YSO Bulletin
- July 2023 -

- Campaigns Under Way -

V347 Aur campaign

AAVSO Alert Notice 830 announces a new campaign for a YSO. Drs. Michael Richmond (Rochester Institute of Technology) and Nicolas Grosso (Laboratoire d'Astrophysique de Marseille) request AAVSO observers' assistance in monitoring the Young Stellar Object V347 Aur in support of XMM-Newton observations scheduled for August and possibly October.
V347 Aur is a young low-mass star transitioning between an evolved protostar and a classical T Tauri star that exhibits quasiperiodic (~155 days) optical outburts, displaying in the V band peak amplitudes from ~1 to ~4 mag above the quiescent level at ~15.8 mag.
These optical brightenings likely signal the onset of rapid mass-infalls, magnetically channelled from the accretion disk onto the stellar surface, which may also produce X-ray outbursts from star-disk magnetic interaction. Dr Richmond says "We predict for V347 Aur an optical high-state in 2023 mid-August with a return to the quiescent phase in 2023 October. Our aim with the AAVSO observations is to monitor the long-timescale behavior of this outburst in the V and B bands and to compare it with the V (plus U and B shorter) time series that will be obtained with the XMM-Newton Optical Monitor and the simultaneously X- ray emission that will be obtained with the XMM-Newton EPIC cameras.
Beginning immediately, please observe V347 Aur a few times per night, with observations spaced about an hour apart to detect rise/decay trends. Please continue these observations on as many nights as possible until about one month after the second XMM-Newton observation (i.e., the expected campaign end date is November 1). Dr. Richmond asks for this cadence in order "to determine the shape of this outburst (the duration and intensity of the outbursts cannot be predicted)."
Johnson V and B (V prioritized) coverage is requested, with observers alternating between the two if possible to obtain nearly simultaneous B-V data. DSLR TB, TG, and TR observations are also welcome. Visual observations are also requested - even upper limits would be helpful. Unfiltered observations are NOT requested. CCD observers should consult the full text of AN 830 for a note about a specific comparison star.

V1117 Her again!

Just 2 days before going to press, I had notice of a new fade taking place. Latest estimate is 13.9 (Gary Poyner, UK) after John Pickett made it 13.5 two days earlier - so this looks like a major dip. These have tended to become fainter with time, so keep an eye out to see how things progress!

Get ready for AB Aur!

At a recent section leaders' meeting - these are great for getting hot news by the way - I learnt that Hubble is due to observe AB Aur this autumn. Steve Shore who runs the spectroscopy group thought that because AB is so bright (it's a binocular star!) amateur spectroscopists could get results from it. Steve said that it's an ideal target for small telescope echelle observations and is also easily done with single gratings.
AB Aur has a very active circumstellar disc producing H-alpha emission, is one of the closest YSOs to us and is also in the process of forming planets!

Circumbinary Discs

A study by Elsender et al reports an analysis of circumbinary discs formed in a simulation of star cluster formation. It considers both pure binary stars and pairs within triple and quadruple systems. The protostellar systems are all young (ages < 10⁵ yrs). They find that the systems that host a circumbinary disc have a median separation of about 11 AU and the median characteristic radius is about 64 AU. They further find that 89 per cent of pure binaries with semi-major axes (a) under 1 AU have a circumbinary disc, and that the occurrence rate of circumbinary discs is bimodal in pure binaries with a second peak at about 50 AU. Systems with a > 100 AU almost never have a circumbinary disc. The median size of a circumbinary disc is between about 5 − 6 times the semi-major axis size, depending on the order of the system, with higher order systems having larger discs relative to binary separation. They find that the underlying distribution of mutual inclinations between circumbinary discs and binary orbit of both observed and simulated discs to not differ statistically.