2,094 research outputs found
Physics of Planet Trapping with Applications to HL Tau
We explore planet formation in the HL Tau disk and possible origins of the
prominent gaps and rings observed by ALMA. We investigate whether dust gaps are
caused by dynamically trapped planetary embryos at the ice lines of abundant
volatiles. The global properties of the HL Tau disk (total mass, size) at its
current age are used to constrain an evolving analytic disk model describing
its temperature and density profiles. By performing a detailed analysis of the
planet-disk interaction for a planet near the water ice line including a
rigorous treatment of the dust opacity, we confirm that water is sufficiently
abundant (1.5x10^-4 molecules per H) to trap planets at its ice line due to an
opacity transition. When the abundance of water is reduced by 50% planet
trapping disappears. We extend our analysis to other planet traps: the heat
transition, dead zone edge, and the CO_2 ice line and find similar trapping.
The formation of planets via planetesimal accretion is computed for dynamically
trapped embryos at the water ice line, dead zone, and heat transition. The end
products orbit in the inner disk (R < 3 AU), unresolved by ALMA, with masses
that range between sub-Earth to 5 Jupiter masses. While we find that the dust
gaps correspond well with the radial positions of the CO_2 , CH_4 , and CO ice
lines, the planetesimal accretion rates at these radii are too small to build
large embryos within 1 Myr.Comment: Accepted for publication in MNRA
Time of origin of opioid peptide-containing neurons in the rat hypothalamus
By using a combined technique of immunocytochemistry and [ 3 H]thymidine autoradiography, we have determined the ābirth dateā of opioid pep-tide-containing neurons in several hypothalamic nuclei and regions. These include proopiomelanocortin (POMC) neurons (represented by ACTH immunoreactivity) in the arcuate nucleus; dynorphin A neurons in the supraoptic and paraventricular nuclei and the lateral hypothalamic area; and leuenkephalin neurons in the periventricular, ventromedial, and medial mammillary nuclei, as well as in preoptic and perifornical areas. Arcuate POMC neurons were born very early in embryonic development, with peak heavy [ 3 H]thymidine nuclear labelling occurring on embryonic day E12. Supraoptic and paraventricular dynorphin A neurons were also labelled relatively early (peak at E13). The lateral hypothalamic dynorphin A neurons showed peak heavy labelling also on day E12, By contrast, leu-enkephalin neurons in the periventricular nucleus and medial preoptic area exhibited peak heavy nuclear labelling on day E14. Furthermore, perifornical and ventromedial leu-enkephalin neurons were also born relatively early (peak on days E12 and E13, respectively). However, the leu-enkephalin neurons in the medial mammillary nucleus were born the latest of all cell groups studied (i.e., peak at E15). The results indicate a differential genesis of these opioid peptide-containing neuronal groups in different hypothalamic nuclei and regions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50027/1/902360409_ftp.pd
Formation of Planetary Populations II: Effects of Initial Disk Size & Radial Dust Drift
Recent ALMA observations indicate that while a range of disk sizes exist,
typical disk radii are small, and that radial dust drift affects the
distribution of solids in disks. Here we explore the consequences of these
features in planet population synthesis models. A key feature of our model is
planet traps - barriers to otherwise rapid type-I migration of forming planets
- for which we include the ice line, heat transition, and outer edge of the
dead zone. We find that the ice line plays a fundamental role in the formation
of warm Jupiters. In particular, the ratio of super Earths to warm Jupiters
formed at the ice line depend sensitively on the initial disk radius. Initial
gas disk radii of 50 AU results in the largest super Earth populations,
while both larger and smaller disk sizes result in the ice line producing more
gas giants near 1 AU. This transition between typical planet class formed at
the ice line at various disk radii confirms that planet formation is
fundamentally linked to disk properties (in this case, disk size), and is a
result that is only seen when dust evolution effects are included in our
models. Additionally, we find that including radial dust drift results in the
formation of more super Earths between 0.1 - 1 AU, having shorter orbital radii
than those produced in models where dust evolution effects are not included.Comment: 24 pages, 13 figures. Submitted to MNRAS; revised in response to
refere
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