The distance to the Vela pulsar gauged with HST parallax oservations

The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed to be 500 pc. Although affected by a significant uncertainty, this value stuck to both the pulsar and the SNR. In an effort to obtain a model free distance measurement, we have applied high resolution astrometry to the pulsar V~23.6 optical counterpart. Using a set of five HST/WFPC2 observations, we have obtained the first optical measurement of the annual parallax of the Vela pulsar. The parallax turns out to be 3.4 +/- 0.7 mas, implying a distance of 294(-50;+76) pc, i.e. a value significantly lower than previously believed. This affects the estimate of the pulsar absolute luminosity and of its emission efficiency at various wavelengths and confirms the exceptionally high value of the N_e towards the Vela pulsar. Finally, the complete parallax data base allows for a better measurement of the Vela pulsar proper motion (mu_alpha(cos(delta))=-37.2 +/- 1.2 mas/yr; mu_delta=28.2 +/- 1.3 mas/yr after correcting for the peculiar motion of the Sun) which, at the parallax distance, implies a transverse velocity of ~65 km/s. Moreover, the proper motion position angle appears specially well aligned with the axis of symmetry of the X-ray nebula as seen by Chandra. Such an alignment allows to assess the space velocity of the Vela pulsar to be ~81 km/s.Comment: LaTeX, 21 pages, 5 figures. Accepted for publication in Ap

Finding a reflexive voice : -- researching the problems of implementing new learning practices within a New Zealand manufacturing organisation : a 100pt thesis presented in partial fulfilment of the requirements for the degree of Master of Management in Human Resources Management at Massey University

This study explored the social forces mediating manager's participation in a new reflexive participative learning practice designed to improve profitability within a New Zealand manufacturing organisation. Despite a large theoretical and managerial body of literature on organisational learning there has been little empirical investigation of how people experience and engage their reflexivity towards challenging the status-quo to create high level learning and new knowledge. Power was identified as a potential moderator of the reflexive learning experience and the variable relations of power and learning were constructed from a review of literature and these relationships were explored and investigated within the case study. Two prevailing discourses were identified as powerful moderators of public reflexivity, the traditionalist discourse which constructed managers actions and conversations towards insularism and survivalist concerns and the productionist discourse in which institutionalised production practices encircled and mediated managers actions and what constituted legitimacy in conversations. This study used a critical action research method to place the reflexive experience of managers and the researcher at the centre of the study and provide data representative of the social discourses that constructed variable freedoms and constraints upon the reflexive voice

A long-period, violently-variable X-ray source in a young SNR

Observations with the Newton X-ray Multimirror Mission (XMM) show a strong periodic modulation at 6.67+/-0.03 hours of the X-ray source at the centre of the 2,000-year-old supernova remnant RCW 103. No fast pulsations are visible. If genetically tied to the supernova remnant, the source could either be an X-ray binary, comprising a compact object and a low-mass star in an eccentric orbit, or an isolated neutron star. In the latter case, its age-period combination would point to a peculiar magnetar, dramatically slowed-down, possibly by a supernova debris disc. Both scenarios require non-standard assumptions on the formation and evolution of compact objects in supernova explosions.Comment: Accepted for publication in Science. Published online via Science Express on 2006, July 6. 17 pages, 7 figure

The ship model basin of Naples' University Federico II: Facilities, experimental tests, measurement systems

This work presents the main facilities of the Naples Towing Tank, LEIN: the instruments and the potential of the laboratory are presented, highlighting some strategies to resolve critical points typical of the towing tank tests. As example we point the attention on three aspects, typically critical: towing point of planing vessels, the accuracy of wave spectra generation and the settings of the radii of gyration for the seakeeping models

X-ray pulsations from the radio-quiet gamma-ray pulsar in CTA 1

Prompted by the Fermi LAT discovery of a radio-quiet gamma-ray pulsar inside the CTA 1 supernova remnant, we obtained a 130 ks XMM-Newton observation to assess the timing behavior of this pulsar. Exploiting both the unprecedented photon harvest and the contemporary Fermi LAT timing measurements, a 4.7 sigma single peak pulsation is detected, making PSR J0007+7303 the second example, after Geminga, of a radio-quiet gamma-ray pulsar also seen to pulsate in X-rays. Phase-resolved spectroscopy shows that the off-pulse portion of the light curve is dominated by a power-law, non-thermal spectrum, while the X-ray peak emission appears to be mainly of thermal origin, probably from a polar cap heated by magnetospheric return currents, pointing to a hot spot varying throughout the pulsar rotation.Comment: 19 pages, 4 figures. Accepted for publication in ApJ Letter

A deep XMM-Newton serendipitous survey of a middle-latitude area

The radio quiet neutron star 1E1207.4-5209 has been the target of a 260 ks XMM-Newton observation, which yielded, as a by product, an harvest of about 200 serendipitous X-ray sources above a limiting flux of 2E-15 erg/cm2/s, in the 0.3-8 keV energy range. In view of the intermediate latitude of our field (b~10 deg), it comes as no surprise that the logN-logS distribution of our serendipitous sources is different from those measured either in the Galactic Plane or at high galactic latitudes. Here we shall concentrate on the analysis of the brightest sources in our sample, which unveiled a previously unknown Seyfert-2 galaxy.Comment: 8 pages, 7 figures, 2 tables. Accepted for publication by Astronomy & Astrophysic

HST and VLT observations of the neutron star 1E 1207.4-5209

1E 1207.4-5209, the peculiar Central Compact object in the G296.5+10.0 supernova remnant, has been proposed to be an "anti-magnetar" - a young neutron star born with a weak dipole field. Accretion, possibly of supernova fallback material, has also been invoked to explain a large surface temperature anisotropy as well as the generation of peculiar cyclotron absorption features superimposed to its thermal spectrum. Interestingly enough, a faint optical/infrared source was proposed as a possible counterpart to 1E 1207.4-5209, but later questioned, based on coarse positional coincidence. Considering the large offset of 1E 1207.4-5209 with respect to the center of its host supernova remnant, the source should move at ~70 mas/yr. Thus, we tested the association by measuring the proper motion of the proposed optical counterpart. Using HST observations spanning 3.75 years, we computed a 3 sigma upper limit of 7 mas/yr. Absolute astrometry on the same HST data set also places the optical source significantly off the 99% confidence Chandra position. This allows us to safely rule out the association. Using the HST data set, coupled to ground-based observations collected at the ESO/VLT, we set the deepest limits ever obtained to the optical/infrared emission from 1E 1207.4-5209. By combining such limits to the constraints derived from X-ray timing, we rule out accretion as the source of the thermal anisotropy of the neutron star.Comment: 8 pages, 3 figures. Accepted for publication in Astronomy & Astrophysic