اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe contact binary VW Cephei revisited: surface activity and period variation
144
0
0.0
(
0
)
تأليف
T. Mitnyan
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Context. Despite the fact that VW Cephei is one of the well-studied contact binaries in the literature, there is no fully consistent model available that can explain every observed property of this system. Aims. Our motivation is to obtain new spectra along with photometric measurements, to analyze what kind of changes may have happened in the system in the past two decades, and to propose new ideas for explaining them. Methods. For the period analysis we determined 10 new times of minima from our light curves, and constructed a new O$-$C diagram of the system. Radial velocities of the components were determined using the cross-correlation technique. The light curves and radial velocities were modelled simultaneously with the PHOEBE code. All observed spectra were compared to synthetic spectra and equivalent widths of the H$alpha$ line were measured on their differences. Results. We have re-determined the physical parameters of the system according to our new light curve and spectral models. We confirm that the primary component is more active than the secondary, and there is a correlation between spottedness and the chromospheric activity. We propose that flip-flop phenomenon occurring on the primary component could be a possible explanation of the observed nature of the activity. To explain the period variation of VW Cep, we test two previously suggested scenarios: presence of a fourth body in the system, and the Applegate-mechanism caused by periodic magnetic activity. We conclude that although none of these mechanisms can be ruled out entirely, the available data suggest that mass transfer with a slowly decreasing rate gives the most likely explanation for the period variation of VW Cep.
قيم البحث
اقرأ أيضاً
YZ Phe is a very short-period contact binary (Sp.= $K2,V$) with an orbital period of 0.2347 days near the short period limit (0.22 d). We present the complete light curves in $VRI$ bands, which photometric data were obtained with the 0.61-m telescope
of PROMPT-8 at CTIO in Chile during June to October 2016 and August 2017. The photometric solutions were determined by using the W-D method and the results reveal that YZ Phe is a W-subtype shallow contact binary ($fsim$ 10%, $q$ = 2.635 or $1/q$ = 0.379 for W subtype) with rotational motion of a large hot spot on the more massive component, showing a strong OConnell effect with variation of maxima in photometric time series at period of 4.20 yr and stellar cycle at period of 1.28 yr. By compiling all available eclipse times, the result shows a long-term period decrease at a rate of $mathrm{d}P/mathrm{d}t = -2.64(pm 0.02)times 10^{-8}$ d $yr^{-1}$, superimposed on a cyclic variation ($A_3$ = 0.0081 days and $P_3$ = 40.76 years). This variation cannot be explained by Applegate mechanism. Thus, the cyclic change may be interpreted as light-travel time effect via the presence of a cool third body. Based on photometric solutions, the third light was detected with 2% contribution of total light in $V$ and $I$ bands. Those support the existence of a third body. For the long-term period decrease, it can be explained by mass transfer from the more massive component ($M_2 sim 0.74 M_{odot}$) to the less massive one ($M_1 sim 0.28 M_{odot}$) or plus AML via magnetic braking. With $1/q$ $<$ 0.4 and long-term period decrease, all suggest that YZ Phe is on the AML-controlled state and its fill-out factor will increase, as well as the system will evolve into a deeper normal contact binary.
This paper presents new CCD BVRI light curves of the newly discovered RS CVn eclipsing binary V1034 Her in 2009 and 2010, which shapes are different from the previous published results. They show asymmetric outside eclipse and we try to use a spot mo
del to explain the phenomena. Using the Wilson-Devinney program with one-spot or two-spots model, photometric solutions of the system and starspot parameters were derived. Comparing the two results, it shows that the case of two spots is better successful in reproducing the light-curve distortions. For all the spot longitudes, it suggests that the trend towards active longitude belts and each active longitude belts might be switch. Comparing the light curves of 2009 and 2010, it indicates that the light curve changes on a long time scale of one year, especially in phase 0.25. In addition, we also collected the values of the maximum amplitudes of photometric distortion of the short-period RS CVn binary. We found for the first time that there is a trend of increasing activity with decreasing the orbital period. Finally, fitting all available light minimum times including our newly obtained ones with polynomial function confirmed that the orbital period of V1034 underwent up increase.
Studying chromospheric activity of contact binaries is an important way of revealing the magnetic activity processes of these systems. An efficient but somewhat neglected method for that is to follow the changes of the H$alpha$ line profiles via opti
cal spectroscopy. Our goal was to perform a comprehensive analysis based on the optical spectral signs of chromospheric activity on the largest sample of contact binaries to date. We collected echelle spectra on 12 bright contact binaries and derived new radial velocity curves from our observations. For quantifying the apparent chromospheric activity levels of the systems, we subtracted self-constructed synthetic spectra from the observed ones and measured the equivalent widths of the residual H$alpha$-profiles at each observed epoch. Our well-sampled data set allowed us to study the short-term variations of chromospheric activity levels as well as to search for correlations between them and some basic physical parameters of the systems. Fitting the radial velocity curves, we re-determined the mass ratios and systemic velocities of all observed objects. We found that chromospheric activity levels of the studied systems show various changes during the orbital revolution: we see either flat, or one-peaked, or two-peaked distributions of equivalent width vs. the orbital phase. The first case means that the activity level is probably constant, while the latter two cases suggest the presence of one or two active longitudes at the stellar surfaces. Our correlation diagrams show that mean chromospheric activity levels may be in connection with orbital periods, B$-$V color indices, inverse Rossby numbers, and temperature differences of the components. At the same time, no clear trend is visible with respect to mass ratios, inclinations and fill-out factors of the systems. A- and W-type contact binaries in our sample show similar distributions.
In this study we determined precise orbital and physical parameters of the very short period low-mass contact binary system CC Com. The parameters are obtained by analysis of the new CCD data with the archival spectroscopic data. The physical paramet
ers of the components derived as $M_textrm{c}$ = 0.717(14) $M_{odot}$, $M_textrm{h}$ = 0.378(8) $M_{odot}$, $R_textrm{c}$ = 0.708(12) $R_{odot}$, $R_textrm{h}$ = 0.530(10) $R_{odot}$, $L_textrm{c}$ = 0.138(12) $L_{odot}$, $L_textrm{h}$ = 0.085(7) $L_{odot}$, and the distance of the system is estimated as 64(4) pc. The times of minima obtained in this study and with those published before enable us to calculate the mass transfer rate between the components which is $1.6times10^{-8}$ M$_{odot}$yr$^{-1}$. Finally, we discuss the possible evolutionary scenario of CC Com.
Binaries are not always neatly aligned. Previous observations of the DI Her system showed that the spin axes of both stars are highly inclined with respect to one another and the orbital axis. Here we report on a measurement of the spin-axis orientat
ion of the primary star of the NY Cep system, which is similar to DI Her in many respects: it features two young early-type stars (~6 Myr, B0.5V+B2V), in an eccentric and relatively long-period orbit (e=0.48, P=15.d3). The sky projections of the rotation vector and the spin vector are well-aligned (beta_p = 2 +- 4 degrees), in strong contrast to DI Her. Although no convincing explanation has yet been given for the misalignment of DI Her, our results show that the phenomenon is not universal, and that a successful theory will need to account for the different outcome in the case of NY Cep.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
