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How to Convert Exoplanet Transit Depth Measurements from Milli-Magnitudes to Percent

-- Sujay | April 7, 2020

Question:

Hello,
I am an amateur exoplanet researcher. One quite annoying problem my team has been running into involves some units. When researching some planets, we get transit depths in units of millimags (ex: wasp-33b is 14mmag transit depth). How does one convert from mmag to percent. We would really like to say X% transit depth instead of mmag.
Thanks

-- Sujay

Answer:

I believe that a measurement in millimagnitudes (mmag) needs to be compared to the un-eclipsed brightness of the host star, in magnitudes, in order to convert its exoplanet transit depth to a percentage. For example, a 14 mmag transit depth against a host star whose brightness is 1.4 mag would convert to a transit depth percentage of 0.014/1.4 = 1%.

-- Jeff Mangum

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