Variations of Interstellar Gas-to-Dust Ratios at High Galactic Latitudes

Interstellar dust at high Galactic latitudes can influence astronomical foreground subtraction, produce diffuse scattered light, and soften the ultraviolet spectra of quasars. In a sample of 94 sight lines toward quasars at high latitude and low extinction, we evaluate the interstellar "gas-to-dust ratio" $N_{\rm H}/E(B-V)$, using hydrogen column densities (H I and H$_2$) and far-infrared estimates of dust reddening. In the Galactic plane, this ratio is $6.0\pm0.2$ (in units of $10^{21}~{\rm cm}^{-2}~{\rm mag}^{-1}$). On average, recent Planck estimates of $E(B-V)$ in low-reddening sight lines are 12% higher than those from Schlafly & Finkbeiner (2011), and $N_{\rm HI}$ exhibits significant variations when measured at different radio telescopes. In a sample of 51 quasars with measurements of both H I and H$_2$ and $0.01 \leq E(B-V) \lesssim 0.1$, we find mean ratios $10.3\pm0.4$ (gas at all velocities) and $9.2\pm0.3$ (low velocity only) using Planck $E(B-V)$ data. High-latitude H$_2$ fractions are generally small (2-3% on average), although 9 of 39 sight lines at $|b| \geq 40^{\circ}$ have $f_{\rm H2}$ of 1-17%. Because FIR-inferred $E(B-V)$ is sensitive to modeled dust temperature $T_d$ and emissivity index $\beta$, gas-to-dust ratios have large, asymmetric errors at low $E(B-V)$. The ratios are elevated in sight lines with high-velocity clouds, which contribute $N_{\rm H}$ but little reddening. In Complex C, the ratio decreases by 40% when high velocity gas is excluded. Decreases in dust content are expected in low-metallicity gas above the Galactic plane, resulting from grain destruction in shocks, settling to the disk, and thermal sputtering in hot halo gas.Comment: Minor changes, accepted to Astrophysical Journal, 37 pages, 7 tables, 8 figure

Demonstration of magnetic field tomography with starlight polarization towards a diffuse sightline of the ISM

The availability of large datasets with stellar distance and polarization information will enable a tomographic reconstruction of the (plane-of-the-sky-projected) interstellar magnetic field in the near future. We demonstrate the feasibility of such a decomposition within a small region of the diffuse ISM. We combine measurements of starlight (R-band) linear polarization obtained using the RoboPol polarimeter with stellar distances from the second Gaia data release. The stellar sample is brighter than 17 mag in the R band and reaches out to several kpc from the Sun. HI emission spectra reveal the existence of two distinct clouds along the line of sight. We decompose the line-of-sight-integrated stellar polarizations to obtain the mean polarization properties of the two clouds. The two clouds exhibit significant differences in terms of column density and polarization properties. Their mean plane-of-the-sky magnetic field orientation differs by 60 degrees. We show how our tomographic decomposition can be used to constrain our estimates of the polarizing efficiency of the clouds as well as the frequency dependence of the polarization angle of polarized dust emission. We also demonstrate a new method to constrain cloud distances based on this decomposition. Our results represent a preview of the wealth of information that can be obtained from a tomographic map of the ISM magnetic field.Comment: 25 pages, 14 figures, published in ApJ, data appear in journa

Monte Carlo analysis of an ODE Model of the Sea Urchin Endomesoderm Network

<p>Abstract</p> <p>Background</p> <p>Gene Regulatory Networks (GRNs) control the differentiation, specification and function of cells at the genomic level. The levels of interactions within large GRNs are of enormous depth and complexity. Details about many GRNs are emerging, but in most cases it is unknown to what extent they control a given process, i.e. the grade of completeness is uncertain. This uncertainty stems from limited experimental data, which is the main bottleneck for creating detailed dynamical models of cellular processes. Parameter estimation for each node is often infeasible for very large GRNs. We propose a method, based on random parameter estimations through Monte-Carlo simulations to measure completeness grades of GRNs.</p> <p>Results</p> <p>We developed a heuristic to assess the completeness of large GRNs, using ODE simulations under different conditions and randomly sampled parameter sets to detect parameter-invariant effects of perturbations. To test this heuristic, we constructed the first ODE model of the whole sea urchin endomesoderm GRN, one of the best studied large GRNs. We find that nearly 48% of the parameter-invariant effects correspond with experimental data, which is 65% of the expected optimal agreement obtained from a submodel for which kinetic parameters were estimated and used for simulations. Randomized versions of the model reproduce only 23.5% of the experimental data.</p> <p>Conclusion</p> <p>The method described in this paper enables an evaluation of network topologies of GRNs without requiring any parameter values. The benefit of this method is exemplified in the first mathematical analysis of the complete Endomesoderm Network Model. The predictions we provide deliver candidate nodes in the network that are likely to be erroneous or miss unknown connections, which may need additional experiments to improve the network topology. This mathematical model can serve as a scaffold for detailed and more realistic models. We propose that our method can be used to assess a completeness grade of any GRN. This could be especially useful for GRNs involved in human diseases, where often the amount of connectivity is unknown and/or many genes/interactions are missing.</p

The globin gene family of the cephalochordate amphioxus: implications for chordate globin evolution

<p>Abstract</p> <p>Background</p> <p>The lancelet amphioxus (Cephalochordata) is a close relative of vertebrates and thus may enhance our understanding of vertebrate gene and genome evolution. In this context, the globins are one of the best studied models for gene family evolution. Previous biochemical studies have demonstrated the presence of an intracellular globin in notochord tissue and myotome of amphioxus, but the corresponding gene has not yet been identified. Genomic resources of <it>Branchiostoma floridae </it>now facilitate the identification, experimental confirmation and molecular evolutionary analysis of its globin gene repertoire.</p> <p>Results</p> <p>We show that <it>B. floridae </it>harbors at least fifteen paralogous globin genes, all of which reveal evidence of gene expression. The protein sequences of twelve globins display the conserved characteristics of a functional globin fold. In phylogenetic analyses, the amphioxus globin BflGb4 forms a common clade with vertebrate neuroglobins, indicating the presence of this nerve globin in cephalochordates. Orthology is corroborated by conserved syntenic linkage of <it>BflGb4 </it>and flanking genes. The kinetics of ligand binding of recombinantly expressed BflGb4 reveals that this globin is hexacoordinated with a high oxygen association rate, thus strongly resembling vertebrate neuroglobin. In addition, possible amphioxus orthologs of the vertebrate globin X lineage and of the myoglobin/cytoglobin/hemoglobin lineage can be identified, including one gene as a candidate for being expressed in notochord tissue. Genomic analyses identify conserved synteny between amphioxus globin-containing regions and the vertebrate <it>β-globin </it>locus, possibly arguing against a late transpositional origin of the <it>β-globin </it>cluster in vertebrates. Some amphioxus globin gene structures exhibit minisatellite-like tandem duplications of intron-exon boundaries ("mirages"), which may serve to explain the creation of novel intron positions within the globin genes.</p> <p>Conclusions</p> <p>The identification of putative orthologs of vertebrate globin variants in the <it>B. floridae </it>genome underlines the importance of cephalochordates for elucidating vertebrate genome evolution. The present study facilitates detailed functional studies of the amphioxus globins in order to trace conserved properties and specific adaptations of respiratory proteins at the base of chordate evolution.</p

IRAS 00450+7401 and the mid-infrared fade/burst cycle of R Coronae Borealis-type stars

We present optical and infrared imaging and spectroscopy of the R Coronae Borealis-type (R Cor Bor) star IRAS 00450+7401. Optical spectra further confirm its classification as a cool R Cor Bor system, having a hydrogen-deficient carbon star spectral sub-class of HdC5 or later. Mid-infrared spectroscopy reveals the typical ~8 um ``hump'' seen in other R Cor Bor stars and no other features. A modern-epoch spectral energy distribution shows bright emission from hot dust having Tdust>600 K. Historical infrared data reveal generally cooler dust color temperatures combined with long-term fading trends, but provide no discernible correlation between flux level and temperature. Investigating the most mid-infrared variable R Cor Bor stars found in IRAS, AKARI, and WISE data reveals similar fading trends, bursts that can show a factor of up to 10 change in flux density between epochs, and blackbody-fit dust color temperatures that span 400-1300 K. While some R Cor Bor stars such as IRAS 00450+7401 appear to undergo fade/burst cycles in the mid-infrared, significant gaps in temporal coverage prevent conclusively identifying any preferred timescale for their mid-infrared variability and circumstellar dust temperature changes.Comment: AJ accepted, 15 pages, 6 figures, 5 tables, and an appendi

A global view of gene expression in lithium and zinc treated sea urchin embryos: new components of gene regulatory networks

Novel territory-specific markers from the sea urchin Strongylocentrotus purpuratus have been identified using screens for genes that are differentially expressed in lithium-treated embryos, which form an excess of endomesoderm, and in zinc-treated embryos, in which endomesoderm specification is blocked

Extreme starlight polarization in a region with highly polarized dust emission

Context. Galactic dust emission is polarized at unexpectedly high levels, as revealed by Planck. Aims. The origin of the observed ≃20% polarization fractions can be identified by characterizing the properties of optical starlight polarization in a region with maximally polarized dust emission. Methods. We measure the R-band linear polarization of 22 stars in a region with a submillimeter polarization fraction of ≃20%. A subset of 6 stars is also measured in the B, V, and I bands to investigate the wavelength dependence of polarization. Results. We find that starlight is polarized at correspondingly high levels. Through multiband polarimetry we find that the high polarization fractions are unlikely to arise from unusual dust properties, such as enhanced grain alignment. Instead, a favorable magnetic field geometry is the most likely explanation, and is supported by observational probes of the magnetic field morphology. The observed starlight polarization exceeds the classical upper limit of [pV/E(B−V)]_(max) = 9% mag^(−1) and is at least as high as 13% mag^(−1), as inferred from a joint analysis of Planck data, starlight polarization, and reddening measurements. Thus, we confirm that the intrinsic polarizing ability of dust grains at optical wavelengths has long been underestimated

Generation, Annotation, Evolutionary Analysis, and Database Integration of 20,000 Unique Sea Urchin EST Clusters

Together with the hemichordates, sea urchins represent basal groups of nonchordate invertebrate deuterostomes that occupy a key position in bilaterian evolution. Because sea urchin embryos are also amenable to functional studies, the sea urchin system has emerged as one of the leading models for the analysis of the function of genomic regulatory networks that control development. We have analyzed a total of 107,283 cDNA clones of libraries that span the development of the sea urchin Strongylocentrotus purpuratus. Normalization by oligonucleotide fingerprinting, EST sequencing and sequence clustering resulted in an EST catalog comprised of 20,000 unique genes or gene fragments. Around 7000 of the unique EST consensus sequences were associated with molecular and developmental functions. Phylogenetic comparison of the identified genes to the genome of the urochordate Ciona intestinalis indicate that at least one quarter of the genes thought to be chordate specific were already present at the base of deuterostome evolution. Comparison of the number of gene copies in sea urchins to those in chordates and vertebrates indicates that the sea urchin genome has not undergone extensive gene or complete genome duplications. The established unique gene set represents an essential tool for the annotation and assembly of the forthcoming sea urchin genome sequence. All cDNA clones and filters of all analyzed libraries are available from the resource center of the German genome project at http://www.rzpd.de