82 research outputs found
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 CHOH, CHDOH, HCO,
H_2\,^{13}CO, HDCO, DCO and CO 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
[CHDOH]/[CHOH] 0.080.02, while the measured deuterium
fractions of formaldehyde at the dust peak are [HDCO]/[HCO]
0.030.02, [DCO]/[HCO] 0.040.03 and [DCO]/[HDCO]
1.20.3. 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 () 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 NH(1-0), ND(1-0),
HCO (1-0) and (2-1), DCO(2-1), and
-NHD(1-1) towards the chosen cores. The missing -NH
and NH(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/HCO is one order of magnitude lower (0.08) than that
of the core central parts traced by the nitrogen-bearing species (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 with core radii,
consistent with the predictions of the chemical model. Our model results show a
good agreement with observations for (ND/NH) and
R(DCO/HCO) and underestimate the (NHD/NH).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
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