101 research outputs found
The orbital elements and physical properties of the eclipsing binary BD+36 3317, a probable member of Lyr cluster
Context. The fact that eclipsing binaries belong to a stellar group is
useful, because the former can be used to estimate distance and additional
properties of the latter, and vice versa. Aims. Our goal is to analyse new
spectroscopic observations of BD along with the photometric
observations from the literature and, for the first time, to derive all basic
physical properties of this binary. We aim to find out whether the binary is
indeed a member of the Lyr open cluster. Methods. The spectra were
reduced using the IRAF program and the radial velocities were measured with the
program SPEFO. The line spectra of both components were disentangled with the
program KOREL and compared to a grid of synthetic spectra. The final combined
radial-velocity and photometric solution was obtained with the program PHOEBE.
Results. We obtained the following physical elements of BD: , , , , ,
. We derived the effective temperatures
K, K. Both components
are located close to ZAMS in the Hertzsprung-Russell (HR) diagram and their
masses and radii are consistent with the predictions of stellar evolutionary
models. Our results imply the average distance to the system d = pc.
We re-investigated the membership of BD in the Lyr
cluster and confirmed it. The distance to BD, given above,
therefore represents an accurate estimate of the true distance for Lyr
cluster. Conclusions. The reality of the Lyr cluster and the cluster
membership of BD have been reinforced.Comment: 10 pages, 7 figures. Accepted for publication in A&
Human impact on the holocene vegetation development in North Macedonia.
This thesis aims to reconstruct the Holocene vegetation development in North Macedonia in relation to human activities; specifically, it focuses on the late Holocene period, when changes in land-use and settlement strategy were simultaneously taking place, which lead to an increased human pressure on the surrounding environment. To describe the vegetation development, a sedimentary profile from a small lake in the Pelister Mountains was chosen for analysis. A total of 25 samples were processed and analysed under a light microscope for the presence of pollen and non-pollen objects. Based on the results of pollen stratigraphy and radiocarbon dating, it was confirmed that the vegetation record covers the entire Holocene period. The early Holocene is characterized by a gradual increase in forest vegetation and a decrease in steppe vegetation. In the middle Holocene, secondary anthropogenic indicators show up in higher numbers. The late Holocene is already showing signs of continuous human presence. Compared to the lowlands, the mountain record shows a rather discontinuous presence of primary indicators, which nevertheless appear after the 5th millennium before present. High percentages of secondary indicators indicate continuous human influence in the mountains. Overall, it has been confirmed that...Tato práce si klade za cíl rekonstruovat holocénní vegetační vývoj v Severní Makedonii s ohledem na lidský vliv; konkrétně se zaměřuje na období pozdního holocénu, kdy současně probíhají změny ve využívání krajiny a ve strategii osídlení, jež vedou ke zvýšenému tlaku člověka na okolní prostředí. K popisu vývoje vegetace byl pro analýzu vybrán sedimentární profil z malého jezera v pohoří Pelister. Celkem 26 vzorků bylo zpracováno a analyzováno pod světelným mikroskopem na přítomnost pylových a nepylových objektů. Na základě výsledků pylové stratigrafie a radiokarbonového datování bylo potvrzeno, že vegetační záznam pokrývá celé období holocénu. Raný holocén je charakterizován postupným nárůstem lesní vegetace a poklesem stepní vegetace. Ve středním holocénu se objevují ve větší míře sekundární antropogenní indikátory. Pozdní holocén již vykazuje známky nepřetržité lidské přítomnosti. Ve srovnání s nížinami vykazuje horský záznam spíše nespojitou přítomnost primárních indikátorů (obilovin); vysoké procento sekundárních ukazatelů nicméně naznačuje nepřetržitý vliv člověka v horských oblastech. Celkově bylo potvrzeno, že horské masivy na území Severní Makedonie poskytují cenný záznam environmentálních změn, který je důležitý pro další paleoenvironmentální rekonstrukce v této oblasti. Klíčová slova:...Department of BotanyKatedra botanikyFaculty of SciencePřírodovědecká fakult
Properties and nature of Be stars: 29. Orbital and long-term spectral variations of \gamma\ Cassiopei\ae
A detailed analysis of more than 800 electronic high-resolution spectra of
gamma Cas, which were obtained during a time interval of over 6000 days (16.84
yrs) at several observatories, documents the smooth variations in the density
and/or extend of its circumstellar envelope. We found a clear anticorrelation
between the peak intensity and FWHM of the H alpha emission, which seems to
agree with recent models of such emission lines. The main result of this study
is a confirmation of the binary nature of the object, determination of a
reliable linear ephemeris T_{min.RV} = HJD (2452081.90.6) +
(203.520.08)*E, and a rather definitive set of orbital elements. We
clearly demonstrated that the orbit is circular within the limits of accuracy
of our measurements and has a semi-amplitude of radial-velocity curve of
4.300.09 (km/s). No trace of the low-mass secondary was found. The time
distribution of our spectra does not allow a reliable investigation of rapid
spectral variations, which are undoubtedly present in the spectra. We postpone
this investigation for a future study, based on series of dedicated whole-night
spectral observations
Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri
Radial-velocity variations of the H-alpha emission measured on the steep
wings of the H-alpha line, prewhitened for the long-time changes, vary
periodically with a period of (218.025 +/- 0.022)d, confirming the suspected
binary nature of the bright Be star Pleione, a member of the Pleiades cluster.
The orbit seems to have a high eccentricity over 0.7, but we also briefly
discuss the possibility that the true orbit is circular and that the
eccentricity is spurious owing to the phase-dependent effects of the
circumstellar matter. The projected angular separation of the spectroscopic
orbit is large enough to allow the detection of the binary with large optical
interferometers, provided the magnitude difference primary - secondary is not
too large. Since our data cover the onset of a new shell phase up to
development of a metallic shell spectrum, we also briefly discuss the recent
long-term changes. We confirm the formation of a new envelope, coexisting with
the previous one, at the onset of the new shell phase. We find that the full
width at half maximum of the H-alpha profile has been decreasing with time for
both envelopes. In this connection, we briefly discuss Hirata's hypothesis of
precessing gaseous disk and possible alternative scenarios of the observed
long-term changes
Hydrodynamical and radiative modeling of temporal H{\alpha} emission V/R variations caused by a discontinuous mass transfer in binaries
H{\alpha} emission V/R variations caused by a discontinous mass transfer in
interacting binaries with a rapidly rotating accreting star are modelled
qualititatively for the first time. The program ZEUS-MP was used for a
non-linear 3-D hydrodynamical modeling of a development of a blob of gaseous
material injected into an orbit around a star. It resulted in the formation of
an elongated disk with a slow prograde revolution. The LTE radiative transfer
program SHELLSPEC was used to calculate the H{\alpha} profiles originating in
the disk for several phases of its revolution. The profiles have the form of a
double emission and exhibit V/R and radial velocity variations. However, these
variations should be a temporal phenomenon since imposing a viscosity in given
model would lead to a circularization of the disk and fading-out of given
variations.Comment: accepted for a publication in Astronomical Journa
Properties and nature of Be stars 30. Reliable physical properties of a semi-detached B9.5e+G8III binary BR CMi = HD 61273 compared to those of other well studied semi-detached emission-line binaries
Reliable determination of the basic physical properties of hot emission-line
binaries with Roche-lobe filling secondaries is important for developing the
theory of mass exchange in binaries. It is a very hard task, however, which is
complicated by the presence of circumstellar matter in these systems. So far,
only a small number of systems with accurate values of component masses, radii,
and other properties are known. Here, we report the first detailed study of a
new representative of this class of binaries, BR CMi, based on the analysis of
radial velocities and multichannel photometry from several observatories, and
compare its physical properties with those for other well-studied systems. BR
CMi is an ellipsoidal variable seen under an intermediate orbital inclination
of ~51 degrees, and it has an orbital period of 12.919059(15) d and a circular
orbit. We used the disentangled component spectra to estimate the effective
temperatures 9500(200) K and 4655(50) K by comparing them with model spectra.
They correspond to spectral types B9.5e and G8III. We also used the
disentangled spectra of both binary components as templates for the 2-D
cross-correlation to obtain accurate RVs and a reliable orbital solution. Some
evidence of a secular period increase at a rate of 1.1+/-0.5 s per year was
found. This, together with a very low mass ratio of 0.06 and a normal mass and
radius of the mass gaining component, indicates that BR CMi is in a slow phase
of the mass exchange after the mass-ratio reversal. It thus belongs to a still
poorly populated subgroup of Be stars for which the origin of Balmer emission
lines is safely explained as a consequence of mass transfer between the binary
components.Comment: 17 pages, 5 figures, accepted for publication in Astronomy and
Astrophysics. appears in Astronomy and Astrophysics 201
A new study of the spectroscopic binary 7 Vul with a Be star primary
We confirmed the binary nature of the Be star 7~Vul, derived a~more accurate
spectroscopic orbit with an orbital period of (69.4212+/-0.0034) d, and
improved the knowledge of the basic physical elements of the system. Analyzing
available photometry and the strength of the \ha emission, we also document the
long-term spectral variations of the Be primary. In addition, we confirmed
rapid light changes with a~period of 0.5592 d, which is comparable to the
expected rotational period of the Be primary, but note that its amplitude and
possibly its period vary with time. We were able to disentangle only the He I
6678 A line of the secondary, which could support our tentative conclusion that
the secondary appears to be a hot subdwarf. A search for this object in
high-dispersion far-UV spectra could provide confirmation. Probable masses of
the binary components are ()~Mnom \ and ()~Mnom. If the
presence of a hot subdwarf is firmly confirmed, 7 Vul might be identified as a
rare object with a B4-B5 primary; all Be + hot subdwarf systems found so far
contain B0-B3 primaries.Comment: 17 pages, 23 figures, accepted for publication in Astronomy and
Astrophysic
Properties and nature of Be stars 31. The binary nature, light variability, physical elements, and emission-line changes of HD~81357
Reliable determination of the basic physical properties of hot emission-line
binaries with Roche-lobe filling secondaries is important for developing the
theory of mass exchange in binaries. It is not easy, however, due to the
presence of circumstellar matter. Here, we report the first detailed
investigation of a new representative of this class of binaries, HD~81357,
based on the analysis of spectra and photometry from several observatories.
HD~81357 was found to be a double-lined spectroscopic binary and an ellipsoidal
variable seen under an intermediate orbital inclination of
, having an orbital period of 33\fd77445(41) and a~circular
orbit. From an automated comparison of the observed and synthetic spectra, we
estimate the component's effective temperatures to be 12930(540)~K and
4260(24)~K. The combined light-curve and orbital solutions, also constrained by
a very accurate Gaia Data Release 2 parallax, give the following values of the
basic physical properties: masses and ~\Mnom, radii
and 13.97\pm0.05~\Rnom, and a~mass ratio 10.0\pm0.5$.
Evolutionary modelling of the system including the phase of mass transfer
between the components indicated that HD~81357 is a~system observed in the
final slow phase of the mass exchange after the mass-ratio reversal. Contrary
to what has been seen for similar binaries like AU~Mon, no cyclic light
variations were found on a~time scale an~order of magnitude longer than the
orbital period.
243,1 15%Comment: 16 pages, 9 figures; accepted for publication in Astronomy and
Astrophysic
The Ultraviolet Spectrum and Physical Properties of the Mass Donor Star in HD 226868 = Cygnus X-1
We present an examination of high resolution, ultraviolet spectroscopy from
Hubble Space Telescope of the photospheric spectrum of the O-supergiant in the
massive X-ray binary HD 226868 = Cyg X-1. We analyzed this and ground-based
optical spectra to determine the effective temperature and gravity of the O9.7
Iab supergiant. Using non-local thermodynamic equilibrium (non-LTE), line
blanketed, plane parallel models from the TLUSTY grid, we obtain T_eff = 28.0
+/- 2.5kK and log g > 3.00 +/- 0.25, both lower than in previous studies. The
optical spectrum is best fit with models that have enriched He and N
abundances. We fit the model spectral energy distribution for this temperature
and gravity to the UV, optical, and IR fluxes to determine the angular size of
and extinction towards the binary. The angular size then yields relations for
the stellar radius and luminosity as a function of distance. By assuming that
the supergiant rotates synchronously with the orbit, we can use the radius -
distance relation to find mass estimates for both the supergiant and black hole
as a function of the distance and the ratio of stellar to Roche radius. Fits of
the orbital light curve yield an additional constraint that limits the
solutions in the mass plane. Our results indicate masses of 23^{+8}_{-6} M_sun
for the supergiant and 11^{+5}_{-3} M_sun for the black hole.Comment: ApJ in pres
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