Search

The advantages of making astrometric observations from space are reviewed, and a project for measuring angular separations between stars along great circle arcs of the order of 90°, by means of a telescope mounted on a TD 1 satellite is described. Positions with accuracy of the order of ±0″.01, parallaxes to ±0″.007 and proper motions to ±0″.005 yr-1 for some 40000 stars brighter than 9m.5 would be obtainable in a two year programme.

The idea of improving star positions from observations of the minor planets was put forward in the first half of our century. In 1928 F. Dyson (1928) suggested using the meridian observations of minor planet Vesta for checking the position of the equator. Then, in 1932 N. I. Dneprovsky investigated the problem concerned with the improvement of fundamental star declinations utilizing the motions of asteroids. At the same time M. F. Subbotin (1932) suggested that a correction to the equinox position could be determined from observations of the minor planets. Theoretical aspects relating to obtaining the solution were set forth by B. V. Numerov (1933, 1936) as well as by D. Brouwer (1935, 1941) and G. Clemence (1948).

Observational information required for determination of the masses of collapsed objects in close binaries is examined. Assumptions commonly used to evaluate the masses or thier lower limits, in the absence of the required observational data, are critically discussed. A reliable determination of the mass of a collapsed object in X-ray emitting binaries is yet to be made. No definitive case has been made for or against the existence of a black-hole in CygX-1.

The evaluation of stellar positions from overlapping plates by rigorous block-adjustment methods leads to a very large system of normal equations containing both stellar positions and plate constants as unknowns. These general normal equations can be reduced to a subsystem with banded-bordered coefficient matrix, containing only the plate constants as unknowns. In the case of a large photographic net covering a hemisphere or sphere with multiple overlap of the plates, the actual number of unknown plate constants may exceed 20000, depending on the adopted reduction model.

The study of planetary companions of stars is at present being carried out through the methods of long-focus photographic astrometry, which are briefly outlined. Tha analysis of a perturbation leads to an orbit, which generally refers to the photocentre of primary of companion. The dynamical interpretation generally yields a lower limit for the mass of the unseen companion for any adopted value of the combined masses; this is a basic limitation in the discovery and evaluation of planetary masses. The results so far are tentative; caution and optimism are recommended for the future.

In order to improve our knowledge of the astronomical constants, great interest must be paid to accurate positions of major planets and their satellites. Likewise, accurate astrometry of the Moon on stellar background is essential to determine the ephemeris time. Both programs are pursued by Bordeaux Observatory.

Before combining the coordinates of the pole obtained by the Dahlgren Polar Monitoring Service (DPMS) with those of the Bureau International de l'Heure (BIH) we investigated the systematic differences between the two series and their relative weights.

Progress in the study of visual binaries depends upon the existence of a series of astrometric observations in addition to observations of their relative motions. The present paper discusses the proper motions, parallaxes and mass-ratios of visual binaries, the detection of astrometric binaries and the photographic astrometry of faint binaries.

The present stage of development of long-baseline interferometry using independent atomic frequency standards is reviewed. The technique is being applied to precision geodesy and astrometry and shows great promise as a means for the intercomparison of national time scales at the 1-ns error level. This paper discusses the development of radio interferometry and, in particular, the theory and practice of interferometry over a very wide (effective) bandwidth. The superb phase stability of the hydrogen maser frequency standard in the range of 100 s to several hours makes it the ideal local oscillator for long-baseline Interferometry.

Analysis of spectroscopic observations of Mars requires values of the effective Martian airmass to obtain true abundances. Semi-arbitrary assumptions for the airmass correction have been used in most of the past publications on the subject. We have computed detailed values corresponding to specified slits superimposed on the disk of the planet, giving useful output in the form of curves presenting the average airmass for different regions of the planet and various conditions of planet diameter, seeing and phase angle.

In 1964 a conference was held at Flagstaff, Arizona, in honour of Ejnar Hertzsprung. At this conference Martin Schwarzschild presented the inaugural address. The title was 'New Impetus to Astrometry'. I was so much impressed by everything what he, as an astrophysicist, had to say that I have always remembered his analysis of important astrometric problems with admiration. Nine years after the Flagstaff Conference, I find it appropriate to open this Symposium in referring to Schwarzschild's lecture and in presenting my views on recent developments and on progress which I expect in the future. Major achievements in astrometry during the past decade resulted mainly from the introduction and development of new instrumental techniques, the application of astrometric methods in new areas of astronomy, and from the vigorous and successful work in large international undertakings. An important part of the recent progress was unforeseen, namely, the progress made in the absolute measurement of positions of objects by means of radio techniques. Let us first consider the classical areas of astrometry. I will follow here Schwarzschild in first citing the determination of the local inertial frame of rest, which in practice, is given by a system of positions and proper motions of fundamental stars and the knowledge of accurate values of the so-called constants of precession, nutation and aberration. While in 1963 the Fourth Fundamental Catalogue {FK4} was completed on the basis of observations before about 1950, an enormous effort began with the aim of improving the system and the individual data of the FK4. The observations have been carried out with the transit circle, the vertical circle, and with Danjon's astrolabe. By means of improved techniques the errors of observations have been decreased by a factor of about two compared with the observations on which the FK4 was based, and it has become possible to push the magnitude limit of meridian circles to stars fainter than visual magnitude nine. Furthermore, considerable contributions have been made to the improvement of the system in the southern sky, which in the FK4 was based almost entirely on observations made at the Cape Observatory alone. The number of absolute and differential observations made since 1950 is already sufficiently large to justify an extensive analysis with the aim of an improvement of the FK4 and its extension from magnitude 7.5 to 9.0. Progress has also been made in determining precession. It has become clear that Newcomb's planetary precession requires a small correction due to recent improvements of the values of the planetary masses. The point has been reached where further correc

Portable equipment for recording millisecond‐integration‐time photoelectric photometric data is described. Digital data are reliably recorded on standard 6.35 mm audio grade magnetic tape via a quadradial audio grade tape deck. The system is designed specifically for recording lunar occulations of stars, but the data recording technique is independent of the data source. Recovery of the data is made via minicomputer.

Recent experience suggests that it is not necessary to introduce a 24-hour information service for following up discoveries of fast-moving objects. Success can be achieved by intelligent action and only a moderate degree of urgency. There is some interest in making deliberate searches for new Apollo objects and hence a great need for follow-up observations.

The advantages of making astrometric observations from space are reviewed, and a project for measuring angular separations between stars along great circle arcs of the order of 90°, by means of a telescope mounted on a TD 1 satellite is described. Positions with accuracy of the order of ±0″.01, parallaxes to ±0″.007 and proper motions to ±0″.005 yr−1 for some 40000 stars brighter than 9m.5 would be obtainable in a two year programme.

The basic techniques of conventional radio interferometry are explained and a review given of the achievements and limitations of the methods as applied to radio astrometry.

The Lick proper motion program with respect to galaxies is summarized. The subject of extragalactic astrometry is introduced with estimates of proper motions for selected members of the Local Group of galaxies and more distant systems. The problems of measuring proper motions for the Magellanic Clouds is described in more detail.

The incorporation of precision inertial control on LST could exert a strong influence on the philosophy of and techniques for carrying out astronomical observations. In conjunction with a fine guidance star sensor, the inertial reference unit (IRU) described herein could easily expand LST capability to include observations such as (1) tracking of solar system objects, including specific points of interest on the planets; (2) rapid repositioning of scanning sensors on distributed objects such as nebulae and galaxies; (3) carrying out unified star catalog measurements to eliminate the overlap problem which exists in all ground procedures; and (4) carrying out various astrometric measurements with 'real time' data reduction capability.

From an evalution of the arguments pro and contra changes in the precessional constants it is concluded that corrections should be made simultaneously with changes in the values of planetary masses at the time when the new fundamental reference system, the FK5, is introduced into the ephemerides. In this case the location and motion of the equinox would be corrected at the same time. An IAU decision on changes in the constants should be made in 1976. Since the completion of the FK5 may be expected around 1980, the introduction into the ephemerides appears practicable in 1984.

The positions of extragalactic radio sources have been determined by very-long-baseline interferometry with uncertainties smaller than 0″.1, and fundamental limits on the accuracy of VLBI astrometry have not yet been reached. Technical improvements within the next five years may enable positions to be determined by VLBI with uncertainties of 0″.005.

A brief summary is given of the plate materials and results obtained at Yale since the advent of photographic astrometry. The distributions of plates not yet measured or reduced are indicated and possible supplementary programmes for their effective utilization are discussed. Interest centres chiefly in the following areas: (1) The unmeasured parallax plates. (2) Reduction of the −60° to −70° zone catalogue. (3) The El Leoncito programmes for the determination of both positions and proper motions relative to faint galaxies. (4) The feasibility of a search for intrinsically faint nearby stars with the Yale 40-in. at Cerro Tololo and the 20-in. double astrograph at El Leoncito.

K. Aa. Strand U. S. Naval Observatory Washington, D. C.Astrometry deals with the space-time behavior of celestial bodies. Important areas within this classical field of astronomy include the determination of stellar distances and motions, studies of star clusters, and construction of photographic star catalogs.Since the turn of the century these studies have been carried out by means of photography with telescopes of high optical and mechanical stability over periods of time measured in major fractions of a century.The major portion of this work has been carried out with long-focus refracting telescopes, considered optically more stable than the reflecting type telescopes.The first reflecting type telescope specifically designed for astrometric work was placed in operation at the U. S. Naval Observatory (USNO) Flagstaff Station, Flag­ staff, Arizona in 1964. The design and operating procedures of the 61-inch (155 cm) astrometric reflector have been described elsewhere (Ref. 1, 2). More than 10 years of operation have proved that the telescope has not only met, but exceeded, the optical stability of the long-focus refractors.In order to attain the maximum accuracy from the photographic material obtained with the telescope an automatic measuring machine was acquired in 1966.Built by Nuclear Research Instruments in Berkeley, California, and based upon design specifications by the USNO, the machine has over the past 8 years proved to be a reliable high speed measuring system, with which more than 50,000 plates have been measured.The following salient features have been incorporated into the machine:1. Automatic centering of images with an opto-mechanical scanner, with a disk with 24 slits rotating at 3600 RPM scanning at the rate of 1 jam in the plate scale in 1 n second.2. Moire fringe measuring system of x, y coordinates with a least count of 1 jim and recording of data on punched cards.3. Automatic prepositioning on selected images with input from punched cards.4. Image projection with 3X and 40X magnification on viewing screen in front of the control console.5. Easy access to the machine with features enabling rapid change over from plate to plate.main structural members of the machine itself are made of heavy granite as are the two carriages which carry the photographic plate over a 25 X cm area.As shown in Figure 1, the lower car­ riage rides over the base plate on eight lift air bearings (pressure 4.2 kg/cm2), and its motion is controlled by granite guideways mounted on the base plate. Guide air bearings maintain the linearity of the motion.The upper carriage (the stage) rests above the base on four lift air bearings (pressure 2.8 kg/cm2) and is held perpen­ dicular to the saddle by two guideways mounted on it, again using guide air bear­ ings moving against the granite guideways.17

A representative system description is given and applications of the system to spectral analysis are considered. Applications of the system are related to stellar photometry, astrometry, interferogram analysis, surface brightness photometry, spatial filtering and image enhancement, and aspects of search and detection.

Radio positional measurements have achieved an accuracy as high as that of optical astrometry, with uncertainties no greater than a few hundredths of an arc second in each coordinate. Declinations and relative right ascensions are determined absolutely. Since the principal sources of systematic error are different for radio and optical astrometry, radio measurements can be useful in the preparation of future fundamental catalogues.

In 1964 a conference was held at Flagstaff, Arizona, in honour of Ejnar Hertzsprung. At this conference Martin Schwarzschild presented the inaugural address. The title was ‘New Impetus to Astrometry’. I was so much impressed by everything what he, as an astrophysicist, had to say that I have always remembered his analysis of important astrometric problems with admiration. Nine years after the Flagstaff Conference, I find it appropriate to open this Symposium in referring to Schwarzschild’s lecture and in presenting my views on recent developments and on progress which I expect in the future.

Discussion of the possible effectiveness of an earth-based ephemeris development program for the outer planet natural satellites. Technologies for obtaining and reducing photographic plates are available and new satellite theories needed for data processing are being developed. It is shown that satellite ephemeris accuracies could be reduced to hundreds of km by the end of the 1970s. An earth-based program would have great benefits to future outer planet missions requiring this level of accuracy.

Publisher Summary This chapter discusses extra-solar planetary systems. The most massive planet in the Solar System is Jupiter, and some theoreticians consider this to be the upper limit for a nonluminous, dense, cosmic sphere of matter. The existing equipment cannot directly reveal an object like Jupiter, even if attached to the nearest star. Such an object, or objects, can be revealed through a study of perturbations in the star's proper motion. This is done through the techniques and methods of long-focus photographic astrometry for which the traditional long-focus refactors are eminently suitable. Contributing factors to the high precision thus obtained are long focal length, the inherent high positional quality and stability of photographic plates, and a precision-measuring engine. The long-focus photographic method is eminently suited for the discovery of extra-solar planets. It is important to keep the optical performance of the telescope and the observing techniques as constant as possible. The measuring technique is of considerable importance.

Absolute determinations of star positions using transit and vertical circles according to the methods developed at Pulkovo are being made at Pulkovo, at Nikolaiev, at the Golossejevo Observatory of the Ukraine Academy of Sciences, and at Santiago de Chile. At this latter observatory Soviet and Chilean astronomers have completed a series of observations of both bright and faint fundamental stars with a photographic vertical circle, and these observations are now being reduced at Pulkovo. Absolute determinations of right ascension will be made at the Cerro Calan Observatory using a large transit instrument recently constructed at Pulkovo. Further details of some of the Southern observations are given in the following paper to be presented by Dr. Anguita.

A photoelectric scanning system has been constructed to determine line positions on the 65-centimeter diameter divided circle of a meridian circle telescope. The system consists of six scanning micrometers attached to microscopes which are aimed at different portions of the circle. Each micrometer has a field of view of 0.35 degrees. Six different quasi-linear segments on the circumference of the divided circle are scanned simultaneously. Profiles of divided circle lines and reference lines are obtained in digital form and analyzed by a data acquisition computer. On repeated scans (n=30) the system achieved a resolu-tion of 0.04 arcsec with a standard devia tion of 0.05 arcsec. The operational characteristics and reliability of the system indicate that it can be used as a real -time primary angular readout method for the accurate determination of the zenith distances of stars.© (1973) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This report consists of a brief summary of the status of a number of programs of an international nature which are now in progress at various observatories of the world. These programs have received strong endorsements from Commission 8 of this Union, as well as from a number of international organizations interested in accurate positions and motions of the stars to the 9th magnitude of brightness. Among the organizations and conferences which have explicitly endorsed the programs are: (1) The Symposium on Coordination of Galactic Research, Groningen, 1953. (2) Conference on the Problems of Astrometry, Evanston, 1953. (3) Astrometric Conference, Pulkovo, 1954. (4) Conference on Astrometry, Brussels, 1955. (5) International Union of Geodesy and Geophysics, 1954 and 1963. (6) International Astronomical Union, 1955. (7) Second Astrometric Conference, Cincinnati, 1959. (8) First Inter-American Conference on Astronomy, La Plata and Cordoba, 1959. (9) Meeting on Problems of Astrometry and Celestial Mechanics, La Plata, 1960. (10) Committee on Space Research, COSPAR, 1966.

The evaluation of stellar positions from overlapping plates by rigorous block-adjustment methods leads to a very large system of normal equations containing both stellar positions and plate constants as unknowns. These general normal equations can be reduced to a subsystem with banded-bordered coefficient matrix, containing only the plate constants as unknowns. In the case of a large photographic net covering a hemisphere or sphere with multiple overlap of the plates, the actual number of unknown plate constants may exceed 20000, depending on the adopted reduction model.

The technique of timing occultation or eclipse events with high-speed photometers, which we shall call “photometric astrometry”, has been used by Evans, Nather, Silverberg and others to obtain lunar occultations with millisecond resolution, to reduce the observation of occultation reappearances to a routine event, to measure the diameter of Io and the diameter and flattening of Jupiter. We propose the possibility of a concerted program to use this technique for the determination of asteroid dimensions and shapes. It appears reasonable to expect that a single observatory could observe about ten events per year in which a sizeable minor planet occults a star that is three magnitudes fainter or less. Such events could be timed to about 10 msec. The development of inexpensive, portable equipment would greatly increase the number of possible events to be observed. Such equipment could open this activity to sophisticated amateur observers, similarly as in the grazing occultation program.

The accuracy of astrometry using the Palomar Sky Survey prints and published reference star positions is examined. It is shown that one-arc-second positions can be obtained with a simple instrument constructod at modest cost. Key words: astrometry - instrumentation

A literature search has yielded nearly 26,000 observations of the satellites of Jupiter, made from 1662 through 1972. The type (photographic; micrometer; eclipse, occultation, transit) and number of observations are tabulated in 5-year increments, and a complete bibliography is cited.

This paper is reproduced from Publ. Astron. Soc. Pac., Vol. 28, p. 61 - 69 (1916) to celebrate the centenary of the Publications. See also 004.055.