1990 photometry of a small amplitude W UMa system LS Delphini

1990 PHOTOMETRY

OF A SMALL

SYSTEM

O. D E M I R C A N ,

AMPLITUDE

W UMA

LS DELPHINI

S. S E L A M ,

andE. DERMAN

Ankara University Observatory and Astronomy and Space Sciences Department, Faculty of Sciences, Ankara, Turkey

(Received 25 January, 1991) Abstract. Differential UBV observations, carried out in 1990 observing season, of a small amplitude (0.'Y15 in V and B) W U M a system LS Del = HD 199497 are presented. Wavelength-dependent light variations from cycle to cycle indicate that the system is in a very active phase, probably due to magnetic flare activity or mass transfer in the system. An analysis of the minima times indicate a probable secular increase of the photometric period which requires a mass transfer from less massive to more massive component. If this is true then the reverse-algol model by Liu et al. (1988) for this system would not be valid.

1. Introduction

LS Del (BD + 19~ HD 199497, A G K + 19~ was discovered as a W UMa system by Bond (1976). He obtained the amplitude of light variation of 0.15 mag and photometric period of 0.3638 days from his 24 photoelectric observations in the y-filter of StrOmgren's four-colour system. Later, the system was observed photoelectrically in B and V colours by Sezer et al. (1984), Ruyou et al. (1987), Derman et al. (1991), and only in V colour by Wieck and Wunder (1989). Two independent photometric analysis were attempted of LS Delphini. By use of the same method (Wilson-Devinney code) Sezer et al. (1985) and Liu et al. (see Leung, 1988) reached different solutions, although almost equal mass ratio (q) and orbital inclination (i) were obtained. Sezer et al.'s analysis preferred a W-type contact solution, while Liu et al. defines a semi-detached, reverse Algol model. Both solutions give very low inclination angle ( ~ 50 ~ as a result of low amplitude light variation. The light curve and period of the system varies in short time intervals. Thus the combination of low amplitude and strong, time-dependent variation of the light curve makes it almost impossible to obtain a reliable model of the system. In order to understand the nature of the light and period variations of the system, LS Del was included in the observing program of Ankara University Observatory in 1987. It was then observed in each observing season. The U B V observations carried out in 1987, 1988, and 1989 observing season have been already presented and discussed by Derman et aL (1991). The 1990 observations and comparative description &the light variation will be presented in Section 2 of this paper. The photometric period will be discussed in Section 3. The final section will be devoted to results of the four years photometry of the system.

Astrophysics and Space Science 186: 57-66, 1991. 9 1991 Kluwer Academic Publishers. Printed in Belgium.

58

O. DEMIRCAN ET AL. TABLE I The UBV observations of LD Delphini in August 1990

HJD

PHASE

DYO

DBO

DUO

2446116.35790 48116.36318 48116,36797 48116.37283 48116.38054 48116.42790 48116.43283 48116.44213 48116,44956 48116.45422 48116.46587 48116.46694 48116,47331

00003 00008 0,0084 0,0144 0.0160 0,0200 0.0219 0.0326 0,0377 0.0399 0.0454 0,0555 0.0568

-0.170 -0.I58 -0.151 -0.143 -0.125 -0,029 -0.038 -0.054 -0,069 -0.071 -0.093 -0. I10 -0.130

-0.657 -0,646 -0.636 -0.622 -0.616 -0.556 -0.553 -0,569 -0,576 -0,583 -0,591 -0,608 -0,620

-1.412 -t.416 -1.415 -I.462 -t,477 -1,144 -1.267 -1.278 -1.432 -I.439 -t.357 -~.362 -1.480

46116.47769

00604

-1.419

0,0686 0.0692 0,0732 0,0610 0,08t5 0.0921 0.0957 0,0997 0,!009 0,1067 0.1078 0.1136 0.1168 0.1200 0.1204 0.1256 0.1314 0.1326 0.1357 0.1377 0.1503 0,1507 0.1519 0.1612 0.1619 0,1626 0.1714 0.1746 0.1749 0.1807 0.1677 0.1897 0.1917 0.1948 0.2051 02067 0.2068 0,2091 0.2185

-0.137 -0.154

-0,629

48116,48227

-0.639

-1.474

-0,169 -0.188 -0,212 -0,221 -0.227 -0.228 -0.233 -0.220 -0.228 -0.224 -0.219 -0.209 -0.201 -0.188 -0.148 -0.152 -0.130 -0. I07 -0.080 -0.067 -0.059 -0.055 -0.052 -0.050 -0.053 -0.058 -0.067 -0.073 -0.078 -0.079 -0.063 -0. I17 -0, t36 -0,173 -0.170 -0.162 -0.160 -0.155

-0.649

-1.500

-0.666 -0.671 -0.695 -0.712 -0.715 -0,714 -0.711 -0,716 -0,709 -0.696 -0.681 -0,689 -0,685 -0.663 -0.662 -0.658 -0,641 -0.615 -0.596 -0.588 -0.581 -0,575 -0.567 -0.561 -0,558 -0.561 -0.562 -0,572 -0,575 -0.587 -0,617 -0.627 -0.716 -0.706 -0.707 -0.691 -0.683

-1.437 -1,591 -1,597 -1.523 -1.507 -1.407 -1.416 -1,513 -1.472 -1.526 -I.644 -1.713 -1,586 -1.210 -1.181 -1.396 -I,428 -1,344 -1.220 -1,228 -1.274 -1.227 -I.359 -1.246 -1,247 -1.296 -1.127 -1.273 -1.200 -1.284 -1.348 -1,292 -1.486 -I.372 -1.372 -1.403 -1.381,

48tt6,48651

48116:49123 46116.49588 48116.50283 48116.5083J 48116.51311 48116.51790 48116.52186 46116.52609 46116,53151 48116.53574 48116.53956 48116.54359 46116,54748 46116.55776 48116.56359 48119.47915 48119,48346 46119.48901 48119,49674 48119,50290 46119,50700 48119,51131 48119.51610 48119.52075 48119.52568 48119.53019 48119,53464 48119.53929 48119.54415 48119.54971 48119.56860 46119.57304 48122.34158 48122.34685 48122.35310 48122,35866 48122.36526

PHOTOMETRY

59

O F LS D E L P H 1 N I

Table I (continued)

HJD

PHASE

24 48122.37067 0.2218 48122.37942 0.2240 48122.36366 0,2261 48122.38763 0.2318 48122.39331 0,2350 48122,40185 0,2378 48122,40824 0,2482 48122.41435 0.2519 48122.41977 0,2543 48122.42442 0.2553 48122.43199 0.2582 48122.43678 0.2591 48122.44297 0.2668 46122,44817 0,2707 48122,45303 0.2731 48122.45652 0.2738 46122.46338 0.2763 46122.46887 0.2856 48122,47498 0,2660 48122.46047 0.2872 48122,48567 0.2947 46122.49373 0.2972 46122.50408 0.2992 46122.50824 0.3013 48122,51241 03021 48122,51658 0.3071 48122.52005 0.3077 48123.28636 0.3139 48123,29115 0.3178 48123.31643 0,3179 46123.32178 0.3188 48123.32907 0.3194 48123.33532 0.3273 48123.33845 0.3295 48123,34652 0.3311 48123.35428 0.3319 48123.36074 0.3343 48123.36553 0.3391 46123.37004 0,3479 48123.37539 0.3508 48123.57977 0,3577 48123.38421 0,3584 48123.36838 0,3607 48123.39921 0,3649 48123.40407 0,3700 48123.41032 -0.3738 48123.41518 0,3756 48123.42004 0.3763 48123.42490 0,3814 48123.43345 0,3871 48123.44018 0.3910 48123.44942 0.3924 48123.45477 0,3965 46123.45963 0,3989

DYO

DBO

DUO

-0.150 -0.130 -0,131 -0.115 -0. I00 -0.095 -0.072 -0.056 -0.052 -0.051 -0.058 -0.058 -0.064 -0,074 -0.069 -0.076 -0.063 -0.092 -0. I03 -0.I17 -0.149 -0.172 -0.178 -0.180 -0.161 -0.183 -0.177 -0.144 -0.115 -0.058 -0.054 -0.041 -0.031 -0.028 -0.034 -0.036 -0.064 -0,061 -0.063 -0.079 -0.106 -0.121 -0.136 -0.161 -0,179 -0,192 -0.204 -0.205 -0.221 -0.230 -0.216 -0,201 -0.213 -0.196

-0.688 -0.650 -0.640 -0.639 -0.630 -0.616 -0.593 -0.578 -0.575 -0.566 -0.559 -0.560 -0.562 -0,568 -0.573 -0.561 -0.607 -0.614 -0.621 -0.643 -0.666 -0.673 -0,684 -0.662 -0.684 -0.689 -0.660 -0.617 -0.614 -0,564 -0.557 -0.551 -0.550 -0.549 -0.550 -0.555 -0.561 -0.566 -0.584 -0.599 -0.600 -0.618 -0.617 -0.660 -0.647 -0.644 -0,666 -0.686 -0.701 -0.701 -0.700 -0,669 -0.663 -0,662

-I.307 -1,357 -I,375 -1.376 -1.429 -I.373 -t.287 -I,197 -1.251 -1.258 -1.309 -1.345 -1.346 -I,307 -1.326 -1.294 -1.260 -1.4t7 -I.476 -I.556 -1,370 -1.247 -1.500 -I.395 -1.365 -1.390 -1.451 -1.128 -1.231 -1.328 -1.198 -1.155 -1.211 -1.156 -I.I17 -i.140 -1.167 -1,289 -1.328 -I.342 -I.307 -1.285 -I.273 -I.334 -I.272 -1.211 -1,366 -1.402 -1.421 -1.410 -1.367 -1.499 -1.360 -1,395

60

O, DEMIRCAN ET AL.

Table 1 (continued) HJD

2446123,46393 48125,41524 48125,42216 48125,42968 48125,43975 48125,44565 46125.45267 46125.46211 48125.46670 48125,47211 46125.47697 48125,48218 48125,48768 48125,49427 48125,49920 48125,50468 48125,51385 48125,51927 48125.52371 48125.52940 48127.32216 48127.37952 48127.38529 48127,39105 48127.39807 48127.40515 46127,41162 46127.41800 46127.42508 48127,43675 48127.44334 48127.45001 48129.27374 46129.27762 46129.28276 48129.26660 48129.29325 46129,29667 46129,30478 46129.30992 48129,31575 48129.32332 48129.32825 48129.33679 46129,34179 48129.34804 48129.35318 48129,35887 48129.36533 48129,37117 48129.37755 48129.38457 48129,39144 46129.39894

PHASE

0,4034 0,4065 0,4142 0,4200 0.4210 0.4226 0,4376 0.4409 0.4434 0.4523 0.4544 0.4569 0,4636 0.4692 0,4754 0.4804 0,4820 0.4886 0,4941 0.5014 05028 0.5113 0.5150 0.5160" 0.5254' 0.5274 0.5330 0.5396 0.5411 0.5473 0.5524 0,5569 0.5607 0.5657 0.5749 0.5758 0.5610 0.5891 0.5924 0,6042 0,6117 0,6210 0,6306 0.6329 0.6361 0,6451 0,6504 0.6512 0,6694 0.6725 0.6869 0.7010 0,7022 0.7026

DYO

-0.153 -0.192 -0,187 -0,207 -0.168 -0.162 -0.149 -0.134 -0.125 -0.124 -0, I18 -0. I07 -0,079 -0.060 -0.056 -0.037 -0,039 -0.035 -0,019 -0.027 -0,035 -0,121 -0,135 -0.134 -0.160 -0.185 -0,195 -0,198 -0.203 -0.208 -0.205 -0.201 -0.190 -0.166 -0,173 -0.158 -0.147 -0.134' -0.129 -0.121 -0.094 -0.066 -0.073 -0.065 -0.057 -0.058 -0.065 -0,074 -0.089 -0.082 -0.100 -0.109 -0.121 -0,151

DBO

DUO

-0,654 -0,688 -0,690 -0,698 -0.691 -0,686 -0.661 -0.658 -0.659 -0,655 -0.625 -0,617 -0,602 -0.595 -0.569 -0.577 -0.563 -0.566 -0.556 -0.563 -0.553 -0.594 -0.599 -0,625 -0.634 -0,639 -0,670 -0,666 -0,666 -0.704 -0.705 -0.661 -0.706 -0,699 -0.692 -0.682 -0.669 -0.663 -0,661 -0,660 -0.645 -0.623 -0,606 -0.595 -0.590 -0.591 -0.593 -0.598 -0.607 -0.614 -0,621 -0,643 -0,658 -0.679

-1,373 -1.492 -1.424 -1.419 -

1 , 4 1 1

1,499 -I,593 - 1,456 -I,422 -1.291 -I,311 -1.358 - 1.323 -1,236 -I,350 - 1,285 -1.224 -1.153 -I.244 - 1.538 - 1.243 1.063 -1.233 -1,301 -1.200 -1,475 -1.638 -1.700 -1.992 -1641 - 1.462 -1.647 1.424 -1.419 - 1,447 -I,413 - 1,440 -1.416 -t,378 -1.338 ,316 .225 ,270 ,317 .318 .356 ,352 ,313 .316 .266 .372 .432 ,384 .401 -

-

-

61

P H O T O M E T R Y OF LS DELPHINI

Table I (continued) HJD

PHASE

DVO

DBO

DUO

2448129.40554 48129.41193 48129.41762 48129.42318 48129.43249 48129.43818 48129.44429 48129,45297 48129.45776 48129.46255 48129,46797 48129.47297 48129.47749 48129.46151 48129.48707 48129.49130 48129.49561 48131.26i90 48131,26787 48131,2730i 48131.27615 48131.28544 48131,29030 48131.29523 46131.29982 48131.30565 48131.31037 48131.31586 48131.32051 48131.32544 48131.32989 48131,33454 48131.34016 48131,34808 48i31.35232 48131.35690 48131.36155 4813i,36572 48131.37023 48131.37468 48131.37857 48131,38384 48131.38884 48131,39440 48131.39989 48131.40419 48131.41079 48131.41593 48131.42114 48131.42655 48131.43155 48131.43669 46131.44440 46131,44954

0.7124 0.7178 0.7213 0.7239 0,7353 0.7419 0.7434 0.7449 0.7591 0,7695 0.7715 02759 0.7858 0.7879 0.7997 0.6020 0.8050 0,8084 0.8i29 0,8162 0,8229 0,8261 0.8310 0.8361 0,8362 0,8409 0,8436 0.8495 0.8496 0.8510 0.8547 0,8585 0.8631 0,8642 0.8671 0.8706 0,87i9 0,8757 0,8782 0.8862 0,8917 0.8934 0,9018 0,9047 0.9051 0.9169 0.9194 0.9198 0,9326 0.9329 0.9337 0.9433 0.9461 0.9460

-0.i62 -0.181 -0.189 -0.196 -0.199 -0.201 -0.190 -0.176 -0.166 -0.160 -0.136 -0.132 -0. Ii7 -0. I09 -0.091 -0.076 -0.070 -0.179 -0.179 -0. i77 -0.165 -0.150 -0. t43 -0. I15 -0. I01 -0.097 -0.068 -0,062 -0.053 -0,046 -0.039 -0.030 -0,025 -0,024 -0,025 -0,031 -0,039 -0.052 -0.059 -0.071 -0.074 -0,102 -0.122 -0.136 -0.147 -0.156 -0.162 -0.172 -0.177 -0.180 -0.189 -0.192 -0.186 -0,182

-0.690 -0.695 -0.696 -0,698 -0,701 -0,694 -0.689 -0,673 -0.663 -0.652 -0.639 -0,619 -0.610 -0.601 -0,597 -0590 -0.588 -0.682 -0.678 -0.673 -0,658 -0,652 -0,640 -0.624 -0.615 -0,603 -0,599 -0,587 -0.582 -0.573 -0.570 -0,568 -0,562 -0.560 -0.561 -0,566 -0.569 -0,579 -0.585 -0,585 -0,593 -0.608 -0.618 -0.622 -0.626 -0.643 -0.662 -0.671 -0.696 -0.698 -0.706 -0.712 -0,714 -0.707

-1.422 -1.404 -1.348 -1.315 -1.498 -1.476 -I,542 -1.344 -1.354 -I.406 -1.427 -1.439 -1.413 -i.4i9 -i.423 -1.369 -1.429 -i.414 -1.376 -1.361 -1.399 -1.368 -1.312 -1.349 -1,342 -1,383 -1.370 -1.338 -1.301 -1.3i0 -1,293 -1.362 -1.313 -I,269 -1.239 -1,224 -1.238 -1.254 -1.343 -1.331 -1.303 -I,372 -1.357 -1.344 -1.340 -1.399 -1.412 -1.406 -1.404 -1.347 -1.366 -1.334 -I,354 -1.380

62

O. D E M I R C A N

E T AL.

Table I (continued) HJD

PHASE

DVO

DBO

DUO

2448131.45495 48131.46072 48131.46551 48131.47266 48131.47780 46131.46266

0.9464 0.9563 0.9684 0.9711 0.9732 0.9856

-0.176 -0.169 -0.160 -0.146 -0.131 -0.124

-0.699 -0.685 -0.672 -0.661 -0.657 -0.642

-1.459 -1.449 -1.405 -1.369 -1.366 -1.326

0,9866 0.9661 0.9942

-0.097 -0,086 -0,070

-0.634

-I,288 -1.284 -1.277

46131,48732 46131.49183 46131.49822

-0.619 -0.608

2. The New Observations New U B V observations of LS De1 on eight full nights in August 1990 were obtained at the Ankara University Observatory, using a single channel unrefrigerated photometer on the 30 cm Maksutov telescope. The same comparison and check stars were chosen as in Sezer et aI. (1984) and Derman et al. (1991). The comparison star BD + 19~ showed no significant variation against the check star BD + 19~ In total 224 differential observations in each passband were obtained. All observations are obtained in a short time interval of only fifteen days. Observations in the U passband are not utilized in defining light curve variations, because of larger scatter. The relatively large standard deviation of differential observations (0.02 mag in V, 0.03 mag in B, 0.09 mag in U) is mostly due to intrinsic variation of light in short time intervals. The magnitude differences in V, B, and U passbands between variable and comparison stars are listed in Table I and the light curves formed by these differential observations in V and B are shown in Figure 1, together with the (B - V) colour curve. The U light curve is not shown in Figure 1. However, it is seen that the shape and the amplitude of light variation is not significantly different in the U band. The phases of the observations in Figure 1 were calculated by using the new light elements (see next section): Hel. J.D. Min. I = 2447790.42696 + 0.3638400E. The light curves in Figure 1 display a few interesting features. Firstly, the level of maxima as well as minima varies up to 0.05 mag from cycle to cycle. The largest variation occurs at the primary maximum at phase 0.25, in V which is surprisingly about three times larger than the same variation in B. The maximum O'Connell effect where the primary maximum is always brighter is seen in V (max II - max I)v < 0m05, (max II - max I)B < 0m03 . More specifically, the level of primary maximum in V fades 0~045 in 8 days (from 19 to 27 August, 1990), but the level of primary maximum in B, brightens about 0T 02 during

PHOTOMETRY OF LS DELPHINI

63

the same interval of time. Similarly, the level of secondary minimum appears to be same on 15 and 18 August, 1990 in both B and V filters, but it was brightened about 0Y03 in B, while it did not change in V on 25 August, 1990. These interesting time and

I

z~(e-v) 9

-0.55

@

-0 .~O

41,~

-0.45

,~

@

~

.

,~+~

~%

9k -0 2 0

#

*

+,,

++

/

A B

z.,

-*"

+

-0.70

?

r176

.

_.. -j-o.s.,

A~ -0.15

2

-0.I0

J

-0.05 PHASE 0,00

l

1

0.7 0.8 Fig. 1.

I

I

0.9

t

I

0.0

I

w

0.1

t

!

0.2

1

1

t

I

0.5 0,4

t

t

0,5

r

I

t

I

0.6 0.7

t

0.8

The B a n d V light curves of LS Del in A u g u s t 1990. The (B - V) colour curve is also shown.

wavelength-dependent variations in the level of secondary minimum is shown in Figure 2. When the light curves are normalized to the level of secondary maximum then it is seen that the system in B behaves very slightly brighter than in V on 25 August, 1990 but 0m.03 fainter in B during 15 and 18 August, 1990 observations. Time-depen-

64

o. DEMIRCAN ET AL.

dent variation in the secondary minimum is very small in V ( _