Stellar Multiplicity via Speckle Interferometry with the 3.6 m Devasthal Optical Telescope

TL;DR

This work demonstrates the viability of speckle interferometry on the 3.6 m DOT to overcome atmospheric limits and achieve diffraction-limited angular resolution for binary stars. The authors develop a forward speckle model for single and binary stars and apply Bayesian inference with Dynesty to extract angular separation $\Delta\theta$, position angle $\phi$, brightness ratio $b$, and PSF scaling $a$ from autocorrelation data. Using short-exposure frames from DOT and observations of 52 Ori and 10 Ari, they show that parameters can be retrieved even for faint companions, with 52 Ori yielding $\Delta\theta \approx 0.80''$, $\theta \approx 0.99''$, $\phi \approx 130^{\circ}$, and $b \approx 1$, while 10 Ari provides constraints on $\phi \approx 77^{\circ}$ among others albeit with exposure-dependent systematics. The work establishes SI as a practical high-angular-resolution technique for Indian astronomy and sets the stage for broader applications in stellar multiplicity studies.

Abstract

Conventional ground-based optical telescopes, even those with large apertures, primarily observe stars, close binaries, and multiple systems as unresolved point sources through photometric measurements. Spectroscopy can identify multiple stellar components within a system, but both techniques are fundamentally limited in resolving stellar surfaces and providing direct angular separations. Although photometric and spectroscopic observations yield critical information on magnitudes/flux, metallicities, and orbital properties, complementary high-angular-resolution methods are required to constrain additional system characteristics, including angular orbital parameters, model-independent distances, radii, and stellar masses. The limitations of these two methods arise due to the Diffraction Limit of the telescopes and atmospheric turbulence. Speckle Interferometry (SI) is a clever and affordable method for ground-based telescopes to work around atmospheric turbulence. In this work, we utilize the speckle images obtained by the 3.6 m DOT and demonstrate the capability of SI to resolve binary systems, measure their orbital separations, and determine their position angles. For systems with faint companions where conventional analysis fails, we employ Bayesian inference to model speckle patterns and estimate orbital parameters with high precision. These results establish the effective methodology for using a medium-sized, 4-m class telescope like the DOT as a high-resolution stellar interferometer and demonstrate the potential of speckle interferometry as a powerful technique to advance optical interferometric studies within Indian astronomy.

Figures (8)

• Figure 1: The left and right panels show the speckle patterns of 52 Orionis with 2 ms and 10 ms exposure times, respectively.
• Figure 2: The left and right panels show the fringe patterns of 52 Orionis obtained by averaging over the Fourier power spectra of 1000 short-exposure image frames with exposure times of 2 ms and 10 ms, as shown in Fig. \ref{['fig:Ori']}. The square root of both data sets has been taken here for clear visualization.
• Figure 3: The left and right panels show the graphical representation of 52 Orionis after taking the inverse Fourier transform of the power spectrum (autocorrelation) of Fig. \ref{['fig:Ori_FT']}, respectively.
• Figure 4: The left and right panels show the results of parameter estimation of 52 Orionis using the Bayesian modeling of autocorrelation (Fig. \ref{['fig:Ori_auto']}) of speckle patterns for 2 ms and 10 ms exposure times (one example shown in Fig. \ref{['fig:Ori']}), respectively.
• Figure 5: The left and right panels show the speckle patterns of 10 Arietis with 10 ms and 100 ms exposure times, respectively.