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003 IN-BaIIA
005 20211108141141.0
008 211028s9999 xx 000 0 eng d
040 _cIIA Library
080 _a043:52
100 _aShylaja, B. S.
245 0 _aEmission line studies of wolf-rayet binaries
_c B. S. Shylaja
_h[Ph.D Thesis]
260 _aBangalore
_bIndian Institute of Astrophysics
300 _avi, 175p.
502 _bDoctor of Philosophy
_cIndian Institute of Astrophysics, Bangalore
520 _aThe construction of a kinematical and physical picture of a Wolf - Rayet atmosphere was attempted by late Prof. M.K.V. Bappu and the present work is a continuation of the understanding of these atmospheres. The binary systems have been chosen with the idea of seeing the variation of the atmospheric structure as it manifests in the presence of the companion. The simple method of observation of the flux variations was suggested by Prof. Bappu for this study. Generally the atmospheres of Wolf - Rayet (WR) stars are known to be extended. This was derived from the velocities of the emission and associated absorption lines. Further studies have shown that there is some type of stratification possibly prevalent in these atmospheres. To study this, the binary systems with WR components are chosen. When the companion passes in front of the primary WR component, atmospheric eclipses are expected to become noticeable. This can be observed as the variation in the total flux of the emission I ines under study. Spectrophotometric techniques provide accurate flux estimates and continuum energy distributions as well. The effect of the earth's atmosphere on the measured value of flux and the role played by the minor constituents of the atmosphere will have to be taken into account for this estimation. For this study, one of the objects chosen was the shortest period binary with WN7 component, CQ Cep. The line profiles have established the complexity of the atmosphere. The eclipse effect is displayed by only one line - N V line at A 4693. The radial veloci ty curves (RV) for different emission 1 ines indicate different orbital solutions. The continuum distribution also does not reveal the identity of the companion. Based on the flux variations, it is possible to arrive at the asymmetric distribution of the line emitting material as a possible cause for non-eclipse effects. The second obj ect chosen for study is HD 513896, which was considered as single earlier. Recent accurate RV and light variation studies have given it the status of a binary. The emission flux variations, which are reported in this work, reflect the asymmetric distribution of the line emitting material. The nature of the companion becomes indirectly evident, in the distortion of the atmosphere. Fast photometric measurements show variations, which may imply mass transfer and accretion. The open cluster NGC 6231 has two WR members associated with it, one of them being HD 152270 (WC7 + 0). This is an established binary with a period of 8.9 d. The measured flux show possible eclipse effects only for the high excitation lines like C III and C IV. On the other hand, the He I and He II show a scatter implying their non participation in the orbit. The photometric measurements in regions, which avoid the effect of emission lines, show that there is no eclipse of the continuum, as expected from the angle of inclination of the orbit, 39. The other member of the cluster, BD 151932 (WN7), considered single, shows irregular variation of flux all through. However, I the photometric variations display a periodicity of about 6 d. Confirmation of this requires better resolution spectra to detect small changes of radial. velocity, if any. The existence of a compact companion puts it to the second WR phase in the evolution of a close massive binary and, at the same time, its membership to the cluster becomes doubtful. From the study of the binaries and suspected binaries, the effect of the companion on the extended atmosphere can be partly understood. The shortest period system, CQ Cep, has the flux variations caused by the asymmetric atmospheric structure, which may be explained by wind dominant Roche surfaces. Similar variations in BD 59896, with a slightly larger period, show that the companion is effective in distorting the line emitting regions. The flux variations of the spectroscopic binary HD 152279 shows that, although the continuum eclipses are not seen, there is a possibility of atmospheric eclipses. Similar study of HD 151932 reveals the important aspect of a possible periodic variation only in the continuum and not of the line flux. This aspect can be established only by more detailed photometric' and spectroscopic investigation. Thus, It appears that there is a general, stratification common to all the above mentioned WR systems - the higher excitation lines arising closer to the photosphere. This leads to the distortion of all the emission lines, like N IV, C IV etc for CQ cep In HD 59896 such high excitation lines show moderate variations, while He II lines are more distorted. In case of the still longer period binary HD 152279, the eclipse effects are seen for the higher excitation lines like C III and C IV, and not for the He II and He I lines. When these results are compared with the available information on other binaries, many interesting results emerge. The atmospheric eclipse is evident in many spectroscopic binaries indirectly. Also the behaviour of the A 4686 line is different from other He II 1 ines in WN binaries. Similarly the WCs are likely to have the A 5696 line of C III as a special case. The results of HD 50896 and HD 151932 show different types of emission and light variations. The possibility of a compact companion in the latter case becomes smaller, especially when the results on another system with suspected, compact companion, HD 76536, are compared. Finally, the evolution of the WR phase in binaries and the possible effect on. the atmospheric structure are discussed, from which it appears that although the subgroups of.WRs are heterogeneous, the stratifications in their atmospheres, in general, are similar.
650 _aAstronomy and Astrophysics Thesaurus
650 _aPh.D.Thesis
650 _aWolf-Rayet Stars
700 _aJ. C. Bhattacharyya
856 _uhttp://prints.iiap.res.in/handle/2248/96
_yClick Here to Access eThesis
942 _cTD
999 _c9276