The Measured Impact of Chromatic Atmospheric Effects on Barycentric Corrections: Results from the EXtreme PREcision Spectrograph

Blackman, Ryan; Ong, J. M. Joel; Fischer, Debra A.

doi:10.3847/1538-3881/ab24c3

Cited by 13 publications

(21 citation statements)

References 36 publications

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“…On the other hand, we do not see any similarly sharp cutoff when extrapolating the chromatic barycentric correction to outside of the wavelength range covered by the exposure meter. This suggests that the wavelength dependences of our barycentric corrections (detailed more fully in Blackman et al 2019) are generally smooth enough for robust extrapolation.…”

Section: Chromatic Dependencesmentioning

confidence: 81%

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An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

Petersburg

Ong

Zhao

et al. 2020

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The EXtreme PREcision Spectrograph (EXPRES) is an environmentally stabilized, fiber-fed, R = 137, 500, optical spectrograph. It was recently commissioned at the 4.3-m Lowell Discovery Telescope (LDT) near Flagstaff, Arizona. The spectrograph was designed with a target radial-velocity (RV) precision of 30 cm s −1 . In addition to instrumental innovations, the EXPRES pipeline, presented here, is the first for an on-sky, optical, fiber-fed spectrograph to employ many novel techniques-including an "extended flat" fiber used for wavelengthdependent quantum efficiency characterization of the CCD, a flat-relative optimal extraction algorithm, chromatic barycentric corrections, chromatic calibration offsets, and an ultra-precise laser frequency comb for wavelength calibration. We describe the reduction, calibration, and radial-velocity analysis pipeline used for EXPRES and present an example of our current sub-meter-per-second RV measurement precision, which reaches a formal, single-measurement error of 0.3 m s −1 for an observation with a per-pixel signal-to-noise ratio of 250. These velocities yield an orbital solution on the known exoplanet host 51 Peg that matches literature values with a residual RMS of 0.895 m s −1 .

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Section: Chromatic Dependencesmentioning

confidence: 81%

“…The reduction steps are as follows, dependent on the type of image being reduced (science, dark, science flat, or extended flat): In the following subsections, we go into detail about each of the above steps. Information about the reduction of exposure meter data can be found in Blackman et al (2019).…”

Section: Reductionmentioning

confidence: 99%

An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

Petersburg

Ong

Zhao

et al. 2020

Self Cite

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“…Barycentric correction-the residual error from the barycentric correction comes from several sources. The accuracy of the correction algorithm, accuracy in the stellar and observatory coordinates, accuracy of the reported shutter times, and accuracy of the chromatic weights measured by the exposure meter all impact the fidelity of the correction (discussed further in Blackman et al 2019). The correction is performed with the weighting scheme of Tronsgaard et al (2019), which improves over the weighted midpoint method commonly used in the past.…”

Section: Definitions Of Termsmentioning

confidence: 99%

“…More details regarding this effect are provided in Petersburg et al (2020). Additionally, it may be important to limit the smearing of stellar spectra across the detector due to barycentric motion as well as minimize the residual barycentric correction errors discussed in Blackman et al (2019). Generally, the brightest the sky will be at a reasonable distance from the Moon will be 12 mag fainter than our target stars.…”

Section: Sky Contamination and Telluric Contaminationmentioning

confidence: 99%

Performance Verification of the EXtreme PREcision Spectrograph

Blackman

Fischer

Jurgenson

et al. 2020

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The EXtreme PREcision Spectrograph (EXPRES) is a new Doppler spectrograph designed to reach a radialvelocity measurement precision sufficient to detect Earth-like exoplanets orbiting nearby, bright stars. We report on extensive laboratory testing and on-sky observations to quantitatively assess the instrumental radial-velocity measurement precision of EXPRES, with a focused discussion of individual terms in the instrument error budget. We find that EXPRES can reach a single-measurement instrument calibration precision better than 10 cm s −1 , not including photon noise from stellar observations. We also report on the performance of the various environmental, mechanical, and optical subsystems of EXPRES, assessing any contributions to radial-velocity error. For atmospheric and telescope related effects, this includes the fast tip-tilt guiding system, atmospheric dispersion compensation, and the chromatic exposure meter. For instrument calibration, this includes the laser fRequency comb (LFC), flat-field light source, CCD detector, and effects in the optical fibers. Modal noise is mitigated to a negligible level via a chaotic fiber agitator, which is especially important for wavelength calibration with the LFC. Regarding detector effects, we empirically assess the impact on the radial-velocity precision due to pixel-position nonuniformities and charge transfer inefficiency (CTI). EXPRES has begun its science survey to discover exoplanets orbiting G-dwarf and K-dwarf stars, in addition to transit spectroscopy and measurements of the Rossiter-McLaughlin effect.

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“…According to Blackman et al (2019), the ADC coupled with the injection on the fiber (controlled by a guiding camera) might affect the observations and introduce chromatic changes in the recorded spectra. To our knowledge, an exhaustive analysis of the problem in the visible range of the spectrum has never been performed.…”

Section: Introductionmentioning

confidence: 99%

The impact of atmospheric dispersion in the performance of high-resolution spectrographs

Wehbé

Cabral

Martins

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Differential atmospheric dispersion is a wavelength-dependent effect introduced by the atmosphere. It is one of the instrumental errors that can affect the position of the target as perceived on the sky and its flux distribution. This effect will affect the results of astronomical observations if not corrected by an atmospheric dispersion corrector (ADC). In high-resolution spectrographs, in order to reach a radial velocity (RV) precision of 10 cm/s, an ADC is expected to return residuals at only a few tens of milli-arcseconds (mas). In fact, current state-of-the-art spectrographs conservatively require this level of residuals, although no work has been done to quantify the impact of atmospheric dispersion. In this work we test the effect of atmospheric dispersion on astronomical observations in general, and in particular on RV precision degradation and flux losses. Our scientific objective was to quantify the amount of residuals needed to fulfil the requirements set on an ADC during the design phase. We found that up to a dispersion of 100 mas, the effect on the RV is negligible. However, on the flux losses, such a dispersion can create a loss of ∼2% at 380 nm, a significant value when efficiency is critical. The requirements set on ADC residuals should take into consideration the atmospheric conditions where the ADC will function, and also all the aspects related with not only the RV precision requirements but also the guiding camera used, the tolerances on the flux loss, and the different melt data of the chosen glasses.

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The Measured Impact of Chromatic Atmospheric Effects on Barycentric Corrections: Results from the EXtreme PREcision Spectrograph

Cited by 13 publications

References 36 publications

An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

Performance Verification of the EXtreme PREcision Spectrograph

The impact of atmospheric dispersion in the performance of high-resolution spectrographs

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