Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHigh-resolution optical spectroscopy of the post-AGB supergiant V340 Ser (=IRAS 17279$-$1119)
80
0
0.0
(
0
)
Added by
Valentina Klochkova G.
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Some evidences of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser (=IRAS 17279$-$1119) taken at the 6-m BTA telescope with a spectral resolution R$ge$60000. The H$alpha$ 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.
rate research
Read More
The optical spectrum of the infrared source IRAS 04296+3429 (optical counterpart-G0 Ia star, V=14.2) was obtained with the echelle spectrometer PFES at the prime focus of the 6 m telescope. We discover emission bands (0,0) and (0,1) of the Swan system of the C2 molecule in the optical spectrum of IRAS 04296+3429. Comparison with the spectrum of the Hale-Bopp comet leads us to propose that in both cases the same mechanism (resonance fluorescence) is responsible for the emission in the C2 molecular bands. Several strong absorption features whose positions coincide with known diffuse interstellar bands are revealed in the spectrum of IRAS 04296+3429. The infrared spectrum of IRAS 04296+3429 shows the famous 21 um feature, but this object has not been observed by KAO. However, like IRAS 05113+1347, IRAS 05341+0852 and IRAS 22223+4327, our detailed modelling of its spectral energy distribution suggested that this source also should show the 30 um band. In fact, ISO discovered a broad, relatively strong feature around 30 um for IRAS 04296+3429. The surface chemical composition of the source IRAS 04296+3429 is metal-deficient (the averaged value of the abundances of the iron group elements Ti, V, Cr and Fe relative to the solar values is [M/H]=-0.9 and has been considerably altered during the evolution: carbon, nitrogen and s-process elements are overabundant relative to the metallicity. The totality of physical and chemical parameters derived for IRAS 04296+3429 confirms a relation between presence of the feature at 21 um in the spectrum of a carbon rich star and an excess of the s-process elements.
High-resolution optical spectroscopy was conducted for the metal-poor post-AGB star CC Lyr to determine its chemical abundances and spectral line profiles. Our standard abundance analysis confirms its extremely low metallicity ([Fe/H]<-3.5) and a clear correlation between abundance ratios and the condensation temperature for 11 elements, indicating that dust depletion is the cause of the abundance anomaly of this object. The very low abundances of Sr and Ba, which are detected for the first time for this object, suggest that heavy neutron-capture elements are not significantly enhanced in this object by the s-process during its evolution through AGB phase. Radial velocity of this object and profiles of some atomic absorption lines show variations depending on pulsation phases, which could be formed by dynamics of the atmosphere rather than by binarity or contributions of circumstellar absorption. On the other hand, the H-alpha emission with double peaks shows no evident velocity shift, suggesting that the emission is originating from the circumstellar matter, presumably the rotating disk around the object.
Aims: To investigate the first high resolution optical spectrum of the B-type star, LS III +52 24, identified as the optical counterpart of the hot post-AGB candidate IRAS 22023+5249 (I22023). Methods: We carried out detailed identifications of the observed absorption and emission features in the high resolution spectrum (4290 - 9015 A) of I22023 obtained with the Utrecht Echelle Spectrograph on the 4.2m William Herschel Telescope. Using Kuruczs WIDTH9 program and the spectrum synthesis code, SYNSPEC, we determined the atmospheric parameters and abundances. The photospheric abundances were derived under the LTE approximation. The NEBULAR package under IRAF was used to estimate the electron temperature (T_e) and the electron density (N_e) from the [N II] and [S II] lines. Results: We estimated T_eff=24000 K, log g=3.0, xi_t=7 kms^{-1}. The derived CNO abundances suggest an evolved star with C/O < 1. P-Cygni profiles of hydrogen and helium indicate ongoing post-AGB mass loss. The presence of [N II] and [S II] lines and the non-detection of [O III] indicate that photoionisation has just started. The derived nebular parameters T_e=7000 K, N_e=1.2X10^{4} cm^{-3} are comparable to those measured in young, compact planetary nebulae (PNe). The nebular expansion velocity was estimated to be 17.5 kms^{-1}. Conclusions: The observed spectral features, large heliocentric radial velocity (-148.31 +/- 0.60 kms^{-1}), atmospheric parameters and chemical composition indicate that I22023, at a distance of 1.95 kpc, is an evolved post-AGB star belonging to the old disk population. The nebular parameters suggest that the central star may be evolving into a compact, young PN, similar to Hen3-1357.
From an analysis of the spectrum (4000AA to 8800AA) of HD~101584 it is found that most of the neutral and single ionized metallic lines are in emission. The forbidden emission lines of [OI] 6300AA and 6363AA and [CI] 8727AA are detected, which indicate the presence of a very low excitation nebula. The H$alpha$, FeII 6383AA, NaI D$_{1}$, D$_{2}$ lines and the CaII IR triplet lines show P-Cygni profiles indicating a mass outflow. The H$alpha$ line shows many velocity components in the profile. The FeII 6383AA also has almost the same line profile as the H$alpha$ line indicating that they are formed in the same region. From the spectrum synthesis analysis we find the atmospheric parameters to be T$_{eff}$=8500K, log g=1.5, V$_{turb}$=13km~s$^{-1}$ and [Fe/H]=0.0. From an analysis of the absorption lines the photospheric abundances of some of the elements are derived. Carbon and nitrogen are found to be overabundant. From the analysis of Fe emission lines we derived T$_{exi}$=6100K$pm$200 for the emission line region.
We are studying a class of binary post-AGB stars that seem to be systematically surrounded by equatorial disks and slow outflows. Although the rotating dynamics had only been well identified in three cases, the study of such structures is thought to be fundamental to the understanding of the formation of nebulae around evolved stars. We present ALMA maps of 12CO and 13CO J=3-2 lines in one of these sources, IRAS08544-4431. We analyzed the data by means of nebula models, which account for the expectedly composite source and can reproduce the data. From our modeling, we estimated the main nebula parameters, including the structure and dynamics and the density and temperature distributions. We discuss the uncertainties of the derived values and, in particular, their dependence on the distance. Our observations reveal the presence of an equatorial disk in rotation; a low-velocity outflow is also found, probably formed of gas expelled from the disk. The main characteristics of our observations and modeling of IRAS08544-4431 are similar to those of better studied objects, confirming our interpretation. The disk rotation indicates a total central mass of about 1.8 Mo, for a distance of 1100 pc. The disk is found to be relatively extended and has a typical diameter of ~ 4 10^16 cm. The total nebular mass is ~ 2 10^-2 Mo, of which ~ 90% corresponds to the disk. Assuming that the outflow is due to mass loss from the disk, we derive a disk lifetime of ~ 10000 yr. The disk angular momentum is found to be comparable to that of the binary system at present. Assuming that the disk angular momentum was transferred from the binary system, as expected, the high values of the disk angular momentum in this and other similar disks suggest that the size of the stellar orbits has significantly decreased as a consequence of disk formation.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
