Ron-Astro Pharmacist wrote:
Ann wrote:This is a golden oldie, although newly processed by Brandon Pimenta. It is certainly a stunning nebula.
Is there any information as to how massive IRS 4 is?
888 is such a nice number. Star Forming Region S106 is loosing so much mass it's probably difficult to calculate.
"In Fig. 5 the star with a mass estimate of 102 M⊙ is source
50, corresponding to the central exciting star S106 IRS 4. The
value of 102 M⊙ is very probably overestimated, due to the
fact that the method we have used to derive a mass value for
each star does not take into account the possible presence of
an IR excess, which in this case is known to be present (e.g.
Felli et al. 1984 and Fig. 4)."
Also stated "For S106 IRS 4 the estimates
in the literature indicate a mass greater than 15 M⊙ (Felli et al.
1984) and therefore the presence of an IR excess does not affect
the placement of S106 IRS 4 in the highest mass bin."
102 M⊙ is a very high mass indeed, and stars that massive are extremely rare in the Milky Way. So yes, such a high mass for S106 IRS 4 is very probably overestimated. Then again, 15 M⊙ represents, comparatively speaking, a rather modest mass for a very high-mass star. It is probably just enough to make an O-type main sequence star. For comparison, Jim Kaler
wrote about O9-type main sequence star 10 Lacertae:
From a surface heated to a quite-amazing 32,000 Kelvin, it radiates a with a luminosity of 26,800 Suns (the majority of the light in the invisible ultraviolet), from which we derive a radius 4.7 times that of the Sun and a great mass of 16 times solar.
S106 IRS 4 is a massive stellar object of spectral type O7–
B0 and luminosity of [0.4–1] × 105 L⊙ (Gehrz et al. 1982;
Felli et al. 1984).
A spectral class of "only" O7-B0 suggests that S106 IRS 4 might lie just at the dividing line between spectral classes O and B, in which case 15 M⊙ would be a reasonable mass estimate. Then again, maybe not. At a very young age, stars belong to a redder, cooler spectral class than when they reach full maturity:
Given their young age however
they could be Herbig Ae/Be stars, which have significant
X-ray activity, or even their precursors, since according to the-
oretical models a two million year old star of 2–3 M⊙ will have
spectral type K–G.
So S106 IRS 4 might be headed for an O3 spectral class, the hottest class, in the future.
I have to say that the whole S106 nebula looks as if it was powered by the bipolar outflow of just one, very massive star. To me, it looks
as if the stellar engine powering the nebula has to be more massive than 15 M⊙! (As if I would know. Oh well.)
Again, thanks, Ron! Very interesting.