Terskol Observatory Research Articles

Thorium-rich halo star HD 221170: Further evidence against the universality of the r-process

We report the abundance determination in the atmosphere of the bright halo star HD221170. The spectra were taken with the Terskol Observatory's 2.0-m telescope with a resolution R=45000 and signal-to-noise ratio up to 250 in the wavelength region 3638-10275 \AA. The adopted atmospheric parameters correspond to an effective temperature \Tef=4475 K, a surface gravity \lgg=1.0, a microturbulent velocity \vmi=1.7 \kms, and a macroturbulent velocity \vma=4 \kms. The abundances of 43 chemical elements were determined with the method of spectrum synthesis. The large overabundances (by 1 dex relative to iron) of elements with Z$>38$ are shown to follow the same pattern as the solar r-abundances. The present HD221170 analysis confirms the non-universality of the r-process, or more exactly the observation that the astrophysical sites hosting the r-process do not always lead to a unique relative abundance distribution for the bulk Ba to Hg elements, the Pb-peak elements, and the actinides.

Correlations between diffuse interstellar bands and atomic lines

We present and discuss correlations between strengths of the well-known, strong interstellar atomic lines of K I and Ca II, and four selected, strong unidentified diffuse interstellar bands (DIBs): 5780, 5797, 5850 and 6614. In order to analyse a homogeneous sample of echelle high-resolution spectra it has been chosen to use measurements from Terskol Observatory in Northern Caucasus plus a selected number of higher resolution observations performed using other instruments. We demonstrate that the strength of certain DIBs correlate well with neutral potassium lines and to a much lower degree with ionized calcium lines. This fact suggests that the degree of irradiation of a cloud with UV photons, capable to ionize interstellar atoms, plays a crucial role in the formation/maintenance of certain molecular species: possible carriers of DIBs.

Chemical composition of 15 photometric analogues of the Sun

The results of a spectroscopic analysis of 15 stars that are photometric analogues of the Sun are reported. The effective temperatures and surface gravities in the stellar atmospheres are derived from published photometric indices and the HIPPARCOS parallaxes. The abundances of 33 elements ranging from lithium to europium are analyzed based on high-dispersion spectra taken with the new Coude echelle spectrometer of the Terskol Observatory in the northern Caucasus. The main parameters of most of the stars agree with the data of an [Fe/H] catalog published in 2001. Our study of the chemical compositions of the sample stars indicates that photometric analogues of the Sun can be divided into three groups according to their elemental abundances: six stars have solar chemical composition, four have abundance excesses, and five have some abundance deficiencies. The sample contains two metal-deficient subgiants (HD 133002 and HD 225239). Our results demonstrate that photometric similarity is not a sufficient criterion to consider a star as solar analogue. When several criteria, including chemical composition, are simultaneously taken into account, only four stars from the sample can be considered true solar analogues: HD 10307, HD 34411, HD 146233 (18 Sco), and HD 186427 (16 Cyg B). These results confirm the previously published suggestion that 18 Sco is the most probable twin of the Sun: essentially all the parameters of the two stars coincide within the errors.

Ground-based photometric observations of Jupiter's inner satellites Thebe, Amalthea, and Metis at small phase angles

We present the results of photometric measurements of the inner jovian satellites Thebe, Amalthea and Metis based on extensive optical observations taken from October 1999 to January 2002. The observations were made in the phase angle range from 8.1° to 0.3°. The Two-Channel Focal Reducer of the Max-Planck Institute for Aeronomy attached to the 2-m RCC telescope at Terskol Observatory (Pik Terskol, Northern Caucasus) was used in coronagraph mode. The observations were performed at a wavelength of 0.887 μm. Mean observational uncertainties corresponding to 1 σ rms errors were 3% for the leading and trailing sides of Amalthea, 7 and 9% for the leading and trailing sides of Thebe and 9% for the leading side of Metis after taking into account the longitude brightness variations. Photometric data calibrated on an absolute scale were used to evaluate the near-opposition behavior of satellite brightness. All three satellites exhibit significant opposition brightening, but the strength of this effect, measured as the ratios of intensities at α 1=1.6° and α 2=6.7° does not vary significantly among these satellites. In order to measure the opposition surge parameters the empirical law proposed by Karkoschka and Hapke's model were used. The parameters of the satellite opposition effects are presented and discussed. The values of geometric albedos calculated with best-fit Hapke parameters are 0.096, 0.157, and 0.24 for Thebe, Amalthea, and Metis respectively. We found that the average leading/trailing ratios of surface reflectance at the measured phase angles are 1.53±0.05, 1.25±0.04, 1.04±0.08 for Amalthea, Thebe, and Metis.

The chemical composition of the mild barium star HD 202109

We present chemical abundances of the mild barium star HD 202109 (ζ Cyg) determined from the analysis of a spectrum obtained by using the 2-m telescope at the Peak Terskol Observatory and a high-resolution spectrometer with R = 80 000, signal to noise ratio > 100. We also present the atmospheric parameters of the star determined using various methods including iron-line abundance analysis. For line identifications, we use whole-range synthetic spectra computed from Kurucz's database and the latest lists of spectral lines. Among the determined abundances of 51 elements, those of P, S, K, Cu, Zn, Ge, Rb, Sr, Nb, Mo, Ru, Rh, Pd, In, Sm, Gd, Tb, Dy, Er, Tm, Hf, Os, Ir, Pt, Tl, and Pb were not investigated previously. Assuming that the overabundance pattern of Ba stars is due to binary accretion, the observed abundance pattern of the neutron-capture process elements in HD 202109 can be explained by combining the AGB star nucleosynthesis and the wind accretion scenario.

Investigation into broad interstellar absorption lines

Diffuse interstellar bands (DIBs) are investigated mainly with high-resolution spectroscopy, which allows very fine structures to be detected. However, the rapidly increasing resolution of echelle spectra becomes a disadvantage when broad absorption structures are involved. These can extend over several dozen angstroms, taking up a significant part of a single echelle order and thus posing an impediment to a proper continuum tracing. This is where low-resolution spectroscopy can regain its importance in DIB research. Recently, an attempt has been made to connect the broader DIBs with polycyclic aromatic hydrocarbons, and more specifically with the naphthalene cation. We present spectra obtained with a spectrograph obtaining information from the 90 cm Torun telescope, accompanied by high-resolution observations made at the Terskol Observatory.

Dust tail of the distant comet C/1999 J2 (Skiff)

CCD observations of comet C/1999 J2 (Skiff) were made at the Pik Terskol Observatory on September 15, 1999. The 2-m telescope equipped with the two-channel focal reducer of the Max-Plank-Institute for Aeronomy was used to study the cometary environment. In spite of the large heliocentric distance, 7.24 AU, a straight dust tail with fairly well defined boundaries was recorded. These data provide an opportunity to study the peculiarity of dust, that is not driven by water vapor. To fit the dust tail, a Monte Carlo model was developed. We trace the trajectories of about 107 sample grains to construct the detailed brightness distribution in the comet tail. The simulated isophote field and the observed one agree very well. In our model we also take into account the heliocentric dependence of the dust production rate and ejection velocity, and the dust ejection anisotropy. To transform the particle population to brightness in the modelled tail we calculate the scattering cross section of a separate particle using Mie theory. The age, ejection velocity, dust size distribution, minimum and maximum size of the involved dust particles have been derived from the model giving the best fit. The intensity map is in agreement with a flow of the slowly travelling icy grains. It has been determined that the age of the dust tail of comet C/1999 J2 (Skiff) was, at the moment of the observations, about 540 days and that the main reason for its appearance is likely phase transition from amorphous to crystalline water ice activated at the heliocentric distance of 8.6 AU.

The Dust in Comet C/1999 S4 (LINEAR) during Its Disintegration: Narrow-Band Images, Color Maps, and Dynamical Models

Comet C/1999 S4 was observed with the 2m-telescopes of the Bulgarian National Observatory and Pik Terskol Observatory, Northern Caucasus, Russia, at the time of its disintegration. Maps of the dust brightness and color were constructed from images obtained in red and blue continuum windows, free from cometary molecular emissions. We analyze the dust environment of Comet C/1999 S4 (LINEAR) taking into account the observed changes apparent in the brightness images and in plots of Afρ profiles as function of the projected distance ρ from the nucleus. We also make use of the syndyne–synchrone formalism and of a Monte Carlo model based on the Finson–Probstein theory of dusty comets. The brightness and color of individual dust particles, which is needed to derive theoretical brightness and color maps of the cometary dust coma from the Monte Carlo model, is determined from calculations of the light scattering properties of randomly oriented oblate spheroids. In general, the dust of Comet C/1999 S4 (LINEAR) is strongly reddened, with reddening values up to 30%/1000 Å in some locations. Often the reddening is higher in envelopes further away from the nucleus. We observed two outbursts of the comet with brightness peaks on July 14 and just before July 24, 2000, when the final disintegration of the comet started. During both outbursts an excess of small particles was released. Shortly after both outbursts the dust coma “turns blue.” After the first outburst, the whole coma was affected; after the second one only a narrow band of reduced color close to the tail axis was formed. This difference is explained by different terminal ejection speeds, which were much lower than normal in case of the second outburst. In particular in the second, final outburst the excess small particles could originate from fragmentation of “fresh” larger particles.

CN, NH$_{\mathsf 2}$, and dust in the atmosphere of comet C/1999 J3 (LINEAR)

Comet C/1999 J3 (LINEAR) was observed with 2 m telescope of the Pik Terskol Observatory on September 19, 1999. Narrow-band CCD images of the CN, NH2 , and dust atmospheres were recorded with the Two-Channel focal reducer of the Max-Plank-Institute for Aeronomy. The distributions of the CN and NH2 molecules in the comet atmosphere were fitted with a Monte Carlo model. For the CN atmosphere the best agreement between observed and calculated surface profiles was reached with the CN photodissociation lifetime s and with the parent photodissociation lifetime s. This result indicates that HCN is the main source of the CN radicals in the atmosphere of comet C/1999 J3 (LINEAR). Regarding the NH2 radicals, there is no doubt that NH3 is the dominant source of this species in the comet atmosphere. The lifetimes s for NH2 and s for its parent are close to theoretical calculations. The gas-production rates of CN, mol s-1 , and NH2 , mol s-1 have also been determined. The appearance of the comet and the obtained data show that the comet is a gaseous one. The values are 21.6 cm for the blue spectral window and 23.4 cm for the red one. The normalized spectral gradient of the cometary dust is low, 4.0% per 1000 A. The ratio log((/Q (CN)) = -24.25 indicates a very low dust to gas ratio as well.

Analysis of Polarimetric, Photometric, and Spectroscopic Observations of Comet C/1996 Q1 (Tabur)

We present the imaging polarimetry and photometry of Comet C/1996 Q1 (Tabur) obtained on October 10, 1996, with a two-channel focal reducer attached to the 2-m Pik Terskol Observatory telescope through blue (λ4430/44 A) and red (λ6420/26 A) continuum filters and through a λ6620/59 A filter that isolated the NH2(0.7.0) band. We analyze the λ3600–9300 A long-slit spectrograms of the comet taken on October 5–6, 1996, with the 2.6-m Crimean Astrophysical Observatory telescope. The NH2(0.8.0) λ6408 A emission and an unidentified λ6428 A emission were found to fall within the pass band of the red filter. The blue filter transmits weak unidentified emissions at λ4424–4444 A and partially C2(λ4360 A). Correction for the depolarizing effect of molecular emissions resulted in an increase of the dust polarization by 2–4% in the near-nucleus region and by almost a factor of 2 in the outer coma regions. However, the polarization and color differences between different coma regions remained even after correction for the contribution of emissions. We found no dust polarization difference between the gas comet Tabur and the dust comet C/1988 A1 (Liller), which are believed to be fragments of a common parent comet. The NH2coma was found to be elongated perpendicular to the comet radius vector. The causes of the spatial asymmetry in the NH2molecular distribution are yet to be established. We study the evolution of activity and the spatial distribution of dust brightness, polarization, and color in the comet. We consider a taxonomic classification of gas and dust comets according to dust polarization properties. The polarization differences between dust and gas comets at large phase angles are most likely related both to the actual differences in dust and to the effect of molecular emissions, nuclear gas- and dust-production rates and to the evolution of grain properties with distance from the nucleus.

Anomalous wavelength dependence of polarization of Comet 21P/Giacobini-Zinner

Results of CCD imaging and aperture polarimetry of Comet 21P/Giacobini-Zinner and Comet C/1989 U5 (Linear) are presented. Observations were carried out with the 2-m telescope of Pik Terskol Observatory and with the 0.7-m telescope of Kharkov State University in November 1998 and January 1999. The new observations and published data indicate an anomalous spectral dependence of polarization of Giacobini-Zinner, namely, a negative wavelength gradient of the degree of polarization. It is shown that this effect is not caused by the presence of molecular emission in the pass band of the employed filter. The uncommon spectral trend of polarization of Comet Giacobini-Zinner may be caused by a large content of organic matter in its dust or an overabundance of large particles as compared to the other comets.

Images of polarization and colour in the inner coma of comet Hale-Bopp

On March 31 and April 1, 1997, simultaneous photometry and polarimetry of comet Hale-Bopp's dust was conducted with the two-channel focal reducer of the Max-Planck-Institute for Aeronomy attached to the 2 m telescope of Pik Terskol Observatory (Northern Caucasus). Interference filters at642 nm and 443 nm selected red and blue narrow-band continuum windows. The observations have been averaged over the one hour of timethe comet could be observed. The polarization maps cover an area of about1 arcmin2 around the nucleus. The values of polarization degree measured close to the nucleus agree very well with observations obtained with aperture polarimetry. They are lower than in the surrounding coma by about 1%. In our field of view the polarization increases along the sun-comet line from the solar to the antisolar side by about 3%. The dust shells are visible in the polarization images. The polarization in the shells is higher by 1 to 2%and this increase is higher in the red than in the blue range. Therefore the ratio of red to blue polarization (≈ 1.2) increases in the shells by ≈ 0.03. In principle, the polarization excess in the shells, the ratio of red/blue polarization and the higher integrated polarization as compared to other comets can be explained by an excess of particles of radius of about 0.1 μm. Such particles, however, are subject to strong radiation pressure and will be pushed back into the tail before they reach the observed location of the shells. Real Rayleigh particles cannot explain the observed increase in the ratio of red/blue polarization. One therefore cannot exclude the possibility that the excess polarization in the shells is caused by fluffy aggregates via effects which are presently not well understood. The colour map shows features not well related to intensity and polarization, perhaps another dust shell of a different particle size.

Comet Hale–Bopp: Velocity Field Of Ions From Fabry-Pérot Imaging

Fabry-Perot interferograms of comet Hale-Bopp were obtained on several nights in March and April 1997. For this purpose we utilized the 2-channel focal reducer of the Max-Planck-Institute for Aeronomy at the 2-m telescope of the Pik Terskol Observatory. Solid Fabry-Perot etalons of resolving power 30000 were used in both channels of the focal reducer. The main aim of this study is to measure the velocities and abundances of OH+ and H2O+, both ions closely related to the same parent molecule, H2O. In the blue channel interferograms we identified several individual OH+ rotational lines of the A3Πi - X3Σ− (0-0) transition and measured their Doppler shifts. The target emissions in the red channel were the H2O+ lines of the A2A1 − X2B1 (10-0) band. We found that the line of sight velocities, obtained from the Doppler shifted wavelengths of emissions in the comet are higher in sunward direction than in the plasma tail and do not exceed 20 km s–1. The corresponding values, deprojected in antisolar direction, are consistent with predictions by magnetohydrodynamical models of the solar-wind-comet interaction, when one accounts for the extremely high gas production rate of comet Hale-Bopp.