288 research outputs found
Centrosymmetric molecules as possible carriers of diffuse interstellar bands
In this paper, we present new data with interstellar C2 (Phillips bands A-X),
from observations made with the Ultraviolet-Visual Echelle Spectrograph of the
European Southern Observatory. We have determined the interstellar column
densities and excitation temperatures of C2 for nine Galactic lines. For seven
of these, C2 has never been observed before, so in this case the still small
sample of interstellar clouds (26 lines of sight), where a detailed analysis of
C2 excitation has been made, has increased significantly. This paper is a
continuation of previous works where interstellar molecules (C2 and diffuse
interstellar bands) have been analysed. Because the sample of interstellar
clouds with C2 has increased, we can show that the width and shape of the
profiles of some diffuse interstellar bands (6196 and 5797 A) apparently depend
on the gas kinetic and rotational temperatures of C2; the profiles are broader
because of the higher values of the gas kinetic and rotational temperatures of
C2. There are also diffuse interstellar bands (4964 and 5850 A) for which this
effect does not exist.Comment: 8 pages, 4 figures, accepted to MNRAS 201
The structure and kinematics of the the Galaxy thin gaseous disc outside the solar orbit
The rotation curve of the Galaxy is generally thought to be flat. However,
using radial velocities from interstellar molecular clouds, which is common in
rotation curve determination, seems to be incorrect and may lead to incorrectly
inferring that the rotation curve is flat indeed. Tests basing on photometric
and spectral observations of bright stars may be misleading. The rotation
tracers (OB stars) are affected by motions around local gravity centers and
pulsation effects seen in such early type objects. To get rid of the latter a
lot of observing work must be involved. We introduce a method of studying the
kinematics of the thin disc of our Galaxy outside the solar orbit in a way that
avoids these problems. We propose a test based on observations of interstellar
CaII H and K lines that determines both radial velocities and distances. We
implemented the test using stellar spectra of thin disc stars at galactic
longitudes of 135{\degr} and 180{\degr}. Using this method, we constructed the
rotation curve of the thin disc of the Galaxy. The test leads to the obvious
conclusion that the rotation curve of the thin gaseous galactic disk,
represented by the CaII lines, is Keplerian outside the solar orbit rather than
flat.Comment: 33 pages, 18 figures, accepted for publication in Publications of the
Astronomical Society of the Pacific, 2015. February
The relation between column densities of interstellar OH and CH molecules
We present a new, close relation between column densities of OH and CH
molecules based on 16 translucent sightlines (six of them new) and confirm the
theoretical oscillator strengths of the OH A--X transitions at 3078 and 3082
\AA (0.00105, 0.000648) and CH B--X transitions at 3886 and 3890 \AA, (0.00320,
0.00210), respectively. We also report no difference between observed and
previously modelled abundances of the OH molecule.Comment: 4 pages, 0 figures, accepted for publication in MNRA
The chemical composition of a mild barium star HD202109
We present the result of chemical abundances of a mild barium star HD202109
(zeta Cyg) determined from the analysis of spectrum obtained by using a 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 by using various methods including iron-line
abundance analysis. For line identifications, we use whole-range synthetic
spectra computed by using the Kurucz 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 have not been previously known. Under the assumption that the
overabundance pattern of Ba stars is due to wind-accretion process, adding
information of more element abundances enables one to show that the heavy
element overabundances of HD202109 can be explained with the wind accretion
scenario model.Comment: 10 pages, Accepted by Astronomy and Astrophysic
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