TCP J18010186-2951258: microlensing event (10.8 mag) in Sgr
https://www.aavso.org/tcp-j18010186-2951258-possible-nova-108-mag-sagittarius

TCP J18292290-1430460: classical nova (10.3 mag) in Scutum
https://www.aavso.org/tcp-j18292290-1430460-likely-nova-103-mag-scutum-0

AAVSO Alert Notice 617

Bob Jacobs (Ph.D. candidate, Radboud University) and Drs. Samaya Nissanke (Radboud University), Jennifer Barnes (Columbia University), and Deanne Coppejans (Northwestern University) have requested AAVSO observers' assistance in monitoring the cataclysmic variables YZ Cnc, SU UMa, and CR Boo. The goal is to build good multicolor light curves of two outbursts of CR Boo and two superoutbursts each of YZ Cnc and SU UMa.

Nightly observations of these stars in any Johnson-Cousins band are requested. When an appropriate outburst occurs, observers should switch to multiple observations per night in 3 or more (more preferred) Johnson-Cousins bands (U, B, V, R, I, J, H, K) spread across the spectrum if possible. It is essential to switch to the higher cadence and multiple bands as soon as possible after the outburst begins. Continue until the star returns to minimum, then resume nightly observations. Visual observations are welcome and are encouraged.

The astronomers want to catch the target outbursts as early as possible. If you see an outburst beginning, please notify the AAVSO immediately via the forum thread for this campaign, and submit your observation(s) as soon as possible.

The astronomers provide the following background information: "Last year's Nobel Prize in Physics went to three researchers in the field of gravitational waves. Two weeks later gravitational wave astronomers announced the discovery of a gravitational wave signal from a merger of two neutron stars. This system also emitted optical light right after the merger and it was observed by many telescopes on the southern hemisphere. The new type of transient was called a "kilonova" or "macronova". When two neutron stars merge, they emit large amounts of matter in ejecta (on the order of 1/100th-1/10th the mass of the Sun). These ejecta are neutron rich. Atoms in the ejecta will capture these neutrons and become much heavier than the atoms created in supernovae. They subsequently decay to stable elements like gold and platinum, heating up the ejecta and making it emit optical and infrared light. Kilonovae could account for all of the gold and platinum in the universe. That's why we would like to observe more kilonovae and test this hypothesis (plus many more). Kilonova observations will also put tighter constraints on gravitational waveforms and therefore the general theory of relativity. Because kilonovae last for only ~10 days, it's important to catch them as early as possible, which requires good observing strategies.

"In order to observe more kilonovae the Radboud University, KU Leuven and NOVA are building the optical telescope BlackGEM in Chile. Upon an alert from the gravitational wave observatories, BlackGEM, together with other observatories, will try to discover the kilonova as quickly as possible. In order to find optimal observing strategies to find the kilonova as quickly as possible, we are trying to simulate how many transients of each type (e.g. Supernovae, dwarf novae, AM CVNs etc.) one would see in what parts of the sky with BlackGEM in each of its color-bands. These transients could be false-positives in the search for the kilonova: they may be indistinguishable from kilonovae. We want to have as few false-positives and as many correctly identified kilonovae as possible. The simulator will also be applicable in other fields of astronomy where estimates are needed for the variability of the night sky.

"For our simulation we use photometry from telescopes to model the temporal evolution of transients. Thanks to the AAVSO community we already have excellent multi-color light curves for SS Cyg and Z Cam type cataclysmic variable outbursts (U Gem and RX And). Unfortunately there aren't yet any light curves available for SU UMa or AM CVn type outbursts with sufficient multi-color coverage to use in our models.

"With your help we look forward to seeing the first well-sampled multi-color observations of CR Boo, SU UMa, and YZ Cnc in outburst."

Coordinates

Charts with comparison star sequences for YZ Cnc, SU UMa, and CR Boo may be plotted using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the names YZ CNC, SU UMA, and CR BOO.

This observing campaign is being followed on the AAVSO Campaigns and Observing Reports online forum at https://www.aavso.org/yz-cnc-su-uma-cr-boo-outburst-observations

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.