Hi folks,
Great section meeting today. Here is a recap. Josch Hambsch started us off with a presentation about his spectacularly productive remote observatory in Chile and some of the recent results and publications that have come from it. Discussion included target selection sources and software he uses for data reduction for such a massive amount of images. You can email me or Josch and we will send you a copy of his presentation.
Brad Schaefer gave us a T CrB update including a discussion on how this eruption will reveal whether T CrB is a neon nova. This goes critically to understanding whether Type 1a supernovae are from single degenerate systems that build mass on the white dwarf or whether they are mergers of doubly degenerate systems that go above the Chandrasekhar Limit via the merger. The key will be identifying extremely prominent neon lines developing in the spectrum in the aftermath of the eruption. I believe he said the expected timing of their appearance was about 45 to 60 days after the eruption. AAVSO spectroscopists are really well positioned to be able to watch these lines develop, or not develop. If they develop strongly, it will confirm the finding in
Bloch & Tcheng, 1953, Ann. Ap., v.16, p73
Spectrophotometrie de T Coronae Borealis de 1946 a 1952
https://ui.adsabs.harvard.edu/abs/1953POHP....2R....B/abstract
Brad also noted the importance of doing time series as soon as T CrB starts to go off. One thing we don’t actually know for sure is how bright the peak will be. There is an observation from the 1946 eruption by a respected observer that it reached magnitude 1.7. This would put it brighter than N1975 Cyg (V1500 Cyg) and make it the brightest nova in the last 80 years (instead of just tied for the brightest). When T CrB goes off, it will rise in just a few hours and start falling back quickly so fast reaction is necessary to see the peak.
Time series immediately after the peak are important as shown by the eruption of recurrent nova U Sco in 2010. U Sco showed two unexpected and previously unseen light curve phenomena soon after it peaked. More info here:
Schaefer et al., 2011, ApJ, 742, 113
Eclipses during the 2010 Eruption of the Recurrent Nova U Scorpii
https://ui.adsabs.harvard.edu/abs/2011ApJ...742..113S/abstract
After the T CrB discussion, Walt discussed how to choose exposure times/cadence for CV’s. For Intermediate Polars in particular, often both the white dwarf spin period (seconds to minutes) and the orbital period (hours) can be seen in the data. A cadence faster than 40% of the white dwarf spin rate is necessary to be able to see the period in Fourier analysis with tools like the AAVSO’s VStar. Walt showed an example of DQ Her data of his from a few weeks ago. Exposures of 8 seconds with 11 second cadence showed the white dwarf spin rate of 71 s prominently in VStar. During the eclipse of the white dwarf and most of the accretion disk behind the companion star, he shifted to 45 second exposures to get better S/N at min light for an accurate Time of Miminum calc. Joe Patterson discussed some of the physics of what is going on in the DQ Her system. One of the things he noted is that the 71s white dwarf spin period can surprisingly still be seen weakly even when the white dwarf is fully behind the companion star. The signal is time shifted indicating it is probably a light echo off other material in the system. Brad asked for observers to continue to monitor DQ Her. He is continuing to track eclipse timings to look at changes and evolution of that system.
Walt presented a spreadsheet where he added approximate magnitude ranges to Dr. Koji Mukai’s IP catalog. It is helpful to quickly see which stars are within range of the telescope and moon phase on a night observing. We hope to make that spreadsheet available on the AAVSO web page. Koji intends to add that info to his IP Catalog web page in the next update. In the mean time, email Walt for a copy.
Clearest skies,
Walt