SN 2005 gj: evidence for LBV supernovae progenitors?

There is mounting observational evidence in favour of Luminous Blue Variables (LBVs) being the direct progenitors of supernovae. Here we present possibly the most convincing evidence yet for such progenitors. We find multiple absorption component P-Cygni profiles of hydrogen and helium in the spectrum of SN 2005gj, which we interpret as being an imprint of the progenitor's mass-loss history. Such profiles have previously only been detected in Luminous Blue Variables. This striking resemblance of the profiles, along with wind velocities and periods consistent with those of LBVs leads us to connect SN 2005gj to an LBV progenitor.

The death of massive stars - I. Observational constraints on the progenitors of Type II-P supernovae

We present the results of a 10.5-yr, volume-limited (28-Mpc) search for supernova (SN) progenitor stars. In doing so we compile all SNe discovered within this volume (132, of which 27 per cent are Type Ia) and determine the relative rates of each subtype from literature studies. The core-collapse SNe break down into 59 per cent II-P and 29 per cent Ib/c, with the remainder being IIb (5 per cent), IIn (4 per cent) and II-L (3 per cent). There have been 20 II-P SNe with high-quality optical or near-infrared pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies and SN environments (distance, metallicity and extinction) and determine masses and upper mass estimates for these 20 progenitor stars using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a Type II-P to form is m(min) = 8.5(-1.5)(+1) M-circle dot and the maximum mass for II-P progenitors is m(max) = 16.5 +/- 1.5 M-circle dot, assuming a Salpeter initial mass function holds for the progenitor population (in the range Gamma = -1.35(-0.7)(+0.3)). The minimum mass is consistent with current estimates for the upper limit to white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations in Local Group galaxies. Red supergiants in the Local Group have masses up to 25 M-circle dot and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30 M-circle dot. The reason we have not detected any high-mass red supergiant progenitors above 17 M-circle dot is unclear, but we estimate that it is statistically significant at 2.4 sigma confidence. Two simple reasons for this could be that we have systematically underestimated the progenitor masses due to dust extinction or that stars between 17-25 M-circle dot produce other kinds of SNe which are not II-P. We discuss these possibilities and find that neither provides a satisfactory solution. We term this discrepancy the 'red supergiant problem' and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. We compare the Ni-56 masses ejected in the SNe to the progenitor mass estimates and find that low-luminosity SNe with low Ni-56 production are most likely to arise from explosions of low-mass progenitors near the mass threshold that can produce a core-collapse.

The Disappearance of the Progenitors of Supernovae 1993J and 2003gd

Using images from the Hubble Space Telescope and the Gemini Telescope, we confirmed the disappearance of the progenitors of two type II supernovae (SNe) and evaluated the presence of other stars associated with them. We found that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed at the SN location and determined its intrinsic brightness using image subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is also no longer present, but its B-supergiant binary companion is still observed. The disappearance of the progenitors confirms that these two supernovae were produced by red supergiants.

On the nature of the progenitors of three Type II-P supernovae: 2004et, 2006my and 2006ov

The pre-explosion observations of the Type II-P supernovae 2006my, 2006ov and 2004et are re-analysed. In the cases of supernovae 2006my and 2006ov we argue that the published candidate progenitors are not coincident with their respective supernova sites in pre-explosion Hubble Space Telescope observations. We therefore derive upper luminosity and mass limits for the unseen progenitors of both these supernovae, assuming they are red supergiants: 2006my (log L/L-circle dot = 4.51; m

Progenitors of Core-Collapse Supernovae

Knowledge of the progenitors of core-collapse supernovae is a fundamental component in understanding the explosions. The recent progress in finding such stars is reviewed. The minimum initial mass that can produce a supernova (SN) has converged to 8 +/- 1 M-circle dot from direct detections of red supergiant progenitors of II-P SNe and the most massive white dwarf progenitors, although this value is model dependent. It appears that most type Ibc SNe arise from moderate mass interacting binaries. The highly energetic, broad-lined Ic SNe are likely produced by massive, Wolf-Rayet progenitors. There is some evidence to suggest that the majority of massive stars above similar to 20 M-circle dot may collapse quietly to black holes and that the explosions remain undetected. The recent discovery of a class of ultrabright type H SNe and the direct detection of some progenitor stars bearing luminous blue variable characteristics suggest some very massive stars do produce highly energetic explosions. The physical mechanism is under debate, and these SNe pose a challenge to stellar evolutionary theory.

Endothelial Progenitors as Tools to Study Vascular Disease

Endothelial progenitor cells (EPCs) have great clinical value because they can be used as diagnostic biomarkers and as a cellular therapy for promoting vascular repair of ischaemic tissues. However, EPCs also have an additional research value in vascular disease modelling to interrogate human disease mechanisms. The term EPC is used to describe a diverse variety of cells, and we have identified a specific EPC subtype called outgrowth endothelial cell (OEC) as the best candidate for vascular disease modelling because of its high-proliferative potential and unambiguous endothelial commitment. OECs are isolated from human blood and can be exposed to pathologic conditions (forward approach) or be isolated from patients (reverse approach) in order to study vascular human disease. The use of OECs for modelling vascular disease will contribute greatly to improving our understanding of endothelial pathogenesis, which will potentially lead to the discovery of novel therapeutic strategies for vascular diseases.

Sca-1+ progenitors derived from embryonic stem cells differentiate into endothelial cells capable of vascular repair after arterial injury

Embryonic stem cells possess the ability to differentiate into endothelium. The ability to produce large volumes of endothelium from embryonic stem cells could provide a potential therapeutic modality for vascular injury. We describe an approach that selects endothelial cells using magnetic beads that may be used therapeutically to treat arterial injury.

Activation of the ACE2/Angiotensin-(1-7)/Mas Receptor Axis Enhances the Reparative Function of Dysfunctional Diabetic Endothelial Progenitors

We tested the hypothesis that activation of the protective arm of the renin angiotensin system, the angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7) [Ang-(1-7)]/Mas receptor axis, corrects the vasoreparative dysfunction typically seen in the CD34(+) cells isolated from diabetic individuals. Peripheral blood CD34(+) cells from patients with diabetes were compared with those of nondiabetic controls. Ang-(1-7) restored impaired migration and nitric oxide bioavailability/cGMP in response to stromal cell-derived factor and resulted in a decrease in NADPH oxidase activity. The survival and proliferation of CD34(+) cells from diabetic individuals were enhanced by Ang-(1-7) in a Mas/phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner. ACE2 expression was lower, and ACE2 activators xanthenone and diminazine aceturate were less effective in inducing the migration in cells from patients with diabetes compared with controls. Ang-(1-7) overexpression by lentiviral gene modification restored both the in vitro vasoreparative functions of diabetic cells and the in vivo homing efficiency to areas of ischemia. A cohort of patients who remained free of microvascular complications despite having a history of longstanding inadequate glycemic control had higher expression of ACE2/Mas mRNA than patients with diabetes with microvascular complications matched for age, sex, and glycemic control. Thus, ACE2/Ang-(1-7)\Mas pathway activation corrects existing diabetes-induced CD34(+) cell dysfunction and also confers protection from development of this dysfunction.

Induction of signalling in non-erythroid cells by pharmacological levels of erythropoietin

Erythropoiesis is maintained by the hormone erythropoietin (Epo) binding to its cognate receptor (EpoR) on erythroid progenitor cells. The Epo-EpoR interaction initiates a signal transduction process that regulates the survival, growth and differentiation of these cells. Originally perceived as highly lineage-restricted, Epo is now recognised to have pleiotropic effects extending beyond the maintenance of red cell mass. Functional interactions between Epo and EpoR have been demonstrated in numerous cells and tissues. EpoR expression on neoplastic cells leads to concern that recombinant human erythropoietin, used to treat anaemia in cancer patients, may augment tumour growth. Here we demonstrate that EPO, at pharmacological concentrations, can activate three major signalling cascades, viz. the Jak2/STAT5, Ras/ERK and PI3K/Akt pathways in non-small cell lung carcinoma (NSCLC) cell lines. EpoR synthesis is normally under the control of GATA-1, but NSCLC cells exhibit decreased GATA-1 levels compared to GATA-2, -3 and -6, suggesting that GATA-1 is not essential for EpoR production. The increased Epo-induced signalling was not associated with a growth advantage for the NSCLC cells.

A review of patents relating to therapeutic angiogenesis using endothelial progenitors and other vasculogenesis-related cell types

Stem and progenitor cells have generated considerable scientific and commercial interest in recent years due to their potential for novel cell therapy for a variety of medical conditions. A highly active research area in the field of regenerative medicine is vascular biology. Blood vessel repair and angiogenesis are key processes with endothelial progenitor cells (EPCs) playing a central role. Clinical trials for ischemic conditions, such as myocardial infarction and peripheral arterial disease, have suggested cell therapies to be feasible, safe, and potentially beneficial. Development of efficient methodologies to deliver EPC-based cytotherapies offers new hope for millions of patients with ischemic conditions. Evidence indicates that EPCs, depending on the subtype, mediate angiogenesis through different mechanisms. Differentiation into endothelium and complete integration into damaged vasculature was the first EPC mechanism to be proposed. However, many studies have demonstrated that vasoregulatory paracrine factor secretion by transplanted cells is also important. Many EPC subsets enhance angiogenesis and promote tissue repair by cytokine release without incorporating into the damaged vasculature. Whatever the mechanism, vascular repair and therapeutic angiogenesis using EPCs represent a realistic treatment option and also provides many commercialization opportunities. This review discusses recent advances in the EPC field whilst recounting relevant patents.

Possible binary progenitors for the Type Ib supernova iPTF13bvn

Cao et al. reported a possible progenitor detection for the Type Ib supernovae iPTF13bvn for the first time. We find that the progenitor is in fact brighter than the magnitudes previously reported by approximately 0.7-0.2 mag with a larger error in the bluer filters. We compare our new magnitudes to our large set of binary evolution models and find that many binary models with initial masses in the range of 10-20M(circle dot) match this new photometry and other constraints suggested from analysing the supernova. In addition, these lower mass stars retain more helium at the end of the model evolution indicating that they are likely to be observed as Type Ib supernovae rather than their more massive, Wolf-Rayet counter parts. We are able to rule out typical Wolf-Rayet models as the progenitor because their ejecta masses are too high and they do not fit the observed SED unless they have a massive companion which is the observed source at the supernova location. Therefore only late-time observations of the location will truly confirm if the progenitor was a helium giant and not a Wolf-Rayet star.

Detecting the progenitors of core collapse supernovae

The masses and the evolutionary states of the progenitors of core-collapse supernovae are not well constrained by direct observations. Stellar evolution theory generally predicts that massive stars with initial masses less than about 30M_sol should undergo core-collapse when they are cool M-type supergiants. However the only two detections of a SN progenitor before explosion are SN1987A and SN1993J, and neither of these was an M-type supergiant. Attempting to identify the progenitors of supernovae is a difficult task, as precisely predicting the time of explosion of a massive star is impossible for obvious reasons. There are several different types of supernovae which have different spectral and photometric evolution, and how exactly these are related to the evolutionary states of the progenitor stars is not currently known. I will describe a novel project which may allow the direct identification of core-collapse supernovae progenitors on pre-explosion images of resolved, nearby galaxies. This project is now possible with the excellent image archives maintained by several facilities and will be enhanced by the new initiatives to create Virtual Observatories, the earliest of which ASTROVIRTEL is already producing results.

Observational Constraints on the Progenitors of Core-Collapse Supernovae: The Case for Missing High-Mass Stars

Over the last 15 years, the supernova community has endeavoured to directly identify progenitor stars for core-collapse supernovae discovered in nearby galaxies. These precursors are often visible as resolved stars in high-resolution images from space-and ground-based telescopes. The discovery rate of progenitor stars is limited by the local supernova rate and the availability and depth of archive images of galaxies, with 18 detections of precursor objects and 27 upper limits. This review compiles these results (from 1999 to 2013) in a distance-limited sample and discusses the implications of the findings. The vast majority of the detections of progenitor stars are of type II-P, II-L, or IIb with one type Ib progenitor system detected and many more upper limits for progenitors of Ibc supernovae (14 in all). The data for these 45 supernovae progenitors illustrate a remarkable deficit of high-luminosity stars above an apparent limit of log L/L-circle dot similar or equal to 5.1 dex. For a typical Salpeter initial mass function, one would expect to have found 13 high-luminosity and high-mass progenitors by now. There is, possibly, only one object in this time-and volume-limited sample that is unambiguously high-mass (the progenitor of SN2009ip) although the nature of that supernovae is still debated. The possible biases due to the influence of circumstellar dust, the luminosity analysis, and sample selection methods are reviewed. It does not appear likely that these can explain the missing high-mass progenitor stars. This review concludes that the community's work to date shows that the observed populations of supernovae in the local Universe are not, on the whole, produced by high-mass (M greater than or similar to 18 M-circle dot) stars. Theoretical explosions of model stars also predict that black hole formation and failed supernovae tend to occur above an initial mass of M similar or equal to 18 M-circle dot. The models also suggest there is no simple single mass division for neutron star or black-hole formation and that there are islands of explodability for stars in the 8-120 M-circle dot range. The observational constraints are quite consistent with the bulk of stars above M similar or equal to 18 M-circle dot collapsing to form black holes with no visible supernovae.