Classroom Creativity: Pedagogical Adaptability in Film

A pair of remarkable cinematic teachers illuminates how adaptability can be central to success in the classroom. Katherine Watson (in “Mona Lisa Smile”) and Mark Thackeray (in “To Sir, With Love”) are able to win over skeptical students because they possess an array of virtues, ranging from openness and responsiveness to humility and courage. These virtues enable Watson and Thackeray to improvise entirely new curricula once they realize that their original pedagogical plans are sill-suited to these particular pupils. The result is that although they teach radically different kinds of students, both groups learn to think for themselves

Hot subdwarf stars in close-up view. I. Rotational properties of subdwarf B stars in close binary systems and nature of their unseen companions

Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO)The origin of hot subdwarf B stars (sdBs) is still unclear. About half of the known sdBs are in close binary systems for which common envelope ejection is the most likely formation channel. Little is known about this dynamic phase of binary evolution. Since most of the known sdB systems are single-lined spectroscopic binaries, it is difficult to derive masses and unravel the companions' nature, which is the aim of this paper. Due to the tidal influence of the companion in close binary systems, the rotation of the primary becomes synchronised to its orbital motion. In this case it is possible to constrain the mass of the companion, if the primary mass, its projected rotational velocity as well as its surface gravity are known. For the first time we measured the projected rotational velocities of a large sdB binary sample from high resolution spectra. We analysed a sample of 51 sdB stars in close binaries, 40 of which have known orbital parameters comprising half of all such systems known today. Synchronisation in sdB binaries is discussed both from the theoretical and the observational point of view. The masses and the nature of the unseen companions could be constrained in 31 cases. We found orbital synchronisation most likely to be established in binaries with orbital periods shorter than . Only in five cases it was impossible to decide whether the sdB's companion is a white dwarf or an M dwarf. The companions to seven sdBs could be clearly identified as late M stars. One binary may have a brown dwarf companion. The unseen companions of nine sdBs are white dwarfs with typical masses. The mass of one white dwarf companion is very low. In eight cases (including the well known system KPD1930+2752) the companion mass exceeds , four of which even exceed the Chandrasekhar limit indicating that they may be neutron stars. Even stellar mass black holes are possible for the most massive companions. The distribution of the inclinations of the systems with low mass companions appears to be consistent with expectations, whereas a lack of high inclinations becomes obvious for the massive systems. We show that the formation of such systems can be explained with common envelope evolution and present an appropriate formation channel including two phases of unstable mass transfer and one supernova explosion. The sample also contains a candidate post-RGB star, which rotates fast despite its long orbital period. The post-RGB stars are expected to spin-up caused by their ongoing contraction. The age of the sdB is another important factor. If the EHB star is too young, the synchronisation process might not be finished yet. Estimating the ages of the target stars from their positions on the EHB band, we found PG 2345+318, which is known not to be synchronised, to lie near the zero-age extreme horizontal branch as are the massive candidates PG 1232-136, PG 1432+159 and PG 1101+249. These star may possibly be too young to have reached synchronisation. The derived large fraction of putative massive sdB binary systems in low inclination orbits is inconsistent with theoretical predictions. Even if we dismiss three candidates because they may be too young and assume that the other sdB primaries are of low mass, PG 1743+477 and, in particular, HE 0532-4503 remain as candidates whose companions may have masses close to or above the Chandrasekhar limit. X-ray observations and accurate photometry are suggested to clarify their nature. As high inclination systems must also exist, an appropriate survey has already been launched to find such binaries.Peer reviewe

KIC7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf

The recently discovered subdwarf B (sdB) pulsator KIC7668647 is one of the 18 pulsating sdB stars detected in the Kepler field. It features a rich g-mode frequency spectrum, with a few low-amplitude p-modes at short periods. We use new ground-based low-resolution spectroscopy, and the near-continuous 2.88 year Kepler lightcurve, to reveal that KIC7668647 consists of a subdwarf B star with an unseen white-dwarf companion with an orbital period of 14.2d. An orbit with a radial-velocity amplitude of 39km/s is consistently determined from the spectra, from the orbital Doppler beaming seen by Kepler at 163ppm, and from measuring the orbital light-travel delay of 27 by timing of the many pulsations seen in the Kepler lightcurve. The white dwarf has a minimum mass of 0.40 M_sun. We use our high signal-to-noise average spectra to study the atmospheric parameters of the sdB star, and find that nitrogen and iron have abundances close to solar values, while helium, carbon, oxygen and silicon are underabundant relative to the solar mixture. We use the full Kepler Q06--Q17 lightcurve to extract 132 significant pulsation frequencies. Period-spacing relations and multiplet splittings allow us to identify the modal degree L for the majority of the modes. Using the g-mode multiplet splittings we constrain the internal rotation period at the base of the envelope to 46-48d as a first seismic result for this star. The few p-mode splittings may point at a slightly longer rotation period further out in the envelope of the star. From mode-visibility considerations we derive that the inclination of the rotation axis of the sdB in KIC7668647 must be around ~60 degrees. Furthermore, we find strong evidence for a few multiplets indicative of degree 3 <= L <= 8, which is another novelty in sdB-star observations made possible by Kepler.Comment: arXiv admin note: text overlap with arXiv:1206.387

UVES and X-Shooter spectroscopy of the emission line AM CVn systems GP Com and V396 Hya

We present time-resolved spectroscopy of the AM CVn-type binaries GP Com and V396 Hya obtained with VLT/X-Shooter and VLT/UVES. We fully resolve the narrow central components of the dominant helium lines and determine radial velocity semi-amplitudes of $K_{\rm spike} = 11.7\pm0.3$ km s$^{-1}$ for GP Com and $K_{\rm spike} = 5.8\pm0.3$ km s$^{-1}$ for V396 Hya. The mean velocities of the narrow central components show variations from line to line. Compared to calculated line profiles that include Stark broadening we are able to explain the displacements, and the appearance of forbidden helium lines, by additional Stark broadening of emission in a helium plasma with an electron density $n_e\simeq 5\times 10^{15}$ cm$^{-3}$. More than $30$ nitrogen and more than $10$ neon lines emission lines were detected in both systems. Additionally, $20$ nitrogen absorption lines are only seen in GP Com. The radial velocity variations of these lines show the same phase and velocity amplitude as the central helium emission components. The small semi-amplitude of the central helium emission component, the consistency of phase and amplitude with the absorption components in GP Com as well as the measured Stark effect shows that the central helium emission component, the so-called central-spike, is consistent with an origin on the accreting white dwarf. We use the dynamics of the bright spot and the central spike to constrain the binary parameters for both systems and find a donor mass of $9.6$ - $42.8$ M$_{\rm Jupiter}$ for GP Com and $6.1$ - $30.5$ M$_{\rm Jupiter}$ for V396 Hya. We find an upper limit for the rotational velocity of the accretor of $v_{\rm rot}<46$ km s$^{-1}$ for GP Com and $v_{\rm rot}<59$ km s$^{-1}$ for V396 Hya which excludes a fast rotating accretor in both systems.Comment: Accepted for publication in MNRAS, 15 pages, 14 figures, 5 table

La oscilación en estructuras de hormigón pretensado y de plantas múltiples

The design of an industrial building intended for the manufacture of precision instruments was carried out taking account of the influence of small vibrations of the structure. Owing to the detailed accuracy of the instruments to be manufactured, this became an important problem. The whole structure was so planned and constructed that the analytical estimates of its dynamic performance could be checked a posteriori by means of direct tests on the building. The building has a ground area of 66 by 15.4 ms and consists of basement, semibasement, four normal floor levels and a top storey, set back about 3 ms from the main frontage. The roof is in metal. As the building has been mainly done with prefabricated units, it was especially important that these should be accurately finished, since the dynamic stability (vibrations) of the structure depended very largely on the prefabricated units. Owing to the large length to width ratio of the building, a design based on the use of portal frames was adopted from the outset. These frames have a 15 ms span, the vertical members being reinforced concrete, and the horizontal beams are prestressed concrete. The central part of the flooring structure, at the various floor levels, consists of a hollow nuit, which carries the air conditioning ducts. As the 15 ms span of the beams could influence considerably the mode of vibration of the structure, provision was made to fit a number of additional struts. They would be easy to put in position and remove, and placed at the midspan of the horizontal beams, would supply a support that would influence notably the overall behaviour of the building structure. The initial test program sought to cover various behaviour hypotheses and systems of induced oscillations. A number of arrangements of the recording oscillographs were also tried. The author of this article describes in considerable detail the various tests and the methods of obtaining the necessary experimental data to analyse the dynamics of the system, its modifications and the natural frequency, harmonics and amplitudes corresponding to each test case. This program of experimental research has led to a final result, giving the basic frequency of the structure, considered as a whole. Finally the author draws a number of general inferences from the investigation.El proyecto para la construcción de un edificio industrial dedicado a la fabricación de mecanismos de precisión se realizó teniendo en cuenta la influencia de las oscilaciones en la estructura, efecto que, dada la precisión de la mecánica que debía fabricarse, presentaba un problema de notable importancia. Todo el dispositivo estructural se resolvió de acuerdo con estas directrices, y de tal forma que pudieran compararse las previsiones analíticas con ensayos directos obtenidos en el propio edificio. El edificio tiene 66x15,4 m en planta y consta de: sótano, entresuelo, cuatro plantas normales, una sexta planta retranqueada unos 3 m respecto de la fachada y cubierta con un entramado metálico. Como la construcción se ha levantado utilizando piezas prefabricadas, debía tenerse especial cuidado en la terminación de las mismas, ya que el sistema vibrante del conjunto se ve altamente influenciado por estas piezas. Dada la gran longitud del edificio y su pequeña anchura relativa, se pensó desde el principio en una solución a base de pórticos, de 15 m de luz, con montantes de hormigón armado, y vigas o cabezales de hormigón pretensado. La parte central de los forjados en las distintas plantas la constituye un elemento de sección hueca, utilizado para alojar los conductos del aire acondicionado. Como la luz de 15 m de las vigas pretensadas podía influir notablemente en el sistema vibrante, se previeron una serie de montantes, independientes, que podrían montarse y desmontarse fácilmente y que, colocados en la parte central de cada pórtico, proporcionarían una especie de apuntalamiento general cuya influencia sería notable. En el programa de ensayos se tuvieron en cuenta distintas hipótesis y dispositivos de excitación ondulatoria y dispositivos de registro en oscilógrafos. El autor se extiende, con gran detalle, en los distintos ensayos realizados y en los métodos utilizados para recoger los datos que permitirían un análisis general del sistema, vibrante, sus modificaciones generales y resonancias, amplitudes y onda propia según los distintos casos experimentados; todo lo cual serviría de base para llegar al resultado final, es decir, conseguir la frecuencia fundamental del conjunto considerado como un todo. Finalmente, el autor llega a una serie de conclusiones que resumen sus deducciones