Atacama Pathfinder Experiment

Atacama Pathfinder Experiment
ESO/H.H.Heyer · CC BY 4.0 · source
Name	APEX
Caption	APEX telescope on Chajnantor
Organization	European Southern Observatory; Max Planck Institute for Radio Astronomy; Onsala Space Observatory; Swedish National Facility
Location	Llano de Chajnantor, Atacama Desert, Chile
Altitude	5100 m
Wavelength	submillimeter (0.2–1.5 mm)
Diameter	12 m
Type	Cassegrain

Atacama Pathfinder Experiment The Atacama Pathfinder Experiment is a 12‑metre submillimetre telescope located on the Llano de Chajnantor plateau in northern Chile. Built as a pathfinder for large aperture facilities, it serves as a technology demonstrator and scientific observatory for studies in star formation, interstellar medium, and high‑redshift galaxies. It operates under partnerships that include European research institutions and Chilean agencies, providing complementarity to facilities such as Atacama Large Millimeter Array and James Clerk Maxwell Telescope.

Overview

APEX is sited near the Chajnantor Plateau at high altitude to exploit low atmospheric water vapour conditions relevant for submillimetre bands shared with instruments like ALMA, Herschel Space Observatory, Submillimeter Array, and South Pole Telescope. The project links organizations including the European Southern Observatory, the Max Planck Society, and national observatories such as Onsala Space Observatory and the Swedish National Facility. Its 12‑metre antenna and suite of heterodyne and bolometer instruments enable continuum and spectral line observations comparable to programs run on IRAM 30m Telescope and complementary to surveys from the Planck satellite.

History and Development

Conceived in the late 1990s to exploit the Atacama Desert's exceptional atmospheric windows, APEX was developed following technical and programmatic interactions with projects including ALMA, the European Space Agency, and the National Radio Astronomy Observatory. The telescope was assembled and commissioned in the early 2000s with contributions from German institutes such as the Max Planck Institute for Radio Astronomy and operational frameworks influenced by observatories like Cerro Tololo Inter-American Observatory and La Silla Observatory. Early milestones involved instrument integration and first light commissioning, paralleling development phases of ALMA and the refurbishment of facilities including James Clerk Maxwell Telescope.

Telescope and Instrumentation

The 12‑metre Cassegrain reflector uses precision panels and active surface control comparable in ambition to design elements from the Nobeyama Radio Observatory and technologies tested at the Institut de Radioastronomie Millimétrique. Instrumentation suites have included heterodyne receivers and bolometer cameras such as LABOCA and CHAMP+, allowing spectral line work on molecules like CO, HCN, and HCO+ and continuum mapping analogous to surveys by SCUBA and Bolocam. APEX supports multi‑band observing across submillimetre windows exploited by missions including Herschel and ground arrays like NANTEN2. Backend spectrometers and data pipelines have been developed in collaboration with institutes such as the Max Planck Institute for Radio Astronomy and the Onsala Space Observatory.

Observing Site and Facilities

Located near ALMA's site on the Llano de Chajnantor, APEX benefits from infrastructure shared with Chajnantor Plateau projects including surface access roads and site operations influenced by examples from Paranal Observatory. At an altitude of about 5100 m, the site offers low precipitable water vapour comparable to the conditions targeted by South Pole Telescope and IRAM. Support facilities in northern Chile and logistics coordination have precedents in operations at Pampa la Bola and coordination with agencies linked to Consejo de Monumentos Nacionales for environmental stewardship. The APEX operations complex includes control rooms, maintenance workshops, and focal plane cryogenic facilities similar to setups at Mauna Kea Observatories.

Science Goals and Key Discoveries

APEX's science program targets star formation in molecular clouds, protostellar disks, extragalactic submillimetre sources, and the interstellar medium chemistry that informs models used at ALMA and in missions like Herschel Space Observatory. Key results include sensitive dust continuum surveys akin to those by SCUBA revealing submillimetre galaxies, spectral line detections of high‑excitation CO in nearby starbursts, and molecular line studies that advance understanding pursued by teams from Max Planck Institute for Radio Astronomy and European Southern Observatory. APEX observations have contributed to the characterization of protostellar outflows studied in contexts similar to Orion Nebula research and complemented redshift determinations for distant dusty star‑forming galaxies alongside measurements from Spitzer Space Telescope and WISE.

Operations and Collaborations

APEX operates under international consortia modeled after cooperative frameworks seen in Atacama Large Millimeter Array governance and partnerships with national facilities such as the Swedish National Facility and the Onsala Space Observatory. Time allocation and science operations follow committees and review processes informed by practices at European Southern Observatory and National Radio Astronomy Observatory. Collaborative programs leverage synergies with instruments and surveys from ALMA, Herschel, James Clerk Maxwell Telescope, and space missions like Spitzer to enable multiwavelength campaigns, calibration efforts, and technology transfer projects relevant to future facilities.

Category:Submillimetre_telescopes Category:Radio_telescopes Category:Astrophysical_observatories_in_Chile