in the
O L D E S T D I S K STARS
by
J O H N B. H E A R N S H A W
A T h e s i s S u b m i t t e d for the D e g r e e of D o c t o r of P h i l o s o p h y
in the
T h e w o r k r e p o r t e d in t h i s t h e s i s is t h a t of the c a n d i d a t e a l o n e , w i t h t h e s e e x c e p t i o n s :
1) S e v e r a l of t h e (R-I) o b s e r v a t i o n s w e r e o b t a i n e d a n d r e d u c e d f o r t h i s p r o j e c t by P r o f e s s o r O . J . E g g e n .
2) T h e m o d e l a t m o s p h e r e an d l i n e p r o f i l e p r o g r a m m e s w e r e w r i t t e n by a g r o u p of s c h o l a r s at M t S t r o m l o O b s e r v a t o r y
A C K N O W L E D G E M E N T S .
It is a p l e a s u r e to a c k n o w l e d g e the c o n t i n u a l a s s i s t a n c e of P r o f e s s o r O.J. E g g e n and Dr. A.W. R o d g e r s for s u g g e s t i n g this p r o j e c t and g u i d i n g me t h r o u g h to its c o n c l u s i o n . P r o f e s s o r E g g e n k i n d l y o b t a i n e d (R-I) c o l o u r s for some of the stars at S i d i n g S p r i n g O b s e r v a t o r y , w h i l e Dr. R o d g e r s i n t r o d u c e d me to b o t h the 50- and 7 4 - i n c h t e l e s c o p e s duri n g the e a rly stages of o b s e r v i n g . Both have g i v e n adv i c e and e n c o u r a g e m e n t t h r o u g h o u t this work, and b o t h r e a d and c o m m e n t e d on the m a n u s c r i p t p r i o r to s ubmis s i o n .
I have had s t i m u l a t i n g d i s c u s s i o n s wi t h ma n y others, e s p e c i a l l y Drs. Bessell, Brooke, Dixon, L y n d e n - B e l l , Norris, P r z y b y l s k i , Sandage, S c h m i d t (E.G.) and W h i t f o r d at Mt Stromlo. Drs. B a s chek, Bell, T a y l o r and W a r n e r have o f f e r e d useful
c o m m e n t s on p a r t of the w o r k d u r i n g the cou r s e of c o r r e s p o n d e n c e . I am very g r a t e f u l to Mrs. P.M. K e n n e d y for a s s i s t a n c e
w i t h c o m p u t e r p r o g r a m m i n g and o p e r a t i o n t h r o u g h o u t this work. The Mt S t r o m l o 7 4 - i n c h n i g h t a s s i s t a n t s , e s p e c i a l l y Mr. J.
M c K i n l a y , have h e l p e d o v e r c o m e n u m e r o u s t e c h n i c a l p r o b l e m s d u r i n g the course of the o b s e r v a t i o n s .
Drs. Brooke, Hain and S c h m i d t very g e n e r o u s l y a l l o w e d me to use their m o d e l a t m o s p h e r e and line p r o f i l e p r o g r a m m e s , w h i c h fo r m an e s s e n t i a l p a r t of this thesis.
My wife, V i c k i e , has w i l l i n g l y a s s i s t e d w i t h many of the
to p u r s u e this w o r k to its c o n c l u s i o n .
L a s t but not least, Mrs. M. Bell ve r y w i l l i n g l y and
e f f i c i e n t l y typed the m a n u s c r i p t , and she took p a i n s t a k i n g care w i t h its layout and p r e s e n t a t i o n .
I am g r a t e f u l to the A u s t r a l i a n G o v e r n m e n t for a
A B S T R A C T .
N i n e t e e n old disk G stars in the solar n e i g h b o u r h o o d have be e n s e l e c t e d whic h , a c c o r d i n g to t h e i r U BV p h o t o m e t r y and
their t r i g o n o m e t r i c p a r a l l a x e s , have e v o l v e d above the ze r o - a g e m a i n s e q u e n c e so as to be a p p a r e n t l y o l d e r than or n e a r l y as old as the old g a l a c t i c c l u s t e r NGC 188. The i n f l u e n c e of
m i c r o t u r b u l e n c e on the UB V c o l o u r s has b e e n comp u t e d , and it is c o n c l u d e d that the p o s i t i o n s of these stars in the HR d i a g r a m c a n n o t be due to a b n o r m a l m i c r o t u r b u l e n c e b l a n k e t i n g e f f e c t s on their c o l o u r s .
E f f e c t i v e t e m p e r a t u r e s for these stars have b e e n o b t a i n e d from :
a ) (R - I ) c o l o u r s
b) p h o t o e l e c t r i c s p e c t r a l scans c) Ha w i n g p r o f i l e s
the latt e r two b e i n g c a l i b r a t e d by m e a n s of flux c o n s t a n t LTE m o d e l a t m o s p h e r e s , c o m p u t e d for this p r o j e c t .
few of the stars is noted, and a tentative explanation is
proposed. The abundance of lithium in old subgiants is
discussed. The view that these stars replenish their surface
lithium supply and then loose it again on a long time scale is consistent with the data.
A model atmosphere analysis of neutral and ionised iron lines has been carried out, and a calibration set up between
gravity and electron pressure. Hence spectroscopic gravities
have been obtained, and it is found that these are significantly less than zero-age main sequence gravities in the majority of
cases. This supports the conclusion that these stars are
evolved, and hence probably old.
Two visual binaries with ..known orbits were included in the nineteen stars observed, and the gravities obtained from their orbital parameters are compared with those obtained
s p e c t r o s c o p i c a l l y .
By means of a grid of helium-rich model atmospheres, the effect of a high helium abundance on the gravity
determinations is considered. Furthermore, it is shown that a
high helium abundance can, in principle, be detected if the
trigonometric parallax is accurately known. Although one star
does show a high helium abundance by this method, the
conclusion is treated with some caution. For the remainder of
the stars, the spectroscopic data do not contradict the view
m u s t be very old to have evolved.
The o r b i t a l p a r a m e t e r s for one of the v i s u a l b i n a r i e s s u g g e s t it is h e l i u m - r i c h , bu t a more p r e c i s e d e t e r m i n a t i o n of the o r b i t w o u l d be n e c e s s a r y to c o n f i r m this a s s e r t i o n .
The ages of the stars have be e n d e r i v e d by c o m p a r i n g their p o s i t i o n s in the (M /log T ) d i a g r a m wi t h i s o c h r o n e s
inter-b o 1 e
p o l a t e d from e v o l u t i o n a r y tracks, u s i n g the p r e m i s s that their h e l i u m c o n t e n t s are normal. A l t h o u g h the i n t e r p r e t a t i o n of the data is h a m p e r e d by a lack of a large sample of stars, it is shown that an a g e - a b u n d a n c e r e l a t i o n p r o b a b l y exists a m o n g old disk stars. On this basis, the rates of f o r m a t i o n of d i f f e r e n t e l e m e n t s d u r i n g the old disk e p o c h are d i s c u s s e d . However, there a p p e a r s to be a small g r o u p of very old m e t a l - r i c h stars w h ich lie s i g n i f i c a n t l y off the a g e - a b u n d a n c e r e l a t i o n for the m a j o r i t y of old di s k stars. An e x p l a n a t i o n for their h i g h a b u n d a n c e s , o t h e r than that of g r a d u a l e n r i c h m e n t of the
i n t e r s t e l l a r m e d i u m by h e a v y e l e m e n t s , may have to be sought. The data are shown to be c o n s i s t e n t w i t h the view that the G a l a x y has u n d e r g o n e a r a pid c o l l a p s e , and i n c o n s i s t e n t with some of the p r e m i s s e s w h i c h lead to the h y p o t h e s i s of the
e j e c t i o n of halo stars from the G a l a c t i c nu c l e u s . F u r t h e r m o r e , it is s h own that, after the r a p i d c o l l a p s e d u r i n g the halo
epoch, the G a l a x y has since then be e n slo w l y c o l l a p s i n g for 9
some 6 x 10 y e ars or more .
Since the o l d e s t stars o b s e r v e d a p p a r e n t l y have ages of 9
T A B L E OF C O N T E N T S .
C H A P T E R O N E ; A S E A R C H F O R O L D S T A R S .
I n t r o d u c t i o n 1
Old s u b g i a n t s in the l i t e r a t u r e 5 The s e l e c t i o n of very old s u b g i a n t s 13 The e f f e c t s of b l a n k e t i n g on the s e l e c t i o n
of s u b g i a n t s 17 The e f f e c t of m i c r o t u r b u l e n c e on UB V
p h o t o m e t r y 19 The e f f e c t of iron a b u n d a n c e on UBV
p h o t o m e t r y 25 C H A P T E R T W O : O B S E R V A T I O N S A N D R E D U C T I O N S .
B r o a d - b a n d p h o t o m e t r y 27
High d i s p e r s i o n sp e c t r a 27
P l a t e t r a c i n g 29
S o l a r p l a t e m a t e r i a l 30
Line i d e n t i f i c a t i o n s 31
E q u i v a l e n t w i d t h m e a s u r e m e n t 32 P h o t o e l e c t r i c s p e c t r a l scans 36
S c a n n e r r e d u c t i o n s 37
D e b l a n k e t i n g of the scans 39
C H A P T E R T H R E E ; M O D E L A T M O S P H E R E S AND LINE P R O F I L E S
I n t r o d u c t i o n 43
A n a l y s i s of the m o d e l res u l t s 47
Ha p r o f i l e 49
I r o n l i n e s 52
I n t e r p r e t a t i o n of the e l e c t r o n p r e s s u r e 54 C H A P T E R F O U R ; THE E F F E C T I V E T E M P E R A T U R E S .
I n t r o d u c t i o n 61
P h o t o e l e c t r i c s c ans 62
Ha w i n g p r o f i l e s 63
(R-I) c o lours 64
B a c k w a r m i n g c o r r e c t i o n s 65 M e a n e f f e c t i v e t e m p e r a t u r e s 66 The d e p e n d e n c e of Ha p r o f i l e s on m e t a l
a b u n d a n c e 67 C H A P T E R F I V E : THE A B U N D A N C E S OF THE E L E M E N T S .
The m e t h o d of coa r s e d i f f e r e n t i a l a n a l y s i s 70 The e x c i t a t i o n t e m p e r a t u r e 71
The curves of g r o w t h 74
The c o n t i n u o u s o p a c i t y 94
P a r t i t i o n f u n c t i o n s 95
The e l e c t r o n p r e s s u r e 95
The deg r e e of i o n i s a t i o n 96
The a b u n d a n c e s and their a c c u r a c i e s 97
The l i t h i u m a b u n d a n c e s 99
The car b o n a b u n d a n c e s 101
N o tes on the a b u n d a n c e s in i n d i v i d u a l stars 105
(Chapter Five Cont.)
C o m p a r i s o n w i t h e a r l i e r w o r k 127 D i s c u s s i o n of a b u n d a n c e s 127
L i t h i u m in old s u b g i a n t s 136
C H A P T E R S I X : G R A V I T I E S , M A S S E S AND THE H E L I U M PR O B L E M .
I n t r o d u c t i o n 141
A c c u r a c y of the g r a v i t i e s 145 C o m p a r i s o n of g r a v i t i e s and a b s o l u t e
m a g n i t u d e s 150
The v i s u a l b i n a r i e s 154
G r a v i t y m e a s u r e m e n t s and the h e l i u m
a b u n d a n c e 159 M o d e l a t m o s p h e r e s for h e l i u m - r i c h stars 160
C o n t i n u o u s fluxes, Ha p r o f i l e s and iron line s t r e n g t h s for h e l i u m - r i c h
stars 162
G r a v i t y e r r o r s and the h e l i u m a b u n d a n c e 165 The h e l i u m a b u n d a n c e of v i s u a l b i n a r i e s 166 C H A P T E R S E V E N ; AGES, K I N E M A T I C S AND G A L A C T I C E V O L U T I O N .
E v o l u t i o n a r y ages and m a s s e s 168
K i n e m a t i c s : the data 173
C o r r e l a t i o n s a m ong the data, and G a l a c t i c
The rates of f o r m a t i o n of d i f f e r e n t
e l e m e n t s 186 H a a s - B o t t l i n g e r d i a g r a m s 189
Old disk m o v i n g groups 191
T A B L E S
I I
1 2]
Old s u b g i a n t s in the l i t e r a t u r e 196
to I
-J
^ Tabl e s for the s e l e c t i o n of old s u b g i a n t s 199
I 8 G e n e r a l data for 19 stars in this p r o g r a m m e 205
II - 1 (R - I ) col o u r s 206
II - 2 S t e l l a r p l a t e d e t a i l s 207
II - 3 S olar p l a t e d e t a i l s 209
II - 4 N u m b e r s of lines used 2 10
II - 5 S c a n n e r w a v e l e n g t h s 211
II - 6 S c a n n e r o b s e r v i n g n i g h t s 212
II - 7 Solar b l a n k e t i n g 213
II - 8 S c a n n e r m o n o c h r o m a t i c m a g n i t u d e s 214
II - 9 E q u i v a l e n t w i d t h s (not C H , Li) 217
II - 10 CH e q u i v a l e n t w i d t h s 235
III- 1 Iron lines for w h i c h e q u i v a l e n t w i d t h s c o m p u t e d 236
III- 2 C o n t i n u u m slopes from mode l s 237
III- 3 S o lar e q u i v a l e n t w i d t h s 238
IV - 1 E f f e c t i v e t e m p e r a t u r e s 239
IV - 2 The d e p e n d e n c e of Ha s t r e n g t h on m e tal a b u n d a n c e 240
IV - 3 O b s e r v e d Ha p r o f i l e s 241
V 1 Iron lines used in d e t e r m i n i n g e x c i t a t i o n
V - 2
t e m p e r a t u r e s
E x c i t a t i o n t e m p e r a t u r e s , e l e c t r o n p r e s s u r e s
242
3 4 5 6 7 8
1 2 3 1 2
245 251 252 253 254
255 256 257 258 259 260 C urve of g r o w t h shifts and a b u n d a n c e s
A c c u r a c y of the a b u n d a n c e s O b s e r v a t i o n s of the Li line L i t h i u m a b u n d a n c e s
C a r b o n a b u n d a n c e s
C o m p a r i s o n s b e t w e e n e a r l i e r a n a l y s e s and the p r e s e n t ones
Gravi ties
M, ,, log T , d i s t a n c e moduli, M
bol e V
S p e c t r o s c o p i c and e v o l u t i o n a r y m a s s e s E v o l u t i o n a r y ages
1
C H A P T E R O N E
A S E A R C H F O R O L D S T A R S
I n t r o d u c t i o n .
T h e y e a r s 1 9 5 7 a n d 19 6 2 m a r k two i m p o r t a n t l a n d m a r k s in o u r u n d e r s t a n d i n g of t he c h e m i c a l e v o l u t i o n of the G a l a x y . T he
f i r s t of t h e s e s a w the p u b l i c a t i o n of the f a m o u s p a p e r b y
B u r b i d g e , B u r b i d g e , F o w l e r a n d H o y l e (1957) w h i c h s h o w e d t h a t all the e l e m e n t s h e a v i e r t h a n h y d r o g e n c o u l d be p r o d u c e d in s t a r s . F u r t h e r m o r e , t h e y c o n c l u d e d t h a t t he p r e s e n t h e a v y e l e m e n t
c o n t e n t of t he G a l a x y c o u l d b e e x p l a i n e d by s t e l l a r s y n t h e s i s of the e l e m e n t s f o l l o w e d b y m a s s l o s s of e n r i c h e d m a t e r i a l
( e s p e c i a l l y f r o m s u p e r n o v a e , r e d g i a n t s a n d s u p e r g i a n t s ) in a 9
t i m e of 6 x 1 0 y r . , t h e i r a s s u m e d age for the G a l a x y . O n l y for h e l i u m w e r e t h e y u n c e r t a i n w h e t h e r s o m e p r i m o r d i a l e n r i c h m e n t w a s n e c e s s a r y or not.
-a n g u l -a r - m o m e n t u m o r b i t s , -a l o w v e l o c i t y d i s p e r s i o n -a n d
[ F e / H ] ^ - 0.6. T h i s t h e o r y of G a l a c t i c c o l l a p s e c l e a r l y b o t h i n v o k e s a n d s u p p o r t s t h e f o r m a t i o n of e l e m e n t s b y s t e l l a r r a t h e r t h a n p r i m o r d i a l s y n t h e s i s .
A c t u a l l y n e i t h e r of t h e s e d e v e l o p m e n t s w e r e e n t i r e l y new; E d d i n g t o n (1930) c o n s i d e r e d t h a t s t a r s m u s t f i n d e n e r g y f r o m s u b a t o m i c p r o c e s s e s , a n d B e t h e (1938) s h o w e d w h a t s o m e of t h e s e p r o c e s s e s w e r e in the c a s e of h y d r o g e n - b u r n i n g . T h e c o n c e p t of s t e l l a r p o p u l a t i o n s (in M 31) w a s d i s c u s s e d in 1 9 4 4 b y B a a d e
(1944) a n d t h a t of G a l a c t i c c o l l a p s e a c c o m p a n i e d by h e a v y
e l e m e n t e n r i c h m e n t w a s d i s c u s s e d b y O o r t in 1 9 5 8 (Oort, 1958) , the s a m e y e a r t h a t S t r ö m g r e n (1958) d i s c u s s e d the c o m p o s i t i o n d i f f e r e n c e s b e t w e e n s t e l l a r p o p u l a t i o n s .
V o n H o e r n e r (1960) a n d D i x o n ( 1 9 6 3 , 1 9 6 6 ) h a v e g i v e n
a d d i t i o n a l o b s e r v a t i o n a l e v i d e n c e c o n c e r n i n g the r a t e s of s t a r f o r m a t i o n a n d t he G a l a c t i c c o l l a p s e . T h e l a t t e r of t h e s e
a u t h o r s c o n s i d e r e d t he d i s t r i b u t i o n in the tw o c o l o u r (U-B, B-V) d i a g r a m of t h o s e s t a r s in a c y l i n d e r p e r p e n d i c u l a r to the
G a l a c t i c p l a n e p a s s i n g t h r o u g h t he sun. He c o n c l u d e d t h a t s t a r s f o r m e d d u r i n g t h e c o l l a p s e p h a s e h a v e [ F e / H ] ^ -0.1; at t he e n d of th i s p h a s e the i r o n a b u n d a n c e is s p a t i a l l y f a i r l y h o m o g e n e o u s
(-0.3 i [ F e / H ] 4 - 0 . 1 ) , a n d s i n c e t h e n s p o r a d i c l o c a l e n r i c h m e n t h a s o c c u r r e d to p r o d u c e d i s k p o p u l a t i o n s t a r s w i t h
- 0 . 3 ^ [ F e / H ] ^ + 0 . 3 . H o w e v e r n e a r l y t w o - t h i r d s of the s t a r s w e r e f o r m e d e a r l y on in an i n i t i a l c o l 1 a p s e - p h a s e b u r s t , a n d
3
rare .
S i n c e the c o l l a p s e p h a s e l a s t e d for o n l y the first few p e r c e n t of the p r e s e n t life time of the Galaxy, and since n e a r l y all the h e a v y e l e m e n t e n r i c h m e n t ha d taken p l ace by the time of this p h a s e ' s c o n c l u s i o n , it f o llows that, if one is to
i n v e s t i g a t e the a g e - a b u n d a n c e r e l a t i o n for the v a r i o u s e l e m e n t s , one has to:
a) use stars at least 95 per cent as old as the G a l a x y i t s e l f .
b) be able to date these stars i d e a l l y to w i t h i n 7
a few 10 y e a r s (about o n e - t e n t h of the total e n r i c h m e n t time)
c) use stars b r i g h t e n o u g h for such an i n v e s t i g a t i o n to be t e c h n i c a l l y f e a s i b l e
if useful i n f o r m a t i o n is to be gained.
The first of these r e q u i r e m e n t s is not h a r d to fulfil; in fact a m a j o r i t y of p r e s e n t l y e x i s t i n g stars s a t i s f y it.
H o w e v e r the s e c o n d is at p r e s e n t i m p o s s i b l e . K i n e m a t i c s p r o v i d e one of the b e s t age crit e r i a , but they are not n e a r l y a c c u r a t e enough, e s p e c i a l l y for sing l e stars (rather than a s t a t i s t i c a l s a m p l e ) . N or are the s t r e n g t h s of the K line e m i s s i o n , w h i c h W i l s o n (1963) and W i l s o n and W o o l l e y (1970) have shown to be a m e a s u r e of s t e l l a r age. S t ars in old c l u s t e r s can be d a t e d r e a s o n a b l y well using e v o l u t i o n a r y theory, b u t t h e i r f a i n t n e s s p r e c l u d e s d e t a i l e d a b u n d a n c e studies. One is t h e r e f o r e
b e d i s c u s s e d .
A c c o r d i n g to e v o l u t i o n a r y t h e o r y , o l d f i e l d s t a r s m u c h m o r e m a s s i v e t h a n the sun a r e n o w h i g h l y e v o l v e d (or no l o n g e r
e x i s t ) , w h i c h p r e c l u d e s an a c c u r a t e d a t i n g b e c a u s e o f p r e s e n t u n c e r t a i n t i e s in t h e t h e o r y . On the o t h e r h a n d , o l d s t a r s m u c h l e s s m a s s i v e t h a n the sun w i l l s t i l l h a v e t h e i r z e r o - a g e m a i n s e q u e n c e l u m i n o s i t i e s a n d t e m p e r a t u r e s , a n d h e n c e c a n n o t be d a t e d b y t h i s t h e o r y . H i g h v e l o c i t y g i a n t s l i k e HD 1 2 2 5 6 3 ar e e x a m p l e s of the f o r m e r , a n d h i g h v e l o c i t y s u b d w a r f s l i k e
H D 2 5 3 2 9 o f the l a t t e r .
T h e o l d e s t f i e l d s t a r s for w h i c h the b e s t a g e s c a n be d e r i v e d are t h e r e f o r e s l i g h t l y e v o l v e d s t a r s of a r o u n d a s o l a r m a s s - t h a t is, s o l a r s p e c t r a l t y p e s u b g i a n t s . T h e c o o l e r t h e s e s t a r s are t he o l d e r t h e y a re l i k e l y to be. A n u m b e r of s u c h s t a r s e x i s t in the s o l a r n e i g h b o u r h o o d w i t h o l d d i s k k i n e m a t i c s ; a c c o r d i n g to the E g g e n , L y n d e n - B e l l a n d S a n d a g e c o l l a p s e t h e o r y t h e y are n o t q u i t e as old, on a v e r a g e , as the h a l o s t a r s , b u t t h e y are the o l d e s t in the s o l a r n e i g h b o u r h o o d w h o s e r e l a t i v e a g e s ca n a l s o be e s t i m a t e d b y e v o l u t i o n a r y t h e o r y . S o m e are b r i g h t e n o u g h for d e t a i l e d o b s e r v a t i o n . O l d s u b g i a n t s in the s o l a r n e i g h b o u r h o o d t h e r e f o r e s a t i s f y the a b o v e t h r e e c o n d i t i o n s the m o s t c l o s e l y , a n d a re t he b e s t s t a r s a v a i l a b l e for an i n v e s t i g a t i o n of the a g e - a b u n d a n c e r e l a t i o n .
5
g r o u p s w i t h o l d d i s k k i n e m a t i c s a n d w i t h c o l o u r - m a g n i t u d e
d i a g r a m s s i m i l a r to the o l d d i s k c l u s t e r M 67. The p o s s i b i l i t y of d a t i n g s o m e o l d u n e v o l v e d s t a r s , or s t a r s w i t h u n c e r t a i n t r i g o n o m e t r i c p a r a l l a x e s , t h u s a r i s e s . In the f o l l o w i n g p r o g r a m m e , t he s t a r s f i n a l l y s e l e c t e d all h a v e e x c e l l e n t
t r i g o n o m e t r i c p a r a l l a x e s . H o w e v e r , the f a c t t h a t six of t h e m h a v e b e e n l i s t e d b y E g g e n as o l d d i s k m o v i n g g r o u p m e m b e r s m u s t
a d d c o n s i d e r a b l y to the a c c u r a c y of t h e i r age d e t e r m i n a t i o n s .
O l d s u b g i a n t s in the l i t e r a t u r e .
T h e f i r s t m e n t i o n t h a t t h e r e m a y e x i s t f i e l d s u b g i a n t s
o l d e r t h a n the o l d e s t g a l a c t i c c l u s t e r k n o w n (at t h a t t i m e , M67) w a s in a p a p e r by J o h n s o n ( 1 9 5 4 ) , a n d o n e of the f i r s t l i s t s of o l d s u b g i a n t s w a s t h a t of E g g e n (1955) w h o d i s c u s s e d t he m a s s e s of f i e l d s t a r s s i m i l a r to th e s u b g i a n t s t a r s in M 67. H is l i s t of t w e n t y n e a r b y s t a r s i n c l u d e d s p e c t r a l t y p e s f r o m F6 to Kl a n d a b s o l u t e m a g n i t u d e s of M -3. H o w e v e r he n o t e d t h a t five s t a r s (X Aur, ß H y i , y Her, 31 A q l , 6 Eri) w e r e s l i g h t l y f a i n t e r t h a n the o t h e r s (M - 3 . 7 5 ) . He c o n s i d e r e d the m a s s e s
©
w e r e all a b o u t 1 . 2 5 M , by c o n s i d e r i n g the o r b i t s of the v i s u a l b i n a r y £ H e r a n d of o t h e r b i n a r i e s w i t h s u b g i a n t l u m i n o s i t y c l a s s i f i c a t i o n s . O f i n t e r e s t a m o n g t h e s e s t a r s w e r e A D S 755
(= 36 And, sgKl) a n d A D S 9 9 0 9 (= £ Sco, F6 I V ) . T he f o r m e r of t h e s e s t a r s h a s b e e n d i s c u s s e d m o r e r e c e n t l y by F a u l k n e r et a l .
(1966) .
t he a g e s of the s u b g i a n t s , S a n d a g e (1958) g a v e a l i s t of
e i g h t e e n s u b g i a n t s w i t h i n o n l y f i f t e e n p a r s e c s of the sun, a nd a f u r t h e r five p r o b a b l y w i t h i n t w e n t y p a r s e c s . A l l t h e s e s t a r s h a v e r e l i a b l e t r i g o n o m e t r i c p a r a l l a x e s , w i t h a m e a n u n c e r t a i n t y
in of o n l y ±0.16. S a n d a g e g a v e n i n e s t a r s s i g n i f i c a n t l y o l d e r t h a n M 67 (ß Vir, t Per, A A u r , ß H y i , y Ara, y Her,
2
31 A q l , 6 Er i , v C M a ) . He c o n s i d e r e d t he age d i f f e r e n c e 9
b e t w e e n t h e s e s t a r s a n d M 67 to be a b o u t 2 x 1 0 y e a r s . P e r h a p s the m o s t i m p o r t a n t p o i n t m a d e by S a n d a g e w a s t h a t t h e s e n i n e v e r y o l d s t a r s h a v e a n o r m a l (B-V) = f(U-B) r e l a t i o n , a n d th u s t h e r e is no e v i d e n c e for l i n e - a n d h e n c e a l s o m e t a l - w e a k n e s s , a s t a t e m e n t w h i c h is t r u e at l e a s t to a r o u g h a p p r o x i m a t i o n .
T h e n e x t d i s c u s s i o n of o l d s u b g i a n t s w a s in 1959 w h e n O k e (1959) p r e s e n t e d the H - R d i a g r a m for 185 s t a r s h a v i n g
u n c e r t a i n t i e s in of ±0.2 or less, a n d l y i n g in the s p e c t r a l t y p e r a n g e o f F5 to K 2 . T h e a b s o l u t e m a g n i t u d e s c a m e f r o m e i t h e r t r i g o n o m e t r i c p a r a l l a x e s a l o n e , or a w e i g h t e d m e a n of t rig, a n d s p e c t r o s c o p i c v a l u e s . O k e g a v e s i x t e e n s t a r s
a p p a r e n t l y o l d e r t h a n M 67, a n d i n c l u d e d in h i s l i s t a re
104 T a u (M = 4.0, B - V = 0 . 6 4 , G4 V) a n d HD 1 9 0 3 6 0 (M = 4.3,
V V
B - V = 0 . 7 5 , d G 8 ) , b o t h o f w h i c h m a y be a m o n g the o l d e s t
m e n t i o n e d . O k e d i s c o u n t s th e p o s s i b i l i t i e s t h a t a n y of t h e s e s i x t e e n s t a r s m a y e i t h e r b e y o u n g s t a r s c o n t r a c t i n g to the m a i n s e q u e n c e , or m o r e m a s s i v e s t a r s w h o s e e v o l u t i o n a r y t r a c k s m a y h a p p e n to p a s s t h r o u g h t h i s p a r t of th e d i a g r a m .
7
m a g n i t u d e s , a n d of f i v e p o s s i b l e e x p l a n a t i o n s , n a m e l y a) u n r e s o l v e d b i n a r i e s
b) c h a n g e s in m a i n s e q u e n c e p o s i t i o n w i t h c h a n g e s in c o m p o s i t i o n .
c) p r e - m a i n s e q u e n c e c o n t r a c t i n g s t a r s d) o l d s t a r s , age a b o u t lO"*-0 yr.
e) l i n e b l a n k e t i n g e f f e c t s on (B-V)
h e c o n s i d e r e d o n l y t h e l a t t e r t w o a r e l i k e l y to b e i m p o r t a n t . At t he s a m e t i m e as O k e ' s p a p e r , W i l s o n (1959) p u b l i s h e d a s i m i l a r s t u d y , u s i n g H a n d K r e v e r s a l w i d t h s or trig.
p a r a l l a x e s as l e a s t as g r e a t as 0 7 0 8 0 to o b t a i n a b s o l u t e
m a g n i t u d e s . H is H - R d i a g r a m is s i m i l a r to O k e ' s ; he f o u n d m a n y e v o l v e d s t a r s b e l o w the M 67 c u r v e , a n d t h e s e h a d a s h a r p l y d e f i n e d r i g h t - h a n d b o u n d a r y , s u g g e s t i n g an a ge for the G a l a x y
1 0
of a b o u t 10 y e a r s .
At t h i s t i m e it w a s c l e a r t h a t G - t y p e s u b g i a n t s m u s t r e p r e s e n t s o m e of t he o l d e s t s t a r s in the G a l a x y , e s p e c i a l l y s i n c e th e f i r s t e v o l u t i o n a r y t r a c k s w e r e n o w b e i n g c o m p u t e d
(Hoy l e , 1959) , a n d c o n s t a n t - a g e l o c i w e r e p r o v i d e d b y t he H - R d i a g r a m s for t he o l d s t r o n g - l i n e c l u s t e r s M 67 ( J o h n s o n , 1954; J o h n s o n a n d S a n d a g e , 1955) and, l a t e r , N G C 188 ( S a n d a g e ,
1 9 6 2 a , b ) . H o w e v e r up t i l l n o w H - R d i a g r a m s w e r e c o m p l i c a t e d by t h e u s e o f a c o l o u r i n d e x ( u s u a l l y (B-V)) u n c o r r e c t e d for the e f f e c t s of l i n e b l a n k e t i n g .
i n t e r m e d i a t e in age b e t w e e n M 67 a n d N G C 188 ( t h e s e w e r e 3 V i r , I Per, 16 C y g A a n d B, A Aur, 99 H e r a n d p CrB) o n l y t w o
(99 Her, [Fe/H] = - 0 . 5 1 ; p CrB, [Fe/H] = -0.20) s h o w e d s i g n s of an u n d e r a b u n d a n c e of ir o n , a n d W a l l e r s t e i n c o n c l u d e d , as S a n d a g e
(1958) a l r e a d y h a d do n e , t h a t ' t h e r e h a s b e e n v e r y l i t t l e
e n r i c h m e n t of the i n t e r s t e l l a r m e d i u m for a l o n g t i m e ' . H o w e v e r , W a l l e r s t e i n a l s o a n a l y s e d f o u r s t a r s a p p a r e n t l y o l d e r t h a n N G C 18 8 (6 T ri , 72 Her, HD 1 5 2 7 9 2 , H D 1 5 7 0 8 9 ) w i t h M v ~ + 4 . 5 , a n d all t h e s e h a v e i r o n u n d e r a b u n d a n t by a f a c t o r of b e t w e e n t w o a n d f o u r w i t h r e s p e c t to t he sun. A l t h o u g h W a l l e r s t e i n d i d n o t d i s c u s s the a g e s of t h e s e l a s t f o u r s t a r s , h i s d a t a w o u l d
s u g g e s t t h a t s i g n i f i c a n t h e a v y e l e m e n t e n r i c h m e n t w a s c o n t i n u i n g b e t w e e n the t i m e s of f o r m a t i o n of t h e s e s t a r s a n d of t h e s e v e n y o u n g e r s t a r s m e n t i o n e d p r e v i o u s l y .
O n e o f t he b e s t k n o w n e x a m p l e s of an o l d s u b g i a n t in the s o l a r n e i g h b o u r h o o d is 6 Eri, w h o s e a b s o l u t e m a g n i t u d e h a s an u n c e r t a i n t y of o n l y ±0^08. B o t h H a z l e h u r s t (1963) a n d P a g e l
(1963) s i m u l t a n e o u s l y p u b l i s h e d a b u n d a n c e a n a l y s e s for t h i s s t a r f i n d i n g a w i d e r a n g e o f e l e m e n t s w i t h s o l a r a b u n d a n c e s , w h i c h a g r e e d w i t h the c o n c l u s i o n s o f W a l l e r s t e i n (1962) for s t a r s of t h i s age. P a g e l in t he s a m e p a p e r a l s o l i s t e d t w e n t y - t w o o t h e r s u b g i a n t s of s i m i l a r age a n d w i t h i n t w e n t y - f i v e p a r s e c s of the sun. O n e o f t h e s e , y S e r ( [Fe/H] = -0.4) , h a d b e e n a n a l y s e d the p r e v i o u s y e a r b y K e g e l (1962), a n d t h r e e w e r e in W a l l e r s t e i n 's
9
Y Ser s h o w e d signs of m etal d e f i c i e n c y (3 H y i , 50 And, 5 S e r , X Her, p o s s i b l y ^ P s c ) . A n o t h e r of the b r i g h t s u b g i a n t s was a n a l y s e d the same year; this was the s o u t h e r n star 3 Hyi, by R o d g e r s and Bell (1963). An u n d e r a b u n d a n c e of iron by a factor of two was found ( [Fe/H] = -0.30). Since E g g e n (1958, 1971b) has s h o w n 3 Hyi to be a m e m b e r of the £ Her m o v i n g group, the a b u n d a n c e s of o t her stars in the g r o u p are of i n terest.
W a l l e r s t e i n (1962) had a n a l y s e d two (HD 30455, [Fe/H] = -0.26; 5 Tri, [Fe/H] = -0.43) and €, Her i t s e l f was a n a l y s e d by H e i f e r
et a l . (1963) who f o und [Fe/H] = +0.07. H o w ev e r the p r e s e n c e of the v e r y close KO V s e c o n d a r y may m a k e this last resu l t u n c e r t a i n .
The a v a i l a b l e data on c o l ours, l u m i n o s i t i e s and m o t i o n s of a large n u m b e r of G - t y p e stars were a n a l y s e d by E g g e n (1964) who gave c o l o u r - m a g n i t u d e d i a g r a m s s h o w i n g s e v e r a l d o z e n stars
a p p a r e n t l y o l der than NGC 188, w i t h v a l u e s of A(B-V) (the c o r r e c t i o n to (B-V) for line b l a n k e t i n g effects) up to +0.15, but none w i t h c o r r e c t i o n s of m o r e t h a n this value. Since
Bergh and Sackmann (1965) and Rodgers (1969) later showed that this star is on or very close to the zero-age main sequence. However other stars in the list included HR 483 ( [Fe/H] = +0.20
(Wallerstein, 1962)), the double stars 104 Tau (ADS 3701) and HR 6516 (ADS 10598), 72 Her ([Fe/H] = -0.36 (Wallerstein, 1962)) and x 1 Ori, although this last star is shown to have the
kinematics of the young Sirius group in the same paper. Two other stars, HD 169822 and HD 169889 are also considered by Eggen to be extremely old; these are a widely separated common proper motion pair, and the former is a G-type subgiant
(Mv = +4.7) lying 1.1 magnitudes above the Hyades main sequence, if the latter fainter star is unevolved. This pair has also been discussed by Eggen (1965a).
The next development came in 1965 when van den Bergh and Sackmann (1965) scanned about 200 stars, mainly G dwarfs, to obtain the narrow-band indices A(UV b l a n k e t i n g ) , r(CN band strength) and s(CH, G-band strength) . These authors formed a function S(r,s) of r and s which showed a good positive
11
m e t a l - r i c h G - t y p e s u b g i a n t s w o u l d b e s t r i k i n g .
T h e a b u n d a n c e of l i t h i u m in s u b g i a n t a t m o s p h e r e s h a s b e e n a t o p i c of g r e a t i m p o r t a n c e , b e c a u s e t h e o r y p r e d i c t s a m a i n
s e q u e n c e c o n v e c t i v e l i t h i u m d e p l e t i o n (by p r o t o n a n n h i l a t i o n ) on a l o n g t i m e s c a l e . O l d s u b g i a n t s s h o u l d t h e r e f o r e h a v e a l o w l i t h i u m a b u n d a n c e . A f t e r C o n t i (1964) d e t e r m i n e d 6 E r i ' s l i t h i u m c o n t e n t to b e a b o u t t w i c e the s o l a r v a l u e , b o t h F e a s t
(1966) a n d H e r b i g a n d W o l f f (1966) d i s c u s s e d t he l i t h i u m a n d
i r o n c o n t e n t s of a n u m b e r o f o l d s u b g i a n t s . F e a s t c o n c l u d e d t h a t m a n y s t a r s s h o w e d s i g n s of L i ^ p r o d u c t i o n s o o n a f t e r l e a v i n g the
6 7
m a i n s e q u e n c e - h is d a t a f or 3 Hyi ([Li/Ca] - +1; Li / L i - 0 . 4 5 ) s u p p o r t e d t his. T h e l a t t e r a u t h o r s d i s c u s s e d a t o t a l of t w e n t y -t w o s -t a r s , i n c l u d i n g H R 4 5 8 7 , a G8 s -t a r l y i n g o n l y h a l f a
m a g n i t u d e a b o v e the z e r o - a g e m a i n s e q u e n c e .
A n u m b e r of s t a r s w i t h o u t g o o d p a r a l l a x d e t e r m i n a t i o n s are t h o u g h t to be o l d s u b g i a n t c o m p o n e n t s of v i s u a l b i n a r i e s ; in t h i s c a s e th e a b s o l u t e m a g n i t u d e c an be e s t i m a t e d by a s s u m i n g t h e f a i n t e r c o m p o n e n t l i e s on t h e m a i n s e q u e n c e . B i d e l m a n (1958) h a s d i s c u s s e d t he s p e c t r a l c l a s s i f i c a t i o n of b i n a r i e s w i t h
p r i m a r i e s a b o v e the m a i n s e q u e n c e . T h e r e are s o m e g i a n t s in h i s l i s t w h i c h a r e r e d d e r t h a n M 67 g i a n t s , b u t no s u b g i a n t s ar e m e n t i o n e d w h i c h a r e o l d e r t h a n M 67. H o w e v e r E g g e n (1967) d i s c u s s e d s e v e r a l b i n a r i e s w i t h o l d s u b g i a n t p r i m a r i e s , i n c l u d i n g A D S 1 4 4 2 4 , A D S 1 5 3 0 0 a n d A D S 1 6 173.
NGC 1 0 8
13
T a y l o r (1969), a n d s e v e n t e e n s u b g i a n t s or o l d g i a n t s w e r e i n c l u d e d . Of t h e s e , t h e y c o n s i d e r e d all b u t <5 Er i (Solar
a b u n d a n c e s ) a n d 91 A q r A a n d x C r B ( s l i g h t l y e n h a n c e d m e t a l s ) to h a v e a m e t a l c o n t e n t g r e a t e r t h a n t h a t of H y a d e s s t a r s . S u c h an o b s e r v a t i o n w a s s i m i l a r to the e a r l i e r o n e of v a n d e n B e r g h a nd S a c k m a n n (1965), and, if c o r r e c t , m i g h t n e e d f u r t h e r e x p l a n a t i o n to be c o m p a t i b l e w i t h t he t h e o r y of g a l a c t i c c o l l a p s e ( E g g e n et a l ., 1962) a n d w i t h the w o r k of D i x o n (1963, 1 9 6 6 ) .
R e c e n t l y G l e b o c k i a n d S t r o b e l (1970) a n n o u n c e d a p r o g r a m m e to m e a s u r e the i r o n a b u n d a n c e s in t w o d o z e n of the i n t r i n s i c a l l y b r i g h t e r s u b g i a n t s . I n c l u d e d in t h e i r l i s t is 31 A q l , f o u n d by t h i s a u t h o r ( H e a r n s h a w , 1971) to be s i g n i f i c a n t l y m e t a l - r i c h
( [Fe/H] = + 0 . 5 2 ) . T h i s is n o t t he o n l y m e t a l - r i c h s u b g i a n t a n a l y s e d by c u r v e of g r o w t h m e t h o d s to d ate; 3 v i r h as b e e n a n a l y s e d b y W a l l e r s t e i n (1962) ([Fe/H] = + 0 . 3 3 ) a n d b y B a s c h e k et al. (1967) ([Fe/H] = + 0 . 2 6 ) a n d t Bo o by S p i t e (1968)
( [Fe/H] = 4 0.28) t h o u g h t h e s e ar e l e s s e x t r e m e in b o t h a g e and a b u n d a n c e t h a n 31 Aql.
Fig. 1 -1 s h o w s the p o s i t i o n o f s u b g i a n t s m e n t i o n e d in the l i t e r a t u r e in t he H - R d i a g r a m , a n d t a b l e 1-1 is a l i s t of t h e s e s t a r s .
T h e s e l e c t i o n of v e r y o l d s u b g i a n t s .
T w o of th e m a i n c o n c l u s i o n s f r o m t h e w o r k on o l d f i e l d s u b g i a n t s up to the p r e s e n t t i m e w e r e :
a b u n d a n c e s , t h o u g h a few m ay be d e f i c i e n t by up to a fac t o r of a b o u t four r e l a t i v e to the sun
b) there may be some a n o m a l o u s s u b g i a n t s with m e t a l a b u n d a n c e s even g r e a t e r than that of the H y a d e s .
So far as the first p o i n t is con c e r n e d , it is s i g n i f i c a n t that NG C 188 i t s e l f is k n own no t to be m e t a l - p o o r (Eggen and Sanda g e , 1969); it may even be m e t a l - r i c h (Demarque and
S c h l e s i n g e r , 1969; S p i n r a d and Taylor, 1969). B e c a u s e of this, it was d e c i d e d that a s e a r c h for w e 1 1 - d o c u m e n t e d e x a m p l e s of s u b g i a n t s a p p a r e n t l y even o l d e r than this c l u s t e r w o u l d be n e c e s s a r y to i n v e s t i g a t e the a g e - a b u n d a n c e r e l a t i o n s h i p in the Galaxy. 6 Tri and 72 Her, a n a l y s e d by W a l l e r s t e i n (1962) may a l r e a d y be e x a m p l e s of such stars, and those a p p e a r i n g in E g g e n 's
(1964) list may be some more.
As a s t a r t i n g point, E g g e n ' s (1964) data w e r e used, as they i n c l u d e (B-V) in d i c e s c o r r e c t e d for line b l a n k e t i n g , and d e t a i l s of s p e c t r o s c o p i c and t r i g o n o m e t r i c l u m i n o s i t i e s for a large
sample of G stars. T h o s e stars in E g g e n ' s tables I and IV
wi t h C >_ 0. 6 0 w e r e p l o t t e d in the (M ,C) d i a g r a m (C=(B-V) ) .
— V c or r .
Th e y were d i v i d e d into three g r o u p s :
-i) T h o s e s u b g i a n t s w i t h i n (i.e. r e d w a r d s of and hence a p p a r e n t l y o l d e r than) the s u b g i a n t and e v o l v e d main s e q u e n c e s d e f i n e d by NGC 188 (Sandage, 1962a) .
15
s u b g i a n t s of NGC 188, but less b r i g h t than those of M 67 ( g e n e r a l l y 3 . <_3.9 )
iii) All o t h e r stars (mainly u n e v o l v e d ma i n se q u e n c e stars; a few b r i g h t e r g i a n t s ) .
T h o s e in g r oup (i) are l i s t e d in table 1-2 t o g e t h e r w i t h II (trig.) f r o m J e n k i n s ( 1952) ( i n c l u d i n g the 1963 supplement) and I1m s , the p a r a l l a x r e q u i r e d to p l a c e the star on the H y a d e s m a i n s e q u e n c e of S a n d a g e and E g g e n ( 1959) , w h i c h is also the m a i n s e q u e n c e u s e d by E g g e n (1964) .
T h o s e stars in table 1-2 for w h i c h
a) II is s i g n i f i c a n t l y g r e a t e r than II, , .
MS J e n k i n s
b) the J e n k i n s p a r a l l a x is w e l l d e t e r m i n e d -g e n e r a l l y s e v e r a l v a l u e s of h i -g h w e i -g h t from d i f f e r e n t o b s e r v a t o r i e s all in a g r e e m e n t
a p p e a r in table 1-3 t o g e t h e r w i t h and C from E g g e n (1964). T h o s e stars in g r o u p (ii) ( a p p a r e n t l y i n t e r m e d i a t e in age b e t w e e n N GC 188 and M 67) are l i s t e d in two c o r r e s p o n d i n g tables
(tables 1-4 and 1-5).
It is p o s s i b l e that some stars not a p p e a r i n g in E g g e n ' s (1964) tables are old s u b g i a n t s . To i n v e s t i g a t e this
p o s s i b i l i t y , all stars in the B r i g h t Star C a t a l o g u e (Hoffleit, 1964) l i s t e d as b e i n g
a) in the s p e c t r a l type r a n g e F9 to G9 i n c l u s i v e b) n . >0"030
t n g
10 Tau •
• HR 1536
• HR 299«
17
w e r e p l o t t e d in the M ^ C t r i g . ) , (B-V) (uncorrected) diagram, and those f i f t e e n stars a p p a r e n t l y o l d e r than or n e a r l y as old as N G C 188 a p p e a r in table 1-6, t o g e t h e r w i t h their t r i g o n o m e t r i c p a r a l l a x e s (Jenkins, 1952), and p a r a l l a x e s r e q u i r e d to p l ace t h e m on the H y a d e s m a i n s e q u e n c e at the o b s e r v e d (rather than corrected) ( B - V ) . T able 1-7 gives the and (B-V) v a l u e s of p r o b a b l e s u b g i a n t s . It is u n l i k e l y th a t they are h i g h l y
b l a n k e t e d m a i n s e q u e n c e stars, t h o u g h this p o s s i b i l i t y is not r u led out.
T a b l e 1-8 lists d e t a i l s of those old s u b g i a n t s o b s e r v e d in this p r o g r a m m e . Stars a p p e a r i n g in lists 1-3, 5 and 7 w e r e c o n s i d e r e d . T h o s e not a p p e a r i n g we r e e i t h e r too far n o r t h
(6>+21°) or too faint for r e a s o n a b l e coude e x p o s u r e times at Mt. Stromlo. Tw o stars not in the above three lists w e r e inclu d e d . T h e s e w e r e HR 4587 (HD 104304) see table 14 -b e c a u s e the R,I p h o t o m e t r y (chapters II, VI) i n d i c a t e d th a t it
is p r o b a b l y a s l i g h t l y e v o l v e d s u b g i a n t , and b e c a u s e it has a UV d e f i c i e n c y (6(U-B = -0.04), i n d i c a t i n g a p o s s i b l y
i n t e r e s t i n g object; and also the w e l l - k n o w n s u b g i a n t 6 Eri. Fig. 1-2 shows the p o s i t i o n s of these stars in the ( t r i g ) , C diagram.
The e f f e c t s of b l a n k e t i n g on the s e l e c t i o n of s u b g i a n t s .
The c o r r e c t i o n p r o c e d u r e d e s c r i b e d by W i l d e y et a l . (1962) for c o r r e c t i n g the o b s e r v e d (B-V) c o l o u r s is a p p l i c a b l e to
T h e v a l u e s of C = (B-V) _ q u o t e d h e r e f r o m E g g e n (1964) c o r r e c t e d
u s e d t h i s p r o c e d u r e ; in the c a s e of U V d e f i c i e n t s t a r s , E g g e n ( p r i v a t e c o m m u n i c a t i o n ) r e v e r s e d t h e s i g n of A ( B - V ) a r i s i n g f r o m a p o s i t i v e 6(U-B) of e q u a l s i z e b u t o p p o s i t e s i g n to t h a t
ob s e r v e d .
T h e i n d e x C m a y n o t r e p r e s e n t o n l y the e f f e c t i v e t e m p e r a t u r e for f o u r r e a s o n s :
-a) g r a v i t y e f f e c t s on (U-B) a n d (B-V)
b) m i c r o t u r b u l e n c e e f f e c t s on t h e s e c o l o u r s c) an u n d e r e s t i m a t i o n of the s i z e of the
c o r r e c t i o n in t he c a s e of U V d e f i c i e n t s t a r s
d) a (He/H) r a t i o n o t e q u a l to t h a t of the H y a d e s .
S t a r s a b o v e the m a i n s e q u e n c e are d e f i c i e n t in th e u l t r a v i o l e t d u e to t h e i r g r e a t e r B a l m e r d i s c o n t i n u i t y . A c c o r d i n g to E g g e n (1963) the e f f e c t is n o t g r e a t for ( B - V ) > 0 . 6 0 . H o w e v e r B a s c h e k ' s (1966) m o d e l a t m o s p h e r e w o r k p r e d i c t e d
3 (U-B)/3]_0 g g = ~ 0 . 1 0 3( B - V ) /3l o g g = + 0 . 0 1
at T = 5 7 8 0 ° K a n d at c o n s t a n t m i c r o t u r b u l e n t v e l o c i t y . F o r a e
19
a f f e c t t h e s e l e c t i o n of s u b g i a n t s .
H e l i u m - r i c h s t a r s are s l i g h t l y m o r e d e f i c i e n t in the UV t h a n n o r m a l h e l i u m s t a r s w i t h the s a m e m e t a l to h y d r o g e n r a t i o ; t h i s is d i s c u s s e d b r i e f l y in c h a p t e r VI. T h e e f f e c t s of
m i c r o t u r b u l e n c e a n d m e t a 1 - r i c h n e s s a re i n v e s t i g a t e d b e l o w .
T h e e f f e c t of m i c r o t u r b u l e n c e on U B V p h o t o m e t r y .
S i n c e l i n e s on t he t r a n s i t i o n a l p a r t of t he c u r v e of g r o w t h a re s e n s i t i v e to m i c r o t u r b u l e n c e , the o v e r a l l b l a n k e t i n g a n d c o l o u r s of a s t a r are a l s o a f u n c t i o n of t h i s p a r a m e t e r . C o n t i a n d D e u t s c h (1966) h a v e g i v e n a t h e o r e t i c a l t r e a t m e n t of
m i c r o t u r b u l e n c e e f f e c t s on t he S t r ö m g r e n i n d i c e s , a nd t h i s h a s b e e n d i s c u s s e d b y C o n t i a n d D e u t s c h (1967) , B a r r y (1967) a n d K r a f t et al. ( 1968). C o n t i a n d D e u t s c h (1966) a l s o g a v e
a p p r o x i m a t e r e s u l t s for U B V p h o t o m e t r y b a s e d on t r a n s f o r m a t i o n s f r o m the S t r ö m g r e n r e s u l t s , a n d t h e i r c o n c l u s i o n w a s t h a t the
(U-B) c o l o u r w a s c o n s i d e r a b l y m o r e s e n s i t i v e to m i c r o t u r b u l e n c e t h a n ( B - V ) , w h i c h w a s m o r e s e n s i t i v e to a b u n d a n c e . B e c a u s e the s l o p e s of the t u r b u l e n c e a n d a b u n d a n c e t r a j e c t o r i e s in the t w o -c o l o u r d i a g r a m d i f f e r , t h e y -c o n -c l u d e d it w a s i m p o s s i b l e to
6 P a v ( R o d g e r s , 1 9 6 9 ) w i t h h i g h m i c r o t u r b u l e n c e , a n d H D 1 9 0 4 0 4 ( C a y r e l de S t r o b e l , 1 9 6 6 ) w i t h l o w m i c r o t u r b u l e n c e .
T h e p r e s e n t r e d i s c u s s i o n o f t h i s e f f e c t is r e s t r i c t e d to s t a r s o f s o l a r t e m p e r a t u r e . S m o l i n s k i ( 1 969) h a s o u t l i n e d a m e t h o d o f c o m p u t i n g b l a n k e t i n g c o e f f i c i e n t s in 2 5 A w i d e b a n d s in t h e s p e c t r u m o f a s t a r d i f f e r i n g f r o m t h e s u n o n l y in t h e v a l u e
O
o f i t s m i c r o t u r b u l e n t v e l o c i t y . T h e 2 5a b a n d s a r e c o n t i g u o u s , a n d t h e s o l a r b l a n k e t i n g in e a c h d u e t o w e a k (n ), i n t e r m e d i a t e
® ®
(n I x ) a n d s t r o n g (n ^ ^ ) l i n e s is g i v e n . F o l l o w i n g t h e a p p r o x i m a t e t h e o r y o f C o n t i a n d D e u t s c h ( 1 9 6 6 ) .
n i ^ n i = A
n
/ n
ii ii
X] / T)
III III
1 3
A 4 V4 I
w h e r e A a n d V a r e r e s p e c t i v e l y t h e r a t i o s o f i r o n a b u n d a n c e a n d t o t a l D o p p l e r v e l o c i t y t o t h e s o l a r v a l u e s a n d n is t h e f r a c t i o n o f t h e f l u x r e m o v e d b y t h e l i n e s . T h u s c h a n g e s in t h e f l u x a r e p r o d u c e d o n l y b y c h a n g e s in w h e n V c h a n g e s . T h e t o t a l
b l a n k e t i n g c o e f f i c i e n t is ®
3
® 4 ©
I + n i i ' v + 11 I II ( A c on s t an t ) If S is t h e m e a n t r a n s m i s s i o n f u n c t i o n o f t h e J o h n s o n U b a n d
U
s y s t e m (as t a b u l a t e d b y M a t t h e w s a n d S a n d a g e (1963) f o r o n e a i r m a s s , t h e U f i l t e r , 1 P 2 1 p h o t o m u l t i p l i e r a n d t w o a l u m i n i u m
O
• ■ mircoturbulence blanketing.
A(U-B)
■ « abundance b la n k e tin g .
-3.00
- 1.80
- 1.00
-0.80
-0.60
- 0.30
- 0.20
- 0.10
+ 0.20
+ 0.30
+0.30
+ 0.40
+0.40
+0.50
0.3
A(B-V)
Zf .s . (i - n ) Au = -2.5 log ----
---Zf . s . ( i - n )
u
w h e r e n = n ^ + ’"’i n ' an<^ AU is the change in the U m a g n i t u d e (minus the c o r r e c t i o n to be a p p l i e d ) . S i m i l a r
e x p r e s s i o n s f o l l o w for AB and AV. V a l u e s for F w e r e i n t e r p o l a t e d from the s o l a r c e n t r e - o f - d i s k c o n t i n u u m fluxes g i v e n by La b s and N e c k e l (1968) . A l t h o u g h the p r e s e n t r e s u l t s are s t r i c t l y only
v a l i d for the centre of the disk of stars of solar a b u n d a n c e , t e m p e r a t u r e and l u m i n o s i t y , they are l i k e l y to be a good
a p p r o x i m a t i o n for the i n t e g r a t e d light of stars not d i f f e r i n g g r e a t l y from the sun in these p a r a m e t e r s . A f u r t h e r d i s c u s s i o n of the S m o l i n s k i m e t h o d and t a b l e s of the a d o p t e d solar
b l a n k e t i n g c o e f f i c i e n t s a p p e a r in c h a p t e r II.
Fi n a l l y , M a t t h e w s and S a n d a g e (1963) have shown that, wh e n u s i n g the t r a n s m i s s i o n f u n c t i o n s that they tabul t e , then, to o b t a i n c o l o u r s w h i c h r e p r o d u c e J o h n s o n ' s system, the c o m p u t e d A(U-B) = Au - AB m u s t be m u l t i p l i e d by 0 . 9 2 1 and A(B-V) by
1.024. This was done to o b t a i n the c h a n g e s in t h ese i n d i c e s from the s o lar values.
6(U-B)
+
0.2
-0.0
-
0.2
--
0
.4
--0
The computed relationship between
S
(U~B)
and A(B-V).
____I__ +
0.2
Pig 1-4
c re
-a
)v
ro
+
00
r
o
-
(A-9)V
t
'
0
*
o
o
r
o
-25
The e f f e c t of iron a b u n d a n c e on UBV p h o t o m e t r y .
A c h eck on the m e t h o d of the p r e v i o u s s e c t i o n is p r o v i d e d by its a b i l i t y to a c c u r a t e l y r e p r o d u c e the k n own (Wildey et al., 1962) r e l a t i o n s h i p b e t w e e n p o s i t i v e 6(U-B) and A(B-V). The
c o m p u t a t i o n s were c a r r i e d o u t in an i d e n t i c a l m a n n e r to those c o n c e r n i n g m i c r o t u r b u l e n c e c h a nges, e x c e p t now V was h e l d at u n ity and [Fe/H] = log A took e i g h t e e n values as f o l l o w s
:--3.0 to -1.0 in i n c r e m e n t s of 0.4 -1.0 to -0.4 in i n c r e m e n t s of 0.2 -0.4 to +0.5 in i n c r e m e n t s of 0.1
The c o m p u t e d r e l a t i o n s h i p b e t w e e n [Fe/H] and A(B-V) is shown in fig. 1-6. The i m p o r t a n t r e s u l t (fig. 1-3) that the
m i c r o t u r b u l e n c e and a b u n d a n c e t r a j e c t o r i e s are i d e n t i c a l is i m m e d i a t e l y seen, in c o n t r a c t i o n to C o nti and D e u t s c h 1s ( 1966) result, and also c o n f i r m i n g the v a l i d i t y of the m e t h o d of
W i l d e y et a l . (1962) even in the case of stars w i t h n o n - s o l a r m i c r o t u r b u l e n c e .
For a star like 31 Aql w i t h 6(U-B) = -0.03 (Eggen, 1964) one d e d u c e s a r e d d e n i n g in (B-V) of 0.03 if its d e f i c i e n c y is due to line b l a n k e t i n g (rather than a g r a v i t y e f f e c t ) . E g g e n 's C of 0.75 s h o u l d t h e r e f o r e not be in e r r o r for this star. In c h a p t e r IV it is shown th a t 31 Aql is o n l y m a r g i n a l l y cooler than the sun (A0 = +0.02) , w h i c h m e a n s C = 0.75 is too red.
e
27
C H A P T E R TWO
O B S E R V A T I O N S AND R E D U C T I O N S .
T h r e e k i n d s of o b s e r v a t i o n s have b e e n used in this thesis. T h e y ar e :
-a) B r o a d - b a n d p h o t o m e t r y . b) High d i s p e r s i o n spectra.
c) P h o t o e l e c t r i c s p e c t r a l scans.
1) B r o a d - b a n d p h o t o m e t r y .
In a d d i t i o n to the U B V data taken from the l i t e r a t u r e and d i s c u s s e d in the p r e v i o u s chapt e r , P r o f e s s o r E g g e n has k i n d l y o b s e r v e d s e v e r a l stars on the Krön (R-I) s y s t e m (Kron, W h i t e and G a s c o i g n e , 1953) for this p r o g r a m m e . The r e m a i n d e r of the stars have (R-I) i n d i c e s on the J o h n s o n s y s t e m (Johnson, 1964) w h i c h appear in the l i t e r a t u r e . T a b l e I I -1 lists this data t o g e t h e r w i t h its source. The J o h n s o n index of those stars o b s e r v e d by E g g e n was d e r i v e d u s i n g the c o n v e r s i o n r e l a t i o n found by E g g e n (1971a) b e t w e e n the two systems. This is:
(R-I) = 1.25 ( (R-I) + 0.05)
J K
and the s c a t t e r is n e g l i b l e .
2) High d i s p e r s i o n s p e c t r a .
All the p l a t e m a t e r i a l used was t a k e n by the a u t h o r on the coude s p e c t r o g r a p h of the 74 in. t e l e s c o p e at Mt S t r o m l o
O b s e r v a t o r y . The 32 in. c a m e r a was used in c o n j u n c t i o n w i t h the
O
600 line s / m m . For each star two good red p l a t e s (Kodak 103aF e m ulsion) and one good blue p l a t e (Kodak IlaO e m u l s i o n , b a k e d
for 48 hours, or o c c a s i o n a l l y less) were used in the r e d u c t i o n s . At the coude focus the slit size was 2 0 0 y , and the s p e c t r a were w i d e n e d to 0.86 mm by the rocker. C o m p a r i s o n s p e c t r a (argon and h y d r o g e n ) and two w e d g e c a l i b r a t i o n s p e c t r a were t a ken on the same p l a t e as each s t e l l a r e x p o s u r e . The c a l i b r a t i o n e x p o s u r e time was g e n e r a l l y 35 min. for the red p l a t e s , and 45 min. for bl u e ones, that is a b o u t a t h i r d to a t e nth of the s t e l l a r e x p o s u r e , and the e n e r g y d i s t r i b u t i o n of the c a l i b r a t i o n s p e c t r u m a b o u t the same as that of a G type star. Red p l a t e s
O
w e r e taken in the s e c o n d o r d e r g i v i n g a d i s p e r s i o n of 10.2 A/mm, and a S c h o t t GG 14 f i l t e r e m p l o y e d in the light p a t h to e l i m i n a t e
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h i g h e r o rders. Blue p l a t e s were in the t h i r d o r d e r at 6.7 A/mm, and a GG 13 filt e r used. If d e n s i t y is d e f i n e d as the f r a c t i o n of l i ght not d i r e c t l y t r a n s m i t t e d by a m i c r o p h o t o m e t e r beam, then the m a x i m u m d e n s i t i e s in the s t e l l a r s p e c t r a w e r e g e n e r a l l y b e t w e e n 30 per cent and 70 pe r cent; a d e n s i t y of 60 per cent was c o n s i d e r e d ideal. M e a s u r e m e n t s on low d e n s i t y p l a t e s have
large r a n d o m errors, w h e r e a s on h i g h l y e x p o s e d p l a t e s , small c a l i b r a t i o n e r r o r s can c a use s y s t e m a t i c err o r s in the e q u i v a l e n t w i d t h s .
T a ble II-2 lists the p l a t e s used. The date refers to the s t a r t of the n i g h t on w h i c h the p l a t e was c o m m e n c e d , p ma x is the m a x i m u m d e n s i t y in the s t e l l a r s p e c t r u m , N is the n u m b e r of lines used in the R vs - log W/Ä c a l i b r a t i o n . A few p l a t e s
29
w e r e c a l i b r a t e d u s i n g the c a l i b r a t i o n s p e c t r a of o t h e r pla t e s , w h o s e n u m b e r s are given. All p l a t e s were d e v e l o p e d for 7 min.
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at 20 C in D-19 d e v e l o p e r unless s t a t e d o t h e r w i s e in the notes.
P l a t e T r a c i n g .
The p l a t e s we r e t r a c e d on the H i l g e r m i r c o p h o t o m e t e r at Mt S t r o m l o O b s e r v a t o r y at a s p e e d of 1 cm. of p l a t e pe r 6 min. The slit wid t h , as p r o j e c t e d on the e m u l s i o n was 24y,
O T O
c o r r e s p o n d i n g to a b o u t for the red s p e c t r a and —a for bl u e 6
ones. The sign a l was r e c o r d e d on a B r o w n r e c o r d e r a f t e r a m p l i f i c a t i o n (Keithley D C a m p l i f i e r ) .
The M o s e l e y X-Y r e c o r d e r has f r e q u e n t l y be e n u s e d (see for e x a m p l e B e s s e l l (1967) and S c h m i d t (19 6 9 ) ) in c o n j u n c t i o n w i t h the Mt S t r o m l o H i l g e r to o b t a i n d i r e c t l y an i n t e n s i t y
tracing. This m e t h o d was, h o w e v e r , not used in this p r o g r a m m e , as there is no simple and a c c u r a t e way of a l l o w i n g for
v a r i a t i o n s in b a c k g r o u n d c h e m i c a l fog over the l e n g t h of the s p e c t r u m . A l s o the X-Y r e c o r d e r was t h o u g h t to h a v e an
u n d e s i r a b l y large time c o n s t a n t . C o n s e q u e n t l y a m e t h o d of
o b t a i n i n g e q u i v a l e n t w i d t h s from a d e n s i t y t r a c i n g was d e v i s e d . The p r o c e d u r e for t r a c i n g was:
a) T r ace the fog level i m m e d i a t e l y b e l o w the
s t e l l a r s p e c t r u m at a s p e e d of 1 cm per 36 sec. (lOx s t e l l a r speed).
