C. Nitschelm - Academia.edu (original) (raw)

Papers by C. Nitschelm

Context. An important goal within the quest for detecting an Earth-like extrasolar planet, will b... more Context. An important goal within the quest for detecting an Earth-like extrasolar planet, will be to identify atmospheric gaseous bio-signatures. Aims. Observations of the light transmitted through the Earth's atmosphere, as for an extrasolar planet, will be the first important step for future comparisons. We have completed observations of the Earth during a lunar eclipse, a unique situation similar to that of a transiting planet. We aim at showing what species could be detected in its atmosphere at optical wavelengths, where a lot of photons are available in the masked stellar light. Methods. We present observations of the 2008 August 16 Moon eclipse performed with the SOPHIE spectrograph at the Observatoire de Haute-Provence (France). Locating the spectrograph's fibers in the penumbra of the eclipse, the Moon irradiance is then a mix of direct, unabsorbed Sun light and solar light that has passed through the Earth's atmosphere. This mixture essentially reproduces what is recorded during the transit of an extrasolar planet. Results. We report here the clear detection of several Earth atmospheric compounds in the transmission spectra, such as ozone, molecular oxygen, and neutral sodium as well as molecular nitrogen and oxygen through the Rayleigh signature. Moreover, we present a method that allows us to derive the thickness of the atmosphere versus the wavelength for penumbra eclipse observations. We quantitatively evaluate the altitude at which the atmosphere becomes transparent for important species like molecular oxygen and ozone, two species thought to be tightly linked to the presence of life. Conclusions. The molecular detections presented here are an encouraging first attempt, necessary to better prepare for the future of extremely-large telescopes and transiting Earth-like planets. Instruments like SOPHIE will be mandatory when characterizing the atmospheres of transiting Earth-like planets from the ground and searching for bio-marker signatures.

https://ui.adsabs.harvard.edu/abs/1990A%26AS...82..331N/abstract, 1990

Description du catalogue de photometrie VBLUW de 5564 etoiles, disponible sur bande magnetique

For over fifteen years, the international collaboration of the Sloan Digital Sky Survey (SDSS) ha... more For over fifteen years, the international collaboration of the Sloan Digital Sky Survey (SDSS) has made terabytes of professional astronomical data freely available to the world. The vast archival imaging and spectroscopic datasets of the SDSS, coupled with its multiple access points and interfaces suitable for users of all levels of experience, provide a novel sandbox for audiences from a wide range of backgrounds to explore and engage with the data while cultivating interests and proficiency in astronomy. SDSS scientists, educators, technicians, and observers involved in the collaboration’s Education and Public Outreach working group have collaborated over the past decade to develop a large and diverse set of educational activities and exhibits built around SDSS data and engineering concepts. The recent expansion of SDSS-IV APOGEE-2 operations to Las Campanas Observatory in Chile has prompted a new emphasis on broadening the accessibility of these educational resources for Spanish...

Astronomy & Astrophysics, 2021

We investigate the inner regions of the Milky Way using data from APOGEE and Gaia EDR3. Our inner... more We investigate the inner regions of the Milky Way using data from APOGEE and Gaia EDR3. Our inner Galactic sample has more than 26 500 stars within |XGal|< 5 kpc, |YGal|< 3.5 kpc, |ZGal|< 1 kpc, and we also carry out the analysis for a foreground-cleaned subsample of 8000 stars that is more representative of the bulge–bar populations. These samples allow us to build chemo-dynamical maps of the stellar populations with vastly improved detail. The inner Galaxy shows an apparent chemical bimodality in key abundance ratios [α/Fe], [C/N], and [Mn/O], which probe different enrichment timescales, suggesting a star formation gap (quenching) between the high- and low-α populations. Using a joint analysis of the distributions of kinematics, metallicities, mean orbital radius, and chemical abundances, we can characterize the different populations coexisting in the innermost regions of the Galaxy for the first time. The chemo-kinematic data dissected on an eccentricity–|Z|max plane rev...

Monthly Notices of the Royal Astronomical Society, 2016

We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observ... more We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observatory Galactic Evolution Experiment for giant stars in five globular clusters located within 2.2 kpc of the Galactic Centre. We detect the presence of multiple stellar populations in four of those clusters (NGC 6553, NGC 6528, Terzan 5 and Palomar 6) and find strong evidence for their presence in NGC 6522. All clusters with a large enough sample present a significant spread in the abundances of N, C, Na and Al, with the usual correlations and anticorrelations between various abundances seen in other globular clusters. Our results provide important quantitative constraints on theoretical models for self-enrichment of globular clusters, by testing their predictions for the dependence of yields of elements such as Na, N, C and Al on metallicity. They also confirm that, under the assumption that field N-rich stars originate from globular cluster destruction, they can be used as tracers of their parental systems in the high-metallicity regime.

The Astrophysical Journal Supplement Series, 2017

Where a licence is displayed above, please note the terms and conditions of the licence govern yo... more Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.

Astronomy & Astrophysics

Context. SDSS-IV APOGEE-2, GALAH, and Gaia-ESO are high-resolution, ground-based, multi-object sp... more Context. SDSS-IV APOGEE-2, GALAH, and Gaia-ESO are high-resolution, ground-based, multi-object spectroscopic surveys providing fundamental stellar atmospheric parameters and multiple elemental abundance ratios for hundreds of thousands of stars of the Milky Way. Data from these and other surveys contribute to investigations of the history and evolution of the Galaxy. Aims. We undertake a comparison between the most recent data releases of these surveys to investigate the accuracy and precision of derived parameters by placing the abundances on an absolute scale. We also discuss the correlations in parameter and abundance differences as a function of main parameters. Uncovering the variants provides a basis to continue the efforts of future sky surveys. Methods. Quality samples from the APOGEE−GALAH (15 537 stars), APOGEE−GES (804 stars), and GALAH−GES (441 stars) overlapping catalogs were collected. We investigated the mean variants between the surveys, and linear trends were also i...

Bulletin of the American Astronomical Society, Sep 30, 2019

SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is de... more SDSS-V will be an all-sky, multi-epoch spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way Galaxy (MW), trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It will also create an integral-field spectroscopic map of the interstellar gas in the Galaxy and the Local Group that is 1,000 times larger than the current state of the art and at high enough spatial resolution to reveal the self-regulation mechanisms of galactic ecosystems. SDSS-V will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. The survey will thus track the flickers, flares, and radical transformations of the most luminous persistent objects in the universe: massive black holes growing at the centers of galaxies. The scope and flexibility of SDSS-V will be unique among both extant and anticipated spectroscopic surveys: it is all-sky, with matched survey infrastructures in both hemispheres; it provides near-infrared and optical multi-object fiber spectroscopy that is rapidly reconfigurable to serve high target densities, targets of opportunity, and time-domain monitoring; and it provides optical, ultrawide-field integral field spectroscopy. SDSS-V, with its programs anticipated to start in 2020, will be perfectly timed to multiply the scientific output from major space missions (e.g., TESS, Gaia, Spektr-RG-eROSITA) and ground-based projects. SDSS-V builds on the 25-year heritage of SDSS's advances in data analysis, collaboration spirit and infrastructure, and product deliverables in astronomy. The project is now refining its science scope, optimizing the survey strategies, and developing new hardware that builds on the SDSS-IV infrastructure. We present here an overview of the current state of these developments. SDSS-V is actively seeking to build its consortium of institutional and individual members for a worldwide, partner-driven collaboration.

The Astrophysical Journal, 2018

In this work, we make use of DR14 APOGEE spectroscopic data to study a sample of 92 known OB star... more In this work, we make use of DR14 APOGEE spectroscopic data to study a sample of 92 known OB stars. We developed a near-infrared semi-empirical spectral classification method that was successfully used in case of four new exemplars, previously classified as later B-type stars. Our results agree well with those determined independently from ECHELLE optical spectra, being in line with the spectral types derived from the "canonical" MK blue optical system. This confirms that the APOGEE spectrograph can also be used as a powerful tool in surveys aiming to unveil and study a large number of moderately and highly obscured OB stars still hidden in the Galaxy.

The Astrophysical Journal, 2022

The APOGEE Open Cluster Chemical Abundances and Mapping survey is used to probe the chemical evol... more The APOGEE Open Cluster Chemical Abundances and Mapping survey is used to probe the chemical evolution of the s-process element cerium in the Galactic disk. Cerium abundances were derived from measurements of Ce ii lines in the APOGEE spectra using the Brussels Automatic Code for Characterizing High Accuracy Spectra in 218 stars belonging to 42 open clusters. Our results indicate that, in general, for ages < 4 Gyr, younger open clusters have higher [Ce/Fe] and [Ce/α-element] ratios than older clusters. In addition, metallicity segregates open clusters in the [Ce/X]–age plane (where X can be H, Fe, or the α-elements O, Mg, Si, or Ca). These metallicity-dependent relations result in [Ce/Fe] and [Ce/α] ratios with ages that are not universal clocks. Radial gradients of [Ce/H] and [Ce/Fe] ratios in open clusters, binned by age, were derived for the first time, with d[Ce/H]/d R GC being negative, while d[Ce/Fe]/d R GC is positive. [Ce/H] and [Ce/Fe] gradients are approximately constan...

$Research paper thumbnail of The eclipsing double-lined binaries V883 Cen and \u3b7 Mus$

VizieR Online Data Catalog, 2021