bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fringe Tracker for the VLTI Spectro-Imager
Authors: Gai M. , Buscher D. F. , Corcione L. , Ligori S. , Young J. S. 
Published: July 2008

AbstractInterferometry in the near IR aims at providing imaging resolution on the mas scale, and astrometry at the few μas level, from ground based infrastructures using current telescope technology. To take advantage of simultaneous combination of four to eight telescopes, an international consortium is proposing to ESO the development of the VLTI Spectro-Imager. One of the key sub-systems, to measure and correct the atmospheric perturbations relative to the beam phase, is the fringe tracker, aimed at providing the science combiner with long, stable observing conditions. The fringe tracker function in interferometer is equivalent to adaptive optics for conventional telescopes. The fringe tracker concept under study, using minimum redundancy combination and bulk optics, is described.
Astrometry from mutual event and small-separation CCD imaging
Authors: Peng Q. Y. , Emelyanov N. V. , Zhou L. , Gu W. R. 
Published: July 2008

AbstractIn order to determine precisely positions of the Galilean satellites of Jupiter, it is useful that shortly before and/or after photometric observations of a mutual event, normal CCD imaging observation is also performed for the two small-separation satellites. Experimental observations showed that the two observational types, on the whole, could derive mean (O-C) s with very good internal and external agreement (about 15–20 mas).
Astrometric performance of the Schmidt telescope at the Xuyi station of the Purple Mountain Observatory
Authors: Yu Y. , Tang Z. H. , Qi Z. X. , Wu J. F. 
Published: July 2008

AbstractOn January 26, 2006, an area of the sky of 80 deg2 at α = 9h, δ= 20o (J2000.0) was observed with the 100/120cm Schmidt telescope at the Xuyi station of the Purple Mountain Observatory. Astrometric performance of the telescope is analyzed by this group of CCD observations. The results show that: (1) the CCD images suffer from complicated distortions, and a third order plate model is recommended for reductions; (2) there is no obvious magnitude equation for objects brighter than 16.5 mag, and (3) for this group of CCD images, the astrometric precision for objects brighter than 16.5 mag is better than 70 mas per coordinate when reduced against the UCAC2 catalog.
VLBI astrometry for the NASA/Stanford gyroscope relativity mission Gravity Probe B
Authors: Bartel N. , Ransom R. R. , Bietenholz M. F. , Lebach D. E. , Ratner M. I. , Shapiro I. I. , Lestrade J.-F. 
Published: July 2008

AbstractWe used VLBI observations at 8.4 GHz between 1991 and 2005 to determine the motion of the RS CVn binary IM Pegasi (HR 8703), the guide star for the NASA/Stanford gyroscope relativity mission, Gravity Probe B (GP-B). The motion was determined relative to our primary reference, the core of the quasar 3C 454.3. The stability of this core was checked relative to two other extragalactic sources, B2250+194 and B2252+172, the former of which was tied to the ICRF. The core of 3C 454.3 is stationary relative to these two sources to within 30 μas yr−1 in each coordinate. IM Pegasi's radio morphology varies, but appears to be on average centered on the primary. We estimate the proper motion of IM Pegasi with a statistical standard error (sse) of 30 μas yr−1 in each coordinate. We also estimate the parallax with a statistical standard error of 75 μas and parameters of the orbit with sse's corresponding to 110 μas on the sky. Coupled with our upper limit of three times the sse on any systematic errors in each parameter %threefold higher upper limit on the systematic error contributions to each parameter estimate, these results ensure that the uncertainty of IM Pegasi's proper motion makes only a small contribution to the uncertainty of GP-B's tests of general relativity.
Astrometry of red supergiant VY Canis Majoris with VERA
Authors: Choi Y. K. , Hirota T. , Honma M. , Kobayashi H. 
Published: July 2008

AbstractWe present observational results on the red supergiant VY Canis Majoris with VERA. We have observed 22 GHz H2O masers and 43 GHz SiO masers (v=1 and 2 J=1-0) around VY CMa for 13 months. We succesfully detected a parallax of 0.87 ± 0.08 mas, corresponding to the distance of 1.15 +0.10−0.09 kpc using H2O masers. As the result of phase-referencing analyses, we have measured absolute positions for both H2O masers and SiO masers. The H2O maser features show rapid expansion off the central star.
A strategy for implementing differential VLBI
Authors: Li J. L. , Wang J. , Qiao S. B. , Tian F. 
Published: July 2008

AbstractBased on past astrometric and geodetic VLBI observations, a strategy for implementing differential VLBI (DVLBI) is developed by interpolating the non-geometric delay (NGD) at the target's direction using observations of several reference sources spreaded out within a circular ring centered on the target. In contrast to the ordinary approach, in our design the limitations in the angular distance are relaxed and the effects of observational uncertainties in reference sources are reduced. Analysis shows that in our design a precision of the NGD correction in S-band reaches about 1ns only. Our design can be adopted for observations of weak sources and in deep space exploration.
The distance to G59.7+0.1 and W3OH
Authors: Xu Y. , Reid M. J. , Menten K. M. , Zheng X. W. , Brunthaler A. , Moscadelli L. 
Published: July 2008

AbstractWe have measured the distance to the high-mass star-forming region G59.7+0.1 (IRAS 19410+2336) and W3OH. Their distances, 2.20 ± 0.11 kpc and 1.95 ± 0.04 kpc, respectively, were determined by triangulation using Very Long Baseline Array (VLBA) observations of 12.2 GHz methanol masers phase-referenced to compact extragalactic radio sources. In addition to the distances, we have also obtained their proper motions.
Gaia: organisation and challenges for the data processing
Authors: Mignard F. , Bailer-Jones C. , Bastian U. , Drimmel R. , Eyer L. , Katz D. , van Leeuwen F. , Luri X. , O'Mullane W. , Passot X. , Pourbaix D. , Prusti T. 
Published: July 2008

AbstractGaia is an ambitious space astrometry mission of ESA with a main objective to map the sky in astrometry and photometry down to a magnitude 20 by the end of the next decade. While the mission is built and operated by ESA and an industrial consortium, the data processing is entrusted to a consortium formed by the scientific community, which was formed in 2006 and formally selected by ESA one year later. The satellite will downlink around 100 TB of raw telemetry data over a mission duration of 5 years from which a very complex iterative processing will lead to the final science output: astrometry with a final accuracy of a few tens of microarcseconds, epoch photometry in wide and narrow bands, radial velocity and spectra for the stars brighter than 17 mag. We discuss the general principles and main difficulties of this very large data processing and present the organization of the European Consortium responsible for its design and implementation.
To determining the mass of a gravitational body with micro-arcsecond astrometric data
Authors: Cheng H. , Tang Z. H. , Huang C. 
Published: July 2008

AbstractA beam of light from a background source to an observer is deflected by a gravitational body when travelling through the space in its vicinity. The deflection changes with configuration of the background source, the gravitational body and the observer, and the amount of deflection is dependent on the gravitational body's mass. It is anticipated that its mass could be determined if the shift can be measured by future precise astrometric projects such as Gaia or SIM-PlanetQuest.
Reference frame linking and tests of GR with Gaia astrometry of asteroids
Authors: Hestroffer D. , Mouret S. , Berthier J. , Mignard F. , Tanga P. 
Published: July 2008

AbstractThe Gaia satellite, an ESA cornerstone mission to be launched at the end of the year 2011, will observe a large number of celestial bodies including also small bodies of the solar system. Albeit spread from the inner to the outer regions of the solar system, these are mainly near-Earth objects and main-belt asteroids. All objects brighter than magnitude V ≤ 20 that cross the field of view (i.e. with solar elongation 45° ≤ L ≤ 135°) of the survey-mode scanning telescope will be observed. The mission will provide, over its 5 years duration, high precision photometry and astrometry with an unprecedented accuracy ranging roughly from 0.3 to 3 milli-arcsecond on the CCD level, and depending on the target's magnitude. In addition, several hundreds of QSOs directly observed by Gaia will provide the kinematically non-rotating reference frame in the visible light, resulting in the construction of a ‘Gaia-ICRF’.The positions of the asteroids hence enable to relate the dynamical reference frame—as defined by the equations of motion—to the kinematic one, and to further check the non-rotating consistency between both frames' definition. Here we show the results of a variance analysis obtained from a realistic simulation of observations for such a link. The simulation takes into account the time sequences and geometry of the observations that are particular to Gaia observations of solar system objects, as well as the instrument sensitivity and photon noise. Additionally, we show the achievable precision for the determination of a possible time variation of the gravitational constant Ġ/G. Taking into account the non-completeness of the actually known population of NEOs, we also give updated values for the nominal precision of the joint determination of the solar quadrupole J2 and PPN parameter β.
The current status of the Nano-JASMINE project
Authors: Kobayashi Y. , Gouda N. , Yano T. , Suganuma M. , Yamauchi M. , Yamada Y. , Sako N. , Nakasuka S. 
Published: July 2008

AbstractNano-JASMINE is a nano-size astrometry satellite that will carry out astrometry measurements of nearby bright stars for more than one year. This will enable us to detect annual parallaxes of stars within 300 pc from the Sun. We expect the satellite to be launched as a piggy-back system as early as in 2009 into a Sun synchronized orbit at the altitude between 500 and 800 km. Being equipped with a beam combiner, the satellite has a capability to observe two different fields simultaneously and will be able to carry out HIPPARCOS-type observations along great circles. A 5 cm all aluminum made reflecting telescope with a aluminum beam combiner is developed. Using the on-board CCD controller, experiments with a real star have been executed. A communication band width is insufficient to transfer all imaging data, hence, we developed an onboard data processing system that extracts stellar image data from vast amount of imaging data. A newly developed 2K × 1K fully-depleted CCD will be used for the mission. It will work in the time delayed integration(TDI) mode. The bus system has been designed with special consideration of the following two points. Those are the thermal stabilization of the telescope and the accuracy of the altitude control. The former is essential to achieve high astrometric accuracies, on the order of 1 mas. Therefore relative angle of the beam combiner must be stable within 1 mas. A 3-axes control of the satellite will be realized by using fiber gyro and triaxial reaction wheel system and careful treatment of various disturbing forces.
Laser interferometric high-precision geometry (angle and length) monitor for JASMINE
Authors: Niwa Y. , Arai K. , Ueda A. , Sakagami M. , Gouda N. , Kobayashi Y. , Yamada Y. , Yano T. 
Published: July 2008

AbstractThe telescope geometry of JASMINE should be stabilized and monitored with the accuracy of about 10 to 100 pm or 10 to 100 prad of rms over about 10 hours. For this purpose, a high-precision interferometric laser metrology system is employed. Useful techniques for measuring displacements on extremely small scales are the wave-front sensing method and the heterodyne interferometrical method. Experiments for verification of measurement principles are well advanced.
Development of a very small telescope for a milli-arcsec space astrometry
Authors: Suganuma M. , Kobayashi Y. , Gouda N. , Yano T. , Yamada Y. , Takato N. , Yamauchi M. 
Published: July 2008

AbstractWe are preparing a reflecting telescope for Nano-JASMINE, a very small satellite for global space astrometry of milli-arcsecond accuracy. The telescope has a 5-cm diameter primary mirror and a beam-combiner in front of it. It occupies only about 12x12x17cm and is entirely made out of aluminum alloy. The telescope and its surrounding structures are carefully designed for thermal stability of the optics, especially to control changes in the relative angle of the beam-combiner.
Space Astrometry JASMINE
Authors: Yano T. , Gouda N. , Kobayashi Y. , Yamada Y. , Tsujimoto T. , Suganuma M. , Niwa Y. , Yamauchi M. 
Published: July 2008

AbstractJASMINE is the acronym of the Japan Astrometry Satellite Mission for INfrared (z-band: 0.9 micron) Exploration, and is planned to be launched around 2017. The main objective of JASMINE is to study the fundamental structure and evolution of the Milky Way bulge components. In order to accomplish these objectives, JASMINE will measure trigonometric parallaxes, positions and proper motions of about ten million stars in the Galactic bulge with a precision of 10 microarcsec at z = 14mag.The primary mirror for the telescope has a diameter of 75cm with a focal length of 22.5m. The back-illuminated CCD is fabricated on a 300 micron thick substrate which is fully depleted. These thick devices have extended near infrared response. The size of the detector for z-band is 3cm×3cm with 2048×2048 pixels. The size of the field of view is about 0.6deg×0.6deg by using 64 detectors on the focal plane. The telescope is designed to have only one field of view, which is different from the designs of other astrometric satellites. JASMINE will observe overlapping fields without gaps to survey a total area of about 20deg×10 deg around the Galactic bulge. Accordingly we make a “large frame” of 20deg×10 deg by linking the small frames using stars in overlapping regions. JASMINE will observe the Galactic bulge repeatedly during the mission life of about 5 years.
From the Roemer mission to Gaia
Authors: Høg E. 
Published: July 2008

AbstractAt the IAU symposium in Shanghai September 1992 the present author made the first proposal for a specific mission concept post-Hipparcos, the first scanning astrometry mission with CCDs in time-delayed integration mode (TDI). Direct imaging on CCDs in long-focus telescopes was described as later adopted for the Gaia mission. The mission called Roemer was designed to provide accurate astrometry and multi-colour photometry of 400 million stars brighter than 18 mag in a five-year mission. The early years of this mission concept are reviewed.
The Infrared Astrometry today
Authors: Kharin A. S. , Vedenicheva I. P. , Zolotukhina A. V. 
Published: July 2008

AbstractInfrared Astrometry is one of the seven subdivisions of astrometry that detects emission in the range from 0.7 to 350 μm. Specific features and some problems of this one are discussed here and more details are provided on our web site “INFRARED ASTROMETRY” with the following URL http://www.mao.kiev.ua/IR. This web page includes 7 sections that will be expanded and regularly updated.
Asteroid astrometry as a link between ICRF and the Dynamical Reference Frames
Authors: Nedelcu D. A. , Souchay J. , Birlan M. , Popescu P. P. , Paraschiv P. V. , Badescu O. 
Published: July 2008

AbstractHighly accurate astrometry of asteroids in the frame of QSOs will provide the direct link between the Dynamical Reference Frame and the International Celestial Reference Frame. We propose a procedure that implies a selection of events for asteroids with accurately determined orbits crossing the CCD field containing the selected quasars. For asteroid ephemerides, a numerical integration method coupled with precise modelling of asteroid brightness will be used for analyzing our observations. A list of predictions for this type of “close approaches” will be presented.
Multi-wavelength VLBI phase-delay astrometry of a complete sample of radio sources
Authors: Martí-Vidal I. , Marcaide J. M. , Guirado J. C. 
Published: July 2008

AbstractWe report on the first global high-precision (differential phase-delay) astrometric analyses performed on a complete set of radio sources. We have observed the S5 polar cap sample, consisting of 13 quasars and BL Lac objects, with the VLBA at 8.4, 15, and 43 GHz. We have developed new algorithms to enable the use of the differential phase-delay observable in global astrometric observations. From our global analyses, we determine the relative positions between all pairs of sources with typical precisions ranging from 10 to 200 μas, depending on observing frequency and source separation. In this paper, we discuss the impact of this observable in the enhancement of the astrometric precision. Since a large fraction of the S5 polar cap sources are ICRF defining sources, this may result in a test of the ICRF stability. Our multi-epoch/multi-frequency approach will also provide both absolute kinematics and spectral information of all sources in the sample. In turn, this will provide an important check on key predictions of the standard jet interaction model.
Solved and unsolved questions in the non-rigid Earth nutation study
Authors: Huang C. L. 
Published: July 2008

AbstractAt the IAU 26th GA held in Prague in 2006, a new precession model (P03) was recommended and adopted to replace the old one, IAU1976 precession model. This new P03 model is to match the IAU2000 nutation model that is for anelastic Earth model and was adopted in 2003 to replace the previous IAU1980 model. However, this IAU2000 nutation model is also not a perfect one for our complex Earth, as stated in the resolution of IAU nutation working group. The Earth models in the current nutation theories are idealized and too simple, far from the real one. They suffer from several geophysical factors: the an-elasticity of the mantle, the atmospheric loading and wind, the oceanic loading and current, the atmospheric and oceanic tides, the (lateral) heterogeneity of the mantle, the differential rotation between the inner core and the mantle, and various couplings between the fluid outer core and its neighboring solids (mantle and inner core). In this paper, first we give a very brief review of the current theoretical studies of non-rigid Earth nutation, and then focus on the couplings near the core-mantle boundary and the inner core-outer core boundary, including the electro-magnetic, viscous, topographic, and gravitational couplings. Finally, we outline some interesting future studies.
Radio interferometric tests of general relativity
Authors: Fomalont E. B. , Kopeikin S. 
Published: July 2008

AbstractSince VLBI techniques produce a microarcsecond positional accuracy of celestial objects, tests of GR using radio sources as probes of a gravitational field have been made. We present the results from two recent tests using the VLBA: in 2005, the measurement of the classical solar deflection; and in 2002, the measurement of the retarded gravitational deflection associated with Jupiter. The deflection experiment measured γ to an accuracy of 3 × 10−4; the Jupiter experiment measured the retarded term to 20% accuracy. The controversy over the interpretation of the retarded term is summarized.
Second post-Newtonian approximation of light propagation in Einstein-Aether theory
Authors: Xie Y. , Huang T. Y. 
Published: July 2008

AbstractFuture deep space laser ranging missions together with astrometry missions will be able to test relativistic gravity to an unprecedented level of accuracy and will require second post-Newtonian approximation of relevant theories of gravity. Einstein-aether theory is adopted as the theory of gravity and the second post-Newtonian approximation of light propagation is studied.
JASMINE data analysis
Authors: Yamada Y. , Gouda N. , Yano T. , Kobayashi Y. , Niwa Y. ,   JASMINE Working group
Published: July 2008

AbstractJapan Astrometry Satellite Mission for Infrared Exploration (JASMINE) aims to construct a map of the Galactic bulge with a 10 μasaccuracy. We use z-band CCD or K-band array detector to avoid dust absorption, and observe about 10 × 20 degrees area around the Galactic bulge region.In this poster, we show the observation strategy, reduction scheme, and error budget. We also show the basic design of the software for the end-to-end simulation of JASMINE, named JASMINE Simulator.
Structure and kinematics of the Milky Way spirals traced by open clusters
Authors: Zhu Z. 
Published: July 2008

AbstractSelecting 301 open clusters with complete spatial velocity measurements and ages, we are able to estimate the disk structure and kinematics of the Milky Way. Our analysis incorporates the disk scale height, the circular velocity of the Galactic rotation, the Galactocentric distance of the Sun and the ellipticity of the weak elliptical potential of the disk. We have derived the distance of the Sun to the Galactic center R0=8.03±0.70 kpc, that is in excellent agreement with the literature. From kinematic analysis, we found an age-dependent rotation of the Milky Way. The mean rotation velocity of the Milky Way is obtained as 235±10 km s−1. Using a dynamic model for an assumed elliptical disk, a clear weak elliptical potential of the disk with ellipticity of ε(R0) = 0.060±0.012 is detected, the Sun is found to be near the minor axis with a displacement of 30°±3°. The motion of clusters is suggested to be on elliptical orbits other than the circular rotation.
15 years of high precision astrometry in the Galactic Center
Authors: Gillessen S. , Genzel R. , Eisenhauer F. , Ott T. , Trippe S. , Martins F. 
Published: July 2008

AbstractIn 1992, we obtained the first observations of S2 a star close to the supermassive black hole at the Galactic Center. In 2002, S2 passed its periastron and in 2007, it completed a first fully observed revolution. This orbit allowed us to determine the mass of and the distance to the supermassive black hole with unprecedented accuracy. Here we present a re-analysis of the data set, enhancing the astrometric accuracy to 0.5 mas and increasing the number of well-determined stellar orbits to roughly 15. This allows to constrain the extended mass distribution around the massive black hole and will lead in the near future to the detection of post-Newtonian effects. We will also give an outlook on the potential of interferometric near-infrared astrometry with 10 microarcsecond accuracy from the VLTI.
Mass segregation effects in very young open clusters
Authors: Chen L. , de Grijs R. , Zhao J. L. 
Published: July 2008

AbstractWe derived proper motions and membership probabilities of stars in the regions of two very young (~ 2–4 Myr-old) open clusters NGC 2244 and NGC 6530. Both clusters show clear evidence of mass segregation, which provides strong support for the suggestion that the observed mass segregation is – at least partially – due to the way in which star formation has proceeded in these complex star-forming regions (“primordial” mass segregation).