ORCID Profile
0000-0001-7212-0835
Current Organisation
Astronomy Australia Ltd
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Astrobiology | Stellar Astronomy and Planetary Systems | Astronomical and Space Sciences | Planetary Science (excl. Extraterrestrial Geology)
Publisher: American Astronomical Society
Date: 26-10-2018
Publisher: Oxford University Press (OUP)
Date: 13-12-2019
Publisher: Oxford University Press (OUP)
Date: 25-01-2021
Abstract: We present high-precision linear polarization observations of four bright hot Jupiter systems (τ Boo, HD 179949, HD 189733, and 51 Peg) and use the data to search for polarized reflected light from the planets. The data for 51 Peg are consistent with a reflected light polarization signal at about the level expected with 2.8σ significance and a false alarm probability of 1.9 per cent. More data will be needed to confirm a detection of reflected light in this system. HD 189733 shows highly variable polarization that appears to be most likely the result of magnetic activity of the host star. This masks any polarization due to reflected light, but a polarization signal at the expected level of ∼20 ppm cannot be ruled out. τ Boo and HD 179949 show no evidence for polarization due to reflected light. The results are consistent with the idea that many hot Jupiters have low geometric albedos. Conclusive detection of polarized reflected light from hot Jupiters is likely to require further improvements in instrument sensitivity.
Publisher: Oxford University Press (OUP)
Date: 29-11-2018
Publisher: Oxford University Press (OUP)
Date: 27-01-2023
Abstract: We have built and tested a compact, low-cost, but very high performance astronomical polarimeter based on a continuously rotating half-wave plate and a high-speed imaging detector. The polarimeter is suitable for small telescopes up to ∼1 m in aperture. The optical system provides very high transmission over a wide wavelength range from the atmospheric ultraviolet cut-off to ∼1000 nm. The high quantum efficiency, low noise, and high speed of the detectors enable bright stars to be observed with high precision as well as polarization imaging of extended sources. We have measured the performance of the instrument on 20 and 60 cm aperture telescopes. We show some ex les of the type of science possible with this instrument. The polarimeter is particularly suited to studies of the wavelength dependence and time variability of the polarization of stars and planets.
Publisher: American Astronomical Society
Date: 03-12-2018
Publisher: Oxford University Press (OUP)
Date: 24-04-2020
Abstract: We use ground-based and space-based eclipse measurements for the near-infrared (IR) bands (JHKs) and Spitzer 3.6- and 4.5-μm bands to construct colour–colour and colour–magnitude diagrams for hot Jupiters. We compare the results with previous observations of substellar objects and find that hot Jupiters, when corrected for their inflated radii, lie near the blackbody line and in the same region of the colour–magnitude diagrams as brown dwarfs, including low-gravity dwarfs that have been previously suggested as exoplanet analogues. We use theoretical emission spectra to investigate the effects of different metallicity, C/O ratios, and temperatures on the IR colours. In general, we find that while differences in C/O ratio and metallicity do correspond to different locations on these diagrams, the measurement errors are too large to use this method to put strong constraints on the composition of in idual objects. However, as a class, hot Jupiters cluster around the location expected for solar metallicity and C/O ratio.
Publisher: Oxford University Press (OUP)
Date: 09-04-2022
Abstract: We report high-precision observations of the linear polarization of the F1III star θ Scorpii. The polarization has a wavelength dependence of the form expected for a rapid rotator, but with an litude several times larger than seen in otherwise similar main-sequence stars. This confirms the expectation that lower-gravity stars should have stronger rotational-polarization signatures as a consequence of the density dependence of the ratio of scattering to absorption opacities. By modelling the polarization, together with additional observational constraints (incorporating a revised analysis of Hipparcos astrometry, which clarifies the system’s binary status), we determine a set of precise stellar parameters, including a rotation rate $\\omega \\, (= \\Omega /\\Omega _{\\rm c})\\ge 0.94$, polar gravity $\\log (g_{\\rm p})= 2.091 ^{+0.042}_{-0.039}$ (dex cgs), mass $3.10 ^{+0.37}_{-0.32}$ M⊙, and luminosity $\\log (L/\\rm{L}_{\\odot }) =3.149^{+0.041}_{-0.028}$. These values are incompatible with evolutionary models of single rotating stars, with the star rotating too rapidly for its evolutionary stage, and being undermassive for its luminosity. We conclude that θ Sco A is most probably the product of a binary merger.
Publisher: Oxford University Press (OUP)
Date: 13-07-2020
Abstract: We report the detection of phase-locked polarization in the bright (mV = 2.98−3.24) semidetached eclipsing binary μ1 Sco (HD 151890). The phenomenon was observed in multiple photometric bands using two different HIPPI-class (HIgh Precision Polarimetric Instrument) polarimeters with telescopes ranging in size from 35 cm to 3.9 m. The peak-to-trough litude of the polarization is wavelength dependent and large, ∼700 ppm in green light, and is easily seen with even the smallest telescope. We fit the polarization phase curve with a synspec/vlidort polarized radiative transfer model and a Wilson–Devinney geometric formalism, which we describe in detail. Light from each star reflected by the photosphere of the other, together with a much smaller contribution from tidal distortion and eclipse effects, wholly accounts for the polarization litude. In the past, polarization in semidetached binaries has been attributed mostly to scattering from extra-stellar gas. Our new interpretation facilitates determining masses of such stars in non-eclipsing systems.
Publisher: American Astronomical Society
Date: 31-07-2017
Publisher: American Astronomical Society
Date: 25-03-2022
Abstract: Measurements of starlight polarized by aligned interstellar dust grains are used to probe the relation between the orientation of the ambient interstellar magnetic field (ISMF) and the ISMF traced by the ribbons of energetic neutral atoms discovered by the Interstellar Boundary Explorer spacecraft. We utilize polarization data, many acquired specifically for this study, to trace the configuration of the ISMF within 40 pc. A statistical analysis yields a best-fit ISMF orientation, B magpol , aligned with Galactic coordinates ℓ = 42°, b = 49°. Further analysis shows the ISMF is more orderly for “downfield” stars located over 90° from B magpol . The data subset of downfield stars yields an orientation for the nearby ISMF at ecliptic coordinates λ , β ≈ 219° ± 15°, 43° ± 9° (Galactic coordinates l , b ≈ 40°, 56°, ±17°). This best-fit ISMF orientation from polarization data is close to the field direction obtained from ribbon models. This agreement suggests that the ISMF shaping the heliosphere belongs to an extended ordered magnetic field. Extended filamentary structures are found throughout the sky. A previously discovered filament traversing the heliosphere nose region, “Filament A,” extends over 300° of the sky, and crosses the upwind direction of interstellar dust flowing into the heliosphere. Filament A overlaps the locations of the Voyager kilohertz emissions, three quasar intraday variables, cosmic microwave background (CMB) components, and the inflow direction of interstellar grains s led by Ulysses and Galileo. These features are likely located in the upstream outer heliosheath where ISMF drapes over the heliosphere, suggesting Filament A coincides with a dusty magnetized plasma. A filament 55° long is aligned with a possible shock interface between local interstellar clouds. A dark spot in the CMB is seen within 5° of the filament and within 10° of the downfield ISMF direction. Two large magnetic arcs are centered on the directions of the heliotail. The overlap between CMB components and the aligned dust grains forming Filament A indicates the configuration of dust entrained in the ISMF interacting with the heliosphere provides a measurable foreground to the CMB.
Publisher: Oxford University Press (OUP)
Date: 20-03-2020
Abstract: Recently we have demonstrated that high-precision polarization observations can detect the polarization resulting from the rotational distortion of a rapidly rotating B-type star. Here, we investigate the extension of this approach to an A-type star. Linear-polarization observations of α Oph (A5IV) have been obtained over wavelengths from 400 to 750 nm. They show the wavelength dependence expected for a rapidly rotating star combined with a contribution from interstellar polarization. We model the observations by fitting rotating-star polarization models and adding additional constraints including a measured vesin i. However, we cannot fully separate the effects of rotation rate and inclination, leaving a range of possible solutions. We determine a rotation rate (ω = Ω/Ωc) between 0.83 and 0.98 and an axial inclination i & 60°. The rotation-axis position angle is found to be 142 ± 4°, differing by 16° from a value obtained by interferometry. This might be due to precession of the rotation axis due to interaction with the binary companion. Other parameters resulting from the analysis include a polar temperature Tp = 8725 ± 175 K, polar gravity log gp = 3.93 ± 0.08 (dex cgs), and polar radius Rp = 2.52 ± 0.06 R⊙. Comparison with rotating-star evolutionary models indicates that α Oph is in the later half of its main-sequence evolution and must have had an initial ω of 0.8 or greater. The interstellar polarization has a maximum value at a wavelength (λmax) of 440 ± 110 nm, consistent with values found for other nearby stars.
Publisher: Oxford University Press (OUP)
Date: 06-12-2019
Publisher: American Astronomical Society
Date: 02-01-2019
Publisher: Oxford University Press (OUP)
Date: 18-07-2018
Start Date: 2014
End Date: 08-2015
Amount: $34,500.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 2014
Funder: Australian Research Council
View Funded Activity