Migration of giant planets in planetesimal discs

Planets orbiting a planetesimal circumstellar disc can migrate inward from their initial positions because of dynamical friction between planets and planetesimals. The migration rate depends on the disc mass and on its time evolution. Planets that are embedded in long-lived planetesimal discs, having total mass of $10^{-4}-0.01 M_{\odot}$, can migrate inward a large distance and can survive only if the inner disc is truncated or because of tidal interaction with the star. In this case the semi-major axis, a, of the planetary orbit is less than 0.1 AU. Orbits with larger $a$ are obtained for smaller value of the disc mass or for a rapid evolution (depletion) of the disc. This model may explain several of the orbital features of the giant planets that were discovered in last years orbiting nearby stars as well as the metallicity enhancement found in several stars associated with short-period planets.Comment: 21 pages; 6 encapsulated figures. Accepted by MNRA

The Supernova Triggered Formation and Enrichment of Our Solar System

We investigate the enrichment of the pre-solar cloud core with short lived radionuclides (SLRs), especially 26Al. The homogeneity and the surprisingly small spread in the ratio 26Al/27Al observed in the overwhelming majority of calcium-aluminium-rich inclusions (CAIs) in a vast variety of primitive chondritic meteorites places strong constraints on the formation of the the solar system. Freshly synthesized radioactive 26Al has to be included and well mixed within 20kyr. After discussing various scenarios including X-winds, AGB stars and Wolf-Rayet stars, we come to the conclusion that triggering the collapse of a cold cloud core by a nearby supernova is the most promising scenario. We then narrow down the vast parameter space by considering the pre-explosion survivability of such a clump as well as the cross-section necessary for sufficient enrichment. We employ numerical simulations to address the mixing of the radioactively enriched SN gas with the pre-existing gas and the forced collapse within 20kyr. We show that a cold clump of 10Msun at a distance of 5pc can be sufficiently enriched in 26Al and triggered into collapse fast enough - within 18kyr after encountering the supernova shock - for a range of different metallicities and progenitor masses, even if the enriched material is assumed to be distributed homogeneously in the entire supernova bubble. In summary, we envision an environment for the birth place of the Solar System 4.567Gyr ago similar to the situation of the pillars in M16 nowadays, where molecular cloud cores adjacent to an HII region will be hit by a supernova explosion in the future. We show that the triggered collapse and formation of the Solar System as well as the required enrichment with radioactive 26Al are possible in this scenario.Comment: 12 pages, 8 figures, accepted for publication in ApJ. Resolution of most figures degraded to fit within arXiv size limits. A full resolution version is available at http://www.usm.uni-muenchen.de/~gritschm/Gritschneder_2011_sun.pd

What We Share Is Who We Are and What We Do: How Emotional Intimacy Shapes Organizational Identification and Collaborative Behaviors

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155930/1/apps12208_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155930/2/apps12208.pd

On the origin of planets at very wide orbits from the re-capture of free floating planets

In recent years several planets have been discovered at wide orbits (>100 AU) around their host stars. Theoretical studies encounter difficulties in explaining their formation and origin. Here we propose a novel scenario for the production of planetary systems at such orbits, through the dynamical recapture of free floating planets (FFPs) in dispersing stellar clusters. This process is a natural extension of the recently suggested scenario for the formation of wide stellar binaries. We use N-body simulations of dispersing clusters with 10-1000 stars and comparable numbers of FFPs to study this process. We find that planets are captured into wide orbits in the typical range ~100-10^6 AU, and have a wide range of eccentricities (thermal distribution). Typically, 3-6 x (f_FFP/1) % of all stars capture a planetary companion with such properties (where f_FFP is the number of FFP per star). The planetary capture efficiency is comparable to that of capture-formed stellar-binaries, and shows a similar dependence on the cluster size and structure. It is almost independent of the specific planetary mass; planets as well as sub-stellar companions of any mass can be captured. The capture efficiency decreases with increasing cluster size, and for a given cluster size the it increases with the host/primary mass. More than one planet can be captured around the same host and planets can be captured into binary systems. Planets can also be captured into pre-existing planetary and into orbits around black holes and massive white dwarfs, if these formed early enough before the cluster dispersal. In particular, stellar black holes have a high capture efficiency (>50 % and 5-10 x (f_FFP/1) % for capture of stars and planetary companions, respectively) due to their large mass. Finally, although rare, two FFPs or brown dwarfs can become bound and form a FFP-binary system with no stellar host.Comment: ApJ, in press. Added two figure

A Keck/HIRES Doppler Search for Planets Orbiting Metal-Poor Dwarfs. I. Testing Giant Planet Formation and Migration Scenarios

We describe a high-precision Doppler search for giant planets orbiting a well-defined sample of metal-poor dwarfs in the field. This experiment constitutes a fundamental test of theoretical predictions which will help discriminate between proposed giant planet formation and migration models. We present here details on the survey as well as an overall assessment of the quality of our measurements, making use of the results for the stars that show no significant velocity variation.Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical Journa

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks II. Extended Simulations with Varied Cooling Rates

In order to investigate mass transport and planet formation by gravitational instabilities (GIs), we have extended our 3-D hydrodynamic simulations of protoplanetary disks from a previous paper. Our goal is to determine the asymptotic behavior of GIs and how it is affected by different constant cooling times. Initially, Rdisk = 40 AU, Mdisk = 0.07 Mo, M* = 0.5 Mo, and Qmin = 1.8. Sustained cooling, with tcool = 2 orps (outer rotation periods, 1 orp ~ 250 yrs), drives the disk to instability in ~ 4 orps. This calculation is followed for 23.5 orps. After 12 orps, the disk settles into a quasi-steady state with sustained nonlinear instabilities, an average Q = 1.44 over the outer disk, a well-defined power-law Sigma(r), and a roughly steady Mdot ~ 5(-7) Mo/yr. The transport is driven by global low-order spiral modes. We restart the calculation at 11.2 orps with tcool = 1 and 1/4 orp. The latter case is also run at high azimuthal resolution. We find that shorter cooling times lead to increased Mdots, denser and thinner spiral structures, and more violent dynamic behavior. The asymptotic total internal energy and the azimuthally averaged Q(r) are insensitive to tcool. Fragmentation occurs only in the high-resolution tcool = 1/4 orp case; however, none of the fragments survive for even a quarter of an orbit. Ring-like density enhancements appear and grow near the boundary between GI active and inactive regions. We discuss the possible implications of these rings for gas giant planet formation.Comment: Due to document size restrictions, the complete manuscript could not be posted on astroph. Please go to http://westworld.astro.indiana.edu to download the full document including figure

TB Peritonitis Mistaken for Ovarian Carcinomatosis Based on an Elevated CA-125

Background. In the United States, tuberculosis (TB) is of relatively low prevalence and most newly diagnosed patients are born outside of the United States. In addition, a large percentage (20.6%) of TB cases initially present with extrapulmonary manifestations (CDC, 2010). Cases of TB peritonitis are a diagnostic challenge in women due to the nonspecific clinical features overlapping with signs of ovarian cancer. (Kosseifi et al., 2009; Rashed et al., 2007; and Xi et al., 2010). We present a 27 year-old woman thought to have ovarian carcinomatosis based on elevated levels of CA-125 who was ultimately diagnosed with TB salpingitis, endometritis, and peritonitis. Methods. This brief report is a retrospective case report. Results. This case outlines the unfortunate consequences of the misdiagnosis of what probably was an antibiotic responsive illness, resulting in an unnecessarily aggressive surgical procedure. The delay in the diagnosis of tuberculous pertitonitis resulted in an unnecessary radical resection of the patient's reproductive organs. Conclusions. Patients with TB peritonitis present with non-specific signs that may be misdiagnoses as ovarian cancer. In differentiating between ovarian carcinomatosis and peritoneal TB, it is vital to consider country of origin, age, CA-125, ascitic fluid analysis, and the use of intra-operative frozen sections

Observing biogeochemical cycles at global scales with profiling floats and gliders: prospects for a global array

Chemical and biological sensor technologies have advanced rapidly in the past five years. Sensors that require low power and operate for multiple years are now available for oxygen, nitrate, and a variety of bio-optical properties that serve as proxies for important components of the carbon cycle (e.g., particulate organic carbon). These sensors have all been deployed successfully for long periods, in some cases more than three years, on platforms such as profiling floats or gliders. Technologies for pH, pCO2, and particulate inorganic carbon are maturing rapidly as well. These sensors could serve as the enabling technology for a global biogeochemical observing system that might operate on a scale comparable to the current Argo array. Here, we review the scientific motivation and the prospects for a global observing system for ocean biogeochemistry