Modeling and budgeting fiber injection efficiency for the Maunakea Spectroscopic Explorer (MSE)

Abstract

The Maunakea Spectroscopic Explorer (MSE) will each year obtain millions of spectra in the optical to nearinfrared, at low (R 3, 000) to high (R 40, 000) spectral resolution by observing >4,000 spectra per pointing via a highly multiplexed fiber-fed system. Key science programs for MSE include black hole reverberation mapping, stellar population analysis of faint galaxies at high redshift, and sub-km/s velocity accuracy for stellar astrophysics.One key metric of the success of MSE will be its survey speed, i.e. how many spectra of good signal-to-noise ratio will MSE be able to obtain every night and every year. The survey speed is directly linked to the allocation efficiency -how many fibers in the focal surface can be allocated to targets -and to the injection efficiencywhat fraction of light from a target can enter the fiber at the focal surface.In this paper we focus on the injection efficiency and how to optimize it to increase the signal-to-noise ratio of targets observed in sky dominated conditions. The injection efficiency depends on the size of the fiber and requires highly precise, repeatable and stable positioning of the fiber in the focal surface. We present the allocation budget used for Conceptual Design Review and the modeling that allows to estimate the injection efficiency, which is just one part necessary to meet the science requirements on sensitivities.

Maximising the sensitivity of next generation multi-object spectroscopy: system budget development and design optimizations for the Maunakea Spectroscopic Explorer

“…The IE budget is discussed in detail in Ref. 30. A critical budget that is related to the IE budget is the Image Quality budget, that describes the expected contributions to the IQ as measured at the focal plane of MSE: bigger images due to poorer IQ mean that less light is able to enter the fiber.…”

Maunakea spectroscopic explorer advancing from conceptual design

“…Table 2 Screen shot of the positioner and metrology system down-select matrix In addition, the survey efficiencies between the two systems, which are the product of injection efficiency 3 (IE) and target allocation efficiency, were compared quantatively. Despite concerns in IE losses in focal ratio degradation (FRD) and defocus from the Sphinx spine tilt, the difference in the system-level IE [9] between the two systems after all losses are accounted is negligible. The point spread function variations due to spine tilt will be corrected by the science calibration system using our prescribed calibration plan [17] .…”

Maunakea Spectroscopic Explorer (MSE): the prime focus subsystems: requirements and interfaces

“…Keeping the fiber input ends aligned with the targets in the sky is critical to the IE of MSE, which is defined as the percentage of flux entering the input fibre with respect to the total flux of a point source at the focal surface. IE is modelled [9] as deviations from the ideal fibre location in two directions, longitudinal (z) and lateral (xy), in units of microns. The maximum amount of attainable flux would enter the fibre at z=0 and xy=0.…”

“…Since the amount of defocus will vary from positioner to positioner, PFHS will position the system to correspond to the mean of the spine tilts. As well, the tilt distribution per field has been modeled [9] for which the defocus is much smaller for the median tilt, so 80 um (max) is a conservative estimate of the error. Regardless, the median distribution was used to estimate IE and the sensitivity requirements are met.…”