264 research outputs found
Relative velocities among accreting planetesimals in binary systems: the circumprimary case
We investigate classical planetesimal accretion in a binary star system of
separation ab<50AU by numerical simulations, with particular focus on the
region at a distance of 1 AU from the primary. The planetesimals orbit the
primary, are perturbed by the companion and are in addition subjected to a gas
drag force. We concentrate on the problem of relative velocities dv among
planetesimals of different sizes. For various stellar mass ratios and binary
orbital parameters we determine regions where dv exceed planetesimal escape
velocities v_esc (thus preventing runaway accretion) or even the threshold
velocity v_ero for which erosion dominates accretion. Gaseous friction has two
crucial effects on the velocity distribution: it damps secular perturbations by
forcing periastron alignment of orbits, but at the same time the
size--dependence of this orbital alignment induces a significant dv increase
between bodies of different sizes. This differential phasing effect proves very
efficient and almost always increases dv to values preventing runaway
accretion, except in a narrow domain of almost circular companion orbits. The
erosion threshold dv>v_ero is reached in a wide (ab,eb) space for small (<10km)
planetesimals, but in a much more limited region for bigger ~50km objects. In
the intermediate v_esc<dv < v_ero domain, a possible growth mode would be the
type II runaway growth identified by Kortenkmap et al.(2001)Comment: to appear in Icarus (accepted 30 january 2006
Planet formation in Binaries
Spurred by the discovery of numerous exoplanets in multiple systems, binaries
have become in recent years one of the main topics in planet formation
research. Numerous studies have investigated to what extent the presence of a
stellar companion can affect the planet formation process. Such studies have
implications that can reach beyond the sole context of binaries, as they allow
to test certain aspects of the planet formation scenario by submitting them to
extreme environments. We review here the current understanding on this complex
problem. We show in particular how each of the different stages of the
planet-formation process is affected differently by binary perturbations. We
focus especially on the intermediate stage of kilometre-sized planetesimal
accretion, which has proven to be the most sensitive to binarity and for which
the presence of some exoplanets observed in tight binaries is difficult to
explain by in-situ formation following the "standard" planet-formation
scenario. Some tentative solutions to this apparent paradox are presented. The
last part of our review presents a thorough description of the problem of
planet habitability, for which the binary environment creates a complex
situation because of the presence of two irradation sources of varying
distance.Comment: Review chapter to appear in "Planetary Exploration and Science:
Recent Advances and Applications", eds. S. Jin, N. Haghighipour, W.-H. Ip,
Springer (v2, numerous typos corrected
Eccentricity of radiative discs in close binary-star systems
Discs in binaries have a complex behavior because of the perturbations of the
companion star. Planet formation in binary-star systems both depend on the
companion star parameters and on the properties of the circumstellar disc. An
eccentric disc may increase the impact velocity of planetesimals and therefore
jeopardize the accumulation process. We model the evolution of discs in close
binaries including the effects of self-gravity and adopting different
prescriptions to model the disc's radiative properties. We focus on the
dynamical properties and evolutionary tracks of the discs. We use the
hydrodynamical code FARGO and we include in the energy equation heating and
cooling effects. Radiative discs have a lower disc eccentricity compared to
locally isothermal discs with same temperature profile. As a consequence, we do
not observe the formation of an internal elliptical low density region as in
locally isothermal disc models. However, the disc eccentricity depends on the
disc mass through the opacities. Akin to locally isothermal disc models,
self-gravity forces the disc's longitude of pericenter to librate about a fixed
orientation with respect to the binary apsidal line (). The disc's
radiative properties play an important role in the evolution of discs in
binaries. A radiative disc has an overall shape and internal structure that are
significantly different compared to a locally isothermal disc with same
temperature profile. This is an important finding both for describing the
evolutionary track of the disc during its progressive mass loss, and for planet
formation since the internal structure of the disc is relevant for
planetesimals growth in binary systems. The non-symmetrical distribution of
mass in these discs causes large eccentricities for planetesimals that may
affect their growth.Comment: accepted for publication in A&A (abstract truncated to comply with
astro-ph rules
Silver nanoparticle embedded copper oxide as an efficient core–shell for the catalytic reduction of 4-nitrophenol and antibacterial activity improvement
International audienc
Against all odds? Forming the planet of the HD196885 binary
HD196885Ab is the most "extreme" planet-in-a-binary discovered to date, whose
orbit places it at the limit for orbital stability. The presence of a planet in
such a highly perturbed region poses a clear challenge to planet-formation
scenarios. We investigate this issue by focusing on the planet-formation stage
that is arguably the most sensitive to binary perturbations: the mutual
accretion of kilometre-sized planetesimals. To this effect we numerically
estimate the impact velocities amongst a population of circumprimary
planetesimals. We find that most of the circumprimary disc is strongly hostile
to planetesimal accretion, especially the region around 2.6AU (the planet's
location) where binary perturbations induce planetesimal-shattering of
more than 1km/s. Possible solutions to the paradox of having a planet in such
accretion-hostile regions are 1) that initial planetesimals were very big, at
least 250km, 2) that the binary had an initial orbit at least twice the present
one, and was later compacted due to early stellar encounters, 3) that
planetesimals did not grow by mutual impacts but by sweeping of dust (the
"snowball" growth mode identified by Xie et al., 2010b), or 4) that HD196885Ab
was formed not by core-accretion but by the concurent disc instability
mechanism. All of these 4 scenarios remain however highly conjectural.Comment: accepted for publication by Celestial Mechanics and Dynamical
Astronomy (Special issue on EXOPLANETS
Chasing extreme planetary architectures: I- HD196885Ab, a super-Jupiter dancing with two stars?
Planet(s) in binaries are unique architectures for testing predictions of
planetary formation and evolution theories in very hostile environments. We
used the IRDIS dual-band imager of SPHERE at VLT, and the speckle
interferometric camera HRCAM of SOAR, to acquire high-angular resolution images
of HD 196885 AB between 2015 and 2020. Radial velocity observations have been
extended over almost 40 yr extending the radial velocity measurements HD 196885
A and resolving both the binary companion and the inner giant planet HD 196885
Ab. Finally, we took advantage of the exquisite astrometric precision of the
dual-field mode of VLTI/GRAVITY (down to 30 {\mu}as) to monitor the relative
position of HD 196885 A and B to search for the 3.6 yr astrometric wobble of
the circumprimary planet Ab imprinted on the binary separation. Our
observations enable to accurately constrain the orbital properties of the
binary HD 196885 AB, seen on an inclined and retrograde orbit (iAB = 120.43
deg) with a semi-major axis of 19.78 au, and an eccentricity of 0.417. The
GRAVITY measurements confirm for the first time the nature of the inner planet
HD 196885 Ab by rejecting all families of pole-on solutions in the stellar or
brown dwarf masses. The most favored island of solutions is associated with a
Jupiter-like planet (MAb = 3.39 MJup), with moderate eccentricity (eAaAb =
0.44), and inclination close to 143.04 deg. This results points toward a
significant mutual inclination (Phi = 24.36 deg) between the orbital planes
(relative to the star) of the binary companion B and the planet Ab. Our
dynamical simulations indicate that the system is dynamically stable over time.
Eccentricity and mutual inclination variations could be expected for moderate
von Zipele Kozai Lidov cycles that may affect the inner planet.Comment: 12 pages, 6 figures, accepted in A&
Expression of TRPC6 channels in human epithelial breast cancer cells
<p>Abstract</p> <p>Background</p> <p>TRP channels have been shown to be involved in tumour generation and malignant growth. However, the expression of these channels in breast cancer remains unclear. Here we studied the expression and function of endogenous TRPC6 channels in a breast cancer cell line (MCF-7), a human breast cancer epithelial primary culture (hBCE) and in normal and tumour breast tissues.</p> <p>Methods</p> <p>Molecular (Western blot and RT-PCR), and immunohistochemical techniques were used to investigate TRPC6 expression. To investigate the channel activity in both MCF-7 cells and hBCE we used electrophysiological technique (whole cell patch clamp configuration).</p> <p>Results</p> <p>A non selective cationic current was activated by the oleoyl-2-acetyl-sn-glycerol (OAG) in both hBCE and MCF-7 cells. OAG-inward current was inhibited by 2-APB, SK&F 96365 and La<sup>3+</sup>. TRPC6, but not TRPC7, was expressed both in hBCE and in MCF-7 cells. TRPC3 was only expressed in hBCE. Clinically, TRPC6 mRNA and protein were elevated in breast carcinoma specimens in comparison to normal breast tissue. Furthermore, we found that the overexpression of TRPC6 protein levels were not correlated with tumour grades, estrogen receptor expression or lymph node positive tumours.</p> <p>Conclusion</p> <p>Our results indicate that TRPC6 channels are strongly expressed and functional in breast cancer epithelial cells. Moreover, the overexpression of these channels appears without any correlation with tumour grade, ER expression and lymph node metastasis. Our findings support the idea that TRPC6 may have a role in breast carcinogenesis.</p
Circumstellar discs: What will be next?
This prospective chapter gives our view on the evolution of the study of
circumstellar discs within the next 20 years from both observational and
theoretical sides. We first present the expected improvements in our knowledge
of protoplanetary discs as for their masses, sizes, chemistry, the presence of
planets as well as the evolutionary processes shaping these discs. We then
explore the older debris disc stage and explain what will be learnt concerning
their birth, the intrinsic links between these discs and planets, the hot dust
and the gas detected around main sequence stars as well as discs around white
dwarfs.Comment: invited review; comments welcome (32 pages
- …