Astronomy:Caltech Submillimeter Observatory

Short description: Decommissioned radio telescope in Hawaii, USA

The Caltech Submillimeter Observatory (CSO) was a 10.4-meter (34 ft) diameter submillimeter wavelength telescope situated alongside the 15-meter (49 ft) James Clerk Maxwell Telescope (JCMT) at Mauna Kea Observatories. It was engaged in submillimeter astronomy, of the terahertz radiation band. The telescope closed on September 18, 2015. As of April 2019, the telescope is set to be dismantled and its site remediated in the near future as part of the Mauna Kea Comprehensive Management Plan.[1]

History

In 1973 Robert Leighton proposed to the NSF to build four 10.4 meter diameter parabolic dish radio antennas. Three of these Leighton antennas were to be used as a mm-wave interferometer to be sited at OVRO, and the fourth was to be used as a single submillimeter telescope at a high mountain site. The proposal was approved (AST 73-04908[2]), but the NSF insisted that the mm-wave array had to be completed before work on the submillimeter telescope could be started, which delayed the construction of the submillimeter telescope by almost a decade. Mauna Kea was selected as the site for the submillimeter telescope, which became the Caltech Submillimeter Observatory, after a site survey by Thomas G. Phillips.[3] The three antenna mm-wave interferometer at OVRO was eventually expanded to six elements, and ultimately became part of the CARMA array in California's Inyo Mountains.

The CSO antenna, named the Leighton Telescope after the death of Robert Leighton in 1997, has a more precise surface than the CARMA array antennas, enabling it to make use of the superior Mauna Kea site by operating at higher frequencies. Heating elements were also added to the stand-off pins which support the hexagonal panels, to allow active control of the surface.[4]

Before being deployed to Hawaii, both the antenna (without its dish) and the dome building were assembled on the Caltech campus, at the current site of the IPAC building, in order to ensure that the building and its shutter operated correctly. Despite having assembled the building once on the Caltech campus, the construction contractor had difficulty re-assembling the building in the high altitude environment of Mauna Kea, and the contractor went bankrupt. After the bankruptcy Caltech staff had to supervise completion of the observatory construction.

Operation

The Horsehead Nebula, as seen in visible light on the left, and on the right as a false color image made from data taken at the CSO, of the intensity of the 230 GHz rotational transition of carbon monoxide.

Throughout its nearly three decade operational lifetime, the CSO was funded primarily by the NSF. The University of Texas provided additional funding from the start of 1988 through the end of 2012.

The CSO emphasized heterodyne receiver work, while the neighboring James Clerk Maxwell Telescope emphasized continuum detector observations. Most of the heterodyne receivers were built on the Caltech campus, and were placed at the Nasmyth focus. The University of Texas team built instruments for the CSO, including a re-imaging system which effectively converted the 10.4 meter telescope into a 1 meter off-axis telescope with a 3 arc minute wide beam at 492 GHz. This wide beam system was used to map the atomic carbon line at 492 GHz over large regions of the sky.[5] The UT team also provided an 850 GHz receiver for the telescope's Cassegrain focus.

In 1986, the CSO obtained official "first light" by producing a spectrum of the carbon monoxide J=2-1 line from the nearby starburst galaxy Messier 82 (although continuum detections of the Moon and some planets had been made earlier).

The CSO and JCMT were combined to form the first submillimeter interferometer. The success of this experiment was important in pushing ahead the construction of the Submillimeter Array and the Atacama Large Millimeter Array interferometers. The CSO was also a part of the Event Horizon Telescope array during the early test observations which proved the feasibility of intercontinental mm-wave interferometry.

Research Highlights:

• The first detection of the Sunyaev-Zel'dovich Effect at millimeter wavelengths, and the first measurement of cluster temperature using the Sunyaev-Zel'dovich Effect.[6][7]
• The Bolocam Galactic Plane Survey, a survey of continuum emission at 1.1 mm, which covered 170 square degrees of the galactic plane. This survey resulted in the publication of at least 14 journal papers with over 1000 aggregate citations.[8]
• Discovery of new submillimeter water maser spectral lines at 321, 325, 437, 439, 471, and 658 GHz.[9][10][11][12]
• Molecular line surveys in the submillimeter band of the star formation regions Sagittarius B2 and Orion KL; the carbon star IRC+10216; and the planets Jupiter and Saturn.[13][14][15][16][17]
• Discovery of a ~200 km/sec fast molecular wind from the protoplanetary nebula CRL 618. This fast neutral wind will interact with the slow AGB wind to shape the final planetary nebula.[18]
• Submillimeter observations of the Solar eclipse of July 11, 1991, a very unusual eclipse in that it passed over several major observatories.[19] Observing the Sun would normally have constituted a severe violation of the telescope's sun-avoidance limits, as it was normally forbidden to allow any sunlight to fall upon even a portion of the telescope's primary mirror. However for this special event a tent-like membrane was deployed over the dish, which prevented focused visible and infrared light from destroying the secondary mirror assembly.

The last observation from the telescope was made on 8 September 2015, and was of Orion KL.[20]

Over 100 students from 25 institutions used the CSO for doctoral research projects.[21]

Decommissioning

Caltech Submillimeter Observatory.

In order to get a permit to build the Thirty Meter Telescope project on Mauna Kea, the University of Hawaii had to commit to closing and dismantling three existing observatories on the mountain. The three chosen were the CSO, the UKIRT, and the Hoku Keʻa telescope.[1] Two additional telescopes must also be removed by 2033, but those have not been selected as of 1 April 2019.[22]

On April 30, 2009, Caltech announced plans to decommission the CSO, transferring ongoing research to the next-generation Cerro Chajnantor Atacama Telescope (CCAT) in Chile. The plans called for CSO to be dismantled, beginning in 2016, with its site returned to a natural state by 2018.[23] Delays in the environmental assessment and permitting processes have led to postponement of the telescope removal. On 24 January 2019, Robert McLaren, the interim Director of the University of Hawaii Institute of Astronomy, gave an update to state lawmakers and suggested the permitting will be accomplished in 2019 with dismantling and removal taking a year or less.[22]

References

1. Phillips, T. G. (June 2007). "The Caltech Submillimeter Observatory". 2007 IEEE/MTT-S International Microwave Symposium: 1849–1852. doi:10.1109/MWSYM.2007.380111. ISBN 978-1-4244-0687-6. Bibcode2007ims..confE...1P. Retrieved 30 October 2020.
2. Leong, Melanie; Peng, Ruisheng; Yoshida, Hiroshige; Chamberlin, Richard; Phillips, Thomas G. (2009). "A Caltech Submillimeter Observatory Active Optics System". Submillimeter Astrophysics and Technology: A Symposium Honoring Thomas G. Phillips. ASP Conference Series. 417. pp. 131–135. ISBN 978-1-58381-714-8. Retrieved 30 October 2020.
3. Plume, Rene; Jaffe, Daniel T. (May 1995). "The World's Smallest 10-meter Submillimeter Telescope". Publications of the Astronomical Society of the Pacific 107: 488–495. doi:10.1086/133579. Bibcode1995PASP..107..488P. Retrieved 19 November 2020.
4. Wilbanks, T. M.; Ade, P. A. R.; Fischer, M. L.; Holzapfel, W. L.; Lange, A. E. (June 1994). "Measurement of the Sunyaev-Zel'dovich Effect toward Abell 2163 at a Wavelength of 2.2 Millimeters". Astrophysical Journal Letters 427: L75–L78. doi:10.1086/187368. Bibcode1994ApJ...427L..75W. Retrieved 31 October 2020.
5. Hansen, Steen H.; Pastor, Sergio; Semikoz, Dmitry V. (July 2002). "First Measurement of Cluster Temperature Using the Thermal Sunyaev-Zel'dovich Effect". Astrophysical Journal Letters 573 (2): L69–L71. doi:10.1086/342094. Bibcode2002ApJ...573L..69H. Retrieved 31 October 2020.
6. Aguirre, James E.; Ginsburg, Adam G.; Dunham, Miranda K.; Drosback, Meredith M.; Bally, John; Battersby, Cara; Bradley, Eric Todd; Cyganowski, Claudia et al. (January 2011). "The Bolocam Galactic Plane Survey: Survey Description and Data Reduction". Astrophysical Journal Supplement Series 192 (1): 4. doi:10.1088/0067-0049/192/1/4. Bibcode2011ApJS..192....4A. Retrieved 6 November 2020.
7. Menten, K. M.; Melnick, G. J.; Phillips, T. G. (1990). "Submillimeter Water Masers". Astrophysical Journal Letters 350: L41–L44. doi:10.1086/185663. Bibcode1990ApJ...350L..41M. Retrieved 6 November 2020.
8. Menten, K. M.; Melnick, G. J.; Phillips, T. G.; Neufeld, D. A. (1990). "A New Submillimeter Water Maser Transition at 325 GHz". Astrophysical Journal Letters 363: L27–L31. doi:10.1086/185857. Bibcode1990ApJ...363L..27M. Retrieved 31 October 2020.
9. Menten, K. M.; Young, K. (1995). "Discovery of Strong Vibrationally Excited Water Masers at 658 GHz Toward Evolved Stars". Astrophysical Journal Letters 450: L67–L70. doi:10.1086/316776. Bibcode1995ApJ...450L..67M. Retrieved 31 October 2020.
10. Melnick, Gary J.; Menten, Karl M.; Phillips, Thomas G.; Hunter, Todd (October 1993). "Discovery of Interstellar Water Lines at 437, 439, and 471 GHz: Strong Case for Water Maser Formation behind C-Type Shocks". Astrophysical Journal Letters 416: L37–L40. doi:10.1086/187065. Bibcode1993ApJ...416L..37M. Retrieved 31 October 2020.
11. Sutton, E. C.; Jaminet, P. A.; Danchi, W. C.; Blake, Geoffrey A. (October 1991). "Molecular Line Survey of Sagittarius B2(M) from 330 to 355 GHz and Comparison with Sagittarius B2(N)". Astrophysical Journal Supplement Series 77: 255–285. doi:10.1086/191603. Bibcode1991ApJS...77..255S. Retrieved 31 October 2020.
12. Groesbeck, T. D.; Phillips, T. G.; Blake, Geoffrey A. (1994). "The Molecular Emission-Line Spectrum of IRC +10216 between 330 and 358 GHz". Astrophysical Journal Supplement Series 94 (1): 147–162. doi:10.1086/192076. PMID 11539132. Bibcode1994ApJS...94..147G. Retrieved 31 October 2020.
13. Weisstein, Eric W.; Serabyn, E. (September 1996). "Submillimeter Line Search in Jupiter and Saturn". Icarus 123 (1): 23–36. doi:10.1006/icar.1996.0139. Bibcode1996Icar..123...23W. Retrieved 31 October 2020.
14. Schilke, P.; Groesbecj, T. D.; Blake, G. A.; Phillips, T. G. (January 1997). "A Line Survey of Orion KL from 325 to 360 GHz". Astrophysical Journal Supplement Series 108 (1): 301–337. doi:10.1086/312948. PMID 11539874. Bibcode1997ApJS..108..301S. Retrieved 31 October 2020.
15. Schilke, P.; Benford, D. J.; Hunter, T. R.; Lis, D. C.; Phillips, T. G. (February 2001). "A Line Survey of Orion-KL from 607 to 725 GHZ". Astrophysical Journal Supplement Series 132 (2): 281–364. doi:10.1086/318951. Bibcode2001ApJS..132..281S. Retrieved 31 October 2020.
16. Gammie, C. F.; Knapp, G. R.; Young, K.; Phillips, T.G.; Falgarone, E. (1989). "A Very Fast Molecular Outflow from the Protoplanetary Nebula CRL 618". Astrophysical Journal Letters 345: L87–L89. doi:10.1086/185559. Bibcode1989ApJ...345L..87G. Retrieved 31 October 2020.
17. Ewell, M. W., Jr; Zirin, H.; Jensen, J. B.; Bastian, T. S. (January 1993). "Submillimeter Observations of the 1991 July 11 Total Solar Eclipse". Astrophysical Journal 403: 426–433. doi:10.1086/172213. Bibcode1993ApJ...403..426E. Retrieved 31 October 2020.
18. McGuire, Brett A.; Carroll, P. Brandon (31 October 2017). "The Final Integrations of the Caltech Submillimeter Observatory". Research Notes of the AAS 1 (1): 4. doi:10.3847/2515-5172/aa9657. ISSN 2515-5172. Bibcode2017RNAAS...1a...4M.
19. "Caltech Submillimeter Observatory in Hawaii to be Decommissioned" (Press release). Caltech.edu. April 30, 2009. Archived from the original on June 10, 2010. Retrieved December 22, 2010.