Photometric observations and Numerical modeling of SDSS J162520.29+120308.7, an SU UMa in the CV period gap

We present R-band photometric observations of Cataclysmic Variable dwarf nova SU UMa SDSS J162520.29+120308.7 during the July 2010 superoutburst, from near maximum through decline and into a single rebrightening. We find a maximum superoutburst amplitude of ∼ 6.1 magnitudes and a maximum rebrightening amplitude of ∼4 magnitudes. Near superoutburst maximum, we find 0.09604(3) days for the mean Stage B positive superhump period and a much longer period for the hump shaped modulation during the rebrightening. For the orbital period, we find P_orb = 0.09113(30) days. As all periods both agree and disagree with values reported by others, additional observations are needed. Our 2015 observations of this system in quiescence reveal a 0.09080(20) day orbital period. As our 2010 value is within the error bars of a spectroscopically determined value and our 2015 photometrically determined value, we suggest 0.09113(30) days as the orbital period for this system. As for the secondary-to-primary mass ratio, analytical models using observed orbital and Stage B positive superhump periods as input suggest q = 0.221. As a check, we present a 3D SPH simulation of the rise to, and during the plateau stage of, the SU UMa in superoutburst, assuming P_orb=0.09113 days. For Stages A and B, we find 0.09717 days and 0.09702 days, respectively, for the average simulated positive superhump periods. Analytical models using these simulated Stages A and B and the simulated orbital period suggest q = 0.1920(4) and q = 0.221, respectively, for this system. Due to the poorly constrained observational data and the similar mass ratio estimates regardless of stage, we can neither confirm nor deny that Stage A is better than Stage B for determining mass ratio in CV dwarf novae SU UMa systems. Additional observations and simulations are needed to further test this recently proposed hypothesis. For now, we suggest an average q = 0.21(1) for this system.     

First photometric study of the W UMa system GSC 1042-2191

We present new photometric observations covering eight minima times for the eclipsing binary GSC 1042-2191. The light curves in $\mathit{BVRI}$ colors were analyzed by using WD-code for the system parameters. Eight minima times were obtained from the new observations. The system is found a low mass ratio (q = 0.148), A-type over-contact binary with a fill out parameter of f = 65.01 ± 12.18%. The preliminary absolute dimensions (M₁= 1.26 ± 0.06 M_⊙, M₂ = 0.18 ± 0.06 M_⊙, R₁ = 1.54 ± 0.20 R_⊙, R₂ = 0.69 ± 0.01 R_⊙, ${\mathit{L}}_1$ =3.30 ± 0.30 L_⊙ and ${\mathit{L}}_2$ = 0.59 ± 0.20 L_⊙) indicate the very much oversized and over-luminous secondary component, by assuming the present luminosity of the secondary is its main sequence luminosity, we predict the original mass is about 0.8 M_⊙, this means the present secondary could be transferred and/or lost 77% of its original mass and only its core is left.     

Period and light-curve study of the contact eclipsing binary V523 Cas

CCD photometry of the eclipsing W Uma binary system V523 Cas in U, B, V and R_C filters was carried out during eight nights in 2012. The physical and geometrical parameters of this system are obtained. A possible pulsation period of one of the components is obtained by analyzing the residuals of the ephemeris light curve. Our observations contain 16 times of minimum light. We combined these with all available published times of minimum. By fitting a quadratic curve to the O-C values, a new ephemeris of the system is calculated. By attributing the period change to mass transfer, we find a mass transfer rate of $4\times {10}^{-12}$$\frac{M_{\odot }}{yr}$. Also, Period (80.58 yr) and the minimum mass (0.3 M_⊙) of a possible third body is estimated. In addition, the possible existence of a fourth body with a mass of order 0.15 M_⊙ is discussed. These third and fourth bodies could be low-mass main-sequence stars (red dwarfs).     

Eclipsing binary UU Cas: Radial-velocity curves

This paper reports the results of spectroscopic observations of UUCas obtained with the highresolution (R = 15 000) fiber-fed echelle spectrometer of the 1.2-m telescope of Kourovka Astronomical Observatory of Ural Federal University. The radial velocities of the secondary, more massive and fainter component are measured for the first time. The component mass ratio is found to be q = M ₁/M ₂ = 0.54. The component masses, M ₁ = 9.5M _⊙ and M ₂ = 17.7M _⊙, and the radius of the or bit, A = 52.7R _⊙, are computed for the published orbital inclination of i ~ 69°. Evidence is presented for a disk surrounding the more massive component and a common expanding envelope.     

The most metal-poor quadruple system of subdwarfs G89-14

The system of subdwarfs G89-14 is one of the most metal-poor multiple stars with an atmospheric metal abundance [m/H] = ?1.9. Speckle interferometry at the 6-m BTA telescope has revealed that G89-14 consists of four components. Measurements of the magnitude difference between the components and published data have allowed their masses to be estimated: M _A ≈ 0.67 M _⊙, M _B ≈ 0.24M _⊙,M _C ≈ 0.33M _⊙, andM _D ≈ 0.22M _⊙. The ratio of the orbital periods of the subsystems has been obtained, 0.52 yr: 3000 yr: 650 000 yr (1: 5769: 1 250 000), indicative of a high degree of hierarchy o fG89-14 and its internal dynamical stability. The calculated Galactic orbital elements and the low metallicity of the quadruple system suggest that it belongs to the Galactic halo.     

A Model of the Mira–Type Star T UMi

Stellar evolution calculations were carried out from the main sequence to the final stage of the asymptotic giant branch for stars with initial masses 1 M_⊙ ≤ M_ZAMS ≤ 2 M_⊙ and metallicity Z = 0.01. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of radiation hydrodynamics and time–dependent convection describing radial stellar pulsations. The study was aimed to construct the hydrodynamic models of Mira–type stars that show the secular decrease in the pulsation period Π commenced in 1970th at Π = 315 day. We show that such a condition for the period change is satisfied with evolutionary sequences 1 M_⊙ ≤ M_ZAMS ≤ 1.2 M_⊙ and the best agreement with observations is obtained for M_ZAMS = 1.2 M_⊙. The pulsation period reduction is due to both the stellar radius decrease during the thermal pulse of the helium burning shell and mode switch from the fundamental mode to the first overtone. Theoretical estimates of the fundament parameters of the star at the onset of pulsation period reduction are as follows: the mass is M = 0.93 M_⊙, the luminosity is L = 4080 L_⊙, and the radius is R = 220 R_⊙. The mode switch occurs 35 years after the onset of period reduction.     

Pulsations of intermediate–mass stars on the asymptotic giant branch

Evolutionary tracks from the zero age main sequence to the asymptotic giant branch were computed for stars with initial masses 2 M _⊙ ≤ M _ZAMS ≤ 5 M _⊙ and metallicity Z = 0.02. Some models of evolutionary sequences were used as initial conditions for equations of radiation hydrodynamics and turbulent convection describing radial stellar pulsations. The early asymptotic giant branch stars are shown to pulsate in the fundamental mode with periods 30 day ? Π ? 400day. The rate of period change gradually increases as the star evolves but is too small to be detected (Π?/Π < 10^?5 yr^?1). Pulsation properties of thermally pulsing AGB stars are investigated on time intervals comprising 17 thermal pulses for evolutionary sequences with initial masses M _ZAMS = 2 M _⊙ and 3 M _⊙ and 6 thermal pulses for M _ZAMS = 4 M _⊙ and 5 M _⊙. Stars with initial masses M _ZAMS ≤ 3 M _⊙ pulsate either in the fundamental mode or in the first overtone, whereas more massive red giants (M _ZAMS ≥ 4 M _⊙) pulsate in the fundamental mode with periods Π ? 10³ day. Most rapid pulsation period change with rate ?0.02 yr^?1 ? Π?/Π ? ?0.01 yr^?1 occurs during decrease of the surface luminosity after the maximum of the luminosity in the helium shell source. The rate of subsequent increase of the period is Π?/Π ? 5 × 10^?3 yr^?1.     

Orbital period analysis of eclipsing post-novae T Aurigae: Evidence of magnetic braking and an unseen companion

Four new CCD times of light minimum of T Aurigae are presented. The orbital period variation is analyzed by means of the standard O–C technique. The new times of light minimum indicate that a ～24 yr sine-like period variation superimposed on a secular orbital period decrease is obviously seen in the O–C diagram. However, the orbital period should increase because of mass transfer between components. In order to solve this apparent paradox, three possibilities including magnetic braking mechanism, which plays an important role in angular moment loss of binary, are proposed. The mass loss rate $\dot{M}={10}^{-10.4}{M}_{\odot }{\text{yr}}^{-1}$ is derived by assuming that the Alfvén radius of secondary is the same as that of the sun (i.e. $R_A?15R_{\odot }$). Using the observational relationship of ${\dot{M}}_{\mathit{mb}}-P_{\mathit{orb}}(h)$ (McDermott and Taam, 1989, Rappaport et al., 1983), the Alfvén radius of secondary is estimated as $R_A?1.9R_{\odot }$, which only requires a weak magnetic field in secondary. Since the brightness variations of T Aurigae caused by Applegate’s mechanism need large energy beyond the total radiant energy in the time interval of 24 yr, the third body light travel-time effect is the most likely explanation for the 24-yr variation. The third body may be a brown-dwarf star in case of the high orbital inclination.     

Superhump evolution of WZ Sge-type dwarf nova ASASSN-14cv at rebrightening stage

We report the results of observations of a WZ Sge-type dwarf nova ASASSN-14cv, acquired in 2014 and covering the end of a superoutburst and a rebrightening stage. We detected 8 rebrightenings of this star. Based on the light curve profiles of the rebrightenings, we conclude on the existence of both the “inside-out” and “outside-in” outbursts. During the entire course of the rebrightening stage, a brightness variability with the mean period of P = 0.^d06042(8) was detected, which was identified as a superhump period during the stage B of the superoutburst. The character of the registered superhump evolution can be either described by a parabolic approximation with the negative P_dot = ?1.1 × 10^?5, or by an approximation with 2 linear areas with the corresponding periods of 0.^d06074(3) and 0.^d06046(9).     

Spectral and photometric studies of polar CRTS CSS 130604 J 215427+155714

We present the results of spectroscopic and photometric studies of a new polar CRTS CSS130604 J 215427+155714, conducted at the telescopes of the SAO RAS. Analysis of the photometric series of observations allowed to clarify the orbital period of the system, P _o = 0_. ^d 0672879 (±0.0000003). We build radial velocity curves and trace the intensity variations in the Hβ and H_γ hydrogen lines and He II λ 4686 ?A ionized heliumline. Based on the Hβ and He II lines we build Doppler maps. It is shown that the line formation region is localized near the Lagrange point. The following parameter estimates of the system are obtained:M ₁ = 0.83 ± 0.10M _⊙, M ₂ = 0.15 ± 0.01M _⊙, q = M ₂/M ₁ = 0.18 ± 0.03, i = 53? ± 5?. Based on the results of spectral, photometric and previously published polarimetric observations the possible geometric model of the system is discussed.     

Photometric and spectral studies of the eclipsing polar CRTS CSS081231 J071126+440405

We present the results of the study of the eclipsing polar CRTS CSS081231 J071126+440405. Photometric observations allowed us to refine the orbital period of the system \(P_ \circ = 0_ \cdot ^d 0.08137673\). Considerable changes in the appearance of the object’s spectra have occurred over the period of September 20–21, 2001: the slope of the continuum changed from “red” to “blue”, and the variability of the line profiles over the duration of the orbital period has also changed. Doppler maps have shown a shift of the emission line-forming region along the accretion stream closer to the white dwarf. We measured the duration of the eclipse of the system and imposed constraints on the inclination angle \(78_ \cdot ^ \circ 7 < i < 79_ \cdot ^ \circ 3\). The derived radial velocity amplitude was used to obtain the basic parameters of the system: M₁ = 0.86 ± 0.08M_⊙, M₂ = 0.18 ± 0.02 M_⊙, q = 0.21 ± 0.01, R_L2 = 0.20 ± 0.03 R_⊙, A = 0.80 ± 0.03 R_⊙. The spectra of the object exhibit cyclotron harmonics. Their comparison with model spectra allowed us to determine the parameters of the accretion column: B = 31–34 MG, T_e = 10–12 keV, θ = 80–90°, and Λ = 10⁵.