Hi CBAers,The AM CVn campaign - the main effort this month - is going well. But not much data at European longitudes; I hope the Euros will pick up the pace for a few weeks. The star is ideally placed for March-April.
There are two objectives in this campaign.(1) Timing the phase of the 1028 s orbital signal. It's always invisible in the light curve - just 0.005 mag peak-to-trough - and dominated by the 1051 s ("positive") superhump, the 1011 s ("negative") superhump, and flickering. However, because the periods are so short, one can average these signals over a long time series - and thus extract the phase of the orbital signal. This is of great interest because the slow drift of orbital phase defines the rate of period change - one of the great unknowns in the theory of these pure helium stars. I attach a paper we wrote for SAS in 2019; this year, we want to upgrade it into a regular journal paper (and we will!).
For this goal, VERY LONG RUNS are highly desirable. Great for March-April.(2) For goal (1), the two superhumps are noise - to be overcome! But one man's noise is another man's signal. In theory, as positive superhumps drift to longer period, negative superhumps drift to shorter period. But this has never been tested. Only two stars offer the test, because only rise winterest because The only star which reliably *offers* the test is AM CVn, because no other star reliably offers both types of superhump.
For this goal, what matters is the total length of the campaign. We should definitely extend it through March-April-May. But the runs need not be particularly long; 2-3 hours is fine after the next 2-3 weeks.
Info on other targets tomorrow... joe
Attachment:
amcvn-sas2019.pdf
Description: Adobe PDF document
____________________________________________________________ Center for Backyard Astrophysics (CBA) mailing lists https://cbastro.org/communications/mailing-lists/