WASP-22 b: A transiting "hot Jupiter" planet in a hierarchical triple system

in Astronomical Journal (The) (2010), 140(6), 2007-2012

We report the discovery of a transiting planet orbiting the star TYC 6446-326-1. The star, WASP-22, is a moderately bright (V=12.0) solar-type star (T_eff = 6000 +/- 100K, [Fe/H]= -0.05 \pm 0.08). The ... [more ▼]

We report the discovery of a transiting planet orbiting the star TYC 6446-326-1. The star, WASP-22, is a moderately bright (V=12.0) solar-type star (T_eff = 6000 +/- 100K, [Fe/H]= -0.05 \pm 0.08). The lightcurve of the star obtained with the WASP-South instrument shows periodic transit-like features with a depth of about 1% and a duration of 0.14d. The presence of a transit-like feature in the lightcurve is confirmed using z-band photometry obtained with Faulkes Telescope South. High resolution spectroscopy obtained with the CORALIE and HARPS spectrographs confirm the presence of a planetary mass companion with an orbital period of 3.533d in a near-circular orbit. From a combined analysis of the spectroscopic and photometric data assuming that the star is a typical main-sequence star we estimate that the planet has a mass M_p = (0.56 +/- 0.02)M_Jup and a radius R_p = (1.12 +/- 0.04)R_Jup. In addition, there is a linear trend of 40m/s/y in the radial velocities measured over 16 months, from which we infer the presence of a third body with a long period orbit in this system. The companion may be a low mass M-dwarf or a second planet. [less ▲]

A transiting giant planet with a temperature between 250K and 430K

in Nature (2010), 464

Of the over 400 known exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their ... [more ▼]

Of the over 400 known exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their atmospheres. Some short-period planets, including the first terrestrial exoplanet (CoRoT-7b), have been discovered using a space mission designed to find smaller and more distant planets than can be seen from the ground. Here we report transit observations of CoRoT-9b, which orbits with a period of 95.274days on a low eccentricity of 0.11+/-0.04 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a `temperate' photospheric temperature estimated to be between 250 and 430K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models with an inferred interior composition consistent with that of Jupiter and Saturn. [less ▲]

Wasp-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit

in Astrophysical Journal (2010), 709

We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses, but 1.5-2 Jupiter radii, giving a density of 6%-14% that of Jupiter. WASP ... [more ▼]

We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses, but 1.5-2 Jupiter radii, giving a density of 6%-14% that of Jupiter. WASP-17b is in a 3.7 day orbit around a sub-solar metallicity, V = 11.6, F6 star. Preliminary detection of the Rossiter-McLaughlin effect suggests that WASP-17b is in a retrograde orbit (λ â â 150°), indicative of a violent history involving planet-planet or star-planet scattering. WASP-17b's bloated radius could be due to tidal heating resulting from recent or ongoing tidal circularization of an eccentric orbit, such as the highly eccentric orbits that typically result from scattering interactions. It will thus be important to determine more precisely the current orbital eccentricity by further high-precision radial velocity measurements or by timing the secondary eclipse, both to reduce the uncertainty on the planet's radius and to test tidal-heating models. Owing to its low surface gravity, WASP-17b's atmosphere has the largest scale height of any known planet, making it a good target for transmission spectroscopy. Based in part on data collected with the HARPS spectrograph at ESO La Silla Observatory under programme ID 081.C-0388(A). [less ▲]

WASP-17b: an ultra-low density planet in a probable retrograde orbit

in Astrophysical Journal (2010), 709(1), 159-167

We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses but 1.5-2 Jupiter radii, giving a density of 6-14 per cent that of Jupiter ... [more ▼]

We report the discovery of the transiting giant planet WASP-17b, the least-dense planet currently known. It is 1.6 Saturn masses but 1.5-2 Jupiter radii, giving a density of 6-14 per cent that of Jupiter. WASP-17b is in a 3.7-day orbit around a sub-solar metallicity, V = 11.6, F6 star. Preliminary detection of the Rossiter-McLaughlin effect suggests that WASP-17b is in a retrograde orbit (lambda ~ -150 deg), indicative of a violent history involving planet-planet or planet-star scattering. WASP-17b's bloated radius could be due to tidal heating resulting from recent or ongoing tidal circularisation of an eccentric orbit, such as the highly eccentric orbits that typically result from scattering interactions. It will thus be important to determine more precisely the current orbital eccentricity by further high-precision radial velocity measurements or by timing the secondary eclipse, both to reduce the uncertainty on the planet's radius and to test tidal-heating models. Owing to its low surface gravity, WASP-17b's atmosphere has the largest scale height of any known planet, making it a good target for transmission spectroscopy. [less ▲]

The CoRoT-7 planetary system: two orbiting super-Earths

in Astronomy and Astrophysics (2009), 506

We report on an intensive observational campaign carried out with HARPS at the 3.6 m telescope at La Silla on the star CoRoT-7. Additional simultaneous photometric measurements carried out with the Euler ... [more ▼]

We report on an intensive observational campaign carried out with HARPS at the 3.6 m telescope at La Silla on the star CoRoT-7. Additional simultaneous photometric measurements carried out with the Euler Swiss telescope have demonstrated that the observed radial velocity variations are dominated by rotational modulation from cool spots on the stellar surface. Several approaches were used to extract the radial velocity signal of the planet(s) from the stellar activity signal. First, a simple pre-whitening procedure was employed to find and subsequently remove periodic signals from the complex frequency structure of the radial velocity data. The dominant frequency in the power spectrum was found at 23 days, which corresponds to the rotation period of CoRoT-7. The 0.8535 day period of CoRoT-7b planetary candidate was detected with an amplitude of 3.3 m s[SUP]-1[/SUP]. Most other frequencies, some with amplitudes larger than the CoRoT-7b signal, are most likely associated with activity. A second approach used harmonic decomposition of the rotational period and up to the first three harmonics to filter out the activity signal from radial velocity variations caused by orbiting planets. After correcting the radial velocity data for activity, two periodic signals are detected: the CoRoT-7b transit period and a second one with a period of 3.69 days and an amplitude of 4 m s[SUP]-1[/SUP]. This second signal was also found in the pre-whitening analysis. We attribute the second signal to a second, more remote planet CoRoT-7c . The orbital solution of both planets is compatible with circular orbits. The mass of CoRoT-7b is 4.8±0.8 (M[SUB]â [/SUB]) and that of CoRoT-7c is 8.4± 0.9 (M[SUB]â [/SUB]), assuming both planets are on coplanar orbits. We also investigated the false positive scenario of a blend by a faint stellar binary, and this may be rejected by the stability of the bisector on a nightly scale. According to their masses both planets belong to the super-Earth planet category. The average density of CoRoT-7b is Ï =5.6± 1.3 g cm[SUP]-3[/SUP], similar to the Earth. The CoRoT-7 planetary system provides us with the first insight into the physical nature of short period super-Earth planets recently detected by radial velocity surveys. These planets may be denser than Neptune and therefore likely made of rocks like the Earth, or a mix of water ice and rocks. Based on observations made with HARPS spectrograph on the 3.6-m ESO telescope and the EULER Swiss telescope at La Silla Observatory, Chile. The HARPS results presented in this paper (Appendix A) are available in electronic form at http://www.aanda.org and 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/506/303 [less ▲]

WASP-16b: A New Jupiter-Like Planet Transiting a Southern Solar Analog

in Astrophysical Journal (2009), 703

We report the discovery from WASP-South of a new Jupiter-like extrasolar planet, WASP-16b, which transits its solar analog host star every 3.12 days. Analysis of the transit photometry and radial velocity ... [more ▼]

We report the discovery from WASP-South of a new Jupiter-like extrasolar planet, WASP-16b, which transits its solar analog host star every 3.12 days. Analysis of the transit photometry and radial velocity spectroscopic data leads to a planet with R [SUB]p[/SUB] = 1.008 ± 0.071 R [SUB]Jup[/SUB] and M [SUB]p[/SUB] = 0.855 ± 0.059 M [SUB]Jup[/SUB], orbiting a host star with R [SUB]*[/SUB] = 0.946 ± 0.054 R [SUB]sun[/SUB] and M [SUB]*[/SUB] = 1.022 ± 0.101 M [SUB]sun[/SUB]. Comparison of the high resolution stellar spectrum with synthetic spectra and stellar evolution models indicates the host star is a near-solar metallicity ([Fe/H] =0.01 ± 0.10) solar analog (T [SUB]eff[/SUB] = 5700 ± 150 K and log g = 4.5 ± 0.2) of intermediate age (tau = 2.3[SUP]+5.8[/SUP] [SUB]--2.2[/SUB] Gyr). [less ▲]

Discovery and characterization of WASP-6b, an inflated sub-Jupiter mass planet transiting a solar-type star

in Astronomy and Astrophysics (2009), 501

We report the discovery of WASP-6b, an inflated sub-Jupiter mass planet transiting every 3.3610060[SUP]+ 0.0000022 [/SUP][SUB]- 0.0000035 [/SUB] days a mildly metal-poor solar-type star of magnitude V ... [more ▼]

We report the discovery of WASP-6b, an inflated sub-Jupiter mass planet transiting every 3.3610060[SUP]+ 0.0000022 [/SUP][SUB]- 0.0000035 [/SUB] days a mildly metal-poor solar-type star of magnitude V = 11.9. A combined analysis of the WASP photometry, high-precision followup transit photometry and radial velocities yield a planetary mass M[SUB]p[/SUB] = 0.503[SUP]+0.019[/SUP][SUB]-0.038[/SUB] M[SUB]J[/SUB] and radius R[SUB]p[/SUB] = 1.224[SUP]+0.051[/SUP][SUB]-0.052[/SUB] R_J, resulting in a density rho[SUB]p[/SUB] = 0.27 ± 0.05 rho_J. The mass and radius for the host star are M_ast = 0.88[SUP]+0.05[/SUP][SUB]-0.08[/SUB] M_o and R_ast = 0.870[SUP]+0.025[/SUP][SUB]-0.036[/SUB] R_o. The non-zero orbital eccentricity e = 0.054^+0.018[SUB]-0.015[/SUB] that we measure suggests that the planet underwent a massive tidal heating 1 Gyr ago that could have contributed to its inflated radius. High-precision radial velocities obtained during a transit allow us to measure a sky-projected angle between the stellar spin and orbital axis beta = 11[SUP]+14[/SUP][SUB]-18[/SUB] deg. In addition to similar published measurements, this result favors a dominant migration mechanism based on tidal interactions with a protoplanetary disk. Based on data collected with the HARPS spectrograph at ESO La Silla Observatory in the programs 082.C-0040(E) and 082.C-0608. The photometric time-series and radial velocities (Tables 4, 5) used in this work are only 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/501/785 [less ▲]

The HARPS search for southern extra-solar planets. XIV. Gl 176b, a super-Earth rather than a Neptune, and at a different period

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 ▲]

TW ;Hydrae: evidence of stellar spots instead of a Hot Jupiter

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 ▲]

WASP-5b: a dense, very hot Jupiter transiting a 12th-mag Southern-hemisphere star

in Monthly Notices of the Royal Astronomical Society (2008), 387

We report the discovery of WASP-5b, a Jupiter-mass planet orbiting a 12th-mag G-type star in the Southern hemisphere. The 1.6-d orbital period places WASP-5b in the class of very hot Jupiters and leads to ... [more ▼]

We report the discovery of WASP-5b, a Jupiter-mass planet orbiting a 12th-mag G-type star in the Southern hemisphere. The 1.6-d orbital period places WASP-5b in the class of very hot Jupiters and leads to a predicted equilibrium temperature of 1750K. WASP-5b is the densest of any known Jovian-mass planet, being a factor of 7 denser than TrES-4, which is subject to similar stellar insolation, and a factor of 3 denser than WASP-4b, which has a similar orbital period. We present transit photometry and radial velocity measurements of WASP-5 (= USNO-B10487-0799749), from which we derive the mass, radius and density of the planet: M[SUB]P[/SUB] = 1.58[SUP]+0.13[/SUP][SUB]-0.08[/SUB]M[SUB]J[/SUB],R[SUB]P[/SUB] = 1.090[SUP]+0.094[/SUP][SUB]-0.058[/SUB]R[SUB]J[/SUB] and rho[SUB]P[/SUB] = 1.22[SUP]+0.19[/SUP][SUB]-0.24[/SUB]rho[SUB]J[/SUB]. The orbital period is P = 1.6284296[SUP]+0.0000048[/SUP][SUB]-0.0000037[/SUB]d and the mid-transit epoch is T[SUB]C[/SUB](HJD) = 2454375.62466[SUP]+0.00026[/SUP][SUB]-0.00025[/SUB]. [less ▲]