CoRoT 102931335: a candidate γ Dor in an eclipsing binary

We present an on-going study of CoRoT 102931335. Our preliminary results indicate that the target is an eclipsing binary system with an orbital period of $3{.\!\!\vphantom{0}^{\mathrm{d}}}979$ and a primary component pulsating in the frequency range 0.6–0.8 c/d. The results of a ground-based follow-up program provided four-colour Strömgren photometry and allowed us to infer the spectral class and the primary effective temperature. We devised and applied an iterative procedure to disentangle the effects of binarity from those of pulsations and could test that a detailed binary modelling is essential for the purpose. Our results suggest that the pulsating component of CoRoT 102931335 could be a γ Dor variable, a rare occurrence in an eclipsing system.     

The high amplitude delta Scuti star SZ Lyncis revisited

Nine new times of light maximum are given for SZ Lyn and the time base of observations is herewith extended to 26 years. 154 light maxima have been used to calculate the orbital elements and the secular change in the period of the pulsating component. The results provided here support the post-Main Sequence, high mass hypothesis for the evolutionary state of this dwarf cepheid.     

The connection between the pulsational and orbital periods for eclipsing binary systems

Considering a sample of 20 eclipsing binary systems with δ Scuti type primaries, we discovered that there is a possible relation among the pulsation periods of the primaries and the orbital periods of the systems. According to this empirical relation, the longer the orbital period of a binary, the longer the pulsation period of its pulsating primary. Among the sample, the masses of the secondaries and the separations between the components are known for eight systems for which a  log  P _puls  versus log  F (the gravitational pull exerted per gram of the matter on the surface of the primaries by the secondaries) diagram also verifies such an interrelation between the periods. So, as the gravitational force applied by the secondary component onto the pulsating primary increases, its pulsation period decreases. The detailed physics underlying this empirical relation between the periods needs further confirmation, especially theoretically. However, one must also consider the fact that the present sample does not contain a sufficiently large sample of longer period  ( P > 5 d)  binaries.     

White dwarfs: Recent developments

Summary. During the last decade white dwarfs have become important as tools in many areas beyond traditional stellar physics: from the age determination of the stars in the solar neighborhood to the dating of open clusters and the distance determination of globular clusters. They are primary candidates for the MACHO microlensing events, possibly for a stellar component of the dark halo, and for the supernova Ia progenitors. The recent developments in these areas are reviewed, but some highlights from more “mature” areas such as stellar parameters, mass distributions, magnetic, and pulsating white dwarfs are also summarized briefly. Received 5 October 2001 / Published online 11 January 2002     

Radioheliograph observations of a pulsating structure associated with a moving type IV burst

Observations of a pulsating structure with the Mark II Nançay Radioheliograph are reported. These fluctuations are found to occur early in the development of a moving type IV burst. It is confirmed that the source of these fluctuations is of small extent and that it is embedded in the moving type IV continuum, plausibly at the top of an expanding arch.The observations suggest that the pulsating structure consists of recurrent enhanced pulses (mean recurrency time 1.7 s) followed by trains of periodic pulses (mean periodicity 0.37 s). The intensity of the enhanced pulses has a damping time of about 5 s. It is shown that previous interpretation of the pulsating structure by Rosenberg (1970) cannot account for the present observations.     

Y Leonis: light curve solution revised and search for photometric variations of the primary minima

The interest in the study of the Algol binary system Y Leonis is justified not only by its light curve having a very deep primary minimum, and pulsating character of its primary component, but also by the complex behavior of its O–C curve which is featured by the presence of long and short time scale modulations. Taking into account the previously inferred K spectral type of the secondary component, one may expect that one of the involved periodicities could be related to magnetic cycles of this star. We gave the Wilson-Devinney solution of the eclipse light curve using our observational data obtained during 2009. The long- and short-term photometric variability of Y Leo is approached both through literature data and new CCD data. Even though these data are scarce, they revealed significant variability in the maximum and minimum brightness of this binary system at long time-scale. The nature of the rapid photometric variations during the deepest phase of primary minima can hardly be explained only by weak δ Scuti pulsations of the primary component which is still visible in partial eclipses.     

Variations of the pulse profile and the X-ray intensity of GX301-2 (4U1223-62)

Two successive X-ray outbursts of the recurrent X-ray pulsar GX301-2 were observed in April and May, 1982 from Hakucho. Apart from general increase during flares lasting for several days, the X-ray intensity was highly variable on a time-scale of the order of an hour. The outstanding feature is that the amplitude of 700 s pulsation of GX301-2 changes rapidly in a very wide range. When the pulsation is distinct, the depth of modulation is as large as 60%; whereas, the pulse amplitude occasionally diminishes almost to an undetectable level so that the observed X-rays become unpulsed. Such drastic changes are found to occur at any intensity levels observed. In several cases of abrupt changes of pulse amplitude, the intensity at the pulse bottom remained essentially unchanged. These properties suggest a hypothesis that the X-ray emission from GX301-2 consists of a pulsating component with variable amplitude and a non-pulsating component of less variable intensity.     

Radiation of magnetoacoustic waves in the interstellar medium by physical variable stars

Radially pulsating stars are shown to radiate fast and slow magnetoacoustic waves into the interstellar gas. No Alfvén waves are excited, because the oscillations are radially symmetric. Calculations were performed for the following two limiting cases: hot, weakly magnetized interstellar plasma and cold plasma with a strong magnetic field. In these limiting cases, pulsating stars excite mostly fast magnetoacoustic waves, while the excitation of slow magnetoacoustic waves is weak. Magnetogasdynamic fields of density, velocity, and magnetic-field perturbations in the interstellar medium were found. Relations were derived to calculate the radiated power and its estimates are given for various conditions in the medium. It is shown that radially stratified wave structures with wavelengths from 1 AU to several tenths of a parsec must exist in the vicinity of pulsating stars.     

Mid-latitude pulsating auroras

Pulsating auroras were recorded at Bedford, Massachusetts, cgm lat. 55.4°, 24 March 1969 during a worldwide magnetic storm, the only known published observations of pulsating auroras at such low magnetic latitudes. Spectral density analysis of several minutes of 5577A pulsations indicated a dominant period of 7.2 sec at 0300 EST. The following characteristics were noted: (1) occurrence during a negative bay in H; (2) location toward the equatorial boundary of the auroral display; (3) occurred a few hours after local midnight; (4) characteristic period of 6–10 sec; (5) quasi-sinusoidal or superposition of sinusoids rather than isolated pulses; (6) modulation of the background intensity by 15–30 per cent. These characteristics have previously been observed by others in pulsating auroras in the auroral oval. Other mid-latitude geophysical measurements at the same time show similarities to typical auroral oval behavior. These observations indicate that the auroral oval expanded during the worldwide magnetic storm until the boundary of the auroral oval was near cgm latitude 55°. If this observation of one mid-latitude pulsating aurora is in general valid, then the agreement of the characteristic period of pulsating auroras when the oval has expanded to mid-latitudes with the period of pulsating auroras when the oval is not expanded should be useful in distinguishing between proposed source mechanisms for these pulsating auroras.     

Discovery of magnetic fields in three He variable Bp stars with He and Si spots

It is essential for the understanding of stellar structure models of high mass stars to explain why constant stars, nonpulsating chemically peculiar hot Bp stars and pulsating stars co‐exist in the slowly pulsating B stars and β Cephei instability strips. We have conducted a search for magnetic fields in the four Bp stars HD55522, HD105382, HD131120, and HD138769 which previously have been wrongly identified as slowly pulsating B stars. A recent study of these stars using the Doppler Imaging technique revealed that the elements He and Si are inhomogeneously distributed on the stellar surface, causing the periodic variability. Using FORS 1 in spectropolarimetric mode at the VLT, we have acquired circular polarisation spectra to test the presence of a magnetic field in these stars. A variable magnetic field is clearly detected in HD55522 and HD105382, but no evidence for the existence of a magnetic field was found in HD131120. The presence of a magnetic field in HD138769 is suggested by one measurement at 3σ level. We discuss the occurrence of magnetic B stars among the confirmed pulsating B stars and find strong magnetic fields of order kG and oscillations to be mutually exclusive. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Population i pulsating stars

On the basis of our age estimations of Population I pulsating stars in our Galaxy (Tsvetkov, 1986a), the mean ages of 6 open star clusters containing 21 Delta Scuti-variables and of 8 star clusters and associations containing 13 classical cepheids, have been evaluated. These mean cluster age estimations weighted according to the probabilities for different evolutionary phases of the pulsating stars, are obtained in the evolutionary track systems of Iben (1967) and Paczyski (1970); the cluster ages are larger in the former system. Our results are compared with those obtained from various methods by other authors. Clusters with classical cepheids and with Delta Scuti-stars have ages, respectively, in the ranges 10⁷–10⁸ years and 10⁶–10⁹ years. It is shown that the use of simple period-age(-colour) relations for Population I pulsating stars gives sufficiently accurate cluster age estimations. By use of our period-age relations for classical cepheids (Tsvetkov, 1986a), the mean ages of 56 other star clusters and associations in our Galaxy, the Magellanic Clouds, and M 31 galaxy have been estimated in both systems of tracks. The results are generally in agreement with those obtained from various methods by other authors. The use of Population I pulsating stars in star clusters and associations is one of the simplest and most easily applied methods for determining cluster ages; but there are some limitations in its application.     

HD 172189, a Cluster Member Binary System with a δ Scuti Component in the Field of View of COROT

Photometric and spectroscopic results for the star HD 172189, member of the open cluster IC 4756 in the summer field of the space mission COROT, are presented. From photometric observations in the Strömgren system carried out at various epochs, its binary nature as well as the presence of a δ Scuti-type pulsating component have been discovered. The frequency analysis of the whole dataset confirms a dominant frequency of 19.5974 c d^?1 with a maximum amplitude near 0.02 mag plus other frequencies in the range 18–20 c d^?1. A preliminary orbital solution from the light curve and from four FEROS spectra reveals two similar components of around 1.5 M _⊙ orbiting with a period of 5.702 d.     

Optical and magnetic pulsations

Based on data from the PULSAUR-rocket (1980) and ground observations, a correlation study between optical and magnetic pulsations has been carried out. By use of All-Sky TV along with the measured flux of electrons we have also simulated the ground magnetic field. The simulation is based on a model of pulsating currents caused by conductivity changes in the ionosphere. Our simulated field well represents the observed field. The time delay between the optical and magnetic signal is discussed in relation to our model, and so is the lack of correlation between the high frequency component of the two types of pulsations.     

Discovery and asteroseismological analysis of a new pulsating DB white dwarf star, PG 2246+121

We report 36.6 h of time-resolved CCD photometry of the DB white dwarf star PG 2246+121 and the discovery that it is a new pulsating variable. Analysis of our compact single-site data set allowed the detection of three mode multiplets, two triplets at 256 and 329 s, respectively, and one doublet at 286 s. The frequency splitting within those structures is exactly the same within the length and accuracy of our data set.
We argue that these multiplets are the result of non-radial g-mode pulsations, most probably of spherical degree ℓ=1, which then yields a formal stellar rotation period of 2.00±0.12 d. We suggest that the excited modes are three consecutive radial overtones of order 3–7, most likely k =4,5,6. This discovery's impact on the understanding of pulsating DB white dwarfs is discussed.     

Classical Cepheids: a New version of the Baade-Becker-Wesselink method

We propose a new version of the Baade-Becker-Wesselink technique, which allows one to independently determine the color excess and the intrinsic color of a radially pulsating star, in addition to its radius, luminosity, and distance. The method is a generalization of the Balona approach. It also allows the function F(CI ₀) = BC(CI ₀) + 10 × log(T _eff (CI ₀)) for the class of pulsating stars considered to be calibrated. The reddenings of several classical Cepheids with very accurate light and radial-velocity curves and with bona fide membership in open clusters (SZ Tau, CF Cas,USgr, DL Cas,GY Sge) agree well with the reddening estimates of the host open clusters. The new technique can also be applied to other pulsating variables, e.g. RR Lyrae.     

Spectroscopic mode identification of main-sequence non-radially pulsating stars

We are undertaking an extensive observational campaign of a number of non-radially pulsating stars using the high-resolution HERCULES spectrograph on the 1.0-m telescope at the Mt John University Observatory. This is part of a large world-wide multi-site campaign to improve mode-identification techniques in non-radially pulsating stars, particularly for g-mode pulsators. This paper outlines our campaign and presents preliminary results for one γ Doradus star, HD 40745, and one β Cephei star, HD 61068. We have used a representative cross-correlation line-profile technique presented by Wright in 2008 to extract line profiles and these have then been analyzed using the FAMIAS package due to Zima published in 2006 to derive a spectroscopic mode identification.     

Intensity ratio I(5577)/I(3914) in morning and evening pulsating aurora

The ratio of the intensity of the oxygen green line at 5577 A to that of the N₂⁺ First Negative band (0, 0) at 3914 A in morning and evening pulsating aurora has been observed using a ground-based scanning photometer which scans the entire sky in 2.6 sec with 2° resolution.The ratio I(5577)/I(3914), after corrections for scattering and extinction made on the basis of hemispheric averages of the intensities at each wavelength, is up to 50% lower in the pulsations than in the surrounding diffuse aurora and in pre-breakup discrete auroras. In morning pulsations this ratio showed systematic decreases with time and with increasing intensity.We report here what we believe to be the first quantitative intensity measurements made of the rare phenomenon evening pulsations. These also show a reduced ratio and a tendency for the ratio to decrease with time.The range of previously published values of the 5577 A time constant in pulsating auroras would lead to ratio variations of the same magnitude as those reported here, suggesting that quenching effects may be more important than atmospheric composition changes in determining intensity ratios within the altitude range of pulsating auroras.     

Pulsations at the Onset of the Great Solar Burst of 22 October 1989

The onset phase of the 22 October 1989 great solar burst was observed at 48 GHz using the multiple beam technique, which allows unambiguous flux determination irrespective of spatial angular position changes in time. We found strong quasi-periodic pulsating structures as the flux started to rise. Two significantly different time scales of 2.5–4.5 s and 0.2–0.5 s have been observed. These pulsations might be related to magnetohydrodynamic perturbations in the active region. However the fast component also might be a signature of the acceleration and/or injection of energetic electrons.     

Effects of rotation and tidal distortions on the shapes of radial velocity curves of polytropic models of pulsating variable stars

Anharmonic oscillations of rotating stars have been studied by various authors in literature to explain the observed features of certain variable stars. However, there is no study available in literature that has discussed the combined effect of rotation and tidal distortions on the anharmonic oscillations of stars. In this paper, we have created a model to determine the effect of rotation and tidal distortions on the anharmonic radial oscillations associated with various polytropic models of pulsating variable stars. For this study we have used the theory of Rosseland to obtain the anharmonic pulsation equation for rotationally and tidally distorted polytropic models of pulsating variable stars. The main objective of this study is to investigate the effect of rotation and tidal distortions on the shapes of the radial velocity curves for rotationally and tidally distorted polytropic models of pulsating variable stars. The results of the present study show that the rotational effects cause more deviations in the shapes of radial velocity curves of pulsating variable stars as compared to tidal effects.     

A model of the gamma-ray burst event of 1979 March 5 (paper I)

We discuss the time profiles and the energy spectra of the γ-ray burst event of 1979 March 5. We find: (1) the energy spectrum in the burst phase (< 0^s, 3) can be fitted by a thermal bremsstrahlung with kT ? 50KeV, plus a bremsstrahlung of relativistic electrons with equivalent Lorentz factor γ = 3.3 and a broad line at 430KeV. (2) The average spectrum in the pulsating phase can be fitted with a bremsstrahlung of thermal electrons with kT ? 40KeV. (3) The time profile in the pulsating phase can be fitted by the bremsstrahlung of a radiative region which is cooling in time. Accordingly, we propose the following morphological model: somehow a large amount of matter is suddenly injected onto the surface of a neutron star at its magnetic poles. The gravitational energy of the electrons is transformed into radiation during the burst phase through the bremsstrahlung of the electrons. The gravitational energy of the protons is first transformed into heat in a radiative region, which then radiates during the pulsating phase by the bremsstrahlung of the thermal electrons.