Linear and circular spectropolarimetry of diffuse interstellar bands
Abstract
Context. The identification of the carriers of diffuse interstellar bands (DIBs) remains one of the long-standing mysteries in astronomy. The detection of a polarisation signal in a DIB profile can be used to distinguish between a dust or gas-phase carrier. The polarisation profile can give additional information on the grain or molecular properties of the absorber.
Aims: To measure the polarisation efficiency of the carriers of the diffuse interstellar bands.
Methods: In order to detect and measure the linear and circular polarisation of the DIBs we observed reddened lines of sight showing continuum polarisation. For this study we selected two stars
Results: High S/N and high resolution Stokes V (circular), Q and U (linear) spectra were obtained. We constrained upper limits by a factor of 10 for previously observed DIBs. Furthermore, we analysed ~30 additional DIBs for which no spectropolarimetry data has been obtained before. This included the 9577 Å DIB and the 8621 Å DIB. The former is attributed to the C60^+ fullerene, which could become aligned in a magnetic field. The latter shows a tight correlation with the amount of dust in the line-of-sight and therefore most likely may show a polarisation signal related the aligned grains.
Conclusions: The lack of polarisation in 45 DIB profiles suggests that none of the absorption lines is induced by a grain-type carrier. The strict upper limits, less than ~0.01%, derived for the observed lines-of-sight imply that if DIBs are due to gas-phase molecules these carriers have polarisation efficiencies which are at least 6 times, and up to 300 times, smaller than those predicted for grain-related carriers.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- July 2011
- DOI:
- 10.1051/0004-6361/201016365
- arXiv:
- arXiv:1104.4581
- Bibcode:
- 2011A&A...531A..25C
- Keywords:
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- astrochemistry;
- polarization;
- dust;
- extinction;
- ISM: lines and bands;
- ISM: molecules;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 6 pages + 13 pages online material, submitted to A&