The environment of supernova remnant VRO 42.05.01 as probed with IRAM 30m molecular line observations

Abstract

The environment of supernova remnants (SNRs) is a key factor in their evolution, particularly at later stages of their existence. It is often assumed that mixed-morphology (MM) SNRs evolve in very dense environments, and that their centre-filled X-ray morphology is due to interactions between the SNRs and their surroundings. We aim to determine whether MMSNR VRO 42.05.01 is embedded in, and interacting with, a dense molecular environment. We used the IRAM telescope in Pico Veleta, Spain, to search for interaction between the SNR and neighbouring molecular clouds. We observed a region of $26'\times14'$ towards the west of VRO 42.05.01 and a region of $8'\times4'$ towards the north of the remnant in the $^{12}$CO $J=1-0$, $^{13}$CO $J=1-0$, and $^{12}$CO $J=2-1$ transitions with the EMIR receiver. We made maps of the properties of the observed molecular clouds (peak temperatures, central velocities, velocity dispersions), column density along the line of sight, and ratio of the $^{12}$CO $J=2-1$ to $^{12}$CO $J=1-0$ transitions. We analyse archival optical, infrared, and radio spectroscopic data for other hints on the nature of the medium. We do not find conclusive physical proof that the SNR is interacting with the few, clumpy molecular clouds that surround it in the region of our observations, although there is some suggestion of such interaction (in a region outside our map) from infrared emission. There is a velocity gradient in one of the molecular clouds that is consistent with a stellar wind blown by a $12-14$ $M_{\odot}$ progenitor star. We reassess the literature distance to VRO 42.05.01, and propose that it has a local standard of rest velocity of $-6$ km s$^{-1}$, and that it is located $1.0\pm0.4$ kpc away (the earlier distance value was $4.5\pm1.5$ kpc). We find that a dust sheet intersects VRO 42.05.01 and is possibly related to its double shell-shaped morphology.