Search

Extensive photometric multisite campaigns of the δScuti variable FG Vir are presented. For the years 2003 and 2004, 926 h of photometry at the millimag precision level were obtained. The combinations with earlier campaigns lead to excellent frequency resolution and high signal/noise. A multifrequency analysis yields 79 frequencies. This represents a new record for this type of star. The modes discovered earlier were confirmed.
Pulsation occurs over a wide frequency band from 5.7 to 44.3 c/d with amplitudes of 0.2 mmag or larger. Within this wide band the frequencies are not distributed at random, but tend to cluster in groups. A similar feature is seen in the power spectrum of the residuals after 79 frequencies are prewhitened. This indicates that many additional modes are excited. The interpretation is supported by a histogram of the photometric amplitudes, which shows an increase of modes with small amplitudes. The old question of the “missing modes” may be answered now: the large number of detected frequencies as well as the large number of additional frequencies suggested by the power spectrum of the residuals confirms the theoretical prediction of a large number of excited modes.
FG Vir shows a number of frequency combinations of the dominant mode at 12.7162 c/d ($m = 0$) with other modes of relatively high photometric amplitudes. The amplitudes of the frequency sums are higher than those of the differences. A second mode (20.2878 c/d) also shows combinations. This mode of azimuthal order $m = -1$is coupled with two other modes of $m = +1$.

Generally, chemical peculiarity found for stars on the upper main sequence excludes δScuti type pulsation (e.g. Ap and Am stars), but for the group of λBootis stars it is just the opposite. This makes them very interesting for asteroseismological investigations. The group of λBootis type stars comprises late B- to early F-type, Population I objects which are basically metal weak, in particular the Fe group elements, but with the clear exception of C, N, O and S. The present work is a continuation of the studies by Paunzen et al. ([CITE], [CITE]), who presented first results on the pulsational characteristics of the λBootis stars. Since then, we have observed 22 additional objects; we found eight new pulsators and confirmed another one. Furthermore, new spectroscopic data (Paunzen [CITE]) allowed us to sort out misidentified candidates and to add true members to the group. From 67 members of this group, only two are not photometrically investigated yet which makes our analysis highly representative. We have compared our results on the pulsational behaviour of the λBootis stars with those of a sample of δScuti type objects. We find that at least 70% of all λBootis type stars inside the classical instability strip pulsate, and they do so with high overtone modes (Q< 0.020 d). Only a few stars, if any, pulsate in the fundamental mode. Our photometric results are in excellent agreement with the spectroscopic work on high-degree nonradial pulsations by Bohlender et al. ([CITE]). Compared to the δScuti stars, the cool and hot borders of the instability strip of the λBootis stars are shifted by about 25 mmag, towards smaller $(b-y)_0$. Using published abundances and the metallicity sensitive indices of the Geneva 7-colour and Strömgren $uvby\beta$systems, we have derived [ Z] values which describe the surface abundance of the heavier elements for the group members. We find that the Period-Luminosity-Colour relation for the group of λBootis stars is within the errors identical with that of the normal δScuti stars. No clear evidence for a statistically significant metallicity term was detected.

We present the results of multisite observations of the δScuti star V 1162 Ori. The observations were done in the period October 1999 -May 2000, when 18 telescopes at 15 observatories were used to collect 253 light extrema during a total of 290 hours of time-series observations. The purpose of the observations was to investigate amplitude and period variability previously observed in this star, and to search for low-amplitude frequencies. We detect, apart from the main frequency and its two first harmonics, four additional frequencies in the light curves, all with low amplitudes (1-3 mmag). Combining the present data set with data obtained in 1998-99 at ESO confirms the new frequencies and reveals the probable presence of yet another pulsational frequency. All five low-amplitude frequencies are statistically significant in the data, but at least one of them (f5) suffers from uncertainty due to aliasing. Using colour photometry we find evidence for a radial main frequency (f1), while most or all low-amplitude frequencies are likely non-radial. We show that the main frequency of V 1162 Ori has variable amplitude and period/phase, the latter is also displayed in the O-C diagram from light extrema. The amplitude variability in our data is cyclic with a period of 282 d and a range of nearly 20 mmag, but earlier amplitude values quoted in the literature cannot be explained by this cyclic variation. O-C analysis including data from the literature show that the period of V 1162 Ori displays a linear period change as well as sudden or cyclic variations on a time scale similar to that of the amplitude variations. ]

The ß Cep variables are characterised by light variations of a few per cent and velocity variations of up to a few tens of km/s over periods of from about 2.5 to 7 hours. Spectral types range from BO to B2 and luminosity classes from IV to II-III, corresponding to masses from 8 to 18 M ?. The light and velocity curves are 90° out of phase, so that maximum light (and also maximum temperature) occur at minimum radius.

AbstractContinuum photometry of high accuracy with Strömgren uand yfilters was used to observe the LMC supernova 1987a for a period of 7 days just two weeks after the outburst.