1,471 research outputs found
Models of infrared spectra of Sakurai's Object (V4334 Sgr) in 1997
Theoretical spectral energy distributions computed for a grid of
hydrogen-deficient and carbon-rich model atmospheres have been compared with
the observed infrared (1--2.5 m) spectra of V4334 Sgr (Sakurai's Object)
on 1997 April 21 and July 13. The comparison yields an effective temperature of
\Tef = 5500 200 K for the April date and \Tef = 5250 200 K for
July. The observed spectra are well fitted by Asplund et al. (1999) abundances,
except that the carbon abundance is higher by 0.3 dex. Hot dust produces
significant excess continuum at the long wavelength ends of the 1997 spectra.
\keywords{Stars: individual: V4334 Sgr (Sakurai's Object) -- Stars: AGB and
post-AGB evolution -- Stars: model atmospheres -- Stars: energy distributions
-- Stars: effective temperatures}Comment: 6 pages, 7 eps figs, accepted for A
Ultracool dwarfs
We present results of modeling of spectra of M-, L-, T-dwarfs. Theoretical
spectra are fitted to observed spectra to study the main parameters of the
low-mass objects beyond the bottom of Main Sequence. Application of ``lithium''
and ``deuterium'' tests for assessment of ultra-cool dwarfs are discussed.Comment: Talk for MAO2004 Meeting (Kyiv, July 15-17, 2004), see more details
on http://www.mao.kiev.ua/mao-2004/public.htm, 6 pages, 3fig
12C/13C in atmospheres of red giants and peculiar stars
We determine the carbon isotopic ratios in the atmospheres of some evolved
stars in both globular clusters and the disk of our Galaxy. Analysis of 12CO
and 13CO bands at 2.3 micron was carried out using fits to observed spectra of
red giants and Sakurai's object (V4334 Sgr). The dependence of theoretical
spectra on the various input parameters was studied in detail. The computation
of model atmospheres and a detailed abundance analysis was performed in a
self-consistent fashion. A special procedure for determining the best fits to
observed spectra was used. We show, that globular cluster giants with [Fe/H] <
-1.3 have a low 12C/13C = 4 +/- 1 abundance ration. In the spectra of Sakurai's
object (V4334 Sgr) taken between 1997-98, the 2.3 micron spectral region is
veiled by hot dust emission. By fitting UKIRT spectra we determined 12C/13C = 4
+/- 1 for the July, 1998 spectrum. CO bands in the spectra of ultracool dwarfs
are modelled as well.Comment: Poster for IAU Symposium No. 228, "From Lithium to Uranium: Elemental
Tracers of Early Cosmic Evolution", V. Hill, P. Francois & F. Primas, eds.
(2005); 2 pages, ppt is available on
ftp://ftp.mao.kiev.ua/%2f/pub/users/yp/12C13C_for_IAU228.pp
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