V839 Cep – a new quadruple doubly eclipsing system

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Abstract

New high-precision photometric measurements of the eclipsing star V839 Cep (P = 9.96d, VA+B = 9.64m, e = 0.07, B6 V + B7 V), which is the “A” component of the visual double star J21035+5925AB, have established that component “B” is also an eclipsing variable (P = 4.075d, B9 V + G8 V). For component “A”, the apsidal rotation rate was measured to be ω˙obs = 0.027° /year, which exceeds the theoretical value under the condition of synchronism ω˙theor = 0.021° /year. The physical parameters of the component stars of the eclipsing pair “A” were obtained: T1 = 13 200 ± 300 K, M1 = (3.7 ± 0.15) M⊙, R1 = (2.57 ± 0.05) R⊙, T2 = 11 900 ± 250 K, M2 = (3.2 ± 0.15) M⊙, R2 = (2.42 ± 0.05) R⊙ and components of the eclipsing pair “B”:  T1 = 10 600 ± 200 K, M1 = (2.6 ± 0.2) M⊙, R1 = (1.97 ± 0.05) R⊙, T2 = 5540 ± 50 K, M2 = (0.88 ± 0.05) M⊙, R2 = (0.84 ± 0.05) R⊙. The age of the system is determined to be 70 million years with solar chemical composition. The components of star “A” are pulsating variable stars of the slow β Cephei (SBC) type.

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About the authors

I. M. Volkov

Lomonosov Moscow State University

Author for correspondence.
Email: hwp@yandex.ru

Sternberg Astronomical Institute

Russian Federation, Moscow

A. S. Volkova

Lomonosov Moscow State University

Email: kravts@yandex.ru

Sternberg Astronomical Institute

Russian Federation, Moscow

L. A. Bagaev

Lomonosov Moscow State University

Email: baglev@yandex.ru

Sternberg Astronomical Institute

Russian Federation, Moscow

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Supplementary files

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2. Fig. 1. Bicolor diagram {U – B, B – V}. Black circles are the color indices of the “A” components. Black diamonds are the color indices of the “B” components. Empty circles and empty diamonds are the individual color indices corrected for interstellar reddening (shown by arrows). The solid line corresponds to the normal color indices of stars of the fifth luminosity class according to the data of Straizys [21]. Gray background – data from the catalog [17]. Oblique crosses are the comparison stars.

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3. Fig. 2. Bicolor diagram {B – V, V – R}. Black circle – color indices of V839 Cep. Empty circle – color indices of V839 Cep corrected for interstellar reddening (shown by arrow). Gray dots show data from the GAISh catalog [16]. Solid line corresponds to normal color indices of stars of the fifth luminosity class according to [21]. It lies above the GAISh data due to the difference in calibrations of GAISh and the Johnson system. Oblique crosses – comparison stars.

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4. Fig. 3. Bicolor diagram {B – V, V – I}. The black circle shows the position of V839 Cep. The empty circle is the color indices of V839 Cep, corrected for interstellar reddening, which is shown by the arrow. The solid line corresponds to the normal color indices of stars of the fifth luminosity class according to [21]. The empty circles are the data for M67, as in [34] in Figs. 4 and 5.

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5. Fig. 4. TESS (Ic) band observations convolved with the period of rotation of component “A” (P = 9.9633d). The chaotically located main minima of component “B” are visible. Pulsations are not corrected.

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6. Fig. 5. Pulsations on the plateau, folded with each of the found periods, from top to bottom, P1, P2, P3, P4 from Table 4. Residual deviations after subtracting all the presented periods σ = 0.0028m.

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7. Fig. 6. Example of physical variability in the course of JD 2458718 – 2458723 (top) and JD 2459845 – 2459850 (bottom). The accuracy of an individual measurement is σ = 0.0010m. The solid line shows the theoretical course of brightness variations in accordance with the found pulsation parameters.

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8. Fig. 7. TESS observations of component V839 Cep “B”, folded with the period P = 4.075d. Eclipses of component “A” are excluded, pulsations are corrected. It is seen that residual oscillations are preserved.

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9. Fig. 8. The course of the residual deviations O – C of the TESS light curve solution for component “A” depending on the radius ratio k = r2 – r1.

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10. Fig. 9. TESS observations in the Ic band in the primary (left) and secondary (right) minima (upper panel). Below are the deviations of the O–C observed points from the model curves for all photometric bands. The vertical scale is the same for all observation bands, which gives a clear idea of ​​both the accuracy of the observations and their correspondence to the found model. It is evident that the scatter in the secondary minimum has small residual systematic deviations.

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11. Fig. 10. The left half of the figure shows TESS observations of component “B” in the primary minimum, the right half – in the secondary minimum. The deviations of the O – C observed points from the model curve are presented below. The pulsations are subtracted in accordance with the parameters of component “A” found in this work. The residual deviation of an individual measurement, corrected for level and pulsation corrections, is σ = 0.00135m.

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12. Fig. 11. Evolutionary tracks showing the dependence of the gravity acceleration on the temperature of the star, constructed according to the data of [43] for selected stellar masses. The solid bold line shows the position of the Initial Main Sequence, ZAMS. The primary component “A” is indicated by a filled square, the secondary – by a circle; components “B” are open square and circle. Errors in determining the parameters are shown. To estimate the scale, the solid curved lines show isochrones for ages from 63 to 100 million years. All theoretical data are given for the solar chemical composition. The gray curves are evolutionary tracks for different masses indicated in the figure.

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13. Fig. 12. Dependence of stellar luminosity in solar units on temperature for selected masses [43]. The designations are the same as in Fig. 11.

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14. Fig. 13. Graphs of residual deviations of the moments of minima from linear formulas, plotted separately for the main and secondary minima, each with its own period, see (4). The upper panel – the main minima, indicated by empty squares. The lower panel – the secondary minima – empty circles. It is clearly seen that the scatter for the secondary minima is significantly larger. This may be due to the presence of spots on the surface of the secondary component.

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