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YSO Bulletin
- Mayday! Mayday! Follow this star -

For this month only I am going to be self-indulgent and dedicate the issue to one star only, and one that I feel should have more observers, both visual and electronic. That star is just rising at a decent hour round about now, and its name is V1117 Herculis, which was originally classed as a Mira variable, thus adding to the list of YSOs that were previously thought to be something else. For many reasons it is a very important object and I urge you to consult the couple of papers mentioned at the end if you want to find out more.
So - what is so special about it? First, its lightcurve as well as its spectrum (type A) looks like a typical UXOR, with its semi-regular fading episodes, but its position on the sky is highly peculiar, being over 30° from the plane of the galaxy, where the vast majority of star-forming material is found. True, UX Orionis itself is at a similar galactic latitude but all the intervening space between it and the galactic plane is taken up with the huge starforming region that includes M42 and friends, so the two in that sense are not comparable. But the really weird thing is its proper motion. It might be thought that V1117 was born in a starforming region and has since moved away (even though you may have spotted a problem there too) but in fact the opposite is true - it is actually heading towards the galaxy, not away from it!
One question may present itself here - is V1117 Herculis not a YSO at all? It was, after all, thought to be a pulsating star. There are several reasons to discount this possibility, the most obvious being the lightcurve. Below is the smoothed 2000-day activity of the star at 10-day means, and you can see that it looks:- (1) Unlike a pulsating variable (2) Very like a YSO! Add to that a recent study by Konkoly Observatory in Hungary using data from GAIA which said
'We performed a detailed analysis of the variable star V1117 Herculis. The star turned out to be a young variable with cyclic dimming events caused by the circumstellar material.'
The star also shows infrared excess which in the circumstances further suggests the presence of circumstellar material.

From the curve above there appears to be a rough period of 400 days to the fades, though they are - as would be expected - hardly occurring on a predictable basis, and there are additional irregularities, most un-Mira like! Likewise, slightly away from the astrophysics again, if you are going to observe this star there is something to bear in mind. V1117 is located near an 8th-magnitude star, seen in the chart snippet here (N at top). Be very careful not to confuse the 8m - 120 - 123 arrangement with the 8m - 123 - 132 group, since they look very similar to one another. As an additional check, note that comp 129 makes an isosceles triangle with 120 and 123.
There is another difference between early-type YSOs, the so-called HAeBe's and (say) their T Tauri type brothers. V1117 Her is not part of a starforming region and is not associated with nebulosity. We find large collections of lower-mass, cooler stars in areas like the Taurus-Auriga starforming region where there is nebular material, whether bright or dark. Hotter YSOs, such as V730 Cep and UX Ori itself, may not be intimately involved in nebulae but they are in OB-associations (large groups of hot, massive youngish stars). Our featured star here however is a true self-isolator - and it maintains its seductive aloofness by presenting us with a series of mysteries, which conituned observation may help to unravel.
Stay safe everyone.

Two High-latitude UXORs