"c" == chornedsnorkack writes:

c Joseph Lazio wrote:

c What would happen if Epsilon Indi B orbited Sun, not Epsilon Indi
c A?
[...]
c Would anyone discover it as a modest source of infrared?

In the discovery observations, the combined system has an infrared
J-band magnitude of approximately 12. That's at a distance of 3.6
pc. Move it about 500 times closer (to a distance of about 1500
pc). That means that it should become about 13.5 magnitudes
^^
Clearly I meant 1500 AU.

brighter. Its apparent J-band magnitude would be approximately
-1.5.

Ah, but these calculations are for eps Ind Ba at its current
temperature. [...] So our hypothetical Sun Ba would be expected
to have a J-band magnitude of 1.5.

There have been all-sky surveys in the J band (e.g., 2MASS). I
think there's little chance that they would have missed either a
-1.5 or 1.5 magnitude object. (Missing a -1.5 magnitude object
would be like conducting a survey at visual wavelengths and not
seeing Sirius.)

c So, it would be noted in 2MASS. Would an near-IR object this bright
c have been noticed before 2MASS survey?

There were the IRAS surveys. The shortest wavelength survey was at 12
microns. One would have to run the numbers, but, again, a 1.5 J-band
magnitude object is bright, really bright. I don't see how IRAS could
have missed it (short of extreme molecular absorption in the object's
atmosphere).

c Also, what about Bb? Epsilon Indi Bb is known to be about 600
c Celsius at the age of 1,3 milliards of years and allegedly 27
c Jupiter masses. Would an object older than this, at 4,5 milliards
c of years, be discovered in infrared?

Without running the numbers, I'd still expect a hypothetical Sun
Bb, similar to eps Ind Bb but older, to still be detectable easily.

c How cold objects would be detectable?

c Jupiter, at 5 a. u. is about 120 K temperature and radiates twice
c the heat received from Sun. So, if Jupiter were at 1500 a. u. it
c would still have temperature of about 100 K.

Above, I concluded that a 500 K object at a distance of 1500 AU would
have a J-band magnitude of 1.5. A 100 K object would be about 7
magnitudes dimmer, or magnitude 8.5. A quick check of the 2MASS
documentation indicates that, at J band, it should be complete down to
15.8. Even a 100 K object should still be detectable.

(Of course, I've made a few assumptions, such as ignoring any effects
due to molecular line absorption, that the radius of the various
objects are all about the same. To zeroth order, these seem reasonable.)


c Would it be seen in IR in absence of visible reflection showing
c where to look for IR radiation?

Yes. One doesn't need to see something via visible reflection in
order to look for IR radiation from it. One can observe the sky at IR
wavelengths without regard to how the sky looks at visible
wavelengths. That was part of the point behind IRAS, 2MASS, and other
surveys in the IR. I encourage you to visit the 2MASS site at URL:
http://www.ipac.caltech.edu/2mass/ .

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