A SEARCH FOR FLARE STARS Paul E. Roques Griffith Observatory

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1 A SEARCH FOR FLARE STARS Paul E. Rques Griffith Observary A survey f dme stars was started in September 1952 with the knwn flare star L Tw flares f this star were bserved and reprted. 1 Late in December f the same year the phmeter began shw erratic behavir, and its recnstructin pstpned resumptin f bservatins f dme stars until late in March The investigatin f dme stars is being cntinued with the 12-inch visual Zeiss refracr and a new phmeter which cntains (in increasing distance frm the bjective) a shutter, a filter slide, a diaphragm slide, a 3-inch fcal length Fabry lens, a dark slide, and a General Electric 1P21 phmultiplier tube. The utput f the phcell is amplified by a three-stage, directcurrent amplifier, and fed in a Brwn recrding ptentimeter. The phcell cmbined with a CG 335 filter gives a maximum respnse near À The bserving prcedure is recrd the starlight cntinuusly, with interruptins at 30-minute intervals check the sky brightness and zer reading. As a precautin against instrumental truble, the bserver watches the recrding and a visual cnfirmatin f a flare is btained at the telescpe befre it fades. Each star n ur list f fifty will be mnired fr a tal f 100 hurs. The list includes stars a limiting apparent magnitude f As reprted earlier, the dme star BD (23 h 26 7, ', 1900) was fund be a flare star. 2 Unlike the extrardinarily rapid increase in brightness f sme f the flares f L 726-, that f BD n September 5, 1954, brightened much mre slwly.. Figure 1 is the light-curve f the flare after crrectin fr zer drift f the recrder. These mre accurate results increase the principal maximum 0.07 mag. ver the estimate first annunced. BD is a duble star f 3'/5 separatin (dm4e and dm5.5e ; = 10.3, 12. and M v == 11.1, 13.6). It was nt pssible determine which cmpnent had flared withut interrupting the recrding. At the time it 34

2 A SEARCH FOR FLARE STARS 35 UNIVERSAL TIME Fig. 1. Light-curve f the flare f BD-j , September 5, seemed mre desirable btain a detailed recrd f the lightcurve. The three flares f L 726- bserved phelectrically with high time reslutin were all characterized by an extremely rapid brightening, 3 while the flares f BD bserved phelectrically by Grdn and Krn 4 and Liller 5 and the flare f BD brightened at a much slwer rate. Althugh the characteristics f flares n a given dme star are prbably as diversified as thse f slar flares, the pssibility that flare characteristics may differ frm star star cannt be entirely dismissed. Red-dwarf flare stars are a type f variable that may play an imprtant rle in stellar evlutin. The need fr mre infrmatin abut them is apparent. Unfrtunately, hwever, the accumulatin f gd phelectric light-curves f flares is extremely time-cnsuming. Since all dme stars may nt flare enugh prduce detectable variatins in brightness, it seemed desirable search fr sme feature that wuld distinguish a dme star that flared frm ne that shwed nly small variatins in the intensity f the emissin lines but n appreciable variatin in the cntinuum. Spectrgrams f the knwn flare stars were examined, with particular attentin the hydrgen emissin lines Hy, Hb, Hs and the K line f Can. The utstanding feature nted in the spectra f knwn flare stars relative many f the ther dme stars was the greater intensity f the hydrgen emissin lines (als the H and K lines f Can) during their quiescent perid. Table I lists these stars with the apparent magnitude, the abslute magnitude, the spectral type, the maximum bserved flare amplitude, and an estimate f the intensity f the H emissin lines.

3 36 PAUL E. ROQUES a 3 S W b b b b C a C bbgbpg^bpbpbgb ^^Sc^ i-< ft. ft. ft ft ft u & C/3 C/3 C/3 ^ C/3 C/3 C/3 ft C/3 > > > > s < to r-i O T-1 (VI O T-H u «-M Q< & ^ w O O <V <U. «4> c m* 4> <D 4> V <v <v T ö T 0 T 0 T 0'0'd'0 T 0 r, d'd, i3 T 0 Knwn Flare Stars O H tono'tforfooh^o VO WO^OrcOHHfO voooccco C^i CO r-l rh Os 't TH O -H O i «ON Q * 00 tooownionno\ c loçnlohloh't r-h CO O M* NO CO tv. CO Ti- On I I ++ + J < -J W T-t ON VO 6- Ti- 00 ON TÍ- ó c CO a A *-H O h 00 n CO a VO JO $ m ft H c PQ ON S3 js^ i t $ a M S < PQ NO NO pq i I r-i t-h t-h ^ On On HK «tfl n T n ^ O r U N.» Q Q ^» ft ^ _ Q Q Q KjH-ícMPSSSií^wSpqpq

4 A SEARCH FOR FLARE STARS 37 The spectrum f Prxima Centauri des nt seem resemble clsely the nrmal spectra f the ther flare stars. Thackeray has btained nine slit spectrgrams f Prxima, nly five f which shw emissin lines. 6 One f these five spectra has intense emissin features clsely resembling the nrmal spectra f the ther flare stars. Shapley, as a result f an examinatin f Harvard plates, reprted variatins in the brightness f Prxima f as much as ne magnitude. 7 Hwever, because the nrmal spectrum des nt shw strng emissin lines f hydrgen as d the ther knwn flare stars, it might be desirable classify it temprarily with the pssible flare star HD bserved by Ppper. These stars might tentatively be thught f as having slightly different characteristics frm the ther flare stars. RD-f A, B were selected fr study because f the strng emissin lines f hydrgen in bth spectra and because f the abslute magnitude (13.6) f the fainter cmpnent. The flare was recrded after 26.6 hurs f bserving. AC A, B (dm4e and dm4.5e, M*=11.5, 12.4), which have very weak emissin lines, had been fllwed previusly, but n flares were fund in 36 hurs f bserving. A variatin f 0.5 mag. with a pssible 6-hur perid was suspected n tw cnsecutive nights. Rss 67 (dm5e, M v = 13.6), with mderately strng emissin lines, and Rss 6 (dm4e, M v = 11.4), with rather weak emissin lines, were each bserved fr 35.9 hurs with n evidence f flare activity. Table II lists several dme stars, with abslute magnitudes f 11.5 r fainter, that shw relatively strng emissin lines. This partial list is given nly as a pssible clue aid in the TABLE II Ptential Flare Stars R.A. Star 1900 Rss 15 l h C Rss Rss C Decl m v M v +5 r Spectral Type Remarks dm4e dm4.5e Unseen cmp. 9 dm5e Spec, binary dm4.5e dm5.5e

5 3 PAUL E. ROQUES search fr flare stars. Whether r nt the suspected cnnectin between the intensity f the H emissin lines in the nrmal spectra f dme stars and detectable flare activity is real, will, f curse, have await the gathering f cnsiderably mre data. The writer wishes express his appreciatin Dr. Ira S. Bwen, direcr f the Munt Wilsn and Palmar Observa- ries, fr permissin study the Munt Wilsn spectrgrams f dme stars, and Dr. Alfred H. Jy fr his cntinued interest in the prgram. Als, the authr wishes thank Dr. Gerge Herbig, f the Lick Observary, fr furnishing a print f the spectrum f Orinis. 1 P. E. Rques, Pub. AS.P., 65, 19, P. E. Rques, Pub. A.S.P., 66, 256, V. Oskanjan, Bulletin de VObservaire Astrnmique de Begrad, 1, 24, *Pub. A.S.P., 61, 210, Pub. A.S.P.y 64, 129, *M.N.y 110, 45, Prc. N.A.S., 37, 15, Pub. A.S.P., 65, 27, D. Reuyl, AJ., 45, 133, 1936.

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