Adv. Space Res.
V o l . 5, No. 3, p p . 5 7 - 5 9 , 1985 0 2 7 3 - 1 1 7 7 / 6 3 S0 0U + 50 P r i n t e d zn G r e a t B r i t a i n . All rights r e s e r v e d . C o p ~ r z g h t ~ C 0 q P A RX - R A Y EMISSION F R O M T H E
P L A N E T A R Y N E B U L A N G C 1360
P A. J de Korte. J. J. Claas, F. A Jansen and
S P_ McKechme
Laho,ator~ tbl Space Research Letden. Wasse,~aa,-~eweg 78.
P 0
Boa 9504. 2300 RA Leiden. The Nethelland~
A B S T R A C T T h e E ~ O S A T o b s e r v a t o r y has d e t e c t e d t h e n u c l e u s of N G C 1360 an f o u r p h o t o m e t r l c e n e r g y b a n d s . T h e d a t a r u l e s out t h a t the e m i s s i o n is f r o m b l a c k b o d y o r a g a n . I n a t a a l f i t s m a d e w l t h L T E m o d e l a t m o s p h e r e s p e c t r a r e q u i r e t h e p r e s e n c e of h i g h l y a o n l z e d O x y g e n a n d N e o n in the s t e l l a r a t m o s p h e r e . I N T R O D U C T I O N C e n t r a l s t a r s of p l a n e t a r y n e b u l a e are b e l i e v e d to be a s h o r t s t a g e in the e v o l u t i o n of a r e d g a a n t t o w a r d s a w h i t e dwarf. A f t e r e l e c t i o n of t h e n e b u l a t h e c e n t r a l s t a r e v o l v e s f r o m a r e l a t a v e l y cool star (40.000 K) of I R Q i n t o an e x t r e m e l y h o t s t a r ( 1 5 0 . 0 0 0 K) of 0.01 R o. T h e r e a f t e r It c o o l s d o w ~ to a w h i t e d w a r f . S i n c e t h e d l s c o v e r y of s o f t X - r a y e m a s s i o n f r o m t h e w h i t e d w a r f HZ 43 / I / n u m e r o u s h o t w h i t e d w a r f s h a v e b e e n d e t e c t e d as X - r a y s o u r c e s . B e c a u s e of t h e i r h i g h e r t e m p e r a t u r e , n u c l e i of p l a n e t a r y n e b u l a e a r e e x p e c t e d t o b e s t r o n g e r X - r a y s o u r c e s , a l t h o u g h s o f a r n o t h a n g h a s b e e n p u b l i s h e d . O B S E R V A T I O N S E X O S A T o b s e r v a t a o n s of N G C 1360 h a v e b e e n c a r r i e d o u t on A u g u s t 20, 1983. A l l f l v e a v a i l a b l e f a l t e r s h a v e b e e n u s e d t o o b t a a n m a x i m u m s p e c t r a l i n f o r m a t i o n a n d t o be a b l e to c o r r e c t the d a t a for U V - c o n t a m l n a t l o n . S o u r c e f l u x e s h a v e b e e n d e t e r m i n e d f r o m a c i r c u l a r b o x of 2 arc m i n u t e daameter c e n t e r e d on the source. An a n n u l u s of 10 arc m i n u t e o u t e r d l a m e t e r a r o u n d the s o u r c e cell d e f i n e s t h e b a c k g r o u n d .
T h e d a t a h a v e b e e n c o r r e c t e d for U V - c o n t a m l n a t l o n b y m a k a n g u s e of x n f l a g h t c a l l b r a t a o n s /2/. F o r t h e d e t e r m i n a t i o n of the c o n t a m i n a t i o n l e v e l s , the A N S - s p e c t r u m for N G C 1360 w a s u s e d /3/. A l s o an I n d e p e n d e n t c h e c k h a s b e e n m a d e b y u s a n g the i n t e r n a l c o n s i s t e n c y of all f a l t e r data. T h e O V - c o n t e m i n a t i o n for t h e d a t a u s e d In the X - r a y anal y s l s as at m o s t 7%. P o l y p r o p y l e n e d a t a are, due to a h i g h e r O V - c o n t e m a n a t l o n , not u s e d .
T h e c o r r e c t e d s o u r c e f l u x e s t o g e t h e r w i t h I ~ e r r o r s a r e g l v e n xn t a b l e I.
A N A L Y S I S ~ N D I N T E R P R E T A T I O N
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F a g u r e I: 90% c o n f a d e n c e c o n t o u r for a b l a c k b o d y X - r a y data. fat to the NGC 1360 l n t e n s l t y , r e p r e s e n t e d b y (R/D) 2 , ~s g l v e n for the N h, T b b v a l u e s on t h e 90% c o n f i d e n c e c o n t o u r an f l g u r e 2. F o r the i n t e r s t e l l a r c o l u m n d e n s a t y in the d a r e c t i o n of N G C 1 3 6 0 , ( 1 . 4 Z 0 . I ) ~ 0 2 0 8 - a t ~ s / c m 2 / 6 / , the b l a c k b o d y temperature e q u a l s 3 8 . 0 0 0 2 8 . 0 0 0 K. In case N h is left f r e e the m a x i m u m a l l o w e d t e m p e r a t u r e is 6 5 . 0 0 0 K. T h i s v a l u e as t o t a l l y i n c o n s i s t e n t w l t h t e m p e r a t u r e s d e r l v e d s o l a r . T h e He II Z a n s t r a t e m p e r a t u r e e q u a l s 8 5 . 0 0 0 K /7/, w h l l e c o l o u r t e m p e r a t u r e s d e r z v e d f r o m the o p t i c a l a n d UV c o n t i n u u m are b e t w e e n 100.000 and ~ 2 0 . 0 0 0 K / 3 , 4 / . T h e o n l y t e m p e r a t u r e c l o s e to o u r s ~s an e f f e c t l v e t e m p e r a t u r e d e r l v e d f r o m n o n - L T E ~ o ~ e l a t m o s p h e r e f ~ t s to a b s o r p t i o n lane p r o f a l e s /8/, w h i c h r e s u l t s in an e f f e c t i v e t e m p e r a t u r e e q u a l to 6 5 . 0 0 0 ± 1 5 . 0 0 0 K.T h e r a a g e of (R/D) 2 in f i g u r e 2 is c o m p a r e d w i t h v a l u e s d e r l v e d on the b a s i s of m v /7/ and a l s o o , t h e b a s a s of t h e s u r f a c e g r a v i t y , log g = 5.2 /8/, the d l s t a n c e D = 350 pc /7/, and a ~ n l y a c c e p t e d v a l u e for t h e s t e l l a r mass, i.e. 0.8 M o. T h e [R/D) 2 d e r l v e d f r o m the X - r a y ~ a t a as o n e or t w o o r d e r s of m a q n l t u d e too hlgh,
A b l a c k b o d y o r l g l n can t h e r e f o r e c l e a r l y be r u l e d out. The X - r a y d a t a r e q u i r e a s t e l l a r f l u x c o n s l s t e n t w l t h a b l a c k b o d y t e m p e r a t u r e of at least 8 5 , 0 0 0 K, w h i l e its s p e c t r a l s h a p e s h o u l d b e as s t e e p as for 3 8 . 0 0 0 K.
In a d d i t i o n w e h a v e a n v e s t l g a t e d a g r i d of L T E - a t m o s p h e r e s c a l c u l a t e d b y H u m ~ e r a n d M 1 h a l a s /9/. T h e s e m o d e l s i n c l u d e b e s l d e s H and He a l s o C , E , O and Ne w h i c h h a v e a b s o r p t i o n e d g e s in the X - r a y r a n g e .
In f i g u r e 3 m o d e l a t m o s p h e r e s p e c t r a an the X - r a y r a n g e are d r a w n for an e f f e c t l v e t e m p e r a t u r e of 1 0 0 . 0 0 0 K, log g=5 and for t h r e e d i f f e r e n t e l e m e n t a l a b u n d a n c e s , i.e. the 200 (1), 300 (If) and 400 Jill) m o d e l s p e c t r a s e r l e s of Hulmaer and M l h a l a s . T h e b e s t flt as o b t a i n e d f o r t h e h i g h e s t a b u n d a n c e , i.e. the 4 0 0 - s e r l e s ( K b u n d a n c e III) s p e c t r u m , as I n d l c a t e d b y the r e d u c e d c h l - s q u a r e . F r o m the s p e c t r a in flgttre 3 at as c l e a r t h a t the
P l a n e t a r y N e b u l a N G C 1360 59 ' ' \ ' ' ' d ~ ~ A . A ~ E ~ f • C log g:SC i A b u n ~ ¢ e
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' ~ l =/.=15 - ~ I a = 2 ! ll'l~ 200 Elllrllly levi F i g u r e 3: L T E m o d e l a t m o s p h e r e s p e c t r a o f M u s h e r a n d M ~ h a l a s / 9 / for Tel f = 1 0 0 . 0 0 0 K, log g = 5 a n d t h r e e d i f f e r e n t a b u n d a n c e s . T h e q u a l i t y of the flt to t h e X - r a y d a t a as g z v e n b y a r e d u c e d c h i - s q u a r e . r e q u i r e d s t e e p n e s s of t h e s p e c t r u m in the r a n g e o b s e r v e d b y E X O S A T is c a u s e d b y the o p a c l t y of the O v and Ne v ions. T h o s e o p a c z t i e e a l l o w for a c o m b a n a t l o n of a l a r g e X - r a y flux, i.e. h z g h e f f e c t z v e t e m p e r a t u r e , a n d s s t e e p s p e c t r a l s h a p e in the s p e c t r a l r a n g e o b s e r v e d .For o b 3 e c t s c l o s e to the E d d z n g t o n lamat, l i k e N G C 1360, n o n - L T E m o d e l a t m o s p h e r e s p e c t r a s h o u l d h o w e v e r be used. R e c e n t l y a g r a d o f m o d e l s h a v e b e e n p u b l 2 s h e d b y H u a f e l d et al. /10/. T h e s e c a l c u l a t l o n s m a k e o n l y u s e of H y d r o g e n a n d H e l i u m . T h e i r s p e c t r a l s h a p e s h o r t w a r d of 228 A zs e v e n f l a t t e r t h a n for a b l a c k b o d y s p e c t r u m , so t h a t t h e y d o n ' t flt the X - r a y d a t a at all. N o n - L T E m o d e l s p e c t r a i n c l u d i n g a b u n d a n c e s of C , N , O and N e w 1 1 1 be r e q u i r e d t o c a r r y out a m o r e q u a n t a t i v e a n a l y s i s on t h e a v a i l a b l e s p e c t r a l data. D I S C U S S I O N A N D C O N C L U S I O N T h e X - r a y d a t a c a n n o t be r e p r e s e n t e d b y a b l a c k b o d y s p e c t r u m . L T E m o d e l a t m o s p h e r e s p e c t r a l e a d t o g o o d f l t s if o p a c ~ t l e s f r o m 0 V a n d Ne V i o n s are i n c l u d e d . T h e d e r a v a t l o n of a b u n d a n c e s for p l a n e t a r y n e b u l a n u c l e l is v e r y i m p o r t a n t . W h l t e d w a r f s are k n o w n t o h a v e a l m o s t p u r e H y d r o g e n or H e l l u m a t m o s p h e r e s , w h i c h as e x p l a i n e d b y g r a v l t a t l o n a l s e t t l i n g d u r l n g the c o o l l n 9 p h a s e . S o l a r a b u n d a n c e s for p l a n e t a r y n e b u l a e n u c l e z , 3 u s t o n e e v o l u t l o n s t a g e b e f o r e chat of the w h i t e d w a r f , are u n k n o w n .
T h e X - r a y m e a s u r e m e n t s d e m o n s t r a t e the p o s s l b i l i t y to d e t e r m i n e t h e O x y g e n a n d N e o n a b u n d a n c e . N o n L T E - c a l c u l a t z o n s w a t h t e m p e r a t u r e , H e l l u m a b u n d a n c e a n d g r a v i t y f i x e d to v a l u e s o b t a z n e d f r o m o p t z c a l lane p r o f z l e s / 8 / w 1 1 1 b e c a r r i e d o u t zn o r d e r t o e x t r a c t the a b u n d a n c e s of O x y g e n and N e o n , f r o m the a v a a l a b l e X - r a y d a t a . R E F E R E N C E S 9 . 10. D. H u s f e l d , R.P. K u d r l t z k z , K.P. Simon, a n d R . E . S . C l e g g : A a t r o n . A s t r o p h y s . 134, (1984) I. B. M a r g o n , R. M a l l n a , S. B o w y e r , R. C r u d d a c e , a n d M. L a m p t o n : A ~ . J . , 203, L 2 5 (1976) 2 . P . A . J . de K o r t e , E X O S A T i n t e r n a l c o m m u n i c a t i o n (1983) 3. S.R. P o t t a s c h , P.R. W e s s e l i u s , C.C. Wu, N. F i e t e n , a n d R.J. v a n D u l n e n : A s t r o n . A s t r o p h y s . 62, 95 (1978) 4. R.P. K u d r l t z k z , p r z v a r e c o m m u n z c a t l o n (1984) 5. W . C a s h ; Ap.J. 228, 9 3 9 (1979) 6. C. H e i l e s : A s t r o n . A s t r o p h y s . S u p p l . 20, 37 (1975) 7. 3.B. Kaler: A p . 3 . 271, 188 (1983) 8. R.H. M e n d e z , R.P. K u d r z t z k z , J. G r u s c h l n s k e , a n d K.P. S i m o n : A s t r o n . A s t r o ~ h y s . 101, 323 (1981)
D.G. Hun~ner, a n d D. M 1 h a l a s : Mort. N o t . R. astr. Soc. 147, 339 (1970)
