New data-mining project - Finding the offending eclipsing binary

American Association of Variable Star Observers (AAVSO)
Thu, 10/15/2020 - 14:03

Finding the offending eclipsing binary - A data-mining project

We have added a list of 935 false positives (eclipsing binaries originally suspected as being exoplanets) from the KELT survey to VSX.
176 of them are properly identified but there are 759 that were added as "not-checked". This means that their identities need confirmation.
They are stars with close (in terms of the KELT large photometric aperture) bright companions that have been wrongly identified as the variable because a transit-like signal was detected in their photometry due to blending.
Among those 759, we have 148 objects that are perfectly suited for a novice to work with.
These ones have eventually been identified from follow up data but their coordinates have not been published in the KELT paper. Instead they just provided positions and directions pointing to the correct star. That information can be found in the remarks field of each object's page and you may use it to revise them and provide the corrected parameters.

So we have two projects here:

A) Identifying the eclipsing binary following the remark

This is the easiest and most straightforward project.

1) Go to the VSX search page and unfold the dropdown menu in the Special searches section at the top of the page.

2) Select "Finding the offending eclipsing binary..." and click on Go.

3) Go to the star's detail sheet and look at the remark. Identify the object on an image according to its separation and direction from the contaminating bright star. We recommend to use Aladin to easily find the target.

4) Use VSX external links to go to VizieR and find a star that matches the coordinates determined from the image.

5) Confirm the identification by looking at different surveys photometric data (keep in mind each survey's resolution to check if splitting the two objects is possible at the given separation. More info on surveys resolution in the VSX FAQ page). You can use the VSX external links to find survey data. ZTF DR3 data and TESS data can be used too but keep in mind that you won't be able to identify objects with TESS due to the large pixel size.

6) Once the existence of eclipses is confirmed, revise the entry adding the Gaia DR2 position of the star. If you can, combine survey data to confirm/improve the elements. Periods are likely twice the value currently given in VSX. Revise the range/amplitude too. The eclipse duration is underestimated in the source catalogue so you can also determine an improved value.

7) Add other names from VizieR catalogues or SIMBAD.

8) Check VizieR to see if the star is included in the ATLAS catalog of variable stars.
If so, you should replace the current KELT primary name by the ATO identifier, add A. N. Heinze et al. (ATLAS) as discoverers and list their paper in the references.

Reference name:  Heinze, A. N.; et al., 2018, A First Catalog of Variable Stars Measured by the Asteroid Terrestrial-impact Last Alert System (ATLAS)
Reference bibcode:  2018AJ....156..241H

9) Mention all you changed in the Revision comment (and add proper references in the References section)

Read more on how to properly revise or submit objects to VSX:

VSX Manual
VSX FAQ page

B) General: confirmation of all not-checked KELT stars (taking the chance to get used to VSX searches...)

1) Go to the VSX search page and click on the More button twice to get extended search options.

2) Write KELT% in the Name field at the top of the form.

3) Scroll down to find the four different variability classes near the bottom. Check the "Not checked" box and uncheck all the others.

When you get the results:

4) Click on an individual star link to get to its VSX detail sheet. If there is a remark indicating distance and direction to the actual EB, jump back to project A.

5) Download survey data on it and confirm its identification. If you find the object to be constant, investigate nearby objects until you can identify the true variable.

Proceed the same way as in the previous project's point 6.