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Title:
The Local Environment of the FU-Orionis-Like Objects AR 6A and 6B
Authors:
Moriarty-Schieven, Gerald H.; Aspin, Colin; Davis, Gary R.
Affiliation:
AA(National Research Council of Canada, Joint Astronomy Centre, 660 North A'ohoku Place, Hilo, HI 96720, USA ), AB(Institute for Astronomy, University of Hawaii, 640 North A'ohoku Place, Hilo, HI 96720-2700, USA ), AC(Joint Astronomy Centre, 660 North A'ohoku Place, Hilo, HI 96720, USA )
Publication:
The Astronomical Journal, Volume 136, Issue 4, pp. 1658-1666 (2008). (AJ Homepage)
Publication Date:
10/2008
Origin:
IOP
AJ Keywords:
accretion, accretion disks, stars: formation, stars: individual: AR 6, stars: pre-main sequence
DOI:
10.1088/0004-6256/136/4/1658
Bibliographic Code:
2008AJ....136.1658M

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 m James Clerk Maxwell Telescope (JCMT). AR 6 was previously found to be a double source with both components exhibiting several characteristics of FU Orionis (FUor) eruptive variable stars. The aims of this investigation were to determine if the AR 6 sources are associated with molecular outflows and if a significant reservoir of natal molecular gas and dust exists around the stars. These observations form a part of a large-scale study of the outflow and circumstellar environment characteristics of FUors and FUor-like objects to place constrains on the age and evolutionary state of sources exhibiting FUor-like tendencies. Our data indicate that AR 6, like FUor itself, does not possess a CO outflow and likewise, does not show evidence for large amounts of molecular gas in its circumstellar environment. In fact, AR 6 seems to lie in a local minimum of HCN emission. This is also found in 850 μm dust emission seen in JCMT archival data. We conclude that from the near-infrared to the sub-millimeter, AR 6 is similar to FUor 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-infrared (NIR) 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 study the stellar environment around AR 6 using Two Micron All Sky Survey, Spitzer Infrared Array Camera, and Chandra ACIS images and show that, being part of the "Spokes" young stellar cluster, AR 6 is unlike many FUors which are typically located in more sparsely populated regions.
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