Person: Glenday, Alexander
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Glenday
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Alexander
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Glenday, Alexander
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Publication Calibration of an Astrophysical Spectrograph Below 1 m/s Using a Laser Frequency Comb(Optical Society of America, 2012) Phillips, David; Glenday, Alexander; Li, Chih-Hao; Cramer, Claire; Furesz, Gabor; Chang, Guoqing; Benedick, Andrew J.; Chen, Li-Jin; Szentgyorgyi, Andrew; Walsworth, RonaldWe deployed two wavelength calibrators based on laser frequency combs (“astro-combs”) at an astronomical telescope. One astro- comb operated over a 100 nm band in the deep red (∼ 800 nm) and a second operated over a 20 nm band in the blue (∼ 400 nm). We used these red and blue astro-combs to calibrate a high-resolution astrophysical spectrograph integrated with a 1.5 m telescope, and demonstrated calibration precision and stability sufficient to enable detection of changes in stellar radial velocity < 1 m/s.Publication Conjugate Fabry–Perot Cavity Pair for Improved Astro-Comb Accuracy(Optical Society of America, 2012) Li, Chih-Hao; Guoqing, Chang; Glenday, Alexander; Langellier, Nicholas; Zibrov, Alexander; Phillips, David; Kärtner, Franz X.; Szentgyorgyi, Andrew; Walsworth, RonaldWe 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.Publication Visible Wavelength Astro-Comb(Optical Society of America (OSA), 2010) Benedick, Andrew J.; Chang, Guoqing; Birge, Jonathan R.; Chen, Li-Jin; Glenday, Alexander; Li, Chih-Hao; Phillips, David; Szentgyorgyi, Andrew; Korzennik, Sylvain; Furesz, Gabor; Walsworth, Ronald; Kärtner, Franz X.We demonstrate a tunable laser frequency comb operating near 420 nm with mode spacing of 20-50 GHz, usable bandwidth of 15 nm and output power per line of ~20 nW. Using the TRES spectrograph at the Fred Lawrence Whipple Observatory, we characterize this system to an accuracy below 1m/s, suitable for calibrating high-resolution astrophysical spectrographs used, e.g., in exoplanet studies.Publication In-Situ Determination of Astro-Comb Calibrator Lines to Better Than 10 cm \(s^{-1}\)(Optical Society of America (OSA), 2010) Li, Chih-Hao; Glenday, Alexander; Benedick, Andrew J.; Chang, Guoqing; Chen, Li-Jin; Cramer, Claire; Fendel, Peter; Furesz, Gabor; Kärtner, Franz X.; Korzennik, Sylvain; Phillips, David; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, RonaldImproved wavelength calibrators for high-resolution astrophysical spectrographs will be essential for precision radial velocity (RV) detection of Earth-like exoplanets and direct observation of cosmological deceleration. The astro-comb is a combination of an octave-spanning femtosecond laser frequency comb and a Fabry-Pérot cavity used to achieve calibrator line spacings that can be resolved by an astrophysical spectrograph. Systematic spectral shifts associated with the cavity can be 0.1-1 MHz, corresponding to RV errors of 10-100 cm/s, due to the dispersive properties of the cavity mirrors over broad spectral widths. Although these systematic shifts are very stable, their correction is crucial to high accuracy astrophysical spectroscopy. Here, we demonstrate an in-situ technique to determine the systematic shifts of astro-comb lines due to finite Fabry-Pérot cavity dispersion. The technique is practical for implementation at a telescope-based spectrograph to enable wavelength calibration accuracy better than 10 cm/s.Publication An astro-comb calibrated solar telescope to search for the radial velocity signature of Venus(2016) Phillips, David; Glenday, Alexander; Dumusque, Xavier; Buchschacher, Nicolas; Cameron, Andrew Collier; Cecconi, Massimo; Charbonneau, David; Cosentino, Rosario; Ghedina, Adriano; Haywood, Raphaelle; Latham, David; Li, Chih-Hao; Lodi, Marcello; Lovis, Christophe; Molinari, Emilio; Pepe, Francesco; Sasselov, Dimitar; Szentgyorgyi, Andrew; Udry, Stephane; Walsworth, RonaldWe recently demonstrated sub-m/s sensitivity in measuring the radial velocity (RV) between the Earth and Sun using a simple solar telescope feeding the HARPS-N spectrograph at the Italian National Telescope, which is calibrated with a green astro-comb. We are using the solar telescope to characterize the effects of stellar (solar) RV jitter due to activity on the solar surface with the goal of detecting the solar RV signal from Venus, thereby demonstrating the sensitivity of these instruments to detect true Earth-twin exoplanets.Publication HARPS-N Observes the Sun as a Star(IOP Publishing, 2015) Dumusque, Xavier; Glenday, Alexander; Phillips, David; Buchschacher, Nicolas; Cameron, Andrew Collier; Cecconi, Massimo; Charbonneau, David; Cosentino, Rosario; Ghedina, Adriano; Latham, David; Li, Chih-Hao; Lodi, Marcello; Lovis, Christophe; Molinari, Emilio; Pepe, Francesco; Udry, Stéphane; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, RonaldRadial velocity (RV) perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to RV changes. Over seven days of observing in 2014, we show an average 50 cm s−1 RV rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly RV rms to 60 cm s−1. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the RV technique.