Thermal Evolution and Core Formation on Asteroid 4 Vesta in the Magma Ocean Regime

Geochemical observations of the eucrite and diogenite meteorites, together with observations made by NASAs Dawn spacecraft while orbiting asteroid 4 Vesta, indicate that Vesta has differentiated to form a crust, mantle, and core. Eucrite and diogenite petrology is best explained by solidification of the crust from a magma ocean constituting 60-70% of Vestas silicates [3], or a temperature of ~1550 C. The abundances of moderately siderophile elements (Ni, Co, Mo, W, and P) in eucrites require that essentially all of the metallic phase in Vesta segregated to form a core prior to eucrite formation and likely reached a temperature of 1450- 1575 C. These observations provide important constraints on Vestas thermal evolution. The high inferred temperature indicates that convective heat transport must have been important during part of Vestas thermal evolution. In this study, we model Vestas thermal evolution in the magma ocean regime

Galactic masers and the Milky Way circular velocity

Masers found in massive star-forming regions can be located precisely in six-dimensional phase space and therefore serve as a tool for studying Milky Way dynamics. The non-random orbital phases at which the masers are found and the sparseness of current samples require modeling. Here we model the phase-space distribution function of 18 precisely measured Galactic masers, permitting a mean velocity offset and a general velocity dispersion tensor relative to their local standards of rest, and accounting for different pieces of prior information. With priors only on the Sun's distance from the Galactic Center and on its motion with respect to the local standard of rest, the maser data provide a weak constraint on the circular velocity at the Sun of V_c = 246 +/- 30 km/s. Including prior information on the proper motion of Sgr A* leads to V_c = 244 +/- 13 km/s. We do not confirm the value of V_c \approx 254 km/s found in more restrictive models. This analysis shows that there is no conflict between recent determinations of V_c from Galactic Center analyses, orbital fitting of the GD-1 stellar stream, and the kinematics of Galactic masers; a combined estimate is V_c = 236 +/- 11 km/s. Apart from the dynamical parameters, we find that masers tend to occur at post-apocenter, circular-velocity-lagging phases of their orbits.Comment: ApJ in pres

The Circular Velocity Curve of the Milky Way from 55 to 2525 kpc

We measure the circular velocity curve $v_{\rm c}(R)$ of the Milky Way with the highest precision to date across Galactocentric distances of $5\leq R \leq 25$ kpc. Our analysis draws on the $6$-dimensional phase-space coordinates of $\gtrsim 23,000$ luminous red-giant stars, for which we previously determined precise parallaxes using a data-driven model that combines spectral data from APOGEE with photometric information from WISE, 2MASS, and Gaia. We derive the circular velocity curve with the Jeans equation assuming an axisymmetric gravitational potential. At the location of the Sun we determine the circular velocity with its formal uncertainty to be $v_{\rm c}(R_{\odot}) = (229.0\pm0.2)\rm\,km\,s^{-1}$ with systematic uncertainties at the $\sim 2-5\%$ level. We find that the velocity curve is gently but significantly declining at $(-1.7\pm0.1)\rm\,km\,s^{-1}\,kpc^{-1}$, with a systematic uncertainty of $0.46\rm\,km\,s^{-1}\,kpc^{-1}$, beyond the inner $5$ kpc. We exclude the inner $5$ kpc from our analysis due to the presence of the Galactic bar, which strongly influences the kinematic structure and requires modeling in a non-axisymmetric potential. Combining our results with external measurements of the mass distribution for the baryonic components of the Milky Way from other studies, we estimate the Galaxy's dark halo mass within the virial radius to be $M_{\rm vir} = (7.25\pm0.26)\cdot 10^{11}M_{\odot}$ and a local dark matter density of $\rho_{\rm dm}(R_{\odot}) = 0.30\pm0.03\,\rm GeV\,cm^{-3}$.Comment: Accepted for publication in ApJ. All data can be downloaded here: https://doi.org/10.5281/zenodo.146805

ECONOMIC MODELING OF FARM PRODUCTION AND CONSERVATION DECISIONS IN RESPONSE TO ALTERNATIVE RESOURCE AND ENVIRONMENTAL POLICIES

Environmental Economics and Policy, Farm Management,

Determination of Flaw Growth Characteristics of Ti-6Al-4V Sheet in the Solution-Treated and Aged Condition

The specific experimental investigation undertaken was designed to answer these questions on Ti-6Al-4V in the solution treated and aged condition. The defect growth and fracture characteristics were studied in parent (unwelded) and welded sheet material. The results of the study indicate that cryogenic proof testing will screen smaller size defects than proof testing at ambient conditions. However some unusual crack growth behavior during the proof test simulation suggests that some further study be made of stress and time duration effects

Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: Revealing the inner funnel of dust

We present new interferometric data obtained with MIDI (MID infrared Interferometric instrument) for the Seyfert II galaxy NGC 1068, with an extensive coverage of sixteen uv points. These observations resolve the nuclear mid-infrared emission from NGC 1068 in unprecedented detail with a maximum resolution of 7 mas. For the first time, sufficient uv points have been obtained, allowing us to generate an image of the source using maximum entropy image reconstruction. The features of the image are similar to those obtained by modelling. We find that the mid-infrared emission can be represented by two components, each with a Gaussian brightness distribution. The first, identified as the inner funnel of the obscuring torus, is hot (800K), 1.35 parsec long, and 0.45 parsec thick in FWHM at a PA=-42 degrees (from north to east). It has an absorption profile different than standard interstellar dust and with evidence for clumpiness. The second component is 3 by 4 pc in FWHM with T=300K, and we identify it with the cooler body of the torus. The compact component is tilted by 45 degrees with respect to the radio jet and has similar size and orientation to the observed water maser distribution. We show how the dust distribution relates to other observables within a few parsecs of the core of the galaxy such as the nuclear masers, the radio jet, and the ionization cone. We compare our findings to a similar study of the Circinus galaxy and other relevant studies. Our findings shed new light on the relation between the different parsec-scale components in NGC 1068 and the obscuring torus.Comment: Accepted to MNRA