The QUEST-La Silla AGN Variability Survey

We present the characterization and initial results from the QUEST-La Silla AGN variability survey. This is an effort to obtain well sampled optical light curves in extragalactic fields with unique multi-wavelength observations. We present photometry obtained from 2010 to 2012 in the XMM-COSMOS field, which was observed over 150 nights using the QUEST camera on the ESO-Schmidt telescope. The survey uses a broadband filter, the $Q$-band, similar to the union of the $g$ and the $r$ filters, achieving an intrinsic photometric dispersion of $0.05$ mag, and a systematic error of $0.05$ mag in the zero-point. Since some detectors of the camera show significant non-linearity, we use a linear correlation to fit the zero-points as a function of the instrumental magnitudes, thus obtaining a good correction to the non-linear behavior of these detectors. We obtain good photometry to an equivalent limiting magnitude of $r\sim 20.5$. Studying the optical variability of X-ray detected sources in the XMM-COSMOS field, we find that the survey is $\sim75-80$% complete to magnitudes $r\sim20$, and $\sim67$% complete to a magnitude $r\sim21$. The determination and parameterization of the structure function (${SF}_{norm}(\tau) = A \tau^{\gamma}$) of the variable sources shows that most BL AGN are characterized by $A > 0.1$ and $\gamma > 0.025$. It is further shown that variable NL AGN and GAL sources occupying the same parameter space in $A$ and $\gamma$ are very likely to correspond to obscured or low luminosity AGN. Our samples are, however, small, and we expect to revisit these results using larger samples with longer light curves obtained as part of our ongoing survey.Comment: Accepted for publication in Ap

A possible surviving companion of the SN Ia in the Galactic SNR G272.2-3.2

We use the {\it Gaia} EDR3 to explore the Galactic supernova remnant SNR G272.2-3.2, produced by the explosion of a Type Ia supernova (SNIa), about 7,500 years ago, to search for a surviving companion. From the abundances in the SNR ejecta, G272.2-3.2 is a normal SN Ia. The {\it Gaia} parallaxes allow to select the stars located within the estimated distance range of the SNR, and the {\it Gaia} proper motions to study their kinematics. From the {\it Gaia} EDR3 photometry, we construct the HR diagram of the selected sample, which we compare with the theoretical predictions for the evolution of possible star companions of SNIa. We can discard several proposed types of companions by combining kinematics and photometry. We can also discard hypervelocity stars. We focus our study on the kinematically most peculiar star, {\it Gaia} EDR3 5323900215411075328 (hereafter MV-G272), a 8.9 $\sigma$ outlier in proper motion. It is of M1-M2 stellar type. Its trajectory on the sky locates it at the center of the SNR, 6,000--8,000 years ago, a unique characteristic among the the sample. Spectra allow a stellar parameters determination and a chemical abundance analysis. In conclusion, we have a candidate to be the surviving companion of the SN Ia that resulted in SNR G272.2-3.2. It is supported by its kinematical characteristics and its trajectory within the SNR. This opens the possibility of a single-degenerate scenario for a SN Ia with an M-type dwarf companion.Comment: 35 pages, 19 Figures, 5 Tables, published as ApJ 947, 90

SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features

We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d ≈ 16.2 Mpc) starting 10 hr after explosion and continuing for ~300 days. SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRT–discovered X-ray emission (L_x ≈ 10⁴¹ erg s⁻¹ at 3 days; L_x ∝ t⁻³), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v ≈ 500 km s⁻¹) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r (0.1–1) × 10¹⁷ cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of t_r = 13.4 ± 0.210 days and a peak B-band magnitude of M_B = −15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) × 10⁻² M_⊙ of ⁵⁶Ni and ejected M_(ej) = (0.72 ± 0.040) M⊙ total with a kinetic energy E_k = (1.8 ± 0.10) × 10⁵⁰ erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (~10 M_⊙) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries

Signatures of circumstellar interaction in the Type IIL supernova ASASSN-15oz

Hydrogen-rich, core-collapse supernovae are typically divided into four classes: IIP, IIL, IIn, and IIb. Recent hydrodynamic modelling shows that circumstellar material is required to produce the early light curves of most IIP/IIL supernovae. In this scenario, IIL supernovae experience large amounts of mass-loss before exploding. We test this hypothesis on ASASSN-15oz, a Type IIL supernova. With extensive follow-up in the X-ray, UV, optical, IR, and radio, we present our search for signs of interaction and the mass-loss history indicated by their detection. We find evidence of short-lived intense mass-loss just prior to explosion from light-curve modelling, amounting in 1.5 M-circle dot of material within 1800 R-circle dot of the progenitor. We also detect the supernova in the radio, indicating mass-loss rates of 10(-6) to 10(-7) M-circle dot yr(-1) prior to the extreme mass-loss period. Our failure to detect the supernova in the X-ray and the lack of narrow emission lines in the UV, optical, and NIR do not contradict this picture and place an upper limit on the mass-loss rate outside the extreme period of <10(-4) M-circle dot yr(-1). This paper highlights the importance gathering comprehensive data on more Type II supernovae to enable detailed modelling of the progenitor and supernova which can elucidate their mass-loss histories and envelope structures and thus inform stellar evolution models

Weak mass loss from the Red Supergiant progenitor of the type II SN 2021yja

We present high-cadence optical, ultraviolet (UV), and near-infrared data of the nearby (D ≈ 23 Mpc) Type II supernova (SN) 2021yja. Many Type II SNe show signs of interaction with circumstellar material (CSM) during the first few days after explosion, implying that their red supergiant (RSG) progenitors experience episodic or eruptive mass loss. However, because it is difficult to discover SNe early, the diversity of CSM configurations in RSGs has not been fully mapped. SN 2021yja, first detected within ≈ 5.4 hours of explosion, shows some signatures of CSM interaction (high UV luminosity and radio and x-ray emission) but without the narrow emission lines or early light-curve peak that can accompany CSM. Here we analyze the densely sampled early light curve and spectral series of this nearby SN to infer the properties of its progenitor and CSM. We find that the most likely progenitor was an RSG with an extended envelope, encompassed by low-density CSM. We also present archival Hubble Space Telescope imaging of the host galaxy of SN 2021yja, which allows us to place a stringent upper limit of ≲ 9 M ☉ on the progenitor mass. However, this is in tension with some aspects of the SN evolution, which point to a more massive progenitor. Our analysis highlights the need to consider progenitor structure when making inferences about CSM properties, and that a comprehensive view of CSM tracers should be made to give a fuller view of the last years of RSG evolution

Photometric and Spectroscopic Properties of Type Ia Supernova 2018oh with Early Excess Emission from the Kepler 2 Observations

Supernova (SN) 2018oh (ASASSN-18bt) is the first spectroscopically confirmed Type Ia supernova (SN Ia) observed in the Kepler field. The Kepler data revealed an excess emission in its early light curve, allowing us to place interesting constraints on its progenitor system. Here we present extensive optical, ultraviolet, and near-infrared photometry, as well as dense sampling of optical spectra, for this object. SN 2018oh is relatively normal in its photometric evolution, with a rise time of 18.3 ± 0.3 days and Δm 15(B) = 0.96 ± 0.03 mag, but it seems to have bluer B − V colors. We construct the "UVOIR" bolometric light curve having a peak luminosity of 1.49 × 1043 erg s−1, from which we derive a nickel mass as 0.55 ± 0.04 M ⊙ by fitting radiation diffusion models powered by centrally located 56Ni. Note that the moment when nickel-powered luminosity starts to emerge is +3.85 days after the first light in the Kepler data, suggesting other origins of the early-time emission, e.g., mixing of 56Ni to outer layers of the ejecta or interaction between the ejecta and nearby circumstellar material or a nondegenerate companion star. The spectral evolution of SN 2018oh is similar to that of a normal SN Ia but is characterized by prominent and persistent carbon absorption features. The C ii features can be detected from the early phases to about 3 weeks after the maximum light, representing the latest detection of carbon ever recorded in an SN Ia. This indicates that a considerable amount of unburned carbon exists in the ejecta of SN 2018oh and may mix into deeper layers

Utilization of synthetic NLS-sequences for nonviral gene delivery into human tumors

Titelseite und Inhalt Abkürzungen Zusammenfassung Abstract 1\. Einleitung 12 2\. Ergebnisse 51 3\. Material und Methoden 32 4\. Diskussion 99 Literaturverzeichnis 132 DanksagungDer Transfer von exogener DNA in den Zellkern ist ein ineffizienter Prozess und gilt als wesentlichen limitierenden Faktor für nicht-virale Gentransfersysteme. Eine Strategie besteht in der Verwendung von peptidischen Kernlokalisationssignalen (NLS), um durch Nutzung von zellulären Transportmechanismen den Kernimport von Plasmid-DNA zu erleichtern. Inhalt der vorliegenden Arbeit ist die Rolle von synthetischen NLS-Peptiden in DNA- Komplexen während des Transfektionsvorgangs. Dazu wurden unterschiedliche Peptide konstruiert, die jeweils eine NLS-Sequenz viralen Ursprungs enthalten und zusätzlich an einer Oligolysin-DNA-Bindungsdomäne fusioniert sind. Die resultierenden Peptid/DNA-Komplexe wurden in in vitro-Tranfektionsversuchen mit humanen Tumorzellen eingesetzt und führten zu einer NLS- sequenzspezifischen 1.5-2.5-fachen Erhöhung der Reportergenexpression. Die Transfektionseffizienz hing sowohl von der NLS-Sequenz als auch von dem eingesetzten Peptid/DNA-Ladungsverhältnis ab. Um ein besseres Verständnis über den Transfektionsvorgang zu erlangen, wurden die physikochemischen Eigenschaften der Peptid/DNA-Komplexe näher untersucht und mit der Transfektionseffizienz verglichen. Die NLS-Sequenz hatte einen Einfluss auf den Kondensierungsgrad der DNA, das Zeta-Potential und das Aggregationsverhalten der resultierenden Komplexe. Mit HCT 116-Zellen wurde die Transfektionseffizienz im wesentlichen von der Größe und Kompaktheit der Komplexe bestimmt. Transmissionelektronenmikroskopische Untersuchungen von transfizierten Zellen zeigten zudem die Internalisierung von Mikrometer-großen Aggregaten und bestätigten das Ergebnis der physikochemischen Untersuchung. Somit wurde ein unspezifischer, aber sequenzabhängiger Effekt des NLS-Peptids auf den Gentransferprozess nachgewiesen. Eine nähere Analyse der Daten deuten auf unspezifische Wechselwirkungen innerhalb des Komplexes aufgrund der Aminosäurenzusammensetzung des Peptids. Auswirkungen dieses Ergebnisses auf den Optimierungsprozess von nicht-viralen Multikomponentensysteme wurden diskutiert. Insbesondere bedeutete die Aggregation eine weitere Hürde für eine in vivo-Applikation des Systems im Hinblick einer gentherapeutischen Anwendung. Die kolloidale Stabilisierung von DNA-Komplexen war daher ein weiterer Schwerpunkt dieser Arbeit. Aufbauend auf jüngste Entwicklungen im Bereich der Nanobiotechnologie wurde versucht, eine Beschichtungstechnik aufbauend auf die schrittweise Adsorption von entgegengesetzt geladenen Polyelektrolyten zur elektrostatischen Stabilisierung der DNA-Komplexe anzuwenden. Als Modellsystem wurde zunächst mit Polyethylenimin- vorkondensierte Plasmid-DNA unter salzfreien Bedingungen mit den synthetischen Polyanionen Polyvinylsulfat (PVS) bzw. Polystyrensulfonat (PSS) kombiniert. Als Ergebnis wurden erstmals stark negativ geladene DNA-Nanopartikel generiert, die unter physiologischen Salzbedingungen kolloidal stabil waren. Darüber hinaus führte die direkte Injektion der Partikel in Transplantationstumore von Nude-Mäusen zu relativ hohen Reportergenexpressionen ohne Anzeichen auf Toxizität. Dieses Ergebnis ist daher ein wichtiger Schritt in der Entwicklung von nicht-viralen Gentransfersystemen zu Virus-ähnlichen Partikeln. Im nächsten Schritt wurden NLS-Peptide eingebaut. Mit dem PVS wurden etwa 100 nm-große, kolloidal stabile Partikel generiert, die in Abhängigkeit des Peptids und des eingesetzten Ladungsverhältnisses ein Zeta-Potential von - 42 mV bis - 62 mV aufwiesen. In vitro-Transfektionsversuche zeigten mit diesen Nanopartikeln keine messbare Reportergenexpression, was mit anderen publizierten Untersuchungen mit negativ geladenen Komplexen übereinstimmt. Da eine in vivo-Applikation den Einbau von zusätzlichen funktionellen Komponenten voraussetzt, wurde danach der Bildungsmechanismus der Nanopartikel durch physiko-chemische und morphologische Untersuchungen näher charakterisiert. Als Ergebnis wurde festgestellt, daß das PVS den Peptid/DNA-Komplex durchdrang und entgegen dem ursprünglichen Modell zur Generierung von durchmischten Partikeln führte. Ein weiteres wichtiges Resultat war die starke beobachtete Empfindlichkeit der DNA-Nanopartikel gegenüber Schwankungen der Salzkonzentration. Dies wurde auf den besonderen Einfluss der Ionenstärke sowohl auf elektrostatische Wechselwirkungen zwischen den Polyelektrolyten als auch auf die Flexibilität der DNA zurückgeführt. Als Folge wurde schließlich das Herstellungsverfahren auf physiologische Salzbedingungen angepasst. Dies gelang mit dem PSS als Polyanion durch eine drastische Erhöhung des Peptid/DNA-Ladungsverhältnisses von 3.0 auf 20 und eine zusätzliche Erhöhung des Polyanion/DNA- Gewichtsverhältnisses von 1.2 auf 50. Darüber hinaus deuten die Ergebnisse auf einem strukturierten Aufbau der Partikel bestehend aus einem Peptid/DNA-Kern, der von einer negativ geladenen PSS-Hülle umgeben ist. Somit wurde eine für die Entwicklung mehrschichtiger Virus-ähnlicher Nanopartikel für den in vivo- Gentransfer wichtige Grundlage geschaffen.The transfer of exogenous DNA into the nucleus is an inefficient process and is considered as a major limiting step for the nonviral gene delivery. One of the strategies to improve nuclear uptake of DNA is taking advantage of the cellular nuclear import machinerie by coupling a peptide bearing a nuclear localization signal (NLS) to the DNA. The aim of the present work is to analyse the role of synthetic NLS-peptides non covalently bound to DNA- complexes during the transfection process. Peptides containing a virus derived NLS-sequence fused to an oligolysin-DNA-bindung domain were designed. Subsequently, peptide/DNA-complexes were generated and used to transfect human tumor cells in vitro. The result showed a 1.5 to 2.5-fold NLS-sequence specific increase of reporter gene expression. The transfection efficiency was related both to the used NLS-sequence and the employed peptide to DNA charge ratio. In order to gain an insight into the transfection process the physicochemical properties of peptide/DNA-complexes were examined and compared to the transfection efficiency. As a result, the NLS-sequence was shown to influence the DNA condensation rate, the Zeta-potential as well as the aggregation behavior of the resulting DNA-complexes. The transfection efficiency was mainly determined by the size and the compaction rate of the complexes. Moreover, transmission electron microscopy observations showed the effective internalization of micrometer-sized aggregates, thus confirming the physicochemial study. Therefore, this result demonstrates an unspecific effect of the NLS-peptide on the gene transfer process. However, this effect strongly depended on the particular NLS-sequence. A more thorough analysis of the data was performed and suggests the occurence of unspecific interactions within the DNA-complex due to the particular amino acid composition of the peptide. This has strong implications for the optimization of nonviral multicomponent systems which was also discussed. In particular, the aggregation tendency represents an additional hurdle for the in vivo-application in the frame of human gene therapy. As a consequence, the ability to generate colloidal stable DNA-complexes became a major issue of the present work. A potential solution arose from recent advances in the field of nanobiotechnology. The layer-by- layer technique consists in the stepwise deposition of oppositely charged polyelectrolytes resulting in the formation of well defined multilayers systems. Therefore, the aim was to use this technique in order to achieve stabilization of DNA-complexes by electrostatic repulsion. As a model system, preformed polyethyleneimine/plasmid-DNA-complexes were combinded to the synthetic polyanions polyvinyl sulfate (PVS) or polystyrene sulfonate (PSS) under salt-free conditions. The results showed the generation of negatively charged DNA-nanoparticles which were colloidal stable in physiological salt conditions. Moreover, intratumoral injection of particles into transplantation tumors of nude mice resulted in relatively high reporter gene expression without apparent toxicity. Therefore, this result represents a significant advance in the development of DNA-containing nanoparticles for nonviral gene delivery. The following step was the incorporation of NLS-peptides. Using PVS as the polyanion, 100 nm-sized colloidal stable particles were generated. A Zeta-potential lying between - 42 mV and - 62 mV was measured depending on the incorporated peptide. Following in vitro-transfection, no significant reporter gene expression could be found. This is in agreement with other published studies using negatively charged particles. The in vivo delivery of the particles would require the incorporation of additional functional elements. Therefore, the nano-particle formation process was investigated using physicochemical and morphological approaches. The results showed a penetration of the PVS into the peptide/DNA-complex leading to the generation of scrambled interpolyelectrolyte complexes. This was in contradiction to the original model of a core-shell-structure of the particle. Additionally, the DNA- containing particles showed a strong sensitivity regarding variations in the salt concentration. This was attributed to the influence of the ionic strength to electrostatic interactions between the polyelectrolytes as well as to the flexibility of the DNA molecule. Consequently, the entire particle formation procedure was adapted to physiological salt conditions. Using PSS as the polyanion, this was achieved following a dramatic increase of the peptide to DNA charge ratio from 3.0 to 20 and the subsequent increase of the PSS to DNA weight ratio from 1.2 to 50. Moreover, these results suggest a structured assembly of the particle consisting in a peptide/DNA-core surrounded by a PSS- shell. As a consequence, this work may provide a basis for the development of multilayered virus-like particles for nonviral gene delivery

Experimental study of trace element partitioning between enstatite and melt in enstatite chondrites at low oxygen fugacities and 5 GPa

International audienceIn order to investigate the influence of very reducing conditions, we report enstatite-melt trace element partition coefficients (D) obtained on enstatite chondrite material at 5 GPa and under oxygen fugacities (fO2) ranging between 0.8 and 8.2 log units below the iron-wustite (IW) buffer. Experiments were conducted in a multianvil apparatus between 1580 and 1850 °C, using doped (Sc, V, REE, HFSE, U, Th) starting materials. We used a two-site lattice strain model and a Monte-Carlo-type approach to model experimentally determined partition coefficient data. The model can fit our partitioning data, i.e. trace elements repartition in enstatite, which provides evidence for the attainment of equilibrium in our experiments. The precision on the lattice strain model parameters obtained from modelling does not enable determination of the influence of intensive parameters on crystal chemical partitioning, within our range of conditions (fO2, P, T, composition). We document the effect of variable oxygen fugacity on the partitioning of multivalent elements. Cr and V, which are trivalent in the pyroxene at around IW − 1 are reduced to 2+ state with increasingly reducing conditions, thus affecting their partition coefficients. In our range of redox conditions Ti is always present as a mixture between 4+ and 3+ states. However the Ti3+-Ti4+ ratio increases strongly with increasingly reducing conditions. Moreover in highly reducing conditions, Nb and Ta, that usually are pentavalent in magmatic systems, appear to be reduced to lower valence species, which may be Nb2+ and Ta3+. We propose a new proxy for fO2 based on D(Cr)/D(V). Our new data extend the redox range covered by previous studies and allows this proxy to be used in the whole range of redox conditions of the solar system objects. We selected trace-element literature data of six chondrules on the criterion of their equilibrium. Applying the proxy to opx-matrix systems, we estimated that three type I chondrules have equilibrated at IW − 7 ± 1, one type I chondrule at IW − 4 ± 1, and two type II chondrules at IW + 3 ± 1. This first accurate estimation of enstatite-melt fO2 for type I chondrules is very close to CAI values