E. Rodríguez

Asteroseismic analysis of the CoRoT δ Scuti star HD 174936

We present an analysis of the delta-Scuti star object HD 174936 (ID 7613) observed by CoRoT during the first short run SRc01 (27 days). A total number of 422 frequencies we are extracted from the light curve using standard prewhitening techniques. This number of frequencies was obtained by considering a spectral significance limit of sig = 10 using the software package SigSpec. Our analysis of the oscillation frequency spectrum reveals a spacing periodicity of around 52 muHz. Although modes considered here are not in the asymptotic regime, a comparison with stellar models confirms that this signature may stem from a quasi-periodic pattern similar to the so-called large separation in solar-like stars.

An in-depth study of HD 174966 with CoRoT photometry and HARPS spectroscopy - Large separation as a new observable for δ Scuti stars

Aims. The aim of this work was to use a multi-approach technique to derive the most accurate values possible of the physical parameters of the δ Sct star HD 174966, which was observed with the CoRoT satellite. In addition, we searched for a periodic pattern in the frequency spectra with the goal of using it to determine the mean density of the star. Methods. First, we extracted the frequency content from the CoRoT light curve. Then, we derived the physical parameters of HD 174966 and carried a mode identification out from the spectroscopic and photometric observations. We used this information to look for the models fulfilling all the conditions and discussed the inaccuracies of the method because of the rotation effects. In a final step, we searched for patterns in the frequency set using a Fourier transform, discussed its origin, and studied the possibility of using the periodicity to obtain information about the physical parameters of the star. Results. A total of 185 peaks were obtained from the Fourier analysis of the CoRoT light curve, all of which were reliable pulsating frequencies. From the spectroscopic observations, 18 oscillation modes were detected and identified, and the inclination angle (62.5 ◦+7.5 −17.5 ) and the rotational velocity of the star (142 km s −1 ) were estimated. From the multi-colour photometric observations, only three frequencies were detected that correspond to the main ones in the CoRoT light curve. We looked for periodicities within the 185 frequencies and found a quasiperiodic pattern Δν ∼ 64 μHz. Using the inclination angle, the rotational velocity, and an Echelle diagram (showing a double comb outside the asymptotic regime), we concluded that the periodicity corresponds to a large separation structure. The quasiperiodic pattern allowed us to discriminate models from a grid. As a result, the value of the mean density is achieved with a 6% uncertainty. So, the Δν pattern could be used as a new observable for A-F type stars.

The γ Doradus CoRoT target HD 49434 - II. Frequency analysis of the CoRoT data

Context. HD 49434 is a bright (V = 5. m 75) and multiperiodic γ Dor-type pulsator that has been selected for the asteroseismic core programme of the CoRoT satellite. Aims. An extensive and detailed study has been carried out to investigate the pulsational content of this object on the basis of the 136.9d (331291 useful datapoints) time series collected by the CoRoT satellite during the long-run LRa01 (October 2007-March 2008). Methods. The frequency analysis was carried out using the recently available software package SigSpec and Period04. Results. The results confirm HD49434 as a complex pulsator with a very dense pulsation spectrum. A total of 1686 significant peaks are formally detected, essentially in the region below 15 d ―1 . No significant pulsation peaks are detected for frequencies higher than 30 d ―1 . Solar-type oscillations are not detected in this star. The reliability of such a high number of detected peaks has been investigated on the basis of two independent methods. As a result, we propose a total of 840 frequencies that can be assumed to be intrinsic to the star. Conclusions. The CoRoT mission provides very high-quality light curves and datasets, which are excellent for asteroseismic studies of complex pulsating stars beacause they allow investigation of the frequency content down to amplitude levels of a few μmag, unattainable with ground-based observations. In this way, hundreds of excited modes were detected in HD 49434. This is the first time that so many frequencies have been found in a γ Dor-type pulsator.

A multisite photometric study of two unusual β Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph

We report a multisite photometric campaign for theCep stars V2052 Oph and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l = 4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54 ◦ < i < 58 ◦ and the magnetic obliquity 58 ◦ < � < 66 ◦ . The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l = 3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent, light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotatingCep stars, which appear to prefer modes of higher l, are briefly discussed.

HD 172189: another step in furnishing one of the best laboratories known for asteroseismic studies

HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti component. It is also a member of the open cluster IC 4756. These combined characteristics make it an excellent laboratory for asteroseismic studies. To date, HD 172189 has been analysed in detail photometrically but not spectroscopically. For this reason we have compiled a set of spectroscopic data to determine the absolute and atmospheric parameters of the components. We determined the radial velocities (RV) of both components using four different techniques. We disentangled the binary spectra using KOREL, and performed the first abundance analysis on both disentangled spectra. By combining the spectroscopic results and the photometric data, we obtained the component masses, 1.8 and 1.7 Mȯ, and radii, 4.0 and 2.4 Rȯ, for inclination i = 73.2°, eccentricity e = 0.28, and orbital period Π = 5.70198 days. Effective temperatures of 7600 K and 8100 K were also determined. The measured v sin i are 78 and 74 km s-1, respectively, giving rotational periods of 2.50 and 1.55 days for the components. The abundance analysis shows [Fe/H] = -0.28 for the primary (pulsating) star, consistent with observations of IC 4756. We also present an assessment of the different analysis techniques used to obtain the RVs and the global parameters.

MOST observations of the Herbig Ae δ-Scuti star HD 34282

ABSTRACT MOSTobservations and model analysis of the Herbig Ae star HD 34282 (V1366 Ori)reveal δScuti pulsations. 22 frequencies are observed, 10 of which confirm those pre-viously identified by Amado et al. (2006), and 12 of which are newly discovered inthis work. We show that the weighted-average frequency in each group fits the radialp-mode frequencies of viable models. We argue that the observed pulsation spectrumextends just to the edge to the acoustic cut-off frequency and show that this also isconsistent with our best-fitting models.Key words: asteroseismology – techniques: photometric – stars: pre-main sequence– stars: individual: HD 34282 – stars: variables: δScuti. 1 HD 34282 PECULIARITIESHD 34282 (V1366 Ori, PDS 176) is a Herbig Ae (HAe) star(the cool A-range subset of the Herbig AeBe stars) thatis also a δ Scuti star. Pulsations were originally discoveredby Amado et al. (2004), with ten frequencies later identi-fied by Amado et al. (2006) using multi-site ground-basedphotometry. The observed frequencies, from 64.7 to 79.4 cy-cles/day (d

γ Doradus stars in the COROT exoplanets fields: first inspection

We present here preliminary results concerning 32 stars identified as main γ Doradus candidates by the COROT Variable Classifier (CVC) among the 4 first fields of the exoplanet CCDs.

Searching for δ Scuti-type pulsation and characterising northern pre-main-sequence field stars

Context. Pre-main-sequence stars (PMS) are objects evolving from the birthline to the zero-age main sequence (ZAMS). Given a mass range near the ZAMS, the temperatures and luminosities of pre-main-sequence and main-sequence stars are very similar. Moreover, their evolutionary tracks intersect one another causing some ambiguity in the determination of their evolutionary status. In this context, the detection and study of pulsations in pre-main-sequence stars is crucial for differentiating between both types of stars by obtaining information of their interiors via asteroseismic techniques. Aims. A photometric variability study of a sample of northern field stars, which previously classified as either PMS or Herbig Ae/Be objects, has been undertaken with the purpose of detecting δ Scuti-type pulsations. Determination of physical parameters for these stars has also been carried out to locate them on the HR diagram and check the instability strip for this type of pulsators. Methods. Multichannel photomultiplier and CCD time series photometry in the uvby Strömgren and BVI Johnson bands were obtained during four consecutive years from 2007 to 2010. The light curves have been analysed, and a variability criterion has been established. Among the objects classified as variable stars, we have selected those which present periodicities above 4 d−1, which was established as the lowest limit for δ Scuti-type pulsations in this investigation. Finally, these variable stars have been placed in a colour-magnitude diagram using the physical parameters derived with the collected uvbyβ Strömgren-Crawford photometry. Results. Five PMS δ Scutiand three probable β Cephei-type stars have been detected. Two additional PMS δ Scuti stars are also confirmed in this work. Moreover, three new δ Scutiand two γ Doradus-type stars have been detected among the main-sequence objects used as comparison or check stars.

γ Doradus variable stars in the Pleiades cluster: results from a photometric multiste campaign

The variability of the two γ Doradus star belong to Pleiades cluster, HD 22702 and HD 23585, have been confirmed by using new photometric measurements collected during a multisite campaign in 1998. Respect to previous observing runs, the frequency analysis shows new peaks close the 3 cd-1 for both stars. With the aim of performing a modal identification, the method based on amplitudes ratios and phase shifts with non-adiabatic time dependent convection (TDC) has been applied. The physical parameters obtained from the photometry put the star HD 23585 out the blue observational edge of the γ Dor region in the HR diagram. This behaviour together with the high value of vsini have not allowed us to perform an identification of the excited modes. Respect to the the star HD 22702, a preliminary study of stability provides results consistent with a l = 2 identification for the found oscillation frequencies except for f3, where a l = 1 mode is also probable. Also for this star, the TDC treatment has not been able to discrimante the found modes. Therefore, in addition to new vsini measurements, it is fundamental to carry out an exhaustive modelling by considering the pertinent corrections in the rotation.

The tip of the iceberg: The frequency content of the δ Sct star HD 50844 from CoRoT space photometry

It has been suggested that the detection of a wealth of very low amplitude modes in δ Sct stars was only a matter of signal‐to‐noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10−5u2009mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0–30u2009d−1. The initial guess that δ Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high‐degree modes (up to lu2009=u200914) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground‐based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy ele...