A new radio recombination line maser object toward the MonR2 HII region

Abstract

We report the detection of a new radio recombination line (RRL) maser object toward the IRS2 source in the MonR2 ultracompact HII region. The continuum emission at 1.3mm and 0.85mm and the H30a and H26a lines were observed with the Submillimeter Array (SMA) at angular resolutions of about 0.5"-3". The SMA observations show that the MonR2-IRS2 source is very compact and remains unresolved at spatial scales <=400AU. Its continuum power spectrum at millimeter wavelengths is almost flat (alpha=-0.16, with S_nu proportional to nu^alpha), indicating that this source is dominated by optically thin free-free emission. The H30a and H26a RRL emission is also compact and peaks toward the position of the MonR2-IRS2 source. The measured RRL profiles are double-peaked with the H26a line showing a clear asymmetry in its spectrum. Since the derived line-to-continuum flux ratios (80 and 180kms-1 for H30a and H26a, respectively) exceed the LTE predictions, the RRLs toward MonR2-IRS2 are affected by maser amplification. The amplification factors are however smaller than those found toward the emission line star MWC349A, indicating that MonR2-IRS2 is a weakly amplified maser. Radiative transfer modelling of the RRL emission toward this source shows that the RRL masers arise from a dense and collimated jet embedded in a cylindrical ionized wind, oriented nearly along the direction of the line-of-sight. High-angular resolution observations at sub-millimeter wavelengths are needed to unveil weakly amplified RRL masers in very young massive stars.

5 pages, 2 figures, 3 tables. Accepted for publication in ApJ Letters

References in corpus (3)

• The Early Evolution of Massive Stars: Radio Recombination Line Spectra
• Extremely broad radio recombination maser lines toward the high-velocity ionized jet in Cepheus A HW2
• SMA Imaging of the Maser Emission from the H30$\alpha$ Radio Recombination Line in MWC349A

Cited by in corpus (18)

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• Massive Protostars in a Protocluster -- A Multi-Scale ALMA View of G35.20-0.74N
• The ionized warped disk and disk wind of the massive protostar Monoceros R2-IRS2 seen with ALMA
• Submillimeter Array High-angular Resolution Observations of the Monoceros R2 Star Forming Cluster
• Origin of the ionized wind in MWC 349A
• Herschel Planetary Nebula Survey (HerPlaNS): Hydrogen Recombination Laser Lines in Mz 3
• Probing the kinematics and chemistry of the hot core Mon R 2 IRS 3 using ALMA observations
• A rotating fast bipolar wind and disk system around the B[e]-type star MWC 922
• Evidence for the First Extragalactic Hydrogen Recombination Line Maser in NGC 253
• Imaging the jet of MWC 349A with resolved Radio Recombination Line emission from ALMA
• ngVLA Synthetic Observations of Ionized Gas in Massive Protostars
• The SOFIA Massive (SOMA) Star Formation Q-band Follow-up. II. Hydrogen Recombination Lines Toward High-Mass Protostars
• Massive envelopes and filaments in the NGC 3603 star forming region