Spectroscopy of planetary nebulae in M 33^*

¹ Dipartimento di Astronomia e Scienza dello Spazio, Universitá di Firenze, L.go E. Fermi 2, 50125 Firenze, Italy
² Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de La Palma, Canarias, Spain
³ Instituto de Astrofísica de Canarias, c. Vía Láctea s/n, 38200, La Laguna, Tenerife, Canarias, Spain

Corresponding author: L. Magrini laura@arcetri.astro.it

Received: 7 August 2002
Accepted: 29 November 2002

Abstract

Spectroscopic observations of 48 emission-line objects of M 33 have been obtained with the multi-object, wide field, fibre spectrograph AF2/WYFFOS at the 4.2 m WHT telescope (La Palma, Spain). Line intensities and logarithmic extinction, , are presented for 42 objects. Their location in the Sabbadin & D'Odorico diagnostic diagram (Hα/ [S ii] vs. Hα/[N ii]) suggests that >70% of the candidates are Planetary Nebulae (PNe). Chemical abundances and nebular physical parameters have been derived for the three of the six  PNe where the 4363 Å  [O iii] emission line was measurable. These are disc PNe, located within a galactocentric distance of 4.1 kpc, and, to date, they are the farthest PNe with a direct chemical abundance determination. No discrepancy in the helium, Oxygen and Argon abundances has been found in comparison with corresponding abundances of PNe in our Galaxy. Only a lower limit to the sulphur abundance has been obtained since we could not detect any [S iii] line. N/H appears to be lower than the Galactic value; some possible explanations for this under-abundance are discussed.