Relative astrometry of the J=1-0, v=1 and v=2 SiO masers towards R Leonis Minoris using VERA

Oxygen-rich Asymptotic Giant Branch (AGB) stars are intense emitters of SiO and H$_2$O maser lines at 43 (J=1-0, v=1 and 2) and 22 GHz, respectively. VLBI observations of the maser emission provides a unique tool to sample the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned v=1 and v=2 SiO maser maps have traditionally prevented a unique interpretation of the observations in terms of physical underlying conditions, which depend on the nature of the SiO pumping mechanism. We have carried out observations of the SiO and H$_2$O maser emission towards RLMi, using the astrometric capabilities of VERA. Due to the too-weak emission of the reference calibrator we had to develop a special method to accurately relate the coordinates for both transitions. We present relative astrometrically aligned v=1 and v=2 J=1-0 SiO maser maps, at multiple epochs, and discuss the astrophysical results. The incorporation of astrometric information into the maps of SiO masers challenges the weak points in the current theoretical models, which will need further refinements to address the observations results.Comment: 17 pages, 8 figure

The Location of the Core in M81

We report on VLBI observations of M81*, the northwest-southeast oriented nuclear core-jet source of the spiral galaxy M81, at five different frequencies between 1.7 and 14.8 GHz. By phase referencing to supernova 1993J we can accurately locate the emission region of M81* in the galaxy's reference frame. Although the emission region's size decreases with increasing frequency while the brightness peak moves to the southwest, the emission region seems sharply bounded to the southwest at all frequencies. We argue that the core must be located between the brightness peak at our highest frequency (14.8 GHz) and the sharp bound to the southwest. This narrowly constrains the location of the core, or the purported black hole in the center of the galaxy, to be within a region of +/-0.2 mas or +/-800 AU (at a distance of ~4 Mpc). This range includes the core position that we determined earlier by finding the most stationary point in the brightness distribution of M81* at only a single frequency. This independent constraint therefore strongly confirms our earlier core position. Our observations also confirm that M81* is a core-jet source, with a one-sided jet that extends to the northeast from the core, on average curved somewhat to the east, with a radio spectrum that is flat or inverted near the core and steep at the distant end. The brightness peak is unambiguously identified with the variable jet rather than the core, which indicates limitations in determining the proper motion of nearby galaxies and in refining the extragalactic reference frame.Comment: LaTeX, 10 pages with 3 figures. Typos fixed and slight rewording for clarity from previous version. Accepted for publication in the Astrophysical Journa

Physical properties of high-mass clumps in different stages of evolution

(Abridged) Aims. To investigate the first stages of the process of high-mass star formation, we selected a sample of massive clumps previously observed with the SEST at 1.2 mm and with the ATNF ATCA at 1.3 cm. We want to characterize the physical conditions in such sources, and test whether their properties depend on the evolutionary stage of the clump. Methods. With ATCA we observed the selected sources in the NH3(1,1) and (2,2) transitions and in the 22 GHz H2O maser line. Ammonia lines are a good temperature probe that allow us to accurately determine the mass and the column-, volume-, and surface densities of the clumps. We also collected all data available to construct the spectral energy distribution of the individual clumps and to determine if star formation is already occurring, through observations of its most common signposts, thus putting constraints on the evolutionary stage of the source. We fitted the spectral energy distribution between 1.2 mm and 70 microns with a modified black body to derive the dust temperature and independently determine the mass. Results. The clumps are cold (T~10-30 K), massive (M~10^2-10^3 Mo), and dense (n(H2)>~10^5 cm^-3) and they have high column densities (N(H2)~10^23 cm^-2). All clumps appear to be potentially able to form high-mass stars. The most massive clumps appear to be gravitationally unstable, if the only sources of support against collapse are turbulence and thermal pressure, which possibly indicates that the magnetic field is important in stabilizing them. Conclusions. After investigating how the average properties depend on the evolutionary phase of the source, we find that the temperature and central density progressively increase with time. Sources likely hosting a ZAMS star show a steeper radial dependence of the volume density and tend to be more compact than starless clumps.Comment: Published in A&A, Vol. 556, A1

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

Water masers in the massive protostar IRAS 20126+4104: ejection and deceleration

We report on the first multi-epoch, phase referenced VLBI observations of the water maser emission in a high-mass protostar associated with a disk-jet system. The source under study, IRAS 20126+4104, has been extensively investigated in a large variety of tracers, including water maser VLBA data acquired by us three years before the present observations. The new findings fully confirm the interpretation proposed in our previous study, namely that the maser spots are expanding from a common origin coincident with the protostar. We also demonstrate that the observed 3-D velocities of the maser spots can be fitted with a model assuming that the spots are moving along the surface of a conical jet, with speed increasing for increasing distance from the cone vertex. We also present the results of single-dish monitoring of the water maser spectra in IRAS 20126+4104. These reveal that the peak velocity of some maser lines decreases linearly with time. We speculate that such a deceleration could be due to braking of the shocks from which the maser emission originates, due to mass loading at the shock front or dissipation of the shock energy.Comment: 11 pages, 8 figures. Accepted for publication in A&

Spanish Preanalytical Quality Monitoring Program (SEQC), an overview of 12 years' experience

Preanalytical variables, such as sample collection, handling and transport, may affect patient results. Preanalytical phase quality monitoring should be established in order to minimize laboratory errors and improve patient safety. A retrospective study (2001-2013) of the results obtained through the Spanish Society of Clinical Biochemistry and Molecular Pathology (SEQC) External quality assessment (preanalytical phase) was performed to summarize data regarding the main factors affecting preanalytical phase quality. Our aim was to compare data from 2006 to 2013 with a previously published manuscript assessing the 2001-2005 period. A significant decrease in rejection rates was observed both for blood and urine samples. For serum samples, the most frequent rejection causes in the first period were non-received samples (37.5%), hemolysis (29.3%) and clotted samples (14.4%). Conversely, in the second period, hemolysis was the main rejection cause (36.2%), followed by non-received samples (34.5%) and clotted samples (11.1%). For urine samples, the main rejection cause overall was a non-received sample (up to 86.1% of cases in the second period, and 81.6% in the first). For blood samples with anticoagulant, the number of rejections also decreased. While plasma-citrate-ESR still showed the highest percentages of rejections (0.980% vs. 1.473%, p<0.001), the lowest corresponded to whole-blood EDTA (0.296% vs. 0.381%, p<0.001). For the majority of sample types, a decrease in preanalytical errors was confirmed. Improvements in organization, implementation of standardized procedures in the preanalytical phase, and participation in a Spanish external quality assessment scheme may have notably contributed to error reduction in this phase

Absolute kinematics of radio source components in the complete S5 polar cap sample. IV. Proper motions of the radio cores over a decade and spectral properties

We have carried out a high-precision astrometric analysis of two very-long-baseline-interferometry (VLBI) epochs of observation of the 13 extragalactic radio sources in the complete S5 polar cap sample. The VLBI epochs span a time baseline of 10 years and enable us to achieve precisions in the proper motions of the source cores up to a few micro-arcseconds per year. The observations were performed at 14.4 GHz and 43.1 GHz, and enable us to estimate the frequency core-shifts in a subset of sources, for which the spectral-index distributions can be computed. We study the source-position stability by analysing the changes in the relative positions of fiducial source points (the jet cores) over a decade. We find motions of 0.1-0.9 mas among close-by sources between the two epochs, which imply drifts in the jet cores of approximately a few tens of micro-as per year. These results have implications for the standard Active Galactic Nucleus (AGN) jet model (where the core locations are supposed to be stable in time). For one of our sources, 0615+820, the morphological and spectral properties in year 2010, as well as the relative astrometry between years 2000 and 2010, suggest the possibility of either a strong parsec-scale interaction of the AGN jet with the ISM, a gravitational lens with ~1 mas diameter, or a resolved massive binary black hole

Inverse Multview I: Multi-Calibrator inverse phase referencing for Microarcsecond VLBI Astrometry

Very Long Baseline Interferometry (VLBI) astrometry is a well established technique for achieving $\pm10~\mu$as parallax accuracies at frequencies well above 10~GHz. At lower frequencies, uncompensated interferometer delays associated with the ionosphere play the dominant role in limiting the astrometric accuracy. Multiview is a novel VLBI calibration method, which uses observations of multiple quasars to accurately model and remove time-variable, directional-dependent changes to the interferometer delay. Here we extend the Multiview technique by phase referencing data to the target source ("inverse Multiview") and test its performance. Multiple observations with a four-antenna VLBI array operating at 8.3~GHz show single-epoch astrometric accuracies near $20~\mu$as for target-reference quasar separations up to about 7 degrees. This represents an improvement in astrometric accuracy by up to an order of magnitude compared to standard phase referencing.Comment: 11 pages, 5 figure