Instrumental magnitude

[sscygni]

Dear Karen
we are teaching broad-band photometry (B, V, R, I) to high school students and we would like to use your wonderful software not only for exoplanets but also for variable stars. We have a little problem. We could not find in the user guide how to derive the instrumental magnitudes of the target and the comparison stars. Our goal is to use the instrumental magnitudes in two bands (usually B and V) to compute the apparent magnitudes through a linear regression of the comparison stars (V-v = alpha * (b-v) + k) and check in the resulting graph the presence of outliers. How can we proceed?
Thank you so much
Marta

[karenacollins]

Hi Marta,

Sorry for the delayed response. AIJ currently provides the option to enter apparent magnitudes of comparison stars. The apparent magnitudes should be specified for the filter used for the observations. Then AIJ calculates the apparent magnitude of the "Target" stars in that filter, based on the comparison star apparent magnitudes. If you do this for B and then V observations separately, would this provide what you need to do the linear regression you mentioned? To enter comp star magnitudes, enable the option circled in the figure below on the Multi-Aperture setup panel. Apparent magnitudes of comp star can also be entered after running photometry in the Reference Star settings panel below clicking the "Show Magnitudes" button. Also, see section 4.2 in the Expanded edition of the AIJ paper on arXiv here:
https://arxiv.org/abs/1701.04817




If this does not provide what you need, I could add a feature request to the AIJ developement to-do list, but unless the implementation is trivial, it may take a few months to get to the implementation. If you would like to pursue this, could you explain how you expect instrumental magnitude to be calculated?

Thanks,
Karen

On 12/14/2017 6:53 AM, sscygni [via AstroImageJ] wrote:

Dear Karen
we are teaching broad-band photometry (B, V, R, I) to high school students and we would like to use your wonderful software not only for exoplanets but also for variable stars. We have a little problem. We could not find in the user guide how to derive the instrumental magnitudes of the target and the comparison stars. Our goal is to use the instrumental magnitudes in two bands (usually B and V) to compute the apparent magnitudes through a linear regression of the comparison stars (V-v = alpha * (b-v) + k) and check in the resulting graph the presence of outliers. How can we proceed?
Thank you so much
Marta

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[karenacollins]

Hi Marta,

Sorry for the delayed response. AIJ currently provides the option to enter apparent magnitudes of comparison stars. The apparent magnitudes should be specified for the filter used for the observations. Then AIJ calculates the apparent magnitude of the "Target" stars in that filter, based on the comparison star apparent magnitudes. If you do this for B and then V observations separately, would this provide what you need to do the linear regression you mentioned? To enter comp star magnitudes, enable the option circled in the figure below on the Multi-Aperture setup panel. Apparent magnitudes of comp star can also be entered after running photometry in the Reference Star settings panel below clicking the "Show Magnitudes" button. Also, see section 4.2 in the Expanded edition of the AIJ paper on arXiv here:
https://arxiv.org/abs/1701.04817




If this does not provide what you need, I could add a feature request to the AIJ developement to-do list, but unless the implementation is trivial, it may take a few months to get to the implementation. If you would like to pursue this, could you explain how you expect instrumental magnitude to be calculated?

Thanks,
Karen