The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Kevin A Schug - One of the best experts on this subject based on the ideXlab platform.
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Rapid Profiling and Authentication of Vanilla Extracts Using Gas Chromatography-Vacuum Ultraviolet Spectroscopy
Food Analytical Methods, 2017Co-Authors: Ines C Santos, Jonathan Smuts, Kevin A SchugAbstract:Vanilla extracts are widely used as flavoring ingredients in foods, beverages, perfumes, and pharmaceuticals. Due to the high cost of producing high-quality natural extracts, artificial flavorings, such as ethyl vanillin and coumarin, are often used. For food safety and to ensure high-quality products, it is important to differentiate between natural and artificial extracts. In this work, gas chromatography-vacuum Ultraviolet Spectroscopy (GC-VUV) was used for the determination of natural and artificial flavoring compounds in vanilla extract samples. Since the GC-VUV software is able to deconvolve co-eluting peaks based on their unique VUV/UV absorption spectra (125–240 nm), a compromise between resolution and speed of analysis (6- and 14-min runs on different polarity columns) could be made. LODs between 0.42 and 2.0 μg mL^−1 were obtained for the tested flavoring compounds. Vanillin was present in extracts at the highest concentrations, from 108 to 5817 μg mL^−1.
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recent advances and applications of gas chromatography vacuum Ultraviolet Spectroscopy
IEEE Journal of Solid-state Circuits, 2017Co-Authors: Ines C Santos, Kevin A SchugAbstract:The vacuum Ultraviolet spectrophotometer was developed recently as an alternative to existing gas chromatography detectors. This detector measures the absorption of gas-phase chemical species in the range of 120-240 nm, where all chemical compounds present unique absorption spectra. Therefore, qualitative analysis can be performed and quantification follows standard Beer-Lambert law principles. Different fields of application, such as petrochemical, food, and environmental analysis have been explored. Commonly demonstrated is the capability for facile deconvolution of co-eluting analytes. The concept of additive absorption for co-eluting analytes has also been advanced for classification and speciation of complex mixtures using a data treatment procedure termed time interval deconvolution. Furthermore, pseudo-absolute quantitation can be performed for system diagnosis, as well as potentially calibrationless quantitation. In this manuscript an overview of these features, the vacuum Ultraviolet spectrophotometer instrumentation, and performance capabilities are given. A discussion of the applications of the vacuum Ultraviolet detector is provided by describing and discussing the papers published thus far since 2014.
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analysis and deconvolution of dimethylnaphthalene isomers using gas chromatography vacuum Ultraviolet Spectroscopy and theoretical computations
Analytica Chimica Acta, 2016Co-Authors: Jamie Schenk, Jonathan Smuts, James X Mao, Peter Kroll, Phillip Walsh, Kevin A SchugAbstract:An issue with most gas chromatographic detectors is their inability to deconvolve coeluting isomers. Dimethylnaphthalenes are a class of compounds that can be particularly difficult to speciate by gas chromatography – mass spectrometry analysis, because of their significant coelution and similar mass spectra. As an alternative, a vacuum Ultraviolet spectroscopic detector paired with gas chromatography was used to study the systematic deconvolution of mixtures of coeluting isomers of dimethylnaphthalenes. Various ratio combinations of 75:25; 50:50; 25:75; 20:80; 10:90; 5:95; and 1:99 were prepared to test the accuracy, precision, and sensitivity of the detector for distinguishing overlapping isomers that had distinct, but very similar absorption spectra. It was found that, under reasonable injection conditions, all of the pairwise overlapping isomers tested could be deconvoluted up to nearly two orders of magnitude (up to 99:1) in relative abundance. These experimental deconvolution values were in agreement with theoretical covariance calculations performed for two of the dimethylnaphthalene isomers. Covariance calculations estimated high picogram detection limits for a minor isomer coeluting with low to mid-nanogram quantity of a more abundant isomer. Further characterization of the analytes was performed using density functional theory computations to compare theory with experimental measurements. Additionally, gas chromatography – vacuum Ultraviolet Spectroscopy was shown to be able to speciate dimethylnaphthalenes in jet and diesel fuel samples.
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gas chromatography vacuum Ultraviolet Spectroscopy for analysis of fatty acid methyl esters
Food Chemistry, 2016Co-Authors: Jonathan Smuts, Phillip Walsh, Daniel W Armstrong, Kevin A SchugAbstract:Abstract A new vacuum Ultraviolet (VUV) detector for gas chromatography was recently developed and applied to fatty acid methyl ester (FAME) analysis. VUV detection features full spectral acquisition in a wavelength range of 115–240 nm, where virtually all chemical species absorb. VUV absorption spectra of 37 FAMEs, including saturated, monounsaturated, and polyunsaturated types were recorded. Unsaturated FAMEs show significantly different gas phase absorption profiles than saturated ones, and these classes can be easily distinguished with the VUV detector. Another advantage includes differentiating cis/trans-isomeric FAMEs (e.g. oleic acid methyl ester and linoleic acid methyl ester isomers) and the ability to use VUV data analysis software for deconvolution of co-eluting signals. As a universal detector, VUV also provides high specificity, sensitivity, and a fast data acquisition rate, making it a powerful tool for fatty acid screening when combined with gas chromatography. The fatty acid profile of several food oil samples (olive, canola, vegetable, corn, sunflower and peanut oils) were analyzed in this study to demonstrate applicability to real world samples.
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gas chromatography vacuum Ultraviolet Spectroscopy for multiclass pesticide identification
Journal of Chromatography A, 2015Co-Authors: Hui Fan, Phillip Walsh, Jonathan Smuts, Dale A Harrison, Kevin A SchugAbstract:Abstract A new vacuum Ultraviolet detector for gas chromatography was recently developed and applied to multiclass pesticide identification. VUV detection features full spectral acquisition in a wavelength range of 115–240 nm, where virtually all chemical species absorb. VUV absorption spectra of 37 pesticides across different classes were recorded. These pesticides display rich gas phase absorption features across various classes. Even for isomeric compounds, such as hexachlorocyclohexane (HCH) isomers, the VUV absorption spectra are unique and can be easily differentiated. Also demonstrated is the ability to use VUV data analysis software for deconvolution of co-eluting signals. As a universal detector, VUV provides both qualitative and quantitative information. It offers high specificity, sensitivity (pg on-column detection limits), and a fast data acquisition rate, making it a powerful tool for multiclass pesticide screening when combined with gas chromatography.
Sagi Benami - One of the best experts on this subject based on the ideXlab platform.
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Ultraviolet Spectroscopy of type iib supernovae diversity and the impact of circumstellar material
The Astrophysical Journal, 2015Co-Authors: Sagi Benami, Stephan Hachinger, A Galyam, P A Mazzali, Alexei V Filippenko, A Horesh, T Matheson, Maryam Modjaz, Daniel SauerAbstract:We present new Hubble Space Telescope (HST) multi-epoch Ultraviolet (UV) spectra of the bright Type IIb SN 2013df, and undertake a comprehensive analysis of the set of four SNe IIb for which HST UV spectra are available (SN 1993J, SN 2001ig, SN 2011dh, and SN 2013df). We find strong diversity in both continuum levels and line features among these objects. We use radiative-transfer models that fit the optical part of the spectrum well, and find that in three of these four events we see a UV continuum flux excess, apparently unaffected by line absorption. We hypothesize that this emission originates above the photosphere, and is related to interaction with circumstellar material (CSM) located in close proximity to the SN progenitor. In contrast, the spectra of SN 2001ig are well fit by single-temperature models, display weak continuum and strong reverse-fluorescence features, and are similar to spectra of radioactive 56Ni-dominated SNe Ia. A comparison of the early shock-cooling components in the observed light curves with the UV continuum levels which we assume trace the strength of CSM interaction suggests that events with slower cooling have stronger CSM emission. The radio emission from events having a prominent UV excess is perhaps consistent with slower blast-wave velocities, as expected if the explosion shock was slowed down by the CSM that is also responsible for the strong UV, but this connection is currently speculative as it is based on only a few events.
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Ultraviolet Spectroscopy of type iib supernovae diversity and the impact of circumstellar material
arXiv: High Energy Astrophysical Phenomena, 2014Co-Authors: Sagi Benami, Stephan Hachinger, A Galyam, P A Mazzali, Alexei V Filippenko, A Horesh, T Matheson, Maryam Modjaz, Daniel SauerAbstract:We present new Hubble Space Telescope (HST) multi-epoch Ultraviolet (UV) spectra of the bright Type IIb SN 2013df, and undertake a comprehensive anal- ysis of the set of four Type IIb supernovae for which HST UV spectra are available (SN 1993J, SN 2001ig, SN 2011dh, and SN 2013df). We find strong diversity in both continuum levels and line features among these objects. We use radiative-transfer models that fit the optical part of the spectrum well, and find that in three of these four events we see a UV continuum flux excess, apparently unaffected by line absorption. We hypothesize that this emission originates above the photosphere, and is related to interaction with circumstel- lar material (CSM) located in close proximity to the SN progenitor. In contrast, the spectra of SN 2001ig are well fit by single-temperature models, display weak continuum and strong reverse-fluorescence features, and are similar to spectra of radioactive 56Ni-dominated Type Ia supernovae. A comparison of the early shock-cooling components in the observed light curves with the UV continuum levels which we assume trace the strength of CSM interaction suggests that events with slower cooling have stronger CSM emission. The radio emission from events having a prominent UV excess is perhaps consistent with slower blast-wave velocities, as expected if the explosion shock was slowed down by the CSM that is also responsible for the strong UV, but this connection is currently speculative as it is based on only a few events.
Jonathan Smuts - One of the best experts on this subject based on the ideXlab platform.
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Rapid Profiling and Authentication of Vanilla Extracts Using Gas Chromatography-Vacuum Ultraviolet Spectroscopy
Food Analytical Methods, 2017Co-Authors: Ines C Santos, Jonathan Smuts, Kevin A SchugAbstract:Vanilla extracts are widely used as flavoring ingredients in foods, beverages, perfumes, and pharmaceuticals. Due to the high cost of producing high-quality natural extracts, artificial flavorings, such as ethyl vanillin and coumarin, are often used. For food safety and to ensure high-quality products, it is important to differentiate between natural and artificial extracts. In this work, gas chromatography-vacuum Ultraviolet Spectroscopy (GC-VUV) was used for the determination of natural and artificial flavoring compounds in vanilla extract samples. Since the GC-VUV software is able to deconvolve co-eluting peaks based on their unique VUV/UV absorption spectra (125–240 nm), a compromise between resolution and speed of analysis (6- and 14-min runs on different polarity columns) could be made. LODs between 0.42 and 2.0 μg mL^−1 were obtained for the tested flavoring compounds. Vanillin was present in extracts at the highest concentrations, from 108 to 5817 μg mL^−1.
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resolution of isomeric new designer stimulants using gas chromatography vacuum Ultraviolet Spectroscopy and theoretical computations
Analytica Chimica Acta, 2017Co-Authors: Jonathan Smuts, Ludovit Skultety, Petr Frycak, Changling Qiu, Lindsey Shearlaude, Karel Lemr, James X Mao, Peter KrollAbstract:Abstract Distinguishing isomeric representatives of “bath salts”, “plant food”, “spice”, or “legal high” remains a challenge for analytical chemistry. In this work, we used vacuum Ultraviolet Spectroscopy combined with gas chromatography to address this issue on a set of forty-three designer drugs. All compounds, including many isomers, returned differentiable vacuum Ultraviolet/Ultraviolet spectra. The pair of 3- and 4-fluoromethcathinones (m/z 181.0903), as well as the methoxetamine/meperidine/ethylphenidate (m/z 247.1572) triad, provided very distinctive vacuum Ultraviolet spectral features. On the contrary, spectra of 4-methylethcathinone, 4-ethylmethcathinone, 3,4-dimethylmethcathinone triad (m/z 191.1310) displayed much higher similarities. Their resolution was possible only if pure standards were probed. A similar situation occurred with the ethylone and butylone pair (m/z 221.1052). On the other hand, majority of forty-three drugs was successfully separated by gas chromatography. The detection limits for all the drug standards were in the 2–4 ng range (on-column amount), which is sufficient for determinations of seized drugs during forensics analysis. Further, state-of-the-art time-dependent density functional theory was evaluated for computation of theoretical absorption spectra in the 125–240 nm range as a complementary tool.
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analysis and deconvolution of dimethylnaphthalene isomers using gas chromatography vacuum Ultraviolet Spectroscopy and theoretical computations
Analytica Chimica Acta, 2016Co-Authors: Jamie Schenk, Jonathan Smuts, James X Mao, Peter Kroll, Phillip Walsh, Kevin A SchugAbstract:An issue with most gas chromatographic detectors is their inability to deconvolve coeluting isomers. Dimethylnaphthalenes are a class of compounds that can be particularly difficult to speciate by gas chromatography – mass spectrometry analysis, because of their significant coelution and similar mass spectra. As an alternative, a vacuum Ultraviolet spectroscopic detector paired with gas chromatography was used to study the systematic deconvolution of mixtures of coeluting isomers of dimethylnaphthalenes. Various ratio combinations of 75:25; 50:50; 25:75; 20:80; 10:90; 5:95; and 1:99 were prepared to test the accuracy, precision, and sensitivity of the detector for distinguishing overlapping isomers that had distinct, but very similar absorption spectra. It was found that, under reasonable injection conditions, all of the pairwise overlapping isomers tested could be deconvoluted up to nearly two orders of magnitude (up to 99:1) in relative abundance. These experimental deconvolution values were in agreement with theoretical covariance calculations performed for two of the dimethylnaphthalene isomers. Covariance calculations estimated high picogram detection limits for a minor isomer coeluting with low to mid-nanogram quantity of a more abundant isomer. Further characterization of the analytes was performed using density functional theory computations to compare theory with experimental measurements. Additionally, gas chromatography – vacuum Ultraviolet Spectroscopy was shown to be able to speciate dimethylnaphthalenes in jet and diesel fuel samples.
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gas chromatography vacuum Ultraviolet Spectroscopy for analysis of fatty acid methyl esters
Food Chemistry, 2016Co-Authors: Jonathan Smuts, Phillip Walsh, Daniel W Armstrong, Kevin A SchugAbstract:Abstract A new vacuum Ultraviolet (VUV) detector for gas chromatography was recently developed and applied to fatty acid methyl ester (FAME) analysis. VUV detection features full spectral acquisition in a wavelength range of 115–240 nm, where virtually all chemical species absorb. VUV absorption spectra of 37 FAMEs, including saturated, monounsaturated, and polyunsaturated types were recorded. Unsaturated FAMEs show significantly different gas phase absorption profiles than saturated ones, and these classes can be easily distinguished with the VUV detector. Another advantage includes differentiating cis/trans-isomeric FAMEs (e.g. oleic acid methyl ester and linoleic acid methyl ester isomers) and the ability to use VUV data analysis software for deconvolution of co-eluting signals. As a universal detector, VUV also provides high specificity, sensitivity, and a fast data acquisition rate, making it a powerful tool for fatty acid screening when combined with gas chromatography. The fatty acid profile of several food oil samples (olive, canola, vegetable, corn, sunflower and peanut oils) were analyzed in this study to demonstrate applicability to real world samples.
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gas chromatography vacuum Ultraviolet Spectroscopy for multiclass pesticide identification
Journal of Chromatography A, 2015Co-Authors: Hui Fan, Phillip Walsh, Jonathan Smuts, Dale A Harrison, Kevin A SchugAbstract:Abstract A new vacuum Ultraviolet detector for gas chromatography was recently developed and applied to multiclass pesticide identification. VUV detection features full spectral acquisition in a wavelength range of 115–240 nm, where virtually all chemical species absorb. VUV absorption spectra of 37 pesticides across different classes were recorded. These pesticides display rich gas phase absorption features across various classes. Even for isomeric compounds, such as hexachlorocyclohexane (HCH) isomers, the VUV absorption spectra are unique and can be easily differentiated. Also demonstrated is the ability to use VUV data analysis software for deconvolution of co-eluting signals. As a universal detector, VUV provides both qualitative and quantitative information. It offers high specificity, sensitivity (pg on-column detection limits), and a fast data acquisition rate, making it a powerful tool for multiclass pesticide screening when combined with gas chromatography.
Scott K Cushing - One of the best experts on this subject based on the ideXlab platform.
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hot phonon and carrier relaxation in si 100 determined by transient extreme Ultraviolet Spectroscopy
Structural Dynamics, 2018Co-Authors: Scott K Cushing, Michael Zurch, Peter M Kraus, Lucas M Carneiro, Angela Lee, Hungtzu Chang, Christopher J Kaplan, Stephen R LeoneAbstract:The thermalization of hot carriers and phonons gives direct insight into the scattering processes that mediate electrical and thermal transport. Obtaining the scattering rates for both hot carriers and phonons currently requires multiple measurements with incommensurate timescales. Here, transient extreme-Ultraviolet (XUV) Spectroscopy on the silicon 2p core level at 100 eV is used to measure hot carrier and phonon thermalization in Si(100) from tens of femtoseconds to 200 ps, following photoexcitation of the indirect transition to the Δ valley at 800 nm. The ground state XUV spectrum is first theoretically predicted using a combination of a single plasmon pole model and the Bethe-Salpeter equation with density functional theory. The excited state spectrum is predicted by incorporating the electronic effects of photo-induced state-filling, broadening, and band-gap renormalization into the ground state XUV spectrum. A time-dependent lattice deformation and expansion is also required to describe the excited state spectrum. The kinetics of these structural components match the kinetics of phonons excited from the electron-phonon and phonon-phonon scattering processes following photoexcitation. Separating the contributions of electronic and structural effects on the transient XUV spectra allows the carrier population, the population of phonons involved in inter- and intra-valley electron-phonon scattering, and the population of phonons involved in phonon-phonon scattering to be quantified as a function of delay time.
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photoexcited small polaron formation in goethite α feooh nanorods probed by transient extreme Ultraviolet Spectroscopy
Journal of Physical Chemistry Letters, 2018Co-Authors: Scott K Cushing, Lucas M Carneiro, Angela Lee, Ilana J Porter, Justin C Ondry, Jakob C DahlAbstract:Small polaron formation limits the mobility and lifetimes of photoexcited carriers in metal oxides. As the ligand field strength increases, the carrier mobility decreases, but the effect on the photoexcited small polaron formation is still unknown. Extreme Ultraviolet transient absorption Spectroscopy is employed to measure small polaron formation rates and probabilities in goethite (α-FeOOH) crystalline nanorods at pump photon energies from 2.2 to 3.1 eV. The measured polaron formation time increases with excitation photon energy from 70 ± 10 fs at 2.2 eV to 350 ± 30 fs at 2.6 eV, whereas the polaron formation probability (85 ± 10%) remains constant. By comparison to hematite (α-Fe2O3), an oxide analogue, the role of ligand composition and metal center density in small polaron formation time is discussed. This work suggests that incorporating small changes in ligands and crystal structure could enable the control of photoexcited small polaron formation in metal oxides.
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photoexcited carriers phonons and their scattering measured in semiconductor junctions by transient extreme Ultraviolet Spectroscopy
2017 IEEE 44th Photovoltaic Specialist Conference (PVSC), 2017Co-Authors: Scott K Cushing, Lucas M Carneiro, Ilana J Porter, Brett M Marsh, Mihai E Vaida, S LeoneAbstract:We use transient XUV Spectroscopy to measure the carrier and phonon dynamics for each atomic-species in a semiconductor or semiconductor heterojunction, giving the technique potential for table-top photovoltaic device characterization. First, the electron populations, phonon populations, and their scattering pathways are measured in the $\Delta$ , L, and r valleys of Si(100) from femtoseconds to hundreds of picosecond. Second, the Si(100) is coated with Ti0 2 and Ni to form a metal-insulator-semiconductor (MIS) junction. The Si L23, Ni M23, and Ti M23 edges are probed using XUV radiation from 20 eV to 150 eV, measuring the photoexcited charge-transfer, equilibration, and lattice dynamics for each component of the MIS junction.
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hot phonon and carrier relaxation in si 100 determined by transient extreme Ultraviolet Spectroscopy
arXiv: Materials Science, 2017Co-Authors: Scott K Cushing, Michael Zurch, Peter M Kraus, Lucas M Carneiro, Angela Lee, Hungtzu Chang, Christopher J Kaplan, Stephen R LeoneAbstract:The thermalization of hot carriers and phonons gives direct insight into the scattering processes that mediate electrical and thermal transport. Obtaining the scattering rates for both hot carriers and phonons currently requires multiple measurements with incommensurate timescales. Here, transient extreme-Ultraviolet (XUV) Spectroscopy on the silicon 2p core level at 100 eV is used to measure hot carrier and phonon thermalization in Si(100) from tens of femtoseconds to 200 ps following photoexcitation of the indirect transition to the {\Delta} valley at 800 nm. The ground state XUV spectrum is first theoretically predicted using a combination of a single plasmon pole model and the Bethe-Salpeter equation (BSE) with density functional theory (DFT). The excited state spectrum is predicted by incorporating the electronic effects of photo-induced state-filling, broadening, and band-gap renormalization into the ground state XUV spectrum. A time-dependent lattice deformation and expansion is also required to describe the excited state spectrum. The kinetics of these structural components match the kinetics of phonons excited from the electron-phonon and phonon-phonon scattering processes following photoexcitation. Separating the contributions of electronic and structural effects on the transient XUV spectra allows the carrier population, the population of phonons involved in inter- and intra-valley electron-phonon scattering, and the population of phonons involved in phonon-phonon scattering to be quantified as a function of delay time.
Daniel Sauer - One of the best experts on this subject based on the ideXlab platform.
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Ultraviolet Spectroscopy of type iib supernovae diversity and the impact of circumstellar material
The Astrophysical Journal, 2015Co-Authors: Sagi Benami, Stephan Hachinger, A Galyam, P A Mazzali, Alexei V Filippenko, A Horesh, T Matheson, Maryam Modjaz, Daniel SauerAbstract:We present new Hubble Space Telescope (HST) multi-epoch Ultraviolet (UV) spectra of the bright Type IIb SN 2013df, and undertake a comprehensive analysis of the set of four SNe IIb for which HST UV spectra are available (SN 1993J, SN 2001ig, SN 2011dh, and SN 2013df). We find strong diversity in both continuum levels and line features among these objects. We use radiative-transfer models that fit the optical part of the spectrum well, and find that in three of these four events we see a UV continuum flux excess, apparently unaffected by line absorption. We hypothesize that this emission originates above the photosphere, and is related to interaction with circumstellar material (CSM) located in close proximity to the SN progenitor. In contrast, the spectra of SN 2001ig are well fit by single-temperature models, display weak continuum and strong reverse-fluorescence features, and are similar to spectra of radioactive 56Ni-dominated SNe Ia. A comparison of the early shock-cooling components in the observed light curves with the UV continuum levels which we assume trace the strength of CSM interaction suggests that events with slower cooling have stronger CSM emission. The radio emission from events having a prominent UV excess is perhaps consistent with slower blast-wave velocities, as expected if the explosion shock was slowed down by the CSM that is also responsible for the strong UV, but this connection is currently speculative as it is based on only a few events.
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Ultraviolet Spectroscopy of type iib supernovae diversity and the impact of circumstellar material
arXiv: High Energy Astrophysical Phenomena, 2014Co-Authors: Sagi Benami, Stephan Hachinger, A Galyam, P A Mazzali, Alexei V Filippenko, A Horesh, T Matheson, Maryam Modjaz, Daniel SauerAbstract:We present new Hubble Space Telescope (HST) multi-epoch Ultraviolet (UV) spectra of the bright Type IIb SN 2013df, and undertake a comprehensive anal- ysis of the set of four Type IIb supernovae for which HST UV spectra are available (SN 1993J, SN 2001ig, SN 2011dh, and SN 2013df). We find strong diversity in both continuum levels and line features among these objects. We use radiative-transfer models that fit the optical part of the spectrum well, and find that in three of these four events we see a UV continuum flux excess, apparently unaffected by line absorption. We hypothesize that this emission originates above the photosphere, and is related to interaction with circumstel- lar material (CSM) located in close proximity to the SN progenitor. In contrast, the spectra of SN 2001ig are well fit by single-temperature models, display weak continuum and strong reverse-fluorescence features, and are similar to spectra of radioactive 56Ni-dominated Type Ia supernovae. A comparison of the early shock-cooling components in the observed light curves with the UV continuum levels which we assume trace the strength of CSM interaction suggests that events with slower cooling have stronger CSM emission. The radio emission from events having a prominent UV excess is perhaps consistent with slower blast-wave velocities, as expected if the explosion shock was slowed down by the CSM that is also responsible for the strong UV, but this connection is currently speculative as it is based on only a few events.
