Eight new δ Scuti stars

HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes.     

Time series photometric spot modelling – V. Phase coherence of spots on UZ Librae

We present spot models for nine years of continuous VI_c photometry of UZ Lib from 1993–2001. The relatively stable double‐humped light curve shape suggests extreme phase coherence. From the spot‐modelling analysis, we found that the major spots or spot groups are always located on the hemisphere facing the secondary star and exactly in the opposite hemisphere anti‐facing the secondary. Several single‐humped light curves and our suggested binary scenario rule out a pure ellipsoidal variability as the cause of the double‐humped light curve shape. We try to explain this preferred spot pattern with a magnetic‐field structure that connects the two components, as suggested earlier for RS CVn stars in general. A possible 4.8 years spot cycle is found from the long‐term brightness variations but needs confirmation. We rediscuss the basic astrophysical data of UZ Lib. The Hipparcos parallax is likely wrong, a possible reason could be that UZ Lib is e.g., a triple system.     

A new determination of the orbit and masses of the Be binary system δ Scorpii

The binary star δ Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital elements. The subsequent observations can only be explained by assuming that an optically bright emission region with an angular size of  ≳2 ± 1 mas  formed around the primary in 2000. By 2006/2007 the size of this region grew to an estimated ≳4 mas.
We have determined a consistent set of orbital elements by simultaneously fitting all the published interferometric and spectroscopic data as well as the SUSI data reported here. The resulting elements and the brightness ratio for the system measured prior to the outburst in 2000 have been used to estimate the masses of the components. We find   M_A = 15 ± 7 M_⊙  and   M_B = 8.0 ± 3.6 M_⊙  . The dynamical parallax is estimated to be  7.03 ± 0.15 mas  , which is in good agreement with the revised Hipparcos parallax.     

UBVRIJH photometry of two new luminous δ Scuti stars and the discovery of δ Scuti pulsation in the most evolved Ap star known

Time-series photometry of the Hipparcos variable stars HD 199434 and 21190 is reported. Both stars are pulsators of the δ Scuti type. Reclassifications of the MK types of the stars, based on new spectrograms, are given. HD 21190 is found to be F2III SrEuSi:, making it the most evolved Ap star known. Its Strömgren photometric indices support the peculiar spectral type. It is also one of the most evolved δ Scuti stars known. Its combined Ap– δ Scuti nature makes it an important test of models of pulsation in peculiar stars recently developed by Turcotte et al., although it is more extreme than any model they examined. Physical parameters of both stars are estimated from Strömgren and H β photometry, and Hipparcos absolute magnitudes. We attempt mode identifications based on amplitude ratios and phase differences from our photometry. The dominant pulsation of HD 21190 may be an overtone radial mode. The model fits for HD 199434 are even less satisfactory, but favour an ℓ=2 mode. Given the good quality and wavelength coverage of our data, the poor results from the application of the photometric theory of mode identification may call into question the use of that technique.     

Photometric properties of the δ Scuti star BR Cancri

We present the results of a three-year Johnson V and Strömgren uvby H β photometric study of the δ Scuti star BR Cancri (BR Cnc). Our data sets consist of 1293 discrete differential magnitudes in Johnson V and yellow y filters, 883 in Strömgren v and 239 in ub filters. The Fourier analysis of the data suggests four pulsation frequencies for the variable: f ₁=24.978, f ₂=11.358, f ₃=11.808 and f ₄=27.914 cycle d⁻¹. During the three observing years, the main frequency f ₁ kept its V ( y ) amplitude constant at about 6 mmag but its v amplitude seems to be changing. Amplitude variations for all the three other frequencies are also claimed. The pulsation modes of the frequencies are discussed based on the colour data. Using uvbyβ data and calibrations in the literature, we derive the physical parameters for BR Cnc.     

Mode identification in the δ Scuti Star 1 Mon

We present new multicolour photometry and simultaneous high-dispersion spectroscopy for the δ Scuti star 1 Mon. The two main periodicities in the star are still present, but the third known period is not directly detected in the new radial velocities or light variations. However, it is detected in the periodogram of the second moment of the line profile variations. We use the cross-correlation function as an approximation for the line profile variations. By computing theoretical profiles for a given mode and comparing them with phased cross-correlation profiles, we are able to determine a goodness-of-fit criterion and estimate the most probable spherical harmonic degree,     the azimuthal order, m , of the pulsation and also the angle of inclination. We then compare the relative amplitudes and phases of the photometric variations in five wavebands and obtain the best estimates of     for the two visible periodicities. We confirm the earlier determinations that the main periodicity is a radial mode and that the other periodicity is probably         We show that the line profile variations and light variations give consistent results. We point out the importance of a long wavelength range when using the photometric mode identification technique. Finally, we attempt to match the two periods with unstable modes from linear, non-adiabatic calculations. We are able to show that the principal period is well matched by either the fundamental or first overtone radial mode, but could not find a satisfactory fit to the     mode. We discuss implications for mode identification of δ Scuti stars based on what we have learned from this star.     

Towards mode selection in δ Scuti stars: regularities in observed and theoretical frequency spectra

Only a fraction of the theoretically predicted non-radial pulsation modes have so far been observed in δ Scuti stars. Nevertheless, the large number of frequencies detected in recent photometric studies of selected δ Scuti stars allow us to look for regularities in the frequency spacing of modes. Mode identifications are used to interpret these results.
Statistical analyses of several δ Scuti stars (FG Vir, 44 Tau, BL Cam and others) show that the photometrically observed frequencies are not distributed at random, but that the excited non-radial modes cluster around the frequencies of the radial modes over many radial orders.
The observed regularities can be partly explained by modes trapped in the stellar envelope. This mode selection mechanism was proposed by Dziembowski & Królikowska and shown to be efficient for  ℓ= 1  modes. New pulsation model calculations confirm the observed regularities.
We present the s – f diagram, which compares the average separation of the radial frequencies ( s ) with the frequency of the lowest frequency unstable radial mode ( f ). This provides an estimate for the  log  g   value of the observed star, if we assume that the centres of the observed frequency clusters correspond to the radial mode frequencies. This assumption is confirmed by examples of well-studied δ Scuti variables in which radial modes were definitely identified.     

The multiperiodic δ Scuti star 4 Canum Venaticorum: amplitude variability

Recent multisite campaigns of the Delta Scuti Network have revealed 34 frequencies of pulsation for the star 4 CVn. Our present knowledge of the frequencies makes it possible to reanalyse the shorter data sets in the literature, photometric observations from 1966 to 1997.
4 CVn shows strong amplitude variability with time-scales of ten years or longer, although for neighbouring years the amplitudes usually are similar. Seven of the eight dominant modes show annual variability of ∼12 per cent. The variability increases to ∼40 per cent over a decade. The formally derived time-scale of variation of 30 years can only be a rough estimate, since this is also the length of the available data span. The variability is compared with that of FG Vir, which shows lower amplitude variability.
The cyclic behaviour of the amplitude variations excludes an evolutionary origin. There exists some evidence that a mode at 6.12 d⁻¹, which appeared during 1996 and 1997, may have been present with small amplitudes in the 1976–1978 time period.
The pulsation mode at 7.375 d⁻¹ exhibited the most rapid decrease found so far: the V amplitude dropped from the highest known value of 15 mmag in 1974 to 4 mmag in 1976 and 1 mmag in 1977. After that the mode has been increasing in amplitude. There exists a phase jump between 1976 and 1977, suggesting the growth of a new mode. It is interesting to note that this mode also has the strongest coupling with other modes with combination frequencies, f _i ± f _j . The amplitudes of these combination frequencies are also strongly variable from year to year. We speculate that power is transferred between the modes through mode-coupling.     

On the orbital periods of the AM CVn stars HP Librae and V803 Centauri

We analyse high time resolution spectroscopy of the AM CVn stars HP Librae and V803 Centauri, taken with the New Technology Telescope (NTT) and the Very Large Telescope (VLT) of the European Southern Observatory, Chile.
We present evidence that the literature value for V803 Cen's orbital period is incorrect, based on an observed ' S -wave' in the binary's spectrogram. We measure a spectroscopic period   P _V803 Cen= 1596.4 ± 1.2 s  of the S -wave feature, which is significantly shorter than the 1611-s periods found in previous photometric studies. We conclude that the latter period likely represents a 'superhump'. If one assumes that our S -wave period is the orbital period, V803 Cen's mass ratio can be expected to be much less extreme than previously thought, at   q ∼ 0.07  rather than   q ∼ 0.016  . This relaxes the constraints on the masses of the components considerably: the donor star then does not need to be fully degenerate, and the mass of the accreting white dwarf no longer has to be very close to the Chandrasekhar limit.
For HP Lib, we similarly measure a spectroscopic period   P _HP Lib= 1102.8 ± 0.2 s  . This supports the identification of HP Lib's photometric periods found in the literature, and the constraints upon the masses derived from them.     

The δ Scuti star 38 o1 Eri

We present and discuss 247 high dispersion échelle spectra of the δ Scuti star 38 o ¹ Eri. We find at least three periods, but all are affected by aliasing problems. We attempt to identify the modes by a technique involving both temporal and spatial pre-whitening. All modes are of high degree, probably ℓ≈4 and ℓ≈7.