We find well pronounced and rather symmetric wine-bottle structures in
the profiles of HR 335, 1660, 2749, 2825, 3237, 8773, and pronouncedly
asymmetric wine-bottle inflexions in the profiles of HR 1622 and 6118.
The average vsini for these eight stars is 124 km s-1 which is well
below the sample average of
.
This clearly indicates that
wine-bottle structures are associated with Be stars with low
inclination as shown by Hummel (1994) and
Hanuschik et al. (1996). This
effect can be clearly seen in Fig. 9 where we have plotted the
ratio versus the equivalent width and marked the eight stars
on it.
It may be pointed out that in twelve of the stars viz. HR 264, 496, 1087, 1789, 1858, 1910, 2356, 3858, 5440, 5778, 5941 and 7106, the line profiles appear to be broader than the 25 Å coverage of the spectrum. Therefore in Fig. 9, the equivalent widths of these stars may be marginally underestimated. However, this will not affect the above conclusions, because this underestimation, if corrected, will only enhance the separation between the wine bottle stars and the rest.
A comprehensive review of the mechanisms which broaden the line profiles
has been given by Hanuschik et al. (1996). The principal amongst
them are the thermal broadening, the kinematical broadening, the shear
broadening (Horne & Marsh 1986) and the non-coherent scattering
broadening (NSB) (Avrett & Hummer 1965; Hummel &
Dachs 1992; Hummel 1994). As shown there, the amount
of broadening due to each of
these mechanisms depends largely on the inclination of the rotation
axis of the star. For symmetrical profiles, and for most ranges
of inclination (except for almost pole-on or low inclination stars),
kinematic broadening is the largest and most important contributor to
the profile width. The kinematic broadening occurs because of the
supposedly Keplerian motion of the gas in the disc. Since the
projected Keplerian velocity in the disc (
)
is expected to
increase with the stellar rotational velocity
,
the observed widths of the line should also increase with the
stellar
values. Although simple, this scenario still gives a
useful qualitative picture. In Figs. 10 and 11 we have plotted the
observed fullwidths (E') and the halfwidths (l) of the profiles
versus
.
It, however, does not mean that the contribution of NSB and other mechanisms to the line widths is always negligible. NSB, in particular, is equally important in the case of low inclination or near pole-on stars as pointed out by Hanuschik (1996). In such cases, since NSB and kinematic broadening are of the same order (Hanuschik 1996), the convolution of the two is not expected to lead to a final width much different than that caused by each mechanism separately. Thus the effects of NSB broadening may be lost in the scatter of the points in Figs. 10 and 11.
Regarding the shape of the profiles, Hummel (1994) has shown how
emission lines of symmetric shape, ranging from the wine-bottle
structure type to the shell profiles, can be satisfactorily explained
by the NSB mechanism. His model calculations show how the peak
separation of the V and R components and also the equivalent width
should relate to the changes in the inclination (or
)
of the
circumstellar disc. From our data we have selected nineteen sources
for which the line profiles are symmetric or nearly symmetric with
respect to the V and R components. These sources are HR 496, 1087,
1165, 1508, 1789, 1858, 1934, 1956, 2284, 2356, 2492, 2845, 3858, 3946,
4787, 5193, 5440, 6510 and 6712. In Fig. 12 we have plotted the peak
separation
versus vsini.
![]() |
Figure 12:
A plot of
![]() ![]() |
The equivalent width W versus
plot for the sample of
these nineteen stars is shown in Fig. 13.
![]() |
Figure 13: A plot of the observed equivalent widths versus peak separation between the V and R components for those stars that showed symmetrical profiles |
Acknowledgements
The authors wish to thank D.B. Pancholi for his able assistance on the telescope floor during some of the observational runs. We thank the referee for his valuable suggestions. The work was supported by the Department of Space, Government of India.
Copyright The European Southern Observatory (ESO)