arXiv subjects

D. Semenov

Publications and source records attributed to D. Semenov.

At least 19 recordsLinked to original sources

arXiv2026

Search for two-neutrino double electron capture in $^{36}$Ar with the DarkSide-50 detector

Two-neutrino double electron capture is a rare nuclear decay where two electrons are simultaneously captured from the atomic shells and two neutrinos are emitted. We report on the first search for two-neutrino double electron capture in the $\textit{KK}$- and $\textit{KL}$-shells of $^{36}$Ar using the low-radioactivity liquid argon target from underground sources in the DarkSide-50 experiment. No statistically significant excess was observed with approximately 12 ton-day exposure of underground argon (UAr) and, taking into account the $^{36}$Ar isotopic abundance in UAr (0.007%), we set a limit on the half-life of the two-electron capture process in $^{36}$Ar of $T_{1/2} > 9.2 \times 10^{19}$ yr at 90% C.L. The sensitivity of the DarkSide-20k experiment, which will become operational in the next few years, was also evaluated and is expected to increase by a factor $\sim$100 with 10 years of expected operation and assuming the same $^{36}$Ar abundance as in the DarkSide-50 underground argon target.

nucl-ex↗

arXiv2026

New limits on the Pauli forbidden transitions in 12C nuclei obtained with the complete Borexino dataset

The Pauli exclusion principle (PEP) was tested for nucleons in $\rm{^{12}C}$ nuclei using the Borexino dataset from 2007 to 2021. %the complete Borexino detector data. The approach consists of searching for $γ$-quanta, neutrons, protons, as well as electrons and positrons emitted in non-Paulian transitions of nucleons from the $1P_{3/2}$ shell to the filled $1S_{1/2}$ shell. Due to the uniquely low background level, the large mass, and long measurement time of the Borexino detector, the most stringent experimental constraints to date on the lifetime of the $\rm{^{12}C}$ nucleus with respect to PEP-forbidden transitions were obtained: $τ({^{12}\rm{C}}\rightarrow{^{12}\widetilde{\rm{C}}}+γ) \geq {1.1\times10^{32}}$ y, $τ({^{12}\rm{C}}\rightarrow{^{11}\widetilde{\rm{B}}}+ p) \geq {1.0\times10^{31}}$ y, $τ({^{12}\rm{C}}\rightarrow{^{11}\widetilde{\rm{C}}}+ n) \geq 2.0 \times 10^{31}$ y, $τ({^{12}\rm{C}}\rightarrow{^{12}\widetilde{\rm{N}}}+ e^- + \widetilde{ν_e}) \geq 6.4 \times 10^{30}$ y and $τ({^{12}\rm{C}}\rightarrow{^{12}\widetilde{\rm{B}}}+ e^+ + ν_e) \geq 6.6 \times 10^{30}$ y (90\% C.L.). The upper limits on the relative strengths for the non-Paulian electromagnetic, strong, and weak transitions have been obtained: $δ^2_γ\leq 1.0\times 10^{-57}$, $δ^2_{N}\leq 7.0\times 10^{-61}$ and $δ^2_β\leq 9.6\times 10^{-36}$, all at 90\% C.L..

nucl-ex↗

arXiv2026

The CepA disk-outflow system at <=0.2'' or <=100au resolution

Context: Although there has been significant progress, the physical properties and potential fragmentation of accretion disks around high-mass protostars remain poorly constrained. Aims: We characterize at high angular resolution one of the most nearby (~700pc) high-mass accretion disk candidates CepA HW2. Methods: Using the new long baseline array configuration (~1700m) of the Northern Extended Millimeter Array (NOEMA), we study CepA HW2 with a resolution of <=0.2'' or <=100au at 1.3mm in dust continuum and spectral line emission. Results: The mm continuum emission resolves the central disk candidate into several sub-structures. Conducting a Toomre Q stability analysis based on CH_3CN and continuum data, and a comparison to 3D radiation hydrodynamic simulations shows that the data are consistent with an almost edge-on disk where the observed sub-structures may represent fragments within the disk. The CO and SiO spectral line data confirm a second bipolar outflow (in addition to the well-known jet) emanating from the central peak position. This indicates that this central peak should host at least a binary if not even a higher order multiple system. The usually assumed dense gas tracer CH_3CN shows also contributions from the outflows which complicates further kinematic analysis of the disk. Conclusions: The high-resolution outflow-disk data of CepA reveal a multiply fragmented disk that drives several outflows. These observations enforce the picture of high-mass star formation where multiplicity and fragmentation can happen on the smallest spatial scales related to the inner accretion disks.

astro-ph.SR↗

arXiv2026

Protostellar Outflows at the EarliesT Stages (POETS). IX. Magnetohydrodynamic disk winds traced by SO and SO$_2$ in luminous protostars

We investigate two massive young stellar objects (YSOs), IRAS21078+5211 and G035.02+0.35, where evidence for magnetohydrodynamic (MHD) disk winds (DWs) has been obtained at scales of 10-100 au through measurements of the 22GHz water maser velocity distribution within the Protostellar Outflows at the EarliesT Stages (POETS) survey. We employ IRAM Northern Extended Millimeter Array and archival Atacama Large Millimeter Array observations of IRAS21078+5211 and G035.02+0.35, respectively, to study kinematics and physical conditions of the corresponding protostellar winds on scales of 100-1000 au using the same molecular tracers. In IRAS21078+5211, the emissions of several molecules, particularly SO, SO2, CH3CN and CH3OH, are distributed along the axis of the radio jet, and present a LSR velocity (Vlsr) gradient transversal to the jet axis. Position-velocity (PV) plots of the SO lines show patterns consistent with Keplerian rotation. The SO2 emission comes from high velocity gas flowing close to the jet axis, while CH3CN and CH3OH present larger radial extension than the S-bearing species. In G035.02+0.35, the same molecules are instead distributed along the major axis of the rotating disk, and their Vlsr gradients consistently trace the disk rotation. The corresponding PV plots present Keplerian profiles. SO is the only molecular species whose emission extends well outside the disk. In both YSOs, the spatial and velocity distributions of SO are consistent with a rotating wind magneto-centrifugally launched from the YSO disk. The comparison with models of molecule formation and excitation in shocks indicates that the different radial extension of the molecular species observed in the protostellar wind of IRAS21078+5211, as well as the lack of molecules, except SO, in the G035.02+0.35's wind, can be explained in terms of a radially extended MHD DW, rather than a compact X-wind.

astro-ph.SR↗

arXiv2026

PRODIGE - envelope to disk with NOEMA: VII. (Complex) organic molecules in the NGC1333 IRAS4B1 outflow: A new laboratory for shock chemistry

Shock chemistry is an excellent tool to shed light on the formation and destruction mechanisms of complex organic molecules (COMs). The L1157-mm outflow is the only low-mass protostellar outflow that has extensively been studied in this regard. Using the data taken as part of the PRODIGE (PROtostars & DIsks: Global Evolution) large program, we aim to map COM emission and derive the molecular composition of the protostellar outflow driven by the Class 0 protostar NGC1333 IRAS4B1 to introduce it as a new laboratory to study the impact of shocks on COM chemistry. In addition to typical outflow tracers such as SiO and CO, outflow emission is seen from H2CO, HNCO, and HC3N, as well as from the COMs CH3OH, CH3CN, and CH3CHO, and even from deuterated species such as DCN, D2CO, and CH2DOH. Maps of integrated intensity ratios between CH3OH and DCN, D2CO, and CH3CHO reveal gradients with distance from the protostar. Intensity ratio maps of HC3N and CH3CN with respect to CH3OH peak in the southern lobe where temperatures are highest. Rotational temperatures derived towards two positions, one in each lobe, are found in the range ~50-100 K. Abundances with respect to CH3OH are higher by factors of a few than for the L1157-B1. In conclusion, for the first time, we securely detected the COMs CH3CN, CH3CHO, and CH2DOH in the IRAS 4B1 outflow, serendipitously with limited sensitivity and bandwidth. Targeted observations will enable the discovery of new COMs and a more detailed analysis of their emission. Morphological differences between molecules in the IRAS 4B1 outflow lobes and their relative abundances provide first proof that this outflow is a promising new laboratory for shock chemistry, which will offer crucial information on COM formation and destruction as well as outflow structure and kinematics.

astro-ph.GA↗

arXiv2026

Constraints on non-standard neutrino interactions from Borexino extended data-set

Neutrino non-standard interactions (NSI) constitute an active research field, as they are closely related to potential new physics associated with dark matter searches and exotic interactions arising from fundamental symmetry violations. The Borexino's unprecedented sensitivity to solar neutrinos, derived from its low background and precision spectral measurements, enables stringent constraints on potential deviations from the standard three-flavor neutrino oscillation paradigm. This work presents an update on the analysis of flavor-diagonal NSI using the full Borexino Phase-III data set, extending the study previously reported in Constraints on flavor-diagonal non-standard neutrino interactions from Borexino Phase-II (JHEP 2020, 38). The updated analysis incorporates the extended temporal and statistical coverage of Phase-III. The results indicate improved sensitivity to the diagonal NSI parameters, with constraints exceeding those obtained in Phase-II. Furthermore, a more general analysis that includes all possible off-diagonal NSI terms is presented for the first time, providing a comprehensive exploration of the NSI parameter space associated with the flavors of the incoming and outgoing neutrinos. This work once again underlines Borexino's critical role in probing new physics scenarios and reinforces its legacy in neutrino research. Detailed comparisons with Phase-II results are discussed, along with implications for theoretical models of NSI.

hep-ex↗

arXiv2026

The converging gas flow around the infrared dark cloud G28.3

Aims: The G28.37+0.07 star-forming region is a prototypical infrared dark cloud (IRDC) located at the interface of a converging gas flow. This study characterizes the properties of this dynamic gas flow. Methods: Combining data from the Northern Extended Millimeter Array (NOEMA) with single-dish data from the IRAM30m observatory, we mapped large spatial scales (~81pc^2) at high angular resolution (7.0''x2.6'' corresponding ~2.3x10^4au or ~0.1pc) down to core scales. The spectral setup in the 3mm band covers many spectral lines as well as the continuum emission. Results: The data reveal the proposed west-east converging gas flow in all observed dense gas tracers. We estimate a mass-flow rate along that flow around 10^-3M_sun/yr. Comparing these west-east flow rates to infall rates toward sources along the line of sight, the gas flow rates are roughly a factor of 25 greater than than those along the line of sight. This confirms the dominance of longitudinal motions along the converging gas flow in G28.37. For comparison, in the main north-south IRDC formed by the west-east converging gas flow, infall rates along the line of sight are about an order of magnitude greater than those along the west-east flow. In addition to the kinematic analysis, a comparison of CH_3CN-derived gas temperatures with Herschel-derived dust temperatures typically show higher gas temperatures toward high-density sources. We discuss whether mechanical heating from the conversion of the flow's kinetic energy into thermal energy may explain some of the observed temperature differences. Conclusions: The differences between flow rates along the converging flow, perpendicular to it, and toward the sources at the IRDC center indicate that at the interfaces of converging gas flows - where most of the active star formation takes place - originally more directed gas flows can convert into multidirectional infall motions.

astro-ph.GA↗

arXiv2025

CASCADE: Filamentary accretion flows in Cygnus X DR20

Aims. We investigate the role of filaments in high-mass star formation, whether gas flows from large to small scales along them, and what their properties might reveal about the region they are found in. Methods. The Max Planck IRAM Observatory Program (MIOP), the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE), includes high spatial resolution (~3'') data of HCO+(1-0) and H13CO+(1-0) emission in the star-forming DR20 region in the Cygnus X complex. In this data we identify filaments with the structure identification algorithm DisPerSE. We further analyze these filaments using Gaussian fits to the spectra to determine the line peak velocity and full width half maximum along them. The Python package FilChaP was used to determine filament widths. Results. We find projected velocity gradients inside several filaments between 0.4 to 2.4km/s over projected length-scales of 0.1pc toward star-forming cores. This can be interpreted as a sign of gas flowing along the filaments toward the cores. The filament width distributions exhibit median values between 0.06 and 0.14pc depending on the core, the tracer, and the method. Standard deviations are approximately 0.02 to 0.06pc. These values are roughly in agreement with the filament width of 0.1pc typically found in nearby low-mass star-forming regions. Conclusions. This first analysis of filamentary properties within the Cygnus X CASCADE program reveals potential signatures of gas flows along filaments onto star-forming cores. Furthermore, the characteristics of the filaments in this high-mass star-forming region can be compared to those of filaments in low-mass star-forming regions typically studied before. Extending such studies to the entire CASCADE survey will enhance our knowledge of high-mass filament properties on solid statistical grounds.

astro-ph.GA↗

arXiv2025

Observations of sulfuretted species in HL Tau

Protoplanetary disks inherit their chemical composition from their natal molecular cloud, but the extent to which this material is preserved versus reset through chemical reprocessing remains an open question. Understanding this balance is a major topic in astrochemistry. Comparing the chemical composition of the envelope and the protoplanetary disk is key to solving the topic. The goal of this paper is to investigate the chemical differences between the disk and the surrounding envelope by comparing the column density ratios of a few selected species in each region. The source we focus on is HL Tau. We present new NOEMA observations of HL Tau targeting the following species: CS, H2CO, H2S, and SO2. We produced zeroth-, first-, and second-moment maps for the species where emission was detected and used them to analyze the spatial distribution and kinematic properties of the different molecules in the disk and the envelope. We derived the column densities and compared the values derived for the envelope and disk. We also computed the rotational diagram for the SO2 detected transitions. Assuming two different temperature regimes, 17 and 58 K, we derived column densities for the species surveyed in the disk and compared them with values derived for the envelope. We find large differences in the derived column density ratios of the surveyed molecules, especially for N(CS)/N(H2S), which is 40 to 50 times larger in the envelope. We attribute these variations to the different excitation and UV-irradiation regimes in the disk and envelope. We also note strong gradients in the ratios between different positions of the disk and tentatively attribute them to different levels of turbulence at different azimuths. The observed differences in molecular ratios in the envelope and the disk are suggestive of chemical reprocessing of the gas during the formation and evolution of the protoplanetary disk.

astro-ph.SR↗

arXiv2025

Edge-On Disk Study (EODS) II: HCO$^+$ and CO vertical stratification in the disk surrounding SSTTau042021

Context. Edge-on disks offer a unique opportunity to directly examine their vertical structure, providing valuable insights into planet formation processes. We investigate the dust properties, as well as the CO and HCO$^+$ gas properties, in the edge-on disk surrounding the T Tauri star 2MASS J04202144+281349 (SSTTau042021). Aims. We estimate the radial and vertical temperature and density profile for the gas and the dust. Methods. We use ALMA archival data of CO isotopologues and continuum emission at 2, 1.3 and 0.9 mm together with new NOEMA HCO$^+$ 3-2 observations. We retrieve the gas and dust disk properties using the tomographic method and the \textsc{DiskFit} model. Results. The vertical CO emission appears very extended, partly tracing the H$_2$ wind observed by JWST. C$^{18}$O, $^{13}$CO and HCO$^+$ emission characterize the bulk of the molecular layer. The dust and gas have a mid-plane temperatures of $\sim 7-11$ K. The temperature of the molecular layer (derived from $^{13}$CO and HCO$^+$) is on the order of 16 K. HCO$^+$ 3-2 being thermalized, we derive a lower limit for the H$_2$ volume density of $\sim 3 \times 10^6$ cm$^{-3}$ at radius 100-200 au between 1 and 2 scale heights. The atmosphere temperature of the CO gas is of the order $\sim$ 31 K at a radius of 100 au. We directly observe CO and HCO$^+$ gas onto the mid-plane beyond the dust outer radius ($\ge 300$ au). The (gas+dust) disk mass estimated up to a radius of 300 au is on the order of $4.6 \times 10^{-2} \mathrm{M}_\odot$. Conclusions. Thanks to the favorable disk inclination, we present the first quantitative evidence for vertical molecular stratification with direct observation of CO and HCO$^+$ gas along the mid-plane. We estimate the temperature profile with temperature of 7-11 K near the mid-plane, and 15-20 K in the dense part of the molecular layer up to $\sim$ 35 K above.

astro-ph.EP↗

arXiv2025

Edge-On Disk Study (EODS) III: Molecular Stratification in the Flying Saucer Disk

Context: Investigating the vertical distribution of molecular content in protoplanetary disks remains difficult in most disks mildly inclined along the line of sight. In contrast, edge-on disks provide a direct (tomographic) view of the 2D molecular brightness. Aims: We study the radial and vertical molecular distribution as well as the gas temperature and density by observing the Keplerian edge-on disk surrounding the Flying Saucer, a Class II object located in Ophiuchus. Methods: We use new and archival ALMA data to perform a tomography of $^{12}$CO, $^{13}$CO, C$^{18}$O, CN, HCN, CS, H$_2$CO, c-C$_3$H$_2$, N$_2$D$^+$, DCN and $^{13}$CS. We analyze molecular tomographies and model data using the radiative transfer code DiskFit. Results: We directly measure the altitude above the mid-plane for each observed species. For the first time, we unambiguously demonstrate the presence of a common molecular layer and measure its thickness: most molecules are located at the same altitude versus radius. Beyond CO, as predicted by chemical models, the CN emission traces the upper boundary of the molecular layer, whereas the deuterated species (DCN and N2D+) resides below one scale-height. Our best fits from DiskFit show that most observed transitions in the molecular layer are thermalized because their excitation temperature is the same, around 17-20 K. Conclusions: These long-integration observations clearly reveal a molecular layer predominantly located around 1-2 scale height, at a temperature above the CO freeze-out temperature. The deuterated molecules are closer to the mid-plane and N2D+ may be a good proxy for the CO snowline. Some molecules, such as CN and H2CO, are likely influenced by the disk environment, at least beyond the mm dust disk radius. The direct observation of the molecular stratification opens the door to detailed chemical modeling in this disk which appears representative of T Tauri disks.

astro-ph.EP↗

arXiv2025

Time-resolved protoplanetary disk physics in DQ Tau with JWST

Accretion variability is ubiquitous in YSOs. While large outbursts may strongly affect the disk, the effects of moderate bursts are less understood. We aim to study the physical response of the disk around the eccentric binary system DQ Tau to its periodic accretion changes. We organized a multi-wavelength campaign centered on four JWST/MIRI spectra. We targeted three periastrons (high accretion state) and one apastron (quiescence). We used optical and near-infrared spectroscopy and photometry to measure how the accretion luminosity varies. We decomposed the multi-epoch SEDs into stellar, accretion, and rim components. We fitted the solid-state features using various opacity curves and the molecular features using slab models. We find the inner disk of DQ Tau to be highly dynamic. The temperature, luminosity, and location of the inner dust rim vary in response to the movement of stars and the L_acc variations. This causes variable shadowing of the outer disk, leading to an anti-correlation between the rim temperature and the strength of the silicate feature. The dust mineralogy remains constant, dominated by large amorphous olivine and pyroxene grains, with smaller fractions of crystalline forsterite. The excitation of CO (1550-2260 K), HCN (880-980 K), and hot H2O (740-860 K) molecules as well as the luminosity of the [NeII] line correlate with the accretion rate, while the warm (650 K) and cold (170-200 K) H2O components are mostly constant. CO emission, originating from a hot (>1500 K) region likely within the dust sublimation radius, is most sensitive to L_acc changes. In comparison with other T Tauri disks, DQ Tau is highly C-poor and displays moderately inefficient pebble drift. We conclude that even moderate accretion rate changes affect the thermal structure in the planet-forming disk regions on short timescales, providing a crucial benchmark for understanding disk evolution.

astro-ph.SR↗

arXiv2025

ANTIHEROES-PRODIGE: Quantifying the connection from envelope to disk with the IRAM 30m telescope and NOEMA I. Attack of the streamers: L1448N's fight for order in the chaos

Star formation is a hierarchical process ranging from molecular clouds down to individual protostars. In particular how infalling asymmetric structures, called streamers, delivering new material onto protostellar systems, are connected to the surrounding envelope is not understood. We investigate the connection between the cloud material at 10000 au scales down to 300 au scales towards L1448N in the Perseus star-forming region hosting three young Class 0/I protostellar systems. Sensitive molecular line observations taken with the IRAM 30m telescope and NOEMA at 1.4 mm are used to study the kinematic properties in the region traced by the molecular lines. Several infalling streamers are associated with the protostellar systems, some of them traced by C18O and DCN, while one of them is bright in SO and SO2. The kinematic properties of the former streamers are consistent with the velocities observed at large envelope scales of 10000 au, while the latter case show different kinematics. The masses and infall rates of the streamers are 0.01 Msun and 0.01-0.1 Msun and 10^-6 Msun/yr and 5-18x10^-6 Msun/yr for IRS3A and IRS3C, respectively. The envelope mass in the L1448N region is ~16Msun, thus the mass of a single streamer is low compared to the envelope mass (<1%). However, compared to the estimated mass of the protostellar systems a single streamer could deliver up to 1% and 8-17% of mass towards IRS3A (M*~1.2 Msun) and IRS3C (M*~1 Msun), respectively. The rotational signatures of structures in L1448N are all connected - from the large-scale envelope, infalling streamers, down to the rotation of all three disks. Two of the three Class 0/I protostellar systems are still fed by this surrounding material, which can be associated to the remnant envelope. However, we also find a streamer that is bright in SO and SO2 towards IRS3C that could be connected to a nearby sulfur reservoir.

astro-ph.SR↗

arXiv2025

MINDS: Detection of an inner gas disk caused by evaporating bodies around HD 172555

Mechanisms such as collisions of rocky bodies or cometary activity give rise to dusty debris disks. Debris disks trace the leftover building blocks of planets, and thus also planetary composition. HD 172555, a stellar twin of beta Pic, hosts a debris disk thought to have resulted from a giant collision. It is known for its extreme mid-infrared silica dust feature, indicating a warm population of silica-rich grains in the asteroid belt (~5 au), cold CO observed by ALMA, and small bodies evaporating as they approach close to the star. Our JWST MIRI/MRS observations now reveal emission from an inner gaseous disk (<0.5 au) that arises from the evaporation of close-in material. For the first time in a debris disk, we detect neutral atomic chlorine and sulfur, as well as ionized nickel. We recovered the neutral sulfur line in ~20-year-old Spitzer data, showing it is long-lived and stable. Ionized iron, previously seen only in beta Pic, is also detected. All lines are broadened by Keplerian rotation, pinpointing the gas location. The HD 172555 system serves as a unique laboratory to study the composition of planetesimals, asteroids, and comets beyond the Solar System. The comparison to beta Pic reveals, that the gas in HD 172555 is hotter, closer to the star, and poor in argon -- suggesting it originates from evaporating rocky bodies near the star, while beta Pic's gas may trace volatile-rich bodies from larger separations.

astro-ph.EP↗

arXiv2025

PRODIGE VI -- Envelope to Disk with NOEMA: VI. The Missing Sulfur Problem

Determining the amount of sulfur in volatiles and refractories in the ISM remains one of the main problems in astrochemistry. The detection of H$_2$S ices, which are thought to be one of the main sulfur reservoirs, has not been achieved yet, and the only S-bearing species detected in the ices to date is OCS. PRODIGE large survey observations with NOEMA of several Class 0/I protostars in the Perseus Molecular Cloud provide a perfect opportunity to study the H$_2$S and OCS composition of the ices through the volatiles sublimated in the warm inner core (T$>$100K, n $\sim10^6$cm$^{-3}$) of these protostars. Our aim is to determine the H$_2$S/OCS ratio in the warm inner core of 24 protostars in order to study how it is affected by different factors during its evolution. We used the NOEMA millimeter observations from the PRODIGE program of H$_2$S, H$_2^{33}$S, OCS, OC$^{33}$S and OC$^{34}$S to estimate the H$_2$S and OCS column densities in the warm inner cores. We used SO and SO$_2$ data from the ALMA archive to give a rough estimate of the total sulfur abundance. We explore the chemistry of H$_2$S and OCS in the warm cores using chemical and dynamical simulations of the collapse of a dense core to form a protostar. The estimated H$_2$S/OCS ratio reveals a segregation of the sources into ``OCS-poor'' and ``OCS-rich'' protostars, where the OCS-poor protostars present higher H$_2$S/OCS ratios than the OCS-rich ones. Total sulfur abundance is always dominated by either H$_2$S or OCS, grows with evolution during the Class 0 phase up to $D_S<8$, and decreases again in the Class I. Simulations show that temperature changes in the pre-stellar phase and during the collapse can produce substantial differences in the H$_2$S and OCS abundances and in the H$_2$S/OCS ratio. Our analysis shows that the H$_2$S/OCS ratio is strongly influenced by the environment and the initial conditions of the cloud.

astro-ph.GA↗

arXiv2025

Edge-On Disk Study (EODS) II: Thermal Structure of the Flying Saucer Disk

Context. The dust and gas temperature in proto-planetary disks play critical roles in determining their chemical evolution and influencing planet formation processes. Aims. We attempted an accurate measurement of the dust and CO temperature profile in the edge-on disk of the Flying Saucer. Methods. We used the unique properties of the Flying Saucer, its edge-on geometry and its fortunate position in front of CO clouds with different brightness temperatures to provide independent constraints on the dust temperature. We compared it with the dust temperature derived using the radiative transfer code DiskFit and the CO gas temperature. Results. We find clear evidence for a substantial gas temperature vertical gradient, with a cold (10 K) disk mid-plane and a warmer CO layer where T(r) is 27 K at 100 au, dropping with exponent 0.3. Direct evidence for CO depletion in the mid-plane, below about 1 scale height, is also found. At this height, the gas temperature is 15-20 K, consistent with the expected CO freeze out temperature. The dust disk appears optically thin at 345 GHz, and exhibits moderate settling.

astro-ph.EP↗

arXiv2025

PRODIGE - envelope to disk with NOEMA: V. Low 12C/13C ratios for CH3OH and CH3CN in hot corinos

The 12C/13C isotope ratio has been derived towards numerous cold clouds (20-50 K) and a couple protoplanetary disks and exoplanet atmospheres. However, direct measurements of this ratio in the warm gas (>100 K) around young low-mass protostars remain scarce, but are required to study its evolution during star and planet formation. We derived 12C/13C ratios from the isotopologues of the complex organic molecules (COMs) CH3OH and CH3CN in the warm gas towards seven Class 0/I protostellar systems to improve our understanding of the evolution of the 12C/13C ratios during star and planet formation. We used the data that were taken as part of the PRODIGE large program with the NOEMA at 1mm. The emission of CH3OH and CH3CN is spatially unresolved in the PRODIGE data (300au scale). Derived rotational temperatures exceed 100K, telling us that they trace the gas of the hot corino, where CH3CN probes hotter regions than CH3OH on average (290 K versus 180 K). The column density ratios between the 12C and 13C isotopologues, derived from LTE analysis, range from 4 to 30, thus, are significantly lower than the expected local ISM isotope ratio of about 68. Assuming that CH3CN and CH3OH may inherit the 12C/13C ratio from their precursor species, astrochemical models were conducted for the latter and compared with our observational results. We conclude that an enrichment in 13C in COMs at the earliest protostellar stages is likely inherited from the COMs' precursor species, whose 12C/13C ratios are set during the prestellar stage via isotopic exchange reactions. This also implies that low 12C/13C ratios observed at later evolutionary stages could at least partially be inherited. A final conclusion on 12C/13C ratios in protostellar environments requires improved observations to tackle current observational limitations and additional modelling efforts.

astro-ph.GA↗

arXiv2025

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. IV. Unveiling the hidden structures in DR18

The Cygnus-X complex is a massive, nearby (1.4 kpc) star-forming region with several OB associations. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations ($\sim$ 3 - 4$''$) toward DR18, covering several molecular species with the Northern Extended Millimeter Array (NOEMA) and the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. In addition, multi-wavelength archival datasets were used to provide a comprehensive analysis of the region. A comparison of the 3.6mm and 6 cm continuum emission confirms that a B2 star (DR18-05) shapes the cometary HII region in the DR18 cavity, with ionized gas escaping toward the OB2 association. On the other hand, the extended 3.6mm and 6 cm continuum emission are likely to trace photoevaporating ionized gas from ultraviolet radiation from the Cyg OB2 association, not from DR18-05. The shell structure around DR18-05 indicates photodissociation regions (PDRs) formed by the expanding HII region and photo-erosion from DR18-05 and OB2 stars. We also identified 18 compact cores with N$_2$H$^+$ emission, half of which are gravitationally bound and mostly located in colder regions behind the PDRs. The SiO emission is found only in PDRs, with narrow-line widths ( 0.8 - 2.0 km s$^{-1}$) and lower abundances (X(SiO) $\sim$ 5$\times$10$^{-11}$ - 1$\times$10$^{-10}$). Comparing with the UV irradiated shock models, we suggest that the SiO emission partially encompassing the HII region arises from the molecular gas region, marginally compressed by low-velocity shocks with $\sim$ 5 km s$^{-1}$, irradiated by external UV radiation (G$_{\rm 0} \sim 10^{2} - 10^{3}$), as they traverse through a medium with $n_{\rm H} \sim 10^{4}$ to 10$^5$ cm$^{-3}$.

astro-ph.GA↗