Toward Understanding the B[e] Phenomenon. VII. AS 386, a Single-lined Binary with a Candidate Black Hole Component

Abstract

We report the results of spectroscopic and photometric observations of the emission-line object AS 386. For the first time we found that it exhibits the B[e] phenomenon and fits the definition of an FS CMa

Not so fast: LB-1 is unlikely to contain a 70 M⊙ black hole

“…Like LB-1, and in contrast to most classical Be stars, AS 386 is slowly rotating. Also in contrast to classical Be stars (Dachs et al 1990), both LB-1 and AS 386 have stronger Balmer decrements than predicted for low-density nebular gas, case-B recombination, and a temperature near 10 4 K. The spectral energy distributions of AS 386 and LB-1 both reveal infrared excess; Khokhlov et al (2018) find that in AS 386, this stems primarily from dust emission in a circumbinary disk.…”

“…There are several similarities between LB-1 and the recently-identified binary AS 386 (Khokhlov et al 2018), which contains a 7 M B-star primary and a detached 7M unseen companion suspected to be a BH. That system also has a strong Hα emission line whose shape changes between epochs.…”

“…AS 386 exhibits periodic variability in the infrared. Khokhlov et al (2018) attribute this to dust temperature variations in the Earth-facing inner rim of the circumbinary disk as the distance from the B star to the rim changes. We do not find evidence of such variability in the WISE light curves of LB-1, although the light curves are sparse.…”

Toward understanding of the origin of the B[e] phenomenon in FS CMa type objects

“…Nevertheless, we have recently managed to find orbital periods in two moderately bright FS CMa objects, MWC 728 (period 27.5 days, V ∼9.8 mag, and AS 386 (period 131.3 days, V ∼10.9 mag, Khokhlov et al 2018). The former object shows absorption lines of a cool star in the optical spectrum (see Fig.…”

“…A dozen other objects show radial velocity variations possibly due to orbital motion or were detected by spectro-astrometry (Baines et al 2006) and interferometry (Millour et al 2009). Two FS CMa objects are known to have compact secondary components: CI Cam (a white dwarf or a neutron star, Robinson et al 2002) and AS 386 (probably a black hole, Khokhlov et al 2018).…”