Spectroscopy and orbital periods of the old novae V533 Herculis, V446 Herculis and X Serpentis

We report spectroscopic orbital periods of 0.147 d (=3.53 h) for V533 Her, 0.207 d (=4.97 h) for V446 Her and 1.478 d for X Ser. V533 Her (Nova Herculis 1963) shows absorption features in its He  i and Balmer lines which appear only in a limited range of orbital phase, suggesting that it is a low-inclination SW Sextantis star. V446 Her is unusual in that it has started normal dwarf nova eruptions after a nova outburst, but we find nothing else unusual about it – in particular, a distance estimate based on its dwarf nova outbursts agrees nicely with another based on the rate of decline of its nova eruption, both giving d ∼1 kpc. In X Ser, unlike in other old novae with long periods, no spectral features of the secondary star are visible. This and its outburst magnitude both suggest that it is quite distant and luminous, and at least 1 kpc from the Galactic plane.     

Superhumps in V348 Pup

The eclipsing nova-like cataclysmic variable star V348 Pup exhibits a persistent luminosity modulation with a period 6 per cent longer than its 2.44-h orbital period ( P _orb). This has been interpreted as a 'positive superhump' resulting from a slowly precessing non-axisymmetric accretion disc gravitationally interacting with the secondary. We find a clear modulation of mid-eclipse times on the superhump period, which agrees well with the predictions of a simple precessing eccentric disc model. Our modelling shows that the disc light centre is on the far side of the disc from the donor star when the superhump reaches maximum light. This phasing suggests a link between superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the full light curve and maximum entropy eclipse mapping both show that the disc emission is concentrated closer to the white dwarf at superhump maximum than at superhump minimum. We detect additional signals consistent with the beat periods between the implied disc precession period and both and     

An analysis of early spectroscopic observations and the light curve of the nova V1663 Aql (Nova Aql 2005)

I report the results of a spectroscopic follow‐up of the nova V1663 Aql performed at the Loiano telescope. The emission lines in the spectra have been identified to study the early evolution. The spectra measured some weeks after the maximum show Balmer lines, several Fe multiplets and low ionization lines. The presence of Fe multiplets confirms the original classification of V1663 Aql as a Fe II nova. I have built the light curve using the observations of IAU circulars, VSNET, AFOEV, ASAS databases to estimate the parameters of the nova: time and magnitude of maximum, and the decline rates by two or three magnitudes. The parameters have been used to deduce a distance of V1663 Aql in the range 7.3÷11.3 kpc. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A transient event in AD 775 reported by al‐Tabarī: A bolide – not a nova,supernova, or kilonova

Given that the cause for the strong increase in ¹⁴C in AD 774/5 in Japanese and German trees is still a matter of debate (e.g. short gamma‐ray burst or solar super‐flare), we have searched in Arabic chronicles for reports about unusual transient celestial events. In the History of al‐Tabarī we found two (almost identical) reports about such an event. The group around caliph al‐Mansūr observed a transient event while on the way from Baghdad to Mecca on AD 775 Augusst 29– September 1 (Julian calendar). A celestial object (kawkab) was seen to fall or set (inqadda), and its trace (atharuhu) was seen for at least tens of minutes (up to 70–90 min) during morning twilight. The reports use the Arabic words kawkab and athar(uhu), which were also used in the known Arabic reports about supernovae SN 1006 and 1054, so that one might consider an interpretation as a nova‐like event. The kawkab (celestial object) was observed only during the morning twilight at a brightness of probably between about –3 and 0 mag. Such a brightness and time‐scale would be expected for optical kilonovae (at ∼3 to 9 kpc) in the context of short gamma‐ray bursts. There are no similar reports from eastern Asia for this time. However, the short reports are fully consistent with a bolide: The word kawkab can be used for meteor, the verb inqad_. d_. a normally means falling down, the word atharuhu can mean its trace. We therefore prefer the interpretation as bolide. We discuss in detail how to convert the Muslim calendar date to a date in the Julian calendar using first the calculated Islamic calendar and then considering the time when the crescent new moon could be visible at the given location. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

矮新星概述与研究进展

矮新星是爆发频繁的激变变星,主星是白矮星,次星是充满洛希瓣的晚型矮星;白矮星周围有吸积盘,物质流与吸积盘的碰撞区域即热斑。与大多数密近双星系统相比,矮新星最大的特点是吸积盘的存在以及频繁的爆发现象。首先介绍了矮新星的研究历史和现状,对吸积盘的形成过程进行总结,给出了矮新星的基本物理图像;其次简要介绍了矮新星的各种次型的特征和形成原因,对目前的爆发模型进行归纳;回顾了矮新星中著名的轨道周期空缺现象和最短轨道周期截止现象,并给出其在标准化模型下的解释以及标准化模型面临的挑战;举例说明了矮新星的轨道周期变化分析不仅对研究其演化起着重要作用,而且是探测褐矮星和地外行星的重要手段;对食光变曲线的分析方法和矮新星中罕见的高低态变化进行了简单小结;最后,进行总结并讨论矮新星领域的发展趋势和目前的一些热点问题。     

激变双星的磁滞效应

本文研究了激变双星中较冷次星的星风在磁场耦合作用下造成的角动量损失，以及对激变双星演化的影响。本文特别注意到双星成员的星风物质损失和角动量损失应该与单星情况明显不同，这就是：双星成员的星风物质损失受到潮汐效应和系统自转效应的影响而增大，同时双星成员的角动量是由轨道角动量和自转角动量所组成，并且轨道角动量远大于自转角动量。研究结果表明，由于次星的星风物质损失率很小，星风的速度也不大，因而磁滞效应造成的角动量损失极小，不能成为驱动周期大于３小时的激变双星演化的机制。     

Clusters of galaxies with modified Newtonian dynamics

I consider X-ray emitting clusters of galaxies in the context of modified Newtonian dynamics (MOND). Self-gravitating isothermal gas spheres are not good representations of rich clusters; the X-ray luminosity at a given temperature is typically an order of magnitude larger than observed, and the predicted X-ray surface brightness distribution is not well-matched by the standard 'β-model' fits to the observations. Pure gas spheres with a density distribution described by a β-model also fail because, with MOND, these objects are far from isothermal and again overluminous. These problems may be resolved by adding an additional dark mass component in the central regions, here modelled by a constant density sphere contained within two core radii and having a mass typically of one to two times the total cluster mass in the gas. With this additional component, the observed luminosity–temperature relation for clusters of galaxies is reproduced, and the typical mass discrepancy in actual clusters is three to four times smaller than implied by Newtonian dynamics. Thus, while MOND significantly reduces the mass of the dark component in clusters it does not remove it completely. I speculate on the nature of the dark component and argue that neutrinos, with mass near the experimental upper limit are a possible candidate.     

Nova Sagittarii 1998 (V4633 Sgr): a permanent superhump system or an asynchronous polar?

We report the results of observations of V4633 Sgr (Nova Sagittarii 1998) during     . Two photometric periodicities were present in the light curve during the three years of observations: a stable one at     , which is probably the orbital period of the underlying binary system; and a second one of lower coherence, approximately 2.5 per cent longer than the former. The latter periodicity may be a permanent superhump, or, alternatively, the spin period of the white dwarf in a nearly synchronous magnetic system. A third period, at     , corresponding to the beat between the two periods was probably present in 1999. Our results suggest that a process of mass transfer has taken place in the binary system since no later than two-and-a-half months after the nova eruption. We derive an interstellar reddening of     from our spectroscopic measurements and published photometric data, and estimate a distance of     to this nova.     

The accretion flow in the discless intermediate polar V2400 Ophiuchi

RXTE observations confirm that the X-ray light curve of V2400 Oph is pulsed at the beat cycle, as expected in a discless intermediate polar. There are no X-ray modulations at the orbital or spin cycles, but optical line profiles vary with all three cycles. We construct a model for line-profile variations in a discless accretor, based on the idea that the accretion stream flips from one magnetic pole to the other, and show that this accounts for the observed behaviour over the spin and beat cycles. The minimal variability over the orbital cycle implies that (1) V2400 Oph is at an inclination of only ≈10°, and (2) much of the accretion flow is not in a coherent stream, but is circling the white dwarf, possibly as a ring of denser, diamagnetic blobs. We discuss the light that this sheds on disc formation in intermediate polars.