Gravitational wave detection with optical lattice atomic clocks

We propose a space-based gravitational wave (GW) detector consisting of two spatially separated, drag-free satellites sharing ultrastable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident GWs at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, and the detection window can be tuned through the control sequence applied to the atoms’ internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, with frequencies ranging fromPhysic

Identifying exoplanets with deep learning. IV. Removing stellar activity signals from radial velocity measurements using neural networks

Funding: This project has received funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation program (SCORE grant agreement No. 851555). A.C.C. acknowledges support from the Science and Technology Facilities Council (STFC) consolidated grant No. ST/R000824/1 and UKSA grant ST/R003203/1. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC)’s Ernest Rutherford Fellowship (grant number ST/V004735/1). M.P. acknowledges financial support from the ASI-INAF agreement No. 2018-16-HH.0. A.M. acknowledges support from the senior Kavli Institute Fellowships.Exoplanet detection with precise radial velocity (RV) observations is currently limited by spurious RV signals introduced by stellar activity. We show that machine-learning techniques such as linear regression and neural networks can effectively remove the activity signals (due to starspots/faculae) from RV observations. Previous efforts focused on carefully filtering out activity signals in time using modeling techniques like Gaussian process regression. Instead, we systematically remove activity signals using only changes to the average shape of spectral lines, and use no timing information. We trained our machine-learning models on both simulated data (generated with the SOAP 2.0 software) and observations of the Sun from the HARPS-N Solar Telescope. We find that these techniques can predict and remove stellar activity both from simulated data (improving RV scatter from 82 to 3 cm s−1) and from more than 600 real observations taken nearly daily over 3 yr with the HARPS-N Solar Telescope (improving the RV scatter from 1.753 to 1.039 m s−1, a factor of ∼1.7 improvement). In the future, these or similar techniques could remove activity signals from observations of stars outside our solar system and eventually help detect habitable-zone Earth-mass exoplanets around Sun-like stars.Publisher PDFPeer reviewe

Bell, Alexander D.

Martha J. Bell - wifehttps://stars.library.ucf.edu/cfm-ch-memoranda-1931/1091/thumbnail.jp

Operation of a Broadband Visible-Wavelength Astro-Comb with a High-Resolution Astrophysical Spectrograph

Searches for Earth-like exoplanets using the periodic Doppler shift of stellar absorption lines require 10 cm∕s precision in the measurement of stellar radial velocity (RV) over timescales of years. Current techniques have led to the discovery of short-period exoplanets that induce RV wobbles as small as ≈1 m∕s on their parent stars. It has been suggested that order-of-magnitude improved RV precision may be achievable using an astro-comb, a laser frequency comb optimized for astrophysical spectrograph wavelength calibration. Here we report the development of a broadband visible-wavelength astro-comb and its operation with the HARPS-N spectrograph at the Telescopio Nazionale Galileo in the Canary Islands. This green astrocomb has >7000 narrow (<1 MHz) spectral lines spaced by 16 GHz with relatively uniform line power from 500 to 620 nm. The line frequencies are locked to GPS, enabling us to realize HARPS-N wavelength calibration with RV measurement precision and stability <10 cm∕s

Femtosecond laser frequency comb for astrophysical spectrograph calibration

We describe the development of a broadband astro-comb providing wavelength coverage of 500 - 620 nm, which is deployed as a wavelength calibration source for the HARPS-N spectrograph to detect and characterize long-period exoplanets

Conjugate Fabry-Perot cavity pair for improved astro-comb accuracy

We propose a new astro-comb mode-filtering scheme composed of two Fabry-Perot cavities (coined "conjugate Fabry-Perot cavity pair"). Simulations indicate that this new filtering scheme makes the accuracy of astro-comb spectral lines more robust against systematic errors induced by nonlinear processes associated with power-amplifying and spectral-broadening optical fibers