When reporting eclipsing binary photometry data to the BAA or AAVSO, the simplest way is using ASTAP. It can produce files to upload in both formats, which is the easiest and quickest way to upload bulk data.

Choosing a star and capturing data is described in this article: How to record an eclipsing binary transit light curve

After you have installed ASTAP these are the steps:

1. Add your lights, darks and flats

Drag your light files into the Lights tab. Do the same for the Darks, Flats and Flat darks. If you already have masters then you can use those instead.

Note that we sometimes use 50% subframes for targets that require a small area and lots of subs (vastly reduce the filesize) so you’ll need to have appropriately sized calibration frames too.

If you already have fully calibrated and aligned frames (eg from a Seestar) you can skip the Calibration and Alignment section and go straight to Photometry. You may still need to do the Alignment though, depending on what you have.

2. Calibrate and Align the frames

Because the variable and comparison stars will have moved slightly from frame to frame, as well as calibrating you will need to align them too.

From the Stack method tab select Calibration and alignment only.

On the Alignment tab select Star alignment

Click on the STACK button.

3. Do the photometry

After the calibration and alignment has been done you should see new files under the Results tab. Highlight all the files , right click and select Copy selected images to tab Photometry.

On the Photometry tab, double click on the first image and you should see it in the viewer window. You can adjust the Histogram levels to improve how the images looks. Click on the Solve button to platesolve the image and then Save new header.

You will see that there are 3 items on the image now, asking you to select the Variable star and 2 Comparison stars, Check and 3. To chose these correctly you will need to use a finder chart, prepared with VSP – the AAVSO Variable Star Plotter. There is one other “neat” way of doing this which sometimes works: setting the Annotation to “Annotation online DB mag 13/15” on the Photometry tab. This means it will download annotations directly from the AAVSO and annotate the variable and comparison stars for you. (It doesn’t always work because the data is not always available – or can take some time.)

In any case you should always set the Database to Online Gaia -> V (assuming you are using a V filter).

If the annotation download has worked (and it usually does) then after platesolving, select Tools -> Variable star annotation. This will mark any variable stars and comparison stars, as listed in the AAVSO database. Yellow text is for variables and green for comparisons.

Now we need to select the Variable, Check and 3 stars. Choose comparison stars that are close in proximity, brightness and colour to the variable. Left click to cycle through them and select. This shows the ones chosen here:

You should choose Aperture and Annulus values to appropriate sizes (not clear how to know what sizes these are this until after the photometry when they show up on the image! so possibly select large sizes initially).

To run the photometry, go back the Photometry tab and click on

This will run through all the files and do the photometry.

4. Produce the reports

If everything works as it should then you can now produce the report files in either AAVSO or BAA format. Click on the AAVSO report button on the photometry tab. This dialog will be displayed. The red line shows the variable star data, the green and blue are the comparisons. As you can see, there is variability although it is not shown well here. Other graphing tools (spreadsheet) can show it better, or AstroImageJ.

  • Check that your Observer Code is correct (it will be different for AAVSO and BAA)
  • Check the variable name is exact
  • Select the Check star you used (should be automatically selected)
  • Check correct filter
  • If you want a BAA format report, select the BAA style check box
  • Select report to file

You should now have a text file in the same folder as your lights in the right format. If you are doing a BAA report straight after an AAVSO one, rename the AAVSO one first otherwise it may get overwritten. You will also get a .png file with the above dialog saved to it.

You can also import the report file into a spreadsheet and use it to produce nicer charts of the variability.

You can now upload the text file to the AAVSO (WebOBS – Observation Files) or BAA (Photometry Database) as described on their websites. You will need accounts for both systems.

Mark Phillips