18 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
Connecting planet formation and astrochemistry: Refractory carbon depletion leading to super-stellar C/O in giant planetary atmospheres
[Abridged] Combining a time-dependent astrochemical model with a model of
planet formation and migration, we compute the carbon-to-oxygen ratio (C/O) of
a range of planetary embryos starting their formation in the inner solar system
(1-3 AU). The volatile and ice abundance of relevant carbon and oxygen bearing
molecular species are determined through a complex chemical kinetic code which
includes both gas and grain surface chemistry. This is combined with a model
for the abundance of the refractory dust grains to compute the total carbon and
oxygen abundance in the protoplanetary disk available for incorporation into a
planetary atmosphere. We include the effects of the refractory carbon depletion
that has been observed in our solar system, and posit two models that would put
this missing carbon back into the gas phase. This excess gaseous carbon then
becomes important in determining the final planetary C/O because the gas disk
now becomes more carbon rich relative to oxygen (high gaseous C/O). One model,
where the carbon excess is maintained throughout the lifetime of the disk
results in Hot Jupiters that have super-stellar C/O. The other model deposits
the excess carbon early in the disk life and allows it to advect with the bulk
gas. In this model the excess carbon disappears into the host star within 0.8
Myr, returning the gas disk to its original (sub-stellar) C/O, so the Hot
Jupiters all exclusively have sub-stellar C/O. This shows that while the solids
will tend to be oxygen rich, Hot Jupiters can have super-stellar C/O if a
carbon excess can be maintained by some chemical processing of the dust grains.
Whether the carbon and oxygen content of the atmosphere was accreted primarily
by gas or solid accretion is heavily dependent on the mass of the atmosphere
and where in the disk the growing planet accreted.Comment: 13 pages, 7 figures, resubmitted to A&A after referee's comment
Vertical gas accretion impacts the carbon-to-oxygen ratio of gas giant atmospheres
Recent theoretical, numerical, and observational work have suggested that
when a growing planet opens a gap in its disk the flow of gas into the gap is
dominated by gas falling vertically from a height of at least one gas scale
height. Our primary objective is to include, for the first time, the chemical
impact that accreting gas above the midplane will have on the resulting C/O. We
compute the accretion of gas onto planetary cores beginning at different disk
radii and track the chemical composition of the gas and small icy grains to
predict the resulting carbon-to-oxygen ratio (C/O) in their atmospheres. In our
model, all of the planets which began their evolution inward of 60 AU open a
gap in the gas disk, and hence are chemically affected by the vertically
accreting gas. Two important conclusions follow from this vertical flow: (1)
more oxygen rich icy dust grains become available for accretion onto the
planetary atmosphere. (2) The chemical composition of the gas dominates the
final C/O of planets in the inner ( 20 AU) part of the disk. This implies
that with the launch of the James Webb Space Telescope we can trace the disk
material that sets the chemical composition of exoplanetary atmospheres.Comment: Accepted for publication in A&
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
Single-nucleus transcriptomes reveal evolutionary and functional properties of cell types in the Drosophila accessory gland.
Many traits responsible for male reproduction evolve quickly, including gene expression phenotypes in germline and somatic male reproductive tissues. Rapid male evolution in polyandrous species is thought to be driven by competition among males for fertilizations and conflicts between male and female fitness interests that manifest in postcopulatory phenotypes. In Drosophila, seminal fluid proteins secreted by three major cell types of the male accessory gland and ejaculatory duct are required for female sperm storage and use, and influence female postcopulatory traits. Recent work has shown that these cell types have overlapping but distinct effects on female postcopulatory biology, yet relatively little is known about their evolutionary properties. Here, we use single-nucleus RNA-Seq of the accessory gland and ejaculatory duct from Drosophila melanogaster and two closely related species to comprehensively describe the cell diversity of these tissues and their transcriptome evolution for the first time. We find that seminal fluid transcripts are strongly partitioned across the major cell types, and expression of many other genes additionally defines each cell type. We also report previously undocumented diversity in main cells. Transcriptome divergence was found to be heterogeneous across cell types and lineages, revealing a complex evolutionary process. Furthermore, protein adaptation varied across cell types, with potential consequences for our understanding of selection on male postcopulatory traits
Population biology of accessory gland-expressed de novo genes in Drosophila melanogaster.
Early work on de novo gene discovery in Drosophila was consistent with the idea that many such genes have male-biased patterns of expression, including a large number expressed in the testis. However, there has been little formal analysis of variation in the abundance and properties of de novo genes expressed in different tissues. Here, we investigate the population biology of recently evolved de novo genes expressed in the Drosophila melanogaster accessory gland, a somatic male tissue that plays an important role in male and female fertility and the post mating response of females, using the same collection of inbred lines used previously to identify testis-expressed de novo genes, thus allowing for direct cross tissue comparisons of these genes in two tissues of male reproduction. Using RNA-seq data, we identify candidate de novo genes located in annotated intergenic and intronic sequence and determine the properties of these genes including chromosomal location, expression, abundance, and coding capacity. Generally, we find major differences between the tissues in terms of gene abundance and expression, though other properties such as transcript length and chromosomal distribution are more similar. We also explore differences between regulatory mechanisms of de novo genes in the two tissues and how such differences may interact with selection to produce differences in D. melanogaster de novo genes expressed in the two tissues