Neutral helium line profiles through the simulation of local interactions

For the past 25 years, we have been considering the Stark effect for neutral helium lines in DB white dwarfs using the standard Stark broadening theory in both the impact regime (in the center of the lines) and the quasi-static regime (in the wings) for the electrons, while neglecting the effect of ions in motion. Although this is probably a good approximation based on previous theoretical work, the transition between the two regimes for the electrons and the contribution of the ions very near the core might be poorly represented. To better represent these particularities, we report here the results of a new series of simulations that treat the local dynamics and interactions of both electrons and ions around a neutral helium atom. From these simulations, we produce new improved line profiles, which we compare with our previous analytical results.

Optical and X-ray study of V404 Cyg during its activity in the Summer 2015

The black hole X-ray binary V404Cyg was studied during of the 2015 outburst. Optical photometry and spectroscopy were performed by using 1.5-meter Russian-Turkish telescope (RTT-150) facilities at the TUBITAK National Observatory (Antalya, Turkey). From June 22 to June 28, 2015, shell expansion velocity decreased from 650 to 400 km s–1 as measured by Hα and Hβ lines and from 450 to 330 km s–1 as measured by HeI and HeII lines. Thus, the shell expansion occurred with deceleration, where the hydrogen and helium line formation regions are at different radial distances from the center of the star. The correlation of flow variability in the optical and X-ray ranges is caused by fluctuations in the rate of accretion near a compact source where X-ray photons are generated.

Perturbations Observed in The Orbital Elements of the Spectroscopic Binary 57 Cygni

We present spectroscopy that confirms periodic Doppler-shifts along with photometry that reinforces a lack of eclipsing in the double-lined spectroscopic binary 57 Cygni. Our spectroscopy concentrates on a range encompassing H-alpha and the helium 667.8 nm line, where we find Doppler-shifts of both stars resolved in the helium line but less so in the broader H-alpha profile. Although we find the radial velocities derived from both lines reasonably consistent, we retained only the helium-line derived velocities for sinusoidal curve-fits to the orbital dependence. The fit-amplitudes specify the ratio of the stellar masses as 1.03 ± 0.05, in agreement with previous assessments. We find an eccentricity of 0.028 ± 0.024 and a longitude of periastron of 163.5 ± 2.5°. The former is significantly lower than that previously reported, while the latter is in agreement but calls into question the apsidal motion predicted four decades ago. Our modeling suggests the presence of an external third body implicit in this previous apsidal motion, as well as the dominant mechanism for our reported change in eccentricity. Based upon the spectral type assignment, the near-circular orbit, and the well-established mass ratio, we can place restrictions on the orbital inclination from 51.5-to-53.0°, in reasonable agreement with previous estimates.