Christian Nitschelm
A5047181870- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Galaxies: Formation, Evolution, Phenomena
- Atmospheric Ozone and Climate
- Astrophysical Phenomena and Observations
- Solar and Space Plasma Dynamics
- History and Developments in Astronomy
- Astronomical and nuclear sciences
- Cosmology and Gravitation Theories
- Historical Astronomy and Related Studies
- Astrophysics and Cosmic Phenomena
- Scientific Computing and Data Management
- History and Theory of Mathematics
- Historical Studies and Socio-cultural Analysis
- Chemical Thermodynamics and Molecular Structure
- Calibration and Measurement Techniques
- Computational Physics and Python Applications
- Space Exploration and Technology
- Spectroscopy and Chemometric Analyses
- Solar Radiation and Photovoltaics
- Geophysics and Gravity Measurements
University of Antofagasta
2014-2024
National Astronomical Observatories
2022
Pontificia Universidad Católica de Chile
2017
Universidad Católica del Norte
2009-2012
University of Antwerp
2007
Royal Observatory of Belgium
2007
Centre National de la Recherche Scientifique
1988-2000
Institut d'Astrophysique de Paris
2000
University of Lausanne
1989
Abstract Multi-epoch radial velocity measurements of stars can be used to identify stellar, substellar, and planetary-mass companions. Even a small number observation epochs informative about companions, though there multiple qualitatively different orbital solutions that fit the data. We have custom-built Monte Carlo sampler ( The Joker ) delivers reliable (and often highly multimodal) posterior samplings for companion parameters given sparse Here we use perform search companions 96,231 red...
Abstract We present a measurement of baryonic acoustic oscillations (BAOs) from Ly α absorption and quasars at an effective redshift <?CDATA $z=2.33$?> using the complete extended Baryonic Oscillation Spectroscopic Survey (eBOSS). The 16th final eBOSS data release (SDSS DR16) contains all its predecessor, (BOSS), providing 210,005 with z q > 2.10 that are used to measure absorption. BAO scale both in autocorrelation cross-correlation 341,468 1.77. Apart statistical gain new deeper...
Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG impacts the measurements emission-line ratios, hence interpretation diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced [S ii]/Hα, [N [O ii]/Hβ i]/Hα. The gradients these line ratios are determined ΣHα. In ratio diagrams, contamination moves...
We combine high-resolution spectroscopic data from APOGEE-2 Survey Data Release 16 (DR16) with broad-band photometric several sources, as well parallaxes {\it Gaia} 2 (DR2). Using the Bayesian isochrone-fitting code {\tt StarHorse}, we derive distances, extinctions and astrophysical parameters for around 388,815 APOGEE stars, achieving typical distance uncertainties of $\sim 6\%$ giants, 2\%$ dwarfs, extinction 0.07$ mag when all information is available, 0.17$ if optical photometry missing....
We present large-scale structure catalogs from the completed extended Baryon Oscillation Spectroscopic Survey (eBOSS). Derived Sloan Digital Sky (SDSS) -IV Data Release 16 (DR16), these provide data samples, corrected for observational systematics, and random positions sampling survey selection function. Combined, they allow clustering measurements suitable testing cosmological models. describe methods used to create eBOSS DR16 Luminous Red Galaxy (LRG) Quasar samples. The quasar catalog...
The eighteenth data release of the Sloan Digital Sky Surveys (SDSS) is first one for SDSS-V, fifth generation survey. SDSS-V comprises three primary scientific programs, or "Mappers": Milky Way Mapper (MWM), Black Hole (BHM), and Local Volume (LVM). This contains extensive targeting information two multi-object spectroscopy programs (MWM BHM), including input catalogs selection functions their numerous objectives. We describe production databases calibration- scientifically-focused...
Context. In November 2019, eROSITA on board of the Spektrum-Roentgen-Gamma (SRG) observatory started to map entire sky in X-rays. After four-year survey program, it will reach a flux limit that is about 25 times deeper than ROSAT. During SRG performance verification phase, observed contiguous 140 deg 2 area down final depth all-sky (eROSITA Final Equatorial-Depth Survey; eFEDS), with goal obtaining census X-ray emitting populations (stars, compact objects, galaxies, clusters and active...
Galactic haloes in a $\Lambda$-CDM universe are predicted to host today swarm of debris resulting from cannibalised dwarf galaxies. The chemo-dynamical information recorded their stellar populations helps elucidate nature, constraining the assembly history Galaxy. Using data APOGEE and \textit{Gaia}, we examine chemical properties various halo substructures, considering elements that sample nucleosynthetic pathways. systems studied Heracles, \textit{Gaia}-Enceladus/Sausage (GES), Helmi...
We study the internal gradients of stellar population properties within 1.5 Re for a representative sample 721 galaxies, with masses ranging between 109 M⊙ and 1011.5 from SDSS-IV MaNGA Integral-Field-Unit survey. Through use our full spectral fitting code firefly, we derive light- mass-weighted their radial gradients, as well star formation metal enrichment histories. also quantify impact that different models routines have on derived gradient measurements. In analysis, find age tend to be...
We find two chemically distinct populations separated relatively cleanly in the [Fe/H] - [Mg/Fe] plane, but also distinguished other chemical planes, among metal-poor stars (primarily with metallicities $< -0.9$) observed by Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of Sloan Digital Sky Survey. These stellar show most significant differences their [X/Fe] ratios $\alpha$-elements, C+N, Al, Ni. In addition to these having differing...
We present an analysis of spectrosopic and astrometric data from APOGEE-2 Gaia DR2 to identify structures towards the Orion Complex. By applying a hierarchical clustering algorithm 6-dimensional stellar data, we spatially and/or kinematically distinct groups young objects with ages ranging 1 12 Myr. also investigate star forming history within Complex, peculiar sub-clusters. With this method reconstruct older populations in regions that are presently largely devoid molecular gas, such as C...
We present a catalog of stellar properties for large sample 6676 evolved stars with APOGEE spectroscopic parameters and \textit{Kepler} asteroseismic data analyzed using five independent techniques. Our includes evolutionary state, surface gravity, mean density, mass, radius, age, the measurements used to derive them. employ new empirical approach combining from different methods, calibrating inferred parameters, estimating uncertainties. With high statistical significance, we find that...
We report the first APOGEE metallicities and alpha-element abundances measured for 3600 red giant stars spanning a large radial range of both Large (LMC) Small Magellanic Clouds (SMC), largest Milky Way dwarf galaxies. Our sample is an order magnitude larger than that previous studies, extends to much distances. These are results presented make use newly installed Southern instrument on du Pont telescope at Las Campanas Observatory. unbiased LMC spans in metallicity, from [Fe/H]=-0.2 very...
The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey has obtained high-resolution spectra for thousands of red giant stars distributed among the massive satellite galaxies Milky Way (MW): Large and Small Magellanic Clouds (LMC/SMC), Sagittarius Dwarf (Sgr), Fornax (Fnx), now fully disrupted \emph{Gaia} Sausage/Enceladus (GSE) system. We present analyze APOGEE chemical abundance patterns each galaxy to draw robust conclusions about their star formation histories,...
We investigate the inner regions of Milky Way with a sample unprecedented size and coverage thanks to APOGEE DR16 Gaia EDR3 data. Our Galactic has more than 26,000 stars within $|X_{\rm Gal}| <5$ kpc, $|Y_{\rm <3.5$ $|Z_{\rm <1$ we also make analysis for foreground-cleaned sub-sample 8,000 representative bulge-bar populations. The Galaxy shows clear chemical discontinuity in key abundance ratios [$\alpha$/Fe], [C/N], [Mn/O], probing different enrichment timescales, which suggests star...
Studies of the kinematics and chemical compositions Galactic globular clusters (GCs) enable reconstruction history star formation, evolution, mass assembly Galaxy. Using latest data release (DR16) SDSS/APOGEE survey, we identify 3,090 stars associated with 46 GCs. a previously defined kinematic association, break sample down into eight separate groups examine how kinematics-based classification maps composition space, considering only $\alpha$ (mostly Si Mg) elements Fe. Our results show...
Chemical abundances are an essential tool in untangling the Milky Way's enrichment history. However, evolution of interstellar medium abundance gradient with cosmic time is lost as a result radial mixing processes. For first time, we quantify many observational across Galactic disk function lookback and birth radius, $R_\text{birth}$. Using empirical approach, derive $R_\text{birth}$ estimates for 145,447 APOGEE DR17 red giant stars, based solely on their ages [Fe/H]. We explore detailed 6...
We report chemical abundances obtained by SDSS-III/APOGEE for giant stars in five globular clusters located within 2.2 kpc of the Galactic centre. detect presence multiple stellar populations four those (NGC 6553, NGC 6528, Terzan 5, and Palomar 6) find strong evidence their 6522. All present a significant spread N, C, Na, Al, with usual correlations anti-correlations between various seen other clusters. Our results provide important quantitative constraints on theoretical models...
We study the internal radial gradients of stellar population properties within $1.5\;R_{\rm e}$ and analyse impact galaxy environment. use a representative sample 721 galaxies with masses ranging between $10^{9}\;M_{\odot}$ to $10^{11.5}\;M_{\odot}$ from SDSS-IV survey MaNGA. split this by morphology into early-type late-type galaxies. Using full spectral fitting code FIREFLY, we derive light mass-weighted age metallicity, calculate these properties. three independent methods quantify...
Abstract We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by Apache Point Observatory Galactic Evolution Experiment (APOGEE). These giants exhibit strong Al and N enhancements accompanied C Mg depletions, strikingly similar to those in so-called second-generation (SG) globular clusters (GCs). Remarkably, we find low abundances ([Mg/Fe] < 0.0) together with overabundances majority (5/7) metal-rich ([Fe/H] ≳ −1.0) sample stars,...
We present an overview of the distributions 11 elemental abundances in Milky Way's inner regions, as traced by APOGEE stars released part SDSS Data Release 14/15 (DR14/DR15), including O, Mg, Si, Ca, Cr, Mn, Co, Ni, Na, Al, and K. This sample spans ~4000 with R_GC<4 kpc, enabling most comprehensive study to date these their variations within innermost few kiloparsecs Way. describe observed abundance patterns ([X/Fe]-[Fe/H]), compare previous literature results at solar Galactic radius,...
Stellar ages are a crucial component to studying the evolution of Milky Way. Using Gaia DR2 distance estimates, it is now possible estimate stellar for larger volume evolved stars through isochrone matching. This work presents [M/H]-age and [$α$/M]-age relations derived different spatial locations in Way disc. These by hierarchically modelling star formation history within given chemical abundance bin. For first time, we directly observe that significant variation apparent relation as...
Baade's window (BW) is one of the most observed Galactic bulge fields in terms chemical abundances. Due to its low and homogeneous interstellar absorption it considered as a calibration field for studies. In era large spectroscopic surveys, such BW are necessary cross calibrate stellar parameters individual abundances APOGEE survey. We use stars derive their metallicity distribution function (MDF) abundances, $\alpha$- iron-peak elements ASPCAP pipeline (DR13), well age BW. determine MDF...
The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based spectroscopic dataset for hundreds of open clusters, constrain key Galactic dynamical chemical parameters from this sample. This second contribution the OCCAM presents analysis 259 member stars with [Fe/H] determinations in 19 using Sloan Digital Sky Survey Data Release 14 (SDSS/DR14) data Apache Point Observatory Evolution Experiment (APOGEE) ESA Gaia. analysis, which...
We use data of $\sim$13,000 stars from the SDSS/APOGEE survey to study shape bulge MDF within region $|\ell|\leq11^\circ$ and $|b|\leq13^\circ$, spatially constrained ${\rm R_{GC}\leq3.5}$ kpc. apply Gaussian Mixture Modeling Non-negative Matrix Factorization decomposition techniques identify optimal number properties components. find spatial variations (at [Fe/H]\geq-1}$ dex) are well represented as a smoothly varying contribution three overlapping components located at [Fe/H]=+$0.32$,...