IAU Commission 8

Talks for the Commission 8 science meeting @ IAU GA 28

We have been allocated 3 sessions for our business and science sessions. The business meeting will be on Monday, 27 August 18:15 in the NAOC Room A208. The science sessions will be on Wednesday, 29 August 16:00-19:30 in Room 406 of the CNCC.

Note that the venue of the business meeting is not the CNCC, where the rest of the General Assembly is being held. The NAOC is about 15 minutes walk away. A map can be found on the GA information page.

The following are the talks for our scientific meeting. The talk lengths are indicted by N+2 minutes. N minutes are allocated to the talks and 2 minutes for discussion. Please keep to time. Clicking on the title will give you access to the presentation if available.

    Science Sessions

  1. J.H.J. de Bruijne
    Gaia is the next astrometry mission of the European Space Agency (ESA), following up on the success of the Hipparcos mission. Gaia's primary science goal is to unravel the kinematical, dynamical, and chemical structure and evolution of the Milky Way. In addition, Gaia's data will touch a wide variety of science topics, e.g., stellar physics, solar-system bodies, fundamental physics, and exo-planets. With a launch in the second half of 2013, the final catalogue is expected in 2021 - the first intermediate data release is envisaged to take place some two years after launch. Gaia will survey the entire sky and repeatedly observe the brightest 1,000 million objects, down to 20th magnitude, during its 5-year lifetime. Parallaxes will be measured with standard errors less than 10 micro-arcsecond (μas) for stars brighter than 12th magnitude, 25 μas for stars at 15th magnitude, and 300 μas at magnitude 20. The properties of the final astrometric catalogue depend, among others, on the adopted scanning law and on the payload-operation and on-ground calibration concepts, in particular the calibration of radiation-induced systematic effects in the data. The importance of these elements is highlighted. In addition, this presentation focuses on expected correlations and systematic errors in the data and on the expected astrometric performance of Gaia in high-density regions on the sky.
    18+2 minutes

  2. Brian Mason
    The resolution of binaries first detected astrometrically has a long history. In the early 19th Century Friedrich Wilhelm Bessel found periodic oscillations in the motions of Sirius and Procyon and reported them in a letter to Humboldt in 1834. The large flux ratio and much smaller mass ratio made these the easiest pairs to detect astrometrically. However, the large magnitude difference made resolution difficult and it was not until Alvan Clark and sons built two of their large refractors that this was accomplished. Sirius B was seen by Alvan G. Clark at the end of January 1862 testing the Dearborn 18.5" instrument and Procyon B was first seen by John Schaeberle in 1896 with the Lick 36" telescope. While pairs of this extreme flux ratio will continue to be a problem for resolution, the situation has improved markedly with smaller flux ratios being detected astrometrically with improvements to accuracy and precision of wide-angle astrometry. Also, new techniques and enhanced resolution capability for narrow-angle astrometry has allowed these pairs to be more easily resolved. The complimentary nature of these disparate techniques is exemplified with the new relative solutions of the astrometric binaries kappa For and HIP 42916 recently presented (Hartkopf et al. AJ 143, 42; 2012). A single resolution of a binary with an astrometric orbit allows for the determination of the relative orbit by scaling the a_phot to a" appropriately. If the Delta-m and parallax is known individual masses will also be forthcoming. Solutions of binaries of these type are presented.
    13+2 minutes

  3. Naoteru Gouda
    National Astronomical Observatory of Japan
    I will talk about the following present status of JASMINE projects:
    JASMINE is an abbreviation of Japan Astrometry Satellite Mission for Infrared Exploration. Three satellites are planned as a series of JASMINE projects, as a step-by-step approach, to overcome technical issues and promote scientific results. These are Nano-JASMINE, Small-JASMINE and (medium-sized) JASMINE.

    Nano-JASMINE uses a very small nano-satellite and is scheduled to be launched in November 2013 at the Alcantara space center in Brazil by a Cyclone-4 rocket developed in Ukraine. Nano-JASMINE will operate in zw-band (0.6---1.1 micron) to perform an all sky survey with an accuracy of 3 milli-arcseconds for position, parallaxes and proper motions. Moreover high-accuracy proper motions (0.1 milli-arcseconds/year) can be obtained by combining the Nano-JASMINE catalogue with the Hipparcos catalogue.

    Small-JASMINE will observe towards a region around the Galactic center and other small regions, which include interesting scientific targets, with accuracies of 10 to 50 micro- arcseconds in an infrared Hw-band (1.1---1.7 micron). The target launch date is around 2017.

    (Medium-sized) JASMINE is an extended mission of Small-JASMINE, which will observe towards almost the whole region of the Galactic bulge with accuracies of 10 micro-arcseconds in Kw-band (1.5---2.5 micron). The target launch date is the first half of the 2020s.
    18+2 minutes

  4. Youfen Wang
    Shanghai Astronomical Observatory
    We report the parallax and proper motions of five L dwarfs obtained with observations from the robotic Liverpool Telescope. These parallaxes represent new values and we use them to discuss the physical properties of L dwarfs. Our derived proper motions are consistent with the published values and have considerably smaller errors. The objects appear to be normal L dwarfs, with space velocities that locate them in the disk and with normal metal abundances according to spectroscopic and model comparisons. For all five objects, we derive effective temperature, luminosity, radius, gravity and mass from evolutional model. We have derived the effective temperature combining observational optical and NIR spectra with model synthetic spectra for three of our L dwarfs. We found the degeneracy of temperature, gravity and metallicity in affecting the absorption line strength through comparison among model spectra and among observational spectra. Robotic Telescope provide us convenient in doing parallax program which need a lot of repeated observations. Such robotic telescopes are able enhance our efficiency in parallax programs, thus they are continuously needed in future.
    13+2 minutes

  5. Catia Cardoso, NPARSEC Collaboration
    Osservatorio Astrofisico di Torino
    We discuss the NPARSEC (NTT PARallaxes of Southern Extremely Cool objects) program to determine parallaxes of ~80 objects covering the T dwarf spectral range. The areas of research directly impacted by this sample will be wide spread. On an individual object basis distances are key for assignments of binarity, metallicity and gravity and more generally the sample will provide key input for the substellar luminosity and mass functions, the connection to exo-planetary models as well as complex atmospheric processes such as non-equilibrium chemistry and turbulent mixing. Eventually these objects will provide new insights into the history of our galaxy, the kinematics of the solar neighborhood and our understanding of differing formation scenarios from stars to brown dwarfs to giant planets. In particular we will discuss the observational and data reduction procedures adopted with a emphasis on the centroiding which is fundamental to the final astrometric precision.
    13+2 minutes

  6. W. F. van Altena, T. M. Girard, D. I. Casetti-Dinescu and K. Vieira
    Yale University & CIDA
    The fourth installment of the Yale/San Juan Southern Proper Motion Catalog, SPM4, contains absolute proper motions, celestial coordinates, and B, V photometry for over 103 million stars and galaxies between the south celestial pole and -20° declination. The catalog is roughly complete to V = 17.5 and is based on photographic and CCD observations taken with the Yale Southern Observatory's double astrograph at Cesco Observatory in El Leoncito, Argentina. The proper-motion precision is 2-3 mas/yr for well-measured stars; systematic uncertainties are on the order of 1 mas/yr.
    In parallel with the SPM4 construction, and using the same SPM observations, a more accurate catalog of proper motions was made over a 450 sq-deg contiguous area that encloses both Magellanic Clouds. That catalog of 1.4 million objects was used to derive the mean absolute proper motions of the LMC and the SMC and, importantly, to make the most precise determination to date of the proper motion of the SMC relative to the LMC. The absolute proper motions are consistent with the Clouds' orbits being marginally bound to the Milky Way, albeit on an elongated orbit.
    Combining UV, optical and IR photometry from existing large-area surveys with SPM4 proper motions, we have identified young, OB-type candidates in an extensive 8000 sq-deg region that includes the LMC/SMC, the Bridge, part of the Magellanic Stream and the Leading Arm. Additionally, a proper-motion analysis has been made of a radial-velocity selected sample of red giants and supergiants in the LMC, shown by Olsen et al. (2011) to be a kinematically and chemically distinct subgroup, most likely captured from the SMC. These results help constrain the Cloud-Cloud interaction, suggesting a near collision that took place 100 to 200 Myr ago.
    Finally, SPM4 absolute proper motions have been cross-identified with radial velocities from the second release of the Radial Velocity Experiment (RAVE) and the resulting three-dimensional space motions of ~4400 red clump stars used to derive the kinematical properties of the thick disk, including the rotational velocity gradient, dispersions, and velocity-ellipsoid tilt angle.
    13+2 minutes

  7. W. F. van Altena
    Yale University
    Astrometry for Astrophysics is intended to fill a serious gap in texts available to introduce advanced undergraduates, beginning graduate students and researchers in related fields to the science of Astrometry. This text provides an introduction to the field with examples of current applications to a variety of astronomical topics of current interest.
    Astrometry for Astrophysics is intended for a one-semester introductory course that will hopefully lead to further study by students or serve as a primer on the field for researchers in related astronomical fields. To accomplish the above goals, the book is divided into five parts. Part one provides the impetus to study Astrometry by reviewing the opportunities and challenges of micro-arcsecond positions, parallaxes and proper motions that will be obtained by the new space astrometry missions as well as ground-based telescopes that are now yielding milli-arcsecond data for enormous numbers of objects. Part two includes introductions to the use of vectors, the relativistic foundations of astrometry and the celestial mechanics of n-body systems, as well as celestial coordinate systems and positions. Part three introduces the deleterious effects of observing through the atmosphere and methods developed to compensate or take advantage of those effects by using techniques such as adaptive optics and interferometric methods in the optical and radio parts of the spectrum. Part four provides introductions to selected topics in optics and detectors and then develops methods for analyzing the images formed by our telescopes and the relations necessary to project complex focal plane geometries onto the celestial sphere. Finally, Part five highlights applications of astrometry to Galactic structure, binary stars, star clusters, Solar System astrometry, extrasolar planets and cosmology. I hope that those chapters will stimulate students and researchers to further explore our exciting field.
    Astrometry for Astrophysics consists of 28 chapters written by 28 specialists in the field from 15 different countries. The book is edited by van Altena and will be published by Cambridge University Press in November 2012.
    5 minutes

    10 minute break

  8. Ralph Gaume
    Current USNO Astrometry catalogs and products will be discussed, including NOMAD and UCAC4. Prospects for future USNO astrometric catalogs will be reviewed, including the status of on-going programs such as URAT and UNAC, catalogs derived from large A-Omega programs, and prospects for a future bright-star catalog from the JMAPS space astrometry mission. The fundamental astrometric reference frame is based on the radio interferometric positions of quasars. Prospects for improvement of the fundamental astrometric reference frame will be discussed.
    13+2 minutes

  9. N.Zacharias, C.Finch
    Reduction details, properties and notes for users are presented about the final USNO CCD Astrograph Catalog (UCAC) release #4 which becomes public in June 2012. Accurate positions (20 to 100 mas) of 113 million stars to R = 16 are given based on over 200,000 CCD images taken by the 20cm astrograph at CTIO and NOFS between 1998 and 2004. Proper motions of most stars are based on SPM and NPM data with average errors of about 4 to 7 mas/yr and smaller errors for stars brighter than 13 utilizing many more catalogs. UCAC4 includes 5-band photometry for about 50 million stars from APASS and near IR photometry for over 100 million stars from 2MASS. FK6, Hipparcos and Tycho2 data are used to supplement bright stars in order to arrive at a complete all-sky catalog.
    13+2 minutes

  10. N.Zacharias, G.Bredthauer, M.DiVittorio, C.Finch, F.Harris, T.Rafferty, G.Wieder
    The USNO Robotic Astrometric Telescope (URAT) achieved first light in 2011 at USNO in Washington DC and is now deployed at the Naval Observatory Flagstaff Station (NOFS). The red-lens of the UCAC program is again utilized for URAT, however, with a completely new tube assembly, upgraded mount, new electronics and a new 4-shooter camera containing 4 large CCDs (STA1600) each with 10,560 by 10,560 pixels of 9 micrometer size. A single exposure of URAT covers 28 square degrees of sky with a resolution of 0.9 arcsec/pixel. The URAT all-sky survey will reach about magnitude 17.5 in a bandpass between R and I with first data release expected by end of 2013. Several built-in features allow URAT to observe stars as bright as 1st magnitude. Multiple sky-overlaps taken over more than 2 years per hemisphere allow determination of accurate positions (10 mas level), proper motions, and parallaxes.
    13+2 minutes

  11. James L. Hilton
    Included in the UCAC observations made at Cerro Tololo Inter-American Observatory (CTIO) are 5864 positions of asteroids. The number of observations of individual asteroids varies from 49 observations of (2) Pallas made over three oppositions to 556 asteroids with a single observation each. Analysis of 47 observations of (692) Hippodamia and 10 observations of (755) Sulamitis each made over two oppositions suggest that the accuracy of the these positions is approximately 50 mas in right ascension and 80 mas in declination. The accuracy of the UCAC may be somewhat better than this as the mean apparent diameters at opposition of these two bodies are approximately 60 and 30 mas, respectively, and no adjustments have been made for phase or possible albedo markings on the surface. A preliminary analysis of 41 of the observations of Pallas (mean apparent diameter 410 mas) are in good agreement with those of Hippodamia and Sulamitis. However, the remaining eight observations show a systematic offset in both right ascension and declination. These discrepant observations may indicate an albedo marking on the surface rotating into view.
    13+2 minutes

  12. Erik Høg
    Niels Bohr Institute, Copenhagen University
    The approval in 1980 of the Hipparcos global astrometry mission and the subsequent development gave rise to ideas and work towards a Hipparcos follow-up mission which culminated with the approval of the ESA cornerstone mission Gaia in the year 2000. Ideas for a successor for global astrometry were studied in Russia (then USSR), and ideas for space astrometry by interferometry were studied in the USA, both beginning in the 1980s. The ESA community was however fully occupied with Hipparcos and nobody there thought of a follow-up mission. That changed in 1990 when I visited Russia, became interested in the Russian ideas and began discussions with Russian colleagues which led to the development in the 1990s, the main subject of the presentation.
    13+2 minutes

  13. Erik Høg
    Niels Bohr Institute, Copenhagen University
    A modest astrometric experiment in Copenhagen in 1925 led to the Hipparcos and Gaia space astrometry missions. - Astrophysicists need accurate positions, distances and motions of stars in order to understand the evolution of stars and the universe. Astrometry provides such information, but this old branch of astronomy was facing extinction during much of the 20th century in the competition with astrophysics. The direction forward was shown by observations at the Copenhagen Observatory in 1925 with a new technique: photoelectric astrometry. Digital techniques were introduced in photoelectric astrometry at the Hamburg Observatory in the 1960s by the present author. This development paved the way for space technology as pioneered in France and implemented in the European satellite Hipparcos approved in 1980.
    13+2 minutes


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Last Modified: 12 September 2012
Published by Dafydd Wyn Evans / IoA / dwe @ ast.cam.ac.uk