@article{Knobloch2013, author = {Knobloch, Eberhard}, title = {„Es w{\"a}re mir unm{\"o}glich nur ein halbes Jahr so zu leben wie er"}, series = {HiN : Alexander von Humboldt im Netz ; International review for Humboldtian studies}, volume = {XIV}, journal = {HiN : Alexander von Humboldt im Netz ; International review for Humboldtian studies}, number = {26}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, issn = {1617-5239}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-66766}, pages = {49 -- 68}, year = {2013}, language = {de} } @phdthesis{Streich2015, author = {Streich, David}, title = {Understanding massive disk galaxy formation through resolved stellar populations}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-81027}, school = {Universit{\"a}t Potsdam}, pages = {ix, 140}, year = {2015}, abstract = {In this thesis we utilize resolved stellar populations to improve our understanding of galaxy formation and evolution. In the first part we improve a method for metallicity determination of faint old stellar systems, in the second and third part we analyze the individual history of six nearby disk galaxies outside the Local Group. A New Calibration of the Color Metallicity Relation of Red Giants for HST data: It is well known, that the color distribution of stars on the the Red Giant Branch (RGB) can be used to determine metallicities of old stellar populations that have only shallow photometry. Based on the largest sample of globular clusters ever used for such studies, we quantify the relation between metallicity and color in the widely used HST ACS filters F606W and F814W. We use a sample of globular clusters from the ACS Globular Cluster Survey and measure their RGB color at given absolute magnitudes to derive the color-metallicity relation. We find a clear relation between metallicity and RGB color; we investigate the scatter and the uncertainties in this relation and show its limitations. A comparison with isochrones shows reasonably good agreement with BaSTI models, a small offset to Dartmouth models, and a larger offset to Padua models. Even for the best globular cluster data available, the metallicity of a simple stellar population can be determined from the RGB alone only with an accuracy of 0.3 dex for [M/H]<-1, and 0.15 dex for [M/H]>-1. For mixed populations, as they are observed in external galaxies, the uncertainties will be even larger due to uncertainties in extinction, age, etc. Therefore caution is necessary when interpreting photometric metallicities. The Structural History of Nearby Low Mass Disk Galaxies: We study the individual evolution histories of three nearby, low-mass, edge-on galaxies (IC5052, NGC4244, NGC5023). Using the color magnitude diagrams of resolved stellar populations, we construct star count density maps for populations of different ages and analyze the change of structural parameters with stellar age within each galaxy. The three galaxies show low vertical heating rates, which are much lower than the heating rate of the Milky Way. This indicates that heating agents, as giant molecular clouds and spiral structure are weak in low mass galaxies. We do not detect a separate thick disk in any of the three galaxies, even though our observations cover a larger range in equivalent surface brightness than any integrated light study. While scaleheights increase with age, each population can be well described by a single disk. Only two of the galaxies contain a very weak additional component, which we identify as the faint halo. The mass of these faint halos is less than 1\% of the mass of the disk. All populations in the three galaxies exhibit no or only little flaring. While this finding is consistent with previous integrated light studies, it poses strong constraints on galaxy formation models, because most theoretical simulations often find strong flaring due to interactions or radial migration. Furthermore, we find breaks in the radial profiles of all three galaxies. The radii of these breaks are independent of age, and the break strength is decreasing with age in two of the galaxies (NGC4244 and NGC5023). This is consistent with break formation models, that combine a star formation cutoff with radial migration. The differing behavior of IC5052 can be explained by a recent interaction or minor merger. The Structural History of Massive Disk Galaxies: We extend the structural analysis of stellar populations with distinct ages to three massive galaxies, NGC891, NGC4565 and NGC7814. While confusion effects due to the high stellar number densities in their central region, and the prominent dust lanes inhibit an detailed analysis of the radial profiles, we can study their vertical structure. These massive galaxies also have a slower heating than the Milky Way, comparable to the low mass galaxies. This can be traced back to their already thick young populations and thick layers of their interstellar medium. We do not find a clear separate thick disk in any of these three galaxies; all populations can be described by a single disk plus a S\'ersic bulge/halo component. In contrast to the low mass galaxies, we cannot rule out the presence of thick disks in the massive galaxies, because of the strong influence of the halo, that might hide the possible contribution of the thick disk to the vertical star count profiles. However, the faintness of the possible thick disks still points to problems in the earlier ubiquitous findings of thick disks in external galaxies.}, language = {en} } @phdthesis{Kerutt2019, author = {Kerutt, Josephine Victoria}, title = {The high-redshift voyage of Lyman alpha and Lyman continuum emission as told by MUSE}, doi = {10.25932/publishup-47881}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-478816}, school = {Universit{\"a}t Potsdam}, pages = {152}, year = {2019}, abstract = {Most of the matter in the universe consists of hydrogen. The hydrogen in the intergalactic medium (IGM), the matter between the galaxies, underwent a change of its ionisation state at the epoch of reionisation, at a redshift roughly between 6>z>10, or ~10^8 years after the Big Bang. At this time, the mostly neutral hydrogen in the IGM was ionised but the source of the responsible hydrogen ionising emission remains unclear. In this thesis I discuss the most likely candidates for the emission of this ionising radiation, which are a type of galaxy called Lyman alpha emitters (LAEs). As implied by their name, they emit Lyman alpha radiation, produced after a hydrogen atom has been ionised and recombines with a free electron. The ionising radiation itself (also called Lyman continuum emission) which is needed for this process inside the LAEs could also be responsible for ionising the IGM around those galaxies at the epoch of reionisation, given that enough Lyman continuum escapes. Through this mechanism, Lyman alpha and Lyman continuum radiation are closely linked and are both studied to better understand the properties of high redshift galaxies and the reionisation state of the universe. Before I can analyse their Lyman alpha emission lines and the escape of Lyman continuum emission from them, the first step is the detection and correct classification of LAEs in integral field spectroscopic data, specifically taken with the Multi-Unit Spectroscopic Explorer (MUSE). After detecting emission line objects in the MUSE data, the task of classifying them and determining their redshift is performed with the graphical user interface QtClassify, which I developed during the work on this thesis. It uses the strength of the combination of spectroscopic and photometric information that integral field spectroscopy offers to enable the user to quickly identify the nature of the detected emission lines. The reliable classification of LAEs and determination of their redshifts is a crucial first step towards an analysis of their properties. Through radiative transfer processes, the properties of the neutral hydrogen clouds in and around LAEs are imprinted on the shape of the Lyman alpha line. Thus after identifying the LAEs in the MUSE data, I analyse the properties of the Lyman alpha emission line, such as the equivalent width (EW) distribution, the asymmetry and width of the line as well as the double peak fraction. I challenge the common method of displaying EW distributions as histograms without taking the limits of the survey into account and construct a more independent EW distribution function that better reflects the properties of the underlying population of galaxies. I illustrate this by comparing the fraction of high EW objects between the two surveys MUSE-Wide and MUSE-Deep, both consisting of MUSE pointings (each with the size of one square arcminute) of different depths. In the 60 MUSE-Wide fields of one hour exposure time I find a fraction of objects with extreme EWs above EW_0>240A of ~20\%, while in the MUSE-Deep fields (9 fields with an exposure time of 10 hours and one with an exposure time of 31 hours) I find a fraction of only ~1\%, which is due to the differences in the limiting line flux of the surveys. The highest EW I measure is EW_0 = 600.63 +- 110A, which hints at an unusual underlying stellar population, possibly with a very low metallicity. With the knowledge of the redshifts and positions of the LAEs detected in the MUSE-Wide survey, I also look for Lyman continuum emission coming from these galaxies and analyse the connection between Lyman continuum emission and Lyman alpha emission. I use ancillary Hubble Space Telescope (HST) broadband photometry in the bands that contain the Lyman continuum and find six Lyman continuum leaker candidates. To test whether the Lyman continuum emission of LAEs is coming only from those individual objects or the whole population, I select LAEs that are most promising for the detection of Lyman continuum emission, based on their rest-frame UV continuum and Lyman alpha line shape properties. After this selection, I stack the broadband data of the resulting sample and detect a signal in Lyman continuum with a significance of S/N = 5.5, pointing towards a Lyman continuum escape fraction of ~80\%. If the signal is reliable, it strongly favours LAEs as the providers of the hydrogen ionising emission at the epoch of reionisation and beyond.}, language = {en} } @article{Reich2011, author = {Reich, Karin}, title = {Sternschnuppen und Erdmagnetismus, ein von Alexander von Humboldt und Carl Friedrich Gauß w{\"a}hrend der Universit{\"a}tsfeierlichkeiten in G{\"o}ttingen im September 1837 initiiertes Projekt}, series = {Alexander von Humboldt im Netz ; international review for Humboldtian studies}, volume = {XII}, journal = {Alexander von Humboldt im Netz ; international review for Humboldtian studies}, number = {23}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, issn = {2568-3543}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57575}, pages = {41 -- 67}, year = {2011}, abstract = {W{\"a}hrend der im September 1837 in G{\"o}ttingen stattfindenden Universit{\"a}tsfeierlichkeiten initiierten Alexander von Humboldt und Carl Friedrich Gauß gemeinsam ein Projekt; es ging dabei um die Frage, ob Sternschnuppen die erdmagnetischen Erscheinungen beeinflussen w{\"u}rden, dem Nordlicht vergleichbar. Dies sollte im folgenden November, anl{\"a}sslich des zu erwartenden großen Sternschnuppenschauers, {\"u}berpr{\"u}ft werden. Im Zentrum dieser Untersuchung steht der Brief von Alexander von Humboldt an Gauß vom 30. November 1837 (Briefwechsel Humboldt-Gauß, S. 63-65); in diesem wurden zwei Beilagen bzw. Anlagen angesprochen, die zwar noch existieren, die aber bei der Ausgabe des Humboldt-Gaußschen Briefwechsels fast ganz unber{\"u}cksichtigt blieben. Es handelt sich erstens um einen Brief von dem in Breslau wirkenden Astronomen Boguslawski an Humboldt vom 15. November 1837, den Humboldt, versehen mit eigenen Anmerkungen, Gauß zukommen ließ, und zweitens um ein Dokument, enthaltend die von Humboldt und Herter in Berlin w{\"a}hrend der Zeit vom 12. bis 21. November angestellten erdmagnetischen Beobachtungen. Diese Dokumente sollen hier erstmals in den historischen Kontext eingebettet, vorgestellt werden, zusammen mit dem Bericht {\"u}ber die in Marburg gemachten Sternschnuppenbeobachtungen vom 12. bis 14. November, die Gerling veranlasst hatte.}, language = {de} } @phdthesis{Hoischen2018, author = {Hoischen, Clemens}, title = {Multi-Messenger Astronomy with H.E.S.S: the Starburst Galaxy NGC253 and the Search for Short Time-Scale Transients}, doi = {10.25932/publishup-42452}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-424521}, school = {Universit{\"a}t Potsdam}, pages = {135}, year = {2018}, abstract = {Gamma-ray astronomy has proven to provide unique insights into cosmic-ray accelerators in the past few decades. By combining information at the highest photon energies with the entire electromagnetic spectrum in multi-wavelength studies, detailed knowledge of non-thermal particle populations in astronomical objects and systems has been gained: Many individual classes of gamma-ray sources could be identified inside our galaxy and outside of it. Different sources were found to exhibit a wide range of temporal evolution, ranging from seconds to stable behaviours over many years of observations. With the dawn of both neutrino- and gravitational wave astronomy, additional messengers have come into play over the last years. This development presents the advent of multi-messenger astronomy: a novel approach not only to search for sources of cosmic rays, but for astronomy in general. In this thesis, both traditional multi-wavelength studies and multi-messenger studies will be presented. They were carried out with the H.E.S.S. experiment, an imaging air Cherenkov telescope array located in the Khomas Highland of Namibia. H.E.S.S. has entered its second phase in 2012 with the addition of a large, fifth telescope. While the initial array was limited to the study of gamma-rays with energies above 100 GeV, the new instrument allows to access gamma-rays with energies down to a few tens of GeV. Strengths of the multi-wavelength approach will be demonstrated at the example of the galaxy NGC253, which is undergoing an episode of enhanced star-formation. The gamma-ray emission will be discussed in light of all the information on this system available from radio, infrared and X-rays. These wavelengths reveal detailed information on the population of supernova remnants, which are suspected cosmic-ray accelerators. A broad-band gamma-ray spectrum is derived from H.E.S.S. and Fermi-LAT data. The improved analysis of H.E.S.S. data provides a measurement which is no longer dominated by systematic uncertainties. The long-term behaviour of cosmic rays in the starburst galaxy NGC253 is finally characterised. In contrast to the long time-scale evolution of a starburst galaxy, multi-messenger studies are especially intriguing when shorter time-scales are being probed. A prime example of a short time-scale transient are Gamma Ray Bursts. The efforts to understand this phenomenon effectively founded the branch of gamma-ray astronomy. The multi-messenger approach allows for the study of illusive phenomena such as Gamma Ray Bursts and other transients using electromagnetic radiation, neutrinos, cosmic rays and gravitational waves contemporaneously. With contemporaneous observations getting more important just recently, the execution of such observation campaigns still presents a big challenge due to the different limitations and strengths of the infrastructures. An alert system for transient phenomena has been developed over the course of this thesis for H.E.S.S. It aims to address many follow-up challenges in order to maximise the science return of the new large telescope, which is able to repoint much faster than the initial four telescopes. The system allows for fully automated observations based on scientific alerts from any wavelength or messenger and allows H.E.S.S. to participate in multi-messenger campaigns. Utilising this new system, many interesting multi-messenger observation campaigns have been performed. Several highlight observations with H.E.S.S. are analysed, presented and discussed in this work. Among them are observations of Gamma Ray Bursts with low latency and low energy threshold, the follow-up of a neutrino candidate in spatial coincidence with a flaring active galactic nucleus and of the merger of two neutron stars, which was revealed by the coincidence of gravitational waves and a Gamma-Ray Burst.}, language = {en} } @misc{EtteKnoblochSchwarzetal.2014, author = {Ette, Ottmar and Knobloch, Eberhard and Schwarz, Oliver and Werner, Petra and Suckow, Christian and Jobst, Anne and Schmuck, Thomas and Ringmacher, Manfred and Tintemann, Ute and Leitner, Ulrike and Holl, Frank and Panwitz, Sebastian and P{\´e}aud, Laura and Holtz, B{\"a}rbel and Folkerts, Menso and P{\"a}ßler, Ulrich and Roba, Bill}, title = {HiN : Alexander von Humboldt im Netz = Ingo Schwarz zum 65. Geburtstag}, series = {HIN : Alexander von Humboldt im Netz ; international review for Humboldtian studies}, volume = {XV}, journal = {HIN : Alexander von Humboldt im Netz ; international review for Humboldtian studies}, number = {29}, editor = {Ette, Ottmar and Knobloch, Eberhard}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, issn = {1617-5239}, doi = {10.18443/hinvol15iss292014}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85033}, pages = {201}, year = {2014}, abstract = {Inhalt: Alexander von Humboldt-Forschungsstelle: Ingo Schwarz zum 65. Geburtstag Ottmar Ette: Findung und Erfindung einer Leserschaft. Neuere Editionsprojekte zu Alexander von Humboldt als Grundlage und Herausforderung k{\"u}nftigen Forschens Eberhard Knobloch: Alexandre de Humboldt et le Marquis de Laplace Oliver Schwarz: Alexander von Humboldt als astronomischer Arbeiter, Diskussionspartner und Ideengeber Petra Werner: Innenwelten und bleiche G{\"a}rten. Alexander von Humboldt untertage und in der Caripe-H{\"o}hle Christian Suckow: Alexander von Humboldt in Ust'-Kamenogorsk Anne Jobst: Neue Briefe Christian Gottfried Ehrenbergs an Alexander von Humboldt Thomas Schmuck: Humboldt, Baer und die Evolution Manfred Ringmacher: Zwei Briefe auf Guaran{\´i} in Alexander von Humboldts Handschrift Ute Tintemann: Julius Klaproths Mithridates-Projekt, Alexander von Humboldt und das Verlagshaus Cotta Ulrike Leitner: „Ja! Wenn Berlin Bonn w{\"a}re!" Friedrich R{\"u}ckerts Berufung nach Berlin Frank Holl: „Zur Freiheit bestimmt" - Alexander von Humboldts Blick auf die Kulturen der Welt Sebastian Panwitz: Das Humboldt-Mendelssohn-Haus J{\"a}gerstraße 22. Ein Quellenfund Laura P{\´e}aud: Du Mexique {\`a} l'Oural : l'expertise humboldtienne au service du politique B{\"a}rbel Holtz: „Cicerone" des K{\"o}nigs? Alexander von Humboldt und Friedrich Wilhelm III. Menso Folkerts: Ein unerwartetes Zusammentreffen in Sanssouci. Alexander von Humboldt und Karl Ludwig Hencke an der Tafel Friedrich Wilhelms IV. Ulrich P{\"a}ßler: Preußens Mann in Washington. F{\"u}nf Briefe Friedrich von Gerolts an Alexander von Humboldt (1858/1859) Bill Roba: German-Iowan Strategies in Celebrating the Centennial of Alexander von Humboldt's Birth Regina Mikosch: Ingo Schwarz' Ver{\"o}ffentlichungen zur Alexander von Humboldt {\"U}ber die Autoren}, language = {mul} } @misc{KnoblochSchwarzEtteetal.2011, author = {Knobloch, Eberhard and Schwarz, Ingo and Ette, Ottmar and P{\´e}aud, Laura and Reich, Karin and Biermann, Kurt-Reinhard}, title = {HiN : Alexander von Humboldt im Netz}, volume = {XII}, number = {23}, editor = {Ette, Ottmar and Knobloch, Eberhard}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, issn = {1617-5239}, doi = {10.18443/hinvol12iss232011}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57517}, pages = {73}, year = {2011}, abstract = {Inhalt: - Eberhard Knobloch/Ingo Schwarz: Die Feuer von Baku - ein wiederentdeckter Brief von Alexander von Humboldt - Ottmar Ette: Alexander von Humboldt: Wissenschaft im Feld - Transareale Wissenschaftsfelder in den Tropen - Laura P{\´e}aud: Le politique, op{\´e}rateur de la construction des savoirs g{\´e}ographiques modernes: l'exemple des voyages d'Alexander von Humboldt - Karin Reich: Sternschnuppen und Erdmagnetismus, ein von Alexander von Humboldt und Carl Friedrich Gauß w{\"a}hrend der Universit{\"a}tsfeierlichkeiten in G{\"o}ttingen im September 1837 initiiertes Projekt - Kurt-R. Biermann: War Alexander von Humboldt ein „Freiherr" (oder „Baron")?}, language = {mul} } @phdthesis{Fritzewski2021, author = {Fritzewski, Dario Jasper}, title = {From fast to slow rotation in the open clusters NGC 2516 and NGC 3532}, doi = {10.25932/publishup-53135}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-531356}, school = {Universit{\"a}t Potsdam}, pages = {viii, 137}, year = {2021}, abstract = {Angular momentum is a particularly sensitive probe into stellar evolution because it changes significantly over the main sequence life of a star. In this thesis, I focus on young main sequence stars of which some feature a rapid evolution in their rotation rates. This transition from fast to slow rotation is inadequately explored observationally and this work aims to provide insights into the properties and time scales but also investigates stellar rotation in young open clusters in general. I focus on the two open clusters NGC 2516 and NGC 3532 which are ~150 Myr (zero-age main sequence age) and ~300 Myr old, respectively. From 42 d-long time series photometry obtained at the Cerro Tololo Inter-American Observatory, I determine stellar rotation periods in both clusters. With accompanying low resolution spectroscopy, I measure radial velocities and chromospheric emission for NGC 3532, the former to establish a clean membership and the latter to probe the rotation-activity connection. The rotation period distribution derived for NGC 2516 is identical to that of four other coeval open clusters, including the Pleiades, which shows the universality of stellar rotation at the zero-age main sequence. Among the similarities (with the Pleiades) the "extended slow rotator sequence" is a new, universal, yet sparse, feature in the colour-period diagrams of open clusters. From a membership study, I find NGC 3532 to be one of the richest nearby open clusters with 660 confirmed radial velocity members and to be slightly sub-solar in metallicity. The stellar rotation periods for NGC 3532 are the first published for a 300 Myr-old open cluster, a key age to understand the transition from fast to slow rotation. The fast rotators at this age have significantly evolved beyond what is observed in NGC 2516 which allows to estimate the spin-down timescale and to explore the issues that angular momentum models have in describing this transition. The transitional sequence is also clearly identified in a colour-activity diagram of stars in NGC 3532. The synergies of the chromospheric activity and the rotation periods allow to understand the colour-activity-rotation connection for NGC 3532 in unprecedented detail and to estimate additional rotation periods for members of NGC 3532, including stars on the "extended slow rotator sequence". In conclusion, this thesis probes the transition from fast to slow rotation but has also more general implications for the angular momentum evolution of young open clusters.}, language = {en} } @article{Schwarz2014, author = {Schwarz, Oliver}, title = {Alexander von Humboldt als astronomischer Arbeiter, Diskussionspartner und Ideengeber}, series = {HiN : Alexander von Humboldt im Netz ; International Review for Humboldtian Studies}, volume = {XV}, journal = {HiN : Alexander von Humboldt im Netz ; International Review for Humboldtian Studies}, number = {29}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, issn = {1617-5239}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-84823}, pages = {36 -- 47}, year = {2014}, abstract = {Auf welche Weise sich unsere Einsch{\"a}tzung des wissenschaftlichen Wirkens Alexander von Humboldts auf Grundlage der best{\"a}ndig voranschreitenden Erschließung seiner Handschriften ver{\"a}ndern konnte und welche aktuellen wissenschaftshistorischen Fragestellungen dadurch aufgeworfen wurden, verdeutlicht Oliver Schwarz an Beispielen aus der Astronomie.}, language = {de} }