Re: Multiplot magnitude issue

Posted by ChristopheM. on Feb 17, 2016; 9:07am
URL: http://astroimagej.170.s1.nabble.com/Multiplot-magnitude-issue-tp267p347.html

Karen,

A few questions about magnitudes and plotting.

The issue is : how can we get a direct plot in magnitude ?

Magnitude measurements are easy to obtain in the measurement table, following your different posting on this subject, thanks for that. Now,  I would like to get a plot automaticaly scaled and labelled with proper magnitude scale/legend on it. I suspect this could be made under AIJ plotting facilities, but didn't found the right way to do it.

What I did to draw the following plot was to pick up the max and min  magnitude value  (source_AMag_T1) in the mesurement table , and then to adjust the scale and « then shift » in order the T1 light curve match the custom predefined Y scale in the multi-plot main. My variable varies between 9.97 and 10.56 in magnitude during observation/sequence (source_AMag_T1).

The plot seems ok at first sight, but still, this is an arbitrarily scaled and shifted one.

Plus, I would like to add an airmass detrended plot for comparison purpose, which I did. But I would like this detrended measurement also to be added as a new column and saved.
Because my target was low above the horizon, this data are essential and must be considered as true brightness of my target.
What is the proper name of the column in the table of measurement, if any ; I couldn't find one matching this requirement but I could have missed it, I confess. Maybe it is already there.

I understand source_AMag_T1 is the observed real flux – sky, converted in mag, but it's not the « absolute » magnitude (as if observed from space) ; that's why I added an airmass detrended plot. Is my understanding correct ?

Finally, I added a comp to the plot (also manualy shifted and scaled) just for showing the error bar growing as the star gets lower in altitude. Incidentaly, when the comp star is plotted at the same scale than that of T1, the error bar is just enormous, how can it be ?

Ps : sorry  about the images : iIdont'know how to add them to this message. I can send you privately, if needed.

That's all for today;-)
Thanks for any answer,
Cheers,
Christophe