High Precision Astrometric Millimeter VLBI Using a New Method for Atmospheric Calibration

We describe a new method which achieves high precision Very Long Baseline Interferometry (VLBI) astrometry in observations at millimeter wavelengths. It combines fast frequency-switching observations, to correct for the dominant non-dispersive tropospheric fluctuations, with slow source-switching observations, for the remaining ionospheric dispersive terms. We call this method Source-Frequency Phase Referencing. Provided that the switching cycles match the properties of the propagation media, one can recover the source astrometry. We present an analytic description of the two-step calibration strategy, along with an error analysis to characterize its performance. Also, we provide observational demonstrations of a successful application with observations using the Very Long Baseline Array at 86 GHz of the pairs of sources 3C274 & 3C273 and 1308+326 & 1308+328, under various conditions. We conclude that this method is widely applicable to millimeter VLBI observations of many target sources, and unique in providing bona-fide astrometrically registered images and high precision relative astrometric measurements in mm-VLBI using existing and newly built instruments.Comment: Astronomical Journal, accepted for publicatio

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

srGAP2 deactivates RhoA to control the duration of thrombin-mediated endothelial permeability

The endothelial barrier is a tightly regulated gateway in the transport of material between circulation and the tissues. Inflammatory mediators such as thrombin are able to open paracellular spaces in the endothelial monolayer to allow the extravasation of plasma proteins and leukocytes. Here we show that the protein SLIT-ROBO Rho GTPase-activating protein 2 (srGAP2) plays a critical role in regulating the extent of thrombin-mediated opening. We show that srGAP2 is not required for normal barrier function in resting endothelial cells, but that depletion of srGAP2 significantly increases the magnitude and duration of junctional opening in response to thrombin. We show that srGAP2 acts to switch off RhoA signaling after the contraction phase of thrombin-induced permeability, allowing respreading of cells and reformation of the barrier. srGAP2 is also required for effective restoration of the barrier after treatment with two other vasoactive agents that active RhoA – TNFα and angiotensin II. Taken together, we show that srGAP2 has a general function in controlling RhoA signaling in endothelial permeability, acting to limit the degree and duration of opening, by triggering the switch from endothelial cell contraction to respreading

Population fluctuations of lepus flavigularis (lagomorpha: leporidae) at tehuantepec isthmus, Oaxaca, México

Through six years Lepus flavigularis population density data were analyzed, at two localities south Tehuantepec Isthmus, Oaxaca, Mexico. The fluctuation index (FI) was calculated for this lagomorph in two localities. FI refers to ranges in fluctuations between maximum and minimum population levels evaluated according to the average number of years required for the changes to take place. Density was obtained by the fixed-width transect method. Lepus flavigularis exhibited low density values in both populations. High FI values in Montecillo Santa Cruz indicate high amplitude of change in population’s size in a short period of time. This probably caused by extensive grazing and prescribed burnings. In San Francisco del Mar Viejo L. flavigularis exhibited low FI values, indicating low population changes over the same period of time. This probably because there is slight grazing and no prescribed burns.Se analizaron datos sobre densidad poblacional de la liebre de Tehuantepec, Lepus flavigularis durante seis años de monitoreo en las poblaciones de Montecillo Santa Cruz y San Francisco del Mar Viejo, al sur del Istmo de Tehuantepec, Oaxaca, México. Se calculó el índice de fluctuación poblacional (IF) para esta especie de lagomorfo en las dos localidades. Los intervalos en fluctuación entre niveles poblacionales máximos y mínimos fueron evaluados de acuerdo al número promedio de años requeridos para que los cambios ocurran. Se llevó a cabo el método de transecto de ancho fijo para la obtención de valores de densidad. La liebre de Tehuantepec presenta en general, valores en densidad bajos en ambas poblaciones de estudio, con IF altos en Montecillo Santa Cruz, lo que indica que presenta una gran amplitud de cambios en su tamaño poblacional en periodos de tiempo cortos, debido probablemente a las prácticas de uso de suelo de la zona, mismas que incluyen una intensa ganadería extensiva y la aplicación de quemas controladas. En San Francisco del Mar Viejo, zona con menor intensidad de pastoreo y sin quemas, la liebre de Tehuantepec presentó valores de IF bajos, por lo que es probable que en esta población la especie se mantenga más estable a lo largo del tiempo

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&

La pericia perceptivo-motriz y la cognición en el deporte: del enfoque ecológico y dinámico a la enacción

En el presente artículo se discuten tres corrientes teóricas alter-nativas al cognitivismo, para explicar el desarrollo hacia la pericia en el ám-bito del aprendizaje y del control motor en deporte, haciendo especial énfa-sis en el enactivismo. En la primera parte se tratan las principales nociones de la psicología ecológica, como la regulación del movimiento, la percep-ción directa o la reciprocidad entre percepción y acción. A continuación se explican las principales aportaciones de la teoría de los sistemas dinámicos a la comprensión de la coordinación del movimiento, de la emergencia de la motricidad y de la interacción de las diferentes variables o restricciones. En el siguiente apartado, se expone el enfoque enactivo como una extensión conceptual proveniente de las ciencias cognitivas y que trasciende a los otros paradigmas. Desde esta orientación, se aboga por una fusión entre el cuerpo y la mente del deportista que es indisociable al medio ambiente y que se opone al dualismo y reduccionismo imperante. Por último, se pre-sentan algunas directrices y aplicaciones de investigaciones enactivas que en la actualidad están en pleno desarrollo. Palabras clave: Enactivismo; cognición; acoplamiento información-movimiento; post-cognitivismo; deporte; pericia