View source for Very Small Array

{{short description|Radio telescope in the Canary Islands}}
{{Use dmy dates|date=April 2022}}
{{Infobox Telescope
|locmapin=Spain Canary Islands
}}

The '''Very Small Array''' ('''VSA''') was a 14-element [[interferometer|interferometric]] radio telescope operating between 26 and 36&nbsp;GHz that is used to study the [[cosmic microwave background radiation]]. It was a collaboration between the [[University of Cambridge]], [[University of Manchester]] and the [[Instituto de Astrofisica de Canarias]] ([[Tenerife]]), and was located at the [[Observatorio del Teide]] on [[Tenerife]]. The array was built at the [[Mullard Radio Astronomy Observatory]] by the [[Cavendish Astrophysics Group]] and [[Jodrell Bank Observatory]], and was funded by [[PPARC]] (now [[Science and Technology Facilities Council|STFC]]). The design was strongly based on the [[Cosmic Anisotropy Telescope]].<ref name="cam" /><ref name="jbo" />

The telescope was comparable in terms of capabilities to several other CMB experiments, including the balloon-based [[BOOMERanG]] and [[Millimeter Anisotropy eXperiment IMaging Array|MAXIMA]], and the ground-based [[Degree Angular Scale Interferometer|DASI]] and [[Cosmic Background Imager|CBI]].<ref name="watson" />

== Design ==
[[File:Teide Observatory 2018 116.jpg|thumb|right|The ground shield that used to hold the VSA]]
The telescope consists of 14 elements (yielding 91 baselines), each of which have a horn reflector antenna focusing astrophysical signals into individual receivers (pseudomorphic [[HFET]] amplifiers, with a system temperature around 25 K and a physical temperature of 12 K,<ref name="cam" /> based on an [[NRAO]] design).<ref name="jbo_dev" /> The separate elements are combined using a correlator to form an [[aperture synthesis]] array.<ref name="jbo_dev" /> The elements are mounted on a tip-table, which is capable of tracking the sky and can tilt up to 35 degrees from the zenith.<ref name="cam" />

The telescope has been used in three different configurations – "compact", "extended" and "super-extended", each of which differ in the separation distance between the elements (the difference between compact and extended is a factor of 2.25), and the size of the antennas.<ref name="cam" /> While the compact array has antennas 143{{nbsp}}mm in diameter, the extended array uses 322{{nbsp}}mm diameter antennas.<ref name="grainge" /> This means that the compact array has a primary beam of 4.5 degrees, and a resolution of 30 arcminutes (multipoles between 100 and 800), while the extended array has a primary beam of 2 degrees, a resolution of 12 arcminutes and can hence observe multipoles between 250 and 1500.<ref name="jbo_techspecs" /> The extended array is also a factor of 5 more sensitive than the compact array.<ref name="grainge" /> The super-extended array will be able to measure multipoles up to 3000,<ref name="dickinson" /> and has 550{{nbsp}}mm antenna mirrors. The front-end amplifiers were also upgraded.<ref name="cleary" />

The telescope can be tuned to frequencies between 26 and 36&nbsp;GHz, with 1.5&nbsp;GHz bandwidth, meaning that the telescope can carry out observations at different frequencies.<ref name="taylor" />

It also includes two 3.7{{nbsp}}m radio telescopes, also working at 30&nbsp;GHz,<ref name="jbo_sources" /> which are dedicated to monitoring foreground sources.<ref name="watson" /> These source subtraction dishes were upgraded to more accurate ones following the first series of observations, to allow the monitoring of much weaker sources than previously.<ref name="grainge" />

Both the source subtractor dishes, and the VSA itself, are surrounded by large metal ground shields.<ref name="jbo" />

As the VSA is an [[interferometer]], it directly measures the angular power spectrum of the CMB, rather than having to construct a map of the sky first.<ref name="jbo" /><ref name="scott" />

== Results ==
[[Image:WMAP TT power spectrum.png|thumb|right|300px|The power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale (or [[multipole moment]]). The data shown come from the [[WMAP]] (2006), [[Arcminute Cosmology Bolometer Array Receiver|Acbar]] (2004) [[BOOMERanG experiment|Boomerang]] (2005), [[Cosmic Background Imager|CBI]] (2004) and Very Small Array (2004) instruments.]]

The fields observed with the VSA were chosen to minimize the amount of bright radio sources and large clusters in the field (the latter to avoid the [[Sunyaev-Zel'dovich effect]]), as well as to avoid contamination by emission from [[Milky Way|our galaxy]].<ref name="dickinson" /> The radio point sources present in the VSA fields were observed with the [[Ryle Telescope]] at 15&nbsp;GHz, then monitored by the VSA source subtracters during the VSA observations.<ref name="watson" />

In the compact array configuration, the telescope observed three 7×7 degree areas of the sky to high precision<ref name="cam" /> in an observing session between August 2000 and August 2001.<ref name="maisinger" /> These observations were taken at the highest frequency of the telescope, centered at 34&nbsp;GHz, to reduce foreground contamination.<ref name="taylor" /> Another, larger area of the sky was also observed, but less precisely.<ref name="taylor" /> The data from these observations were reduced independently at all three involved institutions.<ref name="jbo_dev" /> The results from these observations were published in a series of four papers in 2003; those by Watson et al., Taylor et al., Scott et al. and Rubino-Martin et al. (see References below). The key results were the power spectra of the [[Cosmic Microwave Background]] between multipoles of 150 and 900,<ref name="scott" /> and the resulting limits on [[Lambda-CDM model#Parameters|cosmological parameters]] when combined with data from observations from other experiments.<ref name="rubino" />

The second observing session ran between September 2001<ref name="maisinger" /> and July 2003, and was using the extended array.<ref name="vsaextendedobs" /> The first results from the extended array were published as a Letter in 2003, simultaneously with the first four publications, using data taken up until April 2002. The sections of the sky observed were located within the previously-observed fields, with the measurements being both more accurate and in greater detail. The result was an improved power spectrum of the CMB, going out to a multipole of 1400,<ref name="grainge" /> and refined cosmological parameters.<ref name="slosar" /> The second set of results were published in 2004, and consisted of the original observations plus more observations taken in the same regions of the sky, as well as observations in three new regions. This yielded measurements of the CMB power spectra out to l of 1500 much more accurately than previously,<ref name="dickinson" /> and more accurate cosmological parameter estimates.<ref name="rebolo" />

Observations with the VSA continued until the end of August 2008, using the Super-Extended configuration. Also, the Ryle Telescope has been upgraded to detect lower flux point sources, and the OCRA receiver on a telescope in Poland will be used to more accurately subtract the point sources.<ref name="cleary" />

{| class="wikitable"
|- style="text-align:center;"
| [[Image:VSA CMB spectra 1.png|250px|First results.<ref name="scott" />]]
| [[Image:VSA spectra 2.png|250px|Second results.<ref name="grainge" />]]
| [[Image:VSA spectra 3.png|250px|Third results.<ref name="dickinson" />]]
|-
| colspan=3 | The Very Small Array's measurements of the [[Cosmic Microwave Background|CMB]] power spectra. From left to right: from first observations,<ref name="scott" /> the first results from the second observing session<ref name="grainge" /> and the final results from the second observing session.<ref name="dickinson" />
|}

== See also ==
{{commons category}}
* [[Very Large Array]]

== References ==
{{Reflist|30em|refs=
<ref name="cam">{{cite web | url=http://www.mrao.cam.ac.uk/telescopes/vsa/ | title=University of Cambridge webpage on the VSA | access-date=2007-06-23}}</ref>
<ref name="jbo_dev">{{cite web | url=http://www.jb.man.ac.uk/tech/technology/vsa.html | title=Jodrell Bank Observatory - VSA Receivers | access-date=2007-06-23}}</ref>
<ref name="jbo">{{cite web | url=http://www.jb.man.ac.uk/research/cmb/vsa/ | title=Jodrell Bank webpage on the VSA | access-date=2007-06-23}}</ref>
<ref name="watson">{{cite journal | title=First results from the Very Small Array I: Observational Methods | first=R. A. | last=Watson |display-authors=etal  | date=2003 | journal=[[MNRAS]] | volume=341 | issue=4 | pages=1057–1065 | arxiv=astro-ph/0205378 | bibcode=2003MNRAS.341.1057W | doi=10.1046/j.1365-8711.2003.06338.x| doi-access=free | s2cid=17592336 }}</ref>
<ref name="grainge">{{cite journal | title=The CMB Power Spectrum out to l = 1400 measured by the VSA | first=Keith | last=Grainge |display-authors=etal  | date=2003 | journal=[[MNRAS]] | volume=341 | issue=4 | pages=L23–L28 | bibcode=2003MNRAS.341L..23G | arxiv=astro-ph/0212495 | doi=10.1046/j.1365-8711.2003.06563.x| doi-access=free }}</ref>
<ref name="jbo_techspecs">{{cite web | url=http://www.jb.man.ac.uk/research/cmb/vsa/VSA_Technical_Specs.html | title=Technical specifications of the VSA | publisher=[[Jodrell Bank Observatory]] | access-date=2007-06-23}}</ref>
<ref name="dickinson">{{cite journal | first=Clive | last=Dickinson |display-authors=etal  | title=High sensitivity measurements of the CMB power spectrum with the extended Very Small Array | date=2004 | journal=[[MNRAS]] | volume=353 | issue=3 | page=732 | arxiv=astro-ph/0402498 | bibcode=2004MNRAS.353..732D | doi=10.1111/j.1365-2966.2004.08206.x| doi-access=free | s2cid=2806871 }}</ref>
<ref name="cleary">{{cite journal | title=Source subtraction for the extended Very Small Array and 33-GHz source count estimates | first1=Kieran | last1=Cleary | date=2005 | arxiv=astro-ph/0412605 | bibcode=2005MNRAS.360..340C | journal=[[MNRAS]] | volume=360 | issue=1 | pages=340–353 | doi=10.1111/j.1365-2966.2005.09037.x | last2=Taylor | first2=Angela C. | last3=Waldram | first3=Elizabeth | last4=Battye | first4=Richard A. | last5=Dickinson | first5=Clive | last6=Davies | first6=Rod D. | last7=Davis | first7=Richard J. | last8=Genova-Santos | first8=Ricardo | last9=Grainge | first9=Keith | last10=Jones | first10=Michael E. | last11=Kneissl | first11=Rüdiger | last12=Pooley | first12=G. G. | last13=Rebolo | first13=Rafael | last14=Alberto Rubiño-Martín | first14=José | last15=Saunders | first15=Richard D. E. | last16=Scott | first16=Paul F. | last17=Slosar | first17=Anže | last18=Titterington | first18=David | last19=Watson | first19=Robert A. | doi-access=free | s2cid=10370174 | display-authors=8 }}</ref>
<ref name="taylor">{{cite journal | title=First Results From The Very Small Array II: Observations of the CMB | first=Angela C. | last=Taylor |display-authors=etal  | date=2003 | journal=[[MNRAS]] | volume=341 | issue=4 | pages=1066–1075 | arxiv=astro-ph/0205381 | bibcode=2003MNRAS.341.1066T | doi=10.1046/j.1365-8711.2003.06493.x| doi-access=free | s2cid=15605923 }}</ref>
<ref name="jbo_sources">{{cite web | url=http://www.jb.man.ac.uk/research/cmb/vsa/VSA_source_Subtractors.html | title=VSA Source Subtractors | publisher=[[Jodrell Bank Observatory]] | access-date=2007-06-23}}</ref>
<ref name="scott">{{cite journal | title=First results from the Very Small Array III: The CMB Power Spectrum | first=P. F. | last=Scott |display-authors=etal  | date=2003 | journal=[[MNRAS]] | volume=341 | issue=4 | pages=1076–1083 | bibcode=2003MNRAS.341.1076S | arxiv=astro-ph/0205380 | doi=10.1046/j.1365-8711.2003.06354.x| doi-access=free | s2cid=119088948 }}</ref>
<ref name="maisinger">{{cite journal | title=Maximum-likelihood astrometric geometry calibration of interferometric telescopes: application to the Very Small Array | last1=Maisinger | first1=Klaus | date=2003 | bibcode=2003MNRAS.345..800M | journal=[[MNRAS]] | volume=345 | issue=3 | pages=800–808 | arxiv=astro-ph/0212210 | doi=10.1046/j.1365-8711.2003.06995.x | type=abstract | last2=Hobson | first2=M. P. | last3=Saunders | first3=Richard D. E. | last4=Grainge | first4=Keith J. B. | doi-access=free | s2cid=11987021 }}</ref>
<ref name="rubino">{{cite journal | title=First results from the Very Small Array IV: Cosmological Parameter Estimation | first=J. A. | last=Rubino-Martin |display-authors=etal  | date=2003 | journal=[[MNRAS]] | volume=341 | issue=4 | pages=1084–1092 | arxiv=astro-ph/0205367 | bibcode=2003MNRAS.341.1084R | doi=10.1046/j.1365-8711.2003.06494.x| doi-access=free | s2cid=18192370 }}</ref>
<ref name="vsaextendedobs">{{cite web | url=http://www.jb.man.ac.uk/research/cmb/vsa/vsa_results.html | title=VSA Extended Array Power Spectrum Data | access-date=2007-06-23}}</ref>
<ref name="slosar">{{cite journal | title=Cosmological Parameter Estimation and Bayesian model comparison using VSA data | first=Anze | last=Slosar |display-authors=etal  | date=2003 | journal=[[MNRAS]] | volume=341 | issue=4 | pages=L29–L34 | arxiv=astro-ph/0212497 | bibcode=2003MNRAS.341L..29S | doi=10.1046/j.1365-8711.2003.06564.x| doi-access=free | s2cid=12420402 }}</ref>
<ref name="rebolo">{{cite journal | title=Cosmological parameter estimation using Very Small Array data out to l=1500 | first=Rafael | last=Rebolo |display-authors=etal  | date=2004 | arxiv=astro-ph/0402466 | journal=[[MNRAS]] | volume=353 | issue=3 | pages=747–759 | bibcode=2004MNRAS.353..747R | doi=10.1111/j.1365-2966.2004.08102.x| doi-access=free | s2cid=13971059 }}</ref>
}}

== Further reading ==
{{refbegin}}
* {{cite journal | first1=Richard | last1=Savage | date=2004 | title=Searching for non-Gaussianity in the Very Small Array data | journal=[[MNRAS]] | volume=349 | issue=3 | pages=973–982 | bibcode=2004MNRAS.349..973S | arxiv=astro-ph/0308266 | doi=10.1111/j.1365-2966.2004.07578.x | last2=Battye | first2=Richard A. | last3=Carreira | first3=Pedro | last4=Cleary | first4=Kieran | last5=Davies | first5=Rod D. | last6=Davis | first6=Richard J. | last7=Dickinson | first7=Clive | last8=Genova-Santos | first8=Ricardo | last9=Grainge | first9=Keith| last10=Gutiérrez | first10=Carlos M. | last11=Hafez | first11=Yaser A. | last12=Hobson | first12=Michael P. | last13=Jones | first13=Michael E. | last14=Kneissl | first14=Rüdiger | last15=Lancaster | first15=Katy | last16=Lasenby | first16=Anthony | last17=Leahy | first17=J. P. | last18=Maisinger | first18=Klaus | last19=Pooley | first19=Guy G. | last20=Rajguru | first20=Nutan | last21=Rebolo | first21=Rafael | last22=Rocha | first22=Graca | last23=Alberto Rubiño-Martin | first23=José | last24=Saunders | first24=Richard D. E. | last25=Scott | first25=Paul | last26=Slosar | first26=Anžce | last27=Molina | first27=Pedro Sosa | last28=Taylor | first28=Angela C. | last29=Titterington | first29=David | last30=Waldram | first30=Elizabeth | doi-access=free | s2cid=16877915 | display-authors=8 }}
* {{cite journal | title=Estimating the bispectrum of the Very Small Array data | first=Sarah | last=Smith |display-authors=etal  | journal=[[MNRAS]] | date=2004 | volume=352 | issue=3 | pages=887–902 | arxiv=astro-ph/0401618 | bibcode=2004MNRAS.352..887S | doi=10.1111/j.1365-2966.2004.07885.x| doi-access=free | s2cid=14172358 }}
* {{cite journal | title=Very Small Array observations of the Sunyaev-Zel'dovich effect in nearby galaxy clusters | first1=Katy | last1=Lancaster | journal=[[MNRAS]] | year=2005 | volume=359 | issue=1 | pages=16–30 | arxiv=astro-ph/0405582 | bibcode=2005MNRAS.359...16L | doi=10.1111/j.1365-2966.2005.08696.x | last2=Genova-Santos | first2=Ricardo | last3=Falcon | first3=Nelson | last4=Grainge | first4=Keith | last5=Gutierrez | first5=Carlos | last6=Kneissl | first6=Rudiger | last7=Marshall | first7=Phil | last8=Pooley | first8=Guy | last9=Rebolo | first9=Rafael| last10=Rubino-Martin | first10=J.-A. | last11=Saunders | first11=R. D. E. | last12=Waldram | first12=E. | last13=Watson | first13=R. A. | doi-access=free | s2cid=14038645 | display-authors=8 }}
* {{cite journal | title=A Very Small Array search for the extended Sunyaev-Zel'dovich effect in the Corona Borealis supercluster | last=Génova-Santos | first=Ricardo |display-authors=etal  | journal=[[MNRAS]] | volume=363 | issue=1 | pages=79–92 | bibcode=2005MNRAS.363...79G | arxiv=astro-ph/0507285 | date=2005 | doi=10.1111/j.1365-2966.2005.09405.x| doi-access=free | s2cid=16018448 }}
* {{cite journal | title=Cosmic microwave background observations from the Cosmic Background Imager and Very Small Array: a comparison of coincident maps and parameter estimation methods | last=Rajguru | first=Nutan |display-authors=etal  | date=2005 | journal=[[MNRAS]] | volume=363 | issue=4 | pages=1125–1135 | bibcode=2005MNRAS.363.1125R | arxiv=astro-ph/0502330 | doi=10.1111/j.1365-2966.2005.09519.x| doi-access=free | s2cid=118112483 | url=http://discovery.ucl.ac.uk/182789/1/182789.pdf }}
* {{cite journal | title=Non-Gaussianity in the Very Small Array cosmic microwave background maps with smooth goodness-of-fit tests | last1=Rubiño-Martín | first1=José Alberto | date=2006 | journal=[[MNRAS]] | volume=369 | issue=2 | pages=909–920 | arxiv=astro-ph/0604070 | bibcode=2006MNRAS.369..909R | doi=10.1111/j.1365-2966.2006.10341.x | last2=Aliaga | first2=Antonio M. | last3=Barreiro | first3=R. B. | last4=Battye | first4=Richard A. | last5=Carreira | first5=Pedro | last6=Cleary | first6=Kieran | last7=Davies | first7=Rod D. | last8=Davis | first8=Richard J. | last9=Dickinson | first9=Clive| last10=Génova-Santos | first10=Ricardo | last11=Grainge | first11=Keith | last12=Gutiérrez | first12=Carlos M. | last13=Hafez | first13=Yaser A. | last14=Hobson | first14=Michael P. | last15=Jones | first15=Michael E. | last16=Kneissl | first16=Rüdiger | last17=Lancaster | first17=Katy | last18=Lasenby | first18=Anthony | last19=Leahy | first19=J. P. | last20=Maisinger | first20=Klaus | last21=Martínez-González | first21=Enrique | last22=Pooley | first22=Guy G. | last23=Rajguru | first23=Nutan | last24=Rebolo | first24=Rafael | last25=Sanz | first25=José Luis | last26=Saunders | first26=Richard D. E. | last27=Savage | first27=Richard S. | last28=Scaife | first28=Anna | last29=Scott | first29=Paul | last30=Slosar | first30=Anže | doi-access=free | s2cid=55713539 | display-authors=8 }}
{{refend}}

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