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Th e Zeema n effec t i n stella r spectr a
Revie w
I.I . Romanyu k
Specia l Astrophysica l Observator y o f th e Russia n AS , Nizhni j Arkhy z 357147 , Russi a

Abstract . A shor t biograph y o f Piete r Zeema n i s presented . Th e mai n formula e for th e normal , anomalous , quadrati c Zeema n effec t an d Paschen-Bac k effec t ar e given . Instrumentatio n fo r Zeema n effect measurement s i n stella r spectr a i s de scribed , th e mos t importan t scientifi c achievement s i n magneti c sta r investigation s wit h th e world' s larges t telescope s fo r 5 0 year s ar e demonstrated . Th e device s fo r magneti c measurement s mad e a t SA O an d th e mai n result s o f stella r magneti c observation s obtaine d wit h th e 6 m telescop e ar e describe d i n detail .

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Introductio n

Since th e discover y o f th e Zeema n effect b y Piete r Zeema n i n 1896 , i t ha s prove n t o b e a n extremel y powerful too l for th e stud y o f atoms , radiatio n an d thei r interaction . Th e Zeema n effect ha s pro vided th e mos t importan t techniqu e for derivin g ne w informatio n abou t th e physic s o f stars . A few decade s ag o th e famou s astrophysicis t H.W . Babcoc k (wh o ha d discovere d stella r magneti c field s i n 1946) wrote : "Becaus e o f fundamenta l natur e o f th e Zeema n effect an d becaus e i t permit s no t onl y quantitativ e measuremen t o f fiel d strengt h bu t als o determinatio n o f th e directio n o f th e fiel d an d its obliquit y t o th e lin e o f sight , i t offers a n analytica l too l o f tremendou s importance " (Babcock , 1967). Thank s t o a remarkabl e contingency , i n 1996 w e celebrat e th e occasio n o f th e 100t h anniversar y o f th e Zeema n effect discovery , th e 50t h anniversar y o f firs t Babcock' s measurement s and , finally , 2 0 year s ag o w e starte d magneti c observation s wit h th e 6 m telescop e o f ou r observatory . W e hav e assemble d her e t o recal l histor y an d discus s importan t problem s o f Zeema n effect measurement s i n stella r spectr a an d t o celebrat e th e occasio n o f all thes e jubilees .

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Piete r Zeema n an d hi s discover y

(Following th e addres s o f professo r A.D . Fokke r a t th e Zeema n Centennia l Conference , Septembe r 6, 1965) Piete r Zeema n wa s bor n o n th e 25t h o f May , 1865 i n a villag e name d Zonnemair e fiv e mile s fro m th e provincia l tow n o f Zierikzee , Holland . His fathe r wa s a clergyman . H e taugh t hi m French , s o tha t h e coul d b e admitte d t o th e secondar y schoo l i n th e town . A t th e ag e o f eighteen , Zeema n happene d t o see a magnificen t auror a borealis . H e describe d i t an d mad e a drawin g whic h h e sen t t o th e edito r o f th e Britis h weekl y "Nature" . Th e edito r wa s well please d t o tak e i t an d sen d a lette r t o Zeema n addressin g i t t o "Professo r Zeema n i n th e observator y of Zonnemaire" . 11


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Afte r finishing th e secondar y schoo l h e ha d stil l t o pas s a supplementar y examinatio n i n Gree k an d Lati n for admissio n t o th e Universit y i n th e cit y o f Delft . I n tha t period , b y a fortunat e chance , Zeema n me t Kamerling h Onnes , a youn g professo r o f experimenta l physic s i n Leiden . H e wa s ver y muc h struc k b y th e ope n inteligenc e o f youn g Zeeman , wh o ha d alread y rea d Maxwell' s Heat , an d bee n s o eage r t o becom e a n experimenter . To-da y everybod y i s familia r wit h th e ide a tha t th e constituent s o f atom s o f matte r ar e nucle i an d electrons . A t th e tim e o f th e discover y o f th e Zeema n effect nothin g wa s know n abou t electrons . I t shoul d b e kep t i n min d tha t i n atom s the y hav e bee n detecte d for th e first tim e b y mean s o f th e Zeema n effect. Th e effect o f spectra l lin e splittin g i n th e externa l magneti c field wa s discovere d b y Zeema n i n th e Laborator y o f Kamerling h Onne s i n Leide n i n th e summe r o f 1896 . Th e thin g h e sa w wa s a broadenin g o f th e yellow spectra l line s radiate d b y sodiu m atoms . A t onc e professo r Lorent z interprete d th e effect a s a modificatio n o f th e motion s o f radiatin g particle s unde r th e influenc e o f magneti c force . Withi n a half-yea r afte r hi s discover y Zeema n wa s appointe d a lecture r i n th e Universit y o f Amsterdam . I n January , 1897 h e starte d t o wor k there . Unfortunatel y th e room s rendere d a t hi s disposa l i n th e laborator y wer e o n to p o f th e building . Th e floors wer e ordinar y timber , no t a t al l a n adequat e suppor t for th e ver y sensitiv e apparatu s an d mountin g require d for makin g reliabl e observation s an d measurements.. . Zeema n wa s greatl y please d when , i n 1908 , a t th e Moun t Wilso n Observator y Hal e use d wit h grea t succes s th e Zeema n effect t o investigat e magneti c fields i n th e Su n spots . Zeema n an d Lorent z wer e awarde d Nobe l priz e o f 1901 . Piete r Zeema n died o n th e 9t h o f October , 1943 .

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3. 1

Genera l informatio n o n th e Zeema n effec t theor y
Basi c definition s

Stella r magneti c field stud y i s base d o n th e Zeema n effect, whic h consist s i n splittin g an d polarizatio n o f spectra l line s i n th e externa l magneti c fields. A single lin e i n a magneti c field i s splitte d int o 3 component s i n th e simples t case . On e o f thes e component s ( component ) i s i n th e unshifte d positio n an d th e othe r tw o ( components ) ar e shifte d symmetricall y t o th e sam e distanc e o n bot h side s o f th e component . Th e shift i s proportiona l t o magneti c field strengt h H , all lin e component s ar e polarized . Polarizatio n propertie s depen d o n th e angl e betwee n th e magneti c field directio n an d th e lin e o f sight . Full explanatio n o f th e Zeema n effect wa s give n i n th e quantu m theor y o f atom . I n th e cas e o f wea k magneti c field (whe n L- S couplin g i s assumed ) tw o kind s o f Zeema n effect ar e present : norma l (simple ) effect wit h th e triple t splittin g o f a spectra l lin e an d anomalou s (complex ) effect, whe n a spectra l lin e i s spli t int o a larg e numbe r o f an d components , whil e th e Paschen Bac k effect an d th e quadrati c Zeema n effect ar e observe d i n ver y stron g magneti c fields (whe n L- S couplin g i s broken) . 3.1. 1 Norma l Zeema n effec t

Th e triple t splittin g i s realize d for single t line s only . Single t levels o f ato m (spi n S = 0 ) ar e spli t i n a magneti c field int o 2J+ 1 sublevels , wher e J i s th e full angula r momentum . Ever y single t lin e i s spli t int o 3 components : componen t wit h th e sam e frequenc y an d tw o wit h th e frequenc y component s wit h frequencie s : (1 )


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( H i s th e magneti c fiel d strength , Gauss) . All lin e component s ar e ellipticall y polarized . Tw o extrem e cases ar e o f specia l interest : observation s alon g an d acros s th e magneti c field direction . Whe n w e observe alon g th e magneti c fiel d directio n (longitudina l Zeema n effect) , th e centra l componen t i s absen t whil e th e tw o component s o f th e sam e intensit y ar e circularl y polarize d i n opposit e directions . I n th e observation s acros s th e fiel d directio n (transvers e Zeema n effect) , th e component s componen t i s polarize d i n th e directio n paralle l wit h tha t o f are linearl y polarized : howeve r th e the magneti c field , whil e th e component s -- i n th e directio n perpendicula r t o th e magneti c field . Th e lin e splittin g i n th e Zeema n effect i s ver y small : aroun d 0.0 1 i n a magneti c fiel d o f 1000 Gauss i n th e generall y observe d spectra l rang e nea r 500 0 . 3.1. 2 Anomalou s Zeema n effec t

Most stella r spectra l line s (mor e tha n 80% ) sho w th e anomalou s Zeema n effect (for example , see Romanyuk , 1984) . Here w e will no t conside r th e lin e splittin g i n th e anomalou s effect i n detail , w e recommen d papers o f Mathy s an d Stenfl o (1987a,b) . W e will restric t ourselve s t o som e genera l remarks . I n th e cas e o f smal l fiel d whe n th e Russel-Saunder s (L-S ) couplin g i s assume d (Beckers , 1969) , the spin S 0 an d eac h atomi c level i s spli t int o 2J+ 1 sublevel s wit h energie s E :
M

(2 ) where: E i s th e level energ y i n a zer o fiel d (erg) , H -- magneti c fiel d strengt h (Gauss) , q -- Land e facto r o f th e level , M -- J projectio n on th e directio n of H.
0

Land e facto r for eac h level i s determine d as : (3 ) wher e L , S an d J ar e A spectra l lin e i n th e splittin g pictur e i s fully i n th e quantu m theor y experimenta l investigatio 3.1. 3 th e orbital , spi n an d tota l momenta , respectively . anomalou s effect ca n b e spli t int o a few ten s o f an d components . Th e determine d b y electro n configuration s i n th e ato m an d i s fully explaine d i n th e vecto r mode l o f th e atom . Th e theor y o f Boh r i s verified b y th e n o f th e Zeema n effect whic h ca n b e foun d i n th e text-book s o f physics .

Paschen-Bac k effec t

I n ver y stron g (mor e tha n 1 0 kG ) fields , whe n th e magneti c splittin g become s stronge r tha n th e multiple t splitting , th e comple x Zeema n splittin g graduall y get s mor e simple . Thi s phenomenon , known a s th e Paschen-Bac k effect, i s th e resul t o f L- S couplin g broke n i n a ver y stron g field . I n thi s case , th e energ y o f level splittin g E is :
M

(4 )

where M an d M ar e th e orbita l an d spi n magneti c momenta , respectively . Th e Paschen-Bac k effect for variou s lines appear s i n th e field s o f different strengths , dependin g o n th e multiple t structure . Th e partia l Paschen-Bac k effect need s t o b e take n int o accoun t i n all the case s whe n field s ar e stronge r tha n 1 0 k G (Mathys , 1990a ; Mathy s an d Stenflo , 1987a,b) . W e will conside r th e influenc e o f th e partia l Paschen-Bac k effect a littl e later .
L S


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3 . 1 . 4

Q u a d r a t i c Z e e m a n e f f e c t
6 9

R e a l m e a s u r e m e n t o f t h e q u a d r a t i c Z e e m a n e ffe c t m a y b e e x p e c t e d i n s u p e r s t r o n g , 1 0 - 1 0 G , m a g n e t i c f i e l d s o f w h i t e d w a r f s a n d n e u t r o n s t a r s a s a s h i f t s c a l e . F o r h y d r o g e n l i n e s t h i s s h i f t i s a s f o l l o w s : ( 5 ) w h e r e : n i s t h e m a i n q u a n t u m n u m b e r , M -- m a g n e t i c q u a n t u m n u m b e r , H -- m a g n e t i c fie ld s t r e n g t h s . U n f o r t u n a t e l y , t h e s p e c t r a o f w h i t e d w a r f s a n d n e u t r o n s t a r s a r e v e r y d e f i c i e n t i n s p e c t r a l l i n e s , a n d m a g n e t i c m e a s u r e m e n t s p r e s e n t a p r o b l e m . T h e c i r c u l a r p o l a r i z a t i o n o f t h e r m a l r a d i a t i o n ( K e m p , 1 9 7 0 ) w a s u s e d f o r s t r o n g m a g n e t i c fie ld d e t e c t i o n i n w h i t e d w a r f s ( A n g e l a n d L a n d s t r e e t , 1 9 7 1 ) . T h e s t u d y o f q u a d r a t i c Z e e m a n e ffe c t i n s t e l l a r s p e c t r a h a s b e e n i n i t i a t e d b y P r e s t o n ( 1 9 7 0 a ) , H a m a d a ( 1 9 7 1 ) , T r i m b l e ( 1 9 7 1 ) . H y d r o g e n l i n e p r o f i l e s i n D A - t y p e w h i t e d w a r f s h a v e b e e n c a l c u l a t e d b y B o r r a ( 1 9 7 3 a ) . 3 . 2 C a l c u l a t i o n a n d d e t e r m i n a t i o n o f L a n d e f a c t o r s o f l i n e s s h o r t w a r d o f t h e w a v e l e n g t h

F o r m o s t s t a r s w e c a n n o t o b s e r v e t h e Z e e m a n s p l i t t i n g d i r e c t l y a n d t h a t i s w h y c o r r e c t c a l c u l a t i o n o f t h e L a n d e f a c t o r z i s i m p o r t a n t , z i s t h e w e i g h t e d m e a n p a r a m e t e r f o r g r o u p s o f ( i n t h e a n o m a l o u s e f f e c t ) , w h i c h c h a r a c t e r i z e s t h e m a g n e t i c s e n s i t i v i t y o f a l i n e . E x t e n s i v e c a l c u l a t i o n s o f t h e L a n d e f a c t o r s h a v e b e e n p e r f o r m e d , h o w e v e r B e c k e r s ' ( 1 9 6 9 ) T a b l e s h a v e b e e n t h e m o s t p o p u l a r . T h e L a n d e f a c t o r s f o r t h e u p p e r l e v e l q u a n d t h e l o w e r l e v e l q i i n t h e c a s e o f L - S c o u p l i n g f o r m u l t i p l e t s o f a s t r o p h y s i c a l i n t e r e s t h a v e b e e n c a l c u l a t e d : a n d c o m p o n e n t s

N o t e t h a t i n V A L D ( V i e n n a A t o m i c L i n e D a t a B a s e ) ( P i s k u n o v e t a l . , 1 9 9 5 ) t h e L a n d e f a c t o r s h a v e b e e n c a l c u l a t e d a c c o r d i n g t o B e c k e r s ( 1 9 6 9 ) . T h e L a n d e f a c t o r s f o r d i f f e r e n t t y p e s o f c o u p l i n g a r e d i s c u s s e d . F o r e x a m p l e , i n t h e p a p e r b y M a t h y s ( 1 9 9 0 a ) t h e L a n d e f a c t o r z i s c a l c u l a t e d f o r t h e c a s e o f J - l c o u p l i n g

w h e r e J , L a n d S a r e r e p l a c e d b y t h e J , L a n d S q u a n t u m n u m b e r s o f t h e p a r e n t l e v e l . i s t h e q u a n t u m n u m b e r o f c o r r e s p o n d i n g t o t h e c o u p l i n g o f t h e t o t a l a n g u l a r m o m e n t u m l o f t h e e l e c t r o n . T h e L a n d e f a c t o r v a l u e s c a n b e d e t e r m i n e d i n l a b o r a t o r y e x p e r i m e n t s , m o s t o f w h i c h c a n b e f o u n d i n e x t e n s i v e c o m p i l a t i o n s o f a t o m i c d a t a . T h e a c c u r a c y o f t h e s e e x p e r i m e n t a l v a l u e s i s g e n e r a l l y r a t h e r g o o d a n d q u i t e s u f f i c i e n t f o r a s t r o p h y s i c a l a p p l i c a t i o n s ( M a t h y s , 1 9 9 0 a ) . H o w e v e r , t h e L a n d e f a c t o r s o f m a n y l e v e l s o f a s t r o p h y s i c a l l y i n t e r e s t i n g i o n s h a v e n e v e r b e e n d e t e r m i n e d i n l a b o r a t o r y . I n t h e m a g n e t i c t a p e o f a t o m i c d a t a f o r l i n e s o f i r o n - p e r i o d e l e m e n t s K u r u c z ( 1 9 6 9 ) h a s i n c l u d e d t h e v a l u e s o f t h e L a n d e f a c t o r s . T h e s e v a l u e s a r e e x p e r i m e n t a l o n e s , w h e n e v e r a v a i l a b l e , o r h a v e b e e n d e r i v e d f r o m d e t a i l e d c o m p u t a t i o n o f t h e a t o m i c e i g e n v e c t o r s . M a t h y s { 1 9 9 0 a ) c o m p a r e d t h e L a n d e f a c t o r s c o m p u t e d b y K u r u c z a n d t h o s e c o m p u t e d b y s i m p l e f o r m u l a e a s i n ( 3 ) , ( 6 ) a n d ( 7 ) . I t i s h o w e v e r l i k e l y t h a t s o m e o f K u r u c z ' s v a l u e s a r e s t i l l r a t h e r


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inaccurate , an d i n particular , muc h less accurat e tha n mos t experimenta l values . Nevertheless , i n view o f incompletenes s o f th e laborator y data , Kurucz' s ne w magneti c tap e o f atomi c dat a for th e lines o f iron-perio d element s i s a majo r contributio n t o improve d studie s o f stella r magneti c fields , and it s us e i n thi s contex t ca n b e recommended . More tha n 95 % o f well measure d spectra l lines i n magneti c star s hav e th e Land e factor s z withi n a 0.5 -- 2.0 range . O f course , line s wit h z > 2 ar e preferabl e for magneti c measurements , bu t usuall y the y ar e weak. W e presen t line s wit h z > 3 (Romanyuk , 1984) , practicall y useles s for old photographi c measurements , bu t ca n b e usefull for moder n CC D measurement s (Tabl e 1) .

3. 3

Partia l Paschen-Bac k effec t quadrati c Zeema n effect i s th e fin e structur e splittin g for th e fiel d strengt h o f a 1 0 kG , th e energ y shift o f

The above-sai d refer s t o th e cas e o f wea k magneti c fiel d wher e th e negligible, an d th e magneti c splittin g o f th e levels i s smal l compare d t o o f th e ter m wher e the y belong . Thes e condition s ar e generall y fulfilled few ten s o f kG , bu t doe s no t alway s hol d true . I n a magneti c fiel d o f


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th e atomi c levels mus t b e studie d usin g th e theor y o f partia l Paschen-Bac k effect (Mathys , 1990a ; Mathy s an d Stenflo , 1987) . Th e shap e o f th e Stoke s lin e profiles forme d i n th e presenc e o f magneti c fiel d depend s no t onl y o n th e magneti c fiel d structur e an d effective Land e factor , bu t als o o n th e typ e o f anomalou s Zeema n splittin g pattern , whic h i s determine d b y th e atomi c structure . Mathys ' conclusio n ha s t o b e take n int o account : · whil e a line forme d i n th e pur e Zeema n effect ha s th e sam e centra l wavelengt h a s i n th e absenc e o f magneti c field , line s forme d i n th e partia l Paschen-Bac k regim e ar e globall y shifted ; · lines forme d i n th e partia l Paschen-Bac k effect ar e no t symmetri c abou t thei r centre , contrar y t o lines forme d i n th e pur e Zeema n effect; · i n th e partia l Paschen-Bac k effect th e tota l strengt h o f a lin e differs fro m it s strengt h i n th e absenc e o f magneti c field .

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4. 1 4.1. 1

Zeema n effec t observation s i n stella r spectr a
Instrumentatio n fo r magneti c measurement s Som e genera l remark s

Observation s sho w tha t th e grea t majorit y o f mai n sequenc e magneti c star s hav e field s less tha n 1 0 kG . Onl y 3- 4 star s ar e i n exception . A s a result , th e Zeema n splittin g i s n o large r tha n 0.2 A i n th e visua l spectra l range . An d tha t i s wh y direc t observation s o f splittin g i n stella r spectr a ar e practicall y impossibl e becaus e th e lin e width s ar e usuall y large r tha n 0. 1 A , mainl y du e t o rotatio n o f th e star . Ther e ar e onl y a few star s wit h th e splittin g measurabl e directl y (Mathys , 1990b) . Bu t th e Zeema n effect consist s no t onl y i n splittin g bu t als o i n polarizatio n o f spectra l lines . Usin g thes e propertie s astronomer s hav e develope d different method s o f magneti c fiel d measurements : magneti c shift measurements , narrow-ban d circula r an d linea r polarizatio n measurement s acros s th e spectra l lin e profiles , magneti c broadenin g measurement s an d others . Beginnin g i n 1946 magneti c observation s hav e bee n carrie d ou t o n th e larges t telescope s o f th e world . Base d o n th e observations , w e kno w tha t magnetis m i s a wide-sprea d phenomeno n i n stars : different kind s o f explosions , flare s an d othe r non-stationar y processe s ar e th e resul t o f magneti c fiel d action . Magneti c field s hav e bee n discovere d i n different type s o f star s bu t th e mos t reliabl e measurement s hav e bee n mad e for th e mai n sequenc e C P stars . I n connectio n wit h th e 20t h anniversar y o f magneti c measurement s wit h th e 6 m telescope , w e conside r i t worthwhil e t o give sufficient attentio n t o descriptio n o f stella r magneti c fiel d observa tion s i n Russi a an d especiall y wit h th e 6 m telescope . Not e tha t usuall y larg e coud e spectrograph s ar e use d for magneti c measurements . Sta r ligh t reache s a spectrograph , havin g bee n reflecte d from severa l incline d mirrors , whic h cause s stron g an d variabl e instrumenta l linea r an d circula r polariza tion , dependin g o n th e angl e o f inclinatio n o f th e mirrors . Th e altazimutha l mountin g o f th e 6 m telescop e (Ioannisiani , 1977 ) permit s larg e spectrograph s a t it s Nasmyt h foci t o b e installed . Sta r light i s reflecte d fro m a singl e incline d (a t a constan t angle=45° ) mirror , whic h permit s th e effect o f instrumenta l polarizatio n t o b e take n int o accoun t i n a simplie r manner . Thi s make s th e 6 m telescop e especiall y attractiv e for magneti c observations . Magneti c fiel d investigatio n i s on e o f th e mos t importan t problem s i n moder n astrophysics . Tha t i s wh y different kind s o f apparatu s for magneti c fiel d measurement s hav e bee n develope d an d mad e i n ou r observator y for th e 6 m telescop e (Bychko v e t al. , 1988) . No w w e will conside r different kind s o f magneti c observations .


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4.1. 2

Magneti c shif t measurement s th e attempt s t o find stella r wh o constructe d a specia l c field i n peculia r A stars . th e shift o f line s i n stella r

Since th e discover y o f magneti c fields o f sola r spot s b y Hal e (1908 ) all magnetic fields hav e ende d i n failure . Th e proble m wa s first resolve d successfully b y Babcoc k i n 1946 , differential analyze r o f circula r polarizatio n an d foun d a dipol e magneti Double-polarize d spectra , obtaine d b y Babcock , permitte d measurin g spectra, i n th e presenc e o f large-scal e magneti c field. Th e valu e o f th e shift i s defined b y th e formul a (Babcock , 1958 )

where: H i s th e longitudina l magneti c field strength , z -- th e Land e facto r of a line . A more detaile d explanatio n yo u ca n find i n (Babcock , 1958) . Not e tha t Babcoc k mad e observation s o f a few hundre d stars . U p t o no w magneti c observer s have used th e same , slightl y modernize d Babcock' s analyze r wit h th e larges t telescope s o f th e world : 5 m Paloma r an d 2. 5 m Mt.Wilso n (Babcock , 1947 , 1958) , 3 m Lick (Presto n an d Pyper , 1965) , 2.2 m Hawai i (Wolff an d Bonsack , 1972) , 2.7 m M c Donal d ( Vog t e t al. , 1980) , 3.6 m ES O (Mathy s and Stenflo, 1986) , 2 m Tautenbur g (Schol z an d Gerth , 1981) an d others . A specific achromati c circula r polarizatio n analyze r for th e 6 m telescop e wa s mad e b y Najde nov an d Chuntono v (1976) . Becaus e w e canno t observ e a clea r Zeema n splittin g i n stella r spectra , observation s o f magneti c displacement s o f oppositel y circularl y polarize d spectr a o r measurement s o f circula r polarizatio n insid e spectra l lines ar e use d (bot h for longitudina l field determination) . Transversa l field observation s nee d linea r polarimetri c measurement s an d th e difference i n sharp ness o f lines i n tw o opposit e linea r polarization s t o b e found . Th e accurac y o f transversa l fiel d determinatio n i s ove r on e tent h a s hig h a s for longitudina l field. I t shoul d b e born e i n min d tha t relativel y low accurac y photographi c measurement s ha d bee n used u p t o th e lat e 80s . Moder n observation s wit h precisio n CC D equipmen t hav e a shor t history . The accurac y o f shift measurement s depend s strongl y o n th e lin e width . I n particular , i t i s impossibl e t o measur e magneti c field o n photographi c plate s i f th e lin e widt h i s large r tha n 1 . Th e us e o f CCD move d thi s limi t t o 2- 3 . Fo r suc h lines a n accurac y o f 500 G i s possibl e t o achieve . Th e magneti c measurement s o f th e first 1 0 year s wer e collecte d i n th e well-know n Babcoc k catalogu e (1958) , containin g 8 9 magneti c stars . Durin g th e 5 0 year s o f measurement s astronomer s have obtaine d abou t 2000 0 Zeema n spectra . Abou t 1000 star s hav e bee n measure d an d 150 o f the m have bee n foun d t o hav e magneti c fields. Th e accurac y o f measurement s i s generall y 100 - 200 G , dependin g o n th e typ e o f stars . Mos t o f th e measurement s hav e bee n mad e i n US A b y G . Preston , S . Wolff, W . Bonsack , K . Stepien , D . Pyper . A grea t activit y i s demonstrate d b y G . Mathy s (ESO ) an d J . Landstree t (Canada) . Measurement s wit h th e 6 m telescop e wer e starte d 2 0 year s ago , i n 1976 (Glagolevski j e t al. , 1977). Mor e tha n 200 0 Zeema n spectr a hav e bee n obtained . Th e greates t activit y i n magneti c obser vation s wit h th e 6 m telescop e i s exercise d b y th e astrophysicist s i n SA O (Yu.V . Glagolevskij , V.D . Bychkov , V.G . Elkin , I.I . Romanyuk , an d occasionall y I.M . Kopylov , V.G . Klochkova , S.N. Fabrik a an d others) ; institute s i n Russi a (Mosco w group : V.L . Khokhlova , T.A . Ryabchikova , N.E . Piskunov ; St.Petersbur g group : Yu.N . Gnedin , T.N . Natsvlishvili) ; Ukrain e (Crimea n observatory : A.B . Severny, V.M . Kuvshinov , S.I. Plachinda , N.S . Polosukhina , V.P . Malanushenko) ; German y (E . Gerth , G . Scholz , S . Hubrig , E . Zelwanova , W . Schoneic h an d others) , Czec h an d Slovak Republic s (Z . Miku lashek , J . Ziznovsky , Yu . Zverko , J . Budaj) ; Bulgari a (I . Iliev) , Switzerlan d (P . North) ; Canad a (W . Wehlau , J . Matthews , G . Wade) .


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Th e first attemp t o f linearl y polarize d spectru m observation s hav e bee n mad e b y Kodair a an d Unn o (1969 ) an d the y showe d n o evidenc e o f transvers e field i n th e know n brigh t sta r H D 112413 . SA O an d Mosco w group s mad e attempt s t o tak e linea r Zeema n spectr a for th e sam e sta r wit h measurabl e Q an d U Stoke s parameter s (Glagolevski j e t al. , 1984) . 4.1. 3 Circula r polarizatio n measurement s

Circula r polarimetr y insid e spectra l line s wa s propose d independentl y b y A.B . Severn y (1970 ) an d J . Landstree t (1970) . Ne w devices , photoelectri c magnetometer s wit h electrooptica l modulators , wer e create d for thi s purpose . Device s o f thi s kin d measur e circula r polarizatio n wit h a ver y hig h accurac y (bette r tha n 0.01%) . I t i s possibl e t o discove r an d measur e ver y wea k (ten s o f Gauss ) magneti c fields i n different typ e brigh t star s provide d tha t th e distributio n o f th e V Stoke s paramete r acros s th e lin e profile i s know n wit h tha t accuracy . Crimea n astrophysicist s starte d thei r observation s wit h a modernize d sola r magnetomete r mounte d a t th e coud e focu s o f th e 2.6 m telescop e (Kuvshino v e t al. , 1974) , late r o n a t th e Cassegrai n focus (Bukac h e t al. , 1977) . Kuvshino v (1974 ) ha s don e muc h wor k for instrumenta l polarizatio n investigation's . I t ha s bee n show n i n practic e tha t hig h resolutio n V Stoke s paramete r measurement s wit h a one-channe l photoelectri c magnetomete r ca n b e mad e for th e brightes t star s onl y an d requir e to o muc h observin g time . Th e resul t i s th e smal l numbe r o f measurement s obtaine d a t CrAO . J.D . Landstree t an d hi s colleague s mad e a few different magnetometers : hig h resolutio n mag netomete r (Borr a an d Landstreet , 1973) , Balmer-lin e magnetomete r (Borr a an d Landstreet , 1980) an d others . Ther e i s n o nee d t o us e hig h spectra l resolutio n i n th e Balmer-lin e magnetomete r an d the n narrow-ban d ( 5 ) filter s ar e use d for selectio n o f a require d spectra l range . Th e Balmer lin e magnetomete r o f Landstree t i s know n t o magneti c peopl e a s a ver y goo d an d long-live d device . Mos t photoelectri c magneti c measurement s wer e mad e b y Landstree t an d hi s collaborators . Th e tota l numbe r o f suc h measurement s canno t b e overestimated , i t amount s t o a few thousan d (Land stree t e t al. , 1975 ; Borr a an d Landstreet , 1977 ; Borr a an d Landstreet , 1980 ; Landstreet , 1982 an d others) . Observation s wit h thi s magnetomete r wer e carrie d ou t a t variou s telescopes : fro m th e 5 m Paloma r gian t telescop e t o th e 1.2 m telescop e o f th e Universit y o f Wester n Ontario . Th e magneti c field H fro m th e measure d V Stoke s paramete r i s determine d b y th e formul a belo w (Borr a an d Landstreet , 1977) . V an d V polarization s ar e measure d i n th e righ t an d th e left win g o f th e line . Averag e polarizatio n = (V V )/2. depend s o n th e fiel d strengt h H i n th e following manner :
R L R L

wher e I i s th e observe d profile , z -- th e Land e factor , approximatel y equa l t o 1.0 for hydroge n lines . For mos t A star s i n th e cas e o f observatio n

Th e shap e o f hydroge n lin e profiles i s mor e o r less constan t for variou s stars , thu s for th e magneti c fields measure d fro m hydroge n lines th e following correlatio n i s true : 1 % o f correspond s t o a 10-2 0 k G magneti c field. Th e shap e o f narro w metalli c line s i s essentiall y highe r an d i n thi s case : 1 % o f equal s t o a 500 G magneti c field. ar e ver y difficult t o achiev e a s a Hig h accurac y (bette r tha n 0.01% ) measurement s o f resul t o f variabl e instrumenta l polarization . Brigh t star s wit h wea k fields ar e mor e preferabl e for


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high resolutio n measurement s o f metalli c lines , whil e extende d measurement s o f 6- 8 magnitud e star s (especially fas t rotating ) wit h th e Balmer-lin e magnetomete r ar e mor e effective. Bot h type s o f magnetometer s for th e 6 m telescop e wer e made . 1 . Th e high-resolutio n ( 0.0 8 ) magnetomete r wit h a Fabry-Pero t interferomete r permit s ob servation s withou t loosin g ligh t o n th e slit o f th e spectrograp h (whic h i s typical ) (Glagolevski j e t al. , 1979 ; 1988) . Th e us e of th e Fabry-Pero t interferomete r increase s th e efficiency of th e magnetometer , bu t eve n s o i t ca n b e effectively use d onl y for magneti c measurement s o f brigh t stars . 2 . Th e hydrogen-lin e magnetomete r o f th e 6 m telescop e i s base d o n th e spectrograph . Fo r spectra l ban d selectio n specia l movabl e mask-slit s ar e use d (in contras t t o th e narro w ban d filters in Landstreet' s magnetometer ) (Shtol' , 1984 ; Shtol ' e t al. , 1985) . Mask s of variou s sizes wer e mad e an d spectra l ban d fro m 3 t o 30 0 i s possibl e t o select . Thi s make s i t possibl e t o measur e th e circula r polarization , bot h insid e th e spectra l line s an d i n th e continuu m i n a wid e spectra l range , 400 0 -- 600 0 . A few hundre d measurement s of magneti c field an d broad-ban d circula r polarizatio n wer e mad e wit h thi s magnetometer-spectropolarimeter . A detaile d descriptio n of bot h magnetometer s ca n b e foun d in th e pape r of Bychko v e t al .
(1988) .

4.1. 4

Linea r polarimetri c measurement s

The linea r polarizatio n of spectra l line s in th e Zeema n effect is ver y small , 0.1 % - 0.01% . Th e theor y i s well develope d (for example , th e boo k o f Dolgino v e t al. , 1979 , an d th e ne w editio n o f Dolgino v e t al. , 1995 , an d reference s therein) . J-L . Lero y (1962 ) develope d a theor y of broad-ban d linea r polarizatio n measurements . Th e results o f 5 5 magneti c sta r measurement s wer e publishe d i n th e serie s o f paper s (Landolf i e t al. , 1993 ; Lero y e t al. , 1993 ; 1995 ; Bagnul o e t al. , 1995 ; Leroy , 1995) , an d in th e presen t issue . Lero y (1993 ) publishe d a catalogu e of linea r polarizatio n measurement s of 100 0 neares t stars . Th e transvers e Zeema n effect in th e C P sta r 5 3 Ca m wa s investigate d b y Borr a (1973 ) an d Kem p and Wolstencrof t (1974) . Borr a an d Vaugha n (1976 ) carrie d ou t a hig h resolutio n linea r polarimetr y of Cr B acros s th e Fe I 452 0 line . The y foun d th e Stoke s U an d Q parameter s t o rotat e wit h th e rotationa l perio d o f th e sta r an d thu s confirme d th e obliqu e rotato r mode l for th e magneti c field o f CrB . Th e smal l numbe r o f hig h resolutio n linea r polarimetri c measurement s i s explaine d a s follows: th e signa l o f Q an d U Stoke s parameter s i n th e transvers e Zeema n effect i s ove r 1 0 time s smalle r tha n th e V Stoke s paramete r signa l i n th e sam e intensit y longitudina l effect (i n a field o f a few thousan d Gauss) .

4.1. 5

Fou r Stoke s parameter s

Full informatio n o n th e Zeema n effect ca n b e derive d from measurin g th e 4 Stoke s parameter s wit h a hig h spectra l resolution . Bu t thi s i s a ver y involve d observin g proble m becaus e to o muc h ligh t from a sta r i s neede d an d i t ca n b e resolve d well onl y for th e Sun . W e measure d th e 4 Stoke s parameter s in a broa d ban d centere d o n th e 520 0 depressio n know n in man y C P stars , usin g th e Balmer-lin e magnetomete r (Shtol ' e t al. , 1988) . N o rea l polarizatio n was measure d wit h th e 6 m telescop e for som e stars . Th e mai n problem s i n ou r measurement s ar e 1 ) to o muc h observin g tim e i s neede d t o measur e eac h Stoke s paramete r separately ; 2 ) calibratio n an d standardizatio n o f measurements .


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4.1. 6

Magneti c broadenin g measurement s

Magneti c fields exis t no t onl y i n C P stars . Field s ca n b e o f comple x structure , o f ver y larg e o r ver y smal l intensit y an d canno t b e foun d b y Zeema n effect measurements . Variou s method s o f magneti c field investigatio n ar e give n i n th e revie w o f Gnedi n an d Natsvlishvil i (1996 , thi s issue) . W e presen t i n thi s sectio n a variet y o f method s o f magneti c field measurements , base d o n inves tigation s o f spectra l lin e magneti c broadenin g (i.e . Zeema n effect investigations) . I t i s no t possibl e t o observ e a clea r pictur e o f Zeema n splittin g i n th e cas e o f comple x stella r magneti c field structur e eve n i n ver y stron g fields. Fin e polarizatio n profile analysi s permit s u s t o investigat e th e magneti c field structur e o f different stars . O f course , i t i s possibl e t o measur e th e magneti c broadenin g o f a lin e i n a dipol e magneti c field (for example , Glagolevski j e t al. , 1988) , bu t th e sensitivit y o f thi s metho d i s low i n compariso n t o th e magneti c shift measuremen t method . Practic e show s tha t magneti c shift measurement s ar e essentiall y easie r an d mor e sensitiv e i n measurin g th e longitudina l componen t o f th e magneti c field. Bu t th e magneti c broadenin g i s possibl e t o b e measure d usin g ordinar y (no t Zeeman ) spectra . Th e numbe r o f non-Zeema n spectr a i s man y time s ove r th e numbe r o f Zeema n spectr a sinc e ther e i s n o nee d t o us e additiona l specialize d polarimetri c equipmen t i n observations , an d i t i s possibl e t o us e librar y spectr a for analysis . Modelin g o f measurement s need s full informatio n o f lin e profiles t o b e used . I t shoul d b e born e i n min d tha t for magneti c broadenin g measurement s ver y high-resolutio n (0. 1 A ) an d hig h S/ N rati o (>200 ) spectr a ar e required . Usin g suc h spectr a for shar p lin e star s i t i s possibl e t o detec t a 1 k G magneti c field o r large r eve n usin g ver y hig h S/ N spectra , tha t i s abou t on e orde r large r uncertaintie s tha n th e accurac y o f Zeema n spectr a measurements . Startin g fro m th e pape r o f Boyarchu k e t al . (1960 ) a series o f paper s describin g th e magneti c intensificatio n investigation s hav e bee n publishe d (for example , Ryabchikov a an d Piskunov , 1984; Ryabchikov a e t al. , 1988) . Mathy s (1994 ; 1995) develope d moment s method , whic h wa s successfully use d for analyse s of a lo t of magneti c stars . 4. 2 Som e result s o f magneti c measurement s

A numbe r o f excellen t review s o f magneti c star s hav e bee n publishe d i n las t few decade s (Babcock , 1958; Ledou x an d Renson , 1966; Preston , 1971a ; Landstreet , 1980; Khokhlova , 1983 , an d others) . Th e purpos e o f th e presen t revie w i s t o clea r u p som e importan t point s i n th e histor y o f stella r magneti c investigations . 15-2 0 astronomer s wh o demonstrat e th e highes t activit y i n magneti c field mesurement s ca n b e name d (reference s t o thei r paper s ar e presen t i n m y review) . Bu t th e mos t importan t contributio n t o Zeema n effect investigation s ha s bee n mad e b y H.Babcock , G . Presto n an d J.Landstreet . · H.Babcoc k designe d an d buil t th e first Zeema n analyzer , discovere d stella r magneti c fields. Fo r 1 0 year s h e wa s one , wh o observe d magneti c fields usin g th e 5 m an d 2.5 m telescopes . Th e result s o f thes e observation s wer e publishe d i n hi s well-know n lis t (Babcock , 1958) , 8 9 magneti c star s wer e discovere d i n thi s catalogue . Babcoc k continue d his observation s i n th e 60s an d discovered , i n particular , th e larges t magneti c field i n th e A O sta r H D 21544 1 (Babcock , 1960) . A s a result , afte r Babcock' s investigation s i t becam e clea r tha t stella r magneti c fields ar e present , tha t thes e ar e measurabl e an d tha t A p star s hav e stron g (few kG ) fields o f dipol e structure . · G.Presto n an d hi s colleague s hav e foun d tha t th e longitudina l componen t o f th e magneti c field o f A p star s (B ) varie s periodically . Th e correlation s betwee n periodica l magneti c field variation s an d periodica l variation s o f ligh t an d equivalen t width s o f spectra l lines convince d astronomer s o f validit y o f th e obliqu e rotato r mode l for A p stars . G.Presto n ha s detecte d 8
e


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star s wit h resolve d Zeema n component s and , a s a result , ha s foun d i n thos e star s (Preston , 1971) . Th e correlatio n betwee n th e surfac e fiel d variation s als o confirme d th e obliqu e rotato r mode l o f A p sta r 1970 a,b ; 197 1 a,b ; Presto n an d Pyper, , 1965 ; Presto n an d Stepien , 1969, an d others) .

th e surfac e magneti c fiel d an d longitudina l magneti c (Preston , 1967 ; 1969 a,b ; 1968 a,b,c ; Presto n e t al. ,

· H.Babcoc k an d G.Presto n cease d thei r activit y i n magneti c fiel d measurements . An d J . Land street , th e las t o f th e thre e "magneti c Mohikans" , continue s magneti c investigations . J . Land street an d hi s colleague s hav e designe d an d buil t a ver y effective Balmer-lin e photoelectri c magnetometer . The y measure d rapidl y rotatin g peculia r A star s an d som e o f the m wer e foun d t o b e magnetic . Practicall y all measurement s for a ne w class o f magneti c star s (He-ric h an d He-wea k peculia r stars ) wer e mad e b y Landstree t an d collaborators . Som e unusua l star s wit h a comple x magneti c fiel d structur e wer e discovere d amon g thos e star s (Landstreet , 1990; Borr a an d Landstreet , 1979 ; Thompso n an d Landstreet , 1985 ; Bohlende r an d Landstreet , 1990) . Landstree t an d hi s co-author s foun d magneti c whit e dwarf s (Ange l an d Landstreet , 1971) wit h a megagaus s fiel d an d mad e measurement s for a few doze n object s o f thi s kind . His contributio n t o th e proble m o f correlatio n o f magneti c fiel d an d abundanc e distributio n geometr y i s know n too . Magneti c fiel d an d abundanc e modelin g wa s don e firs t for 2 stars , 5 3 Ca m an d H D 215441 , an d showe d a n importan t rol e o f th e multipola r component s o f thei r magneti c field s (Landstreet , 1988 ; Landstree t e t al. , 1989) . Th e list o f th e mos t importan t supplemen tar y paper s o f J.Landstree t an d his collaborator s are : Ange l an d Landstreet , 1971 , 1972 , 1974; Kem p e t al , 1970 ; Borr a e t al. , 1973 , 1983 ; Borr a an d Landstree t 1973 , 1977 , 1978 , 1979 , 1980; Landstreet , 1978 ; Bohlende r e t al. , 1987 an d man y others . A larg e numbe r o f observation s hav e bee n mad e for A p stars . Bu t othe r star s hav e bee n studie d too . A goo d revie w pape r o n magneti c whit e dwar f investigation s wa s presente d b y Ange l (1978) . Long serie s measurement s o f circula r polarizatio n i n th e continuu m o f 100 whit e dwarf s an d Zeeman effect measurement s o f 1 2 whit e dwarf s wer e presente d b y Ange l e t al . (1981) . Cool star s wit h loca l magneti c field s o f comple x structur e ar e bein g investigate d a t th e presen t time. I t i s no t possibl e t o observ e a clea r Zeema n effect i n thi s cas e a s i n a dipol e field . Accurat e modeling is neede d for s u c h field determination . Variou s method s for suc h field investigatio n hav e been develope d (Donat i e t al. , 1989 ; Semel , 1989; Chugajnov , 1991 ; Gnedi n an d Natsvlishvili , 1996 , and others) . 4. 3 Mai n result s o f stella r magneti c investigation s i n Russi a

Stellar magneti c measuremen t i s on e o f th e mos t importan t observationa l program s o n th e 6 m telescope . Toda y i s th e 20t h anniversar y o f th e firs t measuremen t an d a shor t summar y o f th e principal result s o f magneti c investigation s i n th e forme r USS R (an d Russia) , an d o f observation s with th e 6 m telescope , i n particular , ha s t o b e given . A larg e contributio n t o th e theor y o f polarizatio n an d line formatio n i n a magneti c fiel d wa s mad e b y Leningra d (St.Petersbur g now ) astrophysicist s Yu.N . Gnedin , A.Z . Dolginov , N.A . Silant'e v (Dolginov e t al. , 1979 , 1995 ; Silant'ev , 1988; Gnedi n e t al. , 1972; Pavlo v e t al. , 1975 ; Gnedi n an d Silant'ev , 1976 , 1984 ; Gnedi n an d Pogodin , 1985) an d others . Th e theorist s o f St.Petersbur g schoo l propose d man y observatio n test s for checkin g th e theor y an d explaine d man y fin e polarizatio n effects inside spectra l line s an d i n th e continuum . For example , Gnedi n an d Red'kin a (1984 ) propose d a theor y o f magneti c fiel d o f Herbi g Ae/B e star s an d possibl e wa y o f it s estimatio n b y polarimetri c measurements . Astrophysicist s fro m th e Crime a (Ukrain e now ) wer e th e firs t t o measur e magneti c field s o f brigh t star s usin g a modernize d sola r magnetograp h (Kuvshino v e t al. , 1974; Bukac h e t al. , 1977) . Now CC D measurement s wit h th e 2.6 m telescop e ar e continued .


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Th e Mosco w grou p (V.L . Khokhlova , T.A . Ryabchikova , N.E . Piskuno v an d others ) hav e bee n th e leade r i n th e investigatio n o f non-unifor m distributio n o f element s o n th e stella r surfaces . The y hav e develope d a mappin g technique . A s a resul t o f thei r wor k i t i s show n tha t th e non-unifor m chemica l compositio n i s a n ordinar y phenomeno n i n th e atmosphere s o f peculia r stars . I t i s show n tha t th e mos t peculia r rar e element s ar e concentrate d i n smal l stron g spot s aroun d th e magneti c pole s o f a star . Thi s i s evidenc e o f th e corellatio n betwee n th e distributio n o f element s o n th e surfac e an d th e fiel d configuratio n (Khokhlova , 1983 ; Goncharski j e t al. , 1983 ; Piskuno v an d Khokhlova , 1983 , 1984; Piskuno v e t al , 1990 , 1994; Wehla u e t al. , 1991 ; Piskuno v an d Rice , 1993 , an d others) . Now abou t th e mai n observin g program s wit h th e 6 m telescope . Extensiv e observation s o f magneti c star s i n ope n cluster s o f different ag e wer e conducte d i n 1980-1987 . I t wa s show n tha t peculiaritie s an d magneti c field s appea r a t a ver y earl y stag e o f stella r evolution , befor e th e mai n sequenc e (Glagolevski j e t al. , 1987) . Magneti c field s wer e foun d i n ver y youn g star s (see , for example , Straizy s e t al. , 1991) . Man y ten s o f star s wit h predicte d Genev a field s (Crame r an d Maeder , 1980) wer e measure d for discover y o f ne w magneti c stars . W e hav e foun d mor e tha n 1 0 ne w magneti c stars , th e larges t magneti c fiel d ha s bee n detecte d i n H D 147010 , a membe r o f th e Sco-Ce n associatio n (Glagolevski j e t al. , 1981 , 1986) . Detaile d magneti c measurement s wit h rotationa l perio d hav e bee n mad e for a few C P stars . Th e mos t interestin g result s hav e bee n obtaine d for 3 o f them : 1 ) C Q UM a show s sinusoida l magneti c fiel d variations , whil e spectra l variation s ar e comple x (Mikulashe k e t al. , 1984 ; Glagolevski j e t al. , 1985) ; 2 ) th e informatio n o n th e magneti c fiel d presenc e i n 2 1 Pe r i s inconsistent . W e hav e foun d a ver y wea k (10 0 G ) fiel d an d thu s verified th e hypothesi s tha t all peculia r star s ar e magneti c star s (Glagolevski j e t al. , 1995 ; Elki n e t al. , 1987) ; 3 ) for H D 19267 8 w e hav e foun d a magneti c fiel d (Glagolevski j e t al. , 1981) an d performe d a cooperativ e comple x investigatio n an d propose d a magneti c mode l for thi s sta r (Wad e e t al. , 1996) . W e hav e searche d for magneti c field s i n Hg-M n star s an d showe d tha t 10-1 5 G field s ar e possibl e i n thei r atmosphere s (Glagolevski j e t al. , 1985) . Ther e ar e n o measurabl e magneti c field s i n som e Bo o star s (Iliev e t al. , 1988) an d i n F-S r 407 7 star s (Nort h e t al. , 1992) . W e hav e investigate d th e Zeema n effect i n supergiant s (Schol z e t al. , 1984) , A p star s wit h wea k peculiaritie s (Ziznovsk y an d Romanyuk , 1990) . W e hav e foun d direc t evidenc e o f a ver y stron g an d comple x magneti c fiel d o f th e He- r sta r H D 3777 6 (Kopylov a an d Romanyuk , 1992; Romanyu k e t al. , 1996 , an d thi s issue) . Takin g advantag e o f th e goo d viole t transparenc y o f th e telescop e an d th e spectrograp h optic s w e hav e take n a serie s o f Zeema n spectr a i n th e 3300-400 0 ban d for 3 C P star s (H D 112413 , H D 137909 an d H D 152107) . Thu s th e Balme r jum p i s locate d i n th e middl e o f th e plate . Spectr a wer e use d for searc h for radia l gradien t o f magneti c field . I t i s show n tha t for H D 11241 3 th e magneti c fiel d increase s wit h depth , for H D 137909 w e hav e foun d a phas e shift o f 0.1 5 P betwee n th e longitudina l magneti c fiel d curve s observe d o n bot h side s o f th e Balme r jum p (Romanyuk , 1984; 1986; 1991) . Ne w CC D detector s enabl e investigatio n o f polarizatio n an d magneti c fiel d propertie s o f Herbi g Ae/B e star s (Glagolevskij , 1990; 1996) . Principa l difficulties i n th e investigatio n o f thes e object s ar e th e smal l numbe r o f line s an d thei r comple x structure . A t last , magneti c observation s o f whit e dwarf s wit h th e 6 m telescop e hav e bee n conducte d for th e las t 1 0 year s (Bychko v e t al , 199 1 an d a series o f paper s i n th e presen t book) . Th e magneti c fiel d o f su b dwarf s ha s bee n studie d b y Elki n (1996) .

5

Conclusion s

Th e fat e o f Zeema n effect measurement s i n astrophysic s differs strongl y fro m tha t o f Dopple r effect measurements . Althoug h a 1 k G fiel d cause s approximatel y th e sam e magneti c shift (0.0 2 ) a s


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t h e D o p p l e r s h i f t o f m o v i n g o b j e c t s a t a s p e e d o f 1 k m / s ( i n t h e g e n e r a l l y u s e d s p e c t r a l r a n g e a r o u n d 5 0 0 0 ) , t h e n u m b e r o f r a d i a l v e l o c i t y m e a s u r e m e n t s a r e b y 3 - 4 o r d e r s l a r g e r t h a n m a g n e t i c m e a s u r e m e n t s . T h e m a i n r e a s o n s f o r t h i s s i t u a t i o n a r e t h e t e c h n i c a l d i f f i c u l t i e s o f Z e e m a n e ffe c t m e a s u r e m e n t s , i n s t r u m e n t a l e f f e c t s , w h i c h c a n h a v e i n f l u e n c e o n m e a s u r e m e n t r e s u l t s , d i f f i c u l t i e s i n g e t t i n g o b s e r v ing t i m e a t t h e l a r g e s t t e l e s c o p e s , a n d f i n a l l y , t h e r e i s n o p o l a r i m e t r i c e q u i p m e n t a t l a r g e t e l e s c o p e s . N e v e r t h e l e s s t h e i n t r o d u c t i o n o f n e w d e t e c t o r s , a b e t t e r a c c u r a c y o f o b s e r v a t i o n s a n d m o d e l i n g in s p ire s o n e w i t h o p t i m i s m f o r t h e f u t u r e a n d w e b e l i e v e t h a t m a g n e t i c i n v e s t i g a t i o n s o f s t a r s a r e a t t h e i n i t i a l s t a g e .
A c k n o w l e d g e m e n t s . I w o u l d l i k e t o a k n o w l e d g e fin a n c ia l s u p p o r t f r o m R F B R u n d e r t h e g r a n t 9 6 - 0 2 - 2 6 0 4 8 .

R e f e r e n c e s
A n g e l J . R . P . : 1 9 7 5 , I n : A n n . N . Y . S c i . , 2 5 7 , 8 0 A n g e l J . R . P . : 1 9 7 8 , " M a g n e t i c w h i t e d w a r f s " I n : A n n u . R e v . A s t r o n . A s t r o p h y s . , 1 6 , P a l o A l t o , C a l i f . , 4 8 7 . A n g e l J . R . P . , L a n d s t r e e t J . D . : 1 9 7 1 , A s t r o p h y s . J . , 1 6 4 , 1 . 1 5 . A n g e l J . R . P . , L a n d s t r e e t J . D . : 1 9 7 2 , A s t r o p h y s . J . , 1 7 8 , 2 1 . A n g e l J . R . P . , L a n d s t r e e t J . D . : 1 9 7 4 , A s t r o p h y s . J . , 1 9 1 , 4 5 7 . B a b c o c k H . W . : 1 9 4 7 , A s t r o p h y s . J . , 1 0 5 , 1 0 5 . B a b c o c k H . W . : 1 9 5 8 , A s t r o n . A s t r o p h y s . S u p p l . S e r . , 3 0 , 1 . B a b c o c k H . W . : 1 9 6 0 , A s t r o p h y s . J . , 1 3 2 , 5 2 1 . B a b c o c k H . W . : 1 9 6 7 , P h y s i c a , 3 3 , 1 0 2 . B a g n u l o S . , L a n d i D e g l ' I n n o c e n t i E . , L a n d o l f i M . : 1 9 9 5 , A s t r o n . A s t r o p h y s . , 2 9 5 , 4 5 9 . B e c k e r s J . M . : 1 9 6 9 , S a c r a m e n t o P e a k C o n t r . , 1 4 1 . B o r r a E . F . , V a u g h a n A . H . : 1 9 7 6 , A s t r o p h y s . J . , 2 1 0 , 1 . 1 4 5 . B o r r a E . F . , L a n d s t r e e t J . D . : 1 9 8 0 , A s t r o p h y s . J . S u p p l . S e r . , 4 2 , 4 2 1 . B o r r a E . F . : 1 9 7 3 a , A s t r o p h y s . J . , 1 8 3 , 5 8 7 . B o r r a E . F . : 1 9 7 3 b , A s t r o p h y s . J . , 1 8 6 , 1 . 9 5 9 . B o r r a E . F . , L a n d s t r e e t J . D . , V a u g h a n A . H . : 1 9 7 3 , A s t r o p h y s . J . , 1 8 5 , 1 . 1 4 5 . B o r r a E . F . , L a n d s t r e e t J . D . : 1 9 7 3 , A s t r o p h y s . J . , 1 8 5 , 1 . 1 3 9 . B o r r a E . F . , L a n d s t r e e t J . D . : 1 9 7 7 , A s t r o p h y s . J . , 2 1 2 , 1 4 1 . B o r r a E . F . , L a n d s t r e e t J . D . : 1 9 7 8 , A s t r o p h y s . J . , 2 2 2 , 2 2 6 . B o r r a E . F . , L a n d s t r e e t J . D . : 1 9 7 9 , A s t r o p h y s . J . , 2 2 8 , 8 0 9 . B o r r a E . F . , L a n d s t r e e t J . D . : 1 9 8 0 , A s t r o n . A s t r o p h y s . S u p p l . S e r . , 4 2 , 4 2 1 . B o y a r c h u k A . A . , E f i m o v Y u . S . , S t e p a n o v V . E . : I 9 6 0 , I z v e s t i y a C r A O , 2 4 , 5 2 . B u k a c h . . , G r a n i t s k i j L . V . , K o m i s s a r o v V . N , K u v s h i n o v V . M . : 1 9 7 7 , I z v e s t i y a C r A O , 5 7 , 2 0 9 . B y c h k o v V . D . , G a z h u r E . B . , G l a g o l e v s k i j Y u . V . , E l k i n V . G . , N a z a r e n k o A . F . , N a j d e n o v I . I . , R o m a n y u k C h u n t o n o v G . A . , S h t o l ' V . G . : 1 9 8 8 , I n : M a g n e t i c s t a r s , E d s . : G l a g o l e v s k i j Y u . V . , K o p y l o v I . M . , L e n i n g r a d , 1 2 . B y c h k o v V . D . , F a b r i k a S . N . , S h t o l ' V . G . : 1 9 9 1 , P i s ' m a A s t r o n . Z h . , 1 7 , 4 3 . C h u g a j n o v P . F . : 1 9 9 1 , A s t r o f i z i k a , 3 4 , 2 7 1 . C r a m e r N . , M a e d e r A . : 1 9 8 0 , A s t r o n . A s t r o p h y s . S u p p l . S e r . , 4 1 , 1 1 1 . D o l g i n o v A . Z . , G n e d i n Y u . N . , S i l a n t ' e v N . A . : 1 9 7 9 , I n : R a s p r o s t r a n e n i e i p o l y a r i z a c i y a i z l u c h e n i y a v k o s m i c h e s k o j s r e d e , E d . : A . Z . D o l g i n o v , M o s c o w , N a u k a ( i n R u s s i a n ) . D o l g i n o v A . Z . , G n e d i n Y u . N . , S i l a n ' e v N . A . : 1 9 9 5 , P r o p a g a t i o n a n d p o l a r i z a t i o n o f r a d i a t i o n i n c o s m i c m e d i a , G o r d o n a n d B r e a c h P u b l i s h e r s . D o n a t i J - F . , S e m e l F . , P r a d e r i e F . : 1 9 8 9 , A s t r o n . A s t r o p h y s . , 2 2 5 , 4 6 7 . E l k i n V . G . , G l a g o l e v s k i j Y u . V . , R o m a n y u k I . I . : 1 9 8 7 , A s t r o f i z . I s s l e d . ( I z v . S A O ) , 2 5 , 2 4 . E l k i n V . G . : 1 9 9 6 , A s t r o n . A s t r o p h y s . , 3 1 2 , 2 5 . F o k k e r A . D . : 1 9 6 7 , P h y s i c a , 3 3 , 1 . G l a g o l e v s k i j Y u . V . , K o z l o v a K . I . , K o p y l o v I . M . , K u m a j g o r o d s k a j a R . N . , L e b e d e v V . S . , N a j d e n o v I . D . , R o m a n y u k I . I . , C h u n a k o v a N . M . , C h u n t o n o v G . A . : 1 9 7 7 , P i s ' m a A s t r o n . Z h . , 3 , 5 0 0 . G l a g o l e v s k i j Y u . V . , C h u n t o n o v G . A . , N a j d e n o v I . D . , R o m a n y u k I . I . , R y a d c h e n k o V . P . , B o r i s e n k o A . N . , D r a b e k S . V . : 1 9 7 9 , S o o b s h c h . S p e t s . A s t r o f i z . O b s . , 2 5 , 5 .


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G l a g o l e v s k i j Y u . V . , E l k i n V . G . , R o m a n y u k I . I . , S h t o l ' V . G . : 1 9 8 8 , I n : M a g n e t i c s t a r s , E d s . : G l a g o l e v s k l i j Y u . V . , K o p y l o v I . M . , L e n i n g r a d , N a u k a , 2 2 . G l a g o l e v s k i j Y u . V . , E l k i n V . G . , R o m a n y u k 1 . 1 . , P i s k u n o v N . E . : 1 9 8 8 , I n : M a g n e t i c s t a r s , E d s . : G l a g o l e v s k l i j Y u . V . , K o p y l o v I . M . , L e n i n g r a d , N a u k a , 3 2 . G l a g o l e v s k i j Y u . V . , R o m a n y u k I . I . , B y c h k o v V . D . , L e b e d e v V . S . : 1 9 8 4 , A s t o f i z . I s s l e d . ( I z v . S A O ) , 1 8 , 5 7 . G l a g o l e v s k i j Y u . V . , R o m a n y u k I . I . , B y c h k o v V . D . , N a j d e n o v I . D . : 1 9 8 5 , P i s ' m a A s t r o n . Z h . , 1 1 , 1 0 7 . G l a g o l e v s k i j Y u . V . , R o m a n y u k I . I . , N a j d e n o v I . D . , S h t o l ' V . G . : 1 9 8 9 , A s t r o f i z . I s s l e d . ( I z v . S A O ) , 2 7 , 3 4 . G l a g o l e v s k i j Y u . V . , K l o c h k o v a V . G . , K o p y l o v I . M . : 1 9 8 7 , A s t r o n . Z h . , 6 4 , 3 6 0 . G l a g o l e v s k i j Y u . V . , K o p y l o v a F . G . , L y u b i m k o v L . S . : 1 9 9 0 , A s t r o f i z i k a , 3 3 , 3 6 3 . G l a g o l e v s k i j Y u . V , E l k i n V . G , R o m a n y u k I . I , S h t o l ; V . G . : 1 9 9 5 , P i s ' m a A s t r o n . Z h , 2 1 , 1 9 0 . G e r t h E . : 1 9 8 8 , I n : M a g n e t i c s t a r s , E d s . : G l a g o l e v s k l i j Y u . V , K o p y l o v I . M , L e n i n g r a d , N a u k a , 7 8 . G e r t h E , B y c h k o v V . D , G l a g o l e v s k i j Y u . V , R o m a n y u k 1 . 1 . : 1 9 9 2 , I n : S t e l l a r m a g n e t i s m , E d s . : G l a g o l e v s k l i j Y u . V , R o m a n y u k I . I . S t . P e t e r s b u r g , N a u k a , 6 0 . G n e d i n Y u . N , S i l a n t ' e v N . A . : 1 9 7 6 , A s t r o n . Z h , 5 3 , 3 3 8 . G n e d i n Y u . N , S i l a n t ' e v N . A . : 1 9 8 4 , A s t r o n . A s t r o p h y s . S u p p l . S e r , 1 0 2 , 3 7 5 . G n e d i n Y u . N , P o g o d i n M . A . : 1 9 8 5 , P i s ' m a A s t r o n . Z h , 1 1 , 3 7 . G n e d i n Y u . N , D o l g i n o v A . Z , P o t a s h n i k E . L , S i l a n t ' e v N . A . : 1 9 7 2 , A s t r o n . Z h , 4 9 , 9 9 0 . G o n c h a r s k i j A . V , R y a b c h i k o v a T . A , S t e p a n o v A . V , K h o k h l o v a V . L , Y a g o l a A . G . : 1 9 8 3 , A s t r o n . Z h , 6 0 , 8 3 . H a m a d a T . : 1 9 7 1 , P A S J a p a n , 2 3 , 2 7 1 . I l i e v I . K h , B a r s o v a I . S , G l a g o l e v s k i j Y u . V , B y c h k o v V . D , E l k i n V . G , R o m a n y u k I . I , S h t o l ' V . G . : 1 9 8 8 , I n : M a g n e t i c s t a r s , E d s . : G l a g o l e v s k l i j Y u . V , K o p y l o v I . M , L e n i n g r a d , N a u k a , 8 7 . I o a n n i s i a n i B . K . : 1 9 7 7 , S k y T e l e s c , 5 4 , 3 5 6 . K e m p J . C . : 1 9 7 0 , A s t r o p h y s . J , 1 6 2 , 1 6 9 . K e m p J . C , W o l s t e n c r o f t R . D . : 1 9 7 4 , M o n . N o t . R . A s t r o n . S o c , 1 6 6 , 1 . K e m p J . C , S w e d l u n d J . B , L a n d s t r e e t J . D , A n g e l J . R . P . : 1 9 7 0 , A s t r o p h y s . J , 1 6 1 , 1 . 7 7 . K h o k h l o v a V . L . : 1 9 8 3 , I n : I t o g i n a u k i i t e k h n i k i ( V I N I T I ) , 2 4 , 2 8 3 , ( i n r u s s i a n ) . K o d a i r a K , U n n o W . : 1 9 6 9 , A s t r o p h y s . J , 1 5 7 , 7 6 9 . K o p y l o v a F . G , R o m a n y u k I . I . : 1 9 9 2 , I n : S t e l l a r m a g n e t i s m , E d s . : G l a g o l e v s k l i j Y u . V , R o m a n y u k I . I , S t . P e t e r s b u r g , N a u k a , 5 4 . K u v s h i n o v V . M . : 1 9 7 4 , I z v . C r A O , 5 0 , 5 4 . K u v s h i n o v V . M , N i k u l i n N . S , S e v e r n y . . : 1 9 7 4 , I z v . C r A O , 5 0 , 3 . L a n d s t r e e t J . D , B o r r a E . F , A n g e l J . R . P , I l l i n g R . M . E . : 1 9 7 5 , A s t r o p h y s . J , 2 0 1 , 6 2 4 . L a n d s t r e e t J . D . : 1 9 7 8 , A s t r o p h y s . J , 2 2 4 , 1.5 L a n d s t r e e t J . D . : 1 9 8 2 , A s t r o p h y s . J , 2 5 8 , 6 3 9 . L a n d s t r e e t J . D . : 1 9 8 0 , A s t r o n . J , 8 5 , 6 1 1 . L a n d s t r e e t J . D . : 1 9 9 0 , A s t r o p h y s . J , 3 5 2 , 1 5 . L a n g K . R . : 1 9 7 4 , A s t r o p h y s i c a l f o r m u l a e , S p r i n g e r V e r l a g , N . Y , 2 4 3 . L a n d o l f i M , L a n d i D e g l ' I n n o c e n t i E , L e r o y J . L . : 1 9 9 3 , A s t r o n . A s t r o p h y s , 2 7 2 , 2 8 5 . L e d o u x P , R e n s o n P . : 1 9 6 6 , A n n u . R e v . A s t r o n . A s t r o p h y s , 4 , 2 9 3 . L e r o y J . L . : 1 9 6 2 , A n n . A s t r o p h y s , 2 5 , 1 2 7 . L e r o y J . L . : 1 9 9 3 , A s t r o n . A s t r o p h y s . S u p p l . S e r , 1 0 1 , 5 5 1 . L e r o y J . L , 1 9 9 5 , A s t r o n . A s t r o p h y s . S u p p l . S e r , 1 1 4 , 7 9 . L e r o y J . L , L a n d o l f i M , L a n d i D e g l ' I n n o c e n t i E . : 1 9 9 3 , A s t r o n . A s t r o p h y s , 2 7 0 , 3 3 5 . L e r o y J . L , L a n d o l f i M , L a n d i D e g l ' I n n o c e n t i M : 1 9 9 5 , A s t r o n . A s t r o p h y s . S u p p l . S e r , 3 0 1 , 7 9 7 . M a t h y s G . : 1 9 9 0 a , A s t r o n . A s t r o p h y s , 2 3 2 , 1 5 1 . M a t h y s G . : 1 9 9 0 b , B u l l . A m e r . A s t r o n . S o c , 2 2 , 1 2 0 1 . M a t h y s G . : 1 9 9 5 , A s t r o n . A s t r o p h y s , 2 9 3 , 7 3 3 . M a t h y s G . : 1 9 9 5 , A s t r o n . A s t r o p h y s , 2 9 3 , 7 4 6 . M a t h y s G , S t e n f l o J . O . : 1 9 8 6 A s t r o n . A s t r o p h y s , 1 6 8 , 1 8 4 . M a t h y s G , S t e n f l o J . O . ; 1 9 8 7 a , A s t r o n . A s t r o p h y s , 1 7 1 , 3 6 8 . M a t h y s G , S t e n f l o J . O . : 1 9 8 7 b , A s t r o n . A s t r o p h y s . S u p p l . S e r , 6 7 , 5 5 7 . N a i d e n o v I . D , C h u n t o n o v G . A . : 1 9 7 6 , S o o b s h c h . S p e t s . A s t r o f i z . O b s , 1 6 , 6 3 . " N o r t h P , B r o w n D . N , L a n d s t r e e t J . D . : 1 9 9 2 , A s t r o n . A s t r o p h y s , 2 5 8 , 3 8 9 . P a v l o v G . G , S h i b a n o v Y u . A , G n e d i n Y u . N . : 1 9 7 5 , A s t r o n . Z h , 5 2 , 9 5 6 . P i s k u n o v N . E , K h o k h l o v a V . L . : 1 9 8 3 , P i s ' m a A s t r o n . Z h , 9 , 6 6 5 .


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