Z CamPaign Update March 2016

Z CamPaign Update March 2016

We are now in the seventh year of the Z CamPaign. I want to thank all the CCD and visual observers who have contributed to this campaign since 2009. With your help we have met all the original science goals, published several papers, identified new Z Cams, unearthed a poorly understood group of anomalous Z Cams and whittled down the list of Z Cam suspects and impostors.  

I'm happy to report, there is still plenty to do.   

All the bona fide Z Cams should be observed every night. They still have surprises in store for us and now that we have classified them unambiguously we need to maintain a historical record of their unique and interesting behavior. The gold is buried in the long-term light curves of these stars. So if you adopt them into your program, consider it a multi-year, or lifetime, commitment.

There are plenty of bright Z Cams that visual observers can follow throughout their range of variability. CCD observers should concentrate on Z Cams that get fainter than 15.0V, especially the handful of challenging faint targets mentioned later in this update.

The Z Cam List website lists all the bona fide and suspected Z Cams.

New Discoveries

In the February 2015 Z CamPaign Update I asked observers to concentrate on a new Z Cam candidate, 1RXS J062954.6-033520 (J0629). Fortunately, patience and persistence has paid off. I am making the call on this one as a new bona fide Z Cam system. As you can see in the light curve below, J0629 was in standstill coming out of the seasonal gap, hovering between 13.0 and 13.2V. The standstill lasted through the month of August 2015, and then J0629 went into outburst from standstill at the end of September. A paper is in preparation.

(click on any light curve to enlarge)

Click on image to enlarge

Almost all the CCD data in this light curve are from Josch Hambsch, but this is a great star for everyone to follow. It ranges from 12.3 - 14.5V, so it’s observable visually in a 10” telescope throughout its range, and at -3 degrees declination it is observable from both northern and southern observatories.

UY Pup: Déjà vu 

In February of 2014 Rod Stubbings wrote to me telling me he had discovered a new Z Cam star hiding in the dwarf novae weeds, OQ Car. I wrote about his discovery here. This year Rod wrote to me with an almost identical story. This time the subject was UY Pup. Rod has been following this star for years and had become familiar with its normal dwarf nova pattern of outburst and quiescence.

After an outburst in the end of December 2015 UY Pup had failed to return to quiescence and by the time he wrote me in February UY Pup looked like it was stuck in the low to mid 14th magnitude range, right where I would expect to see a standstill occur in a dwarf nova that ranges from 13.0 to 16.1.

I immediately got it on the observing queues for AAVSOnet and enlisted a few friends to begin nightly monitoring of it with their CCDs. As luck would have it, UY Pup dropped out of standstill almost as soon as we began collecting CCD data, but Rod’s visual data look like they will be enough to write another discovery paper.

After the first historic standstill of OQ Car, that system went into a very active phase with several unambiguous standstills occurring since mid 2014. Those have all been well observed with visual and CCD data. With any luck, UY Pup will reward us with more confirmation in the coming months now that we have trained a bunch of telescopes and observers on her.

Z Cam Stars needing more data

AY Psc- We did a pretty good job of covering this star in the second half of 2014 but most of us forgot all about once the observing window came around in 2015. This is an active and rewarding star to follow as well as one of only three eclipsing Z Cams known.

BP CrA- Almost the same story with BP CrA. It was well covered in 2014, but there has been some drop off in 2015. We almost missed the standstill in November. Weather has been an issue for many southern observers, but let’s try to get better coverage going forward.

ES Dra- This one has been in standstill more than the active phase in the last few years. In fact, it may be in standstill right now. At 62 degrees declination, this one is circumpolar for most northern observers. We should have year-round coverage. Please redouble your efforts, or consider adding this one to your CCD program.

HX Peg- The practical observing window for this interesting Z Cam is only about 6 months, so we really need to make the most of it when it is well placed. Coverage dropped off significantly in 2015. It should be back in view by the end of July. I’ll try to remind everyone then.

MV Leo (Leo5)- This is one of the few Z Cam targets visible during the dregs of spring. There is a real dearth of Z Cams between 10 and 16 hours, so we should be killing this one, but coverage has trailed off recently.

Z Cam Suspects

The full list of Z Cam suspects can be found on the Z Cam List page. As a rule of thumb, if I still have the object listed as UGZ: in the table, I still believe there is a chance the object may yet turn out to be a Z Cam. Otherwise, I am fairly convinced they are whatever else is listed under type. Here are a few suspects of particular interest for various reasons.

ASASSN-14kh- This is a new Z Cam suspect with no data in the AID. The data from ASASSN looks like it could contain a standstill. The sequence team has created a sequence for this star so you can plot charts and start observing it now.

PY Per- I was almost certain this star was in a standstill in February 2015, but it didn’t materialize. This star seems to be switching between high accretion rate states with normal frequent dwarf novae outbursts and low accretion rate periods where outbursts are rare and VY Scl-type fading events dominate the light curve. I’m now leaning towards NL/VY but clinging to hope for very unscientific reasons. I just happen to like this star. I mean look at this crazy light curve. What’s not to love?

V416 Dra- Although there are no signs of any standstills in the light curve for this star, many Z Cams can go for years without a standstill while exhibiting very UGSS-like behavior. Coverage has begun to drop off a bit on this one, and I would like to encourage you to continue getting nightly snapshot data for at least another year. At 71 degrees declination, this is a circumpolar star for all northern observers. There shouldn’t be any seasonal gaps. If it turns out to be a Z Cam it will be very interesting because it is an eclipsing system.

NSV 14581- This star (also known as HS 2325+8205) is interesting for many of the same reasons as V416 Dra. It is circumpolar (+82 degrees dec), not too faint and a potential eclipsing Z Cam if it is a Z Cam. This one is getting plenty of attention. Please keep up the good work!

SSS 120514:105640-312212- This one is new for 2016. Discovered by the Catalina Real Time Survey, the CRTS light curve shows what looks like a possible standstill. This star does not have any data reported to the AID yet, but it does have an AUID and I just created a sequence for it, so you can observe and report your data to the AAVSO starting right now.

Z Cam Challenges

These stars are all challenging targets and are not for the faint at heart.

V433 Ara- This is a faint system, not well covered at all. I have essentially been the lone wolf on this one, getting data from OC61 whenever possible. In P.A. Woudt, B. Warner, M. Spark, 2005, MNRAS 364, 107, they saw it stuck around 16.8 for extended periods, which led them to believe it might be a Z Cam. Because it exhibits ~1.2 mag eclipses, this and the other eclipsing Z Cams could provide an opportunity to study the structural changes among outburst, standstill and quiescent states.

V868 Cyg- This one is in a very crowded field and extra care needs to be taken to correctly identify the star in quiescence and bright states. Some photometry software, including VPHOT, will misplace the aperture onto the nearest bright star in the image instead of leaving it where is should be. Coverage has fallen off dramatically in the last couple years, possibly because it is such a difficult star to observe and has not shown any standstills since the beginning of the Z CamPaign in 2009.

V1404 Cyg- A faint CV in another crowded Milky Way field, this Z Cam suspect has an 18th magnitude companion 4 arc second WSW that can be misidentified as the variable at or near quiescence. Coverage has dropped off lately for this pathological star also.

CSS 100624:220031+033431- Another candidate from the CRTS introduced last year as a potential Z Cam based on the Catalina team’s light curve, which seems to show a standstill around mag 18. Obviously, this one is very faint, varying from ~16-20V. If you have access to a big scope and are looking for a project, this is one possibility.

MN Lac- Most of us dropped this star (at my suggestion) last year because it is so faint. The outburst cycle time looks too long to be a Z Cam (180 days), but I’m not positive we have that cycle time nailed down either due to the paucity of data. Bill Goff helped flesh out the range (14.5V – 22.5CV). This is definitely a project star for big glass if you are looking for target suggestions.

Here's wishing you clear skies and happy hunting,

Mike Simonsen