Microlensing by compact objects associated with gas clouds

¹ Dipartimento di Fisica “E.R. Caianiello”, Universitá di Salerno, 84081 Baronissi (SA), Italy
² Istituto Nazionale di Fisica Nucleare, sez. Napoli, Gruppo Collegato di Salerno, Italia
³ Institut für Theoretische Physik der Universität Zürich, 8057 Zürich, Switzerland
⁴ Institut für Theoretische Physik der ETH, 8093 Zürich, Switzerland
⁵ International Institute for Advanced Scientific Studies, Vietri sul Mare (SA), Italy

Corresponding authors: V. Bozza, valboz@sa.infn.it jetzer@physik.unizh.ch mancini@physik.unizh.ch scarpetta@sa.infn.it

Received: 4 May 2001
Accepted: 25 October 2001

Abstract

We investigate gravitational microlensing of point-like lenses surrounded by diffuse gas clouds. Besides gravitational bending, one must also consider refraction and absorption phenomena. According to the cloud density, the light curves may suffer small to large deviations from Paczyński curves, up to complete eclipses. Moreover, the presence of the cloud endows this type of microlensing event with a high chromaticity and absorption lines recognizable by spectral analysis. It is possible that these objects populate the halo of our galaxy, giving a conspicuous contribution to the fraction of the baryonic dark matter. The required features for the extension and the mass of the cloud to provide appreciable signatures are also met by several astrophysical objects.