Unravelling the stellar Initial Mass Function of early-type galaxies with hierarchical Bayesian modelling

Wanneer nieuwe sterren gevormd worden, dan gebeurt dit volgens een bepaalde massaverdeling. Deze massaverdeling wordt de initiële massafunctie (IMF) genoemd. In algemene zin kan gesteld worden dat er veel meer lichte dan zware sterren worden gevormd. De laatste jaren is er steeds meer bewijs gekomen dat in de zwaarste sterrenstelsels van het heelal de verhouding tussen lage-massa sterren en hoge-massa sterren anders is dan in onze eigen Melkweg. Deze mogelijke variatie van de massaverdeling kan ons meer vertellen over het proces van stervorming en heeft consequenties voor andere onderzoeken binnen de sterrenkunde waarbij een zogenaamde ‘universele IMF’ wordt aangenomen. Het nauwkeurig bepalen van de stellaire massaverdeling en eventuele variaties hiervan is dan ook van groot belang voor de sterrenkunde. In veraf gelegen sterrenstelsels kunnen we geen individuele sterren waarnemen. De stellaire massaverdeling van deze stelsels is hierdoor alleen indirect af te leiden. In dit proefschrift hebben we een nauwkeurig statistisch model ontwikkeld om de stellaire massaverdeling van onopgeloste sterrenstelsels te bepalen met behulp van spectroscopie. De resultaten van dit proefschrift bevestigen dat de zwaarste sterrenstelsels in het heelal een andere massaverdeling hebben dan de Melkweg. Onze resultaten laten zien dat de (relatieve) hoeveelheid hoge-massa sterren ongeveer constant is als functie van de massa van het sterrenstelsel. De (relatieve) hoeveelheid lage-massa sterren verander echter als functie van de massa van het sterrenstelsel, zodanig dat zwaardere sterrenstelsels meer lage-massa sterren bevatten

Mathematical equivalence of non-local transport models and broadened deposition profiles

Old and recent experiments show that there is a direct response to the heating power of transport observed in modulated electron cyclotron heating (ECH) experiments both in tokamaks and stellarators, which is commonly known as non-local transport. This is most apparent for modulated experiments in stellarators such as LHD and W7-AS. We show that this power dependence and its corresponding experimental observations such as the so-called hysteresis in flux [Inagaki, NF, 113006, 2013] can be reproduced by broadened ECH deposition profiles. In other words, many mathematical models proposed to describe non-local transport are equivalent to an deposition (effective) profile in its linearized forms [vanBerkel, NF, 106042, 2018]. This also connects with new insights on microwave scattering due to density fluctuations in the edge plasma which shows that in reality the deposition profiles are much broader than expected [Chellai, PRL, 105001, 2018] but it is unclear if this effect is sufficient to explain non-local transport. These relationships can be further studied by separating the transport in a slow (diffusive) and a fast (heating/non-local) time-scale using perturbative experiments

The X-shooter Spectral Library (XSL): Data Release 3

We present the third data release (DR3) of the X-shooter Spectral Library (XSL). This moderate-to-high resolution, near-ultraviolet-to-near-infrared ($350-2480$ nm, R $\sim$ 10 000) spectral library is composed of 830 stellar spectra of 683 stars. DR3 improves upon the previous data release by providing the combined de-reddened spectra of the three X-shooter segments over the full $350-2480$ nm wavelength range. It also includes additional 20 M-dwarf spectra from the ESO archive. We provide detailed comparisons between this library and Gaia EDR3, MILES, NGSL, CaT library, and (E-)IRTF. The normalised rms deviation is better than $D=0.05$ or 5$\%$ for the majority of spectra in common between MILES (144 spectra of 180), NGSL (112$/$116), and (E-)IRTF (55$/$77) libraries. Comparing synthetic colours of those spectra reveals only negligible offsets and small rms scatter, such as the median offset(rms) 0.001$\pm$0.040 mag in the (box1-box2) colour of the UVB arm,-0.004$\pm$0.028 mag in (box3-box4) of the VIS arm, and -0.001$\pm$0.045 mag in (box2-box3) colour between the UVB and VIS arms, when comparing stars in common with MILES. We also find an excellent agreement between the Gaia published (BP-RP) colours and those measured from the XSL DR3 spectra, with a zero median offset and an rms scatter of 0.037 mag for 449 non-variable stars. The unmatched characteristics of this library, which combine a relatively high resolution, a large number of stars, and an extended wavelength coverage, will help us to bridge the gap between the optical and the near-IR studies of intermediate and old stellar populations, and to probe low-mass stellar systems.Comment: 26 pages, 25 figures, accepted to Astronomy & Astrophysics. The data are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/ or on the XSL web-page http://xsl.astro.unistra.f

A comparative analysis on genome pleiotropy for evolved soft robots

Biological evolution shapes the body and brain of living creatures together over time. By contrast, in evolutionary robotics, the co-optimization of these subsystems remains challenging. Conflicting mutations cause dissociation between morphology and control, which leads to premature convergence. Recent works have proposed algorithmic modifications to mitigate the impact of conflicting mutations. However, the importance of genetic design remains underexposed. Current approaches are divided between a single, pleiotropic genetic encoding and two isolated encodings representing morphology and control. This design choice is commonly made ad hoc, causing a lack of consistency for practitioners. To standardize this design, we performed a comparative analysis between these two configurations on a soft robot locomotion task. Additionally, we incorporated two currently unexplored alternatives that drive these configurations to their logical extremes. Our results demonstrate that pleiotropic representations yield superior performance in fitness and robustness towards premature convergence. Moreover, we showcase the importance of shared structure in the pleiotropic representation of robot morphology and control to achieve this performance gain. These findings provide valuable insights into genetic encoding design, which supply practitioners with a theoretical foundation to pursue efficient brain-body co-optimization