A laser frequency comb featuring sub-cm/s precision for routine operation on HARPS

Probst, Rafael A.; Curto, G. Lo; Ávila, G.; Martins, B. L. Canto; Medeiros, J. R. De; Esposito, M.; Hernández, J. I. González; Hänsch, Theodor W.; Holzwarth, Ronald; Kerber, F.; Leão, I. C.; Manescau, A.; Pasquini, L.; Rebolo, R.; Steinmetz, Tilo; Udem, Thomas; Wu, Yuanting

doi:10.1117/12.2055784

Cited by 35 publications

(27 citation statements)

References 22 publications

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“…Furthermore, owing to the finite width of the comb modes, the mode filtering can shift their center of gravity by skewing their shape, in case the filter transmission peaks are not perfectly centered at their position [25]. In analogy to the discussion in [26] we estimate, that this effect can cause line shifts of up to − 2.1 cm s 1 for this LFC.…”

Section: Introductionsupporting

confidence: 57%

Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel

et al. 2015

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We investigate a new scheme for astronomical spectrograph calibration using the laser frequency comb at the Solar Vacuum Tower Telescope on Tenerife. Our concept is based upon a single-mode fiber channel, that simultaneously feeds the spectrograph with comb light and sunlight. This yields nearly perfect spatial mode matching between the two sources. In combination with the absolute calibration provided by the frequency comb, this method enables extremely robust and accurate spectroscopic measurements. The performance of this scheme is compared to a sequence of alternating comb and sunlight, and to absorption lines from Earth's atmosphere. We also show how the method can be used for radial-velocity detection by measuring the well-explored 5 min oscillations averaged over the full solar disk. Our method is currently restricted to solar spectroscopy, but with further evolving fiber-injection techniques it could become an option even for faint astronomical targets. − 1 m s 1 over large time spans. LFCs hold promise to enable RV measurements at an accuracy of − 1 cm s 1 over arbitrary time horizons, and a − 2.5 cm s 1 calibration repeatability has already been demonstrated on a time scale of hours [9]. Unlike other calibration sources, LFCs are not only repeatable, but to the same degree also accurate, i.e. they allow assigning wavelengths, or optical frequencies, that come close to the true values. Most applications would profit from LFCs mainly for OPEN ACCESS RECEIVED their high repeatability, but the high accuracy of LFCs can also be beneficial, e.g. to compare spectra from different instruments. This property has also been exploited by [10] to create an improved atlas of the solar lines in the visible.Current high-precision spectrographs are usually connected to their telescopes via optical fibers, to detach them from telescope guiding, increasing the stability of the measurements. The spectrographs are usually equipped with a second fiber channel that is used to simultaneously calibrate the spectrograph during each measurement, to track spectrograph drifts. Differential drifts between the two channels are minimized by a rigid mechanical connection between the fiber outputs. However, since it is challenging to couple light from astronomical objects efficiently into single-mode fibers (SMFs), current high-precision spectrographs are fed with multimode fibers. While an SMF guides only a single, approximately Gaussian shaped beam profile, a multimode fiber supports a variety of beam profiles. The profile at the output of a multimode fiber depends on the beam alignment at its input, and therefore on telescope guiding. This translates into uncertainties in RV measurements.In this work, the use of SMFs for LFC-based calibration of astronomical spectrographs is explored. The tests presented here have been made at the Vacuum Tower Telescope (VTT), a solar telescope in Tenerife, Canary Islands, that is operated by the KIS. The very high optical powers available from the Sun allow the use of SMFs to feed the spectrograph b...

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Section: Introductionsupporting

confidence: 57%

Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel

et al. 2015

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“…The ideal tool for this task is a laser frequency comb optimized for calibrating spectrographs. These specialized instruments, known as "astro-combs" [29][30][31][32][33][34], may be referenced to GPS-disciplined atomic clocks. Thus, spectrograph wavelength solutions are easily trustworthy over a decade; and even measurements from multiple comb-calibrated observatories can be combined into a single data set if the same reference clock is used for the astro-combs at all observatories.…”

Section: Observational Considerationsmentioning

confidence: 99%

Probing Dark Matter Using Precision Measurements of Stellar Accelerations

et al. 2019

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Dark matter comprises the bulk of the matter in the universe but its particle nature and cosmological origin remain mysterious. Knowledge of the dark matter density distribution in the Milky Way Galaxy is crucial to both our understanding of the standard cosmological model and for grounding direct and indirect searches for the particles comprising dark matter. Current measurements of Galactic dark matter content rely on model assumptions to infer the forces acting upon stars from the distribution of observed velocities. Here, we propose to apply the precision radial velocity method, optimized in recent years for exoplanet astronomy, to measure the change in the velocity of stars over time, thereby providing a direct probe of the local gravitational potential in the Galaxy. Using numerical simulations, we develop a realistic strategy to observe the differential accelerations of stars in our Galactic neighborhood with next-generation telescopes, at the level of 10 −8 cm/s 2 . Our simulations show that detecting accelerations at this level with an ensemble of 10 3 stars requires the effect of stellar noise on radial velocity measurements to be reduced to <10 cm/s. The measured stellar accelerations may then be used to extract the local dark matter density and morphological parameters of the density profile.

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“…As of 2019, it has been responsible for more exoplanet discoveries than all other techniques apart from transit photometry; and together, the RV and transit methods have been responsible for the discovery of around 95% of all confirmed exoplanets. 1 Apart from being an important tool for exoplanet discovery in its own so-called 'simultaneous reference' technique: Baranne et al 1996;Probst et al 2014) have yielded the highest precisions. The most ambitious plans for next-generation RV instruments call for stability at the 1 cm s −1 level (Pasquini et al 2008;Fischer et al 2016).…”

Section: Introductionmentioning

confidence: 99%

A robust, template-free approach to precise radial velocity extraction

Rajpaul

Aigrain

Buchhave

2020

Monthly Notices of the Royal Astronomical Society

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Doppler spectroscopy is a powerful tool for discovering and characterizing exoplanets. For decades, the standard approach to extracting radial velocities (RVs) has been to cross-correlate observed spectra with a weighted template mask. While still widely used, this approach is known to suffer numerous drawbacks, and so in recent years increasing attention has been paid to developing new and improved ways of extracting RVs. In this proof-of-concept paper we present a simple yet powerful approach to RV extraction. We use Gaussian processes to model and align all pairs of spectra with each other; without constructing a template, we combine pairwise RV shifts to produce accurate differential stellar RVs. Doing this on a highly-localized basis enables a datadriven approach to identifying and mitigating spectral contamination, even without the input of any prior astrophysical knowledge. We show that a crude implementation of this method applied to an inactive standard star yields RVs with comparable precision to and significantly lower rms variation than RVs from industry-standard pipelines. Though amenable to numerous improvements, even in its basic form presented here our method could facilitate the study of smaller planets around a wider variety of stars than has previously been possible.

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A laser frequency comb featuring sub-cm/s precision for routine operation on HARPS

Cited by 35 publications

References 22 publications

Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel

Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel

Probing Dark Matter Using Precision Measurements of Stellar Accelerations

A robust, template-free approach to precise radial velocity extraction

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