[Paper Review] Multiple protostellar systems. I. A deep near infrared survey of Taurus and Ophiuchus protostellar objects

Gaspard Duchêne, J. Bouvier+3 more|ArXiv.org|Jul 22, 2004

Astrophysics and Star Formation Studies43 references83 citations

TL;DR

This study presents a deep near-infrared survey of 63 embedded protostars in Taurus and Ophiuchus, finding a companion star fraction of 27% ± 6% for systems with separations of 110–1400 AU—twice the frequency seen in solar neighborhood G dwarfs. The results indicate that core dynamical fragmentation into multiple protostellar systems is a common outcome of star formation, with multiplicity rates insensitive to initial or environmental conditions in these regions.

ABSTRACT

(Abridged) We performed a deep infrared imaging survey of 63 embedded young stellar objects (YSOs) located in the Taurus and Ophiuchus clouds to search for companions. The sample includes Class I and flat infrared spectrum protostellar objects. We find 17 companions physically bound to 15 YSOs with angular separations in the range 0.8-10" (110-1400 AU) and derive a companion star fraction of 23+/-9 % and 29+/-7 % for embedded YSOs in Taurus and Ophiuchus, respectively. In spite of different properties of the clouds and especially of the prestellar cores, the fraction of wide companions, 27+/-6 % for the combined sample, is identical in the two star-forming regions. This suggests that the frequency and properties of wide multiple protostellar systems are not very sensitive to specific initial conditions. Comparing the companion star fraction of the youngest YSOs still surrounded by extended envelopes to that of more evolved YSOs, we find evidence for a possible evolution of the fraction of wide multiple systems, which seems to decrease by a factor of about 2 on a timescale of about 10^5 yr. Somewhat contrary to model predictions, we do not find evidence for a sub-clustering of embedded sources at this stage on a scale of a few 100 AU that could be related to the formation of small-N protostellar clusters. Possible interpretations for this discrepancy are discussed.

Motivation & Objective

• To measure the multiplicity frequency of deeply embedded protostars in two contrasting star-forming regions: Taurus (quiescent, low-density) and Ophiuchus (dense, cluster-forming).
• To assess whether the properties of wide multiple protostellar systems depend on initial prestellar core conditions or environmental density.
• To investigate the evolution of multiplicity during the embedded phase by comparing Class 0/I YSOs with extended envelopes to more evolved Class I/II/III sources.
• To test predictions of numerical simulations of molecular cloud collapse by comparing observed subcluster morphology at ~100 AU scales.
• To determine whether early protostellar systems show signs of sub-clustering, which could indicate formation of small-N clusters during collapse.

Proposed method

• Conducted deep near-infrared imaging (J, H, K bands) using the Canada-France-Hawaii Telescope and ESO’s New Technology Telescope to detect faint companions.
• Targeted 63 Class I and flat-spectrum protostars in Taurus and Ophiuchus, selected to be representative of the embedded YSO population.
• Measured angular separations and flux ratios of detected companions to determine physical separation and luminosity ratios.
• Defined a separation range of 0.8–10″ (110–1400 AU) to focus on wide multiple systems relevant to core fragmentation.
• Calculated companion star fractions with error estimates using Poisson statistics and combined samples from both regions.
• Compared multiplicity rates between YSOs with and without millimeter-wave extended envelopes to infer evolutionary trends.

Experimental results

Research questions

• RQ1 What is the frequency of wide multiple protostellar systems (separations 110–1400 AU) in the Taurus and Ophiuchus star-forming regions?
• RQ2 How does the multiplicity frequency of embedded YSOs compare between low-density Taurus and high-density Ophiuchus, and what does this imply about environmental dependence?
• RQ3 Does the multiplicity fraction of protostellar systems evolve during the embedded phase, particularly as envelopes dissipate?
• RQ4 Are embedded protostars in Taurus and Ophiuchus organized into subclusters on scales of a few hundred AU, as predicted by some simulations?
• RQ5 To what extent do observed multiplicity properties match predictions from numerical simulations of prestellar core collapse?

Key findings

• The companion star fraction for embedded YSOs in Taurus is 23% ± 9%, and in Ophiuchus it is 29% ± 7%, with a combined fraction of 27% ± 6% across both regions.
• This multiplicity rate is approximately twice that observed for G dwarfs in the solar neighborhood in the same separation range.
• Despite significant differences in prestellar core size, morphology, and average stellar density between Taurus and Ophiuchus, the multiplicity properties of their embedded systems are statistically identical.
• The fraction of wide multiple systems appears to decrease by a factor of about two over a timescale of ~10⁵ yr during the embedded phase, suggesting rapid disruption of wide systems.
• No evidence for sub-clustering of embedded YSOs on scales of a few hundred AU is found, contradicting predictions from some global simulations of cloud collapse.
• The similarity in multiplicity outcomes despite different initial and environmental conditions suggests that protostellar multiplicity is primarily governed by local dynamical processes rather than global or initial conditions.