arXiv subjects

Loránt O. Sjouwerman

Publications and source records attributed to Loránt O. Sjouwerman.

21 records · Page 2Linked to original sources

arXiv2007

Structure of W3(OH) from Very High Spectral Resolution Observations of 5 Centimeter OH Masers

Recent studies of methanol and ground-state OH masers at very high spectral resolution have shed new light on small-scale maser processes. The nearby source W3(OH), which contains numerous bright masers in several different transitions, provides an excellent laboratory for high spectral resolution techniques. We present a model of W3(OH) based on EVN observations of the rotationally-excited 6030 and 6035 MHz OH masers taken at 0.024 km/s spectral resolution. The 6.0 GHz masers are becoming brighter with time and show evidence for tangential proper motions. We confirm the existence of a region of magnetic field oriented toward the observer to the southeast and find another such region to the northeast in W3(OH), near the champagne flow. The 6.0 GHz masers trace the inner edge of a counterclockwise rotating torus feature. Masers at 6030 MHz are usually a factor of a few weaker than at 6035 MHz but trace the same material. Velocity gradients of nearby Zeeman components are much more closely correlated than in the ground state, likely due to the smaller spatial separation between Zeeman components. Hydroxyl maser peaks at very long baseline interferometric resolution appear to have structure on scales both smaller than that resolvable as well as on larger scales.

astro-ph↗

arXiv2006

Observations of the 6 Centimeter Lines of OH in Evolved (OH/IR) Stars

Recent observational and theoretical advances have called into question traditional OH maser pumping models in evolved (OH/IR) stars. The detection of excited-state OH lines would provide additional constraints to discriminate amongst these theoretical models. In this Letter, we report on VLA observations of the 4750 MHz and 4765 MHz lines of OH toward 45 sources, mostly evolved stars. We detect 4765 MHz emission in the star forming regions Mon R2 and LDN 1084, but we do not detect excited-state emission in any evolved stars. The flux density and velocity of the 4765 MHz detection in Mon R2 suggests that a new flaring event has begun.

astro-ph↗

arXiv2006

A Very High Spectral Resolution Study of Ground-State OH Masers in W3(OH)

We present VLBA observations of the ground-state hydroxyl masers in W3(OH) at 0.02 km s-1 spectral resolution. Over 250 masers are detected, including 56 Zeeman pairs. Lineshapes are predominantly Gaussian or combinations of several Gaussians, with normalized deviations typically of the same magnitude as in masers in other species. Typical FWHM maser linewidths are 0.15 to 0.38 km s-1 and are larger in the 1665 MHz transition than in the other three ground-state transitions. The satellite-line 1612 and 1720 MHz masers show no evidence of sigma^+/-2,3 components. The spatial positions of most masers are seen to vary across the line profile, with many spots showing clear, organized positional gradients. Equivalent line-of-sight velocity gradients in the plane of the sky typically range from 0.01 to 1 km s-1 AU-1 (i.e., positional gradients of 1 to 100 AU (km s-1)-1). Small velocity gradients in the 1667 MHz transition support theoretical predictions that 1667 MHz masers appear in regions with small velocity shifts along the amplification length. Deconvolved maser spot sizes appear to be larger in the line wings but do not support a spherical maser geometry.

astro-ph↗