230 research outputs found
Monitoring evolved stars for binarity with the HERMES spectrograph
Binarity is often invoked to explain peculiarities that can not be explained
by the standard theory of stellar evolution. Detecting orbital motion via the
Doppler effect is the best method to test binarity when direct imaging is not
possible. However, when the orbital period exceeds the duration of a typical
observing run, monitoring often becomes problematic. Placing a high-throughput
spectrograph on a small semi- robotic telescope allowed us to carry out a
radial-velocity survey of various types of peculiar evolved stars. In this
review we highlight some findings after the first four years of observations.
Thus, we detect eccentric binaries among hot subdwarfs, barium, S stars, and
post- AGB stars with disks, which are not predicted by the standard binary
interaction theory. In disk objects, in addition, we find signs of the on-
going mass transfer to the companion, and an intriguing line splitting, which
we attribute to the scattered light of the primary.Comment: To appear in the proceedings of the conference "Setting a new
standard in the analysis of binary stars", A. Tkachenko (ed.), European
Astron. Soc. Publ. Se
Debris Disks around Solar-Type Stars: Observations of the Pleiades with Spitzer Space Telescope
We present Spitzer MIPS observations at 24 um of 37 solar-type stars in the
Pleiades and combine them with previous observations to obtain a sample of 71
stars. We report that 23 stars, or 32 +/- 6.8%, have excesses at 24 um at least
10% above their photospheric emission. We compare our results with studies of
debris disks in other open clusters and with a study of A stars to show that
debris disks around solar-type stars at 115 Myr occur at nearly the same rate
as around A-type stars. We analyze the effects of binarity and X-ray activity
on the excess flux. Stars with warm excesses tend not to be in equal-mass
binary systems, possibly due to clearing of planetesimals by binary companions
in similar orbits. We find that the apparent anti-correlations in the incidence
of excess and both the rate of stellar rotation and also the level of activity
as judged by X-ray emission are statistically weak.Comment: 34 pages; accepted for publication in ApJ; new version included
corrections of typos, etc to match published versio
IRAS 19135+3937: An SRd variable as interacting binary surrounded by a circumbinary disc
Semi-regular (SR) variables are not a homogeneous class and their variability
is often explained due to pulsations and/or binarity. This study focuses on
IRAS 19135+3937, an SRd variable with an infra-red excess indicative of a dusty
disc. A time-series of high-resolution spectra, UBV photometry as well as a
very accurate light curve obtained by the Kepler satellite, allowed us to study
the object in unprecedented detail. We discovered it to be a binary with a
period of 127 days. The primary has a low surface gravity and an atmosphere
depleted in refractory elements. This combination of properties unambiguously
places IRAS 19135+3937 in the subclass of post-Asymptotic Giant Branch stars
with dusty discs.
We show that the light variations in this object can not be due to
pulsations, but are likely caused by the obscuration of the primary by the
circumbinary disc during orbital motion. Furthermore, we argue that the
double-peaked Fe emission lines provide evidence for the existence of a gaseous
circumbinary Keplerian disc inside the dusty disc. A secondary set of
absorption lines has been detected near light minimum, which we attribute to
the reflected spectrum of the primary on the disc wall, which segregates due to
the different Doppler shift. This corroborates the recent finding that
reflection in the optical by this type of discs is very efficient. The system
also shows a variable Halpha profile indicating a collimated outflow
originating around the companion. IRAS 19135+3937 thus encompasses all the
major emergent trends about evolved disc systems, that will eventually help to
place these objects in the evolutionary context.Comment: Accepted to MNRA
THz transition radiation of electron bunch laser-accelerated in long-scale near-critical density plasmas
Direct laser electron acceleration in near-critical density plasma produces
collimated electron beams with high charge (up to C). This regime
could be of interest for high energy THz radiation generation, as many of the
mechanisms have a scaling . In this work we focused specifically
on challenges that arise during numerical investigation of transition radiation
in such interaction. Detailed analytical calculations that include both
diffraction and decoherence effects of characteristics of transition radiation
in the THz range were conducted with the input parameters obtained from 3D PIC
and hydrodynamic simulations. The calculated characteristics of THz radiation
are in good agreement with the experimentally measured ones. Therefore, this
approach can be used both to optimize properties of THz radiation and
distinguish the transition radiation contribution if several mechanisms of THz
radiation generation are considered
Universal quantum technologies of semantic comprehension skills formation in junior schoolchildren
The aim of the study is to consider a range of issues related to the difficulties in the development of universal learning actions (ULA) of pupils, presented in the Conception of the same name, from the position of psychology and to explore the essence of innovative quantum technologies of semantic comprehension skills formation as a universal metasubject competence of learners.Π ΡΡΠ°ΡΡΠ΅ ΡΠ°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°ΡΡΡΡ ΡΡΡΠ΄Π½ΠΎΡΡΠΈ Π² ΡΠ°Π·Π²ΠΈΡΠΈΠΈ ΡΠ½ΠΈΠ²Π΅ΡΡΠ°Π»ΡΠ½ΡΡ
ΡΡΠ΅Π±Π½ΡΡ
Π΄Π΅ΠΉΡΡΠ²ΠΈΠΉ ΡΡΠ°ΡΠΈΡ
ΡΡ ΠΈ ΡΠ°ΡΠΊΡΡΠ²Π°Π΅ΡΡΡ ΡΡΡΠ½ΠΎΡΡΡ ΠΈΠ½Π½ΠΎΠ²Π°ΡΠΈΠΎΠ½Π½ΡΡ
ΠΊΠ²Π°Π½Ρ-ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠΉ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΡΠΌΡΡΠ»ΠΎΠ²ΠΎΠ³ΠΎ Π°ΡΠ΄ΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΊΠ°ΠΊ ΡΠ½ΠΈΠ²Π΅ΡΡΠ°Π»ΡΠ½ΠΎΠΉ ΠΌΠ΅ΡΠ°ΠΏΡΠ΅Π΄ΠΌΠ΅ΡΠ½ΠΎΠΉ ΠΊΠΎΠΌΠΏΠ΅ΡΠ΅Π½ΡΠΈΠΈ ΠΌΠ»Π°Π΄ΡΠΈΡ
ΡΠΊΠΎΠ»ΡΠ½ΠΈΠΊΠΎΠ²
Southern Infrared Proper Motion Survey I: Discovery of New High Proper Motion Stars From First Full Hemisphere Scan
We present the first results from the Southern Infrared Proper Motion Survey.
Using 2 Micron All Sky Survey data along with that of the SuperCOSMOS sky
survey we have been able to produce the first widefield infrared proper motion
survey. Having targeted the survey to identify nearby M, L and T dwarfs we have
discovered 72 such new objects with proper motions greater than 0.5''/yr with
10 of these having proper motions in excess of 1''/yr. The most interesting of
these objects is SIPS1259-4336 a late M dwarf. We have calculated a
trigonometric parallax for this object of milliarcseconds
yielding a distance of pc. We have also discovered a common proper
motion triple system and an object with a common proper motion with LHS 128.
The survey completeness is limited by the small epoch differences between many
2MASS and UKI observations. Hence we only recover 22% of Luyten objects with
favourable photometry. However the Luyten study is itself unquantifiably
incomplete. We discuss the prospect of enhancing the survey volume by reducing
the lower proper motion limit.Comment: 20 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Transition Metall-Free C-H/C-H and C-LI/C-H Coupling in the Synthesis of New Azaheterocycles Derivatives
The study was carried out with the financial support of the Russian Foundation for Basic Research in the framework of a research project 18-33-00226 and Russian Science Foundation as part of a research project 18-73-00088
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