Two periods - one or two sources?

American Association of Variable Star Observers (AAVSO)
Tue, 07/17/2018 - 19:14


During my data-mining survey for variable stars around X-ray sources, I found something interesting with shorter period (< 0.5d). I use both ASAS-SN and SuperWASP data for phase plot, but only the first one to calculate period.

At first, I have found magnitude variations using SWASP data. It looked a little untypically multiperiodic for me, so I spent some more time on this one. ASAS-SN data have scatter that clearly shows there’s something variable. After putting into periodogram, the most significant period was 0.45072 days (plot no. 1). Looks good for ASAS-SN, but not for SuperWASP. I decided to find a second period (after reducing the first one) also to clarify what’s wrong with SWASP data. I got 0.35087 days which looks a worse for ASAS-SN (but definitely there are), however it’s perfect for SuperWASP (plot no. 2). Based on properties of the target (J-K= 0.65; B-V= 0.90), it cannot be a GDOR, but another source with spots (not surprising while it’s an 1RXS object). Both periods look to have different amplitude, so these must have rotational origin. An additional 0.05 magnitude flare detected by SuperWASP proves that, together with quite large proper motion value.

But what I find interesting, the main target is possibly K-type star. Periods are too short for this star to be rotationally variable. The first period is 28% longer than the second one, so the difference is quite large (like two spots on 0° and 75° latitude on our Sun). Could this come from a single (binary system) or two M-type sources (trinary system)? Gaia DR2 doesn’t find any other source, so these would be very close. Two blended stars (left for both SWASP and ASAS-SN and upper for SWASP only) are unrelated to this system (totally different proper motion).This upper star isn’t variable too (already checked on ASAS-SN, no large variations). Star on the left lies too close to separate in ASAS-SN data, but I gave a try by putting a center point a bit to the opposite side from the blended star (21 26 5.430 +55 50 24.92) and I still could find variability with that period.

Because of that, I have doubts to classify this as BY+UV or BY+BY+UV type.

Here’s some data if they become useful:*%20IC%201396%20%20%20%20SBZ%20%201-15&submit=submit


Gabriel Murawski

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