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With the clocks changing, its time to review the behaviour of some of the ER Uma stars. First up: V1159 Ori.
VSSC 193 covered V1159 Ori in detail suggesting a irregular trend towards longer superoutburst periods ( 45 days to upto 70 days). The nominal definition of ER Uma is that they have superoutbursts between 20 and 90 days apart. Recent V1159 Ori observations support the trend but also make a definitive statement difficult.
This trend appears to be strengthening with only two superoutbursts ( JD 2460611 and 2460741) in the most recent complete observing season – 130 days apart. Interestingly the frequent normal outbursts continue which are perhaps a better definition for this group of stars.
The difficulty of interpreting the light curve is compounded as two superoutbursts may have occurred either side of the observing season. The good news is that a superoutburst was observed in early 2025 September meaning that we a have a chance to observe the next superoutburst over this winter. After the next superoutburst I will prepare an update for the VSSC.Regards
Stewart Bean
For V1159 Ori an observer on the equator would be able to fill in, to some extent, the summer gap in observations.
How do I look up the ZTF code for ER Uma? It will be something like ZTF******* Stewart
VSX lists synonyms, but not for ER UMa it seems. In the case of V1159 Ori it is ZTF22abhvjny
If you need ZTF photometry on ER UMa, you can access it from the the VSX entry on ER UMa, using the “External Links” drop down and selecting “ZTF”.
Hi all,
Here’s a run I did on V1159 Ori the night before last from my C11 in Spain (2025-10-27). Interesting short term variability. The SNR of the target star was around 100. The average V mag was 14.89 over the 21 frames.
I will carry on monitoring it…
Cheers
Ian.Attachments:
Ian,
Interesting that you are in Spain. One of the challenges is to observe V1159 Ori ( Declination only -3 degrees) around conjunction. The best place would be from the Equator. All my reported observations have been via an AAVSOnet project.
I forgot to use the Slooh Canary 2 (27 deg latitude) instrument this summer for the job – especially as it now has a V filter.VSX gives a period of 90min for V1159 Ori.
Stewart
VSX gives a period of 90min for V1159 Ori.
Hi Stewart,
Well, I’m not in Spain but my kit is. I’ll try and get a really long run on it to see if I can pick up the period. The weather in Spain is not cooperating!
Cheers
Ian.A milestone for V1159 is approaching.
According to the observations in the AVVSO record for V1159 Ori, it is now 98 days since the last superoutburst. This exceeds the previous interval of about 70 days. So either the observations have missed a superoutburst or we continue to see normal outbursts but no superoutburst. I am inclined to think that conditions for triggering a superoutburst are not present. Longer intervals between superoutbursts has been the trend for V1159 Ori. At this rate, if V1159 Ori were discovered today it would not meet the criteria for being classed as a ER Uma type CV. However, normal outbursts do continue and these may be a better guide to classification – which is arbitrary anyway.
Once the next superoutburst occurs and provides another data point on the graph, I will write up for the VSSC.
Hi Stewart,
I’ve noticed a brightening from around 15.2V on 16th Dec. to around 14.6V last night (20th Dec). See attached.
Cheers
Ian.Attachments:
Hi Ian,
Yes there was a normal outburst peaking on the 19th peaking at about 13.5 and returning to 15 on subsequent days. Thanks for the observation.
However, Still no super outburst . So we are at 110 days since the last superoutburst – which is the longest wait yet.
Seems as if the flow of material from the donor star is not stable for V1159 Ori.
Stewart
PS I see you are in the ALTAIR group with one Sebastian Von Harriach. Is this Sebastian a electron microscope professional? I am ex ZeissInteresting stuff, Stewart. I see Eddy Muyllaert had it at 13.9 vis on Dec 28, but Ian’s latest data on Dec 29-30 showed it has faded. So another normal outburst….
Guys, Thank you all who have contributed observations over Xmas.
The pattern remains of continuing normal outbursts – see upto date light curve attached. It is now ~120 days since the last superoutburst. I have worried about having missed a superoutburst but cannot see where it may have occurred.
Is there a category for stars only showing normal outbursts?Will check on the deadline for the next VSSC in preparation for a write up.
Stewart
Attachments:
V1159 Ori has now shown a superoutburst event starting on Jan 7 and running to Jan 15 approximately.
It has been 126 days since the last superoutburst making this interval in the observing record that I am aware of. This continues an irregular trend towards longer intervals between superoutbursts. Normal outbursts have continued as usual. Ian’s observations above are the last before the outburst started.
I interpret this as showing that the flow of material from the donor star has not stopped. Rather the quantity flowing has fallen to a point where conditions needed for a superoutburst have not been present.Time now to write the work up and submit to VSSC.
Thanks to all who have contributed. As usual the interest continues. Has this been an outlier or is the next superoutburst only 40 days away?
STewart
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