Revealing signatures of planets migrating in protoplanetary discs with ALMA multi-wavelength observations

Recent observations show that rings and gaps are ubiquitous in protoplanetary discs. These features are often interpreted as being due to the presence of planets; however, the effect of planetary migration on the observed morphology has not been investigated hitherto. In this work we investigate whether multiwavelength mm/submm observations can detect signatures of planet migration, using 2D dusty hydrodynamic simulations to model the structures generated by migrating planets and synthesising ALMA continuum observations at 0.85 and 3 mm. We identify three possible morphologies for a migrating planet: a slowly migrating planet is associated with a single ring outside the planet's orbit, a rapidly migrating planet is associated with a single ring inside the planet's orbit while a planet migrating at intermediate speed generates one ring on each side of the planet's orbit. We argue that multiwavelength data can distinguish multiple rings produced by a migrating planet from other scenarios for creating multiple rings, such as multiple planets or discs with low viscosity. The signature of migration is that the outer ring has a lower spectral index, due to larger dust grains being trapped there. Of the recent ALMA observations revealing protoplanetary discs with multiple rings and gaps, we suggest that Elias 24 is the best candidate for a planet migrating in the intermediate speed regime.Comment: Accepted for publication in MNRA

Is the ring inside or outside the planet?: The effect of planet migration on dust rings

Planet migration in protoplanetary discs plays an important role in the longer term evolution of planetary systems, yet we currently have no direct observational test to determine if a planet is migrating in its gaseous disc. We explore the formation and evolution of dust rings { now commonly observed in protoplanetary discs by ALMA { in the presence of relatively low mass (12-60 M$_{\oplus}$) migrating planets. Through two dimensional hydrodynamical simulations using gas and dust we find that the importance of perturbations in the pressure profile interior and exterior to the planet varies for different particle sizes. For small sizes a dust enhancement occurs interior to the planet, whereas it is exterior to it for large particles. The transition between these two behaviours happens when the dust drift velocity is comparable to the planet migration velocity. We predict that an observational signature of a migrating planet consists of a significant outwards shift of an observed midplane dust ring as the wavelength is increased.FM acknowledges support from The Leverhulme Trust, the Isaac Newton Trust and the Royal Society Dorothy Hodgkin Fellowship. GR, RB and CC are supported by the DISC- SIM project, grant agreement 341137 funded by the European Research Council under ERC-2013-ADG

ALMA observations of the Extended Green Object G19.01-0.03 : II. A massive protostar with typical chemical abundances surrounded by four low-mass prestellar core candidates

Funding: GMW acknowledges support from the UK’s Science and Technology Facilities Council (STFC) under ST/W00125X/1. CJC acknowledges support from the UK’s STFC under ST/M001296/1. PN acknowledges support by grant 618.000.001 from the Dutch Research Council (NWO) and support by the Danish National Research Foundation through the Center of Excellence "InterCat" (Grant agreement no.: DNRF150).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 Millimeter/submillimeter 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 Submillimeter Array observations. In our ∼0.4″-resolution ALMA data, MM1 has four low-mass millimetre companions within 0.12 pc, all lacking maser or outflow emission, indicating they may be prestellar 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 Tex=162.7+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″ ∼ 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.Publisher PDFPeer reviewe

ALMA observations of the Extended Green Object G19.01−-0.03: II. A massive protostar with typical chemical abundances surrounded by four low-mass prestellar core candidates

We present a study of the physical and chemical properties of the Extended Green Object (EGO) G19.01$-$0.03 using sub-arcsecond angular resolution Atacama Large Millimeter/submillimeter Array (ALMA) 1.05mm and Karl G. Jansky Very Large Array (VLA) 1.21cm data. G19.01$-$0.03 MM1, the millimetre source associated with the central massive young stellar object (MYSO), appeared isolated and potentially chemically young in previous Submillimeter Array observations. In our $\sim0.4''$-resolution ALMA data, MM1 has four low-mass millimetre companions within 0.12pc, all lacking maser or outflow emission, indicating they may be prestellar 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 1.05mm continuum peak of MM1, $\mathrm{N}(\mathrm{CH}_{3}\mathrm{OH})=(2.22\pm0.01)\times10^{18}$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 CH$_{3}$OH $T_{\mathrm{ex}}=165.5\pm0.6$ K is offset from MM1's millimetre continuum peak by $0.22''\sim880$au, and a region of elevated CH$_{3}$OH $T_{\mathrm{ex}}$ coincides with free-free VLA 5.01cm continuum, adding to the tentative evidence for a possible unresolved high-mass binary in MM1. In our VLA 1.21cm data, we report the first NH$_{3}$(3,3) maser detections towards G19.01$-$0.03, along with candidate 25GHz CH$_{3}$OH $5(2,3)-5(1,4)$ maser emission; both are spatially and kinematically coincident with 44GHz Class I CH$_{3}$OH masers in the MM1 outflow. We also report the ALMA detection of candidate 278.3GHz Class I CH$_{3}$OH maser emission towards this outflow, strengthening the connection of these three maser types to MYSO outflows.Comment: 24 pages, 15 figures, 7 tables, Accepted for publication in MNRA

Discovery of a collimated jet from the low luminosity protostar IRAS 16253−-2429 in a quiescent accretion phase with the JWST

Investigating Protostellar Accretion (IPA) is a JWST Cycle~1 GO program that uses NIRSpec IFU and MIRI MRS to obtain 2.9--28~$\mu$m spectral cubes of young, deeply embedded protostars with luminosities of 0.2 to 10,000~L$_{\odot}$ and central masses of 0.15 to 12~M$_{\odot}$. In this Letter, we report the discovery of a highly collimated atomic jet from the Class~0 protostar IRAS~16253$-$2429, the lowest luminosity source ($L_\mathrm{bol}$ = 0.2 $L_\odot$) in the IPA program. The collimated jet is detected in multiple [Fe~II] lines, [Ne~II], [Ni~II], and H~I lines, but not in molecular emission. The atomic jet has a velocity of about 169~$\pm$~15~km\,s$^{-1}$, after correcting for inclination. The width of the jet increases with distance from the central protostar from 23 to~60 au, corresponding to an opening angle of 2.6~$\pm$~0.5\arcdeg. By comparing the measured flux ratios of various fine structure lines to those predicted by simple shock models, we derive a shock {speed} of 54~km\,s$^{-1}$ and a preshock density of 2.0$\times10^{3}$~cm$^{-3}$ at the base of the jet. {From these quantities and using a suite of jet models and extinction laws we compute a mass loss rate between $0.4 -1.1\times10^{-10}~M_{\odot}$~yr~$^{-1}$.} The low mass loss rate is consistent with simultaneous measurements of low mass accretion rate ($2.4~\pm~0.8~\times~10^{-9}~M_{\odot}$~yr$^{-1}$) for IRAS~16253$-$2429 from JWST observations (Watson et al. in prep), indicating that the protostar is in a quiescent accretion phase. Our results demonstrate that very low-mass protostars can drive highly collimated, atomic jets, even during the quiescent phase.Comment: Accepted to ApJL. Comments and feedback welcom

Early planet formation in embedded protostellar disks

Recent surveys of young star formation regions have shown that the dust mass of the average class II object is not high enough to make up the cores of giant planets. Younger class O/I objects have enough dust in their embedded disk, which raises the question whether the first steps of planet formation occur in these younger systems. The first step is building the first planetesimals, which are generally thought to be the product of the streaming instability. Hence the question can be restated to read whether the physical conditions of embedded disks are conducive to the growth of the streaming instability. The streaming instability requires moderately coupled dust grains and a dust-to-gas mass ratio near unity. We model the collapse of a dusty proto-stellar cloud to show that if there is sufficient drift between the falling gas and dust, regions of the embedded disk can become sufficiently enhanced in dust to drive the streaming instability. We include four models to test a variety of collapse theories: three models with different dust grain sizes, and one model with a different initial cloud angular momentum. We find a sweet spot for planetesimal formation for grain sizes of a few 10s of micron because they fall sufficiently fast relative to the gas to build a high dust-to-gas ratio in the disk midplane, but their radial drift speeds are slow enough in the embedded disk to maintain the high dust-to-gas ratio. Unlike the gas, which is held in hydrostatic equilibrium for a time as a result of gas pressure, the dust can begin to collapse from all radii at a much earlier time. The dust mass flux in class O/I systems can thus be higher than the gas flux. This builds an embedded dusty disk with a global dust-to-gas mass ratio that exceeds the inter-stellar mass ratio by at least an order of magnitude. The streaming instability can produce at least between 7 and 35 M⊕ of planetesimals in the class O/I phase of our smooth embedded disks, depending on the size of the falling dust grains. This mass is sufficient to build the core of the first giant planet in the system, and could be further enhanced by dust traps and/or pebble growth. This first generation of planetesimals could represent the first step in planet formation. It occurs earlier in the lifetime of the young star than is traditionally thought

A state-of-the-art review of the recent advances in exosome isolation and detection methods in viral infection

Abstract Proteins, RNA, DNA, lipids, and carbohydrates are only some of the molecular components found in exosomes released by tumor cells. They play an essential role in healthy and diseased cells as messengers of short- and long-distance intercellular communication. However, since exosomes are released by every kind of cell and may be found in blood and other bodily fluids, they may one day serve as biomarkers for a wide range of disorders. In many pathological conditions, including cancer, inflammation, and infection, they play a role. It has been shown that the biogenesis of exosomes is analogous to that of viruses and that the exosomal cargo plays an essential role in the propagation, dissemination, and infection of several viruses. Bidirectional modulation of the immune response is achieved by the ability of exosomes associated with viruses to facilitate immunological escape and stimulate the body's antiviral immune response. Recently, exosomes have received a lot of interest due to their potential therapeutic use as biomarkers for viral infections such as human immunodeficiency virus (HIV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), Epstein–Barr virus (EBV), and SARS-CoV-2. This article discusses the purification procedures and detection techniques for exosomes and examines the research on exosomes as a biomarker of viral infection. Graphical abstrac

Early planet formation in embedded protostellar disks

Recent surveys of young star formation regions have shown that the dust mass of the average class II object is not high enough to make up the cores of giant planets. Younger class O/I objects have enough dust in their embedded disk, which raises the question whether the first steps of planet formation occur in these younger systems. The first step is building the first planetesimals, which are generally thought to be the product of the streaming instability. Hence the question can be restated to read whether the physical conditions of embedded disks are conducive to the growth of the streaming instability. The streaming instability requires moderately coupled dust grains and a dust-to-gas mass ratio near unity. We model the collapse of a dusty proto-stellar cloud to show that if there is sufficient drift between the falling gas and dust, regions of the embedded disk can become sufficiently enhanced in dust to drive the streaming instability. We include four models to test a variety of collapse theories: three models with different dust grain sizes, and one model with a different initial cloud angular momentum. We find a sweet spot for planetesimal formation for grain sizes of a few 10s of micron because they fall sufficiently fast relative to the gas to build a high dust-to-gas ratio in the disk midplane, but their radial drift speeds are slow enough in the embedded disk to maintain the high dust-to-gas ratio. Unlike the gas, which is held in hydrostatic equilibrium for a time as a result of gas pressure, the dust can begin to collapse from all radii at a much earlier time. The dust mass flux in class O/I systems can thus be higher than the gas flux. This builds an embedded dusty disk with a global dust-to-gas mass ratio that exceeds the inter-stellar mass ratio by at least an order of magnitude. The streaming instability can produce at least between 7 and 35 M⊕ of planetesimals in the class O/I phase of our smooth embedded disks, depending on the size of the falling dust grains. This mass is sufficient to build the core of the first giant planet in the system, and could be further enhanced by dust traps and/or pebble growth. This first generation of planetesimals could represent the first step in planet formation. It occurs earlier in the lifetime of the young star than is traditionally thought

JWST/MIRI Detection of Suprathermal OH Rotational Emissions: Probing the Dissociation of the Water by Lyα Photons near the Protostar HOPS 370

Using the MIRI medium-resolution spectrometer on JWST, we have detected pure rotational, suprathermal OH emissions from the vicinity of the intermediate-mass protostar HOPS 370 (OMC2/FIR3). These emissions are observed from shocked knots in a jet/outflow and originate in states of rotational quantum number as high as 46 that possess excitation energies as large as E _U / k = 4.65 × 10 ^4 K. The relative strengths of the observed OH lines provide a powerful diagnostic of the ultraviolet radiation field in a heavily extinguished region ( A _V ∼ 10–20) where direct UV observations are impossible. To high precision, the OH line strengths are consistent with a picture in which the suprathermal OH states are populated following the photodissociation of water in its $\tilde{B}-X$ band by ultraviolet radiation produced by fast (∼80 km s ^−1 ) shocks along the jet. The observed dominance of emission from symmetric ( $A^{\prime}$ ) OH states over that from antisymmetric ( A ″) states provides a distinctive signature of this particular population mechanism. Moreover, the variation of intensity with rotational quantum number suggests specifically that Ly α radiation is responsible for the photodissociation of water, an alternative model with photodissociation by a 10 ^4 K blackbody being disfavored at a high level of significance. Using measurements of the Br α flux to estimate the Ly α production rate, we find that ∼4% of the Ly α photons are absorbed by water. Combined with direct measurements of water emissions in the ν _2 = 1 − 0 band, the OH observations promise to provide key constraints on future models for the diffusion of Ly α photons in the vicinity of a shock front