3,702 research outputs found
The fate of cannibalized fundamental-plane ellipticals
Evolution and disruption of galaxies orbiting in the gravitational field of a
larger cluster galaxy are driven by three coupled mechanisms: 1) the heating
due to its time dependent motion in the primary; 2) mass loss due to the tidal
strain field; and 3) orbital decay. Previous work demonstrated that tidal
heating is effective well inside the impulse approximation limit. Not only does
the overall energy increase over previous predictions, but the work is done
deep inside the secondary galaxy, e.g. at or inside the half mass radius in
most cases. Here, these ideas applied to cannibalization of elliptical galaxies
with fundamental-plane parameters. In summary, satellites which can fall to the
center of a cluster giant by dynamical friction are evaporated by internal
heating by the time they reach the center. This suggests that true
merger-produced multiple nuclei giants should be rare. Specifically,
secondaries with mass ratios as small as 1\% on any initial orbit evaporate and
those on eccentric orbits with mass ratios as small as 0.1\% evolve
significantly and nearly evaporate in a galaxian age. Captured satellites with
mass ratios smaller than roughly 1\% have insufficient time to decay to the
center. After many accretion events, the model predicts that the merged system
has a profile similar to that of the original primary with a weak increase in
concentration.Comment: 19 pages, 10 Postscript figures, uses aaspp4.sty. Submitted to
Astrophysical Journa
The effect of dust obscuration in RR Tel on optical and IR long-term photometry and Fe II emission lines
Infrared and optical photometric and spectroscopic observations of the
symbiotic nova RR Tel are used to study the effects and properties of dust in
symbiotic binaries containing a cool Mira component, as well as showing
"obscuration events" of increased absorption, which are typical for such Miras.
A set of photometric observations of the symbiotic nova RR Tel in different
wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975
to 2002 - are presented. The variability due to the normal Mira pulsation was
removed from the JHKL data, which were then compared with the AAVSO visual
light curve. The changes of the Fe II emission line fluxes during the 1996-2000
obscuration episode were studied in the optical spectra taken with the
Anglo-Australian telescope.
We discuss the three periods during which the Mira component was heavily
obscured by dust as observed in the different wavelength bands. A change in the
correlations of J with other infrared magnitudes was observed with the colour
becoming redder after JD2446000. Generally, J-K was comparable, while K-L was
larger than typical values for single Miras. A distance estimate of 2.5 kpc,
based on the IR data, is given. A larger flux decrease for the permitted than
for the forbidden Fe II lines, during the obscuration episode studied, has been
found. There is no evidence for other correlations with line properties, in
particular with wavelength, which suggests obscuration due to separate
optically thick clouds in the outer layers.Comment: 19 pages, 11 figures, 3 table
Plant-soil feedbacks promote coexistence and resilience in multi-species communities
Both ecological theory and empirical evidence suggest that negative frequency dependent
feedbacks structure plant communities, but integration of these findings has been limited.
Here we develop a generic model of frequency dependent feedback to analyze coexistence
and invasibility in random theoretical and real communities for which frequency dependence
through plant-soil feedbacks (PSFs) was determined empirically. We investigated community
stability and invasibility by means of mechanistic analysis of invasion conditions and numerical
simulations. We found that communities fall along a spectrum of coexistence types ranging
from strict pair-wise negative feedback to strict intransitive networks. Intermediate community
structures characterized by partial intransitivity may feature âkeystone competitorsâ which disproportionately
influence community stability. Real communities were characterized by stronger
negative feedback and higher robustness to species loss than randomly assembled
communities. Partial intransitivity became increasingly likely in more diverse communities.
The results presented here theoretically explain why more diverse communities are characterized
by stronger negative frequency dependent feedbacks, a pattern previously encountered
in observational studies. Natural communities are more likely to be maintained by strict negative
plant-soil feedback than expected by chance, but our results also show that community
stability often depends on partial intransitivity. These results suggest that plant-soil feedbacks
can facilitate coexistence in multi-species communities, but that these feedbacks may also initiate
cascading effects on community diversity following from single-species loss.DEB - 0919434, DEB - 1050237, DEB-1556664, DEB-173804
The Influence of Magnetic Field on Oscillations in the Solar Chromosphere
Two sequences of solar images obtained by the Transition Region and Coronal
Explorer in three UV passbands are studied using wavelet and Fourier analysis
and compared to the photospheric magnetic flux measured by the Michelson
Doppler Interferometer on the Solar Heliospheric Observatory to study wave
behaviour in differing magnetic environments. Wavelet periods show deviations
from the theoretical cutoff value and are interpreted in terms of inclined
fields. The variation of wave speeds indicates that a transition from dominant
fast-magnetoacoustic waves to slow modes is observed when moving from network
into plage and umbrae. This implies preferential transmission of slow modes
into the upper atmosphere, where they may lead to heating or be detected in
coronal loops and plumes.Comment: 8 pages, 6 figures (4 colour online only), accepted for publication
in The Astrophysical Journa
Opacity in the upper atmospheres of active stars II. AD Leonis
We present FUV and UV spectroscopic observations of AD Leonis, with the aim
of investigating opacity effects in the transition regions of late-type stars.
The C III lines in FUSE spectra show significant opacity during both the
quiescent and flaring states of AD Leonis, with up to 30% of the expected flux
being lost during the latter. Other FUSE emission lines tested for opacity
include those of O VI, while C IV, Si IV and N V transitions observed with STIS
are also investigated. These lines only reveal modest amounts of opacity with
losses during flaring of up to 20%. Optical depths have been calculated for
homogeneous and inhomogeneous geometries, giving path lengths of ~20-60 km and
\~10-30 km, respectively, under quiescent conditions. However path lengths
derived during flaring are ~2-3 times larger. These values are in excellent
agreement with both estimates of the small-scale structure observed in the
solar transition region, and path lengths derived previously for several other
active late-type stars.Comment: 13 pages, 4 figures, 4 Tabels, accepted A&
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