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  • 1
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    500 days of SN 2013dy: spectra and photometry from the ultraviolet to the infrared (2015)
    Oxford University Press
    Details
    Publikationsdatum: 2015-08-14
    Beschreibung: SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to ~ 500 d after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with Hubble Space Telescope /Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve ( m 15 ( B ) = 0.92 mag), shallow $\mathrm{Si}\,\small {II}\,\lambda 6355$ absorption, and a low velocity gradient. We detect strong C ii in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of $10.0^{+4.8}_{-3.8} \times 10^{42}$  erg s –1 . We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 2
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    Loss of MITF expression during human embryonic stem cell differentiation disrupts retinal pigment epithelium development and optic vesicle cell proliferation (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-11-07
    Beschreibung: Microphthalmia-associated transcription factor ( MITF ) is a master regulator of pigmented cell survival and differentiation with direct transcriptional links to cell cycle, apoptosis and pigmentation. In mouse, Mitf is expressed early and uniformly in optic vesicle (OV) cells as they evaginate from the developing neural tube, and null Mitf mutations result in microphthalmia and pigmentation defects. However, homozygous mutations in MITF have not been identified in humans; therefore, little is known about its role in human retinogenesis. We used a human embryonic stem cell (hESC) model that recapitulates numerous aspects of retinal development, including OV specification and formation of retinal pigment epithelium (RPE) and neural retina progenitor cells (NRPCs), to investigate the earliest roles of MITF. During hESC differentiation toward a retinal lineage, a subset of MITF isoforms was expressed in a sequence and tissue distribution similar to that observed in mice. In addition, we found that promoters for the MITF-A , -D and -H isoforms were directly targeted by Visual Systems Homeobox 2 (VSX2), a transcription factor involved in patterning the OV toward a NRPC fate. We then manipulated MITF RNA and protein levels at early developmental stages and observed decreased expression of eye field transcription factors, reduced early OV cell proliferation and disrupted RPE maturation. This work provides a foundation for investigating MITF and other highly complex, multi-purposed transcription factors in a dynamic human developmental model system.
    Print ISSN: 0964-6906
    Digitale ISSN: 1460-2083
    Thema: Biologie , Medizin
    Publiziert von Oxford University Press
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  • 3
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    Spectral models for early time SN 2011fe observations (2015)
    Oxford University Press
    Details
    Publikationsdatum: 2015-10-15
    Beschreibung: We use observed UV through near-IR spectra to examine whether SN 2011fe can be understood in the framework of Branch-normal Type Ia supernovae (SNe Ia) and to examine its individual peculiarities. As a benchmark, we use a delayed-detonation model with a progenitor metallicity of Z /20. We study the sensitivity of features to variations in progenitor metallicity, the outer density profile, and the distribution of radioactive nickel. The effect of metallicity variations in the progenitor have a relatively small effect on the synthetic spectra. We also find that the abundance stratification of SN 2011fe resembles closely that of a delayed-detonation model with a transition density that has been fit to other Branch-normal SNe Ia. At early times, the model photosphere is formed in material with velocities that are too high, indicating that the photosphere recedes too slowly or that SN 2011fe has a lower specific energy in the outer 0.1 M than does the model. We discuss several explanations for the discrepancies. Finally, we examine variations in both the spectral energy distribution and in the colours due to variations in the progenitor metallicity, which suggests that colours are only weak indicators for the progenitor metallicity, in the particular explosion model that we have studied. We do find that the flux in the U band is significantly higher at maximum light in the solar metallicity model than in the lower metallicity model and the lower metallicity model much better matches the observed spectrum.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 4
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    Distribution and magnitude of post-seismic deformation of the 2009 L’Aquila earthquake (M6.3) surface rupture measured using repeat terrestrial laser scanning (2012)
    Oxford University Press
    Details
    Publikationsdatum: 2012-04-15
    Beschreibung: SUMMARY We captured post-seismic deformation close to the surface rupture of the 2009 L’Aquila earthquake ( M 6.3, central Italy) using repeat terrestrial laser scan (TLS) methods. From 8 to 126 d after the earthquake, we repeatedly laser scanned four road surfaces that intersected the earthquake surface rupture. We modelled vertical near-field deformation, at millimetre-level precision, by comparing subsequent laser scan data sets to the first acquired at each site. The horizontal post-seismic deformation at each site was measured between reflectors paired across the rupture. The TLS data were supplemented by total station data from a fifth site which measured the vertical and horizontal components of post-seismic deformation between two points spanning the rupture. We find post-seismic deformation increased between 44 and 126 d at the southeastern end of the rupture, beneath which a significant gradient in coseismic slip exists within the fault zone. The location, rate of decay and spatially-localized nature of the post-seismic deformation, within tens of metres of the surface rupture suggests it is due to afterslip in the fault zone, driven by increased shear stresses at the edges of regions which slipped coseismically. We note that the magnitude of post-seismic deformation in the far field obtained from InSAR and GPS is not significantly greater than the deformations we have measured close to the rupture. We suggest that shallow, localized afterslip within the fault zone is responsible for the majority of the regional post-seismic deformation field.
    Print ISSN: 0956-540X
    Digitale ISSN: 1365-246X
    Thema: Geologie und Paläontologie
    Publiziert von Oxford University Press im Namen von The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
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    Microbial diversity in European alpine permafrost and active layers (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-02-25
    Beschreibung: Permafrost represents a largely understudied genetic resource. Thawing of permafrost with global warming will not only promote microbial carbon turnover with direct feedback on greenhouse gases, but also unlock an unknown microbial diversity. Pioneering metagenomic efforts have shed light on the permafrost microbiome in polar regions, but temperate mountain permafrost is largely understudied. We applied a unique experimental design coupled to high-throughput sequencing of ribosomal markers to characterize the microbiota at the long-term alpine permafrost study site ‘Muot-da-Barba-Peider’ in eastern Switzerland with an approximate radiocarbon age of 12 000 years. Compared to the active layers, the permafrost community was more diverse and enriched with members of the superphylum Patescibacteria (OD1, TM7, GN02 and OP11). These understudied phyla with no cultured representatives proposedly feature small streamlined genomes with reduced metabolic capabilities, adaptations to anaerobic fermentative metabolisms and potential ectosymbiotic lifestyles. The permafrost microbiota was also enriched with yeasts and lichenized fungi known to harbour various structural and functional adaptation mechanisms to survive under extreme sub-zero conditions. These data yield an unprecedented view on microbial life in temperate mountain permafrost, which is increasingly important for understanding the biological dynamics of permafrost in order to anticipate potential ecological trajectories in a warming world.
    Print ISSN: 0168-6496
    Digitale ISSN: 1574-6941
    Thema: Biologie
    Publiziert von Oxford University Press
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  • 6
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    SN 2009N: linking normal and subluminous Type II-P SNe (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-01-16
    Beschreibung: We present ultraviolet, optical, near-infrared photometry and spectroscopy of SN 2009N in NGC 4487. This object is a Type II-P supernova with spectra resembling those of subluminous II-P supernovae, while its bolometric luminosity is similar to that of the intermediate-luminosity SN 2008in. We created synow models of the plateau phase spectra for line identification and to measure the expansion velocity. In the near-infrared spectra we find signs indicating possible weak interaction between the supernova ejecta and the pre-existing circumstellar material. These signs are also present in the previously unpublished near-infrared spectra of SN 2008in. The distance to SN 2009N is determined via the expanding photosphere method and the standard candle method as D  = 21.6 ± 1.1 Mpc. The produced nickel-mass is estimated to be ~0.020 ± 0.004 M . We infer the physical properties of the progenitor at the explosion through hydrodynamical modelling of the observables. We find the values of the total energy as ~0.48 10 51  erg, the ejected mass as ~11.5 M , and the initial radius as ~287 R .
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    Analysis of blueshifted emission peaks in Type II supernovae (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-05-04
    Beschreibung: In classical P-Cygni profiles, theory predicts emission to peak at zero rest velocity. However, supernova spectra exhibit emission that is generally blueshifted. While this characteristic has been reported in many SNe, it is rarely discussed in any detail. Here, we present an analysis of Hα emission peaks using a data set of 95 Type II supernovae, quantifying their strength and time evolution. Using a post-explosion time of 30 d, we observe a systematic blueshift of Hα emission, with a mean value of –2000 km s –1 . This offset is greatest at early times but vanishes as supernovae become nebular. Simulations of Dessart et al. match the observed behaviour, reproducing both its strength and evolution in time. Such blueshifts are a fundamental feature of supernova spectra as they are intimately tied to the density distribution of ejecta, which falls more rapidly than in stellar winds. This steeper density structure causes line emission/absorption to be much more confined; it also exacerbates the occultation of the receding part of the ejecta, biasing line emission to the blue for a distant observer. We conclude that blueshifted emission-peak offsets of several thousand km s –1 are a generic property of observations, confirmed by models, of photospheric-phase Type II supernovae.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 8
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    Distribution and magnitude of post-seismic deformation of the 2009 L’Aquila earthquake (M6.3) surface rupture measured using repeat terrestrial laser scanning (2012)
    Oxford University Press
    Details
    Publikationsdatum: 2012-03-17
    Beschreibung: SUMMARY We captured post-seismic deformation close to the surface rupture of the 2009 L’Aquila earthquake ( M 6.3, central Italy) using repeat terrestrial laser scan (TLS) methods. From 8 to 126 d after the earthquake, we repeatedly laser scanned four road surfaces that intersected the earthquake surface rupture. We modelled vertical near-field deformation, at millimetre-level precision, by comparing subsequent laser scan data sets to the first acquired at each site. The horizontal post-seismic deformation at each site was measured between reflectors paired across the rupture. The TLS data were supplemented by total station data from a fifth site which measured the vertical and horizontal components of post-seismic deformation between two points spanning the rupture. We find post-seismic deformation increased between 44 and 126 d at the southeastern end of the rupture, beneath which a significant gradient in coseismic slip exists within the fault zone. The location, rate of decay and spatially-localized nature of the post-seismic deformation, within tens of metres of the surface rupture suggests it is due to afterslip in the fault zone, driven by increased shear stresses at the edges of regions which slipped coseismically. We note that the magnitude of post-seismic deformation in the far field obtained from InSAR and GPS is not significantly greater than the deformations we have measured close to the rupture. We suggest that shallow, localized afterslip within the fault zone is responsible for the majority of the regional post-seismic deformation field.
    Print ISSN: 0956-540X
    Digitale ISSN: 1365-246X
    Thema: Geologie und Paläontologie
    Publiziert von Oxford University Press im Namen von The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
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    Photometric and spectroscopic observations, and abundance tomography modelling of the Type Ia supernova SN 2014J located in M82 (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-11-09
    Beschreibung: Spectroscopic and photometric observations of the nearby Type Ia Supernova (SN Ia) SN 2014J are presented. Spectroscopic observations were taken –8 to +10 d relative to B -band maximum, using FRODOSpec, a multipurpose integral-field unit spectrograph. The observations range from 3900 to 9000 Å. SN 2014J is located in M82 which makes it the closest SN Ia studied in at least the last 28 yr. It is a spectroscopically normal SN Ia with high-velocity features. We model the spectra of SN 2014J with a Monte Carlo radiative transfer code, using the abundance tomography technique. SN 2014J is highly reddened, with a host galaxy extinction of E ( B  –  V ) = 1.2 ( R V  = 1.38). It has a m 15 ( B ) of 1.08 ± 0.03 when corrected for extinction. As SN 2014J is a normal SN Ia, the density structure of the classical W7 model was selected. The model and photometric luminosities are both consistent with B -band maximum occurring on JD 245 6690.4 ± 0.12. The abundance of the SN 2014J behaves like other normal SN Ia, with significant amounts of silicon (12 per cent by mass) and sulphur (9 per cent by mass) at high velocities (12 300 km s –1 ) and the low-velocity ejecta ( v  〈 6500 km s –1 ) consists almost entirely of 56 Ni.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
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  • 10
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    Type II Plateau supernovae as metallicity probes of the Universe (2014)
    Oxford University Press
    Details
    Publikationsdatum: 2014-04-15
    Beschreibung: We explore a method for metallicity determinations based on quantitative spectroscopy of Type II-Plateau supernovae (SNe II-P). For consistency, we first evolve a set of 15 M main-sequence stars at 0.1, 0.4, 1, and 2 times the solar metallicity. At the onset of core collapse, we trigger a piston-driven explosion and model the resulting ejecta and radiation. Our theoretical models of such red supergiant star explosions at different metallicity show that synthetic spectra of SNe II-P possess optical signatures during the recombination phase that are sensitive to metallicity variations. This sensitivity can be quantified and the metallicity inferred from the strengths of metal-line absorptions. Furthermore, these signatures are not limited to O, but also include Na, Ca, Sc, Ti, or Fe. When compared to a sample of SNe II-P from the Carnegie SN Project and previous SN followup programmes, we find that most events lie at a metallicity between 0.4 and 2 times solar, with a marked scarcity of SN II-P events at small magellanic cloud metallicity. This most likely reflects the paucity of low-metallicity star-forming regions in the local Universe. SNe II-P have high-plateau luminosities that make them observable spectroscopically at large distances. Because they exhibit signatures of diverse metal species, in the future they may offer a means to constrain the evolution of the composition (e.g. the O/Fe ratio) in the Universe out to a redshift of 1 and beyond.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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