Sun-Sized Water Vapor Masers in Cepheus A
| Autor: | Malcolm Gray, Andrej M. Sobolev, Hiroshi Imai, James M. Moran, D. A. Ladeyshchikov, A. Alakoz, W. A. Baan, V. A. Samodurov, A. M. Tolmachev |
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| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: |
Brightness
Flux FOS: Physical sciences Astrophysics 01 natural sciences law.invention symbols.namesake masers Angular diameter law 0103 physical sciences Very-long-baseline interferometry Maser 010306 general physics 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics Line (formation) Physics formation [stars] Zeeman effect individual objects (Cepheus A) [ISM] magnetic fields [ISM] Astronomy and Astrophysics Astrophysics - Astrophysics of Galaxies interferometric [techniques] Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) symbols Halo |
| Zdroj: | Astrophysical Journal Sobolev, A M, Moran, J M, Gray, M D, Alakoz, A, Imai, H, Baan, W A, Tolmachev, A M, Samodurov, V A & Ladeyshchikov, D A 2018, ' Sun-sized Water Vapor Masers in Cepheus A ', Astrophysical Journal, vol. 856, no. 1, 60 . https://doi.org/10.3847/1538-4357/aab096 |
| DOI: | 10.3847/1538-4357/aab096 |
| Popis: | We present the first VLBI observations of a Galactic water maser (in Chepeus A) made with a very long baseline interferometric array involving the RadioAstron Earth-orbiting satellite station as one of its elements. We detected two distinct components at -16.9 and 0.6 km/s with a fringe spacing of 66 microarcseconds. In total power, the 0.6 km/s component appears to be a single Gaussian component of strength 580 Jy and width of 0.7 km/s. Single-telescope monitoring showed that its lifetime was only 8~months. The absence of a Zeeman pattern implies the longitudinal magnetic field component is weaker than 120 mG. The space-Earth cross power spectrum shows two unresolved components smaller than 15 microarcseconds, corresponding to a linear scale of 1.6 x 10^11 cm, about the diameter of the Sun, for a distance of 700 pc, separated by 0.54 km/s in velocity and by 160 +/-35 microarcseconds in angle. This is the smallest angular structure ever observed in a Galactic maser. The brightness temperatures are greater than 2 x 10^14K, and the line widths are 0.5 km/s. Most of the flux (about 87%) is contained in a halo of angular size of 400 +/- 150 microarcseconds. This structure is associated with the compact HII region HW3diii. We have probably picked up the most prominent peaks in the angular size range of our interferometer. We discuss three dynamical models: (1) Keplerian motion around a central object, (2) two chance overlapping clouds, and (3) vortices caused by flow around an obstacle (i.e., von Karman vortex street) with Strouhal number of about~0.3. 15 pages, 9 figures. Accepted for publication in ApJ, February 16, 2018 |
| Databáze: | OpenAIRE |
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