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YSO Bulletin
- 1 September 2020 -

- Successful YSO Webinar -

Webinar online

Yesterday (I write this on 30th August) we had a really good webinar, attended by lots of people from around the world, including a high proportion of participants who are not members of the section, which is a very good prospect for its future. We now have several professional astronomers on our mailing list, which has always been one of my aims. Two of these of course were in attendance at the webinar, profs Bill Herbst and Bo Reipurth, who I like to think of as the Bach and Beethoven of YSO studies (I won't say which is which!)
You can now find the complete presentation online here, and I'm pretty sure it will be up on the AAVSO's youtube channel soon. The channel also features past presentations apart from many other things.

Disc Alignments?

A recent Japanese study looked at spatial correlations among proto-planetary disk orientations, which can carry unique information on the physics of multiple star formation processes. They selected five nearby star-forming regions feauting several protoplanetary disks with spatially-resolved images with ALMA and HST. They applied tests to examine the statistical uniformity of the PA orientation. The disks located in the star-forming regions, except the Lupus clouds, do not show any such signature, supporting a random orientation. Examination of 16 disks in the Lupus III cloud however, exhibit a weak and possible departure from the random distribution, and the inclination angles of the disks are not uniform as well. Furthermore, the mean direction of the disk PAs in the Lupus III cloud is parallel to the direction of its filament structure, and approximately perpendicular to the magnetic field direction. The absence of a significant alignment of the disk orientation is consistent with the turbulent origin of the disk angular momentum. Further observations are required to confirm/falsify the possible disk alignment in the Lupus III cloud.

A new high-mass YSO

Massive molecular clumps fragment into cores where star formation takes place, hence star-forming studies should be done at different spatial scales. Using near-IR data obtained with a mass of sources including public surveys, a team from South America performed a deep study of the YSO G29.86−0.004 at core and clump spatial scales which revealed a host of organic molecules. The near-IR emission shows two nebulosities separated by a dark lane, suggesting a typical disk-jets system, but highly asymmetric. They are likely produced by scattered light in cavities carved out by jets on an infalling envelope of material. The CH3CN emission concentrates at the position of the dark lane and appears slightly elongated from southwest to northeast in agreement with the inclination of the system as observed at near-IR. The morphology of the CH3OCHO emission is more complex and extends along some filaments and concentrates in knots and clumps, mainly southwards of the dark lane, suggesting that the southern jet is encountering a dense region. The northern jet flows more freely, generating more extended features. The configurations can be explained by considering that the YSO is located at the furthest edge of the molecular clump along the line of sight. The detection of HCN, HNC, HCO+, and C2H allowed them to characterize the dense gas at clump scales, yielding results that are in agreement with the presence of a high-mass protostellar object.

Almost a Coup!

Just a few hours before the YSO webinar was due to take place I received a set of emails from AAVSO HQ saying that an observer had reported detection of a sudden brightening of an object in NGC7129. Remembering past rare occurrences like this (McNeil's nebula for instance) and bearing in mind that NGC7129 is an area of very intense star formation - and also cognisant of the fact that it woul even be featuring in the webinar! - I was, to say the least, interested - a new YSO to astound you all with, discovered by one of our members to boot! Unfortunately it turned out that the ASASSN survey had recorded this region and found nothing out of the ordinary. However, in the position given there is a knot of outflows from a forming star as can be seen here.
So - no actual discovery but still an interesting detection of a strange object!

RW Aur again!

One of the stars I presented at the webinar was RW Aurigae and its fadings. A Russian study has found that its companion is probably a UX Orionis star. They say:

"The secondary of the famous young binary RW Aur is much less studied than the primary. To compensate, we present here the results of UBVRIJHK photometric, VRI polarimetric and optical spectral observations of RW Aur B. The star demonstrates chaotic brightness variations in the optical band with irregular, short(~1day) dimmings with an amplitude of up to 1.3mV. The dimmings are accompanied by an increase in the linear polarization (up to 3 per cent in the I band), presumably due to the scattering of the stellar radiation by dust in the circumstellar disc that means that RW Aur B can be classified as a UX Ori type star."

They concluded that some excess emissions as well as a variability of fluxes and profiles of several lines are due to the accretion process and that emission components of Ca II lines indicate that RW Aur B has a powerful chromosphere. Assuming the solar elemental abundances, they found parameters of the star to be :

Teff = 4100−4200K
AV = 0.6±0.1 (out of the dimming events)
L* ≈ 0.6 L☉
R* ≈ 1.5 R☉
M* ~ 0.85 M☉
Macc < 5×10-9 M☉yr-1