BVRcIc photometric evolution and flickering during the 2010 outburst of the recurrent nova U Scorpii

CCD BVRcIc photometric observations of the 2010 outburst of the recurrent nova U Scorpii are presented. The light-curve has a smooth development characterized by t2(V)=1.8 and t3(V)=4.1 days, close to the t2(V)=2.2 and t3(V)=4.3 days of 1999 outburst. The plateau phase in 2010 has been brighter, lasting shorter and beginning earlier than in the 1999 outburst. Flickering, with an amplitude twice larger in $I_{\rm C}$ than in $B$ band, was absent on day +4.8 and +15.7, and present on day +11.8, with a time scale of about half an hour.Comment: published March 1

Asiago eclipsing binaries program. III. V570 Per

The orbit and physical parameters of the previously unsolved SB2 EB V570 Per are derived using high resolution Asiago Echelle spectroscopy and B, V photo-electric photometry. The metallicity from chi^2 analysis is [M/H]=+0.02 +/- 0.03, and reddening from interstellar NaI and KI absorption lines is E(B-V) =0.023 +/- 0.007. The two components have masses of 1.449 +/- 0.006 and 1.350 +/- 0.006 Msun and spectral types F3 and F5, respectively. They are both still within the Main Sequence band (T_1 =6842 +/- 25 K, T_2 =6562 +/- 25 K from chi^2 analysis, R_1 =1.523 +/- 0.030, R_2 =1.388 +/- 0.019 Rsun) and are dynamically relaxed to co-rotation with the orbital motion (Vrot sin i_{1,2} =40 and 36 (+/-1) km/sec). The distance to V570 Per obtained from the orbital solution is 123 +/- 2 pc, in excellent agreement with the revised Hipparcos distance of 123 +/- 11 pc. The observed properties of V570 Per components are compared to BaSTI models computed on purpose for exactly the observed masses and varied chemical compositions. This system is interesting since both components have their masses in the range where the efficiency of convective core overshooting has to decrease with the total mass as a consequence of the decreasing size of the convective core during the central H-burning stage. Our numerical simulations show that, a small but not null overshooting is required, with efficiencies lambda_{OV} =0.14 and 0.11 for the 1.449 and 1.350 Msun components, respectively. This confirms the finding of Paper II on the similar system V505 Per. At the approx 0.8 Gyr age of the system, the element diffusion has reduced the surface metallicity of the models from the initial [M/H]=+0.17 to [M/H]=+0.02, in perfect agreement with the spectroscopically derived [M/H]=+0.02 +/- 0.03 value.Comment: accepted by A&A. This revised upload to astro-ph correct a formatting error generated by uncorrect A&A style fil

The 2016-2017 peak luminosity of the pre-main sequence variable V2492 Cyg

V2492 Cyg is a young pre-main sequence star presenting repetitive brightness variations of significant amplitude (Delta R > 5 mag) whose physical origin has been ascribed to both extinction (UXor-type) and accretion (EXor-type) variability, although their mutual proportion has not been clarified yet. Recently, V2492 Cyg has reached a level of brightness ever registered in the period of its documented activity. Optical and near-infrared photometry and spectroscopy have been obtained in October 2016 and between March and July 2017. The source has remained bright until the end of May 2017, then it started to rapidly fade since the beginning of June at a rate of about 0.08 mag/day. On mid-July 2017 the source has reached the same low-brightness level as two years before. Extinction and mass accretion rate were derived by means of the luminosity of the brightest lines, in particular Halpha and Hbeta. A couple of optical high-resolution spectra are also presented to derive information on the gas kinematics. Visual extinction variations do not exceed a few magnitudes, while the mass accretion rate is estimated to vary from less than 10^-8 up to a few 10^-7 M_sun/yr. This latter is comparable to that estimated on the previous high-state in 2010, likely occurred under more severe extinction conditions. The combined analysis of the optical and near-infrared (NIR) observations extends to the present event the original suggestion that the V2492 Cyg variability is a combination of changing extinction and accretion.Comment: Accepted by A&