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EPIC 216747137 is a new HW Virginis system discovered by the Kepler spacecraft during its K 2 'second life'. Like the other HW Vir systems, EPIC 216747137 is a post-common-envelope eclipsing binary consisting of a hot subluminous star and a cool low-mass companion. The short orbital period of 3.87 h produces a strong reflection effect from the secondary (∼9 per cent in the R band). Together with AA Dor and V1828 Aql, EPIC 216747137 belongs to a small subgroup of HW Vir systems with a hot evolved sdOB primary. We find the following atmospheric parameters for the hot component: T eff = 40400 ± 1000 K, log  g  = 5.56 ± 0.06, and log(N (He)/ N (H)) = −2.59 ± 0.05. The sdOB rotational velocity v  sin   i  = 51 ± 10 km s−1 implies that the stellar rotation is slower than the orbital revolution and the system is not synchronized. When we combine photometric and spectroscopic results with the Gaia parallax, the best solution for the system corresponds to a primary with a mass of about 0.62 M⊙ close to, and likely beyond, the central helium exhaustion, while the cool M-dwarf companion has a mass of about 0.11 M⊙. [ABSTRACT FROM AUTHOR]

We report the discovery of an eclipsing binary - PTF1 J072456+125301- composed of a subdwarf B (sdB) star (g'= 17.2m) with a faint companion. Subdwarf B stars are core helium-burning stars, which can be found on the extreme horizontal branch. About half of them reside in close binary systems, but few are known to be eclipsing, for which fundamental stellar parameters can be derived. We conducted an analysis of photometric data and spectra from the Palomar 60" and the 200" Hale telescope, respectively. A quantitative spectral analysis found an effective temperature of Teff = 33 900 ± 350 K, log g = 5.74 ± 0.08, and log(nHe/nH) = -2.02 ± 0.07, typical for an sdB star. The companion does not contribute to the optical light of the system, except through a distinct reflection effect. From the light curve an orbital period of 0.09980(25) d and a system inclination of 83.56 ± 0.30 were derived. The radial velocity curve yielded an orbital semi-amplitude of K1 = 95.8 ± 8.1 kms-1. The mass for the M-type dwarf companion is 0.155 ± 0.020 M☉. PTF1 J072456+125301 has similar atmospheric parameters to those of pulsating sdB stars (V346 Hya stars). Therefore it could be a high-priority object for asteroseismology, if pulsations were detected such as in the enigmatic case of NY Vir. [ABSTRACT FROM AUTHOR]

Aims. We determine the temporal evolution of the luminosity (LWD), radius (RWD) and effective temperature (Teff) of thewhite dwarf (WD) pseudophotosphere of V339 Del from its discovery to around day 40. Another main objective was studying the ionization structure of the ejecta. Methods. These aims were achieved by modelling the optical/near-IR spectral energy distribution (SED) using low-resolution spectroscopy (3500-9200 Å), UBVRCIC and JHKLM photometry. Important insights in the physical conditions of the ejecta were gained from an analysis of the evolution of the Hα and Raman-scattered 6825Å Ovi line using medium-resolution spectroscopy (R ∼ 10 000). Results. During the fireball stage (Aug. 14.8-19.9, 2013), Teff was in the range of 6000-12 000 K, RWD was expanding non-uniformly in time from ∼66 to ∼300 (d/3 kpc) R☉, and LWD was super-Eddington, but not constant. Its maximum of ∼9 × 1038 (d/3 kpc)2 erg s-1 occurred around Aug. 16.0, at the maximum of Teff, half a day before the visual maximum. After the fireball stage, a large emission measure of 1.0-2.0×1062 (d/3 kpc)2 cm-3 constrained the lower limit of LWD to be well above the super-Eddington value. The mass of the ionized region was a few ×10-4 M☉, and the mass-loss rate was decreasing from ∼5.7 (Aug. 22) to ∼0.71×10-4 M☉ yr-1 (Sept. 20). The evolution of the Hα line and mainly the transient emergence of the Raman-scattered Ovi 1032 Å line suggested a biconical ionization structure of the ejecta with a disk-like Hi region persisting around the WD until its total ionization, around day 40. On Sept. 20 (day 35), the model SED indicated a dust emission component in the spectrum. The dust was located beyond the Hi zone, where it was shielded from the hard, ≳105 K, radiation of the burning WD at that time. Conclusions. Our extensive spectroscopic observations of the classical nova V339 Del allowed us to map its evolution from the very early phase after its explosion. It is evident that the nova was not evolving according to the current theoretical prediction. The unusual non-spherically symmetric ejecta of nova V339 Del and its extreme physical conditions and evolution during and after the fireball stage represent interesting new challenges for the theoretical modelling of the nova phenomenon. [ABSTRACT FROM AUTHOR]

HW Vir systems are rare eclipsing binary systems including a subdwarf B star (sdB) with a faint companion, mostly M-dwarfs. Up to now, 19 HW Vir systems have been published, three of them with substellar companions. We report the spectroscopic as well as photometric observation of the eclipsing sdB binary PTF1 J011339.09+225739.1 (PTF1 J0113) in a close (a=0.722 ± 0.023 R⊙), short period (P = 0.0933731(3)d) orbit. A quantitative spectral analysis of the sdB yields Te.=29280 ± 720 K, log(g)=5.77 ± 0.09 dex, and log(y)=−2.32 ± 0.12. The circular orbital velocity of the sdB of K1=74.2 ± 1.7 km s−1 is derived from the radial velocity curve. Except for the strong reflection effect, no other light contribution of the companion could be detected. The light curves - recorded with ULTRACAM - were analyzed using the Wilson-Devinney code. We find an inclination angle of i=79.88 ± 0.18∘. Because our first attempts to determine q failed, we calculated large grids of synthetic lightcurves for several mass ratios. Because of degeneracy, good solutions for different mass ratios were found - the one at q = 0.24 is consistent with the sdB’s canonical mass (MsdB = 0.47 M⊙). Accordingly, the mass of the companion is M2=0.112 ± 0.003 M⊙. The radii of the two components were also derived: RsdB=0.178 ± 0.006 R⊙ and R2 = 0.158 ± 0.009 R⊙. Thus, the results for the secondary are consistent with an M-dwarf as secondary

We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246−2707, and present multicolour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.118 507 9936 ± 0.000 000 0009 d, or about 3 h. Analysis of our time series spectroscopy reveals a velocity semi-amplitude of K1 = 71.6 ± 1.7 km s−1 for the sdB and best-fitting atmospheric parameters of Teff = 28 900 ± 500 K, log g = 5.64 ± 0.06 and log N(He)/N(H) = −2.5 ± 0.2. Although we cannot claim a unique solution from modelling the light curve, the best-fitting model has an sdB mass of 0.45 M⊙ and a cool companion mass of 0.12 M⊙. These results are roughly consistent with a canonical-mass sdB and M dwarf separated by a ∼ 0.84 R⊙. We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to <0.08 per cent. Using 15 yr of eclipse timings, we construct an observed minus calculated (O − C) diagram but find no statistically significant period changes; we rule out $|\dot{P}| > 7.2 \times 10^{-12}$. If EC 10246−2707 evolves into a cataclysmic variable, its period should fall below the famous cataclysmic variable period gap. [ABSTRACT FROM AUTHOR]

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions (white dwarfs with masses M > 1.0 M⊙, neutron stars or black holes). The existence of such systems is predicted by binary evolution calculations and some candidate systems have been found. We identified ≃1100 hot subdwarf stars from the Sloan Digital Sky Survey (SDSS). Stars with high velocities have been reobserved and individual SDSS spectra have been analysed. About 70 radial velocity variable subdwarfs have been selected as good candidates for follow-up time resolved spectroscopy to derive orbital parameters and photometric follow-up to search for features like eclipses in the light curves. Up to now we found nine close binary sdBs with short orbital periods ranging from ≃0.07 d to 1.5 d. Two of them are eclipsing binaries with companions that are most likely of substellar nature (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract We give a brief summary of common basic characteristics of active phases during the whole (1963–2000) observed symbiotic life of CH Cygni. We identify two types of outbursts: (1) those with pronounced signatures of a high-velocity mass outflow, and (2) those displaying signatures of only a mass inflow to the central star. On the basis of the observed Hα emission, we investigate mass loss from the active star during the period from when radio jets appeared (1984.6) to the most recent activity (1998–2000). A simple expression, which relates the observed Hα luminosity to the mass-loss rate, is derived. We obtained mass-loss rates of and 1.8 ± 0.7 × 10[sup -6] M[sub ⊙] yr[sup -1] in 1984 October, 1992 August and 1998 September, respectively. Our values are in very good agreement with radio mass-loss rates determined previously. Mass loss from CH Cygni is a transient effect connected only with active phases of type (1), and is very variable. The ejected material, which is accelerated to the same v[sub ∞] at a distance of ≈ 100 R[sub ⊙] , is heavily decelerated at much larger distances (≈ 1000 au) . The most recent ejecta reflect a larger deceleration. [ABSTRACT FROM AUTHOR]

In this study we present and re-analyse the historical, 1889–1998, light curve (LC) of the eclipsing symbiotic binary AR Pav. For the first time, we show that the timing of mid-points of eclipses observed during a quiescent phase obeys a quadratic ephemeris, with an initial orbital period P[sub 0]=605.18 d and a rate of period change P·=-3.5±0.8×10[sup -5]. We determined a distance to the system of 5.8±1.5 kpc, the mass ratio of the giant to the hot star, M[sub g]M[sub h]=0.4±0.1, the mass of the giant, M[sub g]=1.8+1/-0.5 M[sub ⊙] and its radius, R[sub g]=167±15 R[sub ⊙]. During quiescence, the LC has characteristic features similar to those observed in cataclysmic variables (CVs). It can be well reproduced by a model of a large accretion disc surrounding the hot star. However, it is probable that the geometry of the transferred material in the Roche lobe of the accretor in AR Pav is different from that of CVs. During active phases the shape of the LC changes considerably. A complex wave-like variation developed as a function of the orbital phase with an amplitude of ∼1 mag. It is interpreted in terms of a collisionally heated emission region located on the giant surface and arising from the hot star eruption. [ABSTRACT FROM AUTHOR]

MY Ser is an eclipsing early-type contact system. Both components are of spectral type O6 III. Using ESO archive spectra, we show that the radial velocity of the third body, which contributes about half of the total luminosity, changed from 2006 to 2009. The line profiles of the eclipsing system have peculiar shapes and strengths; namely around conjunctions, they are affected by circumbinary matter. [ABSTRACT FROM PUBLISHER]