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YSO Bulletin
- December 2020 -

- No Pretty Pictures but Two Pro-Am Campaigns instead! -

First Campaign

Dr. Fred Walter (Stony Brook University) requests AAVSO observers to monitor 13 Northern T Tau stars in support of a multi-site multiwavelength campaign being carried out in November and December. He provides the following information:
The HST ULLYSES project (Ultraviolet Legacy Library of Young Stars as Essential Standards – ); is designed to obtain a statistically complete catalog of ultraviolet observations of a set of galactic stars while the HST can still obtain UV spectra. Our interest is in a sample of T Tauri stars. This AAVSO campaign will be part of a larger program called ODYSSEUS (Outflows and Disks around Young Stars: Synergies for the Exploration of Ullyses Spectra), which includes ground-based optical and near-IR photometry and spectroscopy.
The first part of this project involves obtaining UV spectra of 13 stars in the Orion OB1 and σ Ori star forming regions in November/December 2020. These targets will be observed with the HST while they are in the TESS field of view. TESS gets broadband (600-1000nm) optical photometry on a 10 minute cadence for typically 27 days. The HST will obtain ultraviolet spectroscopy. The goal of this observing campaign is to supplement the TESS photometry with filter photometry. It is hard to beat the time coverage of the S/N of the TESS data, or the continuous 27 day cadence, but AAVSO observers can get the color information which helps distinguish the possible causes of brightenings and fadings in the light curve, which may include magnetic flares, enhanced accretion rates, starspots, and obscuration by a warped dust disk.
The science goals are to understand the disk accretion processes that build up stars and drive their outbursts.
The dates in the table are the current windows for the HST observations. The orbits column gives the number of 96 minute orbits that will be scheduled for each target. The exact times of the HST observations will be known about 2 weeks in advance.

Primary Name Alternate Name RA (2000) Dec (2000) Range (VSX) Mean V (not midpoint) Orbits Dates (2020)
TX Ori 05 38 33.69 -02 44 14.1 11.7 - 14.2 V 12.1 4 8-11 DEC
CVSO-165* 05 39 02.57 -01 20 32.4 13.5 - 15.6 V 13.7 5 13-15 DEC
V462 ORI CVSO-109 05 32 32.65 -01 13 45.8 13.0 - 14.5 V 14.0 3 26-29 NOV
V499 ORI CVSO-146 05 35 46.00 -00 57 52.2 13.6 - 15.1 V 14.0 4 6-9 DEC
V505 ORI 05 38 27.26 -02 45 09.7 14.1 - 17.2 V 14.2 4 2-5 DEC
NSV 2091* CVSO-104 05 32 06.38 -01 11 00.1 13.9 - 15.8 V 14.2 4 25-28 NOV
V510 ORI 05 39 39.83 -02 31 21.9 13.5 - 15.3 V 14.3 5 4-7 DEC
CVSO-90 05 31 20.63 -00 49 19.8 13.3 - 16.7 V 14.6 3 15-16 DEC
CVSO-107 05 32 25.78 -00 36 53.4 14.1 - 15.5 V 14.8 5 3-6 DEC
CVSO-58 05 29 23.26 -01 25 15.5 14.5 - 16.0 V 14.9 6 19-20 NOV
V609 ORI CVSO-176 05 40 24.15 -00 31 21.4 15.1 - 16.7 V 15.6 5 30 NOV-3 DEC
CVSO-36 05 25 50.37 +01 49 37.1 15.85 - 16.25 V 16.1 4 28 NOV-1 DEC
CVSO-17 05 23 04.70 +01 37 14.9 16.02 - 16.25 V 16.2 7 29 NOV-1 DEC
Note: It is essential, if you are wanting to participate, that you read the various notes after the table in the Alert Notice.

Second Campaign

This will be similar, but for Southern-hemisphere stars and will be announced soon.

Lupus Survey

A pan-European study revealed details of star counts and their space motions within the spatially-close Lupus starforming region, using largely GAIA data. They identified 137 high-probability members of the Lupus association of young stars, including 47 stars that had never been reported as members before. Many of the historically known stars associated with the Lupus region are more likely to be field stars or members of the adjacent Scorpius-Centaurus association. Their new sample of members covers the magnitude and mass range from about 8-18 Gmag and from 0.03 to 2.4 M☉, respectively.
The Lupus association appears to be younger (at 1-6 Myr) than the population of young stars in the Corona Australis star-forming region recently investigated by their team using a similar methodology.

Orion Supernovae

The Orion Complex is a notable star forming region that is fragmented into several different populations. Marina Kounkel of Western Washington Uni has proposed a model that attempts to explain the how the Complex has evolved to its current configuration. In this model, the large scale expansion can be attributed to a supernova that exploded 6 Myr ago, the remnant of which can be seen as Barnard’s loop, as the centre of the expansion is consistent with the geometrical centre of the HII bubble. This is also similar to the ballistic expansion associated with λ Ori, a region which has also been the site of an ancient supernova. Assuming that the Orion Complex originally formed as one long filament spanning from the bottom of Orion A to ψ2 Ori (or, potentially, as far as λ Ori), Barnard’s loop supernova could have split the cloud, which led to the formation of Orion C & D. Furthermore, the shockwave that has propagated into the filament could have swept along the gas through several pc, which led to the formation of the singularly most massive cluster in the Solar Neighborhood, the ONC. She also discusses other related nearby events, such as the formation of the Monogem ring, and various runaways that have been ejected from the Orion Complex