RADIO SEARCH FOR H ₂ CCC TOWARD HD 183143 AS A CANDIDATE FOR A DIFFUSE INTERSTELLAR BAND CARRIER

Abstract

To clarify the authenticity of a recently proposed identification of H 2 CCC (linear-C 3 H 2 ) as a diffuse interstellar band carrier, we searched for the rotational transition of H 2 CCC at a frequency of 103 GHz toward HD 183143 using a 45-m telescope at the Nobeyama Radio Observatory. Although rms noise levels of 32 mK in the antenna temperature were achieved, detection of H 2 CCC was unsuccessful, producing a 3 σ upper limit corresponding to a column density of 2.0 × 10 13 cm −2 . The upper limit indicates that the contribution of H 2 CCC to the diffuse interstellar band at 5450 Å is less than 1/25; thus, it is unlikely that the laboratory bands of the B 1 B 1 -X 1 A 1 transition of H 2 CCC and the diffuse interstellar bands at 5450 Å (and also 4881 Å) toward HD 183143 are related.

Constraining the size of the carrier of the λ5797.1 diffuse interstellar band

“…Araki et al [81] searched for the 5 1,5 → 4 1,4 rotational emission at 102.99238 GHz toward HD 183143. Based on the non-detection of the line, they set the upper limit of the H 2 C 3 column density to be 1.1 × 10 13 cm −2 or 2.0 × 10 13 cm −2 for the excitation temperatures of 10 K and 60 K, respectively, assumed by Maier et al [76].…”

“…When Maier et al proposed H 2 C 3 as the carrier of the λλ4881 and 5450 DIBs, the main objection was that the required H 2 C 3 column densities on the order of 5 × 10 14 toward HD 183143 and 2 × 10 14 toward HD 206267 were far too high [51,[79][80][81]. Araki et al [81] searched for the 5 1,5 → 4 1,4 rotational emission at 102.99238 GHz toward HD 183143.…”

“…When Maier et al proposed H 2 C 3 as the carrier of the λλ4881 and 5450 DIBs, the main objection was that the required H 2 C 3 column densities on the order of 5 × 10 14 toward HD 183143 and 2 × 10 14 toward HD 206267 were far too high [51,[79][80][81]. Araki et al [81] searched for the 5 1,5 → 4 1,4 rotational emission at 102.99238 GHz toward HD 183143. Based on the non-detection of the line, they set the upper limit of the H 2 C 3 column density to be 1.1 × 10 13 cm −2 or 2.0 × 10 13 cm −2 for the excitation temperatures of 10 K and 60 K, respectively, assumed by Maier et al [76].…”

Analysis of Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36

“…But then we are caught by a dilemma. When Maier et al (2011) proposed H 2 CCC as the carrier of DIBs λ4881 and λ5450, it was negated by radio observations by Araki et al (2012) and Liszt et al (2012) because the column density of that molecule determined from radio observations is orders of magnitude smaller than 5 × 10 14 cm −2 inferred from DIBs. This dilemma applies to any molecules of medium size, but there must be a solution.…”

A framework for resolving the origin, nature and evolution of the diffuse interstellar band carriers?

“…and m n, Jones, 2012a,c) could also be potential DIB carriers. This is perhaps indicated by the coincidence between the bands of l-C3H2 and several DIBs (Maier et al, 2011;Stanton et al, 2012), even though this specific radical may not be the main contributor to these DIBs (Oka and McCall, 2011;Kre lowski et al, 2011;Liszt et al, 2012;Araki et al, 2012).…”