We use Gaia Data Release 2 proper motions of field OB stars from the Runaways and Isolated O-Type Star Spectroscopic Survey of the Small Magellanic Cloud (SMC) to study the kinematics of runaway ...stars. The data reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar of and relative radial velocity . This unambiguously demonstrates that these two regions are kinematically distinct: the Wing is moving away from the Bar, and towards the Large Magellanic Cloud with a 3D velocity of . This is consistent with models for a recent, direct collision between the Clouds. We present transverse velocity distributions for our field OB stars, confirming that unbound runaways comprise on the order of half our sample, possibly more. Using eclipsing binaries and double-lined spectroscopic binaries as tracers of dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers of runaways accelerated by supernova kicks, we find significant contributions from both populations. The data suggest that HMXBs have lower velocity dispersion relative to dynamically ejected binaries, consistent with the former group corresponding to less energetic supernova kicks that failed to unbind the components. Evidence suggests that our fast runaways are dominated by dynamical, rather than supernova, ejections.
The two rings of (50000) Quaoar Pereira, C. L.; Sicardy, B.; Morgado, B. E. ...
Astronomy & astrophysics,
05/2023, Letnik:
673
Journal Article
Recenzirano
Odprti dostop
Context.
Quaoar is a classical trans-Neptunian object (TNO) with an area-equivalent diameter of 1100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations ...observed between 2018 and 2021, an inhomogeneous ring (Q1R, i.e., Quaoar’s first ring) has been detected around this body.
Aims.
A new stellar occultation by Quaoar was observed on August 9, 2022, with the aim of improving Quaoar’s shape models and the physical parameters of Q1R, while searching for additional material around the body.
Methods.
The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements).
Results.
Quaoar’s elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of 579.5 ± 4.0 km, apparent oblateness of 0.12 ± 0.01, and area-equivalent radius of 543 ± 2 km. Quaoar’s limb orientation is consistent with Q1R and Weywot orbiting in Quaoar’s equatorial plane. The orbital radius of Q1R is refined to a value of 4057 ± 6 km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of ∼5 km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of 2520 ± 20 km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of ∼0.004. Just as Q1R, it also lies outside Quaoar’s classical Roche limit.
We use GAIA DR2 proper motions of the RIOTS4 field OB stars in the Small Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data reveal that the SMC Wing has a systemic peculiar ...motion relative to the SMC Bar of (v_RA, v_Dec) = (62 +/-7, -18+/-5) km/s and relative radial velocity +4.5 +/- 5.0 km/s. This unambiguously demonstrates that these two regions are kinematically distinct: the Wing is moving away from the Bar, and towards the Large Magellanic Cloud with a 3-D velocity of 64 +/- 10 km/s. This is consistent with models for a recent, direct collision between the Clouds. We present transverse velocity distributions for our field OB stars, confirming that unbound runaways comprise on the order of half our sample, possibly more. Using eclipsing binaries and double-lined spectroscopic binaries as tracers of dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers of runaways accelerated by supernova kicks, we find significant contributions from both populations. The data suggest that HMXBs have lower velocity dispersion relative to dynamically ejected binaries, consistent with the former corresponding to less energetic supernova kicks that failed to unbind the components. Evidence suggests that our fast runaways are dominated by dynamical, rather than supernova, ejections.
The
14
N nuclear magnetic resonance (n.m.r.) signals of alkylamines and ammonium ions are shifted to lower magnetic fields with the increasing number of alkyl groups at the carbon atom directly ...bonded to the nitrogen atom, and at the nitrogen atom itself. The resonance of an ammonium ion always occurs at a field lower than that for the corresponding amine. It seems that high-lying excited states, not only those corresponding to lowest-wavelength transitions, are important for an explanation of the observed resonance shifts. A downfield shift of the
14
N resonance and a substantial increase in signal width, as compared with the spectra of neat amines, are observed for aqueous solutions of amines. There is a very characteristic chemical shift for the R—CH
2
—NH
2
molecules (R = alkyl, phenyl, vinyl) in the
14
N n.m.r. spectra.
The
14
N nuclear magnetic resonance (n.m.r.) signals of alkylamines and ammonium ions are shifted to lower magnetic fields with the increasing number of alkyl groups at the carbon atom directly ...bonded to the nitrogen atom, and at the nitrogen atom itself. The resonance of an ammonium ion always occurs at a field lower than that for the corresponding amine. It seems that high-lying excited states, not only those corresponding to lowest-wavelength transitions, are important for an explanation of the observed resonance shifts. A downfield shift of the
14
N resonance and a substantial increase in signal width, as compared with the spectra of neat amines, are observed for aqueous solutions of amines. There is a very characteristic chemical shift for the RCH
2
NH
2
molecules (R = alkyl, phenyl, vinyl) in the
14
N n.m.r. spectra.
Reconstruction of neural circuits from volume electron microscopy data requires the tracing of cells in their entirety, including all their neurites. Automated approaches have been developed for ...tracing, but their error rates are too high to generate reliable circuit diagrams without extensive human proofreading. We present flood-filling networks, a method for automated segmentation that, similar to most previous efforts, uses convolutional neural networks, but contains in addition a recurrent pathway that allows the iterative optimization and extension of individual neuronal processes. We used flood-filling networks to trace neurons in a dataset obtained by serial block-face electron microscopy of a zebra finch brain. Using our method, we achieved a mean error-free neurite path length of 1.1 mm, and we observed only four mergers in a test set with a path length of 97 mm. The performance of flood-filling networks was an order of magnitude better than that of previous approaches applied to this dataset, although with substantially increased computational costs.
The synthesis and characterization of two biphenyl phosphates of different structures, as substrates for preparation of two series of functionalized addition silicone rubbers of different crosslink ...density and amount of pendant functional groups, is presented. Obtained materials were applied as flame retardant protective coatings for cotton fabric and characterized by TG and MMC techniques. The relationship between thermal stability, flame-retardant properties, and structure of prepared silicone rubbers is discussed.
•The synthesis and characterization of two new biphenyl phosphates•One-pot synthesis of phosphate functionalized, crosslinked silicone rubbers•TG and MMC characterization of flame retardant protective coatings for cotton fabric
PDF
