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1

Radial Velocity Variations of the Hα and NaI D Lines for the High-Latitude Supergiant Star 89 Her

Khalilov A. M., Hajiyeva G. M., Hasanova A. R., Hasanova A. B.

Acta Astronomica

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2022

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Vol. 72, No. 4

297--313

EN

The variations in the spectral parameters of the Hα and sodium doublet NaI D lines of the high-latitude supergiant 89 Her were investigated on the basis of the spectrograms obtained at the 2-m telescope of Shamakhy Astrophysical Observatory between 1975 and 2017. The research has shown that, in addition to shorter periodic changes, which were found earlier by various authors, there are also long period changes in the atmosphere of this star. It has been found that the Hα and sodium doublet NaI D line's radial velocity and the equivalent width of the absorption component vary with a period of 5000 d. The orbital elements of the binary system were determined for the first time within the spectroscopic-binary system model.

2

V2676 Oph: Estimating Physical Parameters of a Moderately Fast Nova

Raj A., Pavana M., Kamath U. S., Anupama G. C., Walter M. F.

Acta Astronomica

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2018

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Vol. 68, No. 1

79--88

EN

Using our previously reported observations, we derive some physical parameters of the moderately fast nova V2676 Oph 2012 #1. The best-fit Cloudy model of the nebular spectrum obtained on 2015 May 8 shows a hot white dwarf source with TBB≈1.0×105 K having a luminosity of 1.0×1038 erg/s. Our abundance analysis shows that the ejecta are significantly enhanced relative to solar, He/H=2.14, O/H=2.37, S/H=6.62 and Ar/H=3.25. The ejecta mass is estimated to be 1.42×10-5 M⊙. The nova showed a pronounced dust formation phase after 90 d from discovery. The J-H and H-K colors were very large as compared to other molecule- and dust-forming novae in recent years. The dust temperature and mass at two epochs have been estimated from spectral energy distribution fits to infrared photometry.

3

High Proper Motion Objects toward the Inner Milky Way: Characterization of Newly Identified Nearby Stars from the VISTA Variables in the Vía Láctea Survey

Gromadzki M., Kurtev R., Beamán J. C., Tekola A., Ramphul R., Ivanov V. D., Minniti D., Folkes S. L., Vaisanen P., Kniazev A. Y., Borissova J., Parsons S. G., Villanueva V.

Acta Astronomica

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2016

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Vol. 66, No. 3

293--306

EN

The census of the Solar neighborhood is still incomplete, as demonstrated by recent discoveries of many objects within 5-10 pc from the Sun. The area around the mid-plane and bulge of the Milky Way presents the most difficulties in searches for such nearby objects, and is therefore deficient in the known population. This is largely due to high stellar densities encountered. Spectroscopic, photometric and kinematic characterization of these objects allows better understanding of the local mass function, the binary fraction, and provides new interesting targets for more detailed studies. We report the spectroscopic follow-up and characterization of twelve bright high proper motion objects, identified from the VISTA Variables in Vía Láctea survey (VVV). We used the 1.9-m telescope of the South African Astronomical Observatory (SAAO) for low-resolution optical spectroscopy and spectral classification, and the MPG/ESP 2.2-m telescope Fiber-fed Extended Range Optical Spectrograph (FEROS) high-resolution optical spectroscopy to obtain the radial and space velocities for three of them. Six of our objects have co-moving companions. We derived optical spectral types and photometric distances, and classified all of them as K and M dwarfs within 27-264 pc from the Sun. Finally, we found that one of the sources, VVV J141421.23-602326.1 (a co-moving companion of VVV J141420.55-602337.1), appears to be a rare massive white dwarf located close to the ZZ Cet instability strip in the CMD and CC diagrams. Many of the objects in our list are interesting targets for exoplanet searches.

4

Oxygen Issue in Core Collapse Supernovae

Elmhamdi A.

Acta Astronomica

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2011

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Vol. 61, No. 2

179--198

EN

We study the spectroscopic properties of a selected sample of 26 events within Core Collapse Supernovae (CCSNe) family. Special attention is paid to the nebular oxygen forbidden line [OI] 6300, 6364 Å doublet. We analyze the line flux ratio F6300/F6364 and infer information about the optical depth evolution, densities, volume-filling factors in the oxygen emitting zones. The line luminosity is measured for the sample events and its evolution is discussed on the basis of the bolometric light curve properties in type II and in type Ib-c SNe. The luminosities are then translated into oxygen abundances using two different methods. The results are combined with the determined 56Ni masses and compared with theoretical models by means of the [O/Fe] vs. Mms diagram. Two distinguishable and continuous populations, corresponding to Ib-c and type II SNe, are found. The higher mass nature of the ejecta in type II objects is also imprinted in the [CaII] 7291, 7324Å to [OI] 6300, 6364Å luminosity ratios. Our results may be used as input parameters for theoretical models studying the chemical enrichment of galaxies.

5

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.

6

Orbital Solutions for Three RS CVn Systems: WY Cnc, SV Cam and XY UMa

Pojmański G.

Acta Astronomica

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1998

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Vol. 48, No. 4

711--727

EN

Near IR spectroscopic observations of WY Cnc, SV Cam and XY UMa binary systems of RS CVn type are presented. Systemic velocity and radial velocity semi-amplitudes of primary components in each system are derived using cross-correlation between cleaned spectra and G2 noiseless templates. Secondary semi amplitudes are determined from the primary subtracted spectra using the cross-correlation function maps and direct cross-correlation. Masses of the stars are derived and system properties briefly discussed. Primary components in all three systems seem to be more massive than was earlier deduced from their spectral classification. Regarding stellar masses, SV Cam should be classified as F5V+K0V pair. Observations of XY UMa fully confirm results obtained previously using a method for detecting faint secondaries in the low signal-to-noise spectra.