14 research outputs found
YETI observations of the young transiting planet candidate CVSO 30 b
CVSO 30 is a unique young low-mass system, because, for the first time, a
close-in transiting and a wide directly imaged planet candidates are found
around a common host star. The inner companion, CVSO 30 b, is the first
possible young transiting planet orbiting a previously known weak-lined T-Tauri
star. With five telescopes of the 'Young Exoplanet Transit Initiative' (YETI)
located in Asia, Europe and South America we monitored CVSO 30 over three years
in a total of 144 nights and detected 33 fading events. In two more seasons we
carried out follow-up observations with three telescopes. We can confirm that
there is a change in the shape of the fading event between different
observations and that the fading event even disappears and reappears. A total
of 38 fading event light curves were simultaneously modelled. We derived the
planetary, stellar, and geometrical properties of the system and found them
slightly smaller but in agreement with the values from the discovery paper. The
period of the fading event was found to be 1.36 s shorter and 100 times more
precise than the previous published value. If CVSO 30 b would be a giant planet
on a precessing orbit, which we cannot confirm, yet, the precession period may
be shorter than previously thought. But if confirmed as a planet it would be
the youngest transiting planet ever detected and will provide important
constraints on planet formation and migration time-scales.Comment: 14 pages (20 with appendix), 7 figures (16 with appendix), 6 tables
(7 with appendix
Dust and Metal Column Densities in Gamma-Ray Burst Host Galaxies
In this paper we present the results from the analysis of a sample of 28
gamma-ray burst (GRB) afterglow spectral energy distributions, spanning the
X-ray through to near-infrared wavelengths. This is the largest sample of GRB
afterglow spectral energy distributions thus far studied, providing a strong
handle on the optical depth distribution of soft X-ray absorption and
dust-extinction systems in GRB host galaxies. We detect an absorption system
within the GRB host galaxy in 79% of the sample, and an extinction system in
71% of the sample, and find the Small Magellanic Cloud (SMC) extinction law to
provide an acceptable fit to the host galaxy extinction profile for the
majority of cases, consistent with previous findings. The range in the soft
X-ray absorption to dust-extinction ratio, N_{H,X}/Av, in GRB host galaxies
spans almost two orders of magnitude, and the typical ratios are significantly
larger than those of the Magellanic Clouds or Milky Way. Although dust
destruction could be a cause, at least in part, for the large N_{H,X}/Av
ratios, the good fit provided by the SMC extinction law for the majority of our
sample suggests that there is an abundance of small dust grains in the GRB
environment, which we would expect to have been destroyed if dust destruction
were responsible for the large N_{H,X}/Av ratios. Instead, our analysis
suggests that the distribution of N_{H,X}/Av in GRB host galaxies may be mostly
intrinsic to these galaxies, and this is further substantiated by evidence for
a strong negative correlation between N_{H,X}/Av and metallicity for a
subsample of GRB hosts with known metallicity. Furthermore, we find the
N_{H,X}/Av ratio and metallicity for this subsample of GRBs to be comparable to
the relation found in other more metal-rich galaxies.Comment: 23 pages, 10 figures, accepted for publication in MNRA
Herculid meteor shower in the night of 30/31 May 2022 and the meteoroid properties
Context. A Ď„ Herculid meteor outburst or even storm was predicted to occur by several models around 5 UT on 31 May 2022 as a consequence of the break-up of comet 73P/Schwassmann-Wachmann 3 in 1995. The multi-instrument and multi-station experiment was carried out within the Czech Republic to cover possible earlier activity of the shower between 21 and 1 UT on 30/31 May.
Aims. We report meteor shower activity that occurred before the main peak and provide a comparison with the dynamical simulations of the stream evolution. The physical properties of the meteoroids are also studied.
Methods. Multi-station observations using video and photographic cameras were used to calculate the atmospheric trajectories and heliocentric orbits of the meteors. Their arrival times were used to determine the shower activity profile. The physical properties of the meteoroids were evaluated using various criteria based on meteor heights. The evolution of the spectra of three meteors were studied as well.
Results. This annual but poor meteor shower was active for the whole night many hours before the predicted peak. A comparison with dynamical models shows that a mix of older material ejected after 1900 and fresh particles originating from the 1995 comet fragmentation event was observed. The radiant positions of both groups of meteors were identified and were found to agree well with the simulated radiants. Meteoroids with masses between 10 mg and 10 kg were recorded. The mass distribution index was slightly higher than 2. The study of the physical properties shows that the Ď„ Herculid meteoroids belong to the most fragile particles observed ever, especially among higher masses of meteoroids. The exceptionally bright bolide observed during the dawn represents a challenge for the dynamical simulations as it is necessary to explain how a half-metre body was transferred to the vicinity of the Earth at the same time as millimetre-sized particles
A study of asteroid pole-latitude distribution based on an extended set of shape models derived by the lightcurve inversion method
Context. In the past decade, more than one hundred asteroid models were derived using the lightcurve inversion method. Measured by the number of derived models, lightcurve inversion has become the leading method for asteroid shape determination.
Aims. Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population.
Methods. We use sparse photometry from selected observatories from the AstDyS database (Asteroids – Dynamic Site), either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We investigate various correlations between several asteroid parameters and characteristics such as the rotational state and diameter or family membership. We focus on the distribution of ecliptic latitudes of pole directions. We create a synthetic uniform distribution of latitudes, compute the method bias, and compare the results with the distribution of known models. We also construct a model for the long-term evolution of spins.
Results. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. For another 30 asteroids we present their partial models, i.e., an accurate period value and an estimate of the ecliptic latitude of the pole. The addition of new models increases the total number of models derived by the lightcurve inversion method to  ~200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D  60 km) exhibits an evident excess of prograde rotators, probably of primordial origin
Copper deoxidation kinetics utilizing carbon monoxide
Gaseous deoxidation of liquid copper with carbon monoxide as the reducing gas has been examined. The reducing gas was introduced at a submerged orifice so that well characterized, single bubbles were formed. The deoxidation kinetics are determined primarily by the mass transport of oxygen in liquid copper. No effect of sulfur over the range of 10 to 200 ppm was observed. Increasing the temperature from 1113 to 1173°C slightly inhibit the kinetics of oxygen removal. © 1977 The Metallurgical of Society of AIME
Hydrogen peroxide route to Sn-doped titania photocatalysts
<p>Abstract</p> <p>Background</p> <p>The work aims at improving photocatalytic activity of titania under Vis light irradiation using modification by Sn ions and an original, simple synthesis method. Tin-doped titania catalysts were prepared by thermal hydrolysis of aqueous solutions of titanium peroxo-complexes in the presence of SnCl<sub>4</sub> or SnCl<sub>2</sub> using an original, proprietary "one pot" synthesis not employing organic solvents, metallo-organic precursors, autoclave aging nor post-synthesis calcination. The products were characterized in details by powder diffraction, XPS, UV–vis, IR, and Raman spectroscopies, electron microscopy and surface area and porosity measurements</p> <p>Results</p> <p>The presence of tin in synthesis mixtures favors the formation of rutile and brookite at the expense of anatase, decreases the particle size of all formed titania polymorphs, and extends light absorption of titania to visible light region >400 nm by both red shift of the absorption edge and introduction of new chromophores. The photocatalytic activity of titania under UV irradiation and >400 nm light was tested by decomposition kinetics of Orange II dye in aqueous solution</p> <p>Conclusions</p> <p>Doping by Sn improves titania photoactivity under UV light and affords considerable photoactivity under >400 nm light due to increased specific surface area and a phase heterogeneity of the Sn-doped titania powders.</p