RR Ari: Not a variable star

NewV standard measures of RR Ari are presented and the star is found not to be variable. The light of the star Ari BCSV 5954 seems also to be constant.     

Predicting variable star light curves

I present a new method to test determinism, in particular the nonlinear behavior, in observed time series of pulsating stars, based on a recent prediction method which exploits the dynamical system theory. A method for filling gaps in data has thereby been constructed. Estimated bounds to the necessary embedding dimension can be obtained and chaotic divergences can be estimated.     

Light variation of the variable star OO Aquilae

PhotoelectricB andV observations of the W UMa-type system OO Aql have been obtained for 11 nights during the period from 22 June–30 July, 1987. A total of 978 observations were obtained in eachB andV filter. All these observations were transformed to theB andV colours of theUBV standard system. Five light curves for primary and secondary eclipses were obtained, its times of minima were determined and a new linear ephemeris was given. The period changes of the system were discussed.     

BV photometry of the RRc variable star DH Pegasi

Revised light elements of the RR Lyrae variable star DH Pegasi are presented together with a newBV light curve.     

Ultraviolet observations of the hydrogen-deficient variable star MV sagittarii

IUE observations of the hydrogen-deficient irregular variable star MV Sgr obtained in 1980 June-October and also in 1979 November are discussed. These observations show a prominent λ 2200 absorption feature. A value ofE(B — V) = 0.55 is deduced from the strength of λ 2200 band assuming that this absorption is caused by interstellar medium. The dereddened continuum obtained at different times can be fitted to a theoretical energy distribution of a helium star model with T_eff = 18000 K and log g = 2.5, similar to that of BD + 10^‡ 2179. This theoretical energy distribution, after applying interstellar extinction, givesV = 12.7 mag, agreeing with the observed visual magnitude of ≃ 13 in 1979 November and 1980 June-October. Even though there was no change in the continuum flux, the ultraviolet line-spectrum shows variations. The IUE spectra of 1980 October show enhanced (circumstellar) absorption lines of Fe II, Si II, O I, C I and others along with the absorption lines of a B star. In view of the similarity of the spectroscopic phenomena of MV Sgr with that of α Sco system, a model is proposed in which a cool companion star, surrounded by dust, occasionally blows gas towards the hotter hydrogen-poor B star. This model explains the irregular light variations and the spectroscopic phenomena. Based on observations obtained with IUE satellite at the Villafranca Satellite Tracking Station of the European Space Agency.     

On the dynamics of superfluid neutron star cores

We discuss the nature of the various modes of pulsation of superfluid neutron stars using comparatively simple Newtonian models and the Cowling approximation. The matter in these stars is described in terms of a two-fluid model, where one fluid is the neutron superfluid, which is believed to exist in the core and inner crust of mature neutron stars, and the other fluid represents a conglomerate of all other constituents (crust nuclei, protons, electrons, etc.). In our model, we incorporate the non-dissipative interaction known as the entrainment effect, whereby the momentum of one constituent (e.g. the neutrons) carries along part of the mass of the other constituent. We show that there is no independent set of pulsating g-modes in a non-rotating superfluid neutron star core, even though the linearized superfluid equations contain a well-defined (and real-valued) analogue to the so-called Brunt–Väisälä frequency. Instead, what we find are two sets of spheroidal perturbations whose nature is predominately acoustic. In addition, an analysis of the zero-frequency subspace (i.e. the space of time-independent perturbations) reveals two sets of degenerate spheroidal perturbations, which we interpret to be the missing g-modes, and two sets of toroidal perturbations. We anticipate that the degeneracy of all these zero-frequency modes will be broken by the Coriolis force in the case of rotating stars. To illustrate this we consider the toroidal pulsation modes of a slowly rotating superfluid star. This analysis shows that the superfluid equations support a new class of r-modes, in addition to those familiar from, for example, geophysical fluid dynamics. Finally, the role of the entrainment effect on the superfluid mode frequencies is shown explicitly via solutions to dispersion relations that follow from a 'local' analysis of the linearized superfluid equations.     

HR 7275: A new variable star

Differential photometry of the KI IV-III RS CVn-type binary HR 7275 in 1978, 1979, and 1980 at nine different observatories shows it definitely to be variable, thus confirming the suspicion of Herbst. The photometric period determined two ways was 27 _. ^d 91 or 27 _. ^d 65, thus about 3% shorter than the spectroscopically determined orbital period of 28 _. ^d 59. The total variation observed during the three years was 0 _. ^m 22 in theV. The light curve was always asymmetrical, with a stillstand on the rising branch in 1978 but on the falling branch in 1980.Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.Of the AAVSO.     

54 Cam: A new variable star

Differential photometry of the RS CVn-type binary 54 Cam in 1978, 1979, and 1980 shows its light to be variable with a period of 10 _. ^d 163±0 _. ^d 009 and an amplitude inV (max. to min.) which increased from 0 _. ^m 03 to 0 _. ^m 06 between 1979.19 and 1980.82. An epoch of light minimum was JD 2444529.7. The 9% difference betweenP(phtm.)=10 _. ^d 163 andP(orb.)=11 _. ^d 0764,a much larger difference than is characteristic of other RS CVn binaries, is suggested as an explanation for the radio emission.Guest Investigator, Kitt Peak National Observatory,which is operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.Of the AAVSO.     

The variable star SBS 0150+339

Plates from the Second Byurakan Survey reveal two large increases in the brightness of this star in 1972 and 1975. Spectra of this variable have been obtained for the first time. It is not visible in plate H2133 from the Hamburg survey, which has a limiting brightness of ~18m. Our data confirm that the star is an eruptive variable, most likely of the U Gem type.     

An unusual variable star: CH Cyg

Conclusions The existing observational data on CH Cyg agrees well with a model consisting of a semiregular M6 III giant and a white dwarf with a transient accretion disk formed at the time of the large maxima. The model can be tested by means of x-ray and speckle-interferometric observations.Institute of Astrophysics and Physics of the Atmosphere, Estonian Academy of Sciences. Translated from Astrofizika, Vol. 16, No. 3, pp. 443–455. July–September, 1980.     

Problem of the motion of a star inside a layered inhomogeneous elliptical galaxy with a variable mass

The problem of the motion of a star inside a layered inhomogeneous rotating elliptical galaxy with a variable mass is considered. We have found an analogue of the Jacobi integral and determined the possible regions of motion. A solution to the equations of perturbed motion has been obtained.     

A new red variable star in the globularcluster M4

G302 = L3107 is a red star located at the lowest end of the red giant branch of the globular cluster M4. According to its location on the C-M diagram, G302 may be a cluster member. No proper motion or radial velocity determinations are available up to date.

We discovered that C302 is a new variable star with a main period of 1.24719 day and a peak to peak amplitude of about 0.3 mag in V. It may have a second period of 2.38249 day with an amplitude of about 0.05 mag. If it is a cluster member, then there will be interesting implications for the the theory of stellar evolution.     

The ejecta from the luminous blue variable star P Cygni

Further optical observations have been made with the Manchester Occulting Mask Imager and Manchester Echelle Spectrometer of the inner and outer shells of P Cygni, and of the 7-arcmin long giant lobe projecting from this luminous blue variable star.
An image in the light of the fluorescently excited [Ni  ii ] 7378-Å line has revealed the knottiness of the inner shell. Well defined 'velocity ellipses' for the position/velocity arrays across the outer shell indicate that its expansion velocity is 160 km s⁻¹ which is somewhat lower than the previously reported value.
The kinematical behaviour of the giant lobe, both in the vicinity of P Cygni, and further away, emphasizes its strange nature, although close association with P Cygni is again suggested by these new observations. One possibility is that this lobe is a 'trail' of collimated ejected material.
The observations are compared with a 60-μm IRAS high-resolution map of the region.
A variety of possible explanations of the observed phenomena are explored, e.g. radio knots in the outer stellar wind either coalesce or expand to become the [Ni  ii ]7378-Å emitting knots in the inner shell; that a mass-loaded wind overunning slower moving clumps explains the kinematics of the inner shell; that the one-sided giant lobe could be a 'trail' of ejected material from P Cygni funnelled through the outer shell.     

The reclassification of the suspected R coronae borealis star SY hyi as a semiregular variable

SY Hyi is classified as a suspected R Coronae Borealis-type variable star. Photometric and spectroscopic observations of SY Hyi lead to the star’s reclassification as a semiregular variable of spectral type M5-6.