Angular momentum evolution of young low-mass stars and brown dwarfs: observations and theory

This chapter aims at providing the most complete review of both the emerging concepts and the latest observational results regarding the angular momentum evolution of young low-mass stars and brown dwarfs. In the time since Protostars & Planets V, there have been major developments in the availability of rotation period measurements at multiple ages and in different star-forming environments that are essential for testing theory. In parallel, substantial theoretical developments have been carried out in the last few years, including the physics of the star-disk interaction, numerical simulations of stellar winds, and the investigation of angular momentum transport processes in stellar interiors. This chapter reviews both the recent observational and theoretical advances that prompted the development of renewed angular momentum evolution models for cool stars and brown dwarfs. While the main observational trends of the rotational history of low mass objects seem to be accounted for by these new models, a number of critical open issues remain that are outlined in this review.Comment: 22 pages, 8 figures, accepted for publication in Protostars & Planets VI, 2014, University of Arizona Press, eds. H. Beuther, R. Klessen, K. Dullemond, Th. Hennin

Coronal structure of the cTTS V2129 Oph

The nature of the magnetic coupling between T Tauri stars and their disks determines not only the mass accretion process but possibly the spin evolution of the central star. We have taken a recently-published surface magnetogram of one moderately-accreting T Tauri star (V2129 Oph) and used it to extrapolate the geometry of its large-scale field. We determine the structure of the open (wind-bearing) field lines, the closed (X-ray bright) field lines and those potentially accreting field lines that pass through the equatorial plane inside the Keplerian co-rotation radius. We consider a series of models in which the stellar magnetic field is opened up by the outward pressure of the hot coronal gas at a range of radii. As this radius is increased, accretion takes place along simpler field structures and impacts on fewer sites at the stellar surface. This is consistent with the observed variation in the Ca II IRT and HeI lines which suggests that accretion in the visible hemisphere is confined to a single high-latitude spot. By determining the density and velocity of the accretion flows, we find that in order to have most of the total mass accretion rate impacting on a single high-latitude region we need disk material to accrete from approximately 7R*, close to the Keplerian co-rotation radius at 6.8R*. We also calculate the coronal density and X-ray emission measure. We find that both the magnitude and rotational modulation of the emission measure increase as the source surface is increased. For the field structure of V2129 Oph which is dominantly octupolar, the emission forms a bright, high-latitude ring that is always in view as the star rotates. Since the accretion funnels are not dense enough to cause significant scattering of coronal X-ray photons, they provide only a low rotational modulation of around 10% at most.Comment: 10 pages, 9 figure

A changing inner radius in the accretion disc of Q0056-363?

Q0056-363 is the most powerful X-ray quasar known to exhibit a broad, likely relativistic iron line (Porquet & Reeves 2003). It has been observed twice by XMM-$Newton$, three and half years apart (July 2000 and December 2003). In the second observation, the UV and soft X-ray fluxes were fainter, the hard X-ray power law flatter, and the iron line equivalent width (EW) smaller than in the 2000 observation. These variations can all be explained, at least qualitatively, if the disc is truncated in the second observation. We report also on the possible detection of a transient, redshifted iron absorption line during the 2003 observation.Comment: Accepted for publication in A&

Proceedings of the 38th Annual Biochemical Engineering Symposium

The 38th Annual Biochemical Engineering Symposium was held at the Pingree Park Campus and Conference Center, Colorado State University, 22-23 May 2009. The following institutions were represented; Colorado State University, Iowa State University, Kansas State University and the South Dakota School of Mines. This Proceeding contains papers based on most of the oral presentations. The first symposium was first held in 1971. It has been held annually since then except for a one year break. The following institutions have hosted the symposium. Contents History of the Annual Biochemical Engineering Symposium - Larry E. Erickson, Department of Chemical Engineering Kansas State University, Manhattan, Kansas 66506 Enhanced Solid-Liquid Clarification of Lignocellulosic Slurries Using Polyelectrolyte Flocculating Agents - Devon R. Burke, Jason Anderson, Patrick C. Gilcrease and Todd J. Menkhaus, Department of Chemical and Biological Engineering South Dakota School of Mines and Technology, Rapid City, SO 57701 Removal and Recovery of Inhibitory Compounds from Pine Slurry Hydrolysates using a Polyelectrolyte Flocculating Agent - Brian Carter, Todd J. Menkhaus, and Patrick C. Gilcrease Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SO 57701 The thioesterases: A new perspective based on their primary and tertiary structures - David C. Cantu, Yingfei Chen, and Peter J. Reilly Department of Chemical and Biological Engineering, Iowa State University, Ames, lA 50011 Tailoring Polysaccharide-Based Nanostructured Biomaterials for Guided Mesenchymal Stem Cell (MSC) Response - Jorge Almodóvar, Matt J. Kipper, Department of Chemical and Biological Engineering, Colorado State University, School of Biomedical Engineering, Colorado State University, Fort Collins, CO 80523-1370 Nanoassembly of polysaccharide based polyelectrolytes: Tuning morphology and Size - Soheil Boddohit, Jorge Almodóvar, Hao Zhang, Patrick A. Johnson, and Matt J. Kipper, Department of Chemical and Biological Engineering, Colorado State University, School of Biomedical Engineering, Colorado State University, Fort Collins CO, 80523, Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie WY, 82071 Vertical Cell Assembly of Colloidal Crystal Films for Making Inverse Colloidal Crystal Membrane: A New Generation Ultrafiltration Membrane for Protein Separation - Xinying Wang, Scott M. Husson, Xianghong Qian, S. Ranil Wickramasinghe, Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, CO 80523, Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC 29634, Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523https://lib.dr.iastate.edu/bce_proceedings/1037/thumbnail.jp

Resonant Absorption in the AGN spectra emerging from photoionized gas: differences between steep and flat ionizing continua

We present photoionization models accounting for both photoelectric and resonant absorption. Resonance absorption lines from C, O, Ne, Mg, Si S and Fe between 0.1 and 10 keV are treated. In particular we consider the complex of almost 60 strong Fe L absorption lines around 1 keV. We calculate profiles, intensities and equivalent widths of each line, considering both Doppler and natural broadening mechanisms. Doppler broadening includes a term accounting for turbulence of the gas along the line of sight. We computed spectra transmitted by gas illuminated by drastically different ionizing continua and compared them to spectra observed in flat X-ray spectrum, broad optical emission line type 1 AGN, and steep X-ray spectrum, narrow optical emission line type 1 AGN. We show that the $\sim 1$ keV absorption feature observed in moderate resolution X-ray spectra of several Narrow Line Seyfert 1 galaxies can be explained by photoionization models, taking into account for resonance absorption, without requiring relativistic outflowing velocities of the gas, if the physical properties of these absorbers are close to those found in flat X-ray spectrum Seyfert 1 galaxies.Comment: 22 pages, 10 figures. Accepted for publication on Ap

Abell 1201: a Minor merger at second core passage

We present an analysis of the structures and dynamics of the merging cluster Abell~1201, which has two sloshing cold fronts around a cooling core, and an offset gas core approximately 500kpc northwest of the center. New Chandra and XMM-Newton data reveal a region of enhanced brightness east of the offset core, with breaks in surface brightness along its boundary to the north and east. This is interpreted as a tail of gas stripped from the offset core. Gas in the offset core and the tail is distinguished from other gas at the same distance from the cluster center chiefly by having higher density, hence lower entropy. In addition, the offset core shows marginally lower temperature and metallicity than the surrounding area. The metallicity in the cool core is high and there is an abrupt drop in metallicity across the southern cold front. We interpret the observed properties of the system, including the placement of the cold fronts, the offset core and its tail in terms of a simple merger scenario. The offset core is the remnant of a merging subcluster, which first passed pericenter southeast of the center of the primary cluster and is now close to its second pericenter passage, moving at ~1000 km/s. Sloshing excited by the merger gave rise to the two cold fronts and the disposition of the cold fronts reveals that we view the merger from close to the plane of the orbit of the offset core.Comment: accepted by Ap

Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure

The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide strong evidence for an accretion disk near a supermassive black hole as a source of the line emission. These lines serve as powerful probes for examining the structure of inner regions of accretion disks. Previous studies of line emission have considered geometrically thin disks only, where the gas moves along geodesics in the equatorial plane of a black hole. Here we extend this work to consider effects on line profiles from finite disk thickness, radial accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution, and find that within this framework, turbulent broadening is the dominant new effect. The most prominent change in the skewed, double-horned line profiles is a substantial reduction in the maximum flux at both red and blue peaks. The effect is most pronounced when the inclination angle is large, and when the accretion rate is high. Thus, the effects discussed here may be important for future detailed modeling of high quality observational data.Comment: 21 pages including 8 figures; LaTeX; ApJ format; accepted by ApJ; short results of this paper appeared before as a conference proceedings (astro-ph/9711214

Mechanisms and dynamics of the metastable decay in Ar-2(+)

A detailed experimental as well as theoretical investigation of the properties of the metastable dissociation Ar-2(+)--\u3eAr++Ar is presented. The mass-analyzed ion kinetic energy (MIKE) scan technique has been performed using a three sector field mass spectrometer. The possible mechanisms of the metastability of Ar-2(+) have been examined and the observed decay process is assigned to the II(1/2)(u)--\u3eI(1/2)(g) bound to continuum radiative transition, in agreement with earlier work. The calculation of the theoretical shape of the kinetic energy release distribution of fragment ions allowed us to construct the theoretical MIKE peak and compare it with the raw experimental data. The accuracy of various sets of potential energy curves for Ar-2(+) is discussed, as well as the way of production of the metastable Ar-2(+)[II(1/2)(u)] electronic state by electron impact. Excellent agreement between the experimental data and theoretical model has been observed. (C) 2004 American Institute of Physics

The nature of a broad line radio galaxy: Simultaneous RXTE and Chandra HETG observations of 3C 382

We present the results from simultaneous chandra and rxte observations of the X-ray bright Broad-Line Radio Galaxy (BLRG) 3C 382. The long (120 ks) exposure with chandra HETG allows a detailed study of the soft X-ray continuum and of the narrow component of the Fe Kalpha line. The rxte PCA data are used to put an upper limit on the broad line component and constrain the hard X-ray continuum. A strong soft excess below 1 keV is observed in the time-averaged HETG spectrum, which can be parameterized with a steep power law or a thermal model. The flux variability at low energies indicates that the origin of the soft excess cannot be entirely ascribed to the circumnuclear diffuse emission, detected by chandra on scales of 20-30 arcsec (22-33 kpc). A narrow (sigma<90 eV) Fe Kalpha line (with EW< 100 eV) is observed by the chandra HEG. Similar values for the line parameters are measured by the rxte PCA, suggesting that the contribution from a broad line component is negligible. The fact that the exposure is split into two observations taken three days apart allows us to investigate the spectral and temporal evolution of the source on different timescales. Significant flux variability associated with spectral changes is observed on timescales of hours and days. The spectral variability is similar to that observed in radio-quiet AGN ruling out a jet-dominated origin of the X-rays.Comment: 19 pages, 10 figures, 3 tables, accepted for publication in Ap