Radio Properties of Pinwheel Nebulae

Abstract

A small number of dusty Wolf-Rayet stars have been resolved into pinwheel nebulae, defined by their ``rotating'' spiral dust shells observed in the infrared. This morphology is naturally explained by dust formation associated with colliding winds in a binary system. In order to confirm and further explore this hypothesis, we have observed the known pinwheel nebulae (WR 104 and WR 98a) as well as the suspected binary WR 112 at multiple radio wavelengths with the Very Large Array to search for non-thermal radio emission from colliding winds. The spectrum of each target is nearly flat between 5 and 22 GHz, consistent with the presence of non-thermal emission that is reduced at low frequencies by free-free absorption. This emission must lie outside the radio ``photosphere,'' leading us to estimate a lower limit to the physical size of the non-thermal emitting region that is larger than expected from current theory. Based on a radio and infrared comparison to WR 104 and 98a, we conclude that WR 112 is a likely candidate pinwheel nebula, but its temporal variability indicates an eccentric binary orbit or a pinwheel viewed nearly edge-on. A sensitive radio survey of IR-bright WRs would stringently test the hypothesis that colliding winds lie at the heart of_all_ dusty WR systems. We also discuss the effects of dust obscuration in the ultra-violet and how radio-determined mass-loss rates of pinwheel nebulae (and dusty WR stars in general) may be underestimated due to shadowing effects.

21 pages, 5 figures. Accepted for publication in Astrophysical Journal (2002 Feb 10)

References in corpus (4)

• A dusty pinwheel nebula around the massive star WR 104
• The Proper Motion of SgrA*: I. First VLBA Results
• Pinwheel nebula around WR 98a
• Radio Variability of Sagittarius A* - A 106 Day Cycle

Cited by in corpus (25)

• Catalogue of particle-accelerating colliding-wind binaries
• The prototype colliding-wind pinwheel WR 104
• Radio emission models of Colliding-Wind Binary Systems
• Radio emission models of Colliding-Wind Binary Systems - Inclusion of IC cooling
• A Very Large Array 3.6cm continuum survey of Galactic Wolf-Rayet stars
• A Spectroscopic study of the non-thermal radio emitter Cyg OB2 #8A: Discovery of a new binary system
• Orbitally modulated dust formation by the WC7+O5 colliding-wind binary WR140
• Massive Binary WR112 and Properties of Wolf-Rayet Dust
• The Keck Aperture Masking Experiment: Near-Infrared Sizes of Dusty Wolf-Rayet Stars
• Pinwheels in the sky, with dust: 3D modeling of the Wolf-Rayet 98a environment
• Recurrent dust formation by WR 48a on a 30-year timescale
• Disentangling the Nature of the Radio Emission in Wolf Rayet Stars
• The SPHERE view of Wolf-Rayet 104
• Modeling Forbidden Line Emission Profiles from Colliding Wind Binaries
• New X-ray detections of known Wolf-Rayet stars
• Stagnant Shells in the Vicinity of the Dusty Wolf-Rayet-OB Binary WR 112
• Puzzling X-rays from the new colliding wind binary WR65
• Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep
• Smoke on the wind: dust nucleation in archetype colliding wind pinwheel WR104
• A model for the thermal radio-continuum emission from radiative shocks in colliding stellar winds
• Two-wind interactions in binaries with two orbiting giant stars
• Collision of two identical hypersonic stellar winds in binary systems
• Infrared Observations of the Quintuplet Proper Members using SOFIA/FORCAST and Gemini/TReCS
• Revealing the accelerating wind in the inner region of the colliding-wind binary WR 112
• Constraining properties of dust formed in Wolf-Rayet binary WR 112 using mid-infrared and millimeter observations