Close binary systems in star-forming regions: EQ Ori in the Ori I association

Photoelectric (UBVR) observations of the eclipsing variable EQ Ori are presented. The ephemerides of primary minima are refined, and the range of the star’s light variations is determined. All light curves are solved by Lavrov’s direct method, and highly accurate photometric orbital elements are obtained for the system. The magnitudes and colors of each component are calculated and analyzed in two-color (U-B)-(B-V) and (U-B)-(V-R) diagrams. The system’s primary component is classified as a metallic-line Am star. The absolute parameters of the components are estimated, and the binary is classified as a detached system with a subgiant: A0 V and K2 IV. EQ Ori has a faint physical companion, which causes the epochs of primary minimum to be systematically displaced with a period of about 30 years. The expected parameters of the distant companion are estimated. The system’s components are at a pre-ZAMS evolutionary stage, with their age being 2×10⁶ years. EQ Ori is thought to be a member of the Ori I association.     

Minimum on the light curve of the classical symbiotic star AS 338 in 1999

We present our UBVRI photometry and spectroscopy of AS 338 performed in 1999–2000. Another eclipse of the hot component in this symbiotic binary system, the deepest one ever observed, occurred in September 1999. The U brightness declined by ～2^m, the Hβflux decreased by a factor of ～2.3, and the [O III]γ5007 flux did not change. The hot component is eclipsed at orbital phases ?≈0.045–0.057. The U-B color index begins to appreciably fluctuate during an eclipse of the hot component and its circumstellar envelope. About 100 days after a strong outburst of 1995, the mean UBV brightness of AS 338 declined linearly in the ensuing five years at the same rate in all bands (ΔU/Δt≈10^?3 mag/day). The brightness of the outer, uneclipsed parts of the circumstellar envelope also decreased, which is attributable to a reduction in the luminosity of the hot component against the rise in its temperature. The appearance of He II lines has not yet been recorded, though the optical brightness of AS 338 has already dropped by ～2^m after the outburst.     

UGC 5119: A galaxy with a stellar polar ring?

We present our photometric BV R_c observations of UGC 5119, a candidate polar-ring galaxy. We have determined its absolute magnitude, \(M_{0,B} = - 20\mathop m\limits_. 3\), and total color indices, \((B - V)_t^0 = + 0\mathop m\limits_. 73 \pm 0\mathop m\limits_. 10\) and \((V - R_c )_t^0 = + 0\mathop m\limits_. 54 \pm 0\mathop m\limits_. 10\). A Fourier analysis of the shape of its isophotes shows that UGC 5119 is most likely an elliptical galaxy with a disk component in the central part and a “boxy” feature on the periphery. At distances larger than 8″, the galaxy exhibits a turn of its major axis and a change in the phase of the fourth harmonic. Assuming the position angle of the major axis to be constant, a stellar ringlike structure is distinguished in the galaxy. The age of the ring stars is the same as that of the stars in the host galaxy. The distinguished ringlike structure cannot be attributed to typical polar rings rich in gas and in young stars.     

Spectral and photometric evolution of the symbiotic nova HM Sagittae in 1986–2002

We present the results of our photometric and spectroscopic observations of the symbiotic nova HM Sge in 1994–2002. After its outburst in 1975, the star was shown to fade in the U, B, V bands at a rate of about \(0\mathop m\limits_. 05\) per year. The behavior of the B-V and U-B color indices reflects the variations of emission lines and, in part, the fading of the erupted component. We have studied the evolution of the emission spectrum in the range from Hδ to λ7751 Å over the period 1986–2002. The absolute fluxes in the hydrogen lines decreased by half, the ionization of the gaseous envelope continued to increase, and the Raman O VI lines appeared and strengthened. The significant (threefold) decrease in the ratio of the auroral and nebular O III lines is interpreted as a drop in the electron temperature of the envelope as its density decreased by a factor of about 1.5. We have measured the absolute intensity of the near-infrared continuum up to 10 000 Å and show that the infrared continuum follows the pulsations of the Mira star in the system HM Sge. We conclude that the dust envelope around the cool component became noticeably transparent in the 1990s.     

Axisymmetric magnetic fields in stars: relative strengths of poloidal and toroidal components

In this third paper in a series on stable magnetic equilibria in stars, I look at the stability of axisymmetric field configurations and, in particular, the relative strengths of the toroidal and poloidal components. Both toroidal and poloidal fields are unstable on their own, and stability is achieved by adding the two together in some ratio. I use Tayler's stability conditions for toroidal fields and other analytic tools to predict the range of stable ratios and then check these predictions by running numerical simulations. If the energy in the poloidal component as a fraction of the total magnetic energy is written as E_p / E , it is found that the stability condition is a ( E / U ) < E_p / E ≲ 0.8 where E /U is the ratio of magnetic to gravitational energy in the star and a is some dimensionless factor whose value is of order 10 in a main-sequence star and of order 10³ in a neutron star. In other words, whilst the poloidal component cannot be significantly stronger than the toroidal, the toroidal field can be very much stronger than the poloidal–given that in realistic stars we expect E / U < 10⁻⁶. The implications of this result are discussed in various contexts such as the emission of gravitational waves by neutron stars, free precession and a 'hidden' energy source for magnetars.     

FG Sagittae: New observations in the R CrB photometric phase

In 1999–2002, we continued our photometric and spectroscopic observations of FG Sge. This star has been in a new R CrB photometric phase since 1992. We constructed the BV RI light curves and studied the behavior of the color indices as a function of the fading amplitude. As previously, all of the three deep minima observed during this period were found to be blue on the descent; this was interpreted as the result of strong stellar light scattering in dust clouds formed on the line of sight. We analyzed the wavelength dependence of extinction in the circumstellar shell outside fadings, which was similar to Whitford's standard reddening law. Low-resolution spectroscopic observations allowed us to study the changes in the intensities of Swan bands and the Na I D doublet during deep and shallow (up to 1^m) fadings. We confirmed the reversal of the spectrum of the extended stellar envelope on the descending branches of deep minima.