Spectrophotometric Variability of Mira

Data from the Pulkovo spectrophotometric data base on the absolute quasimonochromatic fluxes from oCet in the 320–1080 nm range are used to determine the physical parameters of this star in different phases of its light curve. The continuum emission layer is found to expand between the phases of the cycle corresponding to the rising and falling branches of the light curve. The average expansion velocity is 32 km/s. By the time the star’s brightness has fallen by roughly three magnitudes, its radius has increased by almost a factor of three. Over this same time the temperature of the layer has fallen from 3000 K to 2200 K. For this expansion velocity, the calculated mass rate loss is ⊙ M /year.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 175–189 (May 2005).     

Low frequency flickering of TT arietis: Hard and soft X-ray emission region

Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures 1 keV and 10 keV. A coherent feature at 0.643 mHz appeared in the power spectra during the observation.     

A new model for the periodic outbursts of the BL Lac object OJ287

Recent observations provide strong evidence for the BL Lac object OJ287 exhibiting a 11.6±0.5 yr periodicity with a double-peaked maxima in its optical flux variations. Several models have been proposed for the optical behavior. The 2005 November outburst in OJ287 gives us a surprising result since calculation based on the periodicity was predicting such an outburst in late 2006. Here we suggest a new model, it can not only explain the optical quasi-periodic behavior, but also the radio flares behavior which is and simultaneous with the optical flares. We propose that OJ287 is a binary pair of super-massive black holes, both of them creating a jet. The quasi-periodic double peaks would be due to the relativistic beaming effect on the emission coming from the double helix jets. We used “core flares” to explain the large lags between light curves at different frequencies, and the assumption of two jets appear to be merged with each other partly in the radio frequency emitting regions provides a viable interpretation that we can see only a broad maximum which contains two radio flares that we cannot distinguish.     

A self-similar solution for a supernova explosion with allowance for accelerated relativistic particles

A self-similar solution to Sedov’s problem of a strong explosion in a homogeneous medium is generalized to the case of relativistic-particle generation in a supernova remnant; the particles are accelerated by Fermi’s mechanism at the shock front and in the perturbed post-shock region. Self-similarity takes place if the thickness of the prefront is small compared to its radius and if the pressure ratio of the relativistic and nonrelativistic components at the shock front is kept constant. In the presence of relativistic particles, the time dependence of the shock-front radius remains the same as that in their absence, but the plasma parameters in the inner perturbed region change appreciably. The shell of the matter raked up by the explosion is denser and thinner than that in the nonrelativistic case, the relativistic-particle pressure in the central region remains finite, and the nonrelativistic-gas pressure at the explosion center approaches zero. The influence of relativistic particles on the transition to the radiative phase of expansion of the supernova remnant and on its dynamics is studied. It is shown that relativistic particles can decrease several-fold the remnant radius at which the transition to the radiative phase occurs.     

Orbital periods of the binary sdB stars PG 0940+068 and PG 1247+554

We have used the radial velocity variations of two sdB stars previously reported to be binaries to establish their orbital periods. They are PG 0940+068 ( P =8.33 d) and PG 1247+554 ( P =0.599 d). The minimum masses of the unseen companions, assuming a mass of 0.5 M_⊙ for the sdB stars, are 0.090±0.003 M. for PG 1247+554 and 0.63±0.02 M_⊙ for PG 0940+068. The nature of the companions is not constrained further by our data.     

Modelling the bar in the centre of the starburst galaxy M82

We present VLA A-array 21-cm atomic hydrogen (H  i ) absorption observed against the central region of the starburst galaxy M82 with an angular resolution of ∼1.3 arcsec (≃20 pc). These observations, together with MERLIN H  i absorption measurements, are compared with the molecular (CO) and ionized ([Ne  ii ]) gas distributions and are used to constrain the dynamics and structure of the ionized, neutral and molecular gas in this starburst.
A position–velocity diagram of the H  i distribution reveals an unusual 'hole' feature which, when previously observed in CO, has been interpreted as an expanding superbubble contained within a ring of gas in solid body rotation. However, we interpret this feature as a signature of a nearly edge-on barred galaxy. In addition, we note that the CO, H  i and [Ne  ii ] position–velocity diagrams reveal two main velocity gradients, and we interpret these as gas moving on x₁- and x₂-orbits within a bar potential. We find the best fit to the data to be produced using a bar potential with a flat rotation curve velocity v _b=140 km s⁻¹ and a total length of 1 kpc, a non-axisymmetry parameter q =0.9, an angular velocity of the bar Ω_b=217 km s⁻¹ arcsec⁻¹, a core radius R _c=25 pc, an inclination angle i =80° and a projected angle between the bar and the major axis of the galaxy φ '=4°. We also discuss the orientation of the disc and bar in M82.     

Has the crab pulsar magnetic field grown after its birth?

We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for by the field growth theories.     

Discovery of 13 New Variable Stars in the Field of the Open Cluster NGC 2168 （M35）

A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δScuti stars.