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B.R.N.O. Contributions #37 - Times of minima
Abstract
Paper presents observations of eclipsing binaries acquired by the Variable Star and Exoplanet Section of Czech Astronomical Society members (B.R.N.O. observing project) and cooperating observers. Paper contains 1270 minima timings for 478 eclipsing binaries, obtained by 45 observers during 2009 - 2011 period. Some neglected southern eclipsing binaries are included in the list. New accurate orbital elements have been found for 28 binary systems. Times of minima of an extraordinary quadruple sytem V994 Her are presented as well.
LM And is a neglected close binary system with a period about 18 h. First complete multi-colors CCD light curves are presented which reveals that LM And is β Lyrae-type eclipsing binary. By analyzing two spectrums, we determined its spectral type of F6 for this binary. Photometric solutions of the binary were obtained by analyzing our multi-colors light curves and the TESS Light curve with the Wilson-Devinney method. The orbital inclination is about 84 degree revealing that the binary is a total eclipsing system. The mass ratio is determined to be about 0.54 and 0.58 for two sets of light curves. It is discovered that LM And is a semi-detached near-contact binary where the secondary component is filling the critical Roche lobe, while the primary is more than 90% filling its Roche lobe. A period investigation suggests that the orbital period of the binary is increasing continuously at a rate of dP/dt=4.2(±0.6)×10−7 days/year,which may be attributed to mass transfer from the less-massive component, which fills its Roche-lobe. Therefore, LM And with period increasing will evolve into the contact configuration.
New BVR CCD photometric observations of eclipsing binary V2240 Cyg were performed in the summer of 2017 and 2018. Using four observed times of minimum, a new ephemeris of V2240 Cyg is presented. For the first time, the light curves of V2240 Cyg were analyzed. The new observed light curves show that the light maxima are asymmetric. Considering one cool spot on the primary component, the photometric and physical parameters of V2240 Cyg were determined (e.g, Mp=1.497M⊙, Ms=0.167M⊙, Rp=1.601R⊙, Rs=0.637R⊙ and a=2.71R⊙). The results of the simulations show that V2240 Cyg is an A-type W UMa binary with a low mass ratio and high overcontact degree f=59.6%. The position of both components of V2240 Cyg are shown in the H-R diagram. Collecting all times of minima and using the new ephemeris, the O−C curve was plotted and the orbital period of this binary system was investigated. The O−C curve indicates that the orbital period of V2240 Cyg is decreasing at a rate of dP/dt=−1.56×10−6dyr−1, which can be due to mass transfer (M˙=2.42×10−7M⊙yr−1) from the primary to the secondary component.
The light curve of V921 Her in ultraviolet band observed by the Lunar-based
Ultraviolet Telescope (LUT) is analyzed by the Wilson-Devinney code. Our solutions conclude
that V921 Her is an early type marginal contact binary system with an additional close-in
component. The binary system is under poor thermal contact with a temperature difference
of nearly 700K between the two components. The close-in component contributes about 19%
of the total luminosity in the triple system. Combining the radial velocity study together with
our photometric solutions, the mass of the primary star and secondary one are calculated to be
M1 = 1.784(±0.055)M⊙, M2 = 0.403(±0.012)M⊙. The evolutionary scenario of V921 Her is
discussed. All times of light minimum of V921 Her available in the bibliography are taken into
account and the O − C curve is analyzed for the first time. The most probable fitting results
are discussed in the paper, which also confirm the existence of a third component (P3 = 10.2
year) around the binary system. The period of V921 Her is also undergoing a continuously
rapid increase at a rate of dP/dt = +2.79 × 10−7day · year−1, which may due to mass transfer
from the less massive component to the more massive one.
An intensive analysis of 148 timings of V700 Cyg was performed, including our new timings and 59 timings calculated from the super wide angle search for planets (SWASP) observations, and the dynamical evidence of the W UMa W subtype binary was examined. It was found that the orbital period of the system has varied over approximately in two complicated cyclical components superposed on a weak upward parabolic path. The orbital period secularly increased at a rate of day/year, which is one order of magnitude lower than those obtained by previous investigators. The small secular period increase is interpreted as a combination of both angular momentum loss (due to magnetic braking) and mass-transfer from the less massive component to the more massive component. One cyclical component had a period with an amplitude of , and the other had a period with an amplitude of . The components had an approximate 1:3 relation between their periods and a 1:7 ratio between their amplitudes. Two plausible mechanisms (i.e., the light-time effects [LTEs] caused by the presence of additional bodies and the Applegate model) were considered as possible explanations for the cyclical components. Based on the LTE interpretation, the minimum masses of 0.29 for the shorter period and 0.50 for the longer one were calculated. The total light contributions were within 5%, which was in agreement with the 3% third-light obtained from the light curve synthesis performed by Yang & Dai (2009). The Applegate model parameters show that the root mean square luminosity variations (relative to the luminosities of the eclipsing components) are 3 times smaller than the nominal value (), indicating that the variations are hardly detectable from the light curves. Presently, the LTE interpretation (due to the third and fourth stars) is preferred as the possible cause of the two cycling period changes. A possible evolutionary implication for the V700 Cyg system is discussed.
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