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We present a new study of the eclipsing cataclysmic variable SDSS J154453.60+255348.8 to determine the object’s nature and its system parameters together with the probe of the accretion flow structure in the system. Based on analyses of new simultaneous time-resolved photometric and spectroscopic observations of SDSS J154453.60+255348.8 and using our light-curve modelling techniques and the Doppler tomography method, we found that the system contains a white dwarf with the mass of MWD = 0.62(7) M⊙ and an evolved red dwarf as a secondary. The system inclination is close to 90° and the mass ratio is q = 0.49(2). The secondary has an effective temperature T2 = 3400(40) K and a radius about 1.35(15) times larger than a zero-age main-sequence star with similar mass. From observation of the system in high- and low-brightness states, we conclude that SDSS J154453.60+255348.8 is a long-orbital period VY Scl-type system. The accretion disc in the high state is about two times less than the truncation radius, and is completely missing during the low state of the system.

Some Cataclysmic Variables (CVs) exhibits a very long photometric period (VLPP). We calculate the properties of a hypothetical third body, initially assumed on circular--planar orbit, by matching the modelled VLPP to the observed one of four CVs studied here: {\sl LU Camelopardalis} (LU Cam), QZ Serpentis (QZ Ser), V1007 Herculis (V1007 Her) and BK Lyncis (BK Lyn). The eccentric and low inclination orbits for a third body are considered using analytical results. The chosen parameters of the binary components are based on the orbital period of each CV. The smallest corresponding semi-major axis permitted before the third body's orbit becomes unstable is also calculated. A first-order analytical post-Newtonian correction is applied, and the rate of precession of the pericentre is found, but it can not explain any of the observed VLPP. For the first time, we also estimate the effect of secular perturbations by this hypothetical third body on the mass transfer rate of such CVs. We made sure that the observed and calculated amplitude of variability was comparable too. The mass of the third body satisfying all constrains range from 0.63 to 97 Jupiter masses. Our results show further evidence supporting the hypothesis of a third body in three of these CVs, but only marginally in V1007 Her., 11 pages, 6 figures

The 840 kyr old pulsar PSR J1957+5033, detected so far only in $\gamma$- and X-rays, is a nearby and rather cool neutron star with a temperature of 0.2--0.3 MK, a distance of $\la$1 kpc, and a small colour reddening excess $E(B-V) \approx 0.03$. These properties make it an ideal candidate to detect in the optical to get additional constraints on its parameters. We thus performed the first deep optical observations of the pulsar with the 10.4-meter Gran Telescopio Canarias in the $g'$ band and found its possible counterpart with $g'=27.63\pm 0.26$. The counterpart candidate position is consistent with the X-ray coordinates of the pulsar within the 0.5 arcsec accuracy. Assuming that this is the real counterpart, we analysed the pulsar X-ray spectrum together with the derived optical flux density. As a result, we found that the thermal emission from the bulk surface of the cooling neutron star can significantly contribute to its optical flux. Our multi-wavelength spectral analysis favours the pulsar nature of the detected optical source, since it provides physically adequate parameters of the pulsar emission. We show that the optical data can provide new constraints on the pulsar temperature and distance., Comment: 7 pages, 3 figures, published in MNRAS

We analysed a wealth of optical spectroscopic and photometric observations of the bright (V=11.9) cataclysmic variable BG Tri. TheGaiaDR2 parallax gives a distance d=334(8)pc to the source, making the object one of the intrinsically brightest nova-like variables seen under a low orbital inclination angle. Time-resolved spectroscopic observations revealed the orbital period of P(orb)=3.h8028(24). Its spectroscopic characteristics resemble RW Sex and similarnova-like variables. We disentangled the H alpha emission line into two components, and show that one component forms on the irradiated face of the secondary star. We suggest that the other one originates at a disc outflow area adjacent to the L3 point., Accepted for publication in MNRAS, 11 pages, 10 figures

We obtained photometric observations of the nova-like cataclysmic variable RW Tri and gathered all available AAVSO and other data from the literature. We determined the system parameters and found their uncertainties using the code developed by us to model the light curves of binary systems. New time-resolved optical spectroscopic observations of RW Tri were also obtained to study the properties of emission features produced by the system. The usual interpretation of the single-peaked emission lines in nova-like systems is related to the bi-conical wind from the accretion disc's inner part. However, we found that the Halpha emission profile is comprised of two components with different widths. We argue that the narrow component originates from the irradiated surface of the secondary, while the broader component's source is an extended, low-velocity region in the outskirts of the accretion disc, located opposite to the collision point of the accretion stream and the disc. It appears to be a common feature for long-period nova-like systems -- a point we discuss., Comment: 14 pages, 8 figures, Accepted to MNRAS

The X-ray source CXO\, J085201.4$-$461753in the few kyr-old Vela Jr. supernova remnant (G266.2-1.2) belongs to the peculiar class of isolated neutron stars dubbed "Central Compact Objects" (CCOs). At variance with the other CCOs, which are only detected in the X-rays, \cxo\ has been possibly detected also at other wavelengths. In particular, a candidate near-infrared counterpart (H = 21.6 $\pm$0.1) was detected by the Very Large Telescope (VLT) in addition to a 6\arcsec-wide nebula detected in H$\alpha$, interpreted as a velocity-driven bow-shock. Here, we present new near-infrared and optical VLT observations of the candidate counterpart to \cxo\ and its nebula to confirm the proposed associations. Moreover, we used archival Chandra observations to measure for the first time the CXO\, J085201.4$-$461753 proper motion. The comparison between the two sets of near-infrared VLT images, taken 10.56 year apart, do not show evidence of proper motion for the candidate counterpart to CXO\, J085201.4$-$461753, expected from its 4\arcmin\ offset from the SNR geometrical centre, with a $3\sigma$ upper limit of $\sim 10$ mas yr$^{-1}$. This is much smaller than the expected proper motion of $\sim$50--100 mas yr$^{-1}$, which, in turn, is below the $3\sigma$ upper limit of $\sim$ 300 mas yr$^{-1}$ that we obtained with Chandra. At the same time, VLT spectroscopy resolved the nebula optical emission, which is dominated by the NII doublet at 6548 and 6584 \AA\ and not by H$\alpha$. To summarise, we conclude that the proposed near-infrared counterpart is likely unassociated with \cxo\ and that the nebula is not a velocity-driven bow-shock., Comment: 10 pages, 8 figures. MNRAS, accepted for publication

We report detection of the binary companion to the millisecond pulsar J2302+4442 based on the deep observations performed with the Gran Telescopio Canarias. The observations revealed an optical source with $r'$ = 23.33$\pm$0.02 and $i'$=23.08$\pm$0.02, whose position coincides with the pulsar radio position. By comparing the source colour and magnitudes with the white dwarf cooling predictions, we found that it likely represents a He or CO-core white dwarf and estimated its mass of 0.52$^{+0.25}_{-0.19}$ M$_{\odot}$ and effective temperature of 6300$^{+1000}_{-800}$ K. Combining our results with the radio timing measurements, we set constraints on the binary system inclination angle $i=73^{+6}_{-5}$ degrees and the pulsar mass $m_p=3.1^{+2.7}_{-2.0}$ M$_{\odot}$., Accepted for publication in MNRAS

New time-resolved optical spectroscopic echelle observations of the nova-like cataclysmic variable RW Sextantis were obtained, with the aim to study the properties of emission features in the system. The profile of the H_alpha emission line can be clearly divided into two (`narrow' and `wide') components. Similar emission profiles are observed in another nova-like system, 1RXS~J064434.5+33445, for which we also reanalysed the spectral data and redetermined the system parameters. The source of the `narrow', low-velocity component is the irradiated face of the secondary star. We disentangled and removed the `narrow' component from the H_alpha profile to study the origin and structure of the region emitting the wide component. We found that the `wide' component is not related to the white dwarf or the wind from the central part of the accretion disc, but is emanated from the outer side of the disc. Inspection of literature on similar systems indicates that this feature is common for some other long-period nova-like variables. We propose that the source of the `wide' component is an extended, low-velocity region in the outskirts of the opposite side of the accretion disc, with respect to the collision point of the accretion stream and the disc., Comment: 11 pages, 7 figures, accepted for publication in MNRAS

HD170582 is an interacting binary of the Double Periodic Variable (DPV) type, showing ellipsoidal variability with a period of 16.87 days along with a long photometric cycle of 587 days. It was recently studied by Mennickent et al. (2015), who found a slightly evolved B-type star surrounded by a luminous accretion disc fed by a Roche-lobe overflowing A-type giant. Here we extend their analysis presenting new spectroscopic data and studying the Balmer emission lines. We find orbitally modulated double-peak Halpha and Hbeta emissions whose strength also vary in the long-term. In addition, Doppler maps of the emission lines reveal sites of enhanced line emission in the 1st and 4th velocity quadrants, the first one consistent with the position of one of the bright zones detected by the light curve analysis. We find a difference between Doppler maps at high and low stage of the long cycle; evidence that the emission is optically thicker at high state in the stream-disc impact region, possibly reflecting a larger mass transfer rate. We compare the system parameters with a grid of synthetic binary evolutionary tracks and find the best fitting model. The system is found to be semi-detached, in a conservative Case-B mass transfer stage, with age 7.68E7 yr and mass transfer rate 1.6E-6 Msun/yr. For 5 well-studied DPVs, the disc luminosity scales with the primary mass and is much larger than the theoretical accretion luminosity., Accepted for publication in MNRAS, 11 pages, 4 tables, 11 figures

PSR J1357$-$6429 is a young radio pulsar that was detected in X-rays and $\gamma$-rays. We present the high spatial resolution near-infrared imaging of the pulsar field in $J$, $H$ and $K_s$ bands obtained with the VLT/NaCo using the Adaptive Optic system. We found a faint source at the most precise pulsar radio position which we propose as the pulsar near-infrared counterpart candidate. It is confidently detected in the $J$ and $K_s$ bands, with $J$ = 23.51$\pm$0.24 and $K_s$ = 21.82$\pm$0.25. There is a hint of the source in the $H$ band with an upper limit $H$ $>$ 22.8. The dereddened source fluxes are compatible with the extrapolation of the pulsar X-ray spectrum towards the near-infrared. If the candidate is the true counterpart, by this property PSR J1357$-$6429 would be similar to the nearby middle-age pulsar PSR B0656+14. In this case, both pulsars demonstrate an unusually high near-infrared efficiency relative to the X-ray efficiency as compared to other pulsars detected in both ranges., Comment: 6 pages, 4 figures, 3 tables

MWC 314 is a bright candidate luminous blue variable that resides in a fairly close binary system, with an orbital period of 60.753$\pm$0.003 d. We observed MWC 314 with a combination of optical spectroscopy, broad-band ground- and space-based photometry, as well as with long baseline, near-infrared interferometry. We have revised the single-lined spectroscopic orbit and explored the photometric variability. The orbital light curve displays two minima each orbit that can be partially explained in terms of the tidal distortion of the primary that occurs around the time of periastron. The emission lines in the system are often double-peaked and stationary in their kinematics, indicative of a circumbinary disc. We find that the stellar wind or circumbinary disc is partially resolved in the K\prime-band with the longest baselines of the CHARA Array. From this analysis, we provide a simple, qualitative model in an attempt to explain the observations. From the assumption of Roche Lobe overflow and tidal synchronisation at periastron, we estimate the component masses to be M1 $\approx 5$ M$_\odot$ and M2$\approx 15$ M$_\odot$, which indicates a mass of the LBV that is extremely low. In addition to the orbital modulation, we discovered two pulsational modes with the MOST satellite. These modes are easily supported by a low-mass hydrogen-poor star, but cannot be easily supported by a star with the parameters of an LBV. The combination of these results provides evidence that the primary star was likely never a normal LBV, but rather is the product of binary interactions. As such, this system presents opportunities for studying mass-transfer and binary evolution with many observational techniques., Comment: 26 pages, 7 figures, 5 tables, 2 appendices with 7 additional tables and 2 additional figures. Accepted for publication in MNRAS

The black hole (BH) candidate SWIFT J1753.5-0127 has remained active since the onset of its 2005 outburst. Emission lines in the optical spectrum were observed at the very beginning of the outburst, but since then the spectrum has been featureless making a precise BH mass estimation impossible. Here we present results from our optical and UV observations of SWIFT J1753.5-0127 taken in 2012-2013. Our new observations show extremely broad, double-peaked emission lines in the optical and UV spectra. The optical data also show narrow absorption and emission features with nearly synchronous and significant Doppler motions. A radial velocity study of these lines which we associate with the secondary star, yields a semi-amplitude of K_2=382 km/s. A time-series analysis of the spectral and photometric data revealed a possible orbital periodicity of 2.85 h, significantly shorter than the reported 3.2 h periodic signal by Zurita et al. The observed variability properties argue against a low orbital inclination angle and we present several observational arguments in favour of the BH interpretation. However, the measured radial velocity semi-amplitude of the donor star and the short orbital period imply that SWIFT J1753.5-0127 has one of the lowest measured mass function for a BH in a low-mass X-ray binary. We show that the compact object mass in excess of 5 Msun is highly improbable. Thus, SWIFT J1753.5-0127 is a BH binary that has one of the shortest orbital period and hosts probably one of the smallest stellar-mass BH found to date., Comment: 16 pages, 15 figures, Matches to MNRAS published version, typos corrected

We report the results of optical spectroscopy of a candidate evolved massive star in the Cygnus X region, TYC 3159-6-1, revealed via detection of its curious circumstellar nebula in archival data of the Spitzer Space Telecope. We classify TYC 3159-6-1 as an O9.5-O9.7 Ib star and derive its fundamental parameters by using the stellar atmosphere code FASTWIND. The He and CNO abundances in the photosphere of TYC 3159-6-1 are consistent with the solar abundances, suggesting that the star only recently evolved off the main sequence. Proper motion and radial velocity measurements for TYC 3159-6-1 show that it is a runaway star. We propose that Dolidze 7 is its parent cluster. We discuss the origin of the nebula around TYC 3159-6-1 and suggest that it might be produced in several successive episodes of enhanced mass-loss rate (outbursts) caused by rotation of the star near the critical, \Omega-limit., Comment: 12 pages, 6 figures, accepted for publication in MNRAS

FS Aur is famous for a variety of uncommon and puzzling periodic photometric and spectroscopic variabilities. It was previously proposed that the precession of a fast-rotating magnetically accreting white dwarf can successfully explain these phenomena. We present a study of FS Aur based on two extensive sets of optical photometric observations and three X-ray data sets in which we intended to verify whether the observational properties of the long period modulations observed in FS Aur and V455 And are similar in appearance to the spin modulation in ordinary IPs. These new optical observations have revealed, for the first time in photometric data, the variability with the presumed precession period of the white dwarf, previously seen only spectroscopically. We also found that the modulations with the precession and orbital periods are evident in X-ray data. We show that the observed properties of FS Aur closely resemble those of other intermediate polars, thus confirming this cataclysmic variable as a member of the class. Our analysis of multicolour observations of intermediate polars has shown that time-series analysis of colour indices appears to be a powerful technique for revealing hidden variabilities and shedding light on their nature. We have found that the (B-I) power spectrum of V1223 Sgr indicates the presence in the data of the spin pulsation which is not seen in the optical light curve at all. Also, the analysis of the colour indices of V455 And revealed the presence of the photometric variations which, similarly to FS Aur, was previously observed only spectroscopically., 19 pages, 17 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal

The Vela and Geminga pulsars are rotation powered neutron stars, which have been identified in various spectral domains, from the near-infrared to hard $\gamma$-rays. In the near-infrared they exhibit tentative emission excesses, as compared to the optical range. To check whether these features are real, we analysed archival mid-infrared broadband images obtained with the Spitzer Space Telescope in the 3.6--160 $\mu$m range and compared them with the data in other spectral domains. In the 3.6 and 5.8 $\mu$m bands we detected at $\sim$ (4--5)$\sigma$ significance level a point-like object, that is likely to be the counterpart of the Vela pulsar. Its position coincides with the pulsar at < 0.4 arcsec 1$\sigma$-accuracy level. Combining the measured fluxes with the available multiwavelength spectrum of the pulsar shows a steep flux increase towards the infrared, confirming the reality of the near-infrared excess reported early, and, hence, the reality of the suggested mid-infrared pulsar identification. Geminga is also identified, but only at a marginal 2$\sigma$ detection level in one 3.6 $\mu$m band. This needs a farther confirmation by deeper observations, while the estimated flux is also compatible with the near-infrared Geminga excess. The detection of the infrared excess is in contrast to the Crab pulsar, where it is absent, but is similar to the two magnetars, 4U 0142+61 and 1E 2259+586, showing similar features. We discuss X-ray irradiated fall-back discs around the pulsars, unresolved pulsar nebula structures, and pulsar magnetospheres as possible origins of the excesses. We note also possible infrared signatures of an extended tail behind Geminga and of the Vela plerion radio lobes.

We report simultaneous photometric and echelle-spectroscopic observations of the dwarf nova BZ UMa during which we were lucky to catch the system at the onset of an outburst, the development of which we traced in detail from quiescence to early decline. The outburst had a precursor, and was of a short duration (~5 days) with a highly asymmetrical light curve. On the rise we observed a `jump' during which the brightness almost doubled over the course of half an hour. Power spectra analysis revealed well-defined oscillations with period of ~42 minutes. Using Doppler tomography we found that the unusual emission distribution detected in quiescence held during the outburst. After the maximum a new emission source arose, from the inner hemisphere of the secondary star, which became the brightest at that time. We analyse this outburst in terms of `inside-out' and `outside-in' types, in order to determine which of these types occured in BZ UMa., Comment: 8 pages, 8 figures (12 eps files). Accepted for publication in MNRAS. The paper with high resolution colour images can be downloaded from http://urania.it.nuigalway.ie/papers/bz_outburst.pdf

We present the analysis of high-speed photometric observations of FS Aur taken with the 4.2-m William Herschel Telescope and the high-speed camera ULTRACAM in late 2003. These observations were intended to determine whether there was any evidence of photometric variability with a period in the range 50-100 seconds. The discovery of such variations would help to explain existence, in FS Aur, of the very coherent photometric period of 205.5 min that exceeds the spectroscopic period by 2.4 times. Such a discrepancy in the photometric and spectroscopic periods is an unusual for a low mass binary system that is unambiguously identified as a Cataclysmic Variable. Using various methods, including wavelet-analysis, we found that with exception of the 205.5-minute periodicity, the main characteristic of variability of FS Aur is usual flickering and Quasi-Periodic Oscillations. However, we detected variability with a period of ~101 and/or ~105 sec, seen for a short time every half of the orbital period. These oscillations may be associated with the spin period of the white dwarf, not ruling out the possibility that we are observing a precessing rapidly rotating white dwarf in FS Aur.