Molecular remnant of Nova 1670 (CK Vulpeculae)

II. A three-dimensional view of the gas distribution and velocity field^★

¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Rabiańska 8, 87-100 Toruń, Poland
e-mail: tomkam@ncac.torun.pl
² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
³ Instituto de Astronomía, OAN, UNAM, Ensenada, Mexico
⁴ Observatorio Astronomico Nacional (OAN, IGN), Campus Universitario, Ctra. NII km 33,600, Apartado 112, 28803 Alcala de Henares, Spain
⁵ Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, ul. Oczapowskiego 2, 10-719 Olsztyn, Poland

Received: 9 October 2020
Accepted: 19 December 2020

Abstract

CK Vul is the remnant of an energetic eruption known as Nova 1670 that is thought to be caused by a stellar merger. The remnant is composed of (1) a large hourglass nebula of recombining gas (of 71′′ in size), very similar to some classical planetary and pre-planetary nebulae (PPNe), and (2) a much smaller and cooler inner remnant that is prominent in millimeter-wave emission from molecules. We investigate the three-dimensional spatio-kinematic structure of both components. Our analysis of the hourglass structure yields a revised distance to the object of >2.6 kpc, at least 3.7 times greater than previously assumed. At this distance, the stellar remnant has a bolometric luminosity >12 L_⊙ and is surrounded by molecular material with a total mass >0.8 M_⊙ (the latter value has a large systematic uncertainty). We also analyzed the architecture of the inner molecular nebula using ALMA observations of rotational emission lines obtained at subarcsecond resolution. We find that the distribution of neutral and ionized gas in the lobes can be reproduced by several nested and incomplete shells or jets with different velocity fields and varying orientations. The analysis indicates that the molecular remnant was created in several ejection episodes, possibly involving an interacting binary system. We calculated the linear momentum (≈10⁴⁰ g cm s⁻¹) and kinetic energy (≈10⁴⁷ erg) of the CK Vul outflows and find values that are within the limits typical for classical PPNe. Given the similarities of the CK Vul outflows to PPNe, we suggest there may be CK Vul analogs among wrongly classified PPNe with low intrinsic luminosities, especially among PPNe with post-red-giant-branch central stars.