24 research outputs found
Elemental Abundance Analysis of Single and Binary Late-B Stars Using Sub-meter Class Telescopes: HR 342, HR 769, HR 1284, and HR 8705
We test the capabilities of 0.4 m telescopes equipped with an \'{e}chelle
spectrograph to derive fundamental parameters and elemental abundances of four
late-B type stars: HR 342, HR 769, HR 1284, and HR 8705. The medium resolution
(R~14000) spectra covering the wavelength range of 4380-7350 {\AA} of the four
stars have been obtained using the 40-cm-telescope in Ankara University Kreiken
Observatory (AUKR). Using spectrum synthesis, we were able to derive the
abundances of eleven chemical elements. We find that these stars do not show
remarkable departures from the solar abundances, except for HR 8705 and the
primary component of HR 1284, which exhibit slight underabundances of a few
elements, i.e., O, Mg, Al, Si, and Fe. We also find that HR 1284 is probably a
new spectroscopic binary star. In order to model the spectrum of this object,
one of us (TK) has developed a new graphic interface which allows us to
synthesize the composite spectrum of binary stars.Comment: 3 pages, 2 figures and 1 table. Accepted proceeding of the Observing
techniques, instrumentation and science for metre-class telescopes II
conference, September 24-28, 2018, Tatransk\'a Lomnica, Slovaki
Observing and modelling the young solar analogue EK Draconis: starspot distribution, elemental abundances, and evolutionary status
Observations and modelling of stars with near-solar masses in their early
phases of evolution is critical for a better understanding of how dynamos of
solar-type stars evolve. We examine the chemical composition and the spot
distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from
the HERMES Spectrograph (La Palma), we obtain the abundances of 23 elements
with respect to the solar ones, which lead to a , with
significant overabundance of Li and Ba. The s-process elements Sr, Y, and Ce
are marginally overabundant, while Co, Ni, Cu, Zn are marginally deficient
compared to solar abundances. The overabundance of Ba is most likely due to the
assumption of depth-independent microturbulent velocity. Li abundance is
consistent with the age and the other abundances may indicate distinct initial
conditions of the pre-stellar nebula. We estimate a mass of 1.04 and
an age of \,Myr using various spectroscopic and photometric
indicators. We study the surface distribution of dark spots, using 17 spectra
collected during 15 nights using the CAFE Spectrograph (Calar Alto). We also
conduct flux emergence and transport (FEAT) simulations for EK Dra's parameters
and produce 15-day-averaged synoptic maps of the likely starspot distributions.
Using Doppler imaging, we reconstruct the surface brightness distributions for
the observed spectra and FEAT simulations, which show overall agreement for
polar and mid-latitude spots, while in the simulations there is a lack of
low-latitude spots compared to the observed image. We find indications that
cross-equatorial extensions of mid-latitude spots can be artefacts of the less
visible southern-hemisphere activity.Comment: 15 pages, 16 figures, accepted for publication in MNRAS; corrections
in Abstract and Introductio
Electrical properties and I–V characteristics of 5,14-dihydro-5,7,12,14-tetraazapentacene doped Schottky barrier diode
Physical Parameters of Some Close Binaries: ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg
With the aim of providing new and up-to-date absolute parameters of some
close binary systems, new BVR CCD photometry was carried out at the Ankara
University Observatory (AUG) for five eclipsing binaries, ET Boo, V1123 Tau,
V1191 Cyg, V1073 Cyg and V357 Peg between April, 2007 and October, 2008. In
this paper, we present the orbital solutions for these systems obtained by
simultaneous light and radial velocity curve analyses. Extensive orbital
solution and absolute parameters for ET Boo system were given for the first
time through this study. According to the analyses, ET Boo is a detached binary
while the parameters of four remaining systems are consistent with the nature
of contact binaries. The evolutionary status of the components of these systems
are also discussed by referring to their absolute parameters found in this
study.Comment: this accepted paper will be published in New Astronom
Physical parameters of close binaries QX Andromedae, RW Comae Berenices, MR Delphini, and BD +07{\circ} 3142
Aims. We analyze new multicolor light curves and recently published radial
velocity curves for close binaries QX And, RW Com, MR Del, and BD +07{\circ}
3142 to determine the physical parameters of the components. Methods. The light
curves are analyzed using a binary star model based on Roche geometry to fit
the photometric observations. Spectroscopic parameters, such as the mass ratios
and spectral types, were taken from recent spectroscopic studies of the systems
in question. Results. Our findings provide consistent and reliable sets of
stellar parameters for the four studied binary systems. Of particular interest
is the BD +07{\circ} 3142 system, since this is the first analysis of its light
curves. We find that it is an overcontact binary of W UMa type and W subtype,
and that each component has a large cool spot in the polar region. QX And is an
A subtype, and RW Com a W subtype W UMa binary, and in both systems we find a
bright spot in the neck region between the components. MR Del is a detached
binary with a complex light curve that we could model with two cool spots on
the hotter component.Comment: 10 pages, 4 figures. Accepted for publication by A&
Mass–effective temperature–surface gravity relation for intermediate-mass main-sequence stars
Context. In this work a mass–effective temperature–surface gravity relation (MTGR) is developed for main-sequence stars in the range 6400 K ≤ Teff ≤ 20 000 K with log g ≳ 3.44. The MTGR allows the simple estimation of the masses of stars from their effective temperatures and surface gravities. It can be used for solar metallicity and can be rescaled for any metallicity within −1.0 ≤ [Fe/H] ≤ 0.7. The effect of α-enhanced compositions can also be considered with the help of correction terms.
Aims. It is aimed to develop an MTGR that can estimate the masses of main-sequence stars from their atmospheric parameters. One advantage of an MTGR over the classical mass–luminosity relations is that its mass estimation is based on parameters that can be obtained by purely spectroscopic methods, and, therefore, the interstellar extinction or reddening do not have to be known. The use of surface gravity (g) also relates an MTGR with stellar evolution and provides a more reliable mass estimation.
Methods. A synthetical MTGR is obtained from theoretical isochrones using a Levenberg-Marquardt χ2 minimization algorithm. The validity of the MTGR is then checked by testing over 278 binary components with precise absolute masses.
Results. Very good agreement has been obtained between the absolute masses of 278 binary star components and their masses estimated from the MTGR. A mathematical expression is also given to calculate the propagated uncertainties of the MTGR masses.
Conclusions. For the typical uncertainties in atmospheric parameters and metallicity (i.e., ±2.8% for Teff, ±0.1 dex for log g and ±0.15 dex for [Fe/H]) the typical uncertainties in the masses estimated from the MTGR mostly remain around 5–9%. The fact that this uncertainty level is only on average about three times as large as that of the absolute masses indicates that the MTGR is a very powerful tool for stellar mass estimation. A computer code, mtgr.pr
The Chemical Compositions of the Two New HgMn Stars HD 30085 and HD 30963: Comparison to χ Lupi A, ν Cap, and HD 174567
International audienc
Physical parameters of close binaries QX Andromedae, RW Comae Berenices, MR Delphini, and BD +07° 3142
Aims. We analyze new multicolor light curves and recently published
radial velocity curves for close binaries QX And, RW Com, MR Del, and BD +07°
3142 to determine the physical parameters of the components.
Methods. The light curves are analyzed using a binary star model based
on Roche geometry to fit the photometric observations. Spectroscopic parameters, such as
the mass ratios and spectral types, were taken from recent spectroscopic studies of the
systems in question.
Results. Our findings provide consistent and reliable sets of stellar
parameters for the four studied binary systems. Of particular interest is the BD
+07° 3142 system, since this is the first analysis of its light curves. We
find that it is an overcontact binary of W UMa type and W subtype, and that each component
has a large cool spot in the polar region. QX And is an A subtype, and RW Com a W subtype
W UMa binary, and in both systems we find a bright spot in the neck region between the
components. MR Del is a detached binary with a complex light curve that we could model
with two cool spots on the hotter component