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

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 $P_{1} = 2190 \pm 270 \: \rm d$ and $P_{2} = 417 \pm 17 \: \rm d$, while the dominant optical radial velocity periods are $P_{1, v_{\rm r}} = 2510 \pm 440 \: \rm d$ and $P_{2, v_{\rm r}} = 415 \pm 11 \: \rm d$. 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 $\sim 200 \: \rm d$.Comment: 12 pages, 4 figures, 5 table