Brown dwarf oddness

[omega13a]

I'm working on a star system. One of the objects in it is a brown dwarf. For some odd reason, when I'm like 4000 AU from the brown dwarf, its invisable despite Celestia saying it has a visable magnitude of 0.22 and a diameter comparable to the G type stars in the same system. The odd thing is that when I change the brown dwarf to a type M star but keep everything else about it the same (like absolute magitude and radius), it shows up.

Attached are somethings to show you what I mean.

If it would help, here's the zip file for the star system: http://fedtrek.com/staff/omega13a/celes ... ad&star=49

[John Van Vliet]

--- edit ---

[symaski62]

http://en.wikipedia.org/wiki/Spectral_c ... ane_dwarfs

[Hungry4info]

seeing as brown dwarves do not emit much in the visible spectrum
in IR yes
but in visible , not much
...
so this is behavior that i would expect

But Celestia lists the Visible magnitude, not the Infrared one. Would you not expect an object with a visible magnitude of V = 0.22 to be visible, regardless of where it's peak emission is?

[omega13a]

seeing as brown dwarves do not emit much in the visible spectrum
in IR yes
but in visible , not much
...
so this is behavior that i would expect

But Celestia lists the Visible magnitude, not the Infrared one. Would you not expect an object with a visible magnitude of V = 0.22 to be visible, regardless of where it's peak emission is?

I agree. It not being visible makes as much sense as standing infront of a mirror and seeing the reflections of everything in the room except for your self.

[ajtribick]

I think this may have something to do with the disappearance of the glowing halo at temperatures <1000 K (based on experimentation, I'm not sure where in the code this is defined)

From the source code (star.cpp), the temperatures for T-type objects are defined as follows:

Code: Select all

static float tempT[10] =
{
    1425, 1350, 1275, 1200, 1140, 1080, 1020, 900, 800, 750
};


So types T7-T9 should lack halos. Your screenshot uses a T8 dwarf, which ends up with no glowing halo. If you replace your brown dwarf with a T6 spectral type (which defaults to 1020K) do you still see the same effect?

[omega13a]

I can see it when its a T6 dwarf.

BTW, the zip file I linked to in my first post is regenerated about once every 10 minutes to reflect any changes I make so the brown dwarf in there may or may not be the same spectral type as I originally had it.

[ajtribick]

Yes confirmed that the transition happens at T6/T7 for standard spectral types (without modification of temperature).

On the other hand the properties of this brown dwarf are highly implausible! If you don't force the radius to be 0.87 times solar, the absolute magnitude you have assigned causes Celestia to calculate the radius as 6800 times solar.

Question then arises about whether it even makes sense to use V-magnitudes for such cool objects anyway, these things are hardly putting out any visible light at all. (And the situation gets worse once you go to spectral type Y)

[omega13a]

(And the situation gets worse once you go to spectral type Y)

Which judging by the source code, the current version of Celestia doesn't support.

[ajtribick]

Have to allow stars to reflect light first...

[PlutonianEmpire]

Yes confirmed that the transition happens at T6/T7 for standard spectral types (without modification of temperature).

On the other hand the properties of this brown dwarf are highly implausible! If you don't force the radius to be 0.87 times solar, the absolute magnitude you have assigned causes Celestia to calculate the radius as 6800 times solar.

Question then arises about whether it even makes sense to use V-magnitudes for such cool objects anyway, these things are hardly putting out any visible light at all. (And the situation gets worse once you go to spectral type Y)

Actually, a while back, I looked up blackbody temperatures, and what temperatures give what appearances, and came up with this:

480 c = 753.15 k = faint red glow
580 c = 853.15 k = dark red
730 c = 1003.15 k = bright red, slightly orange
930 c = 1203.15 k = bright orange
1100 c = 1373.15 k = pale yellowish orange
1300 c = 1573.15 k = yellowish white
> 1400 c = 1673.15 k = white (yellowish if seen from a distance through atmosphere)

And on top of that, I looked up known visual magnitudes of known brown dwarves, and used this calculator, and along with some number crunching, was able to come up with with how bright they might look if looking at a particular incandescent light bulb of a particular brightness from a certain distance away, and found that the brighter brown dwarves can indeed emit noticeable lights.

I don't know how accurate my calculations were though.