Earths in Other Solar Systems N-body simulations: the Role of Orbital Damping in Reproducing the Kepler Planetary Systems

The population of exoplanetary systems detected by Kepler provides opportunities to refine our understanding of planet formation. Unraveling the conditions needed to produce the observed exoplanets will sallow us to make informed predictions as to where habitable worlds exist within the galaxy. In this paper, we examine using N-body simulations how the properties of planetary systems are determined during the final stages of assembly. While accretion is a chaotic process, trends in the ensemble properties of planetary systems provide a memory of the initial distribution of solid mass around a star prior to accretion. We also use EPOS, the Exoplanet Population Observation Simulator, to account for detection biases and show that different accretion scenarios can be distinguished from observations of the Kepler systems. We show that the period of the innermost planet, the ratio of orbital periods of adjacent planets, and masses of the planets are determined by the total mass and radial distribution of embryos and planetesimals at the beginning of accretion. In general, some amount of orbital damping, either via planetesimals or gas, during accretion is needed to match the whole population of exoplanets. Surprisingly, all simulated planetary systems have planets that are similar in size, showing that the "peas in a pod" pattern can be consistent with both a giant impact scenario and a planet migration scenario. The inclusion of material at distances larger than what Kepler observes has a profound impact on the observed planetary architectures, and thus on the formation and delivery of volatiles to possible habitable worlds.Comment: Resubmitted to ApJ. Planet formation models available online at http://eos-nexus.org/genesis-database

Studying the evolution of galaxies in compact groups over the past 3 Gyr - II. The importance of environment in the suppression of star formation

We present an in depth study on the evolution of galaxy properties in compact groups over the past 3 Gyr. We are using the largest multi-wavelength sample to-date, comprised 1770 groups (containing 7417 galaxies), in the redshift range of 0.01<z<0.23. To derive the physical properties of the galaxies we rely on ultraviolet (UV)-to-infrared spectral energy distribution modeling, using CIGALE. Our results suggest that during the 3 Gyr period covered by our sample, the star formation activity of galaxies in our groups has been substantially reduced (3-10 times). Moreover, their star formation histories as well as their UV-optical and mid-infrared colors are significantly different from those of field and cluster galaxies, indicating that compact group galaxies spend more time transitioning through the green valley. The morphological transformation from late-type spirals into early-type galaxies occurs in the mid-infrared transition zone rather than in the UV-optical green valley. We find evidence of shocks in the emission line ratios and gas velocity dispersions of the late-type galaxies located below the star forming main sequence. Our results suggest that in addition to gas stripping, turbulence and shocks might play an important role in suppressing the star formation in compact group galaxies.Comment: (Accepted for publication in MNRAS, date of submission November 18, 2015

Mixing in the Solar Nebula: Implications for Isotopic Heterogeneity and Large-Scale Transport of Refractory Grains

The discovery of refractory grains amongst the particles collected from Comet 81P/Wild 2 by the Stardust spacecraft (Brownlee et al. 2006) provides the ground truth for large-scale transport of materials formed in high temperature regions close to the protosun outward to the comet-forming regions of the solar nebula. While accretion disk models driven by a generic turbulent viscosity have been invoked as a means to explain such large-scale transport, the detailed physics behind such an ``alpha'' viscosity remains unclear. We present here an alternative physical mechanism for large-scale transport in the solar nebula: gravitational torques associated with the transient spiral arms in a marginally gravitationally unstable disk, of the type that appears to be necessary to form gas giant planets. Three dimensional models are presented of the time evolution of self-gravitating disks, including radiative transfer and detailed equations of state, showing that small dust grains will be transported upstream and downstream (with respect to the mean inward flow of gas and dust being accreted by the central protostar) inside the disk on time scales of less than 1000 yr inside 10 AU. These models furthermore show that any initial spatial heterogeneities present (e.g., in short-lived isotopes such as 26Al) will be homogenized by disk mixing down to a level of ~10%, preserving the use of short-lived isotopes as accurate nebular chronometers, while simultaneously allowing for the spread of stable oxygen isotope ratios. This finite level of nebular spatial heterogeneity appears to be related to the coarse mixing achieved by spiral arms, with radial widths of order 1 AU, over time scales of ~1000 yrs.Comment: 22 pages, 10 figures. Earth & Planetary Science Letters, accepte

Cosmochemical Consequences of Particle Trajectories During FU Orionis Outbursts by the Early Sun

The solar nebula is thought to have undergone a number of episodes of FU Orionis outbursts during its early evolution. We present here the first calculations of the trajectories of particles in a marginally gravitationally unstable solar nebula during an FU Orionis outburst, which show that 0.1 to 10 cm-sized particles traverse radial distances of 10 AU or more, inward and outward, in less than 200 yrs, exposing the particles to temperatures from $\sim$ 60 K to $\sim$ 1500 K. Such trajectories can thus account for the discovery of refractory particles in comets. Refractory particles should acquire Wark-Lovering-like rims as they leave the highest temperature regions of the disk, and these rims should have significant variations in their stable oxygen isotope ratios. Particles are likely to be heavily modified or destroyed if they pass within 1 AU of the Sun, and so are only likely to survive if they formed in the final few FU Orionis outbursts, or were transported to the outer reaches of the solar system. Calcium, aluminum-rich inclusions (CAIs) from primitive meteorites are the oldest known solar system objects and have a very narrow age range. Most CAIs may have formed at the end of the FU Orionis outbursts phase, with an age range reflecting the period between the last few outbursts.Comment: 32 pages, 4 figures, in press, EPS

Lava channel formation during the 2001 eruption on Mount Etna: evidence for mechanical erosion

We report the direct observation of a peculiar lava channel that was formed near the base of a parasitic cone during the 2001 eruption on Mount Etna. Erosive processes by flowing lava are commonly attributed to thermal erosion. However, field evidence strongly suggests that models of thermal erosion cannot explain the formation of this channel. Here, we put forward the idea that the essential erosion mechanism was abrasive wear. By applying a simple model from tribology we demonstrate that the available data agree favorably with our hypothesis. Consequently, we propose that erosional processes resembling the wear phenomena in glacial erosion are possible in a volcanic environment.Comment: accepted for publication in Physical Review Letter

Evolution of the Solar Nebula. IX. Gradients in the Spatial Heterogeneity of the Short-Lived Radioisotopes 60^{60}Fe and 26^{26}Al and the Stable Oxygen Isotopes

Short-lived radioisotopes (SLRI) such as $^{60}$Fe and $^{26}$Al were likely injected into the solar nebula in a spatially and temporally heterogeneous manner. Marginally gravitationally unstable (MGU) disks, of the type required to form gas giant planets, are capable of rapid homogenization of isotopic heterogeneity as well as of rapid radial transport of dust grains and gases throughout a protoplanetary disk. Two different types of new models of a MGU disk in orbit around a solar-mass protostar are presented. The first set has variations in the number of terms in the spherical harmonic solution for the gravitational potential, effectively studying the effect of varying the spatial resolution of the gravitational torques responsible for MGU disk evolution. The second set explores the effects of varying the initial minimum value of the Toomre $Q$ stability parameter, from values of 1.4 to 2.5, i.e., toward increasingly less unstable disks. The new models show that the basic results are largely independent of both sets of variations. MGU disk models robustly result in rapid mixing of initially highly heterogeneous distributions of SLRIs to levels of $\sim$ 10% in both the inner ($$ 10 AU) disk regions, and to even lower levels ($\sim$ 2%) in intermediate regions, where gravitational torques are most effective at mixing. These gradients should have cosmochemical implications for the distribution of SLRIs and stable oxygen isotopes contained in planetesimals (e.g., comets) formed in the giant planet region ($\sim$ 5 to $\sim$ 10 AU) compared to those formed elsewhere.Comment: 37 pages, 1 table, 19 figures, ApJ accepte

Linking dust emission to fundamental properties in galaxies: The low-metallicity picture

In this work, we aim at providing a consistent analysis of the dust properties from metal-poor to metal-rich environments by linking them to fundamental galactic parameters. We consider two samples of galaxies: the Dwarf Galaxy Survey (DGS) and KINGFISH, totalling 109 galaxies, spanning almost 2 dex in metallicity. We collect infrared (IR) to submillimetre (submm) data for both samples and present the complete data set for the DGS sample. We model the observed spectral energy distributions (SED) with a physically-motivated dust model to access the dust properties. Using a different SED model (modified blackbody), dust composition (amorphous carbon), or wavelength coverage at submm wavelengths results in differences in the dust mass estimate of a factor two to three, showing that this parameter is subject to non-negligible systematic modelling uncertainties. For eight galaxies in our sample, we find a rather small excess at 500 microns (< 1.5 sigma). We find that the dust SED of low-metallicity galaxies is broader and peaks at shorter wavelengths compared to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The PAH mass fraction and the dust temperature distribution are found to be driven mostly by the specific star-formation rate, SSFR, with secondary effects from metallicity. The correlations between metallicity and dust mass or total-IR luminosity are direct consequences of the stellar mass-metallicity relation. The dust-to-stellar mass ratios of metal-rich sources follow the well-studied trend of decreasing ratio for decreasing SSFR. The relation is more complex for highly star-forming low-metallicity galaxies and depends on the chemical evolutionary stage of the source (i.e., gas-to-dust mass ratio). Dust growth processes in the ISM play a key role in the dust mass build-up with respect to the stellar content at high SSFR and low metallicity. (abridged)Comment: 44 pages (20 pages main body plus 5 Appendices), 11 figures, 9 tables, accepted for publication in A&

An Initial Application of a Biopsychosocial Framework to Predict Posttraumatic Stress Following Pediatric Injury

Objectives—Each year millions of children suffer from unintentional injuries that result in poor emotional and physical health. This study examined selected biopsychosocial factors (i.e., child heart rate, peritrauma appraisals, early coping, trauma history) to elucidate their roles in promoting emotional recovery following injury. The study evaluated specific hypotheses that threat appraisals (global and trauma-specific) and coping would predict subsequent posttraumatic stress symptoms (PTSS), that coping would mediate the association between early and later PTSS, and that heart rate would predict PTSS and appraisals would mediate this association. Method—Participants were 96 children hospitalized for injury and assessed at 3 time points: T1 (within 2 weeks of injury), T2 (6-week follow-up), and T3 (12-week follow-up). Participants completed measures of trauma history and appraisals at T1, coping at T2, and PTSS at T1, T2, and T3. Heart rate was abstracted from medical records. Structural equation modeling was employed to evaluate study hypotheses. Results—Heart rate was not associated with PTSS or appraisals. Models including trauma history, appraisals, coping, and PTSS were constructed to test other study hypotheses and fit the data well. T1 global and trauma-specific threat appraisals were associated with T1 PTSS; T2 avoidant coping was a significant mediator of the relation between T1 and T3 PTSS. Conclusions—Findings confirm a role for appraisals and coping in the development of PTSS over the weeks following pediatric injury. Early appraisals and avoidant coping may be appropriate targets for prevention and early intervention. Future researchers should further explicate the utility of a biopsychosocial framework in predicting PTSS

Protostellar collapse: rotation and disk formation

We present some important conclusions from recent calculations pertaining to the collapse of rotating molecular cloud cores with axial symmetry, corresponding to evolution of young stellar objects through classes 0 and begin of class I. Three main issues have been addressed: (1) The typical timescale for building up a preplanetary disk - once more it turned out that it is of the order of one free-fall time which is decisively shorter than the widely assumed timescale related to the so-called 'inside-out collapse'; (2) Redistribution of angular momentum and the accompanying dissipation of kinetic (rotational) energy - together these processes govern the mechanical and thermal evolution of the protostellar core to a large extent; (3) The origin of calcium-aluminium-rich inclusions (CAIs) - due to the specific pattern of the accretion flow, material that has undergone substantial chemical and mineralogical modifications in the hot (exceeding 900 K) interior of the protostellar core may have a good chance to be advectively transported outward into the cooler remote parts (beyond 4 AU, say) of the growing disk and to survive there until it is incorporated into a meteoritic body.Comment: 4 pages, 4 figure