High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM

TL;DR

This paper introduces a novel optical speckle imaging method combining traditional speckle techniques with wavelet-based post-processing to achieve diffraction-limited, high-contrast images from ground-based telescopes without coronagraphs.

Contribution

It presents the first integration of high contrast considerations into optical speckle imaging, enabling detection of faint objects near bright stars with simpler instrumentation.

Findings

Achieved high contrast (1e-5) within 0.5-2 arcseconds around bright stars.

Detected brown dwarf companions at contrast DI~12 at 2" without coronagraphs.

Demonstrated potential for studying dense stellar environments and faint objects.

Abstract

In this paper, we present an original observational approach, which combines, for the first time, traditional speckle imaging with image post-processing to obtain in the optical domain diffraction-limited images with high contrast (1e-5) within 0.5 to 2 arcseconds around a bright star. The post-processing step is based on wavelet filtering an has analogy with edge enhancement and high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope (NOT) and the lucky imaging instrument FASTCAM show that we are able to detect L-type brown dwarf companions around a solar-type star with a contrast DI~12 at 2" and with no use of any coronographic capability, which greatly simplifies the instrumental and hardware approach. This object has been detected from the ground in J and H bands so far only with AO-assisted 8-10 m class telescopes (Gemini, Keck), although more recently detected with small-class telescopes in the K band. Discussing the advantage and disadvantage of the optical regime for the detection of faint intrinsic fluxes close to bright stars, we develop some perspectives for other fields, including the study of dense cores in globular clusters. To the best of our knowledge this is the first time that high contrast considerations are included in optical speckle imaging approach.