Allison Zhou

Multi-site, multi-technique survey of gamma Doradus candidates - I. Spectroscopic results for 59 stars

We present the first results of a 2-year high-resolution spectroscopy campaign of 59 candidate γ Doradus stars which were mainly discovered from the HIPPARCOS astrometric mission. More than 60% of the stars present line profile variations which can be interpreted as due to pulsation related to γ Doradus stars. For all stars we also derived the projected rotation velocity (up to more than 200 km s −1 ). The amplitude ratios 2K/∆m for the main HIPPARCOS frequency are in the range 35−96 km s −1 mag −1 . About 50% of the candidates are possible members of binary systems, with 20 stars being confirmed γ Doradus. At least 6 stars present composite spectra, and in all but one case (for which only one spectrum could be obtained), the narrow component shows line profile variations, pointing towards an uncomfortable situation if this narrow component orig- inates from a shell surrounding the star. This paper is the first of a series concerning mode identification using both photometric and spectroscopic methods for the confirmed γ Doradus stars of the present sample.

The field high-amplitude SX Phoenicis variable BL Camelopardalis: results from a multisite photometric campaign. I. Pulsation

Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005–2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f0 = 25.5765 cd −1 (∆V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f1 = 25.2523 cd −1 is identified as a nonradial mixed mode g4 with � = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f6 = 32.6464 cd −1 could correspond to the first radial overtone.

A comprehensive study of the delta Scuti star AN Lyncis

We present new time-series CCD photometry on the δ Scuti star AN Lyn. Analyses based on all the available data show that the amplitude of the main frequency increased from 1994 to 2000 at a rate of 0.006 mmag yr - 1 . Considering all the existing amplitudes, the amplitude variations seem sinusoidal since 1980. In both periods of 1980-1983 and 1994-2001 with data available the amplitudes increased linearly with time. The amplitudes in the earlier 1980s were higher and they increased at a higher rate than those in 1994-2001. Amplitude variations of the other frequencies are also present from season to season. The light variation of AN Lyn can be explained currently by amplitude variability plus multiperiodic pulsation. However, no conclusion can be drawn regarding change of periods and new oscillation contents. The two independent frequencies f 1 = 10.1756 cycle d - 1 and f 2 = 18.1310 cycle d - 1 are confirmed and are suggested to be the solution of the light variation of AN Lyn. The mixture of radial and nonradial modes of the two frequencies most likely characterize the pulsation of the star.

The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign

Context. Short-period high-amplitude pulsating stars of Population I (δ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. Aims. We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O–C) short-term analyses. Methods. An investigation of the O–C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. Results. In addition to a positive (161 ± 3) × 10 −9 yr −1 secular relative increase in the main pulsation period of BL Cam, we detected in the O–C data short- (144.2 d) and long-term (∼3400 d) variations, both incompatible with a scenario of stellar evolution. Conclusions. Interpreted as a light travel-time effect, the short-term O–C variation is indicative of a massive stellar component (0.46 to 1 M� ) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O–C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably ab rown dwarf star (≥0.03 M� ), orbiting in ∼3400 d at a distance of 4.5 AU from the primary.

9+ frequencies for V534 Tauri, a delta Scuti variable in the Pleiades - Results of the STEPHI IX campaign

New observations of V534 Tau were performed during the STEPHI IX campaign in November 1998. An overall run of 285 h of data has been collected from three sites over a period of 23 days. Period analysis reveals a rich oscillation spectrum with nine frequencies above the 99% confidence level. This oscillation spectrum spans a large range of frequencies, from 179 to 525 µHz (15.52 to 45.36 cycles per day). A preliminary comparison with models suggests that the observed modes would lie in the range of modes from g1 or g2 to p4 or p5, depending on the rotation rate considered for V534 Tau.

New

We report here the discovery of very low amplitude oscillations in the Pleiades star HD 23628. The 14-nights high quality light curve designates HD 23628 as a new member of the Scuti stars class. Amplitude spectra indicate a multi-periodic pulsation behaviour, and four pulsation frequencies have been detected so far. The frequency distribution suggests the presence of nonradial modes. Pulsation constant values of the four modes are distributed in the range corresponding to fundamental f to p4 radial modes.

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We present a comprehensive investigation of the variations of period and amplitude in the high- amplitude Scuti star AE UMa based on our new Johnson V time-series measurements and the existing data. No additional frequencies were detected even though all the available data sets from 1974 to 2001 were analysed. The light variations of AE UMa can be well-reproduced with the fundamental and rst-overtone radial modes and their coupled terms. New observations and analyses support the most recent results of P ocs & Szeidl (2001). The fundamental period was essentially constant over the past 27 years with its standard value of 0: d 086017066 (f0 =1 1:625600 cd 1 ), while the rst overtone period decreased at a rate of 1 P1 dP1 dt = 4:3 10 8 yr 1 .T he amplitude variations in the two modes of AE UMa are detected at the milli-magnitude level on a time-scale of years. It seems that the amplitudes vary in opposite phases, implying an energy conservation or some kind of intrinsic variability cause. We deny the over-interpretation of the period change given by Hintz et al. (1997) and explore its reason.

Scuti variable in the Pleiades: HD 23628

The results of Johnson V time-series CCD photometry of the δ Scuti star V1821 Cygni are presented. Our data set consists of 2431 differential magnitudes and spans the period of July 1999 to September 2000. We detect two best-fit pulsation frequencies representing the light variations of the variable. V1821 Cyg is most likely pulsating in a mixture of radial and nonradial modes. The

Period and amplitude variations in the high-amplitude

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data in the existing catalogues have been used to derive the main physical parameters for the variable. We obtain: