Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 10/24/2014 - 22:07
AAVSO Alert Notice 505 announces a new AAVSO observing campaign on several Northen dwarf novae. The purpose for monitoring these CVs is to detect the beginning of an outburst in time to trigger VLA observations to search for radio jets. Please see the Alert Notice for details.
Many thanks for your participation in this campaign - it will be crucial!
Good observing,
Elizabeth Waagen, AAVSO HQ
U Gem brightenend to 13.7 at 07:29:21 on February 21st.
Hi everyone
It looks like U Gem is in outburst - thank you for your observations :) I will let you know when we send in the VLA trigger. Please continue to monitor it for us.
Clear skies,
Deanne
Can someone confirm this? Here's my measurements from 5:00 UT February 21.
U GEM 2457074.70387 14.182 +/-0.065 V
U GEM 2457074.70676 14.159 +/-0.065 V
U GEM 2457074.70966 14.194 +/-0.065 V
Thanks,
Vance
PVA
I'm wondering why these alerts need to be directed specifically to a forum topic, when estimates go to “Web obs” anyway, Is this to foster collective effort; Espirit de corps? Could this cause division of attention for interested parties?
Thanks very much for the observation, Gordon!
Good observing,
Elizabeth
SU Uma is at about 12.5. Needs confirming.
SU UMA;2457019.77331;12.446
SU UMA;2457019.77369;12.420
SU UMA;2457019.77407;12.465
SU UMA;2457019.77444;12.479
Richard Campbell CMP
Yes indeed it is! Just observed it visually at 12.4
Mike LMK
Thanks Richard and Mike. I've emailed the research group and will let you know if I hear back.
Clear skies, & happy holidays,
Matthew
Hello everyone,
Following up on this post, project co-I James Miller-Jones is monitoring the incoming data, and is asking for continued monitoring. Their triggering threshold requires a superoutburst, so please continue monitoring SU UMa over the next 48-72 hours to see if it rises beyond its typical normal outburst limit.
Clear skies,
Matthew
Its at v=11.7 now.
Mike LMK
Looking at the historical data on SU Uma, the peak outburst brightness varies from around 12 to 10.7, with many in the mid-11's, such as this one appears to be. So, this begs the question, how to distinguish between a regular and super-outburst, as it is developing? The superhumps at maximum would show it, but that is after the fact?
Mike LMK
Hmm... looking at the last 5000 days, superoutbursts seem to approach or surpass 11 whereas regular outbursts barely seem to exceed 12.0. Just from a visual inspection, it seems fairly easy to distinguish between the two, with a few possibly disputable cases. We'll should know within 24 hours... now if it will only the skies over eastern Arkansas would clear up!
Chris
Its at v=12.2 tonite, a drop of 0.5 magnitudes from 24 hours ago, so it might be that this is one of those shorter "normal" outbursts. Though it did get above mag 12 a bit.
Mike LMK
Hello everyone,
James Miller-Jones and I were in communication throughout the day yesterday (Monday Eastern US), and we came to the decision late in the day to hold off on triggering VLA observations. We made the right call, since as Mike points out it appears to be in decline again and is likely a normal outburst. We will continue to monitor SU UMa, and trigger on the next superoutburst whenever it comes.
Many thanks to everyone who submitted timely observations for this one -- this was a great example of how your work is critically needed for projects like this!
Clear skies,
Matthew
From today evening:
SU UMa, 57025.36792, V, 11.603 +- 0.004
SU UMa, 57025.36632, B, 11.582 +- 0.006
Because VPhot is very busy, I transformed observations just in a spreadsheet. Still, values itself should be OK, just uncertaint budget is not the correct one (reported here only var and comp instrumental uncertainties combined).
Tõnis
SU UMa was 11.51V +/- 0.02 on Jan. 3.176. Regards, Bob
SU UMa peaked at V=11.38 and B=11.35 last night.
I just visually estimated it from a digital image at approx. V=11.4, I had it <13.0 several days ago, and then it looked like it had gone back down, but now here it is, bright again. Do superoutburst behave in this fashion? I don't recall that many instances of double outbursts in such a short interval?
Mike LMK
"Do superoutburst behave in this fashion? I don't recall that many instances of double outbursts in such a short interval?"
Yes, the previous short outburst was that was usually called by CV-expert as "precursor outburst".
Clear skies,
Robert
Hi everyone
Thanks so much for your observations! :) We have just submitted the VLA observations now. I'll let you know when they take them. Please continue to monitor it for us over the next few days.
To answer some of your questions in the posts...
Looking at the long-term light curve for SU UMa's, a V mag of 11.4 or brighter indicates a superoutburst. At 11.4 we were confident that it wouldn't be an ordinary outburst. The high-time series photometry seems to show a superhump as well, which is great.
Usually superoutbursts are preceeded by outbursts - so you will see a rise, a small drop and then a rise into superoutburst - just as SU UMa did now.
Clear skies,
Deanne
Hi everyone
The VLA took the first observation of SU UMa at 3.30 UT this morning :) The second one should be taken in the next day or two. I'll keep you updated.
Best wishes,
Deanne
Hi everyone
The VLA have taken all three sets of observations for SU UMa in superoutburst. Thank you so much for monitoring it! :)
Now we only need to catch U Gem.
Clear skies,
Deanne
what kind of
Deanne,
what kind of observations are you doing with VLA? I mean, is the result a map of the surroundings of a dwarf nova or do you get just different velocity components in the RF spectrum?
Best wishes,
Tõnis
Hi Tonis
I'm sorry for the delay in replying to your post.
The VLA observations will produce an image of the dwarf nova and the surrounding area - like an optical image. It will look like a point source in the radio too. When I have an image I'll post it.
p.s. There are some really beautiful radio maps of extended astronomical objects - just do a google image search for 'radio images astronomy'.
For our observations, hopefully the DN will be bright enough to see in the radio and we'll get a clear detection. In that case we will look at other things to determine what produced the radio emission. The variability, amount of polarization and the spectral index are all really useful. Essentially what you need to do to get this information is to split the observations up into different frequency ranges or time ranges and then make images with just that selected data.
Radio astronomy differs from optical astronomy in that you don't get an image from the telescope. Take the VLA for example - it's comprised of 27 dishes. Each of these measure voltages, so you get a very large table of values out. Then by using computer algorithms we stitch that all together to make an image. So, for example, if we want to find out how bright the target was between 1.20 and 1.30, we select only those 10 minutes in the table make an image of it. There are other ways of getting information out of radio data, but this is what I'm doing.
A non-detection is still useful. From the image we can get upper-limits on the brightness of the radio emission and place some constraints on the timing of the expected radio flare - both of which help us narrow down what could have produced the radio emission.
Best wishes,
Deanne
SU UMa is brightening again after "finishing" the superoutburst - which follow a pre-outburst.
Is this typical?
Hi everyone
There are observations showing U Gem to be at I~12.9 mag, so it may be going into outburst. Can anyone confirm whether it is going up?
Thanks,
Deanne
I measured it at v = 14.79(5) last night, at JD 57059.5039, so it was still at or near a low state at that time.
Shawn Dvorak (DKS)
Florida, USA
As you know, we are waiting for U Gem to go into outburst so that PI Deanne Coppejans can trigger radio observations in fulfillment of her northern dwarf novae campaign (AAVSO Alert Notice 505). Thanks to everyone who has been keeping a vigil on U Gem and submitting their observations!
Thank you, Shawn and Chris, for writing about your observations from last night indicating it is at minimum. Your observations match others that show U Gem has not gone into outburst. U Gem is brighter in I than in BVR, so an I magnitude of 12.9 or 13.0 is not unusual when the system is 14.8 V.
Please continue to keep a close eye on U Gem and report your observations promptly. If you see signs of it going into outburst, please submit your observations immediately and send emails in accordance with the instructions in Alert Notice 505. Very fast notification is cruciual to detecting possible radio emission as the outburst gets underway.
Many thanks, and good observing,
Elizabeth Waagen, AAVSO HQ
Last night (first clear night in days) I couldn't see anything in the field near the 131 comp star, so I reported <13.1 (vis) at 0537 UTC. Since that's consistent with Shawn's positive observation, it seems that U GEM is still quiescent.
I don't see any visual or V estimates above 14th magnitude in the recent light curve. The three estimates by Tonis (ETOA) near 12.9 appear to be in I. I wondered if this is typical for U GEM in its low state. So I took a look at the light curve with 1000 and 2000 day windows with LCG and Vstar. It looks as though this is the case. The most recent example occurs between JD 2456288 and 245629, where the cousins I data cluster around ~13.0.
Also, the cousins I magnitude seems to match the V magnitude pretty well during an outburst (See JD 2456025 to JD 2456035). Given these two sets of data, is it reasonable to conclude that I estimates for U GEM near 13.0 actually confirm that it is in its low state? Any thoughts?
Chris
U Gem may be going into outburst. I have it at 13.7
Richard CMP
U Gem faded to 14.5. Must have been a flare of some kind. I checked several times and it was fainter each time.
CMP
Richard CMP (thank you, Richard) reported a visual observation of U Gem at 13.7 on 2015 Feb. 10.14202 UT. However, he subsequently reported another visual observation at 14.5 on 2015 Feb. 10.26515. Thus, U Gem may not be going into outburst after all - Richard may be seeing eclipsing behavior.
Please check U Gem and report your observations as soon as possible tonight so we may know for sure the status of U Gem.
Many thanks, and good observing,
Elizabeth Waagen, AAVSO HQ
I have triggered the first set of VLA observations on U Gem :) I´ll let you know when they have been taken.
Best wishes,
Deanne
I just want to point out that when I was watching it between UT 11:00 and 11:30, it showed rapid variability in visual, between the upper 12's and lower 13's magnitudes, several tenths in just minutes of time. Is this typical of outbursts in their early stages?
Mike LMK
U Gem 11.7 21.02.2015. 18:06 (UT) KLO
Regards,
Laszlo Kocsmaros (KLO)
Attached
Ladies & Gentleman,
Attached is an AVIS 1000 day light curve for U Gem. Since U Gem is a USS +E star it undergoes significant variability due to orbital position as well as outburst. The orbital period is quite short, about 4h 15m. So there is a lot of variation going on between outbursts over a range of about 1 magnitude. It seems to me, that until you get brighter than about 13.5 magnitude, you don't really know if the system is entering outburst. However, at 11.7 as Laszlo reports, it would definitely be in outburst and from the timing of his observation compared to others it would be on the rise to maximum. VSX lists the range of V magnitudes for U Gem as 14.9 to 8.2.
With regard to LMK's question. These stars rise into outburst quite quickly without apparent "sawtoothing." Look at two much smaller segments of the 1000 day curve: the first of a shorter outburst in April 2010 and the second of a longer outburst in March 2011.Both had relatively dense coverage and the light curves rise steeply and apparently monotonically in about 3 days in both cases to the peak at brighter than 10th magnitude.
Those interested should check out the light curves of U Gem and the other Dwarf Novae. If you are more adventurous you might even try some analysis with VStar.
Brad Walter
[quote=WBY]
With regard to LMK's question. These stars rise into outburst quite quickly without apparent "sawtoothing." Look at two much smaller segments of the 1000 day curve: the first of a shorter outburst in April 2010 and the second of a longer outburst in March 2011.Both had relatively dense coverage and the light curves rise steeply and apparently monotonically in about 3 days in both cases to the peak at brighter than 10th magnitude.
[/quote]
Brad, Those light curves have insufficient time resolution to show the variations I was seeing. The several tenths variations occured on time frames of a minute or less. In fact, it seemed to be slightly fainter about 30 minutes after my initial observation, before apparently resuming its rise.
Mike LMK
Mike,
Dwarf novae flicker dramatically and on a pretty short time scale. See figure 1 of the attached paper on high speed photometry of U Gem done at McDonald in the late 80s. Some of the flickering in this figure amounts to 0.2 mags in about 0.05 phase which for U gem is about 20 minutes. This is normal it goes on all the time. The only time it seems to disappear is when the bright spot is being eclipsed. When the system goes into outburst the whole disk gets bright as the viscosity changes rapidly and the disk heats up. While the whole thing is heating up fast the flickering doesn't show up as much. I'm not saying it doesn't flicker. I am saying it isn't as apparent because the slope is steep just as during the bright spot ingress and egress.
This is one of the problems of obtaining a characteristic shape of orbital effects on light curves for CVs the flickering can sometimes be bigger than the orbital effects you are trying to measure. See the CBA website http://cbastro.org/cataclysmics/light-curves/ You can compare how smooth their averaged curves appear in the "Atlas" section to the ones over averaged over only a few cycles in the McDonald Observatory paper.
Brad Walter
Hi everyone
The VLA took the first set of observations at 7.30 UT this morning, so the timing was perfect - thank you again for the fast notifications :)
The next set of observations will probably be taken around 7.30 tomorrow morning.
Cheers,
Deanne
Hi,
I observed the star at approx 9.5 mag
2457076.64679, 9.58 mag
Probably saturated.
Josch (HMB)
Hi everyone
The VLA took the last two observations of U Gem last night (at 3:00 UT and 4:30 UT), so U Gem is now complete.
Thanks to your observations we now have radio light curves for five dwarf novae in outburst: U Gem, Z Cam, RX And, SU UMa and YZ Cnc! To date this has only been done for SS Cyg, so this is a really amazing dataset and the results will be really exciting. If the radio emission shows the same behaviour as for SS Cyg then this is a very important step towards proving that CVs do in fact form jets. If the radio emission does not show the same behaviour then we have still opened up a new field of study, because currently CVs are generally accepted to not produce (strong) radio emission and they have largely ignored at radio wavelengths since the 1980s.
Thank you so much for all your observations. This project would not have been possible without your prompt outburst notifications and optical light curves. I've really enjoyed working with you:)
I will send you updates on the results as they come through.
Clear skies and good luck with all your other projects,
Deanne
From last night, its down to v=10.0, so the more rapid phase of decline appears to be starting.
Mike LMK