EPoS Contribution
EPoS Contribution
Orion Radio News Update: Insights into High-Energy/Accretion Processes in the Time Domain with VLA/ALMA and Precision Astrometry with the VLBA

Jan Forbrich
Herts, Hatfield, UK
The Orion Nebula Cluster (ONC) is an archetype for nearby clustered star formation. As such, it is an important target for new observational capabilities that may provide further details on the physics of star formation in an already well-characterized environment. One such development concerns progress in interferometric radio astronomy. Almost 40 years after the discovery that young stars are radio stars, obtained with the original NRAO Very Large Array (VLA), recent sensitivity upgrades of both the VLA and the Very Long Baseline Array (VLBA), as well as the advent of the Atacama Large Millimeter Array (ALMA) have begun to provide us with a much improved perspective on stellar radio emission, particularly concerning young stellar objects (YSOs) and the time domain. I will present new results from our ongoing deep ONC radio survey, using the VLA, VLBA, and ALMA. Two years ago, our first set of deep VLA observations showed hundreds of compact radio sources, a sevenfold increase over previous studies, and intricate detail on the radio emission of proplyds. Here, I will focus on:
1) new insights from access to the radio time domain toward hundreds of YSOs, with simultaneous X-ray light curves, providing first constraints on YSO radio flares, of which previously only few examples were known, and their relation with X-ray flares. This produces improved constraints on the overall high-energy irradiation of their surroundings, including protoplanetary disks.
2) first results on precision astrometry from ongoing multi-epoch VLBA follow-up of our VLA sample. Using the VLBA sensitivity upgrade and advances in software correlation, I will highlight the use of the VLBA for precision stellar astrometry in the Gaia era, allowing us to extend the Gaia sample of YSOs by including embedded objects and distant obscured sources in the Galactic plane while providing important opportunities for astrometric cross-calibration.
3) very recent first results from our ALMA program to extend YSO radio time domain studies into the millimeter-wavelength range to study high-energy synchrotron emission and signatures of mass accretion, further complementing the emerging picture of dynamic radio stars in the ONC.
Caption: An extreme cm radio flare in the ONC, with simultaneous X-ray data. Upper panel: VLA C-band radio flux density (mJy) over the course of four observing epochs (separated by vertical lines), taken within a few days. Red points show upper limits. Lower panel: Corresponding Chandra X-ray data, with the blue curves indicating confidence intervals for adaptively smoothed photon counts and the black and red points showing binned counts and median energies, respectively. See Forbrich et al. (2017) for details.
Collaborators:
M. Reid, SAO, US
K. Menten, MPIfR, DE
U. Rau, NRAO, US
C. Chandler, NRAO, US
V. Rivilla, Arcetri, IT
S. Wolk, SAO, US
A. Brunthaler, MPIfR, DE
S. Dzib, MPIfR, DE
M. Guedel, U Vienna, AT
A. Hacar, Leiden, NL
Key publication

Suggested Session: Magnetic fields