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We present the second paper of a series whose aim is to perform a global
study of Galactic A-supergiants. Very little work has been carried out
to determine the stellar parameters of these stars. This is illustrated
with a brief review of some previous works. In this paper we analyze the
determination of absolute magnitudes, spectral types and atmo...
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Context 1
... integrals were evaluated numerically by inter- polating S i (λ) parabolically and F (λ) linearly to a wavelength spacing of 1 ˚ A, then integrating trapezoidally. The results for all the models studied are summarized in Table 5. ...
Citations
Magnetic wind confinement has been proposed as one explanation for the
complex wind structures of supergiant stars of spectral types B and A.
Observational investigation of this hypothesis was undertaken using
high-resolution ({\lambda}/{\Delta}{\lambda} {\sim} 65,000) circular
polarization (Stokes V ) spectra of six late B and early A type supergiants
({\beta} Ori, B8Iae; 4 Lac, B9Iab; {\eta} Leo, A0Ib; HR1040, A0Ib; {\alpha}
Cyg, A2Iae; {\nu} Cep, A2Iab), obtained with the instruments ESPaDOnS and
Narval at the Canada-France-Hawaii Telescope and the Bernard Lyot Telescope.
Least Squares Deconvolution (LSD) analysis of the Stokes V spectra of all stars
yields no evidence of a magnetic field, with best longitudinal field 1{\sigma}
error bars ranging from {\sim}0.5 to {\sim}4.5 G for most stars. Spectrum
synthesis analysis of the LSD profiles using Bayesian inference yields an upper
limit with 95.4% credibility on the polar strength of the (undetected) surface
dipole fields of individual stars ranging from 3 to 30 G. These results
strongly suggest that magnetic wind confinement due to organized dipolar
magnetic fields is not the origin of the wind variability of BA supergiant
stars. Upper limits for magnetic spots may also be inconsistent with magnetic
wind confinement in the limit of large spot size and filling factor, depending
on the adopted wind parameters. Therefore, if magnetic spots are responsible
for the wind variability of BA supergiant stars, they likely occupy a small
fraction of the photosphere.
We present the results of photometric and spectroscopic observations of two A-type stars (HD 19993 and HD 29035), optical counterparts of the IRAS sources (F03108+3729 and 04331+5211, respectively). Halpha line emission is found in the optical spectra of both objects for the first time. Our analysis of the spectral line profiles and the photometric information shows that HD 19993 is an A7/8 II star (Teff ~7500+/-200 K, log g =2.7+/-0.2, v sin i =35+/-2 km s-1, M=4.8+/- 0.8 Msun ) with a mild metal deficit ([Fe/H] ~ -0.3+/-0.1), while HD 29035 is a B9/A0 V star (Teff ~10 000 K, log g ~ 4, vsin i ~ 150 km s-1). The presence of an IR excess and the Halpha emission in combination with a very different location in the Hertzsprung-Russell diagram suggest the different nature and evolutionary stages of the objects. We conclude that HD 29035 is a candidate Herbig Ae type star, a possible member of a group of similar objects. HD 19993 seems to be a post-main-sequence object.
HD 223960, an A0 Ia-type supergiant in the Cas OB5 association, is unusual among Galactic supergiants of its class in having an Halpha profile with double-peaked emission entirely above the continuum. We analyzed 12 high-resolution échelle spectra obtained in 1993-1995 and in 1999 with the 1 m telescope of Ritter Observatory. The radial velocities of photospheric Si, C, He, Ne, and S lines were found to be constant to within +/-2 km s-1, but the data suggest variability in the equivalent widths of Si II lambdalambda6347, 6371 and several other photospheric lines. The radial velocities and equivalent widths and, especially, the ratio V/R of the Halpha components vary. The present data do not indicate a binary explanation for the double-peaked emission feature. Alternative explanations are considered, but none is completely satisfactory. The available evidence is consistent with the star having a weak, fast wind.
Elemental abundance analysis based on high S/N and high resolution
Dominion Astrophysical Observatory spectrograms have been performed for
two early type supergiants: 4 Lac (B9 Iab) and {\msf ν } Cep (A2 Ia).
Lines as weak as of order 5 mÅ are employed in this study. The
projected rotational velocities of these stars are 14 and 26 km
s-1, respectively. Both stars show similar radial velocity
amplitudes, macroturbulent velocities and the same general elemental
abundance trends. Their He, CNO and light element abundances are solar
or overabundant while the iron peak and heavy element abundances are
solar or underabundant. Detailed LTE model atmosphere abundance analysis
shows that 4 Lac has nuclearly processed matter in its photosphere while
{\msf ν } Cep does not.
The year 1999 saw the arrival of a star with three planets, a universe
with three parameters, and a solar corona that could be heated at least
three ways. In addition, there were at least three papers on every
question that has ever been asked in astrophysics, from ``Will the
Universe expand forever?'' to ``Does mantle convection occur in one or
two layers?'' The answers generally were, ``Yes,'' ``No,'' and ``None of
the above,'' to each of the questions. The authors have done their best
to organize the richness around centers defined by objects, methods, and
madnesses.
This study presents a detailed model atmosphere abundance analysis of
Deneb which was performed using Kurucz LTE ATLAS9 model atmospheres. The
atmospheric parameters were determined from Mg I/II and Fe I/II
equilibrium, and by fitting the Hgamma profile and optical
region spectrophotometry. The compromise values which best satisfy these
criteria are T_eff = 9000 K and log g = 1.45. The Mg I, Mg II, Si II, Ti
II, Cr II, Fe I, and Fe II lines yield microturbulences of 3.60, 6.50,
8.50, 8.00, 11.90, 3.60, and 10.40 km s-1, respectively. An
average microturbulence of 7 km s-1 was used for the other
atomic species. From a comparision of the synthetic spectrum with the
observations, the best value for the rotational velocity is v sin i = 25
km s-1, and for the macroturbulent velocity is zeta = 14 km
s-1, which are similar to those of some earlier derived
values. Also, the individual spectrograms have a range of radial
velocity variation of ~ 15 km s-1 which is approximately
equal to macroturbulent velocity. These values of the macroturbulence
and the range of radial velocity variation are close to the sum of the
amplitudes (10.44 km s-1) of all the pulsation periods found
by Lucy (\cite{lucy}), who also suggested that the surface motions of
the atmosphere of Deneb can be identified with macroturbulence. Deneb
showed a definite helium underabundance with a well determined He/H
value = 0.071. The CNO values (C being mildly deficient, N being in
moderate excess, and an O being slightly deficient) are consistent with
the mixing of the CNO-cycled products into the surface layers from the
processed materials presumably dredged-up from the interior. Aluminium
is mildly deficient by ~ 0.24 dex with respect to solar value, while
sulfur is moderately underabundant by ~ 0.43 dex in Deneb. Mg and Si
have the solar abundances. The metal abundances (Ca to Ni) tend to be
greater than solar except for Sc which is slightly deficient. The heavy
elements abundances (Sr, Y, and Zr) are all greater than solar. These
abundance patterns conform to the common tendency seen with other normal
Population I A supergiants found by Venn (\cite{venna}). The rare-earth
elements (Ba, La, and Eu) which have been unexplored in other Galactic
early A-type supergiants are significantly overabundant relative the
Sun. Based on data obtained at the Dominion Astrophysical Observatory,
Herzberg Institute of Astrophysics, National Research Council of Canada.
Table A.1 is only available electronically with the On-Line publication
at http://link.springer.de/link/service/00230/
BA-type supergiants show a high potential as versatile indicators for modern
astronomy. The focus here is on the determination of accurate and precise
atmospheric parameters for a sample of 35 Galactic BA-type supergiants. Some
first applications include a recalibration of functional relationships between
spectral-type, intrinsic colours, bolometric corrections and effective
temperature, and an exploration of the reddening-free Johnson Q and Str\"omgren
[c_1] and beta-indices as photometric indicators for effective temperatures and
gravities of BA-type supergiants. An extensive grid of theoretical spectra is
computed based on a hybrid non-LTE approach. The atmospheric parameters are
derived spectroscopically by line-profile fits to high-resolution and high-S/N
spectra obtained at various observatories. Ionization equilibria of multiple
metals and the Stark-broadened H and the neutral He lines constitute our
primary indicators for the parameter determination, supplemented by
(spectro-)photometry. Data on Teff, logg, helium abundances, microturbulence,
macroturbulence and rotational velocities are presented. The interstellar
reddening and the ratio of total-to-selective extinction towards the stars are
determined. Our empirical spectral-type-Teff scale is steeper than reference
relations, the stars are significantly bluer, and bolometric corrections differ
significantly from established literature values. Photometric
Teff-determinations based on the reddening-free Q-index are found to be of
limited use for studies of BA-type supergiants because of large errors of
typically +-5%+-3% (1sigma statistical, 1sigma systematic), compared to a
spectroscopically achieved precision of 1-2%. The reddening-free [c_1]-index
and beta on the other hand are found to provide useful starting values for
further analyses, with uncertainties of +-1%+-2.5% in Teff, and +-0.04+-0.13dex
in log g. [abriged]
Optical spectra taken in 1997–2008 are used to analyze the spectral peculiarities and velocity field in the atmosphere of
the peculiar supergiant 3 Pup. The profiles of strong Fe II lines and of the lines of other iron-group ions have a specific
shape: the wings are raised by emissions, whereas the core is sharpened by a depression. The latter feature becomes more pronounced
with the increasing line strength, and the increasing wavelength. Line profiles are variable: the magnitude and sign of the
absorption asymmetry, and the blue-to-red emission intensity ratios vary from one spectrum to another. The temporal Vr variations are minimal for the forbidden emissions and sharp shell cores of the absorption features of FeII(42), and other
strong lines of iron-group ions. The average velocity for the above lines can be adopted as the systemic velocity: Vsys = 28.5 ± 0.5 km/s. The weakest photospheric absorptions and photospheric MgII, Si II absorptions exhibit well-defined day-to-day
velocity variations of up to 7 km/s. Quantitative spectral classification yields the spectral type of A2.7±0.3 Ib. The equivalent
widths and profiles of Hδ and Hγ, and the equivalent width of the OI 7774 Å triplet yield an absolute magnitude estimate of Mv=−5.5m ± 0.3m, implying the heliocentric distance of 0.7 kpc.
Key wordsstars—variable and peculiar
We present new spectroscopic observations of the peculiar supergiant IRC+10420. In 1997–2000, we obtained three high signal-to-noise ratio spectra of the object at 4300–8000 Å with a spectral resolution of 15 000 (20 km/ s) using the 6-m telescope of the Special Astrophysical Observatory. From our 2000 spectrum, we estimate the spectral type of IRC+10420 to be A2, corresponding to a temperature of ∼9200 K. Many emission lines were detected, identified with lines of Fe I; Fe II, Ti II, Cr II, and Sc II ions; and [O I], [Fe II], and [Ca II] forbidden lines. The radial velocity derived from absorption lines without obvious emission components (He I λ5876, O I, N I, Si II) and from absorption components of the Balmer lines is 93±1 km/s. The redshift of photospheric lines relative to the star’s center-of-mass velocity is interpreted as a consequence of scattering in the expanding, optically thick dust envelope. Both emission and absorption lines show a correlation between radial velocity and oscillator strength. We found variability in the relative intensities of the H
α
and H
β
emission components. We conclude that IRC+10420 is rapidly evolving towards a Wolf-Rayet stage; the current rate of the photospheric temperature increase is ∼120 K per year. Based on the intensity of the O I (λ7773) triplet, we estimate the star’s luminosity to be M
bol=−9.5m. In all 1997–2000 spectra of IRC+10420, the He I λ5876 line has a significant equivalent width of at least 200 mÅ; this may be possible in the presence of such a low temperature due to the star’s high luminosity and the enhanced helium abundance in the supergiant’s atmosphere.
We emphasize in this paper the importance of the UV range for our knowledge of massive stars and the fundamental role played by past and present space-based UV capabilities (IUE, HST, FUSE and others). Based on a review of the work developed in the last years and the state of the art situation for quantitative spectroscopy of massive stars, we present crucial advances which could be addressed by hypothetical future space-based UV missions. Advantages and unique data that these missions could provide are explained in the context of our present knowledge and theories on massive stars in the Milky Way and nearby galaxies. It is argued that these studies are our key to a correct interpretation of observations of more distant objects.
