Multi-Object Spectrometer
{{Short description|Method in astronomy}}
File:Basic principle of Multi-Object Spectroscopy rearranged.png
A multi-object spectrometer is a type of optical spectrometer capable of simultaneously acquiring the spectra of multiple separate objects in its field of view.{{Cite web |url=http://astro.vaporia.com/start/multiobjectspectrograph.html |title=multi-object spectrograph |access-date=2023-08-07 |website=astro.vaporia.com}} It is used in astronomical spectroscopy and is related to long-slit spectroscopy.{{Cite web |url=https://www.eso.org/sci/facilities/lasilla/instruments/efosc/inst/ObsMOS.html |title=Multi Object Spectroscopy (decommissioned) |access-date=2023-08-07 |website=eso.org |publisher=European Southern Observatory}} This technique became available in the 1980s.{{Cite conference |title=The Large Sky Area Multi-Object Fibre Spectroscopy Telescope ( LAMOST) Project |conference=Conference of the Working Group of IAU Commission 9 on “Wide-Field Imaging” held in Athens, Greece, May 20–25, 1996 |url=https://link.springer.com/chapter/10.1007/978-94-011-5722-3_9 |last=Chu |first=Yaoquan |publisher=Springer Dordrecht |doi=10.1007/978-94-011-5722-3_9|url-access=subscription }}
Description
The term multi-object spectrograph is commonly used for spectrographs using a bundle of fibers to image part of the field. The entrance of the fibers is at the focal plane of the imaging instrument. The bundle is then reshaped; the individual fibers are aligned at the entrance slit of a spectrometer, dispersing the light on a detector.
This technique is closely related to integral field spectrography (IFS), more specifically to fiber-IFS. It is a form of snapshot hyperspectral imaging, itself a part of imaging spectroscopy.
= Apertures =
{{External media|float=right|image1=[https://www2.keck.hawaii.edu/realpublic/inst/newsletters/Vol10/fig-mosfire-2.png Photographs of the Configurable Slit Unit on MOSFIRE] Left: full picture, in a configuration for imaging. Right: close-up on the knife-edge slits.{{Cite journal |title=The Imminent Arrival of MOSFIRE, Keck's New Infrared, Multi-Object, Imaging Spectrograph |journal=Keck Observers' Newsletter |url=https://www2.keck.hawaii.edu/realpublic/inst/newsletters/Vol10/index.html |last1=Goodrich |first1=Bob |issue=10 |last2=Adkins |first2=Sean|year=2011}}{{Cite journal |title=Design and development of MOSFIRE: the multi-object spectrometer for infrared exploration at the Keck Observatory |journal=SPIE Conference Proceedings |url=https://irlab.astro.ucla.edu/instruments/mosfire/documents/MOSFIRE%20SPIE%20paper.pdf |date=2010-07-20 |volume=7735 |publisher=SPIE |doi=10.1117/12.856715 |first1=Ian S. |last1=McLean |first2=Charles C. |last2=Steidel |first3=Epps |last3=Harland |first4=Keith |last4=Matthews |first5=Sean |last5=Adkins |first6=Nicholas |last6=Konidaris |first7=Bob |last7=Weber |first8=Ted |last8=Aliado |first9=George |last9=Brims |first10=John |last10=Canfield |first11=John |last11=Cromer |first12=Jason |last12=Fucik |first13=Kristin |last13=Kulas |first14=Greg |last14=Mace |first15=Ken |last15=Magnone |first16=Hector |last16=Rodriguez |first17=Eric |last17=Wang |first18=Jason |last18=Weiss|editor-first1=Ian S. |editor-first2=Suzanne K. |editor-first3=Hideki |editor-last1=McLean |editor-last2=Ramsay |editor-last3=Takami |series=Ground-based and Airborne Instrumentation for Astronomy III |pages=77351E |bibcode=2010SPIE.7735E..1EM |s2cid=122823326 }}}}
Typically, the apertures of multi-object spectrographs can be modified to fit the needs of the given observation.{{Cite web |url=https://jwst-docs.stsci.edu/methods-and-roadmaps/jwst-multi-object-spectroscopy |title=JWST Multi-Object Spectroscopy |date=2022-10-17 |access-date=2023-08-07 |website=JWST User Documentation}}
For example, the MOSFIRE (Multi-Object Spectrometer for Infra-Red Exploration
){{Cite web |url=https://www2.keck.hawaii.edu/inst/mosfire/home.html |title=MOSFIRE Home Page |date=2020-10-07 |access-date=2023-08-07 |website=www2.keck.hawaii.edu}} instrument on the W. M. Keck Observatory contains the Configurable Slit Unit (CSU){{Cite web |url=https://irlab.astro.ucla.edu/instruments/mosfire/ |title=Multi-Object Spectrometer for Infra-Red Exploration First Light Obtained: April 4, 2012 |access-date=2023-08-07 |website=irlab.astro.ucla.edu}} allowing arbitrary positioning of up to forty-six 18 cm slits by moving opposable bars.
Some fiber-fed spectroscopes, such as the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) can move the fibers to desired position. The LAMOST moves its 4000 fibers separately within designated areas for the requirements of a measurement, and can correct positioning errors in real time.{{Cite web |url=http://www.lamost.org/public/instrument/fiber?locale=en |title=Fiber positioning |date=2012-08-14 |access-date=2023-08-07 |website=lamost.org}}
The James Webb Space Telescope uses a fixed Micro-Shutter Assembly (MSA), an array of nearly 250000 5.1 mm by 11.7 mm shutters that can independently be opened or closed to change the location of the open slits on the device.{{Cite web |url=https://jwst-docs.stsci.edu/jwst-near-infrared-spectrograph/nirspec-instrumentation/nirspec-micro-shutter-assembly |title=NIRSpec Micro-Shutter Assembly |date=2023-04-24 |access-date=2023-08-07 |website=jwst-docs.stsci.edu}}
Uses in telescopes
= Ground-based instruments =
Instruments with multi-object spectrometry capabilities are available on most 8-10 meter-class ground-based observatories. For example, the Large Binocular Telescope,{{Cite web |url=https://www.lbto.org/instruments-in-short.html |title=Instruments - an overview |access-date=2023-08-07 |website=Large Binocular Telescope Observatory}} W. M. Keck Observatory,{{Cite web |url=https://www.keckobservatory.org/about/telescopes-instrumentation/ |title=Keck I And Keck II Telescopes |access-date=2023-08-07 |website=W. M. Keck Observatory}} Gran Telescopio Canarias,{{Cite web |url=http://www.gtc.iac.es/instruments/megara/megara.php |title=MEGARA |date=2023-05-08 |access-date=2023-08-07 |website=Gran Telescopio CANARIAS}} Gemini Observatory,{{Cite web |url=https://www.roe.ac.uk/atc/projects/gmos/main.html |title=The GMOS (Gemini Multi-Object Spectrograph) project at the ATC |date=2003-09-12 |access-date=2023-08-07}} New Technology Telescope,{{Cite web |url=https://www.eso.org/sci/facilities/lasilla/instruments/efosc/overview.html |title=EFOSC Overview |access-date=2023-08-07 |website=eso.org |publisher=European Southern Observatory}} William Herschel Telescope,{{Cite web |url=https://www.ing.iac.es/astronomy/instruments/weave/weaveinst.html |title=WEAVE - instrumental overview |date=2023-07-05 |access-date=2023-08-07 |website=ing.iac.es}} UK Schmidt Telescope{{Cite web |url=https://aat.anu.edu.au/about-us/uk-schmidt-telescope |title=The UK Schmidt Telescope |access-date=2023-08-07 |website=aat.anu.edu.au|date=21 May 2014 }} and LAMOST include such system.
Four instruments in the Very Large Telescope, including the KMOS (K-band multi-object spectrograph){{Cite web |url=https://www.eso.org/sci/facilities/paranal/instruments/kmos.html |title=KMOS - K-band Multi Object Spectrograph |access-date=2023-08-07 |website=eso.org |publisher=European Southern Observatory}} and the VIMOS (Visible Multi Object Spectrograph){{Cite web |url=https://www.eso.org/sci/facilities/paranal/decommissioned/vimos.html |title=VIMOS - VIsible MultiObject Spectrograph |access-date=2023-08-07 |website=eso.org |publisher=European Southern Observatory}} instruments, have multi-object spectroscopic capabilities.
= Space-based instruments =
The Hubble Space Telescope has been operating the NICMOS (Near Infrared Camera and Multi-Object Spectrometer){{Cite web |url=https://esahubble.org/about/general/instruments/nicmos/ |title=Hubble's Instruments: NICMOS - Near Infrared Camera and Multi-Object Spectrometer |access-date=2023-08-07 |website=esahubble.org}} from 1997 to 1999 and from 2002 to 2008.
The James Webb Space Telescope's NIRSpec (Near-Infrared Spectrograph) instrument is a multi-object spectrometer.{{Cite web |url=https://jwst-docs.stsci.edu/jwst-near-infrared-spectrograph/nirspec-observing-modes/nirspec-multi-object-spectroscopy |title=NIRSpec Multi-Object Spectroscopy |date=2023-04-24 |access-date=2023-08-07 |website=JWST User Documentation}}