Single-aperture spectro-interferometry in the visible at the Subaru telescope with FIRST: First on-sky demonstration on Keho'oea (α Lyrae) and Hokulei (α Aurigae)

Abstract

FIRST is a spectro-interferometer combining, in the visible, the techniques of aperture masking and spatial filtering thanks to single-mode fibers. This instrument aims to deliver high contrast capabilities at spatial resolutions that are inaccessible to classical coronagraphic instruments. The technique implemented is called pupil remapping: the telescope is divided into subpupils by a segmented deformable mirror conjugated to a micro-lens array injecting light into single-mode fibers. The fiber outputs are rearranged in a nonredundant configuration, allowing simultaneous measurement of all baseline fringe patterns. The fringes are also spectrally dispersed, increasing the coherence length and providing precious spectral information. The optical setup of the instrument has been adapted to fit onto the SCExAO platform at the Subaru Telescope. We present the first on-sky demonstration of the FIRST instrument at the Subaru telescope. We used eight subapertures, each with a diameter of about 1 m. Closure phase measurements were extracted from the interference pattern to provide spatial information on the target. We tested the instrument on two types of targets : a point source (Keho'oea) and a binary system (Hokulei). An average accuracy of 0.6 degree is achieved on the closure phase measurements of Keho'oea, with a statistical error of about 0.15 degree at best. We estimate that the instrument can be sensitive to structures down to a quarter of the telescope spatial resolution. We measured the relative positions of Hokulei Aa and Ab with an accuracy about 1 mas. FIRST opens new observing capabilities in the visible wavelength range at the Subaru Telescope. With SCExAO being a testing platform for high contrast imaging instrumentation for future 30-meter class telescopes, FIRST is an important stepping stone for future interferometric instrumentation on extremely large telescopes.

Accepted for publication in Astronomy and Astrophysics on July 7th 2023

References in corpus (10)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Interferometric data reduction with AMBER/VLTI.Principle,estimators and illustration
• Efficient injection from large telescopes into single-mode fibres: Enabling the era of ultra-precision astronomy
• The VAMPIRES instrument: Imaging the innermost regions of protoplanetary disks with polarimetric interferometry
• High dynamic range imaging by pupil single-mode filtering and remapping
• High-performance 3D waveguide architecture for astronomical pupil-remapping interferometry
• Visible and Near Infrared Laboratory Demonstration of a Simplified Pyramid Wavefront Sensor
• High dynamic range imaging with a single-mode pupil remapping system : a self-calibration algorithm for redundant interferometric arrays
• Sparse aperture masking at the VLT II. Detection limits for the eight debris disks stars $\beta$ Pic, AU Mic, 49 Cet, $\eta$ Tel, Fomalhaut, g Lup, HD181327 and HR8799
• An aperture masking mode for the MICADO instrument