An upper limit to the interstellar abundance in translucent clouds^*

¹ Special Astrophysical Observatory, Nizhnij Arkhyz 369167, Russia e-mail: faig@sao.ru
² Center for Astronomy, Nicholas Copernicus University, Gagarina 11, 87-100 Toruń, Poland e-mail: jacek@astri.uni.torun.pl
³ Isaac Newton Institute of Chile, SAO Branch, Russia
⁴ Laboratorie d'Astrophysique de Marseille, Traverse du Siphon, Les trois Lucs, BP 8, 13376 Marseille Cedex 12, France e-mail: Claire.Moutou@oamp.fr
⁵ European Southern Observatory, Alonso de Cordova 3107 – Vitacura, Santiago, Chile e-mail: glocurto@eso.org

Corresponding author: J. Krełowski, gala@sao.ru

Received: 26 June 2002
Accepted: 27 August 2002

Abstract

We have analyzed high resolution spectra of several slightly to moderately reddened stars collected at two observatories: ESO (La Silla) and Terskol (Northern Caucasia), to estimate the abundance of the C₅ molecule in the interstellar medium. We confirm the presence of a feature near 4975 Å which appears to be a weak DIB rather than the predicted C₅ band since the origin band near 5109 Å remains invisible even in spectra of high signal–to–noise ratio (~2500) and spectral resolution (). This confirms that the C₅ abundance in translucent interstellar clouds is very low. We estimate its limit as low as 10¹¹ cm^-2 in the scale for “zeta" type objects that is two times lower than that of Maier et al. (2002).