Prime Focus Spectrograph (PFS), a next-generation instrument being installed on the 8.2m Subaru Telescope, is a very wide-field, massively multiplexed, optical and near-infrared spectrograph. For its successful science operation, high-quality sky subtraction is of crucial importance to accurately extract weak galaxy signals. To achieve that, we are now developing modeling algorithms to determine the 2D point spread function (PSF) at arbitrary positions on the spectrograph detectors. The light coming into the detectors is affected by various components of the instrument before being observed as the final PSF, such as the telescope pupil illumination, focal ratio degradation in the fibers, and various aberrations of the spectrograph optics. We model the PSF by combining optical models of all these effects. Comparing the model with the data taken in commissioning observations, we determine over a hundred parameters. We present the current status of this PSF modeling.
The PFS (Prime Focus Spectrograph) instrumentation is nearly complete finally. The only missing hardware is the last two spectrograph modules, but the installations are ongoing well as of this abstract being written and are expected to complete very soon. On-sky engineering tests and observations have been carried out continually since September 2021 and, after the resolutions of some major issues on hardware and software, the team successfully observed many targeted stars over the entire field of view (Engineering First Light) in September 2022. The performances and operation of the instrument are being optimized e.g. in the accuracy and speed of fiber positioning process. Long integrations of relatively faint objects are being taken to validate expected increase of signal-to-noise ratio. Given the science operation will start soon after the commissioning process is complete, various procedures of proposing, planning, & executing observations, processing data & assessing their qualities, and delivering data to observers are being developed and tested. In this contribution, a top-level summary of these achievements and ongoing progresses and future perspectives will be provided.
The predicted efficiency of the Prime Focus Spectrograph (PFS) for the Subaru telescope at Mauna Kea took a serious hit at the discovery of an error in the mounting of its volume phase holographic gratings (VPHG). Alerted by unexpected jumps in spectral flux between the blue and red channels in the first two spectrograph modules as they became available on sky, inspection of the gratings as mounted into the fourth and last module, still present in the lab, confirmed that all its gratings – three low-resolution (blue, red, NIR) gratings and a medium resolution grating and prism assembly (grism) – were indeed all mounted upside down. In this paper, after reporting on the observations leading to this discovery, we describe the corrective actions taken, illustrating by on-sky spectra full recovery of performance. Finally, we discuss the causes for this potentially catastrophic error, with an emphasis on the difficulty of ensuring verification at all levels (preliminary and final design, procurement, manufacturing, and AIT phases) for the giant instruments we are currently building and designing. We provide guidelines for future instrument designers in order to minimize the risk of such flaws happening again.
The Subaru Prime Focus Spectrograph (PFS) will soon be the first massively multiplexed wide-field spectrograph on an 8-meter class telescope. PFS’s spectrograph system covers the optical to near-infrared—380 to 1260 nm—in a single exposure and is fed by 2394 reconfigurable fibers distributed across a 1.3-degree wide field of view. Building upon deep multiband imaging catalogs, particularly from Subaru’s Hyper Suprime-Cam (HSC) imager, PFS will fuel future discoveries in cosmology, galaxy evolution, and galactic archaeology. To fully leverage Subaru’s 8.2 meter aperture and probe the faintest targets, accurate spectral reduction and sky subtraction are critical to PFS’s operation. During commissioning of PFS, the accuracy of the sky-subtraction algorithms is being assessed through direct observations of the night sky. In this paper, we report the current status of the sky-subtraction routines, as determined from the commissioning data.
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