Study of the low-amplitude Z Cam star IX Vel

TL;DR

This study reclassifies IX Vel as a Z Cam-type dwarf nova, revealing its low-amplitude outbursts and standstills, and shows that variations in mass-transfer rate drive state transitions.

Contribution

It provides new observational evidence that IX Vel is a Z Cam star and demonstrates the impact of mass-transfer rate variations on its outburst behavior.

Findings

IX Vel is a low-amplitude Z Cam-type dwarf nova.

Cycle lengths of outbursts vary between 13 and 20 days.

Brighter states correlate with shorter cycle lengths and smaller amplitudes.

Abstract

IX Vel has been considered as one of the prototypical novalike cataclysmic variables with thermally stable accretion disks. Using All-Sky Automated Survey (ASAS-3) and All-Sky Automated Survey for Supernovae (ASAS-SN) observations, I found that IX Vel is a low-amplitude dwarf nova showing standstills. This object has been re-classified as a Z Cam-type dwarf nova. This conclusion is consistent with the mass-transfer rate using the Gaia parallax which places the object near the lower limit of the thermal stability. Using two-dimensional Least Absolute Shrinkage and Selection Operator (Lasso), I found that the cycle lengths of dwarf nova outbursts varied between 13 and 20 d. Analysis of the ASAS-3 data suggested that the cycle lengths are shorter and the amplitudes are smaller when the system is bright. Standstills occurred when the system was bright. These results support the idea that a subtle variation in the mass-transfer rate from the secondary causes transitions between outbursting state and standstills in Z Cam stars.