“School of Astronomy”
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| Paper IPM / Astronomy / 17588 |
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We carried out a sensitive survey of C2 and C3 using the EDIBLES data set. We also expanded our searches to C4, C5, and 13C12C isotopologue in the most molecule-rich sightlines.
We fit synthetic spectra generated following a physical excitation model to the C2 (2-0) Phillips band to obtain the C2 column density (N) as well as the kinetic temperature (Tkin) and number density (n) of the host cloud. The C3 molecule was measured through its A~â??X~ (000-000) electronic origin band system. We simulated the excitation of this band with a double-temperature Boltzmann distribution.
We present the largest combined survey of C2 and C3 to date in which the individual transitions can be resolved. In total we detected C2 in 51 velocity components along 40 sightlines, and C3 in 31 velocity components along 27 sightlines. The two molecules are detected in the same velocity components. We find a very good correlation between N(C2) and N(C3) with Pearson r=0.93 and an average N(C2)/N(C3) ratio of 15.5ñ1.4. A comparison with the behaviour of the C2 DIBs shows that there are no clear differences among sightlines with and without detection of C2 and C3. This is in direct contrast to the better-studied non-C2 DIBs who have reduced strengths in molecule-rich environments. We also identify for the first time the Q(2), Q(3), and Q(4) transitions of the 13C12C (2-0) Phillips band in a stacked average spectrum, and estimate the isotopic ratio of carbon 12C/13C as 79ñ8. Our search for the C4 and C5 optical bands was unsuccessful.
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