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Characterizing the physical and chemical properties of the Class I protostellar system Oph-IRS 44. Binarity, infalling streamers, and accretion shocks

E. Artur de la Villarmois, V. V. Guzmán, M. L. van Gelder, E. F. van Dishoeck, E. A. Bergin, D. Harsono, N. Sakai, J. K. Jørgensen

TL;DR

This study uses ~0.1

Abstract

(Abridged) In the low-mass star formation process, theoretical models predict that material from the infalling envelope could be shocked as it encounters the outer regions of the disk. Nevertheless, only a few protostars show evidence of these shocks at the disk-envelope interface, and the main formation path of shocked-related species is still unclear. We present new ALMA observations of IRS 44, a Class I source that has previously been associated with accretion shocks, taken at high angular resolution (0.1"). We target multiple molecular transitions of CO, H2CO, and simple sulfur-bearing species. In continuum emission, the binary nature of IRS 44 is observed for the first time at sub-millimeter wavelengths. Infalling signatures are seen for the CO line and the emission peaks at the edges of the continuum emission around IRS 44 B, the same region where bright SO and SO2 emission is seen. Weak CS and H2CO emission is observed, while OCS, H2S, and H2CS transitions are not detected. IRS 44 B seems to be more embedded than IRS 44 A, indicating a non-coeval formation scenario or the rejuvenation of source B due to late infall. CO emission is tracing the outflow component at large scales, infalling envelope material at intermediate scales, and two infalling streamer candidates are identified at disk scales. Infalling streamers might produce accretion shocks when they encounter the outer regions of the infalling-rotating envelope. These shocks heat the dust and release S-bearing species as well as promoting a lukewarm chemistry in the gas phase. With the majority of carbon locked in CO, there is little free C available to form CS and H2CS in the gas, leaving an oxygen-rich environment. The high column densities of SO and SO2 might be a consequence of two processes: direct thermal desorption from dust grains and gas-phase formation due to the availability of O and S.

Characterizing the physical and chemical properties of the Class I protostellar system Oph-IRS 44. Binarity, infalling streamers, and accretion shocks

TL;DR

This study uses ~0.1

Abstract

(Abridged) In the low-mass star formation process, theoretical models predict that material from the infalling envelope could be shocked as it encounters the outer regions of the disk. Nevertheless, only a few protostars show evidence of these shocks at the disk-envelope interface, and the main formation path of shocked-related species is still unclear. We present new ALMA observations of IRS 44, a Class I source that has previously been associated with accretion shocks, taken at high angular resolution (0.1"). We target multiple molecular transitions of CO, H2CO, and simple sulfur-bearing species. In continuum emission, the binary nature of IRS 44 is observed for the first time at sub-millimeter wavelengths. Infalling signatures are seen for the CO line and the emission peaks at the edges of the continuum emission around IRS 44 B, the same region where bright SO and SO2 emission is seen. Weak CS and H2CO emission is observed, while OCS, H2S, and H2CS transitions are not detected. IRS 44 B seems to be more embedded than IRS 44 A, indicating a non-coeval formation scenario or the rejuvenation of source B due to late infall. CO emission is tracing the outflow component at large scales, infalling envelope material at intermediate scales, and two infalling streamer candidates are identified at disk scales. Infalling streamers might produce accretion shocks when they encounter the outer regions of the infalling-rotating envelope. These shocks heat the dust and release S-bearing species as well as promoting a lukewarm chemistry in the gas phase. With the majority of carbon locked in CO, there is little free C available to form CS and H2CS in the gas, leaving an oxygen-rich environment. The high column densities of SO and SO2 might be a consequence of two processes: direct thermal desorption from dust grains and gas-phase formation due to the availability of O and S.
Paper Structure (25 sections, 9 equations, 16 figures, 5 tables)

This paper contains 25 sections, 9 equations, 16 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Observations
  3. Results
  4. Continuum emission
  5. Molecular transitions
  6. Streamer candidates
  7. SO and SO$_{2}$ as tracers of accretion shocks
  8. Analysis
  9. SO
  10. CO, CS, and H$_{2}$CO
  11. OCS, H$_{2}$S, and H$_{2}$CS
  12. Discussion
  13. Bright SO and SO$_{2}$
  14. Shocks: Origins of S-bearing species and efficient production of H$_{2}$O
  15. Weak CS and H$_{2}$CO
  16. ...and 10 more sections

Figures (16)

  • Figure 1: Continuum emission of IRS 44 above 3$\sigma$ at different frequencies. The white contour represents a flux value of 10$\sigma$. The synthesized beam is represented by a filled white ellipse in the lower left corner of each panel. IRS 44 A and B can also be found as IRS 44 E and W in the literature, respectively Herczeg2011.
  • Figure 2: Spectral energy distribution (SED) of IRS 44. In the infrared regime (green dots), the flux corresponds to both sources, source A being the brightest one Terebey2001Dunham2015. In ALMA bands, the binary system is resolved and source B (blue dots) is $\sim$10 times brighter than source A (red dots).
  • Figure 3: CO 2--1 emission (moment 8) at large (left) and intermediate scales (right). The white stars represent the position of the A and B components (see Fig. \ref{['fig:cont']}). The synthesized beam is represented by a filled white ellipse in the lower left corner of each panel.
  • Figure 4: CO 2--1 emission at small scales. Left: Maximum value map (moment 8) above a 3$\sigma$ level. Center: Integrated map (moment 0) above a 15$\sigma$ level (1$\sigma$ = 10 mJy beam$^{-1}$ km s$^{-1}$). Right: Velocity map (moment 1) above a 15$\sigma$ level. The white contour represents the continuum emission at 233 GHz at a 10$\sigma$ value and the dashed black curves indicate the direction of the proposed streamers. The synthesized beam is represented by a filled white ellipse in the left panel.
  • Figure 5: Velocity channel maps for CO 2--1 above 1$\sigma$. The systemic velocity (3.7 km s$^{-1}$) is shifted to zero and each map has a velocity width of 2 km s$^{-1}$. The yellow stars show the position of IRS44 A and IRS44 B, while the synthesized beam is represented by a filled white ellipse in the upper left panel.
  • ...and 11 more figures