A dispersed heterodyne design for the planet formation imager

Abstract

The Planet Formation Imager (PFI) is a future world facility that will image the process of planetary formation. It will have an angular resolution and sensitivity sufficient to resolve sub-Hill sphere structures around newly formed giant planets orbiting solar-type stars in nearby star formation regions. We present one concept for this design consisting of twenty-seven or more 4m telescopes with kilometric baselines feeding a mid-infrared spectrograph where starlight is mixed with a frequency-comb laser. Fringe tracking will be undertaken in H-band using a fiber-fed direct detection interferometer, meaning that all beam transport is done by communications band fibers. Although heterodyne interferometry typically has lower signal-to-noise than direct detection interferometry, it has an advantage for imaging fields of view with many resolution elements, because the signal in direct detection has to be split many ways while the signal in heterodyne interferometry can be amplified prior to combining every baseline pair. We compare the performance and cost envelope of this design to a comparable direct-detection design.

The planet formation imager

“…For instance, a mid-infrared wavelength range was chosen over mm-wave or near-infrared to access the most diverse aspects of planet formation in the "warm dust" zone. We also seriously explored a new heterodyne interferometer concept using mid-IR laser combs [11,3], although our current baseline array now favors direct detection method to allow L/M band wavelengths which are key to detect young protoplanets themselves. The infrared surface brightness sensitivity is mostly determined by the size of the individual apertures and not the number of telescopes -this pushed the design towards large-area unit telescopes which drives the cost.…”

Status of the Planet Formation Imager (PFI) concept

“…Mid-infrared signal to noise considerations for a heterodyne architecture were presented in Ireland and Monnier (2014). 3 In this section, we describe point-source detection signal-to-noise, focusing on the case of backgroundlimited observations.…”

“…The computing cost for the heterodyne array scales as the number of baselines, with a 30 telescope array considered in Ireland and Monnier (2014). 3 We assume:…”

Planet formation imager: project update

“…The PFI SWG and TWG have published a large number of articles in SPIE, outlining both the science case 2, 5 and possible technical implementations of PFI. 1,3,4,[6][7][8][9][10] This year there are about 13 contributions directly related to PFI: In addition to this work, the PFI TWG will write at least one paper in the planned Science White Book to define a baseline PFI architecture to reference in the science chapters.…”