YSO Bulletin
- May 2022 -

- ULYSSES continuation -

Three more Stars

The ULYSSES campaign on young stars moves South again, just in time for all you antipodeans! Sequences exist now for all three, with the campaign on TW Hya ending very soon. However - this is an important object in the YSO world so please continue to follow it as part of your normal observing programme. That goes for the others as well of course. Periods below are the times scheduled for HST observations. Details on the individual stars can be found through VSX.

TW Hya
Start time: 25 Apr 2022 11:15:55
End time: 25 Apr 2022 12:09:21
Start time: 26 Apr 2022 09:28:27
End time: 26 Apr 2022 10:21:53
Start time: 27 Apr 2022 04:31:22
End time: 27 Apr 2022 05:24:48

SST c2d J161243.8-381503
Start time: 27 Apr 2022 16:00:40
End time: 28 Apr 2022 07:27:30
Start time: 28 Apr 2022 12:40:04
End time: 28 Apr 2022 15:07:45

Sz 103
Start time: 28 Apr 2022 15:50:27
End time: 29 Apr 2022 03:49:03
Start time: 29 Apr 2022 12:29:54
End time: 29 Apr 2022 16:33:04
Start time: 30 Apr 2022 03:01:34
End time: 30 Apr 2022 05:17:34
Start time: 30 Apr 2022 12:20:01
End time: 30 Apr 2022 16:23:10

Sz 129 (new target)
Posn: 15 59 16.471 -41 57 10.30 V=12.0
Start time: 30 Apr 2022 17:05:54
End time: 01 May 2022 06:39:55
Start time: 01 May 2022 13:45:20
End time: 01 May 2022 20:57:58

Fred Walter, whose campaign this is, says: "it is important to get single BVRI sequences each night, but longer sets of data would be useful if they can be obtained simultaneously with the HST observations. Remember, there will not be any TESS photometry, so we will construct a high-cadence light curve from lots of individual measurements at different sites. In all cases, there is little point getting lots of data past the end time of the last HST observation, though one point after the HST end time will help us interpolate through the HST window. I intend to get nightly high-dispersion spectra extending through the night after the last HST observations."

Fruits of Research!

Understanding the chemical past of our Sun and how life appeared on Earth is no mean feat. The best strategy we can adopt is to study newborn stars located in an environment similar to the one in which our Sun was born and assess their chemical content. A study by Bouvier et al found that in particular, hot corinos (inner envelope regions around YSOs) are prime targets since recent studies showed correlations between interstellar Complex Organic Molecules (iCOMs) abundances from hot corinos and comets. The ORion ALMA New GEneration Survey (ORANGES) aims to assess the number of hot corinos in the closest and best analogue to our Sun’s birth environment, the OMC-2/3 filament. In this context, they investigated the chemical nature of 19 solar-mass protostars and found that 26% of the sample showed warm methanol emission indicative of hot corinos. Compared to the Perseus low-mass star-forming region, where the PErseus ALMA CHEmistry Survey (PEACHES) detected about 60% of hot corinos, the latter seem to be relatively scarce in the OMC-2/3 filament. While this suggests that the chemical nature of protostars in Orion and Perseus is different, improved statistics are needed in order to consolidate this result. If the two regions are truly different, this would indicate that the environment is likely playing a role in shaping the chemical composition of protostars.

More on EXORs and FUORs

An interesting paper by Fischer et al discusses accretion phenomena, saying "Variable accretion in young stellar objects reveals itself photometrically and spectroscopically over a continuum of timescales and amplitudes. Most dramatic are the large outbursts (e.g., FU Ori, V1647 Ori, and EX Lup type events), but more frequent are the less coherent, smaller burst-like variations in accretion rate.
Improving our understanding of time-variable accretion directly addresses the fundamental question of how stars gain their masses. We review variability phenomena, as characterized from observations across the wavelength spectrum, and how those observations probe underlying physical conditions.
The diversity of observed lightcurves and spectra at optical and infrared wavelengths defies a simple classification of outbursts and bursts into well-defined categories. Mid-infrared and sub-millimeter wavelengths are sensitive to lower-temperature phenomena, and it is currently unclear if observed flux variations probe similar or distinct physics relative to the shorter wavelengths. We highlight unresolved issues and emphasize the value of spectroscopy, multiwavelength studies, and ultimately patience in using variable accretion to understand stellar mass assembly."
In this regard, just a couple of days ago I had a note from our member John Pickett that the YSO V347 Aur had entered another outburst, so please follow this one!

Accretion... Take 2

An Italian study describes an optical/near-IR survey of 11 variable young stars (EXors and EXor candidates) aimed at deriving and monitoring their accretion properties. About 30 optical and near-infrared spectra were collected between 2014-2019 with the Large Binocular Telescope (LBT). From the spectral analysis they have derived the accretion luminosity and mass accretion rate, visual extinction, temperature and density of the permitted line formation region, and the signature of the outflowing matter. Two sources (ASASSN-13db and iPTF15afq) have been observed in outburst and quiescence, three during a high-level of brightness (XZ Tau, PV Cep, and NY Ori), and the others in quiescence. These latter have accretion luminosity and mass accretion rates in line with the values measured in classical T Tauri stars of similar mass.
All sources observed more than once present accretion variability. The most extreme case is ASASSN-13db, for which the mass accretion rate decreases by two orders of magnitude from the outburst peak in 2015 to quiescence in 2017. Also, in NY Ori the accretion luminosity decreases by a factor 25 in one year. In 80% of the sample we detect the [OI]630 nm line, a tracer of mass loss. They also conclude that mass accretion variations are larger than mass loss variations.