A windswept cometary tail on the Galactic center supergiant IRS 7

Abstract

High-resolution VLA observations provide evidence of optically thick radio emission from IRS 7, a cool red supergiant star, located at a projected distance of roughly 1 1t-yr from the Galactic center. IRS 7 shows a remarkable tail of ionized gas pointing directly away from the compact nonthermal radio source at the Galactic center, Sgr A(asterisk). Given previous evidence for a strong source of UV emission and for a strong circumnuclear wind emanating from the Galactic center, the free-free emission from IRS 7 and its associated tail are interpreted in terms of the ionization and removal of the circumstellar envelope of the red supergiant either by the ram pressure of the nuclear wind or by the pressure of radiation arising from the immediate vicinity of Sgr A(asterisk). The wind mechanism is preferred because: (1) the force it can potentially exert is much greater; and (2) Sgr A(asterisk) is clearly not a known source of luminous energy in the near-IR, whereas it remains a plausible source of a hot, high-velocity wind. Also considered is the potential effect of a nuclear wind upon the atmospheres of red giants in the inner parsec.