Conny Aerts

Automated supervised classification of variable stars in the CoRoT programme. Method and application to the first four exoplanet fields

Context: Aims: In this work, we describe the pipeline for the fast supervised classification of light curves observed by the CoRoT exoplanet CCDs. We present the classification results obtained for the first four measured fields, which represent a one-year in-orbit operation. Methods: The basis of the adopted supervised classification methodology has been described in detail in a previous paper, as is its application to the OGLE database. Here, we present the modifications of the algorithms and of the training set to optimize the performance when applied to the CoRoT data. Results: Classification results are presented for the observed fields IRa01, SRc01, LRc01, and LRa01 of the CoRoT mission. Statistics on the number of variables and the number of objects per class are given and typical light curves of high-probability candidates are shown. We also report on new stellar variability types discovered in the CoRoT data. The full classification results are publicly available. The CoRoT space mission, launched on 27 December 2006, has been developed and is operated by the CNES, with the contribution of Austria, Belgium, Brazil , ESA, Germany, and Spain. The full classification results will be 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/506/519

Automated supervised classification of variable stars II. Application to the OGLE database

Context. Scientific exploitation of large variability databases can only be fully optimized if these archives contain, besides the actual observations, annotations about the variability class of the objects they contain. Supervised classification of observations produces these tags, and makes it possible to generate refined candidate lists and catalogues suitable for further investigation. Aims. We aim to extend and test the classifiers presented in a previous work against an independent dataset. We complement the assessment of the validity of the classifiers by applying them to the set of OGLE light curves treated as variable objects of unknown class. The results are compared to published classification results based on the so-called extractor methods. Methods. Two complementary analyses are carried out in parallel. In both cases, the original time series of OGLE observations of the Galactic bulge and Magellanic Clouds are processed in order to identify and characterize the frequency components. In the first approach, the classifiers are applied to the data and the results analyzed in terms of systematic errors and differences between the definition samples in the training set and in the extractor rules. In the second approach, the original classifiers are extended with colour information and, again, applied to OGLE light curves. Results. We have constructed a classification system that can process huge amounts of time series in negligible time and provide reliable samples of the main variability classes. We have evaluated its strengths and weaknesses and provide potential users of the classifier with a detailed description of its characteristics to aid in the interpretation of classification results. Finally, we apply the classifiers to obtain object samples of classes not previously studied in the OGLE database and analyse the results. We pay specific attention to the B-stars in the samples, as their pulsations are strongly dependent on metallicity.

Orbital parameters, masses and distance to β Centauri determined with the Sydney University Stellar: Interferometer and high-resolution spectroscopy

The bright southern binary star β Centauri (HR 5267) has been observed with the Sydney University Stellar Interferometer (SUSI) and spectroscopically with the European Southern Observatory Coude Auxiliary Telescope and Swiss Euler telescope at La Silla. The interferometric observations have confirmed the binary nature of the primary component and have enabled the determination of the orbital parameters of the system. At the observing wavelength of 442 nm the two components of the primary system have a magnitude difference of 0.15 ± 0.02. The combination of interferometric and spectroscopic data gives the following results: orbital period 357.00 ± 0.07 d, semimajor axis 25.30 ± 0.19 mas, inclination 67. ◦ 4 ± 0. ◦ 3, eccentricity 0.821 ± 0.003, distance 102.3 ± 1.7 pc, primary and secondary masses M 1 = ( ◦ )( ◦ ) .

Maximum mass-loss rates of line-driven winds of massive stars: The effect of rotation and an application to eta Carinae

We investigate the effect of rotation on the maximum mass-loss rate due to an optically-thin radiatively-driven wind according to a formalism which takes into account the possible presence of any instability at the base of the wind that might increase the mass-loss rate. We include the Von Zeipel effect and the oblateness of the star in our calculations. We determine the maximum surface-integrated mass that can be lost from a star by line driving as a function of rotation for a number of relevant stellar models of massive OB stars with luminosities in the range of 5.0 < log (L/L ○. ) < 6.0. We also determine the corresponding maximum loss of angular momentum. We find that rotation increases the maximum mass-loss rate by a moderate factor for stars far from the Eddington limit as long as the ratio of equatorial to critical velocity remains below 0.7. For higher ratios, however, the temperature, flux and Eddington factor distributions change considerably over the stellar surface such that extreme mass loss is induced. Stars close to the Eddington-Gamma limit suffer extreme mass loss already for a low equatorial rotation velocity. We compare the maximum mass-loss rates as a function of rotation velocity with other predicted relations available in the literature which do not take into account possible instabilities at the stellar surface and we find that the inclusion thereof leads to extreme mass loss at much lower rotation rates. We present a scaling law to predict maximum mass-loss rates. Finally, we provide a mass-loss model for the LBV η Carinae that is able to explain the large observed current mass-loss rate of ∼10 -3 M ○. yr -1 but that leads to too low wind velocities compared to those derived from observations.

Orbital elements, masses and distance of λ Scorpii A and B determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy

The triple system HD 158926 (λ Sco) has been observed interferometrically with the Sydney University Stellar Interferometer, and the elements of the wide orbit have been determined. These are significantly more accurate than the previous elements found spectroscopically. The inclination of the wide orbit is consistent with the inclination previously found for the orbit of the close companion. The wide orbit also has low eccentricity, suggesting that the three stars were formed at the same time. The brightness ratio between the two B stars was also measured at λ= 442 and 700 nm. The brightness ratio and colour index are consistent with the previous classification of λ Sco A as B1.5 and λ Sco B as B2. Evolutionary models show that the two stars lie on the main sequence. Since they have the same age and luminosity class (IV), the mass–luminosity relation can be used to determine the mass ratio of the two stars: M_B/M_A= 0.76 ± 0.04. The spectroscopic data have been reanalyzed using the interferometric values for P, T, e and ω, leading to revised values for a_1 sin i and the mass function. The individual masses can be found from the mass ratio, the mass function, spectrum synthesis and the requirement that the age of both components must be the same: M_A= 10.4 ± 1.3 and M_B= 8.1 ± 1.0 M_⊙. The masses, angular semimajor axis and the period of the system can be used to determine the dynamical parallax. We find the distance to λ Sco to be 112 ± 5 pc, which is approximately a factor of 2 closer than the Hipparcos value of 216 ± 42 pc.

Characterization and parameter determination of CoRoT variable stars with FLAMES

We present preliminary results from the ground‐based ESO/FLAMES observational program set up for the spectroscopic study of variable stars observed in the CoRoT exoplanet fields. In the Initial Run (IRa01) and the two first long anticenter runs LRa01 and LRc01 about 9000 variable stars have been identified by the CVC (Corot Variable Classifier). The multi‐objects FLAMES medium resolution (R∼7000) spectroscopic observation of CoRoT variable stars from the IRa01 and LRa01 fields allows us to classify the variable stars accurately. In particular, we identified the Be stars and will determine their fundamental parameters by synthetic spectral fitting and by taking into account NLTE and rapid rotation effects. Confronting these parameters to the CoRoT light curves of these objects will allow us to test for correlations between stellar parameters and pulsation properties in a statistical way, in particular to study the instability strips. Moreover, knowing the fundamental parameters of the stars will allow us t...

Methodology for Automated Supervised Classification of Light Curves in the CoRoT Exoplanet Database

The exploration of the large databases currently produced by large scale ground‐based surveys and space missions requires the use of automated methods. We present an automated supervised classification method for large datasets containing light curves of variable stars. The methodology was developed in preparation of the CoRoT mission, but is more widely applicable. The classifiers are currently being applied to the data, measured in the CoRoT Exoplanet programme. Here, we give a brief overview of the results and the changes we have made to optimize the classification performance. A detailed analysis of the complete classification results is still ongoing.

A Study of the Orbital and Intrinsic Variability of the Double-Lined Spectroscopic Binary β Centauri

We introduce our observational study of the orbital motion of β Cen. Using 463 high signal-to-noise, high-resolution spectra obtained over a timespan of 12 years it is shown that the radial velocity of β Cen varies with an orbital period of 357.0 days. We derive for the first time the orbital parameters of β Cen and find a very eccentric orbit ( e = 0.81) and similar component masses with a mass ratio M 1 / M 2 = 1.02. Both the primary and the secondary exhibit periodic line-profile variations.