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- | ====== CHARA Array (CHARA) | + | ====== CHARA Array ====== |
{{: | {{: | ||
- | ====== Center for High Angular Resolution Astronomy ====== | + | ====== Center for High Angular Resolution Astronomy |
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+ | [[http:// | ||
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+ | * Gravity darkening and oblateness of rapidly rotating main sequence stars. | ||
+ | * Pulsation and radial velocity projection factor in Cepheids. | ||
+ | * Hot exozodiacal dust around main sequence stars. | ||
+ | * Exoplanet stellar host diameters. | ||
+ | * Diameters of low-mass M dwarfs. | ||
+ | * Angular diameter of halo population stars. | ||
+ | * Images of interacting binaries. | ||
+ | * Images of a binary star system in eclipse. | ||
+ | * Precision stellar masses of spatially resolved spectroscopic binaries. | ||
+ | * Direct detection of high contrast companions around Cepheids, RS CVn, and Be stars. | ||
+ | * Structure and physical properties of circumstellar disks around Be stars. | ||
+ | * Images of disks and winds around young stellar objects. | ||
+ | * Early measurements of the angular expansion of a nova after an eruption. | ||
+ | * Direct images of starspots. | ||
+ | * Images of convection cells on supergiant stars. | ||
- | [[http:// | ||
- | **Diameters of six M dwarfs** measured by CHARA, when combined with results from other interferometers and for eclipsing binaries, show a departure from theory that becomes more apparent with increasing metallicity. Thus, current models may overlook some additional opacity source.\\ | ||
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- | The **first direct measurement of an exoplanet diameter** was accomplished by CHARA measurements of the angular diameter of the host star in the exoplanet transit system HD 189733.\\ | ||
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- | A 4-telescope beam combiner developed for CHARA at the University of Michigan is producing CHARA’s first stellar images. This new program is directed at **imaging binaries, rotationally oblate rapid rotators, and stellar disks**.\\ | ||
===== Overview of the CHARA Array ===== | ===== Overview of the CHARA Array ===== | ||
- | \\ | + | \\ Georgia State University’s Center for High Angular Resolution Astronomy (CHARA) operates an optical/ |
- | Georgia State University’s Center for High Angular Resolution Astronomy (CHARA) operates an optical/ | + | |
- | resolutions for stellar diameter measurements, | + | |
- | (milli-arcseconds) in the K and V bands respectively. For binary star studies, these limits are 0.8 and 0.2 mas.\\ | + | |
- | \\ | + | |
- | The major elements of the Array (ten Brummelaar et al. 2005) consist of light collecting telescopes, vacuum light beam transport tubes, optical path length delay lines, beam management systems, and beam combination systems.\\ | + | |
- | \\ | + | |
- | **Light Collecting Telescopes** – Each of the six telescopes is an afocal beam reducer that injects a 12.5-cm output beam into the vacuum transport tubes. The primary and secondary substrates are of low-CTE materials. Typical primary/ | + | |
- | \\ | + | |
- | **Vacuum Light Beam Transport Tube** – The final mirror in the telescope optical train injects the collimated beam through an optical window into a vacuum tube for transport to the Array’s central beam combination facility. Each Array arm (20,000 liters) can be pumped down to an operating level of ~1 Torr in about an hour.\\ | + | |
- | \\ | + | |
- | **Optical Path Length Compensation** – Maintenance of zero optical path length difference is accomplished at the CHARA Array in two stages. The first occurs in vacuum and employs six parallel systems (referred to as the “Pipes of Pan” or PoP’s). Remotely actuated mechanisms move mirrors to select appropriate delay segments. Upon exiting the PoP’s, the beams leave vacuum and are injected into the continuous delay lines by a pair of “periscope” mirrors. The “optical path length equalizers” (OPLE’s) were provided to CHARA under a contract with JPL. The OPLE’s incorporate cat’s-eye retro-reflectors, | + | |
- | \\ | + | |
- | **Beam Management** – The beams emerging from the OPLE’s are reduced to a final diameter of 1.9 cm by a recently improved, two-element “beam-reducing telescope” (BRT). The beams then pass through the “longitudinal dispersion corrector” (LDC) that corrects for unequal air paths. Finally, the “beam sampling system” (BSS) separates visible from IR light at the 1-μm boundary and turns the two beams through 90° along parallel paths to the visible and IR beam combiners. The BSS assembly moves on a precision stage so as to serve as a switchyard for selecting baseline pairs to be directed to the beam combiners.\\ | + | |
- | \\ | + | |
- | **Beam Combination** – Through formal, collaborative agreements between CHARA and several institutions, | + | |
- | The Beam Combining Laboratory (BCL) contains four, soon to be six, separate beam combiners with complementary regimes of wavelength, sensitivity and measurement precision. The Array control system is capable of running up to three of these in parallel, doubling, and sometimes tripling, the number of scheduled programs. While this approach is very demanding of the Array infrastructure, | + | |