arXiv subjects

Duncan J. Wright

Publications and source records attributed to Duncan J. Wright.

42 records · Page 3Linked to original sources

arXiv2018

Revised Exoplanet Radii and Habitability Using Gaia Data Release 2

Accurate stellar properties are crucial for determining exoplanet characteristics. Gaia DR2 presents revised distances, luminosities, and radii for 1.6 billion stars. Here, we report the calculation of revised radii and densities for 320 exoplanets using this data and present updated calculations of the incident flux received by 690 known exoplanets. This allows the likelihood that those planets orbit in the habitable zone of their host stars to be reassessed. As a result of this analysis, three planets can be added to the catalogue of potentially habitable worlds: HIP~67537~b, HD~148156~b, and HD~106720~b. In addition, the changed parameterisation of BD~+49~898 means that its planet, BD~+49~898~b, now receives an incident flux that places it outside the optimistic habitable zone region, as defined by \citep{Kopparapu2013,Kopparapu2014}. We find that use of the new \textit{Gaia} data results in a mean increase in calculated exoplanet radius of 3.76\%. Previously, CoRoT-3 b had been reported as having the highest density of all known exoplanets. Here, we use updated information to revise the calculated density of CoRoT-3~b from 26.4$g\:cm^{-3}$ to 17.3$\pm2.9g\:cm^{-3}$. We also report the densest exoplanet in our dataset, KELT-1~b, with a density of 23.7$\pm4.0g\:cm^{-3}$. Overall, our results highlight the importance of ensuring the the parameterisation of known exoplanets be revisited whenever significant improvements are made to the precision of the stellar parameters upon which they are based.

astro-ph.EP↗

arXiv2017

Spin-Orbit Misalignments of Three Jovian Planets via Doppler Tomography

We present measurements of the spin-orbit misalignments of the hot Jupiters HAT-P-41 b and WASP-79 b, and the aligned warm Jupiter Kepler-448 b. We obtained these measurements with Doppler tomography, where we spectroscopically resolve the line profile perturbation during the transit due to the Rossiter-McLaughlin effect. We analyze time series spectra obtained during portions of five transits of HAT-P-41 b, and find a value of the spin-orbit misalignment of $λ= -22.1_{-6.0}^{+0.8 \circ}$. We reanalyze the radial velocity Rossiter-McLaughlin data on WASP-79 b obtained by Addison et al. (2013) using Doppler tomographic methodology. We measure $λ=-99.1_{-3.9}^{+4.1\circ}$, consistent with but more precise than the value found by Addison et al. (2013). For Kepler-448 b we perform a joint fit to the Kepler light curve, Doppler tomographic data, and a radial velocity dataset from Lillo-Box et al. (2015). We find an approximately aligned orbit ($λ=-7.1^{+4.2 \circ}_{-2.8}$), in modest disagreement with the value found by Bourrier et al. (2015). Through analysis of the Kepler light curve we measure a stellar rotation period of $P_{\mathrm{rot}}=1.27 \pm 0.11$ days, and use this to argue that the full three-dimensional spin-orbit misalignment is small, $ψ\sim0^{\circ}$.

astro-ph.EP↗

arXiv2014

Searching for Earth-mass planets around $α$ Centauri: precise radial velocities from contaminated spectra

This work is part of an ongoing project which aims to detect terrestrial planets in our neighbouring star system $α$ Centauri using the Doppler method. Owing to the small angular separation between the two components of the $α$ Cen AB binary system, the observations will to some extent be contaminated with light coming from the other star. We are accurately determining the amount of contamination for every observation by measuring the relative strengths of the H-$α$ and NaD lines. Furthermore, we have developed a modified version of a well established Doppler code that is modelling the observations using two stellar templates simultaneously. With this method we can significantly reduce the scatter of the radial velocity measurements due to spectral cross-contamination and hence increase our chances of detecting the tiny signature caused by potential Earth-mass planets. After correcting for the contamination we achieve radial velocity precision of $\sim 2.5\,\mathrm{m\,s^{-1}}$ for a given night of observations. We have also applied this new Doppler code to four southern double-lined spectroscopic binary systems (HR159, HR913, HR7578, HD181958) and have successfully recovered radial velocities for both components simultaneously.

astro-ph.EP↗

arXiv2014

Spectroscopic Pulsational Frequency and Mode Determination of the $γ$ Doradus Star HD 189631

We present improvement and confirmation of identified frequencies and pulsation modes for the $γ$ Doradus star HD 189631. This work improves upon previous studies by incorporating a significant number of additional spectra and precise determination of frequencies. Four frequencies were identified for this star: $1.6774 \pm 0.0002$ d$^{-1}$, $1.4174 \pm 0.0002$ d$^{-1}$, $0.0714 \pm 0.0002$ d$^{-1}$, and $1.8228 \pm 0.0002$ d$^{-1}$ which were identified with the modes ($l$,$m$) = ($1,+1$), ($1,+1$), ($2,-2$), and ($1,+1$) respectively. These findings are in agreement with the most recent literature. The prevalence of ($l$,$m$) = ($1,+1$) modes in $γ$ Doradus stars is starting to become apparent and we discuss this result.

astro-ph.SR↗

arXiv2014

Planets in Spin-Orbit Misalignment and the Search for Stellar Companions

The discovery of giant planets orbiting close to their host stars was one of the most unexpected results of early exoplanetary science. Astronomers have since found that a significant fraction of these 'Hot Jupiters' move on orbits substantially misaligned with the rotation axis of their host star. We recently reported the measurement of the spin-orbit misalignment for WASP-79b by using data from the 3.9 m Anglo-Australian Telescope. Contemporary models of planetary formation produce planets on nearly coplanar orbits with respect to their host star's equator. We discuss the mechanisms which could drive planets into spin-orbit misalignment. The most commonly proposed being the Kozai mechanism, which requires the presence of a distant, massive companion to the star-planet system. We therefore describe a volume-limited direct-imaging survey of Hot Jupiter systems with measured spin-orbit angles, to search for the presence of stellar companions and test the Kozai hypothesis.

astro-ph.EP↗

arXiv2012

Signals embedded in the radial velocity noise. Periodic variations in the tau Ceti velocities

The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. We study an extensive set of radial velocities for the star HD 10700 ($τ$ Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. We perform Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reach our goal by adding artificial signals to the "flat" radial velocity data of HD 10700 and by seeing which one of our statistical noise models receives the greatest posterior probabilities while still being able to extract the artificial signals correctly from the data. We utilise various noise components to assess properties of the noise in the data and analyse the HARPS, AAPS, and HIRES data for HD 10700 to quantify these properties and search for previously unknown low-amplitude Keplerian signals. ...

astro-ph.EP↗