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V. E. Panchuk

Publications and source records attributed to V. E. Panchuk.

At least 19 recordsLinked to original sources
arXiv2026

Long-term high-resolution spectroscopic monitoring of the evolved metal-poor binary PS Gem

We present results of long-term high-resolution spectroscopic monitoring of the extremely low-metallicity star PS Gem (=HD 52961), associated with IRAS 07008+1050. The spectra were obtained with the 6-meter BTA telescope at a resolving power of R=60000 during 1997--2025, providing a homogeneous dataset spanning nearly three decades. Quantitative measurements of the H$α$ two-peaked profile reveal repeatable phase-dependent variations of the peak-intensity ratio $I_{\rm V}/I_{\rm R}$ and the absorption-core velocity over multiple orbital cycles, whereas the peak separation remains nearly constant at $ΔV_r = 78\pm 4$ km s$^{-1}$. The heliocentric radial velocity measurements yield a systemic velocity of $γ=7.46\pm 0.64$ km s$^{-1}$ and an orbital semi-amplitude of $K=2.49$ km s$^{-1}$. No significant long-term secular drift is observed over the monitoring interval. The stellar luminosity, estimated from the equivalent width of the OI 7773 Ȧ triplet ($W_λ=1.16\pm$ 0.02 Ȧ), corresponds to $\log(L/L_{\odot})\approx$3.5. The average radial velocity of diffuse interstellar bands is consistent with the location of PS Gem in the Local Arm. These observations provide rare multi-decade time-domain constraints on the dynamical behavior of this evolved metal-poor star.

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arXiv2023

On the status of the star Schulte 12 in the association Cyg OB2

High-resolution spectra of the LBV candidate Schulte 12 in the Cyg OB2 association were obtained at the 6-meter BTA telescope with the NES echelle spectrograph on the arbitrary dates in 2001-2022. Variability of the emission profile of H$α$ and absorptions of HeI, SiII with time was found. Based on the radial velocity measurements at 10 observation dates, radial velocity variability with an amplitude of $Δ$Vr$\approx$8 km/s relative to the average value of the heliocentric velocity Vr=$-15.6\pm2.6$ km/s was revealed. This indicates the presence of a companion in the system. Based on the reliable intensity measurements of a sample of DIBs, color excess E(B-V)=1.74$\pm0.03^{m}$ was determined. This results in the interstellar extinction value Av$\approx 5.6^m$ that is only about half of the total extinction. Taking current Schulte 12 parameters, including Gaia~EDR3 parallax, we estimated its absolute magnitude as Mv$\approx -9.2^m$ and luminosity log$(L/L_{\odot})\approx$5.5, which does not exceed the Humphreys-Davidson limit.

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arXiv2022

Detailed spectroscopy of post-AGB supergiant GSC 04050$-$02366 in IRAS Z02229+6208 IR source system

In the optical spectra of the cold post-AGB supergiant GSC 04050$-$02366, obtained with the 6-meter BTA telescope with a spectral resolution of R$\ge$60000 on arbitrary dates over 2019$÷$2021, a radial velocity variability is found. Heliocentric Vr based on the positional measurements of numerous absorptions varies from date to date with a standard deviation of $Δ$Vr$\approx$1.4 km/s about the average value of Vr=24.75 km/s, which may stem out of the low-amplitude pulsations in the atmosphere. The spectra of the star are purely absorption type, there are no obvious emissions. Intensity variability of most of absorptions and Swan bands of the C$_2$ molecule was discovered. A slight asymmetry of the H$α$ profile is observed at some observation dates. The position of H$α$ absorption core varies within 27.3$÷$30.6 km/s. Splitting into two components (or asymmetry) of strong low-excitation absorptions (YII, ZrII, BaII, LaII, CeII, NdII) was found. The position of the long-wavelength component coincides with the position of other photospheric absorptions, which confirms its formation in the atmosphere of the star. The position of the shortwave component is close to the position of the rotational features of Swan bands, which indicates its formation in the circumstellar envelope expanding at a velocity of about Vexp=16 km/s.

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arXiv2022

Instability in the system of the distant post-AGB star LS III+52 24 (IRAS 22023+5249)

The optical spectra of the B-supergiant LS III+52 24 (IRAS 22023+5249) obtained at the 6-meter telescope BTA with a resolution R$\ge$60000 in 2010-2021 revealed signs of wind variability and velocity stratification in the extended atmosphere. The H$α$ and H$β$ lines have a P Cyg type profile; their wind absorption changes position in the range from $-270$ to $-290$ km/s. The intensity of the H$α$ emission reaches record values with respect to the local continuum: I/Icont $\approx$70. The stationary radial velocity according to the positions of symmetric forbidden emissions and permitted metal emissions was taken as the systemic velocity Vsys=$-149.6\pm$0.6 km/s. Based on the positions of absorptions of NII and OII ions, a time variability of the radial velocity in the range from $-127.2$ to $-178.3$ km/s was found for the first time for this star. This variability indicates the possible presence of a companion and/or atmospheric pulsations. The change of the oxygen triplet profile OI 7775 A due to the occurrence of unstable emission was registered. The set of interstellar absorptions of the NaI D-lines profile in the range from $-10.0$ to $-167.2$ km/s is formed in the Local Arm and subsequent arms of the Galaxy. The distance to the star, d$\ge$5.3 kpc, combined with the high systemic velocity, indicates that the star is located in the Galaxy beyond the Scutum-Crux arm.

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arXiv2022

Results of selected stellar spectroscopy programs at the 6-m telescope of SAO RAS performed with the NES echelle spectrograph

Over the past two decades the echelle spectrograph NES of the 6-m telescope was used to perform high resolution spectroscopy of far evolved stars spanning a wide range of initial masses. The studies cover a diversity of stars with high mass-loss rates during the preceding and current stages of evolution. All these stars have extended atmospheres and structured circumstellar envelopes produced by strong stellar winds. We have studied luminous blue variables near the Eddington limit; hot supergiants with B[e] phenomenon in spectra, which are very likely intermediate-mass binary systems soon after the fast mass exchange stage; a group of yellow hypergiants, as well as an extensive sample of low-mass post-AGB supergiants. The diverse nature of the types of these stars whose common feature is the presence of a circumstellar envelope makes the spectroscopy of such objects a comprehensive task. Such studies consist of many etapes, which include not only determining the peculiarities of their atmospheric chemical composition and understanding the role of supergiants in the enrichment of the interstellar medium with freshly synthesized elements, but also the determination of the evolution status of the objects considered, as well as search for and analysis of spectroscopic manifestations of kinematic processes in their extended and unstable atmospheres and gas-dust envelopes. We spectroscopically monitored selected objects to study in detail the instability of the kinematic state of the atmospheres of the stars considered. This review reports briefly the most significant observational obtained within the framework of the programs in 1998--2021.

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arXiv2020

High-resolution optical spectroscopy of the post-AGB supergiant V340 Ser (=IRAS 17279$-$1119)

Some evidences of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser (=IRAS 17279$-$1119) taken at the 6-m BTA telescope with a spectral resolution R$\ge$60000. The H$α$ line has a P Cyg profile whose absorption component (V=+34 km/s) is formed in the upper layers of the expanding atmosphere close to the circumstellar environment. For four dates the mean velocity has been derived from the positions of 300-550 symmetric metal absorptions with an accuracy better than $\pm0.1$ km/s: Vr=59.30, 60.09, 58.46, and 55.78 km/s. A lot of low-excitation metal lines have an inverse P Cyg profile. The mean positions of their emission components, Vr=46.3$\pm$0.4 km/s, differ systematically from the velocity inferred from symmetric absorptions, suggesting the presence of a velocity gradient in the supergiant extended atmosphere. The multicomponent profile of the NaI D-lines contains the interstellar, Vr=-11.2 km/s, and circumstellar, Vr=+10 km/s, components and the component forming in the upper atmospheric layers, Vr=+34.0 km/s. The mean velocity from 20-30 diffuse interstellar bands (DIBs) identified in the spectra, Vr(DIBs)=-11.6$\pm0.2$ km/s, agrees with the velocity from interstellar NaI and KI components. The equivalent width of the oxygen triplet W(7774)=1.25 A corresponds to an absolute magnitude of the star Mv$\approx-4.6^m$, which, taking into account the total (interstellar+circumstellar) extinction, leads to a distance to the star d$\approx$2.3 kpc.

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arXiv2019

Extended atmosphere of the yellow hypergiant V509 Cas in 1996-2018

Based on the data of spectral monitoring of the yellow hypergiant V509 Cas performed in 1996-2018 at the 6-m telescope with the spectral resolution of R$\ge$60 000, we studied in detail its kinematic state at various levels of extended atmosphere. No signs of presence of a companion were found. An agreement of radial velocities measured on the permitted and forbidden emissions of metal ions, as well as their strict temporal stability led us to the choice of the systemic velocity of the star Vsys=$-63$ km/s. The position of forbidden [NII] emissions forming in the circumstellar medium is strictly stable and is systematically shifted by $-6$ km/s relative to the metal ion emissions. A conclusion on the variation of the [NII] emission halfwidths and intensities (the lines have become narrower and more intense) is made after the observations in 1996 and these parameters did not vary over the next 22 years of observations. The velocities measured from the shortwave FeII(42) absorption components are located in a narrow interval of Vr=$-$(84$÷$87) km/s, which indicates the stability of expansion of the upper layers of the atmosphere. The overall atmosphere of the hypergiant is stable, excluding the layers close to the photosphere. The velocity variability in range of Vr=$-$(52$÷$71) km/s, identified by the positions of strong metal ion absorption cores, may be a manifestation of pulsations in deep atmospheric layers, where this type of lines are formed.

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arXiv2018

Changes of the optical spectrum of the hypergiant $ρ$ Cas due to a shell ejection in 2013

Spectral monitoring of the yellow hypergiant $ρ$ Cas with the by 6-m telescope of the Special Astrophysical Observatory with a spectral resolution of R$\ge$60000 has led to the detection of new features in the kinematic state of its extended atmosphere following the ejection of matter in 2013. Significant changes in the profile of the H$α$ line were detected: the line had a doubled core for the first time in a 2014 spectrum, an inverse P Cygni profile on December 13, 2017, and the profile was again doubled on August 6, 2017 and September 5, 2017, but its core was strongly shifted toward longer wavelengths, indicating a rapid infall of matter. Splitting of the profiles of strong, low-excitation absorptions into three components was first detected in 2017. There is no correlation between the evolution of the profiles of H$α$ and the splitted absorptions. Pulsation-like variability with an amplitude of about 10 km/s is characteristic only of symmetric weak and moderate-intensity absorption lines. Shell emissions of iron-group elements can be identified in the long-wavelength part of a spectrum obtained in 2013, whose intensity decreased until they completely disappeared in 2017. In the absence of emission in the cores of the H and K lines of CaII, emissions of shell metals are visible in the wings of these lines.

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arXiv2017

Gusty wind in the system of the infrared source RAFGL 5081

For the first time, based on long-term spectral monitoring with high spectral resolution, the optical spectrum of the weak central star of the IR source RAFGL 5081 has been studied. The spectral type of this star is close to G5-8 II, and its effective temperature is Teff ~5400 K. An unusual spectral phenomenon was discovered: splitting of the profiles of broad, stationary absorption lines of medium and low intensity. The heliocentric radial velocities Vr of all components of metal absorption lines, the NaI D lines, and the H$α$ line were measured for all the observation epochs. The constancy of the absorption lines rules out the possibility that the line splitting is due to binarity. The radial velocities of the wind components in the profiles of the NaI D and H$α$ lines reach $-250$ and $-600$ km/s, respectively. These profiles have narrow components, whose number, depth, and position vary with time. The time variability and multicomponent structure of the profiles of the NaI D and H$α$ lines indicates inhomogeneity and instability of the circumstellar envelope of RAFGL 5081. The presence of components with velocity Vr(IS)=$-65$ km/s in the NaI(1) lines provides evidence that RAFGL 5081 is located behind the Perseus arm, i.e., no closer than 2 kpc. It is noted that RAFGL 5081 is associated with the reflection nebula GN 02.44.7.

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arXiv2016

New in the optical spectrum and kinematic state of the atmosphere of the variable V1027\,Cyg (= IRAS 20004+2955)

Based on high-resolution spectroscopy performed with the NES echelle spectrograph of the 6-m telescope, we have studied the peculiarities of the spectrum and the velocity field in the atmosphere and envelope of the cool supergiant V1027 Cyg, the optical counterpart of the infrared source IRAS 20004+2955. For the first time, a splitting of the cores of strong absorptions of metals and their ions (SiII, NiI, TiI, TiII, ScII, CrI, FeI, FeII, BaII) has been detected in the stellar spectrum. The broad profile of these lines contains a stable weak emission in the core whose position may be considered as the systematic velocity Vsys=5.5 km/s. Small radial velocity variations with an amplitude of 5-6 km/s due to pulsations have been revealed by symmetric low- and moderate-intensity absorptions. A long-wavelength shift of the H$α$ profile due to line core distortion is observed in the stellar spectrum. Numerous weak CN molecular lines and the KI 7696 Å line with a P Cyg profile have been identified in the red spectral region. The coincidence of the radial velocities measured from symmetric metal absorptions and CN lines suggests that the CN spectrum is formed in the stellar atmosphere. We have also identified numerous diffuse interstellar bands (DIBs) whose positions in the spectrum, Vr(DIBs)=$-12.0$ km/s, correspond to the velocity of the interstellar medium in the Local arm of the Galaxy.

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arXiv2015

Peculiarities of the atmosphere and envelope of a post-AGB star, the optical counterpart of IRAS 23304+6347

Based on high-spectral resolution observations performed with the echelle spectrograph NES of the 6-meter telescope, we have studied the peculiarities of the spectrum and the velocity field in the atmosphere and envelope of the optical counterpart of the infrared source IRAS 23304+6347. We have concluded about the absence of significant variations in the radial velocity Vr inferred from atmospheric absorptions and about its coincidence with the systemic velocity deduced from radio data. The envelope expansion velocity Vexp=15.5 km/s has been determined from the positions of rotational band lines of the C$_2$ Swan (0; 0) band. A complex emission-absorption profile of the Swan (0; 1) 5635 Å has been recorded. Analysis of the multicomponent NaI~D doublet line profile has revealed interstellar components V(IS)=$-61.6$ and $-13.2$ km/s as well as a circumstellar component with V(CS)=$-41.0$ km/s whose position corresponds to the velocity inferred from C$_2$ features. The presence of the interstellar component with Vr=$-61.6$ km/s in the spectrum allows d=2.5 kpc to be considered as a lower limit for the distance to the star. A splitting of the profiles for strong absorptions of ionized metals (YII, BaII, LaII, SiII) attributable to the presence of a short-wavelength component originating in the circumstellar envelope has been detected in the optical spectrum of IRAS23304+6347 for the first time.

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arXiv2014

Spectral variability of the IR-source IRAS 01005+7910 optical component

Highly-resolution optical spectra of the optical component of the IR-source IRAS01005+7910 are used to determine the spectral type of its central star, B1.5$ \pm $0.3, identify the spectral features, and analyze their profile and radial velocity variations. The systemic velocity Vsys =$-50.5$ km/s is determined from the positions of the symmetric and stable profiles of the forbidden [NI], [NII], [OI], [SII], and [FeII] emission lines. The presence of the [NII] and [SII] forbidden emissions indicates the onset of the ionization of the circumstellar envelope and the fact that the star is very close to undergoing the planetary nebula stage. The broad range of heliocentric radial velocity Vr estimates based on the core lines, which amounts to about 34 km/s, is partly due to the deformations of the profiles caused by variable emissions. The variations of the Vr in the line wings are smaller, about 23 km/s, and may be due to pulsations and/or hidden binarity of the star. The deformations of the profiles of complex absorption-emission lines may result from variations of their absorption components caused by the variations of the geometry and kinematics in the wind base. The H$α$ lines exhibit P Cyg III type wind profiles. Deviations of the wind from spherical symmetry are shown to be small. The relatively low wind velocity (27$÷$74 km/s from different observations) and the strong intensity of the red emission (it exceeds the continuum level by up to a factor of seven) are typical for hypergiants rather than the classical supergiants. IRAS01005 +7910 is an example of spectral mimicry of a low mass post-AGB star masquerading as a massive hypergiant.

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arXiv2013

Instability of the kinematic state in the atmosphere of the hypergiant Rho Cas outside outburst

Observations of the yellow hypergiant Rho Cas obtained in 2007-2011 in a wide wavelength region with spectral resolution about 60000 have enabled studies of features of its optical spectrum in detail and brought to light previously unknown characteristics of the extended atmosphere of the star. The radial velocity measured from symmetric absorptions of metals varies with an amplitude of about +/-7 km/s around the systemic velocity Vsys=-47 km/s, due to low-amplitude pulsations of the atmospheric layers near the photosphere. At some times, a velocity gradient was found in deep atmospheric layers of the star. A slight velocity stratification in the stellar atmosphere was detected for the first time, manifested as a difference of 3-4 km/s in the velocities measured from absorption lines of neutral metals and of ions. The long-wavelength components of split absorptions of BaII, SrII, TiII, and other strong lines with low excitation potentials for their lower levels are distorted by nearby emission lines. It is suggested that the short-wavelength components, whose locations correspond to the narrow velocity range Vr(blue) from approximately -60 to -70 km/s, are formed in a circumstellar envelope; one component of the D~NaI doublet and the emission components of the FeII 6369.46 and 6432.68 ions are also formed there.

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arXiv2013

Spectroscopy of 13 high mass stars in the Cyg OB2 association

Aiming to explore weak spectral features of stellar and interstellar origin we used the NES echelle spectrograph of the 6-m telescope to obtain high-resolution spectra for 13 hot O3 - B4 stars in the Cyg OB2 association, including a high luminous star No. 12. Velocity fields in the atmospheres and interstellar medium, characteristics of optical spectra and line profiles are investigated. The cascade star formation scheme for the association is confirmed. Evidence is presented suggesting that the hypergiant Cyg OB2 No.12 is an LBV object and that its anomalous reddening has a circumstellar nature.

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arXiv2010

Peculiarities and variations in the optical spectrum of the post-AGB star V448Lac=IRAS22223+4327

Repeated observations with high spectral resolution acquired in 1998-2008 are used to study the temporal behavior of the spectral line profiles and velocity field in the atmosphere and circumstellar envelope of the post-AGB star V448Lac. Asymmetry of the profiles of the strongest absorption lines with low-level excitation potentials less 1eV and time variations of these profiles have been detected, most prominently the profiles of the resonance lines of BaII, YII, LaII, SiII. The peculiarity of these profiles can be explained using a superposition of stellar absorption line and shell emission lines. Emission in the (0;1) 5635A Swan band of the C2 molecule has been detected in the spectrum of V448Lac for the first time. The core of the Halpha line displays radial velocity variations with an amplitude ~8 km/s. Radial velocity variations displayed by weakest metallic lines with lower amplitudes, 1-2 km/s, may be due to atmospheric pulsations. Differential line shifts, 0 -- 8 km/s, have been detected on various dates. The position of the molecular spectrum is stationary in time, indicating a constant expansion velocity of the circumstellar shell, Vexp=15.2 km/s, as derived from the C2 and NaI lines.

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arXiv2009

New Spectroscopic Observations of the Post-AGB Star V354Lac=IRAS22272+5435

The strongest absorption features with the lower-level excitation potentials $χ_{\rm low}<1$ eV are found to be split in the high-resolution optical spectra of the post-AGB star V354 Lac taken in 2007--2008. Main parameters, T$_{eff}$=5650 K, $\log g$=0.2, $ξ_t$=5.0 km/s, and the abundances of 22 chemical elements in the star's atmosphere are found. The overabundance of the $s$-process chemical elements (Ba, La, Ce, Nd) in the star's atmosphere is partly due to the splitting of strong lines of the ions of these metals. The peculiarities of the spectrum in the wavelength interval containing the LiI $λ$ 6707 Å line can be naturally explained only by taking the overabundances of the CeII and SmII heavy-metal ions into account. The best agreement with the synthetic spectrum is achieved assuming $ε$(LiI)=2.0, $ε$(CeII)=3.2, and $ε$(SmII)=2.7. The velocity field both in the atmosphere and in the circumstellar envelope of V354 Lac remained stationary throughout the last 15 years of our observations.

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