YY Herculis outburst reveals phase-dependent changes in temperature and brightness

Star system: YY Herculis | Distance from the Sun: 26852 light years

YY Herculis is a symbiotic star system that has experienced several brightening events over the past century. In 2021, astronomers observed a hot-type outburst in YY Herculis using the Himalayan Chandra telescope, focusing on changes that occur during the system's secondary minimum.

This study monitored YY Herculis from 2021 to 2023, covering one and a half orbital cycles. Researchers analyzed how the temperature and brightness of the system changed during and after the outburst, finding that these properties depend on the system's position in its orbit. The most reliable measurements were made at phase 0.5, which corresponds to the secondary minimum.

The results show that YY Herculis can display both hot-type and cool-type outbursts, similar to the star AG Draconis. The study also confirmed that the shape of the system, known as the ellipsoidal effect, influences the observed brightness during the secondary minimum.

Key findings

 
YY Herculis experienced a hot-type symbiotic outburst in 2021, observed with the Himalayan Chandra telescope.
 
Temperature and luminosity estimates vary with the system's orbital phase, with the most reliable values at phase 0.5.
 
Both hot-type (2021) and cool-type (1993) outbursts have been observed in YY Herculis, similar to AG Draconis.
 
The ellipsoidal effect contributes to changes in brightness during the secondary minimum.
 
This study covered 1.5 orbital cycles, providing a detailed look at the system's behavior over time.

Scientific study

The 2021 hot-type symbiotic outburst of YY Herculis: an optical follow-up study (external link)