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We present and discuss the pulsational characteristics of the Delta Scuti star 38 Eri from photometric data obtained at two widely spaced epochs, partly from the ground (1998) and partly from space (MOST, 2011). We found 18 frequencies resolving the discrepancy among the previously published frequencies. Some of the frequencies appeared with different relative amplitudes at two epochs, however, we carried out investigation for amplitude variability for only the MOST (Microvariability and Oscillation of STars) data. Amplitude variability was found for one of the three frequencies that satisfy the necessary frequency criteria for linear-combination or resonant-mode coupling. Checking the criteria of beating and resonant-mode coupling we excluded them as possible reason for amplitude variability. The two recently developed methods of rotational splitting and sequence search were applied to find regular spacings based only on frequencies. Doublets or incomplete multiplets with l = 1, 2, and 3 were found in the rotational splitting search. In the sequence search method we identified four sequences. The averaged spacing, probably a combination of the large separation and the rotational frequency, is 1.724 ± 0.092 d-1. Using the spacing and the scaling relation ... = [0.0394, 0.0554] g cm-3 was derived. The shift of the sequences proved to be the integer multiple of the rotational splitting spacing. Using the precise MOST frequencies and multi- colour photometry in a hybrid way, we identified four modes with l = 1, two modes with l = 2, two modes with l = 3, and two modes as l = 0 radial modes. [ABSTRACT FROM AUTHOR]

We present our analysis of photometric data in the Johnson B and V filter of the southern Blazhko star SS For. In parallel, we analysed the V observations obtained with the All Sky Automated Survey-3 photometry of the star gathered between 2000 and 2008. In the frequency spectra resulting from a Fourier analysis of our data, the triplet structure is detectable up to high order, both in the B and V data. Moreover, we find evidence for quintuplet components. We confirm from our data that the modulation components decrease less steeply than the harmonics of the main frequency. We derived the variations of the Fourier parameters quantifying the light-curve shape over the Blazhko cycle. There is good agreement between the spectroscopic abundance and the metallicity determined from the Fourier parameters of the average light curve. SS For is peculiar as a Blazhko star because of its strong variations around minimum light. [ABSTRACT FROM AUTHOR]

We present results from a three-site photometric and high-resolution spectroscopic campaign on the hottest known extreme helium star V2076 Oph (HD 160641). A core programme of intensive observations covered two weeks and a much lower sampling rate extended over another two months. Despite the fact that the data seem to indicate periodicity near half a day (though the light curves are clearly not formed by a single periodicity), conventional Fourier analysis of the data fails to reveal coherent frequencies. Furthermore, we are unable to recover frequencies which were apparently clear in an earlier campaign on the star. Evidence of monotonic pulsation amplitude changes is seen at the higher frequencies from a wavelet analysis, but more data are needed before this study can be extended to lower frequencies. The application of linear stochastic differential equation (LSDE) methods indicates that the observed light variations could be a result of random variations giving the appearance of intermittent periodicity. High-resolution spectroscopic observations were obtained during the campaign and additional observations were made three years later. Complex line profile variations were observed. It is proposed that the different behaviour of the emission line studied may indicate it is associated with a stellar wind or resident circumstellar material. The frequencies that are extracted from the velocity data do not conform to those identified in the current or previous photometric campaigns. [ABSTRACT FROM AUTHOR]

We have carried out single and multisite photometry of the three β Cephei stars β and 15 CMa as well as KZ Mus. For the two stars in CMa, we obtained 270 h of measurement in the Strömgren uvy and Johnson V filters, while 150 h of time-resolved Strömgren uvy photometry was acquired for KZ Mus. All three stars are multiperiodic variables, with three (β CMa) and four (15 CMa, KZ Mus) independent pulsation modes. Two of the mode frequencies of 15 CMa are new discoveries and one of the known modes showed amplitude variations over the last 33 yr. Taken together, this fully explains the diverse behaviour of the star reported in the literature. Mode identification by means of the amplitude ratios in the different passbands suggests one radial mode for each star. In addition, β CMa has a dominant mode while its third mode is non-radial with unknown ℓ. The non-radial modes of 15 CMa, which are , form an almost equally split triplet that, if physical, would imply that we see the star under an inclination angle larger than 55°. The strongest non-radial mode of KZ Mus is , followed by the radial mode and a dipole mode. Its weakest known mode is non-radial with unknown ℓ, confirming previous mode identifications for the pulsations of the star. The phased light curve for the strongest mode of 15 CMa has a descending branch steeper than the rising branch. A stillstand phenomenon during the rise to maximum light is indicated. Given the low photometric amplitude of this non-radial mode this is at first sight surprising, but it can be explained by the aspect angle of the mode. [ABSTRACT FROM AUTHOR]

We undertook a time-series photometric multisite campaign for the rapidly oscillating Ap (roAp) star HD 99563 and also acquired mean light observations over four seasons. The pulsations of the star, which show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 μHz and some first harmonics of it. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 ± 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break up the distorted oscillation mode into its pure spherical harmonic components and find it is dominated by the ℓ= 1 pulsation, and also has a notable ℓ= 3 contribution, with weak ℓ= 0 and 2 components. The geometrical configuration of the star allows us to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes has been modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the δ Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03-M⊙, object, seen at a rotational inclination of 44°, which then predicts a magnetic obliquity . [ABSTRACT FROM AUTHOR]

We have carried out a three-site photometric campaign for the β Cephei star θ Oph from 2003 April to August. 245 h of differential photoelectric u v y photometry were obtained during 77 clear nights. The frequency analysis of our measurements has resulted in the detection of seven pulsation modes within a narrow frequency interval between 7.116 and 7.973 c d−1. No combination or harmonic frequencies have been found. We have performed a mode identification of the individual pulsations from our colour photometry that shows the presence of one radial mode, one rotationally split triplet and possibly three components of a rotationally split quintuplet. We discuss the implications of our findings and point out the similarity of the pulsation spectrum of θ Oph to that of another β Cephei star, V836 Cen. [ABSTRACT FROM AUTHOR]

We report on the second multisite photometric campaign devoted toν Eridani (ν Eri). The campaign, carried out from 2003 September 11 to 2004 February 16, was very nearly a replica of the first campaign, 2002–2003: the five telescopes and photometers we used were the same as those in the first campaign, the comparison stars and observing procedure were identical, and the numbers and time baselines of the data were comparable.Forν Eri, analysis of the new data adds four independent frequencies to the nine derived previously from the 2002–2003 data: three in the range 7.20–7.93 d−1 and a low one, equal to 0.614 d−1. Combining the new and the old data results in two further independent frequencies, equal to 6.7322 and 6.2236 d−1. Altogether, the oscillation spectrum is shown to consist of 12 high and two low frequencies. The latter haveuamplitudes about twice as large as thevandyamplitudes, a signature of high radial-order g modes. Thus, we confirm the suggestion, put forward on the basis of the data of the first campaign, thatν Eri is both aβ Cephei and a slowly pulsating B (SPB) star.Nine of the 12 high frequencies form three triplets, of which two are new. The triplets represent rotationally splitmodes, although in case of the smallest-amplitude one this may be questioned. Mean separations and asymmetries of the triplets are derived with accuracy sufficient for meaningful comparison with models.The first comparison star,μ Eri, is shown to be an SPB variable with an oscillation spectrum consisting of six frequencies, three of which are equidistant in period. The star is also found to be an eclipsing variable. The eclipse is a transit, probably total, the secondary is fainter than the primary by several magnitudes, and the system is widely detached.The second comparison star,ξ Eri, is confirmed to be aδ Scuti variable. To the frequency of 10.8742 d−1 seen already in the data of the first campaign, another, equal to 17.2524 d−1, is added. [ABSTRACT FROM AUTHOR]

ABSTRACT We have acquired between 127 and 150 h of time-resolved multicolour photometry for each of the three β Cephei stars IL Vel, V433 Car and KZ Mus over a time-span of 4 months from two observatories. All three objects are multiperiodic with at least three modes of pulsation. Mode identification from the relative colour amplitudes is performed. We obtain unambiguous results for the two highest-amplitude modes of IL Vel (both are ℓ= 1 ) and the three strongest modes of KZ Mus ( ℓ= 2, 0 and 1), but none for V433 Car. Spectroscopy shows the latter star to be a fast rotator (v sin i= 240 km s[sup -1]) , whereas the other two have moderate v sin i (65 and 47 km s[sup -1], respectively). We performed model calculations using the Warsaw–New Jersey stellar evolution and pulsation code. We find that IL Vel is an object of about 12 M[sub ⊙] in the second half of its main-sequence evolutionary track. Its two dipole modes are most probably rotationally split components of the mode originating as p[sub 1] on the zero-age main sequence; one of these modes is m= 0 . V433 Car is suggested to be an unevolved 13-M[sub ⊙] star just entering the β Cephei instability strip. KZ Mus seems less massive (≈12.7 M[sub ⊙]) and somewhat more evolved, and its radial mode is probably the fundamental one. In this case its quadrupole mode would be the one originating as g[sub 1] , and its dipole mode would be p[sub 1] . Two of our photometric comparison stars also turned out to be variable. HD 90434 is probably a new slowly pulsating B-type star, the dominant mode of which is a dipole, whereas the variability of HD 89768 seems to be a result of binarity. It is suggested that mode identification of slowly rotating β Cephei stars based on photometric colour amplitudes is reliable; we estimate that a relative accuracy of 3 per cent in the amplitudes is sufficient for unambiguous identifications. Owing to the good agreement of our theoretical and observational results we conclude that the prospects for asteroseismology of multiperiodic slowly rotating β Cephei stars are good. [ABSTRACT FROM AUTHOR]

We undertook two time-series photometric multisite campaigns for the rapidly oscillating Ap star HD 122970. The first one, conducted in 1998, resulted in 119 h of data and in the detection of three pulsation frequencies. The presence of possible further modes which held the promise of deriving a mode identification motivated a second worldwide campaign in the year 2001. This second campaign resulted in 203 h of measurement, but did not reveal further modes. Rather, one of the previously detected signals disappeared. The two modes common to both data sets have different spherical degree. They also showed slight frequency modulation, and one of them varied in amplitude as well. Possible causes of the latter behaviour include intrinsic instability of the pulsation spectrum or precession of the pulsational axis and orbital motion in a binary system. Frequency analysis of the Hipparcos observations of the star did not allow us to determine the stellar rotation period. The amplitude and phase behaviour of the two modes of HD 122970 in the Strömgren uvby bands is quite similar to that observed for other roAp stars. [ABSTRACT FROM AUTHOR]

We report multisite observations devoted to the main-sequence δ Scuti star XX Pyx, conducted as the 17th run of the Delta Scuti Network. Over 125 nights a total of 550 h of usable time-series photometric B- and V-filter data were acquired involving both photoelectric and CCD measurements at eight observatories spread around the world, which represents the most extensive single time-series for any pulsating star other than the Sun obtained so far. We describe our observations and reduction methods, and present the frequency analysis of our new data. First, we detect six new pulsation and five new combination frequencies in the star's light curves. We also discover evidence for amplitude and/or frequency variations of some of the modes during the observations. These can occur on time-scales as short as 20 d and show quite diverse behaviour. To take them into account in the frequency analysis, a so-called non-linear frequency analysis method was developed, allowing us to quantify the temporal variability of the modes and to compensate for it. Following that we continue the frequency search and we also incorporate published multisite observations. In this way, we reveal three more pulsation and two more combination frequencies. In the end, we report a total of 30 significant frequencies – 22 of which correspond to independent pulsation modes. This is the largest number of independent modes ever detected in the light curves of a δ Scuti star. The frequencies of the modes show preferred separations as already suggested by previous work on this star; they are also arranged in clear patterns. These results lead to a refinement of the stellar mean density [equation] and to a new constraint on the rotation rate of XX Pyx (ν[sub rot]=1.1±0.3 d[sup -1]). However, our attempts to identify the modes by pattern recognition failed. Moreover, mode identification from multicolour photometry failed as well because the high pulsation frequencies make this method unfavourable. The diverse behaviour of the amplitude and frequency variations of some of the modes leaves resonances as the only presently known possibility for their explanation. [ABSTRACT FROM AUTHOR]

ABSTRACT We report a multisite photometric campaign for the β Cep stars V2052 Oph and V986 Oph. 670 h of high-quality differential photoelectric Strömgren, Johnson and Geneva time-series photometry was 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 mode. 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° < β < 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 rotating β Cep stars, which appear to prefer modes of higher l, are briefly discussed. [ABSTRACT FROM AUTHOR]