Complex organic molecules (COMs) are considered to be crucial molecules, since they are connected with organic chemistry, at the basis of terrestrial life. More pragmatically, they are molecules ...which in principle are difficult to synthesize in harsh interstellar environments and, therefore, are a crucial test for astrochemical models. Current models assume that several COMs are synthesized on lukewarm grain surfaces (gap30-40 K) and released in the gas phase at dust temperatures of gap100 K. However, recent detections of COMs in lap20 K gas demonstrate that we still need important pieces to complete the puzzle of COMs formation. Here, we present a complete census of the oxygen- and nitrogen-bearing COMs, previously detected in different Interstellar Medium (ISM) regions, toward the solar-type protostar IRAS 16293-2422. The census was obtained from the millimeter-submillimeter unbiased spectral survey TIMASSS. Of the 29 COMs searched for, 6 were detected: methyl cyanide, ketene, acetaldehyde, formamide, dimethyl ether, and methyl formate. Multifrequency analysis of the last five COMs provides clear evidence that they are present in the cold (lap30 K) envelope of IRAS 16293-2422, with abundances of 0.03-2 x 10 super(-10). Our data do not allow us to support the hypothesis that the COMs abundance increases with increasing dust temperature in the cold envelope, as expected if COMs were predominately formed on lukewarm grain surfaces. Finally, when also considering other ISM sources, we find a strong correlation over five orders of magnitude between methyl formate and dimethyl ether, and methyl formate and formamide abundances, which may point to a link between these two couples of species in cold and warm gas.
Formamide (NH sub(2)CHO), the simplest possible amide, has recently been suggested to be a central species in the synthesis of metabolic and genetic molecules, the chemical basis of life. In this ...Letter, we report the first detection of formamide in a protostar, IRAS 16293-2422, which may be similar to the Sun and solar system progenitor. The data combine spectra from the millimeter and submillimeter TIMASSS survey with recent, more sensitive observations at the IRAM 30 m telescope. With an abundance relative to H sub(2) of ~10 super(-10), formamide appears as abundant in this solar-type protostar as in the two high-mass star-forming regions, Orion-KL and SgrB2, where this species has previously been detected. Given the largely different UV-illuminated environments of the three sources, the relevance of UV photolysis of interstellar ices in the synthesis of formamide is therefore questionable. Assuming that this species is formed in the gas phase via the neutral-neutral reaction between the radical NH sub(2) and H sub(2)CO, we predict an abundance in good agreement with the value derived from our observations. The comparison of the relative abundance NH sub(2)CHO/H sub(2)O in IRAS 16293-2422 and in the coma of the comet Hale-Bopp supports the similarity between interstellar and cometary chemistry. Our results thus suggest that the abundance of some cometary organic volatiles could reflect gas phase rather than grain-surface interstellar chemistry.
Abstract
Evidence is mounting that the small bodies of our Solar system, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar ...system formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program ‘Astrochemical Surveys At IRAM’ (ASAI). Its goal is to carry out unbiased millimetre line surveys between 80 and 272 GHz of a sample of 10 template sources, which fully cover the first stages of the formation process of solar-type stars, from pre-stellar cores to the late protostellar phase. In this paper, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies with the evolutionary stage and is found to be very similar to that of massive star-forming regions. The molecular content in O- and C-bearing species allows us to define two chemical classes of envelopes, whose composition is dominated by either (a) a rich content in O-rich complex organic molecules, associated with hot corino sources, or (b) a rich content in hydrocarbons, typical of warm carbon-chain chemistry sources. Overall, a high chemical richness is found to be present already in the initial phases of solar-type star formation.
IRAS 16293-2422 is a very well-studied young stellar system seen in projection towards the L1689N cloud in the Ophiuchus complex. However, its distance is still uncertain; there is a range of values ...from 120 pc to 180 pc. Our goal is to measure the trigonometric parallax of this young star by means of H2O maser emission. We use archival data from 15 epochs of VLBA observations of the 22.2 GHz water maser line. By modeling the displacement on the sky of the H2O maser spots, we derived a trigonometric parallax of 7.1 ± 1.3 mas, corresponding to a distance of 141−21+30 pc. This new distance is in good agreement with recent values obtained for other magnetically active young stars in the L1689 cloud. We relate the kinematics of these masers with the outflows and the recent ejections powered by source A in the system.
We report the detection in space of a new molecular species that has been characterized spectroscopically and fully identified from astrophysical data. The observations were carried out with the IRAM ...30 m telescope. The molecule is ubiquitous as its transition has been found in cold molecular clouds, prestellar cores, and shocks. However, it is not found in the hot cores of Orion-KL and in the carbon-rich evolved star IRC+10216. Three rotational transitions in perfect harmonic relation have been identified in the prestellar core B1b. The molecule has a 1 electronic ground state and its transition presents the hyperfine structure characteristic of a molecule containing a nucleus with spin 1. A careful analysis of possible carriers shows that the best candidate is NS+. The derived rotational constant agrees within 0.3%-0.7% with ab initio calculations. NS+ was also produced in the laboratory to unambiguously validate the astrophysical assignment. The observed rotational frequencies and determined molecular constants confirm the discovery of the nitrogen sulfide cation in space. The chemistry of NS+ and related nitrogen-bearing species has been analyzed by means of a time-dependent gas-phase model. The model reproduces well the observed NS/NS+ abundance ratio, in the range 30-50, and indicates that NS+ is formed by reactions of the neutral atoms N and S with the cations SH+ and NH+, respectively.
Abstract
We report new interferometric images of cyclopropenylidene, c-C
3
H
2
, toward the young protocluster OMC-2 FIR 4. The observations were performed at 82 and 85 GHz with the NOrthern Extended ...Millimeter Array (NOEMA) as part of the project Seeds Of Life In Space (SOLIS). In addition, IRAM-30 m data observations were used to investigate the physical structure of OMC-2 FIR 4. We find that the c-C
3
H
2
gas emits from the same region where previous SOLIS observations showed bright HC
5
N emission. From a non-LTE analysis of the IRAM-30 m data, the c-C
3
H
2
gas has an average temperature of ∼40 K, a H
2
density of ∼3 × 10
5
cm
−3
, and a c-C
3
H
2
abundance relative to H
2
of (7 ± 1) × 10
−12
. In addition, the NOEMA observations provide no sign of significant c-C
3
H
2
excitation temperature gradients across the region (about 3–4 beams), with
T
ex
in the range 8 ± 3 up to 16 ± 7 K. We thus infer that our observations are inconsistent with a physical interaction of the OMC-2 FIR 4 envelope with the outflow arising from OMC-2 FIR 3, as claimed by previous studies. The comparison of the measured c-C
3
H
2
abundance with the predictions from an astrochemical PDR model indicates that OMC-2 FIR 4 is irradiated by an FUV field ∼1000 times larger than the interstellar one, and by a flux of ionizing particles ∼4000 times larger than the canonical value of 1 × 10
−17
s
−1
from the Galaxy cosmic rays, which is consistent with our previous HC
5
N observations. This provides an important and independent confirmation of other studies that one, or more, source inside the OMC-2 FIR 4 region emits energetic (≥10 MeV) particles.
Abstract
Cyclic-C3HD (c-C3HD) is a singly deuterated isotopologue of c-C3H2, which is one of the most abundant and widespread molecules in our Galaxy. We observed IRAS 16293–2422 in the 3-mm band ...with a single frequency set-up using the EMIR heterodyne 3 mm receiver of the IRAM 30-m telescope. We observed seven lines of c-C3HD and three lines of c-C3H2. Observed abundances are compared with astrochemical simulations using the nautilus gas-grain chemical model. Assuming that the size of the protostellar envelope is 3000 au and assuming the same excitation temperatures for both c-C3H2 and c-C3HD, we obtain a deuterium fraction of
$14_{-3}^{+4}$
per cent.
Context. Hot corinos are extremely rich in complex organic molecules (COMs). Accurate abundance measurements of COMs in such objects are crucial to constrain astrochemical models. In the particular ...case of close binary systems this can only be achieved through high angular resolution imaging. Aims. We aim to perform an interferometric study of multiple COMs in NGC 1333 IRAS 4A, which is a protostellar binary hosting hot corino activity, at an angular resolution that is sufficient to distinguish easily the emission from the two cores separated by 1.8′′. Methods. We used the Atacama Large (sub-)Millimeter Array (ALMA) in its 1.2 mm band and the IRAM Plateau de Bure Interferometer (PdBI) at 2.7 mm to image, with an angular resolution of 0.5′′ (120 au) and 1′′ (235 au), respectively, the emission from 11 different organic molecules in IRAS 4A. This allowed us to clearly disentangle A1 and A2, the two protostellar cores. For the first time, we were able to derive the column densities and fractional abundances simultaneously for the two objects, allowing us to analyse the chemical differences between them. Results. Molecular emission from organic molecules is concentrated exclusively in A2, while A1 appears completely devoid of COMs or even simpler organic molecules, such as HNCO, even though A1 is the strongest continuum emitter. The protostellar core A2 displays typical hot corino abundances and its deconvolved size is 70 au. In contrast, the upper limits we placed on COM abundances for A1 are extremely low, lying about one order of magnitude below prestellar values. The difference in the amount of COMs present in A1 and A2 ranges between one and two orders of magnitude. Our results suggest that the optical depth of dust emission at these wavelengths is unlikely to be sufficiently high to completely hide a hot corino in A1 similar in size to that in A2. Thus, the significant contrast in molecular richness found between the two sources is most probably real. We estimate that the size of a hypothetical hot corino in A1 should be less than 12 au. Conclusions. Our results favour a scenario in which the protostar in A2 is either more massive and/or subject to a higher accretion rate than A1, as a result of inhomogeneous fragmentation of the parental molecular clump. This naturally explains the smaller current envelope mass in A2 with respect to A1 along with its molecular richness. The extremely low abundances of organic molecules in A1 with respect to those in A2 demonstrate that the dense inner regions of a young protostellar core lacking hot corino activity may be poorer in COMs than the outer protostellar envelope.
Abstract
The protonated form of CO2, HOCO+, is assumed to be an indirect tracer of CO2 in the millimeter/submillimeter regime since CO2 lacks a permanent dipole moment. Here, we report the detection ...of two rotational emission lines (40,4–30,3 and 50,5–40,4) of HOCO+ in IRAS 16293−2422. For our observations, we have used EMIR heterodyne 3 mm receiver of the IRAM 30 m telescope. The observed abundance of HOCO+ is compared with the simulations using the 3-phase NAUTILUS chemical model. Implications of the measured abundances of HOCO+ to study the chemistry of CO2 ices using JWST-MIRI and NIRSpec are discussed as well.
Context.
There is a diverse chemical inventory in protostellar regions leading to the classification of extreme types of systems. Warm carbon chain chemistry sources, for one, are the warm and dense ...regions near a protostar containing unsaturated carbon chain molecules. Since the presentation of this definition in 2008, there is a growing field to detect and characterise these sources. The details are lesser known in relation to hot cores and in high-mass star-forming regions - regions of great importance in galactic evolution.
Aims.
To investigate the prevalence of carbon chain species and their environment in high-mass star-forming regions, we have conducted targeted spectral surveys of two sources in the direction of Cygnus X - AFGL 2591 and IRAS 20126+4104.
Methods.
We observed these sources in frequency ranges around 85, 96, and 290 GHz with the Green Bank Telescope and the IRAM 30m Telescope. We have constructed a local thermodynamic equilibrium (LTE) model using the observed molecular spectra to determine the physical environment in which these molecules originate. We map both the observed spatial distribution and the physical parameters found from the LTE model. We also determine the formation routes of these molecules in each source using the three-phase NAUTILUS chemical evolution code.
Results.
We detect several lines of propyne, CH
3
CCH, and cyclopropenylidene,
c
-C
3
H
2
as tracers of carbon chain chemistry, as well as several lines of formaldehyde, H
2
CO, and methanol, CH
3
OH, as a precursor and a tracer of complex organic molecule chemistry, respectively. We find excitation temperatures of 20−30 K for the carbon chains and 8−85 K for the complex organics. The observed abundances, used as input for the chemical evolution code, are 10
−9
to 10
−10
for both CH
3
CCH and CH
3
OH. The CH
3
CCH abundances are reproduced by a warm-up model, consistent with warm carbon chain chemistry, while the observed CH
3
OH abundances require a shock mechanism sputtering the molecules into the gas phase.
Conclusions.
Single-dish observations are useful for studying the envelope-scale chemistry of star-forming regions, including mechanisms such as warm carbon chain chemistry. As well, LTE models lend well to the wide-band maps obtained from these telescopes. The physical and chemical environment determined for complex hydrocarbons and complex organics lends understanding to high-mass star formation.