Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies

Superluminous supernovae (SLSNe) are very bright explosions that were only discovered recently and that show a preference for occurring in faint dwarf galaxies. Understanding why stellar evolution yields different types of stellar explosions in these environments is fundamental in order to both uncover the elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In this paper, we present the first results of our project to study SUperluminous Supernova Host galaxIES, focusing on the sample for which we have obtained spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (~50% in our sample) occur in a class of galaxies that is known as Extreme Emission Line Galaxies (EELGs). The probability of this happening by chance is negligible and we therefore conclude that the extreme environmental conditions and the SLSN phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more massive, more metal-rich galaxies with softer radiation fields. Therefore, if SLSNe-II constitute a uniform class, their progenitor systems are likely different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average, not found in as extreme environments as H-poor SLSNe. We propose that H-poor SLSNe result from the very first stars exploding in a starburst, even earlier than GRBs. This might indicate a bottom-light initial mass function in these systems. SLSNe present a novel method of selecting candidate EELGs independent of their luminosity.Comment: Published version, matches proofs. Accepted 2015 February 13. 23 pages, 8 figures, 4 tables. Minor changes with respect to previous versio

A three dimensional finite element model for arterial clamping

Motivation and Introduction Arterial clamps are chosen to compress arteries during surgery so that blood flow is arrested. Arterial compression, however, may lead to injuries of the vessel wall, which are associated with a variety of severe short-term and long-term complications. For example, clamp induced injuries may cause spontaneous occlusion of the vessel after the operation, which leads to infarction of the downstream tissues. Therefore, surgeons require arterial clamps that allow efficient compression and cause only minimal injury. Severity and distribution of injuries depend on ͑i͒ the arterial type ͓1,2͔, the geometry and the nonlinear and anisotropic material behavior of the clamped multi-layered artery, ͑ii͒ the design of the chosen clamp ͓3-7͔ and ͑iii͒ the applied clamping forces ͓2,6,8,9͔. The optimization of this mechanical problem requires a numerical model, which considers appropriately all decisive factors. Yet, such a model is not available in the literature to date. Appropriate numerical models may lead to substantial improvements of arterial clamp designs, and thus are of potential interest for surgeons and clamp suppliers. In the past the demand for appropriate arterial clamps has led to a great variety of different designs and techniques. A suitable clamp design provides easy handling, good vessel grip and efficient vessel occlusion, and it is aimed to minimize arterial injuries. Clamps are named after their inventors as, for example, Blalock, Cooley, DeBakey, Fogarty, Potts, Satinsky, etc. They are available in different sizes with straight, curved or angled branches. Their jaws may be plain or have spikes, and they may be silicone filled. The existing designs are based on surgical intuition rather than on mechanical considerations. Consequently, the effects of clamping and the suitability of clamp designs have been investigated by means of experimental studies rather than by mechanical analyses. To the authors' knowledge, only ͓10͔ presented a mathematical approach with the goal to determine the minimum vascular occlusive force. However, this simplifying analytical model does not consider the crucial constitutive behavior of arterial walls. Thus, it is incapable of calculating wall stresses. Despite the clinical significance of arterial clamping there are relatively few studies, which are concerned with its local effects. Most of the experimental investigations are animal studies and focus on morphological changes. The observed injuries range from mild damage, which involves only the intima, to severe damage with total disruptions of the media, layer delaminations and even total wall disruptions with associated bleeding. In addition, long-term changes such as stenoses ͓11͔ and intimal hyperplasia-excessive thickening of the intima due to tissue growth ͓1͔-have been observed. Beside structural changes also functional changes of clamped arteries have been investigated, for example, the ability to relax or contract upon application of certain drugs ͓7,8͔ and the ability to inhibit blood clotting ͓12,13͔. The influences of the clamping force ͓2,6,8,9͔ and of the duration of clamping ͓14͔ have been studied. Moreover, comparisons of different types of arteries ͓2͔ and different clamp designs ͓3-7͔ in regard to clamp induced wall injury have been performed. These studies have identified the types and the consequences of clamp induced injuries and thus have demonstrated the importance of proper clamp designs. However, experimental studies are afflicted with a number of disadvantages. They are expensive and time-consuming and it is disputable if results of animal arteries are representative for human arteries. The significance of experimental studies is definitely restricted to the chosen arteries, instruments and clamping conditions. A fundamental shortcoming is that the results of existing experimental studies do not provide insights into the mechanical process of arterial clamping. The latter is determined by the three-dimensional stress-strain distributions in the clamped arterial wall. To overcome these shortcomings we developed a threedimensional finite element model for arterial clamping. The essential approach is to model the artery as a two-layer fiber-reinforced material with the fibers corresponding to the collagenous component of the material. The two layers represent the media ͑the middle layer of the artery͒ and the adventitia ͑the outer layer͒. Th

SNe 2013K and 2013am: observed and physical properties of two slow, normal Type IIP events

We present one year of optical and near-infrared photometry and spectroscopy of the Type IIP SNe 2013K and 2013am. Both objects are affected by significant extinction, due to their location in dusty regions of their respective host galaxies, ESO 009-10 and NGC 3623 (M65). From the photospheric to nebular phases, these objects display spectra congruent with those of underluminous Type IIP SNe (i.e. the archetypal SNe 1997D or 2005cs), showing low photospheric velocities (~2 X 10**3 km/s at 50d) together with features arising from Ba II which are particularly prominent in faint SNe IIP. The peak V-band magnitudes of SN 2013K (-15.6 mag) and SN 2013am (-16.2 mag) are fainter than standard-luminosity Type IIP SNe. The ejected Nickel masses are 0.012+-0.010 and 0.015+-0.006 Msol for SN 2013K and SN 2013am, respectively. The physical properties of the progenitors at the time of explosion are derived through hydrodynamical modelling. Fitting the bolometric curves, the expansion velocity and the temperature evolution, we infer total ejected masses of 12 and 11.5 Msol, pre-SN radii of ~460 and ~360 Rsol, and explosion energies of 0.34 foe and 0.40 foe for SN 2013K and SN 2013am. Late time spectra are used to estimate the progenitor masses from the strength of nebular emission lines, which turn out to be consistent with red supergiant progenitors of ~15 Msol. For both SNe, a low-energy explosion of a moderate-mass red supergiant star is therefore the favoured scenario.Comment: accepted for publication MNRA

SN 2015bh: NGC 2770’s 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?

Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, “SN impostors”, but the distinction is not always straightforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 yr that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN (or “main event”) had a precursor peaking ~40 days before maximum. The total energy release of the main event is ~1.8 × 1049 erg, consistent with a <0.5 M⊙ shell plunging into a dense CSM. The emission lines show a single narrow P Cygni profile during the LBV phase and a double P Cygni profile post maximum suggesting an association of the second component with the possible SN. Since 1994 the star has been redder than an LBV in an S-Dor-like outburst. SN 2015bh lies within a spiral arm of NGC 2770 next to several small star-forming regions with a metallicity of ~0.5 solar and a stellar population age of 7–10 Myr. SN 2015bh shares many similarities with SN 2009ip and may form a new class of objects that exhibit outbursts a few decades prior to a “hyper eruption” or final core-collapse. If the star survives this event it is undoubtedly altered, and we suggest that these “zombie stars” may evolve from an LBV to a Wolf-Rayet star over the timescale of only a few years. The final fate of these stars can only be determined with observations a decade or more after the SN-like event

Strangeness nuclear physics: a critical review on selected topics

Selected topics in strangeness nuclear physics are critically reviewed. This includes production, structure and weak decay of $\Lambda$--Hypernuclei, the $\bar K$ nuclear interaction and the possible existence of $\bar K$ bound states in nuclei. Perspectives for future studies on these issues are also outlined.Comment: 63 pages, 51 figures, accepted for publication on European Physical Journal

Spin-Momentum Correlations in Quasi-Elastic Electron Scattering from Deuterium

We report on a measurement of spin-momentum correlations in quasi-elastic scattering of longitudinally polarized electrons with an energy of 720 MeV from vector-polarized deuterium. The spin correlation parameter $A^V_{ed}$ was measured for the $^2 \vec{\rm H}(\vec e,e^\prime p)n$ reaction for missing momenta up to 350 MeV/$c$ at a four-momentum transfer squared of 0.21 (GeV/c)$^2$. The data give detailed information about the spin structure of the deuteron, and are in good agreement with the predictions of microscopic calculations based on realistic nucleon-nucleon potentials and including various spin-dependent reaction mechanism effects. The experiment demonstrates in a most direct manner the effects of the D-state in the deuteron ground-state wave function and shows the importance of isobar configurations for this reaction.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. for publicatio

On the diversity of superluminous supernovae: ejected mass as the dominant factor

We assemble a sample of 24 hydrogen-poor super-luminous supernovae (SLSNe). Parameterizing the light curve shape through rise and decline timescales shows that the two are highly correlated. Magnetar-powered models can reproduce the correlation, with the diversity in rise and decline rates driven by the diffusion timescale. Circumstellar interaction models can exhibit a similar rise-decline relation, but only for a narrow range of densities, which may be problematic for these models. We find that SLSNe are approximately 3.5 magnitudes brighter and have light curves 3 times broader than SNe Ibc, but that the intrinsic shapes are similar. There are a number of SLSNe with particularly broad light curves, possibly indicating two progenitor channels, but statistical tests do not cleanly separate two populations. The general spectral evolution is also presented. Velocities measured from Fe II are similar for SLSNe and SNe Ibc, suggesting that diffusion time differences are dominated by mass or opacity. Flat velocity evolution in most SLSNe suggests a dense shell of ejecta. If opacities in SLSNe are similar to other SNe Ibc, the average ejected mass is higher by a factor 2-3. Assuming $\kappa=0.1\,$cm$^2\,$g$^{-1}$, we estimate a mean (median) SLSN ejecta mass of 10$\,$M$_\odot$ (6$\,$M$_\odot$), with a range of 3-30$\,$M$_\odot$. Doubling the assumed opacity brings the masses closer to normal SNe Ibc, but with a high-mass tail. The most probable mechanism for generating SLSNe seems to be the core-collapse of a very massive hydrogen-poor star, forming a millisecond magnetar.Comment: 28 pages, 22 figs, 4 tables -- Updated on 2016-01-13 to fix typo in Table

Interacting supernovae and supernova impostors. LSQ13zm: an outburst heralds the death of a massive star

We report photometric and spectroscopic observations of the optical transient LSQ13zm. Historical data reveal the presence of an eruptive episode (that we label as ‘2013a’) followed by a much brighter outburst (‘2013b’) three weeks later, that we argue to be the genuine supernova explosion. This sequence of events closely resemble those observed for SN 2010mc and (in 2012) SN 2009ip. The absolute magnitude reached by LSQ13zm during 2013a (MR = ?14.87 ± 0.25?mag) is comparable with those of supernova impostors, while that of the 2013b event (MR = ?18.46 ± 0.21?mag) is consistent with those of interacting supernovae. Our spectra reveal the presence of a dense and structured circumstellar medium, probably produced through numerous pre-supernova mass-loss events. In addition, we find evidence for high-velocity ejecta, with a fraction of gas expelled at more than 20 000?km s?1. The spectra of LSQ13zm show remarkable similarity with those of well-studied core-collapse supernovae. From the analysis of the available photometric and spectroscopic data, we conclude that we first observed the last event of an eruptive sequence from a massive star, likely a Luminous Blue Variable, which a short time later exploded as a core-collapse supernova. The detailed analysis of archival images suggest that the host galaxy is a star-forming Blue Dwarf Compact Galaxy