2008A&A...492L...5C

We investigate the diffuse interstellar band (DIB) spectrum in the interstellar medium of the Local Group spiral galaxy M33. Optical spectra of the M33 supergiant star J013346.96+303642.8 were taken at a resolving power of ∼3000 using the DEIMOS spectrograph of the W. M. Keck Observatory. We report the first detection and measurement of DIBs in M33. The λλ5705, 5780, 5797, 6203, 6269, 6283, and 6613 DIBs are detected at velocities matching the M33 NaI 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. The overall spectrum of DIBs observed in M33 is found to be similar to that observed in the Milky Way. However, along this line-of-sight, the M33 DIB equivalent widths per unit reddening are large compared with those typically observed in the Galaxy.