182 research outputs found
Analysis of first overtone bands of isotopologues of CO and SiO in stellar spectra
The first overtone ( = 2) bands of the monosubstituted
isotopologues of CO at 2.3 m in the spectrum of Arcturus (K2 III), and of
the monosubstituted isotopologues of SiO at 4 m in the spectrum of the red
giant HD196610 (M6 III) are modelled.
To investigate problems involving the computation of the first overtone bands
of isotopologues of CO and SiO in spectra of late-type stars and to determine
isotopic abundances.
We use fits of theoretical synthetic spectra to the observed stellar
molecular bands of CO and SiO to determine abundances of isotopes of C, O and
Si.
Fits of synthetic spectra of the \CO first overtone bands at 2.3 m
computed with three available line lists (Goorvitch, HITEMP2010 and Li et al.)
to the observed spectrum of Arcturus provide the same carbon abundance
[C]= and isotopic ratio of carbon C/C=10 2. However,
the quality of fits to the observed spectrum differ for three line lists used.
Furthermore, the derived oxygen isotopic ratio O/O = 2000
500 is larger than that known in the solar system where O/O =
500. The silicon isotopic ratio in the atmosphere of the red giant HD196610 is
revised. Using the ExoMol SiO line list with appropriate statistical weights
for the SiO isotopologues the `non-solar' ratio Si:Si:Si =
0.860.03:0.120.02:0.020.01 is obtained.
We found that a) the computed isotopic carbon and silicon ratios determined
by the fits to the observed spectrum depend on the adopted abundance of C and
Si, respectively; b) Correct treatment of the nuclear spin degeneracies
parameter is of crucial importance for the use of nowadays HITRAN/ExoMol line
lists in the astrophysical computations.Comment: 9 pages, 6 figures, accepted by A&
Vsini-s for late-type stars from spectral synthesis in K-band region
We analyse medium-resolution spectra (R\sim 18000) of 19 late type dwarfs in
order to determine vsini-s using synthetic rather than observational template
spectra. For this purpose observational data around 2.2 m of stars with
spectral classes from G8V to M9.5V were modelled.
We find that the Na I (2.2062 and 2.2090 m) and CO 2-0 band
features are modelled well enough to use for vsini determination without the
need for a suitable observational template spectra. Within the limit of the
resolution of our spectra, we use synthetic spectra templates to derive vsini
values consistent with those derived in the optical regime using observed
templates. We quantify the errors in our vsini determination due to incorrect
choice of model parameters \Teff, log , , [Fe/H] or FWHM and
show that they are typically less than 10 per cent. We note that the spectral
resolution of our data(\sim 16 km/s) limited this study to relatively fast
rotators and that resolutions of 60000 will required to access most late-type
dwarfs.Comment: 8 pages, 4 figures, 3 tables, accepted to the MNRA
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