PUBLICATIONS OF THE DAVID DUNLAP OBSERVATORY UNIVERSITY OF TORONTO
Volume II Number 17
A STUDY OF THE VARIABLE STARS IN THE GLOBULAR CLUSTER MESSIER 14
I. PERIODS AND LIGHT CURVES OF TWENTY VARIABLES
HELEN SAWYER HOGG AND AMELIA WEHLAl"
1966 TORONTO, CANADA PRINTED AT THE UNIVERSITY OF TORONTO PRESS .
A STUDY OF THE VARIABLE STARS IN THE GLOBULAR CLUSTER MESSIER 14
I. Periods and Light Curves of Twenty Variables
By Helen Sawyer Hogg and Amelia Wehlau
h m The globular cluster Messier 14, NGC 6402, (R.A. 17 35 0, Dec. — 03° 15', 1950) is one of the clusters very rich in variable stars. It is exceeded in number of variables by only seven other clusters at present. Seventy-two variables were discovered by H. B. Sawyer (193S) from a series of plates taken with the 72-inch reflector of the Dominion Astrophysical Observatory at Victoria. A preliminary report of work on their periods appeared at the same time (Sawyer 1937), but cir- cumstances delayed publication of further work until now. For the past three years we have been making a study of the variables in the cluster to determine their periods and the form of their light curves. A total of 258 plates is now available, virtually all of which have been taken by one of us (H.S.H.). Of these, 31 were taken with the 72-inch reflector of the Dominion Astrophysical Observatory, 211 with the 74-inch reflector and 9 with the 19-inch of the David Dunlap Observatory, 2 with the 36-inch Steward Observatory reflector, and 5 early Mount Wilson plates were taken by F. G. Lease and H. Shapley. These plates span an interval of 52 years. Four additional variables have now been found by Amelia Wehlau, bringing the total to 76. These are indicated on figure 1, and are given in Table I of this paper. The first 72 variables were identified in the original paper. One of the first results of the renewed study was the discovery of a nova (by A.W.) on the plates of 1938 taken with the
David Dunlap Observatory 74-inch (Sawyer Hogg and Wehlau 1 *. H > 4 ) All the available plates have been measured (by A.W.) with the Becker iris photometer at the Hume Cronyn Memorial Observatory of the University of Western Ontario. The magnitudes of the sequence previously published have now been revised from five plates taken with superimposed exposures on both the cluster and Kapteyn Area 61, one of the areas where the magnitude values have been standarized to the fainter magnitudes (Stebbins, Whit ford and Johnson 1950). The comparison stars are identified on figure 1, and their revised magnitudes are given in Table II, which includes four auxiliary stars added to the original sequence.
451 4o2 Helen Sawyer Hogg and Amelia Wehlau
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Fig. 1 —The globular cluster Messier 14, photographed with the 74-inch reflector of the David Dunlap Observatory on June 23, L938, when the nova was visible. (Plate 3263, exp. 40 min.) Four new variables, and comparison stars are also identified. Scale of the figure, 7".0/mm.
The variables in this paper are mainly those for which preliminary results were given in 1937, with many additional observations obtained since. They have large ranges, and three bright Cepheids with periods over one day are among them. .Many of the preliminary periods derived Variable Stars in Globular Cluster Messier 14 453
TABLE I New Variable Stars
Variable 454 Helen Sawyer Hogg and Amelia Wehlau material alone is not suitable for a discussion of the frequency of periods in this cluster. Table III gives the observations on all available plates for the following twenty variables, numbers 1, 2, 4, 5, 7, 9, 10, 11, 15, 16, 19, 22, 23, 24, 25, 30, 32, 33, 36 and 43, giving the number of the plate, the Julian Date, and the observation derived from photometer read- ings. There are fewer plates listed in the second section of Table III for the stars with numbers 19 to 43 since on some of the poorer quality plates none of these stars could be measured. Table IV gives for these variables the maximum, minimum and mean magnitudes, the epoch of maximum (chosen as the nearest maximum just before J.D. 2438200 in the 1963 series of observations), and the period, followed by remarks when pertinent. The light curves of these twenty variables, in order of decreasing length of period, are shown in figures 2 and 3. The points are the computed weighted means of all observations at intervals in phase of 0.04 of the period of the star. Observations with colons in Table III have been assigned half weight. A filled circle represents at least three good observations, but averages about ten such. Open circles represent mean points derived from observations which are few in number or of low weight.
Of this first group of stars, three are Cepheids with periods longer than one day. Sixteen are type ab RR Lyrae stars with periods between 0.48 and 0.68 days, and one is a type c with period 0.36 days. A period change is noticeable only for Var. 1, the Cepheid with longest period in the cluster, 18.730 days, whose period seems to be steadily shorten- -7 ing at the rate of (3 = 14 X 10 days/day. In figure 2 two light curves are given for this star to illustrate graphically the change in period from an earlier to a later interval. In the case of this star, the figure shows many open circles which do not represent uncertainty in the magnitudes, but rather fewer obser- vations in the means because of the division of material.
Joy (1949) studied spectroscopically variables 1, 2, 7, and 17 in this cluster. For Var. 1, his classification from two spectrograms was G2 and GO, with an average radial velocity of —115 km/sec, indicating cluster membership.
Variable 2, with period 2.79468 days, is the type of short period Cepheid in clusters mentioned by Joy and C. Payne Gaposchkin (1954). Joy gives the spectrum from one plate as F8, and the radial velocity as —129 km/sec. Variable 7 seems to be a typical W Virginis star with period 13.596 455
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CO 00 os l> t^ l~ X t^ t^ t-- x t^ N X N N X t^ t^ t^- t^- t^ t^ t^ t^ 1^ O t^ t^ X X X Variable Stars in Globular Cluster Messier 14 461 Lt L1 '-1 '" '" 1-1 Ll Ll Ll Ll Ll L~ IO Ll Ll L~ HON^O IO CO •"** CN CI CO CO O: — — II -T O I> r-t CN CN x o. — — >+ X>GOGOI>;0C - I- X X X X X I- XX I-it- X X X X I- I- t- X I- t- '-1 Ll 1-1 1-1 ll .. L~ 115 1_~ L~ IO .. I" Ll 1- Ll L~ CN 1) co "C _ co no: ci li — — -* IN I- li o; X li — — li — dc — -r — t— X X X X I- I- XX) GO XI- XX I- I- X X X XXt-I-I- I-XXl-t- 30QOQOQOCO 1- CO I- t- t- X I- CO r-t-t-i-cO I- t- t- t- t- I-I-t-l-cO 1-1 Ifl Li ...... ll Li Li Li Li Li Li Li Li Li Li Li Li HNIONH OCOOSOC '1 l1 X DO Li t- — CN CO CNC — CO 05 11 CO 11 CO x x x x x t- x t- t- r- i- x x x x x i- i - x x t- t- t- i- x x t- r- '" • '1 • Li Li Li Li . . Li Li L~ Li H 1-1 lOHMOC X X CO * t^I> OS C 1) X o x cn -r -t -f rj< i-1 cO X ri 30 00 00 00 OS I- I- I- i^i^Xl-t- X X X t- X r-XXI-I- i-t-t-i-t- Li 1.1 I- CO co CO CO 462 Helen Sawyer Hogg and Amelia Wehlau l~ l^ l*C Variable Stars in Globular Cluster Messier 1A 4(33 © co x ei c: CO ei — OS l- ei — — x r-H> ei -r o I - i~ t - i- x i- x x x x x - x X 30 30 I X t- X X — ~~ x ei ~ re l- l- — re t co ~ re — — ~) — I- T ' DO l~ re e-1 X X t- X X l^ X X T. X X X X X X. — x x x x x /.i' KN XI- CD X -r C I- N I- CO 3 1^ N C C CO CO t^ t^ t> i-~ t- l> t- ed I- • - CO Lt — cr -r l- 464 Helen Sawyer Hogg and Amelia Wehlau "o x ta t^ t~ - Variable Stars in Globular Cluster Messier 14 465 L- l~ l- . . . U~ . . . 10 . . »o is co i-H co * oo so w t> ~ ~ «o oo OS * o ~ ei -r ~ — 6 t^ o b~ l>l> t^l>t*O0l> cO«0 cOCC t^t^l^l^t- r~t~l-~ 1 L~ l ~~ DO »0 CM 1^ 't re X O t> ~ e-1 t> ~ "* XT O C<1 L.O O I - X b t« i> xx x i^ xx o ei re — x ~ i-' r^ t^ x t~i> i> x t~ i- ~ ~ t~ ei -h oa re i; i (35 l- i- -f ojoso ei to -t r ioooi>i>co x s O 0ON00 t^ X l> X X X «> t^ X CO i- 1^ > X X I- l> OfflNOO t- 1- X tj- re e>i X X ~ l- o »o io w so t^ '-h ei _ to >o x x _ o V" d x— x six xx x t- t- J> OS xn;; - ~ 1 - _- -• X X d X X I - I - I X 3JO> 9 X '_; z; cn ,_, x to i> ec o o «o oo i> no '-e — i ~ ooV" i- 1- i- r-. ~ i- 1- i- x i-x i> co e» i-e * >e — — " — : e5 cb x t> -t o t^ to — O cot^t-t^ i> xjoo NN 00 00 00N X x x c; r- X - -- -+• — >e ei c. i- i 7 - ^ — — -3 x S i — t- co oo eo co iQONNM — ,-k ,~ .-.-Us;,, [.; -~ ,- Scoi>»o«c cot-r^oocc coi>t^t-cO — i- >e co to - ~ ~ ~ re >~. re ~r i- to t> _• -^ t^ . e-) t- ~ re to r- ei o ^ ^i -t U50i0»0«0 r ~~ ( < : ! e* eieieieiei —' eirere~f— — — — S —> e3 — — — to t*- oo oc x x — — X ^ — z; — ?h — : -- — — — eiei ei x x x — ei ei e> 466 Helen Sawyer Hogg and Amelia Wehlau s Ol CO Oi-r- CO CO OS Is- [- CD — I - s s s- s s s s- s s- s- s- t-- I - I - I I - t^ x I - i> x t- I - I to I - I I t- I l^ I- (Z N X N X s X CO co CO CM I - X s s- x I - x I Variable Stars in Globular Cluster Messier 1A 467 OONWC Ol X X ~ t- t^ >-H *h c-1 Ol CO CT. lO CO x M ^t - C -ftrct:! o .... 2" OOOOOOt-OC X>l>O0 0OI> I- l> t- X X 00 J> CO OC I-l-t-XX i-t-xi-x co i-h o 10 © o co c c o m r: os to os 01 to to x t> to l- 01 to r- 1 1 - xx scxaact- 00 1- oci 00 x - - x 1^ 1- 1- t> 1- x ' x' 1 —i 1- Q 468 Helen Sawyer Hogg and Amelia Wehlau i~ x. v- x t~ x x x i^ t- 1^ t- i~ x r^ t^ t^- 1^ x i^ x t> i> i^ i> h- i> o t^ X XXX XI^t-1^1- t^ X X X X t>t^l>OOJ> XXXXX XX1^1-I^ i«xim>z xxx i>ooi>i>i>- t>i>i^i>i> i-xxt^i^ t^t^r- x iO iC i^ X CO 05 CC — Variable Stars in Globular Cluster Messier 1A 469 t- |- t^ t - t- i- r- t- I- l- CO CO i- t^ co to t^ t^ t^ t- X X X X X X X X ~ (M oo t-i eo co **< co «* oo oo oo re oo 01 L oo x ~ o> or O t^t^t^t^t- r^l-I-t-h- X X X X X I- t- x XXI-t-I- l-I-I-t-X O x t^ I— t— I-I-t-XX XXt-I-t- I- i^ t- t^ 1- X X I- t-I-l-Xl- Lt L* L* C LC ^C »0 fcO • • i—1 1— I » ^ I O O iO iO CO CO »0 X CO X X r> t- t- 1^ t- i^ t^ t^ t^ t^ r> r- 1> t- x to i- x x x i^ w i- i- t- t- t- 1- "01 —i 35 00 ^h 470 Helen Sawyer Hogg and Amelia Wehlau Variable Stars in Globular Cluster Messier 14 471 o ir; l- . . . . >o »c L~ Lo io ifl 10 10 CO CO <* O OS CO i-l (N © O "* O (30 N N X N 1^ X I~ x r~ t- t- I~ X X X X X 1^ X I - X X X Z LO LO L~ LT Lt »C L.O L~ »0 'O CC X CI CC CO -^ COOS Oi-H r. C M C CC c ~ x 6 XNB l-l-I^t^t^ l>l>00r>l> t^t^t^XX t*t-t^l>0C z * co os — c x — i- 1 /. :c n — x 01 cc x x oi — x to co Z ~ >0 re C} s 00 CO CO f- iO 35 3 <* os — x 01 >o i^ - t^ t^ co cO t^ i^ r^ i^ i - x i 472 Helen Sawyer Hogg and Amelia Wehlau Notes to Table III Plates 103-4397 taken by F. G. Pease and H. Shapley with Mt. Wilson 60-inch reflector. Plate- 20544-23600 taken by H. Sawyer Hogg with Dominion Astrophysical Ob- servatory, 72-inch reflector. Plates 4209 and 4228 taken by H. Sawyer Hogg with 36-inch reflector, Steward Observatory, University of Arizona. Plates B 1691 to B 1789 taken by various observers with 10-inch David Dunlap reflector. All other plates taken by H. Sawyer Hogg with 74-inch David Dunlap reflector. TABLE IV Magnitude Epoch Period Var. Max. Min. Mean of Maximum davs 1 — Variable Stars in Globular Cluster Messier 14 473 +5 5 5 5 No I No.l 1912-1937 338- 363 15-0- + 150 155+ -155 160- -160 +^ 1 155- 2 79468 155 16-0- 160 165- --I65 17-0- — 170 "d T 677990 655975 171 -175 180-K -180 185 185 17-5- -175 180+ 180 18 i 185 170- -170 175- 175 180+ 180 5 5 5 5 Phase FlG. 2— Mean light curves for the nine stars of longest period in this group of 20. Two curves are given for Var. 1 to show the change in period. days, very similar to Var. 29 in Omega Centauri (Martin 1938), whose period is comparable. From two plates, Joy gives spectral types of F5 and ( i2e3, with an average radial velocity of — L36 km sec. Our comments on the total picture of the variables in this cluster will be reserved till the final paper. The second paper of this series is - 474 Helen Sawyer Hogg and Amelia Wehlau No.15 557727 * 17-5- 175 18-0- 180 185- 185 552342 .. No.5 548796 [75 -175 18-0+ -180 '6 -185 No 19 538831 175- -175 180— 180 I85- L -185 '534226 No. 43 175 175 180 180 185+ + 185 '519901 175 175 18 0-- 180 185 185 17 5-=- No- 25 5 I80--0 Phase I85-- 5050?*• Fig. 3— Mean light curves for 11 variables, arranged by decreasing length of period. Variable Stars in Globular Cluster Messier 1/+ 475 in preparation. A summary of the results for the first forty periods determined in this cluster was presented at the Michigan meetings of the American Astronomical Society in August 1965 (Sawyer Hogg and Wehlau 19(35). It is a pleasure to express our appreciation to the National Research Council of Canada for generous support of this program, and to many observers at the David Dunlap Observatory who assisted with the telescopic part of the program, especially the late Dr. Frank S. Hogg and Mr. G. F. Longworth. April 27, 1966 References Joy, A. H. 1949, A p. J., vol. 110, p. 1 05. Martin, W. Chr. 1938, Leiden Ann., vol. 17, pt. 2. Payne-Gaposchkin, C. 1954, "Variable Stars and Galactic Structure," p. 37. Uni- versity of London. Sawyer, H. B. 1937, R.A.S.C. Jour., vol. 31, pp. 57-59. Sawyer, H. B. 193s, Dom. Ap. Obs. Pub., vol. VII, no. 5. Sawyer Hogg, H. and Wehlau, A. 1904, A. J., vol. 69, no. 2, p. 141 ; R.A.S.C. Jour., vol. 58, no. 4, pp. 163-166; D.D.O. Comm., no. 97. 475. Stebbins, J., Whitford, A. E., and Johnson, H. L. 1950, Ap. J., vol. 112, p.