Emission line studies of wolf-rayet binaries B. S. Shylaja [Ph.D Thesis]

Doctor of Philosophy Indian Institute of Astrophysics, Bangalore 1986

The 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.