YSO Bulletin
- October 2022 -

- Witch is your favourite YSO? -

V730 Cephei plummets

A couple of weeks back the Herbig B star V730 Cephei (previously known as MIS V1147) sunk to what I believe is its faintest ever minimum (though I hope I haven't spook too soon), which I caught at 16.1 visual (0.5m scope with skeleton tube), our member Peter Bealo also having seen it at 15.6 V and 16.3 B at the same time. In the months leading up to this I also observed minima of around or below 15.5 (Aug 8 at 15.7) so this might represent a new coming stage - or at least a change - in the star and its environment, perhaps the growth of planetesimals or some other drastic occurrence. These deep fades have been taking place on a roughly monthly basis and are rapid in action. One other fact of note is that over this period the star has not regained its maximum brightness of about 13 with any regularity.

Beverley Lynds

The current issue of the SFN includes an interview with Beverley Lynds (of LBN and LDN fame) who worked with, and under, many luminaries (sorry!) of stellar astronomy such as Otto Struve and Chandra Wickramasinghe, and who was, and remains, instrumental in broadening astronomical interests among all sorts of minority groups. Her work on nebulae of all types is central to the current position in YSO studies, such as the initial publication in 1962 of her catalogue of dark nebulae, from which the Dark Shark nebula in Cepheus (where else?) is number 1235.

V1180 Cas

In a Bulgarian study, results from the optical photometric observations of the pre-main-sequence star V1180 Cas are reported. The star is a young variable associated with the dark cloud Lynds 1340 (it's that lady again!) located at a distance of 600 pc from the Sun in a star forming region. V1180 Cas shows a large-amplitude variability interpreted as a combination of accretion-induced and extinction-driven effects. Data from VRI CCD photometric observations of the star are collected from September 2011 to February 2022. During monitoring, several brightness dips were recorded with large amplitudes of up to 5 mag. (I-band). At the same time, increases in brightness over periods of several weeks have also been recorded. In this paper they compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.

FUORs again

Borchert et al performed simulations of disc-disc stellar flybys and showed that pre-existing circumstellar discs around both stars result in fast rising (years) outbursts lasting 2-5 times longer than for a star-disc flyby. The perturber always goes into outburst (M > 10^-5 M☉ yr^-1) whereas they find that the primary goes into a decades-long outburst only when the flyby is retrograde to the circumprimary disc rotation. High accretion rates during the outburst are triggered by angular momentum cancellation in misaligned material generated by the encounter. A large fraction of accreted material is alien.

HOYS continues

The British-based HOYS (Hunting Outbursting Young Stars) project, instigated by Dirk Froebich, with whom some of you will have worked, now presents measurements of spot properties on 31 young stellar objects, based on multi-band data. On average the analysis for each object is based on 270 data points during 80 days in at least 3 bands. All the young low-mass stars in their sample show periodic photometric variations. They determine spot temperatures and coverage by comparing the measured photometric amplitudes in optical bands with simulated amplitudes based on atmosphere models, including a complete error propagation. 21 objects in the sample feature cool spots, with spot temperatures 500 - 2500K below the stellar effective temperature (T_eff), and a coverage of 0.05 - 0.4. Six more have hot spots, with temperatures up to 3000K above T_eff and coverage below 0.15. The remaining four stars have ambiguous solutions or are AA Tau-type contaminants. All of the stars with large spots (i.e. high coverage > 0.1) are relatively cool with T_eff < 4500K, which could be a result of having deeper convection zones.