Observations of Binary Stars with the 1.3-m Devasthal Fast Optical Telescope Using Speckle Interferometry: An Attempt

TL;DR

This feasibility study evaluates optical speckle interferometry on the 1.3-m DFOT using a sCMOS backend to image binary stars. Using short exposures and standard speckle analysis, the authors demonstrate that atmospheric fluctuations can be mitigated via autocorrelation for wide binaries, but close binaries remain unresolved without instrumentation upgrades. The results identify tracking errors and instrumental limitations as key barriers to diffraction-limited performance, while validating the approach and motivating further enhancements for meter-class telescopes. Overall, the work provides a practical path toward implementing optical interferometry techniques at DFOT and similar facilities, with clear guidance for future improvements and systematic observing campaigns.

Abstract

We present a feasibility study exploring the implementation of optical interferometry and speckle techniques with the 1.3-m Devasthal Fast Optical Telescope (DFOT) at ARIES, which is currently dedicated to photometric observations. Using the sCMOS camera as the DFOT backend, we perform interferometric speckle observations of several binary stars. Standard Speckle Interferometry (SI) algorithms are applied to analyze the recorded data. While this study does not aim to achieve the diffraction limit of DFOT or address a full science-driven resolution case, it serves as a crucial testbed for instrumentation, data acquisition, and analysis of Speckles with DFOT. Notably, we successfully identify and correct tracking-related positional errors in the observed binary systems, demonstrating the viability of the approach. These results provide strong motivation for more systematic observations and future implementation of optical interferometry techniques at meter-class telescopes.

Figures (4)

• Figure 1: The Devasthal Fast Optical Telescope (DFOT) along with the sCMOS camera at the backend. The attached computer system is kept at the right, and the dome is closed.
• Figure 2: Representative speckle images of six binary systems-A Bootis, $\alpha$ Ophiuchi, $\gamma$ Leonis, $\gamma$ Virginis, $\alpha$ Virginis, and $\zeta$ Herculis-arranged from top left to bottom right. Each frame has an exposure time of 2 ms and has been corrected for instrumental effects through bias subtraction and flat-field normalization.
• Figure 3: The average of speckle patterns over many frames for six binary systems: A Bootis, Alpha Ophiuchi, Gamma Leonis, Gamma Virginis, Alpha Virginis, and Zeta Herculis, arranged from top left to bottom right. The tailed nature in each averaged speckle shows the binary behavior of targets.
• Figure 4: Auto-correlation of speckle patterns averaged over many frames for six binary systems: A Bootis, Alpha Ophiuchi, Gamma Leonis, Gamma Virginis, Alpha Virginis, and Zeta Herculis, arranged from top left to bottom right. The top two and the bottom two panels show the single nature of the respective binary star systems due to unresolved speckle patterns (shown in fig. \ref{['fig:Speck']}), which can be solved with additional instrumentation on detectors, including lenses and narrow filters. The third and fourth panel clearly exhibits the characteristic three-lobed structure, revealing the binary nature and a stable orbital signature of variable speckles over time, shown in fig. \ref{['fig:Speck']}. These results demonstrate that the autocorrelations of many frames effectively suppress atmospheric variability over the resolved binaries, allowing the underlying binary structure to emerge.