As gas giant planets and brown dwarfs radiate away the residual heat from their formation, they cool through a spectral type transition from L to T, which encompasses the dissipation of cloud opacity ...and the appearance of strong methane absorption. While there are hundreds of known T-type brown dwarfs, the first generation of directly imaged exoplanets were all L type. Recently, Kuzuhara et al. announced the discovery of GJ 504 b, the first T dwarf exoplanet. GJ 504 b provides a unique opportunity to study the atmosphere of a new type of exoplanet with a ~500 K temperature that bridges the gap between the first directly imaged planets (~1000 K) and our own solar system's Jupiter (~130 K). Of particular interest, our model fits suggest that GJ 504 b has a superstellar metallicity. Since planet formation can create objects with nonstellar metallicities, while binary star formation cannot, this result suggests that GJ 504 b formed like a planet, not like a binary companion.
We present resolved images of the HR 4796A debris disk using the Magellan adaptive optics system paired with Clio-2 and VisAO. We detect the disk at 0.77 mum, 0.91 mum, 0.99 mum, 2.15 mum, 3.1 mum, ...3.3 mum, and 3.8 mum. We find that the deprojected center of the ring is offset from the star by 4.76 + or - 1.6 AU and that the deprojected eccentricity is 0.06 + or - 0.02, in general agreement with previous studies. We find that the average width of the ring is (ProQuest: Formulae and/or non-USASCII text omitted) ((ProQuest: Formulae and/or non-USASCII text omitted) AU), also comparable to previous measurements. Combining our new scattered light data with archival Hubble Space Telescope images at ~0.5-2 mum, along with previously unpublished Spitzer/MIPS thermal emission data and all other literature thermal data, we set out to constrain the chemical composition of the dust grains. After testing 19 individual root compositions and more than 8400 unique mixtures of these compositions, we find that good fits to the scattered light alone and thermal emission alone are discrepant, suggesting that caution should be exercised if fitting to only one or the other. When we fit to both data sets simultaneously, we find that silicates and organics are generally the most favored, while large abundances of water ice are usually not favored. These results suggest the HR 4796A dust grains are similar to interstellar dust and solar system comets, though improved modeling is necessary to place better constraints on the exact chemical composition of the dust.
In this paper we describe the procedure for the optical calibration of large size deformable mirrors, acting as wavefront correctors for adaptive optics systems. Adaptive optics compensate the ...disturbance due to the atmospheric turbulence to restore the telescope resolution. We will showcase in particular the activities performed for the Adaptive Secondary Mirror (ASM) of the Magellan Adaptive Optics system (MagAO), which is an instrument for the 6.5 m Magellan Clay Telescope, located at Las Campanas Observatory, in Chile. The MagAO ASM calibration is part of the MagAO-2K project, a major MagAO upgrade that started in 2016 with the goal of boosting adaptive optics (AO) correction at visible wavelengths to image exoplanets. For the first time, the optical quality of MagAO mirror is reported. We describe the procedures developed to achieve high SNR interferometric measurements of the ASM modes under the presence of dome convection noise and telescope vibrations. These measurements were required to produce an improved control matrix with up to 500 modes to close the AO loop on sky with enhanced performances. An updated slaving algorithm was developed to improve the control of actuators vignetted by the central obscuration. The calibrations yielded also a new ASM flattening command, updating the one in use since the MagAO commissioning in 2013. With the new flattening command, a 22 nm RMS surface error was achieved. Finally, we present on-sky results showing the MagAO performance achieved with the new calibrations.
Questo contributo riassume la storia del gruppo di ottica adattiva di Arcetri a partire dalla visione di Franco Pacini e Piero Salinari alla fine degli anni '80 fino ad arrivare alla sua messa in ...pratica e al riconoscimento internazionale dei suoi risultati intorno al 2010. Parole chiave. Alta risoluzione angolare, ottica adattiva, strumentazione astronomica. This contribution summarizes the history of the adaptive optics group at Arcetri from the vision of Franco Pacini and Piero Salinari at the end of the 1980s to its entry into operation and the international recognition of the achieved results in around 2010. Keywords. High angular resolution, adaptive optics, astronomical instrumentation.
Cryptophycins are potent tubulin polymerization inhibitors with picomolar antiproliferative potency in vitro and activity against multidrug-resistant (MDR) cancer cells. Because of neurotoxic side ...effects and limited efficacy in vivo, cryptophycin-52 failed as a clinical candidate in cancer treatment. However, this class of compounds has emerged as attractive payloads for tumor-targeting applications. In this study, cryptophycin was conjugated to the cyclopeptide
(RGDfK), targeting integrin α
β₃, across the protease-cleavable Val-Cit linker and two different self-immolative spacers. Plasma metabolic stability studies in vitro showed that our selected payload displays an improved stability compared to the parent compound, while the stability of the conjugates is strongly influenced by the self-immolative moiety. Cathepsin B cleavage assays revealed that modifications in the linker lead to different drug release profiles. Antiproliferative effects of Arg-Gly-Asp (RGD)⁻cryptophycin conjugates were evaluated on M21 and M21-L human melanoma cell lines. The low nanomolar in vitro activity of the novel conjugates was associated with inferior selectivity for cell lines with different integrin α
β₃ expression levels. To elucidate the drug delivery process, cryptophycin was replaced by an infrared dye and the obtained conjugates were studied by confocal microscopy.
This contribution summarizes the history of the adaptive optics group at Arcetri from the vision of Franco Pacini and Piero Salinari at the end of the 1980s to its entry into operation and the ...international recognition of the achieved results in around 2010
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