14 research outputs found
(3200) Phaethon: Bulk density from Yarkovsky drift detection
The recent close approach of the NEA (3200) Phaethon offered a rare
opportunity to obtain high-quality observational data. We used the newly
obtained optical light curves to improve the spin and shape model of Phaethon
and to determine its surface physical properties derived by thermophysical
modeling. We also used the available astrometric observations of Phaethon,
including those obtained by the Arecibo radar and the Gaia spacecraft, to
constrain the secular drift of the orbital semimajor axis. This constraint
allowed us to estimate the bulk density by assuming that the drift is dominated
by the Yarkovsky effect. We used the convex inversion model to derive the 3D
shape model of Phaethon, and a detailed numerical approach for an accurate
analysis of the Yarkovsky effect. We obtained a unique solution for Phaethon's
pole orientation at ecliptic longitude and latitude
(uncertainty of ), and confirm the previously reported
thermophysical properties ( km, SI). Phaethon
has a top-like shape with possible north-south asymmetry. The characteristic
size of the regolith grains is 1-2 cm. The orbit analysis reveals a secular
drift of the semimajor axis of au Myr. With
the derived volume-equivalent size of 5.1~km, the bulk density is
g cm. If the size is slightly larger km, as
suggested by radar data, would decrease to g cm. We
further investigated the suggestion that Phaethon may be in a cluster with
asteroids (155140) 2005 UD and (225416) 1999 YC that was formed by rotational
fission of a critically spinning parent body. Phaethon's is consistent
with typical values for large ( km) C-complex asteroids and supports its
association with asteroid (2) Pallas. These findings render a cometary origin
unlikely for Phaethon.Comment: Accepted for publication in A&
DATABASE CREATION AND DESIGN PROCESS MAPS LESSON
Описывается база данных, которая будет содержать лучшие методические разработки преподавателей и помогать создавать технологические карты уроковThe article describes a database that will contain the best methodological developments of teachers and help to create technological maps of lesson
Collection of Minima of Eclipsing Binaries, part III.
We present CCD times of minima for selected eclipsing binaries,
mainly parts of the multiple systems
On the Polish doughnut accretion disk via the effective potential approach
We revisit the Polish doughnut model of accretion disks providing a
comprehensive analytical description of the Polish doughnut structure. We
describe a perfect fluid circularly orbiting around a Schwarzschild black hole,
source of the gravitational field, by the effective potential approach for the
exact gravitational and centrifugal effects. This analysis leads to a detailed,
analytical description of the accretion disk, its toroidal surface, the
thickness, the distance from the source. We determine the variation of these
features with the effective potential and the fluid angular momentum. Many
analytical formulas are given. In particular it turns out that the distance
from the source of the inner surface of the torus increases with increasing
fluid angular momentum but decreases with increasing energy function defined as
the value of the effective potential for that momentum. The location of torus
maximum thickness moves towards the external regions of the surface with
increasing angular momentum, until it reaches a maximum an then decreases.
Assuming a polytropic equation of state we investigate some specific cases.Comment: 33 pages, 28 figures, 1 table. This is a revised version to meet the
published articl
YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus
The rotation states of small asteroids are affected by a net torque arising
from an anisotropic sunlight reflection and thermal radiation from the
asteroids' surfaces. On long timescales, this so-called YORP effect can change
asteroid spin directions and their rotation periods. We analyzed lightcurves of
four selected near-Earth asteroids with the aim of detecting secular changes in
their rotation rates that are caused by YORP. We use the lightcurve inversion
method to model the observed lightcurves and include the change in the rotation
rate as a free parameter of optimization. We
collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used
thermal infrared data from the WISE spacecraft and estimated their size and
thermal inertia. We also used the currently available optical and radar
astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We
detected a YORP acceleration of for asteroid Cacus. For
Toro, we have a tentative () detection of YORP from a significant
improvement of the lightcurve fit for a nonzero value of . For asteroid
Eger, we confirmed the previously published YORP detection with more data and
updated the YORP value to . We also updated the shape model of
asteroid Ra-Shalom and put an upper limit for the change of the rotation rate
to . Ra-Shalom has a greater than
Yarkovsky detection with a theoretical value consistent with observations
assuming its size and/or density is slightly larger than the nominally expected
values
The first study of 54 new eccentric eclipsing binaries in our Galaxy
We present an analysis of the apsidal motion and light curve parameters of 54 galactic Algol-type binaries never before studied. This is the first analysis of such a large sample of eccentric eclipsing binaries in our Galaxy, and has enabled us to identify several systems that are worthy of further study. Bringing together data from various databases and surveys, supplemented with new observations, we have been able to trace the long-term evolution of the eccentric orbit over durations extending back up to several decades. Our present study explores a rather different sample of stars to those presented in the previously published catalogue of eccentric eclipsing binaries by Bulut & Demircan (2007), sampling to fainter magnitudes, covering later spectral types, sensitive to different orbital periods with more than 50% of our systems having periods longer than 6 days. The typical apsidal motion in the sample is rather slow (mostly of order of centuries long), although in some cases this is less than 50 years. All of the systems, except one, have eccentricities less than 0.5, with an average value of 0.23. Several of the stars also show evidence for additional period variability. In particular we can identify three systems in the sample, HD 44093, V611 Pup, and HD 313631, which likely represent relativistic apsidal rotators
Once in a blue moon: detection of ‘bluing’ during debris transits in the white dwarf WD 1145+017
The first transiting planetesimal orbiting a white dwarf was recently detected in K2 data of WD 1145+017 and has been followed up intensively. The multiple, long and variable transits suggest the transiting objects are dust clouds, probably produced by a disintegrating asteroid. In addition, the system contains circumstellar gas, evident by broad absorption lines, mostly in the u΄ band, and a dust disc, indicated by an infrared excess. Here we present the first detection of a change in colour of WD 1145+017 during transits, using simultaneous multiband fast-photometry ULTRACAM measurements over the u΄g΄r΄i΄ bands. The observations reveal what appears to be ‘bluing' during transits; transits are deeper in the redder bands, with a u΄ − r΄ colour difference of up to ∼−0.05 mag. We explore various possible explanations for the bluing, including limb darkening or peculiar dust properties. ‘Spectral' photometry obtained by integrating over bandpasses in the spectroscopic data in and out of transit, compared to the photometric data, shows that the observed colour difference is most likely the result of reduced circumstellar absorption in the spectrum during transits. This indicates that the transiting objects and the gas share the same line of sight and that the gas covers the white dwarf only partially, as would be expected if the gas, the transiting debris and the dust emitting the infrared excess are part of the same general disc structure (although possibly at different radii). In addition, we present the results of a week-long monitoring campaign of the system using a global network of telescopes
Opt/NIR obs. of M31N 2008-12a 2015 eruption
VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title \u27M31N 2008-12a - the remarkable recurrent nova in M31: panchromatic observations of the 2015 eruption.\u27 (bibcode: 2016ApJ...833..149D