The Local Environment of the FUor-like Objects AR 6A and 6B

TL;DR

This study uses molecular line maps to analyze the environment of FUor-like objects AR 6A and 6B, revealing they are more evolved than typical protostars and suggesting FUor eruptions occur at various early star formation stages.

Contribution

It provides new molecular line observations of AR 6, showing its similarity to FU Orionis and proposing that FUor outbursts happen at different evolutionary stages.

Findings

AR 6 lacks CO outflows and significant molecular gas.

AR 6 is more evolved than Class I protostars.

AR 6 is part of a young stellar cluster, unlike typical FUors.

Abstract

We present new 12CO J=3-2 and HCN J=3-2 molecular line maps of the region surrounding the young star AR 6 using the 15 metre James Clerk Maxwell Telescope. AR 6 was previously found to be a double source with both components exhibiting several characteristics of FU Orionis (FUor) eruptive variable stars. Our data indicates that AR 6, like FU Orionis itself, does not possess a CO outflow and likewise, does not show evidence for large amounts of molecular g as in its circumstellar environment. We conclude that from the near-IR to the sub-mm, AR 6 is similar to FU Orionis in several respects. We interpret the lack of significant dust and molecular gas in the circumstellar environment of AR 6, together with the large near-IR thermal excess, as evidence that the sources have exhausted their natal envelopes, that they have at least small hot circumstellar disks, and that they are more evolved than Class I protostars. This, in itself, suggests that, since FUor eruptions have also been observed in stars with large dust mass envelopes (e.g. V346 Nor) and with CO outflows (e.g. L1551 IRS5), FUor events probably occur at many different stages in the early, formative phase of a star's life, and lends support to the idea that FUor outbursts are repetitive like their shorter-lived relatives occurring in EXor eruptive variables. Finally, we show that, being part of the 'Spokes' young stellar cluster, AR 6 is unlike many FUors which typically are located in more sparsely populated regions.