A neck-line structure in the dust tail of Comet C/2004 F4 (Bradfield)

INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate LC, Italy e-mail: luigi.pansecchi@libero.it; scardia@merate.mi.astro.it

Received: 1 August 2004
Accepted: 4 September 2004

Abstract

Three CCD images of Comet C/2004 F4 (Bradfield), taken on three different dates close to the time of the Earth crossing through the plane of the comet orbit (2004 May 2.9280 UT), show a ray-shaped structure (RSS) in the dust tail, accompanied by a short, sunward spike (SWS). This morphology and behaviour strongly recall a Neck-Line Structure (NLS; Kimura & Liu [CITE]; Pansecchi et al. [CITE]). Astrometric measurements of the images show that, on all the three dates, the position on the sky of the observed RSS is consistent with several sky-projected points of a theoretical Neck-Line, computed for the precise date of each observation. Furthermore, the SWS turns out to be a real (not caused by perspective) antitail, which is predicted by NLS models.