What is the local stellar number density?

Question

Is it just me or does this paper, while providing a great equation for the behaviour of the general stellar number density, never actually give a value for the local stellar number density $\rho(R={\rm R}_\odot, z=0)$? I want to use their relationship for a calculation in my Master's thesis but I'm not sure what value for the local stellar density I should be using.

While some values (dimensionless, I assume number per light-year cubed) are present in figures 21 & 24 and tables 6 & 7 these are only for certain binned-by-colour stellar populations and not the general value. The value is conspicuously absent from table 10 which contains every other parameter. And it is not even addressed in equation 19 where it is introduced. Is there a particular reason for all this?

I hope I'm just missing something, and I could always use a rough value like the '$0.004$ stars per cubic light year' used by Erik Gregersen in 'The Milky Way and beyond' (The Rosen Publishing Group. pp. 35–36. ISBN 1-61530-053-8), but any inside insight would be appreciated.

As an aside, I am also assuming 'stellar number density' includes non-main-sequence stars, i.e. giants and white dwarfs. Is that correct?

Answer 1

The local "stellar" number density is about 0.1 per cubic parsec. This includes stars down to about 0.1 solar masses, giants and white dwarfs. The latter are corrections at the level of a few and 15 per cent respectively. e.g. There are 1000 objects within 15 pc in the Gliese & Jahreiss (1991) 3rd catalogue of nearby stars.

It does not include all brown dwarfs, since the census is incomplete even to modest distances, but there are about 4 times as many stars as brown dwarfs. There will also be some incompleteness even at 15pc for the lowest mass stars. There is also some modest upward correction if you really want the number density of stars rather than stellar systems, since about 25 per cent or so of systems are unresolved multiples.