41 research outputs found
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 C-, 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, HNC, 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 CO.
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&
The whole genome sequence of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), reveals insights into the biology and adaptive evolution of a highly invasive pest species
The Mediterranean fruit fly (medfly), Ceratitis capitata, is a major destructive insect pest due to its broad host range, which includes hundreds of fruits and vegetables. It exhibits a unique ability to invade and adapt to ecological niches throughout tropical and subtropical regions of the world, though medfly infestations have been prevented and controlled by the sterile insect technique (SIT) as part of integrated pest management programs (IPMs). The genetic analysis and manipulation of medfly has been subject to intensive study in an effort to improve SIT efficacy and other aspects of IPM control
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