Snowflakes in a furnace: formation of CO and dust in a recurrent nova eruption

TL;DR

This paper reports the first detection of CO and dust formation in the ejecta of a recurrent nova, occurring under unexpectedly hostile conditions shortly after outburst, suggesting new insights into dust formation mechanisms.

Contribution

It presents the first observation of molecule and dust formation in recurrent nova ejecta, challenging previous assumptions about harsh environment constraints.

Findings

Detection of CO and dust 8.7 days after outburst

Estimated CO mass: (1-5) x 10^-8 solar masses

Dust temperature around 1000 K

Abstract

We report the detection of carbon monoxide (CO) and dust, formed under hostile conditions, in recurrent nova V745 Sco about 8.7 days after its 2014 outburst. The formation of molecules or dust has not been recorded previously in the ejecta of a recurrent nova. The mass and temperature of the CO and dust are estimated to be T(CO) = 2250 +/- 250 K, M(CO) = (1 to 5) E-8 solar masses, and T(dust) = 1000 +/- 50 K, M(dust) approximately E-8 to E-9 solar masses respectively. At the time of their detection, the shocked gas was at a high temperature of approximately E+7 K as evidenced by the presence of coronal lines. The ejecta were simultaneously irradiated by a large flux of soft X-ray radiation from the central white dwarf. Molecules and dust are not expected to form and survive in such harsh conditions; they are like snowflakes in a furnace. However, it has been posited in other studies that, as the nova ejecta plow through the red giant's wind, a region exists between the forward and reverse shocks that is cool, dense and clumpy where the dust and CO could likely form. We speculate that this site may also be a region of particle acceleration, thereby contributing to the generation of gamma-rays.