[vsnet-alert 25503] Re: SS Cyg: standstill

[Mariko Kimura]

I think Fig.10 in our paper is helpful to see the difference between
the small and long outbursts in SS Cyg-type stars.
The time evolution of the disk mass and the angular momentum is
displayed.
https://ui.adsabs.harvard.edu/abs/2020PASJ...72...22K/abstract

In the long outburst, the disk radius reaches the tidal truncation
radius and a lot of mass and angular momentum should be
removed from the disk.
However, the correct treatment of heating by the tidal torque
at the disk outer edge is our future work (Actually I have
investigated a little).
Our paper also proposed a possible model for IW And-type
phenomenon on the basis of the suggestion by Kato (2019).
https://ui.adsabs.harvard.edu/abs/2019PASJ...71...20K/abstract

- Mariko


On 2021/03/03 18:29, Siegfried Vanaverbeke 
siegfriedvanaverbeke at gmail.com via vsnet-alert wrote:
> Are any of these hypotheses about the standstills actually corroborated by
> numerical models of the process ?
>
> Siegfried
>
> Op wo 3 mrt. 2021 om 01:42 schreef Taichi Kato <tkato at kusastro.kyoto-u.ac.jp
>> :
>> 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.
>>
>>