Photometry of variable stars with periods near 1 day

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Norman R Simon Papers Research Papers in Physics and Astronomy 1988 Photometry of variable stars with periods near 1 day Charles G Loomis University of Nebraska - Lincoln Edward G Schmidt University of Nebraska at Lincoln, eschmidt1@unledu Norman R Simon University of Nebraska - Lincoln, nsimon@unledu Follow this and additional works at: http://digitalcommonsunledu/physicssimon Loomis, Charles G; Schmidt, Edward G; and Simon, Norman R, "Photometry of variable stars with periods near 1 day" (1988) Norman R Simon Papers 49 http://digitalcommonsunledu/physicssimon/49 This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln t has been accepted for inclusion in Norman R Simon Papers by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln

1988MNRAS235159L Mon Not R astr Soc (1988) 235, 159-172 Photometry of variable stars with periods near 1 day Charles Loomis, Edward G Schmidt and Norman R Simon Behlen Observatory, Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588, USA Accepted 1988 May 6 Received 1988 April 29; in original form 1988 January 25 Summary We have obtained accurate, well-sampled light curves for seven stars which were candidates for short period type Cepheids One of the stars, CM UMa, was found to have an erroneous period The correct period is 589 day and the star is an RRab star The Fourier decomposition coefficients for the light curve of KP Cyg (period=86 day) combined with its high metallicity are consistent with its being either a type Cepheid or an RR Lyrae star The result for V486Her (period=8day) is inconclusive; it is probably an RRabstar The Fourier coefficients showed that CE Her (period= 121 day) and XX Vir (period=135 day) are type Cepheids as suspected Both stars show excess scatter and rapid variations during declining light which we suggest deserve further attention BB Gem has Fourier coefficients which are appropriate to a short period classical Cepheid, making it the shortest period fundamental pulsator of that class known in the Galaxy 1 ntroduction A period of 1 day is commonly assumed as the boundary between the RRab stars and the type Cepheids The latter stars in the short-period range are a heterogeneous group with metallicities ranging from very low to at least solar (Harris 1981), kinematics appropriate to a range of populations (Harris & Wallerstein 1984) and a variety of light curve shapes Diethelm (1983) sorted the light curves into several categories and subsequently (Diethelm 1986) used photometric abundances to show that at least one of the groups, his RRd stars, was physically distinct Petersen & Diethelm (1986) carried out Fourier decomposition of the light curves of 35 type Cepheids and concluded that their pulsational properties were similar to those of the classical Cepheids However, Simon (1986) rediscussed the Fourier coefficients in connection with pulsation models and reached somewhat different conclusions n particular, he suggested that there

1988MNRAS235159L 16 C Loomis, E G Schmidt and N R Simon may be mass differences between some of Diethelm's groups We are led to conclude that among pulsating stars with periods near 1 day there are several different types of object Although these studies have provided new insights, it is clear that more observations are needed An examination of the light curves (see Diethelm 1983 for plots) shows that the data, drawn from a number of sources, often contain excessive scatter, exceeding 1 mag in some cases For some stars there are gaps in the phase coverage which can introduce difficulties for Fourier decomposition Furthermore, the sample of usable light curves is rather small Peterson & Diethelm considered only five of the 35 light curves they decomposed to be of high quality To improve this situation we have started a program of photometric observations of variable stars with periods from about 75 day to 1 week While the long-period limit is consistent with the usual division between BL Her and W Vir stars, we have extended the sample to somewhat shorter periods since, as Wallerstein & Cox (1984) pointed out, terminating the type Cepheid regime at 1 day is an essentially arbitrary choice This paper presents results for the seven stars listed in Table 1 The first column gives the star name while columns two and three give the period and type of variability from the General Catalogue of Variable Stars (4th edn) As discussed below we have determined new epochs of maximum for all except one of them These are given in column four while column five indicates the type of variability inferred from our data Table 1 The variable stars Star Period Type Epoch of Type (GCVS) Maximum * (revised) CH UMa 589 Cep: 65792 }{Rab 64423 719669 FK Vul 434529 RRab 659388 RRab V486 Her 859317 RRab 662483 RRab? KP Cyg 855936 RRab 669962 Type Cepheid or RR Lyrae CE Her 1294357 CWB 658377 Type Cepheid s- xx XX vir 1348251 CWB 62367 Type Cepheid, s-xx BB Gem 23827 DCep 65678 Classical Cepheid * Determined from present data, Heliocentric Julian Date - 2,44, For CM UMa, the period determined with the present data was not accurate enough to carry the phasing from one season to the next For that reason, we give a date of maximum for each year it was observed 2 The observations We made most of the observations with the automatic filter photometer (Taylor 198) on the Behlen Observatory 76-m telescope An RCA 3134C photomultiplier was used with broadband V- and R-filters matched to the Cousins system Both the telescope and the photometer were under computer control This allowed rapid switching between the star and sky apertures and between the variable and its comparison star t was thus possible to obtain accurate differential magnitudes under somewhat adverse conditions Measurements of the variable through both the V- and R-filter were alternated with observations of the comparison star A sequence consisted of at least four observations of the variable and continued until the internal errors of the differentials were judged to be satisfactory The only exception to this practice occurred when rapid changes in the variable were noted n that case, the sequence was continued as long as possible On photometric quality nights we observed standard stars from Landolt's (1983) list and

1988MNRAS235159L Photometry of variable stars 161 determined transformations to the system of Cousins The nights were grouped into intervals no longer than a month and mean colour terms calculated These were then used for all the nights in the interval When a night was regarded as photometric, zero points were also derived and the magnitudes were reduced to the standard system For nights which were not of photometric quality, only differential magnitudes were derived but they are still on the standard system in the sense of having been corrected for colour terms t was found that the mean colour terms for our filters and photocell changed by less than 2 mag over periods of months Since this is smaller than the error in determining nightly transformations, the use of mean coefficients is justified and will reduce the internal scatter in the final results Once the observations had been placed on the standard system for the photometric nights or corrected for colour terms on the non-photometric nights, differential magnitudes were formed for the variables relative to the comparison stars The observational sequence was generally Table 2 Photometric data for CMUMa (period: 589, epochs of maximum: 24465792 and 2 446 4423) HJD - PHASE V sd R sd HJD - PHASE V sd R sd 2,44, 2,44, 656995 43 271 3 2761 7 67875 288 2512 7 267 13 657796 79 2855 6 2934 16 678768 395 2622 11 279 8 657851 883 275 2775 611612 459 27 8 2737 13 657853 887 2686 2755 611671 56 2773 8 284 7 657856 892 2599 273 611361 534 2763 7 281 17 657859 897 2599 2661 611373 77 279 11 2836 14 657862 92 2483 261 6441941 848 2838 2935 657864 95 2428 2547 6441945 855 2868 2956 657867 911 2378 2496 6441954 87 2746 2883 65787 916 2319 2455 6441957 875 2622 2758 657873 921 2281 2461 644196 88 2681 2855 657881 934 225 2434 6441963 886 2675 2763 657884 939 2199 2372 6441968 894 2613 2711 657886 943 226 2358 6441971 899 2483 26 657889 948 2155 2343 6441974 94 2533 2588 657892 953 2118 231 6441976 98 2472 2599 657894 956 211 2278 6441983 92 247 2533 657897 961 261 2283 6441 985 923 2332 2518 657899 965 279 2266 6441988 928 2375 2557 65792 97 24 2229 6441992 935 2314 2472 65794 973 239 2243 6441995 94 2219 242 65797 978 249 2256 6441997 943 2184 2411 65799 982 259 2266 6442 948 223 2413 657912 987 256 2272 6463889 111 2377 25 657914 99 24 2238 646389 115 2385 253 657917 995 248 2273 6463894 12 2398 2526 657925 9 295 2259 6463896 125 244 2519 657928 14 291 2265 6463899 13 241 2534 65793 17 296 2314 6493788 875 271 2832 657933 23 218 227 6493791 88 2698 281 657936 28 212 2347 6493794 885 2662 2765 657966 79 2234 3 2382 14 6493797 89 2635 2756 657998 133 2326 8 2445 7 64938 895 261 2729 65816 163 2372 8 2525 11 649383 91 2619 278 667952 32 2257 4 248 6 649386 96 2597 268 6683 119 2387 14 2496 21 649389 911 2538 2641 668963 749 2781 1 2853 7 6493812 916 253 269 668988 791 2831 6 2887 27 6493816 923 257 262 6695 82 277 286 6493818 926 2491 259 6697 824 2749 2835 649382 929 246 259 6691 829 2747 2829 6493861 999 2232 2418 66912 832 2734 2842 6493863 2 2219 2383-66915 837 2719 281 6493865 6 2226 2383 6692 846 2734 2826 6493869 13 2212 2382 66922 849 2685 2751 6493889 47 2219 2349 66924 852 2667 274 649389 48 2254 237 66926 856 265 2748 6493892 52 2246 249 66929 861 2634 2722 6493895 57 224 2427

1988MNRAS235159L 162 C Loomis, E G Schmidt and N R Simon started and terminated with an observation of the variable, so usual practice was to form a differential magnitude for the mean of pairs of variable measurements and the intervening comparison star magnitude The differential magnitudes were then averaged for the sequence and the root mean square of the deviations from the mean calculated This rms value was then increased by the square root of two since there are only nl2 statistically independent data points in n differential magnitudes The differential magnitudes of the seven variable stars and their internal standard deviations are listed in Tables 2-8 and are plotted in Figs 1-7 The phases were calculated from the GCVS periods (column 2 of Table 1) and the epochs of maximum determined from our data (column 4) n instances when the variable changed significantly between successive observations, differential magnitudes from single observations are given in Tables 2-8 Such cases can be recognized because they lack an entry in the standard deviation column Observations of this type were only retained when they defined parts of the light curve not otherwise available and when the sky conditions were judged to be stable from the comparison star observations n order to verify the constancy of the comparison stars, a check star was selected for each (with Table 3 Photometric data for FK Vul (period: 434529, epoch of maximum: 244659388) HJD - PHASE V sd R sd HJD - PHASE V sd R sd 2,44, 2,44, 6262846 342 241 25 2395 3 6593877 993 1 835 1 99 6263835 62 2529 8 252 8 6593879 998 1816 1 992 6272771 28 226 1 2339 11 6593881 3 1 817 1 976 6272839 365 241 14 2399 6 6593883 7 1836 1 999 6272885 471 258 7 2477 4 6593886 14 1 856 1 977 627384 671 2617 7 2585 1 6593888 19 1 865 1 983 6315697 14 248 1 2136 2 659389 23 1 856 1 977 631572 116 275 3 2148 4 6593893 3 1865 26 631579 132 2112 16 2191 13 6613784 857 2654 6 2626 13 6315798 337 246 6 2413 11 661381 896 2454 17 2489 3 631589 362 2468 1 2425 1 661387 91 24 2447 6315861 482 2556 1 255 11 661389 915 2347 2438 6316638 272 2339 8 234 6 6613811 919 2341 2344 6316644 286 2363 4 2359 14 6613814 926 2282 2349 6316692 396 2474 6 2468 3 6613816 931 2222 2311 6316764 562 2545 1 2513 1 6613819 938 2197 2277 631686 659 2579 6 2563 18 6613821 942 2127 2218 6316858 779 276 14 2686 23 6613823 947 282 2178 6343785 814 2749 18 2723 23 6613826 954 247 2172 655187 215 224 11 2269 7 6613828 958 23 215 655192 33 2378 8 2378 2 6613831 965 1 928 284 6564826 63 1 819 1 967 6613833 97 1 919 25 6564828 68 1 825 1 973 6613836 977 1 874 24 656483 73 1 832 1 97 6613851 11 1786 4 1 974 1 6564833 8 1 871 1977 6613854 18 1 774 1 95 6564835 84 1 897 1 99 6613857 25 1 83 1 975 6564837 89 192 211 6613859 3 1 837 21 6564895 222 2169 4 228 8 665679 856 2652 2612 659837 989 1 817 7 1 985 4 665684 868 255 2575 6593799 814 2717 4 2669 1 665689 879 2461 2487 6593833 892 2431 2463 665694 891 241 245 6593835 897 2372 2388 665717 944 1 946 244 6593837 91 237 2366 665719 949 1 922 269 659384 98 2266 2324 665721 953 1891 255 6593842 913 2247 2288 665723 958 1 876 24 6593844 917 2231 2264 665726 965 1 83 2976 6593846 922 2168 228 665728 969 1 81 1 948 6593849 929 219 2215 66573 974 1798 1 983 6593851 933 266 2184 665732 979 1 84 1 953 6593853 938 231 2154 665735 985 1 89 1 974 6593856 945 1992 214 666976 694 2644 7 2588 6 6593858 95 1 94 292 6699665 713 2599 14 2568 4 6593861 956 1 933 273 6699699 794 279 8 2694 1 6593874 986 1839 1982

1988MNRAS235159L Photometry of variable stars 163 Table 4 Photometric data for V486 Her (period: 859317, epoch of maximum: 244662483) HJD - PHASE V sd R sd HJD - PHASE V sd R s d 2,44, 2,44, 621879 369 5494 7 5321 7 6582833 89 5324 5228 6238824 43 523 13 5119 13 6582835 892 5328 521 6238858 86 5243 1 5166 17 6582838 896 5289 529 6238899 136 531 2 5184 11 6582841 9 539 5286 6239811 268 5387 8 5245 7 6582844 93 531 5251 6239845 31 5436 11 5291 8 6582846 96 5361 5211 6239855 323 5529 l3 5378 2 6582849 91 538 5233 6239861 33 5416 4 6582854 916 531 521 623989 366 5468 11 5288 31 6582869 934 537 522 6239897 375 5432 7 532 3 6582876 943 5268 4 5211 18 6261826 585 561 8 5435 14 6582886 956 5244 16 5166 8 627273 8 5219 8 5122 1 6583682 943 5282 14 5196 25 627279 188 5311 8 524 2 658372 99 529 16 516 3 6273733 358 5482 7 5328 13 6589699 49 5482 7 5325 8 627383 445 5517 7 5351 14 659725 682 5666 7 5495 1 631669 56 5587 4 541 14 659787 759 578 1 5521 11 6316676 643 563 4 5473 2 659371 375 548 4 5314 4 6316725 74 5667 1 5516 17 6593757 444 555 3 5328 2 649393 545 5568 7 5378 11 6613655 135 5277 13 5162 11 65387 414 5514 6 5325 1 66l379 2 5321 6 524 653916 472 5518 4 536 17 6624682 817 5651 l3 553 11 6551731 299 5419 13 5257 11 6624695 833 5644 7 5471 23 6551796 379 5469 11 533 16 662476 913 5327 11 5223 4 6551893 5 5551 7 5367 11 6624772 928 534 11 5214 2 6582739 773 5728 1 5498 18 6624786 946 5278 3 519 8 6582782 826 5683 5531 662484 968 523 7 514 13 6582784 829 5731 5554 6624818 985 518 11 5114 14 6582787 833 5668 5473 665625 7 5185 7 592 6 6582789 835 5681 5467 665654 42 521 6 516 7 6582792 839 5576 5466 66574 14 5252 6 5143 l3 6582794 841 5655 556 666964 6 569 1 5429 3 6582797 845 5585 5465 6699568 735 5665 554 6582799 848 559 546 6699569 736 5682 5571 658282 851 5586 542 6699572 74 5717 557 658285 855 5536 542 6699574 742 5763 5555 658287 857 5516 5398 6698999 29 5665 5534 658281 861 5542 5354 6699579 749 5676 5528 658283 886 5338 5227 669958 75 5681 5517 Table 5 Photometric data for KPCyg (period: 855936, epoch of maximum: 244669962) HJD - PHASE V sd R sd HJD - PHASE V sd R sd 2,44, 2,44, 6272736 266 335 17 3438 16 6699593 969 3l37 3295 6272814 357 3472 8 3519 6 6699595 971 319 331 6272865 417 3541 3 3569 4 6699597 973 3115 3257 627292 46 3592 7 3623 8 6699599 976 315 3269 6273872 594 3791 8 3769 7 669962 979 372 3256 632744 325 342 1 3484 1 669964 982 381 3243 632756 339 3457 8 3513 8 669966 984 35 3213 6316622 539 371 6 373 2 669969 987 327 3217 631676 637 3841 6 3823 16 6699612 991 34 321 6316752 69 389 7 3873 2 6699614 993 318 3214 6316832 784 3948 18 3921 8 6699616 996 31 3173 6343688 16 324 16 3335 6 6699618 998 2982 3169 6343752 235 3314 7 3412 1 6699621 1 31 3196 6551841 349 347 8 352 8 6699622 3 37 3194 659819 887 3757 6 3784 13 671698 942 3363 3496 659894 975 381 6717 945 335 3494 659896 977 368 3245 67172 947 3326 3458 659898 979 342 3245 67174 949 3323 3436 6599 982 345 32l3 67177 953 337 347 65993 985 334 225 67179 955 3275 3393 6596814 89 3697 6 3743 13 671712 959 3231 3391 6699589 964 3182 3343 671715 962 3174 3345 669959 965 318 3335 671718 966 3161 3278

1988MNRAS235159L 164 C Loomis, E G Schmidt and N R Simon Table 6 Photometric data for CEHer (period: 1294357, epoch of maximum: 244658377) HJD - PHASE V sd R ;::id HJD - PHASE V sd R sd 2,44, 2,44, 5935728 178 1 34 7 1 7 1 655275 352 1 312 24 1 237 18 5938681 62 168 8 1531 11 6564725 253 1182 6 1 18 6 5938728 658 1717 11 1 554 1 6564916 411 142 6 1 33 16 5939676 442 1 495 3 1 355 6 6582673 93 778 1 822 8 5939722 48 1 545 1 1 43 1 6582713 126 876 6 892 8 623853 873 1 831 17 1657 18 6583736 971 112 1 7 62391 92 1791 6 1 648 1 6583741 976 958 953 62679 31 1287 8 1199 14 6583742 977 879 918 62694 395 1 423 6 1 289 13 6583747 981 77 81 621739 566 1 633 8 1486 7 6583758 99 661 723 62179 68 1 691 6 1 529 11 658376 992 636 684 621846 655 1 691 8 1 548 1 6583764 995 563 645 62199 77 1 75 11 1 55 7 6583769 999 568 626 6234771 436 1 489 14 1 372 1 658377 495 591 623481 468 1 551 1 1 412 17 6583774 3 537 63 6234873 521 1 655 7 1 53 18 6589675 882 1 89 6 1 653 7 6234889 534 168 6 1 477 11 6589722 921 1 78 4 1621 14 6236746 69 75 7 755 2 658973 928 1742 4 1 618 23 623684 117 859 8 872 3 6589734 931 1 691 1 56 6236833 141 923 13 925 16 6589736 933 1713 1 553 6236862 165 997 6 976 4 6589739 935 1 67 1 561 6236889 187 1 53 6 1 3 8 6589741 937 1 68 1 492 6238757 732 1 718 11 1577 11 6589746 941 1 613 1 514 6238798 766 173 8 1 595 8 6589748 942 1 576 1 445 6238841 81 1 73 1 1 551 16 658975 944 1 542 1411 6238888 84 176 11 1 62 16 6589752 946 1 56 1413 6239673 489 1 562 1 1434 1 6589754 947 1 464 1 387 623974 515 1 586 8 1 423 8 6589757 95 1 42 L 295 6239742 546 1 621 7 1 478 4 6589759 952 1 386 1 278 6239789 585 1 664 11 1 54 7 6589761 953 1 338 1 224 6239832 621 1 673 1 L 518 6 6589763 955 1 271 1 2 6239877 658 1672 4 1 526 17 6589765 957 1 275 1238 6261798 783 1 738 8 1 586 3 6589768 959 1 263 L 21 6261864 838 1 771 16 1 632 8 6589776 966 1125 1128 6315639 31 1 293 1 1 216 14 6589778 967 1 99 1111 6316599 94 775 6 88 8 6589789 976 88 897 6493919 78 179 1 1 579 8 6589791 978 884 889 659951 964 1155 1126 6589793 98 847 882 659954 967 1148 1 133 6589795 981 784 816 659959 971 1129 1118 6589797 983 738 792 659961 973 1 54 1 37 6589799 985 716 769 659964 975 929 944 658982 987 685 744 659966 977 918 934 658984 989 622 648 659969 979 875 99 658986 99 629 683 659971 981 849 892 658988 992 637 719 6511857 54 1 653 17 1 491 4 6589811 995 627 684 6526822 913 1 852 1712 6589813 996 59 657 6526826 917 1779 1646 6589815 998 569 63 6526829 919 1 745 1 58 6589817 1 552 652 6526862 946 1 494 139 6589818 543 624 6526865 949 1 466 1353 6589836 15 538 6 616 4 6526867 951 1 363 1 267 6589856 32 569 7 638 7 6526869 952 1 359 1276 6589886 57 638 1 7 8 6526872 955 1318 1273 659757 777 1753 1 167 16 6526874 956 1321 1234 6593683 196 172 1 139 13 6526879 96 1227 1183 6593728 233 115 4 11 8 6526882 963 1198 1171 6593816 36 1 293 7 1 22 4 6526884 965 1121 1129 659674 694 1688 1 1545 7 6526887 967 1111 1123 6596715 73 1 724 6 1543 4 6526889 969 1 67 1 83 6596766 745 1 715 6 1 565 13 6526892 971 1 67 1 61 6596829 797 178 6 1 565 14 6526894 973 1 24 1 2 6596884 843 1 767 1 1 628 1 6526897 975 955 977 6624654 84 1 719 1 1584 11 65269 978 894 92 Figure 1 Light curves for CM UMa The two upper panels present the data from the photoelectric photometry while the lower panel contains the data from the CCD photometry All are phased with a period of 589 and the epoch from Table 1 which is appropriate to each observation Here and in subsequent figures open circles denote points based on a single differential or points with standard errors larger than 1 mag When a number of open circles are closely crowded, they are plotted as a single larger circle

1988MNRAS235159L Photometry of variable stars Table 7 Photometric data for XXVir (period: 1348251, epoch of maximum: 24462367) HJD - 2,44, PHASE V sd R sd HJD - 2,44, PHASE V sd 6141 872 6171749 617186 623673 623724 623768 623819 621658 621711 621774 621812 6171886 623672 6239685 6239719 6493837 6493876 649394 6493961 649399 659825 659865 659922 6511796 6511827 653785 653935 653673 6552716 6552768 6552772 6552774 6552776 6552779 6552781 6552784 6552786 6552789 162 323 365 2 4 73 111 183 222 269 297 425 514 7l3 739 224 253 31 316 338 83 113 155 545 568 63 741 19 897 935 938 94 941 943 945 947 948 951 2164 15 215 2396 8 2286 2463 1 2335 1729 4 1781 1 846 8 1864 1945 3 1944 235 1 2]2 2184 6 212 2255 1 2172 2342 6 2233 2362 4 226 2498 4 2336 265 2 2487 2734 6 2578 2749 8 267 2262 1 219 2324 3 221 2384 8 2275 241 3 2296 2442 8 2315 1 993 1 1985 245 17 219 2168 11 2122 2644 7 2479 2676 7 2519 268 11 2524 2733 1 2586 183 4 1 833 2788 7 2626 2311 2249 2258 227 221 2186 2198 2149 2155 2121 2153 2119 2119 29 278 26 1 951 1 95 6552791 1 6552822 14 6556659 1 6556668 1 6556698 6 6556745 8 6556754 11 6556778 4 655678 l3 6556782 7 6556785 28 6556787 7 655679 16 6556792 11 6556795 1 6556798 6 65568 3 655683 8 655685 7 6556824 8 6556826 21 6556828 14 6556831 14 6556833 8 6556835 l3 6556833 8 6564653 13 6564676 1 6564753 6564786 656482 6582645 659675 659471 6596676 6596738 66l3687 6624665 952 1975 975 1 749 1 821 2874 14 828 2848 11 85 2883 11 885 284 8 892 2812 99 2595 911 2571 912 2555 915 2437 916 238 918 2428 92 2367 922 2382 924 2389 926 2365 928 2368 929 2337 944 2183 945 2117 947 294 949 254 95 23 952 248 954 1941 75 2776 '7 767 2771 1 825 2876 8 85 292 7 861 2884 4 96 1991 11 52 1891 7 38 1841 4 53 2626 1 549 2671 6 121 26 11 264 2343 6 R 165 sd 1 972 1785 1 268 7 2674 17 278 11 268 13 2685 249 2422 2437 2321 2275 2329 2234 2266 2314 2293 2266 2255 217 293 255 259 258 238 1 994 264 11 263 1 274 7 2719 8 271 14 1 972 1 1 888 23 1 884 1 2455 1 2514 17 224 1 2231 1 13 v 13 5 12 5 - '1: 3, Je '" ", -!- R 13 ~2!> r-j 8 t"'b o ~ Jl&", g "' of o 'l ~, 12'8 - ''(, ~ v ' 13 3 r- o o CM UMa PEP PEP o CCD ~ :"11 ~\ - '5 Phase Figure 1 o f~o ~'<P 'b & Qj' - o~ y /,> 'b - '/58 o J#,,,,,- o 6 9 ~ d\5 o~ 8/ - --! - o -

1988MNRAS235159L 166 C Loomis, E G Schmidt and N R Simon Table 8 Photometric data for BB Gem (period: 23827, epoch of maximum: 24465678) HJD - PHASE V sd R sd HJD - PHASE V sd R sd 2,44, 2,44, 656795 6 1173 1 1 316 4 6439776 928 1776 1 89 656879 43 124 6 1 331 4 643978 929 1 719 1 74 656937 68 1261 6 1 385 3 6439782 931 175 1721 657662 382 193 3 1 862 4 6439785 932 1718 1 739 657758 424 195 6 1911 4 6439789 933 1734 1 775 657831 455 1 975 7 1 929 7 6439791 935 1681 172 657949 56 236 1 197 6 6439797 937 1 615 1 679 667923 327 2168 6 299 6 643981 939 1595 166 677633 34 1 22 13 1 334 13 643986 941 1 562 1 643 678625 464 1 99 8 1 931 7 6439811 943 1 544 1 67 678682 489 22 7 1 959 4 6439813 944 1525 1594 678732 511 235 3 1 981 6 6439817 945 149 1 571 611573 35 1786 4 1 772 4 6439819 947 1 448 1552 611637 333 1 839 1 1 81 6 6439822 948 1 495 1576 611358 68 2112 3 237 4 6439824 949 1 465 1562 6113616 623 2117 4 243 3 6439827 95 1 451 1 538 6113675 649 2135 4 261 3 644188 88 2199 7 2124 8 6113738 676 2144 1 269 7 6444632 32 119 6 1 332 7 61461 314 1778 11 1 77 8 6444711 66 1 263 4 1 388 4 6]4622 324 1 823 6 1 796 4 6444765 9 1331 7 1433 8 614159 743 219 6 213 3 6444827 116 1 41 7 1 489 7 6141 651 769 222 7 2142 7 6444879 139 1451 4 1 515 7 6146588 98 1 884 7 1 884 7 6463762 319 1 81 4 1787 4 6146618 921 1 84 4 1 823 1 6483689 953 1 427 159 6146634 928 1 747 13 1774 4 6483691 954 1 395 153 6148593 777 227 1 2131 7 6483694 955 1 397 1 483 6148656 84 227 1 2128 1 6483696 956 1 389 1 481 6153584 939 16 16 1648 16 6483699 957 1 381 1462 6153592 943 1567 21 1627 21 648374 959 1365 1457 6153598 945 1 553 21 1 589 21 648377 961 1334 1448 615362 947 1491 21 1572 21 648379 961 1 347 1 476 615369 95 1 44 31 1 549 31 6483711 962 1 356 1485 6164597 71 227 14 211 21 6483714 964 1 321 1 439 6164633 726 2191 17 2111 14 6483718 965 1 32 1 435 617167 747 2197 8 219 1 648372 966 1 321 1 432 6343917 398 1967 8 1934 13 6483723 967 137 1 421 6412682 19 1 574 7 1 613 1 6483743 976 1 234 16 1372 14 6412748 219 1 655 4 1 67 1 6488636 96 1344 17 1 454 13 6412791 237 1 67 6 168 4 6488723 133 1 44 8 1512 8 6413846 694 217 3 293 4 649639 964 1317 7 1 431 8 641387 75 2187 11 213 11 649695 988 1194 7 1 337 7 6413968 747 222 3 2121 3 64974 7 1163 13 1 314 11 6439695 893 222 1 979 6497631 993 1169 4 1313 4 6439698 894 1 99 1 967 6497668 9 1174 1 1 316 3 643974 897 1924 1885 651769 648 2152 7 272 8 643976 898 1 953 1923 653682 312 1 83 1 1774 11 12'r- " J,N\ ~ " 1 FKVul ~- Os g~o go 1- om~ ~ " '19 ~ (t;o (i)o 'tj} ' 6' e'" 8, \s ~& ' ", - V 12'5 :6" 8 - R 13'~ l 1 ' 12 - ~ ~ 12'5~ ' L l 5 Phase Figure 2 Light curve for FK Vul plotted with a period of 434529 and epoch of maximum of 244659388 }9

1988MNRAS235159L V 13 13 4 i- Photometry of variable stars 167 'b~ q,~ o V486 Her o f3 i '/, J>eoQ oil' 8 '11 - ~" ' <1> - L o~ e " 12'7 'r-~o s ~ o R ~~'/, o f 13 - o ~ - 5 Phase Figure 3 Light curve for V486 Her plotted with a period of 859317 and epoch of maximum of 244662483 o o'/,o 12 51- / KP Cyg (- V 13' l- - R 12 2 'r- ( '", (- 12 7 l- Phase Figure 4 Light curve for KP Cyg plotted with a period of 855936 and epoch of maximum of 244669962 n this figure and subsequent figures, the points during rising light are very numerous and too crowded to be plotted individually The solid curve shows their locus 5 CE Her 12 V 12 5 o ' 11 5 " R 12 ~ ~ " ~ c, d o o o o '" '" o~ dj i ' "'11 12 5 /' '5 Phase Figure 5 Light curve for CE Her plotted with a period of 1294357 and epoch of maximum of 244658377

1988MNRAS235159L 168 C Loomis, E G Schmidt and N R Simon V / J ' XXVir ~ 12', - ' "' 12 5 '> ', q,-o o <>: J 11'5 ', ) ' ; 8' R 12 ' ' ',, - O', & <b "",'" ~ 1 5 Phase Figure 6 Light curve for XX Vir plotted with a period of 1348251 and epoch of maximum of 24462367 ~1 11' <ii,, BBGem ~ " V " 11 5 "- 1 5 ~ ~ ' ", SOl / /, " R "- 11 _, - go "' '5 Phase Figure 7 Light curve for BB Gem plotted with a period of 23827 and epoch of maximum of 24465678 the exception of KP Cyg) Differential measurements were made between the check stars and the comparison stars at random times While it is common practice to observe the check stars every night, the present procedure is less time consuming and serves to alert us to any potential variability in our comparison stars Additionally, the constancy of the magnitudes of the comparison stars on photometric nights was found to be consistent with the usual photometric errors There is thus little likelihood that any variation as great as 1 mag would have escaped our notice n Table 9 we list the comparison and check stars for each variable They are identified by the variable name in column one Co indicates a comparison star and Ch a check star Columns 2 and 3 give the coordinates of the check and comparison stars The mean magnitudes, colours and their standard errors, calculated from the nights which were judged to be photometric, are listed in columns 4-9 The last column gives the number of nights included in the means

1988MNRAS235159L Table 9 Comparison and check stars Photometry of variable stars 169 Star* RA Dec V se R se V-R se n (195) CM UMa Co 9:4:16 49:44:59 1667 7 131 8 358 3 5 CM U~la Ch 9:4:8 49:44:57 1438 8 1153 1 285 4 3 FK Vu1 Co 2:5:18 22:26:2 1245 6 9916 7 329 2 7 FK Vu1 Ch 2:5:27 22:23:57 11 22 7 1883 9 319 4 6 V486 Her Co 17:24:32 27:15:31 7591 5 753 5 158 3 9 V486 Her Ch 17:24:59 27:14:37 1748 6 1233 6 515 5 5 KP Cyg Co 2:4:49 41:2:39 9356 1 8833 9 522 6 5 CE Her Co 17:37:47 15:19:38 1997 5 1812 6 186 2 11 CE Her Ch 17:4: 15:9:44 11312 5 1987 6 325 3 5 xx Vir Co 14:13:6-5:53:6 987 9 971 9 152 2 9 xx Vir Ch 14:13:4-6:1:2 1143 1 9747 1 396 3 4 BB Gem Co 6:31:39 13:3:42 9648 5 9128 5 521 1 6 BB Gem Ch 6:31:43 13:4:52 1321 6 112 6 219 3 6 * V486 Her Co is SAO 49185 KP Cyg Co is SAO 8593 Owing to difficulties in determining the period of CM UMa as discussed in the next section, further observations of that star were undertaken on six nights during 1988 January and February with the newly commissioned CCD camera at Behlen Observatory This instrument and data' reduction procedures are described by Schmidt (1988) The instrument was new at that time and its performance was not fully optimized Consequently, the data quality is not completely consistent among the various nights used and the photometry was not reduced accurately to the standard system For these reasons, we do not tabulate the data here However, they are fully adequate for the purpose of resolving the period of CM UMa and it will be seen that the light curve from the CCD is in very good agreement with that from the photoelectric data 3 Discussion of individual stars 31 CM UMa When it became obvious that the period listed in the GCVS for this star (144 day) was grossly in error, we tried to employ the phase dispersion minimization technique (Stellingwerf 1978) to search for a new period in our data However, we could not definitively establish the period owing to the relatively long intervals between the observations which made the cycle count ambiguous When the star again became available in 1988 January we obtained further data with the CCD camera An effort was made to obtain data on successive nights and over as long an interval on a given night as possible Two consecutive nights with 6 and 9 hr of coverage eliminated any period shorter than half a day The fit of all the CCD data then yielded a period of 589 days t should be noted that the cycle count between successive years of data is still ambiguous so we can not refine this period by combining all the data We give a date of maximum for each year in Table 1 The light curves for CM UMa are plotted in Fig 1 The upper panels contain the V and R data from the photoelectric photometer (which is listed in Table 2) while the CCD data are plotted in the lower panel t can be seen that the light curve is typical for a type ab RR Lyrae star A comparison of the photoelectric and the CCD light curves in Fig 1 shows excellent agreement in the overall shape and the actual magnitude levels The scatter during rising light and after maximum is likely to be due to the Blazhko effect Owing to the short time over which the CCD observations were obtained (31 days) compared to the interval for the photoelectric observations (438 days), the Blazhko effect is less evident in the former However, there is excess scatter in the light curve around phase 4 Since the

1988MNRAS235159L 17 C Loomis, E G Schmidt and N R Simon CCD camera was new, we might wonder whether this is an instrumental effect or is due to the star itself We prefer the latter interpretation for several reasons n the first place, this region of the light curve was observed with the CCD on three different nights n each case the data agree well before and after this region but the star follows a different curve (but a curve with little scatter) through this region on each of the three nights Secondly, photometry for other stars of comparable brightness observed with the CCD on the same nights shows scatter much too small to explain the scatter in this part of the light curve of CM UMa Finally, other RR Lyrae stars of similar period show similar scatter in their light curves (see, eg Lub 1977) 32 FK Vul This star was included in our programme because the period given in the third edition of the GCVS, 77 day, fell within the range of interest The fourth edition has corrected this period to 434529 day From the phase dispersion minimization analysis of our data we obtained a period of 4344 day, in good agreement Subjecting the observations to Fourier decomposition yielded the coefficients listed in Table 1 The quantities are as defined by Simon & Lee (1981) The amplitude ratio, R(21), and phase differences, 1>(21) and 1>(31), for FK Vul place it among the RRab stars (Simon & Teays 1982), a classification which is also consistent with its period and amplitude The scatter (in excess of observational error) apparent in Fig 2 is likely due to the Blazhko effect which is common in RR Lyrae stars with periods like that of FK Vul Table 1 Fourier coefficients of the light curves Star Order Std Dev Amp1 R(21) 4>(21) R( 31) tp(31) tp(41) of fit (mag) (mag) FK Vu1 5 56 975 565 392 299 21 69 V486 Her 5 35 551 459 454 26 311 KP Cyg 5 22 966 442 452 224 247 677 CE Her 8 37 136 48 46 375 1 96 62 xx Vir 8 37 119 535 421 369 222 673 BB Gem 7 262 1 6 471 48 24 21 611 33 V486 Her The light curve for this star is plotted in Fig 3 The long period (compared with most RR Lyrae stars) and low amplitude of this star make it comparable to XZ Cet (Simon & Teays 1982) which is best modelled as an anomalous Cepheid (Teays & Simon 1985) similar to the cluster variable NGC5466-V19 (Zinn & Dahn 1976) ndeed, the values of 1>(21) and 1>(31) displayed in Table 1place V 486 Her between the RRab stars and XZ Cet on the corresponding Fourier diagrams However, the amplitude ratio R(21) for V486Her agrees with the RR Lyr stars This is in sharp contrast to both XZ Cet and NGC 5466-V19 whose small values of R(21) set them apart from the RRab stars of similar period Although this may indicate that V486Her is an RRabstar, the unusual still-stand and sudden change in slope about threequarters of the way up the rising branch of the light curve raise doubts The star needs further study

1988MNRAS235159L 34 KP Cyg Photometry of variable stars 171 The light curve for this star is presented in Fig 4 While the phase coverage is not fully adequate for Fourier decomposition, the lower order coefficients seem stable~nough for inclusion in Table 1 The coefficients are consistent with the Fourier diagrams for both field RR Lyr stars (Simon & Teays 1982) and type Cepheids (Simon 1986) A solar metallicity (ils=o) was found by Preston (1959) for KP Cyg This, too, is consistent with either type We are therefore unable to assign this star to a class on the basis of present information f KP Cyg turns out to be a type Cepheid, it will have the shortest period among this class This would extend the domain of these objects well below 1 day For this reason, further study of KP Cyg and similar stars is needed 35 CE Her AND XX Vir Our light curves for these stars are plotted in Figs 5 and 6 Both of these stars were assigned by Diethelm (1983) to the class he designated RRd A light curve for XX Vir was analysed by Simon (1986) who classified it as a type Cepheid of subclass S-XX The Fourier parameters from our light curve (Table 1) agree with his Those for CE Her also place it in the S-XX subclass n both CE Her and XX Vir there is excessive scatter before minimum Fig 8 shows the last part of declining light for both stars on an expanded scale with error bars The observations were made during a number of cycles as indicated by different symbols At phases 52-55 and 66 in CE Her and phases 54 and 82 in XX Vir, the scatter between different cycles is large compared with the error bars We note that at this magnitude level and fainter our internal errors for other stars realistically represent the scatter in the light curves There are also bumps and dips in the light curves which seem to repeat from cycle to cycle For example, there is a local maximum at phase 8 in CE Her which is established by three V - CE Her } y9 Y t 1 ~ 12'8 t- t 12'5 +t t + + i 12 6 f- t i f xx Vir - d 5 6 7 '8 Phose 12'6 y+ } +t + }~ + } ~ 12 7r- V 12 7rt # H Figure 8 Expanded plots of the last part of declining light in CE Her and XX Vir When only ne point is present for a particular night, it is plotted as a fill~d circle Otherwise, each night is represented by a different symbol '7 -

1988MNRAS235159L 172 C Loomis, E G Schmidt and N R Simon concordant data points which are also well determined The dip near phase 6 is also significant Looking at the expanded light curve for XX Vir we see that the behaviour is not so well delineated but is consistent with what we see in CE Her This behaviour is complex and can be interpreted in various ways t is possible to draw several straight lines through the variation ofce Her with breaks near phases 54,63 and 79 On the other hand, we might consider the bumps, dips and intervals of excessive scatter to be small, relatively rapid fluctuations about a smooth overall decline n any event, we suggest that this behaviour is indicative of the pulsational properties of these stars and should be pursued further 36 BB Gem Based on its location, Diethelm (1983) considers this star to be a classical Cepheid Fourier coefficients derived from our light curve (Fig 7) are listed in Table 1 Plotting these in the Fourier diagrams for both the type (Simon 1986) and classical (Simon & Moffett 1985) Cepheids we find the phases 1/>(21),1/>(31) and 1/>(41) to be discrepant with type stars of similar period such as UX Nor and V 465 Oph On the other hand, the Fourier parameters for BB Gem fit extremely well with the sequence of classical Cepheids Thus, the Fourier decomposition strongly supports Diethelm's classification Since the well studied classical Cepheid SU Cas (P=195 day) is almost certainly an overtone pulsator (Gieren 1982; Aikawa, Antonello & Simon 1987), BB Gem becomes the shortest period fundamental mode pulsator known among the classical Cepheids in the Galaxy Acknowledgements Three of the stars were taken from a list of pulsating variables with periods near 8 day compiled by T J Teays This provedvery useful in setting up our program and we are grateful to him for providing it The phase dispersion minimization program used in this project was kindly supplied by R F Stellingwerf References Aikawa, T, Antonello, E & Simon, N R 1987 Astr Astrophys, 181,25 Diethelm, R, 1983 Astr Astrophys, 124,18 Diethelm, R, 1986 Astr Astrophys Suppl, 64,261 Gieren, W, 1982 Publs astr Soc Pacif, 94,36 Harris, H c, 1981 Astr J, 86,719 Harris, H C & Wallerstein, G, 1984 Astr J, 89,379 Landolt, A U, 1983 Astr J, 88,439 Lub, J, 1977 Astr Astrophys Suppl, 29,345 Peterson, J O & Diethelm, R, 1986, Astr Astrophys, 156,337 Preston, G W, 1959 Astrophys J, 13,57 Schmidt, E G, 1988 Proc Ninth Annual Fairborn-Smithsonian-APPP Symposium, ed Hayes, D, Fairborn Observatory Press Simon, N R, 1986 Astrophys J, 311,35 Simon, N R & Lee, A S, 1981 Astrophys J, 248,291 Simon, N R & Moffett, T J, 1985 Publs Astr Soc Pacif, 97, 178 Simon, N R & Teays, T J, 1982 Astrophys J, 261,586 Stellingwerf, R F, 1978 Astrophys J, 224,953 Taylor, D J, 198 Pubis astr Soc Pacif, 92, 18 Teays, T J & Simon, N R, 1985 Astrophys J, 29,683 Wallerstein, G & Cox, A N, 1984 Publs astr Soc Pacif, 96,677 Zinn, R & Dahn, C c, 1976 Astr J, 81,527