Dust Envelope Research Articles

Radiative signatures of circumplanetary disks and envelopes during the late stages of giant planet formation

During the late stages of giant planet formation, protoplanets are surrounded by a circumplanetary disk and an infalling envelope of gas and dust. For systems with sufficient cooling, material entering the sphere of influence of the planet falls inward and approaches ballistic conditions. Due to conservation of angular momentum, most of the incoming material falls onto the disk rather than directly onto the planet. This paper determines the spectral energy distributions of forming planets in this stage of evolution. Generalizing previous work, we consider a range of possible geometries for the boundary conditions of the infall and determine the two-dimensional structure of the envelope, as well as the surface density of the disk. After specifying the luminosity sources for the planet and disk, we calculate the corresponding radiative signatures for the system, including the emergent spectral energy distributions and emission maps. These results show how the observational appearance of forming planets depend on the input parameters, including the instantaneous mass, mass accretion rate, semimajor axis of the orbit, and the planetary magnetic field strength (which sets the inner boundary condition for the disk). We also consider different choices for the form of the opacity law and attenuation due to the background circumstellar disk. Although observing forming planets will be challenging, these results show how the observational signatures depend on the underlying properties of the planet/disk/envelope system.

The factors that influence protostellar multiplicity

Context. Protostellar multiplicity is common at all stages and mass ranges. However, the factors that determine the multiplicity of protostellar systems have not been systematically characterized through their molecular gas. Aims. We characterize the physical properties of the Perseus molecular cloud at ≥5000 AU scales by mapping the diagnostic molecular lines. Methods. We used Nobeyama 45m Radio Observatory (NRO) on-the-fly maps of HCN, HNC, HCO+, and N2H+ (J=1–0) toward five subregions in Perseus, complemented with single-pointing Atacama Pathfinder Experiment (APEX) observations of HNC (J = 4–3), to derive the physical parameters of the dense gas. The spatial resolutions of both observations were ~18″, which is equivalent to ~5000 AU scales at the distance of Perseus. The kinetic gas temperature was derived from the I(HCN)/I(HNC) J ratio, and the H2 density was obtained from the HNC J=4–3/J=1–0 ratio. These parameters were used to obtain the N2H+ (cold) and HCO+ (warm) gas masses. The inferred and derived parameters were then compared to source the parameters, including protostellar multiplicity, bolometric luminosity, and dust envelope mass. Results. The inferred mean kinetic gas temperature (I(HCN)/I(HNC) J=1–0 ratio; ranging between 15 and 26 K), and H2 volumetric density (HNC J=4–3/J=1–0; 105−106 cm−3) are not correlated with multiplicity in Perseus. The derived gas and dust masses, 1.3 to 16 × 10−9 M⊙ for the cold-gas mass (N2H+), 0.1 to 25 M⊙ for the envelope dust masses (850 μm), and 0.8 to 10 × 10−10 M⊙ for the warm-gas mass (HCO+), are correlated to multiplicity and to the number of protostellar components. The warm-gas masses are lower by a factor of 16 than the cold-gas masses. Conclusions. The gas and dust mass is correlated to multiplicity at ~5000 AU scales in Perseus. Higher-order multiples tend to have higher gas and dust masses in general, while close binaries (separations ≤7″) and single protostars have similar gas and dust mass distributions. On the other hand, the H2 density and kinetic gas temperature are not correlated with multiplicity.

Post-AGB candidate IRAS 02143+5852: Cepheid-like variability, three-layer circumstellar dust envelope and spectral features

ABSTRACT We present the results of multicolour UBVRCICJHK photometry, spectroscopic analysis and spectral energy distribution (SED) modelling for the post-AGB candidate IRAS 02143+5852. We detected Cepheid-like light variations with the full peak-to-peak amplitude ΔV ∼ 0.9 mag and the pulsation period of about 24.9 d. The phased light curves appeared typical for the W Vir Cepheids. The period–luminosity relation for the Type II Cepheids yielded the luminosity logL/L⊙ ∼ 2.95. From a low-resolution spectrum, obtained at maximum brightness, the following atmospheric parameters were determined: Teff ∼ 7400 K and logg ∼ 1.38. This spectrum contains the emission lines H α, ${\rm Ba\, {\small II}}$ λ6496.9, ${\rm He\, {\small I}}$λ10830, and Pa β. Spectral monitoring performed in 2019–2021 showed a significant change in the H α profile and appearance of CH and CN molecular bands with pulsation phase. The metal lines are weak. Unlike typical W Vir variables, the star shows a strong excess of infrared radiation associated with the presence of a heavy dust envelope around the star. We modelled the SED using our photometry and archival data from different catalogues and determined the parameters of the circumstellar dust envelope. We conclude that IRAS 02143+5852 is a low-luminosity analogue of dusty RV Tau stars.

Experimental Phase Function and Degree of Linear Polarization of Light Scattered by Hydrogenated Amorphous Carbon Circumstellar Dust Analogs

Astronomical observations of the polarized intensity of scattered visible light have revealed the presence of dust envelopes around different types of evolved stars. These observations have helped determine the diameter and width of dust shells around stars with unprecedented accuracy. Simple geometric particle models are used in order to retrieve dust properties from these observations. In this work, we have synthesized and characterized a particulate sample of hydrogenated amorphous carbon (HAC), which is considered to be a realistic carbonaceous interstellar dust analog based on infrared absorption spectroscopy, and we have measured its phase function and degree of linear polarization curves at 514 nm using the CODULAB apparatus at IAA-CSIC. The experimental light-scattering data has been examined in order to explore possible improvements in the interpretation of astronomical observations of circumstellar dust from the point of view of the retrieval of dust properties, including size and porosity. Our results suggest that circumstellar dust observations of linearly polarized scattered light, which are commonly attributed to a population of spherical grains with a radius of ∼0.1 μm, are consistent with larger porous aggregates composed of nanometer-sized grains. In addition, an internal 50wt% mixture of HAC and ultrafine forsterite powder has been generated to study the effect of the mixing of these two components on the light-scattering behavior of dust in cometary environments and protoplanetary disks. In this case, the HAC component, which is not very absorbent, has a very small effect, and the mixture scatters light similarly to the forsterite sample.

V445 Puppis: Dustier than a Thousand Novae

V445 Puppis, the only known Galactic helium nova, is a unique test bed to verify supernova (SN) theories in the single-degenerate channel that involve a white dwarf (WD) accreting matter from a helium-rich donor. An estimate of the mass of the helium shell on the WD is crucial to deciding whether or not it will undergo an SN detonation. In this context, this study estimates the dust and ejecta masses in the 2000 November eruption of V445 Pup. Subsequent to its outburst, the star became cocooned in a dust envelope. An analysis of the spectral energy distribution (SED) of the dust using infrared data shows that V445 Pup produced at least 10−3 M ⊙ of dust, which is unprecedented for a classical or recurrent nova. The SED can be explained by a combination of a cold dust component at 105 ± 10 K, mass (1.9 ± 0.8) × 10−3 M ⊙, and a warm dust component at 255 ± 10 K, mass (2.2 ± 1.2) × 10−5 M ⊙. For a conservative choice of the gas-to-dust mass ratio in the range 10–100, the mass of the ejecta is 0.01–0.1 M ⊙. Such a high mass range raises the question: why did V445 Pup not detonate as a Type Ia SN as is predicted in certain double-detonation sub-Chandrasekhar supernovae formalisms? We reexamine the nature of V445 Pup and discuss its role as a potential SN progenitor.

Coma environment of comet C/2017 K2 around the water ice sublimation boundary observed with VLT/MUSE

We report a new imaging spectroscopic observation of Oort cloud comet C/2017 K2 (hereafter K2) with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope on its way to perihelion at 2.53 au, around a heliocentric distance where H2O ice begins to play a key role in comet activation. Normalized reflectances over 6500–8500 Å for its inner (cometocentric distance ρ ≈ 103 km) and outer (ρ ≈ 2 × 104 km) comae are 9.7 ± 0.5 and 7.2 ± 0.3 % (103 Å)−1, respectively, the latter being consistent with the slope observed when the comet was beyond the orbit of Saturn. The dust coma of K2 at the time of observation appears to contain three distinct populations: millimeter-sized chunks prevailing at ρ ≲ 103 km; a 105 km steady-state dust envelope; and fresh anti-sunward jet particles. The dust chunks dominate the continuum signal and are distributed over a similar radial distance scale as the coma region with redder dust than nearby. They also appear to be co-spatial with OI1D, suggesting that the chunks may accommodate H2O ice with a fraction (≳1%) of refractory materials. The jet particles do not colocate with any gas species detected. The outer coma spectrum contains three significant emissions from C2(0,0) Swan band, OI1D, and CN(1,0) red band, with an overall deficiency in NH2. Assuming that all OI1D flux results from H2O dissociation, we compute an upper limit on the water production rate QH2O of ~7 × 1028 molec s−1 (with an uncertainty of a factor of two). The production ratio log[QC2/QCN] of K2 suggests that the comet has a typical carbon chain composition, with the value potentially changing with distance from the Sun. Our observations suggest that dust chunks (>0.1 mm) containing water ice and near K2’s nucleus emitted beyond 4 au may be responsible for its very low gas rotational temperature and the discrepancy between its optical and infrared lights reported at similar heliocentric distances.

Spatially resolved mid-infrared observations of the circumstellar environment of the born-again object FG Sge

Context. FG Sge has evolved from the hot central star of the young planetary nebula Hen 1–5 to a G–K supergiant in the last 100 yr. It is one of the three born-again objects that have been identified as of yet, and they are considered to have undergone a thermal pulse in the post-asymptotic giant branch evolution. Aims. We present mid-infrared spectro-interferometric observations of FG Sge and probe its dusty environment. Methods. FG Sge was observed with MIDI at the Very Large Telescope Interferometer at baselines of 43 and 46 m between 8 and 13 µm. Results. The circumstellar dust environment of FG Sge was spatially resolved, and the Gaussian fit to the observed visibilities results in a full width at half maximum of ~10.5 mas. The observed mid-infrared visibilities and the spectral energy distribution can be fairly reproduced by optically thick (τV ≈ 8) spherical dust shell models consisting of amorphous carbon with an inner radius rin of ~30 R★ (corresponding to a dust temperature of 1100 ± 100 K). The dust shell is characterized with a steep density profile proportional to r−3.5±0.5 from the inner radius rin to (5–10) × rin, beyond which it changes to r−2. The dust mass is estimated to be ~ 7 × 10−7 M⊙, which translates into an average total mass-loss rate of ~ 9 × 10−6 M⊙ yr−1 as of 2008 with a gas-to-dust ratio of 200 being adopted. In addition, the 8–13 µm spectrum obtained with MIDI with a field of view of 200 mas does not show a signature of the polycyclic aromatic hydrocarbon (PAH) emission, which is in marked contrast to the spectra taken with the Spitzer Space Telescope six and 20 months before the MIDI observations with wide slit widths of 3″.6–10″. This implies that the PAH emission originates from an extended region of the optically thick dust envelope. Conclusions. The dust envelope of FG Sge is much more compact than that of the other born-again stars’ Sakurai’s object and V605 Aql, which might reflect the difference in the evolutionary status. The PAH emission from the extended region of the optically thick dust envelope likely originates from the material ejected before the central star became H-deficient, and it may be excited by the UV radiation from the central star escaping through gaps among dust clumps and/or the bipolar cavity of a disk-like structure.

CO line observations of OH/IR stars in the inner Galactic Bulge: Characteristics of stars at the tip of the AGB

Context. OH/IR stars are examples of late stellar evolution on the asymptotic giant branch (AGB), and they are, as such, important objects to study. They are also excellent probes of stellar populations, in particular in regions of high interstellar extinction such as the central regions of our Galaxy. Aims. Our goal is to characterise the stellar and circumstellar properties of high-mass-loss-rate OH/IR stars in the inner Galactic Bulge using the Atacama Large Millimeter/submillimeter Interferometer (ALMA). Methods. Rotational lines of 12CO and 13CO, as well as a millimetre-wave continuum, have been observed for a sample of 22 OH/IR stars in directions within 2° of the Galactic Centre. Photometry data (≈1–30 µm) have been gathered from the literature to construct spectral energy distributions (SEDs) and to determine pulsational variability. Radiative transfer models have been used to interpret the line and photometry data. Results. All stars in the sample were detected in at least one CO line, and eight objects were detected in 324 GHz continuum. Based on luminosity criteria, the sample is divided into 17 objects that most likely lie within the inner Galactic Bulge, and five objects that are most likely foreground objects. The median luminosity of the inner-Galactic-Bulge sub-sample, 5600 L⊙, corresponds to an initial mass in the range 1.2–1.6 M⊙, indicating that these inner-Galactic-Bulge OH/IR stars descend from solar-type stars. The objects in this sub-sample are further divided into two classes based on their SED characteristics: Eleven objects have SEDs that are well matched by models invoking dust envelopes extending from a few stellar radii and outwards, while six objects are better modelled as having detached dust envelopes with inner radii in the range 200–600 au and warmer central stars. The former objects have periodic variability, while the latter objects are predominantly non-periodic. The median gas-mass-loss rate, gas terminal expansion velocity, gas-to-dust mass ratio, and circumstellar 12CO/13CO abundance ratio have been estimated to be 2 × 10−5 M⊙ yr−1, 18 km s−1, 200 (excluding the sources with detached dust envelopes, which show markedly lower gas-to-dust ratios), and 5, respectively, for the inner-Galactic-Bulge sub-sample. All line brightness distributions are resolved at an angular scale of ≈0″.15, but only two objects show a structure in their circumstellar envelopes at our resolution and sensitivity. In both cases, this structure takes the form of a cavity and a bipolar morphology. Conclusions. The inner-Galactic-Bulge sub-sample consists of high mass-loss-rate stars that descend from solar-type progenitors and that lie near the tip of the AGB. Some of the sample stars may have recently ceased mass loss and, hence, have begun to evolve beyond the AGB, as evidenced by a change in circumstellar characteristics and indications of warmer central stars. The inferred very low stellar 12C/13C isotope ratios are indicative of CNO-cycle nuclear processing, and they are most likely established at the surfaces of the stars during the first dredge-up on the red giant branch since these stars are not expected to experience hot-bottom burning. The inner-Galactic-Bulge OH/IR stars studied here constitute an excellent sample of equidistant objects for the purpose of understanding the evolution of the mass-loss-rate characteristics at the tip of the AGB.

An Excited-state OH Maser Survey toward WISE Point Sources

We report a survey of excited-state hydroxyl (ex-OH) masers at the 4.7 and 6.0 GHz transitions toward a sample consisting of 3348 massive star-forming region candidates selected from the all-sky Wide-field Infrared Survey Explorer point-source catalog. The survey was conducted with the Shanghai Tianma Radio Telescope. In total, 6, 9, and 30 sources were detected with the ex-OH masers at the 4766, 6031, and 6035 MHz transitions, respectively. Among them, one 4766 MHz, one 6031 MHz, and five 6035 MHz ex-OH maser sources are newly identified. A series of statistical analyses derived that the ex-OH masers were detected efficiently toward the subsamples associated with both the 6.7 GHz CH3OH maser and radio recombination lines (RRLs), whereas compared to the CH3OH masers, the ex-OH masers are more likely to be produced toward the sources with stronger 22 μm band emission. A significant luminosity correlation is found between the ex-OH masers and RRLs. In addition, we found that the magnetic field strength of most sources with the 6.7 GHz CH3OH maser was stronger relative to that of sources without the CH3OH maser. Combined with these, it demonstrates that the ex-OH maser is associated with more evolved star-forming regions, likely associated with thicker dust envelopes. Meanwhile, the ex-OH masers might be a potential tracer for measuring the Galactic magnetic field information on the large-scale views using their Zeeman pairs.

The Nearby Evolved Stars Survey II: Constructing a volume-limited sample and first results from the James Clerk Maxwell Telescope

ABSTRACT The Nearby Evolved Stars Survey (NESS) is a volume-complete sample of ∼850 Galactic evolved stars within 3 kpc at (sub-)mm wavelengths, observed in the CO J = (2–1) and (3–2) rotational lines, and the sub-mm continuum, using the James Clark Maxwell Telescope and Atacama Pathfinder Experiment. NESS consists of five tiers, based on distances and dust-production rate (DPR). We define a new metric for estimating the distances to evolved stars and compare its results to Gaia EDR3. Replicating other studies, the most-evolved, highly enshrouded objects in the Galactic Plane dominate the dust returned by our sources, and we initially estimate a total DPR of 4.7 × 10−5 M⊙ yr−1 from our sample. Our sub-mm fluxes are systematically higher and spectral indices are typically shallower than dust models typically predict. The 450/850 $\mu$m spectral indices are consistent with the blackbody Rayleigh–Jeans regime, suggesting a large fraction of evolved stars have unexpectedly large envelopes of cold dust.

Signs of late infall and possible planet formation around DR Tau using VLT/SPHERE and LBTI/LMIRCam

Context. Protoplanetary disks around young stars often contain substructures like rings, gaps, and spirals that could be caused by interactions between the disk and forming planets. Aims. We aim to study the young (1–3 Myr) star DR Tau in the near-infrared and characterize its disk, which was previously resolved through submillimeter interferometry with ALMA, and to search for possible substellar companions embedded into it. Methods. We observed DR Tau with VLT/SPHERE both in polarized light (H broad band) and total intensity (in Y, J, H, and K spectral bands). We also performed L′ band observations with LBTI/LMIRCam on the Large Binocular Telescope (LBT). We applied differential imaging techniques to analyze both the polarized data, using dual beam polarization imaging, and the total intensity data, using angular and spectral differential imaging. Results. We found two previously undetected spirals extending north-east and south of the star, respectively. We further detected an arc-like structure north of the star. Finally a bright, compact and elongated structure was detected at a separation of 303 ± 10 mas and a position angle 21.2 ± 3.7 degrees, just at the root of the north-east spiral arm. Since this feature is visible both in polarized light and total intensity and has a blue spectrum, itis likely caused by stellar light scattered by dust. Conclusions. The two spiral arms are at different separations from the star, have very different pitch angles, and are separated by an apparent discontinuity, suggesting they might have a different origin. The very open southern spiral arm might be caused by infalling material from late encounters with cloudlets into the formation environment of the star itself. The compact feature could be caused by interaction with a planet in formation still embedded in its dust envelope and it could be responsible for launching the north–east spiral. We estimate a mass of the putative embedded object of the order of few MJup.

Probing infrared excess connection with Li enhancement among red clump giants

ABSTRACT We have performed a search among low-mass red giants for finding evidence for merger scenario for triggering He-flash and subsequent Li enhancement. We chose a sample of red giants from GALAH survey with well-measured Li abundances, and near- and mid-IR fluxes from 2MASS and WISE surveys, respectively. The sample contains 418 cool red clump giants and 359 upper red giant branch (RGB) giants. Most of the giants and majority of super Li-rich giants show no IR excess. Only five red clump giants and one RGB giant show IR excess. Notably, of the five red clump giants with IR excess, three are super Li-rich (A(Li) ≥ 3.2 dex) and two are Li-rich (A(Li) ≥ 1.0 dex). Results suggest that Li enhancement among red clump giants may be due to two channels: one resulting from in situ He-flash in single-star evolution and the other due to He-flash triggered by events like merger of He-white dwarfs with giants’ He-inert core on RGB. In the latter case, IR excess, as a result of mass-loss, is expected from merger events. We have modelled IR excess in all six giants using dusty code and derived dust parameters. The estimated kinematic ages and time-scales of dust envelopes of the super Li-rich phase suggest that Li enhancement took place very recently. Further, the analysis shows a significantly higher proportion (four out of five red clump giants) of rapid rotators (vsini ≥ 8 km s−1) among Li-rich giants with IR excess compared to Li-normal and Li-rich giants with no IR excess.

Repeating Gas Ejection Events from Comet 45P/Honda–Mrkos–Pajdušáková

Abstract Studying materials released from Jupiter-family comets (JFCs)—as seen in their inner comae, the envelope of gas and dust that forms as the comet approaches the Sun—improves the understanding of their origin and evolutionary history. As part of a coordinated, multiwavelength observing campaign, we observed comet 45P/Honda–Mrkos–Pajdušáková during its close approach to Earth in 2017 February. Narrowband observations were taken using the Bok 90″ telescope at Kitt Peak National Observatory on February 16 and 17 UT, revealing gas and dust structures. We observed different jet directions for different volatile species, implying source region heterogeneity, consistent with other ground-based and in situ observations of other comet nuclei. A repeating feature visible in CN and C2 images on February 16 was also observed on February 17 with an interval of 7.6 ± 0.1 hr, consistent with the rotation period of the comet derived from Arecibo Observatory radar observations. The repeating feature’s projected gas velocity away from the nucleus is 0.8 km s−1, with an outflow velocity of 0.5 km s−1. A bright compact spot adjacent to the nucleus provides a lower limit of the amount of material released in one cycle of ∼9.2 kg, depending on composition—a quantity small enough to be produced by repeated exposure of nucleus ices to sunlight. This repeating CN jet, forming within 400 km of the nucleus, may be typical of inner-coma behavior in JFCs; however, similar features could be obscured by other processes and daughter product species when viewed from distances further than the scale length of CN molecules.

Accretion Flows or Outflow Cavities? Uncovering the Gas Dynamics around Lupus 3-MMS

Abstract Understanding how material accretes onto the rotationally supported disk from the surrounding envelope of gas and dust in the youngest protostellar systems is important for describing how disks are formed. Magnetohydrodynamic simulations of magnetized, turbulent disk formation usually show spiral-like streams of material (accretion flows) connecting the envelope to the disk. However, accretion flows in these early stages of protostellar formation still remain poorly characterized, due to their low intensity, and possibly some extended structures are disregarded as being part of the outflow cavity. We use ALMA archival data of a young Class 0 protostar, Lupus 3-MMS, to uncover four extended accretion flow–like structures in C18O that follow the edges of the outflows. We make various types of position–velocity cuts to compare with the outflows and find the extended structures are not consistent with the outflow emission, but rather more consistent with a simple infall model. We then use a dendrogram algorithm to isolate five substructures in position–position–velocity space. Four out of the five substructures fit well (>95%) with our simple infall model, with specific angular momenta between 2.7–6.9 × 10−4 km s−1 pc and mass-infall rates of 0.5–1.1 × 10−6 M ⊙ yr−1. Better characterization of the physical structure in the supposed “outflow cavities” is important to disentangle the true outflow cavities and accretion flows.

Mid-infrared circumstellar emission of the long-period Cepheid ℓ Carinae resolved with VLTI/MATISSE

Context. The nature of circumstellar envelopes (CSEs) around Cepheids is a matter of ongoing debate. The physical origin of their infrared (IR) excess could be shown to either be made up of a shell of ionized gas, a dust envelope, or a combination of both. Aims. This study is aimed at constraining the geometry and the IR excess of the environment of the bright long-period Cepheid ℓ Car (P = 35.5 days) at mid-IR wavelengths in order to understand its physical nature. Methods. We first used photometric observations in various bands (from the visible domain to the infrared) and Spitzer Space Telescope spectroscopy to constrain the IR excess of ℓ Car. Then we analyzed the VLTI/MATISSE measurements at a specific phase of observation in order to determine the flux contribution as well as the size and shape of the environment of the star in the L band. Finally, we tested the hypothesis of a shell of ionized gas in order to model the IR excess. Results. We report the first detection in the L band of a centro-symmetric extended emission around ℓ Car, of about 1.7 R⋆ in full width at half maximum, producing an excess of about 7.0% in this band.This latter value is used to calibrate the IR excess found when comparing the photometric observations in various bands and quasi-static atmosphere models. In the N band, there is no clear evidence for dust emission from VLTI/MATISSE correlated flux and Spitzer data. On the other side, the modeled shell of ionized gas implies a more compact CSE (1.13 ± 0.02 R⋆) that is also fainter (IR excess of 1% in the L band). Conclusions. We provide new evidence supporting a compact CSE for ℓ Car and we demonstrate the capabilities of VLTI/MATISSE for determining common properties of CSEs. While the compact CSE of ℓ Car is likely to be of a gaseous nature, the tested model of a shell of ionized gas is not able to simultaneously reproduce the IR excess and the interferometric observations. Further Galactic Cepheid observations with VLTI/MATISSE are necessary for determining the properties of CSEs, which may also depend on both the pulsation period and the evolutionary state of the stars.

The Planck Submillimeter Properties of Galactic High-mass Star-forming Regions: Dust Temperatures, Luminosities, Masses, and Star Formation Efficiency

Abstract Massive star formation occurs in the interior of giant molecular clouds and proceeds through many stages. In this work, we focus on massive young stellar objects (MYSOs) and ultracompact H ii regions (UCH ii), where the former are enshrouded in dense envelopes of dust and gas, the latter of which has begun dispersing. By selecting a complete sample of MYSOs and UCH ii from the Red MSX Source (RMS) survey database, we combine Planck and IRAS data and build their spectral energy distributions. With these, we estimate the physical properties (dust temperatures, mass, luminosity) of the sample. Because the RMS database provides unique solar distances, it also allows the instantaneous star formation efficiency (SFE) to be investigated as a function of Galactocentric radius. We find that the SFE increases between 2 and 4.5 kpc, where it reaches a peak, likely in correspondence with the accumulation of molecular material at the end of the Galactic bar. It then stays approximately constant up to 9 kpc, after which it linearly declines, in agreement with predictions from extragalactic studies. This behavior suggests the presence of a significant amount of undetected molecular gas at R G > 8 kpc. Finally, we present diagnostic colors that can be used to identify sites of massive star formation.

Extended view on the dust shells around two carbon stars

Context. Stars on the asymptotic giant branch lose considerable amounts of matter through their dust-driven stellar winds. A number of such sources have been imaged by Herschel/PACS, revealing a diverse sample of different morphological types. Among them are a few examples which show geometrically thin, spherically symmetric shells which can be used to probe the mass loss history of their host stars. Aims. We aim to determine the physical properties of the dust envelope around the two carbon stars U Hya and W Ori. With the much-improved spatial constraints from the new far-infrared maps, our primary goal is to measure the dust masses contained in the shells and see how they fit the proposed scenarios of shell formation. Methods. We calculated the radiative transfer of the circumstellar dust envelope using the 1D code More of DUSTY (MoD). Adopting a parametrised density profile, we obtained a best-fit model in terms of the photometric and spectroscopic data, as well as a radial intensity profile based on Herschel/PACS data. For the case of U Hya, we also computed a grid of circumstellar envelopes by means of a stationary wind code and compare the results of the two modelling approaches. Results. The Herschel/PACS maps show U Hya surrounded by a detached shell of 114′′ (0.12 pc) in radius, confirming the observations from previous space missions. The dust masses calculated for the shell by the two approaches are consistent with respect to the adopted dust grain properties. In addition, around W Ori, we detect for the first time a weak spherically symmetric structure with a radius of 92′′ (0.17 pc) and a dust mass of (3.5 ± 0.3) × 10−6 M⊙.

MATISSE first pictures of dust and molecules around R Sculptoris

AbstractCarbon-rich dust is known to form in the atmosphere of the semiregular variable star R Sculptoris. Such stardust, as well as the molecules and gas produced during the lifetime of the star, will be spread into the Galaxy via the mass-loss process. Probing this process is crucial to understand the chemical enrichment of the Galaxy. R Scl was observed using the ESO/VLTI MATISSE instrument in December 2018. Here we show the first images of the star between 3 and 10 R*. Using the complementary MIRA 3D image reconstruction and the RHAPSODY 1D intensity profile reconstruction code, we reveal the location of molecules and dust in the close environment of the star. Indeed, the C2H2 and HCN molecules are spatially located between 1 and 3.4 R* which is much closer to the star than the location of the dust. The R Scl spectrum is fitted by molecules and a dust mixture of 90% of amorphous carbon and 10% of silicone carbide. The inner boundary of the dust envelope is estimated by DUSTY at about 4.6 R*. We derive a mass-loss rate of 1.2 ± 0.4 × 10−6M⊙ yr−1however no clear SiC forming region has been detected in the MATISSE data.

Four annular structures in a protostellar disk less than 500,000 years old.

Annular structures (rings and gaps) in disks around pre-main-sequence stars have been detected in abundance towards classII protostellar objects that are approximately 1,000,000years old1. These structures are often interpreted as evidence of planet formation1-3, with planetary-mass bodies carving rings and gaps in the disk4. This implies that planet formation may already be underway in even younger disks in the classI phase, when the protostar is still embedded in a larger-scale dense envelope of gas and dust5. Only within the past decade have detailed properties of disks in the earliest star-forming phases been observed6,7. Here we report 1.3-millimetre dust emission observations with a resolution of five astronomical units that show four annular substructures in the disk of the young (less than500,000 years old)8 protostar IRS63. IRS63 is a single classI source located in the nearby Ophiuchus molecular cloud at a distance of 144 parsecs9, and is one of the brightest classI protostars at millimetre wavelengths. IRS63 also has a relatively large disk compared to other young disks (greater than 50astronomical units)10. Multiple annular substructures observed towards disks at young ages can act as an early foothold for dust-grain growth, which is a prerequisite of planet formation. Whether or not planets already exist in the disk of IRS63, it is clear that the planet-formation process begins in the initial protostellar phases, earlier than predicted by current planet-formation theories11.

How to disentangle geometry and mass-loss rate from AGB-star spectral energy distributions

Context. High-angular-resolution observations of asymptotic giant branch (AGB) stars often reveal non-spherical morphologies for the gas and dust envelopes. Aims. We aim to make a pilot study to quantify the impact of different geometries (spherically symmetric, spiral-shaped, and disc-shaped) of the dust component of AGB envelopes on spectral energy distributions (SEDs), mass estimates, and subsequent mass-loss rate (MLR) estimates. We also estimate the error made on the MLR if the SED is fitted by an inappropriate geometrical model. Methods. We use the three-dimensional Monte-Carlo-based radiative-transfer code RADMC-3D to simulate emission from dusty envelopes with different geometries (but fixed spatial extension). We compare these predictions with each other, and with the SED of the AGB star EP Aqr that we use as a benchmark since its envelope is disc-like and known to harbour spiral arms, as seen in CO. Results. The SEDs involving the most massive envelopes are those for which the different geometries have the largest impact, primarily on the silicate features at 10 and 18 μm. These different shapes originate from large differences in optical depths. Massive spirals and discs appear akin to black bodies. Optically thick edge-on spirals and discs (with dust masses of 10−4 and 10−5 M⊙) exhibit black-body SEDs that appear cooler than those from face-on structures and spheres of the same mass, while optically thick face-on distributions appear as warmer emission. We find that our more realistic models, combined spherical and spiral distributions, are 0.1 to 0.5 times less massive than spheres with similar SEDs. More extreme, less realistic scenarios give that spirals and discs are 0.01 to 0.05 times less massive than corresponding spheres. This means that adopting the wrong geometry for an AGB circumstellar envelope may result in a MLR that is incorrect by as much as one to two orders of magnitude when derived from SED fitting.