Recent Talks

Canon is using its in-house ultra-precision cutting machines to provide the market with new optical devices for spectroscopy, including the world's first CdZnTe and InP immersion gratings and IFUs. They are used in the VLT and ELT instruments of Europe/ESO and in the instruments of the US/KECK and DKIST. The advantage of high-precision cutting is that surface roughness of less than 1 nm RMS can be obtained by cutting alone, so if the shape can be fabricated by cutting, it becomes an optical device. Since no post-processing such as polishing is required, optical devices with fine and sharp structures can be fabricated, and machined image slicers are a major advance in IFUs.
In my presentation, I will introduce the performance of our original cutting machine and the devices we have fabricated.

Segunda tanda de las charlas de instrumentación de los becarios de verano.

Supermassive black holes (SMBHs) in Active Galactic Nuclei (AGN) play a key role in the formation of galaxies and large-scale structure, but the triggering and impact of AGN feedback across scales and the origin of the observed SMBH–galaxy connection remain major open questions owing to the multi-scale and multi-physics nature of the problem. AGN feedback can also profoundly affect the properties and spatial distribution of baryons on scales that contain a large amount of cosmological information.  Current and upcoming cosmological surveys will provide unprecedented data to constrain the fundamental cosmological parameters, but uncertainties in galaxy formation physics remain a major theoretical obstacle to extract information from cosmological experiments.  In this talk, I will present new simulation techniques that are pushing the frontiers of galaxy formation modeling towards (1) the smallest scales, developing physically predictive models of SMBH accretion and feedback explicitly at sub-pc resolution in a full cosmological context and (2) the largest scales, using thousands of large-volume simulations exploring a wide range of sub-grid feedback implementations to train machine learning algorithms that can maximize the extraction of information from cosmological surveys while marginalizing over uncertainties in galaxy formation physics.  I will demonstrate the feasibility of these orthogonal approaches to address fundamental problems and discuss their potential to advance the fields of galaxy evolution and cosmology.

Zoom link: https://rediris.zoom.us/j/95949230133?pwd=xxXArEDCwNg4iXt4f5vUiCGvUFC9ph.1

Massive stars are real cosmic engines, and they have a large impact onto our Universe from early times on. Unfortunately, their evolution is still uncertain in many aspects, even on the main sequence. To check and improve corresponding predictions (needed, e.g., in galaxy simulations as sub-grid physics), various efficiency factors for internal processes such as core-envelope mixing need to be calibrated, by means of observational constraints. To this end, the measurement of chemical abundances, in particular for C,N,O, is a primary tool. Compared to low and intermediate mass stars and also to massive Red Supergiants, these measurements (by means of quantitative spectroscopy) are much more complex, since particularly deviations from LTE and the presence of inhomogeneous winds affect the observed line-strengths, and lead to significant uncertainties in the derived abundance values. In this talk, I will discuss these problems at hand of specific examples, summarize important results of the current state of the art, and provide a quick outlook what's next to come (within a collaboration with IAC-members).

Zoom link: https://rediris.zoom.us/j/98925990368?pwd=LJDIa3HSX4zIHM74vimXTwiabfrreN.1

In the first two years of scientific operations of JWST, three results have emerged, closely related to each other: an unexpected large abundance of bright galaxies at z>9 as well as AGN at z>5, and the existence of some dust even in the confirmed galaxies at the highest redshifts, with large contents present in some particular sources known as little red dots up to at least z~9. I will discuss the details and reliability of these results based on some of the recent work published by the MIRI European and US GTO, the CEERS, and the JADES-SMILES teams.

25 years ago, a seminal letter was published in Nature where it was concluded that the enigmatic linear polarization signal observed in the solar sodium D1 line implies that the quiet solar chromosphere is practically unmagnetized, in contradiction with other observational inferences and plasma physics arguments. This became known as the paradox of the solar sodium D1 polarization, which has puzzled theoretical physicists for many years, even leading some scientists to question the established quantum theory of radiation-matter interaction. In this talk I will briefly discuss the theoretical basis for this intriguing paradox and present its resolution in terms of a radiative transfer investigation published in Physical Review Letters. The observed linear polarization pattern across the sodium D2 and D1 lines can be reproduced to a remarkable degree in the presence of magnetic fields in the gauss range, if one accounts for the variations in the anisotropy of the solar radiation field over the small spectral interval spanned by the various hyperfine structure components of the sodium D2 and D1 lines. In addition, I will present the results of a series of radiative transfer investigations focused on the D lines of other alkali species, namely K I and Ba II, discussing their interest for probing the magnetism of the solar chromosphere.

Primera tanda de las charlas de instrumentación de los becarios de verano.

As a measure to fight global climate change, legislation is essentially terminating coal mining in Germany. In order to help with the necessary transformation of the economy, the federal government has set aside a total of 40 billion Euros for investment into new infrastructure in the affected regions. The state of Saxony decided to use a significant fraction of these funds to create two major research centers -- in essence to invest in brains, and not only in concrete and steel. As a result of a two-stage competition, the proposal of a group of astrophysicists has won a grant of 1.4 billion Euros to create, over a period of 15 years, the Deutsches Zentrum für Astrophysik (DZA). 
The talk will explain the structure of the institute, the current status, and the main focus on (1) fundamental research in Astrophysics, (2) technology development, and (3) big data & eScience. As for technology development, several examples will be presented that are intended to exploit the regional strength in semiconductor and photonics industry, e.g. CMOS sensors, photonic integrated circuits, photonic lanterns, etc.
In a second part of the talk, I will make a connection from the intended DZA engagement in novel detector technologies to the future WST: perhaps the next big project of ESO once the ELT has been finished. I will briefly touch upon the concept of the telescope, and report on the science case about resolved stellar populations that was developed in collaboration with IAC and others, and published recently as part of the WST White Paper (Mainieri+2024).

Elemental abundances of Sun-like stars are crucial for understanding the detailed properties of their planets. However, measuring elemental abundances in M stars is challenging due to their faintness and pervasive molecular features in optical spectra. To address this, elemental abundances of Sun-like stars have been proposed to constrain those of M stars by scaling [X/H] with measured [Fe/H] – a practice is yet to be well tested. Here we compile elemental abundances for 43 M dwarfs for 10 major rock-forming elements (Fe, C, O, Mg, Si, Al, Ca, Na, Ni, and Ti) from high-resolution near-infrared stellar surveys (APOGEE, CARMENES and Subaru/IRD). We perform bootstrap-based linear regressions on the M dwarfs to determine the trends of [X/H] vs. [Fe/H] and compare them with GK dwarfs (from GALAH + APOGEE). A 2-sample, multivariate Mahalanobis Distance test is applied to assess the significance of differences in [X/H]—[Fe/H] trends for individual elemental pairs between M and GK dwarfs. The null hypothesis of no significant difference in chemical trends between M and GK dwarfs is strongly rejected for all elements except Si, for which rejection is marginal, and Na and Ni, for which results are inconclusive. This suggests that assuming no difference may lead to biased results and inaccurate constraints on rocky planets around M dwarfs. Therefore, it is crucial for both the stellar and exoplanet communities to recognise these differences. To better understand these differences, we advocate for dedicated modelling techniques for M dwarf atmospheres and more homogeneous abundance analyses. Our statistically constrained trends of [X/H]—[Fe/H] for M dwarfs offer a new constraint on estimating M-dwarf elemental abundances given measured [Fe/H], aiding in detailed characterisation of M dwarf-hosted rocky worlds in the era of JWST, PLATO and ELT.

With the arrival of large galaxy surveys such as KiDS, DES or HSC and their ability to observe millions of galaxies, statistical errors have shrunk, making cosmology a precision science. Now, systematic effects are becoming the main source of uncertainty, so dealing with them will be one of the main challenges that next-generation surveys, such as Euclid, DESI or LSST. In this presentation, we will focus on two sources of systematic uncertainty: observational systematics and atmospheric conditions. For the former, we will explore the methods and lessons learnt from the DES-Y3 galaxy clustering analysis, the ongoing work for Y6 and the prospects for LSST-DESC. For the latter, we will introduce LSST’s Auxiliary Telescope (AuxTel), whose purpose is to measure atmospheric transparency and to derive color corrections based on spectroscopic observations.