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1.
The RS CVn-type eclipsing binary MM Her was observed photoelectrically inB andV colours. The light curves obtained in 1984 and 1985 are presented. It was found that the depths of the primary minima are decreased from 1983 to 1985. However, the amplitude of the wave-like distortion outside the eclipses was detected to increase since 1976. The period of migration was determined to be about 3.57±0.08 years.  相似文献   

2.
Light curves of the Z Cam type dwarf nova AT Cnc observed during standstill in 2016 and 2018 are analyzed. On the time scale of hours, previous reports on periodicities, in particular the presence of negative superhumps, could not be confirmed. Instead, a modulation with a period equal to the spectroscopic orbital period was detected which we thus interpret as a manifestations of the binary revolution. It enables us to derive a more accurate value of 0.201634  ±  0.000005 days (or its alias of 0.021580 days) for the period. AT Cnc also exhibits a hitherto unreported modulation of 25.731 ± 0.005 min, stable in period but not in amplitude over the entire time base of two years of the observations. We tentatively interpret this modulation in the context of an intermediate polar model for the system.  相似文献   

3.
Many available published times of light minima of the active binary system UV Psc have been collected and analyzed using a new method proposed by Kalimeris et al. (1994). Similar to what was seen in other RS CVn-type binaries, the orbital period of UV Psc oscillates with a period of about 61 years and an semi-amplitude of 0.21 ×10-5 days. Two possible mechanisms (magnetic activity cycle mechanism and a light-time effect due to a hypothetical third body) that could modulated the orbital period behaviour are studied. We think that the cyclical period change in UV Psc can most probably be attributed to a magnetic activity cycle in the primary component. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
The RS CVn-type eclipsing binary star MM Her has been observed in two colours,B andV, in 1979, 1980, and 1983. Several minima times were obtained during the observations and new light elements calculated. The light curves of the system obtained in blue and yellow lights show a significant wave-like distortion which migrates towards the decreasing orbital phases. Its migration period was estimated to be about 3.5 yr. The amplitudes of the wave-like distortion inB andV appear to change each year. The primary minimum of the system is a total eclipse with a duration of 0d.08.  相似文献   

5.
《New Astronomy》2003,8(5):457-463
Orbital period variations of two chromospherically active binary systems, RT CrB and PW Her, are presented. It is shown that the orbital period of RT CrB undergoes a cyclic oscillation with a period of 53.9 years. For PW Her, an alternate change, with a period of 42.7 years, is found to superimpose on a rapid secular increase (dP/dt=+3.53×10−6 days/year). If the period oscillations of those two systems are caused by the light-time effect of a third body, the analysis for RT CrB indicates that the third body would be a low-mass main-sequence star, while, for PW Her, the mass of the third body should be no less than 7.8 M⊙. Since no spectral lines of the third body were seen in PW Her from the spectroscopic study by Popper [AJ 100 (1990) 247], if there is a third body in the system, it can only be a black hole. However, as both components in the two binary stars were showing strong chromospheric activity, the alternate period variations are more plausibly explained as the result of magnetic activity cycles. No secular period changes of RT CrB are found, which is in agreement with the detached evolved configuration of the system. The long-term period increase of PW Her may indicate that it is on an active phase of mass transfer (dm/dt=2.17×10−6 M⊙/year).  相似文献   

6.
The formations of the blue straggler stars and the FK Com-type stars are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars are a very important source to understand the phenomena of Blue Straggler/FK Com-type stars. Recently, 12 W UMa-type binary stars, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars. We found that the system GSC 619-232 has the highest degree of overcontact (f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries.Of the 12 sample stars, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary stars may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary stars, we proposed two evolutionary scenarios evolving from deep, low-mass ratio overcontact binaries into Blue Straggler/FK Com-type stars.  相似文献   

7.
The changes in the orbital period of the short-period RS CVn-type binaryBH Vir are studied based on the analysis of the O-C curve formed by allphotoelectric times of light minimum. It was discovered that the orbitalperiod of BH Vir may show a periodic variation with a period of 9.12years. A weak evidence also indicating a small amplitude oscillation witha period of 52.7 years in the change of the orbital period. Two possiblemechanisms (light times effects due to two hypothetical additional bodiesand magnetic activity cycle) that could explained the period behavior arestudied. The periodic changes in the orbital period can be explained asdue either to magnetic activity cycles in the two components or to thelight-times effects of the additional bodies.  相似文献   

8.
The blue and yellow light curves of the RS CVn-type eclipsing binary Z Her were analyzed by using Wood's and Nelson. Davis and Etzel's methods. The results obtained by two different approaches are in good agreement. The absolute parameters of the components were also calculated using the parameters derived by Popper from the radial velocities. The physical parameters of the components indicate that the cooler one has separated or has been departing from the Main Sequence.  相似文献   

9.
We present new CCD photometric observations of V1044 Her obtained on May 22, 23 and 24, 2015. From our data, we derived five new light curve minimum times. Combining our new results with previously available CCD light minimum times, we derived an updated ephemeris and discovered that the period of this binary system exhibits an oscillation. The cyclic variation may be caused by the light-time effect via the presence of a third body or magnetic activity cycle. We calculated the corresponding period of the third body to be 14.1 ± 1.4 years or magnetic cycle to be 12.2 ± 0.7 years. We analyzed our new asymmetric light curves to obtain photometric solutions and starspot parameters using the Wilson and Devinney program. The final results show that V1044 Her is a contact binary system with a degree of contact factor f = 3.220( ± 0.002)%.  相似文献   

10.
Based on the available celestial intermediate pole (CIP) coordinate determinations from VLBI observations over the last 25 years, we have constructed a new highly accurate combined series of CIP coordinates. An amplitude-phase analysis of this series has allowed us to improve the previously estimated retrograde free core nutation (RFCN) parameters as functions of time. During this interval, the RFCN period changed several times. It was −418.1 ± 0.2 days before 1992.1 and then −431.6 ± 0.2 days until 1999.0. In 1999, the CIP oscillations damped out almost completely and the processwas restructured. Since 2000, the amplitude of these oscillations has increased and their period has become 450.7± 0.1 days.  相似文献   

11.
We demonstrate the power of the local correlation tracking technique on stellar data for the first time. We recover the spot migration pattern of the long-period RS CVn-type binary σ Gem from a set of six Doppler images from 3.6 consecutive rotation cycles. The resulting surface flow map suggests a weak anti-solar differential rotation with α ≈ –0.0022 ± 0.0016, and a coherent poleward spot migration with an average velocity of 220 ± 10ms-1. This result agrees with our recent findings from another study and could also be confirmed theoretically. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
Two-colour photoelectric light curves of the RS CVn-type eclipsing system UV Psc, obtained in 1985 and 1986, are presented. Present work also deals with the Fourier analysis of the outside-eclipse light variations for five years' light curves (1981, 1982, 1984, 1985, 1986). Based on this analysis, the amplitude variations of the so-called wave-like distortion and its migration period have been investigated. The amplitude of the wave-like distortion seems to vary with a very rough period of 4–5 years, and the migration period of the wave minimum appears to be one of the three different (2.3, 0.7, 0.4 years) but most possible values among some others.  相似文献   

13.
Differential photometry of the KI IV-III RS CVn-type binary HR 7275 in 1978, 1979, and 1980 at nine different observatories shows it definitely to be variable, thus confirming the suspicion of Herbst. The photometric period determined two ways was 27 . d 91 or 27 . d 65, thus about 3% shorter than the spectroscopically determined orbital period of 28 . d 59. The total variation observed during the three years was 0 . m 22 in theV. The light curve was always asymmetrical, with a stillstand on the rising branch in 1978 but on the falling branch in 1980.Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.Of the AAVSO.  相似文献   

14.
We present a photometric study of three chromospherically active stars with long periods (V340 Gem, SAO 62042 and FI Cnc). The observations were made at the ÇOMU Observatory in 2006 and 2007. We have made initial photometric analyses of V340 Gem and SAO 62042, which are newly discovered RS CVn–type SB1 binaries, and established the photometric variations of FI Cnc, which is a single G8III active star. Photometric rotation periods of these stars were obtained by analyzing their light variations. The light variations, observed over three or more consecutive orbital cycles, were investigated by using spot models with the program SPOT. We also discussed the surface differential rotation coefficient for the primary component of the SB1 binary star SAO 62042 in this study, using our own photometric period together with an orbital period taken from the literature.  相似文献   

15.
The semi‐regular variable star RU Vulpeculae (RU Vul) is being observed visually since 1935. Its pulsation period and amplitude are declining since ∼1954. A leading hypothesis to explain the period decrease in asymptotic giant branch (AGB) stars such as RU Vul is an ongoing flash of the He‐burning shell, also called a thermal pulse (TP), inside the star. In this paper, we present a CCD photometric light curve of RU Vul, derive its fundamental parameters, and test if the TP hypothesis can describe the observed period decline. We use CCD photometry to determine the present‐day pulsation period and amplitude in three photometric bands, and high‐resolution optical spectroscopy to derive the fundamental parameters. The period evolution of RU Vul is compared to predictions by evolutionary models of the AGB phase. We find that RU Vul is a metal‐poor star with a metallicity [M/H] = –1.59 ± 0.05 and an effective surface temperature of Teff = 3634 ± 20 K. The low metallicity of RU Vul and its kinematics indicate that it is an old, low‐mass member of the thick disc or the halo population. The present day pulsation period determined from our photometry is ∼108 d, the semiamplitude in the V ‐band is 0.39 ± 0.03 mag. The observed period decline is found to be well matched by an evolutionary AGB model with stellar parameters comparable to those of RU Vul. We conclude that the TP hypothesis is in good agreement with the observed period evolution of RU Vul. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
A 16-inch Schmidt-Cassegrain telescope on the campus of Naresuan University of Thailand and several similar-size telescopes in China equipped with CCD cameras were used to observe 14 high amplitude delta Scuti stars: GP And, CY Aqr, BS Aqr, YZ Boo, AD CMi, VZ Cnc, EH Lib, DY Her, V927 Her, KZ Hya, BE Lyn, V1162 Ori, DY Peg, and CW Ser, between the years 1999 and 2010. Data were also collected from scientific journals and sources on the Internet for these variable stars. Times of light maximum of these delta Scuti stars were then either determined from the observations or obtained from the literature to analyze the pulsation period variations. For the 14 delta Scuti stars we concluded that 7 stars (BS Aqr, CY Aqr, AD CMi, EH Lib, KZ Hya, BE Lyn and DY Peg) are binary or multiple systems. 10 delta Scuti stars are found with periods increasing with rates between 5.86×10−9 and 2.34×10−6 per year and the other 4 stars (BS Aqr, DY Her, BE Lyn and DY Peg) show periods decreasing with rates of about 10−9 to 10−8 per year.  相似文献   

17.
Orbital period variations of two neglected Algol type binaries, CC Her and XZ Aql, are studied based on all available times of minima. In the case of CC Her, it is found that the O –C curve displays a tilted sinusoidal variation with an eccentricity of 0.54 ± 0.03 and a period of 52.4 ± 0.4 yr, which can be explained by the light‐time effect due to the presence of an unseen component. The course of the orbital period change in XZ Aql appears less reliable but its O –C curve can be represented by a periodic variation with a period of 36.7 ± 0.6 yr superimposed on an upward parabola. The parabolic variation indicates a secular period increase with a rate of dP /dt = 7.1 s per century. The corresponding conservative mass transfer from less massive component to the more massive one is about 3.26 × 10–7 M⊙ yr–1. It is interesting to see that the O –C variation of CC Her displays no evidence (as upward parabola) on the mass transfer characteristic for Algols. The periodic change of the orbital period of XZ Aql, like CC Her, may be caused by the presence of the thirdbody. The lower limits of the masses of the hypothetical unseen components for CC Her and XZ Aql are found to be 2.69 M⊙ and 0.47 M⊙, respectively. The third body of CC Her should be detectable not only spectroscopically but also photoelectrically, if it exists. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
The rotation period-activity luminosity and the rotation period-surface activity flux correlations for the components of RS CVn-type binaries are discussed. It is argued that such correlations, although they are required by dynamo generated magnetic fields, do not represent the dominant parameter in determining the level of activity. Evidences are given that these correlations may essentially be induced by the period-radius dependence for the components of RS CVn-type binaries, and in addition, this result may well be valid for all the late-type stars (single or binary components).  相似文献   

19.
The RS CVn-type eclipsing binary star RT Lac has been observed inB andV colours, during 1984, 1985, 1986, 1987, and 1988 observing seasons. The orbital period of the system was found to be decreasing with an amount of 62 s century–1. The brightnesses both at minima and maxima are changing with time. It seems that the variations of the brightnesses at mid-primary and second quarter are similar, but at second first quarters are opposite to each other. We believe that these variations are mainly related with the spots (or spot groups) located on the surface of the component star which is in front during the primary minimum. We also estimate the period of the spot activity cycle to be approximately six years.  相似文献   

20.
Light curve analysis for three short-period RS CVn-type binaries were performed, using: a) Fourier analysis techniques for light curve changes in the frequency domain; b) photometric curve fit by means of numerical quadratures to develop theoretical light curves appropriate to RS CVn stars. The two methods were applied to the systems ER Vul, BH Vir, and UV Psc. Improved physical and geometrical parameters are found by taking the average of the results measured by the above two methods.  相似文献   

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