675 research outputs found
Walker (D. P.). Spiritual and demonic magic from Ficino to Campanella
No full textSchaerer René. Walker (D. P.). Spiritual and demonic magic from Ficino to Campanella. In: Revue belge de philologie et d'histoire, tome 38, fasc. 2, 1960. Histoire (depuis la fin de l'Antiquité) — Geschiedenis (sedert de Oudheid) pp. 538-540
A novel CT-based contrast enhancement technique for markerless lung tumor tracking in X-ray projection images
No full textTime-consistent parametrization from dynamic optical surface detection for respiratory motion recovery in radiation oncology
No full textRealistic ionizing fluxes for young stellar populations from 0.05 to 2 ZÔ
No full textWe present a new grid of ionizing fluxes for O and Wolf–Rayet (W–R) stars for use with evolutionary synthesis codes and single-star H ii region analyses. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Z⊙) using the wm-basic code of Pauldrach, Hoffmann & Lennon for O stars and the cmfgen code of Hillier & Miller for W–R stars. The stellar wind parameters are scaled with metallicity for both O and W–R stars. We compare the ionizing fluxes of the new models with the CoStar models of Schaerer & de Koter and the pure helium W–R models of Schmutz, Leitherer & Gruenwald. We find significant differences, particularly above 54 eV, where the emergent flux is determined by the wind density as a function of metallicity. The new models have lower ionizing fluxes in the He i continuum with important implications for nebular line ratios. We incorporate the new models into the evolutionary synthesis code starburst99 and compare the ionizing outputs for an instantaneous burst and continuous star formation with the work of Schaerer & Vacca (SV98), and Leitherer et al. The changes in the output ionizing fluxes as a function of age are dramatic. We find that, in contrast to previous studies, nebular He ii λ4686 will be at, or just below, the detection limit in low metallicity starbursts during the W–R phase. The new models have lower fluxes in the He i continuum for Z≥ 0.4 Z⊙ and ages ≤7 Myr because of the increased line blanketing. We test the accuracy of the new model atmosphere grid by constructing photoionization models for simple H ii regions, and assessing the impact of the new ionizing fluxes on important nebular diagnostic line ratios. For the case of an H ii region where the ionizing flux is given by the WM-basic dwarf O star grid, we show that He iλ5786/Hβ decreases between 1 and 2 Z⊙ in a similar manner to observations. We find that this decline is caused by the increased effect of line blanketing above solar metallicity. We therefore suggest that a lowering of the upper mass limit at high abundances is not required to explain the diminishing strength of He iλ5786/Hβ , as has been suggested in the past. For an H ii region where the ionizing flux is provided by an instantaneous burst of total mass 106 M⊙ , we plot the softness parameter η' against the abundance indicator R23 for ages of 1–5 Myr. The new models are coincident with the observational data of Bresolin et al., particularly during the W–R phase, unlike the previous models of SV98 which generally over-predict the hardness of the ionizing radiation
Tumour motion tracking technique based on dynamic surface scanning and 4D CT breathing motion model
No full textMulti-dimensional respiratory motion tracking from markerless optical surface imaging based on deformable mesh registration
No full textAn optical and infrared analysis of blue compact dwarf galaxies
No full textAn understanding of Blue Compact Dwarf galaxies (BCDs) and the processes occurring within
their chemically un-evolved environments is fundamental in our understanding of the early universe.
This thesis presents an investigation into their physical conditions, kinematics, chemical
abundances and dust compositions.
An optical integral field spectroscopy investigation of two perturbed BCDs, UM420 and UM462,
is presented. Emission line maps show that both galaxies display signs of ongoing perturbation
and/or interaction. Electron temperatures, densities and chemical abundances are computed from
spectra integrated over the whole galaxies and for each area of star formation.
A similar yet more complicated analysis is undertaken of the BCD Mrk996, which displays
multi-component emission lines. The high excitation energy [O III] \lambda4363 and [N II] \lambda5755 lines
are detected only in the inner regions and purely in broad component form, implying unusual
excitation conditions. A separate physical analysis of the broad and narrow emission line regions
is undertaken, yielding a revised metallicity and N/O ratio typical for the galaxy’s metallicity.
The mid-IR properties of 19 BCDs are studied through Spitzer spectral and imaging data. The
depeletion of PAH emission in BCDs is investigated and found to be due to formation and destruction
effects. The [S III] flux ratio is used as a density diagnostic, showing typically low-densities.
Maps of PAH emission and radiation field hardness are derived from IRS spectral mapping data.
Blackbody fits to IR photometric SEDs typically reveal two dust components.
The observed physical and chemical properties of Mrk 996 are successfully reproduced using
the photoionisation code MOCASSIN. The best-fit model involved the inclusion of a filling factor
and an amorphous carbon dust component with a two-zone dust distribution. A STARBURST99
input spectrum was used, yielding ages consistent with the known young WR stars and old super
star clusters within Mrk 996
Theses philosophicae subitariae
No full textquas ... pro summo in philosophia honore rite consequendo sub praesidio ... Ieremiae Raillard ... publice defendet Fridericus Schaerer, Basiliensis. Ad d. 30. Maii M D CC XLII ...Mit ZierinitialeEnthält 12 ThesenDisputatio mag. phil. Basel, 174
Extremely Red Galaxies in Abell 1835
No full textWe use multi-colour data of the gravitational lensing cluster Abell 1835 to search for high-z candidates (Richard et al. 2006) and extremely red galaxies. Applying a colour criteria of R-K ≥ 5.6 we have selected 12 EROs, of which 10(9) have no R(I)-band detection. Two of these sources posses multiple detections in the ACS z850 band, possibly gravitationally bound objects. Using the method of Pozzetti and Mannucci (2000) to classify an ERO either as evolved elliptical or dusty starburst, we find that two thirds of all objects have colours assigned to evolved ellipticals. One of the remaining 4 sources is the known sub-mm source SMMJ14009+0252. The spectral energy distributions of sources with no optical detection show strong similarities to the SED of the high-z object of Mobasher et al. (2005), i.e. a degeneracy between a low- and high-z solution. However, for objects we accept the low-z solution as the better fit. A detailed analyses of the colour properties and spectral energy distribution will be published in two forthcoming papers (Schaerer et al., Hempel et al.
J1154+2443: a low-redshift compact star-forming galaxy with a 46 per cent leakage of Lyman continuum photons
No full textWe report the detection of the Lyman continuum (LyC) radiation of the compact
star-forming galaxy (SFG) J1154+2443 observed with the Cosmic Origins
Spectrograph (COS) onboard the Hubble Space Telescope. This galaxy, at a
redshift of z=0.3690, is characterized by a high emission-line flux ratio
O32=[OIII]5007/[OII]3727=11.5. The escape fraction of the LyC radiation
fesc(LyC) in this galaxy is 46 per cent, the highest value found so far in
low-redshift SFGs and one of the highest values found in galaxies at any
redshift. The narrow double-peaked Lya emission line is detected in the
spectrum of J1154+2443 with a separation between the peaks Vsep of 199 km/s,
one of the lowest known for Lya-emitting galaxies, implying a high fesc(Lya).
Comparing the extinction-corrected Lya/Hb flux ratio with the case B value we
find fesc(Lya) = 98 per cent. Our observations, combined with previous
detections in the literature, reveal an increase of O32 with increasing
fesc(LyC). We also find a tight anticorrelation between fesc(LyC) and Vsep. The
surface brightness profile derived from the COS acquisition image reveals a
bright star-forming region in the centre and an exponential disc in the
outskirts with a disc scale length alpha=1.09 kpc. J1154+2443, compared to
other known low-redshift LyC leakers, is characterized by the lowest
metallicity, 12+logO/H=7.65+/-0.01, the lowest stellar mass M*=10^8.20 Msun, a
similar star formation rate SFR=18.9 Msun/yr and a high specific SFR of
1.2x10^-7 yr^-1.Comment: 16 pages, 8 figures, accepted for publication in MNRAS. arXiv admin
note: text overlap with arXiv:1605.0516
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