Theia: Faint objects in motion or the new astrometry frontier

2020

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 ...

Proceedings of the International Astronomical Union, 2009

The scientific objectives of the Gaia mission cover areas of galactic structure and evolution, stellar astrophysics, exoplanets, solar system physics, and fundamental physics. Astrometrically, its main contribution will be the determination of millions of absolute stellar parallaxes and the establishment of a very accurate, dense and faint non-rotating optical reference frame. With a planned launch in spring 2012, the project is in its advanced implementation phase. In parallel, preparations for the scientific data processing are well under way within the Gaia Data Processing and Analysis Consortium. Final mission results are expected around 2021, but early releases of preliminary data are expected. This review summarizes the main science goals and overall organisation of the project, the measurement principle and core astrometric solution, and provide an updated overview of the expected astrometric performance.

Eprint Arxiv 1108 4784, 2011

The NEAT (Nearby Earth Astrometric Telescope) mission is a proposition submitted to ESA for its 2010 call for M-size mission. The main scientific goal is to detect and characterize planetary systems in an exhaustive way down to 1 Earth mass in the habitable zone and further away, around nearby stars for F, G, and K spectral types. 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 that mass limit. Extremely- high-precision astrometry, in space, can detect the dynamical effect due to even low mass orbiting planets on their central star, reaching those scientific goals. NEAT will continue the work performed by Hipparcos (1mas precision) and Gaia (7{\mu}as aimed) by reaching a precision that is improved by two orders of magnitude (0.05{\mu}as, 1{\sigma} accuracy). The two modules of the payload, the telescope and the focal plane, must be placed 40m away leading to a formation flying option studied as the reference mission. NEAT will operate at L2 for 5 years, the telescope satellite moving around the focal plane one to point different targets and allowing whole sky coverage in less than 20 days. The payload is made of 3 subsystems: primary mirror and its dynamic support, the focal plane with the detectors, and the metrology. The principle is to measure the angles between the target star, usually bright (R \leq 6), and fainter reference stars (R \leq 11) using a metrology system that projects dynamical Young's fringes onto the focal plane. The proposed architecture relies on two satellites of about 700 kg, offering a capability of more than 20,000 reconfigurations. The two satellites are launched in a stacked configuration using a Soyuz ST launch, and are deployed after launch to individually perform cruise to their operational Lissajous orbit.

2006

Precision ground-based photometric and astrometric measurements enable exciting new astrophysical research programs. The CCD/Transit Instrument with Innovative Instrumentation (CTI-II) is the second generation of a 1.8-m stationary, meridian pointing telescope fundamentally capable of millimagnitude photometry and milliarcsecond astrometry. Our goal is demonstrably to attain and maintain this precision in practice. The optical design for this telescope is complete and a unique real-time metrology system is being tested. An innovative focal plane mosaic including real-time focus feedback is being finalized. We discuss the telescope system design considerations, support instrumentation and calibration techniques that allow this precision, even for measurements made through Earth's turbulent and turbid atmosphere. Ancillary instrumentation includes weather stations, cloud monitors, optical and structural metrology and monitoring instruments, a microbarograph array, an atmospheric extinction lidar and a system of cameras capable of providing real-time extinction measurements. The stationary, fully automated CTI-II uses the time-delay and integrate (TDI) readout mode operated at the sidereal rate on a mosaic of CCD detectors to nightly generate a five bandpass, 1° wide (declination) image, nominally 120° long (corresponding to observing for an eight-hour night) strip image of the sky to limiting magnitudes fainter than 21 per bandpass. After one year CTI-II will have completed observation of a small circle on the sky at a declination of +28°. The CTI-II data, approximately 200 Gbytes nightly, will enable a large number of astrophysical research programs including Galactic astronomy based upon motions and parallaxes of stars in the solar neighborhood, discovery and synoptic monitoring of black-hole related variability in the cores of galaxies, and the discovery of targets of opportunity based upon either luminosity variability (e.g. supernovae) or motion (e.g. asteroids and comets). The same database can be used to construct a calibrated, homogeneous photometric and astrometric standard star catalog for northern hemisphere observers. Multi-night observations are combined to detect, classify and exclude variable stars, enhance the precision of photometry, and refine the positions and motions of more than 10 6 stars distributed in a strip continuous in RA and 1° wide in declination. Multi-year observations allow production of precision astrometry and photometry, and result in a system of faint photometric and astrometric standard stars useful to northern observers of the sky, including past, current and future large-scale surveys such as the Sloan Digital Sky Survey (SDSS), Pan-STARRS and prototypically the Large Synoptic Survey Telescope (LSST). The always observable strip of standard stars will be useful for optical sky surveillance systems, in general. The techniques and technologies under development for CTI-II enable new capabilities in faint object detection and characterization for low Earth orbit (LEO) and geosynchronous transfer orbit (GTO) satellites. CTI-II is being designed and implemented as part of the Near Earth Space Surveillance Initiative (NESSI), which will link CTI-II to the Hobby-Eberly Telescope (HET) at McDonald Observatory, a giant special-purpose spectroscopic telescope capable of obtaining a spectrum of any target of opportunity and synoptically monitoring any object discovered by CTI-II to its faint limiting magnitude. NESSI is funded by AFRL. At the end of the 18 th century William Herschel used transit telescope observations referred to as "sweeps" to correctly deduce the flattened geometry of our Milky Way Galaxy. For astronomers in the 19 th century the transit telescope was the epitome of precision astronomical measurement. Transit instruments aided in defining celestial coordinates, discovering the motion of stars in our Galaxy and determining terrestrial time and longitude. In the 20 th century (1980s) first-generation CCD detectors operated in the time-delay and integrate (TDI) mode were applied for the first time to a stationary transit telescope, the CCD/Transit Instrument (CTI), to accomplish a multicolor survey of a small circle of the sky at +28° declination . The TDI mode of CCD operation has since been applied to other projects, including the Sloan Digital Sky Survey (SDSS) [5], the Palomar-Quest Survey [6], the Flagstaff Astrometric Scanning Transit Telescope (FASTT) [7] and the Carlsberg Meridian Telescope [8]. We resurrect the transit telescope, this generation incorporating modern optics, detectors, metrology, ancillary instruments and structural design concepts to address precise ground-based astronomical measurements. The goal of this telescope and its supporting innovative instrumentation is to break the "1% barrier" to photometric accuracy apparently imposed by techniques using telescopic data alone. A second goal is astrometric measurements with precision significantly better than 0.1 arcsec rms per night. Our approach to these goals is to supplement the photometric and astrometric observations with telescope metrology and monitoring and additional instrumentation to provide calibration data on various effects in Earth's atmosphere.

Planetary and Space Science, 2008

The mission Gaia by European Space Agency (ESA) is expected to fly at the end of 2011 and to perform an all-sky, magnitude-limited survey for 5 years. The probe will not use an input catalogue, and will get high accuracy astrometry and photometry for all sources of magnitude V o20. Low-resolution spectra will also be available. Moving Solar System objects will be observed as well, and their observations will be processed by a specific pipeline in order to retrieve the physical and dynamical characteristics of each object. In this contribution we will mainly focus on the impact of Gaia observations on asteroid dynamics. A dramatic improvement of orbital elements is expected, as well as the measurement of subtle effects such as those related to general relativity (GR). Gaia observations will also be supported by a network of ground-based observation sites, capable of providing follow-up for newly discovered objects that will not receive an adequate coverage from space. Specific strategies for follow-up are being planned and tested. These will need to take into account the peculiar observing geometry (large parallax effect due to the orbit of Gaia around L2) and the time constraints dictated by data processing. r

2001

We explore several exciting projects that could be achieved by Full-Sky Astrometric Mapping Explorer (FAME), or similar astrometric satellites, by including a limited number of faint objects (15 < R � 18) in its observing list, that is, by going beyond the current R < 15 limit. Observing some 50,000 quasars will improve the definition of the reference frame in each direction from 17 µasyr −1 to 8 µasyr −1, allowing the proper motion of the Galactic center (the reflex motion of the Sun) to be determined with an accuracy of 0.1%. It will also allow precision tests of non-axisymmetry of the Galaxy and very accurate proper motions of the Magellanic Clouds. Quasar observations also offer a powerful check on any unmodeled parallax systematics. Observing proper motions of 30,000 faint field blue horizontal branch (BHB) stars will allow stellar halo rotation to be mapped to beyond 35 kpc with errors of a few km s −1. Halo substructures producing clumps in the velocity space will be de...

2019

Experimental Astronomy, 2012

This paper on ASTROD I is based on our 2010 proposal submitted for the ESA call for class-M mission proposals, and is a sequel and an update to our previous paper [Experimental Astronomy 23 (2009) 491-527; designated as Paper I] which was based on our last proposal submitted for the 2007 ESA call. In this paper, we present our orbit selection with one Venus swing-by together with orbit simulation. In Paper I, our orbit choice is with two Venus swing-bys. The present choice takes shorter time (about 250 days) to reach the opposite side of the Sun. We also present a preliminary design of the optical bench, and elaborate on the solar physics goals with the radiation monitor payload. We discuss telescope size, trade-offs of drag-free sensitivities, thermal issues and present an outlook. ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. For this mission, accurate pulse timing with an ultra-stable clock, and a drag-free spacecraft with reliable inertial sensor are required. T2L2 has demonstrated the required accurate pulse timing; rubidium clock on board Galileo has mostly demonstrated the required clock stability; the accelerometer on board GOCE has paved the way for achieving the reliable inertial sensor; the demonstration of LISA Pathfinder will provide an excellent platform for the implementation of the ASTROD I drag-free spacecraft. These European activities comprise the pillars for building up the mission and make the technologies needed ready. A second mission, ASTROD or ASTROD-GW (depending on the results of ASTROD I), is envisaged as a three-spacecraft mission which, in the case of ASTROD, would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth, or in the case of ASTROD-GW, would be dedicated to probe gravitational waves at frequencies below the LISA bandwidth to 100 nHz and to detect solar g-mode oscillations. In the third phase (Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD bandwidth.

2009

Abstract: The Telescope for Habitable Exoplanets and Interstellar/Intergalactic Astronomy (THEIA) is a mission concept study for a flagship-class telescope-occulter system to search for terrestrial planets and perform general astrophysics with a space-based 4m telescope. A number of design options were considered for the occulter and telescope optical systems; in this paper we discuss the design of occulters and coronagraphs for THEIA and examine their merits.

The current status of existing star catalogs of relevance for Space Surveillance applications will be reviewed. Hipparcos and Tycho-2 provided reference stars with milliarcsecond (mas) accuracies at their epoch of 1991.25. During the 18 years since then, the proper motion uncertainties have reduced the accuracies significantly. Ground-based programs, such as the USNO CCD Astrograph Catalog (UCAC), now provide an all-sky, astrometrically accurate (20-70 mas) reference star catalog to 16 th magnitude. The USNO-B astrometric catalog contains over a billion detections, providing astrometric positions (~200 mas) and photometry for stars down to V=21 magnitude. These catalogs and others are incorporated into the Naval Observatory Merged Astrometric Dataset (NOMAD), a 100 GB dataset containing astrometric and photometric data for about 1.1 billion stars. Numerous ground and space-based programs hold the promise of providing better future astrometric star catalogs. Pan-STARRS and similar programs will image large fractions of the observable sky every clear night, producing accurate and deep astrometric catalogs. Dedicated next generation astrometric telescopes, for example the USNO Robotic Astrometric Telescope (URAT), will extend UCAC-like astrometric accuracies to fainter stars. Space-based programs like JMAPS (brighter stars) and Gaia (fainter stars) promise to produce high accuracy, astrometric catalogs in their respective magnitude ranges.