ALMA Insight Into CK Vulpeculae: The Aftermath of a White Dwarf - Brown Dwarf Merger?

In July 1670, observers witnessed a nova in the constellation Cygnus, cited as Nova sub Capite Cygni - "a new star below the head of the swan" (Hevelius, Phil. Trans. 1670, 5, 2087). Modern astronomers studying the remains of Nova Vulpeculae 1670 = CK Vul, initially thought this cosmic event was triggered by the merging of two main-sequence stars. However, our new Atacama Large Millimeter/Sub-millimeter Array (ALMA) observations of the remnant suggest a more intriguing picture. These data (Band 6, in 4 spectral windows 1.875 GHz in width, centered on 224, 226, 240, and 242 GHz) trace obscuring dust in the inner regions of the associated nebulosity. The dust forms two cocoons, each extending approximately 5" N and S of the presumed location of the central stellar remnant. Line emission from organic molecules methanamide (NH2CHO), methanol (CH3OH), formaldehyde (H2CO), and CN and C17O is detected. CN lines trace bubbles within the dusty cocoons; methanol a N-S "S-shaped" jet; and other molecules a central cloud with a structure aligned with the innermost dust structure. The dust emission has approximate point symmetry about the radio source position (Hajduk et al. 2007, MNRAS, 378, 1298), the latter taken to be the putative location of stellar remnant. The inner 2" of the dust distribution is extended E-W with a sub-structure (2" x 1") that includes N-S extension around the peak, suggestive of a warped disk. After examining several possibly scenarios, we suggest 1670 "nova" was due to the merger of a white dwarf primary and a brown dwarf secondary. We argue the brown dwarf impact generated the unusual abundances and isotopic ratios seen in this object via nucleosynthesis (including Lithium). The ejected material formed the extended ejecta and disk observed with ALMA and that in turn drives the jets shaping the inner 6" of the nebulosity N and S of the center of the jet and disk. We find a total dust mass of ~2.04 x 10-4 M⊙ of which ~1.56 x 10-4 M⊙ is in the diffuse extended emission and ~4.81 x 10-5 M⊙ is in the central disk.