Kinematics of dense gas in the L1495 filament

We study the kinematics of the dense gas of starless and protostellar cores traced by the N2D+(2-1), N2H+(1-0), DCO+(2-1), and H13CO+(1-0) transitions along the L1495 filament and the kinematic links between the cores and the surrounding molecular cloud. We measure velocity dispersions, local and total velocity gradients and estimate the specific angular momenta of 13 dense cores in the four transitions using the on-the-fly observations with the IRAM 30 m antenna. To study a possible connection to the filament gas, we use the fit results of the C18O(1-0) survey performed by Hacar et al. (2013). All cores show similar properties along the 10 pc-long filament. N2D+(2-1) shows the most centrally concentrated structure, followed by N2H+(1-0) and DCO+(2-1), which show similar spatial extent, and H13CO+(1-0). The non-thermal contribution to the velocity dispersion increases from higher to lower density tracers. The change of magnitude and direction of the total velocity gradients depending on the tracer used indicates that internal motions change at different depths within the cloud. N2D+ and N2H+ show smaller gradients than the lower density tracers DCO+ and H13CO+, implying a loss of specific angular momentum at small scales. At the level of cloud-core transition, the core's external envelope traced by DCO+ and H13CO+ is spinning up, consistent with conservation of angular momentum during core contraction. C18O traces the more extended cloud material whose kinematics is not affected by the presence of dense cores. The decrease in specific angular momentum towards the centres of the cores shows the importance of local magnetic fields to the small scale dynamics of the cores. The random distributions of angles between the total velocity gradient and large scale magnetic field suggests that the magnetic fields may become important only in the high density gas within dense cores.Comment: Accepted for publication in A&A. The abstract is shortene

Seeds of Life in Space: methanol towards the pre-stellar core L1544

В докладе представлены результаты интерферометрических наблюдений метанола на частоте 96.7 ГГц в направлении метанольного пика дозвездного ядра L1544. Профиль содержания метанола в L1544, полученный с помощью не-ЛТР моделирования спектральных линий, сравнивается с результатами химической модели.We present the results of the interferometric observations of methanol at 96.7 GHz towards the methanol peak near the pre-stellar core L1544. The methanol abundance profile derived with the non-LTE modelling of the methanol spectral lines is compared with the results of chemical modelling.Работа выполнена при поддержке грантов ERC-PALs 320620, ERCDOC 741002; STFC ST/L004801, ST/M004139; CITA National Fellowship

Mapping deuterated methanol toward L1544: I. Deuterium fraction and comparison with modeling

The study of deuteration in pre-stellar cores is important to understand the physical and chemical initial conditions in the process of star formation. In particular, observations toward pre-stellar cores of methanol and deuterated methanol, solely formed on the surface of dust grains, may provide useful insights on surface processes at low temperatures. Here we analyze maps of CO, methanol, formaldehyde and their deuterated isotopologues toward a well-known pre-stellar core. This study allows us to test current gas-dust chemical models. Single-dish observations of CH$_3$OH, CH$_2$DOH, H$_2$CO, H_2\,^{13}CO, HDCO, D$_2$CO and C$^{17}$O toward the prototypical pre-stellar core L1544 were performed at the IRAM 30 m telescope. We analyze their column densities, distributions, and compare these observations with gas-grain chemical models. The maximum deuterium fraction derived for methanol is [CH$_2$DOH]/[CH$_3$OH] $\sim$ 0.08$\pm$0.02, while the measured deuterium fractions of formaldehyde at the dust peak are [HDCO]/[H$_2$CO] $\sim$ 0.03$\pm$0.02, [D$_2$CO]/[H$_2$CO] $\sim$ 0.04$\pm$0.03 and [D$_2$CO]/[HDCO] $\sim$ 1.2$\pm$0.3. Observations differ significantly from the predictions of models, finding discrepancies between a factor of 10 and a factor of 100 in most cases. It is clear though that to efficiently produce methanol on the surface of dust grains, quantum tunneling diffusion of H atoms must be switched on. It also appears that the currently adopted reactive desorption efficiency of methanol is overestimated and/or that abstraction reactions play an important role. More laboratory work is needed to shed light on the chemistry of methanol, an important precursor of complex organic molecules in space.Comment: Accepted for publication in A&

The shocked molecular layer in RCW 120

Expansion of wind-blown bubbles or H ii regions lead to formation of shocks in the interstellar medium, which compress surrounding gas into dense layers. We made spatially and velocity-resolved observations of the RCW 120 photo-dissociation region (PDR) and nearby molecular gas with CO(6-5) and (CO)-C-13(6-5) lines and distinguished a bright CO-emitting layer, which we related with the dense shocked molecular gas moving away from the ionizing star due to expansion of H ii region. Simulating gas density and temperature, as well as brightness of several CO and C+ emission lines from the PDR, we found reasonable agreement with the observed values. Analysing gas kinematics, we revealed the large-scale shocked PDR and also several dense environments of embedded protostars and outflows. We observe the shocked layer as the most regular structure in the CO(6-5) map and in the velocity space, when the gas around Young stellar objects (YSOs) is dispersed by the outflows

Ethynyl Around the HII Regions S255 and S257

Abstract: We present the results of the ethynyl (C2H) emission line observations towards the S255 and S257 HII regions and the molecular cloud between them. Radial profiles of line brightness, column density, and abundance of C2H are obtained. We show that the radial profile of the ethynyl abundance is almost flat towards the HII regions and drops by a factor of two towards the molecular cloud. At the same time, we find that the ethynyl abundance is at maximum towards the point sources in the molecular cloud—the stars with emission lines or emitting in X-ray. Line profiles are consistent with the assumption that both HII regions have front and back neutral walls those move relative to each other. © 2021, Pleiades Publishing, Ltd.We are grateful to L.E. Pirogov, S.V. Kalenskii for valuable advice during the processing of observational data, to D.A. Semenov for a discussion of the chemistry of ethynyl, and to anonymous referee for valuable comments. This study was supported by Russian Foundation for Basic Research (contract No. 20-02-00643 А). Anna Punanova is a member of the Max-Planck-Gesellschaft partner group in the Ural Federal University. Anna Punanova is supported by the Russian Ministry of Science and Higher Education via state assignment FEUZ-2020-0038

Deuterium fractionation in cold dense cores in the low-mass star forming region L1688

In this work, we study deuterium fractionation in four starless cores in the low-mass star-forming region L1688 in the Ophiuchus molecular cloud. We study how the deuterium fraction ($R_D$) changes with environment, compare deuteration of ions and neutrals, core centre and its envelope, and attempt to reproduce the observed results with a gas-grain chemical model. We chose high and low gas density tracers to study both core centre and the envelope. With the IRAM 30m antenna, we mapped N$_2$H$^+$(1-0), N$_2$D$^+$(1-0), H$^{13}$CO$^+$ (1-0) and (2-1), DCO$^+$(2-1), and $p$-NH$_2$D(1$_{11}$-1$_{01}$) towards the chosen cores. The missing $p$-NH$_3$ and N$_2$H$^+$(1-0) data were taken from the literature. To measure the molecular hydrogen column density, dust and gas temperature within the cores, we used the Herschel/SPIRE dust continuum emission data, the GAS survey data (ammonia), and the COMPLETE survey data to estimate the upper limit on CO depletion. We present the deuterium fraction maps for three species towards four starless cores. Deuterium fraction of the core envelopes traced by DCO$^+$/H$^{13}$CO$^+$ is one order of magnitude lower ($\sim$0.08) than that of the core central parts traced by the nitrogen-bearing species ($\sim$0.5). Deuterium fraction increases with the gas density as indicated by high deuterium fraction of high gas density tracers and low deuterium fraction of lower gas density tracers and by the decrease of $R_D$ with core radii, consistent with the predictions of the chemical model. Our model results show a good agreement with observations for $R_D$(N$_2$D$^+$/N$_2$H$^+$) and R$_D$(DCO$^+$/HCO$^+$) and underestimate the $R_D$(NH$_2$D/NH$_3$).Comment: 30 pages with 22 figures, accepted for publication in MNRA

Deuterium fractionation in low-mass star-forming regions

В этой работе мы исследуем, как меняется доля дейтерия в зависимости от физических условий в холодных ядрах на примере молекулярных облаков Тельца, Персея и Змееносца. Результаты показывают, что доля дейтерия в холодных ядрах в среднем разная в разных областях звездообразования. В наиболее плотной и турбулентной из рассматриваемых областей L1688 в Змееносце доля дейтерия в соединениях в два раза выше, чем L1495 в Тельце и в В5 в Персее. В L1495 и L1688 доли дейтерия в центральных частях и оболочке ядер отличаются примерно в 10 раз, тогда как в В5 только в 2—3 раза.In this work, we study how deuterium fraction changes depending on the physical conditions in cold cores embedded in the molecular clouds of Taurus, Perseus and Ophiuchus. The results show that the deuterium fraction in cold cores varies in different star-forming regions. In the densest and most turbulent of the studied regions, L1688 in Ophiuchus, the deuterium fraction is two times higher than that of L1495 in Taurus and B5 in Perseus. In L1495 and L1688, the deuterium fraction in the central parts of the cores and in their envelopes differ by a factor of 10, while in B5 only by a factor of 2—3.Работа выполнена при поддержке Российского научного фонда, проект 19-72-00064

Deuterium fraction in cold dense cores in the star-forming region L1688

В работе изучена доля дейтерия в холодных плотных ядрах в области маломассивного звездообразования L1688. Для изучения доли дейтерия и ее зависимости от физических параметров холодного плотного ядра построены наблюдательные карты трех пар соединений (N2H+ и N2D+, NH3 и NH2D, H13CO+ и DCO+) в направлении четырех холодных плотных ядер. Наблюдения выполнены на телескопе IRAM 30m (кроме данных NH3, взятых из обзора GAS по наблюдениям на GBT).The work presents a study of deuterium fraction in cold dense cores in the low mass starforming region L1688. To study the deuterium fraction and its correlation with physical conditions in a cold dense core, we produced the observational maps of three pairs of species (N2H+ and N2D+, NH3 and NH2D, H13CO+ and DCO+) towards four cold dense cores. The observations were carried out with the IRAM 30m telescope (except for NH3 data taken from the GAS survey based on observations with GBT).Работа выполнена при поддержке Российского научного фонда, проект 19-72-00064