YSO Bulletin
- September 2024 -

- Two recent events -

AB Aurigae

I was recently informed by our member Cledison Marcos da Silva in Brasil that according to the BAAVSS the bright YSO (and planet-forming system) AB Aurigae has undergone a fade from its usual maximum of about 7.0 down to around 8.0 after estimates by John Toone. This system is bright enough for amateur spectroscopy and so the spec group at AAVSO was also contacted with the news.

V1490 Cyg

This time we have Cledison's own observations of a rather fainter object! A few years back the AAVSO ran an observing campaign on this T Tau star which is in the famous Pelican Nebula, and the PI Dirk Froebrich said that "We have recently discovered that the young star V1490 Cyg... is periodically occulted by material in its circumstellar disk. Our light-curves indicate a period of about 32 days, and the obscurations are comparable to UX-Ori type eclipses. We will be conducting a six-week, high cadence, multi-wavelengths optical monitoring campaign (in BVRI) of this source to map out in high resolution the azimuthal distribution of the material in the disk around this young star."

Cledison's observations show a fall from around 15.4m to 16.7 which is consistent with the existing data on the object. An exhaustive paper on the star featuring input from both amateur and professional bodies was produced by the Open University (with whom I was studying for a time) and is well worth reading.

More EXORs

V1118 Ori is a classical EXor source whose light curve has been monitored over the past thirty years (although not continuously). It underwent a powerful outburst in 2005, followed by ten years of quiescence and a less intense outburst in 2015. In 2019, a new intense brightness increase in the g band by about 3 magnitudes was observed, and this new accretion episode offers the opportunity to compare the photometric and spectroscopic properties of different outbursts of the same source.
This allows one to highlight differences and similarities among different events by removing any possible bias related to the intrinsic properties of the star-disk system. The investigators discovered the 2019 outburst by examining the g-band light curve acquired by the ZTF and followed the decreasing phase in the griz bands. Two near-infrared spectra were also acquired at different brightness stages with the Large Binocular Telescope. The most recent event shows an amplitude similar to the 2015 event and lower than that in 2005 but a duration of less than one year as in previous events. The rise (decline) speed is different from previous cases, and with few exceptions, the near-infrared lines are the same as those observed in 2015. The mass accretion rate peaks at 10^-7 solar mass per year and decreases in about a month to a few 10^-8 M☉.
Their analysis shows that the comparison of data from different outbursts of the same source is a non-trivial exercise, which allows obtaining important clues useful to drive theoretical efforts towards a better understanding of the EXor phenomenon.