Letter to the Editor

Diffuse interstellar bands in M 33

¹ Astrophysics Research Centre, School of Mathematics and Physics, Queen's University, Belfast, BT7 1NN, UK e-mail: m.cordiner@qub.ac.uk
² School of Chemistry, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK
³ Herschel Science Centre, European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴ UK ATC, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁵ Dr. Remeis-Sternwarte Bamberg, Sternwartstr. 7, 96049 Bamberg, Germany
⁶ Institute for Astronomy of the University of Hawaii, 2680 Woodlawn Drive, 96822 Honolulu, HI, USA

Received: 3 September 2008
Accepted: 10 October 2008

Abstract

Aims. We investigate the diffuse interstellar band (DIB) spectrum in the interstellar medium of the Local Group spiral galaxy M 33.

Methods. Optical spectra of the M 33 supergiant star J013346.96+303642.8 were taken at a resolving power of ~3000 using the DEIMOS spectrograph of the W. M. Keck Observatory.

Results. We report the first detection and measurement of DIBs in M 33. The λλ5705, 5780, 5797, 6203, 6269, 6283, and 6613 DIBs are detected at velocities matching the M 33 absorption lines. The λ4428 DIB is tentatively detected. The stellar spectrum is classified as A3 Ia and the line-of-sight interstellar reddening is derived. Diffuse interstellar band (DIB) equivalent widths and radial velocities are presented.

Conclusions. The overall spectrum of DIBs observed in M 33 is found to be similar to that observed in the Milky Way. However, along this line-of-sight, the M 33 DIB equivalent widths per unit reddening are large compared with those typically observed in the Galaxy.