L. Parrao

Pulsational frequencies of the eclipsing δ Scuti star HD 172189. Results of the STEPHI XIII campaign

Context. The eclipsing δ Scuti star HD 172189 is a probable member of the open cluster IC 4756 and a promising candidate target for the CoRoT mission. Aims. 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. Methods. We performed a detailed frequency analysis of 210 hours of photometric data of HD 172189 obtained from the STEPHI XIII campaign �� . Results. We have identified six pulsation frequencies with a confidence level of 99% and a seventh with a 65% confidence level of 65%, in the range between 100−300 µHz. In addiction, three eclipses were observed during the campaign, allowing us to improve the determination of the orbital period of the system.

Strömgren photometry and spectroscopy of the δ Scuti stars 7 Aql and 8 Aql

Abstract Photometric ( uvby - β ) and spectroscopic observations of the δ Scuti variables 7 Aql and 8 Aql are described. The Stromgren standard indices and physical parameters of both stars are derived. Spectral types of F0V and F2III have been assigned to 7 Aql and 8 Aql , respectively considering the results from both spectroscopy and photometry. Differential uvby light curves were also analyzed. A attempt of multicolour mode identification is carried out.

Multisite Observations of δ Scuti Stars 7 Aql and 8 Aql (a New δ Scuti Variable): The Twelfth STEPHI Campaign in 2003

We present an analysis of the pulsation behavior of the δ Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589), a new variable star, observed in the framework of the STEPHI XII campaign during 2003 June and July; 183 hr of high-precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multichannel photometry. Observations in different filters were also obtained and analyzed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 190-300 μHz and 100-145 μHz in 7 Aql and 8 Aql, respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p-modes of low radial orders, typical among δ Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n = 1 to 3, while for 7 Aql the range spans from n = 4 to 7. Nonradial oscillations have to be present in both stars as well. The expected range of excited modes according to a nonadiabatic analysis goes from n = 1 to 6 in both stars.

Spectrophotometry of three planetary nebulae

The results of a spectroscopic investigation of three possible planetary nebulae, K4- 53, K4- 55, and K4- 57, are presented. It is shown that K4- 53 and K4- 55 are planetary nebulae while K4- 57 can be considered with high probability to be one. The temperatures of the nuclei of these nebulae are determined by Ambartsumian’s method. The optical depths for Lc photons in the region of λ ≤ 912 Å are determined. An anomalously high nitrogen abundance is observed in K4- 55.

Strömgren Photometry of the Delta Scuti Stars 7 Aql and 8 Aql

The preliminary results of new photometric observations of the δ Scuti stars 7 Aql and 8 Aql are reported. 51 hr of uvby—β photoelectric photometric data were obtained over the period June and July 2007 at the San Pedro Martir Observatory, Mexico. Period analyses confirm the three pulsation modes discovered in 8 Aql in the framework of the STEPHI 2003 multisite campaign. For the star 7 Aql we were able to detect only the main pulsation modes. The standard magnitudes of both stars are obtained. The frequency, amplitude and phases of the frequency modes in different filters are presented.

CCD Photometry of Delta Scuti stars 7 Aql and 8 Aql

As a continuation of the study of the Delta Scuti stars 7 Aql and 8 Aql; new CCD photometric data were acquired in 2007. We present a period analysis on these data that confirm the dominant modes detected in each star in the framework of the STEPHI XII campaign in 2003.