Dynamical mass of the O-type supergiant in Zeta Orionis A

A close companion of Zeta Orionis A was found in 2000 with the Navy Precision Optical Interferometer (NPOI), and shown to be a physical companion. Because the primary is a supergiant of type O, for which dynamical mass measurements are very rare, the companion was observed with NPOI over the full 7-year orbit. Our aim was to determine the dynamical mass of a supergiant that, due to the physical separation of more than 10 AU between the components, cannot have undergone mass exchange with the companion. The interferometric observations allow measuring the relative positions of the binary components and their relative brightness. The data collected over the full orbital period allows all seven orbital elements to be determined. In addition to the interferometric observations, we analyzed archival spectra obtained at the Calar Alto, Haute Provence, Cerro Armazones, and La Silla observatories, as well as new spectra obtained at the VLT on Cerro Paranal. In the high-resolution spectra we identified a few lines that can be associated exclusively to one or the other component for the measurement of the radial velocities of both. The combination of astrometry and spectroscopy then yields the stellar masses and the distance to the binary star. The resulting masses for components Aa of 14.0 solar masses and Ab of 7.4 solar masses are low compared to theoretical expectations, with a distance of 294 pc which is smaller than a photometric distance estimate of 387 pc based on the spectral type B0III of the B component. If the latter (because it is also consistent with the distance to the Orion OB1 association) is adopted, the mass of the secondary component Ab of 14 solar masses would agree with classifying a star of type B0.5IV. It is fainter than the primary by about 2.2 magnitudes in the visual. The primary mass is then determined to be 33 solar masses

The Radio Properties of Composite LINER/HII Galaxies

Arcsec-resolution VLA observations -- newly obtained as well as published -- of 40 nearby galaxies are discussed, completing a study of the radio properties of a magnitude-limited sample of nearby galaxies of the composite LINER/HII type. Our results reveal an overall detection rate of at least 25% AGN candidates among these composite sources. The general properties of these AGN candidates, as compared to non-AGN composite sources and HII galaxies, are discussed.Comment: Accepted for publication in ApJ

Chandra Observations and the Nature of the Anomalous Arms of NGC 4258 (M 106)

This paper presents high resolution X-ray observations with Chandra of NGC 4258 and infers the nature of the so called ``anomalous arms'' in this galaxy. The anomalous arms dominate the X-ray image; diffuse X-ray emission from the ``plateaux'' regions, seen in radio and H$\alpha$ imaging, is also found. X-ray spectra have been obtained at various locations along the anomalous arms and are well described by thermal (mekal) models with kT in the range 0.37 - 0.6 keV. The previously known kpc-scale radio jets are surrounded by cocoons of hot X-ray emitting gas for the first 350 pc of their length. The radio jets, seen in previous VLBA and VLA observations, propagate perpendicular to the compact nuclear gas disk (imaged in water vapor maser emission). The angle between the jets and the rotation axis of the galactic disk is 60$^{\circ}$. The jets shock the normal interstellar gas along the first 350 pc of their length, causing the hot, X-ray emitting cocoons noted above. At a height of z = 175 pc from the disk plane, the jets exit the normal gas disk and then propagate though the low density halo until they reach ``hot spots'' (at 870 pc and 1.7 kpc from the nucleus), which are seen in radio, optical line and X-ray emission. These jets must drive mass motions into the low density halo gas. This high velocity halo gas impacts on the dense galactic gas disk and shock heats it along and around a ``line of damage'', which is the projection of the jets onto the galactic gas disk as viewed down the galaxy disk rotation axis. However, because NGC 4258 is highly inclined ($i$ = 64$^{\circ}$), the ``line of damage'' projects on the sky in a different direction to the jets themselves. We calculate the expected p.a. of the ``line of damage'' on the sky and find that it coincides with the anomalous arms to within 2$^{\circ}$. (Abstract truncated).Comment: 12 pages plus 9 figures, to be published in the Astrophysical Journal, v560, nr 1, pt 1 (Oct 10, 2001 issue

The Nature of Composite LINER/HII Galaxies, As Revealed from High-Resolution VLA Observations

A sample of 37 nearby galaxies displaying composite LINER/HII and pure HII spectra was observed with the VLA in an investigation of the nature of their weak radio emission. The resulting radio contour maps overlaid on optical galaxy images are presented here, together with an extensive literature list and discussion of the individual galaxies. Radio morphological data permit assessment of the ``classical AGN'' contribution to the global activity observed in these ``transition'' LINER galaxies. One in five of the latter objects display clear AGN characteristics: these occur exclusively in bulge-dominated hosts.Comment: 31 pages, 27 figures, accepted by ApJ

Observational Evidence of Accretion Disk-Caused Jet Precession in Galactic Nuclei

We show that the observational data of extragalactic radio sources tend to support the theoretical relationship between the jet precession period and the optical luminosity of the sources, as predicted by the model in which an accretion disk causes the central black hole to precess.Comment: 13 pages, 1 figure, accepted for publication in ApJ Letter

Combining concept maps and interviews to produce representations of personal professional theories in higher vocational education: effects of order and vocational domain

This article is about the use of personal professional theories (PPTs) in Dutch higher vocational education. PPTs are internalised bodies of formal and practical knowledge and convictions, professionals use to direct their behaviour. With the aid of high-quality representations of students’ PPTs teachers can access, monitor, and support the professional development of students. Two qualitatively equivalent techniques for representing PPTs are (computer-supported) concept mapping and interviewing. This article reports on a study of the effects of combining these techniques to determine whether (1) this results in higher quality representations and (2), if so, whether technique order will make a difference. The study was conducted in two very different vocational domains: accountancy with 29 participants and teacher education with 20 participants. The results of a counterbalanced quasi-experiment with two factors (i.e. domain and order) show in both domains that combining the techniques improves quality but order does not matter. This order independence has practical importance as the computer-supported analysis of a student generated concept map and subsequently discussing the results with the student, fosters learning and fits in educational practice well

Making FORS2 fit for exoplanet observations (again)

For about three years, it was known that precision spectrophotometry with FORS2 suffered from systematic errors that made quantitative observations of planetary transits impossible. We identified the Longitudinal Atmospheric Dispersion Compensator (LADC) as the most likely culprit, and therefore engaged in a project to exchange the LADC prisms with the uncoated ones from FORS1. This led to a significant improvement in the depth of FORS2 zero points, a reduction in the systematic noise, and should make FORS2 again competitive for transmission spectroscopy of exoplanets.Comment: To appear in the March issue of the ESO Messenge

Brief Report: Assessment of Intervention Effects on In Vivo Peer Interactions in Adolescents with Autism Spectrum Disorder (ASD)

This study aimed to evaluate the effectiveness of a randomized controlled trial of a social skills intervention, the Program for the Education and Enrichment of Relational Skills (PEERS: Laugeson et al. in J Autism Dev Disord 39(4): 596–606, 2009), by coding digitally recorded social interactions between adolescent participants with ASD and a typically developing adolescent confederate. Adolescent participants engaged in a 10-min peer interaction at pre- and post-treatment. Interactions were coded using the Contextual Assessment of Social Skills (Ratto et al. in J Autism Dev Disord 41(9): 1277–1286, 2010). Participants who completed PEERS demonstrated significantly improved vocal expressiveness, as well as a trend toward improved overall quality of rapport, whereas participants in the waitlist group exhibited worse performance on these domains. The degree of this change was related to knowledge gained in PEERS

Revealing the Nature of Algol Disks through Optical and UV Spectroscopy, Synthetic Spectra, and Tomography of TT Hydrae

We have developed a systematic procedure to study the disks in Algol-type binaries using spectroscopic analysis, synthetic spectra, and tomography. We analyzed 119 H-alpha spectra of TT Hya, an Algol-type eclipsing interacting binary, collected from 1985-2001. The new radial velocities enabled us to derive reliable orbital elements, including a small non-zero eccentricity, and to improve the accuracy of the absolute dimensions of the system. High resolution IUE spectra were also analyzed to study the formation of the ultraviolet lines and continuum. Synthetic spectra of the iron curtain using our new shellspec program enabled us to derive a characteristic disk temperature of 7000K. We have demonstrated that the UV emission lines seen during total primary eclipse cannot originate from the accretion disk, but most likely arise from a hotter disk-stream interaction region. The synthetic spectra of the stars, disk, and stream allowed us to derive a lower limit to the mass transfer rate of 2e-10 solar masses per year. Doppler tomography of the observed H-alpha profiles revealed a distinct accretion disk. The difference spectra produced by subtracting the synthetic spectra of the stars resulted in an image of the disk, which virtually disappeared once the composite synthetic spectra of the stars and disk were used to calculate the difference spectra. An intensity enhancement of the resulting tomogram revealed images of the gas stream and an emission arc. We successfully modeled the gas stream using shellspec and associated the emission arc with an asymmetry in the accretion disk.Comment: 46 pages, 15 figures, 6 tables, accepted by Ap