Laboratory Astrophysics at NASA Ames: Recent Results and Advances

The Cosmic SImulation Chamber (COSmIC) facility was developed at NASA Ames to study, in the laboratory, neutral and ionized molecules and nanoparticles under the low temperature and high vacuum conditions representative of interstellar, circumstellar and planetary environments. COSmIC is composed of a Pulsed Discharge Nozzle expansion that generates a plasma in a free supersonic jet expansion coupled to highsensitivity, complementary in situ diagnostic tools, used for the detection and characterization of the species present in the expansion: a Cavity Ring Down Spectroscopy and fluorescence spectroscopy systems operating in the UV-Visible range, and a Reflectron Time-Of-Flight Mass Spectrometer (ReTOF-MS). We will present recent advances that were achieved in laboratory astrophysics using COSmIC. These include advances in the domain of the diffuse interstellar bands (DIBs) and in the formation of dust grains and aerosols from their gas-phase molecular precursors in environments as varied as circumstellar outflows and planetary atmospheres. An extension of the spectral response of the facility into the infrared (IR) range is in progress with the addition of a high-resolution near-IR to mid-IR CRDS system that will allow to further investigate cosmic molecules and grains with COSmIC. Acquisition of laser induced fluorescence spectra of cosmic molecule analogs and the laser induced incandescence spectra of cosmic grain analogs are also planned. Preliminary results in these fronts will presented and the implications of the on-going studies for astronomy will be addressed

The Need for Laboratory Measurements and Ab Initio Studies to Aid Understanding of Exoplanetary Atmospheres

We are now on a clear trajectory for improvements in exoplanet observations that will revolutionize our ability to characterize their atmospheric structure, composition, and circulation, from gas giants to rocky planets. However, exoplanet atmospheric models capable of interpreting the upcoming observations are often limited by insufficiencies in the laboratory and theoretical data that serve as critical inputs to atmospheric physical and chemical tools. Here we provide an up-to-date and condensed description of areas where laboratory and/or ab initio investigations could fill critical gaps in our ability to model exoplanet atmospheric opacities, clouds, and chemistry, building off a larger 2016 white paper, and endorsed by the NAS Exoplanet Science Strategy report. Now is the ideal time for progress in these areas, but this progress requires better access to, understanding of, and training in the production of spectroscopic data as well as a better insight into chemical reaction kinetics both thermal and radiation-induced at a broad range of temperatures. Given that most published efforts have emphasized relatively Earth-like conditions, we can expect significant and enlightening discoveries as emphasis moves to the exotic atmospheres of exoplanets.Comment: Submitted as an Astro2020 Science White Pape

PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula

The JWST has captured the most detailed and sharpest infrared images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). We investigate the fundamental interaction of far-ultraviolet photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of 0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. A complex, structured, and folded DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate

PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $\mu$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $\mu$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $\mu$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photo-dissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, impacting planet formation within the disks. We report JWST and Atacama Large Millimetere Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modelling their kinematics and excitation allows us to constrain the physical conditions within the gas. We quantify the mass-loss rate induced by the FUV irradiation, finding it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk

PDRs4All: A JWST Early Release Science Program on Radiative Feedback from Massive Stars

22 pags., 8 figs., 1 tab.Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter-and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.Support for JWST-ERS program ID 1288 was provided through grants from the STScI under NASA contract NAS5-03127 to STScI (K.G., D.V.D.P., M.R.), Univ. of Maryland (M.W., M.P.), Univ. of Michigan (E.B., F.A.), and Univ. of Toledo (T.S.-Y.L.). O.B. and E.H. are supported by the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES, and through APR grants 6315 and 6410 provided by CNES. E. P. and J.C. acknowledge support from the National Science and Engineering Council of Canada (NSERC) Discovery Grant program (RGPIN-2020-06434 and RGPIN-2021-04197 respectively). E.P. acknowledges support from a Western Strategic Support Accelerator Grant (ROLA ID 0000050636). J.R.G. and S.C. thank the Spanish MCINN for funding support under grant PID2019-106110GB-I00. Work by M.R. and Y.O. is carried out within the Collaborative Research Centre 956, subproject C1, funded by the Deutsche Forschungsgemeinschaft (DFG)—project ID 184018867. T.O. acknowledges support from JSPS Bilateral Program, grant No. 120219939. M.P. and M.W. acknowledge support from NASA Astrophysics Data Analysis Program award #80NSSC19K0573. C.B. is grateful for an appointment at NASA Ames Research Center through the San José State University Research Foundation (NNX17AJ88A) and acknowledges support from the Internal Scientist Funding Model (ISFM) Directed Work Package at NASA Ames titled: “Laboratory Astrophysics—The NASA Ames PAH IR Spectroscopic Database.”Peer reviewe

La formation de l'hydrogène moléculaire sur des silicates interstellaires : des expériences aux observations

The goal of this thesis is to understand the formation of molecular hydrogen in the interstellar medium (ISM) via laboratory experiments and astronomical observations. The experiments are performed with FORMOLISM, an ultra-high vacuum setup to study the formation of molecules in the ISM. We are interested in the energy disposal during the exhothermic recombination of two H atoms on a cryogenically cooled surface (< 10 K). Resonance Enhanced Multi-Photon Ionization ( REMPI 2 + 1) spectroscopy is used to probe the population of rovibrational levels in the ground electronic state of molecular hydrogen after formation. We have tested different surfaces of astrophysical relevance : amorphous and crystalline silicates, porous amorphous solid water, and a bare silicate pre-dosed with hydrogen molecules. We have confirmed the formation enhancement of molecular hydrogen on a surface pre-dosed with molecules and quantified D₂formation as a non-thermal desorption mechanism. We have also measured the ortho-to-para ratio of newly formed molecular hydrogen on p-ASW, finding that it corresponds to the value expected at statistical equilibrium at high temperature. Silicate analog surfaces (forsterite and fayalite) have been fabricated to test the influence of their morphology and chemical composition on hydrogen formation. We have found that newly formed molecular hydrogen leaves rotationally cooler (with respect to the molecular beam rotational temperature) from crystalline surfaces, and that it is unaffected when it scatters from amorphous surfaces. We have also detected nuclear spin conversion of molecular hydrogen absorbed on bare silicates. Observational predictions from these experiments are tested using long slit near infrared spectroscopy available at the VLT and Keck telescopes. Planetary nebulae with H₂ and X-ray emission were chosen as ideal targets. H₂transitions have been detected throughout our targets. The intensity distribution of these transitions will be compared to models of formation pumping spectra. In addition, part of this thesis addresses the VUV high-resolution spectroscopy of CO and its isotopologues, using the Fourier Transform Spectrometer at the SOLEIL synchroton. This complements the work on hydrogen in the wider context of the astrochemistry of small molecules.L'objectif de cette thèse est de comprendre la formation de l'hydrogène moléculaire dans le milieu interstellaire (MIS) via des expériences de laboratoire et des observations astronomiques. Les expériences ont été réalisées avec FORMOLISM, un montage fonctionnant dans l'ultra-vide pour étudier la formation de molécules dans le MIS. On s'intéresse à la distribution en énergie de molécules d'hydrogène formées sur une surface refroidie par cryogénie (< 10 K). La technique de Resonance Enhanced Multi-Photon Ionization (REMPI 2 + 1) est utilisée pour sonder la population des niveaux rovibrationnels de l'état électronique fondamental de l'hydrogène moléculaire. Nous avons examiné différentes surfaces d'intérêt astrophysique : des silicates amorphes et cristallins, et de la glace d'eau solide amorphe poreuse (p-ASW). Nous avons confirmé l'augmentation du taux de formation de l'hydrogène moléculaire sur une surface recouverte au préalable des molécules d'hydrogène et nous avons quantifié la formation D₂en tant que mécanisme de désorption non-thermique. Nous avons mesuré le rapport ortho-para de l'hydrogène moléculaire nouvellement formée sur la surface de p-ASW, qui correspond à la valeur attendue à l'équilibre statistique à haute température (> 100 K). Nous avons fabriqué au laboratoire de nouvelles surfaces de silicates (forstérite et fayalite) pour examiner l'impact de leur morphologie et de leur composition chimique sur la formation de l'hydrogène moléculaire. On a observé l'abaissement de la température de rotation des molécules d'hydrogène formées (par rapport à la température de rotation du jet moléculaire) émergeant de surfaces cristallines. Nous avons également étudié la conversion de spin nucléaire des molécules d'hydrogène absorbées sur une surface de sillicate. Les prédictions observationnelles qui on été déduites de ces expériences ont été testées par spectroscopie à longue fente dans l'infrarouge proche disponible au VLT et au Keck. Des nébuleuses planétaires présentant simultanément des émissions de H₂ont été détectées sur certains de nos objets. La distribution d'intensité de ces raies est comparée à des modèles théoriques de formation H₂dans l'espace. Une partie de cette thèse traite également de la spectroscopie VUV à haute résolution de CO et de ses isotopes, en utilisant le spectromètre à transformée de Fourier disponible au synchroton SOLEIL. Cela complète le travail sur l'hydrogène dans le contexte plus large de l'astrochimie de petites molécules

La formation de l'hydrogène moléculaire sur des silicates interstellaires : des expériences aux observations

The goal of this thesis is to understand the formation of molecular hydrogen in the interstellar medium (ISM) via laboratory experiments and astronomical observations. The experiments are performed with FORMOLISM, an ultra-high vacuum setup to study the formation of molecules in the ISM. We are interested in the energy disposal during the exhothermic recombination of two H atoms on a cryogenically cooled surface ( 100 K). Nous avons fabriqué au laboratoire de nouvelles surfaces de silicates (forstérite et fayalite) pour examiner l'impact de leur morphologie et de leur composition chimique sur la formation de l'hydrogène moléculaire. On a observé l'abaissement de la température de rotation des molécules d'hydrogène formées (par rapport à la température de rotation du jet moléculaire) émergeant de surfaces cristallines. Nous avons également étudié la conversion de spin nucléaire des molécules d'hydrogène absorbées sur une surface de sillicate. Les prédictions observationnelles qui on été déduites de ces expériences ont été testées par spectroscopie à longue fente dans l'infrarouge proche disponible au VLT et au Keck. Des nébuleuses planétaires présentant simultanément des émissions de H ont été détectées sur certains de nos objets. La distribution d'intensité de ces raies est comparée à des modèles théoriques de formation H dans l'espace. Une partie de cette thèse traite également de la spectroscopie VUV à haute résolution de CO et de ses isotopes, en utilisant le spectromètre à transformée de Fourier disponible au synchroton SOLEIL. Cela complète le travail sur l'hydrogène dans le contexte plus large de l'astrochimie de petites molécules.PARIS-Observatoire (751142302) / SudocSudocFranceF

Optical indices of organic aerosols for oxidizing atmospheres of Earth-like exoplanets

International audiencePhotochemical haze is likely produced in most planetary atmospheres. Optical indices are required to evaluate the haze contribution to the climate of aplanet. Unfortunately few experimental data exist and most of them have been measured with laboratory analogs of Titan’s haze, which can only be amodel scenario fortotally reduced atmospheres. In the present work we studythe optical indices in the UV-Vis range ofanalogs of planetary organic haze produced with CO2/CH4ratios varying between 1 and 4 in order to provide appropriate optical indices for a large range of Earth-like oxidizingatmospheres. Oxidized analogues are found as much as four times better absorbers in the UVthan the reduced ones