Formation of wind-captured discs in Supergiant X-ray binaries : consequences for Vela X-1 and Cygnus X-1

In Supergiant X-ray binaries (SgXB), a compact object captures a fraction of the wind of an O/B supergiant on a close orbit. Proxies exist to evaluate the efficiency of mass and angular momentum accretion but they depend so dramatically on the wind speed that given the current uncertainties, they only set loose constrains. Furthermore, they often bypass the impact of orbital and shock effects on the flow structure. We study the wind dynamics and the angular momentum gained as the flow is accreted. We identify the conditions for the formation of a disc-like structure around the accretor and the observational consequences for SgXB. We use recent results on the wind launching mechanism to compute 3D streamlines, accounting for the gravitational and X-ray ionizing influence of the compact companion on the wind. Once the flow enters the Roche lobe of the accretor, we solve the hydrodynamics equations with cooling. A shocked region forms around the accretor as the flow is beamed. For wind speeds of the order of the orbital speed, the shock is highly asymmetric compared to the axisymmetric bow shock obtained for a purely planar homogeneous flow. With net radiative cooling, the flow always circularizes for wind speeds low enough. Although the donor star does not fill its Roche lobe, the wind can be significantly beamed and bent by the orbital effects. The net angular momentum of the accreted flow is then sufficient to form a persistent disc-like structure. This mechanism could explain the proposed limited outer extension of the accretion disc in Cygnus X-1 and suggests the presence of a disc at the outer rim of the neutron star magnetosphere in Vela X-1, with dramatic consequences on the spinning up of the accretor

Radiation-induced interface phenomena: Decoration of high-energy density ion tracks

The effect of 20 MeV Cl4 + ions incident on Au-SiO2 and Ag-SiO2 interfaces was investigated using high-resolution transmission electron microscopy. Cross-sectional micrographs expose beam-induced gold interfacial transport and migration into the SiO2. No such migration was observed for silver films. The relevance of this phenomenon to the adhesion improvement found at corresponding irradiation doses is discussed

The pumpistor: a linearized model of a flux-pumped SQUID for use as a negative-resistance parametric amplifier

We describe a circuit model for a flux-driven SQUID. This is useful for developing insight into how these devices perform as active elements in parametric amplifiers. The key concept is that frequency mixing in a flux-pumped SQUID allows for the appearance of an effective negative resistance. In the three-wave, degenerate case treated here, a negative resistance appears only over a certain range of allowed input signal phase. This model readily lends itself to testable predictions of more complicated circuits.Comment: 4 pages, 3 figure

Ekososiaalista sivistystä rakentamassa alakoulun musiikinopetuksen avulla

Tiivistelmä. Tutkielmassani tutkin keinoja, joiden avulla voidaan tukea oppilaan ekososiaalisen sivistyksen muotoutumista musiikinopetuksessa. Ekososiaalinen sivistys ja kestävä kehitys ovat muuttuneet entistä polttavammiksi aiheiksi musiikkikulttuurissa, mikä näkyy niin suurempien musiikkitapahtumien, materiaalivalintojen kuin yksittäisten teostenkin tasolla. Useat tutkimukset ovat osoittaneet, että erilaisia ekologisuuteen ja ympäristökysymyksiin suuntautuneita musiikillisen toiminnan muotoja on mahdollista soveltaa myös pedagogiseen toimintaan osana musiikinopetusta. Kandidaatintutkielma on kvalitatiivinen tutkimus, tarkemmin määriteltynä kuvaileva kirjallisuuskatsaus. Tutkielmassani olen koonnut ajankohtaista tietoa tieteellisistä julkaisuista sekä aikaisemmin tehdyistä tutkimuksista ja niiden tutkimustuloksista. Tarkastelen tuloksia ekososiaalisen sivistyksen ja kasvatuksen näkökulmasta. Tutkimustuloksissa nousi esille musiikinopetuksessa hyödynnettäviä erilaisia pedagogisia menetelmiä ekososiaalisen sivistyksen tukemiseksi. Ekomusikologian soveltamisella osana pedagogiikkaa voidaan esimerkiksi auttaa tarkastelemaan ekologisia kysymyksiä useasta eri näkökulmasta sekä hahmottamaan ihmisen vaikutusvaltaa suhteessa ympäristöön. Useiden tutkimustulosten perusteella kävi ilmi, että keskeistä ekososiaalisen sivistyksen muotoutumiselle ja ympäristötietoiselle- ja vastuulliselle toiminnalle on luontosuhteen huomioiminen opetus- ja kasvatustoiminnassa. Tutkimustuloksissa korostui erityisesti moniaistillisuuteen ja kehollisuuteen perustuvien harjoitusten merkitys, sillä ne tarjoavat mahdollisuuksia kokea osallisuutta ja yhteyttä ympäristön kanssa. Näin ollen ne edesauttavat oppimaan ympäristön arvostamista ja tuntemaan empatiaa luontoa ja sen moninaisia elämänmuotoja kohtaan

Unified description of floppy and rigid rotating Wigner molecules formed in quantum dots

Restoration of broken circular symmetry is used to explore the characteristics of the ground states and the excitation spectra of rotating Wigner molecules (RWM's) formed in two-dimensional parabolic N-electron quantum dots. In high magnetic fields, the RWM's are floppy rotors with the energies of the magic angular momentum (L) states obeying aL + b/L^{1/2}. Under such fields the ground-state energies (referenced to the kinetic energy in the lowest Landau level) approach the electrostatic energy of N point charges in the classical equilibrium molecular configuration. At zero field and strong interelectron repulsion, the RWM's behave like quasiclassical rigid rotors whose energies vary as L^2. The particular L-dependence in high B is inherent and natural to a floppy rotating WM, and it can be used as a crucial diagnostic tool for resolving the recently posed question whether the composite-fermion or the RWM picture is appropriate for QD's.Comment: 5 pages. Revtex4 with 3 EPS figures and 2 tables . For related papers, see http://www.prism.gatech.edu/~ph274c

Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis

OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations (NRPs). In this paper, we evaluate the possible relation between large-scale, dipolar magnetic fields and the DAC phenomenon by investigating the magnetic properties of a sample of 13 OB stars exhibiting well-documented DAC behaviour. Using high-precision spectropolarimetric data acquired in part in the context of the Magnetism in Massive Stars (MiMeS) project, we find no evidence for surface dipolar magnetic fields in any of these stars. Using Bayesian inference, we compute upper limits on the strengths of the fields and use these limits to assess two potential mechanisms by which the field may influence wind outflow: magnetic wind confinement and local photospheric brightness enhancements. Within the limits we derive, both mechanisms fail to provide a systematic process capable of producing DACs in all of the stars of our sample. Therefore, this implies that dipolar fields are highly unlikely to be responsible for these structures in all massive stars, meaning that some other mechanism must come into play.Comment: 17 pages, 6 figures, accepted for publication in MNRA

UVMag: stellar formation, evolution, structure and environment with space UV and visible spectropolarimetry

Important insights into the formation, structure, evolution and environment of all types of stars can be obtained through the measurement of their winds and possible magnetospheres. However, this has hardly been done up to now mainly because of the lack of UV instrumentation available for long periods of time. To reach this aim, we have designed UVMag, an M-size space mission equipped with a high-resolution spectropolarimeter working in the UV and visible spectral range. The UV domain is crucial in stellar physics as it is very rich in atomic and molecular lines and contains most of the flux of hot stars. Moreover, covering the UV and visible spectral domains at the same time will allow us to study the star and its environment simultaneously. Adding polarimetric power to the spectrograph will multiply tenfold the capabilities of extracting information on stellar magnetospheres, winds, disks, and magnetic fields. Examples of science objectives that can be reached with UVMag are presented for pre-main sequence, main sequence and evolved stars. They will cast new light onto stellar physics by addressing many exciting and important questions. UVMag is currently undergoing a Research and Technology study and will be proposed at the forthcoming ESA call for M-size missions. This spectropolarimeter could also be installed on a large UV and visible observatory (e.g. NASA's LUVOIR project) within a suite of instruments.Comment: Accepted in ApSS's special volume on UV astronom

Stable isotope records for the last 10 000 years from Okshola cave (Fauske, northern Norway) and regional comparisons

The sensitivity of terrestrial environments to past changes in heat transport is expected to be manifested in Holocene climate proxy records on millennial to seasonal timescales. Stalagmite formation in the Okshola cave near Fauske (northern Norway) began at about 10.4 ka, soon after the valley was deglaciated. Past monitoring of the cave and surface has revealed stable modern conditions with uniform drip rates, relative humidity and temperature. Stable isotope records from two stalagmites provide time-series spanning from c. 10 380 yr to AD 1997; a banded, multi-coloured stalagmite (Oks82) was formed between 10 380 yr and 5050 yr, whereas a pristine, white stalagmite (FM3) covers the period from ~7500 yr to the present. The stable oxygen isotope (δ<sup>18</sup>O<sub>c</sub>), stable carbon isotope (δ<sup>13</sup>C<sub>c</sub>), and growth rate records are interpreted as showing i) a negative correlation between cave/surface temperature and δ<sup>18</sup>O<sub>c</sub>, ii) a positive correlation between wetness and δ<sup>13</sup>C<sub>c</sub>, and iii) a positive correlation between temperature and growth rate. Following this, the data from Okshola show that the Holocene was characterised by high-variability climate in the early part, low-variability climate in the middle part, and high-variability climate and shifts between two distinct modes in the late part. <br><br> A total of nine Scandinavian stalagmite δ<sup>18</sup>O<sub>c</sub> records of comparable dating precision are now available for parts or most of the Holocene. None of them show a clear Holocene thermal optimum, suggesting that they are influenced by annual mean temperature (cave temperature) rather than seasonal temperature. For the last 1000 years, δ<sup>18</sup>O<sub>c</sub> values display a depletion-enrichment-depletion pattern commonly interpreted as reflecting the conventional view on climate development for the last millennium. Although the δ<sup>18</sup>O<sub>c</sub> records show similar patterns and amplitudes of change, the main challenges for utilising high-latitude stalagmites as palaeoclimate archives are i) the accuracy of the age models, ii) the ambiguity of the proxy signals, and iii) calibration with monitoring data

Discovery Of A Magnetic Field In The Rapidly Rotating O-Type Secondary Of The Colliding-Wind Binary HD 47129 (Plaskett\u27s Star)

We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett\u27s star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Telescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 +/- 150 and +680 +/- 190 G, implying a minimum surface dipole polar strength of 2850 +/- 500 G. In contrast, we derive an upper limit (3 sigma) to the primary\u27s surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study

Comparison of CDMS [100] and [111] oriented germanium detectors

The Cryogenic Dark Matter Search (CDMS) utilizes large mass, 3" diameter $\times$ 1" thick target masses as particle detectors. The target is instrumented with both phonon and ionization sensors and comparison of energy in each channel provides event-by-event classification of electron and nuclear recoils. Fiducial volume is determined by the ability to obtain good phonon and ionization signal at a particular location. Due to electronic band structure in germanium, electron mass is described by an anisotropic tensor with heavy mass aligned along the symmetry axis defined by the [111] Miller index (L valley), resulting in large lateral component to the transport. The spatial distribution of electrons varies significantly for detectors which have their longitudinal axis orientations described by either the [100] or [111] Miller indices. Electric fields with large fringing component at high detector radius also affect the spatial distribution of electrons and holes. Both effects are studied in a 3 dimensional Monte Carlo and the impact on fiducial volume is discussed.Comment: Low Temperature Detector 14 conference proceedings to be published in the Journal of Low Temperature Physic