HD 158485 revealed as a binary system containing two pulsating stars

The star HD 158485, used to calibrate the James Webb Space Telescope, has been identified as a binary system. By analyzing light fluctuations from two pulsating stars in the pair, researchers calculated the orbital characteristics of the system. This finding is significant because the presence of an unseen companion star can alter the expected brightness data used for astronomical observations.

Star system: HD 158485 | Distance from the Sun: 390 light years

HD 158485 is a well-known A-type Delta Scuti star used as a standard reference point for calibrating the James Webb Space Telescope. While previous data suggested the star was part of a binary system, no specific orbital details were previously confirmed. New analysis of observations from the Transiting Exoplanet Survey Satellite (TESS) confirms that the system consists of two distinct, pulsating components orbiting each other. Because both stars pulsate, they act as independent clocks that allow for precise timing measurements of their orbital movement.

To determine these orbital parameters, researchers measured the pulsation phases of six distinct modes. As the stars move in their orbit, the light they emit experiences delays due to the time it takes for that light to travel to our instruments. By observing these changes in timing, the team created a model of the orbit. They found that the system completes one orbit every 382.8 days with an eccentric, or non-circular, orbit. This model was successfully validated by using early data to accurately predict the results of subsequent observation campaigns.

The discovery of this companion has implications for how we use HD 158485 to calibrate telescopes. Light from the hidden secondary star can blend with the primary, causing small differences in predicted brightness. Accounting for this companion with a two-star atmosphere model suggests variations of up to 2.5 percent in infrared light data. Recognizing this binary nature improves the accuracy of future space-based observations that rely on this star for flux calibration.

Key findings
HD 158485 is confirmed as a binary system with an orbital period of approximately 382.8 days.
The system has an orbital eccentricity of 0.242.
The secondary star has a mass ratio of 0.818 relative to the primary star.
The presence of the companion causes brightness variations of up to 2.5 percent across infrared wavelengths.
Pulsation timing provides a robust method to measure orbits of unresolved binary systems.

Scientific study

TESS Pulsation Timing Reveals the JWST Calibration Star HD 158485 as a Double-pulsator Binary (external link)