A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.
The measurement or constraint of the masses of neutron stars and their binary companions tests theories of neutron star structure and of pulsar formation and evolution. We have measured the rate of the general relativistic advance of the longitude of periastron for the pulsar PSR B1802−07:ω = 0. • 060 ± 0. • 009 yr −1 , which implies a total system mass, pulsar plus companion star, of M = 1.7 ± 0.4 M ⊙ . We also present a much improved measurement of the rate of periastron advance for PSR B2303+46:ω = 0. • 0099 ± 0. • 0002 yr −1 , implying M = 2.53 ± 0.08 M ⊙ for this system. We discuss the available constraints on distribution of mass between the pulsars and their companions, and we compare the pulsar masses with other determinations of neutron star masses.
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