Volume 3, Issue 1
March 1982, pages 1-92
pp 1-4 March 1982
Photoelectric radial-velocity measurements show that HD 105341 is a spectroscopic binary with a near-circular orbit and a period of 194 days.
pp 5-11 March 1982
The general topology of the braiding in Saturn’s F ring is explained by invoking the theory of invariant surfaces to which a plasma would confine itself. This surface, in the framework of serf-consistent fields, is indeed generated by two helicoids turning in opposite directions and are braided.
pp 13-25 March 1982
Potential curves for theB andX states of I2, NS and PS have been obtained by Rydberg-Klein-Rees (RKR) method. From these RKR potentials, Franck-Condon factors (FCFs) lot the above band systems have been calculated using the best available molecular constants, tested for accuracy on the electronic transition moment (ETM)-r-centroid curve in the case of I2 and used in the study of observed abnormal intensity distribution in some bands of NS. A brief outline of the method used in the calculations of the FCFs is given.
pp 27-38 March 1982
UBV photometry of HR 1099 obtained during the 1979-80 and 1980-81 observing seasons is presented. An analysis of the available data shows that the brightness at the light curve maximum increases as the wave amplitude increases, while the brightness at the light minimum remains almost the same. In terms of the starspot model it implies that there is always a hemisphere of the active component that is nearly ’saturated’ with spots and that spots occupy a larger fraction of the stellar surface when the wave amplitude is smaller. The continuous migration attributed to the photometric wave by various authors is far from certain. The amplitude of the wave has a sharp rise followed by slow decay with a period around 5–6 yr. It is found that the two-spot model proposed by Dorren and Guinan (1982) is inadequate to describe all the observed photometric peculiarities of HR 1099.
pp 39-61 March 1982
A spectroscopic study of Hα has been carried out to investigate the properties of expanding chromospheres of late G and K supergiants. Spectra of 23 stars brighter thanV = 6.0 have been obtained at dispersions of 4–10 å mm-1 using the coude and the coudé-echelle spectrographs at the 102-cm telescope of Kavalur Observatory. The Hα profiles are all asymmetric in the sense that the absorption core is shifted to the blue by amounts ranging between -4 and -24 km s-1.
Hα profiles were theoretically computed using radiative transfer in spherically symmetric expanding atmospheres covering a large range of integrated optical depths. These were compared with the characteristics of the observed line in the programme stars. The analysis shows that the Hα line is formed in a region with velocity increasing outward. The computed equivalent widths and line core displacements were matched with those observed to obtain hydrogen column densities and expansion velocities. From these, the rates of mass loss in these stars were determined to be in the range of 10610-7 M⊙ yr-1.
pp 63-67 March 1982
A new solution of Einstein-Maxwell field equations is presented. The material content of the field described by this solution is a perfect fluid plus sourceless electromagnetic fields. The metric of the solution is explicitly written. This metric is examined as a possible representation of Kerr-Newman metric embedded in Einstein static universe. The Kerr-Newman metric in the background of Robertson-Walker universe is also briefly described.
pp 69-77 March 1982
Fabry-Perot interferometric observations on the green coronal line (λ 5303 å) carried out during the total solar eclipse of 1980 February 16 have yielded relative Doppler shift velocities with an accuracy of ± 7 km s-1. The values show a peak in the 30–50 km s-1 range indicating largescale macroscopic mass motion in the solar maximum corona.
pp 79-92 March 1982
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 Teff = 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.
Volume 40 | Issue 2
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