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SS Cygni: Dense CCD Coverage

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MoFatta
SS Cygni: Dense CCD Coverage

Hi everyone, visual observer here. I just started my observations of SS Cygni for this year, and I noticed something that I don't recall seeing before. Over the last few months, I see very dense groups of CCD V points. One of many such examples is right before midnight June 3: over 700 points from a single observer in just a few hours.

In that particular example, there are variations on timescales of 15 minutes of around 0.3 mag, and there's even a single jump of about 0.8 mag. To me, these seem like fairly large and rapid fluctuations.

I've never heard of SS Cygni doing this. Have these observers found something that was previously unknown? This is very intriguing to me and I'm just wondering if anyone might know anything about these interesting measurements.

My apologies if this has already been discussed. I did some quick searching and didn't see anything about it.

Clear skies,

BADB

LMA
LMA's picture
SS Cygni: Dense CCD Coverage

I am one of the observers who does that kind of dense coverage of SS CVyg when I have some spare time on my observing schedule. Like many CV,  SS Cyg can show rapid erratric changes when observed with high time resolution.

LMA

 

LMN
LMN's picture
Hi!

Hi!

I've also done a few of these. This was in relation to calls for high time resolution observations to identfify short period, quasi-periodic oscillations in the accretion disk. Haven't done since June since my camera is away on service...

I have not seen any systematic analysis of it yet, though. Anything you've seen?

Magnus (LNM)

IanKemp
Dense CCD coverage

Hi guys I am very interested in this thread and the comments.

Last year I observed VW Hyi - a southern sky object which is actually a UGSU variable star (ie red star orbiting a white dwarf). This system has had a lot of study and has unravelled a lot of our understanding of this type of system - which is a precursor to the Type 1A supernovae that we use to measure the expansion of the Universe.

Now my observations last year suggested that the VW Hyi system has some 'high frequency' periods in its light curve. The orbital period of the system is about 2 hours, but I'm talking about fluctuations around 15 minutes. I have published these findings in an NZ/Australian journal https://www.variablestarssouth.org/vss-newsletter-july-2020/ . The southern sky system I studied (VW Hyi) will probably have its next outburst in September or October this year. And I will be there waiting. But if anyone here is collecting similar data on the same type of (UGSU) systems - at high cadence (photometry every 30 sec or so) I would be very interested to speak with you and perhaps we can collaborate on the next paper. Longer term I want to use computer modelling of the accretion processes to understand what type of accretion disk we have in these UGSU stars. Mail me!

hambsch
hambsch's picture
VW Hyi

Hi Ian,

thank you for the link to your journal and your valuation of my 2011 data. I have taken another dense coverage of VW Hyi in 2018 on request of Christian Knigge in B and V filters. Data are with the AAVSO maybe you are interested. He and his collaborators wrote a paper on the results (https://arxiv.org/pdf/2003.03056.pdf). I could also follow the next outburst if you are interested and we could share the data.

Josch

MoFatta
SS Cyg and VW Hyi

Hello and thank you to everyone for the replies! As far as I can tell, it looks like these rapid fluctuations are known, but not *widely* known. Again, these observations are very exciting to me and I wonder if I could catch something like that visually.

Indeed, LMN's description of "short period, quasi-periodic oscillations" is a perfect description of what I see in the lightcurve. There is scatter in the visual data, and I always attributed it to different telescopes and different eyes but perhaps some of it is due to these oscillations. And also to LMN no, I haven't seen any analysis of it but I admit I haven't looked too hard.

The discussion of VW Hyi was all new to me and absolutely fascinating. I looked at some random data from HMB around 8-14-18 and there is clearly some short-timescale activity there. What really got my attention was that VW Hyi and similar systems are thought to be precursors to Type 1a supernovae. Wow!!

Thanks again for the insightful replies and as always, clear skies.

BADB

LMN
LMN's picture
Hi!

Hi!

Ian, I'd be very happy to collaborate on that! Where's your email address?

Magnus (LMN)

IanKemp
VW Hyi and other UGSU

Hi All

Great to hear from you - and great to hear from you again Josch!  I am planning to do some high-cadence data collection on VW Hyi during its next super-outburst. I expect this to start around late september; I'll start doing daily monitoring from early September to catch it. 

I am interested in the high-frequency 'wobbles' as I think these will give a clue to the actual structure of the accretion disk.  The Japanese team who modelled this system (see references in my paper) didn't predict anything higher frequency than the superhump - so I think their model can be improved upon.

Magnus - sorry I don't think VW Hyi can be seen from your location, but the SS Cygni data may show the same behaviour, and I'm sure that other UGSU's will be of interest. The trick is to take a short exposure and do photometry with less than 1 minute cadence. I have access to a number of power-spectrum analysis tools and I'll look at the SS Cygni data probably in about a week's time.

By the way, Type 1A supernovae start out as this type of system (or the magnetic equivalent that accretes at the poles of the white dwarf). VW Hyi does not have enough mass to go supernova - the two stars together need to total more than 1.4 solar mass.

- - -Ian- - -  ian.kemp@icrar.org

IanKemp
VW Hyi

Josch, Hi - I did not get to your 2018 data yet!  Also it is known that the colour of the system can change during the super-outburst, so it's recommended that in addition to the high-cadence measurement (for which I'll just use V filter) once per hour to put in B and R as well so the colour change can be monitored. What scope are you using? (Can't be in Europe, surely :-) )? It might be good if we can both observe VW Hyi this year, thereby get better time coverage and or backup measurements.  I have mentioned to Magnus that it would also be good to do a similar study on other UGSU systems, we might be able to correlate the short period variations with some property of the binary system: orbital period, total mass, colour, etc. This could give a clue as to what's causing the short period signal (if it is real :-) )

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