Transcript

ALAN:

Here we are in the FITS photometry tool. I've got some instructions at the top. And the first thing that I need to do is to open one of the FITS images that I've downloaded from telescope.org.

So I can do that from the Load File window. I can drop an image on here. Or I'm going to click Open FITS file and select the file from a list. So here are my images of variable star EA3. I'm going to open this one, 322184.

And here I've got my image in the viewing window. I've got some information about the image, which I can check here. The date and time, make sure that's what I expected, the coordinates of the star. And importantly, the exposure of the image, 16 seconds for this image, which corresponds to what I expected.

And this is for variable star EA3, which we might recognise from the finder charts is this star here in the centre with this V-shaped formation of stars, easily recognisable. And the reference star over here. And I can use the scroll wheel to zoom in if I want to do that just to confirm. Here's my target star and here's my reference.

Now in order to measure the brightness, I'm going to move these little selection targets, one for the target, one for the reference star, onto the appropriate stars. And again, let me just zoom in here. We can see that for the target I've got the little rings. The software is going to measure the brightness of all the pixels in the central ring and subtract off the background in this outer annulus here, this outer ring.

So I can change the size of these rings. I can change the inner ring. I can change the size of the gap between the inner and outer rings. Or I can change the width of the annulus.

And for this image, I found that values of 10 for each work quite well. You may need to adjust those depending on how large the stars are in your image. So I'm going to move the target rings onto the target star, which is this one, the top of the line of three here, the right-hand one of those.

So I'm going to move the target onto there until the star is centred in the central ring. And the first thing I want to check is that the exposure of my image is OK, which I can do over here by looking at the maximum value 27,637. So that's absolutely fine. It's between 10 and 50,000. So that's OK.

And now I've positioned the target. I've got a readout of the brightness of my target star here, target flux. So all we need to do now is to position the other selection rings onto our reference star, which we'll remember is this one with a fainter star next to it, and this pattern of three stars above it.

And so, I'm just going to move the reference rings until that's centred on the reference star like that. And now I've got a value for the ref flux of the reference star as well. And the maximum value, again, is between that 10 and 50,000. So that's all correctly exposed. The exposure is absolutely fine.

So I'm now going to go ahead and record my observation by selecting Plot Data. And this will send the data to the star plotting software. So I just click on Plot Data, and that gives me an option there.

The data have been added to the light curve plot. I can go to view the plot straight away, or I can press OK and view the plot at a later date, which is what I'm going to do now. And that's the measurement made for this image.