Very low-luminosity Class I/Flat outflow sources in sigma Orionis

TL;DR

This study investigates two very low-luminosity Class I/Flat sources in sigma Orionis, revealing their accretion, outflow activities, and low-mass envelopes, suggesting they may evolve into sub-stellar objects.

Contribution

It provides detailed multi-wavelength observations and measurements of accretion and outflow rates for these faint protostellar systems, highlighting their potential to become sub-stellar objects.

Findings

Both sources show active accretion and outflows similar to low-mass Class I protostars.

Their bolometric luminosities are in the very low-mass range (~0.16-0.18 Lsun).

Envelope masses suggest they might dissipate enough material to become sub-stellar objects.

Abstract

We present an optical through sub-millimetre multi-wavelength study of two very low-luminosity Class I/Flat systems, Mayrit 1701117 and Mayrit 1082188, in the sigma Orionis cluster. We performed moderate resolution (R ~ 1000) optical (~0.4-0.9mu) spectroscopy with the TWIN spectrograph at the Calar Alto 3.5-m telescope. The spectra for both sources show prominent emission in accretion- and outflow-associated lines. The mean accretion rate measured from multiple line diagnostics is 6.4x10^{-10} Msun/yr for Mayrit 1701117, and 2.5x10^{-10} Msun/yr for Mayrit 1082188. The outflow mass loss rates for the two systems are similar and estimated to be ~1x10^{-9} Msun/yr. The activity rates are within the range observed for low-mass Class I protostars. We obtained sub-millimetre continuum observations with the Submillimetre Common-User Bolometer Array (SCUBA-2) bolometer at the James Clerk Maxwell Telescope. Both objects are detected at a >5-sigma level in the SCUBA-2 850mu band. The bolometric luminosity of the targets as measured from the observed spectral energy distribution over ~0.8-850mu is 0.18+/-0.04 Lsun for Mayrit 1701117, and 0.16+/-0.03 Lsun for Mayrit 1082188, and is in the very low-mass range. The total dust+gas mass derived from sub-millimetre fluxes is ~36 M_Jup and ~22 M_Jup for Mayrit 1701117 and Mayrit 1082188, respectively. There is the possibility that some of the envelope material might be dissipated by the strong outflows driven by these sources, resulting in a final mass of the system close to or below the sub-stellar limit.