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星間空間では200種類ほどの星間分子が発見されており，星形成領域では星間分子の組成に多様性 があることが知られている．その多様性の起源を明らかにするためには，星形成に至る前段階の分子 雲における化学組成を明らかにする必要がある．本稿では，銀河系内の分子雲と近傍銀河の分子雲の 化学組成を電波望遠鏡によるスペクトル線サーベイ観測の手法を用いて調べた．その結果，分子雲ス ケールでは化学組成に多様性がほとんどないことが明らかになった．この結果は星形成領域の化学組 成の多様性は，母体となる高密度なコアが形成されてから獲得されたことを示唆する．, More than 200 interstellar molecules have been identified in the universe. Strong diversity has been recognized in the chemical composition of interstellar molecules in star-forming regions. In order to reveal the origin of the chemical diversity,thereisaneedtoexplorethechemicalcharacteristicsatthescaleofthemolecularcloud,which defines the initial conditions for chemical evolution and star formation. With this in mind, we conducted spectral line survey observations of molecular clouds, both in the Milky Way and in other nearby galaxies. We found that the chemical composition was almost uniform at a molecular cloud scale, which implies that the chemical diversity seen in star-forming regions is acquired after the formation of dense parent cores.

Methanol, one of the simplest complex organic molecules in the Interstellar Medium (ISM), has been shown to be present and extended in cold environments such as starless cores. We aim at studying methanol emission across several starless cores and investigate the physical conditions at which methanol starts to be efficiently formed, as well as how the physical structure of the cores and their surrounding environment affect its distribution. Methanol and C$^{18}$O emission lines at 3 mm have been observed with the IRAM 30m telescope within the large program "Gas phase Elemental abundances in Molecular CloudS" (GEMS) towards 66 positions across 12 starless cores in the Taurus Molecular Cloud. A non-LTE radiative transfer code was used to compute the column densities in all positions. We then used state-of-the-art chemical models to reproduce our observations. We have computed N(CH$_3$OH)/N(C$^{18}$O) column density ratios for all the observed offsets, and two different behaviours can be recognised: the cores where the ratio peaks at the dust peak, and the cores where the ratio peaks with a slight offset with respect to the dust peak ($\sim $10000 AU). We suggest that the cause of this behaviour is the irradiation on the cores due to protostars nearby which accelerate energetic particles along their outflows. The chemical models, which do not take into account irradiation variations, can reproduce fairly well the overall observed column density of methanol, but cannot reproduce the two different radial profiles observed. We confirm the substantial effect of the environment onto the distribution of methanol in starless cores. We suggest that the clumpy medium generated by protostellar outflows might cause a more efficient penetration of the interstellar radiation field in the molecular cloud and have an impact on the distribution of methanol in starless cores., Accepted for publication in A&A

The technique of chemical tagging uses the elemental abundances of stellar atmospheres to 'reconstruct' chemically homogeneous star clusters that have long since dispersed. The GALAH spectroscopic survey - which aims to observe one million stars using the Anglo-Australian Telescope - allows us to measure up to 30 elements or dimensions in the stellar chemical abundance space, many of which are not independent. How to find clustering reliably in a noisy high-dimensional space is a difficult problem that remains largely unsolved. Here, we explore t-distributed stochastic neighbour embedding (t-SNE) - which identifies an optimal mapping of a high-dimensional space into fewer dimensions - whilst conserving the original clustering information. Typically, the projection is made to a 2D space to aid recognition of clusters by eye. We show that this method is a reliable tool for chemical tagging because it can: (i) resolve clustering in chemical space alone, (ii) recover known open and globular clusters with high efficiency and low contamination, and (iii) relate field stars to known clusters. t-SNE also provides a useful visualization of a high-dimensional space. We demonstrate the method on a data set of 13 abundances measured in the spectra of 187 000 stars by the GALAH survey. We recover seven of the nine observed clusters (six globular and three open clusters) in chemical space with minimal contamination from field stars and low numbers of outliers. With chemical tagging, we also identify two Pleiades supercluster members (which we confirm kinematically), one as far as 6 degrees-one tidal radius away from the cluster centre.

Context. Phosphorus-bearing species are essential to the formation of life on Earth, however they have barely been detected in the interstellar medium. In particular, towards star-forming regions only PN and PO have been identified so far. Since only a small number of detections of P-bearing molecules are available, their chemical formation pathways are not easy to constrain and are thus highly debatable. An important factor still missing in the chemical models is the initial elemental abundance of phosphorus, that is, the depletion level of P at the start of chemical models of dense clouds. Aims. In order to overcome this problem, we study P-bearing species in diffuse and translucent clouds. In these objects phosphorus is expected to be mainly in the gas phase and therefore the elemental initial abundance needed in our chemical simulations corresponds to the cosmic one and is well constrained. Methods. For the study of P-bearing chemistry we used an advanced chemical model. We updated and significantly extended the P-chemistry network based on chemical databases and previous literature. We performed single-pointing observations with the IRAM 30 m telescope in the 3 mm range towards the line of sight to the strong continuum source B0355+508 aiming for the (2-1) transitions of PN, PO, HCP, and CP. This line of sight incorporates five diffuse and/or translucent clouds. Results. The (2-1) transitions of the PN, PO, HCP, and CP were not detected. We report high signal-to-noise-ratio detections of the (1-0) lines of 13CO, HNC, and CN along with a first detection of C34S towards this line of sight. We have attempted to reproduce the observations of HNC, CN, CS, and CO in every cloud with our model by applying typical physical conditions for diffuse or translucent clouds. We find that towards the densest clouds with vLSR = -10, - 17 km s-1 the best-fit model is given by the parameters (n(H), AV, Tgas) = (300 cm-3, 3 mag, 40 K). Conclusions. According to our best-fit model, the most abundant P-bearing species are HCP and CP (~10-10). The molecules PN, PO, and PH3 also show relatively high predicted abundances of ~10-11. We show that the abundances of these species are sensitive to visual extinction, cosmic-ray ionization rate, and the diffusion-to-desorption energy ratio on dust grains. The production of P-bearing species is favored towards translucent rather than diffuse clouds, where the environment provides a stronger shielding from the interstellar radiation. Based on our improved model, we show that the (1-0) transitions of HCP, CP, PN, and PO are expected to be detectable with estimated intensities of up to ~200 mK. © J. Chantzos et al. 2020. Horizon 2020 Framework Programme, H2020: 66493 lzp-2018/1-0170 We thank the anonymous referee for his/her comments that significantly improved the present manuscript. The authors also wish to thank the IRAM Granada staff for their help during the observations. V.M.R. has received funding from the European Unions Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No 66493. Work by A.V. is supported by the Latvian Science Council via the project lzp-2018/1-0170. J.C. acknowledges Dr. J. C. Laas for his support with the Python programming.

Solar flares are the most powerful events in the solar system. These eruptive phenomena convert magnetic energy to thermal, radiative and kinetic energy, and accelerates particles on timescales of minutes via magnetic reconnection. As a result, the local plasma can be heated to temperatures in excess of 20 MK. In addition, plasma flows from the lower chromosphere to the higher corona have been observed. Hence, elemental abundance values similar to chromospheric and photospheric values have been inferred from soft X-ray measurements. Two of the most comprehensive, independent soft X-ray studies on elemental abundance changes in solar flares disagree on the variations of certain low first ionization potential (fip) elements (Narendranath 2014, Dennis et al. 2015). The Miniature X-ray Solar Spectrometer (MinXSS) CubeSats (Moore et al. 2018) provides new spectrally resolved soft X-ray measurements at higher spectral resolution and broader spectral (0.8 – 12 keV) coverage than the measurements used in Narendranath 2014 and Dennis et al. 2015. These properties allow the MinXSS data set to unambiguously quantify solar flare variations in Fe, Ca, Si, Mg, S, Ar, and Ni abundances. Variations in elemental abundance can provide information on plasma transport and heating processes in the solar corona. I present initial results of an M5.0 flare observed by the MinXSS-1 CubeSat and how it compares to the two aforementioned studies., This work supported by the NSF-REU Solar Physics program at SAO, grant number AGS-1560313 and the NSF- Fisk- Vanderbilt Master's-to-Ph.D. Bridge Program Grant No. HRD-1547757. MinXSS-1 CubeSat mission is supported by NASA Grant NNX14AN84G.

The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS ($\gtrsim$200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main-sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature $T_{\rm eff}$, surface gravity $\log{g}$, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced., Derived labels, associated errors, and relevant metadata are available from the RAVE database (http://www.rave-survey.org) from 19 September 2016

We report the discovery of a group of apparently young CoRoT red-giant stars exhibiting enhanced [alpha/Fe] abundance ratios (as determined from APOGEE spectra) with respect to Solar values. Their existence is not explained by standard chemical evolution models of the Milky Way, and shows that the chemical-enrichment history of the Galactic disc is more complex. We find similar stars in previously published samples for which isochrone-ages could be robustly obtained, although in smaller relative numbers, which could explain why these stars have not received prior attention. The young [alpha/Fe]-rich stars are much more numerous in the CoRoT-APOGEE (CoRoGEE) inner-field sample than in any other high-resolution sample available at present, as only CoRoGEE can explore the inner-disc regions and provide ages for its field stars. The kinematic properties of the young [$\alpha$/Fe]-rich stars are not clearly thick-disc like, despite their rather large distances from the Galactic mid-plane. Our tentative interpretation of these and previous intriguing observations in the Milky Way is that these stars were formed close to the end of the Galactic bar, near corotation -- a region where gas can be kept inert for longer times, compared to other regions shocked more frequently by the passage of spiral arms. Moreover, that is where the mass return from older inner-disc stellar generations should be maximal (according to an inside-out disc-formation scenario), further diluting the in-situ gas. Other possibilities to explain these observations (e.g., a recent gas-accretion event) are also discussed., Comment: Letter in press in Astronomy and Astrophysics (5 pages, 4 figures + 2 pages Appendix)

Bioapatites from teeth and other skeletal hardparts record information about environmental conditions under which the material is deposited. Much like in carbonates, chemical analysis of fossil bioapatite can therefore be used as a means to reconstruct climate and paleoenvironment. Mammal teeth grow sequentially, meaning that large, slow-growing teeth have the advantage of recording sub-annual scale environmental variations in a highly diagenesis-resistant bioapatite record. Extraction of seasonally resolved (paleo)environmental records from tooth enamel requires measurements on a very high spatial resolution. In this study, high-resolution micro-X-Ray Fluorescence line scans are implemented to obtain elemental abundance records at 25 µm resolution along the growth axis of teeth of modern cattle (Bos taurus) and horse (Equus ferus caballus). We also analyzed oxygen (carbonate and phosphate) and carbon stable isotopes of the enamel from the same teeth, and compared the results of stable isotopes and elemental abundance to document changes in the chemical composition of the teeth along the growth axis. Applying both methods on modern teeth of known origin, the relationship between elemental ratios, stable isotopes and known environmental parameters is investigated. Results from different tooth positions within the mammal jaw are also studied and compared. Stable isotope results from teeth in eruption sequence are used to show overlapping records seasonal cyclicity. Differences in results from phosphate-stable oxygen isotopes and carbonate stable oxygen isotopes as well as elemental records are used to test the reliability and reproducibility of different sampling and pretreatment techniques.