TY - JOUR

T1 - Tracking the Evolutionary Stage of Protostars through the Abundances of Astrophysical Ices

AU - Rocha, W. R. M.

AU - Pilling, S.

PY - 2020/6/1

Y1 - 2020/6/1

N2 - The physical evolution of young stellar objects (YSOs) is accompanied by an enrichment of the molecular complexity, mainly triggered by the heating and energetic processing of astrophysical ices. In this paper, a study of how the ice column density varies across the protostellar evolution has been performed. Tabulated data of H2O, CO2, CH3OH, and HCOOH observed by ground- and space-based telescopes toward 27 early-stage YSOs were taken from the literature. The observational data show that ice column density and spectral index (alpha), used to classify the evolutionary stage, are well correlated. A 2D continuum radiative transfer simulation containing bare and ice-covered grains at different levels of cosmic-ray processing were used to calculate the spectral energy distributions in different angle inclinations between face-on and edge-on configurations. The H2O:CO(2)ice mixture was used to address the H2O and CO(2)column density variation, whereas CH3OH and HCOOH are by-products of the virgin ice after energetic processing. The simulated spectra were used to calculate the ice column densities of YSOs in an evolutionary sequence. As a result, the models show that the ice column density variation of HCOOH with alpha can be justified by envelope dissipation and energetic processing of ice. On the other hand, the ice column densities are mostly overestimated in the cases of H2O, CO(2)and CH3OH, even though the physical and cosmic-ray processing effects are taken into account.

AB - The physical evolution of young stellar objects (YSOs) is accompanied by an enrichment of the molecular complexity, mainly triggered by the heating and energetic processing of astrophysical ices. In this paper, a study of how the ice column density varies across the protostellar evolution has been performed. Tabulated data of H2O, CO2, CH3OH, and HCOOH observed by ground- and space-based telescopes toward 27 early-stage YSOs were taken from the literature. The observational data show that ice column density and spectral index (alpha), used to classify the evolutionary stage, are well correlated. A 2D continuum radiative transfer simulation containing bare and ice-covered grains at different levels of cosmic-ray processing were used to calculate the spectral energy distributions in different angle inclinations between face-on and edge-on configurations. The H2O:CO(2)ice mixture was used to address the H2O and CO(2)column density variation, whereas CH3OH and HCOOH are by-products of the virgin ice after energetic processing. The simulated spectra were used to calculate the ice column densities of YSOs in an evolutionary sequence. As a result, the models show that the ice column density variation of HCOOH with alpha can be justified by envelope dissipation and energetic processing of ice. On the other hand, the ice column densities are mostly overestimated in the cases of H2O, CO(2)and CH3OH, even though the physical and cosmic-ray processing effects are taken into account.

KW - Astrochemistry

KW - Infrared sources

KW - Interstellar abundances

KW - Laboratory astrophysics

KW - Star-forming regions

KW - YOUNG STELLAR OBJECTS

KW - SPITZER SPECTROSCOPIC SURVEY

KW - INFRARED-SPECTROSCOPY

KW - ABSORPTION FEATURES

KW - RADIATIVE-TRANSFER

KW - BAND STRENGTHS

KW - SNOW-LINE

KW - SPECTRA

KW - WATER

KW - H2O

U2 - 10.3847/1538-4357/ab91bd

DO - 10.3847/1538-4357/ab91bd

M3 - Journal article

VL - 896

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 27

ER -