Search

X‐ray transients provide the best evidence for the existence of stellar‐mass BHs, with 20 confirmed cases based on dynamical studies. However, these are only the tip of iceberg of an estimated population of a few thousand BH binaries, which slowly reveal themselves through secular X‐ray outbursts. Therefore, new strategies aimed at unveiling this dormant population are clearly needed. We propose to use the IPHAS catalogues, together with several diagnostic diagrams, as a shortcut to unveil the brightest members of the galactic population of BH binaries.

We present high time resolution spectroscopy of the non‐eclipsing old nova V533 Herculis (N Her 1963). It is the second nova remnant affected by the ‘SW Sex syndrome’. A modulation of the equivalent width of the emission lines with a period of 23.33 min has been detected. This, together with the strong He ii λ4686 emission characteristic of magnetic systems, leads us to link this period to the spin of a magnetic white dwarf. Similar flaring activity has been recorded in other SW Sex stars, namely, the old nova BT Mon, LS Peg and DW UMa, supporting the idea of these systems being magnetic accretors. Stationary emission features are also observed in the Balmer lines, which we attribute to the ejected nova shell.