425 research outputs found
Did Fomalhaut, HR 8799, and HL Tauri Form Planets via the Gravitational Instability? Placing Limits on the Required Disk Masses
Disk fragmentation resulting from the gravitational instability has been
proposed as an efficient mechanism for forming giant planets. We use the planet
Fomalhaut b, the triple-planetary system HR 8799, and the potential protoplanet
associated with HL Tau to test the viability of this mechanism. We choose the
above systems since they harbor planets with masses and orbital characteristics
favored by the fragmentation mechanism. We do not claim that these planets must
have formed as the result of fragmentation, rather the reverse: if planets can
form from disk fragmentation, then these systems are consistent with what we
should expect to see. We use the orbital characteristics of these recently
discovered planets, along with a new technique to more accurately determine the
disk cooling times, to place both lower and upper limits on the disk surface
density--and thus mass--required to form these objects by disk fragmentation.
Our cooling times are over an order of magnitude shorter than those of Rafikov
(2005),which makes disk fragmentation more feasible for these objects. We find
that the required mass interior to the planet's orbital radius is ~0.1 Msun for
Fomalhaut b, the protoplanet orbiting HL Tau, and the outermost planet of HR
8799. The two inner planets of HR 8799 probably could not have formed in situ
by disk fragmentation.Comment: 5 pages, 1 figure, accepted for publication in ApJ
Geodynamics and Rate of Volcanism on Massive Earth-like Planets
We provide estimates of volcanism versus time for planets with Earth-like
composition and masses from 0.25 to 25 times Earth, as a step toward predicting
atmospheric mass on extrasolar rocky planets. Volcanism requires melting of the
silicate mantle. We use a thermal evolution model, calibrated against Earth, in
combination with standard melting models, to explore the dependence of
convection-driven decompression mantle melting on planet mass. Here we show
that (1) volcanism is likely to proceed on massive planets with plate tectonics
over the main-sequence lifetime of the parent star; (2) crustal thickness (and
melting rate normalized to planet mass) is weakly dependent on planet mass; (3)
stagnant lid planets live fast (they have higher rates of melting than their
plate tectonic counterparts early in their thermal evolution) but die young
(melting shuts down after a few Gyr); (4) plate tectonics may not operate on
high mass planets because of the production of buoyant crust which is difficult
to subduct; and (5) melting is necessary but insufficient for efficient
volcanic degassing - volatiles partition into the earliest, deepest melts,
which may be denser than the residue and sink to the base of the mantle on
young, massive planets. Magma must also crystallize at or near the surface, and
the pressure of overlying volatiles must be fairly low, if volatiles are to
reach the surface. If volcanism is detected in the Tau Ceti system, and tidal
forcing can be shown to be weak, this would be evidence for plate tectonics.Comment: Revised version, accepted by Astrophysical Journa
Evolutionary Tracks of Trapped, Accreting Protoplanets: the Origin of the Observed Mass-Period Relation
The large number of observed exoplanets ( 700) provides important
constraints on their origin as deduced from the mass-period diagram of planets.
The most surprising features in the diagram are 1) the (apparent) pile up of
gas giants at a period of days ( AU) and 2) the so-called
mass-period relation which indicates that planetary mass is an increasing
function of orbital period. We construct the evolutionary tracks of growing
planets at planet traps in evolving protoplanetary disks and show that they
provide a good physical understanding of how these observational properties
arise. The fundamental feature of our model is that inhomogeneities in
protoplanetary disks give rise to multiple (up to 3) trapping sites for rapid
(type I) planetary migration of planetary cores. The viscous evolution of disks
results in the slow radial movement of the traps and their cores from large to
small orbital periods. In our model, the slow inward motion of planet traps is
coupled with the standard core accretion scenario for planetary growth. As
planets grow, type II migration takes over. Planet growth and radial movement
are ultimately stalled by the dispersal of gas disks via photoevaporation. Our
model makes a number of important predictions: that distinct sub-populations of
planets that reflect the properties of planet traps where they have grown
result in the mass-period relation; that the presence of these sub-populations
naturally explains a pile-up of planets at AU; and that evolutionary
tracks from the ice line do put planets at short periods and fill an earlier
claimed "planet desert" - sparse population of planets in the mass-semi-major
axis diagram.Comment: 20 pages, 11 figures, 9 tables; accepted for publication in ApJ. No
change in our conclusions while more discussion is added for supporting the
importance of planet trap
The Growth & Migration of Jovian Planets in Evolving Protostellar Disks with Dead Zones
The growth of Jovian mass planets during migration in their protoplanetary
disks is one of the most important problems that needs to be solved in light of
observations of the exosolar planets. Studies of the migration of planets in
standard gas disk models routinely show that migration is too fast to form
Jovian planets, and that such migrating planetary cores generally plunge into
the central stars in less than a Myr. In previous work, we have shown that a
poorly ionized, less viscous region in a protoplanetary disk called a dead zone
slows down the migration of fixed-mass planets. In this paper, we extend our
numerical calculations to include dead zone evolution along with the disk, as
well as planet formation via accretion of rocky and gaseous materials. Using
our symplectic-integrator-gas dynamics code, we find that dead zones, even in
evolving disks wherein migrating planets grow by accretion, still play a
fundamental role in saving planetary systems. We demonstrate that Jovian
planets form within 2.5 Myr for disks that are ten times more massive than a
minimum mass solar nebula (MMSN) with an opacity reduction and without slowing
down migration artificially. Our simulations indicate that protoplanetary disks
with an initial mass comparable to the MMSN only produce Neptunian mass
planets. We also find that planet migration does not help core accretion as
much in the oligarchic planetesimal accretion scenario as it was expected in
the runaway accretion scenario. Therefore we expect that an opacity reduction
(or some other mechanisms) is needed to solve the formation timescale problem
even for migrating protoplanets, as long as we consider the oligarchic growth.
We also point out a possible role of a dead zone in explaining long-lived,
strongly accreting gas disks.Comment: 16 pages, 15 figures, accepted for publication in Ap
Association of serum osteoprotegerin with vascular calcification in patients with type 2 diabetes
ESPRESSO Mass determination of TOI-263b: An extreme inhabitant of the brown dwarf desert
The TESS mission has reported a wealth of new planetary systems around bright
and nearby stars amenable for detailed characterization of the planet
properties and their atmospheres. However, not all interesting TESS planets
orbit around bright host stars. TOI-263b is a validated ultra-short period
substellar object in a 0.56-day orbit around a faint (V=18.97) M3.5 dwarf star.
The substellar nature of TOI-263b was explored using multi-color photometry,
which determined a true radius of 0.87+-0.21 Rj, establishing TOI-263b's nature
ranging from an inflated Neptune to a brown dwarf. The orbital period-radius
parameter space occupied by TOI-263b is quite unique, which prompted a further
characterization of its true nature. Here, we report radial velocity
measurements of TOI-263 obtained with 3 VLT units and the ESPRESSO spectrograph
to retrieve the mass of TOI-263b. We find that TOI-263b is a brown dwarf with a
mass of 61.6+-4.0 Mj. Additionally, the orbital period of the brown dwarf is
found to be synchronized with the rotation period of the host star, and the
system is found to be relatively active, possibly revealing a star--brown dwarf
interaction. All these findings suggest that the system's formation history
might be explained via disc fragmentation and later migration to close-in
orbits. If the system is found to be unstable, TOI-263 is an excellent target
to test the migration mechanisms before the brown dwarf becomes engulfed by its
parent star.Comment: Accepted for Publication in Astronomy and Astrophysic
Mutational Profile and Pathological Features of a Case of Interleukin-10 and RGS1-Positive Spindle Cell Variant Diffuse Large B-Cell Lymphoma
Diffuse large B-cell lymphoma with spindle cell morphology is a rare variant. We present the case of a 74-year-old male who initially presented with a right supraclavicular (lymph) node enlargement. Histological analysis showed a proliferation of spindle-shaped cells with narrow cytoplasms. An immunohistochemical panel was used to exclude other tumors, such as melanoma, carcinoma, and sarcoma. The lymphoma was characterized by a cell-of-origin subtype of germinal center B-cell-like (GCB) based on Hans’ classifier (CD10-negative, BCL6-positive, and MUM1-negative); EBER negativity, and the absence of BCL2, BCL6, and MYC rearrangements. Mutational profiling using a custom panel of 168 genes associated with aggressive B-cell lymphomas confirmed mutations in ACTB, ARID1B, DUSP2, DTX1, HLA-B, PTEN, and TNFRSF14. Based on the LymphGen 1.0 classification tool, this case had an ST2 subtype prediction. The immune microenvironment was characterized by moderate infiltration of M2-like tumor-associated macrophages (TMAs) with positivity of CD163, CSF1R, CD85A (LILRB3), and PD-L1; moderate PD-1 positive T cells, and low FOXP3 regulatory T lymphocytes (Tregs). Immunohistochemical expression of PTX3 and TNFRSF14 was absent. Interestingly, the lymphoma cells were positive for HLA-DP-DR, IL-10, and RGS1, which are markers associated with poor prognosis in DLBCL. The patient was treated with R-CHOP therapy, and achieved a metabolically complete response
Discovering the Growth Histories of Exoplanets: The Saturn Analog HD 149026b
The transiting "hot Saturn" HD 149026b, which has the highest mean density of
any confirmed planet in the Neptune-Jupiter mass range, has challenged theories
of planet formation since its discovery in 2005. Previous investigations could
not explain the origin of the planet's 45-110 Earth-mass solid core without
invoking catastrophes such as gas giant collisions or heavy planetesimal
bombardment launched by neighboring planets. Here we show that HD 149026b's
large core can be successfully explained by the standard core accretion theory
of planet formation. The keys to our reconstruction of HD 149026b are (1)
applying a model of the solar nebula to describe the protoplanet nursery; (2)
placing the planet initially on a long-period orbit at Saturn's heliocentric
distance of 9.5 AU; and (3) adjusting the solid mass in the HD 149026 disk to
twice that of the solar nebula in accordance with the star's heavy element
enrichment. We show that the planet's migration into its current orbit at 0.042
AU is consistent with our formation model. Our study of HD 149026b demonstrates
that it is possible to discover the growth history of any planet with a
well-defined core mass that orbits a solar-type star.Comment: 20 pages, including 3 figures. Accepted for publication in ApJ
letters. Discussion updated to include new NICMOS transit photometry (Carter
et al. 2009
Sclerosing mesenteritis affecting the small and the large intestine in a male patient with non-Hodgkin lymphoma: a case presentation and review of the literature
<p>Abstract</p> <p>Introduction</p> <p>Sclerosing mesenteritis is a rare disease resembling a mesenteric tumour. We present here a case of sclerosing mesenteritis that affected both the large and the small intestine of the patient. Therapeutic and diagnostic issues are discussed.</p> <p>Case presentation</p> <p>A 62-year-old man with a history of non-Hodgkin lymphoma presented with fatigue, a palpable tender abdominal mass and clinical signs of progressing intestinal obstruction. The preoperative evaluation failed to prove recurrence of the lymphoma or any other definite diagnosis. A laparotomy was performed through a midline incision. The mesentery resembled a tumour-like thickened and fibrotic mass. Abundant, rigid intestinal loop adhesions were observed. Diffuse fibrotic infiltration of the ileum and of the sigmoid colon, which obviously affected the intestinal vascular supply, were identified. A right colectomy and partial sigmoidectomy were performed. Pathological evaluation revealed extensive myofibroblastic reaction of the mesentery with accompanying loci of fat necrosis and areas of inflammation. A diffuse fibrotic infiltration that focally showed a ground-glass appearance was observed. The post-operative course was complicated by respiratory insufficiency and infections and the patient died 2 months after the operation.</p> <p>Conclusion</p> <p>Sclerosing mesenteritis that affects both the small and the large intestine is extremely rare. The disease is characterized by myofibroblastic reaction, fat necrosis and diffuse fibrosis of the mesentery. Pathological confirmation may be required for definite diagnosis. If the disease is characterized by severe and diffuse fibrosis, then the application of surgical therapy may be problematic.</p
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
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