Modeling Molecular-Line Emission from Circumstellar Disks

Molecular lines hold valuable information on the physical and chemical composition of disks around young stars, the likely progenitors of planetary systems. This invited contribution discusses techniques to calculate the molecular emission (and absorption) line spectrum based on models for the physical and chemical structure of protoplanetary disks. Four examples of recent research illutrate these techniques in practice: matching resolved molecular-line emission from the disk around LkCa15 with theoertical models for the chemistry; evaluating the two-dimensional transfer of ultraviolet radiation into the disk, and the effect on the HCN/CN ratio; far-infrared CO line emission from a superheated disk surface layer; and inward motions in the disk around L1489 IRS.Comment: 6 pages, no figures. To appear in "The Dense Interstellar Medium in Galaxies", Procs. Fourth Cologne-Bonn-Zermatt-Symposiu

Line Emission from Gas in Optically Thick Dust Disks around Young Stars

We present self-consistent models of gas in optically-thick dusty disks and calculate its thermal, density and chemical structure. The models focus on an accurate treatment of the upper layers where line emission originates, and at radii $\gtrsim 0.7$ AU. We present results of disks around $\sim 1{\rm M}_{\odot}$ stars where we have varied dust properties, X-ray luminosities and UV luminosities. We separately treat gas and dust thermal balance, and calculate line luminosities at infrared and sub-millimeter wavelengths from all transitions originating in the predominantly neutral gas that lies below the ionized surface of the disk. We find that the [ArII] 7$\mu$m, [NeII] 12.8$\mu$m, [FeI] 24$\mu$m, [SI] 25$\mu$m, [FeII] 26$\mu$m, [SiII] 35 $\mu$m, [OI] 63$\mu$m and pure rotational lines of H$_2$, H$_2$O and CO can be quite strong and are good indicators of the presence and distribution of gas in disks. We apply our models to the disk around the nearby young star, TW Hya, and find good agreement between our model calculations and observations. We also predict strong emission lines from the TW Hya disk that are likely to be detected by future facilities. A comparison of CO observations with our models suggests that the gas disk around TW Hya may be truncated to $\sim 120$ AU, compared to its dust disk of 174 AU. We speculate that photoevaporation due to the strong stellar FUV field from TW Hya is responsible for the gas disk truncation.Comment: Accepted to Astrophysical Journa

Roles and Regulation of Extracellular Vesicles in Cardiovascular Mineral Metabolism

Cardiovascular calcification is a multifaceted disease that is a leading independent predictor of cardiovascular morbidity and mortality. Recent studies have identified a calcification-prone population of extracellular vesicles as the putative elementary units of vascular microcalcification in diseased heart valves and vessels. Their action is highly context-dependent; extracellular vesicles released by smooth muscle cells, valvular interstitial cells, endothelial cells, and macrophages may promote or inhibit mineralization, depending on the phenotype of their originating cells and/or the extracellular environment to which they are released. In particular, emerging roles for vesicular microRNAs, bioactive lipids, metabolites, and protein cargoes in driving this pro-calcific switch underpin the necessity of innovative strategies to employ next-generation sequencing and omics technologies in order to better understand the pathobiology of these nano-sized entities. Furthermore, a recent body of work has emerged that centers on the novel re-purposing of extracellular vesicles and exosomes as potential therapeutic avenues for cardiovascular calcification. This review aims to highlight the role of extracellular vesicles as constituents of cardiovascular calcification and summarizes recent advances in our understanding of the biophysical nature of vesicle accumulation, aggregation, and mineralization. We also comprehensively discuss the latest evidence that extracellular vesicles act as key mediators and regulators of cell/cell communication, osteoblastic/osteoclastic differentiation, and cell/matrix interactions in cardiovascular tissues. Lastly, we highlight the importance of robust vesicle isolation and characterization when studying these phenomena, and offer a brief primer on working with cardiovascular applications of extracellular vesicles

Complex organics in IRAS 4A revisited with ALMA and PdBI: Striking contrast between two neighbouring protostellar cores

We used the Atacama Large (sub-)Millimeter Array (ALMA) and the IRAM Plateau de Bure Interferometer (PdBI) to image, with an angular resolution of 0.5$''$ (120 au) and 1$''$ (235 au), respectively, the emission from 11 different organic molecules in the protostellar binary NGC1333 IRAS 4A. We clearly disentangled A1 and A2, the two protostellar cores present. For the first time, we were able to derive the column densities and fractional abundances simultaneously for the two objects, allowing us to analyse the chemical differences between them. Molecular emission from organic molecules is concentrated exclusively in A2 even though A1 is the strongest continuum emitter. The protostellar core A2 displays typical hot corino abundances and its deconvolved size is 70 au. In contrast, the upper limits we placed on molecular abundances for A1 are extremely low, lying about one order of magnitude below prestellar values. The difference in the amount of organic molecules present in A1 and A2 ranges between one and two orders of magnitude. Our results suggest that the optical depth of dust emission at these wavelengths is unlikely to be sufficiently high to completely hide a hot corino in A1 similar in size to that in A2. Thus, the significant contrast in molecular richness found between the two sources is most probably real. We estimate that the size of a hypothetical hot corino in A1 should be less than 12 au. Our results favour a scenario in which the protostar in A2 is either more massive and/or subject to a higher accretion rate than A1, as a result of inhomogeneous fragmentation of the parental molecular clump. This naturally explains the smaller current envelope mass in A2 with respect to A1 along with its molecular richness.Comment: Accepted in Astronomy and Astrophysic

Molecular line radiative transfer in protoplanetary disks: Monte Carlo simulations versus approximate methods

We analyze the line radiative transfer in protoplanetary disks using several approximate methods and a well-tested Accelerated Monte Carlo code. A low-mass flaring disk model with uniform as well as stratified molecular abundances is adopted. Radiative transfer in low and high rotational lines of CO, C18O, HCO+, DCO+, HCN, CS, and H2CO is simulated. The corresponding excitation temperatures, synthetic spectra, and channel maps are derived and compared to the results of the Monte Carlo calculations. A simple scheme that describes the conditions of the line excitation for a chosen molecular transition is elaborated. We find that the simple LTE approach can safely be applied for the low molecular transitions only, while it significantly overestimates the intensities of the upper lines. In contrast, the Full Escape Probability (FEP) approximation can safely be used for the upper transitions (J_{\rm up} \ga 3) but it is not appropriate for the lowest transitions because of the maser effect. In general, the molecular lines in protoplanetary disks are partly subthermally excited and require more sophisticated approximate line radiative transfer methods. We analyze a number of approximate methods, namely, LVG, VEP (Vertical Escape Probability) and VOR (Vertical One Ray) and discuss their algorithms in detail. In addition, two modifications to the canonical Monte Carlo algorithm that allow a significant speed up of the line radiative transfer modeling in rotating configurations by a factor of 10--50 are described.Comment: 47 pages, 12 figures, accepted for publication in Ap

Molecular Line Emission from Gravitationally Unstable Protoplanetary Disks

In the era of high resolution submillimeter interferometers, it will soon be possible to observe the neutral circumstellar medium directly involved in gas giant planet (GGP) formation at physical scales previously unattainable. In order to explore possible signatures of gas giant planet formation via disk instabilities, we have combined a 3D, non-local thermodynamic equilibrium (LTE) radiative transfer code with a 3D, finite differences hydrodynamical code to model molecular emission lines from the vicinity of a 1.4 M_J self-gravitating proto-GGP. Here, we explore the properties of rotational transitions of the commonly observed dense gas tracer, HCO+. Our main results are the following: 1. Very high lying HCO+ transitions (e.g. HCO+ J=7-6) can trace dense planet forming clumps around circumstellar disks. Depending on the molecular abundance, the proto-GGP may be directly imageable by the Atacama Large Millimeter Array (ALMA). 2. HCO+ emission lines are heavily self-absorbed through the proto-GGP's dense molecular core. This signature is nearly ubiquitous, and only weakly dependent on assumed HCO+ abundances. The self-absorption features are most pronounced at higher angular resolutions. Dense clumps that are not self-gravitating only show minor self-absorption features. 3. Line temperatures are highest through the proto-GGP at all assumed abundances and inclination angles. Conversely, due to self-absorption in the line, the velocity-integrated intensity may not be. High angular resolution interferometers such as the Submillimeter Array (SMA) and ALMA may be able to differentiate between competing theories of gas giant planet formation.Comment: 10 pages, 13 figures; Accepted by Ap

The effect of scattering on the structure and SED of protoplanetary disks

In this paper we investigate how the inclusion of scattering of the stellar radiation into a passive flaring disk model affects its structure and spectral energy distribution, and whether neglecting it could significantly decrease the model reliability. In order to address these questions we construct a detailed 1+1D vertical structure model in which the scattering properties of the dust can be varied. Models are presented with and without dust scattering, and for different albedos and phase functions. It is found that scattering has the effect of reducing the disk temperature at all heights, so that the disk "shrinks", i.e., the the density at all intermediate heights decreases. However, this effect in most cases is more than compensated by the increase of the total extinction (absorption + scattering) cross section, so that the surface scale height increases, and images in scattered light will see a slightly thicker disk. The integrated infrared emission decreases as the albedo increases, because an increasing part of the flux captured by the disk is reflected away instead of absorbed and reprocessed. The reduction of the infrared thermal emission of the disk is stronger at short wavelengths (near infrared) and practically negligible at millimeter wavelengths. For relatively low albedo (alb <~ 0.5), or for strongly forward-peaked scattering (g roughly >0.8), the infrared flux reduction is relatively small.Comment: Accepted for publication in Astronomy & Astrophysic

Standardization of Human Calcific Aortic Valve Disease in vitro Modeling Reveals Passage-Dependent Calcification

Aortic valvular interstitial cells (VICs) isolated from patients undergoing valve replacement are commonly used as in vitro models of calcific aortic valve disease (CAVD). Standardization of VIC calcification, however, has not been implemented, which impairs comparison of results from different studies. We hypothesized that different culture methods impact the calcification phenotype of human VICs. We sought to identify the key parameters impacting calcification in primary human VICs to standardize CAVD in vitro research. Here we report that in calcification media containing organic phosphate, termed osteogenic media (OM), primary human VICs exhibited a passage-dependent decrease in calcification potential, which was not observed in calcification media containing inorganic phosphate, termed pro-calcifying media (PM). We used Alizarin red staining to compare the calcification potential of VICs cultured in OM and PM between the first and fourth passages after cell isolation from human CAVD tissues. Human VICs showed consistent Alizarin red stain when cultured with PM in a passage-independent manner. VICs cultured in OM did not exhibit consistent calcification potential between donors in early passages and consistently lacked positive Alizarin red stain in late passages. We performed whole cell, cytoplasmic and nuclear fractionation proteomics to identify factors regulating VIC passage-dependent calcification in OM. Proteomics cluster analysis identified tissue non-specific alkaline phosphatase (TNAP) as a regulator of passage-dependent calcification in OM. We verified an association of TNAP activity with calcification potential in VICs cultured in OM, but not in PM in which VICs calcified independent of TNAP activity. This study demonstrates that media culture conditions and cell passage impact the calcification potential of primary human VICs and should be taken into consideration in cell culture models of CAVD. Our results help standardize CAVD modeling as part of a greater effort to identify disease driving mechanisms and therapeutics for this unmet medical need