Star Formation Near Photodissociation Regions: Detection of a Peculiar Protostar Near Ced 201

TL;DR

This study reports the detection and detailed analysis of a peculiar low-mass protostar near Ced 201 PDR, revealing its physical properties, accretion activity, and environmental influences, contributing to understanding triggered star formation.

Contribution

First detailed multi-wavelength characterization of a peculiar protostar near Ced 201, combining dust continuum, IR, and molecular line observations to model its envelope and accretion processes.

Findings

Protostar is a transition Class 0/I object or multiple system.

Presence of collimated molecular outflow indicates ongoing accretion.

Envelope modeling suggests inward motions and specific ionization conditions.

Abstract

We present the detection and characterization of a peculiar low-mass protostar (IRAS 22129+7000) located ~0.4 pc from Ced 201 Photodissociation Region (PDR) and ~0.2 pc from the HH450 jet. The cold circumstellar envelope surrounding the object has been mapped through its 1.2 mm dust continuum emission with IRAM-30m/MAMBO. The deeply embedded protostar is clearly detected with Spitzer/MIPS (70 um), IRS (20-35 um) and IRAC (4.5, 5.8, and 8 um) but also in the K_s band (2.15 um). Given the large "near- and mid-IR excess" in its spectral energy distribution, but large submillimeter-to-bolometric luminosity ratio (~2%), IRAS 22129+7000 must be a transition Class 0/I source and/or a multiple stellar system. Targeted observations of several molecular lines from CO, 13CO, C18O, HCO+ and DCO+ have been obtained. The presence of a collimated molecular outflow mapped with the CSO telescope in the CO J=3-2 line suggests that the protostar/disk system is still accreting material from its natal envelope. Indeed, optically thick line profiles from high density tracers such as HCO+ J=1-0 show a red-shifted-absorption asymmetry reminiscent of inward motions. We construct a preliminary physical model of the circumstellar envelope (including radial density and temperature gradients, velocity field and turbulence) that reproduces the observed line profiles and estimates the ionization fraction. The presence of both mechanical and (non-ionizing) FUV-radiative input makes the region an interesting case to study triggered star formation.