arXiv subjects

R. Alonso

Publications and source records attributed to R. Alonso.

190 records · Page 11Linked to original sources

arXiv2008

Transiting exoplanets from the CoRoT space mission III. The spectroscopic transit of CoRoT-Exo-2b with SOPHIE and HARPS

We report on the spectroscopic transit of the massive hot-Jupiter CoRoT-Exo-2b observed with the high-precision spectrographs SOPHIE and HARPS. By modeling the radial velocity anomaly occurring during the transit due to the Rossiter-McLaughlin (RM) effect, we determine the sky-projected angle between the stellar spin and the planetary orbital axis to be close to zero lambda=7.2+-4.5 deg, and we secure the planetary nature of CoRoT-Exo-2b. We discuss the influence of the stellar activity on the RM modeling. Spectral analysis of the parent star from HARPS spectra are presented.

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arXiv2007

HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit

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 independant 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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arXiv2007

Pulsational frequencies of the eclipsing delta-Scuti star HD 172189

The eclipsing delta-Scuti star HD 172189 is a probable member of the open cluster IC 4756 and a promising candidate target for the CoRoT mission. The detection of pulsation modes is the first step in the asteroseismological study of the star. Further, the calculation of the orbital parameters of the binary system allows us to make a dynamical determination of the mass of the star, which works as an important constraint to test and calibrate the asteroseismological models. From a detailed frequency analysis of 210 hours of photometric data of HD 172189 obtained from the STEPHI XIII campaign we have identified six pulsation frequencies with a confidence level of 99% and a seventh with a 65% confidence level in the range between 100-300 uHz. In addiction, three eclipses were observed during the campaign, allowing us to improve the determination of the orbital period of the system.

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arXiv2007

TRUFAS, a wavelet based algorithm for the rapid detection of planetary transits

Aims: We describe a fast, robust and automatic detection algorithm, TRUFAS, and apply it to data that are being expected from the CoRoT mission. Methods: The procedure proposed for the detection of planetary transits in light curves works in two steps: 1) a continuous wavelet transformation of the detrended light curve with posterior selection of the optimum scale for transit detection, and 2) a period search in that selected wavelet transformation. The detrending of the light curves are based on Fourier filtering or a discrete wavelet transformation. TRUFAS requires the presence of at least 3 transit events in the data. Results: The proposed algorithm is shown to identify reliably and quickly the transits that had been included in a standard set of 999 light curves that simulate CoRoT data. Variations in the pre-processing of the light curves and in the selection of the scale of the wavelet transform have only little effect on TRUFAS' results. Conclusions: TRUFAS is a robust and quick transit detection algorithm, especially well suited for the analysis of very large volumes of data from space or ground-based experiments, with long enough durations for the target-planets to produce multiple transit events.

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arXiv2006

Detecting false alarms in transit data from space: Rejection methods tested in Corot Blind Test 2

Transit searches provide a large number of planet candidates. Before attempting follow-up observations, the best effort should be spent in classifying the light-curves, rejecting false alarms and selecting the most likely ones for real planets. A number of analysis tools has been developed with these objectives. Here, we apply such tools to 237 simulated multi-color light-curves from CoRoT Blind Test 2, which contain simulated planet transits and several configurations of impostors. Their comparison gives indications of the various tools' classification and false-alarm rejection capabilities. In order to arrive at the candidate identifications, we used an automated scheme of weighted punctuations assigned to the individual tests, which avoids that results from a single test dominate a candidate's classification.

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arXiv2005

The double-mode nature of the HADS star GSC 00144-03031 and the Petersen diagram of the class

The double--mode pulsation of GSC 00144-03031 has been detected when searching for COROT targets. A very large dataset composed of 4722 photometric measurements was collected at six observatories in Europe and America. There is no hint of the excitation of additional modes (down to 0.6 mmag) and therefore GSC 00144-03031 seems to be a pure double--mode pulsator, with a very short fundamental radial mode (P=84 min). From Stromgren photometry and evolutionary tracks it appears to be a Pop. I star with M=1.75 solar masses, located in the middle of the instability strip, close to the Zero--Age Main Sequence. We also discovered other new double--mode pulsators in the databases of large--scale projects: OGLE BW2_V142, OGLE BW1_V207, ASAS3 094303-1707.3, ASAS3 000116-6037.0, NSVS 3234596 and NSVS 3324715. An observational Petersen diagram is presented and explained by means of new models. A common sequence connecting Pop. I stars from the shortest to the longest periods is proposed and the spreads in the period ratios are ascribed to different metallicities (at the shortest periods) and to different masses (at the longest ones). The paper is based on data collected at S. Pedro Martir and Sierra Nevada Observatories and on the contributions from several amateur astronomers.

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arXiv2005

A New Detached M Dwarf Eclipsing Binary

We describe a newly-discovered detached M-dwarf eclipsing binary system, the fourth such system known. This system was first observed by the TrES network during a long term photometry campaign of 54 nights. Analysis of the folded light curve indicates two very similar components orbiting each other with a period of 1.12079 +/- 0.00001 days. Spectroscopic observations with the Hobby-Eberly Telescope show the system to consist of two M3e dwarfs in a near-circular orbit. Double-line radial velocity amplitudes, combined with the orbital inclination derived from light-curve fitting, yield Mass total = 0.983 +/- 0.007 solar masses, with component masses M(1) = 0.493 +/- 0.003 and M(2) = 0.489 +/- 0.003 solar masses. The light-curve fit yields component radii of R(1) = 0.453 +/- 0.060 and R(2) = 0.452 +/- 0.050 solar radii. Though a precise parallax is lacking, broadband VJHK colors and spectral typing suggest component absolute magnitudes of M_V(1) = 11.18 +/- 0.30 and M_V(2) = 11.28 +/- 0.30.

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arXiv2005

Preparing the COROT space mission: new variable stars in the galactic Anticenter direction

The activities related to the preparation of the asteroseismic, photometric space mission COROT are described. Photoelectric observations, wide--field CCD photometry, uvbyB calibrations and further time--series have been obtained at different observatories and telescopes. They have been planned to complete the COROT programme in the direction of the galactic Anticenter. In addition to suitable asteroseismic targets covering the different evolutionary stages between ZAMS and TAMS, we discovered several other variable stars, both pulsating and geometrical. We compared results on the incidence of variability in the galactic Center and Anticenter directions. Physical parameters have been obtained and evolutionary tracks fitting them have been calculated. The peculiarities of some individual stars alre pointed out. Paper based on observations collected at the San Pedro Martir, Sierra Nevada, Teide, La Silla, Haute-Provence and Roque de Los Muchachos (Telescopio Nazionale Galileo and Mercator telescopes) observatories.

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arXiv2004

A Prototype for the PASS Permanent All Sky Survey

A prototype system for the Permanent All Sky Survey (PASS) project is presented. PASS is a continuous photometric survey of the entire celestial sphere with a high temporal resolution. Its major objectives are the detection of all giant-planet transits (with periods up to some weeks) across stars up to mag 10.5, and to deliver continuously photometry that is useful for the study of any variable stars. The prototype is based on CCD cameras with short focal length optics on a fixed mount. A small dome to house it at Teide Observatory, Tenerife, is currently being constructed. A placement at the antarctic Dome C is also being considered. The prototype will be used for a feasibility study of PASS, to define the best observing strategies, and to perform a detailed characterization of the capabilities and scope of the survey. Afterwards, a first partial sky surveying will be started with it. That first survey may be able to detect transiting planets during its first few hundred hours of operation. It will also deliver a data set around which software modules dealing with the various scientific objectives of PASS will be developed. The PASS project is still in its early phase and teams interested in specific scientific objectives, in providing technical expertise, or in participating with own observations are invited to collaborate.

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arXiv2003

Preparing the COROT space mission: incidence and characterisation of pulsation in the Lower Instability Strip

By pursuing the goal to find new variables in the COROT field-of-view we characterised a sample of stars located in the lower part of the instability strip. Our sample is composed of stars belonging to the disk population in the solar neighbourhood. We found that 23% of the stars display multiperiodic light variability up to few mmag of amplitude. uvbyBeta photometry fixed most of the variables in the middle of the instability strip and high-resolution spectroscopy established that they have vsin i>100 km/s. The comparison with delta Sct stars in the whole Galaxy shows slightly different features, i.e., most delta Sct stars have a 0.05-mag redder (b-y)_0 index and lower vsin i values. Additional investigation in the open cluster NGC 6633 confirms the same incidence of variability, i.e., around 20%. The wide variety of pulsational behaviours of delta Sct stars (including unusual objects such as a variable beyond the blue edge or a rapidly rotating high-amplitude pulsator) makes them very powerful asteroseismic tools to be used by COROT. Being quite common among bright stars, delta Sct stars are suitable targets for optical observations from space.

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