The enormous outer Galaxy HII region CTB 102

We present new radio recombination line observations of the previously unstudied HII region CTB 102. Line parameters are extracted and physical parameters describing the gas are calculated. We estimate the distance to CTB 102 to be 4.3 kpc. Through comparisons with HI and 1.42 GHz radio continuum data, we estimate the size of CTB 102 to be 100-130 pc, making it one of the largest HII regions known, comparable to the W4 complex. A stellar wind blown bubble model is presented as the best explanation for the observed morphology, size and velocities.Comment: 26 pages, 8 figures. Accepted for publication by The Astrophysical Journa

Iron as recyclable energy carrier: Feasibility study and kinetic analysis of iron oxide reduction

Carbon-free and sustainable energy storage solutions are required to mitigate climate change. One possible solution, especially for stationary applications, could be the storage of energy in metal fuels. Energy can be stored through reduction of the oxide with green hydrogen and be released by combustion. In this work a feasibility study for iron as possible metal fuel considering the complete energy cycle is conducted. On the basis of equilibrium calculations it could be shown that the power-to-power efficiency of the iron/iron oxide cycle is 27 %. As technology development requires a more detailed description of both the reduction and the oxidation, a first outlook is given on the kinetic analysis of the reduction of iron oxides with hydrogen. Thermogravimetric experiments using Fe$_2$O$_3$, Fe$_3$O$_4$ and FeO indicate a three-step process for the reduction. The maximum reduction rate can be achieved with a hydrogen content of 25 %. Based on the experimental results a reaction mechanism and accompanied kinetic data were developed for description of Fe$_2$O$_3$ reduction with H$_2$ under varying experimental conditions

A large local rotational speed for the Galaxy found from proper-motions: Implications for the mass of the Milky-Way

Predictions from a Galactic Structure and Kinematic model are compared to the absolute proper-motions of about 30,000 randomly selected stars with $9 < B_{\rm J} \le 19$ derived from the Southern Proper-Motion Program (SPM) toward the South Galactic Pole. The absolute nature of the SPM proper-motions allow us to measure not only the relative motion of the Sun with respect to the local disk, but also, and most importantly, the overall state of rotation of the local disk with respect to galaxies. The SPM data are best fit by models having a solar peculiar motion of +5 km~s$^{-1}$ in the V-component (pointing in the direction of Galactic rotation), a large LSR speed of 270 km~s$^{-1}$, and a disk velocity ellipsoid that points towards the Galactic center. We stress, however, that these results rest crucially on the assumptions of both axisymmetry and equilibrium dynamics. The absolute proper-motions in the U-component indicate a solar peculiar motion of $11.0 \pm 1.5$ km~s$^{-1}$, with no need for a local expansion or contraction term. The implications of the large LSR speed are discussed in terms of gravitational mass of the Galaxy inferred from the most recent and accurate determination for the proper-motion of the LMC. We find that our derived value for the LSR is consistent both with the mass of the Galaxy inferred from the motion of the Clouds ($3 - 4 \times 10^{12} M_\odot$ to $\sim 50$ kpc), as well as the timing argument, based on the binary motion of M31 and the Milky Way, and Leo I and the Milky Way ($\ge 1.2 \times 10^{12} M_\odot$ to $\sim 200$ kpc).Comment: 7 pages (AAS Latex macro v4.0), 2 B&W postscript figures, accepted for publication on ApJ, Letters sectio

Magnetohydrodynamics of Cloud Collisions in a Multi-phase Interstellar Medium

We extend previous studies of the physics of interstellar cloud collisions by beginning investigation of the role of magnetic fields through 2D magnetohydrodynamic (MHD) numerical simulations. We study head-on collisions between equal mass, mildly supersonic diffuse clouds. We include a moderate magnetic field and two limiting field geometries, with the field lines parallel (aligned) and perpendicular (transverse) to the colliding cloud motion. We explore both adiabatic and radiative cases, as well as symmetric and asymmetric ones. We also compute collisions between clouds evolved through prior motion in the intercloud medium and compare with unevolved cases. We find that: In the (i) aligned case, adiabatic collisions, like their HD counterparts, are very disruptive, independent of the cloud symmetry. However, when radiative processes are taken into account, partial coalescence takes place even in the asymmetric case, unlike the HD calculations. In the (ii) transverse case, collisions between initially adjacent unevolved clouds are almost unaffected by magnetic fields. However, the interaction with the magnetized intercloud gas during the pre-collision evolution produces a region of very high magnetic energy in front of the cloud. In collisions between evolved clouds with transverse field geometry, this region acts like a ``bumper'', preventing direct contact between the clouds, and eventually reverses their motion. The ``elasticity'', defined as the ratio of the final to the initial kinetic energy of each cloud, is about 0.5-0.6 in the cases we considered. This behavior is found both in adiabatic and radiative cases.Comment: 40 pages in AAS LaTeX v4.0, 13 figures (in degraded jpeg format). Full resolution images as well as mpeg animations are available at http://www.msi.umn.edu:80/Projects/twj/mhd-cc/ . Accepted for publication in The Astrophysical Journa

Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 SNR

The N206 supernova remnant (SNR) in the Large Magellanic Cloud (LMC) has long been considered a prototypical "mixed morphology" SNR. Recent observations, however, have added a new twist to this familiar plot: an elongated, radially-oriented radio feature seen in projection against the SNR face. Utilizing the high resolution and sensitivity available with the Hubble Space Telescope, Chandra, and XMM-Newton, we have obtained optical emission-line images and spatially resolved X-ray spectral maps for this intriguing SNR. Our findings present the SNR itself as a remnant in the mid to late stages of its evolution. X-ray emission associated with the radio "linear feature" strongly suggests it to be a pulsar-wind nebula (PWN). A small X-ray knot is discovered at the outer tip of this feature. The feature's elongated morphology and the surrounding wedge-shaped X-ray enhancement strongly suggest a bow-shock PWN structure.Comment: 41 pages including 7 figures, accepted for publication by the Astrophysical Journa

An Expanding HI Photodissociated Region Associated with the Compact HII Region G213.880-11.837 in the GGD 14 Complex

We present high angular and spectral resolution HI 21~cm line observations toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14 complex.The kinematics and morphology of the photodissociated region, traced by the HI line emission, reveal that the neutral gas is part of an expanding flow. The kinematics of the HI gas along the major axis of G213.880-11.837 shows that the emission is very extended toward the SE direction, reaching LSR radial velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the molecular gas is 11.5 km/s, which suggests a champagne flow of the HI gas. This is the second (after G111.61+0.37) cometary HII/HI region known.Comment: Accepted for publication in the Astronomical Journal (10 pages, 4 figures, 1 table

Does the Milky Way have a Maximal Disk?

The Milky Way is often considered to be the best example of a spiral for which the dark matter not only dominates the outer kinematics, but also plays a major dynamical role in the inner galaxy: the Galactic disk is therefore said to be ``sub-maximal.'' This conclusion is important to the understanding of the evolution of galaxies and the viability of particular dark matter models. The Galactic evidence rests on a number of structural and kinematic measurements, many of which have recently been revised. The new constraints indicate not only that the Galaxy is a more typical member of its class (Sb-Sc spirals) than previously thought, but also require a re-examination of the question of whether or not the Milky Way disk is maximal. By applying to the Milky Way the same definition of ``maximal disk'' that is applied to external galaxies, it is shown that the new observational constraints are consistent with a Galactic maximal disk of reasonable $M/L$. In particular, the local disk column can be substantially less than the oft-quoted required \Sigma_{\odot} \approx 100 \msolar pc^{-2} - as low as 40 \msolar pc^{-2} in the extreme case - and still be maximal, in the sense that the dark halo provides negligible rotation support in the inner Galaxy. This result has possible implications for any conclusion that rests on assumptions about the potentials of the Galactic disk or dark halo, and in particular for the interpretation of microlensing results along both LMC and bulge lines of sight.Comment: Accepted for publication in The Astrophysical Journal. 23 Latex-generated pages, one (new) table, three figures (two new). A few additions to the bibliography, an expanded discussion, and slight quantitative changes, none of which affect the conclusion

New Models for a Triaxial Milky Way Spheroid and Effect on the Microlensing Optical Depth to the Large Magellanic Cloud

We obtain models for a triaxial Milky Way spheroid based on data by Newberg and Yanny. The best fits to the data occur for a spheroid center that is shifted by 3kpc from the Galactic Center. We investigate effects of the triaxiality on the microlensing optical depth to the Large Magellanic Cloud (LMC). The optical depth can be used to ascertain the number of Massive Compact Halo Objects (MACHOs); a larger spheroid contribution would imply fewer Halo MACHOs. On the one hand, the triaxiality gives rise to more spheroid mass along the line of sight between us and the LMC and thus a larger optical depth. However, shifting the spheroid center leads to an effect that goes in the other direction: the best fit to the spheroid center is_away_ from the line of sight to the LMC. As a consequence, these two effects tend to cancel so that the change in optical depth due to the Newberg/Yanny triaxial halo is at most 50%. After subtracting the spheroid contribution in the four models we consider, the MACHO contribution (central value) to the mass of the Galactic Halo varies from \~(8-20)% if all excess lensing events observed by the MACHO collaboration are assumed to be due to MACHOs. Here the maximum is due to the original MACHO collaboration results and the minimum is consistent with 0% at the 1 sigma error level in the data.Comment: 26 pages, 2 figures. v2: minor revisions. v3: expanded discussion of the local spheroid density and minor revisions to match version published in Journal of Cosmology and Astroparticle Physics (JCAP

Direct Access to Unnatural Cyclobutane ?-Amino Acids through Visible Light Catalyzed [2+2]-Cycloaddition

In this work, we report the first selective, photocatalyzed [2+2]-cycloaddition of dehydroamino acids with styrene-type olefins. This simple, mild, and scalable approach relies on the use of the triplet energy transfer catalyst [Ir(dFCF(3)ppy(2))dtbpy]PF6 under visible light irradiation and provides fast access to value-added substituted strained cyclobutane alpha-amino acid derivatives. © 2022 The Authors. Published by American Chemical Society