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Surface abundanc e distributio n and radial velocit y pulsation s i n roA p star H D 24712
T.A . Ryabchikova
a b a,b

, V.V . Tsymbal , V.P . Malanushenko , I.S . Savanov

c

d

d

c

d

Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia Visiting scientist, Institute for Astronomy, Vienna University Tavrian National University, Simferopol, Crimea, Ukraine Crimean Astrophysical Observatory, Isaac Newton Institute of Chile, Crimean Branch, 334413 Nauchny, Crimea, Ukraine

Abstract . W e presen t th e abundanc e distributio n o f Mg , Fe , Co , Nd , P r o n th e surfac e o f th e roA p sta r H D 24712 . Co , N d an d P r ar e concentrate d i n on e bi g spo t nea r th e visibl e sout h magneti c pol e o f th e star , whil e M g i s deplete d i n th e sam e region . Intensit y variation s o f th e iro n line s ca n b e explaine d b y th e F e abundanc e distributio n aroun d th e magneti c equator . A searc h for radia l velocit y (RV ) variation s resulte d i n discover y o f rapi d R V variation s i n th e PrII I an d a perio d P=6.3 2 min . Thi s perio d doe s 6160.2 4 lin e wit h a n amplitud e o f 25 0 m s no t coincid e wit h th e know n period , P=6.1 5 min , o f th e photometri c pulsations . W e di d no t find rotationa l modulatio n o f th e R V amplitude , whic h shoul d b e expecte d i n a n obliqu e pulsato r mode l for roA p stars .
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1 . Introductio n
H D 2471 2 (HR1217 , D O Eri , V = 6.00 ) i s a well know n variable , rapidl y oscillatin g A p (roAp ) star . I t possesse s ligh t (Wolff & Morrison , 1973 ) spectru m an d magneti c (Preston , 1972 ) variation s wit h a rota tio n perio d P=12.4 6 days . Kurt z (1981 ) discovere d photometri c oscillation s wit h a perio d o f 6.1 5 min . Late r Kurt z (1982 ) foun d tha t th e maximu m o f th e pulsationa l amplitud e correspond s t o th e maximu m o f th e longitudina l magneti c fiel d (B ) whic h doe s no t chang e polarity . Matthew s e t al . (1988 ) foun d ra dia l velocit y (RV ) variation s wit h a n amplitud e o f 0.4 ± 0.0 5 k m s an d wit h th e mai n frequenc y o f th e photometri c pulsations . Moreover , accordin g t o th e author s th e amplitud e o f th e R V variation s cor relate s wit h th e amplitud e o f th e photometri c pulsa tion s showin g it s maxima l valu e a t th e phase s o f th e magneti c maximum .
l -1

an d magneti c variations . Recen t ver y accurat e B measurement s mad e b y Wad e e t al . (1999 ) see m t o favou r th e photometri c period , althoug h a specia l in vestigatio n i s nedee d t o clarif y th e perio d proble m for H D 24712 , whic h i s importan t for establishin g connectio n betwee n magneti c an d pulsationa l phenom en a an d surfac e abundanc e distribution . W e presen t th e fisrt result s o f abundanc e mappin g o f H D 24712 , an d preliminar y result s o f R V monitor ing .
l

2 . Observation s an d dat a reductio n
High-spee d spectroscop y o f H D 2471 2 wa s performe d i n Decembe r 1998 - Marc h 1999 . Spectr a wer e ob taine d wit h th e Photometrie s CC D camer a installe d i n th e coud e spectrograp h o f th e 2. 6 m Schaj n reflecto r o f th e Crimea n Astrophysica l Observatory . Th e exposur e tim e wa s 6 0 seconds . W e ha d t o us e a wide r sli t correspondin g t o a resolvin g powe r o f R=2000 0 t o obtai n a mea n signal-to-nois e rati o o f abou t 30 6 0 for a n individua l spectrum . Al l observation s wer e whic h con mad e i n th e spectra l regio n 6110-617 5 tain s FeI , BaII , PrII I an d NdII I lines . Th e obser vationa l lo g i s give n i n Tabl e 1 . Th e secon d an d th e thir d column s giv e th e numbe r o f spectr a pe r nigh t an d th e duratio n o f th e observation s i n minutes . Th e las t colum n give s th e rotationa l phas e correspondin g t o th e middl e o f eac h observationa l night . Th e sam e reductio n procedur e a s describe d i n Savano v e t al . (1999 ) for Eq u R V observation s wa s used .

Additiona l magneti c fiel d measurement s wer e publishe d b y Ryabchikov a e t al . (1997) . Th e author s als o investigate d spectra l variabilit y o f H D 24712 , an d provide d a n abundanc e analysi s o f th e sta r a t th e phase s o f th e maximu m an d minimu m o f th e longitudina l magneti c field . The y pointe d ou t tha t th e rotationa l perio d P=12.461 0 day s obtaine d b y Mathy s (1991 ) fro m magneti c measurement s remove s th e phas e shif t betwee n light , spectru m an d magneti c variations , whil e th e rotationa l perio d P=12.457 2 day s obtaine d fro m photometr y (Kurt z & Marang , 1987) give s a 0.0 8 phas e shif t betwee n photometri c

© Specia l Astrophysica l Observator y o f th e Russia n AS , 200 0


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T h e s p e c t r a l r e s o l u t i o n o f t h e C r i m e a n s p e c t r a i s n o t s u f f i c i e n t f o r a b u n d a n c e m a p p i n g o f H D 2 4 7 1 2 ( s e e S e c t . 3 ) , t h e r e f o r e w e u s e d f o r t h i s p u r p o s e t h e o b s e r v a t i o n s d e s c r i b e d i n R y a b c h i k o v a e t a l . ( 1 9 9 7 ) . T h e s e o b s e r v a t i o n s w e r e c a r r i e d o u t w i t h t h e c o u d e s p e c t r o g r a p h o f t h e C a n a d a - P r a n c e - H a w a i i t e l e s c o p e i n 1 9 8 4 o n e i g h t c o n s e c u t i v e n i g h t s , c o v e r i n g a b o u t 2 / 3 o f o n e r o t a t i o n . S p e c t r a w e r e o b t a i n e d i n t h e s p e c t r a l r e g i o n w i t h a 0 . 1 0 resolu4 4 6 0 - 4 5 2 5 t i o n . C r i m e a n o b s e r v a t i o n s w e r e u s e d m a i n l y t o c h e c k a b u n d a n c e m a p s d e r i v e d f r o m C F H T s p e c t r a .

F e , C o , N d w h o s e s p e c t r a l l i n e s v a r y o v e r t h e r o t a t i o n a l p e r i o d . I t w a s n o t p o s s i b l e t o i m p r o v e t h e r o t a t i o n a l p e r i o d u s i n g o u r p r e s e n t o b s e r v a t i o n s , t h e r e f o r e w e u s e d h e r e a n e p h e m e r i s g i v e n b y K u r t z & M a r a n g ( 1 9 8 7 ) : J D ( m a g n e t i c m a x i m u m ) 1 2 . 4 5 7 2 E . A s i t w a s p o i n t e d o u t i n I n t r o d u c t i o n t h e p h o t o m e t r i c p e r i o d a g r e e s b e t t e r w i t h t h e m o s t r e c e n t B l m e a s u r e m e n t s ( W a d e e t a l . , 1 9 9 9 ) . T h e u s e o f t h i s p e r i o d o r t h e p e r i o d f r o m M a t h y s ( 1 9 9 1 ) d o e s n o t c h a n g e s i g n i f i c a n t l y t h e m a i n c o n c l u s i o n s d r a w n i n t h i s p a p e r . A l l a t o m i c l i n e p a r a m e t e r s f o r o u r c a l c u l a t i o n s w e r e t a k e n f r o m V A L D - 2 ( K u p k a e t a l . , 1 9 9 9 ) . F o r t h e P r i l l l i n e t h e o s c i l l a t o r s t r e n g t h w a s t a k e n f r o m B o r d ( 1 9 9 9 ) .
d

=

2 4 4 0 5 7 7 . 2 3

d

+

3 . A b u n d a n c e m a p p i n g
R y a b c h i k o v a e t a l . ( 1 9 9 7 ) f o u n d t h e r o t a t i o n a l v e l o c -1 i t y fo r H D 2 4 7 1 2 t o b e v s i n i = 5 . 6 k m s . T h e s l o w r o t a t i o n m a k e s i t i m p o s s i b l e t o a p p l y u s u a l D o p p l e r i m a g i n g t e c h n i q u e f o r m a p p i n g , b e c a u s e w i t h o u r h i g h e s t s p e c t r a l r e s o l u t i o n w e h a v e 3 r e s o l u t i o n e l e m e n t s p e r s p e c t r a l l i n e ( 5 - 6 p i x e l s ) . T h e r e f o r e w e u s e d h e r e a s i m p l i f i e d m e t h o d d e v e l o p e d b y T s y m b a l . I n s t e a d o f g e t t i n g l o c a l a b u n d a n c e s o n t h e s u r f a c e o f t h e s t a r w e c o n s i d e r e d t h e a b u n d a n c e d i s t r i b u t i o n a s a s e t o f c i r c u l a r s p o t s w i t h a g i v e n a b u n d a n c e . T h e f o l l o w i n g p a r a m e t e r s d e f i n e t h e a b u n d a n c e d i s t r i b u t i o n w h i c h p r o v i d e t h e b e s t fit t o t h e o b s e r v e d l i n e p r o f i l e s : · c o o r d i n a t e s o f t h e c e n t e r o f a s p o t a n d i t s r a d i u s ; · e l e m e n t a b u n d a n c e i n s i d e t h e s p o t ; · e l e m e n t a b u n d a n c e i n t h e p h o t o s p h e r e ; · i n c l i n a t i o n o f t h e r o t a t i o n a l a x i s . T h e l a s t v a l u e , i = 1 3 7 ° , w a s t a k e n f r o m t h e m a g n e t i c g e o m e t r y s o l u t i o n b y B a g n u l o e t a l . ( 1 9 9 5 ) . W e u s e d t h e s a m e a t m o s p h e r i c p a r a m e t e r s f o r t h e w h o l e s t e l l a r s u r f a c e a s d e r i v e d b y R y a b c h i k o v a e t a l . ( 1 9 9 7 ) : T e f f = 7 2 5 0 K , l o g g = 4 . 3 , = 1 . 0 k m s
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3 . 1 . M a g n e s i u m , c o b a l t a n d - e a r t h e l e m e n t s
A l l t h e s e e l e m e n t s h a v e a s i m i l a r a b u n d a n c e d i s t r i b u t i o n w i t h i n o n e s p o t . A s a r e p r e s e n t a t i v e o f t h e g r o u p o f r a r e - e a r t h e l e m e n t s ( R E E ) w e c h o o s e n e o d y m i u m , w h i c h h a s u n b l e n d e d l i n e s i n b o t h s p e c t r a l r e g i o n s . I n t h e r e d s p e c t r a l r e g i o n w e a l s o s t u d i e d t h e l i n e s o f N d l l l 6 1 4 5 . 0 7 , a n d P r I I 6 1 6 5 . 8 9 , P r I I I 6 1 6 0 . 2 4 . T h e N d I I I l i n e i s b l e n d e d w i t h S i I t h e P r I I I l i n e i s b l e n d e d w i t h L u I I S m I I 6 1 4 5 . 0 2 , a n d 6 1 5 9 . 9 3 a n d

6 1 6 0 . 4 1 . A l t h o u g h w e t o o k t h e s e b l e n d s i n t o

a c c o u n t a s s u m i n g t h e s a m e d i s t r i b u t i o n f o r a l l R E E e l e m e n t s , t h e r e s u l t s o b t a i n e d f r o m t h e N d I I I a n d P r i I I l i n e s a r e l e s s c o n f i d e n t . T h i s i s t r u e , i n p a r t i c u l a r , f o r t h e P r d i s t r i b u t i o n b e c a u s e t h e P r I I 6 1 6 5 . 8 9 l i n e i s t o o w e a k t o p r o v i d e a g o o d m a p . C o o r d i n a t e s a n d r a d i i o f t h e s p o t s a n d a b u n d a n c e s i n t h e s p o t s a n d i n t h e p h o t o s p h e r e a r e g i v e n i n T a b l e 2 . F i g s . 1 - 3 s h o w a c o m p a r i s o n b e t w e e n t h e o b s e r v e d l i n e p r o f i l e s a n d c a l c u l a t e d w i t h t h e a d o p t e d a b u n d a n c e d i s t r i b u t i o n f o r M g , C o a n d N d . W e c a n a c h i e v e a b e t t e r fit f o r b o t h N d I I l i n e s , s t r o n g e r 4 4 6 2 . 9 8 a n d

. O u r

m a p p i n g p r o c e d u r e w a s a p p l i e d t o t h e e l e m e n t s M g ,


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weake r 4516.3 2 playin g wit h th e vertica l abundanc e stratification , bu t w e faile d t o fi t NdI I an d NdII I line s wit h an y uniqu e vertica l abundanc e distribution . Thi s mean s tha t simpl e stratificatio n canno t explai n th e abundanc e differenc e obtaine d fro m th e line s o f th e firs t an d th e secon d RE E ions . Th e las t lin e i n Tabl e 2 contain s o f th e visibl e sout h magneti c pol e i n figuratio n calculate d b y S . Bagnul o nication) . H e use d measurement s o f magneti c fiel d b y Presto n (1972) , an th e coordinate th e dipola r con (privat e commu th e longitudina d b y Ryabchiko s l -

v a e t al . (1997) , a s wel l a s broad-ban d linea r polariza tio n measurement s b y Bagnul o e t al . (1995) . Calcula tion s wer e mad e for th e rotationa l perio d P=12.457 2 day s derive d fro m photometry . Th e inclinatio n o f th e rotationa l axi s ( i = 131° ) i n th e ne w mode l coin cide s withi n a few degree s wit h tha t use d b y us . Th e positio n o f th e spot s o f M g (depleted) , Co , Nd , Pr , (enhanced ) roughl y coincide s wit h th e positio n o f th e visibl e magneti c pole . Perio d uncertaintie s ma y b e re sponsibl e for th e differenc e i n longitude s o f th e spot s an d o f th e magneti c pole . Th e accurac y o f th e spot' s radiu s i s abou t 10% .


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Th e accurac y o f longitud e i s ± 10° . Th e erro r i n lat itud e i s les s certain . Th e calculation s wit h th e spo t = -55 ° ar e show n i n Fig. 3 b y th e dashe d latitud e line . Not e tha t th e calculation s wit h th e spo t latitud e = --55° fully coincid e wit h thos e for = --65°. Therefor e i n Tabl e 2 w e giv e th e uppe r limit , -60° . W e als o checke d th e RE E distributio n wit h 2 spot s a t bot h magneti c poles . W e rejec t th e possi bilit y o f tw o symmetri c spot s o f equa l abundances ; a spo t nea r th e invisibl e magneti c pol e i n a dipol e configuratio n mus t b e les s anomalous . 3.2 . Iro n Accordin g t o Presto n (1972 ) an d Ryabchikov a e t al . (1997 ) th e iro n line s var y i n counte r phas e wit h th e RE E lines . Th e amplitude s o f thes e variation s ar e smaller . Thi s typ e o f variation s ca n b e successfull y represente d b y a ring-lik e iro n distributio n aroun d th e magneti c equator . W e approximate d th e equato r ban d b y 5 spot s wit h R=40 ° each . Coordinate s an d F e abundance s i n th e spot s an d i n th e photospher e for blu e spectr a ar e give n i n Tabl e 3 . I n re d spec 6137-3 8 lin e profile s ca n b e success tr a th e Fe l fully fitte d wit h th e abundanc e log(Fe /Ntot )=-5.0 3 i n th e rin g an d wit h log(Fe /Ntot )=-5.3 5 i n th e pho tosphere . Not e smal l abundanc e gradient s betwee n th e equato r bel t an d othe r part s o f th e stella r surface . Th e fit o f th e calculate d lin e profile s t o th e observe d 4461. 6 i s one s for th e blen d o f Fe I + FeI I line s a t show n i n Fig.4 .

4 . Rapi d radia l velocit y variation s
Savano v e t al . (1999 ) foun d R V variation s i n th e PrII I line s i n th e roA p sta r Equ di d no t sho w R V variation whic h wa s estimate d a s 14 0 th e highes t amplitud e o f 616 0 an d NdII I 614 5 . Th e Fe I an d BaI I line s s beyon d th e erro r limi t - 180 m s . Du e t o th e
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184

lowe r S/ N o f th e presen t observation s an d lowe r re solvin g power , w e ge t large r error s o f R V measure ments . W e estimat e the m t o b e 20 0 - 40 0 m s for deepe r line s (BaII , NdIII , PrIII ) an d 400-55 0 m s for F e I lines . A n exampl e o f th e R V variation s for on e o f th e night s i s show n i n Fig.5 .
-1 -1

A searc h for perio d wa s performe d wit h th e pack ag e ISD A (Pelt , 1992 ) an d wit h th e programm e PERDE T (Breger , 1990 ) i n th e frequenc y regio n fro m 2.5 mH z t o 2. 9 mHz , wher e th e mai n photomet ri c frequencie s ar e observed . A powe r spectru m ob taine d fro m th e whol e observationa l ru n i s show n i n Fig. 6 for PrII I (uppe r panel ) an d NdII I line s (lower panel) . Si x photometri c pulsationa l frequen cies (Kurt z e t al. , 1989 ) ar e indicate d b y th e dots . Takin g int o accoun t ou r erro r estimate s show n b y th e dotte d line , w e conclud e tha t margina l pulsation s ar e registere d i n th e P r II I lin e only . Fro m seve n frequen cies wit h amplitude s exceedin g th e erro r limits , onl y tw o frequencies , f =2.636 6 mH z (P =6.3213min ,
3 3

semiamplitude=24 4 ms ) , an d f =2.635 3 mH z (P =6.3243min , semiamplitude=16 0 m s ) ma y b e considere d a s independent ; th e othe r frequencie s ar e dail y aliases .
2 -1 4

-1

Fig . 6 (uppe r panel ) show s th e position s o f al l 7 frequencies , whil e i n th e middl e pane l a powe r spectru m afte r subtractio n o f th e signa l wit h f +f frequencie s i s given . Th e pulsationa l period , P=6.32min , obtaine d fro m th e PrII I 6160.2 4 lin e doe s no t coincid e wit h an y o f th e photometri c pul sationa l period s (Kurt z e t al. , 1989) . O f course , thi s ha s t o b e confirme d o n th e basi s o f mor e accurat e high-spee d spectroscopi c observatons .
3 4


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on e t o exclud e th e existenc e o f thi s kin d o f modula tio n wit h lowe r amplitudes . I t i s no t unlikel y tha t th e rotationa l modulatio n exists , bu t it s amplitud e doe s no t excee d 2 . Nothin g ca n b e sai d concernin g phas e correla tions , becaus e th e photometri c an d R V observation s ar e space d b y 1 8 years , th e lates t longitudina l mag neti c fiel d observation s show n i n Fig . 7 a wer e mad e 1 5 year s ago . Perio d uncertaint y ma y caus e a phas e shif t o f u p t o 0.1 . Acknowledgements . W e than k Stefano Bagnulo wh o provide d u s wit h a magneti c mode l calculate d wit h th e photometri c period . Thi s researc h was supporte d b y th e Austria n Fond s zu r de r wissenschaftlichen Forschung (projec t S7303-AST) an d th e Russia n Foun datio n for Basic Research (gran t 98-02-16734)-

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5 . Discussio n
Accordin g t o th e obliqu e pulsato r mode l for roA p star s (Kurtz , 1982) , pulsation s ar e mor e effective alon g th e magneti c axes . Photometri c pulsation s o f H D 2471 2 suppor t thi s model ; the y hav e th e high es t amplitud e a t th e phas e o f passag e o f th e sout h magneti c pole . Give n th e obtaine d RE E abundanc e distributio n w e woul d expec t a rotationa l modula tio n o f th e R V amplitudes . Fig . 7 show s variation s o f th e magneti c field (a) , photometri c pulsationa l ampli tude s (b ) (Kurtz , 1982) , R V (PrIII ) pulsationa l frequencie s (c) an d amplitude s (d ) wit h th e rotationa l period . W e di d no t fin d suc h a modulation . Th e accu rac y o f th e presen t R V measurement s doe s no t allo w