• M. B. K. Sarma

Articles written in Journal of Astrophysics and Astronomy

• The distortion wave on the light curve of the RS CVn binary UV piscium

The eclipsing binary UV Piscium was observed with the standardUBV filters during 1976-77, 1977-78 and 1978-79 observing seasons with the 1.22-m reflecting telescope of the Japal-Rangapur Observatory. A wave-like distortion on the light curve noticed by Carr (1969), Oliver (1974), Sadik (1979) and Zeiliket al. (1982a) is confirmed by the present observations. Combining our observations with those of Carr, Oliver and Sadik, it is found that the distortion wave is moving towards decreasing orbital phase with a period of about 1200 days. The source of the observed distortion wave is found to be the hotter component.

• Spot activity in the RS CVn binary UX arietis

Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation.

• Orbital elements of the RS CVn eclipsing binary, SV Camelopardalis

The extensiveUBV observations of SV Camelopardalis by Patkos (1982) have been analysed to derive the orbital elements of the system. The data were corrected for the effect of third body (Sarma, Sarma & Abhyankar 1985) and for the ‘RS CVn’ distortion wave (Sarma, Vivekanandarao & Sarma 1988). The cleaned data were used to obtain a preliminary solution by a modified version of Wellmann method (Sarma & Abhyankar 1979) from which we concluded that the primary eclipse is a transit. The final orbital elements of SV Cam were obtained by the modified version (Sarma 1988; Sarmaet al. 1987) of WINK program by Wood (1972). The colour and median brightness variation are discussed. From the spectroscopic mass functionf(m) = 0.118 M (Hiltner 1953), the absolute dimensions of the components are found to be 0.826 Mbd & 0.592 M and 1.236 R & 0.778 R for the primary and secondary components, respectively. The age of the binary system is estimated to be 6.0 ± 1.0 × 108 years

• A study of the distortion wave in the RS CVn eclipsing binary SV Camelopardalis

The light outside the eclipses of the totally eclipsing RS CVn binary SV Camelopardalis (SV Cam) is Fourier analysed and the amplitudes of the distortion waves have been derived. The distribution of the percentage contributions of these amplitudes inV, B andU colours with respect to the luminosities of the binary components indicates that the hotter component is the source of the distortion waves. These distortion waves, attributed to star spots, are modelled according to Budding (1977) and spot parameters like longitude, latitude, temperature and size are obtained. From this study it is noticed that while symmetric waves with two minima could be fitted satisfactorily, asymmetric waves with more than two minima could not be fitted well. From the longitudes of the minima of the best fitted curves, migration periods of four spot groups are determined. Assuming synchronism between rotation and orbital periods, the rotation periods of the four spot groups are derived from their migration periods. The period of rotation of one of the spot groups having direct motion is found to be 0d.5934209 while the periods of the other three spot groups having retrograde motion are 0d.5926588, 0d.592607 and 0d.5924688. As the latitudes of these spots are known from modelling parameters, the latitude having a rotation period equal to that of the orbital period (co-rotating latitude) is found to be about 30°

• BV 690, a new bright Type II Cepheid

B andV observations of the suspected variable BV 690 = NSV 04298 are reported. The star shows light variations with a period of ld.2400 and with amplitudes of 0m.27, 0m.36 and 0m.11 inV, B, andB-V respectively. The light curves show steeper rise than decline, and there is evidence for the presence of a bump in the descending branch around the phase of 0.35. From considerations of the period, spectral type, presence of the bump and high tangential velocity we conclude that BV 690 belongs to the BL Herculis class of Typen Cepheids

• Spot modelling and elements of the RS CVn eclipsing binary WY Cancri

Results of analysis of photoelectric observations of the RS CVn eclipsing binary WY Cancri in the standard passbands ofUBV during 1973-74, 1976-79 and inUBVRI during 1984-86 are reported. A preliminary analysis of the eclipses suggested the primary eclipse to be transit. A study of the percentage contribution of the distortion wave amplitudes in all the colours with respect to the luminosities of both components, showed the hotter component to be the source of the distortion wave. The clean (wave removed) light curves of different epochs have not merged, suggesting residual effects of spot activity. The reason for this is attributed to the presence of either (1) polar spots or (2) small spots uniformly distributed all over the surface of the hotter component. This additional variation is found to have a periodicity of about 50 years or more. The distortion waves in yellow colour are modelled according to Budding’s (1977) method. For getting the best fit of the observations and theory, it was found necessary to assume three or four spots on the surface of the hot component. Out of these four spot groups, three are found to have direct motion with migration periods of 1.01, 1.01 and 2.51 years while the fourth one has a retrograde motion with a migration period of 3.01 years. From these periods and the latitudes of the spots derived from the model a co-rotating latitude of 4ℴ is obtained. The temperatures of these spots are found to be lower than that of the photosphere by about 700ℴK to 800ℴK. Assuming the light curve of 1985-86, which is the brightest of all the observed seasons, to be least affected by the spots, the light curves of the other seasons are all brought up to the quadrature level of this season by applying suitable corrections. The merged curves in theUBVRI colours are analysed for the elements by the Wilson-Devinney method. This analysis yielded the following absolute elements:$$\begin{gathered} m_h = 0.86 \pm 0.03{\text{ }}M_ \odot \hfill \\ m_h = 0.51 \pm 0.03{\text{ }}M_ \odot \hfill \\ R_h = 0.99 \pm 0.02{\text{ }}R_ \odot \hfill \\ R_c = 0.65 \pm 0.02{\text{ }}R_ \odot \hfill \\ T_h = 5520^o K \pm 100^o K \hfill \\ T_c = 3740^o K \pm 20^o K \hfill \\ M_{h(bol)} = 4\mathop .\limits^m 96 \pm 0.10 \hfill \\ M_{c(bol)} = 7\mathop .\limits^m 58 \pm 0.15 \hfill \\ Spectral type hotter component = G5 \pm 1 \hfill \\ cooler component = K9 \pm 1 \hfill \\ \end{gathered}$$ For a mass ratio of 0.506 and with the derived fractional radii rh = 0.241 andrc = 0.157, both the components are found to be within their Roche lobes. Hence we have classified WY Cnc as a detached system. From their positions on the HR diagram it is concluded that both the components of WY Cnc belong to the main sequence.

• Orbital elements and evolutionary nature of the long period RS CVn type eclipsing binary RZ eridani

Light curves of the long period RS CVn type eclipsing binary RZ Eri, obtained during the period 1976–1979 with the 1.2 m telescope of the Japal-Rangapur Observatory are analysed, using Wilson-Devinney method, by fixing the two parametersTh (7400°K) andq(0.963), resulting in the following absolute elements:A = 72.5 ± 1.4R,Rh = 2.84 ± 0.12R,Rc = 6.94 ± 0.20R,Mbol,h = 1.35 ± 0.28,Mbol,c= 1.41 ± 0.28,mh = 1.69 ± 0.6m andmc= 1.63 ± 0.13m. The presence of humps and dips of varying amplitudes at a few phases in the normal UBV light curves is explained as due to residual distortion wave. The derived (B-V) and (U-B) colours of both the components appear to have been reddened to an extent of 0m.20 in (B-V) and 0m.16 in (U-B) colours. This reddening is attributed to the presence of an envelope around the system, the material of which might have come from the loss of mass experienced by the evolving cooler component. Taking into consideration the dereddened colours and temperatures of the components, spectral types ofF0 IV for the primary and G 5–8 III–IV for the secondary component were derived. The fractional radii of 0.039 and 0.096 of the two components, when compared with the radii of their critical Roche lobes of 0.378 and 0.372 suggest that these components are well within their critical sizes. From the position of the components on the. isochrones and the evolutionary tracks of stars of Pop I composition computed by Maeder & Meynet, it is concluded that the evolution of the components of RZ Eri is abnormal. This system is found to be situated at a distance of 185 pc, with an age of about 2.5 × 109 yrs.

• VV Orionis – improved elements

TheUBV light curves obtained by Duerbeck (1975) andHa (wide) and Ha (narrow) light curves obtained by Chambliss & Davan (1987) of the detached eclipsing binary VV Orionis (VV Ori) were analysed using the Wilson-Devinney method fixing the two parametersTh (25,000 K) and q(0.4172), resulting in the following absolute elements:A = 13.605 ± 0.03 LR,Rh = 5.03 ±0.03R, Rc = 2.43 ±0.02R,Mbol,h = -5.18 ± 0.11,Mbol,c = -1.54 ± 0.06,mh =10.81 + 0.42m andmc = 4.51 ± 0.41m. The de-reddened colours obtained from applying the reddening corrections ofE(B-V) = 0m.05 andE(U-B) = Om.04, and the derived temperatures of the components, gave spectral types ofB 1.5V for the primary and 54-5V with anUV excess of 0m·3 for the secondary component. A comparison of the logL and logTe of the components with the observed ZAMS shows the primary component to be a little above and the secondary component to be a little below/or on the ZAMS. A comparison of the properties of the components of VV Ori and a few other detached systems with the normal stars in the logL, logR and logTe versus logm planes, indicated a need for either a readjustment of the scales of the above parameters or modifications in the theoretical models. From the position of the components on the evolutionary tracks of Pop I composition computed by Schaller et al. (1992) it is noticed that while the primary component of W Ori had slightly evolved along the main-sequence, its secondary is still unevolved. The age of VV Ori is found to be 10 ± 1 million years and it is at a distance of 368 ± 10 pc.

• # Journal of Astrophysics and Astronomy

Volume 41, 2020
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• # Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

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Posted on July 25, 2019