Photometry- zero points of telescopes.

[sweep123]

Homework Statement

I need to calculate the zero point of the telescope and camera i used.

Homework Equations

The Attempt at a Solution

I have count rates of various points on the screen in a 19x19 pixel box of a standard star using the two filters V and R. I've used exposure times of 20 seconds. I have been told that the zero point is the magnitude that corresponds to a raw ccd count rate of 1 count per second. I am fairly lost on how to go about finding the zero point. Can anyone give me a push in the right direction. Thanks

 

[lippyka]

. The zero point of a telescope or camera is the numerical value that corresponds to a given magnitude for a particular filter. You can calculate the zero point by measuring the flux of a standard star with known magnitude in a given filter and comparing it to the raw count rate you measure from your telescope/camera. To do this, you need to measure the count rate from the standard star in the same filter as the magnitude you have for the star. You can then calculate the zero point by dividing the count rate by the magnitude of the star. For example, if you have a count rate of 10 counts/second and a magnitude of 10, the zero point would be 1 count/second per magnitude. The zero point you calculate should be consistent with the expected zero point of your instrument. If the calculated zero point differs significantly from the expected zero point, it could indicate a problem with your instrument or data. Once you have calculated the zero point, you can use it to convert raw count rates into magnitudes. To do this, you simply multiply the raw count rate by the zero point. For example, if you have a count rate of 10 counts/second and a zero point of 1 count/second per magnitude, the magnitude would be 10.

 

[Moetasim]

I would suggest starting by reviewing the principles of photometry and how it relates to telescopes and cameras. Specifically, the zero point is a calibration factor that relates the raw CCD count rate to the magnitude of the observed object. This factor can vary depending on the telescope and camera used, as well as the filters and exposure times.

To calculate the zero point, you will need to use the equation:

m = -2.5log(counts) + zero point

Where m is the magnitude, counts is the raw CCD count rate, and zero point is the calibration factor you are trying to find.

To determine the zero point, you will need to use the count rates for your standard star and solve for the magnitude, using the equation above. Once you have the magnitude, you can compare it to the known magnitude of the standard star and calculate the zero point.

It is also important to note that the zero point can change over time due to factors such as changes in the telescope or camera, so it is recommended to recalibrate periodically.

I hope this helps guide you in finding the zero point for your telescope and camera. Good luck!