65 research outputs found
A new catalogue of Stroemgren-Crawford uvbybeta photometry
A new all-sky catalogue of all available uvbybeta measurements from the
literature was generated. The uvbybeta photometric system is widely used for
the study of various Galactic and extragalactic objects. It measures the colour
due to temperature differences, the Balmer discontinuity, and blanketing
absorption due to metals. The data for the individual stars were cross-checked
on the basis of the Tycho-2 catalogue. This catalogue includes very precise
celestial coordinates, but is magnitude and spatial resolution limited.
However, the loss of objects is only marginal and is compensated for by the
gain of homogeneity. In total, 298 639 measurements of 60 668 stars were used
to derive unweighted mean indices and their errors. Photoelectric and CCD
observations were treated in the same way. The presented data set can be used
for various applications such as new calibrations of astrophysical parameters,
the standardization of new observations, and as additional information for
ongoing and forthcoming all-sky surveys.Comment: Accepted for publication in Astronomy and Astrophysics: 3 pages, 3
figures, 1 tabl
The astrophysical parameters of chemically peculiar stars from automatic methods
The chemically peculiar (CP) stars of the upper main sequence are excellent
astrophysical laboratories for investigating the diffusion, mass loss,
rotational mixing, and pulsation in the presence and absence of a stable local
magnetic field. For this, we need a homogeneous set of parameters, such as
effective temperature and surface gravity, to locate the stars in the
Hertzsprung-Russell diagram so that we can then estimate the mass, radius, and
age. In recent years, the results of several automatic pipelines have been
published; these use various techniques and data sets, including effective
temperature and surface gravity values for millions of stars. Because CP stars
are known to have flux anomalies, these astrophysical parameters must be tested
for their reliability and usefulness. If the outcome is positive, these can be
used to analyse the new and faint CP stars published recently. I compared
published effective temperature and surface gravity values of a set of CP
stars, which are mostly based on high-resolution spectroscopy, with values from
four automatic pipeline approaches. In doing so, I searched for possible
correlations and offsets. I present a detailed statistical analysis of a
comparison between the `standard' and published effective temperature and
surface gravity values. The accuracy depends on the presence of a magnetic
field and the spectral type of the CP subgroups. However, I obtain standard
deviations of between 2% and 20%. Considering the statistical errors, the
astrophysical parameters from the literature can be used for CP stars, although
caution is advised for magnetic CP stars.Comment: 4 pages. 2 figures, accepted by Astronomy & Astrophysic
A plethora of new, magnetic chemically peculiar stars from LAMOST DR4
Magnetic chemically peculiar (mCP) stars are important to astrophysics
because their complex atmospheres lend themselves perfectly to the
investigation of the interplay between such diverse phenomena as atomic
diffusion, magnetic fields, and stellar rotation. The present work is aimed at
identifying new mCP stars using spectra collected by the Large Sky Area
Multi-Object Fiber Spectroscopic Telescope (LAMOST). Suitable candidates were
selected by searching LAMOST DR4 spectra for the presence of the characteristic
5200A flux depression. Spectral classification was carried out with a modified
version of the MKCLASS code and the accuracy of the classifications was
estimated by comparison with results from manual classification and the
literature. Using parallax data and photometry from Gaia DR2, we investigated
the space distribution of our sample stars and their properties in the
colour-magnitude diagram. Our final sample consists of 1002 mCP stars, most of
which are new discoveries (only 59 previously known). Traditional mCP star
peculiarities have been identified in all but 36 stars, highlighting the
efficiency of the code's peculiarity identification capabilities. The derived
temperature and peculiarity types are in agreement with manually derived
classifications and the literature. Our sample stars are between 100 Myr and 1
Gyr old, with the majority having masses between 2M(Sun) and 3M(Sun). Our
results could be considered as strong evidence for an inhomogeneous age
distribution among low-mass (M < 3M(Sun)) mCP stars. We identified several
astrophysically interesting objects: two mCP stars have distances and
kinematical properties in agreement with halo stars; an eclipsing binary system
hosting an mCP star component; and an SB2 system likely comprising of an mCP
star and a supergiant component.Comment: 62 pages, 24 figures, 10 tables, corrected some typos and minor
mistakes; corrected wrong number of stars with absolute parallax errors less
than 25
Observation of the Open Clusters in the UltraViolet
My poster is related to observing the new open clusters in Ultraviolet and analyzing their data in photometry.
We observed via the DK1.54 meter telescope in Chile and the CASLEO telescope in Argentina in the Ultraviolet filter because it is the best way of observation for Reddening. Reddening is independent of distance, age, and metallicity.
Our method is Isochrone fitting for our observed open clusters. For Isochrone fitting, we need Reddening.
Our goals are: 1) Are these new open clusters that we observed with DK1.54 and CASLEO telescopes real open clusters or not? 2) Do Reddening for all our observed clusters.
The Gaia Data Release 3 will allow us to precisely study known Galactic open clusters. We collected the available photometric and astrometric data and then observed new open clusters with DK1.54 and CASLEO telescopes photometrically in the Ultraviolet region in a homogeneous way.
With these data, a first homogeneous census of the open clusters in the Milky Way using Ultraviolet photometry can be derived and compared to the literature
The status of Galactic field lambda Bootis stars in the post-Hipparcos era
The lambda Bootis stars are Population I, late B to early F-type stars, with
moderate to extreme (up to a factor 100) surface underabundances of most
Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). To
put constraints on the various existing theories that try to explain these
peculiar stars, we investigate the observational properties of lambda Bootis
stars compared to a reference sample of normal stars. Using various photometric
systems and Hipparcos data, we analyze the validity of standard photometric
calibrations, elemental abundances, and Galactic space motions. There
crystallizes a clear picture of a homogeneous group of Population I objects
found at all stages of their main-sequence evolution, with a peak at about 1
Gyr. No correlation of astrophysical parameters such as the projected
rotational velocities or elemental abundances with age is found, suggesting
that the a-priori unknown mechanism, which creates lambda Bootis stars, works
continuously for late B to early F-type stars in all stages of main-sequence
evolution. Surprisingly, the sodium abundances seem to indicate an interaction
between the stars and their local environment.Comment: 14 pages, 9 figures, accepted by MNRA
Analysis of photometric and spectroscopic variability of red supergiant Betelgeuse
Betelgeuse is a pulsating red supergiant whose brightness is semi
periodically variable and in February 2020 reached a historical minimum, the
Great Dimming. The aims of this study are to characterize Betelgeuse's
variability based on available archival data and to study possible causes of
light variability. Many spectra, from ultraviolet and optical regions, were
evaluated for spectral analysis. The spectra were used primarily to determine
radial velocities from different layers of atmosphere and their long{-}term
evolution. Additionally, photometric data were analyzed in different filters as
well, to construct light curves and to determine periods of the variability.
Spectroscopic and photometric variability are compared to each other and given
into a context with the Great Dimming.
The two most dominant photometric periods are and , while the dominant optical radial
velocity periods are and . In the same time, the radial velocity
determined from ultraviolet spectra also shows variability and is distinctively
different from the variability of photospheric velocity, undergoing longer
periods of variability. We attribute these velocities to the velocities at the
base of outflowing wind. We also report a maximum of stellar wind velocity
during the Great Dimming, accompanied by the previously reported minimum of
brightness and the maximum of photospheric radial velocity. After the Dimming,
Betelgeuse mode of variability has fundamentally changed and is now instead
following a shorter period of .Comment: 12 pages, 4 figures, 5 table
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