Context. In Paper I we showed that the accretion disc radius of the dwarf nova HT Cas in its quiescent state has not changed significantly during many years of observations. It has remained ...consistently large, close to the tidal truncation radius. This result is inconsistent with the modern understanding of the evolution of the disc radius through an outburst cycle. Aims. Spectroscopic observations of HT Cas during its superoutburst offered us an exceptional opportunity to compare the properties of the disc of this object in superoutburst and in quiescence. Methods. We obtained a new set of time-resolved spectra of HT Cas in the middle of its 2017 superoutburst. We used Doppler tomography to map emission structures in the system, which we compared with those detected during the quiescent state. We used solutions of the restricted three-body problem to discuss again the location of emission structures and the disc size of HT Cas in quiescence. Results. The superoutburst spectrum is similar in appearance to the quiescent spectra, although the strength of most of the emission lines decreased. However, the high-excitation lines significantly strengthened in comparison with the Balmer lines. Many lines show a mix of broad emission and narrow absorption components. Hα in superoutburst was much narrower than in quiescence. Other emission lines have also narrowed in outburst, but they did not become as narrow as Hα. Doppler maps of Hα in quiescence and of the Hβ and He I lines in outburst are dominated by a bright emission arc at the right side of the tomograms, which is located at and even beyond the theoretical truncation limit. However, the bulk of the Hα emission in outburst has significantly lower velocities. Conclusions. We show that the accretion disc radius of HT Cas during its superoutburst has become hot but remained the same size as it was in quiescence. Instead, we detected cool gas beyond the Roche lobe of the white dwarf that may have been expelled from the hot disc during the superoutburst.
Abstract
New time-resolved optical spectroscopic echelle observations of the nova-like cataclysmic variable RW Sextantis were obtained, with the aim of studying the properties of emission features in ...the system. The profile of the H α 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 α 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.
ABSTRACT
We obtained photometric observations of the nova-like (NL) 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 NL systems is related to the bi-conical wind from the accretion disc’s inner part. However, we found that the Hα 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 NL systems – a point we discuss.
We report Neutrino-4 experiment results of measurements of reactor antineutrinos flux and spectrum dependence on the distance in range 6–12 m from the center of the reactor core. The fit of ...experimental dependence with the law 1/
L
2
, where
L
is the distance from the reactor center, gave satisfactory result with goodness of fit 81%. However, we discovered that the experimental neutrino spectrum is different from the calculated one. Using experimental spectrum, we performed the model independent analysis of restrictions on oscillation parameters Δ
m
14
2
and sin
2
2θ
14
. The results of this analysis exclude area of reactor and gallium anomaly at CL more than 99.7% (>3σ) for values Δ
m
14
2
< 3 eV
2
and sin
2
2θ
14
> 0.1. However, we observed an oscillation effect at CL 2.8σ in vicinity of Δ
m
14
2
Δ
m
14
2
≈ 7.3 eV
2
and sin
2
2θ
14
≈ 0.39. The method of coherent addition of results of measurements, which allows us to directly observe the effect of oscillations, is proposed. The analysis of that effect is presented. In general, it seems that the effect predicted in gallium and reactor experiments is being confirmed but at sufficiently large value of Δ
m
14
2
. Future prospects of the experiment are discussed.
Aims. The black hole binary Swift J1753.5–0127 is providing a unique data set to study accretion flows. Various investigations of this system and of other black holes have not, however, led to an ...agreement on the accretion flow geometry or on the seed photon source for Comptonization during different stages of X-ray outbursts. We place constraints on these accretion flow properties by studying long-term spectral variations of this source. Methods. We performed phenomenological and self-consistent broad band spectral modeling of Swift J1753.5–0127 using quasi-simultaneous archived data from INTEGRAL/ISGRI, Swift/UVOT/XRT/BAT, RXTE/PCA/HEXTE, and MAXI/GSC instruments. Results. We identify a critical flux limit, F ~ 1.5 × 10-8 erg cm-2 s-1, and show that the spectral properties of Swift J1753.5–0127 are markedly different above and below this value. Above the limit, during the outburst peak, the hot medium seems to intercept roughly 50 percent of the disk emission. Below it, in the outburst tail, the contribution of the disk photons reduces significantly and the entire spectrum from the optical to X-rays can be produced by a synchrotron-self-Compton mechanism. The long-term variations in the hard X-ray spectra are caused by erratic changes of the electron temperatures in the hot medium. Thermal Comptonization models indicate unreasonably low hot medium optical depths during the short incursions into the soft state after 2010, suggesting that non-thermal electrons produce the Comptonized tail in this state. The soft X-ray excess, likely produced by the accretion disk, shows peculiarly stable temperatures for over an order of magnitude changes in flux. Conclusions. The long-term spectral trends of Swift J1753.5–0127 are likely set by variations of the truncation radius and a formation of a hot, quasi-spherical inner flow in the vicinity of the black hole. In the late outburst stages, at fluxes below the critical limit, the source of seed photons for Comptonization is not the thermal disk, but more likely they are produced by non-thermal synchrotron emission within the hot flow near the black hole. The stability of the soft excess temperature is, however, not consistent with this picture and further investigations are needed to understand its behavior.
ABSTRACT
We present an analysis of multi-epoch spectroscopic and photometric observations of the WZ Sge-type dwarf nova BW Scl, a period-bouncer candidate. We detected multiple irradiation-induced ...emission lines from the donor star allowing the radial velocity variations to be measured with high accuracy. Also, using the absorption lines Mg ii 4481 Å and Ca ii K originated in the photosphere of the accreting white dwarf (WD), we measured the radial velocity semi-amplitude of the WD and its gravitational redshift. We find that the WD has a mass of 0.85 ± 0.04 M⊙, while the donor is a low-mass object with a mass of 0.051 ± 0.006 M⊙, well below the hydrogen-burning limit. Using NIR data, we put an upper limit on the effective temperature of the donor to be ≲1600 K, corresponding to a brown dwarf of T spectral type. The optically thin accretion disc in BW Scl has a very low luminosity ≲4 × 1030 erg s−1 which corresponds to a very low-mass accretion rate of ≲7 × 10−13 M⊙ yr−1. The outer parts of the disc have a low density allowing the stream to flow down to the inner disc regions. The brightest part of the hotspot is located close to the circularization radius of the disc. The hotspot is optically thick and has a complex elongated structure. Based on the measured system parameters, we discuss the evolutionary status of the system.
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 intermediate polars (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 IPs, thus confirming this cataclysmic variable as a member of the class.
Our analysis of multicolour observations of IPs has shown that a 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.
Abstract
We report extensive 3-yr multiwavelength observations of the WZ Sge-type dwarf nova SSS J122221.7−311525 during its unusual double superoutburst, the following decline and in quiescence. The ...second segment of the superoutburst had a long duration of 33 d and a very gentle decline with a rate of 0.02 mag d−1, and it displayed an extended post-outburst decline lasting at least 500 d. Simultaneously with the start of the rapid fading from the superoutburst plateau, the system showed the appearance of a strong near-infrared excess resulting in very red colours, which reached extreme values (B − I ≃ 1.4) about 20 d later. The colours then became bluer again, but it took at least 250 d to acquire a stable level. Superhumps were clearly visible in the light curve from our very first time-resolved observations until at least 420 d after the rapid fading from the superoutburst. The spectroscopic and photometric data revealed an orbital period of 109.80 min and a fractional superhump period excess ≲0.8 per cent, indicating a very low mass ratio q ≲ 0.045. With such a small mass ratio the donor mass should be below the hydrogen-burning minimum mass limit. The observed infrared flux in quiescence is indeed much lower than is expected from a cataclysmic variable with a near-main-sequence donor star. This strongly suggests a brown-dwarf-like nature for the donor and that SSS J122221.7−311525 has already evolved away from the period minimum towards longer periods, with the donor now extremely dim.
Long-lived stars in globular clusters exhibit chemical peculiarities with respect to their halo counterparts. In particular, sodium-enriched stars are identified as belonging to a second stellar ...population born from cluster material contaminated by the hydrogen-burning ashes of a first stellar population. We investigate the impact of both age and metallicity on the theoretical sodium spread along the AGB within the framework of the fast rotating massive star (FRMS) scenario for globular cluster self-enrichment. We computed evolution models of low-mass stars for four different metallicities assuming the initial helium-sodium abundance correlation for second population stars derived from the FRMS models and using mass loss prescriptions on the RGB with two realistic values of the free parameter in the Reimers formula. The theoretical trends we obtain provide, in principle, an elegant qualitative explanation to the different sodium spreads that are observed along the AGB in the Galactic globular clusters of different ages and Fe/H values. Therefore, additional parameters may play a role in inducing cluster to cluster variations, that are difficult to disentangle from existing data.
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