations of a few mas) in our sample: of the 9 objects observed to date, 5 are binaries of this type.
The Gaia mission: science, organization and present status
Authors: Lindegren L. , Babusiaux C. , Bailer-Jones C. , Bastian U. , Brown A. G. A. , Cropper M. , Høg E. , Jordi C. , Katz D. , van Leeuwen F. , Luri X. , Mignard F. , de Bruijne J. H. J. , Prusti T. 
Published: July 2008

AbstractThe ESA space astrometry mission Gaia will measure the positions, parallaxes and proper motions of the 1 billion brightest stars on the sky. Expected accuracies are in the 7–25 μas range down to 15 mag and sub-mas accuracies at the faint limit (20 mag). The astrometric data are complemented by low-resolution spectrophotometric data in the 330–1000 nm wavelength range and, for the brighter stars, radial velocity measurements. The scientific case covers an extremely wide range of topics in galactic and stellar astrophysics, solar system and exoplanet science, as well as the establishment of a very accurate, dense and faint optical reference frame. With a planned launch around 2012 and an (extended) operational lifetime of 6 years, final results are expected around 2021. We give a brief overview of the science goals of Gaia, the overall project organisation, expected performance, and some key technical features and challenges.
Testing planet formation models with Gaia μas astrometry
Authors: Sozzetti A. , Casertano S. , Lattanzi M. G. , Spagna A. , Morbidelli R. , Pannunzio R. , Pourbaix D. , Queloz D. 
Published: July 2008

AbstractIn this paper, we first summarize the results of a large-scale double-blind tests campaign carried out for the realistic estimation of the Gaia potential in detecting and measuring planetary systems. Then, we put the identified capabilities in context by highlighting the unique contribution that the Gaia exoplanet discoveries will be able to bring to the science of extrasolar planets during the next decade.
Gaia: how to map a billion stars with a billion pixels
Authors: de Bruijne J. H. J. 
Published: July 2008

AbstractGaia, ESA's ambitious star-mapper mission due for launch late-2011, will provide multi-epoch micro-arcsecond astrometric and milli-magnitude photometric data for the brightest one billion objects in the sky, down to at least magnitude 20. Spectroscopic data will simultaneously be collected for the subset of the brightest 100 million stars, down to about magnitude 17. This massive data volume will allow astronomers to reconstruct the structure, evolution and formation history of the Milky Way. It will also revolutionize studies of the solar system and stellar physics and will contribute to diverse research areas, ranging from extra-solar planets to general relativity.Underlying Gaia's scientific harvest will lie in a Catalogue, built on the fundamental space-based measurements. During the 5-year nominal operational lifetime, Gaia's payload, with its CCD mosaic containing 1 billion pixels, will autonomously detect all objects of interest and observe them throughout their passage of the focal plane. This paper discusses the workings of the Gaia instrument, details its payload, and discusses in depth how the scientific measurements will be collected. It addresses issues like maintenance of the scanning law, on-board data processing, the detection and confirmation of objects (single and multiple stars), the detection and rejection of cosmic rays and solar protons, the fundamental science measurements themselves composed of windows of CCD samples (pixels), and special strategies employed to maximize the science return for moving (i.e., solar-system) objects. The paper also explains how an on-board priority scheme will ensure catalogue completeness down to the faintest magnitudes possible, despite the limited ground-station availability and the enormous data volume that will be sent to the ground.
Gaia and the Astrometric Global Iterative Solution
Authors: Hobbs D. , Lindegren L. , Holl B. , Lammers U. , O'Mullane W. 
Published: July 2008

AbstractGaia is an ESA space astrometry mission due for launch in 2011–12. We describe part of the work carried out in the Gaia Data Processing and Analysis Consortium, namely the Astrometric Global Iterative Solution (AGIS) currently being implemented at the European Space Astronomy Center (ESAC) in Spain and largely based on algorithms developed at Lund Observatory. Some provisional results based on simulated observations of one million stars are presented, demonstrating convergence at microarcsec level independent of initial conditions.
Design of a compact astrometric instrument for the GAME mission
Authors: Loreggia D. , Gai M. , Vecchiato A. , Gardiol D. , Ligori S. , Lattanzi M. G. 
Published: July 2008

AbstractWe present the design of a Fizeau interferometer to be implemented for the GAME mission. The aim is to measure the PPN γ parameter with the same technique used for the first time by Dyson, Eddington et al., but at a 10−6 accuracy level. GAME will observe about 106 sufficiently bright stars at about 2° from the Sun. A dedicated space mission has the advantage of observing the light bending without waiting for an eclipse.
Astrometry by small ground-based telescopes
Authors: Thuillot W. , Stavinschi M. , Assafin M. ,   the IAU Working Group ASGBT
Published: July 2008

AbstractMany small ground-based telescopes (with diameter less than 2m) allow us to perform programs of observations well adapted to astrometric measurements. The improvement of limiting magnitudes thanks to the use of CCD detector and their availability make them very useful for follow-up programs or observations on alert. This communication gives several examples of research carried out by members of the IAU working group “Astrometry by small ground-based telescopes”. We also propose setting up of a network of observers for the Gaia follow-up observations.
Quasar astrophysics with the Space Interferometry Mission
Authors: Unwin S. C. , Wehrle A. E. , Meier D. L. , Jones D. L. , Piner B. G. 
Published: July 2008

AbstractOptical astrometry of quasars and active galaxies can provide key information on the spatial distribution and variability of emission in compact nuclei. The Space Interferometry Mission (SIM PlanetQuest) will have the sensitivity to measure a significant number of quasar positions at the microarcsecond level. SIM will be very sensitive to astrometric shifts for objects as faint as V=19. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. These represent unique data on the spatial distribution and time dependence of quasar emission. It will also probe the use of quasar nuclei as fundamental astrometric references. Comparisons between the time-dependent optical photocenter position and VLBI radio images will provide further insight into the jet emission mechanism. Observations will be tailored to each specific target and science question. SIM will be able to distinguish spatially between jet and accretion disk emission; and it can observe the cores of galaxies potentially harboring binary supermassive black holes resulting from mergers.
Gamma Astrometric Measurement Experiment: testing General Relativity with a small mission
Authors: Vecchiato A. , Lattanzi M. G. , Gai M. , Morbidelli R. 
Published: July 2008

AbstractGAME (Gamma Astrometric Measurement Experiment) is a concept for an experiment whose goal is to measure from space the γ parameter of the Parameterized Post-Newtonian formalism, by means of a satellite orbiting at 1 AU from the Sun and looking as close as possible to its limb. This technique resembles the one used during the solar eclipse of 1919, when Dyson, Eddington and collaborators measured for the first time the gravitational bending of light. Simple estimations suggest that, possibly within the budget of a small mission, one could reach the 10−6level of accuracy with ~106observations of relatively bright stars at about 2° apart from the Sun. Further simulations show that this result could be reached with only 20 days of measurements on stars ofV≤ 17 uniformly distributed. A quick look at real star densities suggests that this result could be greatly improved by observing particularly crowded regions near the galactic center.
Dense optical reference frames: UCAC and URAT
Authors: Zacharias N. 
Published: July 2008

AbstractA series of ground-based, dedicated astrometric, observational programs have been performed or are in preparation which provide a dense and accurate optical reference frame. Integral to all these programs are new observations to link the Hipparcos Celestial Reference Frame (HCRF) to the International Celestial Reference Frame (ICRF), based on compact, extragalactic radio sources.The U.S. Naval Observatory CCD Astrograph Catalog (UCAC) 3rd release is in preparation. A pixel re-reduction is in progress to improve astrometric and photometric accuracy as well as completeness of this all-sky reference catalog to 16th magnitude. Optical counterparts of ICRF radio sources have been observed with 0.9-meter telescopes contemporaneously. Scanning of over 5000 early-epoch astrograph plates on StarScan has been completed. These data will improve the proper motions of stars in the 10 to 14 mag range for the UCAC3 release.A 111 million-pixel CCD was successfully fabricated in 2006 and test observations at the USNO astrograph are underway. Four of such detectors will be used for the USNO Robotic Astrometric Telescope (URAT) focal plane assembly. Phase I of URAT will use the astrograph to reach 18th magnitude, while the new 0.85-meter telescope with a 4.5 deg diameter field of view will reach 21st magnitude. The URAT primary mirror has been fabricated.
Deep Astrometric Standards
Authors: Platais I. , Fey A. L. , Frey S. , Djorgovski S. G. , Ducourant C. , Ivezić Ž. , Rest A. , Veillet C. , Wyse R. F. G. , Zacharias N. 
Published: July 2008

AbstractThe advent of next-generation telescopes with very wide fields-of-view creates a need for deep and precise reference frames for astrometric calibrations. The Deep Astrometric Standards (DAS) program is designed to establish such a frame, by providing absolute astrometry at the 5–10 mas level in four 10 deg2 Galactic fields, to a depth of V=25. The source of our basic reference frame is the UCAC2 catalog, significantly improved by additional observations, and new VLBI positions of radio-loud and optically visible QSOs. We describe all the major steps in the construction of the DAS fields and provide the current status of this project.
VLBI observations of weak extragalactic radio sources for the alignment of the future Gaia frame with the ICRF
Authors: Bourda G. , Charlot P. , Porcas R. , Garrington S. 
Published: July 2008

AbstractThe space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between the optical and radio positions, it will be important to align the Gaia frame and the International Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is found that only 10% of the ICRF sources are suitable to establish this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional high-quality radio sources for aligning the two frames. The sample consists of about 450 sources, typically 20 times weaker than the current ICRF sources, which have been selected by cross-correlating optical and radio catalogues. This paper presents the observing strategy and includes preliminary results of observation of 224 of these sources with the European VLBI Network in June 2007.
Selection of stable sources from VLBI observations from 1984 to 2006
Authors: Qiao S. B. , Li J. L. , Zhang B. , Tian F. 
Published: July 2008

AbstractBased on the Calc/Solve system and aiming at the selection of stable sources, we have obtained a series of global solutions to astrometric/geodetic VLBI observations from 1984 to 2006 by changing the settings of the control parameters. After comparing the solutions and performing statistical analysis we proposed a list of 173 candidate stable sources. We also compared the list with those recommended by others authors.
Re-calibration of GSC2.3 with UCAC2
Authors: Tang Z. H. , Qi Z. X. , Yu Y. , Smart R. L. , Bucciarelli B. , Lattanzi M. G. , Spagna A. 
Published: July 2008

AbstractTo make GSC-II more accurate and useful, it is necessary to re-calibrate GSC-II when a better reference catalogue (UCAC2) is available. With UCAC2 as the reference, preliminary re-calibration of some sample plates from GSC2.3 were carried out with different methods, such as Global, Mask and Filter. The results indicate that a 7th-order polynomial is sufficient to account for the influence of Schmidt plate deformation on the measured coordinates of stars. The magnitude equation can be eliminated after correcting for a common magnitude equation. The RMS of the re-calibrated data is around ±0.2~0.3 arcsec.
The second realization of the ICRF with VLBI
Authors: Ma C. 
Published: July 2008

AbstractThe ICRF derived from VLBI observations of extragalactic radio sources up to 1995.6 and effective since 1998.0 was a radical change from the FK5 stellar/equinox celestial system. Since then the number of geodetic/astrometric VLBI observations has tripled and the number of radio sources with astrometrically useful data has quadrupled. These data along with advances in modeling and estimation will be used to generate the next ICRF realization in the microwave band. Analysis of source position time series and source structure evolution will be used to select better “defining” sources. Working groups have been established by the IAU, IERS and IVS with the goal of presenting the second realization of the ICRF at the IAU General Assembly in 2009.
Opacity in compact extragalactic radio sources and its effect on radio-optical reference frame alignment
Authors: Kovalev Y. Y. , Lobanov A. P. , Pushkarev A. B. , Zensus J. A. 
Published: July 2008

AbstractAccurate alignment of the radio and optical celestial reference frames requires detailed understanding of physical factors that may cause offsets between the positions of the same object measured in different spectral bands. Opacity in compact extragalactic jets (due to synchrotron self-absorption and external free-free absorption) is one of the key physical phenomena producing such an offset, and this effect is well-known in radio astronomy (“core shift”). We have measured the core shifts in a sample of 29 bright compact extragalactic radio sources observed by Very Long Baseline Interferometry (VLBI) at 2.3 and 8.6 GHz. We report the results of these measurements and estimate that the average shift between radio and optical positions of distant quasars could be of the order of 0.1--0.2 mas. This shift exceeds the expected positional accuracy of Gaia and SIM. We suggest two possible approaches to carefully investigate and correct for this effect in order to align accurately the radio and optical positions. Both approaches involve determining a Primary Reference Sample of objects to be used for tying the radio and optical reference frames together.
Asteroid mass determination with the Gaia mission
Authors: Mouret S. , Hestroffer D. , Mignard F. 
Published: July 2008

AbstractThe ESA astrometric mission Gaia, due for launch in late 2011, will observe a very large number of asteroids (~ 350,000 down to the magnitude 20), most from the main belt, with an unprecedented positional precision (at the sub-milliarcsecond level). Such high-precision astrometry will enable to considerably improve the orbits of a large number of objects, and also to determine the masses of the largest asteroids by analyzing their gravitational pull during close encounters with smaller ones. A global solution involving simultaneously all the perturbers and the smaller targets should yield about hundred masses with a precision better than 30 percent. The knowledge of these masses will be a rich source of information on the physics of main-belt asteroids and will increase the accuracy of modern solar system ephemerides. We outline the principle of the mathematical method based on variational equations developed to solve for the orbital parameters and the masses of the largest bodies. Calculations have been performed by taking into account realistic simulation of the Gaia observations such as geometry, time sequence, magnitude and by considering possible close approaches among 350,000 asteroids. We give a list of asteroids whose mass can be estimated along with its formal precision.
The RAMOD astrometric observable and the relativistic astrometric catalogs
Authors: Crosta M. T. , Bucciarelli B. , de Felice F. , Lattanzi M. G. , Vecchiato A. 
Published: July 2008

AbstractWe describe a way to compare current relativistic astrometric models accurate to the micro-arcsecond level. The observed stellar direction can be written as a function of several parts, linking the astrometric observables to the relativistic effects associated to the stellar kinematical properties and distances as seen inside the gravitational field of our Solar System, i.e. the so called relativistic astrometric parameters, providing a tool for comparing the RAMOD framework to the pM/pN approaches.
Stars in the age of micro-arc-second astrometry
Authors: Lebreton Y. 
Published: July 2008

AbstractThe understanding and modelling of the structure and evolution of stars is based on statistical physics as well as on hydrodynamics. Today, a precise identification and proper description of the physical processes at work in stellar interiors are still lacking (one key point being that of transport processes) while comparison of real stars to model predictions, which implies conversions from the theoretical space to the observational one, suffers from uncertainties in model atmospheres. This results in uncertainties on the prediction of stellar properties needed for galactic studies or cosmology (as stellar ages and masses). In the next decade, progress is expected from the theoretical, experimental and observational sides. I illustrate some of the problems we are facing when modelling stars and possible ways toward their solutions. I discuss how future observational ground-based or spatial programs (in particular those dedicated to micro-arc-second astrometry, asteroseismology and interferometry) will provide precise determinations of the stellar parameters and contribute to a better knowledge of stellar interiors and atmospheres in a wide range of stellar masses, chemical composition and evolution stages.
The ESPRI project: narrow-angle astrometry with VLTI-PRIMA
Authors: Launhardt R. , Henning T. , Queloz D. , Quirrenbach A. , Delplancke F. , Elias N. M. , Pepe F. , Reffert S. , Ségransan D. , Setiawan J. , Tubbs R. ,   the ESPRI consortium
Published: July 2008

AbstractWe describe the ongoing hardware and software developments that shall enable the ESO VLTI to perform narrow-angle differential delay astrometry in K-band with an accuracy of up to 10 μarcsec. The ultimate goal of these efforts is to perform an astrometric search for extrasolar planets around nearby stars.