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See detailSearch for a habitable terrestrial planet transiting the nearby red dwarf GJ 1214
Gillon, Michaël ULg; Demory, B.-O.; Madhusudhan, N. et al

E-print/Working paper (2013)

High-precision eclipse spectrophotometry of transiting terrestrial exoplanets represents a promising path for the first atmospheric characterizations of habitable worlds and the search for life outside ... [more ▼]

High-precision eclipse spectrophotometry of transiting terrestrial exoplanets represents a promising path for the first atmospheric characterizations of habitable worlds and the search for life outside our solar system. The detection of terrestrial planets transiting nearby late-type M-dwarfs could make this approach applicable within the next decade, with near-to-come general facilities. In this context, we previously identified GJ 1214 as a high-priority target for a transit search, as the transit probability of a habitable planet orbiting this nearby M4.5 dwarf would be significantly enhanced by the transiting nature of GJ 1214 b, the super-Earth already known to orbit the star. Basing on this observation, we have set-up an ambitious high-precision photometric monitoring of GJ 1214 with the Spitzer Space Telescope to probe its entire habitable zone in search of a transiting planet as small as Mars. We present here the results of this transit search. Unfortunately, we did not detect any second transiting planet. Assuming GJ 1214 hosts a habitable planet larger than Mars, our global analysis of the whole Spitzer dataset leads to a posterior no-transit probability >=97%. Our analysis allows us to significantly improve the characterization of GJ 1214 b, to measure its occultation depth to be 70+-35 ppm at 4.5 microns, and to constrain it to be smaller than 205ppm (3-sigma upper limit) at 3.6 microns. In agreement with the plethora of transmission measurements published so far for GJ 1214 b, these emission measurements are consistent with both a metal-rich and a cloudy hydrogen-rich atmosphere. [less ▲]

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See detailThe HARPS search for southern extra-solar planets. XXXIV. A planetary system around the nearby M dwarf GJ163, with a super-Earth possibly in the habitable zone
Bonfils, X.; Lo Curto, G.; Correia, A. C. M. et al

E-print/Working paper (2013)

The meter-per-second precision achieved by today velocimeters enables the search for 1-10 M_Earth planets in the habitable zone of cool stars. This paper reports on the detection of 3 planets orbiting ... [more ▼]

The meter-per-second precision achieved by today velocimeters enables the search for 1-10 M_Earth planets in the habitable zone of cool stars. This paper reports on the detection of 3 planets orbiting GJ163 (HIP19394), a M3 dwarf monitored by our ESO/HARPS search for planets. We made use of the HARPS spectrograph to collect 150 radial velocities of GJ163 over a period of 8 years. We searched the RV time series for coherent signals and found 5 distinct periodic variabilities. We investigated the stellar activity and casted doubts on the planetary interpretation for 2 signals. Before more data can be acquired we concluded that at least 3 planets are orbiting GJ163. They have orbital periods of P_b=8.632+-0.002, P_c=25.63+-0.03 and P_d=604+-8 days and minimum masses msini = 10.6+-0.6, 6.8+-0.9, and 29+-3 M_Earth, respectively. We hold our interpretations for the 2 additional signals with periods P_(e)=19.4 and P_(f)=108 days. The inner pair presents an orbital period ratio of 2.97, but a dynamical analysis of the system shows that it lays outside the 3:1 mean motion resonance. GJ163c, in particular, is a super-Earth with an equilibrium temperature of T_eq = (302+-10) (1-A)^(1/4) K and may lie in the so called habitable zone for albedo values (A=0.34-0.89) moderately higher than that of Earth (A_Earth=0.2-0.3). [less ▲]

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See detailThe HARPS search for southern extra-solar planets: XXXI. The M-dwarf sample
Bonfils, X.; Delfosse, X.; Udry, S. et al

in Astronomy and Astrophysics (2013), 549

(Abridged) Searching for planets around stars with different masses probes the outcome of planetary formation for different initial conditions. This drives observations of a sample of 102 southern nearby ... [more ▼]

(Abridged) Searching for planets around stars with different masses probes the outcome of planetary formation for different initial conditions. This drives observations of a sample of 102 southern nearby M dwarfs, using a fraction of our guaranteed time on the ESO/HARPS spectrograph (Feb. 11th, 2003 to Apr. 1st 2009). This paper makes available the sample's time series, presents their precision and variability. We apply systematic searches and diagnostics to discriminate whether the observed Doppler shifts are caused by stellar surface inhomogeneities or by the radial pull of orbiting planets. We recover the planetary signals corresponding to 9 planets already announced by our group (Gl176b, Gl581b, c, d & e, Gl674b, Gl433b, Gl 667Cb and c). We present radial velocities that confirm GJ 849 hosts a Jupiter-mass planet, plus a long-term radial-velocity variation. We also present RVs that precise the planetary mass and period of Gl 832b. We detect long-term RV changes for Gl 367, Gl 680 and Gl 880 betraying yet unknown long-period companions. We identify candidate signals in the radial-velocity time series and demonstrate they are most probably caused by stellar surface inhomogeneities. Finally, we derive a first estimate of the occurrence of M-dwarf planets as a function of their minimum mass and orbital period. In particular, we find that giant planets (m sin i = 100-1,000 Mearth) have a low frequency (e.g. f<1% for P=1-10 d and f=0.02^{+0.03}_{-0.01} for P=10-100 d), whereas super-Earths (m sin i = 1-10 Mearth) are likely very abundant (f=0.36^{+0.25}_{-0.10} for P=1-10 d and f=0.35^{+0.45}_{-0.11} for P=10-100 d). We also obtained eta_earth=0.41^{+0.54}_{-0.13}, the frequency of habitable planets orbiting M dwarfs (1<m sin i<10 Mearth). For the first time, eta_earth is a direct measure and not a number extrapolated from the statistic of more massive and/or shorter-period planets. [less ▲]

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See detailA hot Uranus transiting the nearby M dwarf GJ 3470. Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry
Bonfils, X.; Gillon, Michaël ULg; Udry, S. et al

in Astronomy and Astrophysics (2012), 546

We report on the discovery of GJ 3470 b, a transiting hot Uranus of mass m[SUB]p[/SUB] = 14.0 ± 1.8 M[SUB]⊕[/SUB], radius R[SUB]p[/SUB] = 4.2 ± 0.6 R[SUB]⊕[/SUB] and period P = 3.3371 ± 0.0002 day. Its ... [more ▼]

We report on the discovery of GJ 3470 b, a transiting hot Uranus of mass m[SUB]p[/SUB] = 14.0 ± 1.8 M[SUB]⊕[/SUB], radius R[SUB]p[/SUB] = 4.2 ± 0.6 R[SUB]⊕[/SUB] and period P = 3.3371 ± 0.0002 day. Its host star is a nearby (d = 25.2 ± 2.9 pc) M1.5 dwarf of mass M[SUB]⋆[/SUB] = 0.54 ± 0.07 M[SUB]&sun;[/SUB] and radius R[SUB]⋆[/SUB] = 0.50 ± 0.06 R[SUB]&sun;[/SUB]. The detection was made during a radial-velocity campaign with Harps that focused on the search for short-period planets orbiting M dwarfs. Once the planet was discovered and the transit-search window narrowed to about 10% of an orbital period, a photometric search started with Trappist and quickly detected the ingress of the planet. Additional observations with Trappist, EulerCam and Nites definitely confirmed the transiting nature of GJ 3470b and allowed the determination of its true mass and radius. The star's visible or infrared brightness (V[SUP]mag[/SUP] = 12.3, K[SUP]mag[/SUP] = 8.0), together with a large eclipse depth D = 0.57 ± 0.05%, ranks GJ 3470 b among the most suitable planets for follow-up characterizations. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope under the program IDs 183.C-0437 at Cerro La Silla (Chile).Our radial-velocity and photometric time series are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A27">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A27</A> [less ▲]

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See detailThe HARPS search for southern extra-solar planets XXXV. Super-Earths around the M-dwarf neighbors Gl433 and Gl667C
Delfosse, X.; Bonfils, X.; Forveille, T. et al

in Astronomy and Astrophysics (2012), 553

Context. M dwarfs have often been found to have super-Earth planets with short orbital periods. These stars are thus preferential targets in searches for rocky or ocean planets in the solar neighborhood ... [more ▼]

Context. M dwarfs have often been found to have super-Earth planets with short orbital periods. These stars are thus preferential targets in searches for rocky or ocean planets in the solar neighborhood. Aims: Our research group recently announced the discovery of one and two low-mass planets around the M1.5V stars Gl 433 and Gl 667C, respectively. We found these planets with the HARPS spectrograph on the ESO 3.6-m telescope at La Silla Observatory, from observations obtained during the guaranteed time observing program of that instrument. Methods: We obtained additional HARPS observations of those two stars, for a total of 67 and 179 radial velocity measurements for Gl 433 and Gl 667C, respectively, and present here an orbital analysis of these extended data sets and our main conclusions about both planetary systems. Results: One of the three planets, Gl 667Cc, has a mass of only M2sini ~ 4.25 M⊕ and orbits in the central habitable zone of its host star. It receives only 10% less stellar energy from Gl 667C than the Earth receives from the Sun. However, planet evolution in the habitable zone can be very different if the host star is a M dwarf or a solar-like star, without necessarily questioning the presence of water. The two other planets, Gl 433b and Gl 667Cb, both have M2sini of ~5.5 M⊕ and periods of ~7 days. The radial velocity measurements of both stars contain longer timescale signals, which we fit with longer period Keplerians. For Gl 433, the signal probably originates in a magnetic cycle, while data of longer time span will be needed before conclusive results can be obtained for Gl 667C. The metallicity of Gl 433 is close to solar, while Gl 667C is metal poor with [Fe/H] ~ -0.6. This reinforces the recent conclusion that the occurrence of super-Earth planets does not strongly correlate with the stellar metallicity. [less ▲]

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See detailPIONIER: a 4-telescope visitor instrument at VLTI
Le Bouquin, J.-B.; Berger, J.-P.; Lazareff, B. et al

in Astronomy and Astrophysics (2011), 535

Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer ... [more ▼]

Context. PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer (ESO, Chile) using an integrated optics combiner. The instrument was integrated at IPAG in December 2009 and commissioned at the Paranal Observatory in October 2010. It has provided scientific observations since November 2010. <BR /> Aims: In this paper, we explain the instrumental concept and describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. <BR /> Methods: This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries δ Sco and HIP11231. <BR /> Results: PIONIER provides six visibilities and three independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R = 40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag = 7 in dispersed mode under median atmospheric conditions (seeing < 1, τ[SUB]0[/SUB] > 3ms) with the 1.8m Auxiliary Telescopes. We demonstrate a precision of 0.5deg on the closure phases. The precision on the calibrated visibilities ranges from 3% to 15% depending on the atmospheric conditions. <BR /> Conclusions: PIONIER was installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8m Unit Telescopes in March 2011 demonstrates that VLTI is ready for four-telescope operation. Based on observations collected at the European Southern Observatory, Paranal, Chile (commissioning data and 087.C-0709). [less ▲]

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See detailThe HARPS search for southern extra-solar planets XXXII. Only 4 planets in the Gl~581 system
Forveille, T.; Bonfils, X.; Delfosse, X. et al

E-print/Working paper (2011)

The Gl 581 planetary system has generated wide interest, because its 4 planets include both the lowest mass planet known around a main sequence star other than the Sun and the first super-Earth planet in ... [more ▼]

The Gl 581 planetary system has generated wide interest, because its 4 planets include both the lowest mass planet known around a main sequence star other than the Sun and the first super-Earth planet in the habitable zone of its star. A recent paper announced the possible discovery of two additional super-Earth planets in that system, one of which would be in the middle of the habitable zone of Gl 581. The statistical significance of those two discoveries has, however, been questioned. We have obtained 121 new radial velocity measurements of Gl 581 with the HARPS spectrograph on the ESO 3.6 m telescope, and analyse those together with our previous 119 measurements of that star to examine these potential additional planets. We find that neither is likely to exist with their proposed parameters. We also obtained photometric observations with the 2.5 m Isaac Newton Telescope during a potential transit of the inner planet, Gl 581e, which had a 5% geometric transit probability. Those observations exclude transits for planet densities under 4 times the Earth density within -0.2 sigma to +2.7 sigma of the predicted transit center. [less ▲]

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See detailA short-period super-Earth orbiting the M2.5 dwarf GJ 3634. Detection with HARPS velocimetry and transit search with Spitzer photometry
Bonfils, X.; Gillon, Michaël ULg; Forveille, T. et al

in Astronomy and Astrophysics (2011), 528

We report on the detection of GJ 3634b, a super-Earth of mass m sin i = 7.0[SUB]-0.8[SUP]+0.9[/SUP]~M_⊕[/SUB] and period P = 2.64561 ± 0.00066 day. Its host star is a M2.5 dwarf, has a mass of 0.45 ± 0.05 ... [more ▼]

We report on the detection of GJ 3634b, a super-Earth of mass m sin i = 7.0[SUB]-0.8[SUP]+0.9[/SUP]~M_⊕[/SUB] and period P = 2.64561 ± 0.00066 day. Its host star is a M2.5 dwarf, has a mass of 0.45 ± 0.05 M[SUB]ȯ[/SUB], a radius of 0.43 ± 0.03 R[SUB]ȯ[/SUB] and lies 19.8 ± 0.6 pc away from our Sun. The planet is detected after a radial-velocity campaign using the ESO/Harps spectrograph. GJ 3634b had an a priori geometric probability to undergo transit of ~7% and, if telluric in composition, a non-grazing transit would produce a photometric dip of ≲0.1%. We therefore followed-up upon the RV detection with photometric observations using the 4.5-μm band of the IRAC imager onboard Spitzer. Our six-hour long light curve excludes that a transit occurs for 2σ of the probable transit window, decreasing the probability that GJ 3634b undergoes transit to ~0.5%. Based on observations made with the Harps instrument on the ESO 3.6-m telescope at La Silla Observatory under program IDs 082.C-0718(B) and183.C-0437(A), and observations made with Warm Spitzer under program 60027.Radial-velocity and photometric tables (Tables 2 and 3) are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A111">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A111</A> [less ▲]

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See detailAn educated search for transiting habitable planets: (Research Note) Targetting M dwarfs with known transiting planets
Gillon, Michaël ULg; Bonfils, X.; Demory, B-O et al

in Astronomy and Astrophysics (2011), 525

Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to ... [more ▼]

Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. We investigate here the potential of this approach for the M dwarf GJ 1214 that hosts a transiting super-Earth. For this system, we infer the transit probabilities as a function of orbital periods. Using Monte-Carlo simulations we address both the cases for fully coplanar and for non-coplanar orbits, with three different choices of inclinations distribution for the non-coplanar case. GJ 1214 reveals to be a very promising target for the considered approach. Because of its small size, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring could detect any transiting habitable planet down to the size of Mars. The mass measurement of such a small planet would be out of reach for current facilities, but we emphasize that a planet mass would not be needed to confirm the planetary nature of the transiting object. Furthermore, the radius measurement combined with theoretical arguments would help us to constrain the structure of the planet [less ▲]

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See detailThe Fourier-Kelvin Stellar Interferometer: Exploring Exoplanetary Systems with an Infrared Probe-class Mission
Barry, R. K.; Danchi, W. C.; Lopez, B. et al

in Coudé du Foresto, Vincent; Gelino, Dawn; Ribas, Ignasi (Eds.) Pathways Towards Habitable Planets (2010, October 01)

We report results of a recent engineering study of an enhanced version of the Fourier-Kelvin Stellar Interferometer (FKSI) that includes 1-m diameter primary mirrors, a 20-m baseline, a sun shield with a ... [more ▼]

We report results of a recent engineering study of an enhanced version of the Fourier-Kelvin Stellar Interferometer (FKSI) that includes 1-m diameter primary mirrors, a 20-m baseline, a sun shield with a ±45° Field-of-Regard (FoR), and 40K operating temperature. The enhanced FKSI is a two-element nulling interferometer operating in the mid-infrared (e.g. ˜ 5-15 μm) designed to measure exozodiacal debris disks around nearby stars with a sensitivity better than one solar system zodi (SSZ) and to characterize the atmospheres of a large sample of known exoplanets. The modifications to the original FKSI design also allows observations of the atmospheres of many super-Earths and a few Earth twins using a combination of spatial modulation and spectral analysis. [less ▲]

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See detailInfrared Detection and Characterization of Debris Disks, Exozodiacal Dust, and Exoplanets: The FKSI Mission Concept
Danchi, W. C.; Barry, R. K.; Lopez, B. et al

in Coudé du Foresto, Vincent; Gelino, Dawn; Ribas, Ignasi (Eds.) Pathways Towards Habitable Planets (2010, October 01)

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a nulling interferometer for the near-to-mid-infrared spectral region. FKSI is conceived as a mid-sized strategic or Probe class ... [more ▼]

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a nulling interferometer for the near-to-mid-infrared spectral region. FKSI is conceived as a mid-sized strategic or Probe class mission. FKSI has been endorsed by the Exoplanet Community Forum 2008 as such a mission and has been costed to be within the expected budget. The current design of FKSI is a two-element nulling interferometer. The two telescopes, separated by 12.5m, are precisely pointed (by small steering mirrors) on the target star. The two path lengths are accurately controlled to be the same to within a few nanometers. A phase shifter/beam combiner (Mach-Zehnder interferometer) produces an output beam consisting of the nulled sum of the target planet’s light and the host star’s light. When properly oriented, the starlight is nulled by a factor of 10[SUP]-4[/SUP], and the planet light is undiminished. Accurate modeling of the signal is used to subtract the residual starlight, permitting the detection of planets much fainter than the host star. The current version of FKSI with 0.5-m apertures and waveband 3-8 μm has the following main capabilities: (1) detect exozodiacal emission levels to that of our own solar system (Solar System Zodi) around nearby F, G, and K stars; (2) characterize spectroscopically the atmospheres of a large number of known non-transiting planets; (3) survey and characterize nearby stars for planets down to 2 R[SUB]earth[/SUB] from just inside the habitable zone and inward. An enhanced version of FKSI with 1-m apertures separated by 20 m and cooled to 40 K, with science waveband 5-15 μm, allows for the detection and characterization of 2 R[SUB]earth[/SUB] super-Earths and smaller planets in the habitable zone around stars within about 30 pc. [less ▲]

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See detailPIONIER: a visitor instrument for VLTI
Berger, Jean-Philippe; Zins, G.; Lazareff, B. et al

in Danchi, W. C.; Delplancke, F.; Rajagopal, J. K. (Eds.) Optical and Infrared Interferometry II (2010, July)

PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD integrated optics combiner that can also be used ... [more ▼]

PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD integrated optics combiner that can also be used in scanning mode. It provides low spectral resolution in H and K band. PIONIER is designed for imaging with a specific emphasis on fast fringe recording to allow closure-phases and visibilities to be precisely measured. In this work we provide the detailed description of the instrument and present its updated status. [less ▲]

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See detailThe HARPS search for southern extra-solar planets. XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period
Forveille, T.; Bonfils, X.; Delfosse, X. et al

in Astronomy and Astrophysics (2009), 493

A 10.24-day Neptune-mass planet was recently announced as orbiting the nearby M2 dwarf Gl 176, based on 28 radial velocities measured with the HRS spectrograph on the Hobby-Heberly Telescope. We obtained ... [more ▼]

A 10.24-day Neptune-mass planet was recently announced as orbiting the nearby M2 dwarf Gl 176, based on 28 radial velocities measured with the HRS spectrograph on the Hobby-Heberly Telescope. We obtained 57 radial velocities of Gl 176 with the ESO 3.6 m telescope and the HARPS spectrograph, which is known for its sub-m s[SUP]-1[/SUP] stability. The median photon-noise standard error of our measurements is 1.1 m s[SUP]-1[/SUP], significantly lower than the 4.7 m s[SUP]-1[/SUP] of the HET velocities, and the 4-year period over which they were obtained overlaps considerably with the epochs of the HET measurements. The HARPS measurements show no evidence of a signal at the period of the putative HET planet, suggesting that its detection was spurious. We do find, on the other hand, strong evidence of a lower mass 8.4 M_Earth planet, in a quasi-circular orbit and at the different period of 8.78 days. The host star has moderate magnetic activity and rotates on a 39-day period, which we confirm through modulation of both contemporaneous photometry and chromospheric indices. We detect that period, as well, in the radial velocities, but it is well removed from the orbital period and offers no cause for confusion. This new detection of a super-Earth (2 M_Earth < M sin (i) < 10 M_Earth) around an M dwarf adds to the growing evidence that such planets are common around very low-mass stars. A third of the 20 known planets with M sin (i)< 0.1 M_Jup and 3 of the 7 known planets with M sin (i) < 10 M_Earth orbit an M dwarf, in contrast to just 4 of the ~300 known Jupiter-mass planets. Based on observations made with the HARPS instrument on the ESO 3.6-m telescope at La Silla Observatory under program ID 072.C-0488. [less ▲]

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See detailMilli-arcsecond Astrophysics with VSI, the VLTI Spectro-imager in the ELT Era
Malbet, F.; Buscher, D.; Weigelt, G. et al

in Moorwood, Alan (Ed.) Science with the VLT in the ELT Era (2009)

Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be ... [more ▼]

Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain. This instrument will provide information complementary to what is obtained at the same time with ALMA at different wavelengths and the extreme large telescopes. [less ▲]

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See detailTW ;Hydrae: evidence of stellar spots instead of a Hot Jupiter
Huélamo, N.; Figueira, P.; Bonfils, X. et al

in Astronomy and Astrophysics (2008), 489

Context: TW Hya is a classical T Tauri star that shows significant radial-velocity variations in the optical regime. These variations have been attributed to a 10 M_Jup planet orbiting the star at 0.04 AU ... [more ▼]

Context: TW Hya is a classical T Tauri star that shows significant radial-velocity variations in the optical regime. These variations have been attributed to a 10 M_Jup planet orbiting the star at 0.04 AU. Aims: The aim of this letter is to confirm the presence of the giant planet around TW Hya by (i) testing whether the observed RV variations can be caused by stellar spots and (ii) analyzing new optical and infrared data to detect the signal of the planet companion. Methods: We fitted the RV variations of TW Hya using a cool spot model. In addition, we obtained new high-resolution optical & infrared spectra, together with optical photometry of TW Hya and compared them with previous data. Results: Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54° can reproduce the reported RV variations. The model also predicts a bisector semi-amplitude variation <10 m s[SUP]-1[/SUP], which is less than the errors of the RV measurements discussed in Setiawan et al. (2008, Nature, 451, 38). The analysis of our new optical RV data, with typical errors of 10 m s[SUP]-1[/SUP], shows a larger RV amplitude that varies depending on the correlation mask used. A slight correlation between the RV variation and the bisector is also observed although not at a very significant level. The infrared H-band RV curve is almost flat, showing a small variation (<35 m s[SUP]-1[/SUP]) that is not consistent with the published optical orbit. All these results support the spot scenario rather than the presence of a hot Jupiter. Finally, the photometric data shows a 20% (peak to peak) variability, which is much larger than the 4% variation expected for the modeled cool spot. The fact that the optical data are correlated with the surface of the cross-correlation function points towards hot spots as being responsible for the photometric variability. Conclusions: We conclude that the best explanation for the RV signal observed in TW Hya is the presence of a cool stellar spot and not an orbiting hot Jupiter. Based on observations taken at the VLT (Paranal), under programs 280.C-5064(A) and 075.C-0202(A), and with the CORALIE spectrograph and EulerCAM both at the Euler Swiss telescope (La Silla). [less ▲]

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See detailErratum to "Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b"
Gillon, Michaël ULg; Demory, B*-O; Barman, T. et al

in Astronomy and Astrophysics (2008), 490

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See detailVSI: the VLTI spectro-imager
Malbet, F.; Buscher, D.; Weigelt, G. et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at ... [more ▼]

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R = 12000. Targets as faint as K = 13 will be imaged without requiring a brighter nearby reference object; fainter targets can be accessed if a suitable reference is available. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysics. The high level specifications of the instrument are derived from a detailed science case based on the capability to obtain, for the first time, milliarcsecond-resolution images of a wide range of targets including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return. [less ▲]

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See detailProspects for near-infrared characterisation of hot Jupiters with the VLTI Spectro-Imager (VSI)
Renard, Stéphanie; Absil, Olivier ULg; Berger, J.-P. et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

In this paper, we study the feasibility of obtaining near-infrared spectra of bright extrasolar planets with the 2nd generation VLTI Spectro-Imager instrument (VSI), which has the required angular ... [more ▼]

In this paper, we study the feasibility of obtaining near-infrared spectra of bright extrasolar planets with the 2nd generation VLTI Spectro-Imager instrument (VSI), which has the required angular resolution to resolve nearby hot Extrasolar Giant Planets (EGPs) from their host stars. Taking into account fundamental noises, we simulate closure phase measurements of several extrasolar systems using four 8-m telescopes at the VLT and a low spectral resolution (R = 100). Synthetic planetary spectra from T. Barman are used as an input. Standard chi[SUP]2[/SUP]-fitting methods are then used to reconstruct planetary spectra from the simulated data. These simulations show that low-resolution spectra in the H and K bands can be retrieved with a good fidelity for half a dozen targets in a reasonable observing time (about 10 hours, spread over a few nights). Such observations would strongly constrain the planetary temperature and albedo, the energy redistribution mechanisms, as well as the chemical composition of their atmospheres. Systematic errors, not included in our simulations, could be a serious limitation to these performance estimations. The use of integrated optics is however expected to provide the required instrumental stability (around 10[SUP]-4[/SUP] on the closure phase) to enable the first thorough characterisation of extrasolar planetary emission spectra in the near-infrared. [less ▲]

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See detailCharacterization of the hot Neptune GJ 436 b with Spitzer and ground-based observations
Demory, B*-O; Gillon, Michaël ULg; Barman, T. et al

in Astronomy and Astrophysics (2007), 475

We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ 436 b. The observations were obtained using the 8-mum band of the InfraRed Array Camera (IRAC). The data ... [more ▼]

We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ 436 b. The observations were obtained using the 8-mum band of the InfraRed Array Camera (IRAC). The data spanning the predicted time of secondary eclipse show a clear flux decrement with the expected shape and duration. The observed eclipse depth of 0.58 mmag allows us to estimate a blackbody brightness temperature of T[SUB]p[/SUB] = 717 ± 35 K at 8 mum. We compare this infrared flux measurement to a model of the planetary thermal emission, and show that this model reproduces properly the observed flux decrement. The timing of the secondary eclipse confirms the non-zero orbital eccentricity of the planet, while also increasing its precision (e = 0.14 ± 0.01). Additional new spectroscopic and photometric observations allow us to estimate the rotational period of the star and to assess the potential presence of another planet. Our final secondary eclipse, photometric and Ca II H+K index time series are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/1125 [less ▲]

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See detailThe HARPS search for southern extra-solar planets. X. A m sin i = 11 M_â planet around the nearby spotted M dwarf <ASTROBJ>GJ 674</ASTROBJ>
Bonfils, X.; Mayor, M.; Delfosse, X. et al

in Astronomy and Astrophysics (2007), 474

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars that are significantly more massive or less ... [more ▼]

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars that are significantly more massive or less massive than the Sun, and in particular our radial velocity search for planets around very low-mass stars. Methods: As part of that program, we obtained measurements of <ASTROBJ>GJ 674</ASTROBJ>, an M 2.5 dwarf at d = 4.5 pc. These measurements have dispersion much in excess of their internal errors. An intensive observing campaign demonstrates that the excess dispersion is due to two superimposed coherent signals, with periods of 4.69 and 35 days. Results: These data are described well by a 2-planet Keplerian model where each planet has a ~11 M_â minimum mass. A careful analysis of the (low-level) magnetic activity of <ASTROBJ>GJ 674</ASTROBJ>, however, demonstrates that the 35-day period coincides with the stellar rotation period. This signal therefore originates in a spot inhomogeneity modulated by stellar rotation. The 4.69-day signal, on the other hand, is caused by a bona-fide planet, <ASTROBJ>GJ 674b</ASTROBJ>. Conclusions: Its detection adds to the growing number of Neptune-mass planets around M-dwarfs and reinforces the emerging conclusion that this mass domain is much more populated than the Jovian mass range. We discuss the metallicity distributions of M dwarf with and without planets and find a low 11% probability that they are drawn from the same parent distribution. Moreover, we find tentative evidence that the host star metallicity correlates with the total mass of their planetary system. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope under the GTO program ID 072.C-0488 at Cerro La Silla (Chile). Radial-velocity, photometric and Ca II H+K index time series are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strabg.fr/cgi-bin/qcat?J/A+A/474/293 [less ▲]

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