V709 Cas Research Articles

Analysis of fundamental parameters for V477 Lyr

We analyze the photometric and spectroscopic observations of the young pre-cataclysmic variable (pre-CV) V477 Lyr. The masses of both binary components have been corrected by analyzing their radial velocity curves. We show that agreement between the theoretical and observed light curves of the object is possible for several sets of its physical parameters corresponding to the chosen temperature of the primary component. The final parameters of V477 Lyr have been established by comparing observational data with evolutionary tracks for planetary nebula nuclei. The derived effective temperature of the O subdwarf is higher than that estimated by analyzing the object’s ultraviolet spectra by more than 10000 K. This is in agreement with the analogous results obtained previously for the young pre-CVs V664 Cas and UU Sge. The secondary component of V477 Lyr has been proven to have a more than 25-fold luminosity excess compared to main-sequence stars of similar mass. Comparison of the physical parameters for the cool stars in young pre-CVs indicates that their luminosities do not correlate with the masses of the objects. The observed luminosity excesses in such stars show a close correlation with the post-common-envelope lifetime of the systems and should be investigated within the framework of the theory of their relaxation to the state of main-sequence stars.

INTEGRAL broadband X-ray spectrum of the intermediate polar V709 Cassiopeiae

We present the hard X-ray time-averaged spectrum of the intermediate polar V709 Cas observed with INTEGRAL. We performed the observation using data from the IBIS/ISGRI instrument in the 20-100 keV energy band and from JEM-X at lower energy (5-20 keV). Using different multi-temperature and density X-ray post-shock models we measured an improved post-shock temperature of ∼40 keV and estimated the V709 Cas mass to be 0.82 +0.12 -0.25 M ○. . We compare the resulting spectral parameters with previously reported BeppoSAX and RXTE observations.

질량비가 작은 접촉쌍성 V410 Aur과 V776 Cas-II

질량비가 작은 접촉쌍성 V410 Aur과V776 Cas를 소백산천문대의 61cm망원경에 2K CCD 카메라를 부착하여 측광 관측을 하였으며, 그 결과 이 별들의 새로운 3색(BVR)의 완전한 광도곡선을 얻었다. 새로운 광도곡선과 이미 발표된 분광관측으로부터 WD모델을 이용하여 이 두 별의 궤도요소와 절대 물리량을 얻었다. V410 Aur과 V776 Cas를 포함한 절대물리량이 잘 알려진 19개의 질량비가 작은 접촉쌍성들의 진화 상태를 조사하였다. 그 결과 질량비가 작은 접촉쌍성의 주성은 대부분 TAMS상에 놓이며 반성은 ZAMS 아래 놓이고 있음을 재확인하였다. New BVR CCD light curves of the low mass ratio contact binaries, V410 Aur and V776 Cas, were observed with the 61 cm reflector and a 2K CCD camera at the Sobaeksan Astronomical Observatory. The absolute dimensions of the low mass ratio contact binaries, V410 Aur and V776 Cas, were obtained using WD program from the published spectroscopic and newly observed photometric data. The evolutionary status of this type of binary system including V410 Aur and V776 Cas has been considered. We reconfirmed that the primary stars of the low mass contact binary system were located on the TAMS and secondary stars were located under the ZAMS in H-R diagram.

The Physical Nature and Orbital Behavior of V523 Cassiopeiae

V523 Cassiopeiae is a dwarf contact binary with one of the shortest orbital periods among the nondegenerate systems. Its orbital history is marked by large period changes. The photometrically determined mass ratios have historically been inconsistent with those calculated from radial velocity curves. In 1998 we acquired high-precision and standardized Johnson-Cousins UBV light curves. Our simultaneous BV light curve/radial velocity curve solutions provided good fits to both the light curves and the radial velocity curves using standard gravity darkening coefficients with a mass ratio of ~0.5. Seven precision mean epochs of minimum light were determined from these observations. We combine these with all available published times of minimum light, along with 50 times of low light found from a search of the archival Harvard plate stacks in the interval 1901–1942 to give us 567 eclipse timings. Our period study covers nearly 160,000 orbits, or ~102 yr. We find a high-amplitude sinusoidal variation with a period of 101 ± 7 yr, overlaid on a strong continuous period increase. The quadratic term is common in contact binaries, but a sinusoidal one is not. This suggests a hierarchical three-star system. Assuming that this is the case and that the inclination from our orbital solution for the close pair is the same as the larger orbit, we obtain a mass for the third star of 0.41 M⊙. This is similar to the masses of the stars that comprise the contact binary. If this scenario is correct, V523 Cas consists of a trio of late K and early M-type dwarfs having a total mass of ~1.6 M⊙. We show that high-resolution imaging can confirm this suggestion.

FUSEobservations of V592 Cas: the continuing enigma of orbitally modulated spectral signatures of accretion disc winds

By exploiting Far Ultraviolet Spectroscopic Explorer (FUSE) satellite time-series data, we have probed the relation between accretion disc geometry and bipolar outflow in the low-inclination, nova-like cataclysmic variable (CV) V592 Cas. Our results show that the outflow is strictly modulated on the orbital period and not on the (negative or positive) superhump periods of this system. This implies that the precession of either the disc eccentricity or its tilt is not directly affecting the structure and global dynamics of the outflow. The principal variability in the ultraviolet resonance lines is characterized by Doppler shifts of the entire blueward absorption troughs, in concert for a range of low- and high-ionization cases. The repetitive behaviour is asymmetric and highly non-sinusoidal over the orbital cycle of the system. The disc wind characteristics derived here allow V592 Cas to be added to a growing number of non-magnetic CVs which exhibit orbitally modulated wind variability. The origin of the departure in axisymmetry, which has to be fixed in the binary star frame, remains to be established.

The nature of the unique precataclysmic variable V664 Cas with two-peaked Balmer lines in its spectrum

We analyze photometric and spectroscopic observations of the close binary system V664 Cas. All the characteristics of its radiation are consistent with the star being a cataclysmic variable with powerful reflection effects. The orbital period is refined (P=0.5816475 d) and the ephemerides of the system determined. The U, B, V, R light curves of V664 Cas display sinusoidal variations with similar amplitudes near Δm=1.1m. This suggests that a hot spot on the surface of the secondary always dominates the optical radiation of the system. The spectra contain emission lines, two-peaked hydrogen lines, and narrow lines of helium and heavy elements in high ionization states, whose intensities vary synchronously with the brightness. The HeII λ4686 A line has broad absorption wings that form in the atmosphere of the O subdwarf. The mass function, f(m)=0.007M ⊙, is the lowest among all precataclysmic variables: the mass of the secondary exceeds the mass of the primary by more than a factor of 1.6. A full set of fundamental parameters for V664 Cas is determined based on modeling of the spectra and light curves, taking into account reflection effects in the system. Most of the emission lines are formed under conditions of appreciable deviations from local thermodynamic equilibrium. The possibility of carrying out correct modeling of the Balmer-line profiles assuming the stellar radiation is absorbed in a planetary nebula is demonstrated.

A photometric study of the recently discovered eclipsing binary V776 Cassiopei

Photoelectric UBV light curves of the recently discovered eclipsing binary V776 Cas were studied for the first time to derive the physical parameters of the system. The light curves were obtained at the T Ü B İ TAK National Observatory (TUG) during 8–9 October 2002. Due to the proximity of the visual companion the light curves were contaminated by the third light effect which has a relatively small impact on the system parameters estimation. This effect dominantly changes only the degree of overcontact and orbit inclination. The solutions made by using Djuraševic's inverse-problem method describe the V776 Cas system as a high overcontact configuration ( f over∼41% without, and 55% and 58% with two different values of the third light effect – L 3=0.091 and L 3=0.136) with a relatively small temperature differences between the components. Because of the large difference in masses of the components ( q= m c/ m h=0.13) these solutions suggest a significant mass and energy transfer from the hotter – more massive primary onto the cooler – less massive secondary through the connecting neck of the common envelope. The obtained orbital inclination ( i∼53 ∘.9 without, and i∼55 ∘ and i∼56 ∘ with two different values of the third light effect – L 3=0.091 and L 3=0.136) explains the characteristic shape of the light curves with a relatively small amplitude which is due to partial eclipses of the components in both of the photometric minima.

Balmer absorption variability and the disc wind of V592 Cassiopeiae

We present results from time-series optical spectroscopy of the low-inclination, nova-like cataclysmic variable, V592 Cas. The data span the wavelength range from similar to4000 to 5000 Angstrom. and include Balmer lines (Hbeta to Hepsilon) as well as He I and He II. The Balmer lines are generally characterized by shallow absorption troughs with superimposed narrower central emission components. The absorption troughs are variable on time-scales of at least similar to20 min, but the fluctuations are asymmetric such that they are more dominant on the blueward side of the profile out to similar to-2000 km s(-1). Fourier analysis reveals modulation periods for emission radial velocities and absorption changes of similar to0.114 and 0.103 d; we support earlier suggestions that the latter is likely to be 1-day alias of the former, which is essentially the system orbital period. However, there is a phase lag of similar to0.3 between absorption and emission changes. The Balmer absorption changes are compared to the predicted behaviour caused by the (stream overflowing) SW Sex phenomenon. There are several discrepancies in this scenario, including the highly asymmetric nature of blueward changes, the velocity amplitudes, and the phase relation to the emission changes. The role of a disc wind in V592 Cas is also discussed; in particular, with this data set, we cannot rule in or rule out the possibility that axisymmetry of the outflow is broken because it is seated on a warped/tilted inner disc, which is implied by previous evidence for negative superhumps in this system.

Radial Velocity Studies of Close Binary Stars. VIII.

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the seventh set of 10 close binary systems: V410 Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HX UMa, HD 93917, and NSV 223. All systems but three (V523 Cas, HD 93917, NSV 223) were discovered photometrically by the Hipparcos mission. All systems are double-lined (SB2) binaries, and all but the detached, very close system V1130 Tau are contact binaries. The broadening function permitted improvement of the orbital elements for V523 Cas, which was the only system observed before for radial velocity variations. Spectroscopic/visual companions were detected for V410 Aur and HX UMa. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

접촉쌍성 V523 CAS의 광도곡선 분석

보현산 천문대의 1.8m 망원경을 이용하여 1999년 10월 19일부터 21일까지 총 3일간 W UMa형 접촉쌍성 V523 Cas를 CCD 측광관측하여 총 616 (308의 <TEX>${\Delta}$</TEX>b점, 308의 <TEX>${\Delta}$</TEX>v점) 개의 관측점을 얻었다. 우리의 관측점으로부터 4개의 새로운 극심시각(주극심 2개, 부극심 2개)을 산출하였다. 우리가 얻은 BV 광도곡선과 Milone et al.(1985)의 시선속도곡선을 Wilson-Devinney(WD) 방법으로 흑점이 있는 경우와 없는 경우로 나누어 광도곡선의 해를 산출하였다. A total of 616 observations (308 in B, 308 in V) to. V523 Cas was made on three nights from October 19 to 21 in 1999 using the 1.8m telescope with 2K CCD camera of the Bohyunsan Optical Astronomy Observatory of KAO. With our data we constructed the BV light curves and determined 4 times of minimum light. We also obtained physical parameters of the system by combined analysis of both light and radial velocity curves using the Wilson-Devinney code.

Radial Velocity Studies of Close Binary Stars. V.

Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the fifth set of 10 close binary systems: V376 And, EL Aqr, EF Boo, DN Cam, FN Cam, V776 Cas, SX Crv, V351 Peg, EQ Tau, and KZ Vir. All systems are double-lined, spectroscopic contact binaries (KZ Vir may be a low-inclination, close, noncontact binary), with seven (all except EL Aqr, SX Crv, and EQ Tau) being the recent photometric discoveries of the Hipparcos project. The most interesting object is SX Crv, a contact system with an unprecedented low mass ratio, q = 0.066 ± 0.003, whose existence challenges the current theory of tidal stability of contact systems. Several of the studied systems are prime candidates for combined light and radial velocity synthesis solutions.

The white dwarf revealed in the intermediate polar V709 Cassiopeiae

Results are presented from the first detailed spectroscopic observations of the recently identified intermediate polar RXJ0028.8+5917/V709 Cas. The study of the emission line radial velocities allows us to remove the uncertainties on the different aliases of the orbital period and a best value is found at (0.2225 +/- 0.0002) day. It is also found that the system shows significant EW~ (2-4)A, broad absorptions affecting the Balmer lines from Hdelta to Hbeta. These broad absorptions are interpreted as the contribution of an underlying white dwarf atmosphere. The characteristics of the absorptions are found to be consistent with a DA log(g) = 8 white dwarf at a temperature of ~ 23 000 K, contributing ~ 17 % (at 4500 A) to the overall flux. This is the first direct detection of a white dwarf in an intermediate polar system. The absence of significant Zeeman splitting indicates a magnetic field lower than 10 MG, confirming that, at least in some cases, intermediate polars have weaker fields than polars. Different possibilities are discussed to explain the substantial contribution of the white dwarf to the overall flux.

The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae

We present photometry and high SNR spectroscopy in the classification region of V635 Cas, the optical counterpart to the transient X-ray pulsator 4U 0115+63, taken at a time when the circumstellar envelope had disappeared. V635 Cas is classified as a B0.2Ve star at a distance of 7-8 kpc. We use the physical parameters derived from these observations and the orbit derived from X-ray observations to elaborate a model of the system based on the theory of decretion discs around Be stars. We show that the disc surrounding the Be star must be truncated by the tidal/resonant interaction with the neutron star and cannot be in a steady state. This explains many of the observed properties of 4U 0115+63. In particular, because of this effect, under normal circumstances, the neutron star cannot accrete from the disc, which explains the lack of regular Type I outbursts from the source.

Orbital Period Changes of Two Very Short-Period W UMa Stars CC Com and V523 Cas: A Possible Evidence for TRO Plus AML Model

Orbital period changes of the two very short-period contact binaries, CC Com and V523 Cas, are presented. It is shown that the period of CC Com varies in secular decrease with rate of dP/dt = -4.39 x 10(-8) days/year, while the period of V523 Cas is increasing at rate of dP/dt = +9.09 x 10(-8) days/year. The physical parameters of the two W UMa stars are nearly equal which indicates that the physical properties of the two contact binaries are almost the same. The different types of period changes in the two systems may strongly suggest that, although they are undergoing secular angular momentum loss (AML), the oscillatory character predicted by thermal relaxation oscilation (TRO) theory still exist and they are on the different TRO stages, i.e., CC Com is on the shrinking TRO stage, but V523 Cas is on the expending TRO stage. The present period changes of the two systems can be explained by the combination of the TRO and the AML theories.

Science with Small Observatory Instruments

Good science can be done with small instruments. Very productive research in the area of short period interacting binary systems has been conducted by the authors with PMT’s and small CCD cameras attached to 0.28 m to 0.9-m instruments. A summary of important results over the past fourteen years is presented along with current work on the interesting semidetached and contact solar type systems TY UMa, V523 Cas, CN And, VZ Psc and BE Cep. Light curve asymmetries in CN And, BE Cep and possibly others indicate the presence of gas streams. This may signal that they are undergoing evolution into contact, an important but rarely observed stage in binary star evolution. Period studies are presented for each of the systems, documenting interesting orbital histories. V523 Cas and TY UMa display large period changes giving evidence of a light time effect due to a third body. This research has been largely supported at the local level and by small research grants from the American Astronomical Society.

A photometric study of the contact binaries V523 Cas and TY UMa

Broad-band V and I photometry of the short-period W UMa-type contact binaries V523 Cas and TY UMa are reported. From the light curves, the system parameters have been determined and evidence is presented for extensive spot activity in both systems, with V523 Cas being the more active system. A compilation of all the available photoelectric and CCD-based timings of eclipse minima is made; the O–C diagrams show evidence for an increasing period in the case of V523 Cas and a decreasing period in TY UMa. In addition we derive a more accurate astrometric position for V523 Cas from our CCD images.

The Relative Contributions to the Near‐Infrared Emission in Short‐Period Cataclysmic Variables

We present phase-resolved near-infrared broadband photometry of four short-period cataclysmic variables (HU Aqr, WZ Sge, TY Psc, and V592 Cas). Coupled with ultraviolet and optical data obtained from the literature, we have modeled the spectral energy distributions of these four cataclysmic variables, as well as that of the twin of WZ Sge, AL Com. The secondary stars contribute no more than 20%-50% of the near-infrared flux except for the polar HU Aqr, where the secondary contributes ~75% of the near-infrared flux. For the systems located above the orbital period minimum, the temperatures of the secondary stars match those for the expected main-sequence secondary stars. However, our modeling places WZ Sge below the orbital period minimum and shows it containing a secondary star of less than 1700 K—the coldest "star" yet identified.

Time‐resolved Photometry and Spectroscopy of the Cataclysmic Variable V592 Cassiopeiae

ABSTRACTOver the past 10 years, the cataclysmic variable (CV) V592 Cassiopeiae (LS I 55°‐8) has been monitored by one of the authors. We now present time‐resolved optical and infrared photometry and optical spectroscopy of this nova‐like binary. Analysis of these data provides the first orbital solution for this star. We find an orbital period near 0.114 days (2.7 hr), a system inclination of 28°, and a mass ratio (M2/M1) of 0.19. V592 Cas appears to be a nova‐like cataclysmic variable with a massive white dwarf primary and lies inside the CV period gap.

Test of the Optimization Techniques for the Photometric Analysis of Contact Binaries

We present light curve analyses of contact binaries and comparisons with previously published cross-correlations radial velocity data. The critical parameter q (mass-ratio) obtained from a grid technique is confronted with the spectroscopic value. For total eclipsing systems, both values are always in a good or reasonable agreement, including some stars with shallow light curves. For partial eclipsing systems, convergent photometric and spectroscopic results are obtained for an important set of stars. Two exceptions are V523 Cas and XY Boo for which some arguments are suggested. We concluded that reliable parameter determinations can be obtained from pure photometric solutions, by means of grid techniques.

Five-year photometry of V635 Cassiopeiae – the optical counterpart of 4U0115 + 63

VRI photometry of V635 Cas, the optical counterpart of the X-ray source 4U0115+63, obtained during the years 1985-90 is presented. Throughout this period three large optical eruptions were detected, two of which were accompanied by an X-ray outburst. The X-ray activity appeared a few hundred days after the onset of the optical outburst. It is suggested that the optical eruptions are generated by an accretion disc around the neutron star, and that the X-ray delay is due to a centrifugal barrier at the neutron star magnetosphere boundary. This effect might be also responsible for the appearance of an optical outburst without any observable X-ray counterpart