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1

Central Wavelengths and Profile Shapes of Diffuse Interstellar Bands versus Physical Parameters of Intervening Clouds

Krełowski J., Marić T., Karipis A., Strobel A., Galazutdinov G. A.

Acta Astronomica

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2019

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Vol. 69, No. 4

369--380

EN

We investigate whether there are variations of the central wavelengths or the profile shapes of diffuse interstellar bands and whether these variations are caused by different physical parameters of translucent clouds. For this purpose we used spectra of two stars seen through two different single clouds: HD 34078 (AE Aur) and HD 73882. The wavelength displacements of the diffuse interstellar bands at 6196 Å, 6203 Å, 6376 Å, 6379 Å and 6614 Å with respect to the well known interstellar atomic and molecular lines (KI and CH) were measured. The shift is seemingly absent in the diffuse interstellar bands at 4726 Å, 4964 Å, 4763 Å, and 4780 Å. In addition the considered profiles may show (in HD 34078) extended red wings. The observed phenomena are likely related to physical parameters of intervening clouds (rotational temperatures of molecular species) and may help in the identification of the diffuse interstellar band carriers.

2

On the Distance Measurements in the Thin Milky Way Disk

Krełowski J., Strobel A., Galazutdinov G. A., Musaev F., Bondar A.

Acta Astronomica

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2018

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Vol. 68, No. 3

285--300

EN

We present a test how far the direct, trigonometric parallax measurements and those, based on interstellar CaII H and K lines lead to distances to OB stars similar to those, based on spectrophotometrically determined ones. For this we use relatively nearby objects where the extinction effects are negligible. A test is based on observations of interstellar CaII H and K lines, that determine distances, in spectra of bright, nearby objects, free of extinction effects. For these objects one can find also trigonometric parallaxes. CaII H and K lines are weak in spectra of nearby stars and thus measurable only in high S/N ratio spectra. Such spectra being at our disposal also allow us to check the spectral classification of our targets and thus to comment the observed differences between distances acquired using different methods. Using four methods, we determined distances to nearly fifty B0-5 type stars, practically free of any extinction effects. We demonstrate that direct, astrometric, CaII H and K and spectrophotometric distances agree reasonably well in the absence of substantial interstellar extinction and when spectral classification is reliable. Apparently the absolute magnitude calibration, provided by Schmidt-Kaler, appears to be correct.

3

Spectrophotometric Distances - Problem of Interstellar Extinction

Krełowski J., Galazutdinov G. A., Strobel A., Bondar A.

Acta Astronomica

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2017

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Vol. 67, No. 3

281--296

EN

Distances to 112 hot reddened stars in the thin Galactic disk have been estimated with different methods and, their accuracies have been compared. Also, we have applied the CaII-method to test its relation to trigonometric parallax and the spectrophotometric one. Some interstellar clouds apparently contain especially large size dust grains which cause interstellar gray (neutral) extinction. The latter does not correlate with the typical color extinction and may falsify spectrophotometric distance estimates. We conclude that CaII and TiII based method provides in many cases the most correct and reliable distance estimates to hot, bright, distant stars in the thin disk of the Milky Way - more accurate than obtained with the spectrophotometric method.

4

On the Distance Measurements toward Young Milky Way Objects. I. Study of IC 2944

Krełowski J., Strobel A., Godunova V., Bondar A.

Acta Astronomica

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2017

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Vol. 67, No. 4

379--396

EN

We compare distances to a very young stellar aggregate, IC 2944, using three methods: direct parallaxes of Gaia, spectrophotometric parallax and our method based on intensities of interstellar CaII lines. The discrepancies between spectrophotometric distances and those, based on CaII K and H lines, were already reported. The interstellar CaII H and K lines allow one to determine both distances and radial velocities of the intervening clouds. Thus, these data allow us to check the aggregate membership. It is also possible to check the spectral classification of considered targets which is necessary for spectrophotometric parallaxes. Using three methods, we determined distances to IC 2944 stars. We demonstrate that CaII based distances agree very well with the kinematic ones but are generally much smaller than the spectrophotometric ones. We conclude that the majority of IC 2944 objects is obscured by clouds producing neutral ("gray") extinction which diminishes their brightness exactly like extended distances. This influences spectrophotometric parallaxes while those, based on the CaII lines, do not depend on extinction and this method seems to be the most reliable one inside the thin disk of our Galaxy. The Gaia trigonometric parallaxes lead to distances similar to those obtained using the CaII method if their errors are reasonably small.

5

Gray Extinction in the Orion Trapezium

Krełowski J., Galazutdinov G. A., Strobel A., Mulas G.

Acta Astronomica

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2016

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Vol. 66, No. 4

469--480

EN

We estimated distances to several Orion Trapezium stars using our CaII-method and confirm the distance recommended by Menten et al. However, we found that in the case of HD 37020 both individual distances (based on the trigonometric VLBI parallax and/or CaII-method) differ from the spectrophotometric distance by a factor of 2.5. We interpret this fact as a result of presence of gray (neutral) extinction of about 1.8 mag in front of this star. The correctness of the applied spectral type/ luminosity class, Sp/L, (based on new original spectra from HARPS-N) and measurements of color indices is discussed

6

Open Clusters in 2MASS Photometry. I. Structural and Basic Astrophysical Parameters

Bukowiecki Ł., Maciejewski G., Konorski P., Strobel A.

Acta Astronomica

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2011

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Vol. 61, No. 3

231--246

EN

The main goal of our project is to obtain a complete picture of individual open clusters from homogeneous data and then search for correlations between their astrophysical parameters. The near-infrared JHKS photometric data from the 2-Micron All Sky Survey were used to determine new coordinates of the centers, angular sizes and radial density profiles for 849 open clusters in the Milky Way. Additionally, age, reddening, distance, and linear sizes were also derived for 754 of them. For these open clusters our results are in satisfactory agreement with the literature data. The analyzed sample contains open clusters with ages in the range from 7 Myr to 10 Gyr. The majority of these clusters are located up to 3 kpc from the Sun, less than 0.4 kpc from the Galactic plane and 6-12 kpc from the Galactic center. The majority of clusters have core radii of about 1.5 pc and the limiting radii of the order of 10 pc. We notice that in the near-infrared, open clusters seem to be greater than in optical bands. We notice that a paucity of clusters is observed at galactic longitudes range from 140° to 200° which probably reflects the real spatial distribution of open clusters in the Galaxy. The lack of clusters was also found in earlier studies.

7

Statistical Indicators of Astrophysical Parameters

Wąż P., Bielińska-Wąż D., Strobel A., Pleskacz A.

Acta Astronomica

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2010

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Vol. 60, No. 3

283--293

EN

The aim of this paper is to introduce a new tool for a simple identification of spectral types. We use methods of statistical spectroscopy, in particular the method of intensity-distribution moments. The statistical approach revealed a characteristic behavior of moments of the stellar spectra for different spectral types. The transition from one spectral type to another may be expressed as a regular function of appropriate moments of the intensity distribution of the spectra. Moment-based diagrams localize particular spectral types in different areas of the plots. Since the intensity-distribution moments may be easily derived from the observed spectra, the presented method facilitates a simple auxiliary tool for the classification of stars to specific spectral types. It is also helpful in checking the correctness of the existing classifications. The intensity-distribution moments depend on all kinds of stellar characteristics, including the metallicity and the age. Therefore, using an inverse approach, from the knowledge of moments one may predict these properties.