SIMBAD references

We place observational constraints on a recently proposed Galactic population, dubbed the `shroud'. The shroud would be a very thick Galactic disc of low-luminosity objects, most likely old white dwarfs (WDs), proposed to explain the optical depth seen in microlensing surveys towards the Magellanic clouds. The shroud is a simple alternative to the lenses being distributed in a classical, near-spherical dark halo; the advantage of the shroud is that it would compose only a fraction of the total mass of a dark halo.

In this paper, we argue that stars of the Galactic shroud would be detectable in the recent proper motion survey of Oppenheimer et al. if their absolute luminosities were brighter than M_R59F= 19.4 or approximately M_V= 18.6. We adopt a range of simple models of the shroud kinematics and morphology, and the colours and luminosities of its WDs; via Monte-Carlo simulations, we predict the numbers expected in the Oppenheimer et al. survey, which would be clearly separated from the numbers produced by WDs of the disc, thick disc and halo.

The number of WD detections in the proper motion survey (98) is found to be well explained by the disc, thick disc and halo. With the most conservative kinematic and density parameters for the shroud, and an absolute luminosity of the WDs of M_R59F= 17.6, we find that the proper motion survey would detect over 100 WDs, just from the shroud. For a M_R59F= 19.4 shroud, the survey would find 5±2 peculiar objects, whereas only two WDs with such characteristics are found in the original data. M_R59F= 19.4 corresponds to M_V= 18.6 for WDs with (V-I) =-1.030.