Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 06/07/2012 - 10:13
The Z Cam star AH Her has been in standstill for some time now. It looked like it was breaking out in a brightening about April 1, 2012 but that was abortive. It now looks as if it is diminishing from the past many weeks.
Yes, AH Her has been getting excellent coverage. Your data has been an important part of that. Indeed, the light curve in the last 200 days shows a standstill, a mini-outburst, back to standstill and what appears to be a fade to quiescence. Always an bright, interesting, unpredictable, entertaining to watch system.
AH Her has aborted its attempt to breakout of standstill. Right now it looks like a mirror image of the previous hiccup. Interesting star!
As of June 18.1 UT the protracted standstill of AH Her has concluded, the star having dropped to 13.8 magnitude. It will undoubtedly now continue on down to its full minimum, reaching this within the next day, or two.
J.Bortle (BRJ)
"the star having
BRJ wrote:
"the star having dropped to 13.8 magnitude."
Yes, I got it at 13.996 at June 18.26 UT. But I'm wondering how you recognized 13.8 (or something close) as a threshold to decide the standstill was really over?
[quote=roe]
BRJ wrote:
"the star having dropped to 13.8 magnitude."
Yes, I got it at 13.996 at June 18.26 UT. But I'm wondering how you recognized 13.8 (or something close) as a threshold to decide the standstill was really over?
[/quote]
Standstills in Z Cam-type stars generally display a protracted period of sustained brightness near the star's mid range, as we are all aware. In the case of AH Her this would be around magnitude 12.5-12.8 . Once the star has brightened/faded quite significantly beyond that magnitude range - in this instance a full magnitude below the usual standstill brightness and within just 0.5 magnitudes of minimum - it signals that the standstill has definitely ended. That and 50 years experience in observing these variables, becoming intimately familiar with aspects of the strange behavior each exhibits.
BRJ