Editing Large Millimeter Telescope

{{short description|Astronomy telescope in Mexico}}
{{Use dmy dates|date=December 2017}}
{{Infobox telescope}}

The '''Large Millimeter Telescope''' ('''LMT''') ({{langx|es|'''Gran Telescopio Milimétrico'''}}, or '''GTM'''), officially the '''Large Millimeter Telescope Alfonso Serrano''' ({{langx|es|'''Gran Telescopio Milimétrico Alfonso Serrano'''}}), is the world's largest single-aperture [[telescope]] in its frequency range, built for observing [[radio wave]]s in the [[wave length]]s from approximately 0.85 to 4&nbsp;mm. It has an [[active surface]] with a diameter of {{convert|50|m|ft|-1}} and {{convert|1960|m2|sqft|-2}} of collecting area.<ref>{{Cite web|url=http://www.lmtgtm.org/general-2/general/|title=General Information|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en|access-date=2017-06-12}}</ref>

[[File:LMT location.png|200px|thumb|left|Location of the LMT in Mexico]]
The telescope is located at an altitude of {{convert|4850|metre|feet}} on top of [[Sierra Negra]], the fifth-highest peak in [[Mexico]] and an extinct [[volcano|volcanic]] companion to Mexico's highest mountain [[Pico de Orizaba]], inside the National Park Pico de Orizaba in the state of [[Puebla]]. It is a binational [[Mexico|Mexican]] (70%) – [[United States of America|American]] (30%) joint project of the [[Instituto Nacional de Astrofísica, Óptica y Electrónica]] (INAOE) and the [[University of Massachusetts Amherst]].

Millimetre-wavelength observations using the LMT give astronomers a view of regions which are obscured by dust in the [[interstellar medium]], thus increasing our knowledge of [[star formation]]. The telescope is also particularly fitted for observing solar system [[planetesimal]]s and planets as well as extra-solar [[protoplanetary disk]]s which are relatively cold and emit most of their radiation at millimetre wavelengths.<ref>{{Cite news|url=https://www.science.org/content/article/mexicos-large-millimeter-telescope-opens-business|title=Mexico's Large Millimeter Telescope Opens for Business|date=2013-05-08|work=Science {{!}} AAAS|access-date=2017-06-12|language=en}}</ref>

The mission of the LMT is to: 1) pursue pioneering research, 2) train future generations of scientists and engineers, and 3) develop new technology for the benefit of society.<ref>{{Cite web|url=http://www.lmtgtm.org/the-lmt-book/|title=The LMT Book|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en|access-date=2017-06-12}}</ref> The LMT mainly studies thermally cold objects, most of which are associated with large amounts of [[cosmic dust]] and/or molecular gas. Among the objects of interest are [[comet]]s, [[planet]]s, [[Protoplanetary disk|protoplanetary discs]], evolved stars, [[Star formation|star-forming]] regions and [[Galaxy|galaxies]], [[molecular cloud]]s, [[active galaxy|active galactic nuclei]] (AGNs), high-redshift galaxies, [[Galaxy cluster|clusters of galaxies]], and  the [[CMB|cosmic microwave background]].<ref>{{Cite web|url=http://www.lmtgtm.org/general-2/science/|title=Science with the LMT|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en|access-date=2017-06-12}}</ref>

The LMT has a bent [[Cassegrain antenna|Cassegrain optical system]] with a 50m-diameter reflecting primary surface (M1) formed by 180 segments distributed in five concentric rings. The number of segments in the rings, from the center of the dish to the outside, are: 12, 24 and 48 in the three outermost rings. Each segment is connected to the structure of the telescope through four [[actuator]]s, allowing for an [[Active surface|active reflecting primary surface]]. In addition, each segment is formed by eight precision [[Electroforming|electro-formed]] nickel sub-panels. The reflecting secondary surface (M2) has a 2.6-m diameter, also built by nine electro-formed nickel sub-panels, and is attached to the telescope with an active [[Hexapod (robotics)|hexapod]] that allows precise focus, lateral offsets, and tilts. The hexapod is attached to the telescope through a metal tetrapod. Finally, the reflecting tertiary surface (M3) is almost flat, elliptical with a 1.6-m major axis and delivers the light beam to the receivers.<ref>{{Cite web|url=http://www.lmtgtm.org/telescope/telescope-description/|title=Telescope Description|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en|access-date=2017-06-12}}</ref>

==History==
INAOE and UMass-Amherst signed the agreement to develop the Large Millimeter Telescope project on 17 November 1994, but construction of the telescope did not begin until 1998.<ref>{{Cite news|url=http://www.conacytprensa.mx/index.php/ciencia/universo/465-19nov-nota-el-gran-telescopio-milimetrico-observa-el-universo-desde-puebla|title=El Gran Telescopio Milimétrico observa el universo desde Puebla|last=Paz|first=Susana|work=México Ciencia y Tecnología|access-date=2017-06-12|language=es-es}}</ref><ref>{{Cite news|url=https://www.umass.edu/newsoffice/article/ground-breaking-set-umass-amherst-mexico-large-millimeter-telescope|title=Ground-Breaking Set for UMass Amherst-Mexico Large Millimeter Telescope|work=Office of News & Media Relations {{!}} UMass Amherst|access-date=2017-06-12|language=en}}</ref> The first observations were taken in June 2011 at 1.1 and 3&nbsp;mm using the AzTEC camera and Redshift Search Receiver (RSR), respectively.<ref>{{Cite news|url=https://cudi.edu.mx/astronomia/UMass-LMTRelease.pdf|title=UMass Amherst Astronomers, Partnering With Mexican Institute Receive First Light Data from Giant New Telescope|work=Office of News & Media Relations {{!}} UMass Amherst|access-date=2024-08-29|language=en}}</ref> In May 2013, the Early Science phase began, producing over a dozen scientific articles. The official name of the LMT was changed to "Large Millimeter Telescope Alfonso Serrano" on 22 October 2012 in order to honour the initiator of the project, [[Alfonso Serrano Pérez-Grovas]].

== Instrumentation ==
The set of LMT instrumentation is built by heterodyne receivers and broad-band continuum cameras, some of them still under development:

===Broad-band continuum===
;TolTEC<ref>{{Cite web|title=The TolTEC Camera|url=http://toltec.astro.umass.edu/|access-date=2017-06-12|website=toltec.astro.umass.edu}}</ref><ref>{{Cite news|title=UMass Amherst Leads International Astronomical Camera Project|language=en|work=Office of News & Media Relations {{!}} UMass Amherst via Phys.org|url=https://phys.org/news/2016-10-umass-amherst-international-astronomical-camera.html|access-date=2024-08-29}}</ref>

[http://toltec.astro.umass.edu/ TolTEC] is a three-band imaging polarimeter which completed laboratory testing and was installed on the LMT in December of 2021, later undergoing commissioning in several phases up to 2023.<ref>{{Cite web |title=LMT - Large Millimeter Telescope Alfonso Serrano |url=http://lmtgtm.org/telescope/instrumentation/instruments/toltec/ |access-date=2023-09-26 |language=en}}</ref> TolTEC can image the sky at three (1.1, 1.4 and 2.1 millimetre) bands simultaneously using 7000 polarization-sensitive [[kinetic inductance detector]]s (KIDs). Each TolTEC observation produces nine independent images - measuring total intensity (I) and two [[Stokes parameters]] (Q and U) in all three bands. Because of the nearly ubiquitous presence of [[Cosmic dust|dust]] in our universe, TolTEC's science reach includes cosmology, the physics of clusters, galaxy evolution and star-formation along the history of the Universe, the relation between the star-forming process and the molecular clouds, small bodies of the Solar System, and much more. The instrument is designed to be capable of rapid mapping of the sky and is capable of a rate of mapping in excess of eight times greater than the decommissioned AzTEC instrument.<ref>{{Cite web |title=The TolTEC Camera |url=http://toltec.astro.umass.edu/using_toltec.php |access-date=2023-09-26 |website=toltec.astro.umass.edu}}</ref> The TolTEC Project is funded by the [[National Science Foundation|National Science Foundation (NSF)]].

=== Heterodyne Receivers  ===
;SEQUOIA <ref>{{Cite web|title=SEQUOIA|url=http://www.lmtgtm.org/telescope/instrumentation/instruments/sequoia/?lang=en|access-date=2017-06-12|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en}}</ref><ref name=":0">{{Cite journal|last1=Hughes|first1=David H.|last2=Schloerb|first2=F. Peter|last3=Aretxaga|first3=Itziar|author3-link=Itziar Aretxaga|last4=Castillo-Domínguez|first4=Edgar|last5=Chávez Dagostino|first5=Miguel|last6=Colín|first6=Edgar|last7=Erickson|first7=Neal|last8=Ferrusca Rodriguez|first8=Daniel|last9=Gale|first9=David M.|last10=Gómez-Ruiz|first10=Arturo|last11=Hernández Rebollar|first11=José Luis|editor-first1=Heather K |editor-first2=Jason |editor-first3=Tomonori |editor-last1=Marshall |editor-last2=Spyromilio |editor-last3=Usuda |date=2020-12-01|title=The Large Millimeter Telescope (LMT) Alfonso Serrano: current status and telescope performance|journal=Society of Photo-Optical Instrumentation Engineers (Spie) Conference Series |url=http://adsabs.harvard.edu/abs/2020SPIE11445E..22H|volume=1445|pages=1144522|doi=10.1117/12.2561893|bibcode=2020SPIE11445E..22H |isbn=9781510636774 |s2cid=230579334 }}</ref>

SEQUOIA operates in the range 85–116&nbsp;GHz band using a cryogenic focal-plane array of 32 pixels arranged in dual-polarized 4×4 arrays fed by square horns separated by 2 fλ. The arrays are cooled to 18K and use low-noise Indium Phosphide (InP) [[monolithic microwave integrated circuit]] (MMIC) [[preamplifier]]s designed at UMass to provide a characteristic receiver noise of 55K in the range 85–107&nbsp;GHz, increasing to 90K at 116&nbsp;GHz.

;Redshift Search Receiver (RSR)<ref>{{Cite web|title=REDSHIFT|url=http://daisy.astro.umass.edu/~fcrao/instrumentation/redshift/red.html|url-status=dead|archive-url=https://web.archive.org/web/20170523003101/http://daisy.astro.umass.edu/~fcrao/instrumentation/redshift/red.html|archive-date=2017-05-23|access-date=2017-06-12|website=daisy.astro.umass.edu}}</ref><ref>{{Cite web|title=Redshift Search Receiver (RSR)|url=http://www.lmtgtm.org/telescope/instrumentation/instruments/rsr/?lang=en|access-date=2017-06-12|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en}}</ref><ref name=":0" />

A novel MMIC-based receiver designed to maximize the instantaneous receiver bandwidth to cover the 90&nbsp;GHz atmospheric window from 75 to 110&nbsp;GHz in a single tuning. The receiver has four pixels arranged in a dual-beam and dual polarized configuration. Orthogonal polarizations are combined in waveguide-based orthomode transducers. Beam-switching at 1&nbsp;kHz on the sky is achieved using a fast Faraday rotation polarization switch and a wire-grid to interchange the reflected and transmitted beams to each receiver. This ultra-wide-band receiver typically achieves noise temperatures < 50K between 75 and 110&nbsp;GHz. The Redshift Search Receiver has exceptional baseline stability because it does not involve mechanical moving parts, therefore being well-suited to the detection of redshifted transitions of the CO ladder from star-forming galaxies at cosmological distances. An innovative wide-band analog autocorrelator system which covers the full 38&nbsp;GHz with 31&nbsp;MHz (100&nbsp;km/s at 90&nbsp;GHz) resolution serves as the backed spectrometer.

=== Decommissioned ===
;AzTEC<ref>{{Cite web|title=UMass Astronomy – AzTEC|url=http://daisy.astro.umass.edu/AzTEC/|url-status=dead|archive-url=https://web.archive.org/web/20160911092304/http://daisy.astro.umass.edu/AzTEC/|archive-date=2016-09-11|access-date=2017-06-12|website=daisy.astro.umass.edu}}</ref><ref>{{Cite web|title=AzTEC|url=http://www.lmtgtm.org/telescope/instrumentation/instruments/aztec/?lang=en|access-date=2017-06-12|website=LMT – Large Millimeter Telescope Alfonso Serrano|language=en}}</ref>

The AzTEC millimetre camera was developed to operate at 1.1mm. It is formed by a 144 silicon nitride micromesh bolometer array arranged in a compact hexagonal package and fed by an array of horns separated by 1.4 fλ. The detectors are cooled down to ~250 mK inside a 3He closed-cycle [[cryostat]], achieving a ~3 mJy Hz-1/2 pixel sensibility. The AzTEC field of view at the LMT is 2.4 arcminutes square and manages to take completely sampled images through telescope or reflecting secondary surface movements.

==References==
{{Reflist}}

==External links==
{{Commons category|Large Millimeter Telescope}}
*{{official|http://www.lmtgtm.org}}
*[http://www.inaoep.mx Instituto Nacional de Astrofísica, Óptica y Electrónica]
*[http://www.astro.umass.edu/ University of Massachusetts Astronomy Department]
*[http://toltec.astro.umass.edu/ TolTEC instrument website]
*[https://www.nsf.gov/ National Science Foundation (NSF)]

{{radio-astronomy}}
{{University of Massachusetts Amherst}}

[[Category:Radio telescopes]]
[[Category:Astronomical observatories in Mexico]]
[[Category:Buildings and structures in Puebla]]
[[Category:Trans-Mexican Volcanic Belt]]