The process of satellite attitude reconstruction carried out at RGO enables the assumed positions of the stars taken from INCA to be improved. The attitude reconstruction is determined from polynomial fits to the residuals between the observed StarMapper positions and those taken from INCA. The degree of the polynomial is such that smoothing occurs over a typical arc length of about 10°. The positions from different passes are combined, giving a typical internal accuracy for a star of 0"·02 in RA and Dec. The observations discussed here were accumulated from provisional magnetic tapes received from Darmstadt before the end of 1990.

An improved astrometric space mission similar to Hipparcos is proposed for launch ten years after the present Hipparcos. The new mission should provide positions, parallaxes and annual proper motions with an accuracy about one milli-arcsecond for some 400 000 stars. The positions from the two missions would give proper motions for the 120 000 common stars with an accuracy about 0.2 milli-arcsecond per year, ten times less than expected for the first mission. The improvements of the satellite relate e.g. to: larger telescope aperture, smooth attitude motion, enhanced star mapper for four-colour observations (B V U R) of two million stars. The proposal resulted from discussions with members of the Pulkovo Observatory and the Hipparcos Science Team, and it is being considered by the Mission Control Centre, Moscow.

The EO galaxy M87 harbours the prototypical and most studied example of an optical jet. First observed by Curtis in 1918, it remained little more than a curiosity, until Baade and Minkowski studied it in 1954 and first used the term “jet” to describe the sequence of optical knots extending to about 20” from the nucleus. Since then, the jet has been observed at radio (Owen, Hardee & Cornwell, 1989, Biretta, Stern & Harris 1991), optical (de Vaucouleurs & Nieto 1979, Keel 1988, Fraix-Burnet, Le Borgne & Nieto 1989) and X-rays wavelengths (Schreier, Gorenstein & Feigelson, 1982).

High resolution imaging observations of the core of the globular cluster 47 Tucanae with the Faint Object Camera (FOC) on the Hubble Space Telescope (HST) reveal a very high surface density of blue stragglers. This discovery supports the hypothesis that they are among the most massive objects in globular clusters, concentrated in the core by mass segregation. Taken together with the presence in 47 Tue of an X-ray source, eleven millisecond and binary pulsars, and two high-velocity stars ejected out of the core, these observations favour the scenario that blue stragglers are either mergers formed through coalescent collisions, or binaries formed through close encounters.

Accurate measurements of the interstellar deuterium/hydrogen ratio along different lines of sight are needed to test predictions of contemporary cosmologies. I describe our GHRS observations of the Lyman-α, 2600 Å and 2800 Å spectral regions for the spectroscopic binary system Capella, obtained with 3.57 km s resolution and high signal/noise. We are now analyzing these data to infer the column densities of H I, D I, Mg II, and Fe II along this 13 pc line of sight.

As a followup to Bel Campbell’s presentation of Planetary and Galactic images, I am presenting Extragalactic images recently obtained by the WF/PC Instrument Definition Team (IDT) using the Wide Field/Planetary Camera onboard the HST. I have many exciting results and little time/space here, therefore, the descriptions will be quite brief and will only highlight the most interesting new science or capablities of the instrument. Many of the images have been published elsewhere and I refer to them whenever possible.

An image of the region of the binary pulsar PSR1913+16 has been obtained with the Planetary Camera on board the Hubble Space Telescope. This image confirms previous observations of a source coincident with the radio position of the pulsar to within 0,15 arcsec. The image shows a marginal extension not seen in other so urce of similar brightness in the field.

The Goddard High Resolution Spectrograph (GHRS) is an ultraviolet spectrograph developed by the Goddard Space Flight Center and constructed by the Ball Aerospace Systems Group. The basic performance characteristics are given in Table 1. The detectors are Digicons with an approximately 500-diode linear array; the faceplate/photocathode combinations are LiF/CsI for Side 1 and MgF2/CsTe for Side 2. The two science apertures are 2x2 and 0.25 x 0.25 arc seconds square. The GHRS has several undispersed-light modes for target acquisition.

We present and discuss the first images of SN 1987A obtained on day 1278 with the FOC on board the Hubble Space Telescope. The supernova is well detected and resolved spatially in the four observed bands. The UV luminosity of SN 1987A is found to be comparable to that emitted in the visible and infrared spectrum. Narrow-band [OUI] imaging reveals that the circumstellar nebula surrounding SN 1987A has the shape of a perfectly elliptical ring, implying an inclination of 43° ±3°. A comparison of the ring angular size with its absolute size derived from an analysis of the light curves of narrow UV lines measured with IUE, gives an accurate determination of the distance to SN 1987A, i.e. d(1987A) = 51.2±3.1 kpc. Allowing for the relative position of SN 1987A within the LMC, the distance to the center of the LMC turns out to be 50.1 ± 3.1 kpc. This value agrees very well with the determinations obtained from light curve analyses of variable stars.

Hot stars are the natural targets for ultraviolet space observations. The bulk of their energy emerges shortward of the atmospheric cutoff and nearly all of the important atomic transitions required for their analysis are located in the region shortward of λ3000Å. However, since they are intrinsically rare, reddening and distance conspire to make the job of studying these important members of the stellar population of a galaxy a very difficulty task. The Goddard High Resolution Spectrograph (GHRS) adds the new dimension of photon counting to high sensitivity and resolution. This means that the massive stars can be more easily observed within our Galaxy, and also in other galaxies.

I present data acquired during the early operations era of the HST with the Goddard High Resolution Spectrograph (GHRS) on three late-type giant and supergiant stars: α Tau (K5 III non-coronal), λ Dra (K5 III hybrid), and α Ori (M2 lab). Figure 1 shows fits to echelle (R=100,000) line profiles of three ions seen in the spectrum of α Tau. The Co II line can be fit with a single gaussian, the self-reversed Fe II line with a combination of an emission and absorption gaussian, but the unreversed C II lines require two emission gaussians of substantially different FWHM and maxima. The complex shape of the C II profiles suggests that the turbulent velocity distribution in the chromosphere is anisotropic (e.g. Gray 1988) or that the lines are formed in two regions characterized by significantly different Teff and Vturb, as in the hybrid star models of Harper (1991).

Beta Pictoris has attracted special attention since the detection of circumstellar (CS) dust emission by the Infrared Astronomy Satellite (Aumann et al 1984) and subsequent imaging of an extended disk (Smith & Terrile 1984). A central cavity in the dust disk (Telesco et al. 1988) and episodes of infalling high-density gas (Kondo & Bruhweiler 1985) have also been found. The infalling gas is highly variable in infall velocity and mass rate (Bruhweiler, Kondo & Grady 1991). Sporadic mass outflow events have also occurred, implying that some of the CS gas may be stellar ejecta.

These observations of the gas around β Pic by the Goddard High-Resolution Spectrograph (GHRS) represent a significant enhancement in velocity resolution and S/N over previous UV studies of this star and permit for the first time a simultaneous probe of the density and velocity structure of the CSgas.

High resolution, high S/N ultraviolet observations of the ultra-sharp-lined Bp star chi Lupi, obtained with the Goddard High Resolution Spectrograph, reveal an unprecedented level of spectroscopic detail. Spectral synthesis of the Hg II λ1942 resonance line confirms the extreme isotope abundance anomaly of mercury in this star. The data also provide the first positive detections of Ru II and Zr III, and tentative detections of As I and Ge II.

STSDAS is a system of some 750,000 lines of code and documentation designed for the calibration and analysis of data from the Hubble Space Telescope. At its inception in 1981, when it was known simply as ‘SDAS’, the system was dependent on the VAX VMS operating system and architecture and was limited in scope to HST data analysis, excluding calibration. As it was realized that astronomers would want to be able to do their own calibrations of HST data, and that it was not cost-effective, either for end-users or for the software development effort, to have a system dependent on a proprietary operating system, the scope and objectives of the system were modified. The most fundamental change was the decision to fully layer the STSDAS software on the Image Reduction and Analysis Facility -IRAF – from the National Optical Astronomy Observatories. For a review of the historical aspects of the development of STSDAS, please see Hanisch (1989).

Experience gained in a world wide effort to exploit restoration methods in order to improve the scientific return from the degraded HST optics calms down fears that HST might have lost all of its spatial resolving power. However, the problems posed by the characteristics of the point spread function (PSF) and of the detectors are such that “black-box” image restoration in an automatic procedure during pipe-line calibration is not applicable. Results from restoration experiments show the directions for future research: On the practical side ways are required to properly estimate the complicated PSF, to objectively describe errors, to treat undersampling and non-linear detectors, and to gain factors in throughput for large amounts of data; innovative example are methods to combine data obtained with differing PSFs (ground – space, space – space) and sampling.

The HST science program is comprised of two principal components: the General Observer (GO) and the Guaranteed Time Observer (GTO) programs. A third component, the Archival Research (AR) program, will become increasingly important as time goes by. The GOs are selected by peer review of competitive proposals from the worldwide astronomical community, in a process managed by the STScI. The initial GO proposal deadline was October 1, 1988 and the corresponding review meetings took place during April 1989. The GTOs are members of the Investigation Definition and Observatory Scientist Teams who were competitively selected by NASA following an Announcement of Opportunity in 1977, to design and build the HST Science Instruments and participate in the project development, and who were awarded a decreasing fraction of the observing time during the initial two to three years of operations to conduct scientific observations with their instruments. The detailed GTO observing programs were received by the STScI on April 1, 1985, and had been revised a number of times since then.

This paper will not review in any detail the performance problems that have been discovered with the Hubble Space Telescope (HST) after it was placed into orbit on April 25, 1990, but rather it will concentrate on the efforts currently under way to conduct a servicing mission late in 1993 in order to restore both the telescope and the spacecraft to their expected capabilities. The detailed planning for this mission will intentionally be left flexible as long as possible to be able to respond to future changes in spacecraft performance. The descriptions below reflect the state of the hardware and planning as of November, 1991. These developments include four major types of spacecraft hardware, plus the carriers, tools and the plans for the servicing mission itself. In addition, some other hardware items are being considered as desirable additions, if schedules and budgets permit.

Solar System bodies are different. They have different sizes, from large planets to small asteroids, and shapes. They have different structure, from solid body to solid body with fluid atmosphere or core, to gaseous bodies, but all of them rotate. The Solar System is a big laboratory for studying rotation of solid and fluid bodies.

Different observational methods are applied to determine the rotation of the Solar system bodies. They depend on the position of the observer and on the structure of the bodies. The most accurate methods, laser ranging to the Moon and artificial satellites and Very Long Base radio Interferometry have been applied to the determination of the rotation of the Earth and the Moon. Their accuracy is better than 0.001”, which on the surface of the Earth corresponds to about 3 cm. Radiotracking of artifical satellites have been used for Earth, Moon, Venus, Mars. In the case of Jupiter, Saturn, Uranus, Neptune and Pluto-Charon magnetic and photometric observations have been used respectively. Their accuracy is of the order of one tenth of a degree.

An edited review of the presentations given at Joint Commission Meeting II during the 21st General Assembly of the IAU is presented.

Most of our information about the Universe comes to us in the form of photons. In order to understand the messages they carry with them, we must study the origins of the photons and work out their histories as they journeyed through space. By analysis of the events in which the photons participated, we can construct pictures of the diverse physical and chemical environments and processess occurring in the Universe and we can learn about the nature of the astrophysical entities in which the photons were created.

Because many of the astronomical photons are absorbed or redirected by the Earth’s atmosphere, space-based observing techniques have been developed and refined over the past several decades. The 1990’s will see the see the launch of a number of important new space astronomy missions that will produce vast amounts of high-resolution spectral data.