13 research outputs found
High Resolution Optical Spectroscopy of the F Supergiant Proto-Planetary Nebula V887 Her=IRAS 18095+2704
An abundance analysis is presented for IRAS 18095+2704 (V887 Her), a post-AGB
star and proto-planetary nebula. The analysis is based on high-resolution
optical spectra from the McDonald Observatory and the Special Astrophysical
Observatory. Standard analysis using a classical Kurucz model atmosphere and
the line analysis program MOOG provides the atmospheric parameters: Teff = 6500
K, log g = +0.5, and a microturbulent velocity Vt = 4.7 km/s and [Fe/H] = -0.9.
Extraction of these parameters is based on excitation of FeI lines, ionization
equilibrium between neutral and ions of Mg, Ca, Ti, Cr, and Fe, and the wings
of hydrogen Paschen lines. Elemental abundances are obtained for 22 elements
and upper limits for an additional four elements. These results show that the
star's atmosphere has not experienced a significant number of C- and s-process
enriching thermal pulses. Abundance anomalies as judged relative to the
compositions of unevolved and less-evolved normal stars of a similar
metallicity include Al, Y, and Zr deficiencies with respect to Fe of about 0.5
dex. Judged by composition, the star resembles a RV Tauri variable that has
been mildly affected by dust-gas separation reducing the abundances of the
elements of highest condensation temperature. This separation may occur in the
stellar wind. There are indications that the standard 1D LTE analysis is not
entirely appropriate for IRAS 18095+2704. These include a supersonic
macroturbulent velocity of 23 km/s, emission in H-alpha and the failure of
predicted profiles to fit observed profiles of H-beta and H-gamma.Comment: Accepted for publication in MNRA
Spectroscopy of high proper motion stars in the ground--based UV
Based on high quality spectral data (spectral resolution R>60000) within the
wavelength range of 3550-5000 AA we determined main parameters (effective
temperature, surface gravity, microturbulent velocity, and chemical element
abundances including heavy metals from Sr to Dy) for 14 metal-deficient G-K
stars with large proper motions. The stars we studied have a wide range of
metallicity: [Fe/H]=-0.3 \div -2.9. Abundances of Mg, Al, Sr and Ba were
calculated with non-LTE line-formation effects accounted for. Abundances both
of the radioactive element Th and r-process element Eu were determined using
synthetic spectrum calculations. We selected stars that belong to different
galactic populations according to the kinematical criterion and parameters
determined by us. We found that the studied stars with large proper motions
refer to different components of the Galaxy: thin, thick disks and halo. The
chemical composition of the star BD+80 245 located far from the galactic plane
agrees with its belonging to the accreted halo. For the giant HD115444 we
obtained [Fe/H]=-2.91, underabundance of Mn, overabundance of heavy metals from
Ba to Dy, and, especially high excess of the r-process element Europium:
[Eu/Fe]=+1.26. Contrary to its chemical composition typical for halo stars,
HD115444 belongs to the disc population according to its kinematic parameters.Comment: 16 pages, 4 figures, 5 tables, "UV Universe-2010 (2nd NUVA Symposium)
conference
Optical spectrum of the post-AGB star HD56126 in the region 4010-8790 AA
We studied in detail the optical spectrum of the post-AGB star HD56126
(IRAS07134+1005). We use high resolution spectra (R=25000 and 60000) obtained
with the echelle spectrographs of the 6-m telescope. About one and a half
thousand absorptions of neutral atoms and ions, absorption bands of C_2, CN,
and CH molecules, and interstellar bands (DIBs) are identified in the 4010 to
8790 AA wavelength region, and the depths and radial velocities of these
spectral features are measured. Differences are revealed between the variations
of the radial velocities measured from spectral features of different
excitation. In addition to the well-known variability of the Halpha profile, we
found variations in the profiles of a number of FeII, YII, and BaII lines. We
also produce an atlas of the spectrum of HD56126 and its comparison staralpha
Per. The full version of the atlas is available in electronic form from
Web-address: http://www.sao.ru/hq/ssl/Atlas/Atlas.htmlComment: 42 pages, 6 figure
New Spectroscopic Observations of the Post-AGB Star V354Lac=IRAS22272+5435
The strongest absorption features with the lower-level excitation potentials
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=5650 K, =0.2, =5.0 km/s, and the abundances of 22
chemical elements in the star's atmosphere are found. The overabundance of the
-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
6707 \AA{} 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 (LiI)=2.0,
(CeII)=3.2, and (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.Comment: 16 pages, 6 figures, 2 table