Ice features of low-luminosity protostars in near-infrared spectra of AKARI/IRC

TL;DR

This study analyzes near-infrared spectra of low-luminosity protostars to detect ice features, revealing evidence of past accretion bursts and comparing ice abundances across different star-forming environments.

Contribution

It provides new spectroscopic data on low-luminosity protostars and links ice features to their accretion history, enhancing understanding of protostellar evolution.

Findings

Detected water, carbon dioxide, and carbon monoxide ice features in all spectra.

Identified crystalline water and XCN ice components indicating past hot phases.

Ice abundances suggest correlation with prior burst activity and evolutionary timescales.

Abstract

We present near-infrared spectra of three low-luminosity protostars and one background star in the Perseus molecular cloud, acquired using the Infrared Camera (IRC) onboard the \textit{AKARI} space telescope. For the comparison with different star-forming environments, we also present spectra of the massive protostar AFGL 7009S, where the protostellar envelope is heated significantly, and the low-mass protostar RNO 91, which is suspected to be undergoing an episodic burst. We detected ice absorption features of \ch{H2O}, \ch{CO2}, and \ch{CO} at all spectra around the wavelengths of 3.05, 4.27, and 4.67 $\mu$m, respectively. At least two low-luminosity protostars, we also detected the \ch{XCN} ice feature at 4.62 $\mu$m. The presence of the crystalline \ch{H2O} ice and \ch{XCN} ice components indicates that the low-luminosity protostars experienced a hot phase via accretion bursts during the past mass accretion process. We compared the ice abundances of low-luminosity protostars with those of the embedded low-mass protostars and the dense molecular clouds and cores, suggesting that their ice abundances reflect the strength of prior bursts and the timescale after the last burst.