Modelling line emission of deuterated H_3^+ from prestellar cores

Context: The depletion of heavy elements in cold cores of interstellar molecular clouds can lead to a situation where deuterated forms of H_3^+ are the most useful spectroscopic probes of the physical conditions. Aims: The aim is to predict the observability of the rotational lines of H_2D^+ and D_2H^+ from prestellar cores. Methods: Recently derived rate coefficients for the H_3^+ + H_2 isotopic system were applied to the "complete depletion" reaction scheme to calculate abundance profiles in hydrostatic core models. The ground-state lines of H_2D^+(o) (372 GHz) and D_2H^+(p) (692 GHz) arising from these cores were simulated. The excitation of the rotational levels of these molecules was approximated by using the state-to-state coefficients for collisions with H_2. We also predicted line profiles from cores with a power-law density distribution advocated in some previous studies. Results: The new rate coefficients introduce some changes to the complete depletion model, but do not alter the general tendencies. One of the modifications with respect to the previous results is the increase of the D_3^+ abundance at the cost of other isotopologues. Furthermore, the present model predicts a lower H_2D^+ (o/p) ratio, and a slightly higher D_2H^+ (p/o) ratio in very cold, dense cores, as compared with previous modelling results. These nuclear spin ratios affect the detectability of the submm lines of H_2D^+(o) and D_2H^+(p). The previously detected H_2D^+ and D_2H^+ lines towards the core I16293E, and the H_2D^+ line observed towards Oph D can be reproduced using the present excitation model and the physical models suggested in the original papers.Comment: 10 pages, 11 Figures; ver2: updated some of the Figures, added some references, added an entry to acknowledgement

A study of the cc-C3HD\mathrm{C_{3}HD}/cc-C3H2\mathrm{C_{3}H_{2}} ratio in low-mass star forming regions

We use the deuteration of $c$-$\mathrm{C_{3}H_{2}}$ to probe the physical parameters of starless and protostellar cores, related to their evolutionary states, and compare it to the $\mathrm{N_{2}H^{+}}$-deuteration in order to study possible differences between the deuteration of C- and N-bearing species. We observed the main species $c$-$\mathrm{C_{3}H_{2}}$, the singly and doubly deuterated species $c$-$\mathrm{C_{3}HD}$ and $c$-$\mathrm{C_{3}D_{2}}$, as well as the isotopologue $c$-$\mathrm{{H^{13}CC_{2}H}}$ toward 10 starless cores and 5 protostars in the Taurus and Perseus Complexes. We examined the correlation between the $N$($c$-$\mathrm{C_{3}HD}$)/$N$($c$-$\mathrm{C_{3}H_{2}}$) ratio and the dust temperature along with the $\mathrm{H_2}$ column density and the CO depletion factor. The resulting $N$($c$-$\mathrm{C_{3}HD}$)/$N$($c$-$\mathrm{C_{3}H_{2}}$) ratio is within the error bars consistent with $10\%$ in all starless cores with detected $c$-$\mathrm{C_{3}HD}$. This also accounts for the protostars except for the source HH211, where we measure a high deuteration level of $23\%$. The deuteration of $\mathrm{N_{2}H^{+}}$ follows the same trend but is considerably higher in the dynamically evolved core L1544. Toward the protostellar cores the coolest objects show the largest deuterium fraction in $c$-$\mathrm{C_{3}H_{2}}$. We show that the deuteration of $c$-$\mathrm{C_{3}H_{2}}$ can trace the early phases of star formation and is comparable to that of $\mathrm{N_{2}H^{+}}$. However, the largest $c$-$\mathrm{C_{3}H_{2}}$ deuteration level is found toward protostellar cores, suggesting that while $c$-$\mathrm{C_{3}H_{2}}$ is mainly frozen onto dust grains in the central regions of starless cores, active deuteration is taking place on ice

Calculating the 3D magnetic field of ITER for European TBM studies

The magnetic perturbation due to the ferromagnetic test blanket modules (TBMs) may deteriorate fast ion confinement in ITER. This effect must be quantified by numerical studies in 3D. We have implemented a combined finite element method (FEM) -- Biot-Savart law integrator method (BSLIM) to calculate the ITER 3D magnetic field and vector potential in detail. Unavoidable geometry simplifications changed the mass of the TBMs and ferritic inserts (FIs) up to 26%. This has been compensated for by modifying the nonlinear ferromagnetic material properties accordingly. Despite the simplifications, the computation geometry and the calculated fields are highly detailed. The combination of careful FEM mesh design and using BSLIM enables the use of the fields unsmoothed for particle orbit-following simulations. The magnetic field was found to agree with earlier calculations and revealed finer details. The vector potential is intended to serve as input for plasma shielding calculations.Comment: In proceedings of the 28th Symposium on Fusion Technolog

Nitrogen fractionation towards a pre-stellar core traces isotope-selective photodissociation

Context. Isotopologue abundance ratios are important to understand the evolution of astrophysical objects and ultimately the origins of a planetary system such as our own. With nitrogen being a fundamental ingredient of pre-biotic material, understanding its chemistry and inheritance is of fundamental importance to understand the formation of the building blocks of life. Aims. We aim to study the 14N/15N ratio in HCN, HNC, and CN across the prototypical pre-stellar core L1544. This study allows us to test the proposed fractionation mechanisms for nitrogen. Methods. We present here single-dish observations of the ground state rotational transitions of the 13C and 15N isotopologues of HCN, HNC, and CN with the IRAM 30 m telescope. We analyse their column densities and compute the 14N/15N ratio map across the core for HCN. The 15N fractionation of CN and HNC is computed towards different offsets across L1544. Results. The 15 N-fractionation map of HCN towards a pre-stellar core is presented here for the first time. Our map shows a very clear decrease in the 14N/15N ratio towards the southern edge of L1544, where carbon chain molecules present a peak, strongly suggesting that isotope-selective photodissociation has a strong effect on the fractionation of nitrogen across pre-stellar cores. The 14N/15N ratio in CN measured towards four positions across the core also shows a decrease towards the south-east of the core, while HNC shows the opposite behaviour. We also measured the 12CN/13CN ratio towards four positions across the core. Conclusions. The uneven illumination of the pre-stellar core L1544 provides clear evidence that 15 N fractionation of HCN and CN is enhanced towards the region more exposed to the interstellar radiation field. Isotope-selective photodissociation of N2 is then a crucial process to understand 15N fractionation, as already found in protoplanetary disks. Therefore, the 15N fractionation in prestellar material is expected to change depending on the environment within which pre-stellar cores are embedded. The 12CN/13CN ratio also varies across the core, but its variation does not affect our conclusions as to the effect of the environment on the fractionation of nitrogen. Nevertheless, the interplay between the carbon and nitrogen fractionation across the core warrants follow-up studies

A large (~1 pc) contracting envelope around the prestellar core L1544

Prestellar cores, the birthplace of Sun-like stars, form from the fragmentation of the filamentary structure that composes molecular clouds, from which they must inherit at least partially the kinematics. Furthermore, when they are on the verge of gravitational collapse, they show signs of subsonic infall motions. How extended these motions are, which depends on how the collapse occurs, remains largely unknown. We want to investigate the kinematics of the envelope that surrounds the prototypical prestellar core L1544, studying the cloud-core connection. To our aims, we observed the $\rm HCO^+$(1-0) transition in a large map. \hcop is expected to be abundant in the envelope, making it an ideal probe of the large-scale kinematics in the source. We modelled the spectrum at the dust peak by means of a non local-thermodynamical-equilibrium radiative transfer. In order to reproduce the spectrum at the dust peak, a large ($\sim 1\, \rm pc$) envelope is needed, with low density (tens of $\rm cm^{-3}$ at most) and contraction motions, with an inward velocity of $\approx 0.05\,\rm km \, s^{-1}$. We fitted the data cube using the Hill5 model, which implements a simple model {for the optical depth and excitation temperature profiles along the line-of-sight,} in order to obtain a map of the infall velocity. This shows that the infall motions are extended, with typical values in the range $0.1-0.2\,\rm km \, s^{-1}$. Our results suggest that the contraction motions extend in the diffuse envelope surrounding the core, which is consistent with recent magnetic field measurements in the source, which showed that the envelope is magnetically supercritical.Comment: Accepted for publication on ApJ, 24 Oct. 202

Quantitative ultrasound tissue characterization in shoulder and thigh muscles – a new approach

BACKGROUND: The echogenicity patterns of ultrasound scans contain information of tissue composition in muscles. The aim was: (1) to develop a quantitative ultrasound image analysis to characterize tissue composition in terms of intensity and structure of the ultrasound images, and (2) to use the method for characterization of ultrasound images of the supraspinatus muscle, and the vastus lateralis muscle. METHODS: Computerized texture analyses employing first-order and higher-order grey-scale statistics were developed to objectively characterize ultrasound images of m. supraspinatus and m. vastus lateralis from 9 healthy participants. RESULTS: The mean grey-scale intensity was higher in the vastus lateralis muscle (p < 0.05) than in the supraspinatus muscle (average value of middle measuring site 51.4 compared to 35.0). Furthermore, the number of spatially connected and homogeneous regions (blobs) was higher in the vastus lateralis (p < 0.05) than in the supraspinatus (average for m. vastus lateralis: 0.092 mm(-2 )and for m. supraspinatus: 0.016 mm(-2)). CONCLUSION: The higher intensity and the higher number of blobs in the vastus lateralis muscle indicates that the thigh muscle contained more non-contractile components than the supraspinatus muscle, and that the muscle was coarser. The image analyses supplemented each other and gave a more complete description of the tissue composition in the muscle than the mean grey-scale value alone

Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211

In the centre of pre-stellar cores, deuterium fractionation is enhanced due to the low temperatures and high densities. Therefore, the chemistry of deuterated molecules can be used to study the earliest stages of star formation. We analyse the deuterium fractionation of simple molecules, comparing the level of deuteration in the envelopes of the pre-stellar core L1544 in Taurus and the protostellar core HH211 in Perseus. We used single-dish observations of CCH, HCN, HNC, HCO$^+$, and their $^{13}$C-, $^{18}$O- and D-bearing isotopologues, detected with the Onsala 20m telescope. We derived the column densities and the deuterium fractions of the molecules. Additionally, we used radiative transfer simulations and results from chemical modelling to reproduce the observed molecular lines. We used new collisional rate coefficients for HNC, HN$^{13}$C, DNC, and DCN that consider the hyperfine structure of these molecules. We find high levels of deuteration for CCH (10%) in both sources, consistent with other carbon chains, and moderate levels for HCN (5-7%) and HNC (8%). The deuterium fraction of HCO$^+$ is enhanced towards HH211, most likely caused by isotope-selective photodissociation of C$^{18}$O. Similar levels of deuteration show that the process is likely equally efficient towards both cores, suggesting that the protostellar envelope still retains the chemical composition of the original pre-stellar core. The fact that the two cores are embedded in different molecular clouds also suggests that environmental conditions do not have a significant effect on the deuteration within dense cores. Radiative transfer modelling shows that it is necessary to include the outer layers of the cores to consider the effects of extended structures. Besides HCO$^+$ observations, HCN observations towards L1544 also require the presence of an outer diffuse layer where the molecules are relatively abundant.Comment: 27 pages, 17 figures, accepted for publication in A&