Context. Age estimation techniques such as gyrochronology and magnetochronology cannot be applied to stars that have exchanged angular momentum with their close environments. This is especially true ...for a massive close-in planetary companion (with a period of a few days or less) that could have been strongly impacted by the rotational evolution of the host star, throughout the stellar evolution, through the star-planet tidal interaction. Aims. In this article, we provide the community with a reliable region in which empirical techniques such as gyrochronology can be used with confidence. Methods. We combined a stellar angular momentum evolution code with a planetary orbital evolution code to study in detail the impact of star-planet tidal interaction on the evolution of the surface rotation rate of the star. Results. We show that the interaction of a close-in massive planet with its host star can strongly modify the surface rotation rate of this latter, in most of the cases associated with a planetary engulfment. A modification of the surface rotation period of more than 90% can survive a few hundred Myr after the event and a modification of 10% can last for a few Gyr. In such cases, a gyrochronology analysis of the star would incorrectly make it appear as rejuvenated, thus preventing us from using this method with confidence. To try overcome this issue, we proposed the proof of concept of a new age determination technique that we call the tidal-chronology method, which is based on the observed pair Prot, ⋆–Porb of a given star-planet system, where Prot, ⋆ is the stellar surface rotational period and Porb the planetary orbital period. Conclusions. The gyrochronology technique can only be applied to isolated stars or star-planet systems outside a specific range of Prot, ⋆–Porb. This region tends to expand for increasing stellar and planetary mass. In that forbidden region, or if any planetary engulfment is suspected, gyrochronology should be used with extreme caution, while tidal-chronology could be considered. This technique does not provide a precise age for the system yet; however, it is already an extension of gyrochronology and could be helpful to determine a more precise range of possible ages for planetary systems composed of a star between 0.3 and 1.2 M⊙ and a planet more massive than 1 Mjup initially located at a few hundredths of au from the host star.
Context. The consortium of the Spectro-Polarimetric High-contrast Exoplanet REsearch installed at the Very Large Telescope (SPHERE/VLT) has been operating its guaranteed observation time (260 nights ...over five years) since February 2015. The main part of this time (200 nights) is dedicated to the detection and characterization of young and giant exoplanets on wide orbits. Aims. The large amount of data must be uniformly processed so that accurate and homogeneous measurements of photometry and astrometry can be obtained for any source in the field. Methods. To complement the European Southern Observatory pipeline, the SPHERE consortium developed a dedicated piece of software to process the data. First, the software corrects for instrumental artifacts. Then, it uses the speckle calibration tool (SpeCal) to minimize the stellar light halo that prevents us from detecting faint sources like exoplanets or circumstellar disks. SpeCal is meant to extract the astrometry and photometry of detected point-like sources (exoplanets, brown dwarfs, or background sources). SpeCal was intensively tested to ensure the consistency of all reduced images (cADI, Loci, TLoci, PCA, and others) for any SPHERE observing strategy (ADI, SDI, ASDI as well as the accuracy of the astrometry and photometry of detected point-like sources. Results. SpeCal is robust, user friendly, and efficient at detecting and characterizing point-like sources in high contrast images. It is used to process all SPHERE data systematically, and its outputs have been used for most of the SPHERE consortium papers to date. SpeCal is also a useful framework to compare different algorithms using various sets of data (different observing modes and conditions). Finally, our tests show that the extracted astrometry and photometry are accurate and not biased.
Sand patches are one of the precursors to early stage protodunes and occur widely in both desert and coastal aeolian environments. Here we show field evidence of a mechanism to explain the initiation ...of sand patches on non‐erodible surfaces, such as desert gravels and moist beaches. Changes in sand transport dynamics, directly associated with the height of the saltation layer and variable transport law, observed at the boundary between non‐erodible and erodible surfaces lead to sand deposition on the erodible surface. This explains how sand patches can form on surfaces with limited sand availability where linear stability of dune theory does not apply. This new mechanism is supported by field observations that evidence both the change in transport rate over different surfaces and in situ patch formation that leads to modification of transport dynamics at the surface boundary.
Plain Language Summary
Sand patches can be observed in various environments such as beaches and gravel plains in deserts. Expected to be precursors of dunes when sediment supply is limited, these bedforms are typically a few centimeters high and present a reverse longitudinal elevation profile, with a sharp upwind edge and a smooth downwind tail. Based on field measurements, we propose a formation mechanism for these patches associated with the sensitive nature of wind‐blown sand transport to changing bed conditions: sand saltation is reduced at the transition from a solid to an erodible surface, hence favoring deposition on the patches. This allows us to explain their typical meter‐scale length as well as their asymmetric shapes.
Key Points
Sand patches can emerge on non‐erodible surfaces
Differing surfaces characteristics control particle behavior
Field measurements demonstrate the key role of sand transport in bedform initiation
The frequency of severe postpartum haemorrhage did not differ between cephalad-caudad and transverse blunt expansion hysterotomy. Transverse blunt expansion hysterotomy may be associated with ...additional sutures after repair of the hysterotomy..
•Caesarean section is a common method of delivery worldwide, accounting for up to 45% of births in some countries.•Caesarean section remains a major cause of maternal morbidity, particularly postpartum haemorrhage (PPH).•The incidence of PPH is higher for caesarean section than vaginal delivery, ranging from 3% to 15%.•As far as the surgical technique is concerned, French guidelines recommend performing blunt expansion of the low transverse hysterotomy with fingers rather than scissors to reduce bleeding.•The preferences for transverse or cephalad-caudal blunt expansion hysterotomy of the low transverse uterine incision during caesarean section differs between countries.
The global prevalence of caesarean section as a delivery method is increasing worldwide. However, there is notable divergence among countries in their national guidelines regarding the optimal technique for blunt expansion hysterotomy of the low transverse uterine incision during caesarean section (cephalad-caudad or transverse).
To compare the risk of severe postpartum haemorrhage (PPH) between cephalad-caudad and transverse blunt expansion hysterotomy during caesarean section.
This prospective comparative observational study was conducted in a university maternity hospital. All women who gave birth to one infant by caesarean section after 30 weeks of gestation between November 2020 and November 2021 were included in this study. The exclusion criteria were a coagulation disorder, the presence of placenta previa, multiple pregnancies, or enlargement of the hysterotomy with scissors. The choice between cephalad-caudad or transverse blunt expansion of the low transverse hysterotomy was left to the surgeon’s discretion. The primary outcome measure was severe PPH, defined as estimated blood loss ≥ 1000 ml. Univariate and multivariate analyses were employed to assess the risk of severe PPH associated with the two methods of enlarging the low transverse hysterotomy.
The study included 850 women, of whom 404 underwent transverse blunt expansion and 446 underwent cephalad-caudad blunt expansion. The overall incidence of severe PPH was 13.3 %. Univariate analysis revealed no significant difference in the frequency of severe PPH between the cephalad-caudad and transverse blunt expansion groups (13.9 % vs 12.6 %; p = 0.61). However, the use of additional surgical sutures (mainly additional haemostatic stitches) was less common with cephalad-caudad blunt expansion (26.7 % vs 36.9 %; p < 0.05). Multivariate analysis showed no significant difference in risk between the two techniques (odds ratio 1.17, 95 % confidence interval 0.77–1.78).
No significant difference in the risk of severe PPH was found between cephalad-caudad and transverse blunt expansion of the low transverse hysterotomy during caesarean section.
We present the results of photometric surveys for stellar rotation in the Hyades and in Praesepe, using data obtained as part of the SuperWASP exoplanetary transit-search programme. We determined ...accurate rotation periods for more than 120 sources whose cluster membership was confirmed by common proper motion and colour-magnitude fits to the clusters' isochrones. This allowed us to determine the effect of magnetic braking on a wide range of spectral types for expected ages of ∼600 Myr for the Hyades and Praesepe. Both clusters show a tight and nearly linear relation between J−K
s colour and rotation period in the F, G and K spectral range. This confirms that loss of angular momentum was significant enough that stars with strongly different initial rotation rates have converged to the same rotation period for a given mass, by the ages of Hyades and Praesepe. In the case of the Hyades, our colour-period sequence extends well into the M dwarf regime and shows a steep increase in the scatter of the colour-period relation, with identification of numerous rapid rotators from ∼0.5 M⊙ down to the lowest masses probed by our survey (∼0.25 M⊙). This provides crucial constraints on the rotational braking time-scales and further clears the way to use gyrochronology as an accurate age measurement tool for main-sequence stars.
Aims. To understand planet formation it is necessary to study the birth environment of planetary systems. Resolved imaging of young planet forming disks allows us to study this environment in great ...detail and find signs of planet-disk interaction and disk evolution. In the present study we aim to investigate the circumstellar environment of the spectroscopic binary T Tauri star CS Cha. From unresolved mid-to far-infrared photometry it is predicted that CS Cha hosts a disk with a large cavity. In addition, spectral energy distribution modeling suggests significant dust settling, pointing toward an evolved disk that may show signs of ongoing or completed planet formation. Methods. We observed CS Cha with the high contrast imager SPHERE at the ESO Very Large Telescope (VLT) in polarimetric differential imaging mode to resolve the circumbinary disk in near-infrared scattered light. These observations were followed up by VLT/NACO L-band observations and complemented by archival VLT/NACO K-band and Hubble Space Telescope WFPC2 I-band data. Results. We resolve the compact circumbinary disk around CS Cha for the first time in scattered light. We find a smooth, low inclination disk with an outer radius of ~55 au (at 165 pc). We do not detect the inner cavity but find an upper limit for the cavity size of ~15 au. Furthermore, we find a faint comoving companion with a projected separation of 210 au from the central binary outside of the circumbinary disk. The companion is detected in polarized light and shows an extreme degree of polarization (13.7 ± 0.4% in the J band). The J- and H-band magnitudes of the companion are compatible with masses of a few MJup. However, K-, L-, and I-band data draw this conclusion into question. We explore with radiative transfer modeling whether an unresolved circum-companion disk can be responsible for the high polarization and complex photometry. We find that the set of observations is best explained by a heavily extincted low-mass (~20 MJup) brown dwarf or high-mass planet with an unresolved disk and dust envelope.
ABSTRACT
Radial substructure in the form of rings and gaps has been shown to be ubiquitous among protoplanetary discs. This could be the case in exo-Kuiper belts as well, and evidence for this is ...emerging. In this paper, we present ALMA observations of the debris/planetesimal disc surrounding HD 206893, a system that also hosts two massive companions at 2 and 11 au. Our observations reveal a disc extending from 30 to 180 au, split by a 27 au wide gap centred at 74 au, and no dust surrounding the reddened brown dwarf (BD) at 11 au. The gap width suggests the presence of a 0.9MJup planet at 74 au, which would be the third companion in this system. Using previous astrometry of the BD, combined with our derived disc orientation as a prior, we were able to better constrain its orbit finding it is likely eccentric ($0.14^{+0.05}_{-0.04}$). For the innermost companion, we used radial velocity, proper motion anomaly, and stability considerations to show its mass and semimajor axis are likely in the ranges 4–100MJup and 1.4–4.5 au. These three companions will interact on secular time-scales and perturb the orbits of planetesimals, stirring the disc and potentially truncating it to its current extent via secular resonances. Finally, the presence of a gap in this system adds to the growing evidence that gaps could be common in wide exo-Kuiper belts. Out of six wide debris discs observed with ALMA with enough resolution, four to five show radial substructure in the form of gaps.
Context. Direct imaging has led to the discovery of several giant planet and brown dwarf companions. These imaged companions populate a mass, separation and age domain (mass >1 MJup, orbits > 5 AU, ...age < 1 Gyr) quite distinct from the one occupied by exoplanets discovered by the radial velocity or transit methods. This distinction could indicate that different formation mechanisms are at play. Aims. We aim at investigating correlations between the host star’s mass and the presence of wide-orbit giant planets, and at providing new observational constraints on planetary formation models. Methods. We observed 58 young and nearby M-type dwarfs in L′-band with the VLT/NaCo instrument and used angular differential imaging algorithms to optimize the sensitivity to planetary-mass companions and to derive the best detection limits. We estimate the probability of detecting a planet as a function of its mass and physical separation around each target. We conduct a Bayesian analysis to determine the frequency of substellar companions orbiting low-mass stars, using a homogenous sub-sample of 54 stars. Results. We derive a frequency of 4.4+3.2-1.3 for companions with masses in the range of 2−80 MJup, and 2.3+2.9-0.7% for planetary mass companions (2−14 MJup), at physical separations of 8 to 400 AU for both cases. Comparing our results with a previous survey targeting more massive stars, we find evidence that substellar companions more massive than 1 MJup with a low mass ratio Q with respect to their host star (Q < 1%), are less frequent around low-mass stars. This may represent observational evidence that the frequency of imaged wide-orbit substellar companions is correlated with stellar mass, corroborating theoretical expectations. Contrarily, we show statistical evidence that intermediate-mass ratio (1% < Q < 5%) companion with masses >2 MJup might be independent from the mass of the host star.
Context. Though only a handful of extrasolar planets have been discovered via direct-imaging, each of these discoveries had a tremendous impact on our understanding of planetary formation, stellar ...formation, and cool atmosphere physics. Aims. Since many of these newly imaged giant planets orbit massive A or even B stars, we investigate whether giant planets could be found orbiting low-mass stars at large separations. Methods. We have been conducting an adaptive optic imaging survey to search for planetary-mass companions of young M dwarfs in the solar neigbourhood, in order to probe different initial conditions of planetary formation. Results. We report here the direct-imaging discovery of 2MASS J01033563-5515561(AB)b, a 12–14 MJup companion at a projected separation of 84 AU from a pair of young late-M stars, with which it shares proper motion. We also detected a Keplerian-compatible orbital motion. Conclusions. This young L-type object at the planet/brown dwarf mass boundary is the first ever imaged around a binary system at a separation compatible with formation in a disc.
Aims. In 2015, we initiated a survey of Scorpius-Centaurus A-F stars that are predicted to host warm-inner and cold-outer belts of debris similar to the case of the system HR 8799. The survey aims to ...resolve the disks and detect planets responsible for the disk morphology. In this paper, we study the F-type star HIP 67497 and present a first-order modelization of the disk in order to derive its main properties. Methods. We used the near-infrared integral field spectrograph (IFS) and dual-band imager IRDIS of VLT/SPHERE to obtain angular-differential imaging observations of the circumstellar environnement of HIP 67497. We removed the stellar halo with PCA and TLOCI algorithms. The disk emission was modeled with the GRaTeR code. Results. We resolve a ring-like structure that extends up to ~450 mas (~50 au) from the star in the IRDIS and IFS data. It is best reproduced by models of a non-eccentric ring with an inclination of 80 ± 1°, a position angle of −93 ± 1°, and a semi-major axis of 59 ± 3 au. We also detect an additional, but fainter, arc-like structure with a larger extension (0.65 arcsec) South of the ring that we model as a second belt of debris at ~130 au. We detect ten candidate companions at separations ≥1′′. We estimate the mass of putative perturbers responsible for the disk morphology and compare this to our detection limits. Additional data are needed to find those perturbers, and to relate our images to large-scale structures seen with HST/STIS.
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