Related papers: Molecular abundances in low-mass protostellar enve…
The widespread rings and gaps seen in the dust continuum in protoplanetary disks are sometimes accompanied by similar substructures seen in molecular line emission. One example is the outer gap at 100 au in AS 209, which shows that the…
Observations of CO+ suggest column densities on the order 10^12 cm^-2 that can not be reproduced by many chemical models. CO+ is more likely to be destroyed than excited in collisions with hydrogen. An anomalous excitation mechanism may…
Theory predicts, and observations confirm, that the column density ratio of a molecule containing D to its counterpart containing H can be used as an evolutionary tracer in the low-mass star formation process. Since it remains unclear if…
Submillimeter lines of CN, NO, CO+ and SO+, and upper limits on SH+ and N2O are observed with the James Clerk Maxwell Telescope in two high-mass and up to nine low-mass young stellar objects and compared with chemical models. Constant…
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…
We found that in regions of high mass star formation the CS emission correlates well with the dust continuum emission and is therefore a good tracer of the total mass while the N$_2$H$^+$ distribution is frequently very different. This is…
Molecular emission is used to investigate both the physical and chemical properties of protoplanetary disks. Therefore, to accurately derive disk properties, we need a thorough understanding of the behavior of the molecular probes we rely…
Prestellar cores are unique laboratories for studies of the chemical and physical conditions preceding star formation. We observed the prestellar core L1544 in the fundamental transition of ortho-H2D+ (1_1,0-1_1,1) at different positions…
The physical structure of the envelopes around a sample of fourteen massive (1000-100,000 solar L) young stars is investigated on 100- 100,000 AU scales using maps and spectra in submillimeter continuum and lines of C17O, CS and H2CO. The…
We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained with the IRAM and JCMT telescopes. The data have been analyzed with three different methods with increasing level of sophistication. We first…
In regions where stars form, variations in density and temperature can cause gas to freeze-out onto dust grains forming ice mantles, which influences the chemical composition of a cloud. The aim of this paper is to understand in detail the…
We present new results on CO depletion in a sample of nearby pre-stellar cores, based on observations of the millimeter C17O and C18O lines and the 1.3 mm dust emission with the IRAM 30m telescope. In most cases, the distribution of CO is…
We present observations of HDCO and H2CO emission toward a sample of 15 Class 0 protostars in the Orion A and B clouds. Of these, eleven protostars are Herschel-identified PACS Bright Red Sources (PBRS) and four are previously identified…
We observe 84 candidate young high-mass sources in the rare isotopologues C17O and C18O to investigate whether there is evidence for depletion (freeze-out) towards these objects. Observations of the J=2-1 transitions of C18O and C17O are…
We present ISO LWS observations of the proto-planetary nebula CRL 618, a star evolving very fast to the planetary nebula stage. In addition to the lines of 12CO, 13CO, HCN and HNC, we report on the detection of H2O and OH emission together…
Understanding the gas abundance distribution is essential when tracing star formation using molecular line observations. Changing density and temperature conditions cause gas to freeze-out onto dust grains, and this needs to be taken into…
Extremely large deuteration of several molecules has been observed towards prestellar cores and low-mass protostars for a decade. New observations performed towards low-mass protostars suggest that water presents a lower deuteration in the…
IRAS 16293-2422 is a well studied low-mass protostar characterized by a strong level of deuterium fractionation. In the line of sight of the protostellar envelope, an additional absorption layer, rich in singly and doubly deuterated water…
The chemical structure of high-mass star nurseries is important for a general understanding of star formation. Deuteration is a key chemical process in the earliest stages of star formation because its efficiency is sensitive to the…
We have investigated molecular distributions in protoplanetary disks, adopting a disk model with a temperature gradient in the vertical direction. The model produces sufficiently high abundances of gaseous CO and HCO+ to account for line…