AAVSO Alert Notice 617 announces an observing campaign beginning immediately on the cataclysmic variables YZ Cnc, SU UMa, and CR Boo. Please see the notice for details and observing instructions.
Many thanks, and Good observing,
We hope to obtain some great, unique light curves with this observing campaign. It will be of great value to our research. Thank you very much for your observations in advance.
CCD observations by several observers show YZ CNC on the rise from ~14 to m>13 during the last 28 hours or so. Franky Dubois (DUBF) had YZ CNC at ~12.7 about 8 hours ago. I just submitted a visual estimate: m=12.2, so the trend is continuing. I will do at least one more visual estimate before I turn in tonight. More confirmations in all bands are needed.
Over the past 10 days YZ CNC has been in outburst. This was a normal, short, outburst. The AAVSO community has been observing this variable in multiple colors. We would like to thank the observers that have submitted data to the database. Special thanks go to Alexander Purves for the majority of these observations. Even though this wasn't the initial purpose of our observing campaign, it will certainly help our research and we are very grateful to the community for observing this normal outburst.
We hope to see a similar level of community cooperation when YZ Cnc or SU Uma go into a superoutburst. So, please keep on observing these systems and CR Boo to find out when they're outbursting.
I imaged CR Boo this morning....looks like it might be on the rise. B=14.41, V=14.496, I= 14.598. I used iTelescope T21 this morning but T11 for all other CR Boo observations. I plan to keep observing as long as the weather in New Mexico holds out.
YZ Cnc seems to be on the rise (<13th mag). It's still too early to tell whether this will be a normal outburst or a superoutburst. But, because we want to catch superoutbursts as early as possible, we please ask observers to start observing in multiple wavelengths.
We thank the AAVSO observers in advance.
CR Boo has entered one of its rather rare low states. I measured it at v=16.72 at JD 58199.74 (05:45 UT). I'm not sure if the return to normal high state that should occur in the next few days (or less) is of interest.
Shawn Dvorak (DKS)
As reported above, YZ Cnc seems to be in an outburst again. SU UMa is in an outburst too. CR Boo has been in a minimum for a few days now and if it indeed has a 46.5 day period (as suggested by Levitan et al 2014 ), it should go into an outburst soon.
Please observe these systems in your Jonson-Cousins colorbands at least once a night. Hopefully we can create a unique multi-color light curve for these outbursts.
I've got many additional BVRI data points on this star, on 2-3 different dates, but images were taken for a college student I'm working with, so we'll report it as soon as she gets a chance to run the analysis.
CR Boo was too faint for the exposures used the first time (exposures used were based on its outburst mag), but I did get some measurable, though weak data last night (SNR only inthe 30's, and not enough images to stack). If those are at all helpful, I'll post them to WebObs.
Brad Vietje, VBPA
Thank you for observing, Brad! Please post your data to WebObs. Any data will help us get a better idea of CR Boo's behaviour.
On a different note: YZ Cnc is in an outburst again. We ask people to please focus their telescopes on this vibrant system again in the hope that this time we might be able to catch that superoutburst.
Yes. My visual estimate last night was 11.7 (12 April @ 0450 UT).
Bob, I've got two questions, if you get a spare moment:
1) I understand that electronic estimates are most valuable, but would multiple visual observations be of any use? Is one per night per target sufficient?
2) Technical question: The abstract from the 2015 paper you linked says that the behavior of AM CVN stars is not well understood because a) few are known and b) their outbursts are infrequent. But YZ CNC goes up 2 or 3 times monthly. Is YZ CNC just an anomalous member of this class which fits the other criteria for an AM CVN? Is this part of what you are studying? I'm just curious, of course.
Chris, thank you for your interest in this subject.
Visual observations are only useful for determining whether a system is in outburst or not. One observation per night per target is therefore sufficient. Whenever a system is in outburst, it's best to observe it a few times during the night in UBVRI bands.
YZ Cnc is not an AM CVN type star, it's a dwarf nova of the SU Uma type. This means that it has "normal outbursts" of about 6 days and "superoutbursts" of ~3-4 weeks. There are typically 3-10 normal outbursts in between superoutbursts of SU Uma type stars. We selected YZ Cnc along with SU Uma to cover the SU Uma dwarf nova types because they are relatively bright and go into (super-)outburst more frequently than other examples.
CR Boo is the only AM CVn system in our set of CVs of this observing campaign. Not all AM CVns show outbursts (as listed in Table 1 of this publication: https://arxiv.org/abs/1410.6987). For example AM CVn itself does not show outbursts. Of the outbursting systems CR Boo is the only one with a somewhat reasonable brightness on the Northern Hemisphere (most AAVSO members are probably on the Northern Hemisphere). As you can see in Figure 1 of that same paper, we have relatively little knowledge of the behavior of AM CVns. However in Figure 6 the authors have been able to distill a "likely" light curve for CR Boo from the data in Figure 1. We hope to be able to construct a similar light curve in multiple color bands with our observing campaign. The AAVSO observations that have been done for that system indicate that CR Boo's behavior may currently be a little bit more erratic than expected in that paper, which is interesting in its own right.
Various observations in the visible spectrum suggest that YZ Cnc is currently in a superoutburst. Please observe this interesting system in UBVRI filters if you have them. That would greatly help us!
Edit: And CR Boo seems to be in outburst too!