Examinando por Autor "Jenkins, J.S."
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Ítem Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars(EDP Sciences, 2016-06) Jones, M.I.; Jenkins, J.S.; Brahm, R.; Wittenmyer, R.A.; Olivares, E.F.; Melo, C.H.F.; Rojo, P.; Jordán, A.; Drass, H.; Butler, R.P.; Wang, L.Context. Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets. In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and that their fraction increases with the stellar mass. Aims. During the past six years we have conducted a radial velocity follow-up program of 166 giant stars to detect substellar com panions and to characterize their orbital properties. Using this information, we aim to study the role of the stellar evolution in the orbital parameters of the companions and to unveil possible correlations between the stellar properties and the occurrence rate of giant planets. Methods. We took multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we computed precision radial velocities and derived atmospheric and physical parameters. Additionally, velocities computed from UCLES spectra are presented here. By studying the periodic radial velocity signals, we detected the presence of several substellar companions. Results. We present four new planetary systems around the giant stars HIP 8541, HIP 74890, HIP 84056, and HIP 95124. Additionally, we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7 +15.5 −5.9 % around stars with [Fe/H] ∼ 0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M? ∼ 1.0 and 2.1 M , with a maximum of f = 13.0 +10.1 −4.2 % at M? = 2.1 M . Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. In addition, we conclude that they are more efficiently formed around more massive stars, in the stellar mass range of ∼1.0–2.1 M . These observational results confirm previous findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.Ítem Giant planets around two intermediate-mass evolved stars and confirmation of the planetary nature of HIP 67851c(EDP Sciences, 2015-08) Jones, M.I.; Jenkins, J.S.; Rojo, P.; Olivares, F.; Melo, C.H.F.Context. Precision radial velocities are required to discover and characterize exoplanets. Optical spectra that exhibit many hundreds of absorption lines can allow the m s-1 precision levels required for this work. After the main-sequence, intermediate-mass stars expand and rotate more slowly than their progenitors, thus, thousands of spectral lines appear in the optical region, permitting the search for Doppler signals in these types of stars. Aims. In 2009, we began the EXPRESS program, aimed at detecting substellar objects around evolved stars, and studying the effects of the mass and evolution of the host star on their orbital and physical properties. Methods. We obtained precision radial velocity measurements for the giant stars HIP 65891 and HIP 107773, from CHIRON and FEROS spectra. Also, we obtained new radial velocity epochs for the star HIP 67851, which is known to host a planetary system. Results. We present the discovery of two giant planets around the intermediate-mass evolved star HIP 65891 and HIP 107773. The best Keplerian fit to the HIP 65891 and HIP 107773 radial velocities leads to the following orbital parameters: P = 1084.5 d; mb sini = 6.0 MJ; e = 0.13 and P = 144.3 d; mb sini = 2.0 MJ; e = 0.09, respectively. In addition, we confirm the planetary nature of the outer object orbiting the giant star HIP 67851. The orbital parameters of HIP 67851 c are: P = 2131.8 d, mc sini = 6.0MJ, and e = 0.17. Conclusions. With masses of 2.5 M⊙ and 2.4 M⊙, HIP 65891 and HIP 107773 are two of the most massive planet-hosting stars. Additionally, HIP 67851 is one of five giant stars that are known to host a planetary system having a close-in planet (a< 0.7 AU). Based on the evolutionary states of those five stars, we conclude that close-in planets do exist in multiple systems around subgiants and slightly evolved giants stars, but most likely they are subsequently destroyed by the stellar envelope during the ascent of the red giant branch phase. © ESO, 2015.Ítem GJ 832c: a super-earth in the habitable zone(Institute of Physics Publishing, 2014-08) Wittenmyer, Robert A.; Tuomi, Mikko; Butler, R.P.; Jones, H.R.A.; Anglada-Escudé, Guillem; Horner, Jonathan; Tinney, C.G; Marshall, J.P.; Carter, B.D.; Bailey, J.; Salter, G.S.; O'Toole, S.J.; Wright, D.; Crane, J.D.; Schectman, S.A.; Arriagada, P.; Thompson, I.; Minniti, D.; Jenkins, J.S.; Diaz, M.We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly circular 9.4 yr orbit. The combination of precise radial velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68 ± 0.03 days and minimum mass (m sin i) of 5.4 ± 1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e = 0.18±0.13) toward the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a “super-Venus,” featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own solar system.Ítem MagAO IMAGING OF LONG-PERIOD OBJECTS (MILO). II. A PUZZLING WHITE DWARF AROUND THE SUN-LIKE STAR HD 11112(IOP PUBLISHING, 2016-11) Rodigas, T.J.; Bergeron, P.; Simon, A.; Arriagada, P.; Faherty, J.K.; Anglada-Escudé, G.; Mamajek, E.E.; Weinberger, A.; Butler, R.P.; Males, J.R.; Morzinski, K.; Close, L.M.; Hinz, P.M.; Bailey, J.; Carter, B.; Jenkins, J.S.; Jones, H.; O'Toole, S.; Tinney, C.G.; Wittenmyer, R.; Debes, J.HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2 2 (100 au) at multiple wavelengths spanning 0.6-4 mu m. and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9-1.1M(circle dot), which corresponds to very high eccentricity, near edge-on orbits from a. Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is > 2 sigma, which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.Ítem New planetary systems from the Calan-Hertfordshire Extrasolar planet search(Oxford University Press, 2016-11) Jenkins, J.S.; Jones, H.R.A.; Tuomi, M.; Díaz, M.; Cordero, J.P.; Aguayo, A.; Pantoja, B.; Arriagada, P.; Mahu, R.; Brahm, R.; Rojo, P.; Soto, M.G.; Ivanyuk, O.; Becerra Yoma, N.; Day-Jones, A.C.; Ruiz, M.T.; Pavlenko, Y.V.; Barnes, J.R.; Murgas, F.; Pinfield, D.J.; Jones, M.I.; López-Morales, M.; Shectman, S.; Butler, R.P.; Minniti, D.We report the discovery of eight new giant planets, and updated orbits for four known planets, orbiting dwarf and subgiant stars using the CORALIE, HARPS, and MIKE instruments as part of the Calan-Hertfordshire Extrasolar Planet Search. The planets have masses in the range 1.1-5.4 MJ's, orbital periods from 40 to 2900 d, and eccentricities from 0.0 to 0.6. They include a double-planet system orbiting the most massive star in our sample (HD147873), two eccentric giant planets (HD128356b and HD154672b), and a rare 14 Herculis analogue (HD224538b). We highlight some population correlations from the sample of radial velocity detected planets orbiting nearby stars, including the mass function exponential distribution, confirmation of the growing body of evidence that low-mass planets tend to be found orbiting more metal-poor stars than giant planets, and a possible period-metallicity correlation for planets with masses > 0.1 MJ, based on a metallicity difference of 0.16 dex between the population of planets with orbital periods less than 100 d and those with orbital periods greater than 100 d.Ítem VLT/SPHERE survey for exoplanets around young early-type stars, including systems with multi-belt architectures(EDP Sciences, 2020-07) Lombart, M.; Chauvin, G.; Rojo, P.; Lagadec, E.; Delorme, P.; Beust, H.; Bonnefoy, M.; Galicher, R.; Gratton, R.; Mesa, D.; Bonavita, M.; Allard, F.; Bayo, A.; Boccaletti, A.; Desidera, S.; Girard, J.; Jenkins, J.S.; Klahr, H.; Laibe, G.; Lagrange, A.-M.; Lazzoni, C.; Marleau, G.-D.; Minniti, D.; Mordasini, C.Context. Dusty debris disks around pre- and main-sequence stars are potential signposts for the existence of planetesimals and exoplanets. Giant planet formation is therefore expected to play a key role in the evolution of the disk. This is indirectly confirmed by extant submillimeter near-infrared images of young protoplanetary and cool dusty debris disks around main-sequence stars that usually show substantial spatial structures. With two decades of direct imaging of exoplanets already studied, it is striking to note that a majority of recent discoveries of imaged giant planets have been obtained around young early-type stars hosting a circumstellar disk. Aims. Our aim was to create a direct imaging program designed to maximize our chances of giant planet discovery and target 22 young early-type stars. About half of them show indications of multi-belt architectures. Methods. Using the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE to acquire high-constrast coronagraphic differential near-infrared images, we conducted a systematic search in the close environment of these young, dusty, and early-type stars. We used a combination of angular and spectral differential imaging to reach the best detection performances down to the planetary mass regime. Results. We confirm that companions detected around HIP 34276, HIP 101800, and HIP 117452 are stationary background sources and binary companions. The companion candidates around HIP 8832, HIP 16095, and HIP 95619 are determined as background contaminations. Regarding the stars for which we infer the presence of debris belts, a theoretical minimum mass for planets required to clear the debris gaps can be calculated. The dynamical mass limit is at least 0.1 MJ and can exceed 1 MJ. Direct imaging data is typically sensitive to planets down to ~3.6 MJ at 1′′, and 1.7 MJ in the best case. These two limits tightly constrain the possible planetary systems present around each target. These systems will be probably detectable with the next generation of planet imagers. © M. Lombart et al. 2020.