http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:723 We have built and used on several occasions an optical broadband stellar polarimeter, PlanetPol, which employs photoelastic modulators and avalanche photodiodes and achieves a photon-noise-limited sensitivity of at least 1 in 10⁶ in fractional polarization. Observations of a number of polarized standards taken from the literature show that the accuracy of polarization measurements is ~1%. We have developed a method for accurately measuring the polarization of altitude-azimuth mounted telescopes by observing bright nearby stars at different parallactic angles, and we find that the on-axis polarization of the William Herschel Telescope is typically ~15 × 10⁻⁶, measured with an accuracy of a few parts in 10⁷. The nearby stars (distance less than 32 pc) are found to have very low polarizations, typically a few ×10⁻⁶, indicating that very little interstellar polarization is produced close to the Sun and that their intrinsic polarization is also low. Although the polarimeter can be used for a wide range of astronomy, the very high sensitivity was set by the goal of detecting the polarization signature of unresolved extrasolar planets. 2010-10-27T01:23:08.402Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:8301 We present elemental abundances of 118 stars (28 of which are known extrasolar planetary host stars) observed as part of the Anglo-Australian Planet Search. Abundances of O, Mg, Cr, Y, Zr, Ba, Nd, and Eu (along with previously published abundances for C and Si) are presented. This study is one of the first to specifically examine planetary host stars for the heavy elements produced by neutron capture reactions. We find that the abundances in host stars are chemically different from both the standard solar abundances and the abundances in non-host stars in all elements studied, with enrichments over non-host stars ranging from 0.06 dex (for O) to 0.11 dex (for Cr and Y). Such abundance trends are in agreement with other previous studies of field stars and lead us to conclude that the chemical anomalies observed in planetary host stars are the result of normal galactic chemical evolution processes. Based on this observation, we conclude that the observed chemical traits of planetary host stars are primordial in origin, coming from the original nebula and not from a "pollution" process occurring during or after formation, and that planet formation occurs naturally with the evolution of stellar material. 2010-05-24T10:11:06.369Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:730 We demonstrate that artificial bipolar structure can be detected using spectro-astrometry when the point spread function (PSF) of a point source suffers distortion in a relatively wide slit. Spectro-astrometry is a technique which allows us to probe the spatial structure of astronomical sources on milliarcsec (mas) scales making it possible to detect close binaries and to study the geometry and kinematics of outflowing gas on scales much smaller than the seeing or the diffraction limit of the telescope. It is demonstrated that a distorted PSF, caused by tracking errors of the telescope or unstable active optics during an exposure, can induce artificial signals which may be misinterpreted as a real spectro-astrometric signal. Using simulations, we show that these may be minimized by using a narrow slit relative to the seeing. Spectra should be obtained at antiparallel slit position angles (e.g. 0° and 180°) for comparison in order to allow artificial signatures to be identified. 2010-01-27T23:24:48.969Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:731 Wide-field (~8' × 8') and deep near-infrared (JHK bands) polarization images of the Orion Nebula are presented. These data revealed various circumstellar structures as infrared reflection nebulae (IRNe) around young stellar objects (YSOs), both massive and low-mass. We found the IRN around both IRc2 and BN to be very extensive, suggesting that there might be two extended (>0.7 pc) bipolar/monopolar IRNe in these sources. We discovered at least 13 smaller scale (~0.01-0.1 pc) IRNe around less massive YSOs, including the famous source θ² Ori C. We also suggest the presence of many unresolved (<690 AU) systems around low-mass YSOs and young brown dwarfs showing possible intrinsic polarizations. Wide-field infrared polarimetry is thus demonstrated to be a powerful technique in revealing IRNe and hence potential disk/outflow systems among high-mass to substellar YSOs. 2010-01-27T23:24:47.736Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:995 We present infrared echelle spectroscopy of three Herbig-Haro (HH) driving sources (SVS 13, B5-IRS 1, and HH 34 IRS) using Subaru IRCS. The large diameter of the telescope and wide spectral coverage of the spectrograph allowed us to detect several H₂ and [Fe II] lines in the H and K bands. These include H₂ lines arising from v = 1-3 and J = 1-11 , and [Fe II] lines with upper level energies of E/k = (1.1-2.7) × 10⁴ K. For all objects the outflow is found to have two velocity components: (1) a high-velocity (−70 to −130 km s⁻¹) component (HVC), seen in [Fe II] or H₂ emission and associated with a collimated jet; and (2) a low-velocity (−10 to −30 km s⁻¹) component (LVC), which is seen in H₂ emission only and is spatially more compact. Such a kinematic structure resembles optical forbidden emission line outflows associated with classical T Tauri stars, whereas the presence of H₂ emission reflects the low-excitation nature of the outflowing gas close to these protostars. The observed H₂ flux ratios indicate a temperature of (2-3) × 10³ K and a gas density of 10⁵ cm⁻³ or more, supporting shocks as the heating mechanism. B5-IRS 1 exhibits faint extended emission associated with the H₂-LVC, in which the radial velocity slowly increases with distance from the protostar (by ~20 km s⁻¹ at ~500 AU). This is explained as warm molecular gas entrained by an unseen wide-angled wind. The [Fe II] flux ratios indicate electron densities to be ~10⁴ cm⁻³ or greater, similar to forbidden-line outflows associated with classical T Tauri stars. Finally, the kinematic structure of the [Fe II] emission associated with the base of the B5-IRS 1 and HH 34 IRS outflows is shown to support disk-wind models. 2010-01-27T23:21:37.674Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:2926 Ground-based telescopes offer a number of advantages for characterising the Martian atmosphere, including the ability to use high resolution (R ~ 30000) spectroscopy and to simultaneously characterise the atmospheric state across an entire hemisphere. In October/November 2005 we obtained high-resolution ground-based spectra of Mars in the 1.6 μm and 2.0 μm CO2 bands using IRTF/CSHELL and Gemini South/GNIRS with the intention of deriving temperature, pressure and dust optical depth maps from these. We will make use of a forward-modelling technique to iteratively match our observational spectra to simulated spectra created using SMART and VSTAR. We present preliminary results demonstrating our models and observations match closely. 2010-01-27T22:58:59.808Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:2928 We summarize the peliminary results from 3 observing runs with PLANETPOL, a polarimeter designed to achieve sensitivities of order 10⁻⁶ in fractional polarization for nearby hot Jupiter systesm. We also describe some of th problems associated with measuring very small fractional polarizations and the solutions we have adopted. Tese observations were conducted at the 4.2-m William Herschel Telescope. 2010-01-27T22:58:58.504Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:6540 Doppler-shift measurements with a remarkable precision of Δλ/λ=3×10⁻⁹, corresponding to velocities of 1 m s⁻¹, have been made repeatedly of 2500 stars located within 300 light years. The observed gravitational perturbations of the stars have revealed 250 orbiting planets, with 27 that cross in front of the host star, blocking a fraction of the starlight to allow measurement of the planet's mass, radius and density. Two new discoveries are the first good analog of Jupiter (HD 154345b) and the first system of five planets (55 Cancri). The predominantly eccentric orbits of exoplanets probably result from planet–planet gravitational interactions or angular momentum exchange by mean-motion resonances. The planet mass distribution ranges from ~15 MJUP to as low as ~5 MEarth and rises toward lower masses as dN/dM∞M⁻¹·¹. The distribution with orbital distance, a, rises (in logarithmic intervals) as dN/d log a∞a⁺⁰·⁴. Extrapolation and integration suggests that 19% of all Sun-like stars harbor a gas-giant planet within 20 AU, but there remains considerable incompleteness for large orbits. Beyond 20 AU, the occurrence of gas-giant planets may be less than a few per cent as protoplanetary disk material there has lower densities and is vulnerable to destruction. Jupiter-mass planets occur more commonly around more massive stars than low mass stars. The transit of the Neptune-mass planet, Gliese 436b, yields a density of 1.55 g cm⁻³ suggesting that its interior has an iron–silicate core surrounded by an envelope of water����ice and an outer H–He shell. Planets with masses as low as five Earth-masses may be commonly composed of iron–nickel, rock and water along with significant amounts of H and He, making the term 'super-Earth' misleading. The transiting planet HD147506b has high orbital eccentricity but no significant orbital inclination to the line of sight, presenting a puzzle about its history. Its orbit together with the mean motion resonances of 4 of the 22 multi-planet systems provides further evidence for the role of planet–planet interactions in shaping planetary architectures. 2010-01-27T22:16:33.681Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:6642 Despite recent advances in the study of extra-solar planets the detection of reflected light from planetary atmospheres remains a major goal. For the so-called hot-Jupiters, which are unlikely to be spatially resolved from the central star in the foreseeable future, very high sensitivity measurements are required to detect the reflected signal from the very much larger direct starlight. We describe an optical photo-polarimeter designed to have a polarization sensitivity of at least 1 in 10⁶ and some early observations made in an attempt to detect the polarization signature of τ Boo b. We discuss the role of such an instrument for the planned ELTs. 2010-01-27T22:15:17.875Z ]]>