KO13Al KANhZ, ODSERVATORY

BULLETIN Numbcr 204

On tlic Polar Coronal Rays of the Sun

h. Bh~lnnpu and K . C A RRtrheem

A study nrthc polnr mrmd ruys made on t w s l i p w photcgraphq n prcamted. Prom tllc n~qucncy tlhtribution dpolar ra)a, it in ahmu lhat the marrimurn dblnbuh d

nip m u n ~ 111 itn aonulnr aonc am~~nd 10' C n LILC la md a minimum at the ph. gmrn thc M*utrtlm nl [ha ~ m l a r I I L ~ the T h 01 tho $m~I~t Icd by m u p e t LY been detcnninml. A vnrlatlon ln thc langlh or Ihe ypothecicd m~ magnat 4th ihe p b of mLr BC~MIY b mnhetl.

(:;ru~phcll, Mtnrc ant1 Bcll (1923) wcrc ihc first to point out thc simi- larity IlcLwccn tllc o l ~ r coronal rays and a bar rnngnct Thcy ahowed that the distribution an t; orienktion of polar rays m a t h fairly well with the magnetic lincn of forcc duc to a bar m nct, aituirtcd innide thc nun and whm

Ics ~ r c scparutcd hy two tbirda of 2 c nun's dinmetcr. In recent em, Gldmdcr (L961), Bachmann (1957'), Snim (19%, 1965), Syoddard, C!-n

studicrl the geomc!q ofthe polnr rays linca oFforce due to a bar magnet. several eclipse-photographs that the a function OF the solar activity c ~ ~ l e .

Itor rwurlhrx vcri6cation or the h thetical bar magnet, it ia nccesaary YK" to al~nlysc as man 1 scalc eclipse p olographu as posxible. In eoncction oFthc &=a1 Observatory, wc had two largc acale photograph, obtdned during the total eclipse of 1898 and 1922. In

n p 1 wc havc prmnted a study of the orientation and the frequency di~lri- E u h d &c polar rap, rnde on two edipe plat*.

The d i p s 8 of 1898 amq 21. TLb ~ h o ph obtained by Michie Smith at S&dol, Oen t r J Indm (IrL =I9 16=n6=8l021'E), mb camera of 1 5 m aperture and 12 met- focal length, m image fi &:

16'.5/mnl. Thc polar raya could hr traced out to tlirhncrq or ~ I I I - ortlrr of 1 . 2 mlnr radii as m~.asurrti finm thv aun'a ccl~trc. A high cnntml copy or l l ~ c

""5" al nqptive wm cnlargcd and pmjcclcd on a scrccn to obtain all imngc sca c of 3". 9/mm. The oullincs of ~nd~vitlual polar r a F wcrc drawn indcpcn-

1,s thc two authors. A cornpnri~on of the two drawingri slio~vcd no diffc~rcncr. A copy of thc cclipsc p h o t o p p h obtninrd l)y thr Lick

cxpcdition with n similar fncd Icngth cnrnrm, IVIN 'mrrously '? madr nvnilablr h Director, Lick Obscwatory, n~ ld u cornpnnson tr Ll~c two

pict~lrca showmi tKat almost a 1 polar rays nrerc colnmon ou twill picturca. Another small scnlc plnlc (1'.5/mrn , made available from ihc Lick collection 1 showed polar rays, eutcndln~ u to . G I<. Tllc amnll scale platc WIIA enlargcd to yicld nn i l n a ~ c wale of3'.9,krn and bot l~ nrnnll aud l q c rcalc platcs wcw coml~incd to givc ir ccrmpmilc drnwing of tl~c. polar rays, HY nliow11 in Figllrc 1. Tllc polar rnys wcrc exiendrrl rrom ihc lilnh or thc moon to mrri t l~c solnr limb.

Ar illc time of tllc eclipse the n arcni scmidiamckr or ihl- sun WM 16'. 14". R m d t h ~ t or illc moon wm lEp 24.3. Tllc paition lr11~1c P or the eun'a axin i a 7 " nnd the heliographic lntiludc of thc sun's ccntrc, B, wns -5". Thc north-muth ollcntnt~on on Lhc plate WRY tlrtcrminccl, usin the @lion anglc of the pmrnincnrm Men on h e platc. Accordiog to rbc fund- cndorff deflni tion thc 11nnc of ihc strlnr c cle at tllc timc of eclipnr w11n -4 -46. 011 [his photrqrapl~ 2 F nurtll polar rap &.P.R.), anrl 30 snutl~ plrlar mya (S.P.R.) wcrc tlistinctly men. T h c ~lumbr r of rhc plnr my in 5 t l i - p c intcr- vnls of thc pnl;lr an& ie givcn in T:rl~lr I and a h i s t o ~ m in I~igu~r: 2. A d i s h c t pcak in ihc hintopam is sccn a t 10°-150 zonc or the polirr mglc.

T1.t sclipe q 1922 S~ptembar 21. 'Illia platc wtla crl)tninrtl l)y ,11)lln Evcr- s11l-d (1222) at Wn I lal,h1 eskrn Ausm~lin, (Lnt. = 19". WS, Long.=120n. I l'l?,), using n HOc.m lrpcrturc and 6.3 rnctrr To~:nl length Ctwrkc tripl(ml I(*n:l, in con- junction with n w c b ~ t a i . 'rhc imngc sc;~lr on Ll~ia platc wns 33'. 1,/1ii1n. The plate wan pwtly f cd, bu1 for our pilrpox of dc~cminin the polar rays thc "T p ntc war usnble, As in thc case of tllc this platc was c n h r p l nnd prc!jectccl to vicld m image oulLnm or thr indivldlral comnnl polar ruyn wcrc drawn and :\re nhown 111 Pigm 1.

At (Jlc time of totality the appnrcnl ncrnidiametcr of the null wan 15'.56'.0 nntl illat of the moon was 16.4Y.6. Thc osition a q l c P or thc sun'a aKis was +25.S0 and 3, was +7O. The no JI aouth oricn~ntion wad dctcrmined fmm thc aymmctry d thc polar rnya. Tllc nmumpllon is marlr hem that the ma. ctic polcs and ~ h c rotation ~ds orthe sun arc in good coin- cidcncr (Cnmpbc "ir st al 1929 . Al the time of cclipe h e h u e of the solar activity cyclc rraa - -0.14. l i lar rap in the north an x I 7 in the ioulb wcrc identified on thc platc. #c polar rays in thc south wrre not ns clearly secn as in thc north, probably bccallac the aun's south pole was tippcd awa from thc obacrvcr (Bo= + 7"). We give in Tablc I thc nurnl)cr of mya in ca 4 of the 5' i n t e i d of the polar angle.. A hintogram showing the distribution of h a polar rap In givcn in Figure 2. Thia show a pcak at (5'-I 0') zone of p o ] ~ r angle and a minimum at the pole.

D I t m 1 . lo' I.'

-19

a 'p;Lq* 0 *d

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1-l& 2 ICrorn Saiio'n (1958, 1965), dliitr for (i cclipvcs and front thcac two ecli-

Iwe, wc: conclndc thnt tllcre is uo apl~i~rcnl rclation bctwccn the position or L l r ~ ' pol'ir RIIKIC nl UIC pcnk ill thc hislogram and Lhc solar rrr.tivily cycle. Ili~i cluri~l~ nll ph~~stw or ~ h c ~olnr cyclc, thc polar rnys rrrc consivtcntly sccu to nvoitl t l l r - 1n)L3a orU11. sun. 011 ihc conhnry lsubRkia a! el (1964) ham rlho!vll ill lllc 1.m~ oI'tRc 1962 cclip, t l l ~ t ihc distribution of the polnr rays is i r muxirniilil at tlic 1w)lnr olld a minimum ncar Lhc (1T - 15') zone, whilc for llic mmt: cclipcs oC1962, S:dto (1965) 11a1 oobiaincd a mnximum nt thc 10' zonc iuul rr rniniinun~ at tllc polc. Saih llas mplnincd discordnncc ill thc two iraultu its th~c ttr tllc aiaihtical cmrr introduced by Taul~aki sl a/, bccauuc i h ~ y I d rhtrsrn sll~nllrr Llkrvaln oCthc polar angle. ltmm tllcsc obacrvatiom it aliljct~~a t l ~ i ~ i 1~1l;lr rays arc clislributctl in an annular zone 10' away horn the pole. In thin c*onncclfon it is inicmiing to notc that, on cxamilliug the promi- ~~c~llcc dlria koni ~ I C Kodaikmal 0l~scrvat.ory Bullctinn for scvcrnl solar cycles, tltrrc- i n ;L icndrucy for promincnccs to p&t around f B O o latitudc and to avoid lllc. l)oka. Howcver, remily Harvcy (1965) horn siudy or tllc 1963 c-clipc plicitr~fi"ir1~11n, l r i fioul~d a correlation bctwccn tllc polnr fays and surrnce I ~ ~ I I ~ I U C S OIMVTVCCI iu Kr spcc~ullcliograms and h ~ e lakcn this carrclation to rshbliall tllc cloru: association bclwccn polar r a p ~ l l d surCaw magllclic lielcla.

3. A p p k ~ f o l l o ~ Of the pokr rays

1898 ~~lipsu: Thc apparcni ar~glc 01 obliquity W and thc polnr angle0 wcrc n~cmumd irt 1Lc limb of thc stm and also at diatmcee ol 1.1 H,, 1.2 R,, 1.3 R,, 1.4 R,, 1.5 R, 1.6 R,, Goln the sun's ccntrc. W dcllo~~n thc a p p m l q l c betwccn ilrc tangcnt drawn irt a point I' on polar ray and thc radius vccior, and 0 in illc apparent polar auglc of'thc point P an mcaaurcd from the N-S nxin. It has bcrn shown by several authors, on the basin of observations, that a lincur mlation of ihc rorm $~=k 0 cxinta between V and 0 ilnd that h e paramctcr k depend8 on the phasc of thc polar activity cydc.

* / * ' -1 // -4 I,. * -8. . - :, .AqL . a. .#a ..

I., .,. J .. L.)

In 'Tablc 2% and 2b wc givc lllr a ~parcnl ol)licl~~ity nncl lmlar rir cach of tile p o h r my8 and at scvc'rnl A M ~ ~ I ~ C L S 1'Ponl UIC S ~ I I I ' ~ centre, iol. both north and south solnr polar rcgiom. 'l%atl nrc l~lotlcrl in i U . A rcw polar r a p sccm to l w c bccn i~kflucncctl IIY ihr local p r o ~ n i n c ~ , ,

thc pointa arcB rnrlnscd in parenthcacq, I11 F i g ~ ~ r c 41, 1% s l ~ o w ~ the varia- tion or pan~rnclcr k wit11 tllc. rndial distancc Cnrm ~ h r aut~'s cent rc . norill pola~ rcgion, k shows tul incrc:uaing trndcllry with distauces upto 1.2 R, while in rllc south sidc, k shows a pctlk ill 1 . 1 I<, and e l lm a steep decline till 1.2 R, 11rCc-r which it remains conahnt.

I .

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IU II II la u 18 -WIo

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Sairo (1958) ll~u ol~tnincd u rcalatio~~ 1,c~wt:cn i l ~ r p u m m c t e r k and the length of a llypotl~cticnl bar magnct, rdtuulcd insidr ihc nun. U s i n g Snito'a rclalion, we obtain Lhc h ~ l r l e n ~ l h of the bnr magnr t nn 0.43 R, for the north polar r a p and 0.46 R, Tor thc ~ o u t h polar mys. Wc havc measured the paramctcr G, which iy thc dishncc bctw[:c~l thc point nT in tcwect ion of the tnnpnin drawn 011 the polar rap a t ihc limb nT thc .u1111 and the c e n e e of the solar disc. Thc rncan 4 1 , is found LO bc 0.50 R, for ~ l l c syslcm of N . P . b and 0.48 R, Tor the S.P.lis. 'rhc two valucn arc in cltr: a p c m c n t a n d wc can consider that ~ h c two poles ol thc hypohctical m a p 1 orc cclualIy .+=parated apart h m rhc nun's centrr, Thc half-lcnath of ihc 1)nr magnct according to Saito M in fair ngrecmcnt with lllc pammctcr (I.

1922 eclipJe : Thc apparent anglc ol'obliquity \Y and the polar angle 0 WCK: mcasured on thc dfawm of the p l a r raya. Thc vnluw of %' and 0 an: tabulated in Tab lc 9a an 8" 3b, and arc plotted in Fiprr. 3. T h e variation or parameter k, with the radial distancc fmm the suns ccntrc given in figure 4. In thc case of 1922 cclipr the aramclcr k. dccrcasc~ with increa- sing &tan= from the sun's diac up 1.2 and then rcrnains nearly conarant-

Using SRiLo's ~dat ion , thc halllen of thr hypothetical b a r magnet obtained from the N.P.R. aystcm is 0.6 P" R, nnd rar thc s.P.R. qystem in 0.55 RD. The ararnctcr - for Lhc N.P.R. wm 0.69 R, (sN) wd S.P.R. wan 0 . 6 ? ~ . (G#), ?n the cme of 1922 e d p e thc h W ~ * d c d

pole secm to hr llrarcr Lo L ~ I P sun's surracc compamd to ~11c mu& ctic pole, A sinlilar rcsult Tor tllc as~mmelric locnhon or thc l~ypothr-

~ x m a v t in ibc Nun, l u ~ lxcn nhtainecl by Namy~nvich (198), from a study of 8 eclipw pl~otogmphs.

The lcngth of lllc obtaincd in the case of the 1898 and 1922 hasc of t l~c solar active cycle. We havc len th of Ulc magnet

thetical rnagnct with thc pllasc of thc aolar cycle. f for thew eclipses or cngth of thc h p

VPrin(ion of parmmdar k with distpnca from the s d a r Umb

Several authors h ~ v c made dctailcd study of thc variation or papmeter k with diatancc bum ihc sun. Waldmcicr (1965) has nhown For thc 1962 eclipse that k is independent of r, while Rachmnn (1957) and lvnncuk (1M) havc obaavcd that k dccrcgacs with incrcasin distnncc r, Tor 1954 ccli

A f f?k bey and S u d ~ 1966) llavc madc n detai ed shdy of h e varirrtic.11 o wi r for several c ipaca and could not arrive at any definiic conclusion on the dependence of k on r.

, Our rcsulta ohtaind from ihc two cclipscs show a variation of k with I near the sun'e limb hnt at largc diatanccs k becomca nearly constant with r.

T h e autholx nrc indebtccl to Dr M. K. V. Bappu for his helpful au tiom and to the Dimtor of the Lick Observatory for cncroualy m available the Lick Observatory cclipsc photographs.

E TL arc due to Mr. V. Namjan for hie hclp during thc mvestiganon.

Kodaikanal Obacmtory, October 1970.

A 197

RRFKRENCEB

Bachmann H., 1957, Zs. f. Ap., 44, 56, 1957.

Campbell W. W., Moor J. H. and Bell R. H., 1923, P. A, S. P., 35, 163.

Evershed J., 1922, Koclaikanal Oh. Bull.

Harvey J. W., 1965, Aatrophys. J., 141, 892.

Ivancuk V. J., 1964, Materials of IGY, Infor. Bull. No. 6, Kijcv, p. 46.

Koprcky M., Suda J., 1966, B. A. G., 17, 144.

Ncnnlyanovich A. T., 1963, Sovict Astron. A. J., 6, 774.

Saito K., 1958, Publ. A. S. Japan, 10, 49.

Saito K., 1965, ibid, 17, I .

Stoddard L. G., Carson D. G., and Sn ih K., 1966, Aahphya. J., 145, 796.

Taubalci T., Tominaga S., Kubata J., and Kawaguchi I., 1964, Publ. A. S. Japan, 16, 13.

Waldrncier M., 1961 ., 2s. f. Ap. 51, 286.

Waldmeier M., 1965, %s. f. Ap. 61, 186.

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