Survey of Planetary Nebulae at 30 GHz with OCRA-p

TL;DR

This survey of 442 planetary nebulae at 30 GHz aims to identify calibration sources and analyze their emission mechanisms, finding that free-free emission generally explains their spectra without needing additional mechanisms like spinning dust.

Contribution

It provides a new catalog of 93 planetary nebulae flux densities at 30 GHz and evaluates their emission mechanisms, supporting free-free emission as the dominant process.

Findings

Catalog of 93 planetary nebulae flux densities at 30 GHz.

Free-free emission explains observed spectra without requiring spinning dust.

No significant contribution from other emission mechanisms at 30 GHz.

Abstract

We report the results of a survey of 442 planetary nebulae at 30 GHz. The purpose of the survey is to develop a list of planetary nebulae as calibration sources which could be used for high frequency calibration in future. For 41 PNe with sufficient data, we test the emission mechanisms in order to evaluate whether or not spinning dust plays an important role in their spectra at 30 GHz. The 30-GHz data were obtained with a twin-beam differencing radiometer, OCRA-p, which is in operation on the Torun 32-m telescope. Sources were scanned both in right ascension and declination. We estimated flux densities at 30 GHz using a free-free emission model and compared it with our data. The primary result is a catalogue containing the flux densities of 93 planetary nebulae at 30 GHz. Sources with sufficient data were compared with a spectral model of free-free emission. The model shows that free-free emission can generally explain the observed flux densities at 30 GHz thus no other emission mechanism is needed to account for the high frequency spectra.