Ice Features of Low-luminosity Protostars in Near-infrared Spectra of AKARI/IRC

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 on board the 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 H2O, CO2, and CO in all spectra around the wavelengths of 3.05, 4.27, and 4.67 μm, respectively. For at least two low-luminosity protostars, we also detected the XCN ice feature at 4.62 μm. The presence of the crystalline H2O ice and 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 the low-luminosity protostars with those of 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.