The 2018 eruption and long term evolution of the new high-mass Herbig Ae/Be object Gaia-18azl = VES 263

Abstract

Abstract We have been monitoring, at high cadence, the photometric and spectroscopic evolution of VES 263 following the discovery in 2018 of a brightening labeled as event Gaia-18azl. VES 263 is so far a neglected emission-line object discovered in the 1960s on objective prism plates, tentatively classified as a semi-regular AGB cool giant by automated analysis of ASASSN lightcurves. We have discovered that VES 263 is a bonafide massive pre-Main Sequence object (∼12 M⊙), of the Herbig AeBe type. It is located at 1.68±0.07 kpc distance, within the Cyg OB2 star-forming region, and it is highly reddened (EB − V=1.80±0.05) by interstellar extinction. In quiescence, the spectral energy distribution is dominated by the ∼20,000 K photospheric emission from the central B1II star, and at λ≥6μm by emission from circumstellar warm dust (T≤400○K). The 2018-19 eruption was caused by a marked brightening of the accretion disk around the B1II star as traced by the evolution with time of the integrated flux and the double-peaked profile of emission lines. At the peak of the eruption, the disk has a bulk temperature of ∼7500 K and a luminosity L ≥860 L⊙, corresponding to a mass accretion rate M≥1.1 × 10−5 M⊙ yr−1. Spectroscopic signature of possible bipolar jets (at −700 and +700 km s−1) of variable intensity are found. We have reconstructed from Harvard, Moscow and Sonneberg photographic plates the photometric history of VES 263 from 1896 to 1995.