arXiv subjects

F. Pont

Publications and source records attributed to F. Pont.

86 records · Page 5Linked to original sources

arXiv2006

High accuracy transit photometry of the planet OGLE-TR-113b with a new deconvolution-based method

A high accuracy photometry algorithm is needed to take full advantage of the potential of the transit method for the characterization of exoplanets, especially in deep crowded fields. It has to reduce to the lowest possible level the negative influence of systematic effects on the photometric accuracy. It should also be able to cope with a high level of crowding and with large scale variations of the spatial resolution from one image to another. A recent deconvolution-based photometry algorithm fulfills all these requirements, and it also increases the resolution of astronomical images, which is an important advantage for the detection of blends and the discrimination of false positives in transit photometry. We made some changes to this algorithm in order to optimize it for transit photometry and used it to reduce NTT/SUSI2 observations of two transits of OGLE-TR-113b. This reduction has led to two very high precision transit light curves with a low level of systematic residuals, used together with former photometric and spectroscopic measurements to derive new stellar and planetary parameters in excellent agreement with previous ones, but significantly more precise.

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arXiv2006

Refined parameters of the planet orbiting HD 189733

We report on the BVRI multi-band follow-up photometry of the transiting extrasolar planet HD 189733b. We revise the transit parameters and find planetary radius RP = 1.154+/- 0.032RJ and inclination i_P = 85.79+/-0.24deg. The new density (~ 1g cm-3) is significantly higher than the former estimate (~ 0.75g cm-3); this shows that from the current sample of 9 transiting planets, only HD 209458 (and possibly OGLE-10b) have anomalously large radii and low densities. We note that due to the proximity of the parent star, HD 189733b currently has one of the most precise radius determinations among extrasolar planets. We calculate new ephemerides: P = 2.218573+/-0.000020 days, T0 = 2453629.39420+/-0.00024 (HJD), and estimate the timing offsets of the 11 distinct transits with respect to the predictions of a constant orbital period, which can be used to reveal the presence of additional planets in the system.

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arXiv2006

High resolution spectroscopy of stars with transiting planets. The cases of OGLE-TR-10, 56, 111, 113, and TrES-1

Context: During the past years photometric surveys, later complemented by follow-up radial-velocity measurements, have revealed the presence of several new extra-solar transiting planets, in very short period orbits. Many of the host stars are extremely faint (V$\sim$16), making high-precision spectroscopic measurements challenging. Aims: We have used the UVES spectrograph (VLT-UT2 telescope) to obtain high resolution spectra of 5 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111, 113 and TrES-1. The immediate objective is to derive accurate stellar parameters and chemical abundances. Methods: The stellar parameters were derived from an LTE analysis of a set of FeI and FeII lines. Results: Complementing the spectroscopic information with photometric transit curves and radial-velocity data from the literature, we have then refined the stellar and planetary radii and masses. The obtained data were also used to study and discuss the relation between the stellar metallicity and orbital period of the planets.

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arXiv2005

Elodie metallicity-biased search for transiting Hot Jupiters I. Two Hot Jupiters orbiting the slightly evolved stars HD118203 and HD149143

We report the discovery of a new planet candidate orbiting the subgiant star HD118203 with a period of P=6.1335 days. The best Keplerian solution yields an eccentricity e=0.31 and a minimum mass m2sin(i)=2.1MJup for the planet. This star has been observed with the ELODIE fiber-fed spectrograph as one of the targets in our planet-search programme biased toward high-metallicity stars, on-going since March 2004 at the Haute-Provence Observatory. An analysis of the spectroscopic line profiles using line bisectors revealed no correlation between the radial velocities and the line-bisector orientations, indicating that the periodic radial-velocity signal is best explained by the presence of a planet-mass companion. A linear trend is observed in the residuals around the orbital solution that could be explained by the presence of a second companion in a longer-period orbit. We also present here our orbital solution for another slightly evolved star in our metal-rich sample, HD149143, recently proposed to host a 4-d period Hot Jupiter by the N2K consortium. Our solution yields a period P=4.09 days, a marginally significant eccentricity e=0.08 and a planetary minimum mass of 1.36MJup. We checked that the shape of the spectral lines does not vary for this star as well.

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arXiv2005

A planet-sized transiting star around OGLE-TR-122 - Accurate mass and radius near the Hydrogen-burning limit

We report the discovery and characterisation of OGLE-TR-122b, the smallest main-sequence star to date with a direct radius determination. OGLE-TR-122b transits around its solar-type primary every 7.3-days. With M=0.092+-0.009 Mo and R=0.120 +0.024-0.013 Ro, it is by far the smallest known eclipsing M-dwarf. The derived mass and radius for OGLE-TR-122b are in agreement with the theoretical expectations. OGLE-TR-122b is the first observational evidence that stars can indeed have radii comparable or even smaller than giant planets. In such cases, the photometric signal is exactly that of a transiting planet and the true nature of the companion can only be determined with high-resolution spectroscopy.

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arXiv2005

Doppler follow-up of OGLE planetary transit candidates in Carina

We present the results of our high-resolution spectroscopic follow-up of 42 planetary transit candidates in Carina from the OGLE survey. This follow-up has already allowed the discovery of three new transiting exoplanets, OGLE-TR-111, 113 and 132, presented in earlier Letters (Bouchy et al. 2004, Pont et al. 2004). Here we analyse the data for the remaining 39 candidates. The radial velocity data show that most of them are eclipsing binaries, in very varied configurations. Precise radial velocity orbits were derived for 15 binaries, revealing 9 transits of small stars (generally M-dwarfs) in front of F-G dwarfs, 1 grazing equal-mass eclipsing binary, 4 triple and 1 quadruple systems. A remaining 14 systems appear binary, but the exact orbit is uncertain or was not determined. 2 objects do not show any radial velocity variations in phase with the transit signal, and 6 do not possess spectral lines strong enough for a reliable cross-correlation function to be measured. Among these last two categories, up to 6 objects are suspected false positives of the photometric transit detection. Finally 2 objects are unsolved cases that deserve further observations. Our study illustrates the wide variety of cases that can mimic photometric planetary transits, and the importance of spectroscopic follow-up. Multi-fiber capacities and an optimized follow-up strategy, which we present here, can help deal with the high number of candidates that are likely to turn up in the near future. (abridged)

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arXiv2004

Doppler follow-up of OGLE transiting companions in the Galactic bulge

Two years ago, the OGLE-III survey (Optical Gravitational Lensing Experiment) announced the detection of 54 short period multi-transiting objects in the Galactic bulge (Udalski et al., 2002a, 2002b). Some of these objects were considered to be potential hot Jupiters. In order to determine the true nature of these objects and to characterize their actual mass, we conducted a radial velocity follow-up of 18 of the smallest transiting candidates. We describe here our procedure and report the characterization of 8 low mass star transiting companions, 2 grazing eclipsing binaries, 2 triple systems, 1 confirmed exoplanet (OGLE-TR-56b), 1 possible exoplanet (OGLE-TR-10b), 1 clear false positive and 3 unsolved cases. The variety of cases encountered in our follow-up covers a large part of the possible scenarii occuring in the search for planetary transits. As a by-product, our program yields precise masses and radii of low mass stars.

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arXiv2004

Surface Brightness and Stellar Populations at the Outer Edge of the Large Magellanic Cloud: No Stellar Halo Yet

We present a high quality CMD for a 36'x 36' field located 8 degrees (7 kpc) from the LMC center, as well as a precise determination of the LMC surface brightness derived from the resolved stellar population out to this large galactocentric radius. This deep CMD shows for the first time the detailed age distribution at this position, where the surface brightness is V=26.5 mag/sq". At a radius R=474' the main sequence is well populated from the oldest turnoff at I=21.5 to the 2.5 Gyr turnoff at I=19.5. Beyond this radius, a relatively strong gradient in the density of stars with ages in the 2.5-4 Gyr range is apparent. There are some stars brighter and bluer than the main population, quite uniformly distributed over the whole area surveyed, which are well matched by a 1.5 Gyr isochrone and may be indicative of a relatively recent star formation, or merger, event. The surface brightness profile of the LMC remains exponential to this large galactocentric radius and shows no evidence of disk truncation. Combining the information on surface brightness and stellar population we conclude that the LMC disk extends (and dominates over a possible stellar halo) out to a distance of at least 7 kpc. These results confirm that the absence of blue stars in the relatively shallow off-center CMDs of dIrr galaxies is not necessarily evidence for an exclusively old stellar population resembling the halo of the Milky Way.

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arXiv2004

Accurate radius and mass of the transiting exoplanet OGLE-TR-132b

The exoplanet OGLE-TR-132b belongs to the new class of very hot giant planets, together with OGLE-TR-56b and OGLE-TR-113b, detected by their transits. Recently, radial velocity measurements provided a planetary mass estimate for OGLE-TR-132b. The planet parameters, however, were poorly cons trained, because of the very shallow transit in the OGLE light curve. In this letter, based on new VLT/FORS2 photometric follow-up of OGLE-TR-132 of unprecedented quality (1.2 millimagnitude relative photometry), we confirm the planetary nature of the orbiting object, and we derive an accurate measurement of its radius and mass: 1.13 +- 0.08 R_J and 1.19 +- 0.13 M_J. The refined ephemeris of OGLE-TR-132 transits is T_0 = 2453142.5888 and P = 1.689857 days.

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arXiv2004

The Geneva-Copenhagen survey of the Solar neighbourhood: Ages, metallicities, and kinematic properties of 14,000 F and G dwarfs

We present and discuss new determinations of metallicity, rotation, age, kinematics, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased sample of 16,682 nearby F and G dwarf stars. Our 63,000 new, accurate radial-velocity observations for nearly 13,500 stars allow identification of most of the binary stars in the sample and, together with published data complete the kinematic information for 14,139 stars. A major effort has been devoted to the determination of new isochrone ages for all stars for which this is possible. Particular attention has been given to a realistic treatment of statistical biases and error estimates, as standard techniques tend to underestimate these effects and introduce spurious features in the age distributions. We demonstrate, however, how strong observational and theoretical biases cause the distribution of the observed ages to be very different from that of the true age distribution of the sample. Our first results confirm the lack of metal-poor G dwarfs relative to closed-box model predictions (the ``G dwarf problem''), the existence of radial metallicity gradients in the disk, the small change in mean metallicity of the thin disk since its formation and the substantial scatter in metallicity at all ages, and the continuing kinematic heating of the thin disk with an efficiency consistent with that expected for a combination of spiral arms and giant molecular clouds. Distinct features in the distribution of the V component of the space motion are extended in age and metallicity, corresponding to the effects of stochastic spiral waves rather than classical moving groups, and may complicate the identification of thick-disk stars from kinematic criteria. (abridged)

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arXiv2004

Two new "very hot Jupiters" among the OGLE transiting candidates

As a result of a radial velocity follow-up of OGLE planetary transit candidates in Carina, we report the discovery of two new transiting planets with very short orbital periods: OGLE-TR-113 with m=1.35+-0.22 M_{Jup}, r=1.08 {+0.07}{-0.05} R_{Jup}, P=1.43 day, and OGLE-TR-132 with m=1.01+-0.31 M_{Jup}, r=1.15 {+0.80}{-0.13} R_{Jup}, P=1.69 day. These detections bring to three the number of known "very hot Jupiters" (Jovian exoplanets like OGLE-TR-56 with periods much smaller than 3 days), indicating that the absence of such planets in radial velocity survey does not reflect an absolute limit.

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arXiv2002

The ARAUCARIA project. Discovery of Cepheid Variables in NGC 300 from a Wide-Field Imaging Survey

Based on observations of NGC 300, obtained with the Wide-Field Camera at the 2.2 m ESO/MPI telescope during 29 nights spread over a 5.3 month interval, 117 Cepheids and 12 Cepheid candidates were found which cover the period range from 115 to 5.4 days. We present a catalog which provides equatorial coordinates, period, time of maximum brightness, and intensity mean B and V magnitudes for each variable, and we show phased B and V light curves for all the Cepheids found. We also present the individual B and V observations for each Cepheid in our catalog. We find very good agreement between our photometry and that obtained by Freedman et al. from ground-based CCD data for common stars. The Cepheids delineate the spiral arms of NGC 300, and a couple of them were detected very close to the center of the galaxy. From the color-magnitude diagram of NGC 300 constructed from our data, we expect that our Cepheid detection is near-complete for variables with periods larger than about 10 days. We present plots of the PL relations in the B and V bands obtained from our data, which clearly demonstrate the presence of a Malmquist bias for periods below about 10 days. A thorough discussion of the distance to NGC 300 will be presented in a forthcoming paper which will include the analysis of photometry in longer-wavelength bands.

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arXiv2001

A Catalog of OB Associations in the spiral galaxy NGC 300

We present results of a search for OB associations in NGC 300. Using an automatic and objective method (PLC technique) 117 objects were found. Statistical tests indicate that our sample is contaminated by less than 10 % of spurious detections due to random concentrations of blue stars. Spatial distributions of detected associations and H II regions are strongly correlated. The size distribution reveals a significant peak at about 60 $μ$rad which corresponds to 125 parsecs if a distance modulus of 26.66 mag is assumed. Besides the objects with sizes corresponding to typical associations we also found several much larger objects. A second level application of our detection method revealed that most of these are composed of smaller subgroups, with sizes of about 100 pc.

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arXiv1998

Structural Properties of s-Cepheid Velocity Curves

The light curves of the first overtone Pop. I Cepheids (s-Cepheids) show a discontinuity in their phi_21 vs. P diagram, near P=3.2 day. This feature, commonly attributed to the 2:1 resonance between the first and the fourth overtones (omega_4=2 omega_1), is not reproduced by the hydrodynamical models. With the goal of reexamining the resonance hypothesis, we have obtained new CORAVEL radial velocity curves for 14 overtone Cepheids. Together with 10 objects of Krzyt et al. (1999), the combined sample covers the whole range of overtone Cepheid periods. The velocity Fourier parameters display a strong characteristic resonant behavior. In striking contrast to photometric ones, they vary smoothly with the pulsation period and show no jump at 3.2 day. The existing radiative hydrodynamical models match the velocity parameters very well. The center of the omega_4 = 2 omega_1 resonance is estimated to occur at P_r = 4.58+-0.04 day, i.e. at a period considerably longer than previously assumed (3.2 day). We identify two new members of the s-Cepheid group: MY Pup and V440 Per.

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