Doppler tomography of the circumstellar disk ofπAquarii

Abstract

Aims. The work is aimed at studying the circumstellar disk of the bright classical binary Be star π Aqr. Methods. We analysed variations of a double-peaked profile of the H α emission line in the spectrum of π Aqr that was observed in many phases during ∼40 orbital cycles in 2004−2013. We applied the discrete Fourier transform (DFT) method to search for periodicity in the peak intensity ratio (V/R). Doppler tomography was used to study the structure of the disk around the primary. Results. The dominant frequency in the power spectrum of the H α V/R ratio is 0.011873 day −1 , which corresponds to a period of 84.2(2) days and agrees with the earlier determined orbital period of the system, P orb = 84.1 days. The V/R shows a sinusoidal variation that is phase-locked with the orbital period. Doppler maps of all our spectra show a non-uniform structure of the disk around the primary: a ring with the inner and outer radii at V in ≈ 450 km s −1 and V out ≈ 200 km s −1 , respectively, along with an extended stable region (spot) at V x ≈ 225 km s −1 and V y ≈ 100 km s −1 . The disk radius of ≈65 R = 0.33 AU was estimated by assuming Keplerian motion of a particle on a circular orbit at the disk's outer edge.

π Aquarii is another γ Cassiopeiae object

“…1 of Bjorkman et al 2002 and Fig. 3 of Zharikov et al 2013). The BeSS 3 database provides spectra obtained on 15 and 19 November 2013, bracketing our X-ray exposure date.…”

“…In this context, it must be noted that the companion on the circular, 84.1 d orbit is certainly not a compact object (Bjorkman et al 2002;Zharikov et al 2013). Indeed, the large mass of the companion is incompatible with masses of white dwarves and neutron stars (Özel & Freire 2016).…”

“…• ) and the circumstellar disk has a radius of 65 R (Zharikov et al 2013), or one third of the separation. With such a geometry, there is not much room in the system to place a compact object relatively close to the Be star, and a putative compact companion in stable orbit would have to be quite distant from the Be+AF pair, rendering wind accretion much less efficient than required.…”

“…The X-ray emission of π Aqr should now be monitored, along with its optical characteristics, on several timescales; in particular the 84.1 d orbital period (since disk variations occur with this period; Zharikov et al 2013) but also longer timescales to probe outbursts. Only then will the exact relationship between the disk and the X-ray emission be unveiled, and the γ Cas phenomenon fully understood.…”

A Search for Hot Subdwarf Companions to Rapidly-Rotating Early B Stars

“…We employed Hα spectra from the Coudé Feed Telescope at the Kitt Peak National Observatory(KPNO), the Be Star Spectra Database (http://basebe.obspm.fr/basebe/), and 22 images from IUE to determine good orbital parameters for the primary. Zharikov et al (2013) found that excess Hα emission is located on the side of the disk facing the secondary. Since this is seen in other sdO objects, we searched for a hot companion in the FUV using cross-correlation templates for BD+28 4211 (T = 82 kK), BD+75 325 (T = 53 kK), and HD 49798 (T = 48 kK), but did not find a signature of the secondary.…”