! File: 4144C.PROP ! Database: PEPDB ! Date: 20-FEB-1994:10:25:41 coverpage: title_1: LINKING HIPPARCOS TO THE EXTRAGALACTIC REFERENCE FRAME title_2: PART 5 OF 6, NEWC, CYCLE 3,CONTINUATION OF 2565 sci_cat: STELLAR POPULATIONS sci_subcat: ASTROMETRY proposal_for: GO cont_id: 2565 pi_title: DR pi_fname: PAUL pi_mi: D pi_lname: HEMENWAY pi_inst: UNIVERSITY OF TEXAS AT AUSTIN pi_country: USA pi_phone: (512)471-3431 keywords_1: REFERENCE FRAMES, HIPPARCOS, QUASARS hours_pri: 80.00 hours_par: 25.00 num_pri: 175 num_par: 30 wf_pc: Y fgs: Y funds_amount: 292590 funds_length: 36 pi_position: RSSCI ! end of coverpage abstract: line_1: Determination of a non-rotating Reference Frame is crucial line_2: to progress in many areas, including: Galactic motions, line_3: local (Oort's A and B) and global (R0) parameters derived line_4: from them, solar system motion discrepancies (Planet X); line_5: and in conjunction with the VLBI radio reference frame, line_6: the registration of radio and optical images at an accuracy line_7: well below the resolution limit of HST images (0.06 arcsec). line_8: The goal of the Program is to tie the HIPPARCOS and Extra- line_9: galactic Reference Frames together at the 0.0005 arcsec and line_10: 0.0005 arcsec/year level. The HST data will allow a deter- line_11: mination of the brightness distribution in the stellar and line_12: extragalactic objects observed and time dependent changes line_13: therein at the 0.001 arcsec/year level. line_14: The Program requires targets distributed over the whole sky line_15: to define a rigid Reference Frame. GTO observations will line_16: provide initial first epoch data and preliminary proper motions. line_17: The observations will consist of relative positions of Extra- line_18: galactic objects (EGOs) and HIPPARCOS stars, measured with the line_19: FGSs, or with the FGSs and PC together in "transit circle mode". line_20: The combination of HST and HIPPARCOS observations will provide ! ! end of abstract general_form_proposers: lname: HEMENWAY fname: PAUL title: DR mi: D inst: UNIVERSITY OF TEXAS AT AUSTIN country: USA ! lname: ARGUE fname: NOEL title: DR inst: THE OBSERVATORIES country: ENGLAND ! lname: DUNCOMBE fname: RAYNOR title: DR mi: L inst: UNIVERSITY OF TEXAS AT AUSTIN country: USA ! lname: HUGHES fname: JAMES title: DR inst: U.S. NAVAL OBSERVATORY country: USA ! lname: JAUNCEY fname: DAVID title: DR inst: C.S.I.R.O. country: AUSTRALIA ! lname: JOHNSTON fname: KENNETH title: DR inst: U.S. NAVAL RESEARCH LAB country: USA ! lname: KOVALEVSKY fname: JEAN title: DR inst: C.E.R.G.A. country: FRANCE ! lname: LESTRADE fname: JEAN title: DR inst: BUREAU DE LONGITUDE country: FRANCE ! lname: PERRYMAN fname: MICHAEL title: DR inst: E.S.T.E.C. country: HOLLAND ! lname: PRESTON fname: ROBERT title: DR inst: JET PROPULSION LAB country: USA ! lname: TURON fname: CATHERINE title: DR inst: OBSERVATOIRE DE MEUDON country: FRANCE ! lname: DEVEGT fname: CHRISTIAN title: DR inst: HAMBURGER STERNWARTE country: FGR ! lname: WALTER fname: HANS title: DR inst: ANSTRONOMISCHE RECHENINSTITUT country: FGR ! lname: WHITE fname: GRAEME title: DR inst: C.S.I.R.O. country: AUSTRALIA ! lname: KRISTIAN fname: JEROME title: DR inst: CALTECH country: USA ! lname: TAPLEY fname: BYRON title: PROF. inst: UNIV OF TEXAS AT AUSTIN country: USA ! ! end of general_form_proposers block general_form_text: question: 2 section: 1 line_1: The astronomical uses of an accurate coordinate reference frame line_2: are manifest. The reference frame provides the kinematic basis line_3: for all dynamical studies of celestial objects. The HIPPARCOS line_4: satellite will determine positions, proper motions, and line_5: parallaxes for about 100000 stars evenly distributed over the line_6: sky (Kovalevsky, _Space Science Rev._, 39,41,1984). A residual line_7: time dependent rotation of the reference frame would introduce line_8: a systematic effect in the system of proper motions that biases line_9: all the astronomical uses that can be made of the system in line_10: kinematical and dynamical studies of the Galaxy. (Galactic line_11: differential rotation and its variation with distance, asymmetry line_12: of motions with respect to the galactic plane, kinematics of line_13: halo stars and other stellar populations, group motions, and line_14: determining the birth places of stars, are a few examples of line_15: galactic studies which are adversely affected by a residual line_16: rotation of the reference frame.) This proposal is to reduce line_17: this undesirable bias by determining the rotation of the line_18: HIPPARCOS frame with respect to extragalactic objects. The line_19: method is to measure the proper motion of some stars in the line_20: HIPPARCOS system with respect to extragalactic objects (EGOs) line_21: using the Hubble Space Telescope (HST). ! question: 2 section: 2 line_1: HST can provide the information needed to link the HIPPARCOS line_2: proper motion system to the fixed reference system defined by line_3: the EGOs. The object of the overall program is to obtain the line_4: observations necessary to determine this link to an accuracy line_5: of the order of the systematic regional errors that may exist line_6: in the final HIPPARCOS catalogue. line_8: The nominal HIPPARCOS accuracy for stars brighter than 10.5 is line_9: expected to be 0.002 arcsec in position and parallax, and 0.002 line_10: arcsec/year in proper motion. HIPPARCOS will observe objects line_11: between 10.5 and 12 magnitude with reduced accuracy. The basic line_12: HIPPARCOS data will be accurate large angle separations of stars line_13: (chords on the celestial sphere). The system solution will line_14: yield a "solid body" celestial coordinate system an order of line_15: magnitude more accurate systematically than the individual line_16: random errors of the individual stars. Caused by unknown line_17: systematic biases of instrumental origin, they have not been line_18: properly assessed, but they should not exceed 0.1 milliarcsec line_19: in position, or 0.1 milliarcsec/year in proper motion. ! question: 2 section: 3 line_1: However, the nature of the HIPPARCOS reference system is such line_2: that it has a double indeterminacy: an arbitrary "solid body" line_3: rotation proportional to time in its proper motion system, line_4: and an arbitrary solid body rotational offset from any line_5: "standard" (e.g. inertial or quasi-inertial) coordinate line_6: system, in position. line_8: R. L. Duncombe and P. D. Hemenway plan to use about 40 hours line_9: of GTO time to observe HIPPARCOS stars near extragalactic line_10: objects. The stars have been screened from about 300 stars line_11: by a large program of speckle interferometry specifically for line_12: this purpose. (C.f. Hemenway, et al., 1985 ESA special line_13: Publication SP-234, p.281; Argue, et al., _Mon. Not. RAS_, line_14: 206,669, and 216,447.) Drs. Franz and McAlister have done line_15: the northern hemisphere speckle observations (private line_16: communcation to PDH). ! question: 2 section: 4 line_1: Simulations by Froeschle and Kovalevsky (_Astron. Astrophys._, line_2: 116, 89, 1982) show that for observations evenly distribued line_3: over the sky, the elements of the rotation matrix would be line_4: obtained with an accuracy of 0.003 arcsec/year rms for 40 line_5: pairs and 0.0023 arcsec/year for 70 pairs. We have identified line_6: 175 stars around 91 EGOs that are observable astrometrically line_7: with HST. This distribution should allow the determination of line_8: the rotation matrix to an accuracy of the order of 0.0016 line_9: arcsec/year. However, these figures represent measurements line_10: over the lifetime of the HIPPARCOS mission, 2.5 years and the line_11: subsequent accuracy for the tie to EGOs at the end of the line_12: mission. A longer time base will reduce the error propor- line_13: tionally to the time base for the next several years after the line_14: HIPPARCOS mission is completed. The determination of the line_15: components of the rotation matrices depends critically on line_16: the distribution being uniform over the sphere. A loss of the line_17: sources south of -30 degrees declination increases the rms of line_18: the solution by a factor of 1.4, for example. Therefore, the line_19: first priority is to make sure that the EGOs that are observed line_20: are well distributed over the celestial sphere. ! question: 2 section: 5 line_1: Although this result is very accurate, it does not reach the line_2: expected accuracy of the HIPPARCOS system by a factor of 2 line_3: or 3. By reobserving all the HIPPARCOS star-EGO pairs over line_4: the course of the HST lifetime, the error of the individual line_5: motions is reduced proportionally to the time, and the overall line_6: solution should reach the 0.0008 arcsec/year level. If, in line_7: addition, about 15 radio stars are observed by VLBI giving a line_8: precision of proper motion of about 0.002 arcsec/year, then line_9: the expected global accuracy will become: line_10: a) 0.0025 arcsec/year if this proposal is not accepted, line_11: b) 0.0016 arcsec/yr if the GTO plus this proposal is accepted, line_12: c) 0.0012 arcsec/year if the full combined list is observed, and line_13: d) 0.0005 arcsec/yr if all observations of all types over the line_14: HST lifetime are observed. line_16: Some points which need stressing: line_17: a) Two HST time scales are important, one common to the line_18: HIPPARCOS epoch should start AS SOON AS POSSIBLE AFTER LAUNCH line_19: to reach the full potential of the tie between the VLBI frame line_20: and the HIPPARCOS frame, which requires observations of the line_21: same objects at the same epochs. The early epoch observations line_22: will also give the longest time base for the proper motion line_23: determinations, ! question: 2 section: 6 line_1: b) HIPPARCOS can only observe down to 12th magnitude with line_2: reduced accuracy. It cannot observe the Exragalactic objects line_3: directly, line_5: c) The program and object selection have been the subjects of line_6: intensive efforts by many people over the last few years, line_7: including the Working Group on Radio/Optical Identifications line_8: of IAU Commission 24, Subgroup 2130 of the HIPPARCOS Input line_9: Catalogue Consortium, a working group of one of the HIPPARCOS line_10: reduction consortia (F.A.S.T.), the speckle observers headed line_11: by Franz and McAlister in the north and Argue and Morgan in line_12: the south, and the southern hemisphere radio observers headed line_13: by Jauncey and White, who have identified the southern sources line_14: in this proposal through a major effort in the last two years, line_16: d) Jauncey, White, and Preston are working to make all the line_17: radio sources in this proposal part of the VLBI reference line_18: frame, including establishing the Australian VLBI capability, ! question: 2 section: 7 line_1: e) A set of 414 candidate stars near EGOs was included in the line_2: HIPPARCOS Input Catalogue in 1982 to make sure that the stars line_3: would be observed by HIPPARCOS. The speckle programs comprised line_4: these stars and the stars near the southern EGOs subsequently line_5: indentified by Jauncey and White. line_7: The objectives of this program are: line_8: 1) Provide an accurate tie of the HIPPARCOS Coordinate line_9: Reference System (positions and proper motions) to the best line_10: available extragalactic (e.g. VLBI) system, at the epoch of line_11: HIPPARCOS, line_13: 2) Tie the HIPPARCOS Reference System of proper motions to a line_14: (non-rotating) extragalactic system of optical objects, line_16: 3) Thereby establishing the connection between the Radio and line_17: Optical reference frames to the millarcsecond level (allowing line_18: the registration of HST images to radio images (VLA, VLBI, line_19: VLBA) to an accuracy well below the reolution limit of HST), line_20: anywhere in the sky, ! question: 2 section: 8 line_1: 4) Obtain single-epoch information on the brightness distri- line_2: bution of EGOs and stars, and line_4: 5) Obtain time dependent studies of the resolved and unresolved line_5: structure of (4) at the 0.001 arcsec/year level of accuracy. line_7: We have a brief statement from the HIPPARCOS Science Team line_8: supporting the importance of this work to the HIPPARCOS project, line_9: and its usefulness for both HIPPARCOS and HST astrometric data. line_10: The stement is included as an appendix to the proposal. ! question: 2 section: 9 line_1: APPENDIX: line_2: The following statement was communicated at the end of line_3: December, 1985: line_5: The eleven members of the HIPPARCOS Science Team, the scientific line_6: representatives who advise ESA directly on the scientific line_7: conduct, planning and organisation of the HIPPARCOS project, line_8: have expressed their full support for this collaborative line_9: programme. For the reasons set out in the proposal, the line_10: HIPPARCOS Science Team has confirmed the importance of the line_11: propsed observations for the interpretation and exploitation line_12: of both HIPPARCOS and Space Telescope astrometric data. line_14: Professor Adrian Blaauw, chairman of the ESA HIPPARCOS proposal line_15: selection committee; and Professor Walter Fricke*, chairman of line_16: the HIPPARCOS Input Catalogue Consortium steering committee, line_17: have also given their support to the present proposal. line_19: *Deceased 28 March 1988. ! question: 3 section: 1 line_1: The basic datum required is the relative separation line_2: angle of an EGO and a HIPPARCOS star. One would hope to rely on line_3: the knowledge of the FGS calibrations to simply measure one line_4: object and then the other. However, because of thermal and line_5: mechanical instabilities during "exposures", initially we will line_6: follow the GTO observing strategy of measuring two objects line_7: several times with some intermediate background stars as a line_8: stability check. Should the FGS measurements prove to be as line_9: stable as expected, then the number of check stars and the line_10: frequency of measurement may be reduced by a large factor (up line_11: to about 5). Since a single measurement of a single pair is line_12: expected to average about 20 minutes, overall slewing time is line_13: expected to be a major factor in actual time consumption. line_14: Based on OV/SV/GTO observations, we will learn how to optimize line_15: the use of HST for the objectives of this program. ! question: 3 section: 2 line_1: For EGOs brighter than 17.0, the observations will consist of line_2: obtaining FGS reading on: 1) the EGO, 2) the HIPPARCOS star, line_3: and 3-5) 3 background stars (when available) in the pickle. line_4: The following sequence will be observed: 1,3-5,2,1,2,5-3,1. line_5: When a star is brighter than V=9.0, the neutral density filter line_6: will be inserted. Whenever possible, another HIPPARCOS star line_7: will be included as one of the "background" stars. line_9: For EGOs fainter than 16.5, a Planetary Camera frame (P8) will line_10: be obtained for the EGO while the guiding FGS data are recorded. line_11: A PC frame will then be obtained for the HIPPARCOS star using line_12: a narrow filter; recording the FGS data for the guide stars. line_13: THE SAME GUIDE STARS MUST BE USED FOR EACH TARGET. The posi- line_14: tional objects' centroids give the separation. line_15: A third exposure will be taken through a red filter. The line_16: color data will be analysed for astrophysical information about line_17: the objects observed. ! question: 4 section: 1 line_1: Simulations have shown that the expected regional systematic line_2: effects within the HIPPARCOS catalogue should be ~0.0001 arcsec. line_3: The expected individual HIPPARCOS position and motion errors line_4: are expected to be 0.002 arcsec and 0.002 arcsec/year. In line_5: tying the HIPPARCOS Reference Frame to EGOs, the error of the line_6: frame will depend on the errors of observations of the line_7: individual objects used. Two methods of high accuracy line_8: observations have been proposed. First is the VLBI observation line_9: of radio stars in HIPPARCOS directly with respect to EGOs. line_10: VLBI sensitivity limits the stars to a few RS CVn stars, with line_11: an accuracy of 0.002 arcsec. Some of these stars show radio- line_12: optical offsets at the 0.002 arcsec level. ! question: 4 section: 2 line_1: The second method is the one proposed here. The FGS measure- line_2: ments have an accuracy commensurate with both HIPPARCOS and line_3: radio measurements, again 0.002 arcsec. Other proposed line_4: methods rely on photographic astrometry of thousands of stars, line_5: galaxies, and QSOs, with measuring accuracies in the 0.1 to line_6: 0.01 arcsec range. These methods suffer from large systematic line_7: effects. No information about the optical structure of the line_8: EGOs or the stars can be obtained at teh 0.04 to 0.002 arcsec line_9: level. Such information is obtained as a matter of course line_10: during HST observations. line_12: The proposed HST observations are the only optical means which line_13: can approach the expected accuracy of the individual HIPPARCOS line_14: star measurements, and these observations are REQUIRED, to line_15: achieve a reduction to a non-rotating coordinate frame at the line_16: level of the internal systematic accuracy of HIPPARCOS. ! question: 5 section: 1 line_1: The FGS observations are expected to take 51.2 sec/setting= line_2: (1/40 sec/sample)*(32 samples/integration)*(2^6 integrations/ line_3: setting) seconds/setting for the 11 settings/"observation" line_4: described in (3) above, due to the need to average over the line_5: "thermal hunt" cycle of the FGSs. The overhead per observation line_6: is expected to be twice the "time on target". Thus we have line_7: allotted 20 minutes for a single "average" observation with the line_8: FGSs. Similarly, PC exposure times are expected to be of the line_9: order of a few minutes for the EGOs (13.0