arXiv subjects

M. S. Kirsanova

Publications and source records attributed to M. S. Kirsanova.

At least 19 recordsLinked to original sources

arXiv2026

OPTIMus-Survey of massive star-forming regions at OPTical, Infrared, and Millimeter wavelengths

This work presents a description of the scientific goals and objectives of OPTIMus (OPTical, Infrared, Millimeter survey of massive star-forming regions), a survey of massive star-forming regions in the optical, infrared, and millimeter wavelengths. The survey is aimed at constructing a comprehensive characterization of the multicomponent and structurally complex interstellar medium in the vicinity of young massive stars, combining both observational and theoretical aspects. Using multi-wavelength observational data, we will reconstruct the three-dimensional structure and determine the physical parameters of HII regions, photodissociation regions, and the surrounding molecular clouds. The paper describes the observational data obtained with the BTA 6-m and Zeiss-1000 telescopes of the Special Astrophysical Observatory of the Russian Academy of Sciences, the 2.5-m telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University, and the 20-m telescope of the Onsala Space Observatory.

astro-ph.GA↗

arXiv2026

Gas-phase and Surface Chemistry in the Massive Star-Forming Region RCW\,120

We analysed broadband emission spectra of a dense molecular clump in RCW 120, obtained with the APEX telescope in the 200--260 GHz range, in order to investigate molecular formation pathways in regions of massive star formation at an early evolutionary stage. We examined the correlations between the molecular column densities derived under the LTE assumption. An excess of methanol was found in the southern part of the dense clump relative to its northern part, while the abundances of other molecules, such as CH$_3$CN and CH$_3$CCH, remain comparable. The methanol abundance is also elevated relative to that of other oxygen-bearing molecules, such as OCS and SO. To identify possible causes of the enhanced methanol abundance in the southern part of the clump, we carried out simulations with the astrochemical model Presta in a two-phase approximation, accounting for chemical processes both in the gas phase and in the mantles of dust grains. The modelling shows that the enhanced gas-phase methanol abundance may be due to photodesorption from icy mantles. At Av values between $4^{m}$ and $6^{m}$, methanol desorbs efficiently from the ice mantles of dust grains upon interaction with photons, but is not yet destroyed by UV radiation in the gas phase. A strong linear correlation between molecular column densities indicates that the molecules form in the same phase --- either in the gas phase or on dust. Their integrated intensity maps may nevertheless differ, as is the case for CCH and CH$_3$CN. If two molecules form in different phases --- one in the gas phase and the other in dust mantles --- no correlation is observed, as for CCH and CH$_3$OH. The weak correlation between methanol and the oxygen-bearing molecules that form on dust suggests that only the upper part of the dust mantles, rich in CO ice, is destroyed in the southern part of the clump.

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arXiv2026

Complex organic molecules in the young hot core RCW 120 S2

We analyse physical and chemical structure of the hot molecular core RCW120 S2, based on high-sensitivity (2-4 mK) APEX observations at 1.3 mm. The analysis reveals a rich molecular inventory, including complex organic molecules (COMs) such as CH$_3$OH, CH$_3$CHO, CH$_3$OCHO and CH$_3$OCH. We derive gas temperatures (20-300 K), H$_2$ densities (10$^4$-10$^7$cm$^{-3}$), and molecular column densities. The detected emission probes a radially stratified envelope, with cooler (<= 60 K) and less dense (10$^4$-10$^5$cm$^{-3}$) outer layers traced by SO, SO2, and c-C$_3$H$_2$, while warmer (60-100 K) and denser (10$^5$-10$^7$cm$^{-3}$) inner regions are traced by H$_2$CO, OCS, and low-excitation CH$_3$CN. The hot gas (<= 100 K) exhibits broad (8-10 km/s) lines from high-excitation CH$_3$OH, CH$_3$CN, HDO, and CH$_3$OCH$_3$. Relative molecular abundances of COMs generally agree with astrochemical hot-core models, while methanol appears underabundant and CH$_3$CN overabundant compared to predictions. We attribute these discrepancies to the need for interferometric observations at intermediate spatial scales to resolve the core's true filling factor and radial gradients.

astro-ph.GA↗

arXiv2026

Single-dish observations and non-LTE analysis of CH3OH, HCN, and CO line emission in the Oort cloud comet C/2017 K2 (PANSTARRS)

We present pre-perihelion observations of methanol, carbon monoxide, and hydrogen cyanide in the Oort cloud comet C/2017 K2 (PANSTARRS), performed with the APEX 12-m and Onsala 20-m telescopes from April to July 2022. As the comets heliocentric distance decreased from 3.4 to 2.7 AU, CH3OH line intensities increased substantially (by factors of 1.1-4.0), with the most pronounced enhancement in lines with the upper-level energies Eu > 40K. In contrast, the brightness of the CO and HCN lines remained constant. We estimate the best-fit gas kinetic temperatures Tgas > 100 K and water production rate of Q(H2O)=(3-10)*10(28) 1/s. The derived methanol-to-water abundance ratio approx. 0.01-0.04, depending on the observed period. Our results demonstrate that non-LTE effects are dominant in the coma and must be accounted for to accurately derive molecular production rates. We also report weak non-thermal excitation, including potential maser activity in the CH3OH 8(0)-7(1) line.

astro-ph.EP↗

arXiv2026

Sky background accounting in spectral infrared observations of extended objects at the Caucasus Mountain Observatory of the SAI MSU

The Caucasus Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University is the only one in Russia and one of the few in the world where is possible to obtain spectral data in the near-infrared (IR) range at $λ$=1-2.5 $μ$m. However, there is a problem of processing the spectra of extended objects, the angular dimensions of which exceed the length of the slit (4.5 arcmin). Obtaining additional spectra of the sky in the immediate vicinity of such objects does not solve the problem, since bright atmospheric hydroxyl lines at $λ$~2 $μ$m change their intensity significantly over a time shorter than the exposure time of a single frame. We have developed a technique that allows us to correctly account for and exclude the contribution of variable atmospheric lines in the spectra of extended objects. This technique has been successfully tested in spectroscopic studies of the star-forming region NGC 7538 (S158) in our Galaxy.

astro-ph.IM↗

arXiv2026

Identifying Evolutionary Stages of Molecular Clumps through Unsupervised and Supervised Machine Learning

The evolutionary classification of molecular clumps, crucial for understanding star formation, is commonly based on human-assigned categories derived from infrared (IR) emission and well-established morphological criteria. However, due to ambiguous signatures, distance uncertainties or heavily obscured IR emission, a significant fraction of sources often remains unclassified. This work demonstrates the capability of machine learning (ML) as a complementary, data-driven approach to automate the identification and classification of these clumps using data from the MALT90 survey, complemented by Spitzer IR photometry. We applied unsupervised clustering with HDBSCAN on molecular line intensities, revealing distinct groupings that correspond to evolutionary stages. Using only five molecular lines (HCO$^+$, HNC, N$_2$H$^+$, HCN, C$_2$H), we identified stable clusters of protostars and regions without active star formation, driven primarily by C$_2$H and N$_2$H$^+$ emission. Incorporating H$^{13}$CO$^+$ gave rise to a distinct UV-dominant cluster, tracing more evolved regions. Infrared properties appeared as non-significant features implying that envelopes of clumps with different masses are similar in their global infrared characteristics. We then employed supervised learning to classify clumps with previously uncertain categories and provided classifications for 522 objects, predominantly as regions without active star formation. Our results show that ML techniques can effectively uncover intrinsic evolutionary structures in complex astrochemical data and assign categories to uncertain sources, providing a powerful, data-driven complement to traditional methods.

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arXiv2025

Interstellar Medium in Extremely High Star-Formation Regions: A Prospect of Observations on the Millimetron Space Observatory

High star-formation rate and active galactic nucleus' emission can significantly transform the interstellar medium. In ultra-luminous infrared galaxies, in which the star-formation rate reaches thousands of solar masses per year, the gas and dust are considerably affected by the ionizing radiation, cosmic rays and shock waves, that can be about a factor of 100--1000 larger than typical values in quiet star-forming galaxies. In these conditions, the emissivity of the gas and dust changes: in dense gas, high ionic and molecular transitions become excited, while dust grains are heated to high temperatures. In this paper, we analyze the possibilities for studying the interstellar medium in extreme conditions of ultra-luminous infrared galaxies at redshifts of $\sim 0-3$, utilizing the atomic and molecular lines, and dust continuum in far infrared range of $100-500μ$m. We discuss the prospect of observations using the instruments of the Millimetron Space Observatory.

astro-ph.GA↗

arXiv2025

MOLLId: software for automatic identification of spectral molecular lines in the sub-millimeter and millimeter bands and its application to the spectra of protostars from the region RCW 120

In this work, we present the program MOLLId (MOLecular Line Identification) for automated molecular lines approximation with gaussian profile. Molecular identification was performed using multi-level comparison of the lines' center frequencies and rest frequencies from the spectroscopic database. The program was tested using identification of the molecular lines in observational spectra of young stellar objects RCW 120 YSO S1 and RCW 120 YSO S2, located near the border of the RCW 120 PDR. In the spectra of the RCW 120 YSO S1 source, 100 lines of 41 molecules were identified over the level of 4-6 sigma. In the spectra of the RCW 120 YSO S2 source, 407 lines of 79 molecules were identified over the level 3-5 sigma. Using Intel Core i7-12700K CPU, identification time is equal to 6 and 8 minutes per spectral range for the YSOs S1 and S2, respectively. From the analysis of CH3OH, CH3CN, CH3CCH molecules identified in RCW 120 YSO S2 we found a two-component structure and estimated the physical parameters in the LTE approximation for each of the components.

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arXiv2024

A study of the star clusters' population in the giant molecular cloud G174+2.5

We study the structure, interstellar absorption, color-magnitude diagrams, kinematics, and dynamical state of embedded star clusters in the star-forming region associated with the giant molecular cloud G174+2.5. Our investigation is based on photometric data from the UKIDSS Galactic Plane Survey catalog and astrometric data from the Gaia DR3 catalogs. First, we recover all the known embedded clusters and candidate clusters in the region using surface density maps. Then, for the detected clusters, we determine their general parameters: the center positions, radii, number of stars, and reddening. To evaluate the reddening, we use both the NICEST algorithm and the Q-method. Both methods produce consistent extinction maps in the regions of the four studied clusters. However, the Q-method yields a much smaller color scatter in the CMD. For four clusters in particular (S235~North-West, S235~A-B-C, S235~Central, and S235~East1+East2), we were able to compute individual membership probabilities, the cluster distances, the cluster masses, and their average proper motions. By building on these results, we have studied the clusters' kinematics and dynamics. Moreover, we estimate the mass of the gas component and the star formation efficiency (SFE) in the regions of these four clusters. Finally, we provide an estimate of the total energy of the stellar and gas components in the area of these four clusters to determine whether the clusters are bound (here we consider a `cluster' as the system `stars + gas'). The gravitational bound strongly depends on the region for which we estimate the gas mass. If we consider the mass of the entire cloud, all these four clusters turn out to be bound.

astro-ph.GA↗

arXiv2024

Chemical differentiation and gas kinematics around massive young stellar objects in RCW 120

We present results of a spectral survey towards a dense molecular condensation and young stellar objects (YSOs) projected on the border of the HII region RCW 120 and discuss emission of 20 molecules which produce the brightest lines. The survey was performed with the APEX telescope in the frequency range 200 -- 260 GHz. We provide evidences for two outflows in the dense gas. The first one is powered by the RCW 120 S2 YSO and oriented along the line of sight. The second outflow around RCW 120 S1 is aligned almost perpendicular to the line of sight. We show that area with bright emission of CH$_3$OH, CH$_3$CCH and CH$_3$CN are organised into an onion-like structure where CH$_3$CN traces warmer regions around the YSOs than the other molecules. Methanol seems to be released to the gas phase by shock waves in the vicinity of the outflows while thermal evaporation still does not work towards the YSOs. We find only a single manifestation of the UV radiation to the molecules, namely, enhanced abundances of small hydrocarbons CCH and c-C$_3$H$_2$ in the photo-dissociation region.

astro-ph.GA↗

arXiv2023

Near infrared view on the photodissociation regions S255, S257, NGC7538 and S140

We performed photometric observations of the S255, S257, S140, NGC7358 and the Orion~Bar photo-dissociation regions (PDRs) at 2 micron using narrow-band filters centered on the Br-gamma, H2 and [FeII] lines, as well as the narrow-band Kcont and the broad-band H filters for continuum subtraction. The observations were done with the 2.5-m telescope of the SAI Caucasian Mountain Observatory and the near-infrared camera and spectrograph ASTRONIRCAM. We find several high-density arc-like structures in the Br-gamma and [FeII] images of the ionized gas in NGC7538 and extended shells and arcs visible through the H2 emission. The H ionization front and H2 dissociation front are merged in NGC7538. In S255 and S257 we detected only Br-gamma emission from the HII regions and bright H2 emission from the PDRs. The projected distance between the H ionization and H2 dissociation fronts are approx. 0.3-0.4 pc, which cannot be explained using models of a uniform medium. Most probably, the ionized and neutral gas in these PDRs is clumpy. The H-to-H2 transitions in the NGC7538, S255, S257 and S140 PDRs are gradual with no sharp borders. This conclusion also confirms the suggestion of a clumpy medium.

astro-ph.GA↗

arXiv2022

The shocked molecular layer in RCW 120

Expansion of wind-blown bubbles or HII regions lead to formation of shocks in the interstellar medium, which compress surrounding gas into dense layers. We made spatially and velocity-resolved observations of the RCW~120 PDR and nearby molecular gas with CO(6-5) and 13CO(6-5) lines and distinguished a bright CO-emitting layer, which we related with the dense shocked molecular gas moving away from the ionizing star due to expansion of HII region. Simulating gas density and temperature, as well as brightness of several CO and C+ emission lines from the PDR, we found reasonable agreement with the observed values. Analysing gas kinematics, we revealed the large-scale shocked PDR and also several dense environments of embedded protostars and outflows. We observe the shocked layer as the most regular structure in the CO(6-5) map and in the velocity space, when the gas around YSOs is dispersed by the outflows.

astro-ph.GA↗

arXiv2022

Impact of HAC evolution on the formation of small hydrocarbons in the Orion Bar and the Horsehead PDRs

We study evolution of hydrogenated amorphous carbon (HAC) grains under harsh UV radiation in photo-dissociation regions (PDRs) near young massive stars. Our aim is to evaluate the impact of the HAC grains on formation of observed small hydrocarbons: C$_2$H, C$_2$H$_2$, C$_3$H$^+$, C$_3$H, C$_3$H$_2$, C$_4$H, in PDRs. We developed a microscopic model of the HAC grains based on available experimental results. The model includes processes of photo- and thermodesorption, accretion of hydrogen and carbon atoms and subsequent formation of carbonaceous mantle on dust surface. H$_2$, CH$_4$, C$_2$H$_2$, C$_2$H$_4$, C$_2$H$_6$, C$_3$H$_4$, C$_3$H$_6$, C$_3$H$_8$ are considered as the main fragments of the HAC photo-destruction. We simulated evolution of the HAC grains under the physical conditions of two PDRs, the Orion Bar and the Horsehead nebula. We estimated the production rates of the HAC fragments in gas phase chemical reactions and compared them with the production rates of fragments due to the HAC destruction. The latter rates may dominate under some conditions, namely, at A$_V$=0.1 in both PDRs. We coupled our model with the gas-grain chemical model MONACO and calculated abundances of observed small hydrocarbons. We conclude that the contribution of the HAC destruction fragments to chemistry is not enough to match the observed abundances, although it increases the abundances by several orders of magnitude in the Orion Bar at A$_V$=0.1. Additionally, we found that the process of carbonaceous mantle formation on dust surface can be an inhibitor for the formation of observed small hydrocarbons in PDRs.

astro-ph.GA↗

arXiv2022

Star formation timescale in the molecular filament WB 673

We present observations of ammonia emission lines toward the interstellar filament WB~673 hosting the dense clumps WB~673, WB~668, S233-IR and G173.57+2.43. LTE analysis of the lines allows us to estimate gas kinetic temperature ($\lesssim$ 30~K in all the clumps), number density ($7-17\times10^3$~cm$^{-3}$), and ammonia column density ($\approx 1-1.5\times 10^{15}$~cm$^{-2}$) in the dense clumps. We find signatures of collapse in WB 673 and presence of compact spatially unresolved dense clumps in S233-IR. We reconstruct 1D density and temperature distributions in the clumps and estimate their ages using astrochemical modelling. Considering CO, CS, NH$_3$ and N$_2$H$^+$ molecules (plus HCN and HNC for WB~673), we find a chemical age of $t_{\rm chem}=1-3\times 10^5$~yrs providing the best agreement between the simulated and observed column densities in all the clumps. Therefore, we consider $t_{\rm chem}$ as the chemical age of the entire filament. A long preceding low-density stage of gas accumulation in the astrochemical model would break the agreement between the simulated and observed column densities. We suggest that rapid star formation over a $\sim 10^5$~yrs timescale take place in the filament.

astro-ph.GA↗

arXiv2021

The link between gas and stars in the S254-S258 star-forming region

The paper aims to study relation between the distributions of the young stellar objects (YSOs) of different ages and the gas-dust constituents of the S254-S258 star-formation complex. This is necessary to study the time evolution of the YSO distribution with respect to the gas and dust compounds which are responsible for the birth of the young stars. For this purpose we use correlation analysis between different gas, dust and YSOs tracers. We compared the large-scale CO, HCO$^+$, near-IR extinction, and far-IR {\it Herschel} maps with the density of YSOs of the different evolutionary Classes. The direct correlation analysis between these maps was used together with the wavelet-based spatial correlation analysis. This analysis reveals a much tighter correlation of the gas-dust tracers with the distribution of Class I YSOs than with that of Class II YSOs. We argue that Class I YSOs which were initially born in the central bright cluster S255-IR (both N and S parts) during their evolution to Class II stage ($\sim$2 Myr) had enough time to travel through the whole S254-S258 star-formation region. Given that the region contains several isolated YSO clusters, the evolutionary link between these clusters and the bright central S255-IR (N and S) cluster can be considered. Despite the complexity of the YSO cluster formation in the non-uniform medium, the clusters of Class II YSOs in the S254-258 star-formation region can contain objects born in the different locations of the complex.

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arXiv2021

The warm-up phase in massive star-forming cores around RCW 120

We study molecular emission in a massive condensation at the border of the HII region RCW 120, paying particular attention to the Core 1 and Core 2 objects, the most massive fragments of the condensation found previously by ALMA. The latter fragment was previously suggested to host a high-mass analogue of Class 0 young stellar object. We present spectra of molecular emission in the 1 mm range made with the APEX telescope. We detect CH$_3$OH and C$^{34}$S lines in Core 1 and Core 2. The CH$_3$CN series and the SO$_2$ lines are only found in Core 2. We estimate gas physical parameters using methanol lines and obtain gas temperature less than 100 K in both regions. Molecular hydrogen number density in Core 2 is in the range of $10^5-10^7$ cm$^{-3}$ and is more uncertain in Core 1. However, the detection of the CH$_3$CN lines corresponding to highly excited transitions ($E_{\rm u}> 400$~K) in Core~2 indicates that the region contains hot gas, while the abundances of CH$_3$OH, CS, SO$_2$ and CH$_3$CN are quite low for a hot core stage. We propose that Core 2 is in the warm-up phase prior to the establishing of the hot gas chemistry. We suggest that Core 2 is in the beginning of the hot core stage. There are no detected CH$_3$CN lines in Core 1, therefore, it might be on an even less evolved evolutionary stage.

astro-ph.GA↗

arXiv2020

The PDR structure and kinematics around the compact HII regions S235A and S235C with [CII], [13CII], [OI] and HCO+ line profiles

The aim of the present work is to study structure and gas kinematics in the photodissociation regions (PDRs) around the compact HII regions S235A and S235C. We observe the [CII], [13CII] and [OI] line emission, using SOFIA/upGREAT and complement them by data of HCO+ and CO. We use the [13CII] line to measure the optical depth of the [CII] emission, and find that the [CII] line profiles are influenced by self-absorption, while the [13CII] line remains unaffected by these effects. Hence, for dense PDRs, [13CII] emission is a better tracer of gas kinematics. The optical depth of the [CII] line is up to 10 in S235A. We find an expanding motion of the [CII]-emitting layer of the PDRs into the front molecular layer in both regions. Comparison of the gas and dust columns shows that gas components visible neither in the [CII] nor in low-J CO lines may contribute to the total column across S235A. We test whether the observed properties of the PDRs match the predictions of spherical models of expanding HII region + PDR + molecular cloud. Integrated intensities of the [13CII], [CII] and [OI] lines are well-represented by the model, but the models do not reproduce the double-peaked [CII] line profiles due to an insufficient column density of C+. The model predicts that the [OI] line could be a more reliable tracer of gas kinematics, but the foreground self-absorbing material does not allow using it in the considered regions.

astro-ph.GA↗

arXiv2020

Impact of PAH photodissociation on the formation of small hydrocarbons in the Orion Bar and the Horsehead PDRs

We study whether polycyclic aromatic hydrocarbons (PAHs) can be a weighty source of small hydrocarbons in photo-dissociation regions (PDRs). We modeled the evolution of 20 specific PAH molecules in terms of dehydrogenation and destruction of the carbon skeleton under the physical conditions of two well-studied PDRs, the Orion Bar and the Horsehead nebula which represent prototypical examples of PDRs irradiated by "high" and "low" ultraviolet radiation field. PAHs are described as microcanonical systems. The acetylene molecule is considered as the main carbonaceous fragment of the PAH dissociation as it follows from laboratory experiments and theory. We estimated the rates of acetylene production in gas phase chemical reactions and compared them with the rates of the acetylene production through the PAH dissociation. It is found that the latter rates can be higher than the former rates in the Orion Bar at $A_{\rm V}<1$ and also at $A_{\rm V}>3.5$. In the Horsehead nebula, the chemical reactions provide more acetylene than the PAH dissociation. The produced acetylene participate in the reactions of the formation of small hydrocarbons (C$_2$H, C$_3$H, C$_3$H$^{+}$, C$_3$H$_2$, C$_4$H). Acetylene production via the PAH destruction may increase the abundances of small hydrocarbons produced in gas phase chemical reactions in the Orion Bar only at $A_{\rm V}>3.5$. In the Horsehead nebula, the contribution of PAHs to the abundances of the small hydrocarbons is negligible. We conclude that the PAHs are not a major source of small hydrocarbons in both PDRs except some locations in the Orion Bar.

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