CHIRON—A Fiber Fed Spectrometer for Precise Radial Velocities
01 Nov 2013-Publications of the Astronomical Society of the Pacific (University of Chicago Press)-Vol. 125, Iss: 933, pp 1336-1347
TL;DR: The CHIRON optical high-resolution echelle spectrometer as mentioned in this paper was designed for high throughput and stability, with the goal of monitoring radial velocities of bright stars with high precision and high cadence for the discovery of low-mass exoplanets.
Abstract: The CHIRON optical high-resolution echelle spectrometer was commissioned at the 1.5 m telescope at CTIO in 2011. The instrument was designed for high throughput and stability, with the goal of monitoring radial velocities of bright stars with high precision and high cadence for the discovery of low-mass exoplanets. Spectral resolution of R = 79 000 is attained when using a slicer with a total (including telescope and detector) efficiency of 6% or higher, while a resolution of R = 136 000 is available for bright stars. A fixed spectral range of 415–880 nm is covered. The echelle grating is housed in a vacuum enclosure and the instrument temperature is stabilized to ± 0.2°. Stable illumination is provided by an octagonal multimode fiber with excellent light-scrambling properties. An iodine cell is used for wavelength calibration. We describe the main optics, fiber feed, detector, exposure-meter, and other aspects of the instrument, as well as the observing procedure and data reduction.
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TL;DR: The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm/s measurement precision as discussed by the authors.
Abstract: The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm/s measurement precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this precision are summarized here.
Beginning with the HARPS spectrograph, technological advances for precision radial velocity measurements have focused on building extremely stable instruments. To reach still higher precision, future spectrometers will need to produce even higher fidelity spectra. This should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. Key data analysis challenges for the precision radial velocity community include distinguishing center of mass Keplerian motion from photospheric velocities, and the proper treatment of telluric contamination. Success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. Center of mass velocities produce Doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from Keplerian signals.
Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. Higher precision radial velocity measurements are required to serve as a discovery technique for potentially habitable worlds and to characterize detections from transit missions. The future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with Doppler measurements.
343 citations
Yale University1, University of Hertfordshire2, Queen Mary University of London3, Carnegie Institution for Science4, Saint Petersburg State University5, University of Chicago6, University of Copenhagen7, Leibniz Institute for Astrophysics Potsdam8, Physical Research Laboratory9, University of Notre Dame10, Pennsylvania State University11, National Institute of Standards and Technology12, University of Colorado Boulder13, University of Geneva14, Harvard University15, University of Texas at Austin16, University of Porto17, New York University18, University of Washington19, Massachusetts Institute of Technology20, Ohio State University21, University of British Columbia22, Aarhus University23, Institut d'Astrophysique de Paris24, Aix-Marseille University25, Spanish National Research Council26, University of California, Santa Cruz27, Cornell University28, Missouri State University29, Lowell Observatory30, Heidelberg University31, University of Göttingen32, INAF33, Space Telescope Science Institute34, University of New South Wales35, University of Southern Queensland36
TL;DR: The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm s−1 measurement precision as mentioned in this paper.
Abstract: The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm s^(−1) measurement precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this bold precision are summarized here. Beginning with the High Accuracy Radial Velocity Planet Searcher spectrograph, technological advances for precision radial velocity (RV) measurements have focused on building extremely stable instruments. To reach still higher precision, future spectrometers will need to improve upon the state of the art, producing even higher fidelity spectra. This should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. Key data analysis challenges for the precision RV community include distinguishing center of mass (COM) Keplerian motion from photospheric velocities (time correlated noise) and the proper treatment of telluric contamination. Success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. COM velocities produce Doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from Keplerian signals. Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. However, higher precision RV measurements are required to serve as a discovery technique for potentially habitable worlds, to confirm and characterize detections from transit missions, and to provide mass measurements for other space-based missions. The future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with Doppler measurements.
295 citations
TL;DR: In this paper, the authors reported observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away.
Abstract: M-dwarf stars--hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun--are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.
265 citations
TL;DR: The Automated Planet Finder (APF) as discussed by the authors is a facility purpose-built for the discovery and characterization of extrasolar planets through high-cadence Doppler velocimetry of the reflex barycentric accelerations of their host stars.
Abstract: The Automated Planet Finder (APF) is a facility purpose-built for the discovery and characterization of extrasolar planets through high-cadence Doppler velocimetry of the reflex barycentric accelerations of their host stars. Located atop Mount Hamilton, the APF facility consists of a 2.4 m telescope and its Levy spectrometer, an optical echelle spectrometer optimized for precision Doppler velocimetry. APF features a fixed-format spectral range from 374–970 nm, and delivers a “throughput” (resolution × slit width product) of 114,000″, with spectral resolutions up to 150,000. Overall system efficiency (fraction of photons incident on the primary mirror that are detected by the science CCD) on blaze at 560 nm in planet-hunting mode is 15%. First-light tests on the radial-velocity (RV) standard stars HD 185144 and HD 9407 demonstrate sub-meter-per-second precision (rms per observation) held over a 3 month period. This paper reviews the basic features of the telescope, dome, and spectrometer, and gives...
146 citations
Massachusetts Institute of Technology1, University of Texas at Austin2, Harvard University3, Princeton University4, Ames Research Center5, Tsinghua University6, University of Southern Queensland7, Swarthmore College8, University of Louisville9, University of Colorado Boulder10, University of Geneva11, Georgia State University12, Spanish National Research Council13, Lehigh University14, Leidos15, Search for extraterrestrial intelligence16, Konkoly Thege Miklós Astronomical Institute17, University of Chicago18, Technical University of Denmark19, Aarhus University20, NASA Exoplanet Science Institute21, Goddard Space Flight Center22, Vanderbilt University23, Northern Kentucky University24, University of Maryland, College Park25, Lynn University26, Cornell University27, Johns Hopkins University28, Eötvös Loránd University29, Hungarian Academy of Sciences30, Tokyo Institute of Technology31, INAF32
TL;DR: In this article, a hot Earth was detected around LHS 3844, an M-dwarf located 15 pc away from Earth, with a radius of 1.303 ± 0.022 R⊕ and orbits the star every 11 hr.
Abstract: Data from the newly commissioned Transiting Exoplanet Survey Satellite has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of 1.303 ± 0.022 R⊕ and orbits the star every 11 hr. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (I = 11.9, K = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy.
135 citations
References
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TL;DR: The ELODIE spectrograph of the Observatoire de Haute-Provence (OHP) as mentioned in this paper was designed as an updated version of the cross-correlation spectrometer CORAVEL to perform very accurate radial velocity measurements.
Abstract: The bre{fed echelle spectrograph of Observatoire de Haute{Provence, ELODIE, is presented. This instrument has been in operation since the end of 1993 on the 1.93 m telescope. ELODIE is designed as an updated version of the cross{correlation spectrometer CORAVEL, to perform very accurate radial velocity measurements such as needed in the search, by Doppler shift, for brown{dwarfs or giant planets orbiting around nearby stars. In one single exposure a spectrum at a resolution of 42000 (=) ranging from 3906 A to 6811 Ai s recorded on a 10241024 CCD. This performance is achieved by using a tan = 4 echelle grating and a combination of a prism and a grism as cross{disperser. An automatic on{line data treatment reduces all the ELODIE echelle spectra and computes cross{correlation functions. The instrument design and the data reduction algorithms are described in this paper. The eciency and accuracy of the instrument and its long term instrumental stability allow us to measure radial velocities with an accuracy better than 15 m s 1 for stars up to 9th magnitude in less than 30 minutes exposure time. Observations of 16th magnitude stars are also possible to measure velocities at about 1 km s 1 accuracy. For classic spectroscopic studies (S=N>100) 9th magnitude stars can be observed in one hour exposure time.
1,285 citations
TL;DR: The HERMES high-resolution spectrograph project as discussed by the authors is based on the white-pupil beam folding for high resolution spectroscopy with a spectral resolution of 85'000 (63'000) for the low-resolution fiber.
Abstract: The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85 000 (63 000 for the low-resolution fibre), a spectral coverage from 377 to 900 nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena.
480 citations
TL;DR: The HERMES high-resolution spectrograph project as mentioned in this paper is based on the white-pupil beam folding for high resolution spectroscopy with a spectral coverage from 377 to 900nm in a single exposure.
Abstract: The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85000 (63000 for the low-resolution fibre), a spectral coverage from 377 to 900nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena.
437 citations
TL;DR: In this paper, the fundamental limit of radial velocity measurement given by photon noise is presented and illustrated with a representative sample of synthetic solar-type stellar spectra, which is applied to two dedicated spectrographs.
Abstract: In the past 5 years, improvements in radial velocity measurements have led to discovery of extra-solar planets and progress in asteroseismology programs. Doppler measurements with high precision is close to the limit given by photon noise. In this paper the methodology to compute the fundamental limit of radial velocity measurement given by photon noise is presented and illustrated with a representative sample of synthetic solar-type stellar spectra. Stellar rotational broadening, instrumental spectral range as well as spectral resolution influences are also considered. This study is applied to two dedicated spectrographs in order to help the optimization of radial velocity programs. Current methods of Doppler calculation are discussed and compared.
401 citations
TL;DR: REDUCE as mentioned in this paper is a data analysis package for cross-dispersed echelle spectra that can be adapted to handle a variety of instrument types, including spec-trographs with prism or grating crossdispersers, possibly fed by a ber or image slicer.
Abstract: We describe advanced image processing algorithms, implemented in a data analysis package for conven- tional and cross-dispersed echelle spectra. Comparisons with results from other packages illustrate the outstanding quality of the new REDUCE package, particularly in terms of resulting noise level and treatment of CCD defects and cosmic ray spikes. REDUCE can be adapted relatively easily to handle a variety of instrument types, including spec- trographs with prism or grating cross-dispersers, possibly fed by a ber or image slicer, etc. In addition to reduced spectra, an accurate spatial prole is recovered, providing valuable information about the spectrograph PSF and simplifying scattered light corrections.
320 citations