Browsing by Author "Jones, M. I."

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    Four Jovian planets around low-luminosity giant stars observed by the EXPRESS and PPPS
    (2021) Jones, M. I.; Wittenmyer, R.; Aguilera-Gomez, C.; Soto, M. G.; Torres, P.; Trifonov, T.; Jenkins, J. S.; Zapata, A.; Sarkis, P.; Zakhozhay, O.; Brahm, R.; Ramirez, R.; Santana, F.; Vines, J. I.; Diaz, M. R.; Vuckovic, M.; Pantoja, B.
    We report the discovery of planetary companions orbiting four low-luminosity giant stars with M-star between 1.04 and 1.39 M-circle dot. All four host stars have been independently observed by the EXoPlanets aRound Evolved StarS (EXPRESS) program and the Pan-Pacific Planet Search (PPPS). The companion signals were revealed by multi-epoch precision radial velocities obtained in nearly a decade. The planetary companions exhibit orbital periods between similar to 1.2 and 7.1 yr, minimum masses of m(p)sin i similar to 1.8-3.7 M-J, and eccentricities between 0.08 and 0.42. With these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets in the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets (m(p) greater than or similar to 1- 2 M-J) orbiting within 5 AU from their parent star of f = 33.3(-7.1)(+9.0)%. This fraction is slightly higher than but consistent at the 1 sigma level with previous results obtained by different radial velocity surveys. Finally, this value is substantially higher than the fraction predicted by planet formation models of gas giants around stars more massive than the Sun.
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    HD 76920 b pinned down: A detailed analysis of the most eccentric planetary system around an evolved star
    (2021) Bergmann, C.; Jones, M. I.; Zhao, J.; Mustill, A. J.; Brahm, R.; Torres, P.; Wittenmyer, R. A.; Gunn, F.; Pollard, K. R.; Zapata, A.; Vanzi, L.; Wang, Songhu
    We present 63 new multi-site radial velocity (RV) measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focused our observational efforts on the time around the predicted periastron passage and achieved near-continuous phase coverage of the corresponding RV peak. By combining our RV measurements from four different instruments with previously published ones, we confirm the highly eccentric nature of the system and find an even higher eccentricity of , an orbital period of 415.891(-0.039)(+0.043) d, and a minimum mass of 3.13(-0.43)(+0.41) M-J for the planet. The uncertainties in the orbital elements are greatly reduced, especially for the period and eccentricity. We also performed a detailed spectroscopic analysis to derive atmospheric stellar parameters, and thus the fundamental stellar parameters (M-*, R-*, L-*) taking into account the parallax from Gaia DR2, and independently determined the stellar mass and radius using asteroseismology. Intriguingly, at periastron, the planet comes to within 2.4 stellar radii of its host star's surface. However, we find that the planet is not currently experiencing any significant orbital decay and will not be engulfed by the stellar envelope for at least another 50-80 Myr. Finally, while we calculate a relatively high transit probability of 16%, we did not detect a transit in the TESS photometry.
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    THE PAN-PACIFIC PLANET SEARCH. VI. GIANT PLANETS ORBITING HD 86950 AND HD 222076
    (IOP PUBLISHING LTD, 2017) Wittenmyer, Robert A.; Jones, M. I.; Zhao, Jinglin; Marshall, J. P.; Butler, R. P.; Tinney, C. G.; Wang, Liang; Johnson, John Asher
    We report the detection of two new planets orbiting the K giants HD 86950 and HD 222076, based on precise radial velocities obtained with three instruments: AAT/UCLES, FEROS, and CHIRON. HD 86950b has a period of 1270 +/- 57 days at a=2.72 +/- 0.08 AU, and m sin i=3.6 +/- 0.7 M-Jup. HD 222076b has P=871 +/- 19 days at a=1.83 +/- 0.03 AU, and m sin i=1.56 +/- 0.11 M-Jup. These two giant planets are typical of the population of planets known to orbit evolved stars. In addition, we find a high-amplitude periodic velocity signal (K similar to 50 m/s(-1)) in HD 29399, and show that it is due to stellar variability rather than Keplerian reflex motion. We also investigate the relation between planet occurrence and host-star metallicity for the 164-star Pan-Pacific Planet Search sample of evolved stars. In spite of the small sample of PPPS detections, we confirm the trend of increasing planet occurrence as a function of metallicity found by other studies of planets orbiting evolved stars.
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    The properties of planets around giant stars
    (EDP SCIENCES S A, 2014) Jones, M. I.; Jenkins, J. S.; Bluhm, P.; Rojo, P.; Melo, C. H. F.
    Context. More than 50 exoplanets have been found around giant stars, revealing different properties when compared to planets orbiting solar-type stars. In particular, they are super-Jupiters and are not found orbiting interior to similar to 0.5 AU.