On the diffuse bands related to the C₂ interstellar molecule

¹ Korea Astronomy and Space Science Institute, Optical Astronomy Division, 61-1, Whaam-Dong, Yuseong-Gu, Daejeon 305-348, Korea e-mail: [gala;iwhan]@kasi.re.kr
² Special astrophysical observatory, Nizhnij Arkhyz 369167, Russia
³ Institute of Theoretical Physics and Astrophysics, University of Gdańsk, ul. Wita Stwosza 57, 80-952 Gdańsk, Poland e-mail: pg@iftia.univ.gda.pl
⁴ Bohyunsan Optical Astronomy Observatory (BOAO) Jacheon P.O.B.#1, YoungChun, KyungPook 770-820, Korea e-mail: [bclee;kmkim]@boao.re.kr
⁵ Nicolaus Copernicus University, Center for Astronomy, Gagarina 11, 87-100 Toruń, Poland e-mail: jacek@astri.uni.torun.pl

Received: 12 May 2005
Accepted: 4 October 2005

Abstract

The recently published idea that intensities of some weak diffuse interstellar bands (DIBs) are related to the C₂ molecule column density have been examined. We use a set of high quality echelle spectra of heavily reddened stars, acquired at the Bohyunsan Optical Astronomical Observatory (South Korea), with a resolution . The high quality (high S/N ratio) of our spectra is proved by the fact that despite using the most widely used Phillips (2, 0) band of the C₂ molecule (near 8760 Å), we can trace the (3, 0) Phillips band (near 7725 Å) as well. Equivalent widths of four (5176, 5542, 5546 and 5769 Å) out of 16 examined DIBs demonstrate relatively good correlation with C₂ column density. However, a majority of the studied DIBs, already reported as “C₂” ones, most likely are not related to this simplest carbon molecule. A removal of peculiar objects like HD 34078 from the analyzed sample does not substantially change the level of correlations.