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1

Profiles of Interstellar Spectral Features Caused by Physical Parameters of Clouds

Krełowski J., Bondar A.

Acta Astronomica

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2022

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Vol. 72, No. 1

69--76

EN

The disk of our Galaxy is filled with clouds of diffuse matter, modifying spectra of distant stars. These clouds are sources of extinction, polarization and of spectral features such as atomic and molecular lines as well as the diffuse interstellar bands (DIBs), still of unknown origin, though likely molecular. Apparently physical parameters of individual translucent clouds are various. We try to provide some constraints on theoretical models of translucent interstellar clouds. It is demonstrated that intensities and profile details of DIBs can be determined using the ESPRESSO spectrograph fed by VLT. This possibility follows its very high resolution and signal-to-noise ratio, necessary to analyze atomic and molecular features, detectable in spectra of OB-stars, and originated in single (thus - likely optically thin) interstellar clouds. Our set of five high resolution (λ/δλ =140 000) ESPRESSO spectra of hot, reddened stars allows us to analyze profiles of some DIBs. It is argued that more high quality spectra from ESPRESSO are necessary to identify the DIB cariers.

2

On the Relation between Interstellar Spectral Features and Reddening

Krełowski J., Galazutdinov G., Godunova V., Bondar A.

Acta Astronomica

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2019

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Vol. 69, No. 2

159--175

EN

It is well known that interstellar spectral features correlate with color excess E(B-V). This suggests that measuring intensities of these features allows one to estimate reddening of stars. The aim of this paper is to check how tight intensities of interstellar diffuse bands (DIBs) are related to the amount of extinction, measured using E(B-V). We have measured equivalent widths of the strongest DIBs (centered at λλ 5780.6 Å, 5797.0 Å, 6196.0 Å, 6379.3 Å, 6613.5 Å, and 8620 Å), as well as of CH (near 4300.3 Å) and CH+ (near 4232.5 Å) in high resolution, high S/N ratio échelle spectra from several spectrographs. The equivalent widths of the 8620 DIB in noisy spectra were measured using a template which was constructed using the high quality spectrum of BD+40 4220. DIB relations with the color excess in the range 0.1-2.0 mag were examined. Our analysis demonstrates that all the above mentioned interstellar spectral features (except for, perhaps, 6379 DIB) do correlate with E(B-V) relatively tightly (with the Pearson's correlation coefficient of 0.8+). Moreover, the observed scatter is apparently not caused by measurement errors but of physical origin. We present several examples where the strength ratios of a DIB/molecule to E(B-V) are different than the average.

3

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.

4

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.

5

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.

6

Constant Intensities of Diffuse Interstellar Bands in the Spectrum of AE Aur

Krełowski J., Galazutdinov G. A., Bondar A., Byeong-Cheol L.

Acta Astronomica

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2017

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Vol. 67, No. 1

71--80

EN

Using spectra of the star AE Aur (HD 34078), covering the period 1997-2016, we prove that all strong diffuse interstellar bands are of the same intensity during the whole period of observations (inside 3-5% of the intensity). This is in sharp contrast to the behavior of both CH and CH+ features which, during the last six years, declined sharply by 13% and 28% respectively. Diffuse bands seem to behave more or less as interstellar atomic lines. We checked also the behavior of CaII lines which should be of constant intensities as the carrier fills the space evenly. Our observations confirm this and allow us to re-estimate the distance to HD 34078.

7

Variable Intensities of Molecular Features in the Spectrum of AE Aur

Krełowski J., Galazutdinov G. A., Mulas G., Bondar A., Musaev F. A., Shapovalova A., Cecchi-Pestellini C., Beletsky Y., Lee B. C.

Acta Astronomica

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2016

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Vol. 66, No. 3

391--403

EN

Using spectra of the star AE Aur (HD 34078), covering the period 1997-2015, we suggest that two strong molecular features of CH and CH+ underwent detectable changes of intensity. In the last five years both CH and CH+ declined sharply and systematically, with the CH/CH+ ratio steadily growing. No variations in the radial velocities of the observed interstellar features was detected during the covered period.