I'd love to start a campaign on VY Aqr, a cataclysmic variable that is undergoing a dwarf nova outburst (and perhaps a superoutburst) without supplanting Patrick Schmeer who first alerted AAVSO (https://www.aavso.org/vy-aqr-outburst-0#comment-74819). Christian Knigge, severall collaborators, and myself are looking to put together as much as we can on this outburst. In particular, we are also hoping to get radio data (likely due to a relativistic jet) to complement the optical and UV data that largely trace the accretion disk. Multiple filters allow us to constrain the broad band spectrum of the source, which is often an important constraint for science. Elizabeth, can we start a co-requested alert, keeping Patrick involved?
We are still working on setting filter, candence, and SNR requirements. We will update you when we can.
At a minimum I would love to get multiple filters (including Visual, U, B, V, R, I, to your best abilities) a day, perhaps even once per hour. I am unsure if we will request higher cadence observations. Spectroscopy around H alpha (6563 Angstrom) and 5000 Angstrom would be interesting as well.
The source is currently brighter than 11th magnitude (and maybe even brigther than 10th magnitude). The quiescent level is more along 17 th magnitude. We have requested and been granted Swift observations to capture the X-rays and the simultaneous UV, U, B, V magnitude once per day, likely from November 11-20 (we're trying to get on scope faster). We will observe with the South African MeerKAT radio telescope at least once on November 8 at 11:40-13:40 UT. We will likely observe multiple times with MeerKAT.
Oftentimes dwarf nova outbursts only last a week or so, so let's all cross our fingers for clear skies and fireworks.
Sincerely,
Greg Sivakoff
Information from Patrick's post at https://www.aavso.org/vy-aqr-outburst-0#comment-74819
VY Aquarii (UGSU)
https://www.aavso.org/vsx/index.php?view=detail.top&oid=888
Visual magnitude estimates by P. Schmeer, Bischmisheim, Germany:
AQRVY 20201105.74 <130 SPK
AQRVY 20201106.742 112 SPK
Sequence: AAVSO (V magnitudes)
Instrument: 203-mm SCT
Confirmed by Gary Poyner (Birmingham, UK) as follows:
Nov 06.777 11.4 22cm
The previously recorded outburst (a normal one?) was observed from 2015 March 28 to April 1.
Time-resolved photometry during the current outburst is encouraged.
Greg, Christian, et al., thanks a lot for the proposal!
Quote: "Oftentimes dwarf nova outbursts only last a week or so, ..."
The current outburst of VY Aquarii is very likely a superoutburst and is expected to last about two weeks (the usual duration of standard SU UMa-type outbursts).
Clear skies,
Patrick
According to AAVSO data, a normal outburst was observed 2006 October 7–11, and a superoutburst 2008 July 1–16 (followed by a rebrightening July 21–23). An outburst of unclear nature was observed from 2015 March 28 to April 1 by Rod Stubbings and the All-Sky Automated Survey for Supernovae (ASAS-SN).
Patrick
This white dwarf has a companion that orbits it every 0.06309 d (90.85 min) that supplies the material the white dwarf accretes. So changes to the source emission may happen on more rapid timescale than daily observations. AAVSO observers can play a major role in this campaign. To first order, a superoutburst will likely last around two weeks, as Patrick said. Towards the end of the outburst, the source will decay towards its quiescent emission (mostly from the companion star) of 17th mag Visual. So we expect around 7 mags of changing optical emission over the outburst, with the AAVSO observers playing critical roles.
We have six priorities for AAVSO observers. Please pick one given your capacity and interest. For this group, I would skip to Priority 5 & 6.
Can 5/6 be expressed in terms of minimum useful SNR and resolution please so that the optimum equipment setup and exposure can be used ? Are there any other requirements? eg flux calibration (relative or absolute) or are rectified spectra sufficient ?
Thanks
Robin
Hi Robin,
This is a good, but tough question. I am less familiar with the capacities of the AAVSO spectroscopic observers. The issue is that we are going after multiple scientific goals [ and I'm very overworked at the moment ;) ].
In Priority 5, the basic idea is that we want broad-band spectroscopy to complement braod-band photometry. We want to see changes in the continuum slope; you basically just need to exceed photometric "spectroscopic" resolution. So this can be truly low resolution spectroscopy. Here, getting a spectra across as much of the optical bands as possible is important. In terms of line behaviour, the region around 5000 Angstroms is the richest (HeI and II, H beta, Bowen), and 6563 Angstroms (H alpha) is also important. At low resolutions, seeing bulk changes in behaviours of lines may be useful for planning observations at higher spectral resolutions. I have not thought in detail about what SNR is needed to do the different aspects here and the source is much brighter than I've ever done spectroscopy on. I often shoot anywhere from continuum SNR of 5-50 per spectral resolution element for monitoring line emission/absorption, but that is overkill for the continuum slope, especially as one could average across spectral resolution elements. For the latter, you might only need continuum SNR of ~3 per spectral resolution element. In addition to being scientificaly interesting, this might also be a good training ground for low-resolution spectroscopy. To get the continuum slope correct, it's better to do flux calibration. Relative flux calibration is good enough, but if absolute flux calibration can be done (i.e., photometric conditions), that's even better given that the source is varying.
For priority 6, there's two goals. Measuring the radial velocity curve and performing "doppler tomography". The former is demonstrated in papers like http://articles.adsabs.harvard.edu/full/1994A%26A...292..481A http://articles.adsabs.harvard.edu/pdf/1997PASP..109.1359T and https://iopscience.iop.org/article/10.1086/319122/fulltext/. While the latter is shown in https://academic.oup.com/mnras/article/357/1/69/1039160 They used spectral resolutions of ~ 2000, 2000, 400, and 6000 respectively. None of them list their SNR, but by eye, but line SNR of ~ 10 - 20 for the middle two at H beta seems to match their plots. I think the first / last of the three (which both show flux calibrated spectra) were at an SNR of ~100/40 compared to the continuum and NA/10 compared to the H beta line. For the radial velocity work and I think the Doppler Tomography, flux calibration is not too crucial. So, while rectified spectra should be good enough to first-order, I try to do relative (and when the condtions allow absolute) flux calibration whenever possible, in case I do need it.
For Priority 6, it's also important to remember that the period of the source is 90.85 minutes. So shorter exposures that get stacked are needed. I probably would try to not go beyond 9 minutes with readout, and would favour 4.5 minutes or less. You might want to try stacking spectra based on the "phase". In that case, you want to start observations that you will stack at the same phase an integer times 90.85 minutes apart. For instance, if you are doing 9 minute exposures with readout over ~6 hours, start exposures at t_1 = 0, 9.085, 18.0170, ..., 354.315 ,363.40 minutes. You might even be able to pickup a day later as long as you start day two's t_2=0 at an integer times 9.085 minutes after t_1=0.
PS, we have scheduled observations for time-resolved spectroscopy with the SAOO 1.9-m tonight and tomorrow (tonight's weather looks iffy). I'm not sure what spectral resolution they decided to use.
Hi folks, I've just submitted a simple visual observation for 2030UT November 8th.
I estimate it's visual magnitude at 9.5 before clouds rolled in.....
Keith.
I have uploaded my data from Chile which was partly clouded out. I had different comp stars in the first place but realized that the sequence was changed in the mean time (some of my comps did not show up any more). Due to the brightness of the source I have changed the comps but see now that there is lots of scatter.
Probably have to remove the data at a later stage.
Josch
Hi Greg,
Thanks for the detailed information. Here are a couple of spectra which give an idea of my typical limiting magnitude at ~15-20 SNR
SU Uma at R=500 V mag 14.7 9x600sec
https://britastro.org/specdb/data_graph.php?obs_id=7679
Nova Cas 2020 R=2000 covering 5000A V mag 13.3 6x600sec
https://britastro.org/specdb/data_graph.php?obs_id=7109
VY Aqr is low from Northern England though.
This is all academic at the moment for me though as the forecast is poor :-(
Cheers
Robin
>Here are a couple of spectra which give an idea of my typical limiting magnitude at ~15-20 SNR
and for completeness one at my maximum resolution
v346Ori at R=15000 at H alpha V mag 10.1 6x 600sec
https://britastro.org/specdb/data_graph.php?obs_id=3379
AAVSO Alert Notice 724 announces an observing campaign on the cataclysmic variable VY Aqr. Please see the notice for details and observing instructions.
There are threads for this campaign under the following forums:
- Campaigns and Observation Reports: https://www.aavso.org/vy-aqr-campaign
- Cataclysmic Variables: https://www.aavso.org/vy-aqr-outburst
- Spectroscopy: https://www.aavso.org/vy-aqr-campain
- Time-Sensitive Alerts: https://www.aavso.org/comment/74849
Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomers and by HQ. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
AAVSO Alert Notice 724 announces an observing campaign on the cataclysmic variable VY Aqr. Please see the notice for details and observing instructions.
There are threads for this campaign under the following forums:
- Campaigns and Observation Reports: https://www.aavso.org/vy-aqr-campaign
- Cataclysmic Variables: https://www.aavso.org/vy-aqr-outburst
- Spectroscopy: https://www.aavso.org/vy-aqr-campain
- Time-Sensitive Alerts: https://www.aavso.org/comment/74849
Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomers and by HQ. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
Hi All,
I apologize that I have not been able to keep you all updated, especially during the echo outburst. I have been dealing with both COVID-19 related administration issues at my University, and then the moment those cleared, I was dealt two health setbacks (I am currently doing ok).
Thank you so much for the incredible data that you all have collected. Combined with the AAVSO historical record, on the raido side we were able to time our observations when we wanted them to occur during the decay!! I will be checking in with that time to find out if we got any detections from imaging within individual epochs, imaging over a full individual epoch, or stacked analyses of multiple epochs. I will also check in with Professor Knigge to find out what we got from Swift X-ray and Ultraviolet observations.
Due to my health issues, I cannot guarantee that I will get back to you before the new year. If I do not, I wish you all a happy holiday season, clear skies, and safety for you and your families.
- Greg Sivakoff