ER Uma and RZ Lmi: Observations requested.

[Stewart John Bean]

Following on from the IX Dra observations ( which continue at AAVSOnet), I am now monitoring ER Uma and RZ Lmi in order to time their superoutbursts. The supercycle period, P(sc),  for these two are relatively short and apparently increasing as shown below from M. Otulakowska-Hypka‹ and A. Olech MNRAS 433, 1338–1343 (2013).

My estimate from the AAVSO, ASAS-SN and Lasair records suggests that their P(sc) values are around 44 and 24 days. The interest is to determine P(sc) for this observing season and check the above graphs. Fortunately, the AAVSOnet committee have agreed to a request to contribute one of their robotic telescopes to the task. 

ER Uma may be starting a superoutburst now. RZ Lmi could be next week although both dates are long extrapolations. 

I would appreciate help with these observations although both are really morning stars at present: only 35 deg above the horizon at midnight but overhead at 06:00. Ideal for robotic telescopes.

Thanks in advance

Stewart Bean

Attachments:

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   Graph-of-Psc.png
   

[Stewart John Bean]

RZ Lmi was 14.26 at 2020/11/24 11:06:56 UT

ER Uma was at 12.8 at 2020/11/24 11:13:38 UT

Both were measured using  AAVSOnet.

[Stewart John Bean]

ER Uma was at 14.7 last night down from 12.8 at maximum 13 days ago. So that superoutburst has been completed. The superoutburst period is around 40-50 days so about this time next month could be the next one.

RZ Lmi is in quiescence following a normal outburst on 3 Dec. The next superoutburst is due shortly as its super period is only about 20 days.

[Stewart John Bean]

Last night’s result from AAVSOnet gave a V Mag of 13.5. Er Uma has displayed a series of gradually more intense normal outbursts. It is now 40 days since the start of the last superoutburst.

With a supercycle length of around 45-50 days in the present epoch the next superoutburst may occur shortly. The graph below shows how the supercycle period has varied over the last 200 cycles  (27 years).

Previous superoutbursts have reached Mag 12.5.

Stewart

[Graeme Coates]

04-01-2021 0340-0421UT: ER UMa Mag. 14.8-15.0 (TG)

[Stewart John Bean]

That could be the last minimum before the superoutburst begins.

[Jeremy Shears]

Was this also with your 80mm frac, Graeme? Really shows what’s possible with a small scope plus CCD.

[Graeme Coates]

Yes – it needs much longer exposures than with my 350mm newt at home(!) and there’s greater uncertainty, but definitely can determine that it’s not in outburst

Clear skies offer some definite advantage, and it’s much darker there as well than my garden here in the UK! 

Unfortunately, not possible last night.

[Stewart John Bean]

I also got Mag 15 on Jan4 from New Mexico AAVSO BSM NM2. 

The only TESS record happens to show the approach to a superoutburst. The normal outbursts are ‘peaky’ or ‘trianglular’ at least compared to IX Da and RZ Lmi.

[Graeme Coates]

2021-01-07 2154-2208UT  ER UMa Mag 13.6V 
2021-01-07 2218-2234UT RZ LMi Mag 17.1V

(350mm Newt, ST2000XM)

[Stewart John Bean]

I got  ER Uma at 13.44 at 2021/01/06 05:06:59 from AAVSOnet

ER Uma is showing increasing bright normal outbursts. Should  be in a superoutburst during the next 10 days based upon  a 45-50 day period.

RZ Lmi at 16.7 at 2021/01/06 05:18:54 again from AAVSOnet. Will be in superoutburst shortly as its period is only ~ 20 days.

 

[Stewart John Bean]

AAVSOnet BSM_NM gave 14.25 V Mag at UTC 2021/01/12 04:58:12 which is similar to the previous two superoutbursts.

[Stewart John Bean]

ER Uma probably in superoutburst at mag 12.6 V at 2021/01/17 04:44:36.

[Stewart John Bean]

In the next two weeks ER Uma will probably start a new superoutburst. This is based upon a superoutburst period of 55+/-5 days.

A graph of the superoutburst period against supercycle number is further up the thread – which shows this star “wanders” around 50 or 55 days for the super cycle period. 

ER Uma is a good target in the spring. Observations are encouraged.

Stewart

[Stewart John Bean]

ER UMa was last reported to be at a low state at 14.8 visual from Hungary. So a superoutburst should happen soon, but, unlike IX Dra , each period varies by upto +_ 7 days from the last. Observations would be most welcome in the next week – howling gales permitting.

The stream of AAVSOnet images I have relied upon for ER Uma, IX Dra and RZ Lmi ( all UGER stars) has paused for some reason.

Thanks in advance

Stewart

[Stewart John Bean]

James DeYoung (USA) has uploaded three days of results –  including superhumps  starting at JD 2459285.5. So the outburst seems to have started at JD 2459285 giving a superoutburst period of 55.3 days since the last. This compares to 54.7 days for the previous period. So 55 days seems a good number to use for the next outburst although there may be an increasing trend as shown in the graph.

The next superoutburst may be around May 5th  give or take a week.

[Stewart John Bean]

ER Uma is expected to start a superoutburst shortly (due date May 5th) so if anyone can help with observations that would be great. ER Uma is a reasonably bright target when in outburst, at about V mag 13, and is high in the sky in the evenings during May. Yesterday it was down at Vmag 15 so that may have been the minimum before a rise to superoutburst.

Stewart

[Maxim Usatov]

ER UMa, V = 12.88 ± 0.04 on May 5.

[Gary Poyner]

Stewart,

ER UMa at 12.4 visual on May 05.063UT.  My previous observation was 14.6 visual on May 01.965UT

Gary

[Stewart John Bean]

V mag 12.4 and 12.88 would suggest a superoutburst has started about 53 days from the previous start.

Jose Ripero Osorio (AAVSO) also reports 12.2 on May 4th.

If anyone can collect time resolved photometry to record super humps that would be good.

Stewart

 

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