EDP Sciences
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Volume 365, Number 2, January II 2001
Page(s) 157 - 164
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20000176

A&A 365, 157-164 (2001)
DOI: 10.1051/0004-6361:20000176

Classification and properties of UV extinction curves

G. Barbaro1 , P. Mazzei2 , L. Morbidelli3 , P. Patriarchi3 and M. Perinotto4 .

1  Dipartimento di Astronomia, Vicolo Osservatorio 3, 35122 Padova, Italy
2  Osservatorio Astronomico, Vicolo Osservatorio 5, 35122 Padova, Italy
3  CAISMI-CNR, Firenze, Italy
4  Dipartimento di Astronomia, Firenze, Italy

(Received 15 February 2000 / Accepted 2 October 2000)

The catalog of Savage et al. (1985) reporting colour excesses of 1415 stars from ANS photometry offers the opportunity to deeply investigate the characteristics of UV extinction curves which differ from the standard extinction of the diffuse interstellar medium. To this aim we have selected a sample of 252 curves, which have been compared with the relations derived by Cardelli et al. (1989; CCM in the following) for a variety of RV values in the range 2.4-5 and have been classified as normal if they fit at least one of the CCM curves or anomalous otherwise. We find that normal curves with small RV are just as numerous as those with large RV. The anomalous objects are arranged into two groups according to the strength of the bump at $0.217 \mu$. For a given value of c2 this increases along the sequence: type A anomalous, normals and type B anomalous, suggesting that this sequence should correspond to an increase of the amount of small grains along the sightline. Considerations concerning the environmental characteristics indicate that the anomalous behaviour is not necessarily tied to the existence of dense gas clouds along the line of sight.

Key words: stars: circumstellar matter - ISM: dust, extinction -ISM: general

Offprint request: G. Barbaro

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