EPIC210744182 to EB or not to EB?
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Ptd
Possible EB but is it? VSX says otherwise
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Ptd
Folded at .3825 days
Skyview of this patch of sky, but according to NEA none of the other stars within 150 arc seconds have available LCsBut VSX has this star listed, with about the same period but not apparently as an EB?
0.00 Variable HAT 259-0002908 -- 03 43 18.93 +19 01 14.3 Tau ROT 0.38425590 10.98 J (0.099r)
This is what the VSX site says about the ROT classification?
"ROT
Spotted stars that weren't classified into a particular class. All the SPOTTED stars in the UNSW list and the very small amplitude spotted stars found by Kepler are included here. Also, some stars that don't fit the current subtypes due to their physical properties have been classified as such (brown dwarfs and white dwarfs with spots). It may be used as a subtype when a T Tauri star shows rotational variability (TTS/ROT, CTTS/ROT or WTTS/ROT)."Posted
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Ptd
in response to Ptd's comment.
In light of VSX saying this is star spots rather than an EB I've had another go at folding this LC, this time at .38424 days
This is the whole LC which its hard to pick detail out of
This is some of the cleaner bits of the LC from the beginning middle and end of the LCIf its a star spot it doesn't look to me like its moved on the surface of the star during this period, but I don't actually know if that means anything, can someone who knows things about star spots educate me here please?
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davidbundy77
Hi Ptd, I don't know all that much about starspots, but here is what I have managed to find out.
The VSX entry is the result of a single survey by Hartman et al in 2010 of rotational periods of stars in and around the Pleiades cluster. This star is not mentioned explicitly in the paper, but does have an entry in the supplementary data which is the source of the VSX listing. The star is apparently not a member of the Pleiades cluster. Unfortunately very little else is known about this star. In particular, it is not listed on SIMBAD.
As far as starspots are concerned, sunspots usually last less than a month, but T-Tauri stars can apparently have spots which can remain stable for years (see for example Bradshaw and Hartigan) which seems to be what the survey above is suggesting.
My initial reaction on seeing this light curve was also that this could be an eclipsing binary, but I suppose we will have to rely on the better knowledge of the professionals.
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Ptd
Hi davidbundy77 MT for pointing me at these papers. If I've read that Bradshaw and Hartigan paper correctly, then the bigger a star spot is, the longer it lasts magnetically, and that the faster a star spins the less likely it is that a big spot will get torn physically apart by the star's rotation. And that while a 10% dimming of a star is towards the upper end of the range, its doable for these stars. So this star spot, if that is what it is, could well be there for decades. Also apparently it makes it easier for the professionals to study these extra solar star spots, if said star also has a transiting planet, something about it being easier to map the surface of the star, but it didn't say why. So we'd best keep our eyes pealed for those then 😃
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davidbundy77
The possibility of mapping long-lived starspots using exoplanet transits is intriguing. I suppose the idea is that when an exoplanet passes in front of large spot, the total brightness should increase because the exoplanet blocks less light than when it passes in front of another part of the star. To get a good map would however require shorter cadence measurements than the usual 30 minute snapshots from Kepler.
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