Observations of the D/H ratio in Methane in the atmosphere of Saturn's moon, Titan - where did the Saturnian system form?

The details of the Solar system's formation are still heavily debated. Questions remain about the formation locations of the giant planets, and the degree to which volatile material was mixed throughout the proto-planetary system. One diagnostic which offers great promise in helping to unravel the history of planet formation is the study of the level of deuteration in various Solar system bodies. For example, the D/H ratio of methane in the atmosphere of Titan can be used as a diagnostic of the initial conditions of the solar nebula within the region of giant planet formation, and can help us to determine where Titan (and, by extension, the Saturnian system) accreted its volatile material. The level of Titanian deuteration also has implications for both the sources and long term evolution of Titan's atmospheric composition. We present the results of observations taken in the 1.58 microns window using the NIFS spectrometer on the Gemini telescope, and model our data using the VSTAR line--by--line transfer model, which yields a D/H ratio for Titan's atmosphere of 143+/-16) x 10^{-6} [1]. We are currently in the process of modeling the Gemini high resolution GNIRS spectra using new sets of line parameters derived for methane in the region between 1.2-1.7 microns [2].Comment: 12 pages, 4 figures, Accepted for publication in proceedings of the Australian Space Science Conference 201

Colour-colour and colour-magnitude diagrams for Hot Jupiters

We use ground-based and space-based eclipse measurements for the near-infrared ($JHK\!s$) bands and Spitzer 3.6 $\mu$m and 4.5 $\mu$m 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 black body 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 analogs. 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 individual objects. However, as a class hot Jupiters cluster around the location expected for solar metallicity and C/O ratio.Comment: 12 pages, 5 figures, accepted by MNRA

Examining the broadband emission spectrum of WASP-19b: A new z band eclipse detection

WASP-19b is one of the most irradiated hot-Jupiters known. Its secondary eclipse is the deepest of all transiting planets, and has been measured in multiple optical and infrared bands. We obtained a z band eclipse observation, with measured depth of 0.080 +/- 0.029 %, using the 2m Faulkes Telescope South, that is consistent with the results of previous observations. We combine our measurement of the z band eclipse with previous observations to explore atmosphere models of WASP-19b that are consistent with the its broadband spectrum. We use the VSTAR radiative transfer code to examine the effect of varying pressure-temperature profiles and C/O abundance ratios on the emission spectrum of the planet. We find models with super-solar carbon enrichment best match the observations, consistent with previous model retrieval studies. We also include upper atmosphere haze as another dimension in the interpretation of exoplanet emission spectra, and find that particles <0.5 micron in size are unlikely to be present in WASP-19b.Comment: 10 pages, 8 figures, 2 tables, accepted for publication in Ap

A study of the rapid rotator zeta Aql: differential surface rotation?

We report new, extremely precise photopolarimetry of the rapidly-rotating A0 main-sequence star ζ Aql, covering the wavelength range ∼400–900 nm, which reveals a rotationally-induced signal. We model the polarimetry, together with the flux distribution and line profiles, in the framework of Roche geometry with ω-model gravity darkening, to establish the stellar parameters. An additional constraint is provided by TESS photometry, which shows variability with a period, Pphot, of 11.1 h. Modelling based on solid-body surface rotation gives rotation periods, Prot, that are in only marginal agreement with this value. We compute new ESTER stellar-structure models to predict horizontal surface-velocity fields, which depart from solid-body rotation at only the ∼2 per cent level (consistent with a reasonably strong empirical upper limit on differential rotation derived from the line-profile analysis). These models bring the equatorial rotation period, Prot(e), into agreement with Pphot, without requiring any ‘fine tuning’ (for the Gaia parallax). We confirm that surface abundances are significantly subsolar ([M/H] ≃ −0.5). The star’s basic parameters are established with reasonably good precision: M = 2.53 ± 0.16 M☉, log (L/L☉) = 1.72± 0.02, Rp = 2.21 ± 0.02 R☉, Teff = 9693 ± 50 K, i = 85+−75◦, and ωe/ωc = 0.95 ± 0.02. Comparison with single-star solar-abundance stellar-evolution models incorporating rotational effects shows excellent agreement (but somewhat poorer agreement for models at [M/H] ≃ −0.4)

Phase-locked polarization by photospheric reflection in the semidetached eclipsing binary μ1\mu^1 Sco

We report the detection of phase-locked polarization in the bright ($m_V$=2.98-3.24) semidetached eclipsing binary $\mu^1$ 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 amplitude of the polarization is wavelength dependent and large, $\sim$700 parts-per-million 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 amplitude. 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.Comment: 16 pages, 8 figures, 8 tables. Accepted to MNRA