126 research outputs found

    X-Shooter observations of low-mass stars in the Eta Chamaeleontis association

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    The nearby Eta Chamaeleontis association is a collection of 4-10 Myr old stars with a disk fraction of 35-45%. In this study, the broad wavelength coverage of VLT/X-Shooter is used to measure the stellar and mass accretion properties of 15 low mass stars in the Eta Chamaeleontis association. For each star, the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab. Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The accretion rates measured here are similar to those obtained from previous measurements of excess UV emission, but tend to be higher than past measurements from H-alpha modeling. The mass accretion rates are consistent with those of other young star forming regions.Comment: Accepted for publication in Astronomy & Astrophysic

    HD 135344B: a young star has reached its rotational limit

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    We search for periodic variations in the radial velocity of the young Herbig star HD 135344B with the aim to determine a rotation period. We analyzed 44 high-resolution optical spectra taken over a time range of 151 days. The spectra were acquired with FEROS at the 2.2m MPG/ESO telescope in La Silla. The stellar parameters of HD 135344B are determined by fitting synthetic spectra to the stellar spectrum. In order to obtain radial velocity measurements, the stellar spectra have been cross-correlated with a theoretical template computed from determined stellar parameters. We report the first direct measurement of the rotation period of a Herbig star from radial-velocity measurements. The rotation period is found to be 0.16 d (3.9 hr), which makes HD 135344B a rapid rotator at or close to its break-up velocity. The rapid rotation could explain some of the properties of the circumstellar environment of HD 135344B such as the presence of an inner disk with properties (composition, inclination), that are significantly different from the outer disk.Comment: Accepted for publication in Astronomy & Astrophysics, 9 pages, 12 figure

    Photoprocessing of formamide ice: route towards prebiotic chemistry in space

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    Aims. Formamide (HCONH2) is the simplest molecule containing the peptide bond first detected in the gas phase in Orion-KL and SgrB2. In recent years, it has been observed in high temperature regions such as hot corinos, where thermal desorption is responsible for the sublimation of frozen mantles into the gas phase. The interpretation of observations can benefit from information gathered in the laboratory, where it is possible to simulate the thermal desorption process and to study formamide under simulated space conditions such as UV irradiation. Methods. Here, two laboratory analyses are reported: we studied formamide photo-stability under UV irradiation when it is adsorbed by space relevant minerals at 63 K and in the vacuum regime. We also investigated temperature programmed desorption of pure formamide ice in the presence of TiO2 dust before and after UV irradiation. Results. Through these analyses, the effects of UV degradation and the interaction between formamide and different minerals are compared.We find that silicates, both hydrates and anhydrates, offer molecules a higher level of protection from UV degradation than mineral oxides. The desorption temperature found for pure formamide is 220 K. The desorption temperature increases to 250 K when the formamide desorbs from the surface of TiO2 grains. Conclusions. Through the experiments outlined here, it is possible to follow the desorption of formamide and its fragments, simulate the desorption process in star forming regions and hot corinos, and constrain parameters such as the thermal desorption temperature of formamide and its fragments and the binding energies involved. Our results offer support to observational data and improve our understanding of the role of the grain surface in enriching the chemistry in space.Comment: In press Astronomy and Astrophysics, 13 pages, 12 figure

    Advanced European Re-Entry System Based on Inflatable Heat Shields: Detailed Design (EFESTO project)

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    The European Union H2020 EFESTO project is coordinated by DEIMOS Space with the end goals of improving the European TRL of Inflatable Heat Shields for re-entry vehicles (from 3 to 4/5) and paving the way towards further improvements (TRL 6 with a future In-Orbit Demonstrator, IOD). This paper presents the project objectives and the initial results of the detailed design of atmospheric entry missions based on the applications of advanced thermal protection systems implementing inflatable heat shields (flexible TPS and inflatable structures), according to aerothermodynamics constraints for future in-orbit demonstration. Placing the future IOD mission in the context of ongoing and future efforts in the European context is also one of the project goals. Two key applications, Mars Robotic Exploration and Reusable Small Launchers Upper Stages, have been identified. For the Mars Application, the robotic exploration mission class resulted in a 10 m diameter Hypersonic Inflatable Aerodynamic Decelerator (HIAD) class, combined with Supersonic Retro-Propulsion (SRP, activated about Mach 2.3) to deliver about 2800 kg of payload at MOLA +2 km. For the Earth Application, the VEGA upper stage (AVUM) has been selected as baseline case study. The current mission foresees a deorbiting from SSO orbit, a controlled entry phase (BC of about 30 kg/m2) and combines the use of a HIAD (4.5m diameter class) with parachutes and parafoil for Mid-Air-Capturing (MAR) with a helicopter. Beyond feasibility of the entry mission phase and system design with an inflated IAD, integration aspects have a key impact in the specific design solutions adopted, due to the nature of an inflatable heatshield. For both considered application cases feasible architectures are developed responding to the challenge of integrating the HIAD into the system in compliance with geometric and functional requirements. While the HIAD in folded state prior to inflation must fit in the available volume, it has limitations with respect to the density imposing a minimum cross section of the stowage volume. Simultaneously requirements with respect to the centre of gravity position during re-entry with an inflated HIAD must be respected for stability and controllability reasons. Other architectural considerations such as payload integration for the application on a launcher upper stage must be considered. Finally, heat loads constraints are considered for the trajectory and TPS deign choices due to important fluid-structure interactions. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821801

    ALMA observations of polarized emission toward the CW Tau and DG Tau protoplanetary disks: constraints on dust grain growth and settling

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    We present polarimetric data of CW Tau and DG Tau, two well-known Class II disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter Array at 870 μ\mum and 0."2 average resolution. In CW Tau, the total and polarized emission are both smooth and symmetric, with polarization angles almost parallel to the minor axis of the projected disk. In contrast, DG Tau displays a structured polarized emission, with an elongated brighter region in the disk's near side and a belt-like feature beyond about 0."3 from the source. At the same time the total intensity is spatially smooth, with no features. The polarization pattern, almost parallel to the minor axis in the inner region, becomes azimuthal in the outer belt, possibly because of a drop in optical depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4% in DG Tau. Our results are consistent with polarization from self-scattering of the dust thermal emission. Under this hypothesis, the maximum size of the grains contributing to polarization is in the range 100 - 150 μ\mum for CW Tau and 50 - 70 μ\mum for DG Tau. The polarization maps combined with dust opacity estimates indicate that these grains are distributed in a geometrically thin layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such settling is not yet apparent for DG Tau. These results advocate polarization studies as a fundamental complement to total emission observations, in investigations of the structure and the evolution of protoplanetary disks.Comment: 8 pages, 5 figures. Accepted for publication in ApJ Letter

    On the origin of heavy-tail statistics in equations of the Nonlinear Schrödinger type

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    We study the formation of extreme events in incoherent systems described by the Nonlinear Schrödinger type of equations. We consider an exact identity that relates the evolution of the normalized fourth-order moment of the probability density function of the wave envelope to the rate of change of the width of the Fourier spectrum of the wave field. We show that, given an initial condition characterized by some distribution of the wave envelope, an increase of the spectral bandwidth in the focusing/defocusing regime leads to an increase/decrease of the probability of formation of rogue waves. Extensive numerical simulations in 1D+1 and 2D+1 are also performed to confirm the results

    Metabolomic fingerprinting of renal disease progression in Bardet-Biedl syndrome reveals mitochondrial dysfunction in kidney tubular cells.

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    Chronic kidney disease (CKD) is a major clinical sign of patients with Bardet-Biedl syndrome (BBS), especially in those carrying BBS10 mutations. Twenty-nine patients with BBS and 30 controls underwent a serum-targeted metabolomic analysis. In vitro studies were conducted in two kidney-derived epithelial cell lines, where Bbs10 was stably deleted (IMCD3-Bbs10-/-cells) and over-expressed. The CKD status affected plasmatic metabolite fingerprinting in both patients with BBS and controls. Specific phosphatidylcholine and acylcarnitines discriminated eGFR decline only in patients with BBS. IMCD3-Bbs10-/ cells displayed intracellular lipidaccumulation, reduced mitochondrial potential membrane and citrate synthase staining. Mass-Spectrometry-based analysis revealed that human BBS10 interacted with six mitochondrial proteins, in vitro. In conclusion, renal dysfunction correlated with abnormal phosphatidylcholine and acylcarnitines plasma levels in patients with BBS; in vitro, Bbs10 depletion caused mitochondrial defects while human BBS10 interacted with several mitochondria-related proteins, suggesting an unexplored role of this protein

    KMOS study of the mass accretion rate from Class I to Class II in NGC 1333

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    Context. The mass accretion rate (\Mdot;acc) is the fundamental parameter to understand the process of mass assembly that results in the formation of a low-mass star. This parameter has been largely studied in Classical T Tauri stars in star-forming regions with ages of ∼1 − 10 Myr. However, little is known about the accretion properties of young stellar objects (YSOs) in younger regions and early stages of star formation, such as in the Class 0/I phases. Aims: We present new near-infrared spectra of 17 Class I/Flat and 35 Class II sources located in the young ( Methods: For the Class II sources in our sample, we measured the stellar parameters (SpT, AV, and L⋆) through a comparison of the IR spectra with a grid of non-accreting Class III stellar templates. We then computed the accretion luminosity by using the known correlation between Lacc and the luminosity of HI lines (Paβ and Brγ). For the Class I sample, where the presence of a large IR excess makes it impossible to use the same spectral typing method, we applied a procedure that allowed us to measure the stellar and accretion luminosity in a self-consistent way. Mass accretion rates \Mdot;acc were then measured once masses and radii were estimated adopting suitable evolutionary tracks. Results: The NGC 1333 Class II sources of our sample have Lacc ∼ 10−4 − 1 L⊙ and \Mdot;acc ∼ 10−11 − 10−7 M⊙ yr−1. We find a correlation between accretion and stellar luminosity in the form of log Lacc = (1.5 ± 0.2)log L⋆ + ( − 1.0 ± 0.1), and a correlation between the mass accretion rate and stellar mass in the form of log \Mdot;acc = (2.6 ± 0.9) log M⋆ + (−7.3 ± 0.7). Both correlations are compatible within the errors with the older Lupus star-forming region, while only the latter is consistent with results from Chamaeleon I. The Class I sample shows larger accretion luminosities (∼10−2 − 102 L⊙) and mass accretion rates (∼10−9 − 10−6 M⊙ yr−1) with respect to the Class II stars of the same cloud. However, the derived mass accretion rates are not sufficiently high to build up the inferred stellar masses, assuming steady accretion during the Class I lifetime. This suggests that the sources are not in their main accretion phase and that most of their mass has already been accumulated during a previous stage and/or that the accretion is an episodic phenomenon. We show that some of the targets originally classified as Class I through Spitzer photometry are in fact evolved or low accreting objects. This evidence can have implications for the estimated protostellar phase lifetimes. Conclusions: The accretion rates of our sample are larger in more embedded and early stage YSOs. Further observations of larger samples in young star-forming regions are needed to determine if this is a general result. In addition, we highlight the importance of spectroscopic surveys of YSOs to confirm their classification and perform a more correct estimate of their lifetime. Reduced spectra of the sources described in Tables 1 and C.1 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/650/A43 Based on observations collected at the European Southern Observatory under ESO programme 0102.C-0679A
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