Broad Wings around Hα and Hβ in the Two S-type Symbiotic Stars Z Andromedae and AG Draconis

Abstract

Symbiotic stars often exhibit broad wings around Balmer emission lines, whose origin is still controversial. We present the high resolution spectra of the S type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS and the 3.6 m Canada France Hawaii Telescope to investigate the broad wings around Hα and Hβ. When Hα and Hβ lines are overplotted in the Doppler space, it is noted that Hα profiles are overall broader than Hβ in these two objects. Adopting a Monte Carlo approach, we consider the formation of broad wings of Hα and Hβ through Raman scattering of far UV radiation around Lyβ and Lyγ and Thomson scattering by free electrons. Raman scattering wings are simulated by choosing an H I region with a neutral hydrogen column density N HI and a covering factor CF . For Thomson wings, the ionized scattering region is assumed to cover fully the Balmer emission nebula and is characterized by the electron temperature T e and the electron column density N e . Thomson wings of Hα and Hβ have the same width that is proportional to T 1/2 e . However, Raman wings of Hα are overall three times wider than Hβ counterparts, which is attributed to different cross section for Lyβ and Lyγ. Normalized to have the same peak values and presented in the Doppler factor space. Hα wings of Z And and AG Dra are observed to be significantly wider than Hβ counterpart, favoring the Raman scattering origin of broad Balmer wings.

LIN 358: a symbiotic binary accreting above the steady hydrogen fusion limit

“…These kind of emission line profiles have been previously observed in many planetary nebulae and symbiotic binaries (e.g. Arrieta & Torres-Peimbert 2003;Chang et al 2018). There are several different possible formation mechanisms for the broad wings, e.g.…”

3D Grid-Based Monte Carlo Code for Radiative Transfer through Raman and Rayleigh Scattering with Atomic Hydrogen -- STaRS

“…The medium for radiative transfer through Raman and Rayleigh scattering corresponds to a thick H I region that is easily found in the slow stellar wind from a red giant (Lee & Lee 1997;Lee et al 2019). No consideration on the thermal motion of neutral hydrogen is given because the variation of the cross section and the branching ratio in the scale of thermal speed is negligible (Chang et al 2015(Chang et al , 2018.…”

“…Due to the line broadening effect, far UV radiation near Lyman series of hydrogen will be considerably diluted and redistributed around Balmer emission lines to appear as broad wings (e.g. Yoo et al 2002;Chang et al 2015Chang et al , 2018. Another important consequence of the line broadening effect is that the line profiles of Raman-scattered features mainly reflect the relative motion between the far UV emitters and the neutral scatterers and quite independent of the observer's line of sight (Heo et al 2016;.…”

“…The solid lines represent the analytic solutions and open circles show simulation results obtained using STaRS. The analytic solutions are obtained from the non-grid based simulation in Chang et al (2015Chang et al ( , 2018.…”

“…Furthermore, Hα and Hβ in symbiotic stars and young planetary nebulae often display fairly extended wings that may indicate the presence of fast tenuous stellar wind (e.g., Arrieta & Torres-Peimbert 2002). Broad wings around Balmer lines may also arise via Raman scattering far-UV continuum around Lyman lines, which requires further investigation (Lee 2000;Yoo et al 2002;Chang et al 2018).…”