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| APASS | |
|---|---|
| Name | APASS |
| Abbreviation | APASS |
| Type | Astronomical photometric survey |
| Established | 2010s |
| Location | United States, Chile, South Africa, Australia |
APASS
The APASS survey is a broad-sky photometric project that provides calibrated optical photometry across multiple broadband filters for millions of stars. It supports observational programs in stellar astrophysics, exoplanet science, transient astronomy, and space-mission planning by delivering standardized magnitudes tied to established photometric systems. APASS data are widely cross-referenced with catalogs from major observatories, space missions, and survey projects.
APASS is designed to deliver all-sky coverage in Johnson B and V and Sloan g', r', i' bands, producing calibrated photometry for sources spanning a range of magnitudes. Its catalogs are used alongside data from Hipparcos, Gaia, Two Micron All-Sky Survey, Wide-field Infrared Survey Explorer, Sloan Digital Sky Survey, Pan-STARRS, Kepler, Transiting Exoplanet Survey Satellite, and European Southern Observatory programs. The survey operates instruments at sites in the Cerro Tololo Inter-American Observatory, Sutherland, Northern Cape, and Siding Spring Observatory, coordinating with facilities like Cerro Pachón and networks such as Las Cumbres Observatory Global Telescope Network. APASS photometry is frequently cross-matched with catalogs from missions including ROSAT, XMM-Newton, Chandra X-ray Observatory, and radio surveys like NRAO VLA Sky Survey.
APASS originated in response to needs identified by researchers associated with projects at Cerro Tololo, NOAO, and institutions linked to Michigan State University, Indiana University, and Harvard-Smithsonian Center for Astrophysics. Early motivations connected to calibration work for Supernova Cosmology Project, Sloan Digital Sky Survey, and preparatory catalogs for Gaia led to deployments in the 2010s. Over successive data releases, the project incorporated cross-calibration with photometric standards established by Landolt fields, tied to foundational datasets from Johnson and Cousins. Collaborations involved scientists from Yale University, University of Washington, University of California, Berkeley, Max Planck Institute for Astronomy, and Space Telescope Science Institute.
APASS uses medium-aperture telescopes equipped with CCD detectors and standard broadband filters to sample stellar fluxes under photometric conditions. Its calibration pipeline references standard-star networks including Landolt standards and transforms instrumental magnitudes to Johnson and Sloan systems using color terms derived from overlap with Sloan Digital Sky Survey photometry. Data reduction employs image processing techniques developed alongside tools from IRAF, Astrometry.net, SExtractor, and photometric software influenced by methods from DAOPHOT and PSF photometry pipelines. Astrometric solutions are matched to reference frames provided by Gaia and UCAC4 to ensure positional accuracy sufficient for cross-identifications with catalogs from 2MASS, AllWISE, and APOGEE.
APASS photometry underpins stellar-parameter estimation for surveys like APOGEE, LAMOST, and RAVE and supports target selection for spectroscopic campaigns at facilities including Keck Observatory, Very Large Telescope, Subaru Telescope, and Gemini Observatory. It is used in variable-star studies associated with projects such as ASAS-SN and OGLE, and in transient identification pipelines for programs like Zwicky Transient Facility and Pan-STARRS. Planet-hunting teams using TESS and ground-based follow-up from networks like HATNet and SuperWASP rely on APASS for pre-screening candidate hosts. APASS also aids calibration of photometric redshifts in extragalactic surveys connected to DES, Euclid, and Rubin Observatory preparatory work.
The APASS calibration strategy interleaves observations of primary standards with nightly secondary calibrators to correct for atmospheric extinction and instrumental response. It references the Johnson-Cousins and Sloan Digital Sky Survey photometric systems and harmonizes zero-points through comparisons with Landolt and Smith et al. standard stars. Cross-calibration campaigns have tied APASS magnitudes to absolute flux scales established by space-based calibrators from Hubble Space Telescope spectrophotometric standards and to the astrometric and photometric reference frame defined by Gaia. Quality checks include comparison with catalogs such as Pan-STARRS1, APASS DR9-era compilations, and targeted observations with observatories like Las Cumbres Observatory.
APASS catalogs are distributed via online services and are accessible through astronomical data centers including Vizier, NASA Exoplanet Archive, and institutional repositories at participating universities and observatories. The data format facilitates cross-matching with databases like SIMBAD and NED and is commonly incorporated into virtual observatory tools including services from IVOA. Users retrieve calibrated magnitudes, positional data, photometric quality flags, and cross-identifications to surveys such as 2MASS, AllWISE, Gaia, and SDSS.
The astronomical community widely cites APASS for its role in providing homogeneous, intermediate-depth optical photometry useful for calibration and target characterization. It is referenced in publications from groups affiliated with Harvard-Smithsonian Center for Astrophysics, Max Planck Institute for Astronomy, Space Telescope Science Institute, NOAO/NSF's NOIRLab, and survey consortia like DES Collaboration. APASS data have been incorporated into workflows at institutions including University of Cambridge, Princeton University, MIT, Caltech, Stanford University, University of Chicago, and Carnegie Institution for Science for studies spanning stellar variability, exoplanet demographics, and transient follow-up.
Category:Astronomical catalogues