arXiv subjects

Anton Vasyunin

Publications and source records attributed to Anton Vasyunin.

17 recordsLinked to original sources

arXiv2026

Mapping Interstellar Ice Inventory toward Class 0 Protostars in Star-forming Region Orion A with JWST Data

We present a detailed study of the spatial distribution and chemical composition of interstellar ices toward six Class 0 protostars (HOPS-56, HOPS-60, HOPS-73, HOPS-91, HOPS-96, and HOPS-108) in the Orion A molecular cloud. Using high-resolution spectroscopic data from the JWST NIRspec and MIRI MRS instruments (4.3 - 8.1 $\mu$m), we have constructed the first pixel by pixel absorption maps with a resolution of $\sim$100~AU for key ice species, including $^{13}$CO$_2$, OCN$^-$, CO, H$_2$O, NH$_4^+$, and H$_2$CO. CH$_4$ and OCS were analyzed toward the continuum peaks. The column densities were derived by fitting the observed spectra with laboratory ice analogs. We employed radiative transfer modeling, which confirmed the reliability of our column density estimates within the protostellar envelopes. Our analysis reveals significant variations in ice abundances and distributions, reflecting the physical structure and energetic processes within the envelopes. Specifically, we observe the influence of protostellar heating and outflows on the ice mantles, most notably in HOPS-60. The total ice composition is consistent with astrochemical models and covers $\sim$90% of observed ice inventory suggesting that ice is primarily formed during the prestellar stage and subsequently inherited by the protostellar envelope. Based on the abundance relative to water, the sources can be categorized into two distinct groups, possibly indicating evolutionary differences or variations in envelope density and temperature profiles.

astro-ph.GA↗

arXiv2026

Infrared spectra of methane-containing ice mixtures for JWST data analyses

Context. Solid methane (CH$_4$) is an important molecule in interstellar and planetary environments, serving as a precursor to complex organic compounds, and it is a potential biosignature in exoplanetary studies. Despite its significance, laboratory data on the low temperature phase of methane below 10 K remain limited. Aims. We obtained spectra of methane in binary mixtures at 10 K and compared them to the spectra obtained at 6.7 K. These temperatures correspond to phases II and II* of pure methane and are representative of dark molecular clouds and protostars in early stages. We also tested whether the data we obtained can be applied to interpret JWST data. Methods. Laboratory reference spectra were obtained with the ISEAge setup via Fourier transform infrared spectroscopy in transmission mode. A weighted $\chi^2$ minimization was used for the fitting. Results. We present infrared spectra with corresponding band strengths of pure methane and binary mixtures with methane: CH$_4$:H$_2$O, CH$_4$:CO$_2$, CH$_4$:CH$_3$OH, and CH$_4$:NH$_3$ at 6.7 K and 10 K. They show an increase of 20% in mixtures compared to the commonly used 10 K band strength value of pure methane. We also tested whether the spectra can be used on open JWST data by probing the spatial distribution of methane in B335. We also present additional experiments concerning the phase transition of methane between phase II* and phase II. Conclusions. Our results reveal distinct spectral features for methane in non-H$_2$O environments that enable a more accurate interpretation of JWST observations. The dataset of spectra is publicly available on Zenodo and can be used for fitting JWST data.

astro-ph.SR↗

arXiv2026

Using astrochemical models to simulate reactivity experiments on cold surfaces

The development of molecular complexity during stellar and planetary formation owes much to the interaction of gas and dust. When the first astrochemical models including solid-state chemistry were developed more than forty years ago, data from dedicated laboratory experiments were limited. Since then, many groups have developed specific experimental setups to address this issue, but astrochemical models have rarely been directly confronted with these new results. We want to demonstrate whether it is possible to use rate-equation-type astrochemical models developed in the context of the Interstellar Medium to compare them with laboratory astrophysics experiments. In this work, we use the case of low-temperature hydrogenation of CO, which is known to lead to methanol, among other molecules. We carried out 9 experiments, varying the experimental parameters such as temperature and dose. We give quantitative results and take care of detailing the vocabulary used in the experiments. We use astrochemical codes, NAUTILUS, pyRate and MONACO, to reproduce our experimental conditions, which requires good control of the change of vocabulary and scales, especially for fluxes and time scales. This work demonstrates that it is possible to use different astrochemical codes to compare modelling results directly with the output of experiments. There are discrepancies between models and experiments, as well as between models, but a fair agreement is achieved. We discuss the possible origin of the differences, which could originate from the chemical network or the difference in the description of physical processes.

astro-ph.GA↗

arXiv2025

Chemical evolution in high-mass star-forming regions

Growing evidence shows that most stars in the Milky Way, including the Sun, are born in high-mass star-forming regions, but due to both observational and theoretical challenges, our understanding of their chemical evolution is much less clear than that of their low-mass counterparts. Thanks to the capabilities of new generation telescopes and computers, a growing amount of observational and theoretical results have been recently obtained, which have important implications not only for our understanding of the (still mysterious) formation process of high-mass stars, but also for the chemistry that the primordial Solar System might have inherited from its birth environment. In this review, we summarise the main observational and theoretical results achieved in the last decades in the study of chemistry evolution in high-mass star-forming regions, and in the identification of chemical evolutionary indicators. Emphasis is especially given to observational studies, for which most of the work has been carried out so far. A comparison with the chemical evolution occurring in other astrophysical environments, in particular in low-mass star-forming cores and extragalactic cores, is also briefly presented. Current open questions and future perspectives are discussed.

astro-ph.GA↗

arXiv2025

Deuteration of water in protoplanetary discs during luminosity outbursts: model predictions for FU Ori discs

Luminosity outbursts of FU Ori-type objects (FUors) allow us to observe in the gas the molecules that are typically present in the ice in protoplanetary discs. In particular, the fraction of deuterated water, which is usually is mostly frozen in the midplane of a protoplanetary disc, has been measured for the first time in the gas of the disc around a FUor V883 Ori. We test the hypothesis that the observed high HDO/H$_{2}$O ratio in the V883 Ori protoplanetary disc can be explained by luminosity outbursts of different amplitude, including a series of two consecutive outbursts. Using the ANDES astrochemical code, we modelled the distributions of water and deuterated water abundances under the action of luminosity outbursts of different amplitudes (from 400 to 10 000 $L_{\odot}$) and at different stellar luminosities at the pre-outburst stage. We show that the best agreement with the observed HDO/H$_{2}$O profile is obtained for outburst amplitudes of 2 000 and 10 000 $L_{\odot}$, while the observed bolometric luminosity of V883 Ori does not exceed 400 $L_{\odot}$. We discuss possible reasons for this discrepancy, including the presence of past luminosity outbursts, the age of the star, and the influence of additional heating mechanisms in the midplane of the protoplanetary disc. We also consider how the high observed $\rm HDO/H_{2}O$ ratio may be related to the evolution of the chemical composition of the ice in the protoplanetary disc and the chemical processes activated under outburst conditions.

astro-ph.EP↗

arXiv2024

Solid and Gaseous Methane in IRAS 23385+6053 as seen with Open JWST Data

We present a new description of the 7.7~$\mu$m region towards the high-mass star-forming region IRAS 23385+6053 taken from open James Webb Space Telescope Mid-Infrared Instrument Medium Resolution Spectrometer (JWST MIRI/MRS) data. This area is commonly attributed to the $\nu_4$ deformation mode of methane ice. For the first time gaseous and solid methane were analyzed simultaneously in IRAS 23385+6053. The band at 7.58--7.8 $\mu$m (1320--1280 cm$^{-1}$) is interpreted as a wide solid absorption methane feature overlapped by the sharp features of the methane emission. We report the detection of gaseous methane and estimate its emitting area radius~$R$, temperature~$T$ and column density~$N$ as $R=2940$~au, $T=103^{+13}_{-11}$~K, and $N=0.78_{+6.18}^{-0.64}\times10^{17}$~cm$^{-2}$, correspondingly. The ice content was analyzed with the laboratory spectra dataset of methane in different molecular environments obtained on the Ice Spectroscopy Experimental Aggregate (ISEAge). We were able to describe the wide feature of solid methane with the following laboratory spectra: CH$_4$~:~CO$_2$~=~1~:~5 (at $27.4^{+6.0}_{-10.8}$~K) and CH$_4$~:~H$_2$O~=~1~:~10 (at $8.4^{+16.4}_{-1.7}$~K) deposited at 6.7~K and warmed up at a rate of 0.5 K per minute. The derived column densities are $N_{\text{CH}_4}$(CO$_2$)~=~$2.97^{+0.37}_{-0.57}\times10^{17}$~cm$^{-2}$ and $N_{\text{CH}_4}$(H$_2$O)~=~$1.02^{+0.46}_{-0.27}\times10^{17}$~cm$^{-2}$. According to the best fit solid methane is mostly surrounded by CO$_2$ rather than H$_2$O. The residuals analysis reveals the unassigned region at 1283--1297~cm$^{-1}$ (7.71--7.79~$\mu$m) which is tentatively assigned to nitrous oxide (N$_2$O) in various environments.

astro-ph.GA↗

arXiv2024

Infrared Spectra of Solid HCN Embedded in Various Molecular Environments for Comparison with the Data Obtained with JWST

HCN molecules serve as an important tracer for chemical evolution of elemental nitrogen in the regions of star and planet formation. This is largely explained by the fact that N atoms and N$_2$ molecules are poorly accessible for the observation in the radio and infrared ranges. In turn, gas-phase HCN can be observed at various stages of star formation including disks arounds young stars, cometary comas and atmospheres of the planetary satellites. Despite the large geography of gas-phase observations, an identification of interstellar HCN ice is still lacking. In this work we present a series of infrared spectroscopic measurements performed at the new ultra-high vacuum cryogenic apparatus aiming to facilitate the search for interstellar HCN ice. A series of high resolution laboratory infrared spectra of HCN molecules embedded in the H$_2$O, H$_2$O:NH$_3$, CO, CO$_2$ and CH$_3$OH ices at 10~K temperature is obtained. These interstellar ice analogues aim to simulate the surroundings of HCN molecules by the main constituents of the icy mantles on the surface of the interstellar grains. In addition, the spectra of HCN molecules embedded in the solid C$_6$H$_6$, C$_5$H$_5$N and C$_6$H$_5$NH$_2$ are obtained to somehow simulate the interaction of HCN molecules with carbonaceous material of the grains rich in polycyclic aromatic hydrocarbons. The acquired laboratory spectroscopic data are compared with the publicly available results of NIRSpec James Webb Space Telescope observations towards quiescent molecular clouds performed by the ICEAge team.

astro-ph.GA↗

arXiv2022

Multi-line observations of CH$_{3}$OH, c-C$_{3}$H$_{2}$ and HNCO towards L1544: Dissecting the core structure with chemical differentiation

Pre-stellar cores are the basic unit for the formation of stars and stellar systems. The anatomy of the physical and chemical structures of pre-stellar cores is critical for understanding the star formation process. L1544 is a prototypical pre-stellar core, which shows significant chemical differentiation surrounding the dust peak. We aim to constrain the physical conditions at the different molecular emission peaks. This study allows us to compare the abundance profiles predicted from chemical models together with the classical density structure of Bonnor-Ebert (BE) sphere. We conducted multi-transition pointed observations of CH$_{3}$OH, c-C$_{3}$H$_{2}$ and HNCO with the IRAM 30m telescope, towards the dust peak and the respective molecular peaks of L1544. With non-LTE radiative transfer calculations and a 1-dimensional model, we revisit the physical structure of L1544, and benchmark with the abundance profiles from current chemical models. We find that the HNCO, c-C$_{3}$H$_{2}$ and CH$_{3}$OH lines in L1544 are tracing progressively higher density gas, from $\sim$10$^{4}$ to several times 10$^{5}$ cm$^{-3}$. Particularly, we find that to produce the observed intensities and ratios of the CH$_{3}$OH lines, a local gas density enhancement upon the BE sphere is required. This suggests that the physical structure of an early-stage core may not necessarily follow a smooth decrease of gas density profile locally, but can be intercepted by clumpy substructures surrounding the gravitational center. Multiple transitions of molecular lines from different molecular species can provide a tomographic view of the density structure of pre-stellar cores. The local gas density enhancement deviating from the BE sphere may reflect the impact of accretion flows that appear asymmetric and are enhanced at the meeting point of large-scale cloud structures.

astro-ph.GA↗

arXiv2021

Methanol Mapping in Cold Cores: Testing Model Predictions

Chemical models predict that in cold cores gas-phase methanol is expected to be abundant at the outer edge of the CO depletion zone, where CO is actively adsorbed. CO adsorption correlates with volume density in cold cores, and, in nearby molecular clouds, the catastrophic CO freeze-out happens at volume densities above 10$^4$ cm$^{-3}$. The methanol production rate is maximized there and its freeze-out rate does not overcome its production rate, while the molecules are shielded from UV destruction by gas and dust. Thus, in cold cores, methanol abundance should generally correlate with visual extinction that depends both on volume and column density. In this work, we test the most basic model prediction that maximum methanol abundance is associated with a local $A_V\simeq$4 mag in dense cores and constrain the model parameters with the observational data. With the IRAM 30 m antenna, we mapped the CH$_3$OH (2-1) and (3-2) transitions toward seven dense cores in the L1495 filament in Taurus to measure the methanol abundance. We use the Herschel/SPIRE maps to estimate visual extinction, and the C$^{18}$O(2-1) maps from Tafalla & Hacar (2015) to estimate CO depletion. We explored the observed and modeled correlations between the methanol abundances, CO depletion, and visual extinction varying the key model parameters. The modeling results show that hydrogen surface diffusion via tunneling is crucial to reproduce the observed methanol abundances, and the needed reactive desorption efficiency matches the one deduced from laboratory experiments.

astro-ph.GA↗

arXiv2021

Detection of Complex Organic Molecules in Young Starless Core L1521E

Determining the level of chemical complexity within dense starless and gravitationally bound prestellar cores is crucial for constructing chemical models, which subsequently constrain the initial chemical conditions of star formation. We have searched for complex organic molecules (COMs) in the young starless core L1521E, and report the first clear detection of dimethyl ether (CH$_3$OCH$_3$), methyl formate (HCOOCH$_3$), and vinyl cyanide (CH$_2$CHCN). Eight transitions of acetaldehyde (CH$_3$CHO) were also detected, five of which (A states) were used to determine an excitation temperature to then calculate column densities for the other oxygen-bearing COMs. If source size was not taken into account (i.e., if filling fraction was assumed to be one), column density was underestimated, and thus we stress the need for higher resolution mapping data. We calculated L1521E COM abundances and compared them to other stages of low-mass star formation, also finding similarities to other starless/prestellar cores, suggesting related chemical evolution. The scenario that assumes formation of COMs in gas-phase reactions between precursors formed on grains and then ejected to the cold gas via reactive desorption was tested and was unable to reproduce observed COM abundances, with the exception of CH$_3$CHO. These results suggest that COMs observed in cold gas are formed not by gas-phase reactions alone, but also through surface reactions on interstellar grains. Our observations present a new, unique challenge for existing theoretical astrochemical models.

astro-ph.GA↗

arXiv2020

Cosmic ray tracks in astrophysical ices: Modeling with the Geant4-DNA Monte Carlo Toolkit

Cosmic rays are ubiquitous in interstellar environments, and their bombardment of dust-grain ice mantles is a possible driver for the formation of complex, even prebiotic molecules. Yet, critical data that are essential for accurate modeling of this phenomenon, such as the average radii of cosmic-ray tracks in amorphous solid water (ASW) remain unconstrained. It is shown that cosmic ray tracks in ASW can be approximated as a cylindrical volume with an average radius that is mostly independent of the initial particle energy. Interactions between energetic ions and both a low-density amorphous (LDA) and high-density amorphous (HDA) ice target are simulated using the Geant4-DNA Monte Carlo toolkit, which allows for tracking secondary electrons down to subexcitation energies in the material. We find the peak track core radii, $r_\mathrm{cyl}$, for LDA and HDA ices to be 9.9 nm and 8.4 nm, respectively - somewhat less than double the value of 5 nm often assumed in astrochemical models.

astro-ph.GA↗

arXiv2019

Efficient Production of S$_8$ in Interstellar Ices: The effects of cosmic ray-driven radiation chemistry and non-diffusive bulk reactions

In this work, we reexamine sulfur chemistry occurring on and in the ice mantles of interstellar dust grains, and report the effects of two new modifications to standard astrochemical models; namely, (a) the incorporation of cosmic ray-driven radiation chemistry and (b) the assumption of fast, non-diffusive reactions for key radicals in the bulk. Results from our models of dense molecular clouds show that these changes can have a profound influence on the abundances of sulfur-bearing species in ice mantles, including a reduction in the abundance of solid-phase H$_2$S and HS, and a significant increase in the abundances of OCS, SO$_2$, as well as pure allotropes of sulfur, especially S$_8$. These pure-sulfur species - though nearly impossible to observe directly - have long been speculated to be potential sulfur reservoirs and our results represent possibly the most accurate estimates yet of their abundances in the dense ISM. Moreover, the results of these updated models are found to be in good agreement with available observational data. Finally, we examine the implications of our findings with regard to the as-yet-unknown sulfur reservoir thought to exist in dense interstellar environments.

astro-ph.GA↗

arXiv2019

The first steps of Interstellar Phosphorus Chemistry

Phosphorus-bearing species are an essential key to form life on Earth, however they have barely been detected in the interstellar medium. Since only PN and PO have been identified so far towards star-forming regions, the chemical formation pathways of P-bearing molecules are not easy to constrain and are thus highly debatable. An important factor still missing in the chemical models is the initial elemental abundance of phosphorus, i.e. the depletion level of P. In order to overcome this problem, we study P-bearing species in diffuse/translucent clouds. In these objects phosphorus is mainly in the gas phase and therefore the elemental initial abundance needed in our chemical simulations corresponds to the cosmic one and is thus well constrained. An advanced chemical model with an updated P-chemistry network has been used. Single-pointing observations were performed with the IRAM 30m telescope towards the line of sight to the blazar B0355+508 aiming for the (2-1) transitions of PN, PO, HCP and CP. This line of sight incorporates five diffuse/translucent clouds. The (2-1) transitions of the PN, PO, HCP and CP were not detected. We report detections of the (1-0) lines of $\mathrm{^{13}CO}$, HNC and CN along with a first detection of $\mathrm{C^{34}S}$. We have reproduced the observations of HNC, CN, CS and CO in every cloud by applying typical conditions for diffuse/translucent clouds. According to our best-fit model, the most abundant P-bearing species are HCP and CP ($\sim10^{-10}$), followed by PN, PO and $\mathrm{PH_3}$ ($\sim10^{-11}$). We show that the production of P-bearing species is favoured towards translucent rather than diffuse clouds, where the environment provides a stronger shielding from the interstellar radiation. Based on our improved model, the (1-0) transitions of HCP, CP, PN and PO are expected to be detectable with estimated intensities up to $\sim200$ mK.

astro-ph.GA↗

arXiv2019

On Simulating the Proton-Irradiation of O$_2$ and H$_2$O Ices Using Astrochemical-type Models, with Implications for Bulk Reactivity

Many astrochemical models today explicitly consider the species that comprise the bulk of interstellar dust grain ice-mantles separately from those in the top few monolayers. Bombardment of these ices by ionizing radiation - whether in the form of cosmic rays, stellar winds, or radionuclide emission - represents an astrochemically viable means of driving a rich chemistry even in the bulk of the ice-mantle, now supported by a large body of work in laboratory astrophysics. In this study, using an existing rate equation-based astrochemical code modified to include a method of considering radiation chemistry recently developed by us, we attempted to simulate two such studies in which (a) pure O$_2$ ice at 5 K and, (b) pure H$_2$O ice at 16 K and 77 K, were bombarded by keV H$^+$ ions. Our aims are twofold: (1) to test the capability of our newly developed method to replicate the results of ice-irradiation experiments, and (2) to determine in such a well-constrained system how bulk chemistry is best handled using the same gas-grain codes that are used to model the interstellar medium (ISM). We find that our modified astrochemical model is able to reproduce both the abundance of O$_3$ in the 5 K pure O$_2$ ice, as well as both the abundance of H$_2$O$_2$ in the 16 K water ice and the previously noted decrease of hydrogen peroxide at higher temperatures. However, these results require the assumption that radicals and other reactive species produced via radiolysis react quickly and non-diffusively with neighbors in the ice.

astro-ph.GA↗

arXiv2018

The first detections of the key prebiotic molecule PO in star-forming regions

Phosphorus is a crucial element in prebiotic chemistry, especially the P$-$O bond, which is key for the formation of the backbone of the deoxyribonucleic acid. So far, PO had only been detected towards the envelope of evolved stars, and never towards star-forming regions. We report the first detection of PO towards two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30m telescope. PN has also been detected towards the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutral-neutral reactions during the cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches $\sim$35 K. The observed molecular abundances of 10$^{-10}$ are predicted by the model if a relatively high initial abundance of phosphorus, 5$\times$10$^{-9}$, is assumed.

astro-ph.GA↗

arXiv2017

Gas mass tracers in protoplanetary disks: CO is still the best

Protoplanetary disk mass is a key parameter controlling the process of planetary system formation. CO molecular emission is often used as a tracer of gas mass in the disk. In this study we consider the ability of CO to trace the gas mass over a wide range of disk structural parameters and search for chemical species that could possibly be used as alternative mass tracers to CO. Specifically, we apply detailed astrochemical modeling to a large set of models of protoplanetary disks around low-mass stars, to select molecules with abundances correlated with the disk mass and being relatively insensitive to other disk properties. We do not consider sophisticated dust evolution models, restricting ourselves with the standard astrochemical assumption of $0.1~μ$m dust. We find that CO is indeed the best molecular tracer for total gas mass, despite the fact that it is not the main carbon carrier, provided reasonable assumptions about CO abundance in the disk are used. Typically, chemical reprocessing lowers the abundance of CO by a factor of 3, compared to the case of photo-dissociation and freeze-out as the only ways of CO depletion. On average only 13% C-atoms reside in gas-phase CO, albeit with variations from 2 to 30%. CO$_2$, H$_2$O and H$_2$CO can potentially serve as alternative mass tracers, the latter two being only applicable if disk structural parameters are known.

astro-ph.EP↗

arXiv2013

Chemical Evolution in High-Mass Star-Forming Regions: Results from the MALT90 Survey

The chemical changes of high-mass star-forming regions provide a potential method for classifying their evolutionary stages and, ultimately, ages. In this study, we search for correlations between molecular abundances and the evolutionary stages of dense molecular clumps associated with high-mass star formation. We use the molecular line maps from Year 1 of the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey. The survey mapped several hundred individual star-forming clumps chosen from the ATLASGAL survey to span the complete range of evolution, from prestellar to protostellar to H II regions. The evolutionary stage of each clump is classified using the Spitzer GLIMPSE/MIPSGAL mid-IR surveys. Where possible, we determine the dust temperatures and H2 column densities for each clump from Herschel Hi-GAL continuum data. From MALT90 data, we measure the integrated intensities of the N2H+, HCO+, HCN and HNC (1-0) lines, and derive the column densities and abundances of N2H+ and HCO+. The Herschel dust temperatures increase as a function of the IR-based Spitzer evolutionary classification scheme, with the youngest clumps being the coldest, which gives confidence that this classification method provides a reliable way to assign evolutionary stages to clumps. Both N2H+ and HCO+ abundances increase as a function of evolutionary stage, whereas the N2H+ (1-0) to HCO+ (1-0) integrated intensity ratios show no discernable trend. The HCN (1-0) to HNC(1-0) integrated intensity ratios show marginal evidence of an increase as the clumps evolve.

astro-ph.GA↗