Holistic spectroscopy: Complete reconstruction of a wide-field, multi-object spectroscopic image using a photonic comb

Abstract

The primary goal of Galactic archaeology is to learn about the origin of the Milky Way from the detailed chemistry and kinematics of millions of stars. Wide-field multi-fibre spectrographs are increasingly used to obtain spectral information for huge samples of stars. Some surveys (e.g. GALAH) are attempting to measure up to 30 separate elements per star. Stellar abundance spectroscopy is a subtle art that requires a very high degree of spectral uniformity across each of the fibres. However wide-field spectrographs are notoriously non-uniform due to the fast output optics necessary to image many fibre outputs onto the detector. We show that precise spectroscopy is possible with such instruments across all fibres by employing a photonic comb -- a device that produces uniformly spaced spots of light on the CCD to precisely map complex aberrations. Aberrations are parametrized by a set of orthogonal moments with $\sim 100$ independent parameters. We then reproduce the observed image by convolving high resolution spectral templates with measured aberrations as opposed to extracting the spectra from the observed image. Such a forward modeling approach also trivializes some spectroscopic reduction problems like fibre cross-talk, and reliably extracts spectra with a resolution $\sim 2.3$ times above the nominal resolution of the instrument. Our rigorous treatment of optical aberrations also encourages a less conservative spectrograph design in the future.

arXiv commentSubmitted to MNRAS

References in corpus (15)

• The Seventh Data Release of the Sloan Digital Sky Survey
• The 2dF Galaxy Redshift Survey: Spectra and redshifts
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• The New Galaxy: Signatures of its Formation
• The Radial Velocity Experiment (RAVE): first data release
• The GALAH Survey: Scientific Motivation
• The Cannon: A data-driven approach to stellar label determination
• Sun-as-a-Star Spectrum Variations 1974-2006
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• Optimal Extraction of Fibre Optic Spectroscopy
• Probabilistic Catalogs for Crowded Stellar Fields
• High Frame-rate Imaging Based Photometry, Photometric Reduction of Data from Electron-multiplying Charge Coupled Devices (EMCCDs)
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• Accelerated Fitting of Stellar Spectra
• Mapping the aberrations of a wide-field spectrograph using a photonic comb

Cited by in corpus (7)

• The GALAH survey and Gaia DR2: dissecting the stellar disc's phase space by age, action, chemistry and location
• The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities
• A Multi-Band Catalog of 10978 Star Clusters, Associations and Candidates in the Milky Way
• The GALAH Survey: Chemical Clocks
• The GALAH+ Survey: A New Library of Observed Stellar Spectra Improves Radial Velocities and Hints at Motions within M67
• Instrument Simulator and Data Reduction Pipeline for the iLocater Spectrograph
• A Full Implementation of Spectro-Perfectionism for Precise Radial Velocity Exoplanet Detection: A Test Case With the MINERVA Reduction Pipeline