No Arabic abstract
We present R-band photometry of the SW Sex-type cataclysmic variable WX Arietis made in October 1995 and August 1998-February 1999. Contrary to previous results, we find that WX Ari is an eclipsing system with an orbital inclination of ~72 deg. The R-band light curves display highly variable, shallow eclipses ~0.15-mag deep and ~40 min long. The observed eclipse depth suggests a partial eclipse of the accretion disc. The light curves also show a wide dip in brightness centred at orbital phase ~0.75 and a hump close to the opposite phase at ~0.2. The observed dip may be explained by the probable vertical thickening of the outer rim of the accretion disc downstream from the bright spot. We also demonstrate that the disc brightness in all SW Sex systems is nearly the same. This implies that the orbital inclination of these systems is only a function of eclipse depth.
Long-term (up to 10000d) monitoring has been undertaken for 41 Seyferts in the near-IR (JHKL). All but 2 showed variability, with K ampl in the range <0.1 to > 1.1 mags. The timescale for detectable change is from about one week to a few years. A simple cross-correlation study shows evidence for delays of up to several hundred days between the variations seen at the shortest wavelengths and the longest in many galaxies. In particular, the data for F9 now extend to twice the interval covered earlier and the delay between its UV and IR outputs persists. An analysis of the fluxes shows that, for any given galaxy, the colours of the variable component are usually independent of the level of activity. The state of activity can be parameterized. Taken over the whole sample, the colours of the variable components fall within moderately narrowly defined ranges. In particular, the H-K colour is appropriate to a black body of temperature 1600K. The H-K excess for a heavily reddened nucleus can be determined and used to find E_{B-V}, which can be compared to the values found from the visible region broad line fluxes. Using flux-flux diagrams, the flux within the aperture from the underlying galaxy can often be determined without the need for model surface brightness profiles. In many galaxies it is apparent that here must be an additional constant contribution from warm dust.
In this paper we report on $sim10$ years of observations of PSR J2051$-$0827, at radio frequencies in the range 110--4032 MHz. We investigate the eclipse phenomena of this black widow pulsar using model fits of increased dispersion and scattering of the pulsed radio emission as it traverses the eclipse medium. These model fits reveal variability in dispersion features on timescales as short as the orbital period, and previously unknown trends on timescales of months--years. No clear patterns are found between the low-frequency eclipse widths, orbital period variations and trends in the intra-binary material density. Using polarisation calibrated observations we present the first available limits on the strength of magnetic fields within the eclipse region of this system; the average line of sight field is constrained to be $10^{-4}$ G $lesssim B_{||} lesssim 10^2$ G, while for the case of a field directed near-perpendicular to the line of sight we find $B_{perp} lesssim 0.3$ G. Depolarisation of the linearly polarised pulses during the eclipse is detected and attributed to rapid rotation measure fluctuations of $sigma_{text{RM}} gtrsim 100$ rad m$^{-2}$ along, or across, the line of sights averaged over during a sub-integration. The results are considered in the context of eclipse mechanisms, and we find scattering and/or cyclotron absorption provide the most promising explanation, while dispersion smearing is conclusively ruled out. Finally, we estimate the mass loss rate from the companion to be $dot{M}_{text{C}} sim 10^{-12} M_odot$ yr$^{-1}$, suggesting that the companion will not be fully evaporated on any reasonable timescale.
We present long-term photometric observations of the young open cluster IC 348 with a baseline time-scale of 2.4 yr. Our study was conducted with several telescopes from the Young Exoplanet Transit Initiative (YETI) network in the Bessel $R$ band to find periodic variability of young stars. We identified 87 stars in IC 348 to be periodically variable; 33 of them were unreported before. Additionally, we detected 61 periodic non-members of which 41 are new discoveries. Our wide field of view was the key to those numerous newly found variable stars. The distribution of rotation periods in IC 348 has always been of special interest. We investigate it further with our newly detected periods but we cannot find a statistically significant bimodality. We also report the detection of a close eclipsing binary in IC 348 composed of a low-mass stellar component ($M gtrsim 0.09,mathrm{M}_{odot}$) and a K0 pre-main sequence star ($M approx 2.7,mathrm{M}_{odot}$). Furthermore, we discovered three detached binaries among the background stars in our field of view and confirmed the period of a fourth one.
We present X-ray observations of the high-inclination low-mass X-ray binary system X2127+119 (AC211) in the globular cluster M15 (NGC 7078). The observations consist of data acquired in 1996 with the RXTE satellite and in 1995 with the ASCA satellite. Also, the MPC1 data from the 1988 GINGA observations were de-archived and re-analysed. The phase-folded 2-10 keV hardness ratios from all three missions differ significantly indicating that the system can exhibit different spectral behaviours. We find that the X-ray eclipse profiles can be described relatively well using a simple model where the secondary star passes in front of a large X-ray emitting region. For this we require a mass ratio (q=M1/M2) of about one. The radius of this X-ray emitting region is ~0.8 RL1 and its vertical extent 60 degrees above the orbital plane. We suggest that if this X-ray emitting region were an optically thick corona, it would explain various puzzling aspects of this system. We also show that the X-ray dip observed at phases around 0.65 does not conform with the idea that the dip is caused by vertically extended material associated with the stream/disc impact region, but that it could be due to structure in the inner parts of the disc.
We present the discovery of eclipses in the X-ray light curves of the X-ray binary Swift J1858.6-0814. From these, we find an orbital period of $P=76841.3_{-1.4}^{+1.3}$ s ($approx21.3$ hours) and an eclipse duration of $t_{rm ec}=4098_{-18}^{+17}$ s ($approx1.14$ hours). We also find several absorption dips during the pre-eclipse phase. From the eclipse duration to orbital period ratio, the inclination of the binary orbit is constrained to $i>70^circ$. The most likely range for the companion mass suggests that the inclination is likely to be closer to this value than $90^circ$. The eclipses are also consistent with earlier data, in which strong variability (flares) and the long orbital period prevent clear detection of the period or eclipses. We also find that the bright flares occurred preferentially in the post-eclipse phase of the orbit, likely due to increased thickness at the disc-accretion stream interface preventing flares being visible during the pre-eclipse phase. This supports the notion that variable obscuration is responsible for the unusually strong variability in Swift J1858.6-0814.