15 research outputs found
Exposing the Gas Braking Mechanism of the beta Pictoris Disk
Ever since the discovery of the edge-on circumstellar disk around beta
Pictoris, a standing question has been why the gas observed against the star in
absorption is not rapidly expelled by the strong radiation pressure from the
star. A solution to the puzzle has been suggested to be that the neutral
elements that experience the radiation force also are rapidly ionized, and so
are only able to accelerate to an average limiting velocity v_ion. Once
ionized, the elements are rapidly braked by C II, which is observed to be at
least 20x overabundant in the disk with respect to other species. A prediction
from this scenario is that different neutral elements should reach different
v_ion, depending on the ionization thresholds and strengths of driving line
transitions. In particular, neutral Fe and Na are predicted to reach the radial
velocities 0.5 and 3.3 km/s, respectively, before being ionized. In this paper
we study the absorption profiles of Fe and Na from the circumstellar gas disk
around beta Pic, as obtained by HARPS at the ESO 3.6m telescope. We find that
the Fe and Na velocity profiles are indeed shifted with respect to each other,
confirming the model. The absence of an extended blue wing in the profile of
Na, however, indicates that there must be some additional braking on the
neutrals. We explore the possibility that the ion gas (dominated by C II) can
brake the neutrals, and conclude that about 2-5x more C than previously
estimated is needed for the predicted line profile to be consistent with the
observed one.Comment: Accepted by ApJ. 4 figs, 8 page
ALMA Resolves CI Emission from the beta Pictoris Debris Disk
The debris disk around ~Pictoris is known to contain gas. Previous
ALMA observations revealed a CO belt at 85 au with a distinct clump,
interpreted as a location of enhanced gas production. Photodissociation
converts CO into C and O within 50 years. We resolve CI emission at 492
GHz using ALMA and study its spatial distribution. CI shows the same clump as
seen for CO. This is surprising, as C is expected to quickly spread in azimuth.
We derive a low C mass (between and
M), indicating that gas production started only recently (within
5000 years). No evidence is seen for an atomic accretion disk inwards of
the CO belt, perhaps because the gas did not yet have time to spread radially.
The fact that C and CO share the same asymmetry argues against a previously
proposed scenario where the clump is due to an outward migrating planet
trapping planetesimals in an resonance; nor can the observations be explained
by an eccentric planetesimal belt secularly forced by a planet. Instead, we
suggest that the dust and gas disks should be eccentric. Such a configuration,
we further speculate, might be produced by a recent tidal disruption event.
Assuming that the disrupted body has had a CO mass fraction of 10%, its total
mass would be 3 .Comment: 30 pages, 15 figures, accepted by Ap
The surprisingly low carbon mass in the debris disk around HD 32297
Gas has been detected in a number of debris disks. It is likely secondary,
i.e. produced by colliding solids. Here, we report ALMA Band 8 observations of
neutral carbon in the CO-rich debris disk around the 15--30 Myr old A-type star
HD 32297. We find that C is located in a ring at 110 au with a FWHM
of 80 au, and has a mass of M.
Naively, such a surprisingly small mass can be accumulated from CO
photo-dissociation in a time as short as 10 yr. We develop a simple
model for gas production and destruction in this system, properly accounting
for CO self-shielding and shielding by neutral carbon, and introducing a
removal mechanism for carbon gas. We find that the most likely scenario to
explain both C and CO observations, is one where the carbon gas is rapidly
removed on a timescale of order a thousand years and the system maintains a
very high CO production rate of 15 M Myr, much higher
than the rate of dust grind-down. We propose a possible scenario to meet these
peculiar conditions: the capture of carbon onto dust grains, followed by rapid
CO re-formation and re-release. In steady state, CO would continuously be
recycled, producing a CO-rich gas ring that shows no appreciable spreading over
time. This picture might be extended to explain other gas-rich debris disks.Comment: accepted for publication in the Ap
Primordial or Secondary? Testing models of debris disk gas with ALMA
The origin and evolution of gas in debris disks is still not well understood.
Secondary gas production from cometary material or a primordial origin have
been proposed. So far, observations have mostly concentrated on CO, with only
few C observations available. We create an overview of the C and CO content of
debris disk gas and use it test state-of-the-art models. We use new and
archival ALMA observations of CO and CI emission, complemented by CII data from
Herschel, for a sample of 14 debris disks. This expands the number of disks
with ALMA measurements of both CO and CI by ten disks. We present new
detections of CI emission towards three disks: HD 21997, HD 121191 and HD
121617. We use a simple disk model to derive gas masses and column densities.
We find that current state-of-the-art models of secondary gas production
overpredict the neutral carbon content of debris disk gas. This does not rule
out a secondary origin, but might indicate that the models require an
additional C removal process. Alternatively, the gas might be produced in
transient events rather than a steady-state collisional cascade. We also test a
primordial gas origin by comparing our results to a simplified thermo-chemical
model. This yields promising results, but more detailed work is required before
a conclusion can be reached. Our work demonstrates that the combination of C
and CO data is a powerful tool to advance our understanding of debris disk gas.Comment: 90 pages, 60 figures. Accepted for publication in ApJ. version 2:
additional acknowledgement. versions 3, 4: minor edit
Discriminate alternative pluripotency states by means of Endogenous Retroviral Elements
International audienc
Investigating Tunneling Nanotubes in Cancer Cells: Guidelines for Structural and Functional Studies through Cell Imaging
CERVOXYInternational audienceBy allowing insured communication between cancer cells themselves and with the neighboring stromal cells, tunneling nanotubes (TNTs) are involved in the multistep process of cancer development from tumorigenesis to the treatment resistance. However, despite their critical role in the biology of cancer, the study of the TNTs has been announced challenging due to not only the absence of a specific biomarker but also the fragile and transitory nature of their structure and the fact that they are hovering freely above the substratum. Here, we proposed to review guidelines to follow for studying the structure and functionality of TNTs in tumoral neuroendocrine cells (PC12) and nontumorigenic human bronchial epithelial cells (HBEC-3, H28). In particular, we reported how crucial is it (i) to consider the culture conditions (culture surface, cell density), (ii) to visualize the formation of TNTs in living cells (mechanisms of formation, 3D representation), and (iii) to identify the cytoskeleton components and the associated elements (categories, origin, tip, and formation/transport) in the TNTs. We also focused on the input of high-resolution cell imaging approaches including Stimulated Emission Depletion (STED) nanoscopy, Transmitted and Scanning Electron Microscopies (TEM and SEM). In addition, we underlined the important role of the organelles in the mechanisms of TNT formation and transfer between the cancer cells. Finally, new biological models for the identification of the TNTs between cancer cells and stromal cells (liquid air interface, ex vivo, in vivo) and the clinical considerations will also be discussed
Momenta Biennale : Sensing Nature
" Sensing Nature, the title for the 17th edition of MOMENTA, can be read in multiple ways. On the one hand, it assumes a human who is sensing nature, perhaps holding a blueberry picked in a forest, exposed to various modes of perception: sight, smell, taste, hearing, and touch. None of us sense in the same way, and our diverse and differently abled bodies perceive and feel differently. On the other hand, the title assumes nature sensing back. Our doings register like sunlight bleaching the colour of driftwood over time or imprinting itself on the retina of an exposed eye. In acknowledging this reciprocity, the biennale works toward decentring the often- foregrounded European-Enlightenment human creator of knowl- edge concerning the natural world. It makes room for stories that dwell in the blurred boundaries between culture and nature, weaving in both human and nonhuman modes of knowing. Sensing Nature recognizes that we are in relation with nature, that we are of nature. " -- Publisher's website
Is RNASEL:p.Glu265* a modifier of early-onset breast cancer risk for carriers of high-risk mutations?
Abstract Background Breast cancer risk for BRCA1 and BRCA2 pathogenic mutation carriers is modified by risk factors that cluster in families, including genetic modifiers of risk. We considered genetic modifiers of risk for carriers of high-risk mutations in other breast cancer susceptibility genes. Methods In a family known to carry the high-risk mutation PALB2:c.3113G>A (p.Trp1038*), whole-exome sequencing was performed on germline DNA from four affected women, three of whom were mutation carriers. Results RNASEL:p.Glu265* was identified in one of the PALB2 carriers who had two primary invasive breast cancer diagnoses before 50 years. Gene-panel testing of BRCA1, BRCA2, PALB2 and RNASEL in the Australian Breast Cancer Family Registry identified five carriers of RNASEL:p.Glu265* in 591 early onset breast cancer cases. Three of the five women (60%) carrying RNASEL:p.Glu265* also carried a pathogenic mutation in a breast cancer susceptibility gene compared with 30 carriers of pathogenic mutations in the 586 non-carriers of RNASEL:p.Glu265* (5%) (p < 0.002). Taqman genotyping demonstrated that the allele frequency of RNASEL:p.Glu265* was similar in affected and unaffected Australian women, consistent with other populations. Conclusion Our study suggests that RNASEL:p.Glu265* may be a genetic modifier of risk for early-onset breast cancer predisposition in carriers of high-risk mutations. Much larger case-case and case-control studies are warranted to test the association observed in this report