PHOTOELECTRIC OBSERVATIONS OF AN SERPENTIS SUMMARY Three-colour photoelectric photometry of the RRab star AN Serpentis is presented. The period change of the star is investigated. No light curve variation or non-repetitive behaviour were noted during the time interval covered by our observations. INTRODUCTION The light variation of AN Serpentis = 45.1935 was discovered by HOFFMEISTER (1935) and its type and period were first determined by SOLOVIEV (1935). Since the time of its discovery several observers have investigated the variable visually and photographically (SOLOVIEV 1936a, b, 1940a, b; PRAGER 1941; van SCHEWICK 1942; GAPOSCHKIN 1952; PAYNE-GAPOSCHKIN 1954; ALANIJA 1954; BATYREV 1957, 1964; TSESSEVICH 1966) and photoelectrically (SPINRAD 1959, 1961; FITCH et al. 1966; STURCH 1966; SZEIDL 1968; BASU 1968). JOY (1950) measured the radial velocity of the star and found a value of -60 km/sec for its normal radial velocity. From his visual observations BATYREV (1957) came to the conclusion that the star had Blazhko-effect with a period of 22.94 days. His result was, however, uncertain because of the large scattering of the visual observations. Furthermore, it also seemed curious that an RRab star with high metal abundance like AN Serpentis (Delta s=O, PRESTON 1959) had light curve variation. As can be seen from Table 1 the RR Lyrae stars with Blazhko-effect generally have a rather low metal abundance. (SW And is the only exception which is a very strangely behaving RRab star with temporary Blazhko-effect.) In order to disentangle this problem and to investigate the light curve variation suspected by BATYREV we commenced observing AN Serpentis in 1967. Since that time we have collected a large number of photoelectric observations in U, B and V which contradict BATYREV's result. AN Serpentis has not shown Blazhko-effect during the time interval of our observations at least. Table 1 RR Lyrae stars with Blazhko-effect in case the secondary period and Delta s are known Star Type P_0 P_B Delta s TV Boo c 0.313d 33.5d 8 RS Boo ab 0.377 537 2 RU Psc c 0.390 28.8 7 RR Gem ab 0.397 37 3 SW And ab 0.442 36.8 0 RW Dra ab 0.443 41.7 3 RV Cap ab 0.448 225.5 6 XZ Cyg ab 0.467 57.3 6 RV UMa ab 0.468 91 8 AR Her ab 0.470 31.5 6 XZ Dra ab 0.476 78 3 RZ Lyr ab 0.511 116.7 9 SZ Hya ab 0.537 25.8 6: UV Oct ab 0.543 80 9 TT Cnc ab 0.563 89 7 RR Lyr ab 0.567 40.8 6 AR Ser ab 0.575 105 8: DL Her ab 0.592 33.6 6: AT And ab 0.617 82.7 3 Z CVn ab 0.654 22.7 8: OBSERVATIONS Our photoelectric observations were made at both the Konkoly Observatory and the Catania Observatory. 1. At the Konkoly Observatory a total of 396 observations in yellow light, 390 observations in blue light and 193 observations in ultraviolet light were obtained during 17 nights in the years 1967, 1968 and 1971. These observations were made with the photoelectric photometer attached to the 24" reflector of the Konkoly Observatory. The photometer employed an unrefrigerated EMI 9502 B photomultiplier and the following Schott filters: 2 mm UG 1 for ultraviolet light; 1 mm BG 12 plus 2 mm GG 13 for blue light and 2 mm GG 11 for yellow light. A nearby comparison star was observed with AN Serpentis, and 3 nights this comparison star, BD +13 3025 (9.5), was tied to the Johnson and Morgan UBV system by observations of standard stars. The results for BD +13 3025 are as follows: V = 10.66 B - V = +0.63 U - B = +0.17 The U - B, B - V colours of the comparison star fit well the standard U - B, B - V relation for main sequence stars. According to the Sp, B - V relation the star is of spectral type G2V. Very likely STURCH (1966) and BASU (1968) used the same comparison star since the photometric data of their comparison star agree very well with the data given above. They give the following photometric values for their comparison star: STURCH BASU V = 10.682 and 10.670 B - V = +0.637 and +0.625 U - B = +0.187 All the observations of the variable obtained at the Konkoly Observatory are reduced to the time of observations in yellow. Corrections for differential extinction were usually made with extinction coefficients determined for the particular night from the comparison star. On a few occasion a mean extinction coefficient was adopted. Observations of standard stars were used to transform the differential magnitudes and colours in instrumental system to the UBV system. These tie-in observations were made on several good and uniform nights and indicated that Delta V = Delta y + epsilon Delta (B - V) Delta (B - V) = mu Delta (b - y) Delta (U - B) = psi Delta (u - b) where the small letters refer to instrumental quantities reduced to no atmosphere, and epsilon, mu and psi are the scale factors. The scale coefficients derived on different nights of tie-in observations showed some small variations which probably resulted from instrumental and temperature effects, uncertain extinction terms and observational errors. In Table 2 the observations of AN Serpentis on UBV system obtained at the Konkoly Observatory are listed. The magnitude differences are given as variable minus comparison (BD +13 3025). 2. At the Catania Observatory the observations were taken with the 61 cm Cassegrain reflector equipped with a standard three-colour photometer containing an unrefrigerated EMI 6256 photomultiplier tube. In 1970 during two nights 97 observations of AN Serpentis were obtained, 40 in yellow, 40 in blue and 17 in ultraviolet light. As comparison star we used BD +13 3026 (9.5). According to our tie-in observations its brightness and colours are as follows: V = 10.51 B - V = +0.94 U - B = +0.64 Table 2 J.D. Phase Delta Delta Delta J.D. Phase Delta Delta Delta 2400000+ V (B-V) (U-B) 2400000+ V (B-V) (U-B) 39527.6413 .8687 +.679 -.067 39538.6408 .9376 +.168 -.366 -.093 .6461 .8779 .652 .079 .6429 .9416 .143 .366 .081 .6475 .8805 .633 .092 .6471 .9496 .110 .367 .091 .6510 .8872 .632 .148 .6492 .9536 +.079 .375 -.039 .6524 .8899 .624 .155 .6533 .9615 -.003 .450 +.009 .6566 .8980 .571 .174 .6554 .9655 .068 .429 -.012 .6580 .9006 .542 .193 .6595 .9734 .163 .409 +.018 .6607 .9058 .475 .262 .6616 .9774 .192 .400 +.018 .6621 .9085 .453 .232 .6658 .9854 .223 .450 -.015 .6642 .9125 .409 .253 .6679 .9895 .239 .442 .061 .6656 .9152 .374 .246 .6721 .9975 .263 .459 .047 .6677 .9192 .351 .289 .6742 .0015 .273 .443 .038 .6691 .9219 .324 .253 .6783 .0094 .277 .400 .040 .6711 .9257 .246 .251 .6804 .0134 .261 .440 .001 .6725 .9284 .208 .245 .6845 .0213 .233 .470 .014 .6746 .9324 .173 .271 .6866 .0253 .234 .438 -.022 .6760 .9351 .140 .282 .6908 .0333 -.228 -.410 .6781 .9391 .110 .316 .6795 .9419 .106 .320 39547.5203 .9457 +.107 -.342 .6816 .9459 .095 .332 .5217 .9484 .059 .307 .6829 .9483 .077 .318 .5245 .9538 +.003 .310 .6850 .9524 .058 .383 .5286 .9616 -.031 .396 .6864 .9550 +.028 .371 .5300 .9643 .046 .447 .6885 .9591 -.036 .373 .5342 .9723 .095 .476 .6899 .9618 .055 .377 .5369 .9775 .131 .470 .6920 .9658 .091 .376 .5384 .9804 .154 .495 .6934 .9685 .144 .338 .5412 .9858 .202 .479 .6954 .9723 .163 .366 .5426 .9884 .231 .458 .6968 .9750 .168 .401 .5453 .9936 .238 .479 .6989 .9790 .186 .414 .5467 .9963 .243 .472 .7003 .9817 -.219 -.395 .5495 .0016 .236 .483 .5509 .0043 .236 .472 39537.6230 .9880 -.212 -.477 .5536 .0095 .232 .476 .6244 .9907 .213 .497 .5550 .0122 .239 .456 .6272 .9961 .247 .439 .5578 .0175 .235 .418 .6286 .9987 .270 .437 .5592 .0202 -.222 -.407 .6314 .0041 .239 .478 .6356 .0122 .221 .465 39560.5605 .9235 +.301 -.260 .6370 .0148 .259 .442 .5723 .9461 .080 .309 .6397 .0200 .227 .433 .5737 .9487 +.047 .307 .6411 .0227 -.214 -.439 .5946 .9888 -.246 .421 .6015 .0020 .215 .476 39538.6095 .8776 +.645 -.098 -.052 .6029 .0047 .246 .453 .6116 .8816 .626 .110 .078 .6057 .0100 .245 .436 .6158 .8897 .618 .220 .017 .6071 .0127 -.229 -.444 .6179 .8937 .606 .253 .029 .6221 .9017 .554 .273 -.015 39562.5232 .6829 +.643 -.083 -.061 .6242 .9058 .481 .257 +.005 .5253 .6869 .645 .083 .073 .6283 .9136 .397 .223 -.090 .5295 .6950 .635 .074 .049 .6304 .9176 .358 .277 .130 .5316 .6990 .652 .046 .087 .6345 .9255 .266 .290 .159 .5357 .7068 .638 .018 .081 .6366 .9295 +.221 -.314 -.135 .5378 .7109 +.644 -.022 -.013 Table 2 (continued) J.D. Phase Delta Delta Delta J.D. Phase Delta Delta Delta 2400000+ V (B-V) (U-B) 2400000+ V (B-V) (U-B) 39562.5420 .7189 +.664 -.021 -.044 39611.4916 .4790 +.529 -.170 +.011 .5441 .7229 .667 .027 -.026 .4958 .4870 .519 .131 -.032 .5482 .7308 .669 .072 +.001 .4999 .4949 .523 .131 -.060 .5503 .7348 .667 .063 -.051 .5020 .4989 .525 .161 .000 .5545 .7428 .698 .094 .040 .5062 .5070 .527 .161 +.013 .5566 .7469 .707 .085 .011 .5083 .5110 .512 .142 -.011 .5607 .7547 .708 .094 .031 .5134 .5207 .511 .122 -.028 .5628 .7587 .692 .081 .003 .5249 .5428 .518 .086 .5670 .7668 .704 .065 .015 .5305 .5535 .530 .111 +.003 .5732 .7787 .699 .037 .019 .5384 .5686 .509 .086 -.005 .5753 .7827 .708 .076 .012 .5437 .5788 .515 .066 +.016 .5795 .7907 .694 .048 -.008 .5458 .5828 .519 .071 -.022 .5816 .7948 .711 .067 .000 .5499 .5907 .531 .079 .025 .5857 .8026 .723 .059 -.007 .5520 .5947 .543 .094 .037 .5878 .8066 .708 .037 .015 .5562 .6027 .559 .105 .038 .5920 .8147 .710 .033 .007 .5583 .6067 .572 .096 -.044 .5941 .8187 .713 .031 .023 .5624 .6146 .602 .109 .5982 .8266 .715 .046 .020 .5645 .6186 .569 .093 .6003 .8306 .719 .057 -.039 .5687 .6267 .600 .102 .6045 .8386 .722 .057 +.007 .5708 .6307 .610 .088 .6066 .8426 .698 .021 -.054 .5749 .6385 .595 .091 -.009 .6107 .8505 .712 .040 .058 .5770 .6426 .601 .077 .056 .6128 .8545 .721 .040 .074 .5812 .6506 .603 .079 .014 .6177 .8639 .705 .033 .022 .5833 .6546 .621 .108 .020 .6198 .8679 .684 .035 .030 .5874 .6625 .595 .073 .020 .6281 .8838 +.646 -.142 -.034 .5895 .6665 +.610 -.064 -.059 39570.5390 .0367 -.178 -.479 +.011 39617.4375 .8680 +.724 -.087 .5411 .0407 .175 .471 -.007 .4416 .8759 .662 .071 .5464 .0509 .152 .453 .018 .4437 .8799 .646 .076 -.085 .5515 .0606 .134 .428 .038 .4479 .8879 .638 .179 -.040 .5536 .0647 .121 .439 .044 .4499 .8918 .620 .146 .5578 .0727 .118 .397 .071 .4541 .8998 .539 .163 -.003 .5599 .0767 -.100 -.404 -.050 .4562 .9038 .518 .170 -.014 .4604 .9119 .405 .235 39600.4766 .3804 +.405 -.143 -.077 .4625 .9159 .353 .229 +.008 .4787 .3844 .407 .182 .035 .4666 .9238 .292 .314 -.074 .4829 .3925 .430 .189 .040 .4687 .9287 .238 .259 .099 .4850 .3965 .439 .171 .069 .4729 .9358 .161 .288 .124 .4891 .4043 .447 .184 .044 .4750 .9398 .120 .304 .174 .4912 .4084 .444 .190 .051 .4791 .9477 .074 .287 .166 .4954 .4164 .442 .183 -.026 .4812 .9517 .056 .320 .146 .4975 .4204 +.463 -.204 +.036 .4854 .9598 +.008 .379 .073 .4874 .9636 -.022 .399 .071 39611.4385 .3773 +.381 -.140 -.084 .4916 .9716 .121 .390 .103 .4687 .4351 .479 .131 .076 .4937 .9757 .162 .383 .115 .4708 .4391 .466 .121 .037 .4979 .9837 .217 .431 .098 .4759 .4489 .480 .125 .028 .4999 .9875 .234 .439 .079 .4812 .4591 .508 .163 .032 .5041 .9956 .236 .448 .091 .4833 .4631 .515 .161 .030 .5062 .9996 .233 .444 .103 .4874 .4709 +.534 -.200 -.003 .5104 .0076 -.240 -.422 -.114 Table 2 (continued) J.D. Phase Delta Delta Delta J.D. Phase Delta Delta Delta 2400000+ V (B-V) (U-B) 2400000+ V (B-V) (U-B) 39617.5124 .0115 -.235 -.437 -.084 39967.4402 .2776 +.251 -.271 .5166 .0195 .220 .429 .068 .4423 .2817 .281 .265 .5187 .0235 .215 .447 .043 .4465 .2897 .279 .226 -.035 .5229 .0316 .190 .462 .037 .4486 .2937 .265 -.182 -.028 .5249 .0354 .185 .445 .033 .4527 .3016 .280 .5291 .0435 .189 .416 .062 .4548 .3056 .310 -.219 -.015 .5312 .0475 .169 .431 .066 .4590 .3137 .318 .249 -.009 .5354 .0555 .155 .411 .112 .4611 .3177 .326 .246 +.008 .5374 .0594 .157 .390 .084 .4652 .3255 .336 .262 .5416 .0674 .130 .388 .087 .4673 .3295 .347 .251 -.031 .5437 .0714 .119 .366 .115 .4715 .3376 .373 .227 .054 .5479 .0795 .104 .373 .021 .4757 .3456 .419 .223 .059 .5499 .0833 .096 .368 .036 .4819 .3575 .417 .196 .017 .5541 .0914 .091 .339 .053 .4861 .3656 .401 .190 .046 .5562 .0954 .067 .342 .033 .4902 .3734 .387 .166 .031 .5604 .1034 .026 .370 -.018 .4923 .3774 .399 .188 .042 .5624 .1073 .015 .393 +.018 .4965 .3855 .433 .188 .061 .5666 .1153 -.007 .381 +.019 .4986 .3895 .444 .207 .002 .5687 .1193 +.006 .371 -.015 .5027 .3974 .425 .160 .029 .5729 .1274 .005 .312 -.027 .5048 .4014 .420 .145 -.020 .5749 .1312 .015 .331 +.009 .5090 .4094 .446 .179 .5791 .1392 .037 .339 +.011 .5111 .4134 .461 .156 +.008 .5812 .1433 +.055 -.327 -.025 .5152 .4213 .470 .184 +.004 .5173 .4253 .449 .151 -.032 39673.4461 .1492 +.049 -.300 -.071 .5236 .4374 .466 .110 -.043 .4482 .1532 .063 .305 .062 .5277 .4452 .490 .157 +.010 .4523 .1611 .069 .314 -.012 .5298 .4493 .484 .142 -.012 .4544 .1651 .083 .335 +.002 .5340 .4573 .483 .132 .038 .4593 .1745 .073 .312 -.006 .5361 .4613 .479 .104 .082 .4614 .1785 .075 .266 .040 .5402 .4692 .479 .127 .047 .4655 .1864 .122 .290 .046 .5423 .4732 .495 .146 .042 .4676 .1904 .142 .293 .052 .5465 .4813 .505 .142 .038 .4725 .1998 .165 .284 -.053 .5486 .4853 .507 .132 .015 .4787 .2116 .185 .331 .5527 .4931 .536 .179 .026 .4808 .2157 .171 .317 .5548 .4972 .510 .131 -.027 .4850 .2237 .180 .325 .5590 .5052 .478 .119 +.027 .4863 .2262 .196 -.320 .5611 .5092 .495 .141 +.024 .4891 .2316 .199 .5652 .5171 .492 .116 -.021 .4905 .2343 .203 -.310 .5673 .5211 .504 .128 +.002 .4933 .2396 .234 .283 .5715 .5291 .530 .160 +.011 .4947 .2423 .229 .297 .5736 .5332 .508 .151 -.009 .4989 .2503 .241 .296 .5777 .5410 .501 .110 .015 .5016 .2555 .220 -.246 .5798 .5450 .514 .109 .040 .5030 .2582 .223 .5840 .5531 .527 .132 .038 .5120 .2754 .227 -.235 .5861 .5571 +.523 -.128 -.023 .5148 .2808 .271 .233 .5162 .2835 .275 .231 39996.4787 .8992 +.551 -.275 .5190 .2888 .260 .239 .4801 .9019 .521 .277 .5204 .2915 .275 .215 .4829 .9072 .494 .287 .5231 .2967 .271 .214 .4843 .9099 .476 .282 .5245 .2994 +.257 -.210 .4870 .9151 +.406 -.284 Table 2 (continued) J.D. Phase Delta Delta Delta J.D. Phase Delta Delta Delta 2400000+ V (B-V) (U-B) 2400000+ V (B-V) (U-B) 39996.4884 .9178 +.353 -.323 41096.4972 .9201 +.341 -.237 .4912 .9231 .294 .299 .5014 .9281 .270 .301 .4926 .9258 .258 .270 .5028 .9308 .226 .288 .4982 .9365 .162 .345 .5042 .9335 .216 .286 .4996 .9392 .109 .341 .5069 .9386 .149 .319 .5023 .9444 .066 .315 .5083 .9413 .125 .293 .5037 .9471 .050 .294 .5097 .9440 .131 .310 .5065 .9524 .042 .299 .5111 .9467 .122 .310 .5079 .9551 +.026 .310 .5159 .9559 .035 .294 .5141 .9670 -.108 .353 .5180 .9599 +.009 .308 .5155 .9697 .121 .437 .5222 .9679 -.060 .346 .5183 .9750 .175 .388 .5243 .9720 .076 .390 .5197 .9777 .198 .426 .5284 .9798 .167 .367 .5225 .9831 .228 .431 .5305 .9838 .220 .387 .5239 .9858 .231 .456 .5347 .9919 .234 .427 .5266 .9909 .226 .472 .5368 .9959 .223 -.440 .5280 .9936 .233 .485 .5534 .0277 .236 .5308 .9990 .221 .514 .5555 .0317 -.221 .5322 .0017 .223 .512 .5357 .0084 .224 .488 41117.3824 .9244 +.285 -.233 .5371 .0110 .226 -.469 .3845 .9285 .204 .264 .5398 .0162 .247 .451 .3970 .9524 .035 .387 .5412 .0189 .230 .440 .3984 .9551 +.011 .397 .5440 .0243 .234 .426 .4011 .9603 -.063 .359 .5454 .0269 .226 .431 .4025 .9629 .088 .378 .5482 .0323 .206 .463 .4039 .9656 .130 .392 .5496 .0350 .194 .467 .4074 .9723 .146 .395 .5523 .0402 -.202 -.451 .4088 .9750 .167 .433 .4102 .9777 .168 .454 41095.5059 .0213 -.212 -.450 .4136 .9842 .207 .422 .5080 .0253 .203 .453 .4150 .9869 .219 .448 .5121 .0332 .200 .447 .4164 .9896 .226 .441 .5142 .0372 .191 .426 .4254 .0068 .226 .470 .5184 .0452 .196 .413 .4268 .0095 .240 .472 .5212 .0506 .181 .398 .4331 .0215 .243 .449 .5253 .0584 .152 .399 .4345 .0242 .215 .474 .5274 .0625 .149 .381 .4359 .0269 .212 .477 .5315 .0703 .126 .386 .4386 .0321 -.173 -.454 .5336 .0743 -.114 -.356 41119.4846 .9511 +.071 -.371 41096.4722 .8722 +.682 -.112 .4860 .9538 .045 .364 .4736 .8749 .689 .122 .4874 .9564 +.003 .329 .4750 .8775 .690 .127 .4888 .9591 -.029 .356 .4764 .8802 .669 .123 .4923 .9658 .094 .340 .4791 .8854 .652 .158 .4937 .9685 .118 .340 .4805 .8881 .645 .201 .4951 .9712 .141 .382 .4819 .8908 .620 .222 .4965 .9739 .154 .383 .4833 .8934 .588 .183 .5041 .9884 .192 .424 .4861 .8988 .549 .180 .5055 .9911 .201 .451 .4875 .9015 .511 .189 .5068 .9936 .222 -.418 .4944 .9147 .383 .232 .5082 .9963 -.235 .4958 .9174 +.366 -.235 Table 3 Observations at Catania J.D. Phase Delta m J.D. Phase Delta m J.D. Phase Delta m 2440000+ 2440000+ 2440000+ in yellow 707.5424 .9000 +.655 707.5897 .9906 -.148 718.5095 .9068 +.580 .5477 .9101 .565 .5949 .0005 .178 .5134 .9143 .475 .5508 .9161 .478 .5970 .0046 .183 .5195 .9260 .340 .5550 .9241 .360 .6011 .0124 .185 .5224 .9315 .275 .5569 .9277 .303 .6036 .0172 .173 .5285 .9432 .218 .5611 .9358 .233 .6078 .0252 .185 .5329 .9516 +.153 .5632 .9398 .200 .6118 .0329 .153 .5412 .9675 -.001 .5673 .9477 .173 .6150 .0390 -.113 .5530 .9901 .165 .5696 .9521 .148 .5599 .0033 .178 .5738 .9601 .078 718.4799 .8501 +.860 .5632 .0097 .170 .5761 .9645 +.048 .4874 .8645 .875 .5702 .0231 .160 .5804 .9728 -.040 .4909 .8712 .815 .5737 .0298 .148 .5824 .9766 .060 .4992 .8871 .768 .5799 .0417 -.120 .5873 .9860 -.113 .5030 .8944 +.688 in blue 707.5468 .9084 -.010 707.5939 .9986 -.938 718.5084 .9047 +.048 .5490 .9126 .035 .5960 .0026 .958 .5124 .9124 -.095 .5541 .9224 .198 .6001 .0105 .923 .5186 .9242 .255 .5561 .9262 .290 .6022 .0145 .923 .5215 .9298 .353 .5600 .9337 .410 .6067 .0231 .930 .5274 .9411 .460 .5620 .9375 .443 .6089 .0273 .890 .5311 .9482 .520 .5661 .9454 .473 .6126 .0344 .868 .5403 .9658 .720 .5687 .9503 .535 .6188 .0463 -.825 .5519 .9880 .913 .5728 .9582 .608 .5588 .0012 .935 .5750 .9624 .665 718.4809 .8520 +.428 .5621 .0076 .935 .5789 .9699 .740 .4866 .8629 .373 .5690 .0208 .928 .5815 .9749 .800 .4899 .8693 .368 .5728 .0281 .920 .5859 .9833 .888 .4982 .8852 .293 .5789 .0397 -.888 .5888 .9888 -.883 .5019 .8922 +.210 in ultraviolet 718.4857 .8612 -.105 718.5174 .9219 - .780 718.5574 .9986 -1.645 .4887 .8670 .123 .5204 .9277 .915 .5610 .0055 1.650 .4968 .8825 .233 .5259 .9382 1.100 .5677 .0183 1.600 .5005 .8896 .288 .5301 .9463 1.098 .5714 .0254 1.615 .5072 .9024 .433 .5377 .9608 1.248 .5777 .0374 -1.583 .5107 .9091 -.573 .5484 .9813 -1.488 The individual observations in instrumental system are given in Table 3 in the sense variable minus comparison (BD +13 3026). The phases of observations obtained at both the Catania Observatory and the Konkoly Observatory have been calculated by using the formula: phase = (J.D. - 2439538.6734)/0.5220729 LIGHT AND COLOUR CURVES Composite light curve in V is shown in Figure 1. In order to make a more precise analysis of the light and colour curves possible 44 normal points were obtained in V and in both colours which are tabulated in Table 4. Since most of the observations were collected on the ascending branch and near the maxima of the variable, the light curve was not uniformly covered. Therefore, the normal points are not chosen at equal intervals but rather as determined by groups of yellow observations of equal number. Each normal point was formed from nine yellow observations and the colours belonging to these yellow observations. The normal points are plotted against phase in Figure 2. The light and colour curves are very regular and typical of the class of variables which AN Serpentis belongs to.
Figure 1. Light curve of AN Serpentis
Figure 3 shows the observations at Catania Observatory plotted
against phase.
Both Figure 1 and Figure 3 clearly indicate that no irregularities
or non-repetitive behaviour as reported by BATYREV (1957) could
be detected during the time interval covered by our observations.
Figure 2. Normal points as function of phase
Nevertheless, it is possible that the star might have had Blazhko-effect
and then it disappeared. At present there is no doubt about the
stable character of AN Serpentis.
The hump on the ascending branch of AN Ser is conspicuous in
both Figure 2 and Figure 3. The duration of the hump fits well into
the relation found by DETRE (1959) between the duration of the hump and
the visual light amplitude of different RR Lyrae stars.
SPINRAD (1959) observed an unusual hump on the declining
branch of the variable. BASU (1968), however, showed that the suspected
hump was unreal. Our light curves also confirm BASU's result, there is
no unusual hump on the declining branch of AN Serpentis in the phase
region O.20p < Phi < O.40p
Figure 3. Observations obtained at the Catania Observatory
The two-colour diagram of AN Serpentis is shown in Figure 4.
The dashed line represents the main sequence. The phases of AN Ser are
shown as numbers on the loop, with zero phase being that of maximum in
V light. The loop for the variable lies below the luminosity class V
line at all phases. This depression of the loop below the main sequence
has already been noted by SPINRAD (1959) who attributes the effect to
absorption-line blanketing in the ultraviolet as the high galactic
latitude of the variable (bII = 45.02 deg) makes any large amount of
interstellar reddening very unlikely.
Figure 4. Two-colour diagram for AN Serpentis. Phases are
shown as numbers on the loop, with zero phase being that
of maximum light.
Table 4
Normal points
Phase Delta V n Delta (B-V) n Delta (U-B) n
0.0054p -0.236 9 -0.463 9 -0.077 2
.0113 .236 9 .455 9 .043 2
.0189 .232 9 .438 9 .041 2
.0245 .222 9 .448 9 .033 2
.0325 .204 9 .450 7 .035 2
.0436 .181 9 .438 9 .028 5
.0634 .138 9 .399 9 .080 6
.0870 -0.081 9 .371 9 .033 8
.1377 +0.032 9 .331 9 .017 9
.1940 .133 9 .306 9 -0.032 6
.2459 .219 9 .284 7 0
.2871 .270 9 .231 9 -0.031 2
.3196 .330 9 .236 8 .027 6
.3768 .408 9 .178 9 .044 9
.4044 .439 9 .173 9 .034 8
.4358 .472 9 .147 9 .020 9
.4683 .503 9 .149 9 .033 9
.4975 .513 9 .143 9 .011 9
.5290 .510 9 .125 9 .014 8
.5758 .528 9 .097 9 .019 9
.6315 .597 9 .094 9 .029 5
.6922 .636 9 .054 9 .054 9
.7486 .690 9 .069 9 .022 9
.8076 .711 9 .050 9 .015 9
.8585 .703 9 .055 9 .038 6
.8784 .657 9 .100 9 .072 3
.8883 .633 9 .175 9 .030 3
.8985 .557 9 .209 9 .016 3
.9075 .470 9 .251 9 .005 2
.9163 .371 9 .260 9 .071 3
.9238 .290 9 .267 9 .117 2
.9306 .211 9 .279 9 .117 2
.9388 .139 9 .326 9 .118 4
.9455 .092 9 .313 9 .166 1
.9506 .062 9 .340 9 .118 2
.9553 +0.022 9 .347 9 .039 1
.9612 -0.030 9 .377 9 .045 3
.9665 .095 9 .373 9 .012 1
.9721 .131 9 .403 9 .042 2
.9767 .172 9 .419 9 .048 2
.9831 .204 9 .429 9 .056 2
.9881 .226 9 .445 9 .070 2
.9930 .225 9 .457 9 .091 1
0.9985 -0.247 9 -0.461 8 -0.063 3
Table 5 summarizes the most important photometric data for
AN Serpentis.
Table 5
V B U B - V U - B
maximum 10.42 10.57 10.69 +0.15 +0.12
mean 10.97 11.35 11.49 +0.38 +0.14
minimum 11.38 11.97 12.11 +0.59 +0.14
amplitude 0.96 1.40 1.42 0.44 -
The mean values of the colour indices are <B - V> = +0.41
and <U - B> = +0.14, while PRESTON's quantities for the U - B excess
on the rising branch: delta_1 = 0.13 and delta_2 = 0.13. The interval
between minimum and maximum, divided by the period is epsilon = 0.16p
while the time from hump to maximum expressed in period is
epsilon* = O.06p.
PERIOD CHANGES AND O - C DIAGRAM
All the maxima published and known to us are listed in Table
6. In addition to the reference where the maxima observed were published
we denoted the kind of observations: vis=visual, pg=photographic,
and pe=photoelectric.
The O - C values have been calculated by using the formula:
C = J.D. 2414708.9500 + 0.52207162d*E
Having scrutinized our photoelectric blue and yellow light
curves we have not found any measurable phase lag between them. Therefore
we have not applied any corrections to the visual or photographic maxima.
For all the photoelectric observations do not exhibit any
sign of light curve variation we have formed a mean value of O - C's
for each year. These average O - C values are plotted against Julian
Days in Figure 5. If we do not question the very uncertain observation
at J.D. 2426122 we can conclude from the O - C diagram that the period
of AN Serpentis decreased by 0.00001 day around J.D. 2428000. A slight
increase of the period might take place in the last 20 years.
Figure 5. O - C diagram for AN Serpentis
Table 6
Year J.D. 24... Reference O-C E mean(O-C) mean(E)
1899 14708.950 Payne-G.(1954) pg .0000 0 .0000 0
1930 26122.464 Soloviev(1936a) " -.0158 21862 -.0158 21862
1934 27462.673 v.Schewick(1942) " +.0354 24429 +.0141 24580
463.686 " " +.0043 24431 (6)
521.635 " " +.0033 24542
543.546 " " -.0127 24584
599.461 " " +.0406 24691
657.384 " " +.0137 24802
1935 874.620 " " +.0679 25218 +.0294 25471
931.487 " " +.0291 25327 (13)
953.453 " " +.0681 25369
955.488 " " +.0148 25373
28007.193 Soloviev(1935) vis +.0347 25472
010.311 Soloviev(1936a) " +.0203 25478
011.346 " " +.0111 25480
021.266 " " +.0118 25499
033.263 " " +.0011 25522
043.208 " " +.0268 25541
045.337 v.Schewick(1942) pg +.0675 25545
046.331 " " +.0173 25547
155.438 Soloviev(1936b) vis +.0114 25756
1936 219.688 v.Schewick(1942) pg +.0465 25879 +.0309 26095
245.265 Soloviev(1936a) vis +.0420 25928 (12)
256.227 " " +.0405 25949
280.219 " " +.0172 25995
308.430 v.Schewick(1942) " +.0364 26049
332.444: " " +.0351 26095
333.472 " " +.0189 26097
369.513 " " +.0370 26166
391.433 " " +.0300 26208
403.423: " " +.0123 26231
Table 6 (continued)
Year J.D. 24... Reference O-C E mean(O-C) mean(E)
1936 28424.326 v.Schewick(1942) vis +.0325 26271
425.360 " " +.0223 26273
1937 609.131 Soloviev(1940b) " +.0241 26625 +.0241 26625
1938 29156.260 Soloviev(1940a) " +.0221 27673 +.0221 27673
1944 31235.149 Tsessevich(1966) " +.0219 31655 +.0219 31655
1951 33876.303 Batyrev (1957 " +.0155 36714 +.0209 36750
886.233 " " +.0262 36733 (7)
887.271 " " +.0200 36735
898.235 " " +.0205 36756
899.283 " " +.0244 36758
909.202 " " +.0240 36777
910.238 " " +.0159 36779
1952 34128.466 " " +.0180 37197 +.0131 37316
149.344 " " +.0131 37237 (6)
174.410 " " +.0196 37285
184.331 " " +.0213 37304
242.265 " " +.0053 37415
265.232 " " +.0012 37459
1953 515.341 " " +.0379 37938 +.0214 38051
540.403 Alanija(1954) pg +.0404 37986 (5)
562.305 Batyrev (1957 vis +.0154 38028
621.288 " " +.0043 38141
632.256 " " +.0088 38162
1954 986.234 " " +.0223 38840 +.0223 38840
1955 35248.312 " " +.0203 39342 +.0225 39367
274.420 " " +.0247 39392 (2)
1956 606.445 Batyrev (1964) " +.0122 40028 +.0060 40065
628.359 " " -.0008 40070 (4)
629.397 " " -.0070 40072
639.343 " " +.0197 40091
1957 928.552 " " +.0010 40645 +.0126 40745
993.339 " " +.0511 40769 (4)
995.373 " " -.0032 40773
36005.297 " " +.0015 40792
1959 660.497 Tsessevich(1966) pg +.0016 42047 +.0016 42047
1962 37817.400 " " -.0061 44263 -.0061 44263
1963 38205.308 " vis +.0027 45006 -.0055 45068
229.314 " " -.0066 45052 (4)
252.281 " " -.0108 45096
264.292 " " -.0074 45119
1965 845.891 Fitch et al.(1966) pe +.0038 46233 +.0015 46336
846.933 " " +.0016 46235 (3)
39006.6845 Basu 1968) " -.0008 46541
1967 537.631: present paper " -.0011 47558 -.0022 47601
538.6745 " " -.0017 47560 (5)
547.5485 " " -.0030 47577
560.601 " " -.0023 47602
617.5060 " " -.0031 47711
1968 996.5310 " " -.0021 48437 -.0021 48437
1970 40707.5971 " " +.0025 49799 +.0022 49810
718.5600 " " +.0019 49820 (2)
1971 41117.4220 " " +.0012 50584 +.0012 50584
We are indebted to Prof. L. DETRE for drawing our attention
to this star and for useful discussions. One of us (S.K.) is grateful
to Prof. G. GODOLI for providing opportunity to observe this star at
the Catania Observatory. Our thanks are also due to Miss A. FARÁDI and
Mrs. I. KÁLMÁN for preparing the manuscript.
REFERENCES
Alanija, I.F., 1954, Astron.Circ. 146. 14
Basu, B., 1968, Publ. Astr. Soc. Pacific 80. 612
Batyrev, A.A., 1957, Peremennye Zvezdy 12. 137
1964, Peremennye Zvezdy 15. 278
Detre, L., 1959, Kleine Veröff. Bamberg Nr.27, p.23
Fitch, W.S., Wisniewski, W.Z. and Johnson, H.L., 1966, Commun. Lunar
and Planetary Laboratory No.71, Vol.5, Part 2
Gaposchkin, S., 1952, Harvard Ann. 115. 257
Hoffmeister, C., 1935, Astron. Nachr. 255. 401
Joy, A.H., 1950, Publ. Astr. Soc. Pacific 62. 60
Payne-Gaposchkin, C., 1954, Harvard Ann. 113. 153
Prager, R., 1941, Harvard Ann. 111
Preston, G.W., 1959, Astrophys. J. 130. 507
van Schewick, H., 1942, Astron. Nachr. 272, 197
Soloviev, A.V., 1935, Tadjik Observatory Circular No.1O
1936a, Tadjik Observatory Circular No.19
1936b, Tadjik Observatory Circular No.20
1940a, Tadjik Observatory Circular No.43
1940b, Peremennye Zvezdy 5. 313
Spinrad, H., 1959, Publ. Astr. Soc. Pacific 71. 542
Struck, C., 1966, Astrophys. J. 143. 774
Szeidl, B., 1968, IBVS No.291 (IBVS No. 291)
Tsessevich, V.P., 1966, RR Lyrae-Type Variable Stars (Press "Naukova-Dumka"
Kiev, in Russian) p. 118