Alignment options

[7170]

Hi, I'm confused about which alignment option is best to use for different scenarios.

I can see the following ways of doing an alignment:

(1) Align stack using WCS
(2) Align stack using apertures
(3) Align stack using image stabilizer

I do two types of work (a) double stars and measuring PA and distance between pairs, and (b) photometry on variable stars (plotting light curves over time).

For double stars I have always aligned the stack using option (2) and then combined them into a single image using average. And for variables I used to align using (2) and then plot the light curve using apertures. But more recently have note done an alignment but used "Use RA/Dec to locate aperture positions" instead.

I am however wondering if this is an optimal approach for both types of work or not - what do people recommend? One thing I have noticed is that option two does warp the image slightly - namely the x and y pixel scale is usually slightly different after plate solving, yet that is not the case with (1).

Thanks in advance.

[karenacollins]

Hi, if your images are already plate-solved, for time-series photometry I prefer the option you mentioned "Use RA/Dec to locate aperture positions". In general you can leave centroid enabled also to fine tune each apertures location in each image. Avoiding aligning the images retains the x,y centroid information in case that's helpful for post processing, or to measure the tracking/guiding performance of your observation. This approach also avoids the extract step of aligning the images. If your images are not plate-solved, then you can avoid the plate-solving process by aligning with aperture, but this step is not needed in this case either unless your tracking jumps by more than 1 aperture radius from image to image.

Karen

On 12/16/2020 4:09 PM, 7170 [via AstroImageJ] wrote:

Hi, I'm confused about which alignment option is best to use for different scenarios.

I can see the following ways of doing an alignment:

(1) Align stack using WCS
(2) Align stack using apertures
(3) Align stack using image stabilizer

I do two types of work (a) double stars and measuring PA and distance between pairs, and (b) photometry on variable stars (plotting light curves over time).

For double stars I have always aligned the stack using option (2) and then combined them into a single image using average. And for variables I used to align using (2) and then plot the light curve using apertures. But more recently have note done an alignment but used "Use RA/Dec to locate aperture positions" instead.

I am however wondering if this is an optimal approach for both types of work or not - what do people recommend? One thing I have noticed is that option two does warp the image slightly - namely the x and y pixel scale is usually slightly different after plate solving, yet that is not the case with (1).

Thanks in advance.

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