The OAO-A2 observations of two Be stars, 60 Cygnus and gamma Cassiopeia, were analyzed. It is shown that unpolarized radiation produced by continuous Balmer emission in the atmospheres of Be stars is significant in the explanation of the polarization observed below the Balmer discontinuity. Available multicolor polarimetry data was also analyzed with respect to interstellar polarization

Coyne, G. V.

English

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11828
FINAL REPORT
Grant HGR 03-002-193
GUEST OBSERVER PROGRAM OAO
August 29, 1972
Be Stars:
Observations by OAO-A2 of two Be stars, 60 Cyg and Gamma Gas, have been
'analyzed to show that unpolarized radiation produced by Balmer continuous
emission in the atmospheres of Be stars is significant in explaining the
polarization observed shortwards of the Balmer discontinuity. The polar-
ization in the UV in Be stars is relatively less than that in other stars,
because of the added unpolarized energy produced by Balmer continuous emis-
sion in Be stars. The ratio of the energy flux (normalized at 2200A) of
Be stars to normal B stars, with the same amount of reddening, varies from
about l.U at 3600 A to 1.05 at 2500 A. This is interpreted as due to contin-
uous emission in Be stars. For Gamma Cas the polarizations at 3300 A and
3600 A are respectively 0.6 and 0.7 of the values one expects from inter-
stellar polarization. Neutral polarization produced by Thomson scattering
and thence modified by both hydrogen absorption and Balmer continuous emission
is adduced to explain the wavelength dependence of the observed polarization.
These results are now in press (Coyne 1972).
In support of the OAO observations of Be stars, Coyne 1971 has pub-
lished further ground-based observations of Be stars and has given the best
mean values for the wavelength dependence of the intrinsic polarization in Be
stars from 0.3 to 1.0 microns.' Furthermore, in support of the OAO observa-
tions Coyne and Dyck (1972) have shown that the polarization for one Be star,
Zeta Tau, shows an almost flat wavelength dependence from about 0.75 to 1.60
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microns, where the polarization drops into the infrared. It will "be inter-
esting to know whether the Paschen discontinuity is responsible for the pecu-
liar wavelength dependence of the polarization in the red-infrared as the
Balmer continuous emission is responsible for the peculiar wavelength depen-
dence of the polarization in the UV. Infrared polarimetric observations of
Gamma Cas and 60 Cyg will be of interest in that regard.
Interstellar Polarization:
With respect to the interstellar polarization, all of the available
multi-color polarimetry has been analyzed by us (Coyne, Gehrels, Serkowski
19J2a, 1972b) and it has been shown that the wavelength, X > at which
1T1S.X
the maximum polarization occurs is a characteristic parameter of the inter-
stellar grains. Stars with large values of X appear also to have abnor-
mal wavelength dependence of the extinction. We are nov analyzing the OAO
photometric data in conjunction with ground-based photometric data for two
stars, HD 37903 and Rho Oph, both of which have large values of Xmax-
References:
Coyne, G. 1971, Ric. Astron. 8_, 201.
Coyne, G. 1972, in "Proceedings of the Symposium on the Scientific Results
from the Orbiting Astronomical Observatory,", ed. A.D. Code, WASA
SP series (to be published, November 1972).
Coyne, G. and Dyck, H.M. 1972, (to be published). .
Coyne, G., Gehrels, T. and Serkowski, K. 1972a, in "Proceedings of IAU
Symposium 52 on Interstellar Dust and Related Topics", ed. J. M.
Greenberg (to be published).
1972b, Astron. J. (to be published).
G. V. Coyne, S'.J.
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