arXiv subjects

T. M. Louden

Publications and source records attributed to T. M. Louden.

3 recordsLinked to original sources

arXiv2017

K2-110 b - a massive mini-Neptune exoplanet

We report the discovery of the exoplanet K2-110 b (previously EPIC212521166b) from K2 photometry orbiting in a 13.8637d period around an old, metal-poor K3 dwarf star. With a V-band magnitude of 11.9, K2-110 is particularly amenable to RV follow-up. A joint analysis of K2 photometry and high-precision RVs from 28 HARPS and HARPS-N spectra reveal it to have a radius of 2.6$\pm 0.1 R_{\oplus}$ and a mass of 16.7$\pm 3.2$~M$_{\oplus}$, hence a density of $5.2\pm1.2$ g.cm$^{-3}$, making it one of the most massive planets yet to be found with a sub-Neptune radius. When accounting for compression, the resulting Earth-like density is best fitted by a 0.2 M$_{\oplus}$ hydrogen atmosphere over an 16.5 M$_{\oplus}$ Earth-like interior, although the planet could also have significant water content. At 0.1~AU, even taking into account the old stellar age of $8 \pm 3$ Gyr, the planet is unlikely to have been significantly affected by EUV evaporation. However the planet likely disc-migrated to its current position making the lack of a thick H$_2$ atmosphere puzzling. This analysis has made K2-110 b one of the best-characterised mini-Neptunes with density constrained to less than 30%.

astro-ph.EP↗

arXiv2015

Single Transit Candidates from K2: Detection and Period Estimation

Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool ("Namaste: An Mcmc Analysis of Single Transit Exoplanets") to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to 7 candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of $540 ^{+410}_{-230}$ days and a radius of $0.51 \pm 0.05 R_{Jup}$. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia.

astro-ph.EP↗

arXiv2014

WASP-104b and WASP-106b: two transiting hot Jupiters in 1.75-day and 9.3-day orbits

We report the discovery from the WASP survey of two exoplanetary systems, each consisting of a Jupiter-sized planet transiting an 11th magnitude (V) main-sequence star. WASP-104b orbits its star in 1.75 d, whereas WASP-106b has the fourth-longest orbital period of any planet discovered by means of transits observed from the ground, orbiting every 9.29 d. Each planet is more massive than Jupiter (WASP-104b has a mass of $1.27 \pm 0.05 \mathrm{M_{Jup}}$, while WASP-106b has a mass of $1.93 \pm 0.08 \mathrm{M_{Jup}}$). Both planets are just slightly larger than Jupiter, with radii of $1.14 \pm 0.04$ and $1.09 \pm 0.04 \mathrm{R_{Jup}}$ for WASP-104 and WASP-106 respectively. No significant orbital eccentricity is detected in either system, and while this is not surprising in the case of the short-period WASP-104b, it is interesting in the case of WASP-106b, because many otherwise similar planets are known to have eccentric orbits.

astro-ph.EP↗