Searcharxiv⌕ Search

arXiv subjects

M. I. Jones

Publications and source records attributed to M. I. Jones.

31 records · Page 2Linked to original sources
arXiv2015

RAFT I: Discovery of new planetary candidates and updated orbits from archival FEROS spectra

A recent reanalysis of archival data has lead several authors to arrive at strikingly different conclusions for a number of planet-hosting candidate stars. In particular, some radial velocities measured using FEROS spectra have been shown to be inaccurate, throwing some doubt on the validity of a number of planet detections. Motivated by these results, we have begun the Reanalysis of Archival FEROS specTra (RAFT) program and here we discuss the first results from this work. We have reanalyzed FEROS data for the stars HD 11977, HD 47536, HD 70573, HD 110014 and HD 122430, all of which are claimed to have at least one planetary companion. We have reduced the raw data and computed the radial velocity variations of these stars, achieving a long-term precision of $\sim$ 10 m/s on the known stable star tau Ceti, and in good agreement with the residuals to our fits. We confirm the existence of planets around HD 11977, HD 47536 and HD 110014, but with different orbital parameters than those previously published. In addition, we found no evidence of the second planet candidate around HD 47536, nor any companions orbiting HD 122430 and HD 70573. Finally, we report the discovery of a second planet around HD 110014, with a minimum mass of 3.1 Mjup and a orbital period of 130 days. Analysis of activity indicators allow us to confirm the reality of our results and also to measure the impact of magnetic activity on our radial velocity measurements. These results confirm that very metal-poor stars down to [Fe/H]$\sim$ -0.7 dex, can indeed form giant planets given the right conditions.

astro-ph.EP↗
arXiv2015

Giant planets around two intermediate-mass evolved stars and confirmation of the planetary nature of HIP67851 c

Precision radial velocities are required to discover and characterize planets orbiting nearby stars. Optical and near infrared spectra that exhibit many hundreds of absorption lines can allow the m/s precision levels required for such work. However, this means that studies have generally focused on solar-type dwarf stars. After the main-sequence, intermediate-mass stars (former A-F stars) expand and rotate slower than their progenitors, thus thousands of narrow absorption lines appear in the optical region, permitting the search for planetary Doppler signals in the data for these types of stars. We present the discovery of two giant planets around the intermediate-mass evolved star HIP65891 and HIP107773. The best Keplerian fit to the HIP65891 and HIP107773 radial velocities leads to the following orbital parameters: P=1084.5 d; m$_b$sin$i$ = 6.0 M$_{jup}$; $e$=0.13 and P=144.3 d; m$_b$sin$i$ = 2.0 M$_{jup}$; $e$=0.09, respectively. In addition, we confirm the planetary nature of the outer object orbiting the giant star HIP67851. The orbital parameters of HIP67851c are: P=2131.8 d, m$_c$sin$i$ = 6.0 M$_{jup}$ and $e$=0.17. With masses of 2.5 M$_\odot$ and 2.4 M$_\odot$ HIP65891 and HIP107773 are two of the most massive stars known to host planets. Additionally, HIP67851 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 probably they are subsequently destroyed by the stellar envelope during the ascent of the red giant branch phase. As a consequence, planetary systems with close-in objects are not found around horizontal branch stars.

astro-ph.EP↗
arXiv2015

Analysis of combined radial velocities and activity of BD+20 1790: evidence supporting the existence of a planetary companion

This paper presents the simultaneous Bayesian analysis of the radial velocity and activity indices for the K5Ve active star BD+20 1790, that was proposed to host a close-in massive planet by Hernán-Obispo et al. (2010). The Bayesian analysis supports the hypothesis of a planetary companion. We present a new orbital solution after removing the two main contributions to the stellar jitter, one that varies with the photometric period and another that varies with the synodic period of the star+planet system. We use a new method to determine these jitter components, considering them as a second and third signals in the system. A discussion on possible magnetic star-planet-interaction is included, based on the Bayesian analysis of the activity indices. We propose two possible sources for flare events of this star: one related to the geometry of the system and the relative movement of the star+planet, and a second one purely stochastic source that is related to the evolution of stellar active regions. Also, we observe for the first time the magnetic field of the star, from spectropolarimetric data.

astro-ph.EP↗
arXiv2014

A planetary system and a highly eccentric brown dwarf around the giant stars HIP67851 and HIP97233

Context: So far more than 60 substellar companions have been discovered around giant stars. These systems present physical and orbital properties that contrast to those detected orbiting less evolved stars. Aims: We are conducting a radial velocity survey of 166 bright giant stars in the southern hemisphere. The main goals of our project are to detect and characterize planets in close-in orbits around giant stars in order to study the effects of the host star evolution on their orbital and physical properties. Methods: We have obtained precision radial velocities for the giant stars HIP67851 and HIP97233 that have revealed periodic signals, which are most likely induced by the presence of substellar companions. Results: We present the discovery of a planetary system and an eccentric brown dwarf orbiting the giant stars HIP67851 and HIP97233, respectively. The inner planet around HIP67851 has a period of 88.8 days, a projected mass of 1.4 Mjup and an eccentricity of 0.09. After Kepler 91b, HIP67851b is the closest-in known planet orbiting a giant star. Although the orbit of the outer object is not fully constrained, it is likely a super-Jupiter. The brown dwarf around HIP97233 has an orbital period of 1058.8 days, a minimum mass of 20.0 Mjup and an eccentricity of 0.61. This is the most eccentric known brown dwarf around a giant star.

astro-ph.EP↗
arXiv2014

The properties of planets around giant stars

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 $\sim$ 0.5 AU. Aims: We are conducting a radial velocity study of a sample of 166 giant stars aimed at studying the population of close-in planets orbiting giant stars and how their orbital and physical properties are influenced by the post-MS evolution of the host star. Methods: We have collected multi epochs spectra for all of the targets in our sample. We have computed precision radial velocities from FECH/CHIRON and FEROS spectra, using the I$_2$ cell technique and the simultaneous calibration method, respectively. Results: We present the discovery of a massive planet around the giant star HIP105854. The best Keplerian fit to the data leads to an orbital distance of 0.81 $\pm$ 0.03 AU, an eccentricity of 0.02 $\pm$ 0.03 and a projected mass of 8.2 $\pm$ 0.2 \mjup. With the addition of this new planet discovery, we performed a detailed analysis of the orbital properties and mass distribution of the planets orbiting giant stars. We show that there is an overabundance of planets around giant stars with $a \sim$ 0.5-0.9 AU, which might be attributed to tidal decay. Additionally, these planets are significantly more massive than those around MS and subgiant stars, suggesting that they grow via accretion either from the stellar wind or by mass transfer from the host star. Finally, we show that planets around evolved stars have lower orbital eccentricities than those orbiting solar-type stars, which suggests that they are either formed in different conditions or that their orbits are efficiently circularized by interactions with the host star.

astro-ph.EP↗
arXiv2014

No evidence of the planet orbiting the extremely metal-poor extragalactic star HIP13044

CONTEXT: The recent discovery of three giant planets orbiting the extremely metal-poor stars HIP11952 and HIP13044 have challenged theoretical predictions of the core-accretion model. According to this, the metal content of the protoplanetary disk from which giant planets are formed is a key ingredient for the early formation of planetesimals prior to the runaway accretion of the surrounding gas. AIMS: We reanalyzed the original FEROS data that were used to detect the planets to prove or refute their existence, employing our new reduction and analysis methods. METHOD: We applied the cross-correlation technique to FEROS spectra to measure the radial velocity variation of HIP13044 and HIP11952. We reached a typical precision of $\sim$ 35 $ms^{-1}$ for HIP13044 and $\sim$ 25 $ms^{-1}$ for HIP11952, which is significantly superior to the uncertainties presented previously. RESULTS: We found no evidence of the planet orbiting the metal-poor extragalactic star HIP13044. We show that given our radial velocity precision, and considering the large number of radial velocity epochs, the probability for a non-detection of the radial velocity signal recently claimed is lower than 10$^{-4}$. Finally, we also confirm findings that the extremely metal-poor star HIP11952 does not contain a system of two gas giant planets. These results reaffirm the expectations from the core-accretion model of planet formation.

astro-ph.EP↗
arXiv2013

Study of the impact of the post-MS evolution of the host star on the orbits of close-in planets. II. A giant planet in a close-in orbit around the RGB star HIP63242

Context: More than 40 planets have been found around giant stars, revealing a lack of systems orbiting interior to $\sim$ 0.6 AU. This observational fact contrasts with the planetary population around solar-type stars and has been interpreted as the result of the orbital evolution of planets due to the interaction with the host star and/or because of a different formation/migration scenario of planets around more massive stars. Aims: We are conducting a radial velocity study of a sample of 166 giant stars aimed at studying the population of close-in planets orbiting post-main sequence stars. METHODS: We have computed precision radial velocities from multi-epoch spectroscopic data, in order to search for planets around giant stars. Results: In this paper we present the discovery of a massive planet around the intermediate-mass giant star HIP\,63242. The best keplerian fit to the data lead to an orbital distance of 0.57 AU, an eccentricity of 0.23 and a projected mass of 9.2 \mjup. HIP\,63242\,b is the innermost planet detected around any intermediate-mass giant star and also the first planet detected in our survey.

astro-ph.EP↗
arXiv2011

Study of the impact of the post-MS evolution of the host star on the orbits of close-in planets. I. Sample definition and physical properties

Context: To date, more than 30 planets have been discovered around giant stars, but only one of them has been found to be orbiting within 0.6 AU from the host star, in direct contrast to what is observed for FGK dwarfs. This result suggests that evolved stars destroy/engulf close-in planets during the red giant phase. Aims: We are conducting a radial velocity survey of 164 bright G and K giant stars in the southern hemisphere with the aim of studying the effect of the host star evolution on the inner structure of planetary systems. In this paper we present the spectroscopic atmospheric parameters (\Teff, \logg, $ξ$, [Fe/H]) and the physical properties (mass, radius, evolutionary status) of the program stars. In addition, rotational velocities for all of our targets were derived. Methods: We used high resolution and high S/N spectra to measure the equivalent widths of many Fe{\sc\,i} and Fe{\sc\,ii} lines, which were used to derive the atmospheric parameters by imposing local thermodynamic and ionization equilibrium. The effective temperatures and metallicities were used, along with stellar evolutionary tracks to determine the physical properties and evolutionary status of each star. Results: We found that our targets are on average metal rich and they have masses between $\sim$\,1.0\,M$_\odot$ and 3.5\,M$_\odot$. In addition, we found that 122 of our targets are ascending the RGB, while 42 of them are on the HB phase.

astro-ph.EP↗
arXiv2011

Study of Planetary Systems around Giant Stars

More than 450 exoplanets have currently been detected, most of them by the radial velocity (RV) technique. While the majority of exoplanets have been found around main-sequence (MS) FGK stars (M 1.5M*), only a small fraction (- 10%) have been discovered orbiting post- MS stars. However, such stars are known to host exoplanets and the detection fraction appears to be larger than for solar-type dwarfs. To date - 30 planets have been found orbiting giant stars which have revealed interesting properties that contrast with the results found for solar-type stars. We are carrying out a RV search for planets around giant stars in the southern hemisphere in order to study different formation scenarios for planets around intermediate-mass stars and the effect of the post-MS evolution of the host stars on the orbits of close-in planets (a 0.6 AU).

astro-ph.EP↗
arXiv2009

The Calan-Hertfordshire Extrasolar Planet Search

The detailed study of the exoplanetary systems HD189733 and HD209458 has given rise to a wealth of exciting information on the physics of exoplanetary atmospheres. To further our understanding of the make-up and processes within these atmospheres we require a larger sample of bright transiting planets. We have began a project to detect more bright transiting planets in the southern hemisphere by utilising precision radial-velocity measurements. We have observed a constrained sample of bright, inactive and metal-rich stars using the HARPS instrument and here we present the current status of this project, along with our first discoveries which include a brown dwarf/extreme-Jovian exoplanet found in the brown dwarf desert region around the star HD191760 and improved orbits for three other exoplanetary systems HD48265, HD143361 and HD154672. Finally, we briefly discuss the future of this project and the current prospects we have for discovering more bright transiting planets.

astro-ph.EP↗
arXiv2008

Distance determination to 12 Type II Supernovae using the Expanding Photosphere Method

We used early time photometry and spectroscopy of 12 Type II plateau Supernovae (SNe IIP) to derive their distances using the Expanding Photosphere Method (EPM). We performed this study using two sets of Type II supernovae (SNe II) atmosphere models (E96, D05), three filter subsets (BV, BVI, VI) and two methods for the host galaxy extinctions, which led to 12 Hubble diagrams. Using the VI filter subset and the D05 models we obtained a dispersion in the Hubble diagram of sigma = 0.32 mag and a Hubble constant of H0 = 52.4 +/- 4.3 km s-1 Mpc-1. We also applied the EPM analysis to the well-observed SN IIP SN 1999em. With the VI filter subset and the D05 models we derived a distance of 13.9 +/- 1.4 Mpc, agreement with the Cepheid distance of 11.7 +/- 1.0 Mpc to the SN 1999em host galaxy (NGC 1637).

astro-ph↗
arXiv2008

A Metal-biased Planet Search

We have begun a metal-rich planet search project using the HARPS instrument in La Silla, Chile to target planets with a high potential to transit their host star and add to the number of bright benchmark transiting planets. The sample currently consists of 100, bright (7.5 </= V </= 9.5) solar-type stars (0.5 </= B-V </= 0.9) in the southern hemisphere which are both inactive (logR'HK </= -4.5) and metal-rich ([Fe/H] >/= 0.1 dex). We determined the chromospheric activity and metallicity status of our sample using high resolution FEROS spectra. We also introduce the first result from our HARPS planet search and show that the radial-velocity amplitude of this star is consistent with an orbiting planetary-mass companion (i.e. Msini < 0.5MJ) with a period of ~5 days. We are currently engaged in follow-up to confirm this signal as a bonafide orbiting planet.

astro-ph↗