Instrument presentation

The Fibered Imager foR a Single Telescope (FIRST) is a spectro-interferometer operating in the visible wavelengths at a resolution of about 3,000. It is fed by the SCExAO system. FIRST was developed in collaboration with the Paris Observatory.

FIRST feeds a Photonic Lantern device from a focal plane. The Photonic Lantern consists of a multi-mode input slowly transitioning into 19 Single-mode fibers. The multi-mode input’s core has a diameter of 25 micrometers.

Figure 1: Photonic Lantern hardware. The input is a multi-mode fiber, and the outputs are 19 single mode fibers spliced into a V-groove

The 19 outputs of the Photonic Lantern feed a mid resolution spectrograph (R~3,000), optimized for wavelengths ranging from 600 nm to 780 nm. The spectrograph is equipped with a wollaston, allowing to split the polarization for each output, providing a total of 38 spectra (see below). More information on the instrument and its integration on SCExAO are available here.

Figure 2: Example of imaging of `Aua (Betelgeuse) using the Photonic Lantern. This image is averaged from 200,000 frames, and displays 38 spectra, corresponding to the two polarizations from each of the 19 outputs of the Photonic Lantern.

General information

FIRST parameters
Operating wavelength	620 - 780 nm
Spectral resolution	R~3,000
Spatial resolution	25 mas
Spectro-astrometric precision	50 uas
Field of view	80 mas @ f/8	Optimal injection efficiency is for a focal ratio of 8, providing a field of view of 80 mas. The field of view is defined as the area where the injection efficiency drops to 50% compared to the center of the field.
Exposure times	7.2us - 1800 s.	Fast or Slow readout modes possible

Observing Modes

Mode 1: Spectro-astrometry

Capability	Sub-λ/D measurement of photocenter position as a function of wavelength, enabling spatial information retrieval at scales well below the diffraction limit.
Science applications	- Mapping accretion signatures on protoplanets via $H\alpha$ emission - Detecting asymmetries in stellar environments - Measuring spatial distribution of spectral features
Data requirements	- Primary: FIRST-PL camera acquisition - Auxiliary (required): Focal plane images from at least 1 of 2 additional cameras (SCExAO/VAMPIRES and/or SCExAO internal IR camera)
On-sky calibration	- Self-calibrating via tip-tilt telemetry from auxiliary cameras - No separate calibrator star observation required
Off-sky calibration	- Wavelength calibration (Neon lamp) - Flat field calibration (Halogen lamp) - Dark frames

Mode 2: On-Axis Imaging

Capability	λ/D spatial resolution within the field of view of the photonic lantern (~130 mas), with modest contrast capabilities (contrast ~10).
Science applications	- Resolving stellar surfaces and features - Detecting close companions within the field of view - Characterizing compact circumstellar environments
Data requirements	- Primary: FIRST-PL camera acquisition - Auxiliary (optional): Telemetry from SCExAO for additional wavefront/PSF monitoring
On-sky calibration	- Calibrator star observation (similar magnitude to target or brighter)
Off-sky calibration	- Wavelength calibration (Neon lamp) - Flat field calibration (Halogen lamp) - Dark frames

Mode 3: Off-Axis Imaging

Capability	Extended field of view beyond the Photonic Lantern’s intrinsic ±20 mas, enabling observations at separations up to ~1000 mas. Achieves contrast ratios >1000 at separations ≥100 mas.
Science applications	- Characterizing faint companions - Wide binary systems - High contrast imaging
Data requirements	- Primary: FIRST-PL camera acquisition - Auxiliary (optional): Telemetry from SCExAO for additional wavefront/PSF monitoring
On-sky calibration	- On-axis pointing on primary star (serves as calibration) - Interleaved on-axis/off-axis observations recommended
Off-sky calibration	- Wavelength calibration (Neon lamp) - Flat field calibration (Halogen lamp) - Dark frames