Astron. Nachr. 316 (1995) 1, 9-16

The true rotational period of the Ap star HD 193722 = V 1584 Cyg *

G. HILDEBRANDT and G. SCHOLZ, Potsdam, Germany

Astrophysikalisches Institut Potsdam

H . LEHMANN, Tautenburg, Germany

Thiiringer Landessternwarte

K. PANOV, Sofia, Bulgaria

Institute of Astronomy, Bulgarian Academy of Sciences

Received 1994 Juni 2; accepted 1994 August 12

Photometric observations of the Ap star HD 193722 give unambiguous proofs for a rotational period of P=8.5297 days in contradiction to the earlier found value of P=1.13316 days. Spectroscopic measurements yield a line width equivalent to the value u sin 1=44.5 km/s. Both findings show convincingly that HD 193722 is an evolved Ap star with a position in the giant region of the HR diagram. This place falls into a domain occupied by the hypothetic Maia sequence. Die photometrischen Beobachtungen des Ap Sterns HD 193722 liefern eindeutige Beweise f i r eine Rotationsperiode von P=8.5297 Tagen im Gegensatz eu dem friiher gefundenen Wert von P=1.13316 Tagen. Aus den Linienbreiten der spek- troskopischen Messungen ergab sich einen Wert f i r usin i=44.5 km/s. Beide Ergebnisse zeigen iiberzeugend, da6 HD 193722 ein entwickelter Ap Stern im Riesenbereich des HR Diagramms ist. In diesem Bereich befindet sich auch die hypothetische Maia Sequenz.

Key words: Ap stars - rotational period: HD 193772 = V 1584 Cyg

AAA subject classification: 114

1. Introduction

Struve (1955) suggested that a sequence of variable stars having periods between about 1 to 4 hours and spectral types in the range B7III - A2V/II might exist. Up to now a long lasting and controversial discussion has been taken place about the existence of the Maia variable group called after the presumed prototype Pleiadid, Maia (20 Tau). In a collection of the observational evidences about the existence of this group McNamara (1987) concluded that not a single member can be confirmed. But, recently Kuschnig et al. (1990) found that the Ap star E T And, if its location in the HRD is correct, could be an candidate of the Maia variable group. Another Ap star, HD 193722 (BSSi), showing some similar characteristics as ET And, was observed already earlier photometrically in Potsdam. Beside the searching of rapid oscillations first of all investigations are necessary to determine the real rotational period of the star. The rotational period of P=1.13316 days of HD 193722 determined by Aslanov et al. (1973) is consistent only with earlier findings of the star. In contrast to this Hildebrandt (1985) found a period of P=8.5304 days, but he mentioned that more observations are necessary to clarify the difference between the periods. Here we present some recent observations of this star.

2. Observations and Discussions

2.1. Photometrical results

The observations of HD 193722 were obtained during 1993 Sept. 23 to 28 with the 60 cm Cassegrain telescope of the Bulgarian National Observatory at Rozhen. The computer controlled photometer is equipped with an

'Based on observations collected at the National Observatory, Rozhen, Bulgaria

10 Astron. Nachr. 316 (1995) 1

EM1 9789 QB multiplier, a set of v,b,u filters and a diaphragm of 28". The intergration time was ten seconds for each measurement and each filter. The reductions included the corrections for dead-time, the background, the differential extinction and the correction of the data to the standard UBV system. The behaviour of the atmosphere and of the extinction coefficients for the three spectral ranges V, B , U are shown in Fig. 1 to 3.

HD 19231s - HD I93722 23.09.1993 -14.24 , ' ' I ' ' ' ' I " ' ' 1 " ' '

1 -1..22

- s ;-14.2/

' -14 .18

c -,,& -I

Cx-O.Ia3 i HD 192314 - HD 193722 23.09.1993

- 1 5 . 8 1 . . . . I . . . . I . . , . ( . . . ,

i -15.81

-15.80

-15.74

-15.72

j Ex-0.2'4

-1110 I , . I I , . I I , , . , I , , , , 1.05 1.10 1.15 1.20 1.W

w

HD 192314 - HD 193722 2109 1991 - 1 4 . J O I . 1 ' ' I ' . 1 ' 1 - ' ' 1 1 - ' 3 7 1

Fig. 1 to 3. Behaviour of the atmosphere and extinction coefficients in the spectral ranges V, B, U represented by the run from 1993, Sept. 23.

G. Hildebrandt et al.: Rotational period of V 1584 Cyg 11

- O . 9 8 - . " 1 ' . ' I " ' I " ' I " ' I ' "

-

They give an impression of the good photometrical quality in Rozhen observatory in comparison to other sites of observatories. The most interesting run from 1993, Sept. 23 with the filters V, B, U is shown in Fig. 4 to 6 for the further discussion. The comparison star was the well known star HD 192514. The journal of observations is given in Table 1 and the individual measurements of the three runs are listed in Table 2. For the frequency analyses of all photometrical data the very comfortable computer program of Breger (1990) was used.

-1.62

-1.64

- D

- 1 66

B

-1.68

ti0 I92314 - HD 193722 23.09.1993 (2449250s) - t , u , 1 , 1 ' . . I ' ' ' I ' ' ' I . ' ' I ' ,

-1.52 4.28 i40 1.30 4.32 4.3e WO 4.36

-l.w t I 3 0

- E -1.02

- 1 , O b t 1

-1.06 4.10 4.32 4.34 4.36 4 38 6.40

tIJ0 4.28

Fig. 4 to 6. Observational run for the filter V, B, U from 1993, Sept. 23.

12 Astron. Nachr. 316 (1995) 1

The photometrical data of Winzer (1974), Wesselius et al. (1982), Hildebrandt et al. (1985) and the observa- tions of Rozhen (Table 2) were used for a detailed frequency analysis. The obtained power spectra are shown in Fig. 7 to 9. The dominant peak (Fig. 7) has the value of frequency f=0.117237 days-' (P=8.5297 days). The region of power spectra of the two relevant periods - about 8.5 days and 1 day, respectively - are shown in Fig. 8 and 9 with a larger resolution.

Fig. 7 to 9. Power spectra of all photometrical observations and details of the power spectra in the region 8.5 and 1 day.

G. Hildebrandt et al.: Rotational period of V 1584 Cyg 13

-1.44 " ' I " ' 1 I " " I " ' 1

U K 9 I

The frequency f =0.8825 days-' (P=1.13316 days) is obviously an alias value to the period P=8.5297 days. Assuming the period of Pd3.5297 days as the true period the light curves for V, B , U are shown in Fig. 10 to 12. The curves are calculated with the elements:

HJD(Light-Max.) = 2440450.067 + (8.5297&OOO004)x E

HD 192514 - HD 193722 (1969-1994) P-8.5297 d -1.601. ' * I ' ' ' ' I ' ' ' ' I ' ' " I

-1.12 ' 1 t

+ . + f ha.

%I8 I- * + I

- 1 . 4 I

-1.12

A

0 t # u 6 0 0

1 + + + 60 01

I -1.54 A A I

HO 192514 - HD 193722 (1969-1994) P-8.5297 d -0.08 . , ' 7 I " ' ' I ' ' " I ' ' ' ,

+

-1.02 ++i TO

: + * :

- t '-+O

.-.

.E -1.04

a - 1.06 1 +;++ * + + + +

+ + * ? + ++;

:a + : : +

0 0

* + n+

+ a

, , I , , , ; , I ; ,

+j+ 1 +;* -1.08 + : * : . + . +

.+ ' *

. + + +

-1.10 0.0 0.5 I .o I .I 1.0

PM..

Fi . 10 to 12. Light curves of HD 193722 for the filters V,B,U. The symbols mean: + UBV-Aslanov, * BV-Winzer, ASV-Hildebrandt, o 10-Color-Hildebrandt, 0 UBV-Hildebrandt, x ANS-V-Wesselius, 0 UBV-this paper.

14 Astron. Nachr. 316 (1995) I

Table 1 Table 2 Journal of observations of HD 193722 Observational runs of HD 192514 - HD 193722

JD Date t I t HJD AV AB AU HJD AV AB AU 2440000+ 1993 [hr] [sec] 2449000+ [mag] [map] [mag] 2449000+ [mag] [mag] [mag]

9254 Sep.23 9256 Sep.25 9259 Sep.28

2.75 10 254.281 2.05 10 254.285 1.0 10 254.285

254.289 254.289 254.293 254.297 254.297 254.301 254.305 254.305 254.309 254.309 254.313 254.313 254.316 254.320 254.320 254.324 254.324 254.328 254.328 254.332 254.336 254.336 254.340 254.340 254.344 254.344 254.348 254.352 254.355 254.355 254.359 254.359 254.363 254.367 254.367 254.371 254.375 254.375 254.379 254.379 254.383 254.387 254.387 254.391 254.391 254.395 256.262 256.262 256.266 256.266 256.270

-1.664 -1.663 -1.672 -1.669 -1.667 -1.668 -1.661 -1.660

-1.667 -1.664 -1.667 -1.664 -1.663 -1.662 -1.660 -1.670 -1.663 -1.669 -1.670 -1.660 -1.666

-1.666 -1.665

-1.658

-1.661

-1.673 -1.668 -1.667

-1.666 -1.659 -1.657 -1.661 -1.662 -1.663 -1.656 -1.664 -1.668 -1.665 -1.671

-1.665 -1.661

-1.665 -1.669

-1.665

-1.706 -1.697 -1.702

-1.697

-1.666

-1.669

-1.667

-1.670

-1.666

-1.698

-1.489 -1.484 -1.482 -1.491 -1.491 -1.495 -1.490 -1.488 -1.495 -1.485 -1.487 -1.492 -1.491 -1.495 -1.493 -1.486 -1.489

-1.491 -1.496 -1.495 -1.496 -1.497 -1.486 -1.493

-1.492

-1.495 -1.495 -1.498

-1.493 -1.485 -1.493 -1.492 -1.486 -1.493

-1.490 -1.495

-1.495 -1.494 -1.495 -1.495 -1.495 -1.492 -1.496

-1.496

-1.493

-1.438

-1.493

-1.500

-1.496 -1.529 -1.532 -1.533 -1.539 -1.534

-1.022 -1.023 -1.025 -1.015 -1.018 -1.018 -1.026 -1.022 -1.020 -1.015 -1.023 -1.019 -1.018 -1.019 -1.020 -1.020 -1.022 -1.022 -1.027 -1.030 -1.019 -1.021 -1.022 -1.016 -1.018 -1.030 -1.028 -1.031 -1.029 -1.029 -1.022 -1.026 -1.019 -1.023 -1.028 -1.025 -1.024 -1.029 -1.027 -1.028 -1.031 -1.028 -1.029 -1.029 -1.033 -1.029 -1.026 -1.032 -1.031 -1.063 -1.069 -1.079 -1.088 -1.082

256.270 256.273 256.277

25 6.281 256.281 256.2d5 256.2d5 256.2d9 256.2~39 256.297 256.297 256.301 256.301 256.305 256.305 256.309 256.313 256.313 256.316 256.316 256.320 256.320 256.324 256.32d 256.32d 256.332 256.336 256.336 256.340 256.340 256.344 256.344 259.273 259.273 259.277 259.277 259.281 259.281 259.285 259.2d5 259.289 259.2d9 259.293 259.297 259.297 259.301 259.301 259.305 259.305 259.309 259.309 259.313

2 5 6 . 2 n

-1.693 -1.532 -1.693 -1.523 -1.697 -1.522 -1.704 -1.529 -1.698 -1.525 -1.697 -1.531 -1.698 -1.531 -1.696 -1.528 -1.696 -1.529 -1.703 -1.531 -1.699 -1.520 -1.696 -1.522 -1.699 -1.530 -1.687 -1.525 -1.692 -1.520 -1.691 -1.525 -1.698 -1.538 -1.700 -1.531 -1.693 -1.527 -1.700 -1.525 -1.696 -1.525 -1.697 -1.525 -1.698 -1.535 -1.689 -1.523 -1.697 -1.521 -1.698 -1.518 -1.698 -1.525 -1.698 -1.527

-1.700 -1.525 -1.694 -1.529 -1.694 -1.520 -1.693 -1.518 -1.677 -1.508 -1.686 -1.507 -1.680 -1.507 -1.679 -1.509 -1.676 -1.512 -1.673 -1.507 -1.670 -1.497 -1.695 -1.516 -1.685 -1.512 -1.673 -1.505 -1.681 -1.509 -1.679 -1.508 -1.680 -1.509

-1.681 -1.503 -1.680 -1.502 -1.682 -1.505 -1.682 -1.507 -1.684 -1.502 -1.676 -1.504

-1.696 -1.529

-1.682 -1.506

-1.083 -1.072 -1.082

-1.068 -1.070 -1.076 -1.076 -1.084 -1.078 -1.075

-1.088

-1.076 -1.073 -1.075 -1.069 -1.071 -1.074

-1.075 -1.076 -1.071 -1.072 -1.078 -1.074 -1.071 -1.076 -1.072 -1.080 -1.079 -1.072 -1.070 -1.073 -1.075

-1.050 -1.047 -1.047 -1.059

-1.042 -1.049

-1.076

-1.046

-1.048

-1.046 -1.047 -1.051 -1.053 -1.050 -1.048

-1.046 -1.053

-1.051 -1.044

-1.044

-1.051

The following facts are unambiguous hints for the reality of the long period: 1.) The observations of Winzer (1974), which are obtained with a time shift of about 0.4 days in comparison to the sideral time of other observations, are only in agreement sufficently with the other observations accepting the period of 8.5 days but not with the period of 1.13 days. This can be seen in Fig 13. 2.) The same statement is valid for the ANS observations of Wesselius et al. (1982). 3.) The three hours run from 1993, Sept. 23 shows in the filters B and U a clear trend from the brighter to the fainter magnitude. This trend, represented in a phase diagram, matchs only in connection with the long period putting the values in the decending part of the light curve. In the other case, using the period of 1.13 days, our measurements do not fit with the general shape. 4.) Another argument for. the long period is given in the spectroscopical part below.

2.2. Spectroscopical results

In order to give an additional hint a t the validity of the longer or shorter photometric period HD 193722 has been observed spectroscopically a t the 2m telescope of the Rozhen Observatory during the time of the photometrical ob- servations mentioned above. Unfortunately, only one overexposed photographic spectrogram (HJD 2449259.3014, blue spectral region, reciprocal linear dispersion 9 A/mm) has been obtained for determination of the v sin i and

G. Hildebrandt et al.: Rotational period of V 1584 Cyg 15

- 1 . 6 0 - 1 " ' I " " I ' " ' I ' ' ' '

- -1.62 -

-1.64 l o : - 1 . 6 8 1

II

- 1 . 7 0 1

+ + +++ +

+

+ + i

++ +

. . . . . . . . . . . . . - . . ..

A 0 . 0 0 ; x +

x + 0 + x + + * (+

X

+ + + x + X

0 +++ + 1 0 0

0

+

A X

A 0 D O

+ + o d 0 0

0

2.0 -1.72 I * * ~ ~ ' " " " ' ' I ' ' * '

0.5 I .o I .S Phase

0.0

Fig. 13. V-light curve calculated with the period of 1.13 days.

Table 3. Radial velocity and line width of HD 193722

X (Moore) Ele./Mult. RV FWHM* Line depth. [A1 b / s l [A1

4618.830 4616.640 4520.225 4515.337 4481 228 4416.817 4340.468 4303.166 4233.167 4233.250 4130.884 4128.053 4101.737 3970.074 3963.470 3933.664

3905.527 3862.592 3856.021 3853.657

CrII (44) CrII (44) FeII (37) FeII (37)

FeII (27) H5 FeII (27) FeII (27) CrII (31) SiII (3) SiII (3) H6 H7 CaII (1) CaII (1)

MI311 (4)

SiI (3) SiII (1)

-12.68

-12.69 -9.56 -12.50

-11.22

-11.99 -13.69 -12.10 -11.76 -11.32 -12.00 -11.93

-12.17

-13.10 -13.96

0.48 0.47 0.62 0.80 0.72 0.58

0.75

0.80 0.69 0.78

0.24 C 0.42 P 0.70 W 0.60 0.52 0.74

0.09 0.06 0.01 0.09 0.21 0.06

0.04

0.07 0.16 0.12

0.10

0.04

0.07 0.08

'values derived from the trancparency; C core, P profile, W wing;

Considering the measuring accuracy of the vsini values and the radial velocity ones a dependence on the element or line strength does obviously not exist. Therefore it seems to be justified to use the mean values:

RV = (-12.8 f 0.27)km/s and vsini = (44.5 f 2.6)km/s.

The latter value has been derived on the assumption that the line width is produced mainly by the rotation of the star, Comparing our findings with the corresponding data determined by other authors the values agree very well with each other. Apart from the value of w sin i = 265 km/s indicated in the catalogue of Uesugi & h k u d a (1981) all other determinations yield the same magnitude, e.g. for vsini = 40 km/s, Babcock (1958); 42 km/s, Aslanov et al. (1973); 42 km/s, Wolff (1976). For the radial velocity we found RV = -10 km/s and -10.8 km/s, Abt & Biggs (1972) as well as +4, -7 and -8 km/s, Duflot et al. (1990) indicating perhaps the existence of a binary nature of the star.

16 Astron. Nachr. 316 (1995) 1

3. Conclusions

In past the preference of the period of 1.1 days compared with the period of 8.5 days for HD 193722 is based above all on the popular idea that the most Ap stars are main sequence objects. The reinvestigation of the previous photometrical observations and including the observatons notified in this paper gives now unambiguous hints for the true rotational period of P = 8.5297 days. Together with the value of u sin i = 44.5 km/s the radius of the star has to be larger than 7.5 RO, e.g. the star belongs to the luminosity class II/III. This is in good agreement with the value g = 3.3 of the surface gravity determined from the effective temperature (12300K) and the equivalent width of H5, Kroll (1993), which locates the star also in the giant region. As a consequence of this result the deviation of the position of the star in the North’s (1985) log(P) - log(g)-diagram (Fig.2a) can be completly eliminated with the rotational period of 8.5 days, thus confirming likewise the correctness of the longer rotational period. Comparing with ET And the stellar parameters of HD 193722 indicate that both stars have obviously a past main sequence evolutionary state. For this reason it should be useful to look also for rapid variations in HD 193722 but one need observations with a higher accuracy as before. Acknowledgements: The authors have to thank Mr. T. Tomow of the Observatory Rozhen for making of the spectroscopical observations of this and further objects of our programme.

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Kuschnig, R., Weiss, W.W., Kreidel, T.J., Bus, S. J., Osip, D. J., Huang, L., Sareyan, J.-P.,

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1987, Stellar Pulsation, Lecture Not. in Physics, 274, 92 1985, Astron. Astrophys. 148, 165-168 1955, Sky and Telescope, 14, 461

1981, Proc. 7th Intern. CODATA Conf., Strassbourg 1982, Astron. As-

trophys. Suppl. Ser. 49, 427 1974, Thesis, Univ. of Toronto

1976, IAU Coll. 29, 43, Budapest; (Ed. W.S. Fitch)

Addresses of the authors:

Gerald Hildebrandt Astrophysikalisches Institut Potsdam An der Sternwarte 16 D - 14482 Potsdam-Babelsberg Germany

Gerhard Scholz Astrophysikalisches Institut Potsdam Telegraphenberg D - 14473 Potsdam Germany

Holger Lehmann Thiiringer Landessternwarte Karl-Schwarzschild-Observatorium DorfstraBe 73 D - 07778 Tautenburg Germany

K. Panov Institute of Astronomy Bulgarian Academy of Sciences Zarigradsko Chaussee 72 BG - 1784 Sofia Bulgaria