Looking for "New Earth" around Alpha Centauri

In article ,
(Abdul Ahad) writes:
I've managed to patch together a basic magnitude model that lets you
project the expected visual (V-band) magnitude for an extrasolar
planet (exoplanet) having Earth- or Jupiter-like photometric
properties, which is located in the habitable zone and shining by the
light reflected from its parent star, as viewed from our vantage point
here on Earth.

In theory, the model should hold accurate for gauging the brightness
of an exoplanet around *any* star, since by the default definition of
a "habitable zone", a planet would experience a total light flux of a
constant planet/star ratio in all cases.

The model is basically right, but there are a few complications. The
habitable zone is constant in _bolometric magnitude_, i.e. the total
flux at all wavelengths per unit surface area of the planet. But for
detection, what is important is the magnitude at the particular
wavelength of observation, which varies with the temperature of the
star. Look up "bolometric correction" for details.

A second complication is that in the mid to far infrared, a planet
shines not by reflected light but by thermal emission of its own.
This makes the planet quite a lot brighter than the model would
predict. In the long wavelength regime, the brightness ratio is the
ratio of (surface area * temperature) for the planet and star.

A third complication is that the brightness at particular wavelengths
will be modified by a planet's atmosphere, if it has one.

m2 = 5/2 * Log10 R + m1

[where m2 = magnitude of planet, R = star/planet brightness ratio
(Earth = 1,499,684,836, Jupiter = 9,120,108, m1 = apparent visual
magnitude of parent star ]

You can replace (2.5*log10 R) with a magnitude ratio, 22.9 for Earth,
17.4 for Jupiter. Mathematically the same but perhaps easier to
write.

My article in full, is he-

http://uk.geocities.com/aa_spaceagen...r-planets.html

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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