ASA 2007

THE ASTRONOMICAL SOCIETY
OF AUSTRALIA INC.

Annual Scientific Meeting
1st to 5th July, 2007

Program	All Days	Sunday	Monday	Tuesday	Wednesday	Thursday	Posters
Abstracts	Posters A-K	Posters L-Z	Monday	Tuesday	Wednesday	Thursday	Lunch Meetings

Abstracts - Wednesday

Session Nine - Stellar Astronomy

09:00-10:30

Particle acceleration associated with magnetic reconnection

Don Melrose and Alix Nulsen

Magnetic reconnection is an essential ingredient in the release of magnetic energy in solar flares and in flaring in other astrophysical contexts. Some of the released energy appears in energetic particle populations, but the link between the acceleration of these particles and the reconnection is only indirect. One suggestion is that the reconnection leads to fast mass flows that cause shocks, and the acceleration occurs in association with the shocks. Such an acceleration model is nonlocal: the magnetic energy release occurs at one location (a magnetic null) and the energy propagates to another location where acceleration occurs in a manner that is not directly related to the reconnection.

In this paper we outline an alternative type of nonlocal model that is based on phenomena observed in the terrestrial magnetosphere. In so-called substorms, magnetic energy release occurs in the geomagnetic tail, and it results in acceleration of particles much closer to the Earth. The energy transport is due primarily to large-amplitude Alfven waves, generated as a result of the reconnection. The acceleration involves parallel (to the magnetic field) electric fields in the auroral zones, and the location of the acceleration sites is determined by the physical processes (including Pedersen resistivity, anomalous resistivity, double layers and kinetic Alfvenic effects) that allow the parallel electric field to develop. We discuss how this nonlocal model can be adapted to acceleration in solar flares, emphasizing the various possibilities for the development of a parallel electric field.

Asteroseismology and Interferometry of solar-like stars

Julian North

In recent years tremendous progress been made in the study of oscillations in solar-like stars: a field now known as asteroseismology. In a shortperiod of time, ambiguous detections have developed into firm measurements of oscillations in many main sequence and subgiant stars. A new development in this rapidly evolving field, presented here, is the augmentation of these asteroseismic results with diameters obtained from long-baseline optical interferometry. The group investigating pulsating stars at the University of Sydney is in collaboration with the SUSI team on a number of targets, resulting in the constraining of fundamental parameters including the most accurate mass determination of a single, solar-like star to date.

Radio emission and polarization in an oscillating model for pulsar electrodynamics

Matthew Verdon

Two outstanding unsolved problems in the theory of pulsar radio emission are the nature of the plasma instability that underlies the radio emission mechanism, and the origin of the separation into orthogonally polarized modes (OPMs). The conventional models for the emission involve a streaming instability, but the instability is too slow to explain the observed power. To produce radiation in orthogonal modes requires the cyclotron resonance to be at a much lower frequency than most models allow. An electrodynamics model that can potentially solve both problems involves assuming that the parallel electric field oscillates with large amplitude (Levinson et al. 2006). This model implies oscillatory counter-streaming motions between electrons and positrons, which lead to instabilities in a phase where the relative motion is nonrelativistic, and a lowered cyclotron resonance in the highly relativistic phases. As a first step in modeling the plasma physics underlying these processes, we consider the wave properties in a strongly magnetized plasma composed of relativistically counter-streaming cold electrons and positrons. We identify regions of instability and discuss how these may be relevant to pulsar radio emission in the oscillating model for the electrodynamics.

Pulsar Timing and the Astronomical Distance Scale

Joris Verbiest

The astronomical distance scale stands or falls with its most fundamental technique: the measurement of parallax. While the geometric basis of this technique clearly stands beyond doubt, we will show how the practical measurement of parallax in pulsar timing can be corrupted due to correlations with the planetary ephemerides applied in the pulsar timing model.

Based on ten years of timing data on PSR J0437-4715, we will demonstrate the effect of faulty planetary ephemerides on a timing parallax, and as such explain the inconsistencies in literature. We will also demonstrate a new and independent technique for distance determination to binary millisecond pulsars, based on the rate of orbital decay, P'_b. Using this new technique, we derive the distance of PSR J0437-4715 to be 157 ± 1 pc. The unprecedented accuracy of this distance along with the insensitivity of this method to any of the parameters in the timing model allow us to use this new method to confirm the current parallax measurement to within 1% accuracy.

Thermonuclear (type-I) X-ray bursts: progress and problems

Duncan Galloway

Thermonuclear bursts occur on the surface of neutron stars, and arise from nuclear burning of accreted He or mixed H/He from a stellar companion. These events are a unique probe of the surface conditions and can help to constrain the neutron star equation of state. Although the basic physics were established in the 1970s and 80s, a "burst" of recent theoretical work has meant that our understanding of this phenomenon is better than ever before. This work has been motivated in part by the gradual development of a comprehensive phenomenology over the years, as well as several more substantial milestones, including the discovery of burst oscillations and highly-energetic "superbursts".

I will review recent theoretical and observational work on these events, with particular attention to i) predictions of time-dependent nuclear burning models and comparisons with observed lightcurves; ii) the Rossi X-ray Timing Explorer burst catalogue and the global variation of burst rates, energetics and time-scales with accretion rate; iii) recent mass and radius constraints derived for the neutron star in EXO 0748-676; and, time permitting, iv) outstanding problems.

Gravitational waves from freely precessing, accreting millisecond pulsars

Christine Chung

Theoretical models of accreting millisecond pulsars predict that these objects have mass quadrupole moments as large as 1029 kg m2, corresponding to an ellipticity as high as 10-8, produced by magnetic stresses (Melatos & Payne 2005) or thermocompositional gradients (Ushomirsky et al. 2000). The quadrupole is misaligned in general with respect to their rotation axis. Indirect observational evidence for the existence of such a quadrupole comes from the upper cut-off of the spin frequency distribution. Here we present a feasibility study for detecting the quadrupole directly through X-ray observations, via the free precession of the misaligned quadrupole, which causes modulations in pulse arrival times and X-ray intensity at the precession period (~several days). Our simulations predict the phase and intensity modulations as a function of the X-ray emission pattern, precession angle, inclination angle, and ellipticity of the pulsar. Additional information can be extracted from the relative phase and amplitude of the fndamental and first harmonic. These results can be easily combined with data in order to infer the ellipticity, geometrical configuration, and hence gravitational wave strain from a given source. We also investigate the relation between the X-ray and gravitational wave signals, the latter as observed by advanced LIGO.

Session Ten - Extra-solar Planets

11:00-12:30

The University of NSW Extrasolar Planet Search: Updates and candidates

Jessie Christiansen

The University of New South Wales is currently undertaking a transit search for extrasolar planets using the Automated Patrol Telescope. The survey is described, with a focus on updates and changes from previous years. These include implementation of new software for handling systematic noise, and the installation of a new CCD camera which should increase our survey efficiency dramatically. The most recent candidates are presented and the status of previous candidates is updated.

Physical and chemical aeronomy of HD 209458b

Antonio García Muñoz

We have carried out model computations of the composition, temperature and bulk escape of the illuminated upper atmosphere of the hot Jupiter HD 209458b [1]. In spite of the expectedly intense EUV radiation incident on the planet, that orbits its host star at a distance a~0.05 AU, the planet's gaseous envelope appears to remain stable over time scales of hundreds of Gyears. The escape lifetime would however shorten significantly for orbital distances a~0.015 AU or less, largely due to the effect of tidal forces. We have computed the profiles of the main H, He, C, O, N, and Deuterium species forming in the atmosphere. The model results are then compared with the existing observations of H I, C II and O I atoms [2, 3]. A scenario with solar or nearly solar abundances of these three elements at high altitude appears to match best the observations. [1] García Muñoz, Planetary and Space Science (In press). [2] Vidal-Madjar et al. (2003), Nature, 422, 143146. [3] Vidal-Madjar et al. (2004), Astrophys. J. 604, L69L72.

High dynamic range direct imaging of extrasolar planets with LAPCAT

Tui Britton

We present an analysis of the potential for LAPCAT (the Large Antarctic Plateau Clear-Aperture Telescope) to directly observe extrasolar planets using high dynamic range imaging. LAPCAT is a proposed 8.4 metre off-axis telescope to be located at Dome C in Antarctica. The low atmospheric temperatures and minimal high altitude turbulence, along with low wind speeds and the absence of dust, make this a unique site for astronomical observations. LAPCAT’s monolithic primary mirror would be similar to one of the six off-axis primary mirror segments of the Giant Magellan Telescope. As well as achieving unique science goals, LAPCAT can pave the way for the construction of an ELT in Antarctica.

We have run simulations to determine the point spread function (PSF) of LAPCAT and two existing telescopes under both diffraction-limited and adaptive-optics-corrected seeing conditions. To do this we used PAOLA, an analytical adaptive optics simulation package written in IDL. The PSF of LAPCAT was compared with the PSF's produced by Keck, an on-axis segmented telescope, and Gemini, an on-axis monolithic telescope. We have studied the effect of a typical Antarctic atmospheric turbulence profile on these PSFs, and compared this to the effect of a typical Chilean atmosphere. In later stages of this project we will include apodizing, coronagraphy and the subtraction of speckle noise.

Earth: A Prototype Extrasolar Planet?

Sally Langford

The discovery of terrestrial planets around nearby stars is one of the major goals of modern astronomy. Space-based missions such as ESA's Darwin and NASA's Terrestrial Planet Finder are being developed to catalogue the planets orbiting neighbouring stars in habitable zones. The potential to identify these planets as Earth-like objects depends on our capacity to recognise telluric signatures. This motivates an investigation of the observable signatures due to terrestrial features on Earth, such as the variation in the reflected flux of the planet with rotation.

We have investigated the variation of the Earth's photometric flux and the correlation of this variation with surface features of the Earth, using observations of Earthshine. In this talk I will present results showing a ~20% change in the Earths reflected light over a period of ~1.5 hours. This variation corresponds to the continental boundary between the Indian Ocean and Africa's East coast. The consistent trend between terrestrial features and variability of Earthshine measurements suggests that similar characteristics of extra-solar planets may be explored by the same method.

Understanding Anglo-Australian Planet Search observations

Simon O'Toole

The number of known extra-solar planets is growing at a increasing rate. The vast majority of these exoplanets have been discovered by measuring the Doppler velocities of the host star. Before any robust comparison of mass, orbital period and eccentricity distributions can be made with theory, a detailed understanding of the observational selection effects is required. Up to now, no study of these effects has been undertaken by any planet search group. In this talk I present a progress report on our analysis of the selection effects present in the Anglo-Australian Planet Search data, including the methodology used and some preliminary results.

The Anglo-Australian Planet Search - An update

Chris Tinney

In planets detected per star monitored, the AAPS is now the world's most efficient planet search. I will highlight some of our recent results, and update the community on our plans to keep AAPS at the forefront of international exoplanet studies.

Session Eleven - The Solar System, and Astrophysics

13:45-14:30

Thermal Radiation from Large Asteroids

Matthew Chamberlain

New thermal observations are being made at mid-infrared and millimeter wavelengths of Ceres, Vesta and other large asteroids. These planetary bodies represent protoplanets left over from the formation of terrestrial planets. There is evidence for variation in thermophysical properties both between asteriods and on the surface of a single asteroid. Thermal lightcurves are observed as the asteroids rotate and these lightcurves have significant amplitudes that cannot be explained by shape and albedo alone. Repeat observations of the same asteroid are made under different viewing aspects and sub-solar latitudes, and can constrain thermophysical properties of the surface. Results are being used to refine the thermal models applied to asteroids and to begin identifying surface regions with anomalous properties.

Lucky Imaging

Andrew Smith

We have tested the method of selective imaging, or "lucky imaging", in light of the original theories of Fried (1966,1978), with the aim of optimising the technique and broadening its application. Selective imaging involves taking many successive short exposure images of a sufficiently bright source, every frame is analysed for sharpness and only those that meet given quality criteria are selected to combine into a final image. This makes use of the random moments of clarity that occur during imaging, and substantially reduces the distorting and blurring effects of seeing as well as dark current.

Imaging was undertaken on both the AAT and the 1m ANU telescope with various aperture masks, frame exposure times, and colour filters. Results from observations of bright stars using a simple "brightest pixel" criterion are presented. These images show improvements in Strehl ratios with increasing selectivity. In agreement with theory, more usable frames are found when using smaller apertures, and greater improvements in Strehl are obtained at higher wavelengths. The issue of the longest useful frame exposure time is presented. Initial results of planetary images using Fourier analyses are also shown.

Regularisation, Resolution and Revolutions: Bayesian Inference in Astrophysics

Brendon Brewer

Session Twelve - Antarctic Astronomy

16:00-17:45

Ground-layer atmospheric turbulence in Antarctica

Michael Ashley

The atmospheric turbulence over the Antarctic plateau is quite different from that at temperate latitude sites: a thin (tens of metres at Dome C) ground layer is highly turbulent; above this, the seeing averages 0.25 arcseconds at 500nm. 90% of the time the seeing above the ground layer is better than the best 10% of the time at Mauna Kea.

Our knowledge of the thickness and properties of the ground layer is crucial to planning new optical/IR telescopes for Antarctica. Should a telescope be placed on a tower, or will adaptive optics be sufficient?

This talk will review our knowledge of the ground layer at several sites on the Antarctic plateau. Four techniques will be described for measuring the ground layer, as will plans to answer the remaining questions in the next year or two.

Can adaptive optics in Chile compete with an Antarctic telescope?

Jon Lawrence

The unique atmospheric characteristics found at Dome C on the Antarctic plateau offer significant advantages for the operation of adaptive optics systems. The large coherence length, wide isoplanatic angle, and long coherence time of the Dome C atmosphere allow an adaptive optics system located there to correct to high order, observe over wide fields and use faint guide stars, resulting in a lower total wavefront error and a significant increase in sky coverage factor than can be achieved at a typical mid-latitude site, such as Cerro Paranal. An analysis is presented here comparing the performance of both natural guide star and laser guide star adaptive optics systems on telescopes located at Dome C with similar systems located at Cerro Paranal.

Sky brightness, photometry and cloud statistics for Dome C, Antarctica

Tim Leslie

90% of the time the seeing above the ground layer is better than the best 10% of the time at Mauna Kea.

Water vapour radiometry for millimetre phase correction - from Antarctica to Narrabri

Balthasar Indermuehle

Radio interferometry at mm and submm wavelengths is greatly affected by signal path length variations caused by water vapour in the atmosphere. Various methods exist to quantify the radio seeing for site testing as well as for signal correction purposes during observations. Depending on site location and anticipated water vapour content, either 22 GHz or 183 GHz emissions can be measured, the former for locations where high water vapour lading is present, whereas the very narrow emission feature at the higher frequency is suitable for very dry atmospheres encountered in Antarctica. We present data from satellite missions over the Antarctic Plateau used for site testing and evaluation as well as data from the currently installed water vapour radiometers on the Compact Array Telescope.

PILOT and the future of Dome C astronomy

John Storey

Concordia Station, Dome C Antarctica, is now in its third winter of continuous operation. New data being obtained confirm the remarkable site qualities, strengthening the case for a new, large telescope to take advantage of the conditions. PILOT, the Pathfinder for an International Large Optical Telescope, is proposed as a joint Australian-European 2.4 metre optical/infrared telescope. This talk will review the background to the project, and describe its current status and future plans.

The functional requirements and design for PILOT

Will Saunders

The PILOT project aims to do justice to the astronomical potential at Dome-C, particularly in terms in terms of sky background and image quality. The NCRIS-funded design study now underway is intended to achieve this goal, in the face of the many novel environmental challenges. The functional requirements and their implications for the telescope design will be presented, and feedback invited.

PLATO and the 2007/8 site testing expedition to Dome A

Shane Hengst

Dome A, Antarctica, has an elevation of 4100m and temperatures that can fall below -80°C. It is possibly the best astronomical site on the planet, especially at terahertz frequencies. We are currently developing PLATO (PLATeau Observatory), the third generation of our robotic site-testing observatories. PLATO will be deployed to Dome A by the Polar Research Institute of China in the summer season of 2007-8 as part of their "PANDA" International Polar Year expedition.

PLATO differs from its predecessors, the AASTO and AASTINO, in that it consists of a separate power and instrumentation module. A suite of instruments from both UNSW and international collaborators will observe the site conditions. The instruments will be measuring sky emission and opacity in the visible and sub-millimetre, turbulence in the boundary layer and upper atmosphere, and meteorological conditions. These measurements will provide valuable site testing and scientific data. The instrumentation module will be powered by a hybrid system of solar panels and diesel generators. We have constructed a low-pressure environmental chamber and used it to successfully test the diesel engines at simulated Dome A altitudes. PLATO is fully autonomous, but control and data retrieval is also possible via the Iridium satellite network.

Program	All Days	Sunday	Monday	Tuesday	Wednesday	Thursday	Posters
Abstracts	Posters A-K	Posters L-Z	Monday	Tuesday	Wednesday	Thursday	Lunch Meetings

For further information (and additions or corrections), contact: qap@physics.mq.edu.au