AAVSO Alert Notice 814: HST observations of AB Aur this week

February 27, 2023

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns & Observation Reports: https://www.aavso.org/ab-aur-campaign-2023
- Young Stellar Objects: https://www.aavso.org/ab-aur-campaign-2023-01

Please subscribe to these threads if you are observing this star so you can be updated by the astronomers and by HQ. Join in the discussion or ask questions there!

Further to Alert Notice 809, Dr. Lauren Biddle (University of Texas) informs us that a second set of HST observations of the bright (6.9-8.4V) young, accreting A0 Herbig Ae star, AB Aur has been scheduled for:

2023 Mar. 1 18:57:56 UT - Mar. 2 10:13:31 UT

Please continue to observe AB Aur according to the cadence requested by Dr. Biddle in Alert Notice 809: "The science goals of this campaign would be best supported by a time-series with observational cadence that covers a range of timescales: high-cadence (hourly), medium cadence (weekly), and low-cadence (monthly). An ideal observing plan that satisfies the desired cadences would look something like: 3 – 10 observations over the course of the night, with each night separated by a few days to a week, repeated over several months."

Be sure to read Alert Notice 809 for instructions regarding filters.

As was noted in Alert Notice 811 for the first set of HST observations, since the comp and check stars for this campaign are about 5 magnitudes fainter than AB Aur, observers are reminded to take multiple exposures in each filter used and stack the exposures to attain comp star S/N of 100 or more while not overexposing AB Aur.

Coordinates (2000.0):  R.A. 04 55 45.84  Dec. +30 33 04.3  (from VSX page for AB Aur)

Charts with comparison stars for AB Aur may be created using the AAVSO Variable Star Plotter (VSP). Be sure to create new charts for this campaign - do not use ones you may have from observing prior to January 2023, when changes were made to the comparison stars. Observers should be aware that the 116 comp star appeared in earlier versions of the AB Aur sequence as 117. If you are using AUIDs to identify the comp and check stars when you submit your observations, note that the AUID of the 116 is not the same as that star had when it was 117; be sure to use the AUID from the current chart's photometry table.

Important note re charts and the check star to use: There are two 120 stars in the general vicinity, and depending on which scale chart you create, you might not see the correct 120. Please use the 'E' scale version of the chart to see the correct comp (116) and check (120) stars. Below is the chart image. If you have reduced any observations using stars other than these, please remove your observations from the AID (using the WebObs search function), re-reduce your photometry, and re-submit the re-reduced observations.  Thank you!