Affiliation
American Association of Variable Star Observers (AAVSO)
Tue, 07/11/2023 - 16:10
AAVSO Alert Notice 828 announces a campaign beginning immediately on the SU UMa-type cataclysmic variable V844 Her. Please see the notice for details and observing instructions.
There are threads for this campaign under the following AAVSO forums:
- Campaigns and Observing Reports: https://www.aavso.org/v-844-her-campaign
- Cataclysmic Variables: https://www.aavso.org/v-844-her-campaign-01
Please subscribe to these threads if you are participating in the campaign so you can be updated. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
We took a look at V844 Her last night with the Notre Dame campus scope (the Sarah L. Krizmanich telescope). It was near its typical quiescent mag of 17.
It has had two "normal" outbursts since the last super-outburst, although we might have missed a super-outburst when V844 Her was behind the Sun. Either way, I think we are due for a super-outburst soon.
I see several observations in the AAVSO database added in the past week. In particular, Ian Sharpe has done a few time-series observations. Thank you! This sort of observation will be critical when the outburst does happen.
Good observing!
Peter
Greetings,
VSX has this for "period" 0.054643 d (78.686 min). I presume that is the orbital period. Observers should understand the 29 min. WD spin would be modulated onto the super-hump periiod.
I've heard lot about negative detections by TESS for various objects. From what little I have found in my short time searching for it it appears the TESS observing bandpass is very, very wide, 600 to 1000 nm. If we assume the WD produces most of its light in the blue does that mean that TESS may be dominated by light from other physical processes in quiessence and not the WD light? Another that has bothered me is H-Alpha would be in the TESS bandpass for a CV but not in say an Ic filter so TESS might be dominated by H-Alpha light while the narrower Ic filter isn't.
Any comments?
Yes, the 78 minute period is the orbital period of the system. When the disk goes into super-outburst the dominant variation is the superhump oscillation which is a bit longer than this and variable in frequency. So, in the initial outburst, the 29 minute period would not be apparent until several nights of time-series photometry has been analyzed. The 29-minute period was seen in AAVSO data when V844 Her went into super-outburst in 2006, but it was tough to spot with the stronger superhump oscillation dominating.
WD rotation variations often has a higher amplitude in the blue, but generally the broad-band filters are better than narrow-band at picking it up. In the case of V844 Her, the 29-min oscillation is only seen during outburst - probably because the enhanced accretion rate generates continuum emission at the magnetic poles. This emission is seen over a wide wavelength range, even the very red TESS bandpass.
The 29-min period IS seen by TESS during an outburst. The hard part is seeing a low-amplitude 29-min signal from the ground where we only get a few hours of data at a time. 29-min is relatively slow and there are superhumps and harmonics during outburst that has made the WD spin period hard to spot.
Peter
All,
The paper describing the new periodicity in V844 Her has arrived on the astro-ph server:
https://arxiv.org/abs/2308.10344
The 29-min periodicity was seen only during an outburst caught by TESS. It is not observed during quiescence by TESS, X-rays, or optical ground-based monitoring.
There is some evidence of the signal in Arto Oksanen's photometry series in the AAVSO database from an outburst in 2006. I am hoping that we can get great time-series coverage during the up-coming outburst (arriving soon I hope).
Peter
V844 Her 2460218.49665 16.791 0.063 CV
Appears to be early into the rise to an outburst...
Jim (DEY)
All,
Jim DeYoung just reported that V844 Her was unusually bright last night. This may be the start of an outburst - normal or super, it is too early to tell. At V=16.79, it is about twice the brightness it has been. In superoutburst it can reach V~12.
Please do intensify monitoring this star to see if it continues to rise. If this is an outburst, I ask that long time-series photometry be obtained. The unusual period detected in TESS is 29 minutes. This is slow and rather weak compared to the superhumps that will exist. So time-series lasting 2 hours or more are needed. And photometry on several consecutive nights is ideal.
This may only be a blip, but it does look promising.
Peter
All,
Jim DeYoung just reported that V844 Her was unusually bright last night. This may be the start of an outburst - normal or super, it is too early to tell. At V=16.79, it is about twice the brightness it has been. In superoutburst it can reach V~12.
Please do intensify monitoring this star to see if it continues to rise. If this is an outburst, I ask that long time-series photometry be obtained. The unusual period detected in TESS is 29 minutes. This is slow and rather weak compared to the superhumps that will exist. So time-series lasting 2 hours or more are needed. And photometry on several consecutive nights is ideal.
This may only be a blip, but it does look promising.
Peter
Hello Everyone. I wanted to let people know that are interested in this star, that it appears to be very bright right now. Using AUID 000-BBX-846 which is 12.352 mag as a reference, I am getting 12.252 V-mag for V844 Her, (about 0.1 mag difference in quick look photometry using MaximDL). if I am identifying it correctly, which is near its peak brightness for it according to the chart. I will follow it for as long as I can tonight. I took a look at the AAVSO light curves from a a couple weeks ago and it is not this bright. Maybe I am misidentfying it? Anyhow, I thought I should let people know just in case something is happening.
All,
This does look like the real thing. I'm looking at V844 Her now and it is near it is 12th mag, typical of its superoutbursts.
The outburst should decay 3 mags over 2 weeks. It is this entire period where TESS detected the 29 min periodicity. So long time-series over the next two weeks will be very useful.
Good observing!
Peter
Just uploaded a short 40m time series before it got too low for me, around V=12.29.
Keith
Hi All:
I'll be starting another time series this Thursday, running from 20:35 - 21:40 MDT - in case anyone wants to jump in before and/or after I wrap up to get a longer continuous series. Or, is less important to get time series obs when its decreasing?
Enjoy
Gary
V0844 was very bright last night, reaching V magnitude 12.4. It appears to be in outburst.
Greetings,
I don't usually do time-series photometry in my olde age but using the current version of Muniwin, very little experience with it, and using the 128 and 136 comps, both B-V around 1.0 I get "significantly" different results than when using the 124 which has a B-V of around 0.6. Comp minus check star plot is also a bit unexpected. At his point I wouldn't put a lot of confidence in my time-series photometry that has been uploaded so far to the db.. I'm trying to figure things out to see what is zooming what and may upload corrected photometry at some point.
FYI
Jim (DEY)
Jim,
During outburst V844 Her is probably fairly blue, so color differences between it and your comp stars can be causing trouble. You should avoid the very red comp stars and aim to use the most blue you can find.
V844 Her has been reaching an airmass of 2 (elevation of 30 deg) at the end of my observing runs. Just like watching a sunset, the atmosphere scatters blue light and makes stars more red as they get closer to the horizon. So blue stars will get fainter faster than redder stars and make it appear that there is a slow variation in brightness.
Peter
Peter,
The problem turned out to be a simple configuration problem with Muniwin that didn't take. Read noise and CCD gains were wrong on the first attempt. All fixed now and data uploaded.
Btw, I have observed CVs for a long, long time... Ahhh, the olde visual obs. days... calling Janet at night, at home, to alert her to a CV going into outburst so she could decide if it was a false alarm before contacting the HEAO-2 or the IUE so they could schedule obs. Sounds familiar but no blips so far and no blips in the olde days! I think we started doing CCD-based photometry of CVs in 1993 or so, EF Peg and others. Did a lot of photometry on V1974 Cygni and still check it now and then. Others I don't remember of the top of my head.
Best regards,
Jim (DEY)
I started doing…
Jim,
I started doing visual observations for the AAVSO back when I was 16. I was terrible at it. Thank goodness for CCDs as now I can make accurate brightness estimates.
Peter
Yes, I remembered the name... wasn't 100% sure it was "you". Now we know.
Best regards,
Jim (DEY)
AAVSO Alert Notice 834 reports on the outburst of V844 Her and important instructions from Principal Investigator Dr. Peter Garnavich. Please see the notice for details.
There are threads for this campaign under the following AAVSO forums:
- Campaigns and Observing Reports: https://www.aavso.org/v-844-her-campaign
- Cataclysmic Variables: https://www.aavso.org/v-844-her-campaign-01
Please subscribe to these threads if you are participating in the campaign so you can be updated. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
Thank you all for observations of V844 Her and alerting us to the outburst in October. Doing a quick look at the CCD data in the AAVSO archive, we do see the mysterious 29-minute periodicity, as well as the large superhump oscillations. This is certainly the most well-observed outburst of V844 Her, and one of the most extensive datasets covering a superoutburst that I know of.
With your help, we triggered Swift x-ray and UV observations at the start of the outburst and Swift executed 6 visits covering the outburst. I have a student analyzing the x-ray variations and this will become part of her honors thesis when she graduates in the spring!
It has been exciting, thanks again.
Peter