YSO Bulletin
- November 2023 -

- Observational Edition -

AB Aur... and more

This month saw the announcement of an observational campaign on, first of all, AB Aurigae and its forming planet(s). This is a continuing campaign on the star from the HST team headed by Dr. Lauren Biddle, who gave an AAVSO webinar on the project last week (mid-November 2023). She writes: "we [would like] a complete and accurate understanding of the star’s accretion activity and the behavior of its variability, including bright massive accretion events and rare dimming events". Observations with H-alpha filters are ideal but basically longer-wavelength filters are preferred. With the rising prominence of spectroscopy in AAVSO circles, this is also very welcome, especially as AB Aur at 7th mag will be a good target for amateur equipment.
As was outlined at the webinar observers should use the comp star labelled 104 (use a d scale chart, not e scale as in the linked document) exclusively if possible. And although the observations for this campaign are CCD rather than visual there is of course nothing to stop visual observers from following AB Aur and its YSO companion SU Aur, especially as SU Aur has shown some unexpected behaviour over past years.

Another Campaign

Actually just ended is another campaign on 5 Winter YSO's, most of which are AAVSO legacy stars - RY Tau, UX Ori, RR Tau, CO Ori, and R Mon. The idea was to get optical observations for correlation with a large spectroscopic study at the Spanish site of Calar Alto.
While we have improving knowledge of star formation processes among Sun-mass (T Tauri) stars, the objects in this study are a step up in mass, and our knowledge of their starforming details is rather more sketchy; and although by the time you read this this particular study will have run its course, I have included mention of it here to stress the importance of following even legacy stars - something that the study team in fact mention. Many of those objects are highly active and observations going back years can be every bit as valuable as current ones - witness the historical behaviour of RW Aurigae where AAVSO observations are sometimes the sole source.

Stars to Follow

Whilst on the subject of old-fashioned variable stars (surely an oxymoron!) there have been observational reports of a fade on CO Ori - one of those stars studied in the above campaign by the way - by our doughty fademeister John Pickett. It also appears that the YSO V373 Cep has undergone a bit of a protracted fade to about magnitude 13½ and there is a suspicion that the nebulosity around RY Tau may be showing some activity.

More T Tau's

A study by Spanish astronomers examined a list of 63 T Tauri candidates in the Taurus-Auriga Molecular Cloud identified by their ultraviolet and infrared colours, measured from data obtained by the Galaxy Evolution Explorer all sky survey (GALEX-AIS) and 2MASS. The objective is twofold: evaluate whether they are pre-main sequence (PMS) stars, and evaluate the ability of the UV-IR colour-colour diagram to detect PMS stars in wide fields. The astrometric properties of these sources have been retrieved from the Gaia DR3 catalogue and used to evaluate their membership probability. Several classification algorithms were tested to search for the kinematical groups but the final classification has been made by other methods.
In addition, spectroscopic information available in the archive of the Large Sky Area Multi Object Fiber Spectroscopic Telescope has been used to ascertain their PMS nature when available. About 20% of the candidates share the kinematics of the TAMC members. Among them, HD 281691 is a G8-type field star located in front of the cloud and HO Aur is likely a halo star given the very low metallicity provided by Gaia. The rest are three known PMS stars (HD 30171, V600 Aur and J04590305+3003004), two previously unknown accreting M-type stars (J04510713+1708468 and J05240794+2542438) and five additional sources, which are very likely PMS stars. Most of these new sources are concentrated at low galactic latitudes in the Aur-Per region.

DQ Tau

DQ Tau is a unique young high-eccentricity binary system that exhibits regular magnetic reconnection flares and pulsed accretion near periastron. The July 30, 2022 periastron event was used to characterize X-ray, NUV, and optical flaring emissions. X-ray super-flares accompanied by substantial NUV and optical flares were seen, consistent with previous discoveries of periastron flares in 2010 and 2021. These observations, supported by new evidence, strongly establish the magnetosphere collision mechanism as the primary driver of magnetic energy release during DQ Tau’s periastron flares. The energetics of the observed X-ray super-flares remain consistent across the three periastrons, indicating recurring energy sources during each passage, surpassing the capabilities of single stars.
The current study is part of a broader multi-wavelength campaign, which is planned to investigate the influence of DQ Tau’s stellar radiation on gas-phase ion chemistry within its circumbinary disk.