[vsnet-alert 25490] Re: SS Cyg: standstill

[Mariko Kimura]

Thank you for your suggestions.
At least for me, filtered photometry (U, B, V, R, I) is helpful.

- Mariko

On 2021/03/03 12:23, Brian Skiff wrote:
>       Since this event is on-going and occurring on a genuinely bright target, would Kato-san or others suggest the most useful observations to be made?  I think it would be useful to be a little prescriptive about what is to be done with these very many cv outbursts.  It seems that the opportunity exists in this case to do something more use diagnostic than simple unfiltered photometry (i.e. the usual thing).  Would having, say, U, V, I, or Sloan z (= Paschen decrement) time-series photometry be helpful?  Time-resolved H-alpha spectroscopy?  Helium lines?  Polarization?  Spectra in the near-IR?
>
>
> \Brian
>
>
>
> On Mar 2, 2021, at 5:42 PM, Taichi Kato <tkato at kusastro.kyoto-u.ac.jp> wrote:
>
> Re: SS Cyg: standstill
>
>> Akazawa-san and Kasai-san reported their latest observations.
>> The standstill in SS Cyg seems to be accompanied by oscillatory
>> variations even at this moment.  Their timescale is around a week.
>> It would be important to see if SS Cyg enters Z Cam-type standstill
>> with constant luminosity or repeats oscillations.
>    It has been documented that some standstills are
> associated with a hint of mini-outbursts occurring
> within the standstill at the normal interval
> frequency (Szkody and Mattei 1984, PASP 96, 988).
> So, the presence of low-amplitude oscillations
> may not be a surprise.
>
>    It would be noteworthy that the outburst preceding
> this standstill had a "shoulder" in the light curve
> at the end of 2020 Dec., particularly evident in
> Akawaza-san's light curve.  This phenomenon indicates
> that the disk radius reached the tidal truncation
> radius during this outburst.  The angular momentum
> of the disk was maximal during this outburst.
> The present standstill appears (to me) to be a result
> of the insufficient removal of the disk mass and angular
> momentum during this outburst (SS Cyg-type -- currently
> an ironical term -- outbursts reaching the tidal truncation
> radius are usually long ones, but this one lacked
> the flat-topped portion).
>
>    The presence of oscillations during the standstill
> somewhat reminds me of IW And stars.  The present
> phenomenon might provide a clue in understanding
> the IW And-type phenomenon and SS Cyg-type phenomenon
> as a whole.