Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis

TL;DR

This study used low-resolution spectroscopy and spectral energy distributions to analyze nine peculiar sources in the sigma Orionis cluster, revealing their diverse nature including young stars, brown dwarf candidates, and galaxies, thus aiding understanding of stellar and substellar formation.

Contribution

The paper presents detailed classifications and physical characterizations of nine peculiar sources in sigma Orionis using combined spectroscopy and photometry, highlighting their diverse properties and evolutionary states.

Findings

Classified sources into stars, brown dwarf candidates, and galaxies.

Discovered three new infrared sources in a cold cloud region.

Highlighted the importance of spectroscopy and SEDs in studying young stellar objects.

Abstract

Aims: We investigated in detail nine sources in the direction of the young sigma Orionis cluster, which is considered a unique site for studying stellar and substellar formation. The nine sources were selected because of some peculiar properties, such as extremely red infrared colours or too strong Halpha emission for their blue optical colours. Methods: We took high-quality, low-resolution spectroscopy (R ~ 500) of the nine targets with ALFOSC at the Nordic Optical Telescope. We also re-analyzed [24]-band photometry from MIPS/Spitzer and compiled the best photometry available at the ViJHKs passbands and the four IRAC/Spitzer channels for constructing accurate spectral energy distributions covering from 0.55 to 24 mum. Results: The nine targets were classified into: one Herbig Ae/Be star with a scatterer edge-on disc, two G-type stars, one X-ray flaring, early-M, young star with chromospheric Halpha emission, one very low-mass, accreting, young spectroscopic binary, two young objects at the brown dwarf boundary with the characteristics of classical T Tauri stars, and two emission-line galaxies, one undergoing star formation, and another one whose spectral energy distribution is dominated by an active galactic nucleus. Besides, we discover three infrared sources associated to overdensities in a cold cloud in the cluster centre. Conclusions: Low-resolution spectroscopy and spectral energy distributions are a vital tool for measuring the physical properties and the evolution of young stars and candidates in the sigma Orionis cluster.