72 research outputs found
New inclination changing eclipsing binaries in the Magellanic Clouds
Context: Multiple stellar systems are unique laboratories for astrophysics.
Analysis of their orbital dynamics may reveal invaluable information about the
physical properties of the participating stars. Unfortunately, there are only a
few known and well described multiple systems, this is even more so for systems
located outside the Milky Way galaxy. A particularly interesting situation
occurs when the inner binary in a compact triple system is eclipsing. This is
because the stellar interaction, typically resulting in precession of orbital
planes, may be observable as a variation of depth of the eclipses on a long
timescale. Aims: We aim to present a novel method to determine compact triples
using publicly available photometric data from large surveys. Here we apply it
to eclipsing binaries (EBs) in Magellanic Clouds from OGLE III database.
Methods: We analyzed light curves (LCs) of 26121 LMC and 6138 SMC EBs with the
goal to identify those for which the orbital inclination varies in time.
Archival LCs of the selected systems, when complemented by our own observations
with Danish 1.54m telescope, were thoroughly analyzed using the PHOEBE program.
Time dependence of the EB's inclination was described using the theory of
orbital-plane precession. By observing the parameter-dependence of the
precession rate, we were able to constrain the third companion mass and its
orbital period around EB. Results: We identified 58 candidates of new compact
triples in Magellanic Clouds. This is the largest published sample of such
systems so far. Eight of them were analyzed thoroughly and physical parameters
of inner binary were determined together with an estimation of basic
characteristics of the third star. These data may provide important clues about
stellar formation mechanisms for objects with different metalicity than found
in our galactic neighborhood.Comment: Accepted for publication in Astronomy and Astrophysic
Time-dependent spectral-feature variations of stars displaying the B[e] phenomenon III. HD 50138
We analyse spectroscopic observations of the B[e] star HD 50138 (MWC 158,
V743 Mon, or IRAS 06491-0654), a member of the FS CMa group, obtained over the
last twenty years. Four different epochs are identified in the observational
data, where the variability of the spectral features is substantially
different. Additionally, two long periods of (3 000 +/- 500) and (5 000 +/-
1000) days are found in the variations of the equivalent widths of the H alpha
and [OI] 6300 A lines and radial velocities of the H alpha line violet peak.
Modest signatures of a regular period of ~34 days in the radial velocities of
the H alpha red peak and H beta central depression are found in the season
2013/2014. The H alpha V/R changes indicate a periodicity of ~50 days. The
correlations between individual spectral features significantly restricts the
model of the object and suggest that it is most likely a binary system with a
highly distorted disc with spiral arms around the primary component. At the
same time, no obvious signs of the secondary component has been found in the
object's spectrum
Učební úlohy ve výuce fyziky na 2. stupni základní školy: vybrané výsledky CPV videostudie fyziky
Učební úlohy představují soubor specifických požadavků kladených na žákovo učení. Z hlediska didaktiky je klíčovou otázka, jaký potenciál mají učební úlohy pro procesy učení. Předkládané výzkumné sdělení je zaměřeno právě tímto směrem. Na základě systematické analýzy videozáznamů 27 vyučovacích hodin fyziky na 2. stupni základní školy je hledána odpověď na otázky: Kolik učebních úloh je řešeno ve vyučovací hodině a v jakém časovém zastoupení? Kolik času zaujímají fáze zadávání, řešení a kontroly úloh? Kdo je řešitelem úloh? Jaký typ řešení úlohy vyžadují? Výsledky ukazují, že práce s učebními úlohami zaujímá 63 % všech posuzovaných sekvencí, což odpovídá přibližně 6 úlohám za jednu vyučovací hodinu. Dále bylo zjištěno, že nejčastěji řeší úlohy učitel v interakci se žáky, nejvíce úloh vyžaduje slovní řešení a nejméně jsou zastoupeny úlohy řešené experimentálně
DIAMOND DEPOSITION ON WC-Co CUTTING TOOLS AFTER PRE-TREATMENT IN REACTIVE SOLUTIONS
We describe the influence of pre-treatment procedures on the adhesion of diamond films to WC-Co substrates. Annealing of substrates at 600˚C in vacuum and repeated etching in different reactive solutions (Al(OH)2-COOH diluted in acetic acid, Murakami and HCl:HNO3) were studied with respect to their effectiveness in suppressing C diffusion into Co on the WCCo surface. Substrates were coated with polycrystalline diamond films by the dual plasma HF CVD method. Raman spectra confirmed the existence of the diamond phase on all samples. Film surface morphology varied with the pre-treatment method used. Adhesion strength was evaluated using the scratch test
First apsidal motion and light curve analysis of 162 eccentric eclipsing binaries from LMC
We present an extensive study of 162 early-type binary systems located in the
LMC galaxy that show apsidal motion and have never been studied before. For the
ample systems, we performed light curve and apsidal motion modelling for the
first time. These systems have a median orbital period of 2.2 days and typical
periods of the apsidal motion were derived to be of the order of decades. We
identified two record-breaking systems. The first, OGLE LMC-ECL-22613, shows
the shortest known apsidal motion period among systems with main sequence
components (6.6 years); it contains a third component with an orbital period of
23 years. The second, OGLE LMC-ECL-17226, is an eccentric system with the
shortest known orbital period (0.9879 days) and with quite fast apsidal motion
period (11 years). Among the studied systems, 36 new triple-star candidates
were identified based on the additional period variations. This represents more
than 20% of all studied systems, which is in agreement with the statistics of
multiples in our Galaxy. However, the fraction should only be considered as a
lower limit of these early-type stars in the LMC because of our method of
detection, data coverage, and limited precision of individual times of
eclipses.Comment: 24 pages, 18 figures, 5 tables, published in 2020A&A...640A..33
Translanguaging in mainstream education:a sociocultural approach
Due to the monolingual self-understanding of European nation-states, migration-induced multilingualism and the language mixing practices it triggers are not usually acknowledged as resources for learning within mainstream classrooms. The term translanguaging has recently been put forward as both a way of describing the flexible ways in which bilinguals draw upon their multiple languages to enhance their communicative potential and a pedagogical approach in which teachers and pupils use these practices for learning. However, little research has been conducted in how the translanguaging approach can be used in mainstream education to enhance knowledge. This study draws on videographic data recorded in 59 10th grade (15-year-olds) subject-matter classes in 4 secondary schools. Applying sociocultural discourse analysis to peer–peer interaction and therefore considering how learners scaffold one another as they participate in collaborative talk and in the co-construction of knowledge, results describe several functions of translanguaging for ‘exploratory talk’ leading to content-matter learning. Multilingual adolescents in naturalistic settings thus use their multilingualism to cognitively engage with content-based tasks and produce high-order speech acts embedded in complex talk
Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis
CU Vir and V901 Ori belong among these few magnetic chemically peculiar stars
whose rotation periods vary on timescales of decades. We aim to study the
stability of the periods in CU Vir and V901 Ori using all accessible
observational data containing phase information. We collected all available
relevant archived observations supplemented with our new measurements of these
stars and analysed the period variations of the stars using a novel method that
allows for the combination of data of diverse sorts. We found that the shapes
of their phase curves were constant, while the periods were changing. Both
stars exhibit alternating intervals of rotational braking and acceleration. The
rotation period of CU Vir was gradually shortening until the year 1968, when it
reached its local minimum of 0.52067198 d. The period then started increasing,
reaching its local maximum of 0.5207163 d in the year 2005. Since that time the
rotation has begun to accelerate again. We also found much smaller period
changes in CU Vir on a timescale of several years. The rotation period of V901
Ori was increasing for the past quarter-century, reaching a maximum of 1.538771
d in the year 2003, when the rotation period began to decrease. A theoretically
unexpected alternating variability of rotation periods in these stars would
remove the spin-down time paradox and brings a new insight into structure and
evolution of magnetic upper-main-sequence stars.Comment: 5 pages, 3 figure
Science with a small two-band UV-photometry mission II: Observations of stars and stellar systems
We outline the impact of a small two-band UV-photometry satellite mission on
the field of stellar physics, magnetospheres of stars, binaries, stellar
clusters, interstellar matter, and exoplanets. On specific examples of
different types of stars and stellar systems, we discuss particular
requirements for such satellite missions in terms of specific mission
parameters such as bandpass, precision, cadence, and mission duration. We show
that such a mission may provide crucial data not only for hot stars that emit
most of their light in UV, but also for cool stars, where UV traces their
activity. This is important, for instance, for exoplanetary studies, because
the level of stellar activity influences habitability. While the main asset of
the two-band UV mission rests in time-domain astronomy, an example of open
clusters proves that such a mission would be important also for the study of
stellar populations. Properties of the interstellar dust are best explored when
combining optical and IR information with observations in UV. It is well known
that dust absorbs UV radiation efficiently. Consequently, we outline how such a
UV mission can be used to detect eclipses of sufficiently hot stars by various
dusty objects and study disks, rings, clouds, disintegrating exoplanets or
exoasteroids. Furthermore, UV radiation can be used to study the cooling of
neutron stars providing information about the extreme states of matter in the
interiors of neutron stars and used for mapping heated spots on their surfaces.Comment: Submitted to Space Science Review
Quick Ultra-VIolet Kilonova surveyor (QUVIK)
We present a near-UV space telescope on a ~70kg micro-satellite with a
moderately fast repointing capability and a near real-time alert communication
system that has been proposed in response to a call for an ambitious Czech
national mission. The mission, which has recently been approved for Phase 0, A,
and B1 study shall measure the brightness evolution of kilonovae, resulting
from mergers of neutron stars in the near-UV band and thus it shall distinguish
between different explosion scenarios. Between the observations of transient
sources, the satellite shall perform observations of other targets of interest,
a large part of which will be chosen in open competition.Comment: SPIE Astronomical Telescopes and Instrumentatio
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