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C a m O B I
byD av id A n th o n y L y der B .Sc.. U n iv e rsity of A lb e r ta 1982 B .Sc.. U n iv ersity of A lb e rta I9ST M .S c.. U n iv e rsity of A lb e rta 1989
A D isse rta tio n S u b m itte d in P a r tia l Fulfillm ent o f th e R e q u ire m e n ts for th e D egree of
D O C T O R O F P H IL O S O P H Y
in th e D e p a rtm e n t of P h y sics a n d A stron om y
We acc ep t th is th e sis as conform ing to th e re q u ire d s ta n d a r d
D r. C . G ow er. S u p erv iso r ( D e p a rtm e n t of P hv sics and .\s tro n o m v )
__________ D r. C. R. P u rto n . C o -S u p erv iso r (D o m in io n R ad io .A strophysical O b se rv ato ry )
D r. C . D. Scarfe. D e p a rtm e n ta l M e m b e r ( D e p a rtm e n t of P hysics an d .\s tro n o m y )
D r. F / p . H art wick. D e p a rtm e n ta l M e m b e r (D e p a rtm e n t of P hysics an d .A stronom y
V
D r. G . M iller. O u tsid e M em b er ( D e p a rtm e n t of M a th e m a tic s a n d S ta tis tic s)
D r. J / M . M acLeod. E x te rn a l E x a m in e r (.Jam es C lerk M axw ell T elescope)
© D.AVID A N T H O N Y L Y D E R . 1997
L n iv e rs ity of V ic to ria
.All rig h ts reserved. D is se rta tio n m ay n ot b e rep ro d u ced in w hole o r in p a rt, by p h o to co p y in g o r o th e r m e a n s, w ith o u t th e p erm ission of th e a u th o r.
S u p erv iso rs: D rs. A . C. G o w er a n d C. R . P u rto n
A B S T R A C T
S ta r fo rm atio n in th e C am O B I region is in v estig ated . S ta r fo r m a tio n , in g e n e ra l,
is co n sid ere d in te rm s of th r e e e lem en ts: a) th e s tr u c tu r a l r e la tio n s h ip b etw ee n
th e p a re n t m o le c u la r clou ds a n d new ly form ed s ta rs , b) th e te m p o r a l e v o lu tio n
of th e p a re n t m o lecu la r clo u d s, an d c) th e p ro b a b ility of th e o c c u r r e n c e o f s ta r
fo rm a tio n . S ta r fo rm a tio n in C a m O B I . over th e ran g e in I a n d 6 c o n s id e re d in
th is w ork, is c o n c e n tra te d in th e v ic in ity of C am R l a n d a p p e a rs to h a v e led to th e
fo rm a tio n of th re e d is tin c t s te lla r g ro u p s: a) G roup I. fo rm ed ~ I — 50 x 10® y r ago.
a n d lo c a te d sp a tia lly an d k in e m a tic a lly betw een tw o C O c o m p lex es, b ) G ro u p II.
fo rm ed ~ 1 — 3 x 1 0® y r ago . a n d co in cid en t w ith one of th e p re v io u s ly m e n tio n e d
co m p lex es, a n d c) G ro u p III. th e y o u n g e st group, form ed ~ I — 20 x 10"* y r ago . a n d
lo c a te d a t th e c u rre n t p o in t o f in te rs e c tio n betw een th e tw o co m p le x e s in ( a ) . T h e
m ass fu n ctio n (M F ) for G ro u p s I an d II is sim ilar to th e clo ud m ass fu n c tio n o f th e
p a re n t m o lecu lar clo ud s, i.e.. a pow er-law w ith ex p o n en t q ~ 2. .A. s im ila r a n a ly sis
for th e G ro u p III s ta r s a n d a s s o c ia te d m o lecular clouds c a n n o t be p e r f o r m e d d u e
to th e rela tiv e ly sm all n u m b e rs in b o th sam ples. T h e s ta r fo rm in g efficien cy (S E E )
in all cases is ~ 1%. It is p ro p o se d th a t cloud-cloud collisions b e tw e e n th e C O
co m p lex es in th e region trig g e re d th e fo rm atio n of G ro u p s I a n d III. w h ile G ro u p II
was p ro d u ced by a shock in d u c e d by th e rad ia tio n p ressu re a n d s te lla r w in d s from
th e s ta r s in G ro u p I. .An a n a ly sis o f th e m o lecular clo ud s tr u c tu r e in C a m O B I a n d
th e b ack g ro u n d P erseu s a rm also show s th a t th e clouds in b o th region s a r e tu r b u le n t,
a n d ty p ic a l of clouds seen e lse w h e re in th e G alaxy. H owever, th e c lo u d s in C a m O B I
la rg e r, w arm er clo ud s b ein g g ra v 'ita tio n a lly b o u n d .
T h e p rin cip al d a ta set for th is w ork c o m p rise s fully sam p led ( J = l - 0 ) o b
s e rv a tio n s of th e w estern h a lf o f C am O B I . w hich w ere o b ta in e d a t th e C e n te r for
.A strophysics d u rin g th e w in te r of 1992-1993. T h e se d a ta have an effectiv e reso lu
tio n o f 10'. a v elo city reso lu tio n of 0.6-5 k m s ~ ‘ . a n d a sen sitiv ity of 0.11-5 K. H igh
re s o lu tio n (20") o b serv atio n s of th e *^C 0 ( J = 2 - l ) tra n s itio n o f th e m o st a c tiv e s ta r
fo rm in g region w ere o b ta in e d w ith th e J a m e s C le rk M axw ell T elesco pe d u rin g th e
w in te r o f 1994-199-5. T h ese o b serv atio n s le d to th e discovery o f a seco n d outflow .
.AFGL 490 — iki. asso c ia te d w ith IR.AS 032344-5843. in th e im m e d ia te v ic in ity of
t h e v e ry w ell-stu died m o lecu la r outflow .AFGL 490. .A dditional o b se rv a tio n s of th e
C H3O H m aser (5i — Oo-A'*’ ). ta k e n w ith th e 26m telescope at th e D o m in io n R ad io
•A strophysical O b se rv a to ry d u rin g th e fall o f 1994. d id not reveal a n y su ch m a ser-
ing a c tiv ity in th e C am O B I region, b u t d id lead to th e discovery o f a new m a se r.
A B S T R A C T c o n t.
D r. C. G ow er. S u p erv iso r (D e p a rtm e n t of P h ysics an d .\s tro n o m y )
D r. C . R. P u rto n . C o -S u perv isor (D o m in io n R ad io .A strophysical O b serv ato ry )
D r. C . D. S carfe. D e p a rtm e n ta l M em b er (D e p a rtm e n t o f P h y sics an d .A stronom y)
D r. ^ D . H artw ick . D e p a rtm e n ta l M em b er (D e p a rtm e n t o f P h y sics an d .A stronom y)
D r. G . M iller. O u ts id e M em ber (D e p a rtm e n t of M a th e m a tic s a n d S ta tistic s)
) r . / j . M. M acL eod. 1
T itle P age ...i
A b stra c t ... ii
T able o f C o n te n ts ... v
List o f T ab les ...x
List of F ig u res ... xii
A ck no w led gem ents ... xvi
C h a p te r ... P ag e In tro d u c tio n ... 1 C h a p te r I G e n e ra l O verview o f C O O bserv in g ... 15 1 . 1 I n t r o d u c t i o n ...15 1.2 P hy sical P r i n c i p l e s ...16 1.3 P h y sical Q u a n titie s of In te re st ... 25
1.3.1 M easu red P h y sic a l Q u a n titie s ...26
1.3.2 D erived P h y sic a l Q u a n titie s ...29
1.4 S u m m a ry of .A ssum ptions a n d C o n s tr a in ts ... 32 C h a p te r 2 T h e P re se n t S urvey ... 33 2.1 I n t r o d u c t i o n ... 33 2 . 2 T h e Cf.A T elesco p e ...34 2.3 T h e O b se rv atio n s ... 39 2.3.1 O b serv in g P r o c e d u r e ... 40 2.4 T h e D a ta ...43 2.4.1 b L's. V ... 46 2 .4 .2 / vs . V ... 48 2.4.3 I v s. b: Local E m ission ( + 10 to — 5 km s “ ^ ) ...50 2 .4 .4 I v s. b: C am O B I E m ission ( —5 to — 22 k m s “ ^ ) ... 53 2 .4 .5 / C6. b: I n te ra r m E m ission ( —22 to — 30 k m s " M ... 57 2 .4 .6 I v s. b: P erseu s E m ission ( —30 to — 70 k m s “ ^ ) ...59 2 .4 .7 I v s. b: O u te r G a la x y ( — 70 to — 130 k m s " ^ ) ... 62 2.5 C on clusions ... 64 C h a p te r 3 W h y th e New S u rvey ? ...65 3.1 In tro d u c tio n ...65
3.2.1 Q u a lita tiv e C o m p a riso n ... 67
3.2 .2 .A. Q u a n tita tiv e .Analyses ... 71
3 .2 .2.1 .A F F T .Analysis o f th e C O E m issio n S t r u c t u r e ... 71 3.2.2 .2 S tr u c tu r e T ree S t a t i s t i c s ... 79 3.3 D iscussion ... 84 3.4 C onclu sio ns ...87 C h a p te r 4 P o p u la tio n 1 O b je c ts ...8 8 4.1 In tro d u c tio n ...8 8 4.2 P o p u la tio n 1 O b j e c t s ... 90
4.2.1 T h e D ista n c e to th e Local E m ission ... 90
4.2 .2 T h e D ista n c e to th e P erseu s E m ission ...93
4.2 .3 T h e D ista n c e to th e C am O B I E m i s s i o n ... 96
4.3.1 T h e O b se rv e r's HR D iag ram for C am O B I ... 100
4 .3 .2 T h e T h e o re tic ia n 's H R D iag ram for C a m O B I ... 107
4.4 C onclu sio ns ... 113 C h a p te r 5 E x tr e m e P o p u la tio n I O b je c ts ...115 5.1 In tro d u c tio n ... 115 5.2 In frared O b je c ts in C am O B I ... 117 5.2.1 S election o f C a n d id a te In fra re d O b je c ts in C a m O B I .. 117 5.2 .2 T h e N a tu re o f th e In frared O b je c ts in C a m O B I ... 125
5.3 e P Io Id en tified b y th e ir O p tic a l o r R ad io E m issio n ...134
5.4 M eth an o l M asers ... 140
5.4.1 In tro d u c tio n ... 140
5 .4 .2 O b s e r v a tio n s ... 141
5 .4 .4 C onclusions R e g a rd in g M e th a n o l M asers ...147
5.5 M o lecular O utflow s ...148
5.5.1 In tro d u c tio n ... 148
5.5.2 O b s e r v a tio n s ... 150
5.5.3 D iscussion ...153
5 .5 .3.1 G eneral P ro p e rtie s of th e C O S p e c tra ... 153
5.5.3.2 .\FG L49G -iki ...154
5.5.4 C onclusion R eg ard in g O utflow s ...158
5.6 C onclusions R eg ard in g e P Io in C a m O B I ... 159
C h a p te r 6 O n th e .Association o f C a m O B I S ta rs w ith C a m O B I M olecular G as ...160
6 . 1 In tro d u c tio n ... 160
6.2 M orphological .A r g u m e n ts ...161
6.3 P h y sical In te ra c tio n betw een th e C a m O B I CO E m is sio n a n d P o p u latio n I O b je c ts ... 172 6.3.1 Hii Regions ... 172 6.3.2 D u st W arm ed by th e C am O B I S ta rs ... 177 6.4 C onclusions ... 185 C h a p te r 7 S ta r F o rm atio n in C am O B I ... 186 7.1 I n t r o d u c t i o n ...186 7.2 T h e M olecular C lo u d s a n d C lo u d C o m p lex es of C a m O B I 188 7.3 T h e S tellar G ro u p s in C am O B I ...195 7.3.1 G ro u p I ... 195 7.3.2 G ro u p II ... 204 7.3.3 G ro u p I I I ... 212 7.4 D is c u s s io n ... 217
7.5 C onclusions ...220
C h a p te r S O n th e Im p o rta n c e o f T u rb u le n c e a n d G ra v ity to th e M o lecu lar C loud S tr u c tu r e in C a m O B I . P erseus a n d E lsew here in th e G a l a x y ...222
8.1 I n t r o d u c t i o n ... 222
8.2 'M o v in g ' th e C a m O B I CO C lou ds to P e r s e u s ...224
8.3 C lo u d S election in C a m O B I a n d P erseu s ... 224
8.3.1 T h e in situ a n d M odified C a m O B I C l o u d s ...224
8.3 .2 T h e Perseus C lo u d s ...227
8.4 A C o m p ariso n of th e S tru c tu re o f M olecular C lou ds in C am O B I a n d P erseus ... 228
8.4.1 T h e T u rb u len ce Law ...228
8.4.2 Vi rial E q u ilib riu m ...233
8.5 D is c u s s io n ... 237
8 . 6 C onclusions ... 238
C h a p te r 9 C o n clu sio n s an d S u g g estio n s for F u rth e r O b se rv atio n s ...239
B ib lio g rap h y ... 241
.\p p e n d ix \ ... 254
•A.l T h e U n c e rta in ty in th e M easu red a n d D erived Q u a n titie s Used to C h a ra c te riz e M olecu lar C louds ...254
.A ppendix B ... 257
B .l P e r O B I and C as 0 B 6 ... 257
L ist o f T ables
T a b l e ... P a g e T ab le 2.1 O ff P o sitio n s ...40 T ab le 2.2 S u m m a ry o f S u rv e y P a ra m e te rs ...43 T ab le 4.1 O p en C lu s te rs a n d R-.Associations in F i e l d ... 91 T a b le 4.2 O b s c u ra tio n in S u rv ey ed Region ... 92T a b le 4.3 D a ta for B S ta rs . M ain S equence F i t t i n g ... 99
T ab le 4.4 D a ta for C a m O B I P o p u la tio n I O b je c ts ... 103
T ab le 5.1 O c c u p a tio n Zones for /R .4 5 P oint S ources ... 126
T ab le -5.2 [ R A S D a ta for C a m O B I E x tre m e P o p u la tio n I O b je c ts ...133
T ab le 5.3 O p tic a lly Id en tified Hii Regions in C am O B I (w ith R e lia b le D is ta n c e s ) ...137
T a b le 5.4 O p tic a lly Id e n tifie d Hii Regions in C a m O B I (w ith o u t R e lia b le D istan ces) ...137
T ab le 5.5 P ro p e rtie s o f O p tic a lly Identified B R X ... 138
T ab le 5.6 S u m m a ry o f P a r a m e te r s for M eth an o l S urv ey w ith DR.AO 25.6m T e l e s c o p e ... 141
T ab le 5.7 P o sitio n s S earch e d for th e 5i — 6o.4"^ M e th a n o l M a s e r ... 142
T ab le 5.8 S u m m a ry o f O u tflo w S urvey P a ra m e te rs w ith th e J C M T 15m Telescope ...149
T a b le 5.9 P o sitio n s S earch e d for M u ltip le-P eak e d C O E m issio n ...151
T ab le 6.1 C a n d id a te C a m O B I S ta rs w ith S ig nifican t L y m a n F lu x .A ssociated w ith S202 ... 174
T ab le 6.2 P a ra m e te rs for C a m O B I S tars W arm in g D u st .A ssociated w ith C am O B I CO E m ission ... 181
T able 7.2 C a m O B I - S te lla r G rou p I ...199
T able 7.3 C a m O B I - S te lla r G roup I I ... 208
T able 7.4 C a m O B I - S te lla r G rou p I I I ... 214
T able 7.-5 S u m m a r y for C a m O B I: C am R l S te lla r G ro u p s ... 216
T able 8 . 1 C a m O B I C O C lou ds if T hey W ere L o ca ted in th e P erseu s .A r m ...226
T able 8.2 S u m m a r y o f P h y sical P a ra m e te rs of P erseu s C l o u d s ...229
T able 8.3 S ta tis tic s for C o m p ariso n of V'irial P a r a m e te r ...234
T able 8.4 P h y s ic a l P ro p e rtie s o f C am O B I C loud s w ith .Above- a n d B elow -average V irial P a r a m e t e r s 236 T able .A.l S u m m a r y o f T y p ic a l C loud U n c e r ta in ti e s ... 255
T able B .l C as 0 B 6 ...258
T able B.2 P e r O B I ...259
L ist o f F igu res
F ig u re ...P a g e
F ig u re 1.1 A sc h e m a tic d ia g ra m show ing th e re la tio n s h ip b etw ee n
th e ISM a n d s ta rs ... 7
F ig u re 1 . 1 R o -v ib ra tio n a l s ta te s for th e lower tra n s itio n s o f 17 F ig u re 1.2 S a m p le C am O B I C O clou d s p e c tru m ... 27
F ig u re 1.3 S a m p le C am O B I C O c l o u d ... 28
F ig u re 2.1 S c h e m a tic of C f.\ 1.2 m te le s c o p e ...35
F ig u re 2.2 .A uthor s ta n d in g n e x t to th e C f.\ 1.2 m telesco p e ... 36
F ig u re 2.3 S c h e m a tic of receiv er for C f.\ 1 . 2 m t e l e s c o p e ... 38
F ig u re 2.4 S u rv e y b o u n d arie s o f p resen t surv ey (D i96) ... 39
F ig u re 2.5 S a m p le of b a d ' s p e c tr a d e te c te d d u rin g th e ob serv in g r u n 44 F ig u re 2.6 .Average CO s p e c tru m for th e su rv ey ed r e g i o n ... 45
F ig u re 2.7 6 r s . v for p resent s u rv e y ...47
F ig u re 2.8 / c s . v for p resent su rv e y ... 49
F ig u re 2.9 I v s . b: Local e m i s s i o n ...51
F ig u re 2.10 T e m p e ra tu re w eig h ted m o m en t m a p o f th e Local em issio n . . . .5 2 F ig u re 2 . 1 1 I v s . b: C am O B I e m issio n ...55
F ig u re 2.12 T e m p e ra tu re w eig h ted m o m en t m a p o f th e C am O B I em issio n 56 F ig u re 2.13 / r s . b: In te ra rm regio n ... 58
F ig u re 2.14 / c s . 6: P erseu s e m i s s i o n ... 60
F ig u re 2.15 T e m p e ra tu re w eig h ted m o m en t m a p o f th e P erseus em issio n . .61 F ig u re 2.16 I v s . b: O u te r G a la x y ... 63
F ig u re 3.1 .A c o m p a riso n b e tw e e n th e present su rv e y an d
F igu re 3.2 F ig u re 3.3 F ig u re 3.4 F ig u re 3.5 F ig ure 3.6 F ig u re 4.1 F ig u re 4.2 F ig ure 4.3 F ig ure 4.4 F ig ure 4.5 F ig u re 4.6 F ig u re 4.7 F ig u re 4.8 F ig ure 5.1 F ig u re 5.2 F ig u re 5.3 F ig u re 5.4 F ig u re 5.5
.A. c o m p a ris o n o f th e v elo city m o m en t m aps b etw ee n th e
p re se n t su rv ey a n d th e original CfA su rv e y ... 70
T w o d im e n s io n a l F F T o f p re se n t survey ... 73
C lose up o f tw o d im e n sio n a l F F T of p resen t su rv ey ... 74
T w o d im e n s io n a l F F T o f o rig in al survey ...78
S tr u c tu r e tre e s for o rig in al a n d p resen t su rv ey s ...80
.All s te lla r o b je c ts in SIM B.AD co n tain ed w ith in th e su rv ey b o u n d a rie s ...91
O v e rla y o f H eesch en 's (1951) a rea s of o b sc u ra tio n o n to th e Local em issio n ... 92
L o c a tio n of s ta rs in C as 0 B 6 a n d P er O B I. as listed by G S92. in th e P erseu s a rm ...94
B S ta rs for M ain S eq u en ce fittin g . C am O B I ...98
O b s e rv e r's H R d ia g ra m o f C am O B l ... 102
T h e o r e tic ia n 's H R d ia g ra m of C am O B I ...108
T h e s p a tia l d is trib u tio n a n d . h isto g ra m o f th e age d is tr ib u tio n of s ta rs in C am O B l ...I l l O v e rla y o f C a m O B l s ta rs on C am O B l C O e m i s s i o n ...112
L o c a tio n of all in fra re d o b je c ts w ith in th e p re se n t su rv e y b o u n d a rie s ...119
O v e rla y o f e n h a n c e d d e n s ity o f in frared fe a tu re s o n to C O e m i s s i o n ... 120
C o lo r-color p lo ts for in fra re d sources w hich h av e a t le a st tw o a d ja c e n t I R A S fluxes of m o d e ra te q u a l i t y ...124
O c c u p a tio n zones (O Z s) for n o n -eP Io a n d e P Io ...129
F ig u re 5.6 O c c u p a tio n zones (O Z s) in [25-60-100] p la n e for C a m O B I . . 131
F ig u re 5.7 O v e rla y o f e P Io o n to th e C a m O B I C O e m i s s i o n ... 139
F ig u re 5.8 O v e rla y o f I R .\S sources e x a m in e d for m e th a n o l em issio n
o n to C O em ission ... 143
F ig u re 5.9 S p e c tru m for m e th a n o l m a s e r asso c ia te d w ith
I R .\S 02455+ 6034 ... 145
F ig u re 5.10 P o s itio n s o f m e th a n o l m a s e r. IR A S 0 2 4 5 5 + 6 0 3 4 . CS e m issio n .
a n d on ly know n ra d io -d e te c te d H ii reg ion , Lo2.
s u p e rim p o se d on th e a s so c ia te d C O em issio n ... 146
F ig u re 5.11 O v e rla y o f o b serv atio n s o n to in te g ra te d C O em ission
in C a m O B l reg io n ... 153
F ig u re 5.12 ^ ^ C 0 ( 2 - l) em ission for .AFG L490-iki c e n te re d on
I = 141Î580.6 = 1?4T5 ...155
F ig u re 5.13 A v e ra g e ^ ^ C 0 (2 -l) e m issio n for .■\FGL490-iki over
th e velocity ran g e - 3 7 to -1 6 k m s"^ ...156
F ig u re 6 . 1 O v e rla y of P o p u la tio n I o b je c ts in C a m O B l o n to
th e C a m O B l C O em issio n ... 162
F ig u re 6.2 O v e rla y o f C O em ission a n d C a m O B l s ta r s over
th e 1420 M Hz c o n tin u u m em issio n ... 175
F ig u re 6.3 O v e rla y of C O em ission a n d C a m O B l s ta r s over
d u s t te m p e r a tu r e m a p ... 178
F ig u re 6.4 S e le c te d C a m O B l s ta rs s p a tia lly co in c id e n t w ith w arm d u s t
a s s o c ia te d w ith th e C a m O B l C O e m i s s i o n ...181
F ig u re 7.1 A s im p le sc h e m a tic sho w ing clo u d c o m p lex es, se le c te d on th e
basis o f sim ilar ra d ia l velo cities a n d p o sitio n s, in
F ig u re 7.2 H isto g ra m fo r C O C o m p le x e s ... 195
F ig u re 7.3 O v erlay o f G ro u p I s ta rs over C O em ission a t -9 .4 km s " ‘ --- 197
F ig u re 7.4 H R d ia g ra m for th e s ta rs d e s ig n a te d as G ro u p I in
th e C a m R l region ...198
F igu re 7.5 .\g e d is tr ib u tio n o f s ta r s in G ro u p I ... 201
F igu re 7.6 In itia l M ass F u n c tio n for G ro u p 1 s ta rs ...202
F ig u re 7.7 C O clo ud m a ss fu n c tio n for th e clouds m a k in g up
C o m p le x e s A a n d B ... 204
F igu re 7.8 O v erlay o f G ro u p II s ta rs over C O em ission a t -9 .4 km s “ ^ . . .206
F ig ure 7.9 H R d ia g ra m for th e s ta r s d e s ig n a te d as G ro u p 11 in
th e C a m R l region ... 207
F igure 7.10 .\g e d is tr ib u tio n of s ta rs in G ro u p 11 ... 209
F igu re 7.11 In itia l M ass F u n c tio n for G ro u p II sta rs ... 210
F ig u re 7.12 C O clo ud m a ss fu n c tio n for th e clo ud s m a k in g up C o m p lex B 211
F igu re 7.13 O v erlay o f G ro u p III s ta rs over C O em ission a t -9 .4 k m s~^ ..2 1 3
F igu re 8.1 O rig in a l a n d M odified C a m O B l D a t a ...225
F igure 8.2 C o m p a riso n o f th e Turbulence L aw as defined by L81 to th e
m o d ifie d C a m O B l clo ud s an d P erseu s clouds ... 232
F igu re 8.3 P lo t of th e V iria l P a ra m eter. 2 G M /A c ^ L . as a fu n ctio n
o f c lo u d ra d iu s ...235
F igu re . \ . l Effect of th e fin ite reso lu tio n of th e telescop e b e a m on
A ck n o w led g m en ts
I s ta r te d th is a d v e n tu r e so m a n y years ago th a t I am su re I h ave ru n into people
w ho I will forget to th a n k b u t w ho really did help m e very m u ch . P lea se forgive m y
poor m em ory.
W hen I s ta r te d o u t in V ic to ria 1 was fo rtu n ate enou gh to m a k e th e a c q u a in ta n c e
of som e good frien d s a n d d a rn g oo d astro p h y sicists in c lu d in g .\n a . R o b erto , Luc.
.Joanne, S tev e n , P a t, all o f th e D avids, and J o h n , e t al. I en jo y ed y o u r co m p any
very m u ch a n d le a rn e d a lo t from you. I should also like to say a sp ecia l th a n k you
to J e re m y T a tu m for s ta n d in g up for m e when I first la n d ed in V ic to ria an d was
a d ju stin g to m y new s u rro u n d in g s .
I also w ould like to th a n k th e folks in V icto ria o u ts id e of U. V ic. who were
so very kind to m e d u rin g m y s ta y th e re : Russ an d M argie a n d th e kids for m an y
nice d in n e rs a n d a c h a n c e to play, th e Ewings for th e ir very k in d h o sp ita lity , g reat
d in n ers a n d g o od c o m p an y . I w ould be rem iss if I d id n ’t say a sp ecia l th a n k you to
S a m a n th a (S am ) for b e in g so g ood to m e. You w ere really such a g ood friend to m e
S am , I wish you all th e jo y a n d h ap p in ess in th e W orld. I w ould also like to th a n k
S haron a n d .■Mex from S V d P . w ho allow ed m e to help o u t an d keep m y feet p la n ted
firm ly on th e g ro u n d a n d th in k a b o u t w hat is really im p o rta n t in th is W orld.
O n m y way to P e n tic to n I h a d th e chance to m ak e a six -m o n th d e to u r in B oston.
T h is was a g re a t o p p o r tu n ity for m e to stu d y a t th e CfA a n d m e e t m any g re a t
astro n o m ers. I m u st th a n k P a t T h a d d e u s, Tom D am e an d S am P a lm e r for allow ing
m e th e o p p o r tu n ity to u se su ch a g re a t in stru m e n t an d ju s t allow ing m e a chance
to ta lk to th e m a b o u t C O , e tc . I m u st also send a very sp ecial th a n k you to S eth
Digel (a n d his wife J e a n n e ) w ho was a great colleague an d frien d, a n d gave m e a
lot of s u p p o rt w hen I w as d e s p e ra te ly try in g to g et th is p ro je c t underw ay. I do not
crazy co usin. A n n -L e e . fo r le ttin g m e s ta y w ith h e r d u rin g m y s ta y a t t h e CfA - it
was a very in te r e s tin g e x p e rie n c e .
L an d in g in P e n tic to n I quickly le arn ed th a t D R A O w as m a d e u p o f a g re a t
grou p of peo ple. T o m L an d e ck er an d Lloyd Higgs w ere very kind in m a k in g s u re I had aJl th e reso u rces I n eed e d to c o m p le te th is th esis. I h av e to th a n k e v e ry o n e for
m an y in te re s tin g c o n v e rs a tio n s I had w ith th e m over th e y ears a n d all o f th e h elp
th e y have g iv en m e. In p a r tic u la r. I m u st th a n k K en T a p p in g for te a c h in g m e a b o u t
SIS ju n c tio n s . Lew is K n e e for co rrectio n s to an e a rlie r version of th is th e s is a n d his
th o u g h ts o n s ta r fo rm a tio n , a n d Tom B urgess for his e d ito ria l c o m m e n ts .
I have m a n y g o o d m e m o rie s of m y days a t D R A O a n d a (larg e) n u m b e r o f th e m
have to do w ith d a n c in g . M an y th a n k s to little D ianeski for h er little re d n u m b e r, to
C olleen a n d T a ra e t a l. for th e m an y fun n ig h ts c u ttin g a rug . M any th a n k s to P e te r
for th e e n jo y ab le fish in g trip s , an d also to Tom an d K aren for th e ir e x c e lle n t w ine
and an d th e ir good c o m p a n y (I hope we still get to play b rid g e to g e th e r s o m e d a y ).
I m u st also th a n k C h ris a n d S a n d ra for th e ir k in d h o s p ita lity d u rin g m y s ta y in
P e n tic to n a n d H aw ai i - I a m a r a th e r large stray ! A sp ecial th a n k s m u s t also go to
Ricky, one o f th e k in d e s t m e n I have m e t in m y life a n d a good frien d.
M y s ta y in P e n tic to n w ould not have b een c o m p le te /rig h t w ith o u t b e in g ab le
to w ork for S V dP . So m a n y friend s I m e t an d enjoyed th ro u g h m y w ork w ith th e
Society. I w ould like to first rem e m b er th o se w ho have gone before us - D o n n a a n d
M arg aret - we s till th i n k a b o u t you and p ray for you. I m u s t say a s p e c ia l th a n k s to
Rose w ho is very in t u n e w ith th e W orld a n d ta u g h t m e how to pray, a n d M a rg e u rite
who ta u g h t m e how to o rg a n iz e (d eleg ate) an d enjoy m y rig h t b ra in . I a lso w ould
like to th a n k C ecil ( P a p a B e a r) and M a rg u e rite for th e ir good c o m p a n y m a n y a
nig h t p la y in g sc ra b b le . L et m e also say th a n k s to B lanche. J o h n a n d A n ita , S h a ro n ,
of th e ir w ork w hich th e y p u t in to m a k in g th e Society work. G o d bless y ou all.
I a m b ack in E d m o n to n now a n d it does feel as if I a m b ack ho m e. I could n o t
h av e d o n e th is w ork w ith o u t t h e u n q u e stio n in g su p p o rt o f m y p a re n ts . N u ala a n d
B ria n , w ho w ere alw ays th e re fo r m e a n d en co u rag ed m e w hen th in g s w ere not easy.
I m u s t aiso th a n k m y sis te r. M aev e. a n d b ro th er-in -law . D eraid , for all o f th e h elp
th e y g ave m e o v er th e y ears. I know I co u ld be a real p ain s o m e tim e s. I w ould also
like to th a n k Z u lm a a n d M a rc e l for th e ir w onderful d a u g h te r a n d th e re st of th e
C h e r le t clan for all o f th e ir p ra y e rs a n d su p p o rt. I m u st also th a n k D o ro th y a n d
.Andrei for th e ir k in d s u p p o r t o v e r th e y ears - it finally is d o ne, yeah!! T h a n k s also
to T erry . C h ris. R ek h a. D aw n a n d M alco lm , and Ian a n d Jill for m a in ta in in g o u r
ties o v er th e y ears. I t ’s g ood to b e b ack h o m e to enjoy y o u r com p an y.
A th e sis is n o t c o m p le te w ith o u t a big th a n k you to m y su p e rv iso rs. C h ris
P u r to n a n d .Ann G ow er. C h ris s h o u ld b e given a g reat d eal o f c re d it for th e th in g s
w hich w orked well in th e th e s is (T il ta k e th e blam e for th e re s t). He re a lly is a v ery
p a tie n t m a n a n d believes s tro n g ly in bein g u ncon ven tional - th a n k G od! I c a n ’t
th a n k y ou en o u g h K im o sab e. I h o p e I h a v e n 't let you dow n. .Ann has b een k in d
en o u g h to s u p p o rt m e for all o f th e s e y ears an d has been g re a t b rin g in g th is th e sis
h o m e dow n th e final s tr e tc h (I h o p e y o u learned so m eth in g a b o u t s ta r fo rm a tio n
alo n g th e w ay). I m u st also th a n k m y co m m itte e , p a rtic u la rly C olin S carfe, for
re a d in g e a rlie r versions of th is th e sis a n d aJl o f th e e d ito ria l c o m m e n ts th e y m a d e .
I w o uld also like to th a n k J o h n S calo a n d Lynne H illen b ran d w ho also p ro v id ed
e d ito ria l c o m m e n ts a n d in sig h t in to im p ro v in g th e thesis a n d k eep in g m e on th e
rig h t tra c k .
L a st, b u t n ot le a st, I m u s t th a n k th e F a th e r, Son an d H oly S p irit for g ivin g m e
D e d ic a tio n
I have sav ed for m y d e d ic a tio n an acknow ledgem ent o f th a t m o s t sp ecia l person
in m y life, m y b e s te s t b u d d y , m y fiancee, m y C ath y. T h a n k y o u so m u c h for all of
y o u r help an d s u p p o rt y o u h av e giv en m e over th e years. I look fo rw ard so m uch
to th e a d v e n tu re s we sh all s h a re th ro u g h o u t our lives to g e th e r. G o d bless you. keep
Introduction
T h e H isto r ic a l D e v e lo p m e n t o f O ur U n d e r s ta n d in g
o f S ta r F o r m a tio n
T h e first m od el o f s ta r fo rm ation can be a ttr ib u t e d to Im m a n u e l K a n t a n d P ie rre Sim on L ap lace w ho, in th e e ig h te e n th c e n tu ry , p ro p o sed th e n eb u la th e o r y ' to a c c o u n t for th e fo rm a tio n of th e so lar s y ste m . In th e ir o rig in al m od el, th e y e n v isio n ed a large th in disk o f gas. a p p ro x im a te ly th e size a n d méiss of th e c u r r e n t so la r sy ste m , u n d erg o in g c o n tra c tio n , from w hich th e S un fo rm ed a t th e c e n te r w ith th e p la n e ts form in g in rings o f m a teria l w hich h a d b roken aw ay fro m th e c o n tra c tin g disk . P ro b lem s w ith th e d is trib u tio n of a n g u la r m o m e n tu m in th is sy ste m , th e in a b ility to ex p la in p la n e ta ry o rb its in clined to th e p lan e, as w ell as th e in a b ility o f th e rings of th e p ro p o sed size to avoid b ein g d is ru p te d b y tid a l forces p ro v e d in s u rm o u n ta b le . F u rth e rm o re , th e m a n n e r in w hich th e disk first form ed was n o t a d d re s s e d . H ow ever, th e w ork of K ant an d L ap lace has serv ed to p lan t th e seed for c o n te m p o ra ry m o d els of s ta r fo rm atio n an d th e re la te d p ro b le m of p la n e ta r y fo rm a tio n .
In th e n in e te e n th cen tu ry , th e c o n te m p o ra ry m a th e m a tic a l fram ew o rk for ta c k ling th e p ro b lem of s ta r fo rm atio n was fo rm u la te d by R. J . E. C la u siu s in his d e riv a tio n o f th e virial th e o re m . .A. very in te re stin g e x p o sitio n of th e h isto rical d ev e lo p m e n t of th is th e o re m is given by C ollins (1978). .A rigorous d ev elo p m en t of th is fo rm u la tio n is no t th e focus o f th is thesis b u t th e u n d e rly in g p rin c ip le is clear if o n e co n sid ers th a t th e ch an g e in th e d y n am ical s ta t e o f a sy ste m is a b alan ce b e tw e e n th e forces w hich a re try in g to disperse th e sy ste m an d th o se tr y in g to co n d en se it. C la u siu s was ab le to show th a t th e m a th e m a tic a l d e sc rip tio n o f th is b alance is:
1 d^I
5 5^ = 2 r + n , ( U )
w h ere I is th e m o m e n t o f in e rtia of th e sy ste m . T th e k in e tic e n e rg y of th e sy ste m a n d Q th e p o te n tia l en erg y o f th e sy stem . T h e s im p le st a p p lic a tio n o f th is fo rm u la to th e p ro b le m of s ta r fo rm a tio n weis first c arried o u t b y Sir J a m e s J e a n s who co n sid e re d a c lo u d o f gas w hich was s ta b le (i.e., a sy ste m in w hich th e re is no ch ang e in its r o ta tio n a l in e rtia ), in w hich th e k inetic energ y o f th e s y ste m w ould be d u e to its th e r m a l m o tio n a n d its p o te n tia l energy w ould b e d e te rm in e d b y its self-gravity. F o r
G \ P
w here \ I . th e v irial m a ss, is th e to ta l m ass c o n ta in e d w ith in r a d iu s R . v is th e m ean th re e -d im e n sio n a l v e lo c ity of th e p article s d u e to th e ir th e r m a l m o tio n , q is a facto r in c lu d e d to g e n e ra liz e th e e q u a tio n to allow for d iffe re n t g e o m e trie s an d G is N ew to n ’s g ra v ita tio n a l c o n s ta n t. T h e m in im u m m a ss w hich m u s t b e co n tain ed w ith in ra d iu s R su ch th a t th e force due to self-g rav ity o f th e s y s te m a t le ast equals its te n d e n c y to d isp e rse d u e to its th e rm a l m o tio n is g iv e n by E q . 1.2 a n d is known as its J e a n s m ass. m a ss la rg e r th a n th is, for a given g a s te m p e r a t u r e a n d rad iu s, will u ndergo co llap se w hile for a sm aller m ass th e s y s te m w ill d is p e rs e .
O f course it was re a liz e d th a t Eq. 1.2 d id no t c o n ta in all o f th e p o ssib le con trib u tin g forces to th e s y s te m . O v er a perio d o f tim e th e in flu en ce of a d d itio n a l forces, e.g .. m a g n e tic fields a n d ro ta tio n (C h a n d ra s e k h a r Sc L e b o v itz 1962). tu r b u lence (von W eizacker 1951), a n d e x te rn a l p ressu re ( E b e r t 1955. B o n n o r 1956). have been in clu d ed . A m o re c o m p le te fo rm u latio n o f th e p ro b le m , a s s u m in g a stab le sy ste m , m ay now be giv en éis:
P - n = 2 T + B + 2L. (1.3)
w here P re p re se n ts th e c o n trib u tio n to th e en erg y of th e s y s te m d u e to a n y e x te rn a l pressu re. Q. re p re se n ts th e p o te n tia l energy of th e s y s te m as b e fo re . T rep resen ts th e kin etic en erg y of th e s y s te m w hich m u st now in c lu d e th e c o n trib u tio n s d u e to th e rm a l m o tio n a n d tu r b u le n t m o tio n . B is th e to ta l n e t m a g n e tic en e rg y of the sy stem an d L re p re se n ts t h e e n e rg y due to ro ta tio n .
C o n te m p o r a r y A p p r o a c h e s to U n d e r s ta n d in g S ta r F o r m a tio n
V arious a ss u m p tio n s h a v e to b e m ad e in a p p ro a c h in g a th e o ry o f s ta r fo rm atio n for a given region . It is q u it e co m m o n for a p a r tic u la r m o d e l o f th e s ta r form ing process to rely u p o n a re d u c e d fo rm of Eq. 1.3 in th a t o n ly so m e o f th e (relev an t) forces a t play a re c o n sid e re d . As a n exam p le, in th e a n a ly s is o f th e s ta r fo rm atio n in C am elo p ard a lis p re s e n te d in th is thesis, th e role o f e x te r n a l p re s s u re is n o t con sid ered even th o u g h m a n y o f th e C O clouds found in t h e reg io n d o n o t a p p e a r to exceed th e ir v irial m ass a n d s h o u ld quickly d issip a te w ith o u t th is a d d itio n a l force. H owever, o n e of th e m a in p o in ts o f in terest in th is th e s is is th e re la tio n betw eenth e m o le c u la r clouds a n d new ly fo rm ed s ta r s , n o t n ece ssarily th e lo n g ev ity o f th e clo u d s (w h ich would re q u ire d e ta ils of th e e x te r n a l p re s s u re ). T h e a s s u m p tio n th a t th e e x te rn a l p ressu re is c o n s ta n t th ro u g h o u t th e field is co m m o n to m o st s tu d ie s of s ta r fo rm in g regions a n d is a d e q u a te for th e a n a ly sis c o n d u c te d in this th e sis.
F u rth e rm o re , u n d e rs ta n d in g s ta r fo rm a tio n is in h e re n tly difficult as it is difficult to define w h at c o n s titu te s a 's y s te m ' e x a c tly in a p a r tic u la r s itu a tio n . For e x a m p le , a n e x tre m e case w ould b e a s ta r b u r s t g alaxy , in w h ich case th e w hole galax y, o r a t le a st a sig nifican t p o rtio n o f it. c o n s titu te s th e s y s te m u n d e rg o in g th e tra n s fo rm a tio n fro m gas to stars. T h e c o m p le x ity o f th is s y s te m ch anges as it evolves a n d th e im p o r ta n c e of th e d ifferen t forces m ay v ary w ith tim e .
C o n te m p o ra ry m o d els o f s ta r fo rm a tio n h a v e a p p ro a c h e d th e p ro b lem , for th e m o st p a r t, from tw o d ifferen t p o in ts o f view . O n e p o in t o f view co n sid ers s ta r fo rm a tio n in te rm s o f th e s tr u c tu r e of th e m o le c u la r clou ds from w hich th e s ta rs c a m e (von W eizacker 1951. L arson 1979. 1981. 1991. 1992). i.e.. th ey a re p ro d u c e d as a n a tu ra l co n sequ ence of th e s tr u c tu r e seen in th e in te rs te lla r m ed iu m (IS M ). T h e o th e r p o in t o f view c o n sid ers s ta r fo rm a tio n in te rm s o f th e d e ta ils of th e fo rm a tio n a n d ev o lu tio n of in d iv id u a l s ta rs (M y ers & B en so n 1983. S h u et al. 1987. M yers 1991). T h e tw o ap p ro ac h es a re n ot m u tu a lly e x clu siv e. O n th e co n tra ry , one o f th e m a in th r u s ts of c o n te m p o ra ry s ta r fo rm a tio n th e o ry is a n a tte m p t to s y n th e siz e th e o b se rv a tio n s a n d th e o rie s d ev elo p ed from th e s e tw o p o in ts o f view.
O n th e E volu tion o f M oleculsir C lou d s
H isto rically , th e re w ere tw o schools of th o u g h t o n th e o rg a n iz a tio n o f th e ISM . w h ich can b e now be e x te n d e d to m o le c u la r clo u d s. Von W eizacker ( 1951 ) p ro p o sed a m o d e l o f th e ISM w h ere in th e s tr u c tu re o f th e clo u d s co u ld b e d escrib ed by classical tu r b u le n c e (K olm ogorov 1941). w h ereb y d ifferen ces in th e velo city field serv ed to o rg a n iz e m a te ria l in a series o f ed dies w ith a tr a n s f e r o f en erg y , v ia viscous h e a tin g , from th e la rg est scale to th e sm a lle st. A t th e s m a lle s t scale, h e a t is th e n d is s ip a te d v ia ra d ia tiv e cooling. If th e sm allest clo u d s c a n s a tisfy th e J e a n s c rite rio n th e n th e s m a lle s t clouds will co llap se a n d form a s ta r . O n th e o th e r h a n d . Hoyle ( 1953) a rg u e d for a g ra v ita tio n a lly -d riv e n s tr u c tu re , i.e.. tu r b u le n c e in a g ra v ita tio n a l field r a th e r th a n a p re ssu re field, w h ere fra g m e n ta tio n a t all levels o f o rg a n iz a tio n o c c u rre d cis a n a tu r a l re su lt o f th e gas cooling. A g ain , th e fin al u n it in th is fra g m e n ta tio n scen ario w as a J e a n s m ass clo u d w hich p ro d u c e d a s ta r . T h e d ifference b etw een th e se tw o
d e ta il in this c h a p te r. .\s H oyle (1953) very s u c c in c tly su m m a rized :
“T h e rise o f p re ssu re [in a v elo city field] d u e to co m pression in o r d in a r y tu rb u le n c e te n d s to d isru p t th e d en ser e le m e n ts o f m a te ria l. It is for th is reaso n th a t th e d e n sity of a p a rtic u la r sam p le o f m a te r ia l flu c tu a te s in o r d in a ry tu rb u le n c e , so m etim es b ein g d en ser th a n th e g en eral av era g e a n d so m etim es less dense. T h e fo rm a tio n of a d e n se r e le m e n t in g ra v ita tio n a l tu rb u le n c e , o n th e o th e r h a n d , o n ly increases th e a b ility o f th e e le m e n t to h o ld itself to g e th e r. T h u s th e re is a ro o ted d ifferen ce b etw ee n th e tw o cases: d en ser e le m e n ts a re evan escen t in o rd in a ry tu rb u le n c e , d e n se r e le m e n ts te n d to becom e p e rm a n e n t co n d en satio n s in g ra v ita tio n a l tu rb u le n c e .”
W hile th e von W eizacker an d H oyle m odels of m olecu lax clouds a re useful th e y
c a n n o t e n tirely re p re se n t th e tr u th of th e m a tte r . B o th o f th e se m odels a re essen tia lly to p -d o w n ' view s o f th e o rg a n iz a tio n of m o le c u la r clouds in th e G a la x y a n d a re very lim ited in th e ir a p p lic a tio n . If e ith e r th e von W eizack er o r H oyle m o d e l were s tr ic tly correct th e n th e s ta r fo rm a tio n a sso ciated w ith th e s e clouds, a n d all clou ds in th e G alaxy, sh o u ld be rap id , w ith th e m o lecu lar m a te r ia l bein g qu ick ly c o n v e rte d in to s ta rs . T h is is n o t seen in th e G a la x y to d a y w h ere th e observed s ta r fo rm a tio n r a te . ~ 3 .\I j, y r " ^ is con spicuously low an d th e life tim e o f m o lecu lar clo u d s. I - 3 x 1 0 ' y r (B litz & S hu 1980. E lm eg reen 1985) is a p p re c ia b le . T his d ifficu lty w ith tim e scales for b o th th e von W eizacker an d H oyle m o d e ls w as first n o te d by O o rt (1954) an d m o delled by Field & Saslaw (1965). In th e m o d ificatio n to th e th e o ry p ro p o sed by O o rt (1954) it was p ro p o sed th a t th e la rg e st m o lecu lar clo u d s w ere c o n tin u a lly being rep la ced by sm a lle r ones w hich coalesced a n d w hich, in th e ir tu rn , h a d b een built u p fro m even sm aller clouds, a n d so o n , dow n to th e sm a lle st cloud scale. It should b e n o te d th a t a p p lic a tio n of O o rt's (1954) 'b o tto m - u p ' m o d e l alo ne is also u n sa tisfa c to ry as it does not allow for a re a listic b re a k u p of th e m o st m assiv e clo ud s by s te lla r w inds a fte r th e fo rm a tio n of a su fficien tly m assive s ta r (E lm e g re e n 1987) ' a n d /o r su p ern o v ae (T en orio-T agle & B o d e n h e im e r 1989). N or does it
ad-^ E lm egreen (1993) considers th e fo rm atio n o f clo u d s v ia ‘p re ssu riz e d ’ e v e n ts as b ein g a se p a ra te p rocess, a disco n tin u o u s r a th e r th a n a co n tin u o u s p ro cess, from th e tw o d escrib ed h ere. H owever, th e o b je c ts he a t tr ib u t e s to th e se e v e n ts - sh ells, s h e e ts , c o m e ta ry glob ules an d g a la c tic ch im n ey s - m a y b e m o d elled ju s t as w ell in
& Saslaw 1965). o r allow for d e s tru c tiv e collisions b etw een clo u d s (S tru c k -M a rc e l & Scalo 1984).
H ence, an y m o lecu la r clouds we observ e, e.g.. th e C a m O B I clo ud s o r P erseus clou ds, rep resen t a sn ap -sh o t of th e c u rre n t s ta te of affairs, w hich is a balance b etw een th e te n d e n c y for th e clo ud s to b reak up in to sm a lle r c lo u d s a n d th e te n d en cy for sm aller clouds to c o n g lo m e ra te to form la rg e r m o le c u la r co m plexes.
O n th e F o r m a tio n o f In d iv id u a l S ta r s
T h e fo rm atio n of an in d iv id u a l s ta r is still a very p o o rly u n d e rs to o d process b u t th e s ta n d a rd m odel for th is process a t p resen t (S h u e t al. 1987) involves th e in sid e-o u t collapse of a r o ta tin g iso th e rm a l m o lecu la r clo u d co re w hich has a 1/r^ d e n s ity profile. C ollap se of su ch a core lead s to th e fo rm a tio n o f a p ro to -s ta r and disk a t th e c e n te r of th e core. M a te ria l from th e infalling co re c o n tin u e s to acc rete o n to th e p ro to -s ta r a fte r first falling up o n th e m u ch la rg e r d isk . T e rm in a tio n of th e infall occu rs w hen outflow s from th e p ro to -s ta r, e ith e r fro m b ip o la r outflow s or s te lla r w inds, d isp erse th e re m a in in g core m a te ria l.
In th e m odel o f S hu et al. (1987) m a g n e tic fields se rv e as th e m a in su p p o rt m ech an ism re g u la tin g th e size o f th e in itia l core a n d s u b se q u e n t p r o to - s ta r form ed. C ores w hich a re g ra v ita tio n a lly u n s ta b le b u t s u p p o rte d by th e local m a g n e tic field (m a g n e tic a lly s u b -c ritic a l cores), collapse slow ly as th e s u p p o r tin g m a g n e tic field g ra d u a lly escapes (a m b ip o la r diffusion). C ores in w hich th e m a g n e tic field su p p o rt ex ceeds th e m in im u m to p rev en t g ra v ita tio n a l collap se (m a g n e tic a lly s u p e r-c ritic a l cores), avoid co llapse u n til th e m ass c o n tain ed w ith in th e m o le c u la r co re exceeds w h at can be s u p p o rte d , a fte r w hich ra p id collapse o ccu rs. G iven th a t th e su p er c ritic a l cores can be m o re m assiv e th a n th e su b -c ritic a l co res before th e onset of co llap se, it is b eliev ed th a t th e su p e r-c ritic a l cores p ro d u c e m a ssiv e sta rs.
W h ile th e m o d el of Shu e t al. is a ttr a c tiv e in th e sen se t h a t it provides a co m p reh en siv e fram ew ork in w hich to s tu d y th e ev o lu tio n o f th e p ro to -s ta r and is o b s e rv â tionally c o n siste n t w ith th e d en sity profiles seen in clo u d cores, as least as m e a su re d by p resen t tech n iq u es (M yers 1983), it is by no m e a n s u n iv e rsa lly acc ep ted . G o o d m a n et al. (1990) n o te th e re is no u n eq u iv o cal e v id e n c e for an a lig n m e n t of
te rm s o f th e tw o g en eral processes o p e ra tin g in th e e v o lu tio n o f th e ISM so th e re is no a d d itio n a l in sig h t to be g ain e d from m alting th is d is tin c tio n .
cloud fe a tu re s w ith th e a m b ie n t m a g n etic field. T h is a rg u m e n t w as e x te n d e d to cloud cores (M y e rs e t al. 1991) a n d b ipolar outflow s (H eiles e t al. 1993). w h e re it was show n t h a t n e ith e r th e ax is o f ro ta tio n no r th e d ire c tio n o f th e o u tflo w s was c o rre la te d w ith th e a m b ie n t m ag n etic field. F u rth e rm o re , th is m odel o f s ta r fo rm atio n lead s to th e fo rm a tio n o f single s ta rs (B o d e n h e im e r et al. 1993) a n d can n o t a c c o u n t for th e high freq u en cy ( ~ 50%) o f m u ltip le s y s te m s seen in v e ry young s ta r fo rm in g reg io ns.
.A.n a lte r n a tiv e m o d e l by .\d a m s & F atuzzo (1996) p ro p o ses th a t th e S h u et al. m o d el be g e n e ra liz e d to in c lu d e o th e r s u p p o rt m e c h a n ism s, e.g .. tu r b u le n c e and th e rm a l p re s s u re , in w hich case th e rate of b u ild up o n to th e p r o to - s ta r fro m th e s u rro u n d in g c o re m a te r ia l is re la te d to th e ra te of r o ta tio n o f th e core a n d th e effective so u n d s p e e d a , / / , i.e.. th e r a te a t w hich m a te ria l c a n b e tr a n s p o r te d to th e p ro to -s ta r from t h e s u rro u n d in g m o lecu lar core. In his e a rly w o rk, L arson (1981) proposed th a t th e p ro to -s te lla r co re was built up e n tire ly by a c c re tio n p ro cesses, in a m a n n e r s o m e w h a t re m in is c e n t o f th e O ort m od el for c lo u d e v o lu tio n , w ith th e te rm in a tio n o f in fall a g a in o c c u rrin g w hen th e ra d ia tiv e p re s s u re a n d s te lla r w in d s p rev en ted fu r th e r a c c re tio n . In th is m odel L arson a rg u e d th a t th e in itia l p ro to - ste lla r m ass s h o u ld b e a fu n c tio n of th e core d e n sity a n d te m p e r a tu r e {p > 1 0^ cm~^. T % 10 K ) w h ich for ty p ic a l cores sh o u ld y ield a p ro to -s te lla r m a ss ~ 1
Mr,. F in ally , in a r e - e x a m in a tio n o f th e p roblem . L arson (1991. 1992) su g g e ste d an a lte rn a tiv e s o lu tio n in w hich tu rb u le n c e was th e d o m in a n t force for o rg a n iz in g th e ISM a n d m o le c u la r co res re p re s e n te d th e sm allest o rg an iz ed u n it o f th is s tr u c tu r e .
N one o f th e s e m o d e ls a d d re s s th e problem of m u ltip le -s ta r fo rm a tio n d ire c tly . In th e o rig in al w ork o f H oyle ( 1953) no ro ta tio n was a ssu m ed in th e c lo u d fra g m e n ta tio n process b u t th is m o d e l w as e x te n d e d by Zinnecker (1984) to th e s m a lle s t fra g m e n t sizes, re s u ltin g in th e fo rm a tio n o f b in a ry s ta rs . In all th e m o d e ls of in d iv id u a l s ta r fo rm a tio n d is c u s s e d so far. it is assum ed th a t an y c o m p a n io n s ta r s w hich fo rm aro u n d th e m a in p r o to - s ta r form in th e disk p ro d u ced as a re s u lt o f th e co llap se o f a ro ta tin g core. D e ta ils o f th e m e c h a n ism for th e fo rm a tio n o f th e d isk , its size r e la tiv e to th e p r o to - s ta r , t h e a m o u n t o f th e sy ste m 's a n g u la r m o m e n tu m it c o n ta in s , a re still very p o o rly u n d e r s to o d ( B o d e n h e im e r et «d. 1993). F u r th e r m o re , w h e th e r a n y successful m o d e ls fo r th e fo rm a tio n of m u ltip le s ta r sy ste m s c a n b e e x te n d e d to ex p lain th e f o rm a tio n o f c lu ste rs o r w h eth er th e y form by so m e o th e r m e a n s, e.g . fra g m e n ta tio n o f th e co re b efo re collapse, rem ain s to be seen.
4
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i tF i g u r e I . l A s c h e m a tic d ia g ra m o f th e re la tio n s h ip b etw ee n th e ISM a n d s ta rs . T h e cycle o f clo ud s re p re s e n ts th e po ssible s ta te s o f th e m o lecu la r clo u d s, w h ile th e cy cle of s ta rs illu s tr a te s th e e v o lu tio n of sta rs for d iffe re n t m asses. T h e co n v ersio n o f th e ISM in to s ta rs is show n as a solid arrow , w h ile th e e n ric h m e n t o f th e ISM by th e s ta rs v ia s te lla r w in d s a n d su p ern o v ae r e m n a n ts a re show n as b ro k e n arro w s. T h e fu n d a m e n ta l e le m e n ts of th e p ro b le m o f s ta r fo rm a tio n , structural, temporal, a n d stochastic, axe h ig h lig h te d in th e in sert.
F ig u re I .l p ro vides a p ic to r ia l s u m m a ry o f th e c u rre n t s ta te o f s t a r fo rm atio n theo ry . In th is overview o f th e p ro b le m , th e re la tio n sh ip betw een th e ISM an d th e s ta rs - th e G a la c tic ecology - is re p re s e n te d by tw o cycles: th e cy cle o f clouds a n d th e cycle o f s ta rs . T h e cycle o f clo u d s is not really a closed cycle b e c a u se low m ass s ta rs , and to a lesser e x te n t h ig h m ass s ta rs , p e rm a n e n tly rem ove gas fro m th e ISM . H ow ever, th is tim e scale. ~ 10* — 10® y r, is long in co m p ariso n w ith th e le n g th o f a single s ta r fo rm in g e v e n t, e .g .. th e tim e to form an asso ciatio n . ~ 10' y r (H ille n b ra n d e t al. 1993).
T h e re a re sev eral ob servatio ns w hich are useful in c o n s tra in in g a n y m o d e l for th e con version o f th e ISM into stars.
1. L arson (1981. 1982. 1991. 1992) n o te d th a t th e re was a r e la tio n s h ip b e tw e e n
th e m ost m a ssiv e s ta r form ed in a s ta r form ing region a n d th e m o s t m a ssiv e m o lecu la r clou d asso c ia te d w ith th e s ta r form ing region , b ased u p o n a lite r a tu r e search of th e d a t a th e n available. T h is re la tio n sh ip is d e sc rib e d by
M . 3C . M l . , . (1.4)
w ith n = 0.43. L arson argued th a t if th e sta rs w ere form in g in a n h ie ra rc h ic a l m a n n e r i.e.. th e m o st m assive s ta r fo rm ed from a given s u b s y s te m w as re la te d in a sim ila r fash io n to th e m ass in th e su b sy ste m , th e n th e d is tr ib u tio n o f s ta rs w ould follow a pow er-law d is trib u tio n given by.
d \
2C.VC". (1.5)
d l o g M .
w h ere i = 1/ n = 2.33. Larson allow s for b o th a c c re tio n , w hich w as th e p re m ise of his early w ork (L arson 1981). a n d tu rb u le n t fra g m e n ta tio n , w h ich is th e p rem ise of his m o re recent work (L arso n 1992). to be th e re s p o n s ib le a g e n ts .
2. O b se rv atio n s o f m a n y s ta r form ing sy stem s, in c lu d in g b o th h ig h -m a s s s ta r an d low -m ass s ta r fo rm in g regions, th ro u g h o u t th e G alax y show a n in itia l m ass fu n c tio n (IM F ) * w hich is relativ ely c o n s ta n t w ith j* = 1.7 ± 0.5 (S c a lo 1987). 3. S ta r fo rm a tio n is going on th ro u g h o u t th e G alax y in tw o m odes: “lo o sely a g g re
g a te d " s ta r fo rm a tio n occurs in s m a lle r an d sp a rse r clouds w ith p re d o m in a te ly low -m ass s ta r fo rm a tio n s c a tte re d th ro u g h o u t th e region, e.g .. T a u r u s (L arso n 1982. E vans 1991). w hereas “tig h tly packed" s ta r fo rm a tio n o c c u rs in d e n se r, iso la ted m o le c u la r clouds and re su lts in th e fo rm atio n of m o re m a ss iv e s ta r s from th e m o re m assiv e cores, e.g.. p O p h iu c h i (L ad a et al. 1993). H o w ev er, n e ith e r m o d e is c o m p le te ly a b se n t in a s ta r fo rm in g region w here th e o th e r m o d e is m o st e v id e n t, e.g .. O rio n (E v ans 1991).
^ T h e re is som e con fu sion in th e lite r a tu r e a b o u t th e c a lc u la tio n o f t h e IM F in te rm s of m ass b in s o r lo g a rith m m ass b in s. T h ro u g h o u t th is th e s is t h e IM F is defined in te rm s o f th e ch an g e in th e n u m b e r of s ta rs (a n d clou ds) p e r m a ss b in . in w hich Ccise oc
4. N ot all g ia n t m o le c u la r clo u d s (G M C . M > 10® M@) p ro d u ce s ta r s (B litz 1993), a n d so m e a re d o in g so a t a v ery low ra te . e .g .. t h e G M C d e te c te d by M a d d a le n a e t al. (1986).
5. S ta r fo rm a tio n is n o t coeval b u t r a th e r c o n te m p o ra n e o u s (S ta iile r 1985. P a lla &: S ta b le r 1990, 1991. G a rm a n y 1994). T h e re is also ev id en ce for th e fo rm a tio n o f low -m ass s ta r s a f te r la rg e m a ss s ta rs have a p p e a r e d (H ille n b ra n d e t al. 1993).
6. It is n ece ssary b u t n o t sufficient th a t th e r e b e h ig h -d e n sity co res p resen t to e n su re s t a r fo rm a tio n : s ta r fo rm a tio n is s tro n g ly fav ored in reg io n s possessing a s u b s ta n tia l to ta l m a ss ( L a d a e t al. 1993).
7. C ores a p p e a r to b e e lo n g a te d a n d d o m in a te d b y ro ta tio n a l m o tio n w hich does no t a p p e a r to b e w ell c o rre la te d w ith th e la rg e -sc a le s tr u c tu r e o f th e m o lecu la r cloud (M y ers e t al. 1991). As s ta te d in th e p re v io u s sectio n , th e r e is no ov er w h elm in g e v id e n c e for th e a lig n m e n t o f th e co res w ith th e a m b ie n t m a g n e tic field (H eiles e t al. 1993. G o o d m a n e t al. 1990). b u t th is po in t is s till c o n te n tio u s. R ecent w ork b y V allée & B a s tie n (1996) s u g g e sts such an a lig n m e n t m ay b e in effect b u t th e r e a re a la rg e n u m b e r of p o ssib le m a g n e tic field c o n fig u ra tio n s pro p o sed a n d th e u n c e r ta in ty in th e m e a s u re m e n ts is large. F u rth e rm o re , th e m a g n e tic field w hich th e y h av e m e asu re d m a y n o t b e th e o n e d e e p inside th e m o lecu la r clo u d .
8. T h e la rg e st co res a p p e a r to b e e m b e d d e d in th e c e n te r of t h e m o s t m assive
clouds w ith s m a lle r cores d is tr ib u te d a b o u t th e m (B litz 1993).
9. T h e s ta r fo rm in g efficiency for a m o lecu la r c o m p le x as a w hole is low . ty p ically on ly a few p e rc e n t, b u t is v ery hig h, g r e a te r t h a n 50%, for th e s ta r fo rm in g m o lecu la r cores (E v a n s 1991).
10. .A.t least h a lf o f th e s ta r s s tu d ie d w hich c a n b e a sso c ia te d w ith s ta r form ing regions a re m u ltip le s ta r s y ste m s : of th ese 87% a r e b in a ry s y s te m s (B o d e n h e im e r e t al. 1993).
T h e o b s e rv a tio n a l c o n s tr a in ts liste d abo ve su g g e st t h a t the s t a r f o r m i n g process
is regulated in three dif ferent ways; s tr uctur all y (as suggested by p o i n t s 1 through 3), temporall y ( poi nt s 4 o n d 5) a n d stochastically ( poi nt s 6 through 10). A sim
p le overview o f a ty p ic a l s ta r fo rm in g ev en t m a y b e as follows; m o le c u la r m a te ria l fo rm s, by w h a te v e r m e a n s, a n d a rra n g e s itse lf q u ic k ly in to a h ie ra rc h ic a l s tr u c tu re w ith s ta rs b ein g p ro d u c e d d ire c tly fro m th e co res o f th e s e s tr u c tu re s . M assive cores, fo rm e d a t th e c e n te r o f larg e m o le c u la r clouds te n d to form th e m o s t m assiv e s ta rs .
T h ese cores in te ra c t v ia tid a l o r h y d ro d y n a m ic m e c h a n ism s, a n d in a sm all n u m b e r o f e n c o u n te rs, o n e . so m e o r a ll cores involved b eco m e u n s ta b le a n d collapse. S ta r fo rm atio n is fa v o u red in reg io n s o f high den sity gas as th e to ta l n u m b e r o f in te ra c tions in creases a n d th e c ro ss-se c tio n for a s ta r fo rm in g in te ra c tio n increases (d u e to th e d ecreased re la tiv e v e lo c ity o f th e in te ra c tin g co res). C ores a p p e a r to b e fla tte n e d a n d are p ro b a b ly disk-lik e w h ic h m ay b e th e result o f ro ta tio n o r a m b ip o la r diffusion b u t th e ir c o lla p se , in g e n e ra l, a p p e a rs to be u n s ta b le , in w hich case m u ltip le s ta r sy stem s o r p o ssib ly s te lla r c lu s te rs a re form ed.
W h y C a m e lo p a r d a lis? W h a t c a n it te ll us a b o u t
t h e S ta r F orm in g P r o c e s s ?
C a m e lo p a rd a lis O B I ( C a m O B I) is a very e x te n s iv e OB a sso c ia tio n (134° < < 151°. —3° < < -1-7°) ^ lying a t a d is ta n c e of 975 pc (see C h a p te r 4.
H u m p h rey s 1978. D am e e t a l. 1987). S ta r fo rm a tio n in th e v ic in ity in th e recent p ast ( ~ I — 5 X 10' y r) c a n b e tra c e d o u t by th e O B asso ciatio n itse lf as well as
by large, e x te n s iv e a n d old H ii regions, e.g. S202 (S h arp less 1959) o r su p ern o v a re m n a n ts (q C a m is a very w ell s tu d ie d runaw ay s ta r in th e region believ ed to h av e o rig in ated in XGCT5Q2 b u t th e re m n a n t of th e co m p a n io n s ta r to a C am is no longer v isible. B laau w 1964). M o re rece n t s ta r fo rm a tio n in th e region ( ~ 10° — 10® y r) includes th e v ery e n e rg e tic outflow A FG L490 (C a m p b e ll e t al. 1986. M itch ell
et al. 1995). th e new ly d e te c te d outflow A FG L 490-iki (P u r to n et al. 1995). th e R-
.A.ssociation C a m R l (R a c in e 1968). as well as in frare d sources d e te c te d by th e I R A S s a te llite (B e ic h m a n e t al. 1988) w hich h ave th e in fra re d colors of ( u ltr a c o m p a c t)
UC H i i a n d H ii region s, m a se rs . outflow s, etc. (W alk er Sz C ohen 1988). H ence. C a m O B I a p p e a rs to b e an a c tiv e s t a r fo rm in g region p ro d u c in g in te rm e d ia te m ass s ta rs (3 to 25 M g . e a rly .•\- to l a te 0 - ty p e ) alb e it a t a m u c h less p ro d ig io u s r a te th a n som e of th e m o re e n e rg e tic in te r m e d ia te an d m a ssiv e s ta r form in g regions in th e G alaxy, e.g. O rio n a n d M o n o cero s (L arso n 1982).
C am O B I is w o rth y of s tu d y for sev eral reaisons. F irstly , very little is know n
^ In reg ard s to co n v en tio n s; all G a la c tic c o o rd in a te s refer to th e new G a la c tic co o rd in a tes a n d w ill b e referred to éis { L b ) th ro u g h o u t th is th e sis, th e rad ial v elo cities m e a su re d in th e L ocal S ta n d a rd o f R e st are b ased u p o n s ta n d a r d solar m o tio n , a n d all e q u a to r ia l c o o rd in a te s are re fe rre d to th e m e a n eq u in o x a n d e q u a to r of B 1950.0 unless o th e rw is e specified.
a b o u t th is reg io n o f th e G alaxy. E x am in in g th e P a lo m a r O b se rv a to ry S k y S urvey (P O S S ) p rin ts sh ow s th a t C am O B I. in p ro jec tio n , lies n e a r to th e v e ry e n e rg e tic VV'3/4/5 s ta r fo rm in g region an d m ost stu d ie s c a rrie d o u t along th is line-of-sight have c o n c e n tr a te d on th is d y n am ic region. S tu d y in g C a m 0 8 1 is a n e x c e lle n t op p o r tu n ity to in v e s tig a te a relatively poo rly know n reg io n of th e G a la x y w h ere th e p o ssib ility of n ew discov eries, e.g.. .\F G L 4 9 0 -ik i. is g re a t. Secondly. C a m O B I . by v irtu e o f b ein g a so m ew h at q u ie te r a n d g e n tle r s ta r fo rm in g region allow s th e s tu d y of th e fo rm a tio n o f an O B asso ciatio n in w hich th e fo rm a tio n of very m a ssiv e s ta rs a n d th e ir e v o lu tio n , v ia s te lla r w inds o r su p erno va re m n a n ts , h av e n o t d e stro y e d th e p rim a ry m e c h a n is m responsible for p ro d u cin g th e s ta rs . T h ird ly , as in stu d ie s of o th e r s ta r fo rm in g regions. C am O B I can be te s te d for co n siste n cy w ith th e o b serv ab le c o n s tra in ts o u tlin e d in th e previou s section. A n e x h a u s tiv e e x a m in a tio n of s ta r fo rm a tio n in th e C a m O B I region w ould req u ire o b serv atio n s a t m a n y different w av eleng th s w ith d ifferen t in stru m e n ts a n d is bey ond th e scope of th is th e s is . How ever. w h at th is th e s is a tte m p ts to do is prov id e a fram e w o rk for o u r u n d e r s ta n d in g of s ta r fo rm a tio n w ith in th e C am O B I region. T h is th e sis also s u g g e sts fu rth e r o b serv atio n s, w h ic h will su p p o rt or reject th e c laim e d m e th o d o f s t a r fo rm a tio n . F inally, it also c o m m e n ts on th e a p p lic a b ility of th e s ta r form ing m e c h a n is m (s ) seen in C am O B I to else w h e re in th e G alaxy.
O u tlin e o f th e T h e sis
S ince th e p r im a r y d a ta for th is th e sis consist of a C O survey of t h e C a m O B I region, th e first th r e e c h a p te rs will focus on th is m a te ria l. C h a p te r s 4 th ro u g h 7 id e n tify th e s ite s o f s ta r fo rm atio n in th e region a n d con sid er th e s t a r form ing process in te rm s o f th e th re e elem ents prop osed to c h a ra c te riz e it. i.e.. t h e s tr u c tu r a l re la tio n sh ip b e tw e e n th e p a re n t m o lecu lar clouds an d new ly form ed s ta r s , te m p o ra l ev o lu tio n of th e clo u d s, an d th e p ro b a b ility of th e o n set of s ta r fo rm a tio n . C h a p te r S co m p ares th e s tr u c t u r e of th e clouds in C am O B I w ith th e m o re d is ta n t P erseu s region. T h e fin al c h a p te r provides a su m m a ry o f th e c u rre n t k n o w led g e o f s ta r fo rm a tio n in C a m O B I a n d m akes som e suggestions for fu rth e r o b s e rv a tio n s . T h e o u tlin e o f th e th e s is , in d e ta il, is as follows:
