Radio variability and non-thermal components in stars evolving toward planetary nebulae

Abstract

We present new JVLA multi-frequency measurements of a set of stars in transition from the post-AGB to the Planetary Nebula phase monitored in the radio range over several years. Clear variability is found for five sources. Their light curves show increasing and decreasing patterns. New radio observations at high angular resolution are also presented for two sources. Among these is IRAS 18062+2410, whose radio structure is compared to near-infrared images available in the literature. With these new maps, we can estimate inner and outer radii of 0.03$"$ and 0.08$"$ for the ionised shell, an ionised mass of $3.2\times 10^{-4}$ M${}_{\odot }$, and a density at the inner radius of $7.7\times 10^{-5}$ cm${}^{-3}$, obtained by modelling the radio shell with the new morphological constraints. The combination of multi-frequency data and, where available, spectral-index maps leads to the detection of spectral indices not due to thermal emission, contrary to what one would expect in planetary nebulae. Our results allow us to hypothesise the existence of a link between radio variability and non-thermal emission mechanisms in the nebulae. This link seems to hold for IRAS 22568+6141 and may generally hold for those nebulae where the radio flux decreases over time.

11 pages, 9 figures, accepted for publication on MNRAS

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Cited by in corpus (13)

• Radio Stars: from kHz to THz
• The Coordinated Radio and Infrared Survey for High-mass Star Formation. IV: A new radio selected sample of compact Galactic Planetary Nebulae
• A global view on star formation: The GLOSTAR Galactic plane survey. IX. Radio Source Catalog III: 2<l<28, 36<l<40, 56<l<60 and |b|<1, VLA B-configuration
• Evolution of the outflow in the water fountain source IRAS 18043$-$2116
• Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey
• Non-thermal radio emission in Sakurai's Object
• The Nature of the Stingray Nebula from Radio Observations
• Study of the Galactic radio sources in the SCORPIO survey resolved by ATCA at 2.1 GHz
• Long and short term variability of the possible nascent planetary nebula IRAS 22568+6141: A late thermal pulse?
• ASKAP-EMU radio continuum detection of planetary nebula NGC 5189: the "Infinity" nebula
• Structural and spectral properties of Galactic plane variable radio sources
• Magnetic fields in planetary nebulae detected through non-thermal radio continuum emission
• The secular evolution of planetary nebula IC 418 and its implications for carbon star formation