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 λ λ 5705, 5780, 5797, 6203, 6269, 6283, and 6613 DIBs are detected at velocities matching the M 33 absorption lines. The λ 4428 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.
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