Low-mass Cores Research Articles

ALMA-IMF

Context. The star formation process leads to an increased chemical complexity in the interstellar medium. Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. Aims. We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods. We built a comprehensive census of hot core candidates toward the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results. We built a catalog of 76 hot core candidates with masses ranging from ~0.2 M⊙ to ~80 M⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8 M⊙ and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores may be explained as a mixture of contributions from shocks or may correspond to objects in a more evolved state (i.e., beyond the hot core stage). We find that the fraction of hot core candidates increases with the core mass, suggesting that the brightest dust cores are all in the hot core phase. Conclusions. Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH3OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales.

Core to ultracompact HII region evolution in the W49A massive protocluster

Aims. We aim to identify and characterize cores in the high-mass protocluster W49A, determine their evolutionary stages, and measure the associated lifetimes. Methods. We built a catalog of 129 cores extracted from an ALMA 1.3 mm continuum image at 0.26″ (2900 au) angular resolution. The association between cores and hypercompact or ultracompact HII (H/UC HII) regions was established from the analysis of VLA 3.3 cm continuum and H30α line observations. We also looked for emission of hot molecular cores (HMCs) using the methyl formate doublet at 218.29 GHz. Results. We identified 40 cores associated with an H/UC HII region and 19 HMCs over the ALMA mosaic. The 52 cores with an H/UC HII region and/or an HMC are assumed to be high-mass protostellar cores, while the rest of the core population likely consists of prestellar cores and low-mass protostellar cores. We found a good agreement between the two tracers of ionized gas, with 23 common detections and only four cores detected at 3.3 cm and not in H30α. The spectral indexes from 3.3 cm to 1.3 mm range from 1, for the youngest cores with partially optically thick free-free emission, to about −0.1, which is for the optically thin free-free emission obtained for cores that are likely more evolved. Conclusions. Using the H/UC HII regions as a reference, we found the statistical lifetimes of the HMC and massive protostellar phases in W49N to be about 6 × 104 yr and 1.4 × 105 yr, respectively. We also showed that HMCs can coexist with H/UC HII regions during a short fraction of the core lifetime, about 2 × 104 yr. This indicates a rapid dispersal of the inner molecule envelope once the HC HII is formed.

Diagnostics of 3D explosion asymmetries of stripped-envelope supernovae by nebular line profiles

ABSTRACT Understanding the explosion mechanism and hydrodynamic evolution of core-collapse supernovae (SNe) is a long-standing quest in astronomy. The asymmetries caused by the explosion are encoded into the line profiles which appear in the nebular phase of the SN evolution – with particularly clean imprints in He star explosions. Here, we carry out nine different supernova simulations of He-core progenitors, exploding them in 3D with parametrically varied neutrino luminosities using the prometheus-hotb code, hydrodynamically evolving the models to the homologous phase. We then compute nebular phase spectra with the 3D Non-Local Thermodynamic Equilibrium spectral synthesis code extrass (EXplosive TRAnsient Spectral Simulator). We study how line widths and shifts depend on progenitor mass, explosion energy, and viewing angle. We compare the predicted line profile properties against a large set of Type Ib observations, and discuss the degree to which current neutrino-driven explosions can match observationally inferred asymmetries. With self-consistent 3D modelling – circumventing the difficulties of representing $^{56}$Ni mixing and clumping accurately in 1D models – we find that neither low-mass He cores exploding with high energies nor high-mass cores exploding with low energies contribute to the Type Ib SN population. Models which have line profile widths in agreement with this population give sufficiently large centroid shifts for calcium emission lines. Calcium is more strongly affected by explosion asymmetries connected to the neutron star kicks than oxygen and magnesium. Lastly, we turn to the near-infrared spectra from our models to investigate the potential of using this regime to look for the presence of He in the nebular phase.

Deep Search for Phosphine in a Prestellar Core

Understanding in which chemical forms phosphorus exists in star- and planet-forming regions and how phosphorus is delivered to planets are of great interest from the viewpoint of the origin of life on Earth. Phosphine (PH3) is thought to be a key species to understanding phosphorus chemistry, but never has been detected in star- and planet-forming regions. We performed sensitive observations of the ortho-PH3 10 − 00 transition (266.944 GHz) toward the low-mass prestellar core L1544 with the Atacama Compact Array stand-alone mode of the Atacama Large Millimeter/submillimeter Array. The line was not detected down to 3σ levels in 0.07 km s−1 channels of 18 mK. The nondetection provides the upper limit to the gas-phase PH3 abundance of 5 × 10−12 with respect to H2 in the central part of the core. Based on the gas-ice astrochemical modeling, we find the scaling relationship between the gas-phase PH3 abundance and the volatile (gas and ice with larger volatility than water) P elemental abundance for given physical conditions. This characteristic and well-constrained physical properties of L1544 allow us to constrain the upper limit to the volatile P elemental abundance of 5 × 10−9, which is a factor of 60 lower than the overall P abundance in the interstellar medium. Then the majority of P should exist in refractory forms. The volatile P elemental abundance of L1544 is smaller than that in the coma of comet 67P/C-G, implying that the conversion of refractory phosphorus to volatile phosphorus could have occurred along the trail from the presolar core to the protosolar disk through, e.g., sputtering by accretion/outflow shocks.

Low-mass Population III Star Formation due to the HD Cooling Induced by Weak Lyman–Werner Radiation

Lyman–Werner (LW) radiation photodissociating molecular hydrogen (H2) influences the thermal and dynamical evolution of the Population III (Pop III) star-forming gas cloud. The effect of powerful LW radiation has been well investigated in the context of supermassive black hole formation in the early Universe. However, the average intensity in the early Universe is several orders of magnitude lower. For a comprehensive study, we investigate the effects of LW radiation at 18 different intensities, ranging from J LW/J 21 = 0 (no radiation) to 30 (H-cooling cloud), on the primordial star-forming gas cloud obtained from a three-dimensional cosmological simulation. The overall trend with increasing radiation intensity is a gradual increase in the gas cloud temperature, consistent with previous works. Due to the HD cooling, however, the dependence of gas cloud temperature on J LW deviates from the aforementioned increasing trend for a specific range of intensities (J LW/J 21 = 0.025–0.09). In HD-cooling clouds, the temperature remained below 200 K during 105 yr after the first formation of the high-density region, maintaining a low accretion rate. Finally, the HD-cooling clouds have only a low-mass dense core (above 108 cm−3) with about 1–16 M ⊙, inside of which a low-mass Pop III star with ≤0.8 M ⊙ (a so-called “surviving star”) could form. The upper limit of star formation efficiency Mcore/Mvir,gas significantly decreases from 10−3 to 10−5 as HD cooling becomes effective. This tendency indicates that, whereas the total gas mass in the host halo increases with the LW radiation intensity, the total Pop III stellar mass does not increase similarly.

Chemical differences among collapsing low-mass protostellar cores

Context. Organic features lead to two distinct types of Class 0/I low-mass protostars: hot corino sources exhibiting abundant saturated complex organic molecules (COMs) and warm carbon-chain chemistry (WCCC) sources exhibiting abundant unsaturated carbon-chain molecules. Some observations suggest that the chemical variations between WCCC sources and hot corino sources are associated with local environments and the luminosity of protostars. Aims. We aim to investigate the physical conditions that significantly affect WCCC and hot corino chemistry, as well as to reproduce the chemical characteristics of prototypical WCCC sources and hybrid sources, where both carbon-chain molecules and COMs are abundant. Methods. We conducted a gas-grain chemical simulation in collapsing protostellar cores, adopting a selection of typical physical parameters for the fiducial model. By adjusting the values of certain physical parameters, such as the visual extinction of ambient clouds (AVamb), cosmic-ray ionization rate (ζ), maximum temperature during the warm-up phase (Tmax), and contraction timescale of protostars (tcont), we studied the dependence of WCCC and hot corino chemistry on these physical parameters. Subsequently, we ran a model with different physical parameters to reproduce scarce COMs in prototypical WCCC sources. Results. The fiducial model predicts abundant carbon-chain molecules and COMs. It also reproduces WCCC and hot corino chemistry in the hybrid source L483. This suggests that WCCC and hot corino chemistry can coexist in some hybrid sources. Ultraviolet (UV) photons and cosmic rays can boost WCCC features by accelerating the dissociation of CO and CH4 molecules. On the other hand, UV photons can weaken the hot corino chemistry by photodissociation reactions, while the dependence of hot corino chemistry on cosmic rays is relatively complex. The value of Tmax does not affect any WCCC features, while it can influence hot corino chemistry by changing the effective duration of two-body surface reactions for most COMs. The long tcont can boost WCCC and hot corino chemistry by prolonging the effective duration of WCCC reactions in the gas phase and surface formation reactions for COMs, respectively. The scarcity of COMs in prototypical WCCC sources can be explained by insufficient dust temperatures in the inner envelopes that are typically required to activate hot corino chemistry. Meanwhile, the high ζ and the long tcont favors the explanation for scarce COMs in these sources. Conclusions. The chemical differences between WCCC sources and hot corino sources can be attributed to the variations in local environments, such as AVamb and ζ, as well as the protostellar property, tcont.

A Low-mass line-rich Core Found in Massive Star-forming Region IRAS 16351-4722

We present Atacama Large Millimeter/submillimeter Array subarcsecond-resolution observations of both continuum and molecular lines at 345 GHz toward the massive star-forming region IRAS 16351-4722 (hereafter I16351). A total of 12 dust cores were detected based on high-spatial-resolution observations of the continuum. Among them, a high-mass core (11.6 M ⊙) and a low-mass core (1.7 M ⊙) show abundant molecular line emissions. 164 molecular transitions from 29 species and 104 molecular transitions from 25 species are identified in the high-mass and low-mass cores, respectively. Complex organic molecules (COMs) such as CH3OH, CH3OCHO, CH3OCH3, C2H5OH, and C2H5CN are detected in the two cores. Under the assumption of local thermodynamic equilibrium, the rotational temperatures and column densities of the COMs are derived with the XCLASS software. The maximum rotation temperature values in the low-mass core and the high-mass core were found to be approximately 130 K and 198 K, respectively. Additionally, the line widths in the high-mass core are larger than those in the low-mass one. The abundant COM line transitions, high gas temperatures, and smaller line widths indicate the presence of a low-mass line-rich core in the massive star formation region for the first time, while the high-mass line-rich core shows hot core properties. When comparing the molecular abundances of CH3OH, CH3OCHO, CH3OCH3, and C2H5OH of the two cores with other hot cores and hot corinos reported in the literature, we further confirm that both a hot core and a low-mass line-rich core are simultaneously detected in I16351.

ALMA observations of the Extended Green Object G19.01–0.03 – ii. A massive protostar with typical chemical abundances surrounded by four low-mass pre-stellar core candidates

ABSTRACT We present a study of the physical and chemical properties of the Extended Green Object (EGO) G19.01−0.03 using sub-arcsecond angular resolution Atacama Large Millimetre/submillimetre Array (ALMA) 1.05 mm and Karl G. Jansky Very Large Array (VLA) 1.21 cm data. G19.01−0.03 MM1, the millimetre source associated with the central massive young stellar object (MYSO), appeared isolated and potentially chemically young in previous Submillimetre Array observations. In our ∼0.4 arcsec-resolution ALMA data, MM1 has four low-mass millimetre companions within 0.12 pc, all lacking maser or outflow emission, indicating they may be pre-stellar cores. With a rich ALMA spectrum full of complex organic molecules, MM1 does not appear chemically young, but has molecular abundances typical of high-mass hot cores in the literature. At the 1.05 mm continuum peak of MM1, N(CH3OH) = (2.22 ± 0.01) × 1018 cm−2 and $T_{\mathrm{ex}} = 162.7\substack{+0.3 \\ -0.5}$ K based on pixel-by-pixel Bayesian analysis of LTE synthetic methanol spectra across MM1. Intriguingly, the peak CH3OH Tex = 165.5 ± 0.6 K is offset from MM1’s millimetre continuum peak by 0.22 arcsec ∼ 880 au, and a region of elevated CH3OH Tex coincides with free–free VLA 5.01 cm continuum, adding to the tentative evidence for a possible unresolved high-mass binary in MM1. In our VLA 1.21 cm data, we report the first NH3(3,3) maser detections towards G19.01−0.03, along with candidate 25 GHz CH3OH 5(2, 3) − 5(1, 4) maser emission; both are spatially and kinematically coincident with 44 GHz Class I CH3OH masers in the MM1 outflow. We also report the ALMA detection of candidate 278.3 GHz Class I CH3OH maser emission towards this outflow, strengthening the connection of these three maser types to MYSO outflows.

Quantifying the Impact of the Dust Torque on the Migration of Low-mass Planets

Disk solids are critical in many planet formation processes; however, their effect on planet migration remains largely unexplored. Here we assess this important issue for the first time by building on the systematic measurements of dust torques on an embedded planet by Benitez-Llambay & Pessah. Adopting standard models for the gaseous disk and its solid content, we quantify the impact of the dust torque for a wide range of conditions describing the disk/planet system. We show that the total torque can be positive and reverse inward planet migration for planetary cores with M p ≲ 10 M ⊕. We compute formation tracks for low-mass embryos for conditions usually invoked when modeling planet formation processes. Our most important conclusion is that dust torques can have a significant impact on the migration and formation history of planetary embryos. The most important implications of our findings are as follows. (i) For nominal dust-to-gas mass ratios ϵ ≃ 0.01, low-mass planets migrate outwards beyond the water ice-line if most of the mass in the solids is in particles with Stokes numbers St ≃0.1. (ii) For ϵ ≳ 0.02–0.05, solids with small Stokes numbers, St ≃ 0.01, can play a dominant role if most of the mass is in those particles. (iii) Dust torques have the potential to enable low-mass planetary cores formed in the inner disk to migrate outwards and act as the seed for massive planets at distances of tens of au.

Deuterium fractionation across the infrared-dark cloud G034.77−00.55 interacting with the supernova remnant W44

Context. Supernova remnants (SNRs) may regulate star formation in galaxies. For example, SNR-driven shocks may form new molecular gas or compress pre-existing clouds and trigger the formation of new stars. Aims. To test this scenario, we measured the deuteration of N2H+, DfracN2H+ – a well-studied tracer of pre-stellar cores – across the infrared-dark cloud (IRDC) G034.77-00.55, which is known to be experiencing a shock interaction with the SNR W44. Methods. We use N2H+ and N2D+J = 1−0 single pointing observations obtained with the 30m antenna at the Instituto de Radioas-tronomia Millimetrica to infer DfracN2H+ towards five positions across the cloud, namely a massive core, different regions across the shock front, a dense clump, an+d ambient gas. Results. We find DfracN2H+ in the range 0.03−0.1, which is several orders of magnitude larger than the cosmic D/H ratio (~10−5). The DfracN2H+ across the shock front is enhanced by more than a factor of 2 (DfracN2H+ ~ 0.05 - 0.07) with respect to the ambient gas (≤0.03) and simila+r to that measured generally in pre-stellar cores. Indeed, in the massive core and dense clump regions of this IRDC we measure DfracN2H+ ~ 0.01. Conclusions. We find enhanced deuteration of N2H+ across the region of the shock, that is, at a level that is enhanced with respect to regions of unperturbed gas. It is possible that this has been induced by shock compression, which would then be indirect evidence that the shock is triggering conditions for future star formation. However, since unperturbed dense regions also show elevated levels of deuteration, further, higher-resolution studies are needed to better understand the structure and kinematics of the deuterated material in the shock region; for example, to decipher whether it is still in a relatively diffuse form or is already organised in a population of low-mass pre-stellar cores.

ALMA–IMF

Context.The origin of the stellar initial mass function (IMF) and its relation with the core mass function (CMF) are actively debated issues with important implications in astrophysics. Recent observations in the W43 molecular complex of top-heavy CMFs, with an excess of high-mass cores compared to the canonical mass distribution, raise questions about our understanding of the star formation processes and their evolution in space and time.Aims.We aim to compare populations of protostellar and prestellar cores in three regions imaged in the ALMA-IMF Large Program.Methods.We created an homogeneous core catalogue in W43, combining a new core extraction in W43-MM1 with the catalogue of W43-MM2&MM3 presented in a previous work. Our detailed search for protostellar outflows enabled us to identify between 23 and 30 protostellar cores out of 127 cores in W43-MM1 and between 42 and 51 protostellar cores out of 205 cores in W43-MM2&MM3. Cores with neither outflows nor hot core emission are classified as prestellar candidates.Results.We found a similar fraction of cores which are protostellar in the two regions, about 35%. This fraction strongly varies in mass, fromfpro≃ 15–20% at low mass, between 0.8 and 3M⊙up tofpro≃ 80% above 16M⊙. Protostellar cores are found to be, on average, more massive and smaller in size than prestellar cores. Our analysis also revealed that the high-mass slope of the prestellar CMF in W43,α= -1.46-0.19+0.12, is consistent with the Salpeter slope, and thus the top-heavy form measured for the global CMF,α= −0.96 ± 0.09, is due to the protostellar core population.Conclusions.Our results could be explained by ‘clump-fed’ models in which cores grow in mass, especially during the protostellar phase, through inflow from their environment. The difference between the slopes of the prestellar and protostellar CMFs moreover implies that high-mass cores grow more in mass than low-mass cores.

TOI-5678b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS

Context. A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events. Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates. Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements. Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2σ. The planet TOI-5678 b has a mass of 20 ± 4 Earth masses (M⊕) and a radius of 4.91 ± 0.08 R⊕ Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2±1.7−1.3 M⊕. Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 S⊕). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs

The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12 and 7 m arrays from the Atacama Large Millimeter/submillimeter Array. The targets are 70 μm dark massive (220–4900 M ⊙), dense (>104 cm−3), and cold (∼10–20 K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 M ⊙ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass (<1 M ⊙), whereas ≲1% (7/839) are high-mass (≳27 M ⊙). We detect no high-mass prestellar cores. The most massive cores (MMC) identified within individual clumps lack sufficient mass to form high-mass stars without additional mass feeding. We find that the mass of the MMCs is correlated with the clump surface density, implying denser clumps produce more massive cores. There is no significant mass segregation except for a few tentative detections. In contrast, most clumps show segregation once the clump density is considered instead of mass. Although the dust continuum emission resolves clumps in a network of filaments, some of which consist of hub-filament systems, the majority of the MMCs are not found in the hubs. Our analysis shows that high-mass cores and MMCs have no preferred location with respect to low-mass cores at the earliest stages of high-mass star formation.

The Evolution of Protostellar Outflow Cavities, Kinematics, and Angular Distribution of Momentum and Energy in Orion A: Evidence for Dynamical Cores

We present Atacama Large Millimeter/submillimeter Array observations of the ∼10,000 au environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full ∼1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the pixel flux-tracing technique. Our results indicate that by the end of the protostellar phase, outflows will remove ∼2–4 M ⊙ from the surrounding ∼1 M ⊙ low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of cores as well-defined mass reservoirs, and hence to the simplified core-to-star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on 10,000 au scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.

3D radiative transfer modelling and virial analysis of starless cores in the B10 region of the Taurus molecular cloud

ABSTRACT Low-mass stars like our Sun begin their evolution within cold (10 K) and dense (∼105 cm−3) cores of gas and dust. The physical structure of starless cores is best probed by thermal emission of dust grains. We present a high-resolution dust continuum study of the starless cores in the B10 region of the Taurus Molecular Cloud. New observations at 1.2 and 2.0 mm (12 and 18 arcsec resolution) with the NIKA2 instrument on the IRAM 30m have probed the inner regions of 14 low-mass starless cores. We perform sophisticated 3D radiative transfer modelling for each of these cores through the radiative transfer framework pandora, which utilizes RADMC-3D. Model best-fits constrain each cores’ central density, density slope, aspect ratio, opacity, and interstellar radiation field strength. These ‘typical’ cores in B10 span central densities from 5 × 104 to 1 × 106 cm−3, with a mean value of 2.6 × 105 cm−3. We find the dust opacity laws assumed in the 3D modelling, as well as the estimates from Herschel, have dust emissivity indices, β’s, on the lower end of the distribution constrained directly from the NIKA2 maps, which averages to β = 2.01 ± 0.48. From our 3D density structures and archival NH3 data, we perform a self-consistent virial analysis to assess each core’s stability. Ignoring magnetic field contributions, we find nine out of the 14 cores (64 per cent) are either in virial equilibrium or are bound by gravity and external pressure. To push the bounded cores back to equilibrium, an effective magnetic field difference of only ∼15 $\mu$G is needed.

Nested spheroidal figures of equilibrium – III. Connection with the gravitational moments J2n

ABSTRACT We establish, in the framework of the theory of nested figures, the expressions for the gravitational moments J2n of a systems made of ${\cal L}$ homogeneous layers separated by spheroidal surfaces and in relative rotational motion. We then discuss how to solve the inverse problem, which consists in finding the equilibrium configurations (i.e. internal structures) that reproduce ‘exactly’ a set of observables, namely the equatorial radius, the total mass, the shape, and the first gravitational moments. Two coefficients J2n being constrained per surface, ${\cal L}=1+\frac{n}{2}$ layers (n even) are required to fix J2 to J2n. As shown, this problem already suffers from a severe degeneracy, inherent in the fact that two spheroidal surfaces in the system confocal with each other leave unchanged all the moments. The complexity, which increases with the number of layers involved, can be reduced by considering the rotation rate of each layer. Jupiter is used as a test-bed to illustrate the method, concretely for ${\cal L}=2,3$, and 4. For this planet, the number of possible internal structures is infinite for ${\cal L} &amp;gt; 2$. Intermediate layers can have smaller or larger oblateness, and can rotate slower or faster than the surroundings. Configurations with large and massive cores are always present. Low-mass cores (of the order of a few Earth masses) are predicted for ${\cal L} \ge 4$. The results are in good agreement with the numerical solutions obtained from the self-consistent field method.

On the evolution of pebble-accreting planets in evolving protoplanetary discs

ABSTRACTWe examine the migration of luminous low-mass cores in laminar protoplanetary discs where accretion occurs mainly because of disc winds and where the planet luminosity is generated by pebble accretion. Using 2D hydrodynamical simulations, we determine the eccentricities induced by thermal forces as a function of gas and pebble accretion rates, and also evaluate the importance of the torque exerted by the solid component relative to the gas torque. For a gas accretion rate $\dot{M}= 2\times 10^{-8}\, \mathrm{ M}_\odot$ yr−1 and pebble flux $\dot{M}_{\mathrm{ peb}}=170\, \mathrm{ M}_\oplus$ Myr−1, we find that embryo eccentricities attain values comparable to the disc aspect ratio. The planet radial excursion in the disc, however, causes the torque exerted by inflowing pebbles to cancel on average and migration to transition from outward to inward. This is found to arise because the magnitude of thermal torques decreases exponentially with increasing eccentricity, and we provide a fitting formula for the thermal torque attenuation as a function of eccentricity. As the disc evolves, the accretion luminosity becomes at some point too small to make the core eccentricity grow such that the solid component can exert a non-zero torque on the planet. This torque is positive and for gas accretion rates $\dot{M} \lesssim 5\times 10^{-9}$M⊙ yr−1 and pebble fluxes $\dot{M}_{\rm {peb}} \lesssim 120\, \mathrm{ M}_\oplus $ Myr−1, it is found to overcome the gas torque exerted on cores with mass $m_\mathrm{ p}\lesssim \, 1\,\mathrm{ {M}}_\oplus$, resulting in outward migration.

Directly detecting the envelopes of low-mass planets embedded in protoplanetary discs and the case for TW Hydrae

ABSTRACT Despite many methods developed to find young massive planets in protoplanetary discs, it is challenging to directly detect low-mass planets that are embedded in discs. On the other hand, the core-accretion theory suggests that there could be a large population of embedded low-mass young planets at the Kelvin-Helmholtz (KH) contraction phase. We adopt both 1D models and 3D simulations to calculate the envelopes around low-mass cores (several to tens of M⊕) with different luminosities, and derive their thermal fluxes at radio wavelengths. We find that, when the background disc is optically thin at radio wavelengths, radio observations can see through the disc and probe the denser envelope within the planet’s Hill sphere. When the optically thin disc is observed with the resolution reaching one disc scale height, the radio thermal flux from the planetary envelope around a 10 M⊕ core is more than 10 per cent higher than the flux from the background disc. The emitting region can be extended and elongated. Finally, our model suggests that the au-scale clump at 52 au in the TW Hydrae disc revealed by ALMA is consistent with the envelope of an embedded 10–20 M⊕ planet, which can explain the detected flux, the spectral index dip, and the tentative spirals. The observation is also consistent with the planet undergoing pebble accretion. Future ALMA and ngVLA observations may directly reveal more such low-mass planets, enabling us to study core growth and even reconstruct the planet formation history using the embedded ‘protoplanet’ population.

A Catalog of Molecular Clumps and Cores with Infall Signatures

The research of infall motion is a common means to study molecular cloud dynamics and the early process of star formation. Many works had been done in-depth research on infall. We searched the literature related to infall study of molecular cloud since 1994, summarized the infall sources identified by the authors. A total of 456 infall sources are cataloged. We classify them into high-mass and low-mass sources, in which the high-mass sources are divided into three evolutionary stages: prestellar, protostellar and H ii region. We divide the sources into clumps and cores according to their sizes. The H2 column density values range from 1.21 × 1021 to 9.75 × 1024 cm−2, with a median value of 4.17 × 1022 cm−2. The H2 column densities of high-mass and low-mass sources are significantly separated. The median value of infall velocity for high-mass clumps is 1.12 km s−1, and the infall velocities of low-mass cores are virtually all less than 0.5 km s−1. There is no obvious difference between different stages of evolution. The mass infall rates of low-mass cores are between 10−7 and 10−4 M ⊙yr−1, and those of high-mass clumps are between 10−4 and 10−1 M ⊙yr−1 with only one exception. We do not find that the mass infall rates vary with evolutionary stages.

Confronting double-detonation sub-Chandrasekhar models with the low-luminosity suppression of Type Ia supernovae

ABSTRACT Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon–oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recently, Sharon &amp; Kushnir used The Zwicky Transient Facility Bright Transient Survey to construct a synthesized 56Ni mass, MNi56, distribution of SNe Ia. They found that the rate of low-luminosity ($M_\text{Ni56}\approx 0.15\, \mathrm{M}_{\odot }$) SNe Ia is lower by a factor of ∼10 than the more common $M_\text{Ni56}\approx 0.7\, \mathrm{M}_{\odot }$ events. We here show that in order for the double-detonation model (DDM, in which a propagating thermonuclear detonation wave, TNDW, within a thin helium shell surrounding a sub-Chandrasekhar mass CO core triggers a TNDW within the core) to explain this low-luminosity suppression, the probability of a low-mass ($\approx 0.85\, \mathrm{M}_{\odot }$) WD explosion should be ∼100-fold lower than that of a high-mass ($\approx 1.05\, \mathrm{M}_{\odot }$) WD. One possible explanation is that the ignition of low-mass CO cores is somehow suppressed. We use accurate one-dimensional numerical simulations to show that if a TNDW is able to propagate within the helium shell, then the ignition within the CO core is guaranteed (resolved here for the first time in a full-star simulation), even for $0.7\, \mathrm{M}_{\odot }$ WDs, providing no natural explanation for the low-luminosity suppression. DDM could explain the low-luminosity suppression if the mass distribution of primary WDs in close binaries is dramatically different from the field distribution; if the Helium shell ignition probability is suppressed for low-mass WDs; or if multidimensional perturbations significantly change our results.