A new method for instrumental profile reconstruction of high-resolution spectrographs

Milaković, D.; Jethwa, P.

doi:10.1051/0004-6361/202348532

Cited by 3 publications

(1 citation statement)

References 56 publications

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“…Long-range wavelength distortions were later found to be the dominant source of systematic uncertainty in those measurements (e.g., Whitmore & Murphy 2015), but their overall impact may not be as severe as initially thought (e.g., Dumont & Webb 2017). With the advances of precision radial velocity measurements on large telescopes, such as with ESPRESSO on the Very Large Telescope (VLT), and new analysis methods such as artificial intelligence, the wavelength measurement is being improved and systematics associated with the wavelength calibration are being alleviated (e.g., Milaković et al 2020;Lee et al 2021aLee et al , 2021bSchmidt et al 2021;Milaković & Jethwa 2024;Schmidt & Bouchy 2024).…”

Section: Introductionmentioning

confidence: 99%

Constraints on the Spacetime Variation of the Fine-structure Constant Using DESI Emission-line Galaxies

Jiang,

Pan,

Aguilar

et al. 2024

ApJ

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We present strong constraints on the spacetime variation of the fine-structure constant α using the Dark Energy Spectroscopic Instrument (DESI). In this pilot work, we utilize ∼110,000 galaxies with strong and narrow [O iii] λ λ4959, 5007 emission lines to measure the relative variation Δα/α in space and time. The [O iii] doublet is arguably the best choice for this purpose owing to its wide wavelength separation between the two lines and its strong emission in many galaxies. Our galaxy sample spans a redshift range of 0 < z < 0.95, covering half of all cosmic time. We divide the sample into subsamples in 10 redshift bins (Δz = 0.1), and calculate Δα/α for the individual subsamples. The uncertainties of the measured Δα/α are roughly between 2 × 10−6 and 2 × 10−5. We find an apparent α variation with redshift at a level of Δα/α = (2–3) × 10−5. This is highly likely to be caused by systematics associated with wavelength calibration, since such small systematics can be caused by a wavelength distortion of 0.002–0.003 Å, which is beyond the accuracy that the current DESI data can achieve. We refine the wavelength calibration using sky lines for a small fraction of the galaxies, but this does not change our main results. We further probe the spatial variation of α in small redshift ranges, and do not find obvious, large-scale structures in the spatial distribution of Δα/α. As DESI is ongoing, we will include more galaxies, and by improving the wavelength calibration, we expect to obtain a better constraint that is comparable to the strongest current constraint.

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Section: Introductionmentioning

confidence: 99%

Constraints on the Spacetime Variation of the Fine-structure Constant Using DESI Emission-line Galaxies

Jiang,

Pan,

Aguilar

et al. 2024

ApJ

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Ultraviolet astronomical spectrograph calibration with laser frequency combs from nanophotonic lithium niobate waveguides

Ludwig,

Ayhan,

Schmidt

et al. 2024

Nat Commun

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Astronomical precision spectroscopy underpins searches for life beyond Earth, direct observation of the expanding Universe and constraining the potential variability of physical constants on cosmological scales. Laser frequency combs can provide the required accurate and precise calibration to the astronomical spectrographs. For cosmological studies, extending the calibration with such astrocombs to the ultraviolet spectral range is desirable, however, strong material dispersion and large spectral separation from the established infrared laser oscillators have made this challenging. Here, we demonstrate astronomical spectrograph calibration with an astrocomb in the ultraviolet spectral range below 400 nm. This is accomplished via chip-integrated highly nonlinear photonics in periodically-poled, nano-fabricated lithium niobate waveguides in conjunction with a robust infrared electro-optic comb generator, as well as a chip-integrated microresonator comb. These results demonstrate a viable route towards astronomical precision spectroscopy in the ultraviolet and could contribute to unlock the full potential of next-generation ground-based and future space-based instruments.

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Solar photospheric spectrum microvariability

Dravins,

Ludwig

2024

A&A

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The search for small exoplanets around solar-type stars is limited by stellar physical variability, such as a jittering in the apparent photospheric radial velocity. While chromospheric variability has been aptly studied, challenges remain for the observation, modeling. and understanding the much smaller fluctuations in photospheric spectral line strengths, shapes, and shifts. Extreme-precision radial-velocity spectrometers allow for highly precise stellar spectroscopy and time series of the Sun (seen as a star) enable the monitoring of its photospheric variability. Understanding such microvariability through hydrodynamic 3D models would require diagnostics from different categories of well-defined photospheric lines with specific formation conditions. Fluctuations in their line strengths may indeed be correlated with radial-velocity excursions and prove useful in identifying observable proxies for their monitoring. From three years of HARPS-N observations of the Sun-as-a-star at lambda /$ sim 100,000, we selected 1000 low-noise spectra and measured line absorption in Fe i Fe ii Mg i Mn i Halpha , Hbeta , Hgamma Na i and the G -band. We examined their variations and likely atmospheric origins, also with respect to simultaneously measured chromospheric emission and apparent radial velocity. Systematic line-strength variability is seen, largely shadowing the solar-cycle evolution of Ca ii H\ \,K emission, but to smaller extents (typically on a sub-percent level). Among iron lines, the greatest amplitudes have been seen for Fe ii in the blue, while the trends change sign among strong lines in the green Mg i triplet and between Balmer lines. Variations in the G -band core are greater than of the full G -band, in line with theoretical predictions. No variation is detected in the semi-forbidden Mg i lambda \,457.1 nm. Hyperfine split Mn i behaves largely similar to Fe i . For lines at longer wavelengths, telluric absorption limits the achievable precision. Microvariability in the solar photospheric spectrum displays systematic signatures among various features. These measure values that are different than the classical Ca ii H\ \,K index, while still reflecting a strong influence from magnetic regions. Although unprecedented precision can be achieved from radial-velocity spectrometers, current resolutions are not adequate to reveal changes in detailed line shapes; in addition, their photometric calibration is not perfect. A forthcoming priority will be to model microvariability in solar magnetic regions, which could also provide desired specifications for future instrumentation toward exoEarth detections.

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A new method for instrumental profile reconstruction of high-resolution spectrographs

Cited by 3 publications

References 56 publications

Constraints on the Spacetime Variation of the Fine-structure Constant Using DESI Emission-line Galaxies

Constraints on the Spacetime Variation of the Fine-structure Constant Using DESI Emission-line Galaxies

Ultraviolet astronomical spectrograph calibration with laser frequency combs from nanophotonic lithium niobate waveguides

Solar photospheric spectrum microvariability

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