This is time-sensitive.
Rod Stubbings has reported the presence of eclipses during outbursts in the peculiar Z Cam star (UGZ/IW = outbursts from standstills) V0598 Sco.
Years of ASAS-SN and ATLAS data do not show eclipses but the events seem to be short enough that may have been missed (15 minutes).
Rod caught three dimmings and determined a period of 0.1563 d.
The star started another outburst last tuesday so it is a good time to observe it.
However, outbursts last only 3-8 days so it may already be returning to quiescence tonight, although probably still bright.
Outburst cycle is close to 17 days so you can try again soon.
The star is going up and down all the time. Only two standstills have been recorded (light curve attached).
I prepared a list of timings when the eclipses should happen during the next three days.
Dense time series are requested to confirm them.
HJD | Date UT | Time UT | Day of the week
|2460832.4870|5/6/2025|23:41:19|Thursday|
|2460832.6433|6/6/2025|3:26:23|Friday|
|2460832.7996|6/6/2025|7:11:28|Friday|
|2460832.9559|6/6/2025|10:56:32|Friday|
|2460833.1122|6/6/2025|14:41:36|Friday|
|2460833.2685|6/6/2025|18:26:41|Friday|
|2460833.4248|6/6/2025|22:11:45|Friday|
|2460833.5811|7/6/2025|1:56:50|Saturday|
|2460833.7374|7/6/2025|5:41:54|Saturday|
|2460833.8937|7/6/2025|9:26:58|Saturday|
|2460834.0500|7/6/2025|13:12:03|Saturday|
|2460834.2063|7/6/2025|16:57:07|Saturday|
|2460834.3626|7/6/2025|20:42:12|Saturday|
|2460834.5189|8/6/2025|0:27:16|Sunday|
|2460834.6752|8/6/2025|4:12:20|Sunday|
|2460834.8315|8/6/2025|7:57:25|Sunday|
|2460834.9878|8/6/2025|11:42:29|Sunday|
|2460835.1441|8/6/2025|15:27:34|Sunday|
|2460835.3004|8/6/2025|19:12:38|Sunday|
|2460835.4567|8/6/2025|22:57:43|Sunday|
|2460835.6130|9/6/2025|2:42:47|Monday|
|2460835.7693|9/6/2025|6:27:51|Monday|
Elements for predictions of eclipses during future outbursts:
HJD 2460813.262 + 0.156301 x E
Provisional, and based only on 3 dimmings by Rod, not confirmed with survey data.
Observations needed!
Cheers,
Sebastian
3 Likes
What is the eclipse magnitude depth? Is the amplitude variable with location in outburst? I ask so we know if our observing system can do anything. Weather very poor still in the Eastern USA so it probably won’t matter for me…
Jim (DEY)
Hi Jim,
the amplitude is larger than 0.6 mag. according to Rod. He lost it from sight at minimum so he reported a lower limit for the amplitude.
The star gets too faint at minimum for him so we do not know if eclipses are only visible during outbursts.
3 Likes
I have added it to my observing program for tonight from Chile
Josch
an eclipse observed at 832.10 suggests a period of 0.155686 or 0.156985 (+/- 1 cycle)
2 Likes
I caught an eclipse as well. Attached a screen shot of my data at the AAVSO database. Mid eclipse around 834.756. Field is pretty dense and I had to reduce the aperture to 3 pixel (3.5 arcsec) and sometimes (5 times) caught the nearby star of mag 16 about. Have removed those outliers.
Josch
2 Likes
Sebastian, should I continue observing this target?
Josch
I have got another eclipse last night. Data are with the AAVSO database. I have improved focus and will try again tonight.
Josch
Josch, William and all,
I had just finished analyzing the data before your post came through.
With your data I was able to determine a pretty accurate period because we had ATLAS, ASAS-SN data to add to the analysis. On their own, it was impossible to find a period due to their observing cadence, but with your eclipses, we could determine the elements.
HJD 2460813.2625 + 0.1557856 x E
I attach some plots.
Rod’s, Josch’s and William’s data and then combined data (zoomed in the eclipse and full light curve).
I will add your new eclipse(s) to the analysis, but I don’t think we need more data now.
Josch, up to you if you want to follow it tonight or not!
Thank you very much for your help. A great example of amateur collaboration! 
Cheers,
Sebastian
Uploading: V0598ScoFINAL_AAVSO.jpg…
Processing: V0598ScoFINAL_ALL.jpg…
Processing: V0598ScoFINAL_ALL_full.jpg…
3 Likes
Apparently the images can not be downloaded or viewed.
I will take data during one more night as I have improved focus.
Josch
Have to postpone to another night as the moon is too close to the target tonight and maybe tomorrow night.
Josch
There was no way to upload the light curves. No idea why.
Josch, I think that we have enough observations now and the period is well-established.
We’d like to write something up and I don’t think we need more data due to the many years of survey observations we have incorporated into the analysis.
You are welcomed to observe it in the future, but I will use all we have up to now in our analysis to get it done.
Thanks again!
Sebastian
Sebastian,
that’s fine with me.
I will not observe it again.
Josch
