Okay, so I was messing around with ALMA the other day, trying to get a handle on the different sizes of things. You know, like, how big is too big, how small is too small… that kind of stuff.
First, I fired up CASA, like always. Gotta have that running to do anything with ALMA data, right?
Then I grabbed some data I had lying around. I think it was some galaxy observations, nothing too fancy. I just needed something to work with.
Figuring out the sizes
So, the main thing I wanted to see was the image size. I used the `imhead` task for that. It’s pretty simple:
- I typed in `imhead`, then hit enter.
- I set `imagename` to my image file.
- I typed `mode=’summary’ and hit enter again.
Boom! It spit out a bunch of info, including the image shape (like, how many pixels in each direction) and the pixel size (how big each pixel is on the sky). That gave me a good starting point.
Next, I wanted to get a feel for the synthesized beam size. That’s basically how blurry the image is, because of the way ALMA works. You can get that with `imhead` too, but I also like to just look at the image in the viewer.
- I opened the image with the `viewer` task.
- I zoomed in and out, panned around, you know, the usual.
- There are tools there to measure the beam.
I also played around with some of the `imfit` tasks, it does a bunch of image analysis. I used it to fit a Gaussian to the beam, just to get a more precise measurement of the beam size.
Wrapping Up
After all that, I felt like I had a pretty good grasp on the different sizes in my ALMA data. And I was able to successfully finish it.
