Extinction Coefficient

[Chatzisotiriou Marina]

Hello!

I have taken images of Standard Stars and I'm trying to calculate the extinction coefficient for each night. I've been told that in order to do that I need to measure the magnitude of the star and then draw a straight line on the plot airmass - magnitude. Is there a way to measure the magnitude of a star using AstroImageJ?

Thank you very much!
Marina

[karenacollins]

The magnitude of a star can be calculated based on known magnitudes of stars in the same image. To do that, follow these directions:
http://astroimagej.1065399.n5.nabble.com/Enter-apparent-magnitude-of-reference-stars-to-calculate-magnitude-of-target-stars-requires-AIJ-v3-1-td236.html

Karen

On 4/17/2019 6:58 AM, Chatzisotiriou Marina [via AstroImageJ] wrote:

Hello!

I have taken images of Standard Stars and I'm trying to calculate the extinction coefficient for each night. I've been told that in order to do that I need to measure the magnitude of the star and then draw a straight line on the plot airmass - magnitude. Is there a way to measure the magnitude of a star using AstroImageJ?

Thank you very much!
Marina

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NAML

[Chatzisotiriou Marina]

Dear Karen,

Thank you for your reply. In the end I calculated the magnitude using the equation m_instumental=-2.5*log_10(A/t) with A being the counts within the apperurture and t the exposure time.
I would like now to calculate the AB magnitude of my standard stars and to do that I need the flux. Do you know how can I find it?

Thank you,
Marina

[karenacollins]

The total ADU counts in aperture NN are given in the data column Source-Sky_TNN. I think you would need to know what absolute flux an ADU corresponds to for your telescope and camera. Alternatively, I think you would need to relate the Source-Sky_TNN counts to counts from another star for which you know the AB magnitude. I don't have experience using the AB magnitude system, so I can't give much guidance.

Maybe someone else on the forum is able to help?

Karen

[Chatzisotiriou Marina]

Hello Karen,

Thank you for your answer! I would like to ask another one. I want to measure the counts of a star within an aperture but without the background. In order to do that I set the object aperture and around it an inner and outer background aperture and I use the value given in Source-Sky. Is this correct?

Thank you,

Marina

On "karenacollins [via AstroImageJ]" <[hidden email]>, May 16, 2019 5:15 AM wrote:

The total ADU counts in aperture NN are given in the data column Source-Sky_TNN. I think you would need to know what absolute flux an ADU corresponds to for your telescope and camera. Alternatively, I think you would need to relate the Source-Sky_TNN counts to counts from another star for which you know the AB magnitude. I don't have experience using the AB magnitude system, so I can't give much guidance.

Maybe someone else on the forum is able to help?

Karen

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http://astroimagej.1065399.n5.nabble.com/Extinction-Coefficient-tp1128p1157.html

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NAML

[karenacollins]

HI Marina,

That is correct.

Karen

On 5/23/2019 6:13 AM, Chatzisotiriou Marina [via AstroImageJ] wrote:

Hello Karen,

Thank you for your answer! I would like to ask another one. I want to measure the counts of a star within an aperture but without the background. In order to do that I set the object aperture and around it an inner and outer background aperture and I use the value given in Source-Sky. Is this correct?

Thank you,

Marina

On "karenacollins [via AstroImageJ]" <[hidden email]>, May 16, 2019 5:15 AM wrote:

The total ADU counts in aperture NN are given in the data column Source-Sky_TNN. I think you would need to know what absolute flux an ADU corresponds to for your telescope and camera. Alternatively, I think you would need to relate the Source-Sky_TNN counts to counts from another star for which you know the AB magnitude. I don't have experience using the AB magnitude system, so I can't give much guidance.

Maybe someone else on the forum is able to help?

Karen

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http://astroimagej.1065399.n5.nabble.com/Extinction-Coefficient-tp1128p1157.html

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NAML

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NAML