Principal Investigator: Dr. Steven Raymond Majewski
Proposal Title: A Survey of Distant Halo Giant Stars for the SIM Astrometric Grid and a Deep Probe of Galactic Halo Structure
We propose to conduct a ground-based survey for old, distant, intermediate to metal-poor giant stars with telescopes at the Las Campanas Observatory in support of Astrometric Grid needs as well as science goals for SIM. Metal poor giant stars, by virtue of their luminosity, can probe the Galaxy to greater distances than almost any other stellar type at the same apparent magnitude. Distant (> 5 kpc) giants with V < 12 are also highly desirable candidate Astrometric Grid objects. Our Grid Giant Star Survey (GGSS), a patchwork all-sky survey below dec < +20o, is intended to fill partially the need of the SIM mission for a grid of astrometrically stable reference stars and may be used to address a host of problems relating to Galactic structure and kinematics.
Principal Investigator: Dr. David J. Helfand
Proposal Title: A New Bright Quasar Sample for the SIM Extragalactic Frame Tie
Tying the SIM reference grid to the ICRF extragalactic frame will both enable new science with SIM, and be of utility in connecting future astrometric missions to the SIM database. While in principle only a few quasars are required for the frame tie, the stringent constraints on SIM astrometric targets means that hundreds of objects will be required in the sample from which SIM targets are chosen; in addition, the sample must be bright and broadly distributed over the sky. We propose to use the FIRST, NVSS, and SUMSS interferometric radio sky surveys to construct a sample of over 1000 quasars and BL Lac objects brighter than R = 17.5 (>75% previously undiscovered), and to plan a program of followup observations to select the most promising targets for SIM observations.
Principal Investigator: Dr. Thomas E. Corbin
Proposal Title: USNO Grid Star Selection for SIM
The United States Naval Observatory (USNO) proposes to prepare an input catalog of SIM grid stars (the SIM Grid Star Input Catalog) by utilizing existing databases, observing capabilities and instrumental development. Stars in the apparent magnitude range 6.5 < V < 8.5 with spectral types from A5V through G5V will be considered. Known doubles will be eliminated, and proper motions will identify previously unknown, wide pairs. This proposal outlines a comprehensive selection and observing program, the first year of which includes candidate selection and the start of survey observations. In later years, further elimination of doubles will be made astrometrically using observations with the USNO speckle interferometer and the Navy Prototype Optical Interferometer (NPOI). In total, 8,000 candidate stars, evenly distributed over the sky, will be examined observationally. The combination of these three methods will remove double systems in the » 15 arcsec to » 1 mas range with D V of 3.5 magnitudes. In addition, a multichannel Fourier Transform Spectrometer (FTS), with a potential for sub-meter per second radial velocity determinations, will be developed to eliminate spectroscopic pairs. This technique will overlap and complement these astrometric methods, thus ensuring the best possible grid star list. At the end of the first year, the instrumental strategy will be reassessed in light of anticipated upgrades to the NPOI and FTS resulting from other proposals/programs.
Principal Investigator: Dr. Andreas Quirrenbach
Proposal Title: Selection of SIM Grid Stars - Astrophysical Criteria and the Role of Astrometric Catalogs and DIVA
The main objective of this proposal is to provide a list of candidate stars for the SIM grid. They will be selected from the Hipparcos Catalogue, subject to astrometric and astrophysical constraints, with the goal to include only stars with a small expected astrometric jitter. In particular, we will assess the influence of possible sub-stellar companions on each individual grid candidate. We will also discuss the impact of a future small astrometric mission such as DIVA on the quality of the set of grid candidates, by performing a detailed simulation of a combined reduction of Hipparcos and DIVA data. Finally, we will address the question of whether tying together the SIM and ICRS reference frames can be facilitated by including a few radio-loud quasars in the SIM grid observations.
Principal Investigator: Dr. Zoran Ninkov
Proposal Title: A Sensitive Speckle Search for Duplicity of Candidate Objects for the SIM Reference Grid
This proposal seeks funding to observe candidate objects for the SIM Reference Grid to determine if those stars have close companions. The importance of the astrometric stability of the reference grid has been discussed on the SIM web pages and in the NRA. It is important to know in advance if candidate grid objects are binary or multiple star systems. One of the most sensitive and efficient ways to search for close stellar companions continues to be speckle interferometry. We therefore propose to obtain speckle observations of candidate grid stars that have been observed by HIPPARCOS. Our current CCD based observing system is able to detect magnitude differences of better than 5 mag. We have guaranteed observing time on the WIYN 3.5-m telescope at Kitt Peak, Arizona and are arranging for guaranteed observing at the 2.1-m Argentina National Observatory. With these large apertures, we are capable of detecting binaries with separations as small as 3.5 milliarcseconds.
P>Principal Investigator: Dr. Kenneth J. Johnston
Proposal Title: Placing the SIM All-Sky Astrometric Grid onto the ICRS
The International Celestial Reference Frame (ICRF) is a quasi-inertial reference frame based on the radio positions of quasars, and is the realization of the International Celestial Reference System (ICRS) at radio wavelengths. The ICRF has been adopted as the fundamental celestial reference frame, replacing the FK5 optical frame. We propose to support SIM by selecting a list of 50-75 quasars suitable for observation with SIM, and useful for placing SIM observations directly onto the ICRS. We will also begin an observing program to refine and monitor the positions of the SIM quasar list. As a secondary goal, we will select a list of radio stars (brighter than 12mag) from catalogs of recent radio surveys which have uncovered a significant number of new radio stars. We will begin an observing program to determine the suitability of these radio stars for future SIM and VLBI observations to support the SIM placement onto the ICRS.