Showing papers by "Mark J. Reid published in 1993"
768 citations
TL;DR: In observations at long wavelengths, the apparent angular size of Sgr A* decreases in the manner expected for emission from a point source scattered by electron density fluctuations along the line of sight, which is consistent with an extrapolation from results at longer wavelengths.
Abstract: Sagittarius (Sgr) A * is a unique radio source located at the center of our galaxy. The radiation from Sgr A * may be generated in matter accreting onto a massive black hole. In observations at long wavelengths, the apparent angular size of Sgr A * decreases in the manner expected for emission from a point source scattered by electron density fluctuations along the line of sight. Measurements at a wavelength of 7 millimeters with the nearly completed Very Long Baseline Array indicate a size of 0.7 milliarc seconds, which is consistent with an extrapolation from results at longer wavelengths. The true size of Sgr A * must be less than 0.4 milliarc seconds, or 3.3 astronomical units. The inferred black hole mass is less than 1.5 x 10 6 solar masses according to a recent model for the emission.
41 citations
01 Jan 1993
TL;DR: In this article, the relative proper motions of individual maser components were determined for the 22 GHz H2O masers near the compact HII region W3(OH) in order to obtain a full 3D description of the kinematics of the emitting region.
Abstract: We describe the results of three-epoch intercontinental VLBI observations of the 22 GHz H2O masers near the compact HII region W3(OH). We have determined the relative proper motions of individual maser components. Assuming a distance to the source of 2.2 kpc, we are able to obtain a full 3-dimensional description of the kinematics of the emitting region, which indicates that the H2O masers are part of bipolar outflow.
18 citations
01 Jan 1993
TL;DR: The work of the CfA group over the past decade to measure the proper motions of H2O masers in our Galaxy is described in this article, where distances to 7 masers have been measured and the distance to the Galactic Center, Ro, is estimated to be 7.6 ± 0.6 kpc.
Abstract: The work of the CfA group over the past decade to measure the proper motions of H2O masers in our Galaxy is described. The distances to 7 masers have been measured and the distance to the Galactic Center, Ro, is estimated to be 7.6 ± 0.6 kpc. Various technical aspects of the measurements are discussed here.
1 citations
01 Jan 1993
TL;DR: In this article, the VLA was used to locate oppositely polarized Zeeman-pairs and measure the strength and line-of-sight orientation of the magnetic field in the masing regions.
Abstract: We report on observations with the VLA designed to map precisely the OH maser emission from many interstellar OH sources The primary purpose of these observations is to locate oppositely polarized Zeeman-pairs and measure the strength and line-of-sight orientation of the magnetic field in the masing regions The magnetic fields of interstellar OH masers appear to be of Galactic origin and can be used to map the global structure of the magnetic field of the Milky Way Measurements of the line-of-sight direction of the magnetic field for 34 OH maser sources favor axi-symmetric (over bi-symmetric models of the magnetic field of the Milky Way
01 Jan 1993
TL;DR: In this article, preliminary results from a study of the proper motions of water vapor masers associated with HII regions in Cepheus A are presented, showing that the masers lie in two distinct clumps near the peaks in intensity of the HII region.
Abstract: Preliminary results from a study of the proper motions of water vapor masers associated with HII regions in Cepheus A are presented. The masers lie in two distinct clumps near the peaks in intensity of the HII regions. Some 50 maser spots were detected over 3 epochs, but only 11 maser spots were identified at two or more epochs. A statistical parallax analysis from these prelimary results gives a distance between 0.4 and 0.6kpc with a statistical uncertainty of about 0.2kpc.
01 Jan 1993
TL;DR: In this paper, the authors present VLBI synthesis observations of the water vapor megamaser in the south eastern region of IC10 and conclude that the maser is highly variable.
Abstract: We present VLBI synthesis observations of the water vapor megamaser in the south eastern region of IC10. We compare our spectrum with earlier single dish spectra and conclude that the maser is highly variable.