Carbon chemistry and diffuse interstellar bands in the Magellanic Clouds
Abstract
To unravel the carbon chemistry prevailing in (diffuse) interstellar clouds we seek to disentangle the different environmental effects that influence the existence and strength of the diffuse interstellar bands (DIBs). DIBs are weak unidentified interstellar absorption bands observed towards reddened stars. Their carriers are presently believed to be large carbonaceous molecules (e.g PAHs). The Large and Small Magellanic Cloud (LMC and SMC) offer a unique opportunity to link DIB behaviour to widely varying environmental conditions (e.g. metallicity, UV radiation field and star formation activity). This in turn imposes useful constraints on the nature of the DIB carrier, which hopefully leads to its much desired identification.
To this aim we have observed the absorption spectra of reddened OB stars in the Magellanic Clouds at unprecedented high resolution (R ≅100.000) and high S/N (>∼100) with the Ultraviolet Visual Echelle Spectrograph (UVES) mounted at the Very Large Telescope (VLT). These spectra provide the first observational evidence for the presence of DIBs in the SMC (Ehrenfreund et al. 2002, ApJ, 576, L117). Analysis of the spectra of the LMC and SMC targets indicates that a delicate balance must exist for DIBs to be present. Noteworthy in this respect is the 30 Doradus region in the LMC in which these special conditions seem to prevail. Of all LMC stars observed, only the two situated in the 30 Dor region have detectable DIBs. This balance appears to be strongly dependent on the UV radiation field, which is represented by the shape of the extinction curve (i.e. the presence of the 2200Å bump and the steepness of the far-UV rise).- Publication:
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Astrophysics of Dust
- Pub Date:
- 2003
- Bibcode:
- 2003asdu.confE..43C