Astrometric Telescope Research Articles

Compact binary formation in open star clusters – I. High formation efficiency of Gaia BHs and their multiplicities

ABSTRACT Gaia BHs, black hole (BH) binaries discovered from data base of an astrometric telescope Gaia, pose a question to the standard binary evolution model. We have assessed whether Gaia BHs can be formed through dynamical capture in open clusters rather than through isolated binary evolution. We have performed gravitational N-body simulations of 100 open clusters with $10^5 \, \mathrm{M}_\odot$ in total for each metallicity Z = 0.02, 0.01, and 0.005. We have discovered one Gaia BH-like binary escaping from an open cluster, and found that the formation efficiency of Gaia BHs in open clusters ($\sim 10^{-5} \, \mathrm{M}_\odot ^{-1}$) is larger than in isolated binaries ($\sim 10^{-8} \, \mathrm{M}_\odot ^{-1}$) by 3 orders of magnitude. The Gaia BH-like binary is the inner binary of a triple star system. Gaia BHs can have tertiary stars frequently, if they are formed in open clusters. Combining additional N-body simulations with 8000 open clusters with $8 \times 10^6 \, \mathrm{M}_\odot$, we have estimated the number of Gaia BHs in the Milky Way disc to 104–105 (depending on the definitions of Gaia BHs), large enough for the number of Gaia BHs discovered so far. Our results indicate that the discoveries of Gaia BHs do not request the reconstruction of the standard binary evolution model, and that Gaia BHs are a probe for the dynamics of open clusters already evaporated.

URAT South Parallax Results

Abstract We present 916 trigonometric parallaxes and proper motions of newly discovered nearby stars from the United States Naval Observatory Robotic Astrometric Telescope (URAT). Observations were taken at the Cerro Tololo Interamerican Observatory over a 2-year period from 2015 to 2017 October covering the entire sky south of about +25° decl. SPM4 and UCAC4 early epoch catalog data were added to extend the temporal coverage for the parallax and proper motion fit up to 48 years. Using these new URAT parallaxes, optical and near-IR photometry from the AAVSO Photometric All-Sky Survey and Two Micron All-Sky Survey catalogs, we identify possible new nearby dwarfs, young stars, low-metallicity subdwarfs and white dwarfs. Comparison to known trigonometric parallaxes shows a high quality of the URAT-based results confirming the error in parallax of the URAT south parallaxes reported here to be between 2 and 13 mas. We also include additional 729 trigonometric parallaxes from the URAT north 25 pc sample published in Finch & Zacharias here after applying the same criterion as for the southern sample to have a complete URAT 25 pc sample presented in this paper.

PARALLAX RESULTS FROM URAT EPOCH DATA

ABSTRACT We present 1103 trigonometric parallaxes and proper motions from the United States Naval Observatory Robotic Astrometric Telescope (URAT) observations taken at the Naval Observatory Flagstaff Station (NOFS) over a three-year period from 2012 April to 2015 June covering the entire sky north of about decl. We selected two samples: previously suspected nearby stars from known photometric distances and stars showing a large, significant parallax signature in URAT epoch data without any prior selection criteria. All systems presented in this paper have an observed parallax ≥40 mas with no previous published trigonometric parallax. The formal errors on these weighted parallax solutions are mostly between 4 and 10 mas. This sample gives a significant (of the order of 50%) increase to the number of known systems having a trigonometric parallax to be within 25 pc of the Sun (without applying Lutz–Kelker bias corrections). A few of these are found to be within 10 pc. Many of these new nearby stars display a total proper motion of less than 200 mas yr−1. URAT parallax results have been verified against Hipparcos and Yale data for stars in common. The publication of all signifigant parallax observations from URAT data is in preparation for CDS.

Formation flying for very high precision astrometry: NEAT and micro-NEAT mission concepts

The nearest solar-type stars are of prime interest for the science of exoplanets because they are the objects most suitable for direct detection and future spectroscopic study of telluric planets. In addition, the habitable zone is a region of special interest for astrobiology and for comparison with our own Earth. These two features point to astrometry as a unique tool for a systematic study of the architectures of planetary systems in that domain because the astrometric signal is larger the nearer the stars and the wider the planetary orbits whereas the other techniques favour smaller orbits. The astrometric technique is highly complementary and better suited for planets in the habitable zone (HZ). Recently, we have proposed two astrometric missions to ESA with different scales, but both of them use flying formation capability for the platform: Nearby Earth Astrometric Telescope (NEAT) as an M-class mission with a 1 m telescope and μNEAT as an S-class mission with a 0.3 m telescope. μNEAT can search and characterise giant planets, i.e., Neptune’s mass and heavier, in the HZ around these stars, whereas NEAT can detect even smaller planets down to an Earth mass. The scientific impact of NEAT/μNEAT would be tremendous because they would provide the first exhaustive census of terrestrial/giant planet architecture in the HZ and beyond, around the nearest solar-type stars.

The principle of measuring unusual change of underground mass by optical astrometric instrument

Abstract: Optical observations from a ground-based astrometric instrument provide a unique set of data sensitive to variations of local plumb line, which represent the change of local gravitational field on the ground. The local gravitational change could be caused by density variation or movement of underground mass in addition to tidal action. Earthquake was found to be related with gravitational change. A seismic zone could have abnormal underground material density, causing the variation of plume line on the ground. In this frame, the astrometric telescope can measure the variation of local plumb line by observing the local astronomical longitudes and latitudes from stars in the Hipparcos catalog. In this study, we estimate the deflection angle of the plumb line on a ground site, and give a relation between the angle, abnormal mass and site distance (depth and horizontal distance). Then we derive the abnormality of underground material density using the plumb lines measured at different sites, and study the earthquake gestation, development and occurrence. Using the deflection angles of plumb lines observed at two sites, we give a method to calculate the mass and the center of gravity of underground materials. We also estimate the abnormal masses of latent seismic zones with different energy, using thermodynamic relations, and introduce a new optical astrometric instrument we had developed.

NEAT: An Astrometric Mission to Detect and Characterize Nearby Habitable Planetary Systems

AbstractMany planets have been detected so far but very few around nearby stars that could allow characterization of their atmosphere thanks to their proximity. There are known exoplanets around less than 8.3% of the FGK stars of the Solar neighborhood (d<20 pc) and the vast majority of them are giant planets. Within the ESA Cosmic Vision 2015-2025 plan, the scientific goal of the NEAT (Nearby Earth Astrometric Telescope) mission is to detect and characterize planetary systems around these nearby stars in an exhaustive way down to 1 Earth-mass in the habitable zone. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to the Earth-mass limit. NEAT will continue the work performed by Hipparcos and Gaia by reaching a precision that is improved by two orders of magnitude on pointed targets compared to Gaia. We present the free-flyer concept that has been submitted to the 2010 ESA call for M3 missions with two satellites flying in formation 40m apart.

High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)

(abridged) A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT - the Nearby Earth Astrometric Telescope. NEAT is designed to carry out space-borne extremely-high-precision astrometric measurements sufficient to detect dynamical effects due to orbiting planets of mass even lower than Earth's around the nearest stars. Such a survey mission would provide the actual planetary masses and the full orbital geometry for all the components of the detected planetary systems down to the Earth-mass limit. The NEAT performance limits can be achieved by carrying out differential astrometry between the targets and a set of suitable reference stars in the field. The NEAT instrument design consists of an off-axis parabola single-mirror telescope, a detector with a large field of view made of small movable CCDs located around a fixed central CCD, and an interferometric calibration system originating from metrology fibers located at the primary mirror. The proposed mission architecture relies on the use of two satellites operating at L2 for 5 years, flying in formation and offering a capability of more than 20,000 reconfigurations (alternative option uses deployable boom). The NEAT primary science program will encompass an astrometric survey of our 200 closest F-, G- and K-type stellar neighbors, with an average of 50 visits. The remaining time might be allocated to improve the characterization of the architecture of selected planetary systems around nearby targets of specific interest (low-mass stars, young stars, etc.) discovered by Gaia, ground-based high-precision radial-velocity surveys.

Dense optical reference frames: UCAC and URAT

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.

Astrometric reference stars: from UCAC to URAT

AbstractCurrently available astrometric catalogs will be reviewed, and instrumentation and observational issues discussed, particularly systematic errors and their control. The U.S. Naval Observatory (USNO) CCD Astrograph Catalog (UCAC) is an all‐sky astrometric survey to 16th magnitude. It was observed with a semi‐automated telescope on a low budget. The second data release (July 2003) contains positions, proper motions, and photometry for over 48 million stars; the final release is expected in 2006. Design studies have been performed for a new 0.9‐meter aperture USNO Robotic Astrometric Telescope (URAT) with a single chip (≥100 Mpixel), 3 degree FOV and circular symmetric pupil. Its operation is envisioned to be fully automatic, generating stellar positions on the 5 to 10 mas level to at least 18th magnitude with a limiting magnitude of about 20 to 21. These reference stars, being on an inertial system (linked to quasars), will be very beneficial for LSST, PanSTARRS and other projects. With a few years of observing, absolute trigonometric parallaxes (5‐20 mas, depending on magnitude) could be obtained for all stars accessible by URAT from an initially southern hemisphere location. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Astrometry of five major Uranian satellites in 1995–1997

At the oppositions of 1995-1997, a total of 122 CCD frames were taken on the 1.56 m astrometric telescope at the Sheshan station, yielding 864 positions of the major Uranian satellites. The calibration of the images was carried out using a least-squares iterative program by fitting to the well-known orbits of the brighter moons of Uranus, based on the modern theory GUST86 and an ephemeris produced by numerical integration. The residuals lay between 0: 00 03 and 0: 00 05 for each of the inter-satellite positions, except for the innermost and faintest satellite Miranda, whose residuals exceeded 0: 08 due to the proximity of Uranus. No significant systematic errors were found when using satellites themselves for determining calibration parameters. The largest residual in the comparison between GUST86 and the numerical integration was about 0: 00 01.

Using Precise Solar Limb Shape Measurements to Study the Solar Cycle

Despite 20 years of total solar irradiance measurements from space, the lack of high precision spatially resolved observations limits definitive answers to even simple questions like ``Are the solar irradiance changes caused solely by magnetic fields perturbing the radiative flux at the photosphere?" More subtle questions like how the aspheric structure of the sun changes with the magnetic cycle are only now beginning to be addressed with new tools like p-mode helioseismology. Solar 5-min oscillation studies have yielded precise information on the mean radial interior solar structure and some knowledge about the rotational and thermal solar asphericity. Unfortunately this progress has not been enough to generate a self-consistent theory for why the solar irradiance and luminosity vary with the magnetic cycle. We need sharper tools to describe and understand the sun's global aspheric response to its internal dynamo, and we need to be able to measure the solar cycle manifestation of the magnetic cycle on entropy transport from the interior to the photosphere in much the same way that we study the fundamentally more complex problem of magnetic flux transport from the solar interior. A space experiment called the Solar Physics Explorer for Radius, Irradiance and Shape (SPHERIS) and in particular its Astrometric and Photometric Telescope (APT) component will accomplish these goals.

On The Possibility of Identification of the Moving Celestial Objects Observed with the Space Astrometric Telescope

In connection with the creation of the scientific grounds of the Russian Project named “Struve” Space Astrometric System, the main principles of classification and identification of any celestial moving object observed with this System were formulated and basic algorithms were elaborated. These algorithms are invariable for a short or long observational arc, for a known or unknown heavenly body and for an artificial or natural celestial object.For classification of observed celestial bodies the angular velocities of motion are used. These values are calculated from the statistical treatment of the 5 nearest spherical celestial body positions with a time intervalbetween them near 7 seconds.For an identification of well known sky objects ordinary procedure may be used by means of traditional ephemeris calculations. For an identification of unknown natural celestial bodies a special algorithm was developed. Ituses a calculated angular velocity of moving object from one scan to another close scan of observations. Then, having several accurate positions of fixed object during 5-10 hours per day, we can determine an initial elliptical object’s orbit by the Apparent Motion Parameters Method created at Pulkovo Observatory. It deals with a position of object, its angular velocity and acceleration, position’s angle and a curvature of trajectory on a short observational arc. These last four quantities are named the Apparent Motion Parameters.In spite of a preliminary character of the AMP-method orbits we can identify an observed object through a large interval of time, for example over 2-4 months after orbit determination. In this problem the observed and calculated angular velocities of the object’s motion are very useful. They are new and important ephemeris parameters at the epoch of Space Telescope astrometric positional observations. Examples of simulations of orbit determinations will be presented.

Optical photometric monitoring of γ-ray loud blazars.

The results of the optical monitoring between November 1994 and November 1995 of twenty γ-ray loud blazars included in the Torino blazar monitoring program are presented. All data were taken with the REOSC astrometric telescope of the Torino Astronomical Observatory, equipped with a pixels charge-coupled device (CCD) camera. Observations have been carried out in the standard B, V (Johnson), and R (Cousins) bands. Source magnitudes are calculated with respect to reference stars in the same frame. For half blazar fields it was possible to perform a photometric calibration through the observation of Landolt's fields during photometric nights. In the other cases either photometric sequences from the literature were adopted or, when lacking, magnitudes were simply normalized to their minimum value. Most of the monitored objects show a more or less pronounced brightness variability on both short and long time scales. In a few cases also noticeable intranight variations were detected. Data simultaneous to pointings of the Compton Gamma Ray Observatory (CGRO) are present in our light curves: when the γ data are available they will provide a useful information in order to understand the possible correlations between the optical and γ-ray emissions. For one source (PKS 2254+074) we performed also photopolarimetry, deducing magnitudes, amount of polarization, and position angle in the UBVRI bands.

Carlsberg optical astrometry of the outer solar system

The Carlsberg astrometric telescope has made about 17000 observations of outer Solar System objects since it began operation in 1984. The observed positions of the major planets are compared with JPL DE200 and DE403. The agreement with DE403 is good in general, but unresolved discrepancies of the order 0″.1 are found in Jupiter and Saturn. The run-off between the observations and DE200 which was fitted to observations before 1980 emphasize the need to continue optical observations of the outer planets.

Modelling of a space-based ronchi ruling experiment for high-precision astrometry

An end-to-end modelling program for an astrometric telescope employing a Ronchi ruling has been developed. The program models the aberrated images formed anywhere in the field-of-view. It then determines apparent centroids by simulating the motion of a Ronchi ruling across the field. Photo-electron statistics are included. A 6-term plate-constant model is used to determine the apparent motion of a target star within a reference frame as the object is re-observed through both ideal and perturbed optics. The modelling code is accurate at the submicroarcsecond level.

Conceptual design considerations for the Astrometric Telescope Facility

The system of an astrometric telescope on the Space Station and its support by the Station are described and its feasibility demonstrated. The conceptual design shows that such a facility provides a basis for the study of design alternatives and a point of departure for a detailed design. Basic requirements for this preliminary design are outlined.

The Astrometric Telescope Facility

The Astrometric Telescope Facility (ATF) proposed for use on NASA's planned Space Station is similar in form and data output to ground-based long focus astrometric instruments. With a focal plane scale of 12.7 arc seconds/mm, the strawman design has a field size of 10 arc min square and a limiting visual magnitude fainter than 16. Output from an observation includes the X and Y coordinates of each star and its relative brightness. The targeted precision for the AFT is 0.00001 arc seconds.

Newly Installed Radio and Optical Telescopes in China

AbstractNew radio and optical telescopes installed in recent years in China are summarised. These include the 2.16-m optical telescope, the solar magnetic field telescope, the Miyun synthesis radio telescope, the 1.26-m infrared telescope (Beijing Astronomical Observatory), the 25-m radio telescope as the first station of China’s VLBI network, the 1.56-m astrometric telescope (Shanghai Observatory), and the 13.7-m millimetre wave radio telescope.

Astrophysics from The Moon

The moon offers mixed blessings as a site for astronomical observatories, and some of these are presented in Tables I and II (see the paper by Smith for a more complete discussion). The advantages are so strong that they make the moon a unique site for certain kinds of observatories, particularly those which feature very large telescopes or interferometric arrays of large dimensions, and those that require a presence beyond the screening effect of the earth’s magnetic field. More than one hundred scientists gathered at Annapolis, Maryland for a Workshop on Astrophysics from the Moon (Feb. 5-7, 1990), and discussed these questions in considerable detail (Mumma and Smith 1990). The objective was to examine the astrophysical frontiers of the 21st century, and to identify those which require the presence of astrophysical observatories on the moon for their successful address. The scope of the Workshop was defined to include all areas of space astronomy. It was assumed that the base program of space astronomy will have been completed prior to the emplacement of lunar-based observatories, thus that the four Great Observatories, the Solar and Heliospheric Observatory, the Orbiting Solar Laboratory, the Coronagraphic Imaging and Astrometric Telescope Facility, and the Earth-Orbital Planetary Telescope will all have been accomplished. The Workshop participants tried to look beyond the scientific objectives to be addressed with those Earth-orbiting facilities to the next generation of scientific frontiers, which are associated with the very small, the very distant, and the very faint. This paper summarizes some of the ideas presented there, but these are presented in much greater detail in the published Proceedings (Mumma and Smith 1990).

NASA's Astrometric Telescope Facility

NASA is planning an Astrometric Telescope Facility (ATF) for the U.S. Space Station. Space astrometric observations of unprecedented accuracy will yield many important results, including a planetary detection survey. The proposed facility is a dedicated astrometric telescope using the Multichannel Astrometric Photometer (Gatewood et al., 1987). To achieve the goal of sub-milliarcsecond accuracy requires innovative approaches to measuring technique and data analysis.