962 research outputs found
The Binary Galaxies NGC 147 And NGC 185
Contrary to a previously published claim it is found that the spheroidal
galaxies NGC 147 and NGC 185 probably form a stable binary system. Distance
estimates place this pair on the near side of the Andromeda subgroup of the
Local Group. The fact that this system has probably remained stable over a
Hubble time suggests that it does not have a plunging orbit that brings it very
close to M 31. It is noted that the only two Local Group galaxy pairs, in which
the components have comparable masses, also have similar morphological types.
NGC 147 and NGC 185 are both spheroidals, while the LMC and SMC are both
irregulars. This suggests that protogalaxies of similar mass that are spawned
in similar environments evolve into objects having similar morphologies.Comment: To be published in A.J. October 199
The warm circumstellar envelope and wind of the G9 IIb star HR 6902
IUE observations of the eclipsing binary system HR 6902 obtained at various
epochs spread over four years indicate the presence of warm circumstellar
material enveloping the G9 IIb primary. The spectra show Si IV and C IV
absorption up to a distance of 3.3 giant radii (R_g}. Line ratio diagnostics
yields an electron temperature of ~ 78000 K which appears to be constant over
the observed height range.
Applying a least square fit absorption line analysis we derive column
densities as a function of height. We find that the inner envelope (< 3 R_g) of
the bright giant is consistent with a hydrostatic density distribution. The
derived line broadening velocity of ~ 70 kms^{-1} is sufficient to provide
turbulent pressure support for the required scale height. However, an improved
agreement with observations over the whole height regime including the emission
line region is obtained with an outflow model. We demonstrate that the common
beta power-law as well as a P \propto rho wind yield appropriate fit models.
Adopting a continuous mass outflow we obtain a mass-loss rate of M_loss= (0.8 -
3.4)*10^{-11} M_{sun}yr^{-1} depending on the particular wind model.Comment: 11 pages, 8 figures, submitted to Astronomy Astrophysics main Journa
A hydrodynamic study of the circumstellar envelope of alpha Scorpii
Context: Both the absolute mass-loss rates and the mechanisms that drive the
mass loss of late-type supergiants are still not well known. Binaries such as
alpha Sco provide the most detailed empirical information about the winds of
these stars.
Aims: The goal was to improve the binary technique for the determination of
the mass-loss rate of alpha Sco A by including a realistic density distribution
and velocity field from hydrodynamic and plasma simulations.
Methods: We performed 3D hydrodynamic simulations of the circumstellar
envelope of alpha Sco in combination with plasma simulations accounting for the
heating, ionization, and excitation of the wind by the radiation of alpha Sco
B. These simulations served as the basis for an examination of circumstellar
absorption lines in the spectrum of alpha Sco B as well as of emission lines
from the Antares nebula.
Results: The present model of the extended envelope of alpha Sco reproduces
some of the structures that were observed in the circumstellar absorption lines
in the spectrum of alpha Sco B. Our theoretical density and velocity
distributions of the outflow deviate considerably from a spherically expanding
model, which was used in previous studies. This results in a higher mass-loss
rate of (2 +/- 0.5) x 10^-6 M_sun/yr. The hot H II region around the secondary
star induces an additional acceleration of the wind at large distances from the
primary, which is seen in absorption lines of Ti II and Cr II at -30 km/s.Comment: 12 pages, 14 figures, accepted for publication in A&
HE 0515-4414 - an unusual sub-damped Ly alpha system revisited
Using STIS and VLT UVES observations we have examined the ionization,
abundances, and differential dust depletion of metals, the kinematic structure,
and the physical conditions in the molecular hydrogen-bearing sub-damped Ly
alpha system toward HE 0515-4414 at z = 1.15. The velocity interval of
associated metal lines extends for 700 km/s. In addition, saturated H I
absorption is detected in the blue damping wing of the main component. The
column density ratios of associated Al II, Al III, and Fe II lines indicate
that the absorbing material is ionized. 19 of in total 31 detected metal line
components are formed within peripheral H II regions, while only 12 components
are associated with the predominantly neutral main absorber. For the main
absorber the observed abundance ratios of refractory elements to Zn range from
Galactic warm disk [Si/Zn] = - 0.40, [Fe/Zn] = -1.10 to halo-like and
essentially undepleted patterns. The dust-corrected metal abundances indicate a
nucleosynthetic odd-even effect and might imply an anomalous depletion of Si
relative to Fe for two components, but otherwise do correspond to solar ratios.
The intrinsic average metallicity is almost solar [Fe/H] = -0.08, whereas the
uncorrected average is [Zn/H] = -0.38. The ion abundances in the periphery
conform with solar element composition. The detection of H II as well as the
large variation in dust depletion for this sight line raises the question
whether in future studies of damped Ly alpha systems ionization and depletion
effects have to be considered in further detail. Ionization effects, for
instance, may pretend an enrichment of alpha elements. An empirical recipe for
detecting H II regions is provided.Comment: 26 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
Magnetic field detection in the B2Vn star HR 7355
The B2Vn star HR 7355 is found to be a He-rich magnetic star.
Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory
to measure the disk-averaged longitudinal magnetic field at various phases of
the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z
= -2200 and +3200G was found, with confidence limits of 100 to 130G. The field
topology is that of an oblique dipole, while the star itself is seen about
equator-on. In the intensity spectra the HeI-lines show the typical equivalent
width variability of He-strong stars, usually attributed to surface abundance
spots. The amplitudes of the equivalent width variability of the HeI lines are
extraordinarily strong compared to other cases. These results not only put HR
7355 unambiguously among the early-type magnetic stars, but confirm its
outstanding nature: With v sin i = 320 km/s the parameter space in which
He-strong stars are known to exist has doubled in terms of rotational velocity.Comment: 6 pages, 5 figures, 1 Table. Accepted for publication in MNRAS
Letter
The (B0+?)+O6 system FN CMa: A case for tidal-pulsational interaction?
FN CMa is visually double with a separation of about 0.6arcsec. Sixty
high-cadence VLT/UVES spectra permit the A and B components to be disentangled,
as the relative contribution of each star to the total light entering the
spectrograph fluctuates between exposures due to changes in seeing. Component A
exhibits rapid line-profile variations, leading us to attribute the photometric
variability seen by HIPPARCOS (with a derived P=0.08866d) to this component.
From a total of 122 archival and new echelle spectra it is shown that component
A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of
0.6 may result in tidal modulation of the pulsation(s) of component Aa.Comment: 2 pages, 1 figure, IAUS 272 - Active OB Stars: Structure, Evolution,
Mass Loss and Critical Limit
Not in my back yard! Sports stadia location and the property market
In recent years sports stadia have been built in the UK, not only for their intended sporting purpose but with the twin aim of stimulating economic and physical regeneration. However, proposals to locate stadia in urban areas often prompt a negative reaction from local communities, fearing a decline in property prices. This paper will use a case study of the Millennium Stadium in Cardiff and the City of Manchester Stadium to illustrate that in contrast to this widely held belief, sports stadia can actually enhance the value of residential property. Furthermore, it will argue that stadia also contribute indirectly to property value through the creation of pride, confidence and enhanced image of an area.</p
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