scholarly journals Modeling Nitrogen Fractionation in the Protoplanetary Disk around TW Hya: Model Constraints on Grain Population and Carbon-to-oxygen Elemental Abundance Ratio

2021 ◽  
Vol 908 (1) ◽  
pp. 82
Author(s):  
Seokho Lee ◽  
Hideko Nomura ◽  
Kenji Furuya ◽  
Jeong-Eun Lee
Keyword(s):  
Abundance Ratio ◽  
Protoplanetary Disk ◽  
Elemental Abundance

scholarly journals Depletion of 15N in the center of L1544: Early transition from atomic to molecular nitrogen?

2018 ◽  
Vol 615 ◽  
pp. L16 ◽  
Author(s):  
K. Furuya ◽  
Y. Watanabe ◽  
T. Sakai ◽  
Y. Aikawa ◽  
S. Yamamoto
Keyword(s):  
Gas Phase ◽  
Molecular Nitrogen ◽  
Abundance Ratio ◽  
Elemental Abundance ◽  
Evolutionary Stage ◽  
Gas Phase Chemistry ◽  
Far Ultraviolet ◽  
Phase Chemistry ◽  
Grain Surface

We performed sensitive observations of the N15ND+(1–0) and 15NND+(1–0) lines toward the prestellar core L1544 using the IRAM 30 m telescope. The lines are not detected down to 3σ levels in 0.2 km s−1 channels of ~6 mK. The non-detection provides the lower limit of the 14N/15N ratio for N2D+ of ~700–800, which is much higher than the elemental abundance ratio in the local interstellar medium of ~200–300. The result indicates that N2 is depleted in 15N in the central part of L1544, because N2D+ preferentially traces the cold dense gas, and because it is a daughter molecule of N2. In situ chemistry is probably not responsible for the 15N depletion in N2; neither low-temperature gas phase chemistry nor isotope selective photodissociation of N2 explains the 15N depletion; the former prefers transferring 15N to N2, while the latter requires the penetration of interstellar far-ultraviolet (FUV) photons into the core center. The most likely explanation is that 15N is preferentially partitioned into ices compared to 14N via the combination of isotope selective photodissociation of N2 and grain surface chemistry in the parent cloud of L1544 or in the outer regions of L1544, which are not fully shielded from the interstellar FUV radiation. The mechanism is most efficient at the chemical transition from atomic to molecular nitrogen. In other words, our result suggests that the gas in the central part of L1544 has previously gone trough the transition from atomic to molecular nitrogen in the earlier evolutionary stage, and that N2 is currently the primary form of gas-phase nitrogen.

scholarly journals The Fe/O elemental abundance ratio in the solar wind as observed with SOHO CELIAS CTOF

1999 ◽  
Vol 104 (A11) ◽  
pp. 24769-24780 ◽  
Author(s):  
M. R. Aellig ◽  
S. Hefti ◽  
H. Grünwaldt ◽  
P. Bochsler ◽  
P. Wurz ◽  
...  
Keyword(s):  
Solar Wind ◽  
Abundance Ratio ◽  
Elemental Abundance

scholarly journals Measuring elemental abundance ratios in protoplanetary disks at millimeter wavelengths

2020 ◽  
Vol 638 ◽  
pp. A110 ◽  
Author(s):  
D. Fedele ◽  
C. Favre
Keyword(s):  
Protoplanetary Disks ◽  
Abundance Ratio ◽  
Elemental Abundance ◽  
Physical Parameters ◽  
Minor Effect ◽  
Line Flux ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
A Minor

Over million years of evolution, gas dust and ice in protoplanetary disks can be chemically reprocessed. There is evidence that the gas-phase carbon and oxygen abundances are subsolar in disks belonging to nearby star forming regions. These findings have a major impact on the composition of the primary atmosphere of giant planets (but it may also be valid for super-Earths and sub-Neptunes) as they accrete their gaseous envelopes from the surrounding material in the disk. In this study, we performed a thermochemical modeling analysis with the aim of testing how reliable and robust are the estimates of elemental abundance ratios based on (sub)millimeter observations of molecular lines. We created a grid of disk models for the following different elemental abundance ratios: C/O, N/O, and S/O, and we computed the line flux of a set of carbon-nitrogen and sulphur-bearing species, namely CN, HCN, NO, C2H, c–C3H2, H2CO, HC3N, CH3CN, CS, SO, H2S, and H2CS, which have been detected with present (sub)millimeter facilities such as ALMA and NOEMA. We find that the line fluxes, once normalized to the flux of the 13CO J = 2−1 line, are sensitive to the elemental abundance ratios. On the other hand, the stellar and disk physical parameters have only a minor effect on the line flux ratios. Our results demonstrate that a simultaneous analysis of multiple molecular transitions is a valid approach to constrain the elemental abundance ratio in protoplanetary disks.

scholarly journals First detections of H13CO+ and HC15N in the disk around HD 97048

2019 ◽  
Vol 629 ◽  
pp. A75 ◽  
Author(s):  
Alice S. Booth ◽  
Catherine Walsh ◽  
John D. Ilee
Keyword(s):  
Dust Emission ◽  
Line Emission ◽  
Abundance Ratio ◽  
Protoplanetary Disk ◽  
Temperature Structure ◽  
Exchange Reactions ◽  
Gas Kinematics ◽  
Spatially Resolved ◽  
Chemical Models ◽  
Disk Structure

Observations of different molecular lines in protoplanetary disks provide valuable information on the gas kinematics, as well as constraints on the radial density and temperature structure of the gas. With ALMA we have detected H13CO+ (J = 4–3) and HC15N (J = 4–3) in the HD 97048 protoplanetary disk for the first time. We compare these new detections to the ringed continuum mm-dust emission and the spatially resolved CO (J = 3–2) and HCO+ (J = 4–3) emission. The radial distributions of the H13CO+ and HC15N emission show hints of ringed sub-structure whereas, the optically thick tracers, CO and HCO+, do not. We calculate the HCO+/H13CO+ intensity ratio across the disk and find that it is radially constant (within our uncertainties). We use a physio-chemical parametric disk structure of the HD 97048 disk with an analytical prescription for the HCO+ abundance distribution to generate synthetic observations of the HCO+ and H13CO+ disk emission assuming LTE. The best by-eye fit models require radial variations in the HCO+/H13CO+ abundance ratio and an overall enhancement in H13CO+ relative to HCO+. This highlights the need to consider isotope selective chemistry and in particular low temperature carbon isotope exchange reactions. This also points to the presence of a reservoir of cold molecular gas in the outer disk (T ≲ 10 K, R ≳ 200 au). Chemical models are required to confirm that isotope-selective chemistry alone can explain the observations presented here. With these data, we cannot rule out that the known dust substructure in the HD 97048 disk is responsible for the observed trends in molecular line emission, and higher spatial resolution observations are required to fully explore the potential of optically thin tracers to probe planet-carved dust gaps. We also report non-detections of H13CO+ and HC15N in the HD 100546 protoplanetary disk.

scholarly journals The surprisingly carbon-rich environment of the S-type star W Aql,

2020 ◽  
Vol 642 ◽  
pp. A20
Author(s):  
E. De Beck ◽  
H. Olofsson
Keyword(s):  
Line Emission ◽  
Abundance Ratio ◽  
Asymptotic Giant Branch ◽  
Elemental Abundance ◽  
Agb Stars ◽  
Trace Species ◽  
Abundance Estimates ◽  
Chemical Content ◽  
Molecular Abundances ◽  
Circumstellar Environment

Context. W Aql is an asymptotic giant branch (AGB) star with an atmospheric elemental abundance ratio C/O ≈ 0.98. It has previously been reported to have circumstellar molecular abundances intermediate between those of M-type and C-type AGB stars, which respectively have C/O < 1 and C/O > 1. This intermediate status is considered typical for S-type stars, although our understanding of the chemical content of their circumstellar envelopes is currently rather limited. Aims. We aim to assess the reported intermediate status of W Aql by analysing the line emission of molecules that have never before been observed towards this star. Methods. We performed observations in the frequency range 159−268 GHz with the SEPIA/B5 and PI230 instruments on the APEX telescope. We made abundance estimates through direct comparison to available spectra towards a number of well-studied AGB stars and based on rotational diagram analysis in the case of one molecule. Results. From a compilation of our abundance estimates and those found in the literature for two M-type (R Dor, IK Tau), two S-type (χ Cyg, W Aql), and two C-type stars (V Aql, IRC +10 216), we conclude that the circumstellar environment of W Aql appears considerably closer to that of a C-type AGB star than to that of an M-type AGB star. In particular, we detect emission from C2H, SiC2, SiN, and HC3N, molecules previously only detected towards the circumstellar environment of C-type stars. This conclusion, based on the chemistry of the gaseous component of the circumstellar environment, is further supported by reports in the literature on the presence of atmospheric molecular bands and spectral features of dust species which are typical for C-type AGB stars. Although our observations mainly trace species in the outer regions of the circumstellar environment, our conclusion matches closely that based on recent chemical equilibrium models for the inner wind of S-type stars: the atmospheric and circumstellar chemistry of S-type stars likely resembles that of C-type AGB stars much more closely than that of M-type AGB stars. Conclusions. Further observational investigation of the gaseous circumstellar chemistry of S-type stars is required to characterise its dependence on the atmospheric C/O. Non-equilibrium chemical models of the circumstellar environment of AGB stars need to address the particular class of S-type stars and the chemical variety that is induced by the range in atmospheric C/O.

scholarly journals Signature and escape of highly fractionated plasma in an active region

2021 ◽  
Vol 508 (2) ◽  
pp. 1831-1841
Author(s):  
David H Brooks ◽  
Stephanie L Yardley
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Active Region ◽  
Active Regions ◽  
Abundance Ratio ◽  
Elemental Abundance ◽  
Composition Analysis ◽  
Closed Field ◽  
Coronal Loops ◽  
Magnetic Field Model

ABSTRACT Accurate forecasting of space weather requires knowledge of the source regions where solar energetic particles (SEP) and eruptive events originate. Recent work has linked several major SEP events in 2014, January, to specific features in the host active region (AR 11944). In particular, plasma composition measurements in and around the footpoints of hot, coronal loops in the core of the active region were able to explain the values later measured in situ by the Wind spacecraft. Due to important differences in elemental composition between SEPs and the solar wind, the magnitude of the Si/S elemental abundance ratio emerged as a key diagnostic of SEP seed population and solar wind source locations. We seek to understand if the results are typical of other active regions, even if they are not solar wind sources or SEP productive. In this paper, we use a novel composition analysis technique, together with an evolutionary magnetic field model, in a new approach to investigate a typical solar active region (AR 11150), and identify the locations of highly fractionated (high Si/S abundance ratio) plasma. Material confined near the footpoints of coronal loops, as in AR 11944, that in this case have expanded to the AR periphery, show the signature, and can be released from magnetic field opened by reconnection at the AR boundary. Since the fundamental characteristics of closed field loops being opened at the AR boundary is typical of active regions, this process is likely to be general.

scholarly journals Does the structure of Population III supernova ejecta affect the elemental abundance of extremely metal-poor stars?

2020 ◽  
Vol 498 (2) ◽  
pp. 2676-2687
Author(s):  
Gen Chiaki ◽  
Nozomu Tominaga
Keyword(s):  
First Generation ◽  
Abundance Ratio ◽  
Mass Scale ◽  
Elemental Abundance ◽  
Abundance Pattern ◽  
Normal Core ◽  
Structure Of Population ◽  
Population Iii Stars ◽  
The One ◽  
Population Iii

ABSTRACT The first generation of metal-free (Population III) stars are crucial for the production of heavy elements in the earliest phase of structure formation. Their mass scale can be derived from the elemental abundance pattern of extremely metal-poor (EMP) stars, which are assumed to inherit the abundances of uniformly mixed supernova (SN) ejecta. If the expanding ejecta maintains its initial stratified structure, the elemental abundance pattern of EMP stars might be different from that from uniform ejecta. In this work, we perform numerical simulations of the metal enrichment from stratified ejecta for normal core-collapse SNe (CCSNe) with a progenitor mass $25 \ {\rm M_{\bigodot }}$ and explosion energies 0.7–10 B ($1 \ {\rm B} = 10^{51} \ \rm erg$). We find that SN shells fall back into the central minihalo in all models. In the recollapsing clouds, the abundance ratio [M/Fe] for stratified ejecta is different from the one for uniform ejecta only within ±0.4 dex for any element M. We also find that, for the largest explosion energy (10 B), a neighbouring halo is also enriched. Only the outer layers containing Ca or lighter elements reach the halo, where [C/Fe] = 1.49. This means that C-enhanced metal-poor stars can form from the CCSN even with an average abundance ratio [C/Fe] = −0.65.

Sign in / Sign up

Export Citation Format

Share Document