General Photometry Questions

[R L Togni]

I have taken subs with my Seestar and entered them directly into the Photometry tab. I converted them to TG and solved per your instructional video of a few years ago. Results came out very good comparing with visual and V filter results in AAVSO Light Curve. I used the AAVSO reporting feature and it reported each sub. Is there a way to just report the mean? or should I stack first and then solve? or take the mean given after calculating magnitudes of the variable, check, and comp star. and report manually. I don't think stacking works in the Photometry tab. Thanks. Wonderful program for stacking and I'm just beginning to understand the many features.

[han.k]

Hi Robert,

Thanks for the feedback. Stacking is normaly only done when the variable star is very faint and difficult to detect. In the photometry tab you could stack the images in groups using the popup menu. This is done to improve the signal to noise ratio.

If your observing a long period variable where the magnitude doesn't change in a night, you still better report the individual value of each image so the quality of the measurement can be judged later.

cs Han

[R L Togni]

When I try to establish Variable, Check, and Comparison stars it isn't giving me a V or Ck or 3 any more? And there doesn't seem to be a way to change it if you decide to use different stars. I just downloaded the 4/30/25 version., but I think I had messed it up before that. Thanks

[han.k]

Hi Robert,

That is correct. In mode "manual selection" you can select up to 10 stars. The sequence doesn't matter. They do no get a marking except the purple circle. Once you have pressed the play button you can select in the report the variable, check and comp stars as you like. Note you can select more then one comp star. The reported standard deviation in the report helps you to select the proper check and comp stars.

In the same way you can select mode "measure all annotated".

Cheers, Han

[R L Togni]

Thanks Hans, That works really well. I finally got some clear skies and tried a few more with good success. I found with my 10 second Seestar images that Mag 7 or 8 stars are oversaturated and don't have any comparison in the small seestar field, so I am limited to about mag 9 to mag 13. I also stacked a group of total subs - 1. That was a work around because play button doesn't seem to work with one entry. Then when I did the AAVSO report I unchecked the 1. I got a better error and one submission for an LPV. Attached is my workflow. If you see anything wrong please let me know.

[R L Togni]

I had one more subject. I just took VPHOT course . My instructor said my submission looked good but wondered why I used Gaia vs AAVSO Comparison stars. I'm not sure ASTAP has that option. I loaded the AAVSO Variable star database installer. It loaded but I don't see an option to use it. It is just variable stars and not the comparison stars though. Also attached my workflow I forgot to attach.

[han.k]

Hi Robert,

If you uncheck "Ensemble local database" you can select the AAVSO comparison stars starting with 000-. See screenshot.

For brighter stars then magnitude 9, just unfocus a little. Then you can measure brighter then 9. Unfocus a little is always better because you use more pixels and unequality is averaged out. If you unfocus too much the star detection could fail. (HFD 10 or larger).

With respect to saturation. ASTAP takes default the brightest pixel measured as the limit before saturation occurs. You can force it to except pixel values up to 64000 with the check mark "Hi satuation value" (tab photometry, just above the report button. Do this only if your sure the image pixel values can reach above 64000. Just measure a bright star at a long exposure.

Saturation will also be visible in the star profile curve. See viewer option View, Star profile. Activate it and move the mouse cursor to a star. The profile of star r is then displayed in the north-east indicater of the viewer. If the top is flattened then it is saturated.

I looked briefly to the work flow and it looks okay.

Cheers, Han