astro-comb

{{Short description|Type of frequency comb}}

{{update|date=November 2010}}

An astro-comb is a type of frequency comb used in observational astronomy to increase the accuracy of wavelength calibration in spectrographs.{{cite web |title=Frequency Combs to Measure Cosmic Velocities |url=http://www2.mpq.mpg.de/~haensch/astro/combs.html |website=Astrocombs |publisher=LMU University of Munich |access-date=25 January 2022 |date=2015-03-08}}{{cite news |title=NIST 'Astrocomb' Opens New Horizons for Planet-Hunting Telescope |url=https://www.nist.gov/news-events/news/2019/02/nist-astrocomb-opens-new-horizons-planet-hunting-telescope |access-date=25 January 2022 |agency=National Institute of Standards and Technology (NIST) |publisher=National Institute of Standards and Technology (NIST) |date=February 19, 2019}} The increased accuracy reduces systematic errors and enhances detection of small variations in stellar radial velocities caused by smaller orbiting exoplanets (e.g. Earth-mass planets), among other applications.{{cite journal |last1=Chae |first1=Eunmi |last2=Kambe |first2=Eiji |last3=Motohara |first3=Kentaro |last4=Izumiura |first4=Hideyuki |last5=Doi |first5=Mamoru |last6=Yoshioka |first6=Kosuke |title=Compact green Ti:sapphire astro-comb with a 43 GHz repetition frequency |journal=Journal of the Optical Society of America B |date=1 July 2021 |volume=38 |issue=7 |pages=A1 |doi=10.1364/JOSAB.419078|arxiv=2101.05926 |bibcode=2021JOSAB..38A...1C |s2cid=231627499 }}{{cite web |title=Astro Combs |url=https://pweb.cfa.harvard.edu/research/topic/astro-combs |website=Astro Combs |publisher=Harvard & Smithsonian |access-date=25 January 2022 |date=2017-03-03}} Astro-combs are distinguished from conventional frequency combs by their focus on high repetition frequencies (with mode spacings of ≥10 GHz).{{cite journal |last1=Ravi |first1=Aakash |last2=Phillips |first2=David F. |last3=Beck |first3=Matthias |last4=Martin |first4=Leopoldo L. |last5=Cecconi |first5=Massimo |last6=Ghedina |first6=Adriano |last7=Molinari |first7=Emilio |last8=Bartels |first8=Albrecht |last9=Sasselov |first9=Dimitar |last10=Szentgyorgyi |first10=Andrew |last11=Walsworth |first11=Ronald L. |title=Astro-comb calibrator and spectrograph characterization using a turn-key laser frequency comb |journal=Journal of Astronomical Telescopes, Instruments, and Systems |date=17 November 2017 |volume=3 |issue=4 |page=045003 |doi=10.1117/1.JATIS.3.4.045003|arxiv=1705.07192 |bibcode=2017JATIS...3d5003R |s2cid=13676771 }}

A green astro-comb was installed in January 2013 in the high accuracy radial velocity planet searcher in the northern hemisphere (HARPS-N) spectrograph at the Telescopio Nazionale Galileo on the Canary Islands.{{Cite web|url=http://spie.org/newsroom/5730-a-green-astro-comb-to-search-for-earth-like-exoplanets#B1|title=A green astro-comb to search for Earth-like exoplanets|last=|first=|date=|website=spie.org|publisher=|access-date=2016-12-01}} The device was developed by a team led by Chih-Hao Li of Harvard University. This astro-comb uses a pulsed laser to filter starlight before feeding the signal into a spectrograph. As of December 2016, it is gathering data from Venus to demonstrate its ability to discover exoplanets.{{Cite web|url=http://www.tng.iac.es/news/2015/07/28/tng-harps-astrocomb/|title=TNG :: TNG, HARPS-N and Astro Comb ready to characterize the first earth twin|website=www.tng.iac.es|access-date=2016-12-01}}