[vsnet-alert 25508] Re: SS Cyg: standstill

[Mariko Kimura]

As you know, the viscous timescale is much longer than
the dynamical and thermal timescales in the accretion disk
around ~10,000 K, so that the one-zone approximation is
basically applicable.
Of course the 3 dimensional effect works on a warped disk,
but we just assumed the disk is rigidly tilted and not warped
in our paper.
However, if we want to investigate short-term variability on
timescales of less than ~1 day, we should do 3d simulations.
A full 3d treatment is beyond our scope and probably has not
yet been done.

- Mariko

On 2021/03/04 17:53, Siegfried Vanaverbeke wrote:
> Thanks for the abstract.  These are still effective 1d models ?  A 
> full 3d treatment has probably not yet been done.
>
> Siegfried
>
> Op do 4 mrt. 2021 om 02:36 schreef Mariko Kimura 
> <mkimura at kusastro.kyoto-u.ac.jp <mailto:mkimura at kusastro.kyoto-u.ac.jp>>:
>
>     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
>     <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
>     <https://ui.adsabs.harvard.edu/abs/2019PASJ...71...20K/abstract>
>
>     - Mariko
>
>
>     On 2021/03/03 18:29, Siegfried Vanaverbeke
>     siegfriedvanaverbeke at gmail.com
>     <mailto: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 <mailto: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.
>     >>
>     >>
>