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.     

Is WD 1437-008 a cataclysmic variable?

Comprehensive observations of a close binary candidate WD 1437-008 are performed. The shape and amplitude of the observed brightness variations are shown to be inconsistent with the hypothesis of reflection effects, and the photometric period of the system, P _phot = 0. ^d 2775, is found to differ from the period of spectral variations, P _sp = 0. ^d 272060. As a result, WD 1437-008 has been preliminarily classified as a low-inclination cataclysmic variable.     

Spectroscopy and optical/IR photometry of the cataclysmic variable CPD-48°1577

The photometric variability of CPD-48°1577 in the optical and IR ranges is discussed. The structure and variation of prominent emission line profiles are investigated. An estimate of the distance is given.Paper presented at the Lembang-Bamberg IAU Colloquium No 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.Based on data collected at the European Southern Observatory in Chile.     

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.     

Results of a long-term monitoring of the 1.35-cm water-vapor maser source ON 1 (1981–2013)

We present the results of our long-term monitoring of the 1.35-cm water-vapor maser source ON 1 performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory from 1981 to 2013. Maser emissionwas observed in a wide range of radial velocities, from ?60 to +60 km s^?1. Variability of the integrated flux with a period of ～9 years was detected. We show that the stable emission at radial velocities of 10.3, 14.7, and 16.5 km s^?1 belongs to compact structures that are composed of maser spots with close radial velocities and that are members of two water-maser clusters, WMC 1 and WMC 2. The detected short-lived emission features in the velocity ranges from ?30 to 0 and from 35 to 40 km s^?1 as well as the high-velocity ones are most likely associated with a bipolar molecular outflow observed in the CO line.     

A magnetic cycle of τ Bootis? The coronal and chromospheric view

τ Bootis is a late F‐type main sequence star orbited by a Hot Jupiter. During the last years spectropolarimetric observations led to the hypothesis that this star may host a global magnetic field that switches its polarity once per year, indicating a very short activity cycle of only one year duration. In our ongoing observational campaign, we have collected several X‐ray observations with XMM‐Newton and optical spectra with TRES/FLWO in Arizona to characterize τ Boo's corona and chromosphere over the course of the supposed one‐year cycle. Contrary to the spectropolarimetric reconstructions, our observations do not show indications for a short activity cycle (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

κ Velorum: another variable interstellar sightline?

We present ultra-high-resolution ( R = 900 000) observations of interstellar Na  i and K  i absorption lines towards κ Vel (HD 81188) which show clear evidence for temporal variation between 1994 and 2000. Specifically, the column densities of K⁰ and Na⁰ in the main velocity component have increased by 40 and 16 per cent, respectively, over this period. Earlier work had suggested that this component actually consists of two unresolved sub-components; this result is confirmed here, and the overall line profile is found to be consistent with only one of these sub-components having increased in strength since 1994. We argue that this variation is consistent with the line of sight gradually probing a cold, dense interstellar filament of the kind recently proposed by Heiles to explain other observations of small-scale structure in the interstellar medium.     

The period variation of the double mode high amplitude δ Scuti variable VZ Cnc

VZ Cnc is a population I double mode high amplitude δ Scuti variable. We observed the star and collected the data from January 2007 to January 2009 to determine 14 times of maximum light. We also searched its times of maximum light from other papers and from IBVS and got 57 values. We collected a total of 194 times of maximum light and used them to perform an (O-C) analysis and concluded that there may be no tendency of binary orbital light time effect. But by parabola tendency, it shows a continuous period increasing at the rate of 1.4×10⁻⁸ per year; this is compatible with the stellar evolution model calculation both in direction and size.     

What is the nature of RX J0720.4–3125?

RX J0720.4–3125 has recently been identified as a pulsating soft X-ray source in the ROSAT all-sky survey with a period of 8.391 s. Its spectrum is well characterized by a blackbody with a temperature of 8 × 10⁵ K. We propose that the radiation from this object is thermal emission from a cooling neutron star. For this blackbody temperature we can obtain a robust estimate of the object's age of ∼ 3 × 10⁵ yr, yielding a polar field ∼ 10¹⁴ G for magnetic dipole spin-down and a value of P compatible with current observations.     

KIC 5197256: an eclipsing binary containing a δ Scuti variable star

This paper reports analysis of an eclipsing binary system KIC 5197256 with a δ Sct variable component.Utilizing light-curve modeling,several stellar parameters are derived,e.g.,temperature,mass,and mass ratio.The O-C diagram is a straight line with a negative slope which means that its period is almost constant for about 2 yr.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.Large frequency separation is cross-identified with the histogram graph and the Fourier transform method.Based on the large separation and density relationship,the mean density of the δ Sct component is estimated to be 0.05 g·cm~(-3).Five frequencies with the same frequency spacing in the range of 25 d~(-1)-34 d~(-1) are detected.Statistically,the pulsation amplitudes of δ Sct stars increase with decreasing of rotations,so we propose that KIC 5197256 might have a relatively large rotational velocity,and the frequency f_(10) might be the rotation frequency.     

GSC 4560–02157: a new long-period eclipsing cataclysmic variable star

We study the newly discovered variable star GSC 4560–02157. CCD photometry was performed in 2013–2014 at the Tien Shan Astronomical Observatory,and a spectrum was obtained with the 6-m telescope of the Special Astrophysical Observatory in June, 2014. GSC 4560–02157 is demonstrated to be an eclipsing variable star(P = 0.265359d). All its flat-bottom primary minima are approximately at the same brightness level, but the star's out-of-eclipse brightness and brightness at secondary minima vary considerably(by up to 0.6m) from cycle to cycle. Moreover,there are short-term(time scale of 0.03–0.04 days) small-amplitude brightness variations out of eclipse. This behavior suggests a cataclysmic nature for the star, which is confirmed with a spectrum taken on 2014 June 5. The spectrum shows numerous emissions of the hydrogen Balmer series, He Ⅰ and He Ⅱ.     

Strong lensing of submillimetre galaxies: a tracer of foreground structure?

The steep source counts and negative K -corrections of bright submillimetre galaxies (SMGs) suggest that a significant fraction of those observed at high flux densities may be gravitationally lensed, and that the lensing objects may often lie at redshifts above 1, where clusters of galaxies are difficult to detect through other means. In this case, follow-up of bright SMGs may be used to identify dense structures along the line-of-sight. Here, we investigate the probability for SMGs to experience strong lensing, using the latest N -body simulations and observed source flux and redshift distributions. We find that almost all high-redshift sources with a flux density above 100 mJy will be lensed if they are not relatively local galaxies. We also give estimates of the fraction of sources experiencing strong lensing as a function of observed flux density. This has implications for planning follow-up observations for bright SMGs discovered in future surveys with the Submillimetre Common-User Bolometer Array 2 and other instruments. The largest uncertainty in these calculations is the maximum allowed lensing amplification, which is dominated by the presently unknown spatial extent of SMGs.     

Optical afterglows of gamma-ray bursts: a bimodal distribution?

The luminosities of the optical afterglows of gamma-ray bursts, 12 h (rest-frame time) after the trigger, show a surprising clustering, with a minority of events being at a significantly smaller luminosity. If real, this dichotomy would be a crucial clue to understand the nature of optically dark afterglows, i.e. bursts that are detected in the X-ray band, but not in the optical. We investigate this issue by studying bursts of the pre- Swift era, both detected and undetected in the optical. The limiting magnitudes of the undetected ones are used to construct the probability that a generic burst is observed down to a given magnitude limit. Then, by simulating a large number of bursts with pre-assigned characteristics, we can compare the properties of the observed optical luminosity distribution with the simulated one. Our results suggest that the hints of bimodality present in the observed distribution reflect a real bimodality: either the optical luminosity distribution of bursts is intrinsically bimodal, or there exists a population of bursts with a quite significant grey absorption, i.e. wavelength-independent extinction. This population of intrinsically weak or grey-absorbed events can be associated with dark bursts.     

Dune fields on Mars: Recorders of a climate change?

Dunes have similar morphologies on the Earth and Mars. The main differences between Martian and terrestrial dunes are their size, which is larger on Mars, and their duration of formation, which is longer on Mars. As the characteristic time of Martian dunes is in the same order as that of the Martian climatic oscillations, Martian dunes could be recorders of past winds regimes and past climates. In order to test this hypothesis, we performed a morphological study of 550 dune fields with high resolution images and we inferred the directions of the dune formative winds from the orientation of the dune slip faces. Our study shows that 310 dune fields record one to four distinct wind directions with some geometric patterns that do not exist on the Earth such as barchans built by opposite wind directions coexisting in the same dune field. Our study demonstrates that the inferred formative wind directions are only partially in agreement with the current wind-patterns predicted by General Circulation Models (GCM). Several possible causes for the misalignment between dunes and GCM outputs are discussed: these include the local variation of the global circulation due to local topographic effects or the possibility that these dunes could be in a transient geometry or fossil. Such bedforms are considered indeed to be not in equilibrium with the present-day atmospheric conditions. This latter hypothesis is supported by the presence, in some ergs, of closely spaced dunes showing nearly opposite slip face orientations. Therefore, we propose that Martian dune fields are constituted, in some cases, by active and fossil dunes and therefore have the potential to preserve information on paleoclimates over extensive periods.     

Chemistry in grain aggregates: a source of complex molecules?

The aggregation of grains in dense protostellar clouds brings together materials such as silicates, carbons, polycyclic aromatic hydrocarbons and ices to form porous structures with high internal volume. Some physical and chemical properties of these aggregate grains are discussed in the context of the role that they may play in the formation of complex organic and organometallic compounds. One characteristic of such grains that is unique outside planetary systems is the availability of all elements and a number of their common compounds in a composite solid. In dark clouds, the chemistry inside aggregate grains will be driven by cosmic ray heating and sputtering. This occurs in an environment where the products of such reactions can be retained within the dust particle. Hot atom chemistry and secondary reactions are facilitated by the re-entrant nature of such aggregated structures, leading to the possible formation of complex organic compounds. In particular, the sputtering of Si, Mg and Fe from silicate dust is discussed, and it is shown that a variety of organometallic compounds could be expected in ices within aggregate grains. The optical depth for ultraviolet light within aggregates is large, so that materials inside such grains will be effectively shielded from ambient radiation. However, the incorporation of luminifors such as those grain components responsible for the extended red emission converts ultraviolet to visible and near-infrared radiation, and might moderate photochemistry within aggregates. It is suggested that the chemical environment within aggregates may be conducive to the formation and retention of complex molecules such as amino acids, peptides and a variety of organometallic compounds.     

The maximum limit of the density variation parameter λ for a stable neutron star

A static spherically-symmetric model, based on an exact solution of Einstein's equation, gives the permissible matter density 2×10¹⁴ g cm^–3. If we use the change in the ratio of central density to the radiusr=a (i.e., central density per unit radius (₀/a), we call it radius density) minimum, we have estimated the upper limit of the density variation parameter () and minimum mass limit of a superdense star like a neutron star. This limit gives an idea of the domain where the neutron abundance with negligible number of electrons and protons (may be treated as pure neutrons) and equilibrium in neutrons begins.