Identification of Potential Weak Target Radio Quasars for ASTRO-G In-Beam Phase-Referencing

We apply an efficient selection method to identify potential weak Very Long Baseline Interferometry (VLBI) target quasars simply using optical (SDSS) and low-resolution radio (FIRST) catalogue data. Our search is restricted to within 12" from known compact radio sources that are detectable as phase-reference calibrators for ASTRO-G at 8.4 GHz frequency. These calibrators have estimated correlated flux density >20 mJy on the longest ground-space VLBI baselines. The search radius corresponds to the primary beam size of the ASTRO-G antenna. We show that ~20 quasars with at least mJy-level expected flux density can be pre-selected as potential in-beam phase-reference targets for ASTRO-G at 8.4 GHz frequency. Most of them have never been imaged with VLBI. The sample of these dominantly weak sources offers a good opportunity to study their radio structures with unprecedented angular resolution provided by Space VLBI. The method of in-beam phase-referencing is independent from the ability of the orbiting radio telescope to do rapid position-switching manoeuvres between the calibrators and the nearby reference sources, and less sensitive to the satellite orbit determination uncertainties.Comment: 5 pages, accepted for the Publ. Astron. Soc. Japan (Vol. 61, No. 1, Feb 2009

Astrometry of OH/IR stars using 1612 MHz hydroxyl masers. I. Annual parallaxes of WX Psc and OH138.0+7.2

We report on the measurement of the trigonometric parallaxes of 1612 MHz hydroxyl masers around two asymptotic giant branch stars, WX Psc and OH138.0+7.2, using the NRAO Very Long Baseline Array with in-beam phase referencing calibration. We obtained a 3-sigma upper limit of <=5.3 mas on the parallax of WX Psc, corresponding to a lower limit distance estimate of >~190 pc. The obtained parallax of OH138.0+7.2 is 0.52+/-0.09 mas (+/-18%), corresponding to a distance of 1.9(+0.4,-0.3) kpc, making this the first hydroxyl maser parallax below one milliarcsecond. We also introduce a new method of error analysis for detecting systematic errors in the astrometry. Finally, we compare our trigonometric distances to published phase-lag distances toward these stars and find a good agreement between the two methods.Comment: Preprint, accepted for publication in The Astronomical Journal (January 17, 2017

Atrioventricular Nodal Ablation Is Not an Effective Treatment Strategy in Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia is a rare but lethal heritable arrhythmia syndrome associated with both atrial and ventricular arrhythmias. Treatment includes antiarrhythmics, sympathetic denervation, and implantable cardioverter-defibrillators. The use of atrioventricular nodal ablation as a treatment strategy to prevent ventricular arrhythmias in catecholaminergic polymorphic ventricular tachycardia was not found in the literature. This report describes a teenager with a presenting rhythm of atrial and ventricular fibrillation and cardiac arrest. Her clinical arrhythmia was predominantly atrial dysrhythmias, which delayed her diagnosis of catecholaminergic polymorphic ventricular tachycardia. Before her diagnosis, she underwent atrioventricular nodal ablation in an effort to prevent ventricular arrhythmias, which was ultimately ineffective. This report highlights the importance of recognizing atrial arrhythmias in catecholaminergic polymorphic ventricular tachycardia and provides evidence that atrioventricular nodal ablation is not an effective treatment strategy for this disease

ALMA high-frequency long-baseline campaign in 2017: an investigation of phase-referencing cycle times and effective baseline lengths using band-to-band and in-band phase calibration techniques

Interstellar matter and star formatio

ALMA Long Baseline Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z=3.042

We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $z$=3.042 gravitationally lensed galaxy HATLAS J090311.6+003906 (SDP.81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to 15 km. We present continuum imaging at 151, 236 and 290 GHz, at unprecedented angular resolutions as fine as 23 milliarcseconds (mas), corresponding to an un-magnified spatial scale of ~180 pc at z=3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of ~1.5". We also present imaging of CO(10-9), CO(8-7), CO(5-4) and H2O line emission. The CO emission, at an angular resolution of ~170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of H2O line emission, using only the shortest baselines, provides the most resolved detection to date of thermal H2O emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.Comment: 9 pages, 5 figures and 3 tables, accepted for publication in the Astrophysical Journal Letter

The VSOP 5 GHz AGN Survey II. Data Calibration and Imaging

The VSOP mission is a Japanese-led project to study radio sources with sub-milliarcsecond angular resolution using an orbiting 8-m telescope, HALCA and global arrays of Earth-based telescopes. Approximately 25% of the observing time has been devoted to a survey of compact AGN at 5 GHz which are stronger than 1 Jy -- the VSOP AGN Survey. This paper, the second in a series, describes the data calibration, source detection, self-calibration, imaging and modeling, and gives examples illustrating the problems specific to space VLBI. The VSOP Survey web-site which contains all results and calibrated data is described.Comment: 14 pages. To appear in Astrophysical Journal Supplemen

ALMA Long Baseline Campaigns: Phase Characteristics of Atmosphere at Long Baselines in the Millimeter and Submillimeter Wavelengths

We present millimeter- and submillimeter-wave phase characteristics measured between 2012 and 2014 of Atacama Large Millimeter/submillimeter Array long baseline campaigns. This paper presents the first detailed investigation of the characteristics of phase fluctuation and phase correction methods obtained with baseline lengths up to ~15 km. The basic phase fluctuation characteristics can be expressed with the spatial structure function (SSF). Most of the SSFs show that the phase fluctuation increases as a function of baseline length, with a power-law slope of ~0.6. In many cases, we find that the slope becomes shallower (average of ~0.2–0.3) at baseline lengths longer than ~1 km, namely showing a turn-over in SSF. These power law slopes do not change with the amount of precipitable water vapor (PWV), but the fitted constants have a weak correlation with PWV, so that the phase fluctuation at a baseline length of 10 km also increases as a function of PWV. The phase correction method using water vapor radiometers (WVRs) works well, especially for the cases where PWV > 1mm, which reduces the degree of phase fluctuations by a factor of two in many cases. However, phase fluctuations still remain after the WVR phase correction, suggesting the existence of other turbulent constituent that cause the phase fluctuation. This is supported by occasional SSFs that do not exhibit any turn-over; these are only seen when the PWV is low (i.e., when the WVR phase correction works less effectively) or after WVR phase correction. This means that the phase fluctuation caused by this turbulent constituent is inherently smaller than that caused by water vapor. Since in these rare cases there is no turn-over in the SSF up to the maximum baseline length of ~15 km, this turbulent constituent must have scale height of 10 km or more, and thus cannot be water vapor, whose scale height is around 1 km. Based on the characteristics, this large scale height turbulent constituent is likely to be water ice or a dry component. Excess path length fluctuation after the WVR phase correction at a baseline length of 10 km is large ($\gtrsim$200 μm), which is significant for high frequency (>450 GHz or <700 μm) observations. These results suggest the need for an additional phase correction method to reduce the degree of phase fluctuation, such as fast switching, in addition to the WVR phase correction. We simulated the fast switching phase correction method using observations of single quasars, and the result suggests that it works well, with shorter cycle times linearly improving the coherence