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Astron. Astrophys. 346, 441-452 (1999)

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7. Conclusions

We have obtained new observations of the unusual young stellar object, IRAS 05327+3404 (Holoea). We have shown that the central star is directly visible, with only a modest amount of extinction ([FORMULA] mag). The spectral type of the central star is roughly K 2. The spectral energy distribution implies the presence of substantial circumstellar material, and model comparisons suggest the original cloud had significant angular momentum ([FORMULA] 10-13 rad s-1). A detailed study of the flux detected from the reflection nebula also shows the presence of circumstellar material arranged in an equatorial plane, with a 33o wide polar hole. CO mapping shows the presence of a bipolar molecular outflow aligned with the polar hole (P.A. [FORMULA]o) seen via the reflection nebula. This is roughly the same direction as the ionized outflow evident in the H[FORMULA] line profiles. The CO map also shows a small ([FORMULA]0.3 pc) enveloping molecular cloud, and the possible presence of a single, weaker CO outflow. Although IRAS 05327+3404 (Holoea) drives an ionized outflow which is surprisingly fast for a low-mass young stellar object ([FORMULA]650 km s-1), there is little or no evidence for active accretion in the form of strong UV excess, veiling, or high-Balmer line emission. This suggests that an ionized outflow may exist without the simultaneous presence of a hot, active accretion disk. Two possibilities exist: 1) the observed ionized outflow in Holoea was driven by a hot accretion disk in the recent past which has subsequently shut off, leaving behind the fast-moving jet or 2) the observed ionized outflow is currently being driven, not by a hot accretion disk, but by some other component, such as the cool circumsellar disk or the stellar photosphere. The central star has brightened in the past 40 years, but this brightening does not seem to be due to an increase in accretion activity. We suggest that the brightening is due to reduced extinction as the polar regions are cleared. The unusual presence of a massive circumstellar disk, as seen in the far-IR emission, and a visible central star may imply a large angular velocity for the birth cloud. We suggest that the relative isolation of IRAS 05327+3404 (Holoea) during its formation may have allowed a large amount of material to be maintained in a circumstellar disk with high angular momentum. In addition to having a large circumstellar disk, and few nearby neighbors to disrupt the disk, the large angular momentum may inhibit further accretion, and may allow the circumstellar disk to remain longer than in less isolated systems. Thus, the environment may play an important role in determining the evolution of the spectral energy distribution.

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© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999