Herschel-PACS spectroscopy of the intermediate mass protostar NGC7129 FIRS 2

TL;DR

This study presents Herschel-PACS spectroscopic observations of the intermediate mass protostar NGC7129 FIRS 2, revealing strong emission lines that suggest the emission originates from outflow cavity walls rather than the spherical envelope.

Contribution

First Herschel spectroscopic observations of NGC7129 FIRS 2, providing new insights into the origin of high excitation emission lines in intermediate mass protostars.

Findings

Detected 26 emission lines including H2O, CO, OH, O I, and C II.

Most lines are stronger than spherical envelope models predict.

High excitation emission likely arises from outflow cavity walls, not the envelope.

Abstract

Aims: We present preliminary results of the first Herschel spectroscopic observations of NGC7129 FIRS2, an intermediate mass star-forming region. We attempt to interpret the observations in the framework of an in-falling spherical envelope. Methods: The PACS instrument was used in line spectroscopy mode (R=1000-5000) with 15 spectral bands between 63 and 185 microns. This provided good detections of 26 spectral lines seen in emission, including lines of H2O, CO, OH, O I, and C II. Results: Most of the detected lines, particularly those of H2O and CO, are substantially stronger than predicted by the spherical envelope models, typically by several orders of magnitude. In this paper we focus on what can be learned from the detected CO emission lines. Conclusions: It is unlikely that the much stronger than expected line emission arises in the (spherical) envelope of the YSO. The region hot enough to produce such high excitation lines within such an envelope is too small to produce the amount of emission observed. Virtually all of this high excitation emission must arise in structures such as as along the walls of the outflow cavity with the emission produced by a combination of UV photon heating and/or non-dissociative shocks.