On the age of the Milky Way bulge stellar population

Die Milchstraße unterscheidet sich nicht wesentlich von anderen weit entfernten Spiralgalaxien. Allerdings erlaubt es uns unsere Lage innerhalb der Milchstraße, ihre Sternpopulationen mit einer Genauigkeit zu studieren, wie sie für extragalaktische Quellen undenkbar wäre. Der "Bulge" der Milchstraße (d.h. die Sternpopulation innerhalb von ~3 kpc vom Galaktischen Zentrum) ist die massereichste der verschiedenen Komponenten der Milchstraße, die sehr alte Sterne beherbergt (>10 Milliarden Jahre). Die Untersuchung der Eigenschaften dieser Sternpopulation kann deshalb Aufschluss geben über die Entstehung und Entwicklung der Milchstraße als ganzes, und von Spiralgalaxien im breiteren Kontext. Bislang herrscht weitgehend Konsens bezüglich der globalen kinematischen, chemischen und strukturellen Eigenschaften der Bulge-Population. Das Alter der Sterne im Bulge, oder besser gesagt die Altersverteilung, ist noch nicht vollständig verstanden. Das Ziel dieser Arbeit ist es, bei den Fragen "Wie alt ist der Bulge?"' und "Gibt es einen räumlichen Altersgradienten im Bulge?" anzusetzen, indem das Alter von Sternen in mehreren verschiedenen Feldern bestimmt wird, die alle innerhalb einer Zone von 300 Quadratgrad um das Zentrum des Bulges liegen. Zum Einsatz kommen Aufnahmen des "VISTA Variables in the Vía Láctea" (VVV) Surveys, in denen durch Fitten der Point Spread Function die genauen Magnituden und Farben von einer halben Milliarde Sterne im Bereich des Bulges extrahiert werden. Die neu erstellten photometrischen Kataloge, die auch dafür genutzt werden, die Extinktion in Richtung des Bulges zu ermitteln, werden der gesamten wissenschaftlichen Gemeinschaft öffentlich zugänglich gemacht. Der Beitrag der vorgelagerten Disk-Population entlang der verschiedenen Blickachsen in Richtung Bulge wird mit Hilfe eines statistischen Verfahrens ermittelt und entfernt, um einen finalen Satz an Sternen zu erhalten, der ausschließlich die Bulge-Population repräsentiert. Das Alter der Sterne in verschiedenen Feldern wird durch den Vergleich der Beobachtungen mit synthetischen Sternpopulationsmodellen bestimmt, welche sorgfältig so konstruiert wurden, dass Beobachtungseffekte berücksichtigt werden (Streuung in der Entfernung, differenzielle Rötung, photometrische Vollständigkeit, photometrische und systematische Unsicherheiten). Die Simulationen zur Generierung der synthetischen Poulationen wurden auf zweierlei Arten durchgeführt: i) ein Modell, das eine spektroskopisch bestimmte Metallizitätsverteilung verwendet, dient als A-priori-Verteilung, so dass das Alter als einzig freier Parameter übrig bleibt; ii) ein genetischer Algorithmus findet aus allen möglichen Kombinationen von Alter und Metallizität die beste Lösung heraus (entsprechend einer uniformen A-priori-Verteilung in Alter und Metallizität). Wir schlussfolgern letztlich, dass der Bulge selbst über seine gesamte Ausdehnung hinweg ($|l| 9.5 Milliarden Jahre), mit einem schwachen Altersgradienten von 0.16 Milliarden Jahren pro Grad in Richtung Galaktisches Zentrum.The Milky Way (MW) galaxy is not much different from its faraway cousins. However, our position within the MW allows us to study the properties of its stellar populations with exquisite detail in comparison to extragalactic sources. The bulge of the MW (i.e. the stellar population within ~3 kpc from the Galactic center) is the most massive stellar component of the MW that also hosts very old stars (>10 Gyr), therefore the study of its stellar population properties can shed light on the formation and evolution of the MW as a whole, and of other spiral galaxies at large. So far, there is a general consensus on the global kinematic, chemical and structural properties of the bulge populations, however the age, or rather, the distribution of the ages of the stars in the bulge is yet to be completely understood. In this work we aim at addressing the questions "How old is the bulge?" and "Is there a spatial age gradient in the bulge?" through the determination of the stellar ages in the different fields sparsely distributed within a region of 300 sqr. deg centered on the bulge. We use VISTA Variables in the Vía Láctea (VVV) survey images to extract accurate magnitude and color of half a billion stars in the bulge area using point spread function fitting. The newly derived photometric catalogs, used in addition to probe the extinction towards the bulge, are made publicly available to the entire community. The contribution of the intervening disk population along the bulge lines of sight has been detected and removed by using a statistical approach in order to obtain a final stars sample that is representative of the bulge population only. The determination of the stellar ages in different fields is provided through the comparison between the observations and synthetic stellar population models, which have been carefully tailored to account for the observational effects (i.e. distance dispersion, differential reddening, photometric completeness, photometric and systematic uncertainties). The simulations leading to the construction of synthetic populations have been carried out by using two different methods: i) a model that uses a spectroscopically derived metallicity distribution functions as prior, leaving the age as the only free parameter; ii) a genetic algorithm that finds the best solution within all possible combinations of age and metallicity (i.e. uniform prior in age and metallicity). We ultimately find that the bulge itself appears to be on average old (>9.5 Gyr) throughout its extension (|l| < 10 degr and -10 degr < b < +5 degr), with a mild gradient of about 0.16 Gyr/deg towards the Galactic center

Software Engineering for Millennials, by Millennials

Software engineers need to manage both technical and professional skills in order to be successful. Our university offers a 5.5 year program that mixes computer science, software and computer engineering, where the first two years are mostly math and physics courses. As such, our students' first real teamwork experience is during the introductory SE course, where they modify open source projects in groups of 6-8. However, students have problems working in such large teams, and feel that the course material and project are "disconnected". We decided to redesign this course in 2017, trying to achieve a balance between theory and practice, and technical and professional skills, with a maximum course workload of 150 hrs per semester. We share our experience in this paper, discussing the strategies we used to improve teamwork and help students learn new technologies in a more autonomous manner. We also discuss what we learned from the two times we taught the new course.Comment: 8 pages, 9 tables, 4 figures, Second International Workshop on Software Engineering Education for Millennial

Tubulin and Actin Interplay at the T Cell and Antigen-Presenting Cell Interface

T cells reorganize their actin and tubulin-based cytoskeletons to provide a physical basis to the immune synapse. However, growing evidence shows that their roles on T cell activation are more dynamic than merely serving as tracks or scaffold for different molecules. The crosstalk between both skeletons may be important for the formation and movement of the lamella at the immunological synapse by increasing the adhesion of the T cell to the antigen-presenting cells (APC), thus favoring the transport of components toward the plasma membrane and in turn regulating the T-APC intercellular communication. Microtubules and F-actin appear to be essential for the transport of the different signaling microclusters along the membrane, therefore facilitating the propagation of the signal. Finally, they can also be important for regulating the endocytosis, recycling, and degradation of the T cell receptor signaling machinery, thus helping both to sustain the activated state and to switch it off

T-cell trans-synaptic vesicles are distinct and carry greater effector content than constitutive extracellular vesicles

The immunological synapse is a molecular hub that facilitates the delivery of three activation signals, namely antigen, costimulation/corepression and cytokines, from antigen-presenting cells (APC) to T cells. T cells release a fourth class of signaling entities, trans-synaptic vesicles (tSV), to mediate bidirectional communication. Here we present bead-supported lipid bilayers (BSLB) as versatile synthetic APCs to capture, characterize and advance the understanding of tSV biogenesis. Specifically, the integration of juxtacrine signals, such as CD40 and antigen, results in the adaptive tailoring and release of tSV, which differ in size, yields and immune receptor cargo compared with steadily released extracellular vesicles (EVs). Focusing on CD40L+ tSV as model effectors, we show that PD-L1 trans-presentation together with TSG101, ADAM10 and CD81 are key in determining CD40L vesicular release. Lastly, we find greater RNA-binding protein and microRNA content in tSV compared with EVs, supporting the specialized role of tSV as intercellular messenger