Quark deconfinement in neutron star cores: The effects of spin-down

We study the role of spin-down in driving quark deconfinement in the high density core of isolated neutron stars. Assuming spin-down to be solely due to magnetic braking, we obtain typical timescales to quark deconfinement for neutron stars that are born with Keplerian frequencies. Employing different equations of state (EOS), we determine the minimum and maximum neutron star masses that will allow for deconfinement via spin-down only. We find that the time to reach deconfinement is strongly dependent on the magnetic field and that this time is least for EOS that support the largest minimum mass at zero spin, unless rotational effects on stellar structure are large. For a fiducial critical density of $5\rho_0$ for the transition to the quark phase ($\rho_0=2.5\times10^{14}$g/cm$^3$ is the saturation density of nuclear matter), we find that neutron stars lighter than $1.5M_{\odot}$ cannot reach a deconfined phase. Depending on the EOS, neutron stars of more than $1.5M_{\odot}$ can enter a quark phase only if they are spinning faster than about 3 milliseconds as observed now, whereas larger spin periods imply that they are either already quark stars or will never become one.Comment: 4 pages, 4 figures, submitted to ApJ

Tau Aggregation Inhibitor Therapy : An Exploratory Phase 2 Study in Mild or Moderate Alzheimer's Disease

ACKNOWLEDGMENTS We thank patients and their caregivers for their participation in the study and are indebted to all the investigators involved in the study, particularly Drs. Douglas Fowlie and Donald Mowat for their helpful contributions to the clinical execution of the study in Scotland. We thank Sharon Eastwood, Parexel, for assistance in preparing initial drafts of the manuscript. We acknowledge constructive comments provided by Professors G. Wilcock and S. Gauthier on drafts of the article. CMW, CRH, and JMDS are officers of, and hold beneficial interests in, TauRx Therapeutics. RTS, PB, KK, and DJW are paid consultants to TauRx Therapeutics. The study was financed entirely by TauRx TherapeuticsPeer reviewedPublisher PD

Onshore–Offshore Trends in the Size-Frequency Distribution of Death Assemblages: Northwestern Gulf of Mexico

The size-frequency distributions of death assemblages were compared at three sites on the inner continental shelf of Texas by means of three descriptor variables, numerical abundance, paleoproduction (biomass at death), and paleoingestion (lifetime ingestion, a measure of energy flow). These death assemblages were then compared with six other death assemblages covering a transect from the estuary (Copano Bay, TX) to the continental slope. Typically, size-frequency distributions are based on abundance and size classes are set proportional to the largest individual in the collection. Restriction to this one analysis would have identified few of the important trends observed in this study. The evaluation of size frequency on the basis of species\u27 maximum size as well as assemblage maximum size and the comparison of a suite of assemblages on the basis of the largest maximum size provide important new inferences into community dynamics. The distribution of measures of energy flow across the size-frequency spectrum provided an additional, valuable source of information on community structure and habitat optimality. Within-habitat variability was consistently less than between-habitat variability. The autochthonous continental slope assemblages were the most diverse in their size-frequency spectra. Comparison between habitats showed that the continental slope assemblages had the largest proportion of adult individuals. The continental shelf assemblages were dominated by juveniles. The chemoautotrophic and heterotrophic assemblages in Copano Bay and on the continental slope were similar in most respects despite substantial differences in their trophic structure. Similarity existed in the proportion of adults, in the tendency toward bimodality, and in the degree to which species reached maximum size. The shapes of the size-frequency spectra were controlled in large measure by (a) the relative loss of juveniles through taphonomy, (b) the degree of survivorship to adulthood, probably predominately determined by predation, (c) the food and space resources present that control species size, and (d) the optimality of the habitat that allowed animals to approach maximum size. The habitats on the continental slope had the highest proportion of individuals near maximum size. The Copano Bay assemblages were also characterized by a large proportion of adult individuals; however, these normally did not reach sizes above 70% of species\u27 maximum size. The largest individuals were found at the petroleum seeps and in the heterotrophic assemblages from Copano Bay. Continental slope habitats should be temporally most stable, and our information supports that expectation. Food supply should be greatest in estuaries and in cold seeps where chemosynthetic processes dominate. Our data support this expectation

The role of dredge-up in double white dwarf mergers

We present the results of an investigation of the dredge-up and mixing during the merger of two white dwarfs with different chemical compositions by conducting hydrodynamic simulations of binary mergers for three representative mass ratios. In all the simulations, the total mass of the two white dwarfs is $\lesssim1.0~{\rm M_\odot}$. Mergers involving a CO and a He white dwarf have been suggested as a possible formation channel for R Coronae Borealis type stars, and we are interested in testing if such mergers lead to conditions and outcomes in agreement with observations. Even if the conditions during the merger and subsequent nucleosynthesis favor the production of $^{18}{\mathrm O}$, the merger must avoid dredging up large amounts of $^{16}{\mathrm O}$, or else it will be difficult to produce sufficient $^{18}{\mathrm O}$ to explain the oxygen ratio observed to be of order unity. We performed a total of 9 simulations using two different grid-based hydrodynamics codes using fixed and adaptive meshes, and one smooth particle hydrodynamics (SPH) code. We find that in most of the simulations, $>10^{-2}~{\rm M_\odot}$ of $^{16}{\mathrm O}$ is indeed dredged up during the merger. However, in SPH simulations where the accretor is a hybrid He/CO white dwarf with a $\sim 0.1~{\rm M_\odot}$ layer of helium on top, we find that no $^{16}{\mathrm O}$ is being dredged up, while in the $q=0.8$ simulation $<10^{-4}~{\rm M_\odot}$ of $^{16}{\mathrm O}$ has been brought up, making a WD binary consisting of a hybrid CO/He WD and a companion He WD an excellent candidate for the progenitor of RCB stars.Comment: Accepted for publication in Ap

The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results

We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from $\sim10$--$40\:\rm{\mu}\rm{m}$. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based MIR observations and archival {\it{Spitzer}} and {\it{Herschel}} data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses $m_*\sim10$--50$\:M_\odot$ accreting at $\sim10^{-4}$--$10^{-3}\:M_\odot\:{\rm{yr}}^{-1}$ inside cores of initial masses $M_c\sim30$--500$\:M_\odot$ embedded in clumps with mass surface densities $\Sigma_{\rm{cl}}\sim0.1$--3$\:{\rm{g\:cm}^{-2}}$. Fitting Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates $\sim100\times$ smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.Comment: Accepted to ApJ, 32 page

The SOFIA Massive (SOMA) Star Formation Survey. II. High Luminosity Protostars

We present multi-wavelength images observed with SOFIA-FORCAST from $\sim$10 to 40 $\mu$m of seven high luminosity massive protostars, as part of the SOFIA Massive (SOMA) Star Formation Survey. Source morphologies at these wavelengths appear to be influenced by outflow cavities and extinction from dense gas surrounding the protostars. Using these images, we build spectral energy distributions (SEDs) of the protostars, also including archival data from Spitzer, Herschel and other facilities. Radiative transfer (RT) models of Zhang & Tan (2018), based on Turbulent Core Accretion theory, are then fit to the SEDs to estimate key properties of the protostars. Considering the best five models fit to each source, the protostars have masses $m_{*} \sim 12-64 \: M_{\odot}$ accreting at rates of $\dot{m}_{*} \sim 10^{-4}-10^{-3} \: M_{\odot} \: \rm yr^{-1}$ inside cores of initial masses $M_{c} \sim 100-500 \: M_{\odot}$ embedded in clumps with mass surface densities $\Sigma_{\rm cl} \sim 0.1-3 \: \rm g \: cm^{-2}$ and span a luminosity range of $10^{4} -10^{6} \: L_{\odot}$. Compared with the first eight protostars in Paper I, the sources analyzed here are more luminous, and thus likely to be more massive protostars. They are often in a clustered environment or have a companion protostar relatively nearby. From the range of parameter space of the models, we do not see any evidence that $\Sigma_{\rm cl}$ needs to be high to form these massive stars. For most sources the RT models provide reasonable fits to the SEDs, though the cold clump material often influences the long wavelength fitting. However, for sources in very clustered environments, the model SEDs may not be such a good description of the data, indicating potential limitations of the models for these regions.Comment: 30 pages, 19 figures, Accepted for publication in Ap

Childhood intelligence and personality traits neuroticism and openness contributes to social mobility : A study in the Aberdeen 1936 Birth Cohort

Peer reviewedPostprin