Northern dwarf novae monitoring campaign

[posted by Elizabeth Waagen]

Thank you all so much for your observations of RX And. The quick response time was great!

The timing of this outburst was such that we were concerned that RX And would not be visible from the VLA at the time of the optical peak, so we decided to trigger on a more optimally-timed outburst.

The observations you took are helping us to estimate the rise time and peak of outburst more accurately, so please keep it up   We are still focusing on RX And and EM Cyg for now.

Best wishes,

Deanne

--
Deanne Coppejans   (de Bude`)
PhD student
Department of Astrophysics, Radboud University Nijmegen
Astronomy Department, University of Cape Town

Hello Observers,

RX And is in outburst, but it will not be well placed for the VLA to observe it at maximum. Therefore, it will not be observed by the VLA during this outburst - hopefully the next outburst will be better placed. Please follow it through the outburst (and monitor for the next outburst) but please do not send any more emails for THIS (current) outburst of RX And. Please submit your observations to the AAVSO International Database as soon as you reasonably can.

Thanks, and good observing,

Elizabeth

Hello Observers

RX And is due to go into outburst in the next few days. Please monitor it and help us catch the outburst as early as possible so that we can trigger our VLA observations.

Thank you! :)

Deanne

I just made an visual estimate of 11.5.  I've sent emails per the instructions in the campaign announcement.  Thanks.

Chris Maloney 

Hi everyone

Thank you for your observations of RX And - we have triggered the VLA observations :) Please continue to observe it over the course of the outburst, as we will need the optical light curve along with the radio data.

Special thanks to Chris Maloney, Paul Benni and Richard Campbell for the prompt notice of the outburst.

Best wishes,

Deanne

Hi everyone

The first set of VLA observations on RX And was taken yesterday (8 November) at 09:30 UT. Another two sets will probably be taken today and tomorrow.

Please continue to monitor RX And for us so that we know at what stage of the outburst each set of observations were taken.

Thanks :)

Deanne

Hello everyone,

After taking B- and V-filter measurements for RX And during minimum and maximum phases I noticed that (B-V) values are changing substantially.  E.g., during minimum (B-V) values appear to be about 0.4, during early outburst even larger than 0.5, and at maximum (B-V) values approach 0, see   http://tinyurl.com/pths8ye   (or the pdf-attachment) for a recent LCG light curve.

Does anybody know about measured spectra in the visible (especially some covering the B and V filter ranges) during different phases?  I do not know enough about dwarf novae, but is there some simple physics explanation for this behavior?

There is an interesting paper with spectra in the UV ("The Astrophysical Journal, 574:937–941, 2002 August 1"), but I did not find any paper with visible spectra at different phases... 

Maybe Deanne could give some explanation? 

It is exciting to hear that VLA has been triggered for observations! Thanks for letting us know, Deanne!

Best,

Helmar (AHM)

I'll take a stab at an answer:  Assuming the system doesn't deviate much from an ideal (blackbody) radiator, the color index should change in just this way.  At quiescence the energy output is far less, so one would expect a larger B-V (slightly redder) and a lower temperature.  At maximum, when the temperature is higher, the blackbody curve peak shifts toward shorter wavelenghts which results, among other things, in more blue photons, making flux in B and V more comparable..

This somewhat naive answer probably depends on such things as whether we are seeing mostly the accretion disk (which probably isn't in equilbrium) or the primary's surface and whether absorption from dust or various chemical species in a common envelope complicates things etc.  But I thought I'd stick my neck out, because if I'm wrong it should be interesting to hear why.  I do have a copy of Hellier's book on CV's lying around here somewhere (haven't read the chapter on Z Cams yet :)...

Chris

Hi Helmar

Chris and Shawn are correct about the change in colour over the course of the outburst.

In quiescence the colour of the CV depends on the secondary, the cool disc, the bright spot (the point where the accretion stream hits the disc) and various other factors. In outburst, the hot disc dominates. So as the temperature of the disc increases on the rise to outburst, it will become more blue and hence the CV becomes more blue.

There are plots of how the colour changes in VW Hyi and SS Cyg in Bailey 1980 (http://mnras.oxfordjournals.org/content/190/2/119.full.pdf+html ). A lot of our understanding, particularly regarding the cause of the outbursts has changed since then, so I wouldn't recommend reading the discussion in the paper. On pg 148 in Brian Warner's book 'Cataclysmic Variable stars' there is a section on colour changes as well. I haven't been able to find any recent papers on the topic, but I'm going to ask around and get back to you if I find one.

Cheers,
Deanne

Hi everyone

Following your notice that RX And was in outburst we triggered the VLA observations on it.

They were on target exceptionally quickly - only 20 minutes after we sent the trigger. That means that they observed right at the point where we expect the radio emission to peak. Hopefully it's a positive radio detection :) Two more VLA observations were taken - one 24 hours later and another one 24 hours after that.

In combination with your optical observations, we hope to track how the radio emission evolves in comparison to the optical light curve.

Thank you again for catching RX And's outburst! :)

Cheers,

Deanne 

I noticed there are two reference stars labeled 106 in the RX AND field.  Some data uploaded may have used the wrong star id & magnitudes.  Please check.  See Chart 13696AZN

thanks

Paul

Hi Everyone

We are now focusing on U Gem and Z Cam. These are bright and nearby, so we are really keen to get radio observations of these two.

There are also two CVs, namely SU UMa and YZ Cnc, that we need to catch in superoutburst. Please keep monitoring them as well. When your observations indicate that either one is in outburst we will watch it carefully and trigger as soon as we see it brighten enough to indicate a superoutburst.

Thank you and clear skies :)

Deanne

Hi Everyone

SU UMa is currently in outburst. Please can you monitor it to see if it is a superoutburst? If it is a superoutburst we will trigger the VLA observations as soon as we know for sure.

Thank you,

Deanne

12.0 mag by V filter CCD.

Since there is no recent data, difficult to determine if the outburst is beginning or ending.

YZ CNC;2456977.86184;12.029;0.008;V

YZ CNC;2456977.86226;12.045;0.008;V

YZ CNC;2456977.86267;12.035;0.008;V

-Paul

Hi everyone,

I just estimated Z CAM to be 12.4 vis.  It may be on the rise, but confirmations are needed.  Can anyone out there do a ccd time series?  Thanks.

Chris Maloney

Hi everyone

Thanks for your observations of YZ Cnc. Hopefully it will go into superoutburst soon.

As Chris pointed out, Z Cam might be on the rise and it's very close to our VLA triggering criteria, so we need updates on its current magnitude as soon as possible please. It would be great to send in another VLA trigger today! :)

Deanne

Just got Z cam at 12.810.  Will continue to monitor.  Also will monitor YZ Cnc.

Barbara

Hi Barbara

Thank you, that's great :)

For YZ Cnc, we only need low-time resolution (a few times a day) of it for now as it's just come down from outburst. When we see that the next outburst has started we'll ask again for high-time resolution in order to trigger the moment that we see it's a superoutburst.

Best wishes,

Deanne

Z Cam may be going into outburst, according to observations made very early this morning. If you are able to observe it tonight (2014 November 20-21), please report your observations IMMEDIATELY. Because timing is critical, observations from locations East of Greenwich - the farther East the better - will be especially crucial to knowing its status in time to decide whether to trigger VLA observations. Observations from all locations are definitely needed. (see Alert Notice 505 for details)

Many thanks and good observing,

Elizabeth Waagen, AAVSO HQ

Hi everyone

If you have any observations of Z Cam, please can you urgently submit them? I need to decide now whether to trigger the VLA.

Thank you,

Deanne

YZ CNC outburst (V filter CCD)

YZ CNC;2456983.74699;11.499;0.006;V;
YZ CNC;2456983.74741;11.502;0.006;V;
YZ CNC;2456983.74783;11.509;0.006;V;
YZ CNC;2456983.74825;11.510;0.006;V;
YZ CNC;2456983.74866;11.500;0.006;V;
YZ CNC;2456983.74908;11.496;0.006;V;
YZ CNC;2456983.74951;11.502;0.006;V;

-Paul (BPAD)

Hi everyone

We have triggered the VLA observations on YZ Cnc as it was in superoutburst. Thank you all for your observations of it and especially to Paul for the observations confirming it was in superoutburst !:)

Please could you continue observing it for the next few days? We will be using the optical light curve in our analysis.

I'll send you an update as soon as we've heard from the VLA.

Best wishes,

Deanne

My CCD Observation of Z Cam:

Z Cam;2456984.36327;12.70;0.02;V;

Paolo (RPAA)

Hi everyone

The VLA observed YZ Cnc from 06:30 - 08:30 (UTC) this morning :) Thank you again for all your observations! We will submit two more sets of observations (1 hour each) spanning the next 2 to 3 days, so please keep monitoring it for us so that we can compare the optical and radio data.

YZ Cnc is top priority right now, but for those of you monitoring Z Cam please keep on sending in the observations, as it looks like it's going to go into outburst soon (or may even be on it's way up now).

Best wishes,

Deanne

Z CAM 11.7 vis. at 07/05 UT  I've watched it brighten visually over the last couple of hours.  Confirming estimates needed.

Chris

Thanks for your notice that Z Cam is in outburst! :) We have triggered the VLA observations on it.

Update for YZ Cnc: The VLA took another set of observations this morning, so we have one more set of observations to take of it. Hopefully these will be taken around 06:00 UTC tomorrow morning.

Best wishes,

Deanne

Confirming Z Cam rising

Z Cam;2456986.340381;11.140;0.005;V;

Paolo (RPAA)

Hi everyone

Thanks again for your observations of Z Cam! :) The VLA observed it from 02:30 - 04:30 (UTC) this morning. They will take two more observations over the next 2-3 days.

The third observation of YZ Cnc hasn't been taken yet, so please continue to monitor both of these sources.

Thanks,

Deanne

The VLA observed YZ Cnc from 7:35 - 8:35 (UTC) this morning, so the observations are complete :) We no longer need optical monitoring of it.

Z Cam was observed from 3:50 - 4:50 (UTC), so we only need one more radio observation of it. That will hopefully be taken in the next 48 hours, so please continue to monitor it in the optical.

Clear skies,

Deanne

The last VLA observation of Z Cam was taken this morning from 03:00 - 04:00 (UTC) :) Thank you for following it for us! :) From now on we don't need any more optical observations of it.

Best wishes,

Deanne

Hi everyone

You have helped us catch 3 dwarf nova in outburst with the VLA, namely Z Cam, RX And and YZ Cnc - thank you! :) The data from these targets are coming in now. I'll let you know if we've detected radio emission as soon as we know (as radio data takes a long time to reduce, this will take a while).

For this project we still need to observe U Gem in outburst and SU UMa in superoutburst. Their outbursts are fairly unpredictable but it looks like U Gem should go off in the next few weeks, so U Gem is the next priority.

Could I ask anyone who detects an outburst in either U Gem or SU UMa to post the detection to this forum as well please?

Clear skies,

Deanne

Hi Josch

Thank you, that's really great :) I'm keeping an eye on the AAVSO database and have signed up for MyNewsFlash reports, so I will be notified when you enter data indicating U Gem is in outburst.

Also, thank you for the notice of SY Cnc. We have used up our two triggers for Z Cam type dwarf novae though - on RX And and Z Cam. So we only need to catch U Gem and SU UMa now. 

Best wishes,

Deanne

AAVSO Special Notice #391 updates the campaign on northern dwarf novae. Please see the notice for details.

Thank you and good observing!

Elizabeth Waagen, AAVSO HQ

An observation from last night (this morning, Dec 18 UT) showed U Gem brighter by several tenths of a mag in V than the night before (same observer, possible eclipsing taken into account). Please check it tonight and report immediately if it is in outburst - see AAVSO Special Notice #391 for instructions on reporting by email (as well as by WebObs). Many thanks!

Good observing,

Elizabeth Waagen, AAVSO HQ

[In my original post I had the year as 2104 instead of 2014 - sorry!]