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We report new mid-infrared and radio images of the M supergiant (X Orionis. The radio images, taken with MERLIN! and the Very Large Array, resolve the chromosphere of the star at a wavelength of 6 em, showing that the radio-emitting region has between two and three times the diameter of the optical photosphere. The infrared images, taken at the UK Infrared Telescope (UKIRT) using the Berkeley Infrared Camera, show that the dust shell is resolved. Images taken one year apart show great changes in morphology, which suggests that the dust shell is being asymmetrically illuminated by a stellar radiation field that is strongly affected by the presence and evolution of spots on the stellar surface. We present a new model of the circumstellar environment of the star, which fits the infrared and radio images and the spectral energy distribution (SED), and is consistent with recently reported Hubble Space Telescope observations. The chromospheric structure is determined quantitatively and the inner dust shell structure qualitatively with this model. We find that the inner radius of the dust shell is approximately 0.5 arcsec, which disagrees with a number of interferometric measurements that have resulted in an inner radius close to 1.0 arcsec. We are unable to explain this difference.

We present high spatial resolution images, at a wavelength of 6 cm, of the luminous blue variable star P Cygni. The images fully resolve the core of the stellar wind, and show that it is very clumpy. Two images were taken, separated in time by approximately a month, during which the structure in the wind has changed radically. The total flux observed has also changed significantly. We show that the clump sizes and electron densities are consistent with the radio variability being due to recombination of the ionized gas within the clumps, after key cooling lines become optically thin, causing the free-free emission to disappear. This is the first time that resolved radio images of a hot star wind have been obtained. It also represents important confirmation of a previous observation that thermal free-free wind emission can vary rapidly in a not stellar wind.

We present the first high-spatial-resolution radio observations of the Wolf-Rayet star WR 146, obtained at 1.6 and 5 GHz with the MERLIN array. The 5-GHz observations resolve the source into two components separated by 116 ± 14 milliarcsecond (mas). The weaker (southern) source is identified as thermal emission arising from the stellar wind of the WR star and the stronger (northern) source, which is resolved with a diameter of 38 mas and a brightness temperature Tb ", 106 K, as non-thermal emission. New infrared and millimetre photometry of WR 146 is consistent with a stellar-wind origin for the southern radio component, and allows us to estimate the distance to the WR star to be 1.2 ± 0.3 kpc. We also present a blue spectrum of WR 146, which shows evidence for absorption lines attributable to an DB-type companion to the WC6 star. In these respects, WR 146 is similar to the other Wolf - Rayet stars (WR 125 and 140) known to be non-thermal emitters. We suggest that the non-thermal emission arises from the interaction of the WR wind and that of its newly detected luminous companion. The observed size of the non-thermal radio-emitting region is consistent with that expected from colliding-wind theory. We estimate that the non-thermal emission is essentially unabsorbed by the stellar wind of the WR star, providing an unprecedented opportunity for studying colliding winds.

Classical nova outbursts occur in binary systems containing a white dwarf accretor and a Roche-lobe-filling main-sequence star. The outburst is due to a thermonuclear runaway in the accreted material on the surface of the white dwarf, and results in the ejection of up to 10–4 M ⨀ of material at velocities of several hundred to a few thousand kilometres per second. There is now strong evidence that the mass ejection takes place via a wind with secularly increasing velocity. The fast ejecta catches up with slower moving material ejected earlier in the outburst, forming a layer of shock-heated gas which gives rise to a short burst of soft X-ray emission. This emission was observed in V838 Her (Nova Herculis 1991), and was succesfully accounted for by the ‘interacting winds’ model. In this paper, we present 2.5-D numerical hydrodynamics calculations of interacting winds in novae which consider the effects of the binary system on shaping the mass-loss, and show that many of the features seen in the optical shells of novae many years after outburst can be accounted for.

1 Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, Liverpool, L3 5RF, UK e-mail: M.J.Darnley@ljmu.ac.uk 2 Institut de Ciencies de l’Espai (CSIC-IEEC), Campus UAB, C/Can Magrans s/n, 08193 Cerdanyola del Valles, Spain 3 Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands 4 Instituto de Astrofisica de Canarias, Via Lactea, s/n, La Laguna, 38205 Santa Cruz de Tenerife, Spain 5 Departamento de Astrofisica, Universidad de La Laguna, La Laguna, 38206 Santa Cruz de Tenerife, Spain 6 Department of Astronomy, San Diego State University, San Diego, CA 92182, USA 7 Physics Department, Lancaster University, Lancaster, LA1 4YB, UK 8 Department of Earth Science and Astronomy, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, 153-8902 Tokyo, Japan 9 Astronomical Institute, Academy of Sciences, 251 65 Ondřejov, Czech Republic 10 Astronomy Department, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801, USA 11 Department of Astronomy, Keio University, Hiyoshi, 223-8521 Yokohama, Japan 12 Variable Stars Observers League in Japan (VSOLJ), 7-1 Kitahatsutomi, 273-0126 Kamagaya, Japan 13 Astronomical Institute of the Charles University, Faculty of Mathemathics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic 14 Okayama Astrophysical Observatory, NAOJ, NINS, 3037-5 Honjo, Kamogata, Asakuchi, 719-0232 Okayama, Japan 15 European Space Astronomy Centre, Camino Bajo del Castillo s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Canada, Madrid, Spain 16 Departament de Fisica i Enginyeria Nuclear, EUETIB, Universitat Politecnica de Catalunya, c/ Compte d’Urgell 187, 08036 Barcelona, Spain 17 Institut d’Estudis Espacials de Catalunya, c/ Gran Capita 2-4, Ed. Nexus-201, 08034 Barcelona, Spain 18 Isaac Newton Group of Telescopes, Apartado de correos 321, 38700 Santa Cruz de La Palma, Spain

We observed HM Sagittae with the Multi-Element Radio Linked Interferometer Network (MERLIN*) at 6 cm and 18cm. We find non-thermal bipolar outflow in the east-west direction, associated with optical emission lines, and thermal ridges to the north and south associated with the UV nebulosity detected by the HST.

In our preceding paper, Liverpool Telescope data of M31 novae in eruption were used to facilitate a search for their progenitor systems within archival Hubble Space Telescope (HST) data, with the aim of detecting systems with red giant secondaries (RG-novae) or luminous accretion disks. From an input catalog of 38 spectroscopically confirmed novae with archival quiescent observations, likely progenitors were recovered for eleven systems. Here we present the results of the subsequent statistical analysis of the original survey, including possible biases associated with the survey and the M31 nova population in general. As part of this analysis we examine the distribution of optical decline times (t(2)) of M31 novae, how the likely bulge and disk nova distributions compare, and how the M31 t(2) distribution compares to that of the Milky Way. Using a detailed Monte Carlo simulation, we determine that 30 (+13/-10) percent of all M31 nova eruptions can be attributed to RG-nova systems, and at the 99 percent confidence level, >10 percent of all M31 novae are RG-novae. This is the first estimate of a RG-nova rate of an entire galaxy. Our results also imply that RG-novae in M31 are more likely to be associated with the M31 disk population than the bulge, indeed the results are consistent with all RG-novae residing in the disk. If this result is confirmed in other galaxies, it suggests any Type Ia supernovae that originate from RG-nova systems are more likely to be associated with younger populations, and may be rare in old stellar populations, such as early-type galaxies., 15 pages, 11 figures, accepted for publication in the Astrophysical Journal

We report the radio detection of a shell-like HI structure in proximity to, and probably associated with, the nova V458 Vul. High spectral resolution observation with the Giant Metrewave Radio Telescope has made it possible to study the detailed kinematics of this broken and expanding shell. Unlike the diffuse Galactic HI emission, this is a single velocity component emission with significant clumping at ~ 0.5' scales. The observed narrow line width of ~ 5 km/s suggests that the shell consists of mostly cold gas. Assuming a distance of 13 kpc to the system, as quoted in the literature, the estimated HI mass of the nebula is about 25 M_sun. However, there are some indications that the system is closer than 13 kpc. If there is a physical association of the HI structure and the nova system, the asymmetric morphology and the off-centred stellar system indicates past strong interaction of the mass loss in the asymptotic giant branch phase with the surrounding interstellar medium. So far, this is the second example, after GK Per, of a large HI structure associated with a classical nova.

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted.Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit.Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components.Results. We find that the source star is a giant G star with radius 9 R⊙. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s-1. We find that the lens is composed of a brown dwarf secondary of mass MS = 0.05 M⊙ orbiting a primary M-star of mass MP = 0.18 M⊙. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries.Conclusions. As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf. Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted. Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit. Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components. Results. We find that the source star is a giant G star with radius 9 R . The grid search gives two local minima, which correspond to the theoretical degeneracy s s . We find that the lens is composed of a brown dwarf secondary of mass M = 0.05 M orbiting a primary M-star of mass M = 0.18 M . We also reveal a new mass-ratio degeneracy for the central caustics of close binaries. Conclusions. As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf.

International audience; V1280 Sco is one of the slowest dust-forming nova ever historically observed. We performed multi-epoch high-spatial resolution observations of the circumstellar dusty environment of V1280 Sco to investigate the level of asymmetry of the ejecta We observed V1280 Sco in 2009, 2010 and 2011 using unprecedented high angular resolution techniques. We used the NACO/VLT adaptive optics system in the J, H and K bands, together with contemporaneous VISIR/VLT mid-IR imaging that resolved the dust envelope of V1280 Sco, and SINFONI/VLT observations secured in 2011. We report the discovery of a dusty hourglass-shaped bipolar nebula. The apparent size of the nebula increased from 0.30" x 0.17" in July 2009 to 0.64" x 0.42" in July 2011. The aspect ratio suggests that the source is seen at high inclination. The central source shines efficiently in the K band and represents more than 56+/-5% of the total flux in 2009, and 87+/-6% in 2011. A mean expansion rate of 0.39+/-0.03 mas per day is inferred from the VISIR observations in the direction of the major axis, which represents a projected upper limit. Assuming that the dust shell expands in that direction as fast as the low-excitation slow ejecta detected in spectroscopy, this yields a lower limit distance to V1280 Sco of 1kpc; however, the systematic errors remain large due to the complex shape and velocity field of the dusty ejecta. The dust seems to reside essentially in the polar caps and no infrared flux is detected in the equatorial regions in the latest dataset. This may imply that the mass-loss was dominantly polar.

Bipolarity is a common feature in the outbursts of classical, recurrent and symbiotic novae. In this paper, we present the results of numerical calculations of bipolar explosions in which two parcels of gas are ejected at highly supersonic and oppositely directed velocities into a cold surrounding medium. The calculations demonstrate the formation of a dense ring of shocked material in the plane normal to the line of ejection, due to the interaction of two bowshocks. Observational candidates for this hydrodynamic phenomenon are discussed.

We present near-infrared photometry for a number of old classical novae and related objects, and we use the data to estimate the mass-transfer rates in these systems. There is no correlation between mass-transfer rate and time since outburst, at least over the timebase (140 yr) for which we have data, contrary to what is expected in the hibernation model. Our data also point to potential recurrent novae amongst the classicals, namely EU Sct and V3645 Sgr

The Swift GRB satellite is an excellent facility for studying novae. Its rapid response time and sensitive X-ray detector provides an unparalleled opportunity to investigate the previously poorly sampled evolution of novae in the X-ray regime. This paper presents Swift observations of 52 Galactic/Magellanic Cloud novae. We included the XRT (0.3-10 keV) X-ray instrument count rates and the UVOT (1700-8000 Angstroms) filter photometry. Also included in the analysis are the publicly available pointed observations of 10 additional novae the X-ray archives. This is the largest X-ray sample of Galactic/Magellanic Cloud novae yet assembled and consists of 26 novae with super soft X-ray emission, 19 from Swift observations. The data set shows that the faster novae have an early hard X-ray phase that is usually missing in slower novae. The Super Soft X-ray phase occurs earlier and does not last as long in fast novae compared to slower novae. All the Swift novae with sufficient observations show that novae are highly variable with rapid variability and different periodicities. In the majority of cases, nuclear burning ceases less than 3 years after the outburst begins. Previous relationships, such as the nuclear burning duration vs. t_2 or the expansion velocity of the eject and nuclear burning duration vs. the orbital period, are shown to be poorly correlated with the full sample indicating that additional factors beyond the white dwarf mass and binary separation play important roles in the evolution of a nova outburst. Finally, we confirm two optical phenomena that are correlated with strong, soft X-ray emission which can be used to further increase the efficiency of X-ray campaigns., Accepted to ApJ Supplements. Full data for Table 2 and Figure 17 available in the electronic edition. New version of the previously posted paper since the earlier version was all set in landscape mode

We present the analysis result of a gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by 2 adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling of the light curve considering the parallax effect and Keplerian orbital motion, we are able to measure not only the physical parameters but also a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance $6.7\pm 0.3$ kpc from the Earth. The individual lens components with masses $0.9\pm 0.3\ M_\odot$ and $0.5\pm 0.1\ M_\odot$ are separated with a semi-major axis of $a=2.5 \pm 1.0$ AU and orbiting each other with a period $P=3.1 \pm 1.3$ yr. The event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves., 19 pages, 6 figures

Nova V2491 Cyg is one of just two detected pre-outburst in X-rays. The light curve of this nova exhibited a rare "re-brightening" which has been attributed by some as the system being a polar, whilst others claim that a magnetic WD is unlikely. By virtue of the nature of X-ray and spectroscopic observations the system has been proposed as a recurrent nova, however the adoption of a 0.1 day orbital period is generally seen as incompatible with such a system. In this research note we address the nature of the progenitor system and the source of the 0.1 day periodicity. Through the combination of Liverpool Telescope observations with published data and archival 2MASS data we show that V2491 Cyg, at a distance of 10.5 - 14 kpc, is likely to be a recurrent nova of the U Sco-class; containing a sub-giant secondary and an accretion disk, rather than accretion directly onto the poles. We show that there is little evidence, at quiescence, supporting a ~ 0.1 day periodicity, the variation seen at this stage is likely caused by flickering of a re-established accretion disk. We propose that the periodicity seen shortly after outburst is more likely related to the outburst rather than the - then obscured - binary system. Finally we address the distance to the system, and show that a significantly lower distance (~ 2 kpc) would result in a severely under-luminous outburst, and as such favour the larger distance and the recurrent nova scenario., 5 pages, 3 images, accepted for publication in A&A as a research note

We report the results of a multi-year spectroscopic and photometric survey of novae in M31 that resulted in a total of 53 spectra of 48 individual nova candidates. Two of these, M31N 1995-11e and M31N 2007-11g, were revealed to be long-period Mira variables, not novae. These data double the number of spectra extant for novae in M31 through the end of 2009 and bring to 91 the number of M31 novae with known spectroscopic classifications. We find that 75 novae (82%) are confirmed or likely members of the Fe II spectroscopic class, with the remaining 16 novae (18%) belonging to the He/N (and related) classes. These numbers are consistent with those found for Galactic novae. We find no compelling evidence that spectroscopic class depends sensitively on spatial position or population within M31 (i.e., bulge vs. disk), although the distribution for He/N systems appears slightly more extended than that for the Fe II class. We confirm the existence of a correlation between speed class and ejection velocity (based on line width), as in the case of Galactic novae. Follow-up photometry allowed us to determine light-curve parameters for a total of 47 of the 91 novae with known spectroscopic class. We confirm that more luminous novae generally fade the fastest, and that He/N novae are typically faster and brighter than their Fe II counterparts. In addition, we find a weak dependence of nova speed class on position in M31, with the spatial distribution of the fastest novae being slightly more extended than that of slower novae., Accepted for publication in the Astrophysical Journal. The manuscript is 123 pages with 29 figures

Spectra obtained simultaneously both at visual maximum and during eclipse with the International Ultraviolet Explorer satellite and the Isaac Newton Telescope between 1988 September and 1991 August are discussed and interpreted. Ultraviolet line ratios and phase plots are used to confirm that the C III]/Si III] emission-line ratio is subject to phase-related variations, and possible causes are discussed. Visual, photo-electric and ultraviolet light curves are used to determine the physical extent of the emission components. The resulting estimates suggest that AX Per is a detached binary system. The distance is determined bolometrically and by spectroscopic parallax

We report 0.45-2.0 mm continuum observations of Nova Cygni 1992, the brightest classical nova at visual maximum since 1975. Measurements were obtained 66, 104, 224, 234, 357 and 358 d after outburst. At the earliest epoch of our observations, the data are consistent with free-free emission from an optically thick nebula. The measurements obtained one month later show the nebula becoming progressively more transparent, with a turnover to optically thin emission in the millimetre regime. We find that our millimetre/submillimetre data on the early stages of this nova outburst are inconsistent with kinematical models which have been used to fit the radio data on previous novae at later times

Swift X-ray observations of the ~60 day super-soft phase of the recurrent nova RS Ophiuchi 2006 show the progress of nuclear burning on the white dwarf in exquisite detail. First seen 26 days after the optical outburst, this phase started with extreme variability likely due to variable absorption, although intrinsic white dwarf variations are not excluded. About 32 days later, a steady decline in count-rate set in. NLTE model atmosphere spectral fits during the super-soft phase show that the effective temperature of the white dwarf increases from ~65 eV to ~90 eV during the extreme variability phase, falling slowly after about day 60 and more rapidly after day 80. The bolometric luminosity is seen to be approximately constant and close to Eddington from day 45 up to day 60, the subsequent decline possibly signalling the end of extensive nuclear burning. Before the decline, a multiply-periodic, ~35 s modulation of the soft X-rays was present and may be the signature of a nuclear fusion driven instability. Our measurements are consistent with a white dwarf mass near the Chandrasekhar limit; combined with a deduced accumulation of mass transferred from its binary companion, this leads us to suggest RS Oph is a strong candidate for a future supernova explosion. The main uncertainty now is whether the WD is the CO type necessary for a SN Ia. This may be confirmed by detailed abundance analyses of spectroscopic data from the outbursts., Accepted for publication in ApJ

We present Spitzer Space Telescope observations of the "peculiar variable" DZ Cru, identified by Rushton et al. (2008, MNRAS, 386, 289) as a classical nova. A dust shell, on which are superimposed a number of features, is prominent in the 5-35micron range some 4 years after eruption. We suggest that the dust in DZ Cru is primarily hydrogenated amorphous carbon in which aliphatic bands currently predominate, and which may either become predominantly aromatic as the dust is photo-processed by ultraviolet radiation from the stellar remnant, or more likely completely destroyed.

Gravitational microlensing is not only a successful tool for discovering distant exoplanets, but it also enables characterization of the lens and source stars involved in the lensing event. In high magnification events, the lens caustic may cross over the source disk, which allows a determination of the angular size of the source and additionally a measurement of its limb darkening. When such extended-source effects appear close to maximum magnification, the resulting light curve differs from the characteristic Paczynski point-source curve. The exact shape of the light curve close to the peak depends on the limb darkening of the source. Dense photometric coverage permits measurement of the respective limb-darkening coefficients. In the case of microlensing event OGLE 2008-BLG-290, the K giant source star reached a peak magnification of about 100. Thirteen different telescopes have covered this event in eight different photometric bands. Subsequent light-curve analysis yielded measurements of linear limb-darkening coefficients of the source in six photometric bands. The best-measured coefficients lead to an estimate of the source effective temperature of about 4700 +100-200 K. However, the photometric estimate from colour-magnitude diagrams favours a cooler temperature of 4200 +-100 K. As the limb-darkening measurements, at least in the CTIO/SMARTS2 V and I bands, are among the most accurate obtained, the above disagreement needs to be understood. A solution is proposed, which may apply to previous events where such a discrepancy also appeared., Astronomy & Astrophysics in press

We report observations of the flickering variability of the recurrent nova RS Oph at quiescence on the basis of simultaneous observations in 5 bands (UBVRI). RS Oph has flickering source with (U-B)_0=-0.62 \pm 0.07, (B-V)_0=0.15 \pm 0.10, (V-R)_0=0.25 \pm 0.05. We find for the flickering source a temperature T_fl = 9500 \pm 500 K, and luminosity L_fl = 50 - 150 L_sun (using a distance of d=1.6kpc). We also find that on a (U-B) vs (B-V) diagram the flickering of the symbiotic stars differs from that of the cataclysmic variables. The possible source of the flickering is discussed. The data are available upon request from the authors and on the web www.astro.bas.bg/~rz/RSOph.UBVRI.2010.MNRAS.tar.gz., 7 pages, MNRAS (accepted)

The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very low-mass stars just above the hydrogen-burning limit. From the combined measurements of the Einstein radius and microlens parallax, we measure the masses of the binary components of $0.10\pm 0.01\ M_\odot$ and $0.09\pm 0.01\ M_\odot$. This discovery demonstrates that microlensing will provide a method to measure the mass function of all Galactic populations of very low mass binaries that is independent of the biases caused by the luminosity of the population., Comment: 6 pages, 3 figures, 1 table

Ultraviolet observations of the resolved shells of the old novae RR Pic (1925) and GK Per (1901) are presented. On the assumption that the RR Pic nebula is photoionized by the ultraviolet continuum emitted by the stellar remnant, we conclude that nitrogen is overabundant relative to solar in both the «equatorial ring» and «polar blob» regions; there are steep gradients in the C/O ratio, however. We also find possible evidence for emission by molecular hydrogen in the «blob». There is, in addition, some evidence for abundance gradients in the GK Per nebula, in which excitation is likely to be by shocks rather than by the weak ultraviolet emission of the stellar remnant

It has been suggested that free-free emission from symbiotic stars should become optically thin at submillimetre and millimetre wavelengths. 0.45-2.0 mm continuum measurements are presentred for a selected sample of symbiotic stars, H2-38, HM Sagittae, V1016 Cygni, AG Pegasi and R Aquarii. These observations clearly confirm that the D-type symbiotic stars HM Sge and V1016 Cyg exhibit a spectral turnover at a wavelength of ∼ 3 cm. The 1.1-2.0 mm spectral indices for these sources agree well with that expected for optically thin free-free emission

The discovery of an extended nebula of diameter ∼24 arcsec around the symbiotic nova V1016 Cyg from long-slit high-resolution spectroscopy of the Hα, He II λ468.6-nm and [O III] λ500.7-nm emission lines is presented. The existence of the nebula is confirmed by CCD images obtained in [O III]. The nebula was mapped spectroscopically but the profile changes are difficult to explain in simple terms. The extent of the nebulosity is similar to that inferred for a cool dust component by IRAS observations, for a distance of 0.6 kpc

Ealiers papers of this series developed a model for the interaction of ejecta with a circumstellar medium which was principally applied to the 1985 outburst of the recurrent nova RS Ophiuchi. Here the X-ray emission predicted by this model is compared in detail to EXOSAT observations of the outburst. Fits to the first observations 55 days after outburst lead to values for model parameters which are consistent with existing estimates : outburst energy ⇒ 1.1 × 10 43 erg; ejecta mass ⇒ 1.1 × 10 -6 M ⊙ ; and mass-loss rate into the wind of the red giant component ⇒ 6 × 10 12 g/cm. Once these parameters are fixed the model predicts the subsequent evolution of the X-ray emission

We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parameterisation proposed and detailed in Cassan (2008). As an illustration of our methodology, we present an analysis of OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source crossing the whole caustic structure in less than three days. In order to identify all possible models we conduct an extensive search of the parameter space, followed by a refinement of the parameters with a Markov Chain-Monte Carlo algorithm. We find a number of low-chi2 regions in the parameter space, which lead to several distinct competitive best models. We examine the parameters for each of them, and estimate their physical properties. We find that our fitting strategy locates several minima that are difficult to find with other modelling strategies and is therefore a more appropriate method to fit this type of events., Comment: 12 pages, 11 figures

We analyze OGLE-2007-BLG-050, a high magnification microlensing event (A ~ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star. Both finite-source and parallax effects permit a measurement of the angular Einstein radius \theta_E = 0.48 +/- 0.01 mas and the parallax \pi_E = 0.12 +/- 0.03, leading to an estimate of the lens mass M = 0.50 +/- 0.14 M_Sun and its distance to the observer D_L = 5.5 +/- 0.4 kpc. This is only the second determination of a reasonably precise (, Comment: 20 pages, 23 figures

Classical novae are phenomena caused by explosive hydrogen burning on an accreting white dwarf. So far, only one classical nova has been identified in X-rays before the actual optical outburst occurred (V2487 Oph). The recently discovered nova, V2491 Cyg, is one of the fastest (He/N) novae observed so far. Using archival ROSAT, XMM-Newton and Swift data, we show that V2491 Cyg was a persistent X-ray source during its quiescent time before the optical outburst. We present the X-ray spectral characteristics and derive X-ray fluxes. The pre-outburst X-ray emission is variable, and at least in one observation it shows a very soft X-ray source., Comment: 4 pages, 2 figures. Astronomy and Astrophysics, in press

We report MERLIN, VLA, OCRA-p, VLBA, Effelsberg and GMRT observations beginning 4.5 days after the discovery of RS Ophiuchi undergoing its 2006 recurrent nova outburst. Observations over the first 9 weeks are included, enabling us to follow spectral development throughout the three phases of the remnant development. We see dramatic brightening on days 4 to 7 at 6 GHz and an accompanying increase in other bands, particularly 1.46 GHz, consistent with transition from the initial "free expansion" phase to the adiabatic expansion phase. This is complete by day 13 when the flux density at 5 GHz is apparently declining from an unexpectedly early maximum (compared with expectations from observations of the 1985 outburst). The flux density recovered to a second peak by approximately day 40, consistent with behaviour observed in 1985. At all times the spectral index is consistent with mixed non-thermal and thermal emission. The spectral indices are consistent with a non-thermal component at lower frequencies on all dates, and the spectral index changes show that the two components are clearly variable. The estimated extent of the emission at 22 GHz on day 59 is consistent with the extended east and west features seen at 1.7 GHz with the VLBA on day 63 being entirely non-thermal. We suggest a two-component model, consisting of a decelerating shell seen in mixed thermal and non-thermal emission plus faster bipolar ejecta generating the non-thermal emission, as seen in contemporaneous VLBA observations. Our estimated ejecta mass of 4+/-2x10^{-7} M_\odot is consistent with a WD mass of 1.4 M_\odot. It may be that this ejecta mass estimate is a lower limit, in which case a lower WD mass would be consistent with the data., Comment: 8 pages, 4 figures, 3 tables, accepted for MNRAS

To improve the planet detection efficiency, current planetary microlensing experiments are focused on high-magnification events searching for planetary signals near the peak of lensing light curves. However, it is known that central perturbations can also be produced by binary companions and thus it is important to distinguish planetary signals from those induced by binary companions. In this paper, we analyze the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007-BLG-091, OGLE-2007-BLG-355/MOA-2007-BLG-278, and MOA-2007-BLG-199/OGLE-2007-BLG-419, for all of which exhibit short-term perturbations near the peaks of the light curves. From detailed modeling of the light curves, we find that the perturbations of the events are caused by binary companions rather than planets. From close examination of the light curves combined with the underlying physical geometry of the lens system obtained from modeling, we find that the short time-scale caustic-crossing feature occurring at a low or a moderate base magnification with an additional secondary perturbation is a typical feature of binary-lens events and thus can be used for the discrimination between the binary and planetary interpretations., 17 pages, 4 figures, 1 table

Using a new, comprehensive multiwavelength survey of 63 Gamma Ray Bursts (GRBs) with unprecedented temporal coverage, we classify the observed afterglows into four main classes and discuss the underlying physics that can explain them. The presence or absence of temporal breaks in X‐ray and optical bands is used to examine the emission in the context of the standard model; a number of GRBs are shown to deviate from the forward shock model even with the inclusion of energy injection or ambient density gradients. We show that additional emission in the early‐time X‐ray afterglow due to late‐time central engine activity is key and may explain both GRBs whose afterglows do not fit the standard model and those GRBs that appear to be optically dark even at early times.

High and low resolution optical spectroscopy obtained with the Manchester Echelle Spectrography, coupled with optical photometry, of the symbiotic star CH Cygni during the period 1986 to 1990 May is presented. This covers a phase during which the system appears to have reached its least active since its discovery. The variation in Balmer line fluxes correlates with changes in emission from the hot component, and is consistent with the previously published orbital solution

Infrared and optical photometry of the Herbig Be star HD 97048 obtained at intervals over a period of ∼1000 d is discussed. This shows that although the optical (BVRI) magnitude of the star has remained virtually constant, the star appears variable at Stromgren u, Johnson U and near-infrared (JHKL) wavelengths. This behaviour is interpreted as being the result of the variability of an active shell, superimposed on a star that is photospherically inactive. Variations in the flux shortward of the B-band directly influence the U magnitude and, by affecting the temperature of a circumstellar dust shell, cause the variability detected in the infrared

The relationship between optical line flux and 5 GHz radio flux is investigated for a sample of 17 northern sky symbiotic stars. Data were obtained near-simultaneously with the Manchester Echelle Spectrograph mounted on the Isaac Newton Telescope, La Palma and the Broad Band Interferometer at Jodrell Bank. Color excesses, calculated from Balmer hydrogen lines fluxes, are compared with other reddening estimates and also combined with extinction maps to provide improved distance estimates. Optical line fluxes are used in combination with redio fluxes to estimate physical parameters of these objects, including mass-loss rates. The suggestion that the ionized regions of D-type symbiotics are much more extensive than those on S-type is comfirmed.

RoboNet-II uses a global network of robotic telescopes to perform follow-up observations of microlensing events in the Galactic Bulge. The current network consists of three 2m telescopes located in Hawaii and Australia (owned by Las Cumbres Observatory) and the Canary Islands (owned by Liverpool John Moores University). In future years the network will be expanded by deploying clusters of 1m telescopes in other suitable locations. A principal scientific aim of the RoboNet-II project is the detection of cool extra-solar planets by the method of gravitational microlensing. These detections will provide crucial constraints to models of planetary formation and orbital migration. RoboNet-II acts in coordination with the PLANET microlensing follow-up network and uses an optimization algorithm ("web-PLOP") to select the targets and a distributed scheduling paradigm (eSTAR) to execute the observations. Continuous automated assessment of the observations and anomaly detection is provided by the ARTEMiS system., Comment: 8 pages, 4 figures. Astronomical Notes - accepted. Changes:*spelling corrections and rewording. *Expanded sections on how the software interacts to further clarify the procedure. *Clarified further minor points as requested by the referee

In this chapter, we concentrate on describing the physical characteristics and evolution of the nebular remnants of classical novae across the electromagnetic spectrum. We also refer as appropriate to the relationship between the central binary and the ejected nebula, particularly in terms of remnant shaping. Evidence for remnant structure in the spectra of unresolved novae is briefly described before moving on to discuss resolved nebular remnants, first in the optical and infrared, and then in the radio. Over the past two decades, great strides have also been made in understanding the relationship of remnant shape to the evolution of the outburst and the properties of the central binary. The results of various models are presented. Finally, we briefly discuss the idiosyncratic remnant of GK Per ? an object that may provide important clues to the evolution of nova binaries ? before concluding with a discussion of outstanding problems and prospects for future work.

We present nearly simultaneous optical and infrared photometry of RV Tauri stars. From this we deduce stellar and (where appropriate) dust shell parameters. Possible correlations are suggested between dust shell extent, metallicity and type of RV Tauri stars. Grain formation appears to be episodic, rather than continuous.

Nova V458 Vul erupted on 2007 August 8th and reached a visual magnitude of 8.1 a few days later. H$\alpha$ images obtained six weeks before the outburst as part of the IPHAS galactic plane survey reveal an 18th magnitude progenitor surrounded by an extended nebula. Subsequent images and spectroscopy of the nebula reveal an inner nebular knot increasing rapidly in brightness due to flash ionization by the nova event. We derive a distance of 13 kpc based on light travel time considerations, which is supported by two other distance estimation methods. The nebula has an ionized mass of 0.2 M$_{\odot}$ and a low expansion velocity: this rules it out as ejecta from a previous nova eruption, and is consistent with it being a ~14,000 year old planetary nebula, probably the product of a prior common envelope (CE) phase of evolution of the binary system. The large derived distance means that the mass of the erupting WD component of the binary is high. We identify two possible evolutionary scenarios, in at least one of which the system is massive enough to produce a Type Ia supernova on merging., Comment: 5 pages, 2 figures. Accepted for publication in ApJL

We present a multiwavelength analysis of 63 Gamma-Ray Bursts observed with the world's three largest robotic optical telescopes, the Liverpool and Faulkes Telescopes (North and South). Optical emission was detected for 24 GRBs with brightnesses ranging from R = 10 to 22 mag in the first 10 minutes after the burst. By comparing optical and X-ray light curves from t = 100 to about 10^6 seconds, we introduce four main classes, defined by the presence or absence of temporal breaks at optical and/or X-ray wavelengths. While 15/24 GRBs can be modelled with the forward-shock model, explanation of the remaining nine is very challenging in the standard framework even with the introduction of energy injection or an ambient density gradient. Early X-ray afterglows, even segments of light curves described by a power-law, may be due to additional emission from the central engine. 39 GRBs in our sample were not detected and have deep upper limits (R < 22 mag) at early time. Of these, only ten were identified by other facilities, primarily at near infrared wavelengths, resulting in a dark burst fraction of about 50%. Additional emission in the early time X-ray afterglow due to late-time central engine activity may also explain some dark bursts by making the bursts brighter than expected in the X-ray band compared to the optical band., 51 pages, 9 figures, 4 tables, submitted to ApJ

(abridged) The technique of gravitational microlensing is currently unique in its ability to provide a sample of terrestrial exoplanets around both Galactic disk and bulge stars, allowing to measure their abundance and determine their distribution with respect to mass and orbital separation. In order to achieve these goals in reasonable time, a well-coordinated effort involving a network of either 2m or 4 x 1m telescopes at each site is required. It could lead to the first detection of an Earth-mass planet outside the Solar system, and even planets less massive than Earth could be discovered. From April 2008, ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) is planned to provide a platform for a three-step strategy of survey, follow-up, and anomaly monitoring. As an expert system embedded in eSTAR (e-Science Telescopes for Astronomical Research), ARTEMiS will give advice on the optimal targets to be observed at any given time, and will also alert on deviations from ordinary microlensing light curves by means of the SIGNALMEN anomaly detector. While the use of the VOEvent (Virtual Observatory Event) protocol allows a direct interaction with the telescopes that are part of the HTN (Heterogeneous Telescope Networks) consortium, additional interfaces provide means of communication with all existing microlensing campaigns that rely on human observers. The success of discovering a planet by microlensing critically depends on the availability of a telescope in a suitable location at the right time, which can mean within 10 min. Real-time modelling offers the opportunity of live discovery of extra-solar planets, thereby providing ''Science live to your home''., Comment: 4 pages with 2 eps figures embedded. Accepted for publication in Astronomische Nachrichten as part of the Proceedings of the Joint VOEvent & HTN Workshop "Hot-wiring the Transient Universe" held in Tucson, Arizona (US), June 4-7 2007