Isotopic enrichment of planetary systems from Asymptotic Giant Branch stars

Short-lived radioisotopes, in particular 26-Al and 60-Fe, are thought to contribute to the internal heating of the Earth, but are significantly more abundant in the Solar System compared to the Interstellar Medium. The presence of their decay products in the oldest Solar System objects argues for their inclusion in the Sun's protoplanetary disc almost immediately after the star formation event that formed the Sun. Various scenarios have been proposed for their delivery to the Solar System, usually involving one or more core-collapse supernovae of massive stars. An alternative scenario involves the young Sun encountering an evolved Asymptotic Giant Branch (AGB) star. AGBs were previously discounted as a viable enrichment scenario for the Solar System due to the presumed low probability of an encounter between an old, evolved star and a young pre-main sequence star. We report the discovery in Gaia data of an interloping AGB star in the star-forming region NGC2264, demonstrating that old, evolved stars can encounter young forming planetary systems. We use simulations to calculate the yields of 26-Al and 60-Fe from AGBs and their contribution to the long-term geophysical heating of a planet, and find that these are comfortably within the range previously calculated for the Solar System.Comment: 8 pages, 4 figures, accepted for publication in ApJ

Runaway and walkaway stars from the ONC with Gaia DR2

Theory predicts that we should find fast, ejected (runaway) stars of all masses around dense, young star-forming regions. $N$-body simulations show that the number and distribution of these ejected stars could be used to constrain the initial spatial and kinematic substructure of the regions. We search for runaway and slower walkaway stars within 100 pc of the Orion Nebula Cluster (ONC) using $Gaia$ DR2 astrometry and photometry. We compare our findings to predictions for the number and velocity distributions of runaway stars from simulations that we run for 4 Myr with initial conditions tailored to the ONC. In $Gaia$ DR2, we find 31 runaway and 54 walkaway candidates based on proper motion, but not all of these are viable candidates in three dimensions. About 40 per cent are missing radial velocities, but we can trace back 9 3D-runaways and 24 3D-walkaways to the ONC, all of which are low/intermediate-mass (<8 M$_{\odot}$). Our simulations show that the number of runaways within 100 pc decreases the older a region is (as they quickly travel beyond this boundary), whereas the number of walkaways increases up to 3 Myr. We find fewer walkaways in $Gaia$ DR2 than the maximum suggested from our simulations, which may be due to observational incompleteness. However, the number of $Gaia$ DR2 runaways agrees with the number from our simulations during an age of $\sim$1.3-2.4 Myr, allowing us to confirm existing age estimates for the ONC (and potentially other star-forming regions) using runaway stars.Comment: 19 pages, 7 figures, accepted for publication in MNRA

Using ejected stars to constrain the initial conditions of young star-forming regions

Star-forming regions have fascinated observers for many centuries. These regions are the locations where most stars form and are considered to be a fundamental unit of star formation. However, what we observe of these regions now is not necessarily how they formed as dynamical evolution can quickly change the initial density, spatial and kinematic substructure. Knowledge about these initial conditions is essential to be able to constrain star formation theories. Star-forming regions and their likely initial conditions have been studied in the past with different methods, all of which focused on stars that are considered to still be members. In this thesis, I investigate if we can use ejected stars that are often found on the outskirts of young star-forming regions to infer their initial properties. These stars are commonly known as runaway stars, having “run away” from their birth region. These fast-moving stars have been studied since their discovery in the 1940s using simulations and observations. With improvements in computing capabilities, simulations have made huge advances in the past 50 years, allowing us to make our models of the formation and evolution of these star-forming regions increasingly realistic. For many decades, runaway star observations were limited to bright massive stars, but this changed with the launch of the Gaia telescope. This mission has already provided accurate measurements of the positions and velocities for over 1.5 billion stars in our Galaxy. With this data, discoveries of countless new runaways have been made and we now know that they occur across all stellar masses. In this work, I use a combination of simulations and Gaia observations and show that ejected stars can be used to constrain the initial conditions of the ONC and NGC 2264. Both regions appear to have formed from high stellar density, substructured and subvirial initial conditions

Impact of an Interleukin-1 Receptor Antagonist and Erythropoietin on Experimental Myocardial Ischemia/Reperfusion Injury

Background. Revascularization of infarcted myocardium results in release of inflammatory cytokines mediating myocardial reperfusion injury and heart failure. Blockage of inflammatory pathways dampens myocardial injury and reduces infarct size. We compared the impact of the interleukin-1 receptor antagonist Anakinra and erythropoietin on myocardial ischemia/reperfusion injury. In contrast to others, we hypothesized that drug administration prior to reperfusion reduces myocardial damage. Methods and Results. 12–15 week-old Lewis rats were subjected to myocardial ischemia by a 1 hr occlusion of the left anterior descending coronary artery. After 15 min of ischemia, a single shot of Anakinra (2 mg/kg body weight (bw)) or erythropoietin (5000 IE/kg bw) was administered intravenously. In contrast to erythropoietin, Anakinra decreased infarct size (P < 0.05, N = 4/group) and troponin T levels (P < 0.05, N = 4/group). Conclusion. One-time intravenous administration of Anakinra prior to myocardial reperfusion reduces infarct size in experimental ischemia/reperfusion injury. Thus, Anakinra may represent a treatment option in myocardial infarction prior to revascularization

Coronary Artery Bypass Grafting in Patients with Acute Myocardial Infarction and Cardiogenic Shock

Objective: Acute myocardial infarction (AMI) complicated by cardiogenic shock (CS) remains associated with a high rate of mortality and disabling morbidity. Coronary artery bypass grafting (CABG) is seldom considered in this setting due to the fear of peri-operative complications. Here, we analysed the outcome of CS patients undergoing CABG within 48 hours after diagnosed with AMI. Methods: A single-center, retrospective data analysis was performed in 220 AMI patients with CS that underwent CABG within 48 hours between 01/2001 and 01/2018. Results: 141 patients were diagnosed with ST-elevation myocardial infarction (STEMI), 79 with non-STEMI (NSTEMI). Median age was 67 (60; 72) for STEMI, and 68 (60.8; 75.0) years for NSTEMI patients (p = 0.190). 52.5% of STEMI patients and 39.2% of NSTEMI patients had suffered from cardiac arrest (CA) pre-operatively (p = 0.049). Coronary 3-vessel disease was present in most patients (78.0% STEMI vs 83.5% NSTEMI; p = 0.381). Percutaneous coronary interventions (PCI) were performed in 32.6% STEMI and 27.8% NSTEMI patients (p = 0.543) prior to surgery. Time from diagnosis to surgery was shorter in STEMI patients (3.92 (2.67; 5.98) vs 7.50 (4.78; 16.74) hours; p < 0.001). A complete revascularization was achieved in 82.3% of STEMI and 73.4% of NSTEMI cases (p = 0.116). Post-operative low cardiac output occurred in 14.2% of STEMI vs 8.9% of NSTEMI patients (p = 0.289). The rate of cerebrovascular injury–including hypoxic brain damage was 12.1% for STEMI and 10.1% among NSTEMI patients. (p = 0.825). 30-day mortality was 32.6% after STEMI vs 31.6% in NSTEMI cases (p = 0.285). Conclusions: In contrast to the discouraging data concerning the role of PCI in AMI patients with CS and complex coronary artery disease, CABG may represent a treatment option worth considering