Search

Meteorites trace planet formation in the Sun's protoplanetary disk, but they also record the influence of the Sun's birth environment. Whether the Sun formed in a region like Taurus-Auriga with ∼ 10 2 stars, or a region like the Carina Nebula with ∼ 10 6 stars, matters for how large the Sun's disk was, for how long and from how far away it accreted gas from the molecular cloud, and how it acquired radionuclides like 26Al. To provide context for the interpretation of meteoritic data, we review what is known about the Sun's birth environment. Based on an inferred gas disk outer radius ≈ 50 − 90 AU, radial transport in the disk, and the abundances of noble gases in Jupiter's atmosphere, the Sun's molecular cloud and protoplanetary disk were exposed to an ultraviolet flux G 0 ∼ 30 − 3000 during its birth and first ≈ 10 Myr of evolution. Based on the orbits of Kuiper Belt objects, the Solar System was subsequently exposed to a stellar density ≈ 100 M ⊙ pc − 3 for ≈ 100 Myr, strongly implying formation in a bound cluster. These facts suggest formation in a region like the outskirts of the Orion Nebula, perhaps 2 pc from the center. The protoplanetary disk might have accreted gas for many Myr, but a few × 10 5 yr seems more likely. It probably inherited radionuclides from its molecular cloud, enriched by inputs from supernovae and especially Wolf-Rayet star winds, and acquired a typical amount of 26Al. [ABSTRACT FROM AUTHOR]

Molecular clouds are the prime locations of star formation. These clouds contain filamentary structures and cores which are crucial in the formation of young stars. In this work, we aim to quantify the physical properties of structural characteristics within the molecular cloud L1251 to better understand the initial conditions for star formation. We applied the getsf algorithm to identify cores and filaments within the molecular cloud L1251 using the Herschel multi-band dust continuum image, enabling us to measure their respective physical properties. Additionally, we utilized an enhanced differential term algorithm to produce high-resolution temperature maps and column density maps with a resolution of 13.5 ′ ′ . We identified 122 cores in the region. Of those, 23 are protostellar cores, 13 are robust prestellar cores, 32 are candidate prestellar cores (including 13 robust prestellar cores and 19 strictly candidate prestellar cores), and 67 are unbound starless cores. getsf also found 147 filament structures in the region. Statistical analysis of the physical properties (mass (M), temperature (T), size and core brightness (hereafter, we are using the word luminosity (L)) for the core brightness) of obtained cores shows a negative correlation between core mass and temperature and a positive correlation between (M/L) and (M/T). Analysis of the filaments gives a median width of 0.14 pc and no correlation between width and length. Out of those 122 cores, 92 are present in filaments (∼ 75.4%) and the remaining were outside them. Out of the cores present in filaments, 57 (∼ 62%) cores are present in supercritical filaments ( M line > 16 M ⊙ / pc ). [ABSTRACT FROM AUTHOR]

Molecular clouds are prime locations to study the process of star formation. These clouds contain filamentary structures and cores, which are crucial sites for the formation of young stars. The star-formation process has been investigated using various techniques, including polarimetry, for tracing magnetic fields. In this small review-cum-short report, we put together the efforts (mainly from the Indian community) to understand the roles of turbulence and magnetic fields in star formation. These are two components of the ISM competing against gravity, which is primarily responsible for the collapse of gas to form stars. We also include attempts made using simulations of molecular clouds to study this competition. Studies on feedback and magnetic fields are combined and listed to understand the importance of the interaction between two energies in setting the current observed star formation efficiency. We have listed available and upcoming facilities with the polarization capabilities needed to trace magnetic fields. We have also stated the importance of ongoing and desired collaborations between Indian communities and facilities abroad to shed more light on the roles of turbulence and magnetic fields in the process of star formation. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is one of the important elements for the formation of life and plays a crucial role in several biochemical processes. Recent spectral line surveys have confirmed the existence of P-bearing molecules, especially PN and PO, in the star-formation regions, but their formation mechanisms are poorly understood. The P-bearing molecule phosphorus nitride (PN) is detected in several star-forming regions, but this molecule has been poorly studied at high gas densities (≥ 10 6 cm - 3 ) hot molecular cores. In this paper, we presented the detection of rotational emission line of PN with transition J = 3 –2 towards the hot molecular cores G10.47 + 0.03 and G31.41 + 0.31, using the Atacama Compact Array (ACA). The estimated column densities of PN for G10.47 + 0.03 and G31.41 + 0.31 using the local thermodynamic equilibrium model are (3.60 ± 0.2) × 10 13 cm - 2 and (9.10 ± 0.1) × 10 12 cm - 2 with an excitation temperature of 150 ± 25 K. The fractional abundance of PN relative to H 2 is 2.76 × 10 - 10 for G10.47 + 0.03 and 5.68 × 10 - 11 for G31.41 + 0.031. We computed the two-phase warm-up chemical model of PN to understand the chemical evolution in the environment of hot molecular cores. After chemical modeling, we claimed that PN is created in the gas phase via the neutral–neutral reaction between PO and N in the warm-up stage. Similarly, PN is destroyed via the ion–neutral reaction between H 3 O + and PN. [ABSTRACT FROM AUTHOR]

In the interstellar medium (ISM), the complex organic molecules that contain the thiol group (–SH) play an important role in the polymerization of amino acids. We look for SH-bearing molecules in the chemically rich solar-type protostar IRAS 16293–2422. After extensive spectral analysis using the local thermodynamic equilibrium (LTE) model, we have detected the rotational emission lines of trans-isomer monothioformic acid (t-HC(O)SH) towards the IRAS 16293 B using the Atacama Large Millimeter/Submillimeter Array (ALMA). We did not observe any evidence of cis-isomer monothioformic acid (c-HC(O)SH) towards the IRAS 16293 B. The column density of t-HC(O)SH towards the IRAS 16293 B was ( 1.02 ± 0.6) × 10 15 cm - 2 with an excitation temperature of 125 ± 15 K. The fractional abundance of t-HC(O)SH with respect to H 2 towards the IRAS 16293 B is 8.50 × 10 - 11 . The column density ratio of t-HC(O)SH/ CH 3 SH towards the IRAS 16293 B is 0.185. We compare our estimated abundance of t-HC(O)SH towards the IRAS 16293 B with the abundance of t-HC(O)SH towards the galactic center quiescent cloud G + 0.693–0.027 and hot molecular core G31.41 + 0.31. After the comparison, we found that the abundance of t-HC(O)SH towards the IRAS 16293 B is several times of magnitude lower than G + 0.693–0.027 and G31.41 + 0.31. We also discussed the possible formation mechanism of t-HC(O)SH in the ISM. [ABSTRACT FROM AUTHOR]

Protostellar jets are one of the primary signposts of star formation. A handful of protostellar objects exhibit radio emission from ionized jets, of which a few display negative spectral indices, indicating the presence of synchrotron emission. In this study, we characterize the radio spectra of HH80-81 jet with the help of a numerical model that we have developed earlier, which takes into account both thermal free–free and non-thermal synchrotron emission mechanisms. For modeling the HH80-81 jet, we consider jet emission towards the central region close to the driving source along with two Herbig-Haro objects, HH80 and HH81. We have obtained the best-fit parameters for each of these sources by fitting the model to radio observational data corresponding to two frequency windows taken across two epochs. Considering an electron number density in the range of 10 3 – 10 5 cm - 3 , we obtained the thickness of the jet edges and fraction of relativistic electrons that contribute to non-thermal emission in the range of 0. 01 ∘ – 0. 1 ∘ and 10 - 7 – 10 - 4 , respectively. For the best-fit parameter sets, the model spectral indices lie in the range of − 0.15 to + 0.11 within the observed frequency windows. [ABSTRACT FROM AUTHOR]

The studies of the complex organic molecular lines towards the hot molecular cores at millimeter and submillimeter wavelengths provide instructive knowledge about the chemical complexity in the interstellar medium (ISM). We present the detection of the rotational emission lines of the complex nitrogen-bearing molecule ethyl cyanide (C2H5CN) towards the chemically rich hot molecular core G10.47 + 0.03 using the Atacama Large Millimeter/Submillimeter Array (ALMA) band 4 observations. The estimated column density of C2H5CN towards the G10.47 + 0.03 is (7.7 ± 0.5) × 10 16 cm − 2 with the high rotational temperature of 352.9 ± 66.8 K. The estimated fractional abundance of C2H5CN with respect to H2 towards the G10.47 + 0.03 is 5.70 × 10 − 9 . We observe that the estimated fractional abundance of C2H5CN is similar to the existing three-phase warm-up chemical modelling abundance of C2H5CN. We also discuss the possible formation mechanism of C2H5CN towards the hot molecular cores, and we claim the barrierless and exothermic radical-radical reaction between CH2 and CH2CN is responsible for the production of low abundance of C2H5CN (∼ 10 − 9 ) in the grain surface of G10.47 + 0.03. [ABSTRACT FROM AUTHOR]

The amide-related molecules are essential for the formation of the other complex bio-molecules and an understanding of the prebiotic chemistry in the interstellar medium (ISM). We presented the first detection of the rotational emission lines of the amide-like molecule cyanamide (NH2CN) towards the hot molecular core G358.93–0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array (ALMA). Using the rotational diagram model, the derived column density of NH2CN towards the G358.93–0.03 MM1 was (5.9±2.5)×1014 cm−2 with a rotational temperature of 100.6±30.4 K. The derived fractional abundance of NH2CN towards the G358.93–0.03 MM1 with respect to H2 was (4.72±2.0)×10−10, which is very similar to the existent three-phase warm-up chemical model abundances of NH2CN. We compare the estimated abundance of NH2CN towards G358.93–0.03 MM1 with other sources, and we observe the abundance of NH2CN towards G358.93–0.03 MM1 is nearly similar to that of the sculptor galaxy NGC 253 and the low-mass protostars IRAS 16293–2422 B and NGC 1333 IRAS4A2. We also discussed the possible formation mechanisms of NH2CN towards the hot molecular cores and hot corinos, and we find that the NH2CN molecule was created in the grain-surfaces of G358.93–0.03 MM1 via the neutral-neutral reaction between NH2 and CN. [ABSTRACT FROM AUTHOR]

To investigate the star-formation process, we present a multi-wavelength study of a massive star-forming site RAFGL 5085, which has been associated with the molecular outflow, Hii region and near-infrared cluster. The continuum images at 12, 250, 350 and 500 μ m show a central region (having M clump ∼ 225 M ⊙ ) surrounded by five parsec-scale filaments, revealing a hub-filament system (HFS). In the Herschel column density ( N (H 2) ) map, filaments are identified with higher aspect ratios (length/diameter) and lower N (H 2) values (∼ 0.1– 2.4 × 10 21 cm - 2 ), while the central hub is found with a lower aspect ratio and higher N (H 2) values (∼ 3.5– 7.0 × 10 21 cm - 2 ). The central hub displays a temperature range of [19, 22.5] K in the Herschel temperature map, and is observed with signatures of star formation (including radio continuum emission). The JCMT 13 CO(J = 3–2) line data confirm the presence of HFS and its hub is traced with supersonic and non-thermal motions having higher Mach number and lower thermal to non-thermal pressure ratio. In the 13 CO position–velocity diagrams, velocity gradients along the filaments towards the HFS appear to be observed, suggesting the gas flow in the RAFGL 5085 HFS and the applicability of the clump-fed scenario. [ABSTRACT FROM AUTHOR]

In the interstellar medium, the amide-type molecules play an important role in the formation of prebiotic molecules in the hot molecular cores or high-mass star-formation regions. The complex amide-related molecule cyanamide (NH 2 CN) is known as one of the rare interstellar molecule which has a major role in the formation of urea (NH 2 CONH 2 ). In this paper, we presented the detection of the rotational emission lines of cyanamide (NH 2 CN) towards the hot molecular core G10.47 + 0.03 between the frequency range of 158.49–160.11 GHz using the Atacama Large Millimeter/Submillimeter Array (ALMA) interferometric radio telescope. The estimated column density of the emission lines of NH 2 CN using the rotational diagram model was N (NH 2 CN) = (6.60 ± 0.1) × 10 15 cm - 2 with rotational temperature ( T rot) = 201.2 ± 3.3 K. The fractional abundance of NH 2 CN with respect to H 2 towards the G10.47 + 0.03 was f (NH 2 CN) = 5.076 × 10 - 8 . Additionally, the estimated NH 2 CN/NH 2 CHO abundance ratio towards the G10.47 + 0.03 was 0.170, which was nearly similar with NH 2 CN/NH 2 CHO abundance ratio towards the IRAS 16293–2422 B and Sgr B2 (M). We found that the observed abundance of NH 2 CN with respect to H 2 towards the G10.47 + 0.03, fairly agrees with the theoretical value predicted by Garrod (2013). We also discussed the possible formation and destruction pathways of NH 2 CN. [ABSTRACT FROM AUTHOR]

The studies of the complex molecular emission lines in the millimeter and submillimeter wavelengths towards the hot molecular cores reveal valuable details about the chemical complexity in the interstellar medium (ISM). We presented the first detection of the rotational emission lines of the complex organic molecule methyl formate (CH3OCHO) towards the hot molecular core region IRAS 18566+0408 using the high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) band 3 observation. The estimated column density of CH3OCHO using the rotational diagram analysis was (4.1±0.1)×1015 cm−2 with a rotational temperature of 102.8±1.2 K. The estimated fractional abundance of CH3OCHO relative to hydrogen (H2) towards the IRAS 18566+0408 was 3.90×10−9. We noted that the estimated fractional abundance of CH3OCHO is fairly consistent with the simulation value predicted by the three-phase warm-up model from Garrod (2013). We also discussed the possible formation mechanism of CH3OCHO towards the IRAS 18566+0408. [ABSTRACT FROM AUTHOR]

Young massive stars are usually found embedded in dense and massive molecular clumps which are known for being highly obscured and distant. During their formation process, the degree of deuteration can be used as a potential indicator of the very early formation stages. This is particularly effective when employing the abundance of H2D+. However, its low abundances and large distances make detections in massive sources hard to achieve. We present an application of the radiative transfer code POLARIS, with the goal to test the observability of the ortho-H2D+ transition 1 10 - 1 11 (∼372.42 GHz) using simulations of high-mass collapsing cores that include deuteration chemistry. We analyzed an early and a late stage of the collapse of a 60 M⊙ core, testing different source distances. For all cases, we generated synthetic single-dish and interferometric observations and studied the differences in both techniques. The column densities we derive are comparable to values reported for similar sources. These estimates depend on the extent over which they are averaged, and sources with compact emission they can be highly affected by beam dilution. Combined ALMA-ACA observations improve in signal-to-noise ratio and lead to better column density estimates as compared to ALMA alone. We confirm the feasibility to study ortho-H2D+ emission up to distances of ∼7 kpc. We provide a proof-of-concept of our framework for synthetic observations and highlight its importance when comparing numerical simulations with real observations. This work also proves how relevant it is to combine single-dish and interferometric measurements to derive appropriate source column densities. [ABSTRACT FROM AUTHOR]

Young star clusters consisting of massive stars are the ideal sites to study the star formation processes and influence of massive stars on the subsequent star formation. NGC 1893 is a young star cluster associated with the Hii region Sh2-236. It contains about five 'O'-type stars and several early 'B'-type stars. It is located at a moderate distance of ∼ 3.25 kpc and has a reddening, E (B - V) ∼ 0.4 mag. To characterize the young low-mass stellar population in the central portion of the cluster, we carried out deep VI band observations of the region using the 4 K × 4 K CCD IMAGER mounted on the 3.6-m Devasthal Optical Telescope. Our analysis shows that the present data are deep enough to detect stars below V ∼ 24 mag. We found optical counterparts of ∼ 220 candidates, including young stars and unclassified cluster members from Caramazza et al. (2008). We estimated the membership probabilities of the Gaia sources (mostly bright stars with G < 19 mag) located within the cluster radius using the Gaia EDR3. Toward the fainter end, we used the optical color-magnitude diagram (CMD) to select the cluster members from a sample of young stars. The locations of young stars on the CMD show that a majority of them are low-mass stars with age <10 Myr. The unclassified candidates and X-ray sources from Caramazza et al. (2012) are also found to be young low-mass stars. In total, we identified ∼ 425 young stars with age <10 Myr, and 110 of these are new. Most of these stars appear as kinematic members of the cluster. By examining the CMD for the stars in the cluster region, we suggest that the cluster has insignificant contamination due to field stars in the pre-main-sequence zone of the CMD. The slope of the mass function in the mass range 0.2 ≤ M / M ⊙ ≤ 2.5 is found to be Γ = - 1.43 ± 0.15 , consistent with those of other star-forming complexes. The spatial distribution of the young stars as a function of mass suggests that toward the cluster center, most of the stars are massive. [ABSTRACT FROM AUTHOR]

Cosmic history has witnessed the lives and deaths of multiple generations of massive stars, all of them invigorating their host galaxies with ionizing photons, kinetic energy, fresh material, and stellar-mass black holes. Ubiquitous engines as they are, astrophysics needs a good understanding of their formation, evolution, properties and yields throughout the history of the Universe, and with decreasing metal content mimicking the environment at the earliest epochs. Ultimately, a physical model that could be extrapolated to zero metallicity would enable tackling long-standing questions such as "What did the first, very massive stars of the Universe look like?" or "What was their role in the re-ionization of the Universe?" Yet, most of our knowledge of metal-poor massive stars is drawn from one single point in metallicity. Massive stars in the Small Magellanic Cloud (SMC, ∼ 1/5Z⊙) currently serve as templates for low-metallicity objects in the early Universe, even though significant differences with respect to massive stars with poorer metal content have been reported. This White Paper summarizes the current knowledge on extremely (sub-SMC) metal poor massive stars, highlighting the most outstanding open questions and the need to supersede the SMC as standard. A new paradigm can be built from nearby extremely metal-poor galaxies that make a new metallicity ladder, but massive stars in these galaxies are out of reach to current observational facilities. Such a task would require an L-size mission, consisting of a 10m-class space telescope operating in the optical and the ultraviolet ranges. Alternatively, we propose that ESA unites efforts with NASA to make the LUVOIR mission concept a reality, thus continuing the successful partnership that made the Hubble Space Telescope one of the greatest observatories of all time. [ABSTRACT FROM AUTHOR]

The far-infrared (FIR) regime is one of the wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist. None of the medium-term satellite projects like SPICA, Millimetron, or the Origins Space Telescope will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO), light hydrides, and especially from water lines would open the door for transformative science. A main theme will be to trace the role of water in proto-planetary discs, to observationally advance our understanding of the planet formation process and, intimately related to that, the pathways to habitable planets and the emergence of life. Furthermore, key observations will zoom into the physics and chemistry of the star-formation process in our own Galaxy, as well as in external galaxies. The FIR provides unique tools to investigate in particular the energetics of heating, cooling, and shocks. The velocity-resolved data in these tracers will reveal the detailed dynamics engrained in these processes in a spatially resolved fashion, and will deliver the perfect synergy with ground-based molecular line data for the colder dense gas. [ABSTRACT FROM AUTHOR]

A dynamical model has been developed to envisage the star formation scenario in filamentary molecular clouds. In the present work a double well potential has been considered to find the number of stable stationary points as the origin of field star, binary stars or stellar associations. It is found that low density structure can lead to the formation of field stars while an intermediate density structure is favourable for formation of binary stars. Stellar associations are generally prevalent in dense filamentary molecular clouds. [ABSTRACT FROM AUTHOR]

Molecular clouds are a fundamental ingredient of galaxies: they are the channels that transform the diffuse gas into stars. The detailed process of how they do it is not completely understood. We review the current knowledge of molecular clouds and their substructure from scales ∼ 1 kpc down to the filament and core scale. We first review the mechanisms of cloud formation from the warm diffuse interstellar medium down to the cold and dense molecular clouds, the process of molecule formation and the role of the thermal and gravitational instabilities. We also discuss the main physical mechanisms through which clouds gather their mass, and note that all of them may have a role at various stages of the process. In order to understand the dynamics of clouds we then give a critical review of the widely used virial theorem, and its relation to the measurable properties of molecular clouds. Since these properties are the tools we have for understanding the dynamical state of clouds, we critically analyse them. We finally discuss the ubiquitous filamentary structure of molecular clouds and its connection to prestellar cores and star formation. [ABSTRACT FROM AUTHOR]

Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work. [ABSTRACT FROM AUTHOR]

Molecular jets are seen coming from the youngest protostars in the early phase of low-mass star formation. They are detected in CO, SiO, and SO at (sub)millimeter wavelengths down to the innermost regions, where their associated protostars and accretion disks are deeply embedded and where they are launched and collimated. They are not only the fossil records of accretion history of the protostars but also are expected to play an important role in facilitating the accretion process. Studying their physical properties (e.g., mass-loss rate, velocity, rotation, radius, wiggle, molecular content, shock formation, periodical variation, magnetic field, etc) allows us to probe not only the jet launching and collimation, but also the disk accretion and evolution, and potentially binary formation and planetary formation in the disks. Here, the recent exciting results obtained with high-spatial and high-velocity resolution observations of molecular jets in comparison to those obtained in the optical jets in the later phase of star formation are reviewed. Future observations of molecular jets with a large sample at high spatial and velocity resolution with ALMA are expected to lead to a breakthrough in our understanding of jets from young stars. [ABSTRACT FROM AUTHOR]

Primordial clouds are supposed to host the so-called population III stars. These stars are very massive and completely metal-free. The final stage of the life of population III stars with masses between 130 and 260 solar masses is a very energetic hypernova explosion. A hypernova drives a shock, behind which a spherically symmetric very dense supershell forms, which might become gravitationally unstable, fragment, and form stars. In this paper we study under what conditions can an expanding supershell become gravitationally unstable and how the feedback of these supershell stars (SSSs) affects its surroundings. We simulate, by means of a 1-D Eulerian hydrocode, the early evolution of the primordial cloud after the hypernova explosion, the formation of SSSs, and the following evolution, once the SSSs start to release energy and heavy elements into the interstellar medium. Our results indicate that a shell, enriched with nucleosynthetic products from SSSs, propagates inwards, towards the center of the primordial cloud. In a time span of a few Myr, this inward-propagating shell reaches a distance of only a few parsec away from the center of the primordial cloud. Its density is extremely high and its temperature very low, thus the conditions for a new episode of star formation are achieved. We study what fraction of these two distinct populations of stars can remain bound and survive until the present day. We study also under what conditions can this process repeat and form multiple stellar populations. We extensively discuss whether the proposed scenario can help to explain some open questions of the formation mechanism of globular clusters. [ABSTRACT FROM AUTHOR]

In this paper we continue the investigation reported by Arreaga-Garcia (Rev. Mex. Astron. Astrofís. 52(1):1-15, 2016) concerning the morphology of binary configurations obtained via the collapse of rotating parent gas structures with total masses in the range of $M_{T}= 1 \mbox{ to } 5~M_{\odot}$ . Here we extend the mass range and consider the collapse of two uniform gas clumps of $M_{T} = 50 \mbox{ and } 400~M_{\odot}$ , so that they also rotate rigidly in such a way that its approximate virial parameter takes the values of 0.5, 1.5, and 2.5 and their collapse is induced initially by implementing an azimuthal mass perturbation. To assess the effects of the total mass of the parent gas structure on the nature of the resulting binary configurations, we also consider the collapse of two cores of $M_{T} = 1 \mbox{ and } 5~M_{\odot}$ . We calculate the collapse of all these parent gas structures using three values of the ratio of thermal energy to potential energy, $\alpha$ , and for two values of the mass perturbation amplitude. For most of our models, we next calculate the extreme value of the ratio of rotational energy to potential energy, $\beta$ , so that a model with a slightly higher $\beta$ value would no longer collapse. We finally calculate the binary separations, masses and some integral properties of the binary fragments, the $\alpha_{f}$ and $\beta_{f}$ and present them in terms of the total mass of the parent structure. [ABSTRACT FROM AUTHOR]

An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and, therefore, predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates. [ABSTRACT FROM AUTHOR]

Protoplanetary disks are the birthplaces of planetary systems. The evolution of the star-disk system and the disk chemical composition determines the initial conditions for planet formation. Therefore a comprehensive understanding of the main physical and chemical processes in disks is crucial for our understanding of planet formation. We give an overview of the early evolution of disks, discuss the importance of the stellar high-energy radiation for disk evolution and describe the general thermal and chemical structure of disks. Finally we provide an overview of observational tracers of the gas component and disk winds. [ABSTRACT FROM AUTHOR]

Deeply embedded low-mass protostars can be used as testbeds to study the early formation stages of solar-type stars, and the prevailing chemistry before the formation of a planetary system. The present study aims to characterise further the physical and chemical properties of the protostellar core Orion B9-SMM3. The Atacama Pathfinder EXperiment (APEX) telescope was used to perform a follow-up molecular line survey of SMM3. The observations were done using the single pointing (frequency range 218.2-222.2 GHz) and on-the-fly mapping methods (215.1-219.1 GHz). These new data were used in conjunction with our previous data taken by the APEX and Effelsberg 100 m telescopes. The following species were identified from the frequency range 218.2-222.2 GHz: ${}^{13}\mathrm{CO}$, $\mathrm{C}^{18}\mathrm{O}$, SO, para- $\mathrm{H}_{2}\mathrm{CO}$, and $\mathrm{E}_{1}$-type $\mathrm{CH}_{3}\mathrm{OH}$. The mapping observations revealed that SMM3 is associated with a dense gas core as traced by $\mathrm{DCO}^{+}$ and p- $\mathrm{H}_{2}\mathrm{CO}$. Altogether three different p- $\mathrm{H}_{2}\mathrm{CO}$ transitions were detected with clearly broadened linewidths ( $\Delta v\sim8.2\mbox{--}11~\mbox{km}\,\mbox{s}^{-1}$ in FWHM). The derived p- $\mathrm{H}_{2}\mathrm{CO}$ rotational temperature, $64\pm15~\mbox{K}$, indicates the presence of warm gas. We also detected a narrow p- $\mathrm{H}_{2}\mathrm{CO}$ line ( $\Delta v=0.42~\mbox{km}\,\mbox{s}^{-1}$) at the systemic velocity. The p- $\mathrm{H}_{2}\mathrm{CO}$ abundance for the broad component appears to be enhanced by two orders of magnitude with respect to the narrow line value ( ${\sim}3\times10^{-9}$ versus ${\sim}2\times10^{-11}$). The detected methanol line shows a linewidth similar to those of the broad p- $\mathrm{H}_{2}\mathrm{CO}$ lines, which indicates their coexistence. The CO isotopologue data suggest that the CO depletion factor decreases from ${\sim}27\pm2$ towards the core centre to a value of ${\sim}8\pm1$ towards the core edge. In the latter position, the $\mathrm{N}_{2}\mathrm{D}^{+}/\mathrm{N}_{2}\mathrm{H}^{+}$ ratio is revised down to $0.14\pm0.06$. The origin of the subfragments inside the SMM3 core we found previously can be understood in terms of the Jeans instability if non-thermal motions are taken into account. The estimated fragmentation timescale, and the derived chemical abundances suggest that SMM3 is a few times $10^{5}~\mbox{yr}$ old, in good agreement with its Class 0 classification inferred from the spectral energy distribution analysis. The broad p- $\mathrm{H}_{2}\mathrm{CO}$ and $\mathrm{CH}_{3}\mathrm{OH}$ lines, and the associated warm gas provide the first clear evidence of a molecular outflow driven by SMM3. [ABSTRACT FROM AUTHOR]

The evolution of protoplanetary disks is regulated by its interaction with the central forming star. This interaction happens through accretion of matter from the disk onto the star, and its most significant signatures are the continuum excess in the UV part of the spectrum and the presence of various emission lines. With the VLT/X-Shooter spectrograph, the excess emission in the UV due to accretion can being studied simultaneously with the signatures in the visible and in the near-infrared, giving a simultaneous and complete view of this phenomenon. Here we present some results we obtained using observation and modeling of the UV-excess in young forming stars, which are: (1) the determination of stellar and accretion properties in candidate older accreting young stellar objects and (2) the study of the star-disk interaction in the early stages of planetary system evolution in transitional disk systems. [ABSTRACT FROM AUTHOR]

Although the existence of dark matter is generally accepted by the mainstream scientific community, there is no generally agreed direct detection of it. Also, observations show that some Bok globules are prolate in some regions without suitable explanation for its cause. In this paper, we investigate the effect of dark matter sub-halo in transformation of the Bok globules from spherical to the prolate shape. We limit the investigation to a particular case that the magnetic field and turbulent effects are negligible through the Bok globule. We consider the gravitational effect of dark matter sub-halo on the isothermal Bok globule that is exposed to suitable distance of it. The results show that the dark matter sub-halo can justify the transformation of Bok globules in some regions. In this paper, we introduce a new method for proving the existence of dark matter sub halo. [ABSTRACT FROM AUTHOR]

Historically, it has been assumed that globular and open clusters never interact. However, recent evidence suggests that: globular clusters passing through the disk may be able to perturb giant molecular clouds (GMCs) triggering formation of open clusters and some old open clusters may be linked to accreted globulars. Here, we further explore the existence of possible dynamical connections between globular and open clusters, and realize that the most obvious link must be in the form of gravitational interactions. If open clusters are born out of GMCs, they have to move in similar orbits. If we accept that globulars can interact with GMCs, triggering star formation, it follows that globular and open clusters must also interact. Consistently, theoretical arguments as well as observational evidence, show that globular and open clusters certainly are interacting populations and their interactions are far more common than usually thought, especially for objects part of the bulge/disk. Monte Carlo calculations confirm that conclusion. Globular clusters seem capable of not only inducing formation of open clusters but, more often, their demise. Relatively frequent high speed cluster encounters or cluster harassment may also cause, on the long-term, slow erosion and tidal truncation on the globulars involved. The disputed object FSR 1767 (2MASS-GC04) may be, statistically speaking, the best example of an ongoing interaction. [ABSTRACT FROM AUTHOR]

The role of grains in evolution of accretion disc is an important issue in astrophysics. In this paper, we study the effect of vapor pressure of grains in the dead zones of protoplanetary discs. Our study is limited to some particular observed cases in which evaporation of grains would be important and their vapor gas are constrained to an approximately isolated case. Here, we use the Einstein model to investigate the thermodynamics of vapor pressure. The results show that there is a critical temperature as a function of oscillation frequency and binding energy of particles. For temperatures greater than this critical value, the system goes into unstable mode. We show that the dead zone of the disc may reach to enough conditions to condense via instability caused by vapor pressure of grains. This mechanism may play an important role in the formation of planetesimals through protoplanetary disc. [ABSTRACT FROM AUTHOR]

A hybrid JHK− W W W W high-spectral index ( α) selection scheme was employed to identify (sub)-clusters of class I/f candidate protostars (YSOs) in WISE observations (the Wide-Field Infrared Survey Explorer). n>10 candidate YSOs were detected owing to WISE's advantageous all-sky spatial coverage, and a subsample ( n∼200) of their heavily-obscured host (sub)clusters were correlated with the Avedisova (Astron. Rep. 46:193, ) and Dias et al. (Astron. Astrophys. 389:871, ) catalogs of star-forming regions. Forthcoming observations from the VVV/UKIDSS surveys shall facilitate the detection of additional protostars and bolster efforts to delineate the Galactic plane, since the campaigns aim to secure deep JHK photometry for a pertinent fraction of the WISE targets lacking 2MASS detections, and to provide improved data for YSOs near the limits of the 2MASS survey. [ABSTRACT FROM AUTHOR]

Viscosity have a significant effect in evolution of accretion disc. In this paper, we investigate the thermal effect of viscosity in the accretion disc that may cause instability to produce overdense regions through it. For this purpose, the linear perturbation method is used to investigate instability on this so-called viscothermal effect. The results show that instability can occur in accretion disc so that larger overdense regions are formed at far greater distance of protostar. This mechanism may explain formation of larger protoplanets farther from protostars. [ABSTRACT FROM AUTHOR]

Our Sun and planetary system were born about 4.5 billion years ago. How did this happen, and what is the nature of our heritage from these early times? This review tries to address these questions from an astrochemical point of view. On the one hand, we have some crucial information from meteorites, comets and other small bodies of the Solar System. On the other hand, we have the results of studies on the formation process of Sun-like stars in our Galaxy. These results tell us that Sun-like stars form in dense regions of molecular clouds and that three major steps are involved before the planet-formation period. They are represented by the prestellar core, protostellar envelope and protoplanetary disk phases. Simultaneously with the evolution from one phase to the other, the chemical composition gains increasing complexity. In this review, we first present the information on the chemical composition of meteorites, comets and other small bodies of the Solar System, which is potentially linked to the first phases of the Solar System's formation. Then we describe the observed chemical composition in the prestellar core, protostellar envelope and protoplanetary-disk phases, including the processes that lead to them. Finally, we draw together pieces from the different objects and phases to understand whether and how much we inherited chemically from the time of the Sun's birth. [ABSTRACT FROM AUTHOR]

The stellar Initial Mass Function (IMF) suggests that stars with sub-solar mass form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre-main-sequence (PMS) evolutionary phase, i.e., they have not started their lives on the main-sequence yet. The peculiar nature of these objects and the contamination of their samples by the fore- and background evolved populations of the Galactic disk impose demanding observational techniques, such as X-ray surveying and optical spectroscopy of large samples for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the metal-poor companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of the above techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope within the last five years yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of star-forming regions in these galaxies, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of the PMS stellar content of the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the Magellanic Clouds allowed thus a more comprehensive understanding of the star formation process in our neighboring galaxies. [ABSTRACT FROM AUTHOR]

Star formation is thought to be triggered by gravitational collapse of the dense cores of molecular clouds. Angular momentum conservation during the collapse results in the progressive increase of the centrifugal force, which eventually halts the inflow of material and leads to the development of a central mass surrounded by a disc. In the presence of an angular momentum transport mechanism, mass accretion onto the central object proceeds through this disc, and it is believed that this is how stars typically gain most of their mass. However, the mechanisms responsible for this transport of angular momentum are not well understood. Although the gravitational field of a companion star or even gravitational instabilities (particularly in massive discs) may play a role, the most general mechanisms are turbulence viscosity driven by the magnetorotational instability (MRI), and outflows accelerated centrifugally from the surfaces of the disc. Both processes are powered by the action of magnetic fields and are, in turn, likely to strongly affect the structure, dynamics, evolutionary path and planet-forming capabilities of their host discs. The weak ionisation of protostellar discs, however, may prevent the magnetic field from effectively coupling to the gas and shear and driving these processes. Here I examine the viability and properties of these magnetically-driven processes in protostellar discs. The results indicate that, despite the weak ionisation, the magnetic field is able to couple to the gas and shear for fluid conditions thought to be satisfied over a wide range of radii in these discs. [ABSTRACT FROM AUTHOR]

We study details of the UV radiation transfer in a protoplanetary disk, paying attention to the influence of dust growth and sedimentation on the disk density and temperature. Also, we show how the dust evolution affects photoreaction rates of key molecules, like CN and CS. [ABSTRACT FROM AUTHOR]

The study of the stellar constituents of star-forming sites in a wide variety of conditions yields the key to interpreting wide-field UV-optical imaging of extended nearby galaxies, and of distant galaxies. We obtained six-band imaging (from far-UV to I) with HST-WFPC2 of 67 sites of recent star formation in eight Local Group galaxies. HST pointings were selected from GALEX wide-field FUV imaging, which traces the young stellar populations. The HST observations were optimized to characterize the hottest, most massive stars in these regions. From the HST photometry, analyzed with stellar model colors, we derived the physical parameters of the massive stars in each field, and of the extinction by interstellar dust. The HST results are used to interpret GALEX UV measurements of SF across the entire galaxies. Our comprehensive photometric study at HST resolution (sub-pc scale in these galaxies) also provides an ideal selection of targets for follow-up spectroscopy with large ground-based telescopes, and in the UV with HST- or WSO-class telescopes, to clarify the influence of metallicity on the properties and the evolution of massive stars. [ABSTRACT FROM AUTHOR]

We study the magneto-thermal instability in ionized plasmas including the effects of Ohmic, ambipolar and Hall diffusion. The magnetic field in the single-fluid approximation does not allow for transverse thermal condensations; however, non-ideal effects highly diminish the stabilizing role of the magnetic field in thermally unstable plasmas. Therefore, the enhanced growth rate of thermal condensation modes in the presence of the diffusion mechanisms speed up the rate of structure formation. [ABSTRACT FROM AUTHOR]

Infrared dark clouds (IRDCs) are cold, dense molecular clouds identified as extinction features against the bright mid-infrared Galactic background. Our recent 1.2 mm continuum emission survey of IRDCs reveals many compact (<0.5 pc) and massive (10–2100 M⊙) cores within them. These prestellar cores hold the key to understanding IRDCs and their role in star formation. Here, we present high angular resolution spectral-line and mm/sub-mm continuum images obtained with the IRAM Plateau de Bure Interferometer and the Sub-Millimeter Array towards three high-mass IRDC cores. The high angular resolution images reveal that two of the cores are resolved into multiple, compact protostellar condensations, while the remaining core contains a single, compact protostellar condensation with a very rich molecular spectrum, indicating that it is a hot molecular core. The derived gas masses for these condensations suggest that each core is forming at least one high-mass protostar, while two of the cores are also forming lower-mass protostars. The close proximity of multiple protostars of disparate mass indicates that these IRDCs are in the earliest evolutionary states in the formation of stellar clusters. [ABSTRACT FROM AUTHOR]

We review the success of current simulations in reproducing the observed initial mass function (IMF) in clusters and show that whereas the two main types of simulation invoke the same physics to explain the point at which the IMF flattens from a Salpeter slope, they reproduce the Salpeter tail itself by quite different means. We highlight the fact that a proper modelling of the thermal properties of star-forming gas is probably crucial in explaining why the IMF is apparently quite insensitive to cloud parameters. We also explore how the mass of a cluster’s most massive star depends on cluster mass and how this issue impacts the relationship between the IMF in individual clusters and the integrated galactic IMF. We emphasise the importance of a careful statistical treatment of data in this area. [ABSTRACT FROM AUTHOR]

We explore how the expulsion of gas from star-forming cores due to supernova explosions affects the shape of the initial cluster mass function, that is, the mass function of star clusters when cluster infant weight-loss triggered by gas expulsion is over. We demonstrate that if the radii of cluster-forming gas ‘cores’ are roughly constant over the core mass range, as supported by observations, then more massive cores undergo slower gas expulsion. Therefore, for a given star-formation efficiency, more massive cores retain a larger fraction of stars after gas expulsion. The initial cluster mass function may thus substantially differ from the core mass function, with the final shape depending on the star-formation efficiency. A mass-independent star-formation efficiency of about 20% turns a power-law core mass function into a bell-shaped initial cluster mass function, while mass-independent efficiencies of order 40% preserve the shape of the core mass function. [ABSTRACT FROM AUTHOR]

We present the first high-spatial-resolution near-infrared (NIR) imaging of NGC604, obtained with the NICMOS camera onboard the Hubble Space Telescope (HST). These NICMOS broad-band images reveal new NIR point sources, clusters, and diffuse structures. We find an excellent spatial correlation between the 8.4 GHz radio continuum and the 2.2 μm nebular emission. Moreover, massive young stellar object candidates appear aligned with these radio peaks, reinforcing the idea that those areas are star-forming regions. Three different scaled OB associations are recognized in the NICMOS images. The brightest NIR sources in our images have properties that suggest that they are red supergiant stars, of which one was previously known. This preliminary analysis of the NICMOS images shows the complexity of the stellar content of the NGC604 nebula. [ABSTRACT FROM AUTHOR]

This paper has two parts: one about observational constraints related to the empirical differential oxygen abundance distribution (EDOD), and the other about inhomogeneous models of chemical evolution, in particular the theoretical differential oxygen abundance distribution (TDOD). In the first part, the EDOD is deduced from subsamples related to two different samples involving (i) N=532 solar neighbourhood (SN) stars within the range, −1.5<[Fe/H]<0.5, for which the oxygen abundance has been determined both in presence and in absence of the local thermodynamical equilibrium (LTE) approximation (Ramirez et al. in Astron. Astrophys. 465:271, ); and (ii) N=64 SN thick disk, SN thin disk, and bulge K-giant stars within the range, −1.7<[Fe/H]<0.5, for which the oxygen abundance has been determined (Melendez et al. in Astron. Astrophys. 484:L21, ). A comparison is made with previous results implying use of [O/H]–[Fe/H] empirical relations (Caimmi in Astron. Nachr. 322:241, ; New Astron. 12:289, ) related to (iii) 372 SN halo subdwarfs (Ryan and Norris in Astron. J. 101:1865, ); and (iv) 268 K-giant bulge stars (Sadler et al. in Astron. J. 112:171, ). The EDOD of the SN thick + thin disk is determined by weighting the mass, for assumed SN thick to thin disk mass ratio within the range, 0.1–0.9. In the second part, inhomogeneous models of chemical evolution for the SN thick disk, the SN thin disk, the SN thick + thin disk, the SN halo, and the bulge, are computed assuming the instantaneous recycling approximation. The EDOD data are fitted, to an acceptable extent, by their TDOD counterparts with the exception of the thin or thick + thin disk, where two additional restrictions are needed: (i) still undetected, low-oxygen abundance thin disk stars exist, and (ii) a single oxygen overabundant star is removed from a thin disk subsample. In any case, the (assumed power-law) stellar initial mass function (IMF) is universal but gas can be inhibited from, or enhanced in, forming stars at different rates with respect to a selected reference case. Models involving a strictly universal IMF (i.e. gas neither inhibited from, nor enhanced in, forming stars with respect to a selected reference case) can also reproduce the data to an acceptable extent. Our main conclusions are (1) different models are necessary to fit the (incomplete) halo sample, which is consistent with the idea of two distinct halo components: an inner, flattened halo in slow prograde rotation, and an outer, spherical halo in net retrograde rotation (Carollo et al. in Nature 450:1020, ); (2) the oxygen enrichment within the inner SN halo, the SN thick disk, and the bulge, was similar and coeval within the same metallicity range, as inferred from observations (Prochaska et al. in Astron. J. 120:2513, ); (3) the fit to thin disk data implies an oxygen abundance range similar to its thick disk counterpart, with the extension of conclusion (2) to the thin disk, and the evolution of the thick + thin disk as a whole (Haywood in Mon. Not. R. Astron. Soc. 388:1175, ) cannot be excluded; (4) leaving outside the outer halo, a fit to the data related to different environments is provided by models with a strictly universal IMF but different probabilities of a region being active, which implies different global efficiencies of the star formation rate; (5) a special case of stellar migration across the disk can be described by models with enhanced star formation, where a fraction of currently observed SN stars were born in situ and a comparable fraction is due to the net effect of stellar migration, according to recent results based on high-resolution N-body + smooth particle hydrodynamics simulations (Roškar et al. in Astrophys. J. Lett. 684:L79, ). [ABSTRACT FROM AUTHOR]

Half of the energy ever emitted by stars and accreting objects comes to us in the far-infrared (FIR) waveband and has yet to be properly explored. We propose a powerful Far-InfraRed Interferometer mission, FIRI, to carry out high-resolution imaging spectroscopy in the FIR. This key observational capability is essential to reveal how gas and dust evolve into stars and planets, how the first luminous objects in the Universe ignited, how galaxies formed, and when super-massive black holes grew. FIRI will disentangle the cosmic histories of star formation and accretion onto black holes and will trace the assembly and evolution of quiescent galaxies like our Milky Way. Perhaps most importantly, FIRI will observe all stages of planetary system formation and recognise the birth of planets via its ability to image the dust structures in planetary systems. FIRI is an observatory-class mission concept: three cold, 3.5-m apertures, orbiting a beam-combining module, with separations of up to 1 km, free-flying or tethered, operating between 25 and 385 μm, using the interferometric direct-detection technique to ensure μJy sensitivity and 0.02” resolution at 100 μm, across an arcmin2 instantaneous field of view, with a spectral resolution, R ~ 5,000 and a heterodyne system with R ~ 1 million. Although FIRI is an ambitious mission, we note that FIR interferometry is appreciably less demanding than at shorter wavelengths. [ABSTRACT FROM AUTHOR]

In various astrophysical contexts, we analyze self-similar behaviours of magnetohydrodynamic (MHD) evolution of a quasi-spherical polytropic magnetized gas under self-gravity with the specific entropy conserved along streamlines. In particular, this MHD model analysis frees the scaling parameter n in the conventional polytropic self-similar transformation from the constraint of n+ γ=2 with γ being the polytropic index and therefore substantially generalizes earlier analysis results on polytropic gas dynamics that has a constant specific entropy everywhere in space at all time. On the basis of the self-similar nonlinear MHD ordinary differential equations, we examine behaviours of the magnetosonic critical curves, the MHD shock conditions, and various asymptotic solutions. We then construct global semi-complete self-similar MHD solutions using a combination of analytical and numerical means and indicate plausible astrophysical applications of these magnetized flow solutions with or without MHD shocks. [ABSTRACT FROM AUTHOR]

In this study we investigated the effects of external trigger on the characteristics of young stellar objects (YSOs) associated with cometary globules (CGs). We made optical spectroscopy of stars associated with star-forming CGs. We find that the masses of the most massive stars associated with CGs are correlated with the masses of the parent cloud but they are systematically larger than expected for clouds of similar mass from the relation M max-star=0.33 M given by Larson (Mon. Not. R. Astron. Soc. 200:159, ). We have also estimated the luminosities of the IRAS sources found associated with CGs as a function of cloud mass and then compared them with those of the IRAS sources found associated with isolated opacity class 6 clouds (isolated and relatively away from large star forming regions). We find that the luminosities of IRAS sources associated with CGs are larger than those of the opacity class 6 clouds. These findings support results from recent simulations in which it was shown that the Radiation Driven Implosion (RDI) process, believed to be responsible for the cometary morphology and star formation, can increase the luminosity 1–2 orders of magnitudes higher than those of protostars formed without external triggering due to an increase in accretion rates. Thus implying that the massive stars can have profound influence on the star formation in clouds located in their vicinity. [ABSTRACT FROM AUTHOR]

A magnetic torque associated with the magnetic field linking a giant, gaseous protoplanet to its host pre-main-sequence star can halt inward protoplanet migration. This torque results from a toroidal magnetic field generated from the star’s poloidal (dipole) field by the twisting differential motion between the star’s rotation and the protoplanet’s revolution. Outside the corotation radius, where a protoplanet orbits slower than its host star spins, this torque transfers angular momentum from the star to the protoplanet, halting inward migration. Necessary conditions for angular momentum transfer include the requirement that the Alfvén speed v A in the region magnetically linking a protoplanet to its host star exceeds the protoplanet’s orbital speed v K . In addition, the timescale for Ohmic dissipation τ D must exceed the protoplanet’s orbital period P to ensure that the protoplanet is magnetically coupled to its host star. For a Jupiter-mass protoplanet orbiting a solar-mass pre-main-sequence star, v A > v K and τ D > P only when the migrating protoplanet approaches within about 0.1 AU of its host star, primarily because of the rapid drop in the strength of the magnetic field with increasing distance from the central star. Because of this restricted reach, inwardly migrating gaseous protoplanets can be expected to “pile up” very close to their central stars, as is indeed observed for extrasolar planets. The characteristic timescale required for a magnetic torque to transfer angular momentum outward from a more rapidly spinning central star to a magnetically coupled protoplanet is found to be comparable to planet-forming disk lifetimes and protoplanet migration timescales. [ABSTRACT FROM AUTHOR]

In recent years there has been much debate, both observational and theoretical, about the nature of star formation at high redshift. In particular, there seems to be strong evidence of a greatly enhanced star formation rate early in the Universe’s evolution. Simulations investigating the nature of the first stars indicate that these were large, with masses in excess of 100 solar masses. By the use of a chemical model, we have simulated the molecular signature of massive star formation for a range of redshifts, using different input models of metallicity in the early Universe. We find that, as long as the number of massive stars exceeds that in the Milky Way by factor of at least 1000, then several ‘hot-core’ like molecules should have detectable emission. Although we predict that such signatures should already be partly detectable with current instruments (e.g. with the VLA), facilities such as ALMA will make this kind of observation possible at the highest redshifts. [ABSTRACT FROM AUTHOR]

During the past decade we have compiled a large molecular line data base of massive star forming regions in the southern Milky Way. These regions are confined into giant molecular clouds that trace the galactic spiral arms. Their radial distribution has a pronounced peak midway between the Sun and the galactic center, which in the IV quadrant corresponds to the location of the Norma Spiral arm. We study in some detail one of the foremost regions of massive star formation in the Norma arm, using millimeter continuum and line emission maps obtained with the SEST, APEX, and ASTE telescopes. It is a multiple system evolving along a complete GMC core, candidate for future ALMA observations. [ABSTRACT FROM AUTHOR]