Siding Spring Research Articles

Hot White Dwarfs in the Extreme Ultraviolet Explorer Survey. I. Properties of a Southern Hemisphere Sample

We present optical spectroscopy of the Balmer line series (Hβ through H8) of a sample of 18 hot white dwarfs obtained at the Mount Stromlo and Siding Spring Observatories; the stars are a subset of the white dwarfs detected in the Extreme Ultraviolet Explorer (EUVE) all-sky survey. We analyze the Balmer line profiles conjointly with EUV photometric measurements and provide new effective temperature and surface gravity determinations. We also provide determinations of the neutral hydrogen column density in the interstellar medium toward these lines of sight. The spectral and photometric properties of most objects in our sample are consistent with emission from pure hydrogen atmospheres. However, we find evidence for the presence of trace absorbers in the photospheres of five of 18 objects from the sample EUVE J0230-479, EUVE J0809-729, EUVE J1 546-370, EUVE J2004-560, and EUVE J2324-547. The star EUVE J0230-479 figures among the group of DA white dwarfs with the highest level of metallicity, while EUVE J0809-729 is one of the coolest DA stars (≍30,000 K) to show evidence of trace elements. We also report the discovery of three new massive white dwarf stars -- EUVE J1546-367 (M ≍ 1.0 M<SUB>sun</SUB>), EUVE J1727-360 (M ≍ 1.2 M<SUB>sun</SUB>), and EUVE J1746-706 (M ≍ 1.4 M<SUB>sun</SUB>); excluding the two high-mass (M &gt; 1.1 M<SUB>sun</SUB>) objects from our sample, we obtain an average white dwarf mass of 0.64 M<SUB>sun</SUB>.

UV/Optical Continuum Variability In AGNs

The observed strong UV/Optical excess in many Seyfert 1 galactic nuclei and quasars (QSOs) is well described as thermal radiation from the surface of an optically thick accretion disk surrounding a supermassive black hole (Malkan 1983, Sun and Malkan 1989). This scenario naturally leads to a radially symmetric temperature gradient with the innermost regions the hottest. Thus for a perturbation generated in the inner regions propagating outward, sequential variations from higher to lower frequencies should be expected, aside from the bolometric increase of brightness. However, the extremely intensive International AGN watch (Peterson 1993 and references therein) on NGC 5548 and UV/Optical monitoring campaign on Mkn 335 (Sun et al. 1995) point to opposite conclusions on the time lag between UV and Optical continua, with no lag for NGC 5548 and ∼ 50 days for Mkn 335. We thus began two monitoring programs at Lick Observatory and Mount Stromlo and Siding Spring Observatory (MSSSO) on a sample of Seyfert 1 galaxies with CCD direct imaging to search for more conclusive evidence on the sequential variabilities.

Asteroid Discovery Efficiencies for Telescope Systems at Siding Spring

AbstractRelative efficiencies for the discovery of Earth-crossing asteroids (ECAs) are modelled for various telescopes at Siding Spring. It is found that the narrow-field instruments—the Anglo-Australian Telescope and the 40 in and 2·3m reflectors—are not competitive in this regard for present CCD imaging systems. The UK Schmidt Telescope (UKST), if used to take short-exposure stereo pairs of photographs, would be an effective search tool, outperforming all current systems apart from the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) systems now being implemented by the US Air Force for ECA searches. If a CCD mosaic were fitted to the UKST, its performance would far exceed that of any other device at Siding Spring, and it would produce ECA discoveries at a rate around 3–4 times as high as GEODSS, but at considerable expense. The most sophisticated search instrument currently in use is the University of Arizona’s Spacewatch telescope; a notable result found here is that even with its present CCD, the Automated Patrol Telescope (APT) of the University of New South Wales would be able to match or outperform Spacewatch for all ECA sizes, including ~10m objects, should this modelling be a reasonable representation of its real performance. In terms of cost-effectiveness and telescope availability, the conclusion arrived at herein is that the APT, equipped with small-pixel but large-format CCD chips of high quantum efficiency, would be an extremely effective ECA search instrument: if operated with 12 μm pixel chips covering a 4° × 4° field it might produce ECA discoveries at a rate well in excess of the combined rate for all current search programs.

Seeing Measurements at Freeling Heights and Siding Spring Observatory

AbstractA low-cost differential image motion monitor (DIMM), consisting of an 11-inch Celestron, an SBIG ST-4 autoguiding CCD camera and a PC, is described. Two such systems were used during June–July and November–December 1993 to make near-simultaneous seeing measurements at Freeling Heights in the Northern Flinders Ranges and at Siding Spring Observatory. The results of these campaigns show that the seeing-distribution is generally similar at both sites, with the most common seeing value being ~l·2″. Siding Spring does, however, have slightly more bad seeing (&gt;2″) than Freeling Heights. Weather records from Arkaroola Resort (15 km south of Freeling Heights) indicate that there is ~15% less cloud cover at Freeling Heights than at Siding Spring. Episodes of rapid seeing deterioration at Siding Spring in winter are shown to coincide with warm air masses crossing the mountain.

Astronomy with the Automated Patrol Telescope

AbstractThe Automated Patrol Telescope (APT) is a wide-field CCD imaging telescope operated by the University of New South Wales at Siding Spring Observatory in Australia. The optical design employed resembles that of a Schmidt, but uses a 3-element lens to achieve a wide, corrected field of view. The APT was developed by extensively modifying the optical, mechanical and electronic systems of a Baker-Nunn satellite tracking camera. Telescope motion and operation of the CCD have been placed under computer control, allowing automated observations for longterm survey and monitoring projects. The APT has 0.5 m aperture f/1 optics which produce a 5° flat field, of which a 2°×3° field is covered by the CCD currently installed. The telescope is being used for studies of stellar activity in open clusters and regions of star formation, and comet and minor planet investigations. A number of other projects for the APT are being considered, including searches for novae, supernovae in clusters of galaxies, and brown dwarfs.

Searching for Near-Earth Asteroids with the UK Schmidt Telescope at the AAO

AbstractSince 1990 we have operated a program in which all plates and films exposed at the 1.2 m U.K. Schmidt Telescope (UKST) are searched for suspicious trails that may represent fast-moving (Earth-approaching) objects. When a possible near-Earth asteroid is discovered, we obtain follow-up astrometric positions using photography on either the UKST (if the object is faint) or the 0.5 m Uppsala Southern Schmidt at the same site. Further astrometric positions, once a reasonable ephemeris is available, are obtained with a large-format CCD on the 40 inch telescope of the Siding Spring Observatory (SSO).In the near term we plan to extend our use of the UKST making use of time near bright-of-moon when the telescope is currently underused. We will conduct photographic searching by taking dedicated films in pairs of 5-10 minutes exposure, with 30-60 minutes gaps between. These will then be inspected using electronically blinked video cameras to scan the films and look for objects that have moved between the exposures. We believe that we can better than triple our current discovery rate (which is about 8-10 near-Earth asteroids per year) in this way.In the longer term clearly the installation of a mosaic of CCDs covering some reasonable fraction of the UKST focal surface is a desideratum, and this is under consideration.

The relationship between past and present star formation in galactic disks from CCD surface photometry

We present some results of a major new multiband imaging survey of 34 nearby southern spiral galaxies. Images in V, I, Hα, and the adjacent red continuum have been obtained using a CCD and focal reducer on the 1.0 and 2.3 m telescopes at Siding Spring Observatory. Surface photometry using the GASP software package is used first to derive the disk orientation parameters, then to provide deprojected radial surface brightness profiles for each galaxy in V and I, as well as the continuum- subtracted Hα, which traces the present-day rate of massive star formation. In the outer disk, the Hα profile can be reasonably well fitted by an exponential disk, but with a scale length much longer than the V scale length, which itself tends to be slightly longer than the I scale length. An almost universal relationship is observed in the disk between the Hα surface brightness and the I-band surface brightness at a given radius, with any residual offset from the mean trend being a weak function of the morphological type. Thus the rate of massive star formation per unit area in the disk is closely related to the old stellar mass surface density at each radius, and to the mean H I surface density in the disk as a whole. This forms the basis for a law of (or rather, a constraint on) massive star formation in the disks of spiral galaxies, one that has a surprising degree of independence from both galactic dynamics and molecular gas content.

Microspots on IIIa- Emulsions: New Results

This paper continues the investigations carried out at the Royal Observatory Edinburgh into the microspot problem affecting Kodak Spectroscopic plates taken with the UK 1.2m Schmidt Telescope (UKST) at Siding Spring Observatory (SSO). Over 10,000 plate inspections have been made since the previous report. Analysis of all the available data shows that UKST plates on IIIa- emulsions processed up to January 1991 continue to show evidence of microspot contamination. Various changes to the processing procedures are listed and the effects on spot formation are analyzed. The effectiveness of Rapid Selenium Toner in the original processing line and post-processing is discussed.

A NASMYTH COMBINED IMAGER AND LOW-RESOLUTION SPECTROGRAPH

ABSTRACT A Nasmyth mounted combined imaging system and low resolution spectrograph recently constructed for the 2.3-m alt-az Telescope operated by the Mount Stromlo and Siding Spring Observatories is described. The instrument is in modular form, has a telecentric section for uniform interference filter field response, a collimated beam section and a camera operated at f/3.6. The camera scale is 24.8 arc sec/mm and accepts without vignetting the total 6.6 arc minutes field of the telescope. The system optics have been optimised for achromaticity over the wavelength range 3000 to 11000 angstroms.

Evolution from AGB Star to Planetary Nebula

Thesis work conducted at: Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, The Australian National University, Private Bag, Weston Creek Post Office, Weston Creek, ACT 2611, Australia Current address: Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218 Electronic mail: vass@stsci.edu Ph.D. dissertation directed by: Peter R. Wood and Michael A. Dopita Co-director: Donald J. Faulkner

Ring Nebulae Around Population I WR Stars: Is Their Origin Similar to the PNe?

Interference filter CCD images have been obtained in Hα and [O III] λ5007 for all population I WR stars in the LMC and SMC using the 2.4 m telescope at Siding Spring Observatory ANU. We have found new ring nebulae in the LMC around Br#13, 25, 31 and 56. Ring nebulae around Br 31 and Br 13 most probably represent stellar ejecta. Nebula around Br 56 is a filamentary wind-blown bubble type.

No Backside Infall into the Great Attractor

AbstractWe have recently completed a survey of the peculiar velocities of 1355 southern spiral galaxies. The Tully – Fisher relation was used to estimate the distances to the spirals. The photometry was done in the I-band using CCDs on the lm telescope and the Anglo-Australian Telescope at Siding Spring Observatory. The rotational velocities were measured from 1042 H-alpha rotation curves obtained with the 2.3m telescope at SSO and 609 H 1 profiles obtained with the Parkes radio telescope.

Does Gravity Rule the Universe?

AbstractThe initial results of a southern sky survey of the peculiar velocities of 1355 spiral galaxies by a group at Mount Stromlo and Siding Spring Observatories (MSSSO) are discussed against the background of past work in this area. The most important result is that the Great Attractor does not exist; rather, there is bulk flow relative to the cosmic microwave background (CMB) of amplitude 600 km s−1 and scale greater than 130 h−1 Mpc in the Supergalactic plane. This is generated by the assumption that the CMB dipole is Doppler induced by our Galaxy moving at 622 km s−1 relative to the CMB. This may be incorrect, in which case there is no bulk flow and the radiation dipole is cosmological in origin with important implications for the early Universe.

Foreword

A workshop on 'Star Formation in Different Environments' was held at the University of Sydney in October 1991. The workshop was sponsored by the Research Centre for Theoretical Astrophysics, which was set up in 1991 as a Special Research Centre of the Australian Research Council, with the primary objective of fostering theoretical astrophysics in Australia. The major part of the initial organisation of the workshop was carried out by Geoff Bicknell, who was co-opted to the Research Centre for several months from Mount Stromlo and Siding Spring Observatories. About fifty astrophysicists took part, including three distinguished overseas visitors, Leon Mestel, Colin Norman and Joe Silk, who took leading roles in the scientific discussions.

The creation of the Anglo-Australian observatory

Foreword Preface 1. The scientific background 2. The technical background 3. The campaign for a large telescope: aspirations and realities 4. An Anglo-Australian agreement 5. Site, dome and building 6. Optics and tube 7. Mounting, drive and control 8. Telescope or observatory? 9. The beginnings of the observatory 10. Commissioning 11. The UK Schmidt telescope at Siding Spring Observatory 12. Some achievements of the AAT 13. Political winds of change 14. Towards the next century Appendices.

Edinburgh Astronomy and Educational Teaching Packages

AbstractFilm copies of original astronomical plates taken with the 1.2-metre UK Schmidt Telescope (UKST) at Siding Spring Observatory, New South Wales have been used for several years at Edinburgh University. Two teaching packages are intended for undergraduate use; the educational packages are mainly designed as visual aids for colleges, schools and amateur groups.

A Peltier-cooled CCD Camera

AbstractWe describe the application of Peltier effect cooling to charge coupled device (CCD) detectors. We are developing this technique to produce a CCD camera which requires low maintenance, yet has sufficiently small dark-current for long exposure imaging. This camera will be used in an automated imaging telescope at Siding Spring Observatory. The design principles used to maximise cooling of the detector, and hence minimise dark-current, are discussed. A small dark-current can be obtained only if great care is taken to reduce or eliminate convective, conductive and radiative heating of the chip. In addition, a path of high thermal conductivity must be provided for the heat removed from the CCD. A recent laboratory test of our cooling system demonstrates that careful design can lead to sufficiently low CCD dark-current for many astronomical applications.

Orbit determination and analysis for Aureole 2 rocket at 27:2 resonance

The Aureole 2 rocket (1973-107 B) was launched on 26 December 1973 into an orbit of inclination 74° and eccentricity 0.1 and has an estimated lifetime of 30 years. The orbit has been determined from observations for 90 epochs between September 1983 and December 1984, during which time the orbit was expected to be influenced significantly by the effects of 27:2 resonance with the Earth's gravitational field: exact resonance occurred on 28 April 1984. The observations numbered nearly 7400, of which 344 were from the Hewitt cameras of the University of Aston which are sited at Herstmonceux in England, and Siding Spring in Australia. The orbital inclination and eccentricity of the orbits derived had standard deviations corresponding on average to positional accuracies of 130 m cross-track and 80 m in perigee distance. The variations in inclination and eccentricity have been analysed individually to determine values of two pairs of lumped harmonics of order 27 from each parameter; when these parameters were fitted simultaneously they gave three pairs of harmonics with standard deviations corresponding to accuracies of approximately 2.5 cm in geoid height.

Preliminary Results from the Automated Patrol Telescope CCD Camera

Abstract The University of NSW Automated Patrol Telescope (APT), a modified 0.5 m Baker-Nunn Schmidt telescope situated at Siding Spring Observatory, Coonabarabran, Australia, was opened in June 1989. It features the unique combination of an extremely fast (f/1) optical system with a CCD (Charge-Coupled Device) camera at the prime focus, capable of both fast (50 Hz TV-rate) imaging and slow-scan integrated readout via a low noise Correlated Double Sampling amplifier. This combination of optics and detector gives a wide field (0.9° × 1.4°) suited to observing extended objects including the LMC, SMC and galaxies in the Sculptor group. First images from the APT are presented along with the results of noise, linearity and dark current measurements made to date with a 12-bit analog-to-digital converter. Results were (ADU = Analog-Digital Unit):

Radio Polarization Studies of Some Southern Galaxies

We have begun a long-range project to study southern galaxies using the radio telescopes at Parkes and Molonglo, the Siding Spring optical facilities and soon, the Australia Telescope. Here we present the results of polarization mapping at two wavelengths of the galaxies NGC 55, 253,4945, M 83 and the Circinus Galaxy.