CHARA array

CHARA's six telescopes each have a one-meter diameter mirror to reflect light. They are spread across Mount Wilson to increase the angular resolution of the array. Each of the six telescopes provides a different image, to combine it into one image the light from each telescope is transported through vacuum tubes and fed into a single beam, where they are matched up to within one micron. This process is called interferometry, and allows the array to have the same resolving power as a telescope with a 330-meter mirror, and an angular resolution of 200 micro-arcseconds.{{Cite web|url=http://www.chara.gsu.edu/public|title=About|website=www.chara.gsu.edu|language=en-gb|access-date=2017-10-26}}{{Cite journal|last=Hand|first=Eric|date=2010-04-07|title=Telescope arrays give fine view of stars|journal=Nature News|language=en|volume=464|issue=7290|pages=820–821|doi=10.1038/464820a|pmid=20376117|bibcode=2010Natur.464..820H|doi-access=free}}

In 1984 CHARA was founded, and with financial support from the National Science Foundation (NSF), in 1985 planning for the array began. Construction for the array started on July 13, 1996, and with $6.3 million awarded to GSU by the NSF, and the same amount matched by GSU, going towards the effort. In July 1998, GSU was awarded another $1.5 million by W.M. Keck Foundation, which allowed for a sixth telescope to be added to the previously planned five. With a final gift of $574,000 from David and Lucile Packard Foundation, the funding for the array was completed in October 1998.{{Cite web|url=http://www.chara.gsu.edu/public/history|title=History of CHARA|last=Baron|first=Fabien|website=www.chara.gsu.edu|language=en-gb|access-date=2017-10-26}}

After another five years of construction, the CHARA array was completed in 2003. In April of the same year, CHARA was awarded a 3-year grant to support scientific programs at the center, which was renewed in 2006. In 2013 another grant from the NSF worth 3.6 million was given to the center.{{Cite web|url=https://www.eurekalert.org/pub_releases/2016-10/gsu-caa100316.php|title=CHARA Array awarded $3.9 million to provide telescope access to scientists across the nation|website=EurekAlert!|language=en|access-date=2017-10-26}}

Observatories throughout the world have come to CHARA to test beam combining technology.{{Cite book|url=https://books.google.com/books?id=_8SSDQAAQBAJ&dq=C%C3%B4te+d%27Azur+Observatory&pg=PT404|title=Observatories and Telescopes of Modern Times: Ground-Based Optical and Radio Astronomy Facilities since 1945|last=Leverington|first=David|date=2016-11-24|publisher=Cambridge University Press|isbn=9781316841815|language=en}}

File:Beta Lyrae - CHARA.gif eclipsing binary, using images from the CHARA array]]

On January 15, 2007, the diameter of an exoplanet, HD 189733 b, was measured directly, using CHARA. This was achieved by using the observed angular diameter of the star that the planet orbited, and the already known distance of the star from Earth, to get the diameter of the star. With this they could calculate the diameter of the exoplanet when comparing its size to the star when it passed in front of it. This was the first time the diameter of an exoplanet was directly measured, and returned a value slightly different than that obtained from indirect, more conventional methods.{{Cite news|url=http://www.astronomy.com/news/2007/01/chara-measures-an-exoplanet|title=CHARA measures an exoplanet|work=Astronomy.com|access-date=2017-10-26}}

In 2013 CHARA was used to capture images showing the starspots on Zeta Andromedae, a star 181 light years away. This was the first time that images of starspots on stars other than the Sun were taken.{{Cite news|url=http://news.gsu.edu/2016/05/04/starspot-images-that-give-insight-into-early-sun-captured-by-universitys-chara-telescope-array/|title='Starspot' Images that Give Insight into Early Sun Captured by University's CHARA Telescope Array - News Hub -|date=2016-05-04|work=News Hub|access-date=2017-10-26|language=en-US}}{{Cite news|url=http://discovermagazine.com/2017/april-2017/seeing-stars|title=Seeing Stars {{!}} DiscoverMagazine.com|work=Discover Magazine|access-date=2017-10-26}}

CHARA directly observed binary stars, such as Beta Lyrae and Algol.{{Cite journal|last1=Zhao|first1=M.|last2=Gies|first2=D.|last3=Monnier|first3=J. D.|last4=Thureau|first4=N.|last5=Pedretti|first5=E.|last6=Baron|first6=F.|last7=Merand|first7=A.|last8=ten Brummelaar|first8=T.|last9=McAlister|first9=H.|last10=Ridgway|first10=S. T.|last11=Turner|first11=N.|date=September 2008|title=First Resolved Images of the Eclipsing and Interacting Binary β Lyrae|journal=Astrophysical Journal Letters|language=en|volume=684|issue=2|pages=L95|doi=10.1086/592146|bibcode=2008ApJ...684L..95Z|issn=0004-637X|arxiv=0808.0932|s2cid=17510817}}{{Cite journal|last1=Baron|first1=F.|last2=Monnier|first2=J. D.|last3=Pedretti|first3=E.|last4=Zhao|first4=M.|last5=Schaefer|first5=G.|last6=Parks|first6=R.|last7=Che|first7=X.|last8=Thureau|first8=N.|last9=ten Brummelaar|first9=T. A.|last10=McAlister|first10=H. A.|last11=Ridgway|first11=S. T.|date=June 2012|title=Imaging the Algol Triple System in the H Band with the CHARA Interferometer|journal=Astrophysical Journal|language=en|volume=752|issue=1|pages=20|doi=10.1088/0004-637X/752/1/20|arxiv=1205.0754 |bibcode=2012ApJ...752...20B|issn=0004-637X|hdl=2027.42/98563|s2cid=11110989|hdl-access=free}} CHARA directly imaged multiple stars, such as Regulus, Rasalhague, Altair, Alderamin and Beta Cassiopeiae to measure the flattened shape of these rapidly rotating stars. Because the equator is further from the center of the star, it will appear cooler than the poles, an effect called gravity darkening.{{Cite web|url=http://chara.gsu.edu/science-highlights/rapid-rotators|title=CHARA - Rapid Rotators|website=chara.gsu.edu|access-date=2020-01-24}}

The CHARA array can also resolve the circumstellar disks around Be-stars and measure the disk precession variations.{{Cite web|url=http://chara.gsu.edu/science-highlights/be-stars|title=CHARA - Be Stars|website=chara.gsu.edu|access-date=2020-01-24}}

In 2022, the array was used to observe the disc of the hypergiant star RW Cephei during its ongoing dimming event.{{cite journal |bibcode=2023AJ....166...78A |title=The Great Dimming of the Hypergiant Star RW Cephei: CHARA Array Images and Spectral Analysis |last1=Anugu |first1=Narsireddy |last2=Baron |first2=Fabien |last3=Gies |first3=Douglas R. |last4=Lanthermann |first4=Cyprien |last5=Schaefer |first5=Gail H. |last6=Shepard |first6=Katherine A. |last7=Brummelaar |first7=Theo ten |last8=Monnier |first8=John D. |last9=Kraus |first9=Stefan |last10=Le Bouquin |first10=Jean-Baptiste |last11=Davies |first11=Claire L. |last12=Ennis |first12=Jacob |last13=Gardner |first13=Tyler |last14=Labdon |first14=Aaron |last15=Roettenbacher |first15=Rachael M. |last16=Setterholm |first16=Benjamin R. |last17=Vollmann |first17=Wolfgang |last18=Sigismondi |first18=Costantino |journal=The Astronomical Journal |date=2023 |volume=166 |issue=2 |page=78 |doi=10.3847/1538-3881/ace59d |arxiv=2307.04926 |s2cid=259766495 |doi-access=free }}

CHARA holds annual science meetings where recent advancements in science and technologies relevant to the array are discussed. The center also gives access to the array to the astronomical community using the National Optical Astronomy Observatory peer review system for around 50 nights per year. They also have periodic community workshops.

• Interferometry
• Mount Wilson

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Category:Interferometric telescopes