[Paper Review] Radio Sources Embedded in the Dense Core B59, the "Mouthpiece" of the Pipe Nebula

Sergio A. Dzib, Luis F. Rodrı́guez+2 more|Redalyc (Universidad Autónoma del Estado de México)|Aug 12, 2013

Astrophysics and Star Formation Studies1 references3 citations

TL;DR

The paper proposes that the radio emission from five compact sources in the dense B59 core of the Pipe Nebula arises from free-free emission in ionized winds of embedded protostars, with winds optically thick at radio but thin at X-rays, explaining why X-rays from magnetospheres are detected while radio emission is dominated by thermal wind components. This resolves the apparent lack of non-thermal radio emission despite X-ray detections.

ABSTRACT

We present Very Large Array continuum observations made at 8.3 GHz toward the dense core B59, in the Pipe Nebula. We detect six compact sources, of which five are associated with the five most luminous sources at 70 micrometer in the region, while the remaining one is probably a background source. We propose that the radio emission is free-free from the ionized outflows present in these protostars. We discuss the kinematical impact of these winds in the cloud. We also propose that these winds are optically thick in the radio but optically thin in the X-rays and that this characteristic can explain why X-rays from the magnetosphere are detected in three of them, while the radio emission is most probably dominated by the free-free emission from the external layers of the wind.

Motivation & Objective

• To identify and characterize compact radio sources in the dense B59 core of the Pipe Nebula.
• To determine the origin of radio emission from these sources and its connection to protostellar activity.
• To explain the observed X-ray detections in three sources despite the absence of detectable non-thermal radio emission.
• To assess the kinematic impact of ionized winds on the surrounding dense core.
• To reconcile the observed emission properties with theoretical models of stellar winds and radiative transfer.

Proposed method

• Conducted high-resolution 8.3 GHz continuum observations with the Very Large Array (VLA) in C configuration to image the B59 core.
• Used AIPS software for calibration and imaging, with flux and gain calibrators (1331+305 and 1626-298) to ensure flux accuracy.
• Cross-identified radio sources with infrared (2MASS) and X-ray (2XMMi) counterparts to assess source associations.
• Applied the free-free emission formalism of Panagia & Felli (1975) to estimate mass loss rates from observed flux densities.
• Calculated optical depth thresholds for radio and X-ray bands using wind parameters (T_e, Ṁ, V_∞, μ) to determine where τ=1.
• Used the X-ray opacity model of Leutenegger et al. (2010) with κ(E) = 50(E/keV)^{-2} cm² g⁻¹ to estimate X-ray optical depth in the wind.

Experimental results

Research questions

• RQ1 What is the origin of the compact radio emission detected at 8.3 GHz in the B59 core?
• RQ2 Why are X-rays detected from three of the five radio-emitting sources but not non-thermal radio emission?
• RQ3 How do ionized winds from protostars affect the kinematics of the surrounding dense core?
• RQ4 What are the optical depth characteristics of the winds at radio and X-ray wavelengths?
• RQ5 Why do the X-ray and radio emission mechanisms appear independent yet still follow the Guedel & Benz (1993) relation?

Key findings

• Six compact radio sources were detected at 8.3 GHz, with five associated with the most luminous 70 μm sources in the region, indicating a link to embedded protostars.
• The radio emission is best explained by free-free emission from ionized winds, with a derived mass loss rate of 1.2×10⁻⁸ M☉ yr⁻¹ for a typical source.
• The wind is optically thick at radio (τ=1 at ~140 R☉) but optically thin at X-rays (τ=1 at ~2 R☉ for E=1 keV), explaining X-ray detectability.
• The X-ray emission originates from the magnetosphere and is not absorbed by the wind, while radio emission arises from the outer, optically thick layers of the wind.
• The observed X-ray and radio emission properties are consistent with the Guedel & Benz (1993) relation, suggesting stellar winds may be a significant contaminant in such correlations.
• The kinematic impact of the winds is localized near the protostars, with no strong evidence of large-scale disruption of the core.