On the instrument profile of slit spectrographs

Casini, R.; Wijn, A. G. de

doi:10.1364/josaa.31.002002

Cited by 8 publications

(8 citation statements)

References 7 publications

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“…We find that the line profile is flat-topped, with negative h + 4 , as expected for the slitwidth-limited resolution provided by the medium slicer (see, e.g., Casini & de Wijn 2014). There is no clear trend with wavelength, and the average values for the Gauss-Hermite components in three wavelength regions are h + 3 = −0.005 ± 0.005 and h + 4 = −0.094 ± 0.014.…”

Section: Instrumental Line Profilesupporting

confidence: 76%

Spatially Resolved Stellar Kinematics of the Ultra-diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, and Cold Dark Matter Halo Fits

Dokkum

Wasserman

Danieli

et al. 2019

ApJ

109

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We present spatially-resolved stellar kinematics of the well-studied ultra diffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hrs of observations with the Keck Cosmic Web Imager. The luminosity-weighted dispersion within the half-light radius is σ 1/2 = 33 +3 −3 km s −1 , lower than what we had inferred before from a DEIMOS spectrum in the Hα region. There is no evidence for rotation, with V max / σ < 0.12 (90 % confidence) along the major axis, in possible conflict with models where UDGs are the high-spin tail of the normal dwarf galaxy distribution. The spatially-averaged line profile is more peaked than a Gaussian, with Gauss-Hermite coefficient h 4 = 0.13 ± 0.05. The mass-to-light ratio within the effective radius is (M dyn /L I )(< R e ) = 26 +7 −6 M /L , similar to other UDGs and higher by a factor of six than smaller galaxies of the same luminosity. This difference between UDGs and other galaxies is, however, sensitive to the aperture that is used, and is much reduced when the M/L ratios are measured within a fixed radius of 10 kpc. Dragonfly 44 has a rising velocity dispersion profile, from σ = 26 +4 −4 km s −1 at R = 0.2 kpc to σ = 41 +8 −8 km s −1 at R = 5.1 kpc. The profile can only be fit with a cuspy NFW profile if the orbital distribution has strong tangential anisotropy, with β = −0.8 +0.4 −0.5 . An alternative explanation is that the dark matter profile has a core: a Di Cintio et al. (2014) density profile with a mass-dependent core provides a very good fit to the kinematics for a halo mass of log(M 200 /M ) = 11.2 +0.6 −0.6 and β = −0.1 +0.2 −0.3 , i.e. isotropic orbits. This model predicts a slight positive kurtosis, in qualitative agreement with the measured h 4 parameter. UDGs such as Dragonfly 44 are dark matter dominated even in their centers, and can constrain the properties of dark matter in a regime where baryons usually dominate the kinematics: small spatial scales in massive halos. In a companion paper (Wasserman et al. 2019) we provide constraints on the axion mass in the context of "fuzzy" dark matter models.

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Section: Instrumental Line Profilesupporting

confidence: 76%

Spatially Resolved Stellar Kinematics of the Ultra-diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, and Cold Dark Matter Halo Fits

Dokkum

Wasserman

Danieli

et al. 2019

ApJ

109

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“…1, bottom-center panel) broaden the spectral profile of an output channel, thus leading to a higher crosstalk. In astronomical spectroscopy, this is analogous to the line spread function [34]. For astronomical sources, it is more critical to collect all the light at the output FPR than the spectral purity of the channels as long as the spectral leakage is < 30-40% (or crosstalk > 4−5 dB) and the line spread function is well-characterized.…”

Section: Awg Propertiesmentioning

confidence: 99%

Potential of commercial SiN MPW platforms for developing mid/high-resolution integrated photonic spectrographs for astronomy

et al. 2021

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Integrated photonic spectrographs offer an avenue to extreme miniaturization of astronomical instruments, which would greatly benefit extremely large telescopes and future space missions. These devices first require optimization for astronomical applications, which includes design, fabrication and field testing. Given the high costs of photonic fabrication, Multi-Project Wafer (MPW) SiN offerings, where a user purchases a portion of a wafer, provide a convenient and affordable avenue to develop this technology. In this work we study the potential of two commonly used SiN waveguide geometries by MPW foundries, i.e. square and rectangular profiles to determine how they affect the performance of mid-high resolution arrayed waveguide grating spectrometers around 1.5 μm. Specifically, we present results from detailed simulations on the mode sizes, shapes, and polarization properties, and on the impact of phase errors on the throughput and cross talk as well as some laboratory results of coupling and propagation losses. From the MPW-run tolerances and our phase-error study, we estimate that an AWG with R ∼ 10,000 can be developed with the MPW runs and even greater resolving power is achievable with more reliable, dedicated fabrication runs. Depending on the fabrication and design optimizations, it is possible to achieve throughputs ∼ 60% using the SiN platform. Thus, we show that SiN MPW offerings are highly promising and will play a key role in integrated photonic spectrograph developments for astronomy.

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“…In the spectral dimension, we must consider the effects of anamorphic magnification on the spectrograph point-spread function (Casini and de Wijn, 2014), which gets shortened in that dimension by the same factor: r = cos α/ cos β. This required increasing the widths of the camera lenses in order to mitigate vignetting for configurations with β < −α.…”

Section: Spectral Channelsmentioning

confidence: 99%

“…i.e., δβ R ≈ 2 δβ g . In reality, one must also consider the finite width of the slit, which contributes to the line-spread function of the spectrograph along with δβ g (see Casini and de Wijn, 2014). Considering for simplicity the case where the spectrograph is set to the Littrow configuration and with the grating tilted at the blaze angle (β = −α = ϕ), such a sampling condition gives…”

Section: Diffraction Gratingmentioning

confidence: 99%

“…An oversized collimator optic is necessary to avoid loss of instrument throughput as a result of diffraction, because of the matching condition of the entranceslit width to the diffraction limit of the telescope. A rigorous diffraction-model analysis of telescope-spectrograph systems (Casini and de Wijn, 2014) shows that, by making the collimator system faster than the imaging telescope by about 20% (i.e., (f /#) tel /(f /#) coll ≈ 1.2, or (f /#) coll ≈ 27), the diffraction losses of ViSP remain below 10%, when the entrance slit matches the diffraction limit of the DKIST at a given wavelength.…”

Section: Collimatormentioning

confidence: 99%

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The Visible Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope

et al. 2022

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The Daniel K. Inouye Solar Telescope (DKIST) Visible Spectro-Polarimeter (ViSP) is a traditional slit-scanning spectrograph with the ability to observe solar regions up to a $120\times 78~\mbox{arcsec}^{2}$ 120 × 78 arcsec 2 area. The design implements dual-beam polarimetry, a polychromatic polarization modulator, a high-dispersion echelle grating, and three spectral channels that can be automatically positioned. A defining feature of the instrument is its capability to tune anywhere within the 380 – 900 nm range of the solar spectrum, allowing for a virtually infinite number of combinations of three wavelengths to be observed simultaneously. This enables the ViSP user to pursue well-established spectro-polarimetric studies of the magnetic structure and plasma dynamics of the solar atmosphere, as well as completely novel investigations of the solar spectrum. Within the suite of first-generation instruments at the DKIST, ViSP is the only wavelength-versatile spectro-polarimeter available to the scientific community. It was specifically designed as a discovery instrument to explore new spectroscopic and polarimetric diagnostics and test improved models of polarized line formation through high spatial-, spectral-, and temporal-resolution observations of the Sun’s polarized spectrum. In this instrument article, we describe the science requirements and design drivers of ViSP and present preliminary science data collected during the commissioning of the instrument.

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On the instrument profile of slit spectrographs

Cited by 8 publications

References 7 publications

Spatially Resolved Stellar Kinematics of the Ultra-diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, and Cold Dark Matter Halo Fits

Spatially Resolved Stellar Kinematics of the Ultra-diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, and Cold Dark Matter Halo Fits

Potential of commercial SiN MPW platforms for developing mid/high-resolution integrated photonic spectrographs for astronomy

The Visible Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope

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