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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 - Posters: A-K
Mapping the temperature of the Venus upper atmosphere using IRIS2
Jeremy Bailey
Observations with IRIS2 on the AAT have been used to map the
temperature in the upper atmosphere of Venus by using the rotational
line strengths in the 1.27 μm airglow band of molecular oxygen. A
forward modelling scheme has been developed to allow for the
absorption in the Earth's atmosphere in the same molecular band. The
resulting temperatures range from about 178K - 220K with spatial
structure that varies from night to night. The temperatures are higher
than those expected from the Venus International Reference Atmosphere
(VIRA) profile, suggesting the presence of adiabatic heating due to
downwelling of the gas. The results complement data on the height of
the airglow emission obtained with VIRTIS on the ESA Venus Express
spacecraft.
NIFS Observations and Atmospheric Modelling of Titan
Jeremy Bailey and Linda Ahlsved
We present disk resolved near infrared spectra of Titan obtained
using NIFS and the Altair adaptive optics system on Gemini North. The
K-band spectrum has been modelled using a radiative transfer model for
the Titan atmosphere based on the VSTAR code. The model includes
methane absorption which accounts for almost all of the spectral
features observed. The aerosol haze is modelled using tholin particles
with enanced forward scattering. The major problem in fitting the
spectrum was to correctly match the shape of the 2 μm window.
An improved fit is obtained by including absorption due to H2-N2
dimers, and by using a sub-Lorentzian line shape model for the far
wings of the methane lines.
Surface Properties of Asteroids and Their Use as mm-Calibrators
Peter Barnes, Thomas Muller, and Michael Dahlem
(4) Vesta and (9) Metis are large main-belt asteroids with high albedos. There are strong indications for heterogeneous surfaces for both targets from imaging techniques in the visible and near-IR range, very likely connected to impact structures. Despite that, the thermal spectral energy distributions from mid-IR to the mm-range have, until now, been consistent with a homogeneous regolith-covered surface and the thermal light-curves are dominated by the shape and spin vector properties.
With recent ATCA observations at 93.0 and 95.5 GHz we tried to characterise the emission properties of the surface material. The coverage of the full rotation period allowed a detailed study of the heterogeneity of the surface. We combined our carefully-calibrated mm-observations with sophisticated thermophysical modelling techniques. In this way it was possible to derive emissivity properties and to disentangle the effects caused by shape, albedo or various thermal properties.
The thermophysical model predictions match the overall flux levels
very well, but cannot reproduce certain lightcurve features due to the
lack of information on the grain size distribution. The 3mm
observations are very powerful for the study of surface
heterogeneities, but they show MBAs are unlikely to make good
calibration candidates at 3mm, even though they are ideal for this
purpose at submm wavelengths. We have also recently used similar
techniques to refine the ATCA's absolute calibration at 3mm. By
interleaving observations at 85, 95, and 105 GHz of Mars, Uranus, and
Neptune, we are able to define the CA's antennas' gain-elevation curve
much more precisely than has hitherto been done, and from this can also
study the mm-emissivities and spectral indices of these bodies,
refining their use as calibrators at 3mm.
Radio study of MASH planetary Nebulae
Ivan Bojicic, Alan Vaughan and Quentin A. Parker
The recent Anglo-Australian Observatory/UK Schmidt Telescope
(AAO/UKST) Hα survey of the Southern Galactic Plane gaseous
emission, led to discovery of about 1000 new Galactic Planetary
Nebulae (Parker et al., 2005, 2006). Accurate positions, angular
sizes, morphologies, multi-wavelength images and spectroscopy for all
newly discovered planetaries are presented in the MASH
(Macquarie/AAO/Strasbourg Hα PNe project) catalogue
(Parker et al., 2006). We here report on a new multi-frequency radio
measurements of a sample of PNe from the MASH catalogue. With the high
sensitivity observation at 3 and 5cm, carried out with the Australian
Telescope Compact Array, we achieve detection of very faint objects
(>1mJy) with detection rate of about 45%. Small subsample of detected
nebulae is also observed at lower frequencies in order to construct
radio-spectral distribution. Preliminary results show that MASH sample
consists from low-brightness objects, optically thick at lower frequencies,
implying a later stadium of evolution.
Star Formation and the Hall Effect
Catherine Braiding and Mark Wardle
Low-mass stars form as a result of the gravitational collapse of dense molecular cloud cores. The magnetic field in these molecular clouds provides pressure support against gravity and carries away angular momentum prior to and during the collapse of cloud cores into protostars.
The effect of Hall diffusion on the breakdown of flux freezing
within the clouds has not been examined in previous models of
gravitational collapse, where the effect of the magnetic field is
usually approximated by ambipolar diffusion at low densities or
resistive diffusion at high densities. The Hall effect has been shown
to control the evolution of the magnetic field in molecular gas, and
is expected to alter the dynamics of gravitational collapse. This
poster presents the preliminary results from a model of the
self-similar collapse of rotating isothermal molecular cloud cores
with a magnetic field.
Water masers within the G333.2-0.6 giant molecular cloud
Shari Breen, Simon Ellingsen, Melanie Johnston-Hollitt, Simon Wotherspoon, Indra Bains, Michael Burton, Maria Cunningham, Nadia Lo, Cliff Senkbeil and Tony Wong.
We report the results of a blind search for 22 GHz water masers in
two regions, covering approximately half a square degree, within the
giant molecular cloud associated with RCW 106. The complete search of
the two regions was carried out with the 26 m Mount Pleasant radio
telescope and resulted in the detection of nine water masers, five of
which are new detections. Australia Telescope Compact Array
observations of these detections have allowed us to obtain positions
with arcsecond accuracy, allowing meaningful comparison with infrared
and molecular data for the region. We find that for the regions
surveyed there are more water masers than either 6.7 GHz methanol, or
main-line OH masers. The water masers are concentrated towards the
central axis of the star formation region, in contrast to the 6.7 GHz
methanol masers which tend to be located near the periphery. The
colours of the GLIMPSE point sources associated with the water masers
are similar to those of 6.7 GHz methanol masers, but slightly less
red. We have made a statistical investigation of the properties of
the 13CO and 1.2 mm dust clumps with and without associated
water masers. We find that the water masers are associated with the
more massive, denser and brighter 13CO and 1.2 mm dust
clumps. We present statistical models that are able to predict those
13CO and 1.2 mm dust clumps that are likely to have
associated water masers, with a low misclassification
rate.
Flaring OH masers in Mon R2
Shari Breen, Simon Ellingsen, Derck Smits, Anita Richards and Lisa Harvey-Smith
We report a spectacular flare in the excited 4765 MHz OH maser
emission from Mon R2. The current measured flux density of the source
is ~50 Jy, more than 400 times brighter than when it was discovered
by Gardner & Martin-Pintado (1983) with a peak flux density of
0.12 Jy. In 1997 the source exhibited similar flaring behavior and a
peak flux density of ~75 Jy was measured (Smits, Cohen &
Hutawarakorn 1998). The Mon R2 4765 MHz OH maser is by far the
brightest maser of this transition detected to date and is the only
known example of 4765 MHz excited OH maser emission with linear
polarization. This is a unique source and studying it in detail
provides an excellent opportunity to test the models of maser pumping
and hence constrain the physical conditions responsible for flaring
events, as well as the excitation of 4765 MHz masers in star
formation regions. We present new MERLIN target-of-opportunity
observations of the 4765 MHz source as well as the results of a
weekly monitoring program undertaken with the University of Tasmania
26 m radio telescope over a three month period. Observations of the
1612, 1665, 1667, 1720, 6030 and 6035 MHz OH transitions made with
the Parkes radio telescope during the current 4765 MHz flaring
episode will also be presented.
Investigation into the diffuse radio emission in A3128
Anne-Marie L. Brick, Melanie Johnston-Hollitt and HRS collaboration
The Horologium Reticulum Supercluster(HRS) is the second largest
supercluster in the local universe. To date, considerable progress
has been made in understanding the large scale structure of the HRS
(Fleenor et. al., 2005, and references therein), however, there is
still much to do. Of particular interest is the diffuse radio
emission in A3128, near the centre of the HRS, noted by Rose et. al.
(2002) seen at 843MHz, but not at 1.4GHz. It is our belief that this
radio emission is possibly associated with a background cluster at a
redshift of 0.11. The shape of the emission indicates that it is
likely to be a radio relic, and if this is true, it would be the most
distant radio relic found to date. We will discuss the
multi-wavelength data collected from this region, and its implication
on the presence of this distant source.
High-redshift radio galaxies from the MRCR and SUMSS
Jess W. Broderick
High-redshift radio galaxies (HzRGs; z > 2) play a
fundamental role in our understanding of the formation and evolution
of the most massive galaxies in the early Universe. The most
efficient way of finding these rare objects is through ultra-steep
spectrum (USS) selection. We are conducting an extensive program to
find HzRGs in the south by selecting USS sources from a deeper
re-analysis of the 408 MHz Molonglo Reference Catalogue (MRCR), the
843 MHz Sydney University Molonglo Sky Survey (SUMSS) and the 1400 MHz
NRAO VLA Sky Survey (NVSS). High-resolution 20 and 13 cm Australia
Telescope Compact Array (ATCA) observations are used to secure each
host galaxy identification for follow-up spectroscopy, and also to
investigate the environments of the hosts through a combination of
spectral energy distributions, fractional polarization and Faraday
rotation measures. We discuss the radio properties of our sample of
HzRG candidates, as well as a related 12 mm and 3 cm ATCA study that resulted in the discovery of an extreme
rotation measure (-9600 rad m-2) in the z=2.575
source PKS B0529-549, the largest seen thus far in the environment of a
z > 2 radio galaxy.
The 20GHz Sky: Polarization of Bright Extragalactic Radio Sources
Sarah Burke
In this poster we present the results of a high-frequency radio
polarization survey of the brightest sources in the southern sky
region -30 < dec < -70. Using the AT20G Southern Sky Survey as
a tool to collect a complete flux-limited sample of sources selected
at high frequency, we have reobserved the brightest sources (20 GHz
flux >500mJy) with the intention of gathering unbiased statistics
of the polarization of extragalactic sources. The knowledge of high
frequency polarization properties is poor even for sources of high
flux level; the low frequency behaviour of the sources is not a sure
estimator of high frequency behaviour. The results of our observations
hold multifold importance for the CMB missions: from providing an
accurate observational base for predicting and correcting levels of
contamination of CMB polarization signal caused by extragalactic
sources, and the catalogue of individual sources with same-epoch
multifrequency measurements (at 5, 8, and 18 GHz) provide a database
of fluxes, positions, and polarizations to better understand the
physical properties and makeup of the population. Among our catalog
are a few bright, highly polarized sources which may prove to be
formidable candidates for polarization calibrators at high radio
frequency. For nearby sources of large angular extent, we have made
maps of total intensity and polarization.
The Southern Skies Digital Science Partnership
Bradley D. Carter
Mt Kent Observatory is now providing live remote observations of
southern skies as part of a collaborative project between USQ, the
University of Louisville, and Northern Kentucky University.
Telescopes at Mt Kent and Moore Observatory in Kentucky enable
students to remotely observe otherwise inaccessible night-time
skies using a 0.5m aperture telescope located in the opposite
hemisphere. Mt Kent Observatory delivers live remote observing using
multiple CCD cameras for narrow and wide-field imaging, and an
astronomer at the observatory supervising remote use via a
videoconferencing system. This project demonstrates the feasibility
of live remote observing for astronomy education.
Near-Infrared Ground-based Observations of Venus: Technique and Observations of H2O variations in the Lower Atmosphere.
Sarah A. Chamberlain, J. Bailey, V.Meadows, A.Simpson and D.Crisp
Ground-based spatially resolved near infrared spectroscopic
observations of the Venusian night-side have been obtained from Siding
Springs at each inferior conjunction since 2002. Observations have
been made using the IRIS2 on the Anglo-Australian Telescope and Caspir
on the 2.3m ANU Telescope. We are currently in the process of
analysing the data to obtain temporal variations, gradients and spatial
distributions of water in the Venusian lower atmosphere and present
new results.
Topographic and Atmospheric Pressure Mapping of Mars
Sarah A. Chamberlain, J. Bailey, D. Crisp and M. Walter
Near-Infrared images and spectral observations were obtained using
the United Kingdom Infrared Telescope (UKIRT) and the UKIRT Imaging
Spectrometer (UIST) on Mauna Kea, Hawaii. The observations were made
in mid-August and early September 2003, taking advantage of the
close approach of Mars during the August opposition. Narrow band
imaging resulted in possibly the highest resolved images of Mars ever
taken from a ground based telescope, with an image scale of 16km per
pixel. Spectral observations were obtained at wavelengths between
0.9μm and 3.6μm at medium to high spectral
resolving powers. The data were stored in a datacube, enabling images
of Mars to be extracted at any wavelength. CO2 index
images can be produced using spectral regions on and off the
2μm absorption feature, since the Martian atmosphere is
composed of 96% CO2, the resulting image details the planet's surface
topography and correlates well with accurate topographical images
produced by the Mars Orbiting Laser Altimeter (MOLA). However the
CO2 index is a measure of the absorbing column of
CO2 and hence is also influenced by surface pressure
systems on Mars. Pressure systems on Mars have been measured as high
as 50Pa in a total pressure of 800Pa (Barnes 1981, Collins et al 1996).
Preliminary estimates show that our observations are sensitive to
4 - 5Pa and can be improved upon with a more efficient observing
system. This dataset outlines a technique by which weather systems
might be monitored on Mars from future ground-based or space
instruments.
Chemical modelling of hot cores and comparisons with observations
Jacqueline Chapman, Mark Wardle, Andrew Walsh, and Michael Burton
Observations of the abundance of gas phase species inside hot
cores aid in the understanding of the physical and chemical
conditions. However, their interpretation is not straightforward:
first one needs a predictive model based on a accurate physical model
of the source being studied. These models ultimately allows one to
try to reproduce observations and potentially determine the
conditions inside a hot core. Key species act as chemical clocks and
aid in determining the age of the hot core. Second, observed line
intensities must be converted to species abundances for comparison
with predictions. Commonly, one assumes that a species is in local
equilibrium (LTE) and a rotation diagram is used to derive the column
density. This approach is not always accurate and may only roughly
constrain the excitation temperature of a species and its column
density. A radiative transfer (non-LTE) calculation which includes
collisional excitation with H2 and He to model the molecular
excitation and emission is more desirable. We present the results for
a gas phase chemical core model and will discuss the limitations of
these types of models, including issues or initial conditions. We
also present results for a non-LTE molecular excitation model which
can be used to better constrain molecular abundances derived from
observations.
The first high-amplitude delta Scuti star in an eclipsing binary system
Jessie L. Christiansen, A. Derekas, M. C. B. Ashley, J. K. Webb, M. G. Hidas, D. W. Hamacher and L. L. Kiss
We present the discovery data for the first high-amplitude delta
Scuti star to be observed in an eclipsing binary system. It was
discovered in the light curves compiled by the University of New
South Wales Extrasolar Planet Search. By modelling the light curve
and radial velocity curve simultaneously we find an Algol-type
semi-detached eclipsing binary system with an orbital period of
5.3504751 days, containing an A7 spectral type high-amplitude delta
Scuti primary component, and a late K spectral type secondary component.
This model was subtracted and a Fourier analysis performed on the
residuals, detecting a delta Scuti pulsation frequency of 13.6207 cycles
per day.
TenTen : An IACT Array for Multi-TeV Gamma-Ray Astronomy
Jarrad Denman, Victor Stamatescu, Gavin Rowell, Greg Thornton, Roger Clay, Bruce Dawson and Raymond Protheroe
TenTen is a proposed array of Imaging Atmospheric Cherenkov
Telescopes (IACT) optimised for the gamma-ray energy regime above 10
TeV. It will offer a collecting area of 10 km2 above
energies of 10 TeV. In the initial phase, we anticipate a cell of 3
to 5 modest-sized telescopes, each with 10-20 m2 mirror
area. A possible expansion of the array would comprise many such cells.
Here we present recent work on the configuration and technical issues
from our simulation studies of the array. Working topics include array
layout, telescope size and optics, camera field of view, telescope
trigger system, electronics, and site surveys in
Australia.
The brown dwarf binary fraction in the Pleiades
Paul D. Dobbie
We will present an estimate of the brown dwarf binary fraction
from our recent analysis of the UKIDSS DR1 photometric data covering
the Pleiades open cluster. We find a brown dwarf binary fraction
which is somewhat higher than estimated by previous high resolution
imaging studies. We will discuss the implications of this result in
the context of current low mass star/brown dwarf formation
models.
The Magellan Telescopes
David J. E. Floyd
The Magellan Telescopes at Las Campanas Observatory are a pair of 6.5m actively guided optical telescopes with extremely wide-field capability. Current instrumentation includes 2 wide-field imagers / multi-object spectrographs and a high-resolution Echelle spectrograph with extremely high throughput (comparable to HIRES on Keck). Infrared imaging is possible to K short. A host of new instrumentation is arriving in the next 2 years to expand on the current capabilities.
We will present an overview of current and near-future
instrumentation, and be available for questions on all aspects of
observing and applying for time.
Joining the Hubble flow: implications for expanding space
Matthew Francis
The concept of expanding space has come under fire recently as
being inadequate and even misleading in describing the motion of test
particles in the universe. Previous investigations have suffered from a
number of shortcomings, which we seek to correct. We study the motion of
test particles in the universe in detail, solving the geodesic equations
of General Relativity for a number of cosmological models. In
particular, we use analytic methods to examine whether particles removed
from the Hubble flow asymptotically rejoin the Hubble flow, a topic that
has caused confusion because of differing definitions and invalid
reasoning. We conclude that particles in eternally expanding but
otherwise arbitrary universes do not in general rejoin the Hubble flow.
Probing the O2 (a→X) 1.27 μm airglow in the Venusian atmosphere with VIRTIS/VEX
Antonio García Muñoz, F. P. Mills, P. Drossart and the VIRTIS team.
The airglow affords an insight into the chemical composition, dynamics and
thermal balance of planetary atmospheres, and serves to better our
understanding of the spectroscopy and chemical kinetics of the relevant
gas constituents. We have recently started work on the retrieval of the O2
(a—> X) 1.27μm limb and nadir column intensities measured by the
VIRTIS instrument on ESA's Venus Express (VEX) mission, that will
subsequently be used to infer the vertical profiles of the emitting layer.
VIRTIS/VEX commenced observations in 2006 and is scheduled to continue
until 2009, thus providing an extensive seasonal and global coverage of the O2
(a—>X) 1.27μm airglow. In the presentation, we will report on
the current state of our work.
Radio Luminosity Functions of the HR Supercluster
James Gill and M. Johnston-Hollitt
We present the bivariate and univariate 1.4GHz radio luminosity
functions (RLFs) of the A3125/A3128 complex in the centre of the
Horologium-Reticulum Supercluster. We have obtained a deep 1.4 GHz
ATCA image of the are covering the clusters A3125, A3128 and A3158 in
combination with a spectroscopic sample of over 2000 redshifts for the
region. With this unprecedented dataset we can better probe the fainter
end of the RLFs and examine the role environment plays in the generation
of radio emission. We present here the preliminary results of this study
and compare our results to those obtained for the Shapley Supercluster.
High Resolution Spectral Models for Globular Clusters: Construction of the Models and Application to Local Group Globular Clusters
Mita Gopal and Michael D Albrow
We are currently developing high resolution model spectra of simple-stellar-populations for the measurement of chemeical abundances in extragalactic globular clusters. The models are well matched to the available spectral resolution and will allow higher precision studies than those employing the traditional Lick index system.
We describe here the construction of the models and present the
initial comparisons of the models with moderate resolution,
integrated-light spectra of globular clusters in the Milky Way and M31.
Follow-up Observations of UNSW Extrasolar Planet Search Candidates
Duane Hamacher
The University of New South Wales Extrasolar Planet Search
utilizes the wide-field 0.5m Automated Patrol Telescope at Siding
Spring Observatory to search for transiting extrasolar planets.
Follow-up photometric observations are conducted using the ANU
40-inch Telescope at SSO. Since we have collected approximately 35
nights of high precesion photometric data. We present follow-up
photometry and analysis of transit candidates, highlighting new
methods used to identify candidates as well as new reduction methods
incorporated in order to gain more accurate data. UNSW-TR29 and
UNSW-TR-41 remain promising planet candidates that will be further
followed up with additional photometric and spectral observations.
Faraday Rotation in Galaxy Clusters
Warren Hankey
Images of several southern galaxy clusters have been studied for evidence
of Faraday Rotation effects, which imply magnetic fields. Archival data from the
Compact Array radio interferometer at four frequencies were reduced and imaged.
The 128 MHz bands were split into component channels to obtain multiple polarisation images.
Thirty rotation measures were obtained, adjusted for galactic and ionospheric contributions.
An excess of rotation measure was found in extragalactic sources seen
through clusters compared to a control of non-cluster sources. This is seen even when
controversial sources embedded in the clusters are excluded. Statistical tests indicate the
cluster sample and a control of non-cluster sources are two different populations.
The New Green Bank Telescope
Julienne Harnett
The new GBT is the world's largest fully steerable radio telescope, with surface dimensions 100 by 110 meters. The structure allows the telescope to view the entire sky above 5 degrees elevation (85% of the celestial sphere). The track is level to within a few thousandths of an inch in order to provide precise pointing of the structure while bearing 7300 metric tons of moving weight.
The GBT is an unusual design which results in the aperture being unblocked so that incoming radiation meets the surface directly. This increases the useful area of the telescope and simplifies its response pattern.
The 2,004 panels that make up the telescope surface are mounted at their corners on actuators, which make it easier to adjust the surface shape. This is crucial to the high-frequency performance of the GBT for which an accurate surface figure must be maintained.
The frequency coverage is currently 230 MHz to 49 GHz via both prime focus and Gregorian receivers. Backends include digital continuum receivers, a spectral processor and pulsar spigot card, that takes data from the spectrometer's A/D samplers and dumps them to disk. VLBI observations are supported by a Mark 5 recorder.
The next call for observing proposals will be October 1, 2007. We
encourage you to apply.
Fibre losses in astronomical instrumentation due to end-face surface roughness.
Dionne Haynes, Judith Dawes, Roger Haynes and Mick Withford
Fibres have been used in ground based astronomical instrumentation for 30 years and therefore much work has been done on the characterisation of fibres and the losses that can impact the performance of the instrument. However, although the end-face surface roughness of a fibre is recognised as a possible contributor to the losses in the fibre, it has not yet been quantified to our knowledge.
In this poster we present modelling of the effect of scattering from fibre end-face surface roughness and compare with experimental measurements of the fibre losses for a range of surface roughness values.
The AAOmicron instrument
Roger Haynes and Simon Ellis
AAOmicron is one of the concepts being proposed as the new AAT instrument.
It is a fibre fed near infrared spectrograph and if selected it would aim to provide a
frontline facility for the coming decade. The new spectrograph concept builds on the AATs
established strength as a spectroscopic survey telescope, on the successful investment in the
2dF fibre positioner and wide-field corrector as well as much of the AAOmega instrument design.
In this poster I will outline the instrument design and performance goals.
The Phoenix Deep Survey: Extremely red galaxies and cluster candidates
Andrew Hopkins, Anthony Smith, Samuel Schmidt, Jose Afonso and Antonis Georgakakis
We present the results of a study of a sample of 375 Extremely Red
Galaxies (ERGs) in the Phoenix Deep Survey, 273 of which constitute a
subsample which is 80% complete to Ks = 18.5. We calculate the
angular correlation function for ERGs, and explore the association of
ERGs with faint radio sources finding evidence that ERGs and faint
radio sources are associated at z > 0.5. We identify a
number of cluster candidates in our ERG field, and detail an
overdensity-mapping algorithm that we use to characterise the ERG
distribution. We use this algorithm in an attempt to constrain the
environments in which faint radio sources and ERGs are associated, and
find limited evidence that the I - Ks > 4 criterion is more
efficient at selecting dusty star-forming galaxies, rather than
passively evolving ERGs. Amongst the cluster candidates thus
identified we highlight a likely cluster containing ERGs at
z ~ 1.
Radio Synchrotron Emission from Secondary Leptons in the Vicinity of Sgr A*
David Jones, Roland Crocker, David Ballantyne and Fulvio Melia
The Galactic Centre (GC) presents the best laboratory in which to
test theories of particle acceleration, as it is the closest example
of a supermassive black hole, namely Sagittarius A* (Sgr A*).
Exciting recent observations reveal a source of high energy gamma-rays
eminating from the centre of the Galaxy as detected by air Cherenkov
telescopes, such as HESS. This poses the question of how these
energetic gamma rays are produced. We present here modelling and
observations building on previous work done by us investigating proton
diffusion and interaction in the circum-nuclear disk (CND). In this
model, protons are accelerated at Sgr A*, producing neutral pions and
gamma-rays. We further this by modelling charged pions, produced
concomitantly with the neutral pions and their decay into electrons
and positrons. In concert with this modelling, we present new ATCA
observations of the GC at 1384 and 2368 MHz, along with archival 330
MHz VLA data, unpublished 843 MHz SUMSS data and snapshot ATCA 4800
and 8640 MHz data. This data is then used to build a model of emission
which can explain the bulk of the observed broadband emission from the
GC.
Luminosity and Stellar Mass Functions from the 6dFGS
Heath Jones, Bruce Peterson, Matthew Colless and Will Saunders
We present new measures of the stellar mass and luminosity functions in
the local universe (z<0.1) from the 6dF Galaxy Survey. The unprecedented
combination of angular coverage and depth in the 6dFGS offers the best
opportunity to date to minimise systematics in the determination of
local luminosity and stellar mass functions, both in the near-infrared
and the optical. Associated mass and luminosity densities are also
derived and discussed in the context of cosmic star formation history
and mass density evolution. We compare our stellar masses with dynamical
masses from the 6dFGS peculiar velocity survey and find their ratio to
be roughly constant, implying that star formation efficiency, integrated
over time to the present, is largely independent of galaxy dynamical
mass.
The 6dF Galaxy Survey Final Data Release
Heath Jones, Mike Read, Will Saunders, Matthew Colless and the 6dFGS Team
The near-infrared selected 6dF Galaxy Survey covers nearly half the sky and has yielded redshifts, luminosities and stellar mass estimates for more than 120,000 nearby galaxies. It is also being used to derive distances, peculiar velocities and dynamical mass estimates for a subset of about 12,000 bright, early-type galaxies.
We report the completion of the redshift component of the 6dF Galaxy Survey and provide maps of the large scale structures in the local (z<0.1) southern universe showing unprecedented detail. In addition to encompassing well-known superclusters such as Hydra-Centaurus and Shapley, the 6dFGS maps reveal a wealth of new intervening structures. The fainter limiting magnitude and higher sampling density of 6dFGS, compared to earlier surveys of equivalent angular extent, has confirmed the three-dimensional locations for hundreds of voids and furnished the first redshifts for hundreds of southern Abell clusters.
The 6dFGS Final Data Release will be made publicly available in August 2007. The release will comprise a fully-searchable online SQL database with easy-to-use web forms that provide access to the 6dFGS spectra and redshifts together with photometric and imaging data from the 2MASS Extended Source Catalog, the SuperCOSMOS Sky Survey, and a dozen other input catalogues. Velocity dispersions, absorption line indices, distances and peculiar velocities for the brightest 10% of these galaxies will be made available at a later date.
Subaru HDS observations of Tycho Star G
Wolfgang Kerzendorf, B.P. Schmidt, M. Asplund, K. Nomoto, P. Podsiadlowski, A Frebel
It is widely believed that Type Ia supernovae originate in binary
star systems where a white dwarf accretes material from a companion
star until it nears the Chandrasekhar mass, and Carbon ignites near the
star's center. This scenario predicts the donor star to the white
dwarf should remain intact, a calling card to the elusive progenitors
of Type Ia. Ruiz-Lapuente et al. (2004) scrutinised the remnants
central stars and showed strong evidence that a subgiant-G star near
the remnant's centre was the system's donor star. We present R=40000
spectra taken with the High Dispersion Spectrograph on Subaru of this
candidate donor star, and precisely measure the star's radial velocity
and put limits on the star's rotation of less than 10km/s.
We show that the donor star should be rotating at rate faster
than allowed by our observations, arguing against this star being
associated with the supernovae. Furthermore, we compare the star's
observed properties with a model of the galaxy, and conclude that,
except for the star's reported proper motion, all observations are
consistent with that of an unrelated background star. We strongly
urge follow up observations of the star's proper motion be undertaken
ascertain for certain the association between this candidate and
Tycho's supernova.
Mapping age distribution of star forming regions in nearby face-on spirals
Madhura Killedar
The H_alpha-to-FUV flux ratio in young star forming regions is an age sensitive quantity. If this quantity is measured for each pixel in an image of a face-on galaxy, it is possible to map the ages of star forming regions across the disk. We compare the new release GALEX FUV images and extremely narrowband TTF H_alpha images of the nearby face-on spirals: M83, M51 and M77.
The evolutionary synthesis model Starburst99 (Leitherer et al. 1999) (SB99)
describes the predicted decline of the H_alpha-to-FUV flux ratio with the
age of a star forming region. The evolution of the flux ratio is modelled
with the Salpeter IMF, 6% escape fraction and solar metallicity. The flux
ratio found from the images is scaled to the SB99 model assuming an
approx. zero age for the youngest region. In this way, an age is assigned
to each pixel, binned into either 0-4 Myrs, 4-6 Myrs, 6-9 Myrs and >9
Myrs. The resulting age maps show the newest star forming regions tracing
the spiral arms in all three galaxies with the inner edge clear in M83 and
M51. Regions in M83 with no symmetrical counterpart show distinct ages: one
of 4-9 Myrs and the other >6 Myrs. New star formation in the interarm
regions of M51 show possible links to the arms or other independent
structures.
An emission line and kinematic analysis of MASH Galactic PNe
Anna V. Kovacevic and Quentin A. Parker
We present preliminary spectrophotometric and kinematic results for Galactic Planetary Nebulae (PNe) in the Macquarie/AAO/Strasbourg H-alpha Planetary Nebulae Catalogue (MASH) (Parker et al. 2006). MASH PNe generally represent the more evolved end of the luminosity function than previous catalogues due to the inherent depth and resolution of the data. Line-of-sight velocity dispersions as a function of Galactic longitude are presented and compared to previously known PNe to confirm current trends. The radial velocities are compared to other observed PNe properties such as position, excitation class, morphology and environment. Tentative underlying trends between PN type/abundances and kinematic motion are identified and we discuss the impact this has for mixed populations and gradients.
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