S 266: a ring nebula around a Galactic B[e] supergiant?

A narrow-band Hα image and high-resolution spectroscopy have been obtained in order to investigate the nature of S 266 and its central star MWC 137. The analysis of the stellar and nebular spectra suggests that MWC 137 is a B[e] supergiant located ≥ 6 kpc away from the Sun and not a Herbig Ae/Be star, as it has been traditionally classified. Moreover, the morphology and other properties of the nebula suggest that S 266 is a ring nebula, probably produced by the interaction of stellar winds with the ambient interstellar medium or unprocessed ejected matter. This result would imply that S 266 is the first ring nebula around a B[e] supergiant known in the Galaxy.     

The micro-glitch in PSR B1821−24: a case for a strange pulsar?

The single glitch observed in PSR B1821−24, a millisecond pulsar in M28, is unusual on two counts. First, the magnitude of this glitch is at least an order of magnitude smaller  (Δν/ν∼ 10⁻¹¹)  than the smallest glitch observed to date. Secondly, all other glitching pulsars have strong magnetic fields with   B ≳ 10¹¹ G  and are young, whereas PSR B1821−24 is an old recycled pulsar with a field strength of  2.25 × 10⁹ G  . We have earlier suggested that some of the recycled pulsars could actually be strange quark stars. In this work, we argue that the crustal properties of such a strange pulsar are just right to give rise to a glitch of this magnitude, explaining the scarcity of larger glitches in millisecond pulsars.     

“Pathological” Martian craters: Evidence for a transient obliteration event?

Abstract— We have detected three unusual, low-relief circular features, 1.2 to 2.1 km in diameter, in the northwest Noachis highlands, which may be craters that have undergone isostatic deformation. They may shed light on the existence, nature, and timing of suspected widespread Martian erosion/obliteration events, and offer clues to a type of Martian terrain softening. In the surrounding area, we find an anomalous deficiency of craters in the 3–11 km diameter range and evidence that larger, older craters have undergone relief softening and infill. We discuss three different hypotheses to explain these features, two of which involve Martian ice. This region may have undergone a transient event in which a near-surface permafrost layer (several hundred meters deep) underwent partial melting or softening. This would allow relaxation of kilometer-scale craters and softening of larger craters. Crater data presented here suggest that this event happened some time in mid-Martian history. Whether the event was regional or related to global-scale events is uncertain, though it may represent a class of events that also happened in other Martian areas.     

The new intermediate polar RX J1238 − 38: a system below the period gap?

We present optical observations of the recently discovered ROSAT source RX J1238 − 38, which is a new member of the intermediate polar class of asynchronous magnetic cataclysmic variables (CVs). Optical photometry reveals two coherent periodicities at 1860 and 2147 s respectively, with similar amplitudes of ∼ 8 per cent. Infrared ( J -band) intensity variations are detected only at the 1860-s period, at an amplitude of ∼ 15 per cent. The initial hypothesis, that these two periods were the spin and synodic (i.e., beat) period respectively, appears not to be supported by the spectroscopic data. The emission lines vary on the longer photometric period, and radial velocity variations are detected at this period and at a longer period of ∼ 5300 s, which we identify as the spin and orbital periods respectively. The most likely explanation for the 1860-s period is that it is the first harmonic of the ω − Ω sideband, leading to an improved determination of the orbital period as 5077 s (= 84 min). If this interpretation is correct, RX J1238 − 38 joins EX Hya as the only other intermediate polar below the 2–3 h period gap, and with an orbital period close to the minimum for CVs with non-degenerate secondaries. The spin-modulated emission-line radial velocities and widths appear to be anticorrelated, with maximum width occurring at maximum blueshift. Such an anticorrelation is expected for aspect changes of accretion curtains. Polarimetric observations of RX J1238 − 38 were inconclusive, although we can put a limit of 0.4 per cent on any variability on the circular polarization, and certainly there is no indication of variations at the photometric or spectroscopic periods.     

Observations of the extreme-ultraviolet transient RE J1255+266: a short outburst of a WZ Sge system?

We present a previously unpublished ROSAT Wide Field Camera observation of the transient source RE J1255+266 made just 4 d before the discovery observations. The source is not detected, limiting the duration of the outburst to be less than expected for a superoutburst of a WZ Sge system.
We also present a marginal detection of X-ray emission from RE J1255+266 using ASCA . The most probable luminosity is 6×10²⁹ erg s⁻¹, which is very similar to WZ Sge itself.
We discuss the nature of the source in the light of these observations, and conclude that it is most probably a WZ Sge system, but that the observed outburst must have been a normal dwarf nova outburst.     

STELLA and RoboTel – a prototype for a robotic network?

Robotic telescopes are more and more commonly used in today's astronomical research. In fact, several facilities are spread around the globe, already forming a loose net. A big leap forward would lie in the capabilities to share observations between different telescopes. One gains immediately weather independence and the possibility of continuous observations from a working network. In this paper, the three robotic telescope operated under the hood of the Astrophysical Institute Potsdam are introduced, the potential of a robotic telescope network are sketched out and principle hints on accomplishing such a network are outlined. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Oscillations Accompanying a He <Emphasis Type="SmallCaps">i</Emphasis> 10830 Å Negative Flare in a Solar Facula

On 21 September 2012, we carried out spectral observations of a solar facula in the Si?i 10827 Å, He?i 10830 Å, and H\(\upalpha\) spectral lines. Later, in the process of analyzing the data, we found a small-scale flare in the middle of the time series. Based on the anomalous increase in the absorption of the He?i 10830 Å line, we identified this flare as a negative flare.The aim of this article is to study the influence of the negative flare on the oscillation characteristics in the facular photosphere and chromosphere.We measured the line-of-sight (LOS) velocity and intensity of all the three lines as well as the half-width of the chromospheric lines. We also used the Helioseismic and Magnetic Imager (HMI) magnetic field data. The flare caused a modulation of all these parameters. In the location of the negative flare, the amplitude of the oscillations increased four times on average. In the adjacent magnetic field local maxima, the chromospheric LOS velocity oscillations appreciably decreased during the flare. The facular region oscillated as a whole with a 5-minute period before the flare, and this synchronicity was disrupted after the flare. The flare changed the spectral composition of the LOS magnetic field oscillations, causing an increase in the low-frequency oscillation power.     

Radio properties of the Shapley Concentration — II. J1324–3138: a remnant of a radio galaxy in the Abell cluster A3556?

In this paper we present a detailed study of the radio galaxy J1324–3138, located at a projected distance of 2 arcmin from the centre of the Abell cluster of galaxies A3556, belonging to the core of the Shapley Concentration, at an average redshift of z  = 0.05. We have observed J1324–3138 over a wide range of frequencies: at 327 MHz (VLA), 843 MHz (MOST), and at 1376, 2382, 4790 and 8640 MHz (ATCA).   Our analysis suggests that J1324–3138 is a remnant of a tailed radio galaxy, in which the nuclear engine has switched off and the radio source is now at a late stage of its evolution, confined by the intracluster gas. The radio galaxy is not in pressure equilibrium with the external medium, as is often found for extended radio sources in clusters of galaxies. We favour the hypothesis that the lack of observed polarized radio emission in the source is a result of Faraday rotation by a foreground screen, i.e. the source is seen through a dense cluster gas, characterized by a random magnetic field.   An implication of the head–tail nature of the source is that J1324–3138 is moving away from the core of A3556 and that, possibly, a major merging event between the core of A3556 and the subgroup hosting J1324–3138 has already taken place.     

V 361 Lyrae: An exotic binary system with a “Hot Spot” between the components?

A phenomenological model for V 361 Lyr is proposed. Probably it is a binary system which consists of a mass accreting primary star with mass of about M₁ ≈ 0·81 M⊙ and radius R₁ ≈ (6.1 ± 0·4) · 10¹⁰ cm and a mass losing secondary with about M₂ ≈ 0·77 M⊙ and R₂ ≈ 5.8 · 10¹⁰ cm. The secondary fills its Roche lobe, but the primary is something smaller than this lobe, contrary to the models of W UMa-type systems. So the hot spot appears in the atmosphere of the primary, but not in a disk, like in cataclysmic variables. The luminosity of the hot spot, L = (6-15) · 10³² erg/s, is large enough to be the main emission source of the system in visible light. So phenomenologically the object may be somewhat between W UMa-type stars and cataclysmic variables.     

Weak ion-acoustic double layers in a plasma with a <Emphasis Type="Italic">q</Emphasis>-nonextensive electron velocity distribution

Weak ion-acoustic double-layers (IA-DLs) in a two-component plasma are investigated in the context of the nonextensive statistics proposed by Tsallis. Due to the entropic index q, our plasma model can admit compressive as well as rarefactive IA-DLs. It is shown that the values \frac53 < q < 3\frac{5}{3}q-parameters for the existence of small-DLs. As long as the Mach number M is less than ∼1.42, the only admissible q-values which may lead to IA-DLs are all positive. For −1<q<1 (1<q<5/3), the effect of increasing q is to lower (to shift towards higher values) the critical Mach number M _cr above which only compressive IA-DL are admitted. Beyond q=3, only compressive small-amplitude ion-acoustic double layers are observed. Furthermore, due to the flexibility of the q-parameter, the obtained results bring a possibility to deal with small-DLs with relatively high Mach numbers. Our investigation may be of wide relevance to astronomers and space scientists working on interstellar plasmas.     

Glass‐bearing inclusions in Shergotty and Chassigny: Consistent samples of a primary trapped melt?

Glass‐bearing inclusions hosted by different mineral phases in SNC meteorites provide important information on the conditions that prevailed during formation of early phases and/or on the composition of the primary trapped liquids/melts of these rocks. Although extensive previous work has been reported on such inclusions, several questions are still unresolved. We performed a chemical and petrographic study of the constituents (glasses and mineral assemblage) of glassy and multiphase inclusions in Shergotty and Chassigny. We focused on obtaining accurate trace element contents of glasses and co‐existing minerals and discussing their highly variable REE contents. Our results reveal an unusual geochemistry of trace element contents that appear to be independent of their major element compositions. Chemical equilibrium between phases inside inclusions as well as between glasses and host minerals could not be established. The LREE contents of glasses in glass inclusions can vary by up to two orders of magnitude. The depletion in trace element abundances shown by glasses seem to be inconsistent with these phases being residual melts. The light lithophile element contents of glasses are highly variable with enrichment in incompatible elements (e.g., Be, Sr, Ba, and LREE) indicating some processes involving percolation of fluids. All of these features are incompatible with glass‐bearing inclusions in the host minerals acting as closed systems preserving unmodified primary liquids/melts. Glass‐bearing inclusions in Shergotty and Chassigny appear to have been altered (as was the rock itself) by different postformational processes (e.g., shock, metamorphism, metasomatic [?] fluids) that affected these meteorites with different degree of intensity. Our results indicate that these inclusions could not preserve a reliable sample of the primary trapped melt.     

Can ε Carinae be a triple system?

We examine the possibility that ε Carinae is a triple system. We show that a stable hierarchical system is possible, although perhaps only marginally.
We outline a speculative scenario for the history of the system, in which the giant outburst of the last century is associated with an interchange of components in a dynamically unstable triple system. We point out that the currently observed spectroscopic 'event' could be used to distinguish among the different possible configurations of the system.     

Is the semi‐regular variable RU Vulpeculae undergoing a helium‐shell flash?

The semi‐regular variable star RU Vulpeculae (RU Vul) is being observed visually since 1935. Its pulsation period and amplitude are declining since ∼1954. A leading hypothesis to explain the period decrease in asymptotic giant branch (AGB) stars such as RU Vul is an ongoing flash of the He‐burning shell, also called a thermal pulse (TP), inside the star. In this paper, we present a CCD photometric light curve of RU Vul, derive its fundamental parameters, and test if the TP hypothesis can describe the observed period decline. We use CCD photometry to determine the present‐day pulsation period and amplitude in three photometric bands, and high‐resolution optical spectroscopy to derive the fundamental parameters. The period evolution of RU Vul is compared to predictions by evolutionary models of the AGB phase. We find that RU Vul is a metal‐poor star with a metallicity [M/H] = –1.59 ± 0.05 and an effective surface temperature of T_eff = 3634 ± 20 K. The low metallicity of RU Vul and its kinematics indicate that it is an old, low‐mass member of the thick disc or the halo population. The present day pulsation period determined from our photometry is ∼108 d, the semiamplitude in the V ‐band is 0.39 ± 0.03 mag. The observed period decline is found to be well matched by an evolutionary AGB model with stellar parameters comparable to those of RU Vul. We conclude that the TP hypothesis is in good agreement with the observed period evolution of RU Vul. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

EPIC 202843107:a close eclipsing binary containing a δ Scuti variable

This paper reports on the discovery that an eclipsing binary system, EPIC 202843107, has aδ Scuti variable component. The phased light curve from the Kepler space telescope presents a detached configuration. The binary modeling indicates that the two component stars have almost the same radius and may have experienced orbital circularization. Frequency analyses are performed for the residual light curve after subtracting the binary variations. The frequency spectrum reveals that one component star is a δ Scuti variable. A large frequency separation is cross-identified with the corresponding histogram, the Fourier transform and the echelle diagram method. The mean density of the δ Scuti component is estimated to be 0.09 g cm~(-3) based on the large separation and density relation. Systems like EPIC 202843107 are helpful to study the stellar evolution and physical state of binary stars.     

HIDES: a High Dispersion Echelle Spectrograph

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GD 552: a cataclysmic variable with a brown dwarf companion?

GD 552 is a high proper motion star with the strong, double-peaked emission lines characteristic of the dwarf nova class of cataclysmic variable (CV) star, and yet no outburst has been detected during the past 12 yr of monitoring. We present spectroscopy taken with the aim of detecting emission from the mass donor in this system. We fail to do so at a level which allows us to rule out the presence of a near-main-sequence star donor. Given GD 552's orbital period of 103 min, this suggests that it is either a system that has evolved through the ∼80-minute orbital period minimum of CV stars and now has a brown dwarf mass donor, or that has formed with a brown dwarf donor in the first place. This model explains the low observed orbital velocity of the white dwarf and GD 552's low luminosity. It is also consistent with the absence of outbursts from the system.