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.     

Dirac spinor scattering states with positive-energy in rotating spheroid models

There are many rotating spheroids in the universe, and many astronomers and physicists have used theoretical methods to study the characteristics of stellar gravity since Newton's time. This paper derives the solutions of eight scattering states $({\varphi }^{(0)},{\chi }^{(0)},{\varphi }^{(1)},{\chi }^{(1)},{\varphi }^{(2)}$, ${\chi }^{(2)},{\varphi }^{(3)}$, and ${\chi }^{(3)})$ for the Dirac equation with positive-energy $E=\mathit{im}$, and establishes the relationship between the differential scattering cross section ${\sigma }_i(p,\theta ,\phi )$ and the stellar density $\mu$. It is found that: (1) For the eight scattering states, their average scattering cross-sections $\overline{{\sigma }_i}$ are proportional to ${\mu }^2$, and depend on the star's radius, and the higher the stellar density $\mu$, the greater the sensitivity of $\overline{\sigma \mathit{i}}$ to the change of $\mu$; (2) For the four scattering states ${\chi }^{(i)},i=0,1,2,3$, their average scattering amplitudes $\bar{f}(p,\theta )$ and $\bar{\sigma }(p,\theta )$ depend on the mass $m$ of the particles; while for the other four scattering states ${\varphi }^{(i)}$, $i=0,1,2,3$, then $\bar{f}$ and $\bar{\sigma }$ are independent of $m$. This study links the gravitational characteristics of stars with the scattering cross section, creating a new method for studying the gravitational characteristics, which helps to reveal the mystery of the gravity of rotating ellipsoidal stars.     

Description of accretion induced outflows from ultra-luminous sources to under-luminous AGNs

We study the energetics of the accretion-induced outflow and then plausible jet around black holes/compact objects using a newly developed disc-outflow coupled model. Inter-connecting dynamics of outflow and accretion essentially upholds the conservation laws. The energetics depend strongly on the viscosity parameter $\alpha$ and the cooling factor f which exhibit several interesting features. The bolometric luminosities of ultra-luminous X-ray binaries (e.g. SS433) and family of highly luminous AGNs and quasars can be reproduced by the model under the super-Eddington accretion flows. Under appropriate conditions, low-luminous AGNs (e.g. Sagittarius $A^1$) also fit reasonably well with the luminosity corresponding to a sub-Eddington accretion flow with $f\to 1$.     

Decomposition of the central structure of NGC 2273 in the NIR: A case study

The Seyfert 2 galaxy NGC 2273 is a prime target to explore how active nuclei can be fed. It has a star-forming innermost nuclear ring with a radius of 0.33kpc from where material may be funneled to the supermassive black hole in its center. In this article, we discuss high-resolution adaptive optics aided JHKs images of NGC 2273 taken with the Large Binocular Telescope. Using Galfit we decomposed the innermost part of NGC 2273 into a core, a disk, and a ring using 58 parameters, 44 of them were used to describe the ring. The stellar mass of the ring was found to be 12 $\times 10^8{\mathrm{M}}_{\odot }$, a factor of 10 higher than its molecular gas mass. A continuous gas flow via the main stellar bar of NGC 2273 during the lifetime of the bar of up to 10 ${\mathrm{M}}_{\odot }{\text{yr}}^{-1}$ is required to provide the fuel for the formation of the stars unless the star formation efficiency is on the order of 10%. This does not affect the fueling of the nuclear source as the amount of molecular gas required for this low-luminosity active galaxy to achieve this is on the order of $10^4{\mathrm{M}}_{\odot }$ only.     

New orbital solutions and absolute elements of the eclipsing binary TV Cet

We present new differential, four-color photoelectric photometry for the eclipsing binary TV Cet. UBVR light curves and radial velocities published previously are solved simultaneously using the Wilson–Devinney computer program. Our solutions indicate that TV Cet includes a third light contribution with 2.3% in U, 1.9% in B, 1.3% in V and 1.6% in R. The masses of the component stars are $1.34\pm 0.05$ and $1.23\pm 0.05M\odot$, while the radii are $1.47\pm 0.02$ and $1.21\pm 0.01R\odot$ for the primary and secondary components, respectively. Using new absolute properties and our previous results from period analysis, we calculated the observational and theoretical internal structure constants to be ${\overline{k}}_{2\text{,}\mathit{obs}}=-1.66$ and ${\overline{k}}_{2\text{,}\mathit{theo}}=-2.25$, respectively. Taking into account the third light contribution from the Wilson–Devinney solution and properties of the third body orbit from period analysis, the mass of the third body is obtained as $0.56M\odot$, corresponding to the inclination value $i_3=20°$. Evolutionary status of the component stars is also studied. We present the position of the stars in an H–R diagram for solar compositions.     

Analysis of resonant curves and phase portrait in the earth–moon system by using its unperturbed solution and earth’s equatorial ellipticity

In this research article, we have investigated resonant curves due to the rate of change of earth’s equatorial ellipticity parameter $\left(\dot{\gamma }\right)$, steady-state value of the angular velocity of the moon $\left({\dot{\theta }}_{mo}\right)$, and angular velocity of barycenter $\left(\dot{{\alpha }_0}\right)$ in the Earth-Moon system. Equations of motion of the moon are determined in a spherical coordinate system with the help of the gravitational potential of the earth. By using the unperturbed solution, equations of motion of the moon reduced into the second-order differential equation. From the solution it is observed that resonance occurs due to the frequencies $\dot{\gamma }$, ${\dot{\theta }}_{m0}$, and $\dot{{\alpha }_0}$ at the resonant points ${\dot{\theta }}_{m0}=2\dot{\gamma }$, $3{\dot{\theta }}_{m0}=2\dot{\gamma }$, ${\dot{\theta }}_{m0}=\dot{\gamma }$, ${\dot{\theta }}_{m0}={\dot{\alpha }}_0$. Finally, we have analyzed the phase portrait and phase space by method of Poincaré section when the system is free from forces.