How to make good photometric measurements

Over the years Astrolab students have produced many, many excellent light curves of variable stars and asteroids.

For example this is the light curve that was measured for CW Cas which has a period of 7.6 hours.

However there are many, many ways to acquire poor photometric data.

These including

At the telescope

observing in very poor conditions, although observing in mediocre conditions is often possible as only relative photometry within the CCD field-of-view is being undertaken
not checking the photometry in real-time, particular the run of the magnitude difference of the two comparison stars
saturating either the target object or one/both of the comparison stars
letting either the target object or one of the comparison stars drift too close to the CCD field edge
checking that the dome shutter is tracking telescope properly ("re-Home" dome if necessary)
selecting a comparison star that is a variable star (this only happens rarely)
not cooling the CCD down (i.e. this will mean a high dark frame level and many hot pixels)
not noticing that the target asteroid has moved close to a star
using a comparison star that is too faint
observing with an internally or externally dewed up telescope
selecting the wrong photometric filter
observing the target at high airmass (i.e. greater than 2 )
observing close to a bright Moon or bright star
if not flat-fielding the images, placing one of the objects on/near a CCD "dust speck"
observing in windy conditions where the telescope is buffeted
taking short exposures and getting poor S/N data
not switching off the monitors and the lights in the dome

In the Lab

jrl

2020-Jun-17 12:47:08 UTC