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Flares and Proper Motions of Ground-State OH Masers in W75N  [PDF]
Vincent L. Fish,Malcolm Gray,W. M. Goss,A. M. S. Richards
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19297.x
Abstract: The star-forming region W75N hosts bright OH masers that are observed to be variable. We present observations taken in 2008 of the ground-state OH maser transitions with the Very Long Baseline Array (VLBA) and the Multi-Element Radio-Linked Interferometer Network (MERLIN) and with the Nancay Radio Telescope in 2011. Several of the masers in W75N were observed to be flaring, with the brightest 1720-MHz maser in excess of 400 Jy. The 1720-MHz masers appear to be associated with the continuum source VLA 1, unlike the bright flaring 1665- and 1667-MHz masers, which are associated with VLA 2. The 1720-MHz masers are located in an outflow traced by water masers and are indicative of very dense molecular material near the H II region. The magnetic field strengths are larger in the 1720-MHz maser region than in most regions hosting only main-line OH masers. The density falls off along the outflow, and the order of appearance of different transitions of OH masers is consistent with theoretical models. The 1665- and 1667-MHz VLBA data are compared against previous epochs over a time baseline of over 7 years. The median maser motion is 3.5 km/s, with a scatter that is comparable to thermal turbulence. The general pattern of maser proper motions observed in the 1665- and 1667-MHz transitions is consistent with previous observations.
Proper motions of the outer knots of the HH 80/81/80N radio-jet  [PDF]
Josep M. Masqué,Luis F. Rodríguez,Anabella Araudo,Robert Estalella,Carlos Carrasco-González,Guillem Anglada,Josep M. Girart,Mayra Osorio
Physics , 2015,
Abstract: (abridged) The HH 80/81/80N jet extends from the HH 80 object to the recently discovered Source 34 and has a total projected jet size of 10.3 pc, constituting the largest collimated radio-jet system known so far. It is powered by IRAS 18162-2048 associated with a massive young stellar object. We report 6 cm JVLA observations that, compared with previous 6 cm VLA observations carried out in 1989, allow us to derive proper motions of the HH 80, HH 81 and HH 80N radio knots located about 2.5 pc away in projection from the powering source. For the first time, we measure proper motions of the optically obscured HH 80N object providing evidence that HH 81, 80 and 80N are associated with the same radio-jet. We derived tangential velocities of these HH objects between 260 and 350 km/s, significantly lower than those for the radio knots of the jet close to the powering source (600-1400 km/s) derived in a previous work, suggesting that the jet material is slowing down due to a strong interaction with the ambient medium. The HH 80 and HH 80N emission at 6 cm is, at least in part, probably synchrotron radiation produced by relativistic electrons in a magnetic field of 1 mG. If these electrons are accelerated in a reverse adiabatic shock, we estimate a jet total density of $\lesssim1000$ cm$^{-3}$. All these features are consistent with a jet emanating from a high mass protostar and make evident its capability of accelerating particles up to relativistic velocities.
The Optical Proper Motions of HH 7-11 and Cep E (HH 377)  [PDF]
Alberto Noriega-Crespo,Peter M. Garnavich
Physics , 2001, DOI: 10.1086/324451
Abstract: A key ingredient in understanding the dynamics of stellar outflows is their proper motion. We have used optical images in the [SII] emission at 6717/31 A and the red Digitized Palomar Observatory Sky Survey (DSS) plates to determine the proper motion of HH 7-11 system and the optical knot of Cep E (HH 377). The DSS plate measurements span nearly 37 years for both HH 7-11 and HH 377 and have wide field of view, which allows an accurate determination of the proper motions despite their relatively low angular resolution. The optical images, with higher angular resolution, cover a shorter period of 7 and 4 years, respectively, and have been used to complement the DSS measurements. From the DSS plates we have found that HH 377 has a proper motion of 0.031 +/- 0.003 arcsec/yr with a PA = 206 arcdeg, i.e. moving away from IRAS 230111+63, that at a distance of 730 pc corresponds to a tangential velocity of 107 +/- 14 km/s. The values obtained from the optical images are consistent with these measurements. Similarly, the proper motions of HH 7-11 range from 0.015 +/- 0.009 (HH 9) to 0.044 +/- 0.007 (HH 11) arcsec/yr, and the flow is moving away from SVS 13 with a mean PA = 136 arcdeg. At a distance of 330 pc, these motions correspond to tangential velocities of 25 - 70 km/s, i.e. comparable to the original values obtained by Herbig & Jones (1983). The measurements from the optical CCD [SII] images are again consistent with these motions, although in detail there are some difference, particularly for HH 7 and HH 10.
Interpreting the proper motions of the HH 34S bowshock  [cached]
A. C. Raga,P. F. Velu00E1zquez,J. Cantu00F3,E. Masciadri
Revista mexicana de astronomía y astrofísica , 2002,
Abstract: Reipurth et al. (2002) han obtenido movimientos propios muy detallados del choque a proa HH 34S usando imágenes obtenidas con el Hubble Space Telescope (HST). Encontramos que estos movimientos propios pueden ser usados para reconstruir la velocidad de choque y la velocidad más allá de HH 34S en función de posición. De este ejercicio, obtenemos velocidades de choque en el intervalo de 60 a 120 km s1, lo cual concuerda con determinaciones previas basadas en el análisis de cocientes y perfiles de líneas de emisión. También deducimos la presencia de un flujo con velocidades de 200 km s1 más allá de HH 34S, el cual se extiende hasta 10 a cada lado del eje del sistema. Interpretamos este flujo como la estela dejada por eventos de eyección previos, y mostramos que una simulación numérica de una eyección con dependencia temporal logra reproducir las propiedades de este flujo en una forma convincente.
The dangers of deprojection of proper motions  [PDF]
Paul J. McMillan,James J. Binney
Physics , 2009, DOI: 10.1111/j.1745-3933.2009.00775.x
Abstract: We re-examine the method of deprojection of proper motions, which has been used for finding the velocity ellipsoid of stars in the nearby Galaxy. This method is only legitimate if the lines of sight to the individual stars are uncorrelated with the stars' velocities. Very simple models are used to show that spurious results similar to ones recently reported are obtained when velocity dispersion decreases with galactocentric radius in the expected way. A scheme that compensates for this bias is proposed.
Proper motions in cepheus a  [cached]
L. F. Rodru00EDguez,J. M. Torrelles,A. C. Raga,J. Cantu00F3
Revista mexicana de astronomía y astrofísica , 2005,
Abstract: Presentamos un análisis de observaciones de radiocontinuo hechas con el Very Large Array hacia la región de formación estelar masiva Cefeo A. El propósito principal de este análisis es buscar y estudiar movimientos propios en las fuentes de radio a lo largo de las dos décadas de tiempo cubiertas por las observaciones. Las cuatro componentes de la fuente W, ubicada en la parte occidental de Cefeo A, muestran claros movimientos hacia el oeste con velocidades en el intervalo de 120 a 280 km s 1. Creemos que estas componentes están siendo excitadas por el chorro térmico Cep A HW3d, ubicado hacia el este de ellas. Más aún, proponemos que, después de ser deflectado en la posición de la fuente W, el chorro Cep A HW3d se mueve hacia el noroeste y produce la fuente óptica GGD 37. La fuente Cep A HW7 muestra un complejo patrón de movimientos propios para los que se discuten varias posibles explicaciones.
Towards Proper Motions in the Local Group  [PDF]
A. Brunthaler,M. Reid,H. Falcke,L. J. Greenhill,C. Henkel
Physics , 2002,
Abstract: Key and still largely missing parameters for measuring the mass content and distribution of the Local Group are the proper motion vectors of its member galaxies. The problem when trying to derive the gravitational potential of the Local Group is that usually only radial velocities are known, and hence statistical approaches have to be used. The expected proper motions for galaxies within the Local Group, ranging from 20 to 100 $\mu$as/yr, are detectable with VLBI using the phase-referencing technique. We present phase-referencing observations of bright masers in IC~10 and M33 with respect to background quasars. We observed the H$_2$O masers in IC10 three times over a period of two months to check the accuracy of the relative positions. The relative positions were obtained by modeling the interferometer phase data for the maser sources referenced to the background quasars. The model allowed for a relative position shift for the source and a single vertical atmospheric delay error in the correlator model for each antenna. The rms of the relative positions for the three observations is only 0.01 mas, which is approximately the expected position error due to thermal noise. Also, we present a method to measure the geometric distance to M33. This will allow re-calibration of the extragalactic distance scale based on Cepheids. The method is to measure the relative proper motions of two H$_2$O maser sources on opposite sides of M33. The measured angular rotation rate, coupled with other measurements of the inclination and rotation speed of the galaxy, yields a direct distance measurement.
Proper Motions in Compact Symmetric Objects  [PDF]
A. G. Polatidis,J. E. Conway
Physics , 2002, DOI: 10.1071/AS02053
Abstract: We discuss recent measurements of proper motions of the hotspots of Compact Symmetric Objects. Source expansion has been detected in ten CSOs so far and all these objects are very young (<3000 years). In a few sources ages have also been estimated from energy supply and spectral ageing arguments and these estimates are comparable. This argues that these sources are close to equipartition and that standard spectral ageing models apply. Proper motions studies are now constraining hotspot accelerations, side-to-side motions and differences in hotspot advance speeds between the two hotspots within sources. Although most CSOs are young sources their evolution is unclear. There is increasing evidence that in some objects the CSO structure represents a new phase of activity within a recurrent source.
Radio Proper Motions of Wolf-Rayet Stars
Dzib, S.;Rodríguez, L. F.;
Revista mexicana de astronomía y astrofísica , 2009,
Abstract: we present the analysis of observations taken from the very large array archive of six wolf-rayet stars with radio emission, with the purpose of determining their proper motions. typically, these observations cover periods of 10 to 20 years. to verify the method, we included wr 140 in the sample, and found that the proper motions determined by us are a few times more accurate than, and consistent within noise, with those of hipparcos. the other five wr stars were not studied by hipparcos and we report their proper motions for the first time. the proper motions for wr 145a = cyg x-3 are consistent with the source being stationary with respect to its local standard of rest and suggest that the black hole in this binary system formed by direct collapse of a massive star, without expulsion of a supernova remnant.
Radio Proper Motions of Wolf-Rayet Stars  [PDF]
Sergio Dzib,Luis F. Rodriguez
Physics , 2009,
Abstract: We present the analysis of observations taken from the Very Large Array archive of six Wolf-Rayet stars with radio emission, with the purpose of determining their proper motions. Typically, these observations cover periods of 10 to 20 years. To verify the method, we included WR 140 in the sample, finding that the proper motions determined by us are a few times more accurate than and consistent within noise with those of Hipparcos. The other five WR stars were not studied by Hipparcos and we report their proper motions for the first time. The proper motions for WR 145a = Cyg X-3 are consistent with the source being stationary with respect to its local standard of rest and suggest that the black hole in this binary system formed by direct collapse of a massive star, without expulsion of a supernova remnant.
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