The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium

Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, N2O, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293–2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and N2O have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm−2 in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO2, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, N2O, and NO2 abundances, but not the NO, HNO, and NH2OH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NH2OH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.

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Dependence of Gas-Phase Abundances in the Interstellar Medium on Column Density

The Astrophysical Journal ◽

10.1086/317316 ◽

2000 ◽

Vol 544 (2) ◽

pp. L107-L110 ◽

Cited By ~ 68

Author(s):

B. P. Wakker ◽

J. S. Mathis

Keyword(s):

Interstellar Medium ◽

Gas Phase ◽

Column Density

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The ALMA-PILS survey: propyne (CH3CCH) in IRAS 16293–2422

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936323 ◽

2019 ◽

Vol 631 ◽

pp. A137 ◽

Cited By ~ 2

Author(s):

H. Calcutt ◽

E. R. Willis ◽

J. K. Jørgensen ◽

P. Bjerkeli ◽

N. F. W. Ligterink ◽

...

Keyword(s):

Gas Phase ◽

Spatial Scales ◽

Excitation Temperature ◽

Gas Phase Reactions ◽

Star Forming ◽

Physical Conditions ◽

Star Forming Regions ◽

Chemical Modelling ◽

Low Mass ◽

Grain Surface

Context. Propyne (CH3CCH), also known as methyl acetylene, has been detected in a variety of environments, from Galactic star-forming regions to extragalactic sources. These molecules are excellent tracers of the physical conditions in star-forming regions, allowing the temperature and density conditions surrounding a forming star to be determined. Aims. This study explores the emission of CH3CCH in the low-mass protostellar binary, IRAS 16293–2422, and examines the spatial scales traced by this molecule, as well as its formation and destruction pathways. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Protostellar Interferometric Line Survey (PILS) were used to determine the abundances and excitation temperatures of CH3CCH towards both protostars. This data allows us to explore spatial scales from 70 to 2400 au. This data is also compared with the three-phase chemical kinetics model MAGICKAL, to explore the chemical reactions of this molecule. Results. CH3CCH is detected towards both IRAS 16293A and IRAS 16293B, and is found the hot corino components, one around each source, in the PILS dataset. Eighteen transitions above 3σ are detected, enabling robust excitation temperatures and column densities to be determined in each source. In IRAS 16293A, an excitation temperature of 90 K and a column density of 7.8 × 1015 cm−2 best fits the spectra. In IRAS 16293B, an excitation temperature of 100 K and 6.8 × 1015 cm−2 best fits the spectra. The chemical modelling finds that in order to reproduce the observed abundances, both gas-phase and grain-surface reactions are needed. The gas-phase reactions are particularly sensitive to the temperature at which CH4 desorbs from the grains. Conclusions. CH3CCH is a molecule whose brightness and abundance in many different regions can be utilised to provide a benchmark of molecular variation with the physical properties of star-forming regions. It is essential when making such comparisons, that the abundances are determined with a good understanding of the spatial scale of the emitting region, to ensure that accurate abundances are derived.

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Molecular complexity on disc scales uncovered by ALMA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834527 ◽

2019 ◽

Vol 628 ◽

pp. A2 ◽

Cited By ~ 7

Author(s):

Eva G. Bøgelund ◽

Andrew G. Barr ◽

Vianney Taquet ◽

Niels F. W. Ligterink ◽

Magnus V. Persson ◽

...

Keyword(s):

Spatial Distribution ◽

Star Formation ◽

Chemical Composition ◽

Column Density ◽

Angular Resolution ◽

High Mass ◽

High Angular Resolution ◽

Mass Star ◽

Complex Species ◽

Low Mass

Context. The chemical composition of high-mass protostars reflects the physical evolution associated with different stages of star formation. In addition, the spatial distribution and velocity structure of different molecular species provide valuable information on the physical structure of these embedded objects. Despite an increasing number of interferometric studies, there is still a high demand for high angular resolution data to study chemical compositions and velocity structures for these objects. Aims. The molecular inventory of the forming high-mass star AFGL 4176, located at a distance of ~3.7 kpc, is studied in detail at a high angular resolution of ~0.35′′, equivalent to ~1285 au at the distance of AFGL 4176. This high resolution makes it possible to separate the emission associated with the inner hot envelope and disc around the forming star from that of its cool outer envelope. The composition of AFGL 4176 is compared with other high- and low-mass sources, and placed in the broader context of star formation. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA) the chemical inventory of AFGL 4176 has been characterised. The high sensitivity of ALMA made it possible to identify weak and optically thin lines and allowed for many isotopologues to be detected, providing a more complete and accurate inventory of the source. For the detected species, excitation temperatures in the range 120–320 K were determined and column densities were derived assuming local thermodynamic equilibrium and using optically thin lines. The spatial distribution of a number of species was studied. Results. A total of 23 different molecular species and their isotopologues are detected in the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH) with a column density of 5.5 × 1018 cm−2 in a beam of ~0.3′′, derived from its 13C-isotopologue. The remaining species are present at levels between 0.003 and 15% with respect to methanol. Hints that N-bearing species peak slightly closer to the location of the peak continuum emission than the O-bearing species are seen. A single species, propyne (CH3C2H), displays a double-peaked distribution. Conclusions. AFGL 4176 comprises a rich chemical inventory including many complex species present on disc scales. On average, the derived column density ratios, with respect to methanol, of O-bearing species are higher than those derived for N-bearing species by a factor of three. This may indicate that AFGL 4176 is a relatively young source since nitrogen chemistry generally takes longer to evolve in the gas phase. Taking methanol as a reference, the composition of AFGL 4176 more closely resembles that of the low-mass protostar IRAS 16293–2422B than that of high-mass, star-forming regions located near the Galactic centre. This similarity hints that the chemical composition of complex species is already set in the cold cloud stage and implies that AFGL 4176 is a young source whose chemical composition has not yet been strongly processed by the central protostar.

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First detection of NHD and ND2 in the interstellar medium

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038490 ◽

2020 ◽

Vol 641 ◽

pp. A153

Author(s):

M. Melosso ◽

L. Bizzocchi ◽

O. Sipilä ◽

B. M. Giuliano ◽

L. Dore ◽

...

Keyword(s):

Interstellar Medium ◽

Column Density ◽

Molecular Spectroscopy ◽

Far Infrared ◽

Chemical Model ◽

Star Forming ◽

Star Forming Regions ◽

Submillimeter Wavelengths ◽

Order Of Magnitude ◽

Low Mass

Context. Deuterium fractionation processes in the interstellar medium (ISM) have been shown to be highly efficient in the family of nitrogen hydrides. To date, observations have been limited to ammonia (NH2D, NHD2, ND3) and imidogen radical (ND) isotopologues. Aims. We want to explore the high-frequency windows offered by the Herschel Space Observatory to search for deuterated forms of the amidogen radical NH2 and to compare the observations against the predictions of our comprehensive gas-grain chemical model. Methods. Making use of the new molecular spectroscopy data recently obtained at high frequencies for NHD and ND2, we searched for both isotopologues in the spectral survey toward the Class 0 protostar IRAS 16293-2422, a source in which NH3, NH, and their deuterated variants have previously been detected. We used the observations carried out with HIFI (Heterodyne Instrument for the Far-Infrared) in the framework of the key program “Chemical Herschel surveys of star forming regions” (CHESS). Results. We report the first detection of interstellar NHD and ND2. Both species are observed in absorption against the continuum of the protostar. From the analysis of their hyperfine structure, accurate excitation temperature and column density values are determined. The latter were combined with the column density of the parent species NH2 to derive the deuterium fractionation in amidogen. We find a high deuteration level of amidogen radical in IRAS 16293-2422, with a deuterium enhancement about one order of magnitude higher than that predicted by earlier astrochemical models. Such a high enhancement can only be reproduced by a gas-grain chemical model if the pre-stellar phase preceding the formation of the protostellar system has a long duration: on the order of one million years. Conclusions. The amidogen D/H ratio measured in the low-mass protostar IRAS 16293-2422 is comparable to that derived for the related species imidogen and much higher than that observed for ammonia. Additional observations of these species will provide more insights into the mechanism of ammonia formation and deuteration in the ISM. Finally, we indicate the current possibilities to further explore these species at submillimeter wavelengths.

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Exploration of Stellar Processes Through Interstellar Abund Anci Studies

Highlights of Astronomy ◽

10.1017/s153929960002147x ◽

1998 ◽

Vol 11 (1) ◽

pp. 397-397

Author(s):

U.J. Sofia ◽

D.M. Meyer

Keyword(s):

Interstellar Medium ◽

Gas Phase ◽

Neutron Capture ◽

The Sun ◽

Agb Stars ◽

The Past ◽

Apparent Inconsistency ◽

Low Mass ◽

Ism Abundances

Interstellar abundances studies can provide answers to some questions about stellar processes, and they can lead to new questions about others. We will discuss some recent interstellar abundance determinations and their implications for stellar studies. Although Cd and Sn are chemically similar to elements which are moderately to heavily depleted from the gas-phase interstellar medium (ISM), they appear to have solar-like abundances in inter-stellar clouds. This is likelythe result of these elements being depleted from an ISM which has been enriched with Cd and Sn since the formation of the sun. These two elements are mainly produced by s-process neutron capture in intermediate to low mass AGB stars. The present ISM abundances of Cd and Sn can therefore provide information about s-process yields and the cumulative injection of this material into the ISM over the past 4.5 Gy. Recent studies of C and O abundances in the ISM have shown that the C/H and O/H are constant out to approximately 1500pc from the sun. Local B star abundance studies, however, find that C/O is not constant, thereby indicating that the ISM is not well mixed or homogeneous. We currently do not have an explanation for this apparent inconsistency between stars and the ISM.

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ELECTRONIC SPECTROSCOPY OF ORGANIC CATIONS IN GAS-PHASE AT 6 K:IDENTIFICATION OF C60 + IN THE INTERSTELLAR MEDIUM

Proceedings of the 71st International Symposium on Molecular Spectroscopy ◽

10.15278/isms.2016.ma01 ◽

2016 ◽

Author(s):

John Maier

Keyword(s):

Interstellar Medium ◽

Gas Phase ◽

Electronic Spectroscopy ◽

Organic Cations

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Abundances in the Gaseous Galactic Halo

Highlights of Astronomy ◽

10.1017/s1539299600020049 ◽

1998 ◽

Vol 11 (1) ◽

pp. 86-89

Author(s):

Ulysses J. Sofia

Keyword(s):

Interstellar Medium ◽

Gas Phase ◽

High Velocity ◽

Galactic Halo ◽

Solar Neighborhood ◽

Local Interstellar Medium ◽

The Galaxy ◽

Metal Abundances ◽

High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

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