Letter to the Editor

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun^*

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
² European Southern Observatory ESO, Alonso de Cordova 3107, Santiago de Chile, Chile e-mail: hboehnha@eso.org, glocurto@eso.org
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: hboehnha@mpia-hd.mpg.de

Corresponding author: G. P. Tozzi, tozzi@arcetri.astro.it

Received: 20 November 2002
Accepted: 19 December 2002

Abstract

Comet C/2001 Q4 (NEAT) was observed inbound at an heliocentric distance of 8.6 AU. Broadband filter images in the visible and long slit spectroscopy in the 3500–7000 Å range was recorded. No sign of CN emission was detected and an upper limit for CN production rate of  molecules s^-1 is estimated. The color of the dust in the inner coma is very red with a spectral index of 29%/1000 Å. The radial profile of the dust coma displays steep gradients of 1.7 (inner part) to 2.4 (outer part). The af ρ  value, a proxy for the dust production, is measured to be 1500 cm. The coma shows a weak and short conic structure in the northern hemisphere that is interpreted as dust fan produced by an active region on the nuclear surface.