Mass loss in semi-detached binaries

Pre-Main-Sequence contracting objects, post-Main-Sequence expanding stars and mass-losing components of semi-detached systems all occupy more or less the same region in the conventional H-R-diagram. We make a transformation to variables Δ(logL) and Δ(logTe), where Δ is the difference between the observed quantity, logL or logTe, and the value of that quantity which a star of the same mass would have on the empirical Main Sequence. It is demonstrated that a plot between the new variables clearly separates the mass-losing stars from other objects which is essentially an effect of the increasing abundance of helium relative to hydrogen

Intensity and polarization line profiles in a semi-infinite Rayleigh-scattering planetary atmosphere. III. Variation of polarization profiles and the Stokes parameter Q over the disk

The variation of the polarization profiles, the Stokes parameters Q and U, and the angle defining the plane of polarization along the intensity equator and along the mirror meridian, on which μ = μ0, in a Rayleigh scattering atmosphere is studied. It is found that these variations are more complex than thought hitherto, particularly at large phase angles

A reconsideration of the effective depth of line formation in planetary atmospheres

A new definition of the effective depth of line formation is given which incorporates its dependence on the angle of emergence as well as on the position within the line. Solution obtained for isotropic scattering in the third approximation of discrete ordinates explains: (i) Variation of equivalent widths over the disc; (ii) Inverse dependence of this variation on line strength; and (iii) The phase effect for relative equivalent widths

Intensity and Polarization line profiles in a semi-infinite Rayleigh-scattering planetary atmosphere. II. Variations of equivalent width over the disk

The study of the variation of equivalent width in a Rayleighscattering planetary atmosphere along the intensity equator and along the mirror meridian on which μ =μ0 shows that the equivalent widths decrease monotonically towards the poles, the limb and the terminator with the following characteristics: (i) the weakest lines exhibit the maximum change; (ii) the Ier component shows more change than the Iel component; (iii) the decrease towards the limb or the terminator is not as sharp as that towards the poles; (iv)Iel component shows more decrease towards the limb while Ier component shows more decrease towards the terminator; and (v) the relation W (μ,φ;μ0,φ0)= W (μ0,φ0;μ,φ) holds for the total intensity. These results are qualitatively in agreement with the observations of absorption bands in the spectra of Venus, Jupiter and Saturn

Analysis of the UBV light curves of TT hydrae by Kopal's frequency domain method

The light curves of the totally eclipsing system TT Hya in UBV colours observed by Kulkarni and Abhyankar during 1973-77 have been analysed by Kopal's frequency domain method with slight modification. We find rs (primary) = 0.104 ± 0.005, rg (secondary) = 0.215 ± 0.008 and i = 89° ± 1°. The value of rg obtained in this study is smaller than that determined earlier by Kulkarni and Abhyankar by the method of Russell and Merrill; this confirms the undersized nature of the secondary component. The ultraviolet colour excess of the secondary is also confirmed

MK Morphological Study of Am Stars at 66 Å/mm

The pseudo-luminosity effect in the metallic line A-type stars found by Abt & Morgan (1976) is confirmed in a random sample of 27 Am stars. From a morphological study of their spectra in the wavelength interval 3850-4400 Å at a reciprocal dispersion of 66 Å/mm, revised spectral types are given on the MK system for their K-line and metallic-line spectra. This shows that: (a) our segregation of weak Am from the Am stars largely agrees with that by Cowleyet al. (1969); (b) all the stars in the sample are dwarfs according to their K-line classification; (c) more than 80 per cent exhibit the pseudo-luminosity effect significantly, with their metallic-line spectra resembling a giant or even a supergiant in the violet (3850-4100 Å), and a giant rather than a dwarf in the blue region (4260-4400 Å); (d) in two-thirds of the stars under (c), the Sr n 4077 Å line is found to have a markedly brighter luminosity class compared to any region, and in more than one-third of the sample it is comparable to that in Ap stars; (e) at least five stars exhibit characteristics which might suggest a spectrum variability: among these, the most striking example is 41 Sex A which was found to show a phase-modulated spectrum variation hitherto unknown in Am stars; (f) the metallic-line spectra of another five stars appear to be similar to A-shell type in differing degrees; (g) less than 20 per cent of the sample comprises stars which do not show any significant differential luminosity effect; these stars might have been misclassified or perhaps they are in a quiescent state. We also confirm the conclusion arrived at by Bohm-Vitense & Johnson (1978) that all Am stars may vary and our observations suggest that groups may exist among them

The eclipsing binary WX Eridani

The Algol type eclipsing binary WX Eridani was observed on 21 nights with the 48-inch telescope of the Japal-Rangapur Observatory during 1973-74 and 1974-75 seasons in UBV colors. An improved period of P=0d.82327038 was obtained from the analysis of the times of five primary minima. Standstills between phase angles 50-80° , 100-130° , 230-260° and 280-310° were present in the light curves. The analysis of the light curves indicated the eclipses to be grazing with the primary a transit and the secondary an occultation. Elements derived from the solution of the light curve using Russell-Merrill method are given. From the comparison of the fractional radii with Roche lobes, it is concluded that none of the components has filled its respective Roche lobe. The spectral type of the primary component is estimated to be F3 and it is found to be a δ -scuti type variable pulsating with two periods equal to one-fifth and one-sixth of the orbital period

Equivalent widths of atomic lines in sunspot spectra

Equivalent widths of 82 Cr I lines, 70 Fe 1 lines, and 74 Ti I lines are measured in the spectra of four sunspots of average area 55 millionths of the visible hemisphere of the sun. Separate curves of growth for Cr I, Fe t, and Ti I are constructed. Excitation temperatures of 4030° ± 80° , 4200° ± 150° , and 3800° ± 100° are obtained for Cr I, Fe I, and Ti I, respectively

Absolute dimensions of TT hydrae

The photometric elements of the Algol type binary TT Hydrae derived by the authors from their UBV observations during 1973-77 have been combined with the spectroscopic elements given by Sanford (1937) and Sahade and Cesco (1946) to obtain the absolute dimensions of the system. It is found that the spectroscopic orbital elements given by Sanford represent the evolutionary status of the secondary component better than those of Sahade and Cesco. The primary appears to be an Al v main sequence star of mass ~ 3 to 4m⊙ and radius ~2.3R⊙. The secondary fills its Roche lobe; it can be represented by a K0III star of mass ~0.8m⊙ and radius ~6.0Rm⊙. Better spectroscopic data are needed for confirmation of these results

A model of the Algol type close binary TT Hydrae

UBV photometric observations and elements of TT Hydrae obtained by Kulkarni and Abhyankar (1980) are combined with the radial velocity curve of Popper (1979, personal communication) to derive the absolute dimensions and a model of this important Algol system. While the photometric ratios of radii in V and B are in agreement giving k = 0.3812 for a limb darkening coefficient of x = 0.6, application of Irwin's (1947) method gives x = 0.4 for U. The primary is found to be a main sequence A1 V star of mass 2.61M⊙ and radius 2.01 R⊙, and the secondary is classified as a K1 III star of mass 0.70 M⊙ and radius 5.33 R⊙. The observed Fourier coefficients for the light outside the eclipse agree with those calculated from theory for the reflection and ellipticity effects. The system shows an ultraviolet excess of 0.5 to 0.6 magnitudes during primary eclipse, which is attributed to an asymmetric circumstellar distribution of matter around the primary. The evolutionary status of the secondary, which does not appear to fill its Roche lobe completely, is discussed