“Large Latin American Millimeter Array”的意思、由来-开放百科全书

The Large Latin American Millimeter Array (LLAMA) is a single-dish 12 m Nasmyth optics antenna with VLBI capability which is under construction in the Puna de Atacama desert in the Province of Salta, Argentina. The primary mirror accuracy will allow observation from 40 GHz up to 900 GHz. It is also planned to install a bolometer camera at millimeter wavelengths. After installation it will be able to join other similar instruments to perform Very Large Base Line Interferometry or to work in standalone mode. Financial support is provided by the Argentinian government through its Science Ministry, and from Brazil through a FAPESP grant. The total cost of construction, around US$20 million, and operation as well as the telescope time use will be shared equally by the two countries. Construction planning started in July 2014 after the formal signature of an agreement between the main institutions involved.

Overview

LLAMA is a joint project between Argentinian and Brazilian Astronomers to build and operate a radio telescope at submillimeter wavelengths, that can work in stand alone mode or join a VLBI network. It is similar to the APEX antenna, also build by the German firm Vertex Antennentechnik, GmbH (the same firm provided 25 of the ALMA antennae). The main scientific Institutions involved in the project are the Instituto Argentino de Radio Astronomía (IAR), and the Núcleo para o Apoio da Rádio Astronomia (NARA), from the Universidade de São Paulo (Brazil). The telescope is located at a very high altitude (4,825 m) where the atmospheric absorption (mostly due to water vapor) allows the observation at the very short wavelengths of less than 1 mm. It is a multipurpose instrument that will have cryogenic receivers with very high sensitivity in order to observe very faint sources, and filters to observe the Sun. This large receivers input range is quite a big challenge (although is not the first time that it was achieved since ALMA 12 m antennas have the same capacity.)

History

The history of the instrument can be traced back to 2007, during the XII Latin American Regional IAU Metting (LARIM)^[1] held in Isla de Margarita (Venezuela). Argentinian radio astronomers discussed the idea with colleagues from South America.^[2] The search for the best place for a submillimeter (wavelength less than 1 mm) telescope had started in Argentina well earlier, in 2003, with a 210 GHz tipper which was installed in different places to investigate the atmospheric opacity.^[3]^[4] During the XXVII General Assembly^[5] in Rio de Janeiro, the project gained a name in a document authored by the leading scientists of the project.^[6] In the same document, scientists also proposed the initial science, budget, strategies for construction, site, and other matters. The formal presentation before the Argentinian Science Ministry (MinCyT) was in 2010, while a meeting held at the offices of FAPESP in August 2011 was the kickoff in Brazil. In 2011 MinCyT ranked LLAMA as its astronomical project and in 2012 FAPESP approved a €7 M grant. The final agreement, between MinCyT, FAPESP and USP, was signed in June 2014, and on July 9, it was formally presented to the public.^[7]

Measurement of electrical characteristics of the site was done in late 2016, and construction of the road to the summit began in December 2016.^[8]

Origin of the name. The logo

The word llama has different meanings in Spanish. Llama means flame. However, the origin of the observatory acronym comes from the Quechuan word llama that designates the South American camelid that lives in the region where the telescope is being installed. There is some confusion with the word array, since LLAMA will consist of a single dish antenna. The justification goes with the fact that the instrument will have VLBI technology; therefore, it can be part of an antenna array with telescopes of other observatories. Moreover, the LLAMA observatory can be expanded in the future by installing other antennas in different sites.

In different official documents the acronym LLAMA may be found expanded as Long Latin American Millimeter Array and not as Large. It is also possible to read Millimetric (instead of Millimeter). After some debate, the LLAMA Executive Committee stated that Large Latin American Millimeter Array is the right expansion for the LLAMA acronym.^[9]

The observatory logo has as symbols the Southern Cross (upper right), a telescope sketch (bottom right), the acronym (upper left) and a llama profile (bottom left). Although it changed with time, these symbols are present since the beginning. The image illustrating this{{which|date=December 2018}} page is the official logo since August 2014.

Science

LLAMA is a multipurpose instrument, with the capacity to both observe strong sources (the Sun) and very weak sources very far from Earth. The following is a list of different subjects that will be addressed with LLAMA observations.

The Sun

In the unperturbed solar Atmosphere, the shorter the wavelength the deeper the observation. Frequencies near the submillimeter range are produced in the lower Chromosphere or even the Photosphere.^[10]^[11] Therefore, LLAMA observations will bring new information about the structure of the lower Solar Atmosphere, the active and quiescent filaments and the dynamics of the Chromosphere and its Magnetic Field. The possibility to observe Solar Flares at high frequencies with a high sensitive instrument will give clues about the acceleration of the high energetic particles in the Sun, complementing results obtained with the Solar Submillimeter Telescope. In particular the still unexplained spectral inversion above ≈ 100 GHz.^[12] A very challenging experiment would be to make VLBI solar observations. For example, in a joint observation between LLAMA and some of the ALMA antennas, a spatial resolution of 0.001" will be achieved for λ ≈ 1 mm, i.e. 700 m over the solar surface, never attained before at any wavelength.

Planets

Stellar objects

Astrophysical jets and maser emission

Galactic and Intergalactic interstellar medium

Galaxies

High energies

Optics, Receivers

The Nasmyth optics will allow to install as many as 6 different heterodyne receivers. There is a consensus about the frequency for these receivers to adopt the same spectral bands used in ALMA.^[13] With this scheme the Nasmyth cabins will allocate receivers for the bands

It is intended to install in the Cassegrain focus a bolometer multi-wavelength camera, or even a camera plus a small heterodyne array.

Pictures

References

1. ^12th LARIM, 2007
2. ^Mirabel, I.F, Arnal, M.E., Morras, R., Romero, G, Proyecto Latinoamericano de Astronomía en Argentina, 2008, presented during the Annual Meeting of the Astronomical Argentinian Association
3. ^Arnal,E.M, Morras, R., García Lambas, D.G., Recabarren P., ¿Dónde instalamos el telescopio?, Revista Ciencia Hoy, 19, 110, Abril-Mayo, 2009
4. ^Bareilles, F., Opacidad al cénit a 210 GHz (tipper)
5. ^XVII IAU GA, Rio de Janeiro, 3-14 Aug 2009
6. ^Mirabel, I.F, Arnal, E.M., Morras, R., Romero, G., Lepine, J.R.D., Abraham, Z., de Gouveia Dal Pino, E., Long Latin American Millimeter Array,pdf {{webarchive|url=https://web.archive.org/web/20140819125942/http://www.llamaobservatory.org/pdf/LLAMA3.pdf |date=2014-08-19 }})
7. ^Jesús Rodríguez, Diario Clarín, Buenos Aires, 9 July 2014, accessed on 15 August 2014
8. ^LLAMA site at Alto Chorrillos. LLAMA News #2, Feb. 2017. https://www.llamaobservatory.org/LLAMA_newsletter_n_2.pdf. Retrieved 24 September 2018.
9. ^LLAMA Executive Committee Meeting, May 2014, La Plata (personal communication)
10. ^De la Luz, V, Lara, A., Raulin, J.-P., Synthetic spectra of radio, millimeter, sub-millimeter, and infrared regimes with non-local thermodynamic equilibrium approximation, Astrophys. J., 737, 1 (2011)
11. ^Silva, A. V. et al., [https://link.springer.com/article/10.1007%2Fs11207-005-2787-6 Diffuse Component Spectra of Solar Active Regions at Submillimeter Wavelengths], Solar Phys., 227,261 (2005)
12. ^Kaufmann, P et al. , A new solar burst spectral component emitting only in the Terahertz range, Astrophys. J. 603, L121 (2004)
13. ^ALMA frequency bands