Talk:AM Canum Venaticorum star

things I was hoping to find here
How many of these are there ? How are their periods distributed ? Are any visible as a spectroscopic binary ? What are the separations for the various periods (in km) ? What orbital velocity do the components have ? - Rod57 (talk) 12:38, 23 July 2019 (UTC)
 * There are 42 listed in the 2004 Cataclysmic Binary catalogue. Not many!  No doubt more have been discovered since.  AM CVn is the brightest, which should give you some idea why they are hard to find.  Not sure what you mean by visible as a spectroscopic binary.  They are visible, but the spectra lack well-defined lines that could be used to define an orbit.  A normal white dwarf spectrum is almost entirely hydrogen absorption lines, but these are not found in AM CVn systems because the material accreted from the donor lacks hydrogen.  The spectrum is therefore dominated by helium and various emission lines from gas being transferred between the components.  Lithopsian (talk) 13:57, 23 July 2019 (UTC)