arXiv subjects

Shilong Liao

Publications and source records attributed to Shilong Liao.

23 records · Page 2Linked to original sources

arXiv2021

Progress on the Astrometric Gravitation Probe design

The Astrometric Gravitation Probe mission is a modern version of the 1919 Dyson-Eddington-Davidson experiment, based on a space-borne telescope with a permanent built-in eclipse, provided by a coronagraphic system. The expected improvement on experimental bounds to General Relativity and competing gravitation theories is by at least two orders of magnitude. The measurement principle is reviewed, in particular the principle of Fizeau-like combination of a set of individual inverted coronagraphs simultaneously feeding a common high resolution telescope. Also, the payload has a dual field of view property, in order to support simultaneous observations of stellar fields either very close, or far away, from the Sun, i.e. fields affected by either high or low light bending. We discuss a set of solutions introduced in the optical design to improve on technical feasibility and robustness of the optical performance against perturbations, in particular induced by manufacturing and alignment tolerances, and launch stresses.

astro-ph.IM↗

arXiv2021

The ASTRA project: a doorway to future astrometry

Astrometric Science and Technology Roadmap for Astrophysics (ASTRA) is a bilateral cooperation between China and Italy with the goal of consolidating astrometric measurement concepts and technologies. In particular, the objectives include critical analysis of the Gaia methodology and performance, as well as principle demonstration experiments aimed at future innovative astrometric applications requiring high precision over large angular separations (one to 180 degrees). Such measurement technologies will be the building blocks for future instrumentation focused on the "great questions" of modern cosmology, like General Relativity validity (including Dark Matter and Dark Energy behavior), formation and evolution of structure like proto-galaxies, and planetary systems formation in bio compatibles environments. We describe three principle demonstration tests designed to address some of the potential showstoppers for high astrometric precision experiments. The three tests are focused on the key concepts of multiple fields telescopes, astrometric metrology and very fine sub-pixel precision (goal: <1/2000 pixel) in white light.

astro-ph.IM↗

arXiv2019

A wide star-black-hole binary system from radial-velocity measurements

All stellar mass black holes have hitherto been identified by X-rays emitted by gas that is accreting onto the black hole from a companion star. These systems are all binaries with black holes below 30 M$_{\odot}$$^{1-4}$. Theory predicts, however, that X-ray emitting systems form a minority of the total population of star-black hole binaries$^{5,6}$. When the black hole is not accreting gas, it can be found through radial velocity measurements of the motion of the companion star. Here we report radial velocity measurements of a Galactic star, LB-1, which is a B-type star, taken over two years. We find that the motion of the B-star and an accompanying H$α$ emission line require the presence of a dark companion with a mass of $68^{+11}_{-13}$ M$_{\odot}$, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. The gravitational wave experiments have detected similarly massive black holes$^{7,8}$, but forming such massive ones in a high-metallicity environment would be extremely challenging to current stellar evolution theories$^{9-11}$.

astro-ph.SR↗

arXiv2018

The properties of the quasars astrometric solution in Gaia DR2

Gaia data release 2 (DR2) provides the best non-rotating optical frame aligned with the radio frame (ICRF) thanks to the inclusion of about half-million quasars in the 5-parameter astrometric solution. Given their crucial diagnostic role for characterizing the properties of the celestial reference frame, we aim to make an independent assessment of the astrometry of quasars in DR2. We cross-match with Gaia DR2 the quasars from LQAC3, SDSS and LAMOST, obtaining 208743 new sources (denominated as KQCG). With the quasars already identified in DR2, we estimate the global offsets of parallaxes and proper motions of different quasar subsets to check their astrometric consistency. The features of the proper motion field are analyzed by means of vectorial spherical harmonics (VSH); the scalar field of parallaxes is expanded into spherical harmonics to investigate their spatial correlation. We find a bias of $\sim$ $-0.030$ $mas$ in KQCG parallaxes, and a bias of $-9.1$ $μas/yr$ in $μ_{α\ast}$; a $\sim$ +10 $μas/yr$ bias in $μ_δ$ consistently found in the entire quasar sample. The results of the VSH analysis on different subsets indicate good agreement between them. The proper motion field exhibits a ((-6,-5,-5) $\pm$ 1) $μas/yr$ rotation in the northern hemisphere and a rotation of ((0,+1,+3) $\pm$ 1 ) $μas /yr$ in the southern one. The spherical harmonics expansion of the parallax field reveals an angular scale of systematics of $\approx$ 18 degrees with a RMS amplitude of 13 $μ$as. The positional comparison shows that the axes of the current Gaia Celestial Reference Frame and the ICRF2 are aligned within 30 $μ$as.

astro-ph.GA↗

arXiv2018

Identifying quasars with astrometric and mid-infrared methods from APOP and ALLWISE

Context. Quasars are spatially stationary, and they are essential objects in astrometry when defining reference frames. However, the census of quasars is far from complete. Mid-infared colors can be used to find quasar candidates because AGNs show a peculiar appearance in mid-infrared color, but these methods are incapable of separating quasars from AGNs. Aims. The aim of our study is to use astrometric and mid-infrared methods to select quasars and get a reliable quasar candidates catalog. Methods. We used a near-zero proper motion criterion in conjuction with WISE (all-sky Wide-field Infrared Survey Explorer) [W1-W2] color to select quasar candidates. The [W1-W2] color criterion is defined by the linear boundary of two samples: LAMOST DR5 quasars, which serve as the quasar sample, and LAMOST DR5 stars and galaxies, which serve as the non-quasar sample. The contamination and completeness are evaluated. Results. We present a catalog of 662 753 quasar candidates, with a completeness of about 75% and a reliability of 77.2%.

astro-ph.GA↗