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Th e radia l velocitie s o f th e uncommo n SrCrE u magneti c sta r 4 9 Camelopardali s
D.E . Mkrtichian , N.N . Samus , N.A . Gorynya
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Astronomica l Observatory , Odess a Stat e University , Shevchenk o Park , Odessa , Ukraine , 27001 4 e-mail : Institut e fo r Astronomy , Russia n Academ y o f Sciences , 48 , Pyatnitskay a Str. , Moscow , Russia , 10901 7

david@oao.odessa.u a
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samus@sai.msu.s u

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Th e scientifi c goal s

I n 1994-199 5 w e carrie d ou t th e tes t radia l velocit y observation s o f SrCrE u star s wit h th e Mosco w Stat e Universit y CORAVEL-typ e radial-velocit y spectrophotomete r (RVS , Tokovini n (1987)) . Th e mai n goal s o f th e observation s wer e testin g th e fitnes s o f accurat e radia l velocit y (RV ) measurement s wit h CORAVEL-typ e spectrophotometer s wit h cross-correlatio n template s for th e asteroseismolog y o f A p star s (Mkrtichian , 1994) , determinatio n o f typica l accurac y for star s wit h different rotationa l velocities , searc h for pulsationa l R V variability . Th e exces s o f metalli c an d rare-eart h elemen t spec tra l line s i n spectr a o f A p star s hold s ou t hop e t o achiev e a suitabl e accurac y o f V measurement s even for th e earl y A an d F A p stars . Eq u ( v sin i < 5 k m s ) an d 4 9 Ca m ( v sin % = 2 2 k m s Th e typica l FOp SrCrE u star s (Bonsac k e t al. , 1974)) , a s th e tw o star s wit h th e low an d relativel y hig h rotationa l velocitie s wer e include d i n ou r program . Th e complet e result s wit h th e analysi s o f rapi d V variabilit y o f thes e tw o star s will b e publishe d i n a separat e article ; w e not e her e onl y tha t th e typica l interna l error s o f a singl e one-minut e integratio n for Eq u o n th e 1.0 m telescop e o f th e Simeiz Statio n o f th e Sternber g Institut e wer e i n th e rang e o f 120-30 0 ms , th e accurac y o f 8-minut e integratio n tim e for 4 9 Ca m a t th e 0.7 m telescop e o f th e Sternber g Institut e gave s a typica l interna l erro r pe r singl e measuremen t o f 450 - 870 ms .
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Th e 1994-199 5 RV s o f 4 9 Ca m

Th e 1994 observation s o f 4 9 Ca m wer e carrie d ou t o n th e 0.7 m Zeiss telescop e o f th e Sternber g Astronomica l Institut e (Moscow , Russia ) durin g 4 night s i n spring . W e use d th e cross-correlatio n mas k o f Alph a Booti s (Tokovinin , 1987) no t optimize d for A p stars . Ou r first estimate s o f V i n 1994 immediatel y sho w significan t differences (approximatel y + 1 3 k m s ) betwee n ou r estimate s o f th e mea n R V an d th e valu e 1.4 1.5 k m s fro m Wilson' s Genera l Catalo g o f Radia l velocitie s (Wilson , 1953 ; Young , 1945) . A compariso n o f ou r 1994 dat a an d th e availabl e V for th e 4 9 Ca m RVs give n i n th e paper s o f va n de n Heuve l (1971) , Bonsac k e t al . (1974 ) show s a monotoni c increas e o f th e mea n V from 1.4 kms t o abou t 1 5 kms ove r th e las t 5 0 years . W e continue d ou r R V measurement s o f 4 9 Ca m durin g thre e night s i n th e spring-summe r o f 1995 an d detecte d a n unpredictabl e rapi d declin e i n th e RVs durin g 1994-199 5 fro m +1 6 k m s t o -0. 9 k m s . Th e compile d mea n V dat a o f all th e author s ar e presente d i n Tabl e 1 . Th e first an d secon d column s give th e yea r an d th e mea n Julia n Date s o f observations , respec tively, th e thir d an d fourt h -- th e estimate s o f th e mea n V an d th e standar d erro r o f th e mean , th e
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fifth an d sixt h -- th e numbe r o f average d estimate s an d th e rotationa l phase , an d th e las t colum n gives th e references . Th e rotationa l phase s wer e calculate d accordin g t o ephemeride s o f Lero y e t al . (1994 ) JD(negative crossover)= 2441254.0 8 + 4.2866 E days . Th e mea n RVs versu s th e Heliocentri c Julia n Dat e ar e presente d i n Fig . 1 . Unfortunately , for th e mea n valu e o f 1.4 kms give n i n Wilson' s catalo g an d i n th e origina l referenc e (Young , 1945) th e dat e o f observation s i s no t given , w e mar k thi s poin t i n Fig . 1 wit h a n arro w a s relate d t o som e momen t befor e th e dat e o f publicatio n i n 1945 .
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Fig . 2 display s ou r 1994-199 5 observation s wit h thei r erro r bar s a s well a s th e adjuste d linea r fit (dashe d line ) o f th e data . Th e rapi d declin e o f V wit h 0.029 kms day i s well see n from ou r data .
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suppos e tha t th e probabl e reaso n for th e detecte d V variation s i s th e binar y motio n o f Fro m ou r 1994-199 5 dat a th e orbita l perio d mus t b e abou t severa l years . However , i n o ou r result s th e 1971-197 2 observation s o f Bonsac k e t al . (1973 ) spannin g 328 day s did th e pea k t o pea k V change s highe r tha n 2 kms an d an y tendenc y t o monotoni c
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On e ca n 4 9 Cam . contras t t no t sho w changes .

Th e natur e o f suc h significan t differences, i n principle , ca n b e produce d b y th e well-know n effect o f inhomogeneou s surfac e distributio n o f element s an d sta r rotation . Th e rang e o f suc h expecte d rotationa l differences i s limite d b y v sin i valu e an d ca n b e approximatel y 2 2 k m s for 4 9 Cam . Th e tempora l trend s ca n b e estimate d a s
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an d i f w e tak e P = 4.286 6 day s an d v sin i = 2 2 k m s , thi s tren d ca n hav e th e uppe r limi t o f value s 0.8 k m s hour and , i n principle , ca n b e measurabl e wit h th e RVS durin g on e nigh t o f observations . However , i n ou r case , a s th e mad e Alph a Booti s cross-correlatio n mask s ar e no t optimize d for SrCrE u star s (se e Mkrtichia n (1994 ) concernin g th e proble m o f optimizatio n o f mask s for introducin g th e periodi c spatia l filter s an d gainin g th e detectio n sensitivit y t o nonradia l modes ) an d rejecte d all th e visibl e spectra l lines , th e possibl e influenc e o f V variation s cause d b y surfac e inhomogeneitie s an d star s rotatio n wa s minimize d bot h for th e dat a o f Youn g (1945) , Heuve l (1972 ) an d Bonsac k e t al . (1974 ) wher e th e spectra l line s o f different element s wer e involve d i n th e calculatio n o f mea n velocit y pe r singl e plate , an d different rotationa l phase s wer e involve d i n th e calculatio n o f th e mea n velocit y o f stars . Nevertheless , possibl e smal l variation s i n ou r mea n RVs versu s th e rotationa l phas e ca n b e seen from Fig . 3 , wher e w e presen t th e residual s o f ou r estimate s relativ e t o th e linea r fit . Accordin g t o Stift (1985) , th e R V determination s wit h CORAVEL-typ e spectrophotometer s woul d give th e spuriou s phase-dependen t R V variation s du e t o line asymmetr y produce d b y Zeema n splitting . Fo r a n 8 k G magneti c fiel d an d rotationa l velocitie s betwee n 5 an d 1 0 k m s h e gives th e R V amplitud e o f 10-2 0 kms . However , thes e expecte d spuriou s phase-dependen t magneti c R V variation s overlappe d thos e
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produce d b y th e surfac e chemica l element s inhomogeneitie s ar e i n disagreemen t wit h 1994-199 5 drasti c declin e o f RVs coverin g different rotationa l phases . I t i s possibl e tha t a wea k contributio n o f thi s effect occur s i n th e phas e curv e o f R V residual s i n Fig . 3 . Accordin g t o Lero y e t al . (1994 ) 4 9 Ca m ha s stron g an d variabl e linea r polarizatio n (uppe r limi t abou t 0.26 % ) an d th e magneti c field configuratio n depart s from th e simpl e dipol e structure . Amon g 4 0 A p star s the y hav e observe d 4 9 Ca m a s on e o f th e mos t peculia r an d almos t uniqu e object . Th e magneti c natur e o f suc h R V variation s ca n basicall y b e explaine d i f durin g 1994-199 5 4 9 Ca m change s th e magneti c field configuration , a s i n th e ye t unexplaine d cas e for th e magneti c sta r 5 2 Her , whic h twic e showe d th e rapi d reversa l o f magneti c polarit y fro m abou t + 2 t o -2. 8 k G i n 1975-197 8 an d fro m -2. 8 t o +1. 6 k G i n 1978-198 0 (Gerth , 1990) . However , for th e cas e o f 5 2 Her thi s polarit y reversa l wa s no t affected b y an y significant radia l velocit y variations . Note , tha t evidenc e o f low amplitud e cyclic magneti c field variation s i n A p star s (simila r t o th e sola r p-mod e frequenc y change s wit h sola r cycles) i s comin g from th e asteroseismolog y o f roA p stars . Ever y roA p sta r fro m th e sampl e o f th e well-studie d roA p star s show s cyclic frequenc y variation s o f nonradia l mode s (Kurt z e t al. , 1994) . Returnin g t o 4 9 Cam , w e wan t t o not e tha t th e incomplet e tim e coverag e an d th e absenc e o f simultaneou s magneti c field measurement s doe s no t permi t u s a t presen t t o decid e whethe r th e detecte d V variabilit y i s cause d b y th e binar y motio n o f th e sta r o r i t i s drive n b y th e effects o f th e magneti c field influenc e o n asymmetr y o f spectra l lines .
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Conclusion s

Base d o n th e previou s investigation s an d ou r 1994-199 5 radia l velocit y observation s w e ca n sum mariz e th e result s o f ou r wor k a s follows: t W e mad e 4 0 ne w radia l velocit y measurement s o f 4 9 Ca m coverin g different rotationa l phases . · A compariso n betwee n ou r dat a an d all publishe d estimate s o f 4 9 Ca m RVs show s a slow increas e i n R V o f 4 9 Ca m fro m 1.4 k m s i n th e earl y fortie s u p t o 16.2 k m s i n 1994 .
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· Ou r 1994-199 5 RVs sho w a rapi d declin e from 16.2 k m s approximatio n o f suc h a declin e i s 0.029 kms day .
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t o -0. 9 k m s . Th e linea r tren d

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· W e discusse d th e possibl e natur e o f th e ye t unexplaine d characte r o f V variation s i n th e sta r an d mar k th e uncommo n natur e o f suc h variations .
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Th e presen t an d futur e wor k

Du e t o th e uncommo n behaviou r o f 4 9 Ca m th e questio n o f significanc e i s t o revis e th e behaviou r o f 4 9 Ca m RVs i n th e past . I n th e SA O collectio n o f spectrogram s ther e ar e nin e 9 A /m m plate s o f 4 9 Ca m take n wit h th e Mai n Stella r Spectrograph , whic h cove r 1982-1983-198 4 interva l an d coul d b e use d for R V measurements . I n th e sprin g o f 1995 , on e o f th e author s (MDE ) carrie d ou t three-nigh t spectra l observation s o f 4 9 Ca m withi n th e interva l o f rapi d RVs decreas e wit h th e SA O 6 m telescop e echell e spectromete r "LYNX " (Panchu k e t al. , 1993 ) a t th e Nasmyth - 2 focu s coverin g different rotationa l phase s . Th e reductio n o f th e CC D spectr a i s no w i n progres s an d woul d suppor t th e CORAVE L results . Futhe r multisit e comple x investigation s o f 4 9 Ca m base d o n surfac e magneti c field s an d abun danc e mapping , radia l velocit y an d photometri c observation s ar e neede d for definin g th e natur e o f thi s puzzlin g star . Acknowledgments . Th e author s ar e thankfu l t o th e America n Astronomica l Societ y an d ES O C&E E Gran t Committe e for partia l suppor t o f thi s project .

Reference s
Bonsac k W.K. , Pilachowsk i C.A. , an d Wol f S.C. : 1974 , Astrophys . J. , 187 , 265 . Gert h E. : 1990 , Astron . Nachr. , 311 , 41 . Heuve l E.P.J , va n den. : 1971 , Astron . Astrophys. , 11 , 461 . Kurt z D.W. , Sulliva n D.J. , Martine z P . an d Trip e P. : 1994 , Mon . Not . R . Astron . Soc , 270 , 674 * Lero y J.L. , Landstree t J.D . an d Bagnul o S. : 1994 , Astron . Astrophys. , 284 , 481 . Mkrtichia n D.E. : 1994 , Sola r Phys. , 152 , 275 . Panchu k V.E. , Klochkov a V.G. , Galazutdino v G.A. , Ryadchenk o V.P. , Chentso v E.L. : 1993 , Sov . Astron . Lett. , 19 , 11 . Stif t M. : 1985 , Mon . Not . R . Astron . Soc , 217 , 55 . Tokovinin,A.A. : 1987 , Sov . Astron. , 31 , 98 . Wilson , R.E. : 1953 , Washington) . Youn g R.K. : 1945 , Publ . Davi d Dunla p Obs. , 1 , 311 . General Catalogue o f Stellar Radial Velocities, (Washington : Carnegi e Institutio n o f