arXiv subjects

Thierry Forveille

Publications and source records attributed to Thierry Forveille.

At least 73 records · Page 4Linked to original sources

arXiv2015

An Unbiased 1.3 mm Emission Line Survey of the Protoplanetary Disk Orbiting LkCa 15

The outer (>30 AU) regions of the dusty circumstellar disk orbiting the ~2-5 Myr-old, actively accreting solar analog LkCa 15 are known to be chemically rich, and the inner disk may host a young protoplanet within its central cavity. To obtain a complete census of the brightest molecular line emission emanating from the LkCa 15 disk over the 210-270 GHz (1.4 - 1.1 mm) range, we have conducted an unbiased radio spectroscopic survey with the Institute de Radioastronomie Millimetrique (IRAM) 30 meter telescope. The survey demonstrates that, in this spectral region, the most readily detectable lines are those of CO and its isotopologues 13CO and C18O, as well as HCO+, HCN, CN, C2H, CS, and H2CO. All of these species had been previously detected in the LkCa 15 disk; however, the present survey includes the first complete coverage of the CN (2-1) and C2H (3-2) hyperfine complexes. Modeling of these emission complexes indicates that the CN and C2H either reside in the coldest regions of the disk or are subthermally excited, and that their abundances are enhanced relative to molecular clouds and young stellar object environments. These results highlight the value of unbiased single-dish line surveys in guiding future high resolution interferometric imaging of disks.

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arXiv2014

Near-infrared transmission spectrum of the warm-uranus GJ 3470b with the Wide Field Camera-3 on the Hubble Space Telescope

The atmospheric composition of low-mass exoplanets is the object of intense observational and theoretical investigations. GJ3470b is a warm uranus recently detected in transit across a bright late-type star. The transit of this planet has already been observed in several band passes from the ground and space, allowing observers to draw an intriguing yet incomplete transmission spectrum of the planet atmospheric limb. In particular, published data in the visible suggest the existence of a Rayleigh scattering slope, making GJ3470b a unique case among the known neptunes, while data obtained beyond 2 um are consistent with a flat infrared spectrum. The unexplored near-infrared spectral region between 1 and 2 um, is thus key to undertanding the atmospheric nature of GJ3470b. Here, we report on the first space-borne spectrum of GJ3470, obtained during one transit of the planet with WFC3 on board HST, operated in stare mode. The spectrum covers the 1.1--1.7-um region with a resolution of about 300. We retrieve the transmission spectrum of GJ3470b with a chromatic planet-to-star radius ratio precision of 0.15% (about one scale height) per 40-nm bins. At this precision, the spectrum appears featureless, in good agreement with ground-based and Spitzer infrared data at longer wavelengths, pointing to a flat transmission spectrum from 1 to 5 um. We present new simulations of transmission spectra for GJ3470b, which allow us to show that the HST/WFC3 observations rule out cloudless hydrogen-rich atmospheres (>10 sigma) as well as hydrogen-rich atmospheres with tholin haze (>5 sigma). Adding our near-infrared measurements to the full set of previously published data from 0.3 to 5 um, we find that a cloudy, hydrogen-rich atmosphere can explain the full transmission spectrum if, at the terminator, the clouds are located at low pressures (<1 mbar) or the water mixing ratio is extremely low (<1 ppm).

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arXiv2014

Unbiased mm-wave Line Surveys of TW Hya and V4046 Sgr: The Enhanced C2H and CN Abundances of Evolved Protoplanetary Disks

We have conducted the first comprehensive mm-wave molecular emission line surveys of the evolved circumstellar disks orbiting the nearby T Tauri stars TW Hya and V4046 Sgr AB. Both disks are known to retain significant residual gaseous components, despite the advanced ages of their host stars. Our unbiased broad-band radio spectral surveys of the TW Hya and V4046 Sgr disks were performed with the Atacama Pathfinder Experiment (APEX) 12 meter telescope and are intended to yield a complete census of bright molecular emission lines in the range 275-357 GHz (1.1-0.85 mm). We find that lines of 12CO, 13CO, HCN, CN, and C2H, all of which lie in the higher-frequency range, constitute the strongest molecular emission from both disks in the spectral region surveyed. The molecule C2H is detected here for the first time in both disks, as is CS in the TW Hya disk. The survey results also include the first measurements of the full suite of hyperfine transitions of CN N=3-2 and C2H N=4-3 in both disks. Modeling of these CN and C2H hyperfine complexes in the spectrum of TW Hya indicates that the emission from both species is optically thick and may originate from very cold disk regions. It furthermore appears that the fractional abundances of CN and C2H are significantly enhanced in these evolved protoplanetary disks relative to the fractional abundances of the same molecules in the environments of deeply embedded protostars.

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arXiv2013

A search for rocky planets transiting brown dwarfs

Exoplanetary science has reached a historic moment. The James Webb Space Telescope will be capable of probing the atmospheres of rocky planets, and perhaps even search for biologically produced gases. However this is contingent on identifying suitable targets before the end of the mission. A race therefore, is on, to find transiting planets with the most favorable properties, in time for the launch. Here, we describe a realistic opportunity to discover extremely favorable targets - rocky planets transiting nearby brown dwarfs - using the Spitzer Space Telescope as a survey instrument. Harnessing the continuous time coverage and the exquisite precision of Spitzer in a 5,400 hour campaign monitoring nearby brown dwarfs, we will detect a handful of planetary systems with planets as small as Mars. The survey we envision is a logical extension of the immense progress that has been realized in the field of exoplanets and a natural outcome of the exploration of the solar neighborhood to map where the nearest habitable rocky planets are located (as advocated by the 2010 Decadal Survey). Our program represents an essential step towards the atmospheric characterization of terrestrial planets and carries the compelling promise of studying the concept of habitability beyond Earth-like conditions. In addition, our photometric monitoring will provide invaluable observations of a large sample of nearby brown dwarfs situated close to the M/L transition. This is why, we also advocate an immediate public release of the survey data, to guarantee rapid progress on the planet search and provide a treasure trove of data for brown dwarf science.

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arXiv2013

Spitzer Observations of GJ3470b: a Very Low-density Neptune-size Planet Orbiting a Metal-rich M dwarf

We present Spitzer/IRAC 4.5-micron transit photometry of GJ3470b, a Neptune-size planet orbiting a M1.5 dwarf star with a 3.3-day period recently discovered in the course of the HARPS M-dwarf survey. We refine the stellar parameters by employing purely empirical mass-luminosity and surface brightness relations constrained by our updated value for the mean stellar density, and additional information from new near-infrared spectroscopic observations. We derive a stellar mass of M_star = 0.539+0.047-0.043 M_sun and a radius of R_star = 0.568+0.037-0.031 R_sun. We determine the host star of GJ3470b to be metal-rich, with a metallicity of [Fe/H] = +0.20 +/- 0.10 and an effective temperature of Teff = 3600 +/- 100 K. The revised stellar parameters yield a planetary radius R_pl = 4.83+0.22-0.21 R_Earth that is 13 percent larger than the value previously reported in the literature. We find a planetary mass M_pl = 13.9+1.5-1.4 M_Earth that translates to a very low planetary density, rho_pl = 0.72+0.13-0.12 gcm-3, which is 33% smaller than the original value. With a mean density half of that of GJ436b, GJ3470b is an example of a very low-density low-mass planet, similar to Kepler-11d, Kepler-11e, and Kepler-18c but orbiting a much brighter nearby star that is more conducive to follow-up studies.

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arXiv2012

Hint of a transiting extended atmosphere on 55 Cancri b

The naked-eye star 55 Cancri hosts a planetary system with five known planets, including a hot super-Earth (55 Cnc e) extremely close to its star and a farther out giant planet (55 Cnc b), found in milder irradiation conditions with respect to other known hot Jupiters. This system raises important questions on the evolution of atmospheres for close-in exoplanets, and the dependence with planetary mass and irradiation. These questions can be addressed by Lyman-alpha transit observations of the extended hydrogen planetary atmospheres, complemented by contemporaneous measurements of the stellar X-ray flux. In fact, planet `e' has been detected in transit, suggesting the system is seen nearly edge-on. Yet, planet `b' has not been observed in transit so far. Here, we report on Hubble Space Telescope STIS Lyman-alpha and Chandra ACIS-S X-ray observations of 55 Cnc. These simultaneous observations cover two transits of 55 Cnc e and two inferior conjunctions of 55 Cnc b. They reveal the star as a bright Lyman-alpha target and a variable X-ray source. While no significant signal is detected during the transits of 55 Cnc e, we detect a surprising Lyman-alpha absorption of 7.5 +/- 1.8% (4.2 sigma) at inferior conjunctions of 55 Cnc b. The absorption is only detected over the range of Doppler velocities where the stellar radiation repels hydrogen atoms towards the observer. We calculate a false-alarm probability of 4.4%, which takes into account the a-priori unknown transit parameters. This result suggests the possibility that 55 Cnc b has an extended upper H I atmosphere, which undergoes partial transits when the planet grazes the stellar disc. If confirmed, it would show that planets cooler than hot Jupiters can also have extended atmospheres.

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arXiv2012

Dynamical evolution of the Gliese 436 planetary system - Kozai migration as a potential source for Gliese 436b's eccentricity

The close-in planet orbiting GJ 436 presents a puzzling orbital eccentricity considering its very short orbital period. Given the age of the system, this planet should have been tidally circularized a long time ago. Many attempts to explain this were proposed in recent years, either involving abnormally weak tides, or the perturbing action of a distant companion. We address here the latter issue based on Kozai migration. We propose that GJ 436b was formerly located further away from the star and that it underwent a migration induced by a massive, inclined perturber via Kozai mechanism. In this context, the perturbations by the companion trigger high amplitude variations to GJ 436b that cause tides to act at periastron. Then the orbit tidally shrinks to reach its present day location. We numerically integrate the 3-body system including tides and General Relativity correction. We first show that starting from the present-day location of GJ 436b inevitably leads to damping the Kozai oscillations and to rapidly circularizing the planet. Conversely, starting from 5-10 times further away allows the onset of Kozai cycles. The tides act in peak eccentricity phases and reduce the semi-major axis of the planet. The net result is an evolution characterized by two phases: a first one with Kozai cycles and a slowly shrinking semi-major axis, and a second one once the planet gets out of the Kozai resonance characterized by a more rapid decrease. The timescale of this process appears in most cases much longer than the standard circularization time of the planet by a factor larger than 50. This model can provide a solution to the eccentricity paradox of GJ 436b. Depending on the various orbital configurations, it can take several Gyrs to GJ 436b to achieve a full orbital decrease and circularization. According to this scenario, we could be witnessing today the second phase of the scenario where the semi-major axis is already reduced while the eccentricity is still significant. We then explore the parameter space and derive in which conditions this model can be realistic given the age of the system. This yields constraints on the characteristics of the putative companion.

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arXiv2011

High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)

(abridged) A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT - the Nearby Earth Astrometric Telescope. NEAT is designed to carry out space-borne extremely-high-precision astrometric measurements sufficient to detect dynamical effects due to orbiting planets of mass even lower than Earth's around the nearest stars. Such a survey mission would provide the actual planetary masses and the full orbital geometry for all the components of the detected planetary systems down to the Earth-mass limit. The NEAT performance limits can be achieved by carrying out differential astrometry between the targets and a set of suitable reference stars in the field. The NEAT instrument design consists of an off-axis parabola single-mirror telescope, a detector with a large field of view made of small movable CCDs located around a fixed central CCD, and an interferometric calibration system originating from metrology fibers located at the primary mirror. The proposed mission architecture relies on the use of two satellites operating at L2 for 5 years, flying in formation and offering a capability of more than 20,000 reconfigurations (alternative option uses deployable boom). The NEAT primary science program will encompass an astrometric survey of our 200 closest F-, G- and K-type stellar neighbors, with an average of 50 visits. The remaining time might be allocated to improve the characterization of the architecture of selected planetary systems around nearby targets of specific interest (low-mass stars, young stars, etc.) discovered by Gaia, ground-based high-precision radial-velocity surveys.

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arXiv2011

CFBDSIR J1458+1013B: A Very Cold (>T10) Brown Dwarf in a Binary System

We have identified CFBDS J1458+10 as a 0.11" (2.6 AU) physical binary using Keck laser guide star adaptive optics imaging and have measured a distance of 23.1+/-2.4 pc to the system based on near-IR parallax data from CFHT. The integrated-light near-IR spectrum indicates a spectral type of T9.5, and model atmospheres suggest a slightly higher temperature and surface gravity than the T10 dwarf UGPS J0722-05. Thus, CFBDS J1458+10AB is the coolest brown dwarf binary found to date. Its secondary component has an absolute H-band magnitude that is 1.9+/-0.3 mag fainter than UGPS J0722-05, giving an inferred spectral type of >T10. The secondary's bolometric luminosity of ~2 x 10^{-7} L_sun makes it the least luminous known brown dwarf by a factor of 4-5. By comparing to evolutionary models and T9-T10 objects, we estimate a temperature of 370+/-40 K and a mass of 6-15 Mjup for CFBDS J1458+10B. At such extremes, atmospheric models predict the onset of novel photospheric processes, namely the appearance of water clouds and the removal of strong alkali lines, but their impact on the emergent spectrum is highly uncertain. Our photometry shows that strong CH4 absorption persists at H-band; the J-K color is bluer than the latest known T dwarfs but not as blue as predicted by current models; and the J-H color delineates a possible inflection in the blueward trend for the latest T dwarfs. Given its low luminosity, atypical colors and cold temperature, CFBDS J1458+10B is a promising candidate for the hypothesized Y spectral class. However, regardless of its ultimate classification, CFBDS J1458+10AB provides a new benchmark for measuring the properties of brown dwarfs and gas-giant planets, testing substellar models, and constraining the low-mass limit for star formation.

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arXiv2011

CO (2-1) Line Emission in Redshift 6 Quasar Host Galaxies

We report new observations of CO (2-1) line emission toward five z~6 quasars using the Ka-band receiver system on the Expanded Very Large Array (EVLA). Strong detections were obtained in two of them, SDSS J092721.82+200123.7 and CFHQS J142952.17+544717.6, and a marginal detection was obtained in another source, SDSS J084035.09+562419.9. Upper limits of the CO (2-1) line emission have been obtained for the other two objects. The CO (2-1) line detection in J0927+2001, together with previous measurements of the CO (6-5) and (5-4) lines, reveals important constraints on the CO excitation in the central ~10 kpc region of the quasar host galaxy. The CO (2-1) line emission from J1429+5447 is resolved into two distinct peaks separated by 1.2" (~6.9 kpc), indicating a possible gas-rich, major merging system, and the optical quasar position is consistent with the west peak. This result is in good agreement with the picture in which intense host galaxy star formation is coeval with rapid supermassive black hole accretion in the most distant universe. The two EVLA detections are ideal targets for further high-resolution imaging (e.g., with ALMA or EVLA observations) to study the gas distribution, dynamics, and SMBH-bulge mass relation in these earliest quasar-host galaxy systems.

astro-ph.CO↗

arXiv2011

Spin-orbit inclinations of the exoplanetary systems HAT-P-8, HAT-P-9, HAT-P-16 and HAT-P-23

We report the measurement of the spin-orbit angle of the extra-solar planets HAT-P-8 b, HAT-P-9 b, HAT-P-16 b and HAT-P-23 b, thanks to spectroscopic observations performed at the Observatoire de Haute-Provence with the SOPHIE spectrograph on the 1.93-m telescope. Radial velocity measurements of the Rossiter-McLaughlin effect show the detection of an apparent prograde, aligned orbit for all systems. The projected spin-orbit angles are found to be lambda=-17 deg (+9.2,-11.5), -16 deg (8), -10 deg (16), +15 deg (22) for HAT-P-8, HAT-P-9, HAT-P-16 and HAT-P-23 respectively, with corresponding projected rotational velocities of 14.5 (0.8), 12.5 (1.8), 3.9 (0.8), and 7.8 (1.6) km/s. These new results increase to 37 the number of accurately measured spin-orbit angles in transiting extrasolar systems. We conclude by drawing a tentative picture of the global behaviour of orbital alignement, involving the complexity and diversity of possible mechanisms.

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arXiv2010

The HARPS search for southern extra-solar planets: XXVIII. Two giant planets around M0 dwarfs

Fewer giants planets are found around M dwarfs than around more massive stars, and this dependence of planetary characteristics on the mass of the central star is an important observational diagnostic of planetary formation theories. In part to improve on those statistics, we are monitoring the radial velocities of nearby M dwarfs with the HARPS spectrograph on the ESO 3.6 m telescope. We present here the detection of giant planets around two nearby M0 dwarfs: planets, with minimum masses of respectively 5 Jupiter masses and 1 Saturn mass, orbit around Gl 676A and HIP 12961. The latter is, by over a factor of two, the most massive planet found by radial velocity monitoring of an M dwarf, but its being found around an early M-dwarf is in approximate line with the upper envelope of the planetary vs stellar mass diagram. HIP 12961 ([Fe/H]=-0.07) is slightly more metal-rich than the average solar neighborhood ([Fe/H]=-0.17), and Gl 676A ([Fe/H=0.18) significantly so. The two stars together therefore reinforce the growing trend for giant planets being more frequent around more metal-rich M dwarfs, and the 5~Jupiter mass Gl 676Ab being found around a metal-rich star is consistent with the expectation that the most massive planets preferentially form in disks with large condensate masses.

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arXiv2010

SOPHIE velocimetry of Kepler transit candidates. I. Detection of the low-mass white dwarf KOI-74b

The Kepler mission has detected transits and occultations of a hot compact object around an early-type star, the Kepler Object of Interest KOI 74. The mass of this transiting object was photometrically assessed in a previous study using the presence of the relativistic beaming effect (so-called `Doppler boosting') in the light curve. Our aim was to provide a spectroscopic validation of this pioneering approach. We measured the radial velocity variations of the A1V star KOI 74 with the SOPHIE spectrograph at the 1.93-m telescope of the Observatoire de Haute-Provence (France). Radial velocity measurements of this star are challenging because of the high level of stellar pulsations and the few available spectral lines. Using a technique dedicated to early-type main-sequence stars, we measured radial velocity variations compatible with a companion of mass 0.252+/-0.025 Msun, in good agreement with the value derived from the Kepler light curve. This work strengthens the scenario suggesting that KOI 74 is a blue straggler orbited by a stellar core despoiled of its envelope, the low-mass white dwarf KOI 74b.

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arXiv2010

Detection of a Molecular Disk Orbiting the Nearby, "Old," Classical T Tauri Star MP Mus

We have used the Atacama Pathfinder Experiment 12 m telescope to detect circumstellar CO emission from MP Mus (K1 IVe), a nearby (D ~ 100 pc), actively accreting, ~7 Myr-old pre-main sequence (pre-MS) star. The CO emission line profile measured for MP Mus is indicative of an orbiting disk with radius ~120 AU, assuming the central star mass is 1.2 solar masses and the disk inclination is ~30 degrees, and the inferred disk molecular gas mass is ~3 Earth masses. MP Mus thereby joins TW Hya and V4046 Sgr as the only late-type (low-mass), pre-MS star systems within ~100 pc of Earth that are known to retain orbiting, molecular disks. We also report the nondetection (with the Institut de Radio Astronomie Millimetrique 30 m telescope) of CO emission from another ten nearby (D ~ 100 pc or less), dusty, young (age ~10-100 Myr) field stars of spectral type A-G. We discuss the implications of these results for the timescales for stellar and Jovian planet accretion from, and dissipation of, molecular disks around young stars.

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arXiv2010

The HARPS search for southern extrasolar planets. XXIII. 8 planetary companions to low-activity solar-type stars

In this paper, we present our HARPS radial-velocity data for eight low-activity solar-type stars belonging to the HARPS volume-limited sample: HD6718, HD8535, HD28254, HD290327, HD43197, HD44219, HD148156, and HD156411. Keplerian fits to these data reveal the presence of low-mass companions around these targets. With minimum masses ranging from 0.58 to 2.54 MJup, these companions are in the planetary mass domain. The orbital periods of these planets range from slightly less than one to almost seven years. The eight orbits presented in this paper exhibit a wide variety of eccentricities: from 0.08 to above 0.8.

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arXiv2010

Chandra X-ray Detection of the Enigmatic Field Star BP Psc

BP Psc is a remarkable emission-line field star that is orbited by a dusty disk and drives a parsec-scale system of jets. We report the detection by the Chandra X-ray Observatory of a weak X-ray point source coincident with the centroids of optical/IR and submillimeter continuum emission at BP Psc. As the star's photosphere is obscured throughout the visible and near-infrared, the Chandra X-ray source likely represents the first detection of BP Psc itself. The X-rays most likely originate with magnetic activity at BP Psc and hence can be attributed either to a stellar corona or to star-disk interactions. The log of the ratio of X-ray to bolometric luminosity (log(L_X/L_{bol}) lies in the range -5.8 to -4.2. This is smaller than log(L_X/L_{bol}) ratios typical of low-mass, pre-main sequence stars, but is well within the log(L_X/L_{bol}) range observed for rapidly-rotating (FK Com-type) G giant stars. Hence, the Chandra results favor an exotic model wherein the disk/jet system of BP Psc is the result of its very recently engulfing a companion star or giant planet, as the primary star ascended the giant branch.

astro-ph.SR↗

arXiv2010

The Earth as an extrasolar transiting planet: Earth's atmospheric composition and thickness revealed by Lunar eclipse observations

An important goal within the quest for detecting an Earth-like extrasolar planet, will be to identify atmospheric gaseous bio-signatures. Observations of the light transmitted through the Earth's atmosphere, as for an extrasolar planet, will be the first step for future comparisons. We have completed observations of the Earth during a Lunar eclipse, a unique situation similar to that of a transiting planet. We aim at showing what species could be detected in its atmosphere at optical wavelengths, where a lot of photons are available in the masked stellar light. We present observations of the 2008 August 16 Moon eclipse performed with the SOPHIE spectrograph at the Observatoire de Haute-Provence. Locating the spectrograph fibers in the penumbra of the eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun light and solar light that has passed through the Earth's limb. This mixture essentially reproduces what is recorded during the transit of an extrasolar planet. We report here the clear detection of several Earth atmospheric compounds in the transmission spectra, such as ozone, molecular oxygen, and neutral sodium as well as molecular nitrogen and oxygen through the Rayleigh signature. Moreover, we present a method that allows us to derive the thickness of the atmosphere versus the wavelength for penumbra eclipse observations. We quantitatively evaluate the altitude at which the atmosphere becomes transparent for important species like molecular oxygen and ozone, two species thought to be tightly linked to the presence of life. The molecular detections presented here are an encouraging first attempt, necessary to better prepare for the future of extremely-large telescopes and transiting Earth-like planets. Instruments like SOPHIE will be mandatory when characterizing the atmospheres of transiting Earth-like planets from the ground and searching for bio-marker signatures.

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arXiv2009

A super-Earth transiting a nearby low-mass star

A decade ago, the detection of the first transiting extrasolar planet provided a direct constraint on its composition and opened the door to spectroscopic investigations of extrasolar planetary atmospheres. As such characterization studies are feasible only for transiting systems that are both nearby and for which the planet-to-star radius ratio is relatively large, nearby small stars have been surveyed intensively. Doppler studies and microlensing have uncovered a population of planets with minimum masses of 1.9-10 times the Earth's mass (M_Earth), called super-Earths. The first constraint on the bulk composition of this novel class of planets was afforded by CoRoT-7b, but the distance and size of its star preclude atmospheric studies in the foreseeable future. Here we report observations of the transiting planet GJ 1214b, which has a mass of 6.55 M_Earth and a radius 2.68 times Earth's radius (R_Earth), indicating that it is intermediate in stature between Earth and the ice giants of the Solar System. We find that the planetary mass and radius are consistent with a composition of primarily water enshrouded by a hydrogen-helium envelope that is only 0.05% of the mass of the planet. The atmosphere is probably escaping hydrodynamically, indicating that it has undergone significant evolution during its history. As the star is small and only 13 parsecs away, the planetary atmosphere is amenable to study with current observatories.

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