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| BeSSeL Survey | |
|---|---|
| Name | BeSSeL Survey |
| Abbreviation | BeSSeL |
| Type | Astronomical survey |
| Start date | 2007 |
| Status | Ongoing |
| Instruments | Very Long Baseline Array, Green Bank Telescope, phased Karl G. Jansky Very Large Array |
| Wavelength | Radio (22 GHz, 6.7 GHz) |
| Region | Milky Way |
BeSSeL Survey The BeSSeL Survey is a long‑term radio interferometric program mapping the structure and kinematics of the Milky Way by measuring trigonometric parallaxes and proper motions of maser sources associated with high‑mass star formation regions. Using very long baseline interferometry with arrays such as the Very Long Baseline Array and the Green Bank Telescope, the survey delivers direct geometric distances that refine models of Galactic structure, dynamics, and the Galactic rotation curve. It complements complementary efforts by projects like the VLBI Exploration of Radio Astrometry and the European VLBI Network.
The survey targets methanol and water masers in regions cataloged by observatories such as the NASA‑funded surveys and follow‑ups from instruments like the Spitzer Space Telescope and the Arecibo Observatory. Observations primarily employ the Very Long Baseline Array together with the Green Bank Telescope and phased elements of the Karl G. Jansky Very Large Array, achieving milliarcsecond astrometric precision. Teams include investigators from institutions such as the Bar‑Ilan University, the Harvard–Smithsonian Center for Astrophysics, the Max Planck Institute for Radio Astronomy, and the National Radio Astronomy Observatory.
The principal aims are to produce a three‑dimensional map of major spiral arms like the Perseus Arm, the Sagittarius Arm, and the Scutum–Centaurus Arm; to measure the distance to the Galactic Center (associated with Sagittarius A*); and to constrain parameters including the circular rotation speed (Theta_0) and the distance from the Sun to the Galactic Center (R_0). The program seeks to test theories of spiral structure developed by proponents such as Lin and Shu and to compare with results from surveys like Gaia and the APOGEE project. Additional goals include improving estimates of peculiar motions of star‑forming regions and informing models of Galactic bar dynamics connected to studies of the Milky Way bar and the Long Bar.
Observing strategy relies on phase‑referenced very long baseline interferometry using maser lines (e.g., 6.7 GHz methanol, 22 GHz water) discovered in catalogs compiled by facilities like the Methanol Multibeam Survey and the Parkes Observatory. Multi‑epoch campaigns spaced over one to three years permit measurement of annual parallax and secular proper motion with reference to quasars in catalogs maintained by the International Celestial Reference Frame and the International VLBI Service. Calibration techniques incorporate models from the International Earth Rotation and Reference Systems Service and ionospheric corrections informed by the Global Positioning System. Scheduling coordinates involve coordination with projects such as the VERA array and data comparisons with radio continuum surveys by the Very Large Array Sky Survey.
Correlation and fringe fitting are performed with correlators developed by facilities such as the NRAO correlator and the Joint Institute for VLBI ERIC. Imaging and astrometric modeling use software like AIPS, CASA, and specialized scripts adapted from groups at the Jet Propulsion Laboratory and the Max Planck Institute for Radio Astronomy. Statistical analyses employ Bayesian and Monte Carlo methods developed in collaborations with teams at the University of Virginia and the University of Tokyo, allowing rigorous estimation of parallaxes, proper motions, and noncircular motions that are then incorporated into Galactic rotation models by groups led from the University of Cincinnati and the University of Wisconsin–Madison.
The survey produced precise parallaxes to dozens of high‑mass star formation regions, refining distances to structures such as the Perseus Arm and demonstrating large‑scale streaming motions in the Sagittarius Arm. BeSSeL measurements contributed to updated values of the distance to the Galactic Center and the rotation speed at the Sun’s orbit, challenging earlier estimates by teams using optical tracers like the Hipparcos mission and complementing infrared results from the Keck Observatory and the European Southern Observatory. Results uncovered peculiar motions associated with regions such as W49 and W51, impacting models of spiral arm pitch angles advanced by researchers at the University of Cambridge and the University of Chicago.
Instrumental partners include the Very Long Baseline Array, the Green Bank Telescope, the phased Karl G. Jansky Very Large Array, and international stations from the European VLBI Network and the VERA project. Collaborators span institutions such as the Harvard–Smithsonian Center for Astrophysics, the Jet Propulsion Laboratory, the Max Planck Institute for Radio Astronomy, the National Radio Astronomy Observatory, the University of Tokyo, and the Chinese Academy of Sciences. Funding and programmatic support have involved agencies like the National Science Foundation and national observatories including the National Astronomical Observatory of Japan.
By delivering geometric distances and motions, the project has become a cornerstone for contemporary models of the Milky Way and a benchmark for cross‑validation with optical astrometry from Gaia and infrared studies by the Spitzer Space Telescope and the Two Micron All Sky Survey. Its datasets inform Galactic dynamical models employed by research groups at the University of California, Berkeley and the Princeton University and underpin investigations into star formation, Galactic structure, and kinematics pursued at institutions like the Max Planck Institute for Astronomy and the Leiden Observatory. The survey’s legacy includes catalogs used by the SIMBAD database and influence on planning for future facilities such as the Square Kilometre Array.
Category:Astronomical surveys Category:Radio astronomy