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

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1. Introduction

A major problem in the study of the early stages of star formation is the fact that they are obscured by large amounts of circumstellar dust, making them invisible at optical wavelengths. By observing at longer wavelengths, we can study more obscured, and thus generally younger, sources but at these wavelengths we are looking more at the circumstellar material than the photosphere of the protostar itself. Choosing only the less obscured stars selects older objects. Only a few sources are known which show features of the young, embedded systems, but which are visible in the optical or the near IR. The flat spectrum sources, at the boundary between the Class I and Class II systems, are thought to be close to this transition.

We are studying a young star which is an excellent example of an object close to the Class I / Class II boundary. This transitional Young Stellar Object (YSO), which is associated with IRAS 05327+3404, was first discussed by Magnier et al. (1996; Paper I). We refer to the outflow source by the nickname "Holoea" because of the unusually powerful ionized outflow (see Paper I) and to distinguish it from the other, weaker sources of far-IR emission in the vicinity. In Paper I, we showed that IRAS 05327+3404 (Holoea) has some features typical of Class I sources (rising spectral energy distribution, molecular bipolar outflow) and some features typical of Class II sources (visible central star, ionized outflow). Furthermore, the outflow is of an unusually high velocity ([FORMULA]650 km s-1) for a low-mass star (roughly K2), and the central star has brightened by [FORMULA] magnitudes since the 1954 POSS plates. All of these pieces of evidence suggest that this source is not only close to the Class I / Class II (Lada & Wilking 1984) boundary, but in fact in the process of becoming exposed. We are continuing the study of this transitional YSO to gain further understanding of this short-lived stage of stellar evolution. We have recently obtained new observations from optical to sub-millimeter wavelengths. In this paper, we discuss the implications of these new data on our understanding of the circumstellar material and the reflection nebula of IRAS 05327+3404 (Holoea).

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© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999