Re: paper on transits by extrasolar planets in OGLE data

[Fraser Farrell <fraser@trilobytes.com.au>]

On Sun, 24 Mar 2002 03:58, Stupendous Man wrote:
>   Very impressive!  The OGLE group looks at stars in the Large
> Magellanic Cloud with a big telescope, so they are searching a very
> different portion of parameter space than the Mark IV would.

Actually the OGLE group looks mostly towards the galactic centre. It's the 
MACHO group who check out the Large Magellanic Cloud (and who comes up 
with these contrived acronyms anyway?).  Both groups search primarily for 
gravitational lensing events; but as an inevitable byproduct also discover 
vast numbers of variable stars. And the occasional transiting "planet"...

If I simplistically assume all stars imaged are 0.005 AU radius, and also 
have a planet 1/10 this size (ie: a tad bigger than the sun & Jupiter) in 
a randomly oriented circular orbit, then I calculate the following 
probabilities for seeing a transit for any star:

orbital radius 0.05 AU (period ~4 days)  =  0.09 (for "total" transit only)

orbital radius 0.05 AU (period ~4 days)  =  0.11 (for total or partial 
transit)

orbital radius 1 AU (period ~1 year)  =  0.0045 (for total transit)

orbital radius 5 AU (period ~11 years)  =  0.0009 (for total transit)

Maximum durations of total transits would be about one hour (for a 
limiting non-central transit) every four days, or about 1.7 hours for a 
central transit every 4 days, up to about 17 hours (central transit) every 
11 years. For all total transits the star would fade by about one percent.

Therefore if all these stars were accompanied by "hot jupiters" then we 
could expect to see total transits on any given night for about 1 in 650 
of them ( = 0.11 * (1.35h / 4d) ). If they are all accompanied by our sort 
of jupiter then we could expect transits for about 1 in 6.3 million per 
night.

Of course not all these stars would actually have planets - or indeed 
anything bigger than rocks - circling them, and the size ratio isn't 
always 10:1. Like I said, this is a simplistic calculation.

Meanwhile, for a Real World check, why not aim the Mark IV at some stars 
already known to have transiting planets?


cheers,

-- 

Fraser Farrell

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