Young eccentric binary KL CMa revisited in the light of spectroscopy

The absolute dimensions of the components of the eccentric eclipsing binary KL CMa have been determined. The solution of light and radial velocity curves of high ($\mathrm{\Delta }\lambda =0.14$ Å) and intermediate ($\mathrm{\Delta }\lambda =1.1$ Å) resolution spectra yielded masses M₁ = 3.55 ± 0.27 M_⊙, M₂ = 2.95 ± 0.24 M_⊙ and radii R₁ = 2.37 ± 0.09 R_⊙, R₂ = 1.70 ± 0.1 R_⊙ for primary and secondary components, respectively. The system consists of two late B-type components at a distance of 220 ± 20 pc for an estimated reddening of $E(B-V)=0.127$.The present study provides an illustration of spectroscopy’s crucial role in the analysis of binary systems in eccentric orbits. The eccentricity of the orbit ($e=0.20$) of KL CMa is found to be bigger than the value given in the literature ($e=0.14$). The apsidal motion rate of the system has been updated to a new value of $\dot{w}=0°.0199\pm 0.0002{\text{cycle}}^{-1}$, which indicates an apsidal motion period of $U=87\pm 1$ yrs, two times slower than given in the literature. Using the absolute dimensions of the components yielded a relatively weak relativistic contribution of ${\dot{w}}_{\mathit{rel}}=0°.0013{\text{cycle}}^{-1}$. The observed internal-structure component ($\log k_{2\text{,}\mathit{obs}}=-2.22\pm 0.01$) is found to be in agreement with its theoretical value ($\log k_{2\text{,}\mathit{theo}}=-2.23$).Both components of the system are found very close to the zero-age main-sequence and theoretical isochrones indicate a young age ($\tau =50$ Myr) for the system. Analysis of the spectral lines yields a faster rotation ($V_{\mathit{rot}1\text{,}2}=100$ km s⁻¹) for the components than their synchronization velocities ($V_{\mathit{rot}\text{,}\mathit{syn}1}=68$ km s⁻¹, $V_{\mathit{rot}\text{,}\mathit{syn}1}=49$ km s⁻¹).     

Absolute parameters of the newly-identified contact binary star IS Canis Major

This paper presents the results of the first high-resolution spectroscopic observations of the Southern W UMa type system IS CMa. Spectroscopic observations of the system were made at Mt. John University Observatory using a HERCULES fibre-fed échelle spectrograph in September 2007. The first radial velocities of the component stars of the system were determined by using the spectral disentangling technique. The resulting orbital elements of IS CMa are: $a_1\sin i=0.0041\pm 0.0001$ AU, $a_2\sin i=0.0135\pm 0.0001$ AU, $M_1{\sin }^{3}i=1.48\pm 0.01{\mathrm{M}}_{\odot }$, and $M_2{\sin }^{3}i=0.44\pm 0.01{\mathrm{M}}_{\odot }$. The components were found to be in synchronous rotation taking into account the disentangled ${\mathrm{H}}_{\delta }$ line profiles of both components of the system. The Hipparcos light curve was solved by means of the Wilson–Devinney method supplemented with a Monte Carlo type algorithm. The radial velocity curve solutions including the proximity effects give the mass ratio of the system as 0.297 ± 0.001. The combination of the Hipparcos light and radial velocity curve solutions give the following absolute parameters of the components: $M_1=1.68\pm 0.04{\mathrm{M}}_{\odot }\text{,}{\mathrm{M}}_2=0.50\pm 0.02{\mathrm{M}}_{\odot }\text{,}{R}_1=2.00\pm 0.02{\mathrm{R}}_{\odot }\text{,}{R}_2=1.18\pm 0.03R_{\odot }\text{,}{L}_1=7.65\pm 0.60$ ${\mathrm{L}}_{\odot }$ and $L_2=1.99\pm 0.80{\mathrm{L}}_{\odot }$. The distance to IS CMa was calculated as $87\pm 5$ pc using the distance modulus with corrections for interstellar extinction. The position of the components of IS CMa in the HR diagram are also discussed: the system seems to have an age of 1.6 Gyr.     

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.     

Signature of slow acoustic oscillations in a non-flaring loop observed by EIS/Hinode

We study intensity oscillations near the apex of a coronal loop to find the signature of MHD oscillations. We analyse the time series of the strongest Fe XII 195.12 Å image data, observed by 40″ SLOT of the EUV Imaging Spectrometer (EIS) onboard the Hinode spacecraft. Using a standard wavelet tool, we produce power spectra of intensity oscillations at location ‘${\mathrm{L}}_3$’ near the apex of a clearly visible coronal loop. We detect intensity oscillations of a period of ≈322 s with a probability of 96%. This oscillation period of ≈322 s is found to be in good agreement with theory of the (second) harmonics of standing slow acoustic oscillations of $P_{2\mathit{nd}\mathit{slow}}\approx 313\pm 31\text{s}$. We detect, for the first time, the observational signature of multiple (first and second) harmonics of slow acoustic oscillations in the non-flaring coronal loop. Such oscillations have been observed in the past in hot and flaring coronal loops only, but have been predicted recently to exist in comparatively cooler and non-flaring coronal loops as well. We find the periodicities ～497 s and ～592 s with the probability 99–100% at the ‘L₁’ and ‘L₂’ locations, respectively, near the clearly visible western footpoint of the loop. We interpret these oscillations to be likely associated with the first harmonics (fundamental mode) of slow acoustic oscillations. Using the period ratios $P_1/P_2=1.54\text{and}1.84$, we estimate the density scale heights in the EUV loop as ～10 Mm and 21 Mm, respectively, in which the latter value (～21 Mm) is compared well with the loop half length. We also find an evidence of propagating bright blob at its lower bound sub-sonic speed of ≈6.4 km/s, suggesting that they are caused by the mass flow from one end to the other in the coronal loop. We also suggest that standing oscillations, and propagating bright blobs caused probably by the pulse of plasma flow, co-exist in comparatively cooler and non-flaring coronal loop.     

An application of the tensor virial theorem to hole + vortex + bulge systems

The tensor virial theorem for subsystems is formulated for three-component systems and further effort is devoted to a special case where the inner subsystems and the central region of the outer one are homogeneous, the last surrounded by an isothermal homeoid. The virial equations are explicitly written under the additional restrictions: (i) similar and similarly placed inner subsystems, and (ii) spherical outer subsystem. An application is made to hole + vortex + bulge systems, in the limit of flattened inner subsystems, which implies three virial equations in three unknowns. Using the Faber-Jackson relation, $R_{\text{e}}\propto {\sigma }_0^2$, the standard $M_{\text{H}}$-${\sigma }_0$ form $(M_{\text{H}}\propto {\sigma }_0^4)$ is deduced from qualitative considerations. The projected bulge velocity dispersion to projected vortex velocity ratio, $\eta =({\sigma }_{\text{B}}{)}_{33}/\{[(v_{\text{V}}{)}_{\mathit{qq}}{]}^2+[({\sigma }_{\text{V}}{)}_{\mathit{qq}}{]}^2{\}}^{1/2}$, as a function of the fractional radius, $y_{\text{BV}}=R_{\text{B}}/R_{\text{V}}$, and the fractional masses, $m_{\text{BH}}=M_{\text{B}}/M_{\text{H}}$ and $m_{\text{BV}}=M_{\text{B}}/M_{\text{V}}$, is studied in the range of interest, $0?m_{\text{VH}}=M_{\text{V}}/M_{\text{H}}?5$ [Escala, A., 2006. ApJ, 648, L13] and $229?m_{\text{BH}}?795$ [Marconi, A., Hunt, L.H., 2003. ApJ 589, L21], consistent with observations. The related curves appear to be similar to Maxwell velocity distributions, which implies a fixed value of $\eta$ below the maximum corresponds to two different configurations: a compact bulge on the left of the maximum, and an extended bulge on the right. All curves lie very close one to the other on the left of the maximum, and parallel one to the other on the right. On the other hand, fixed $m_{\text{BH}}$ or $m_{\text{BV}}$, and $y_{\text{BV}}$, are found to imply more massive bulges passing from bottom to top along a vertical line on the $(\mathsf{O}{y}_{\text{BV}}\eta )$ plane, and vice versa. The model is applied to NGC 4374 and NGC 4486, taking the fractional mass,$m_{\text{BH}}$, and the fractional radius, $y_{\text{BV}}$, as unknowns, and the bulge mass is inferred from the knowledge of the hole mass, and compared with results from different methods. In presence of a massive vortex $(m_{\text{VH}}=5)$, the hole mass has to be reduced by a factor 2–3 with respect to the case of a massless vortex, to get the fit. Finally, the assumptions of homogeneous inner bulge and isotropic stress tensor are discussed.     

The age of cataclysmic variables: A kinematical study

Using available astrometric and radial velocity data, the space velocities of cataclysmic variables (CVs) with respect to Sun were computed and kinematical properties of various sub-groups of CVs were investigated. Although observational errors of systemic velocities (γ) are high, propagated errors are usually less than computed dispersions. According to the analysis of propagated uncertainties of the computed space velocities, available sample was refined by removing the systems with the largest propagated uncertainties so that the reliability of the space velocity dispersions was improved. Having a dispersion of $51\pm 7\mathrm{km}{\mathrm{s}}^{-1}$ for the space velocities, CVs in the current refined sample (159 systems) are found to have 5 ± 1 Gyr mean kinematical age. After removing magnetic systems from the sample, it is found that non-magnetic CVs (134 systems) have a mean kinematical age of 4 ± 1 Gyr. According to 5 ± 1 and 4 ± 1 Gyr kinematical ages implied by 52 ± 8 and 45 ± 7 km s^?1 dispersions for non-magnetic systems below and above the period gap, CVs below the period gap are older than systems above the gap, which is a result in agreement with the standard evolution theory of CVs. Age difference between the systems below and above the gap is smaller than that expected from the standard theory, indicating a similarity of the angular momentum loss time scales in systems with low-mass and high-mass secondary stars. Assuming an isotropic distribution, $\gamma$ velocity dispersions of non-magnetic CVs below and above the period gap are calculated ${\sigma }_{\gamma }=30\pm 5\mathrm{km}{\mathrm{s}}^{-1}$ and ${\sigma }_{\gamma }=26\pm 4\mathrm{km}{\mathrm{s}}^{-1}$. The small difference of $\gamma$ velocity dispersions between the systems below and above the gap may imply that magnetic braking does not operate in the detached phase, during which the system evolves from the post-common envelope orbit into contact.