T H E C A U S E S OF T H E L I G H T V A R I A T I O N S
B.
Sternberg
State
F.
IN AG
Peg
Yudin
Astronomical
U.S.S.R.
Institute,
Moscow,
It can be s h o w n that t h e l o n g - t e r m p e r i o d i c v a r i a t i o n s in the U b a n d , d i s t i n c t l y o b s e r v e d in AG peg by
UBV p h o t o m e t r y ( B e l y a k i n a 1 9 7 0 ) from the e a r l y 1 9 6 0 ' s
with a m p l i t u d e i n c r e a s i n g , o v e r s i n c e , h a v e in fact two
p r i n c i p a l r e a s o n s for t h e i r e x i s t e n c e . O n e of t h e s e is
t r a n s p a r e n c y of the e n v e l o p e to the L c - e m i s s i o n of the
hot c o m p o n e n t in AG Peg a r i s e n in the 1 9 5 0 ' s and i n c r e a sing s i n c e t h e n . T h e s e c o n d o n e is c o n n e c t e d with the c h a n ges of the t r a n s p a r e n c y of the c o m p a c t part of the gas e n v e l o p e l o c a t e d c l o s e to t h e hot c o m p o n e n t w h e n in m o v e s
a l o n g its o r b i t ( Y u d i n 1 9 8 7 ) . It is i n t e r e s t i n g to n o t e
that for the o r b i t a l s o l u t i o n with n o n - z e r o e c c e n t r i c i t y
( H u n c h i n g s et a l . 1 9 7 5 ) the t r a n s p a r e n c y m i n i m u m and
cons e q u e n t l y the flux e m i s s i o n m a x i m u m for t h e gas e n v e l o p e
in AG Peg a r e o b s e r v e d in the m o m e n t w h e n the hot c o m p o n e n t
is c l o s e to its a p o a s t r o n . T h e a m p l i t u d e of the p e r i o d i c
v a r i a t i o n s in V i n c r e a s e s due to the e x i s t e n c e in AG Peg
of the e f f e c t of n o t i c e a b l e h e a t i n g of t h e cool c o m p o n e n t ' s
h e m i s p h e r e f a c i n g its hot c o m p a n i o n . U s i n g the T i O b a n d s in
the red the cool c o m p o n e n t in AG Peg is c l a s s i f i e d as
s l i g h t l y e a r l i e r than M2 from i l l u m i n a t e d s i d e and s l i g h t l y
later than M3 from the o p p o s i t e o n e ( I p a t o v and Y u d i n
1986).
N o w a d a y s the r a d i a t i o n flux from the gas e n v e l o p e ,
that is its o p t i c a l d e p t h , c h a n g e s from m a x i m u m to m i n i m u m
by a b o u t a f a c t o r of 2 . 5 . In 1 9 8 4 , at the m a x i m u m of its
b r i g h t n e s s , o n l y a b o u t 3 7 % of the t o t a l a m o u n t of the L c q u a n t a w e r e a b s o r b e d in the gas e n v e l o p e . At the s a m e t i m e ,
the hot s t a r ' s t e m p e r a t u r e and boloraetric l u m i n o s i t y w e r e
e q u a l to a b o u t 7.9 1 0 ^ K and 5.7 1 0 ^ Lo r e s p e c t i v e l y
( L ( h , b o l ) 4 L ( c , b o l ) ; I p a t o v and Y u d i n 1 9 8 6 ) .
A comparison of the hot c o m p o n e n t ' s b o l o m e t r i c l u m i n o s i t y at p r e sent with that d e r i v e d for the m o m e n t of its v i s u a l b r i g h t ness m a x i m u m show that the d e c l i n e from t h e m a x i m u m h a v e
not been a c c o m p a n i e d by the n o t i c e a b l e l u m i n o s i t y c h a n g e s
261
/. Mikolajewska et al. (eds.), The Symbiotic Phenomenon, 261-262.
© 1988 by Kluwer Academic Publishers.
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262
yet
(Boya rchu k 1 9 6 7 )
The uni que ligh t cur ve of the AG Peg d u r i n g its
o u t b u r s t , whi ch has b e e n cont i nui ng s i n c e 1 8 5 0 ' s , and its
very
Ion g-li ved W - R pha se ac c o m p a n i ed by the v e r y hi gh
rate of i a s s loss by the hot c o m p o n ent (M> 1 0 - 6 Mo y r - * ) ,
Mo from its h y d r o g e n
havi ng sh ed a I ready m o r e t h a n
e n v e l o p e , cou Id be u nde r s t o o d i f we s u p p o s e th at the p r e sent o u t b urst of the hot comp o n e n t in AG P eg w as c o n n e c t e d
with the heli um (but not h y d r o g e n ) s h e l l f lash
T h e di f f e r e n c e s in t he Li g ht curv es o f sym bi oti c
n o v a e (AG Peg , V 1 0 1 6 Cyg , HM S g e ) a nd c las s i caI sym bi oti c
star s (Z A n d , CI Cyg , AG D r a ) are d ue to a dif f e r e n t role
of t he ac cret ion pro cess in t h e s e s y s t e m s . In symbi ot i c
nova e, ac cret ion is not a not i ceab I e e n e r g y so u r c e s of the
hot s u b d w arf . It can pla y on I y role of a s uppl i er of h y d roge n fue I to its su rf ac e w h e n the hot sub dwar f air eady is
cool ing d o w n . In c la ssi c a I sy mbi ot i c s y s t e B I S , at le ast d u ring the o u t b u r s t s o f th ei r h ot com p o n e n t s , ac c ret i on b e come s a p redo mi nant s o u r ce of e n e r g y of th e ho t sub d w a r f .
The t r a n s i t ion from a symb i ot i c nova to a c l a s si ca I syra biot i c s t a r tak es pi ace at the mo ment w h e n the
coo I corap o n e n t' s si z e i s a p p r oach i ng the s i ze of it s R o c h e
lobe , res ulti ng i n a sha rp in c r e a s e of the ace ret i on rate
of i ts ma t t e r o n t o t he h ot co m p o n e n t (Yudi n 19 8 7 ) . The
n o n s tat i onari ty of t his p r o c e ss lea ds to t he e m e r g e nee of
the n o v a - like o u t b u r st s on th e ligh t c u r v e s of symb i oti c
s t a r s whi ch a re now call ed c Iassi ca I.
References
B e l y a k i n a , T. S.: 1 9 7 0 , A s t r o f i z i k a 6, 4 9 .
B o y a r c h u k , A. A.: 1 9 6 7 , A s t r o n . Zh. 4 4 , 1 2 2 2 .
Hutchi n g s , J. B . , C o w l e y , A. P. and R e d m a n , R. 0.:
1 9 7 5 , A s t r o p h y s . J. 2 Q 1 , 4 0 4 .
I p a t o v , A. H. and Y u d i n , B. ?.: 1 9 8 6 , P i s ' m a A s t r o n
Zh.
12, 9 3 6 .
Y u d i n , B. F : 1 9 8 7 , A s t r o p h y s . and Space Sci
in press,
Y u d i n , B . F.: 1 9 8 7 , A s t r o n . T s i r k . , in p r e s s .
Downloaded from https://www.cambridge.org/core. IP address: 88.99.165.207, on 31 Jul 2017 at 21:28:25, subject to the Cambridge Core terms of
use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100103586