Detection of the Red Supergiant Wind from the Progenitor of Cassiopeia A

Abstract

Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While providing a rare opportunity to study in detail the remnant of a Type IIb supernova, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Hα emission nebulosities concentrated 10-15 pc (10-15 arcminutes) to the north and east. First reported by Minkowski as a faint H II region, these nebulosities exhibit distinct morphological and spectroscopic properties relative to the surrounding diffuse emissions. Compared to neighboring H II regions, these nebulae show stronger [N II] 6548, 6583Å and [S II] 6716, 6731Å emissions relative to Hα. We show that Cas A's highest-velocity ejecta knots are interacting with some of the closest projected emission nebulae, thus providing strong evidence that these nebulae lie at the same distance as the remnant. We interpret these surrounding nebulosities to be the remains of the progenitor's red supergiant wind which accumulated against the southern edge of a large extended H II region located north of Cas A. Our findings are consistent with the view that Cas A's progenitor underwent considerable mass-loss, first from a fast main-sequence wind, then from a slower, clumpy red supergiant wind, and finally from a brief high-velocity wind, like that from a yellow supergiant.

Formation pathway for lonely stripped-envelope supernova progenitors: implications for Cassiopeia A

“…We choose the total RSG lifetime of the secondary as ∆t but this can also be smaller depending on the mass ratio of the binary, so we consider r sh ∼ 100 pc as a conservative upper limit. It is known that there is an Hα cloud located 10-15 pc outside of Cas A in the North East direction (van den Bergh 1971;Weil et al 2020). The location of this cloud is within the ballpark of our inner shell estimate and the one-sided Figure 12.…”

“…There are no obvious X-ray features that appear to be the remnant of the primary supernova within 50 pc. The yellow box shows the faint H II region called "Minkowski's H II region" (see van den Bergh 1971;Weil et al 2020).…”

The forward and reverse shock dynamics of Cassiopeia A

“…The debris of this overrun shell may be associated with the quasi-stationary flocculi in the western part of Cas A (Koo et al 2018). If true, the current reverse shock dynamics may reveal some information about the mass loss history of the Cas A progenitor, which could be combined with the optical information about unshocked CSM as reported by Weil et al (2020) to shed light on the nature of the progenitor star.…”

“…The standard scenario for the evolution of Cas A is that of a remnant of a core-collapse SN of Type IIb (Krause et al 2008;Rest et al 2011), with a low ejecta mass of 2-4 M evolving in the clumpy, dense wind of its progenitor (Vink et al 1996;Willingale et al 2003;Chevalier & Oishi 2003;Vink 2004;Hwang & Laming 2012;Weil et al 2020). The observed deviations from spherical symmetry, like the jet and ejecta rings, are usually attributed to asymmetries in the explosion itself, for which light echos from different directions indeed provide evidence (Rest et al 2011).…”

“…Lawrence et al 1995;Fesen et al 2001;Alarie et al 2014;Koo et al 2018), with a large concentration in the northern part, and a protruding arc of QSFs in the Southwest. Weil et al (2020) recently reported the detection of faint optical emission from clumpy CSM outside the current shock radius.…”