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HD 17156
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Title: Characterisation of the HD 17156 planetary system
Authors: M. Barbieri, R. Alonso, S. Desidera, A. Sozzetti, A.F. Martinez Fiorenzano, J. M. Almenara, M. Cecconi, R.U. Claudi, D. Charbonneau, M. Endl, V. Granata, R. Gratton, G. Laughlin, B. Loeillet

AIMS : To improve the parameters of the HD 17156 system (peculiar due to the eccentric and long orbital period of its transiting planet) and constrain the presence of stellar companions.
METHODS : Photometric data were acquired for 4 transits, and high precision radial velocity measurements were simultaneously acquired with SARG@TNG for one transit. The template spectra of HD 17156 was used to derive effective temperature, gravity, and metallicity. A fit of the photometric and spectroscopic data was performed to measure the stellar and planetary radii, and the spin-orbit alignment. Planet orbital elements and ephemeris were derived from the fit. Near infrared adaptive optic images was acquired with ADOPT@TNG.
RESULTS: We have found that the star has a radius of R_S = 1.430.03 R_sun and the planet R_P =1.020.08 R_jup. The transit ephemeris is T_c = 2454\756.731340.00020+N*21.216630.00045 BJD. The analysis of the Rossiter-Mclaughlin effect shows that the system is spin orbit aligned with an angle lambda = 4.8 5.3 deg. The analysis of high resolution images has not revealed any stellar companion with projected separation between 150 and 1000 AU from HD 17156.

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RE: HD17156b
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Title: Constraining Orbital Parameters Through Planetary Transit Monitoring
Authors: Stephen R. Kane, Kaspar von Braun

The orbital parameters of extra-solar planets have a significant impact on the probability that the planet will transit the host star. This was recently demonstrated by the transit detection of HD 17156b whose favourable eccentricity and argument of periastron dramatically increased its transit likelihood. We present a study which provides a quantitative analysis of how these two orbital parameters affect the geometric transit probability as a function of period. Further, we apply these results to known radial velocity planets and show that there are unexpectedly high transit probabilities for planets at relatively long periods. For a photometric monitoring campaign which aims to determine if the planet indeed transits, we calculate the expected transiting planet yield and the significance of a potential null result, as well as the subsequent constraints that may be applied to orbital parameters.

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Title: Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit
Authors: M. Gillon (1, 2), A. H. M. J. Triaud (1), M. Mayor (1), D. Queloz (1), S. Udry (1), P. North (3) ((1) Observatoire de Geneve, Sauverny, Switzerland; (2) Institut d'Astrophysique et de Geophysique, Universite de Liege, Liege, Belgium; (3) Laboratoire d'Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire de Sauverny, Versoix, Switzerland)
(Version v3)

We report high-precision transit photometry for the recently detected planet HD 17156b. Using these new data with previously published transit photometry and radial velocity measurements, we perform a combined analysis based on a Markov Chain Monte Carlo approach. The resulting mass M_p = 3.09 (+0.22-0.17) M_Jup and radius R_p = 1.23 (+0.17-0.20) R_Jup for the planet places it at the outer edge of the density distribution of known transiting planets with rho_p = 1.66 (+1.37-0.60) rho_Jup. The obtained transit ephemeris is T_tr = 2454438.48271 (+0.00077-0.00057) + N x 21.21747 (+0.00070-0.00067) BJD. The derived plausible tidal circularisation time scales for HD 17156b are larger than the age of the host star. The measured high orbital eccentricity e = 0.6719 (+0.0052-0.0063) can thus not be interpreted as the clear sign of the presence of another body in the system.

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RE: HD17156c
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Title: Orbital Dynamics Of A Second Planet In HD17156
Authors: Donald Short, William F. Welsh, Jerome A. Orosz, Gur Windmiller

In this letter we report the possible existence of a second planet in the transiting extrasolar planet system HD17156 and its interactive dynamics with the previously known planet. The analysis is achieved through the POFP optimisation software which is based on a full integration of the system's multiple-body Newtonian equations of motion. The two-planet solution yields a significantly improved fit to the previously published radial velocities. The two planets are strongly interacting and exchange angular momentum, yet remain stable as they mutually excite orbital eccentricities and periastron advances.

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HD 17156b
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Title: A Possible Spin-Orbit Misalignment in the Transiting Eccentric Planet HD 17156b
Authors: Norio Narita, Bun'ei Sato, Osamu Ohshima, Joshua N. Winn

We present simultaneous photometric and spectroscopic observations of HD 17156b spanning a transit on UT 2007 November 12. This system is of special interest because of its 21-day period (unusually long for a transiting planet) and its high orbital eccentricity of 0.67. By modelling the Rossiter-McLaughlin effect, we find the angle between the sky projections of the orbital axis and the stellar rotation axis to be 62 25. Such a large spin-orbit misalignment, as well as the large eccentricity, could be explained as the relic of a previous gravitational interaction with other planets or with a binary companion star.

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HD 17156

Position(2000): RA 02h 49m 44.487s +71 45' 11.64''

V=8.15
Spectral type: G5
G0V

The ephemeris table for transits

HD 17156.kmz
Google Sky file (2kb, kmz)

-- Edited by Blobrana at 15:06, 2008-01-12

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Title: Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit
Authors: M. Gillon (1, 2), A. H. M. J. Triaud (1), M. Mayor (1), D. Queloz (1), S. Udry (1), P. North (3) ((1) Observatoire de Geneve, Sauverny, Switzerland; (2) Institut d'Astrophysique et de Geophysique, Universite de Liege, Liege, Belgium; (3) Laboratoire d'Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire de Sauverny, Versoix, Switzerland)

We report here high-precision transit photometry for the recently detected planet HD 17156b. Using these new data with previously published transit photometry and radial velocity measurements, we perform a combined analysis based on a Markov Chain Monte Carlo approach. The resulting mass M_p = 3.111 (+0.035-0.013) M_Jup and radius R_p = 0.964 (+0.016-0.027) R_Jup for the planet places it at the outer edge of the density distribution of known transiting planets with a density = 3.47 (+0.35-0.18) Jupiter's one. The obtained transit ephemeris is T_tr = 2454438.4835 (+0.0009-0.0025) + N 21.21725 (+0.00048-0.00043) BJD. The derived plausible tidal circularisation time scales for HD 17156b are larger than the age of the host star. The measured high orbital eccentricity e = 0.6717 (+0.0028-0.0027) can thus not be interpreted as the clear sign of the presence of another body in the system.

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RE: HD17156b
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An international network of astronomers has announced one of the most impressive discoveries ever made that involves amateurs. The group has found an extrasolar planet that crosses the face of its host star, an event known as a transit. Better yet, this object is unlike any of the 28 other known transiting exoplanets, and follow-up observations will yield precious insights into the diversity of planets throughout our galaxy.

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Transits of HD 17156b have been confirmed.
The Sep. 9/10, 2007 transit of HD 17156 was observed by Transitsearch.org participants C. Lopresti and D. Gasparri from Italy, and by J. Almenara of the IAC in the Canary Islands. Analysis of the data was led by M. Barbieri and R. Alonso of LAM, Marseille, France.
On Sep 30/ Oct 1, the transit was confirmed by W. Welsh, A. Rajan, J. Irwin, P. Nutzman, and D. Charbonneau, and by Transitsearch.org participant D. Davies. A discovery paper, Barbieri et al. 2007 (157 KB) has been submitted for publication in the journal Astronomy and Astrophysics. With an orbital period of 21.22 days and an orbital eccentricity of e=0.67, HD 17156b has both the longest period and highest eccentricity of any known transiting extrasolar planet. It is also the first transit to be discovered under the auspices of Transitsearch.org.

transitsearch.org

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Title: HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit
Authors: M. Barbieri, R. Alonso, G. Laughlin, J. M. Almenara, R. Bissinger, D. Davies, D. Gasparri, E. Guido, C. Lopresti, F. Manzini, G. Sostero

We report the detection of transits by the 3.1 M_Jup companion to the V=8.17 G0V star HD 17156. The transit was observed by three independent observers on Sept. 9/10, 2007 (two in central Italy and one in the Canary Islands), who obtained detections at confidence levels of 3.0 sigma, 5.3 sigma, and 7.9 sigma, respectively. The observations were carried out under the auspices of the Transitsearch.org network, which organizes follow-up photometric transit searches of known planet-bearing stars during the time intervals when transits are expected to possibly occur. Analyses of the 7.9 sigma data set indicates a transit depth d=0.0062 0.0004, and a transit duration t=186 5 min. These values are consistent with the transit of a Jupiter-sized planet with an impact parameter b=a*cos(i)/R_star ~ 0.8. This planet occupies a unique regime among known transiting extrasolar planets, both as a result of its large orbital eccentricity (e=0.67) and long orbital period (P=21.2 d). The planet receives a 26-fold variation in insolation during the course of its orbit, which will make it a useful object for characterization of exoplanetary atmospheric dynamics.

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