34 research outputs found
Cytochemical and ultrastructural aspects of aquatic carnivorous plant turions
Turions, which are modified shoot apices, are vegetative, dormant overwintering organs produced by perennial aquatic plants. In this study, the turion cytochemistry and ultrastructure of Aldrovanda vesiculosa, Utricularia vulgaris and U. stygia were compared with particular emphasis placed on storage substances. These three aquatic, rootless carnivorous plant species were studied at the end of their winter dormancy. At this stage, the turions of all species had starch as their main storage material. In contrast with A. vesiculosa, Utricularia turions were rich in protein storage vacuoles, and proteins were also accumulated as crystalline inclusions in the nuclei. All examined species accumulated lipid droplets in cells of epidermal glands
The Evolved Red Stellar Contents of the Sculptor Group Galaxies NGC55, NGC300, and NGC7793
Deep J, H, and K images are used to probe the evolved stellar contents in the
central regions of the Sculptor group galaxies NGC55, NGC300, and NGC7793. The
brightest stars are massive red supergiants (RSGs) with K ~ 15 - 15.5. The peak
RSG brightness is constant to within ~0.5 mag in K, suggesting that NGC55,
NGC300, and NGC7793 are at comparable distances. Comparisons with bright RSGs
in the Magellanic Clouds indicate that the difference in distance modulus with
respect to the LMC is = 7.5. A rich population of asymptotic giant branch (AGB)
stars, which isochrones indicate have ages between 0.1 and 10 Gyr, dominates
the (K, J-K) color-magnitude diagram (CMD) of each galaxy. The detection of
significant numbers of AGB stars with ages near 10 Gyr indicates that the disks
of these galaxies contain an underlying old population. The CMDs and luminosity
functions reveal significant galaxy-to-galaxy variations in stellar content.
Star-forming activity in the central arcmin of NGC300 has been suppressed for
the past Gyr with respect to disk fields at larger radii. Nevertheless,
comparisons between fields within each galaxy indicate that star-forming
activity during intermediate epochs was coherent on spatial scales of a kpc or
more. A large cluster of stars, which isochrones suggest has an age near 100
Myr, is seen in one of the NGC55 fields. The luminosity function of the
brightest stars in this cluster is flat, as expected if a linear
luminosity-core mass relation is present.Comment: 30 pages, including 13 figure
Correcting for the Effects of Interstellar Extinction
This paper addresses the issue of how best to correct astronomical data for
the wavelength-dependent effects of Galactic interstellar extinction. The main
general features of extinction from the IR through the UV are reviewed, along
with the nature of observed spatial variations. The enormous range of
extinction properties found in the Galaxy, particularly in the UV spectral
region, is illustrated. Fortunately, there are some tight constraints on the
wavelength dependence of extinction and some general correlations between
extinction curve shape and interstellar environment. These relationships
provide some guidance for correcting data for the effects of extinction.
Several strategies for dereddening are discussed along with estimates of the
uncertainties inherent in each method. In the Appendix, a new derivation of the
wavelength dependence of an average Galactic extinction curve from the IR
through the UV is presented, along with a new estimate of how this extinction
law varies with the parameter R = A(V)/E(B-V). These curves represent the true
monochromatic wavelength dependence of extinction and, as such, are suitable
for dereddening IR--UV spectrophotometric data of any resolution, and can be
used to derive extinction relations for any photometry system.Comment: To appear in PASP (January 1999) 14 pages including 4 pages of
figures Uses emulateapj style. PASP, in press (January 1999
Extinction Curves, Distances, and Clumpiness of Diffuse Interstellar Dust Clouds
We present CCD photometry in UBVRI of several thousand Galactic field stars
in four large (>1 degree^2) regions centered on diffuse interstellar dust
clouds, commonly referred to as ``cirrus'' clouds (with optical depth A_V less
than unity). Our goal in studying these stars is to investigate the properties
of the cirrus clouds. A comparison of the observed stellar surface density
between on-cloud and off-cloud regions as a function of apparent magnitude in
each of the five bands effectively yields a measure of the extinction through
each cloud. For two of the cirrus clouds, this method is used to derive UBVRI
star counts-based extinction curves, and U-band counts are used to place
constraints on the cloud distance. The color distribution of stars and their
location in (U-B, B-V) and (B-V, V-I) color-color space are analyzed in order
to determine the amount of selective extinction (reddening) caused by the
cirrus. The color excesses, A_lambda-A_V, derived from stellar color histogram
offsets for the four clouds, are better fit by a reddening law that rises
steeply towards short wavelengths [R_V==A_V/E(B-V)<=2] than by the standard law
(R_V=3.1). This may be indicative of a higher-than-average abundance of small
dust grains relative to larger grains in diffuse cirrus clouds. The shape of
the counts-based effective extinction curve and a comparison of different
estimates of the dust optical depth (extinction optical depth derived from
background star counts/colors; emission optical depth derived from far infrared
measurements), are used to measure the degree of clumpiness in clouds. The set
of techniques explored in this paper can be readily adapted to the Sloan
Digital Sky Survey data set in order to carry out a systematic, large-scale
study of cirrus clouds.Comment: 22 pages, 13 figures (postscript, gif, jpg). Accepted for publication
in the Astronomical Journal, scheduled for the May 1999 issue. Full
resolution postscript versions of all figures are available at
http://www.ucolick.org/~arpad
An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology
We study the IR-through-UV interstellar extinction curves towards 328
Galactic B and late-O stars. We use a new technique which employs stellar
atmosphere models in lieu of unreddened "standard" stars. This technique is
capable of virtually eliminating spectral mismatch errors in the curves. It
also allows a quantitative assessment of the errors and enables a rigorous
testing of the significance of relationships between various curve parameters,
regardless of whether their uncertainties are correlated. Analysis of the
curves gives the following results: (1) In accord with our previous findings,
the central position of the 2175 A extinction bump is mildly variable, its
width is highly variable, and the two variations are unrelated. (2) Strong
correlations are found among some extinction properties within the UV region,
and within the IR region. (3) With the exception of a few curves with extreme
(i.e., large) values of R(V), the UV and IR portions of Galactic extinction
curves are not correlated with each other. (4) The large sightline-to-sightline
variation seen in our sample implies that any average Galactic extinction curve
will always reflect the biases of its parent sample. (5) The use of an average
curve to deredden a spectral energy distribution (SED) will result in
significant errors, and a realistic error budget for the dereddened SED must
include the observed variance of Galactic curves. While the observed large
sightline-to-sightline variations, and the lack of correlation among the
various features of the curves, make it difficult to meaningfully characterize
average extinction properties, they demonstrate that extinction curves respond
sensitively to local conditions. Thus, each curve contains potentially unique
information about the grains along its sightline.Comment: To appear in the Astrophysical Journal, Part 1, July 1, 2007. Figures
and Tables which will appear only in the electronic version of the Journal
can be obtained via anonymous ftp from ftp://ftp.astronomy.villanova.edu .
After logging in, change directories to "fitz/FMV_EXTINCTION". A README file
describes the various files present in the director
The Disk and Extraplanar Regions of NGC 55
The stellar content of the nearby SB(s)m galaxy NGC 55 is investigated using
images covering the visible and near-infrared wavelength regions. A
well-defined plume, which stellar evolution models suggest contains stars with
masses near the RSG - AGB transition, is detected in CMDs of the disk, and it
is concluded that star formation in the thin disk of NGC 55 has ocurred at a
significant rate for at least the past 0.1 - 0.2 Gyr. The disk also contains a
large population of old (log(t_yr) ~ 10) stars, and it is argued that a stable
disk has been in place in NGC 55 for a significant fraction of the age of the
Universe. At projected distances in excess of 2 kpc off of the disk plane the
brightest AGB stars have ages 10(+3)(-2) Gyr. Thus, despite indications that
dust and gas are present in the envelope surrounding the NGC 55 disk, the AGB
content suggests that recently formed stars do not occur in large numbers in
the extraplanar region. The mean metallicity of extraplanar RGB stars is in
excellent agreement with that measured in the extraplanar HII regions EHR 1 and
2, suggesting that the age-metallicity relation in this part of NGC 55 has been
flat for at least a few Gyr. Finally, the RGB-tip occurs near i' = 23.1 in the
extraplanar region, and a distance modulus of 26.5 is computed from this
feature.Comment: 27 pages of text, 20 postscript figures. Accepted for publication in
the Ap
Embryogenesis in Sedum acre L.: structural and immunocytochemical aspects of suspensor development
The changes in the formation of both the actin and the microtubular cytoskeleton during the differentiation of the embryo-suspensor in Sedum acre were studied in comparison with the development of the embryo-proper. The presence and distribution of the cytoskeletal elements were examined ultrastructurally and with the light microscope using immunolabelling and rhodamine-phalloidin staining. At the globular stage of embryo development extensive array of actin filaments is present in the cytoplasm of basal cell, the microfilament bundles generally run parallel to the long axis of basal cell and pass in close to the nucleus. Microtubules form irregular bundles in the cytoplasm of the basal cell. A strongly fluorescent densely packed microtubules are present in the cytoplasmic layer adjacent to the wall separating the basal cell from the first layer of the chalazal suspensor cells. At the heart-stage of embryo development, in the basal cell, extremely dense arrays of actin materials are located near the micropylar and chalazal end of the cell. At this stage of basal cell formation, numerous actin filaments congregate around the nucleus. In the fully differentiated basal cell and micropylar haustorium, the tubulin cytoskeleton forms a dense prominent network composed of numerous cross-linked filaments. In the distal region of the basal cell, a distinct microtubular cytoskeleton with numerous microtubules is observed in the cytoplasmic layer adjacent to the wall, separating the basal cell from the first layer of the chalazal suspensor cells. The role of cytoskeleton during the development of the suspensor in S. acre is discussed
New data about the suspensor of succulent angiosperms : ultrastructure and cytochemical study of the embryo-suspensor of Sempervivum arachnoideum L. and Jovibarba sobolifera (Sims) Opiz
The development of the suspensor in two species - Sempervivum arachnoideum and Jovibarba sobolifera - was investigated using cytochemical methods, light and electron microscopy. Cytological processes of differentiation in the embryo-suspensor were compared with the development of embryo-proper. The mature differentiated suspensor consists of a large basal cell and three to four chalazal cells. The basal cell produces haustorial branched invading ovular tissues. The walls of the haustorium and the micropylar part of the basal cell form the wall ingrowths typical for a transfer cells. The ingrowths also partially cover the lateral wall and the chalazal wall separating the basal cell from the other embryo cells. The dense cytoplasm filling the basal cell is rich in: numerous polysomes lying free or covering rough endoplasmic reticulum (RER), active dictyosomes, microtubules, bundles of microfilaments, microbodies, mitochondria, plastids and lipid droplets. Cytochemical tests (including proteins, insoluble polysaccharides and lipids are distributed in the suspensor during different stages of embryo development) showed the presence of high amounts of macromolecules in the suspensor cells, particularly during the globular and heart-shaped phases of embryo development. The protein bodies and lipid droplets are the main storage products in the cells of the embryo-proper. The results of Auramine 0 indicate that a cuticular material is present only on the surface walls of the embryo-proper, but is absent from the suspensor cell wall. The ultrastructural features and cytochemical tests indicate that in the two species - S. arachnoideum and J. sobolifera - the embryo-suspensor is mainly involved in the absorption and transport of metabolites from the ovular tissues to the developing embryo-proper
The F-actin cytoskeleton in syncytia from non-clonal progenitor cells
The actin cytoskeleton of plant syncytia (a multinucleate cell arising through fusion) is poorly known: to date, there have only been reports about F-actin organization in plant syncytia induced by parasitic nematodes. To broaden knowledge regarding this issue, we analyzed F-actin organization in special heterokaryotic Utricularia syncytia, which arise from maternal sporophytic tissues and endosperm haustoria. In contrast to plant syncytia induced by parasitic nematodes, the syncytia of Utricularia have an extensive F-actin network. Abundant F-actin cytoskeleton occurs both in the region where cell walls are digested and the protoplast of nutritive tissue cells fuse with the syncytium and also near a giant amoeboid in the shape nuclei in the central part of the syncytium. An explanation for the presence of an extensive F-actin network and especially F-actin bundles in the syncytia is probably that it is involved in the movement of nuclei and other organelles and also the transport of nutrients in these physiological activity organs which are necessary for the development of embryos in these unique carnivorous plants. We observed that in Utricularia nutritive tissue cells, actin forms a randomly arranged network of F-actin, and later in syncytium, two patterns of F-actin were observed, one characteristic for nutritive cells and second—actin bundles—characteristic for haustoria and suspensors, thus syncytia inherit their F-actin patterns from their progenitors
Radiative Transfer Analysis of Far-UV Background Observations Obtained with the Far-Ultraviolet Space Telescope (FAUST)
In 1992 the Far-Ultraviolet Space Telescope (FAUST) provided measurements of
the ultraviolet (140-180nm) diffuse sky background at high, medium, and low
Galactic latitudes. A significant fraction of the detected radiation was found
to be of Galactic origin, resulting from scattering by dust in the diffuse
interstellar medium. To simulate the radiative transfer in the Galaxy, we
employed a Monte Carlo model which utilized a realistic, non-isotropic
radiation field based on the measured fluxes (at 156nm) and positions of 58,000
TD-1 stars, and a cloud structure for the interstellar medium. The comparison
of the model predictions with the observations led to a separation of the
Galactic scattered radiation from an approximately constant background,
attributed to airglow and extragalactic radiation, and to a well constrained
determination of the dust scattering properties. The derived dust albedo a =
0.45 +/- 0.05 is substantially lower than albedos derived for dust in dense
reflection nebulae and star-forming regions, while the phase function asymmetry
g = 0.68 +/- 0.10 is indicative of a strongly forward directed phase function.
We show the highly non-isotropic phase function to be responsible, in
conjunction with the non-isotropic UV radiation field, for the wide range of
observed correlations between the diffusely scattered Galactic radiation and
the column densities of neutral atomic hydrogen. The low dust albedo is
attributed to a size distribution of grains in the diffuse medium with average
sizes smaller than those in dense reflection nebulae.Comment: 35 pages, 10 figures included, to be published in the Ap