[extropy-chat] Most star systems are single

[Amara Graps]

Robert:

>What I don't understand is if there are so many M class stars, why
>doesn't the IMF trend continue?  I.e. there should be even more brown
>dwarfs, methane dwarfs and superplanets (all "non-orbiting" / "rogue")
>running around the galaxy?

---
Lada says in his paper:

"First, the functional form of the stellar initial mass function (IMF)
has been better constrained by observations of both field stars (e.g.,
Kroupa 2002) and young embedded clusters (e.g., Muench et al. 2002). The
IMF has been found to peak broadly between 0.1 and 0.5 M_s, indicating
that most stars formed in the Galactic disk are M stars. Second, surveys
for binary stars have suggested that the binary star frequency may be a
function of spectral type (e.g., Fischer & Marcy 1992). In particular,
there have been a number of attempts to ascertain the binary frequency
of M-type stars and even of L and T dwarfs, objects near and below the
hydrogen-burning limit."

---

The IMF is constrained by observations, and those faint objects are
difficult to detect. Also, according to my old astronomy text, the
definition and the derivation of the IMF assumes stars. The IMF is the
number of stars formed per unit mass interval in a unit volume as a
function of mass M. Usually it is derived by first deriving the initial
luminosity function, and then calculating the mass function via the
mass-luminosity relationship for main-sequence stars. The mass-lumino-
sity relationship is empirical; do you know if such a relationship
exists for brown dwarfs? I honestly don't know. Perhaps there are other
ways to derive the IMF using non-main sequence objects. This is much more
in your area than in mine, maybe a derivation like this is one of your
texts. (My galactic astronomy text is from 1981)

Amara

-- 

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Amara Graps, PhD          email: amara at amara.com
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