J. Harju

Low upper limits on the O2 abundance from the Odin satellite

For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O2, using the Odin satellite. Equipped with a sensitive 3 mm receiver (Tsy ...

HD depletion in starless cores

Aims: We aim to investigate the abundances of light deuterium-bearing species such as HD, H2D+ and D2H+ in a gas-grain chemical model including an extensive description of deuterium and spin state chemistry, in physical conditions appropriate to the very centers of starless cores. Methods: We combine a gas-grain chemical model with radiative transfer calculations to simulate density and temperature structure in starless cores. The chemical model includes deuterated forms of species with up to 4 atoms and the spin states of the light species H2, H2+ and H3+ and their deuterated forms. Results: We find that HD eventually depletes from the gas phase because deuterium is efficiently incorporated to grain-surface HDO, resulting in inefficient HD production on grains. HD depletion has consequences not only on the abundances of e.g. H2D+ and D2H+, whose production depends on the abundance of HD, but also on the spin state abundance ratios of the various light species, when compared with the complete depletion model where heavy elements do not influence the chemistry. Conclusions: While the eventual HD depletion leads to the disappearance of light deuterium-bearing species from the gas phase in a relatively short timescale at high density, we find that at late stages of core evolution the abundances of H2D+ and D2H+ increase toward the core edge and the disributions become extended. The HD depletion timescale increases if less oxygen is initially present in the gas phase, owing to chemical interaction between the gas and the dust predecing the starless core phase. Our results are greatly affected if H2 is allowed to tunnel on grain surfaces, and therefore more experimental data not only on tunneling but also on the O + H2 surface reaction in particular is needed.

Modelling line emission of deuterated H3+ 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 + are the most useful spectroscopic probes of the physical conditions. Aims. The aim is to predict the observability of the rotational lines of H2D + and D2H + from prestellar cores. Methods. Recently derived rate coefficients for the H + + H2 isotopic system were applied to the “complete depletion” reaction scheme to calculate abundance profiles in hydrostatic core models. The ground-state lines of H2D + (o) (372 GHz) and D2H + (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 H2. 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 + abundance at the cost of other isotopologues. Furthermore, the present model predicts a lower H2D + (o/p) ratio, and a slightly higher D2H + (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 H2D + (o) and D2H + (p). The previously detected H2D + and D2H + lines towards the core I16293E, and the H2D + line observed towards Oph D can be reproduced using the present excitation model and the physical models suggested in the original papers.

SiO and CH3CCH abundances and dust emission in high-mass star-forming cores ,

Aims. We determine the fractional SiO abundance in high-mass star-forming cores, and investigate its dependence on physical conditions, to provide constraints on the chemistry models of the formation of SiO in the gas phase or via grain mantle evaporation. The work addresses also CH3CCH chemistry, as the kinetic temperature is determined using this molecule. Methods. We estimate the physical conditions of 15 high-mass star-forming cores and derive the fractional SiO and CH3CCH abundances using spectral line and dust continuum observations with the SEST. Results. The kinetic temperatures as derived from CH3CCH range from 25 to 39 K, the average being 33 K. The average gas density in the cores is 4.5 × 10 6 cm −3 . The SiO emission regions are extended and typically half of the integrated line emission comes from the velocity range traced out by CH3CCH emission. The upper limit of SiO abundance in this “quiescent” gas component is ∼10 −10 . The average CH3CCH abundance is about 7 × 10 −9 . It shows a shallow, positive correlation with the temperature, whereas SiO shows the opposite tendency. Conclusions. We suggest that the high CH3CCH abundance and its possible increase when the clouds become warmer is related to the intensified desorption of the chemical precursors of the molecule from grain surfaces. In contrast, the observed tendency of SiO does not support the idea that the evaporation of Si-containing species from the grain mantles would be important, and it contradicts models where neutral reactions with activation barriers dominate SiO production. A possible explanation for the decrease is that warmer cores represent more evolved stages of core evolution with fewer high-velocity shocks and thus less efficient SiO replenishment.

A (sub)millimetre study of dense cores in Orion B9

Context. Studies of dense molecular-cloud cores at (sub)millimetre wavelengths are needed to understand the early stages of star formation. Aims. We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The prime objective of this study is to examine the dust emission of the cores near the peak of their spectral energy distributions, and to determine the degrees of CO depletion, deuterium fractionation, and ionisation. Methods. The central part of Orion B9 was mapped at 350 μm with APEX/SABOCA. A sample of nine cores in the region were observed in C 17 O(2−1), H 13 CO + (4−3) (towards 3 sources), DCO + (4−3), N2H + (3−2), and N2D + (3−2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-μm dust continuum data. Results. All the LABOCA cores in the region covered by our SABOCA map were detected at 350 μm. The strongest 350 μm emission is seen towards the Class 0 candidate SMM 3. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image. In particular, we report on the discovery of multiple very low-mass condensations in the prestellar core SMM 6. Based on the 350-to-870 μm flux density ratios, we determine dust temperatures of Tdust � 7.9−10.8 K, and dust emissivity indices of β ∼ 0.5−1.8. The CO depletion factors are in the range fD ∼ 1.6−10.8. The degree of deuteration in N2H + is � 0.04−0.99, where the highest value (seen towards the prestellar core SMM 1) is, to our knowledge, the most extreme level of N2H + deuteration reported so far. The level of HCO + deuteration is about 1–2%. The fractional ionisation and cosmic-ray ionisation rate of H2 could be determined only towards two sources with the lower limits of ∼2−6 × 10 −8 and ∼2.6 × 10 −17 −4.8 × 10 −16 s −1 , respectively. We also detected D2CO towards two sources. Conclusions. The detected protostellar cores are classified as Class 0 objects, in agreement with our previous SED results. The detection of subcondensations within SMM 6 shows that core fragmentation can already take place during the prestellar phase. The origin of this substructure is likely caused by thermal Jeans fragmentation of the elongated parent core. Varying levels of fD and deuteration among the cores suggest that they are evolving chemically at different rates. A low fD value and the presence of gas-phase D2CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N2H + deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase.

HCN and HNC mapping of the protostellar core Chamaeleon-MMS1

Aims. The purpose of this study is to investigate the distributions of the isomeric molecules HCN and HNC and estimate their abundance ratio in the protostellar core Cha-MMS1 located in Chamaeleon i. Methods. The core was mapped in the

The kinetic temperature of Barnard 68

J=1{-}0

First detection of NH3 (10 -g 00) from a low mass cloud core. On the low ammonia abundance of the rho Oph A core

rotational lines of HCN, HCN, and

Detection of 6 K gas in Ophiuchus D

\mathrm{HN^{13}C}

The ratio of N(C

. The column densities of