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&

Genome of the house fly, <i>Musca domestica</i> L., a global vector of diseases with adaptations to a septic environment

Background: Adult house flies, Musca domestica L., are mechanical vectors of more than 100 devastating diseases that have severe consequences for human and animal health. House fly larvae play a vital role as decomposers of animal wastes, and thus live in intimate association with many animal pathogens. Results: We have sequenced and analyzed the genome of the house fly using DNA from female flies. The sequenced genome is 691 Mb. Compared with Drosophila melanogaster, the genome contains a rich resource of shared and novel protein coding genes, a significantly higher amount of repetitive elements, and substantial increases in copy number and diversity of both the recognition and effector components of the immune system, consistent with life in a pathogen-rich environment. There are 146 P450 genes, plus 11 pseudogenes, in M. domestica, representing a significant increase relative to D. melanogaster and suggesting the presence of enhanced detoxification in house flies. Relative to D. melanogaster, M. domestica has also evolved an expanded repertoire of chemoreceptors and odorant binding proteins, many associated with gustation. Conclusions: This represents the first genome sequence of an insect that lives in intimate association with abundant animal pathogens. The house fly genome provides a rich resource for enabling work on innovative methods of insect control, for understanding the mechanisms of insecticide resistance, genetic adaptation to high pathogen loads, and for exploring the basic biology of this important pest. The genome of this species will also serve as a close out-group to Drosophila in comparative genomic studies

Deuteration of c-C

Context. In the centre of pre-stellar cores, the deuterium fractionation is enhanced due to the cold temperatures and high densities. Therefore, the chemistry of deuterated molecules can be used to probe the evolution and the kinematics in the earliest stages of star formation. Aims. We analyse emission maps of cyclopropenylidene, c-C3H2, to study the distribution of the deuteration throughout the prototypical pre-stellar core L1544. Methods. We used single-dish observations of c-C3H2, c-H13CC2H, c-C3HD, and c-C3D2 towards the pre-stellar core L1544, performed at the IRAM 30 m telescope. We derived the column density and deuterium fraction maps, and compared these observations with non-local thermodynamic equilibrium radiative transfer simulations. Results. The highest deuterium fractions are found close to the dust peak at the centre of L1544, where the increased abundance of H2D+ ions drives the deuteration process. The peak values are N(c-C3HD)/N(c-C3H2) = 0.17 ± 0.01, N(c-C3D2)/N(c-C3H2) = 0.025 ± 0.003, and N(c-C3D2)/N(c-C3HD) = 0.16 ± 0.03, which is consistent with previous single-pointing observations. The distributions of c-C3HD and c-C3D2 indicate that the deuterated forms of c-C3H2 in fact trace the dust peak and not the c-C3H2 peak. Conclusions. The N(c-C3D2)/N(c-C3HD) map confirms that the process of deuteration is more efficient towards the centre of the core and demonstrates that carbon-chain molecules are still present at high densities. This is likely caused by an increased abundance of He+ ions destroying CO, which increases the number of carbon atoms in the gas phase