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L. Arnold

Publications and source records attributed to L. Arnold.

70 records · Page 4Linked to original sources
arXiv2012

The SOPHIE search for northern extrasolar planets. V. Follow-up of ELODIE candidates: Jupiter-analogs around Sun-like stars

We present radial-velocity measurements obtained in a programs underway to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Haute-Provence Observatory. Targets were selected from catalogs observed with ELODIE, mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 years. Two new Jupiter-analog candidates are reported to orbit the bright stars HD150706 and HD222155 in 16.1 and 10.9 yr at 6.7 (+4.0,-1.4) and 5.1(+0.6,-0.7) AU and to have minimum masses of 2.71 (+1.44,-0.66) and 1.90 (+0.67,-0.53) M_Jup, respectively. Using the measurements from ELODIE and SOPHIE, we refine the parameters of the long-period planets HD154345b and HD89307b, and publish the first reliable orbit for HD24040b. This last companion has a minimum mass of 4.01 +/- 0.49 M_Jup orbiting its star in 10.0 yr at 4.92 +/- 0.38 AU. Moreover, the data provide evidence of a third bound object in the HD24040 system. With a surrounding dust debris disk, HD150706 is an active G0 dwarf for which we partially corrected the effect of the stellar spot on the SOPHIE radial-velocities. HD222155 is an inactive G2V star. On the basis of the previous findings of Lovis and collaborators and since no significant correlation between the radial-velocity variations and the activity index are found in the SOPHIE data, these variations are not expected to be only due to stellar magnetic cycles. Finally, we discuss the main properties of this new population of long-period Jupiter-mass planets, which for the moment, consists of fewer than 20 candidates. These stars are preferential targets either for direct-imaging or astrometry follow-up to constrain the system parameters and for higher precision radial-velocity to search for lower mass planets, aiming to find a Solar System twin.

astro-ph.EP↗
arXiv2011

The SOPHIE search for northern extrasolar planets. IV. Massive companions in the planet-brown dwarf boundary

The mass domain where massive extrasolar planets and brown dwarfs lay is still poorly understood. Indeed, not even a clear dividing line between massive planets and brown dwarfs has been established yet. This is partly due to the paucity of this kind of objects orbiting close to solar-type stars, the so-called brown dwarf desert, that hinders setting up a strong observational base to compare to models and theories of formation and evolution. We search to increase the current sample of massive sub-stellar objects with precise orbital parameters, and to constrain the true mass of detected sub-stellar candidates. The initial identification of sub-stellar candidates is done using precise radial velocity measurements obtained with the SOPHIE spectrograph at the 1.93-m telescope of the Haute-Provence Observatory. Subsequent characterisation of these candidates, with the principal aim of identifying stellar companions in low-inclination orbits, is done by means of different spectroscopic diagnostics, as the measurement of the bisector velocity span and the study of the correlation mask effect. With this objective, we also employed astrometric data from the Hipparcos mission and a novel method of simulating stellar cross-correlation functions. Seven new objects with minimum masses between ~ 10 Mjup and ~90 Mjup are detected. Out of these, two are identified as low-mass stars in low-inclination orbits, and two others have masses below the theoretical deuterium-burning limit, and are therefore planetary candidates. The remaining three are brown dwarf candidates; the current upper limits for their the masses do not allow us to conclude on their nature. Additionally, we have improved on the parameters of an already-known brown dwarf (HD137510b), confirmed by astrometry.

astro-ph.EP↗
arXiv2011

Higher-precision radial velocity measurements with the SOPHIE spectrograph using octagonal-section fibers

High-precision spectrographs play a key role in exoplanet searches using the radial velocity technique. But at the accuracy level of 1 m.s-1, required for super-Earth characterization, stability of fiber-fed spectrograph performance is crucial considering variable observing conditions such as seeing, guiding and centering errors and, telescope vignetting. In fiber-fed spectrographs such as HARPS or SOPHIE, the fiber link scrambling properties are one of the main issues. Both the stability of the fiber near-field uniformity at the spectrograph entrance and of the far-field illumination on the echelle grating (pupil) are critical for high-precision radial velocity measurements due to the spectrograph geometrical field and aperture aberrations. We conducted tests on the SOPHIE spectrograph at the 1.93-m OHP telescope to measure the instrument sensitivity to the fiber link light feeding conditions: star decentering, telescope vignetting by the dome,and defocussing. To significantly improve on current precision, we designed a fiber link modification considering the spectrograph operational constraints. We have developed a new link which includes a piece of octagonal-section fiber, having good scrambling properties, lying inside the former circular-section fiber, and we tested the concept on a bench to characterize near-field and far-field scrambling properties. This modification has been implemented in spring 2011 on the SOPHIE spectrograph fibers and tested for the first time directly on the sky to demonstrate the gain compared to the previous fiber link. Scientific validation for exoplanet search and characterization has been conducted by observing standard stars.

astro-ph.IM↗
arXiv2011

The Swift/Fermi GRB 080928 from 1 eV to 150 keV

We present the results of a comprehensive study of the gamma-ray burst 080928 and of its afterglow. GRB 080928 was a long burst detected by Swift/BAT and Fermi/GBM. It is one of the exceptional cases where optical emission had already been detected when the GRB itself was still radiating in the gamma-ray band. For nearly 100 seconds simultaneous optical, X-ray and gamma-ray data provide a coverage of the spectral energy distribution of the transient source from about 1 eV to 150 keV. In particular, we show that the SED during the main prompt emission phase agrees with synchrotron radiation. We constructed the optical/near-infrared light curve and the spectral energy distribution based on Swift/UVOT, ROTSE-IIIa (Australia), and GROND (La Silla) data and compared it to the X-ray light curve retrieved from the Swift/XRT repository. We show that its bumpy shape can be modeled by multiple energy-injections into the forward shock.Furthermore, we investigate whether the temporal and spectral evolution of the tail emission of the first strong flare seen in the early X-ray light curve can be explained by large-angle emission (LAE). We find that a nonstandard LAE model is required to explain the observations. Finally, we report on the results of our search for the GRB host galaxy, for which only a deep upper limit can be provided.

astro-ph.HE↗
arXiv2011

The retrograde orbit of the HAT-P-6b exoplanet

We observed with the SOPHIE spectrograph (OHP, France) the transit of the HAT-P-6b exoplanet across its host star. The resulting stellar radial velocities display the Rossiter-McLaughlin anomaly and reveal a retrograde orbit: the planetary orbital spin and the stellar rotational spin point towards approximately opposite directions. A fit to the anomaly measures a sky-projected angle lambda = 166 +/- 10 degrees between these two spin axes. All seven known retrograde planets are hot jupiters with masses M_p < 3 M_Jup. About two thirds of the planets in this mass range however are prograde and aligned (lambda ~ 0). By contrast, most of the more massive planets (M_p > 4 M_Jup) are prograde but misaligned. Different mechanisms may therefore be responsible for planetary obliquities above and below ~3.5 M_Jup.

astro-ph.EP↗
arXiv2010

The SOPHIE search for northern extrasolar planets III. A Jupiter-mass companion around HD 109246

We report the detection of a Jupiter-mass planet discovered with the SOPHIE spectrograph mounted on the 1.93-m telescope at the Haute-Provence Observatory. The new planet orbits HD109246, a G0V star slightly more metallic than the Sun. HD109246b has a minimum mass of 0.77 MJup, an orbital period of 68 days, and an eccentricity of 0.12. It is placed in a sparsely populated region of the period distribution of extrasolar planets. We also present a correction method for the so-called seeing effect that affects the SOPHIE radial velocities. We complement this discovery announcement with a description of some calibrations that are implemented in the SOPHIE automatic reduction pipeline. These calibrations allow the derivation of the photon-noise radial velocity uncertainty and some useful stellar properties (vsini, [Fe/H], logR'HK) directly from the SOPHIE data.

astro-ph.EP↗
arXiv2010

Observation of the full 12-hour-long transit of the exoplanet HD80606b. Warm-Spitzer photometry and SOPHIE spectroscopy

We present new observations of a transit of the 111-day-period exoplanet HD80606b. Using the Spitzer Space Telescope and its IRAC camera on the post-cryogenic mission, we performed a 19-hour-long photometric observation of HD80606 that covers the full transit of 13-14 January 2010. We complement this photometric data by new spectroscopic observations that we simultaneously performed with SOPHIE at Haute-Provence Observatory. This provides radial velocity measurements of the first half of the transit that was previously uncovered with spectroscopy. This new data set allows the parameters of this singular planetary system to be significantly refined. We obtained a planet-to-star radius ratio R_p/R_* = 0.1001 +/- 0.0006 that is slightly lower than the one measured from previous ground observations. We detected a feature in the Spitzer light curve that could be due to a stellar spot. We also found a transit timing about 20 minutes earlier than the ephemeris prediction; this could be caused by actual TTVs due to an additional body in the system or by underestimated systematic uncertainties. The sky-projected angle between the spin-axis of HD80606 and the normal to the planetary orbital plane is found to be lambda = 42 +/- 8 degrees thanks to the fit of the Rossiter-McLaughlin anomaly. This allows scenarios with aligned spin-orbit to be definitively rejected. Over the twenty planetary systems with measured spin-orbit angles, a few of them are misaligned; this is probably the signature of two different evolution scenarios for misaligned and aligned systems, depending if they experienced or not gravitational interaction with a third body. As in the case of HD80606b, most of the planetary systems including a massive planet are tilted; this could be the signature of a separate evolution scenario for massive planets in comparison with Jupiter-mass planets.

astro-ph.EP↗
arXiv2010

The SOPHIE search for northern extrasolar planets. II. A multi-planet system around HD9446

We report the discovery of a planetary system around HD9446, performed from radial velocity measurements secured with the spectrograph SOPHIE at the 193-cm telescope of the Haute-Provence Observatory during more than two years. At least two planets orbit this G5V, active star: HD9446b has a minimum mass of 0.7 M_Jup and a slightly eccentric orbit with a period of 30 days, whereas HD9446c has a minimum mass of 1.8 M_Jup and a circular orbit with a period of 193 days. As for most of the known multi-planet systems, the HD9446-system presents a hierarchical disposition, with a massive outer planet and a lighter inner planet.

astro-ph.EP↗
arXiv2007

Three-dimensional MHD simulation of expanding magnetic flux ropes

Three-dimensional, time-dependent numerical simulations of the dynamics of magnetic flux ropes are presented. The simulations are targeted towards an experiment previously conducted at CalTech (Bellan, P. M. and J. F. Hansen, Phys. Plasmas, 5, 1991 (1998)) which aimed at simulating Solar prominence eruptions in the laboratory. The plasma dynamics is described by ideal MHD using different models for the evolution of the mass density. Key features of the reported experimental observations like pinching of the current loop, its expansion and distortion into helical shape are reproduced in the numerical simulations. Details of the final structure depend on the choice of a specific model for the mass density.

physics.plasm-ph↗
arXiv2005

Near-UV to near-IR disk-averaged Earth's reflectance spectra

We report 320 to 1020nm disk-averaged Earth reflectance spectra obtained from Moon's Earthshine observations with the EMMI spectrograph on the NTT at ESO La Silla (Chile). The spectral signatures of Earth atmosphere and ground vegetation are observed. A vegetation red-edge of up to 9% is observed on Europe and Africa and ~2% upon Pacific Ocean. The spectra also show that Earth is a blue planet when Rayleigh scattering dominates, or totally white when the cloud cover is large.

astro-ph↗
arXiv2005

Detectability of planetary rings around an extrasolar planet from reflected-light photometry

The next generation of high-contrast imaging instruments will provide the first unresolved image of an extrasolar planet. While the emitted infrared light from the planet in thermal equilibrium should show almost no phase effect, the reflected visible light will vary with the orbital phase angle. We study the photometric variation of the reflected light with orbital phase of a ringed extrasolar planet. We show that a ring around an extrasolar planet, both obviously unresolved, can be detected by its specific photometric signature. Keywords: Stars: planetary systems -- Planets: rings -- Extrasolar planet characterization

astro-ph↗
arXiv2005

Near-UV to near-IR disk-averaged Earth's spectra from Moon's Earthshine observations

We discuss a series of Earthshine spectra obtained with the NTT/EMMI instrument between 320nm and 1020nm with a resolution of R~450 in the blue and R~250 in the red. These ascending and descending Moon's Earthshine spectra taken from Chile give disk-averaged spectra for two different Earth's phases. The spectra show the ozone (Huggins and Chappuis bands), oxygen and water vapour absorption bands, and also the stronger Rayleigh scattering in the blue. Removing the known telluric absorptions reveals a spectral feature around 700nm which is attributed to the vegetation stronger reflectivity in the near-IR, so-called vegetation red-edge.

astro-ph↗
arXiv2002

The STAR Silicon Strip Detector (SSD)

The STAR Silicon Strip Detector (SSD) completes the three layers of the Silicon Vertex Tracker (SVT) to make an inner tracking system located inside the Time Projection Chamber (TPC). This additional fourth layer provides two dimensional hit position and energy loss measurements for charged particles, improving the extrapolation of TPC tracks through SVT hits. To match the high multiplicity of central Au+Au collisions at RHIC the double sided silicon strip technology was chosen which makes the SSD a half million channels detector. Dedicated electronics have been designed for both readout and control. Also a novel technique of bonding, the Tape Automated Bonding (TAB), was used to fullfill the large number of bounds to be done. All aspects of the SSD are shortly described here and test performances of produced detection modules as well as simulated results on hit reconstruction are given.

physics.ins-det↗
arXiv2002

A test for the search for life on extrasolar planets: Looking for the terrestrial vegetation signature in the Earthshine spectrum

We report spectroscopic observations (400 to 800nm, R = approx 100) of Earthshine in June, July and October 2001 from which normalised Earth albedo spectra have been derived. The resulting spectra clearly show the blue colour of the Earth due to Rayleigh diffusion in its atmosphere. They also show the signatures of oxygen, ozone and water vapour. We tried to extract from these spectra the signature of Earth vegetation. A variable signal (4 to 10 +/-3%) around 700nm has been measured in the Earth albedo. It is interpreted as being due to the vegetation red edge, expected to be between 2 to 10% of the Earth albedo at 700nm, depending on models. We discuss the primary goal of the present observations: their application to the detection of vegetation-like biosignatures on extrasolar planets.

astro-ph↗
arXiv2000

First images on the sky from a hyper telescope

We show star images obtained with a miniature ``densified pupil imaging interferometer'' also called a hyper-telescope. The formation of such images violates a ``golden rule of imaging interferometers'' which appeared to forbid the use of interferometric arrangements differing from a Fizeau interferometer. These produce useless images when the sub-apertures spacing is much wider than their size, owing to diffraction through the sub-apertures. The hyper-telescope arrangement solves these problems opening the way towards multi-kilometer imaging arrays in space. We experimentally obtain an intensity gain of 24 +- 3X when a densified-pupil interferometer is compared to an equivalent Fizeau-type interferometer and show images of the double star alpha Gem. The initial results presented confirm the possibility of directly obtaining high resolution and high dynamic range images in the recombined focal plane of a large interferometer if enough elements are used.

astro-ph↗