# Discovery of Standstills in the SU UMa-Type Dwarf Nova NY Serpentis

## TL;DR

This study reports the first clear observation of standstills occurring between superoutbursts in an SU UMa-type dwarf nova, revealing new insights into disk behavior and resonance conditions during these phases.

## Contribution

It demonstrates that standstills can occur in SU UMa-type dwarf novae and provides evidence linking disk radius growth and tidal instability to these phenomena.

## Key findings

- Standstills observed twice in 2018 in NY Ser.
- No superhumps detected during standstills.
- Superoutbursts can start directly from standstills.

## Abstract

We found that the SU UMa-type dwarf nova NY Ser in the period gap [orbital period 0.097558(6) d] showed standstills twice in 2018. This is the first clear demonstration of a standstill occurring between superoutbursts of an SU UMa-type dwarf nova. There was no sign of superhumps during the standstill, and at least one superoutburst directly started from the standstill. This provides strong evidence that the 3:1 resonance was excited during standstills. This phenomenon indicates that the disk radius can grow during standstills. We also interpret that the condition close to the limit of the tidal instability caused early quenching of superoutbursts, which resulted substantial amount of matter left in the disk after the superoutburst. We interpret that the substantial matter in the disk in condition close to the limit of the tidal instability is responsible for standstills (as in the high mass-transfer system NY Ser) or multiple rebrightenings (as in the low mass-transfer system V1006 Cyg).