Astrometric observation of the Galactic LPVs with VERA; Mira and OH/IR stars

We present studies of Long Period Variables (LPVs) in our Galaxy based on astrometric VLBI observations of H2O and SiO masers. The Galactic Miras and OH/IR stars are our main targets. For Miras, we present the distribution of the LPVs on the MK – log P plane. Galactic Miras show consistency with PLR in the LMC except for some fainter sources. Parallaxes of the LPVs determined from VLBI and Gaia are compared. There seems to be some offset.

Astrometric Reduction of Cassini ISS Images of Enceladus in 2015 Based on Gaia DR1

The Gaia DR1 catalogue stars are taken as reference ones to reduce the Cassini ISS images of Enceladus in 2015, and a total of 494 Cassini-centered astrometric observation are obtained in right ascension(α) and declination (δ) in the international Celestial Reference Frame(ICRF). Compared with JPL ephemerides SAT367, we derive that their mean residuals are a few tens meters in α*cos(δ) and a few kilometers in δ, and their standard deviation is not over 2 kilometers. Compared with the results from UCAC4 catalogue stars, The Gaia DR1 has the equivalent precision of reduction.

The second post-Newtonian light propagation and its astrometric measurement in the solar system

The relativistic theories of light propagation are generalized by introducing two new parameters ς and η in the second post-Newtonian (2PN) order, in addition to the parametrized post-Newtonian (PPN) parameters γ and β. This new 2PN parametrized (2PPN) formalism includes the nonstationary gravitational fields and the influences of all kinds of relativistic effects. The multipolar components of gravitating bodies are taken into account as well at the first post-Newtonian (1PN) order. The equations of motion and their solutions of this 2PPN light propagation problem are obtained. Started from the definition of a measurable quantity, a gauge-invariant angle between the directions of two incoming photons for a differential measurement in astrometric observation is discussed and its formula is derived. For a precision level of a few microarcsecond (μas) for space astrometry missions in the near future, we further consider a model of angular measurement, the Laser Astrometric Test of Relativity (LATOR)-like missions. In this case, all terms with aimed at the accuracy of ~1μas are estimated.

Overview of Gaia Multi-Color Photometry

Gaia will obtain multi-color photometry for astrometric and astrophysical purposes. A photometry in five broad bands and with high angular resolution will be obtained after every astrometric observation of a star, especially for the sake of correcting slight astrometric chromaticity errors of the optical system. A separate smaller telescope will obtain photometry in eleven passbands of medium width designed to serve the astrophysical analysis of the mission results. The medium-band photometry (MBP) has less angular resolution, but much longer effective integration time than the broad-band photometry (BBP).

The Potential of Differential Astrometric Interferometry from the High Antarctic Plateau

The low infrared background and high atmospheric transparency are the principal advantages of Antarctic Plateau sites for astronomy. However, the poor seeing (between 1 and 3 as) negates much of the sensitivity improvements that the Antarctic atmosphere offers, compared to mid-latitude sites such as Mauna Kea or Cerro Paranal. The seeing at mid-latitude sites, though smaller in amplitude, is dominated by turbulence at altitudes of 10–20 km. Over the Antarctic Plateau, virtually no high altitude turbulence is present in the winter. The mean square error for an astrometric measurement with a dual-beam, differential astrometric interferometer in the very narrow angle regime is proportional to the integral of h2C2N(h). Therefore, sites at which the turbulence occurs only at low altitudes offer large gains in astrometric precision. We show that a modest interferometer at the South Pole can achieve 10 μ as differential astrometry 300 times faster than a comparable interferometer at a good mid-latitude site, in median conditions. Science programs that would benefit from such an instrument include planet detection and orbit determination, and astrometric observation of stars microlensed by dark matter candidates.

Precision of Studies From Astrometric Observations: Recent Progress and Future Prospects

Recent progress of precision in astrometric studies is summarized and the weights of systematic errors in astrometric observation are analysed.