84 research outputs found
Zur Kenntnis der Taxonomie und Verbreitung der Alpenpflanzen
Abstract.: Landolt E. 2006. Remarks on the present taxonomic and chorological knowledge of the Alpine flora. Bot. Helv. 116: 79-90. Recently published Floras of the Alps or of parts of the Alps show that our taxonomic and chorological knowledge of the Alpine flora is still incomplete regarding the morphology, delimitation and distribution of many taxa. The situation is demonstrated and discussed by different examples. Compared to Floras of the 20th century only few of the many critical aggregates of taxa have been clarified despite new study methods. A proposal is given to survey and improve our information on Alpine plant tax
Speciation in Duckweeds (Lemnaceae): Phylogenetic and Ecological Inferences
Species of duckweeds (Letnnaceae) that were resolved as sister taxa in a phylogeny based on combined molecular and non-molecular data were compared for morphological, physiological, and ecological attributes to infer factors important in the initial divergence leading to speciation. The ability to survive extreme conditions such as desiccation and cold temperatures is the most common difference identified between species. Two morphological characters facilitating survival in extreme environments are production of special resting buds called turions and increased seed production. The prevalent geographic pattern for species pairs consists of one restricted species occurring on the periphery of a more widespread taxon; this pattern indicates that divergence of peripheral isolates is a common geographical mode of speciation in duckweeds. Other species differ in optimal environmental conditions for growth, and these species are largely sympatric. In only one instance does it appear that divergence and speciation occurred following long-distance dispersal. Sympatric species pairs have the lowest molecular divergence; widespread primarily allopatric, and distantly allopatric species have the highest molecular divergence. Despite infrequent sexual reproduction, some degree of detectable variation (molecular, physiological, etc.) occurs within populations and among populations of the same species. Molecular evidence indicates that variation within duckweeds extends from the population and intraspecific levels to very different levels of divergence among recognized species. Contrary to the appearance of morphological and ecological uniformity implied by their reduced morphology and restricted occurrence in fresh water habitats, duckweeds are not a group in evolutionary stasis. Rather, these smallest of all flowering plants are dynamic evolutionarily, and comprise a model system for studying plant evolution and speciation
Late-time emission of type Ia supernovae: optical and near-infrared observations of SN 2001el
We present optical and near-infrared light curves of SN 2001el from 310 to
445 days past maximum light, obtained with the Very Large Telescope. The
late-time optical (UBVRI) light curves decay in a nearly linear fashion with
decay time scales of 1.43\pm0.14, 1.43\pm0.06, 1.48\pm0.06, 1.45\pm0.07, and
1.03\pm0.07 magnitudes (per hundred days) in the U, B, V, R and I bands,
respectively. In contrast, in the near-infrared (JHKs) bands the time evolution
of the flux appears to be nearly constant at these epochs. We measure decline
rates (per hundred days) of 0.19\pm0.10 and 0.17\pm0.11 magnitudes in the J and
H bands, respectively. We construct a UVOIR light curve, and find that the
late-time luminosity has a decay time scale nearly consistent with complete
depostion of positron kinetic energy. The late-time light curves of the normal
type Ia SN 2001el demonstrate the increased importance of the near-infrared
contribution. This was previously observed in the peculiar SN 2000cx, and the
results for SN 2001el thus ensure that the conclusions previously based on a
single peculiar event are applicable to normal type Ia supernovae. The measured
late-time UVOIR decline rate suggests that a majority of the positrons are
trapped within the ejecta. This results does not favor the predictions of a
weak and/or radially combed magnetic field configuration.Comment: 4 pages with 2 figures plus 7 tables. Accepted for publication in A&A
letter. Constructive comments welcome
Allozyme variation and the taxonomy of Wolffiella
Abstract Allozyme electrophoresis was carried out to estimate genetic diversity within and assess divergence between the 10 recognized species in three sections of the aquatic angiosperm genus Wolffiella. Eleven presumptive loci were used in the calculations. Crawford et al. /Aquatic Botany 58 (1997) [43][44][45][46][47][48][49][50][51][52][53][54] Allozyme data support the recognition of sect. Stipitatae as now constituted and provide evidence for the circumscription of sect. Wolffiella as presently recognized. However, W. denticulata is rather isolated within this section. © 1997 Elsevier Science B.V
Close binary companions of the HAeBe stars LkHa 198, Elias 1, HK Ori and V380 Ori
We present diffraction-limited bispectrum speckle interferometry observations
of four well-known Herbig Ae/Be (HAeBe) stars, LkHa 198, Elias 1, HK Ori and
V380 Ori. For two of these, LkHa 198 and Elias 1, we present the first
unambiguous detection of close companions. The plane of the orbit of the new
LkHa 198 companion appears to be significantly inclined to the plane of the
circumprimary disk, as inferred from the orientation of the outflow. We show
that the Elias 1 companion may be a convective star, and suggest that it could
therefore be the true origin of the X-ray emission from this object. In the
cases of HK Ori and V380 Ori, we present new measurements of the relative
positions of already-known companions, indicating orbital motion. For HK Ori,
photometric measurements of the brightness of the individual components in four
bands allowed us to decompose the system spectral energy distribution (SED)
into the two separate component SEDs. The primary exhibits a strong infrared
excess which suggests the presence of circumstellar material, whereas the
companion can be modelled as a naked photosphere. The infrared excess of HK Ori
A was found to contribute around two thirds of the total emission from this
component, suggesting that accretion power contributes significantly to the
flux. Submillimetre constraints mean that the circumstellar disk cannot be
particularly massive, whilst the near-infrared data indicates a high accretion
rate. Either the disk lifetime is very short, or the disk must be seen in an
outburst phase.Comment: 14 pages, 10 figures, 22 separate figure file
Near-IR search for lensed supernovae behind galaxy clusters: I. Observations and transient detection efficiency
Massive galaxy clusters at intermediate redshift can magnify the flux of
distant background sources by several magnitudes and we exploit this effect to
search for lensed distant supernovae that may otherwise be too faint to be
detected. A supernova search was conducted at near infrared wavelengths using
the ISAAC instrument at the VLT. The galaxy clusters Abell 1689, Abell 1835 and
AC114 were observed at multiple epochs of 2 hours of exposure time, separated
by a month. Image-subtraction techniques were used to search for transient
objects with light curve properties consistent with supernovae, both in our new
and archival ISAAC/VLT data. The limiting magnitude of the individual epochs
was estimated by adding artificial stars to the subtracted images. Most of the
epochs reach 90% detection efficiency at SZ(J) ~= 23.8-24.0 mag (Vega). Two
transient objects, both in archival images of Abell 1689 and AC114, were
detected. The transient in AC114 coincides - within the position uncertainty -
with an X-ray source and is likely to be a variable AGN at the cluster
redshift. The transient in Abell 1689 was found at SZ=23.24 mag, ~0.5 arcsec
away from a galaxy with photometric redshift z=0.6 +/-0.15. The light curves
and the colors of the transient are consistent with a reddened Type IIP
supernova at redshift z=0.59 +/- 0.05. The lensing model of Abell 1689 predicts
~1.4 mag of magnification at the position of the transient, making it the most
magnified supernova ever found and only the second supernova found behind a
galaxy cluster. Our pilot survey has demonstrated the feasibility to find
distant gravitationally magnified supernovae behind massive galaxy clusters.
One likely supernova was found behind Abell 1689, in accordance with the
expectations for this survey, as shown in an accompanying analysis paper.Comment: Language-edited version, 9 pages, 6 figures, accepted by A&
The short-duration GRB 050724 host galaxy in the context of the long-duration GRB hosts
We report optical and near-infrared broad band observations of the
short-duration GRB 050724 host galaxy, used to construct its spectral energy
distribution (SED). Unlike the hosts of long-duration gamma-ray bursts (GRBs),
which show younger stellar populations, the SED of the GRB 050724 host galaxy
is optimally fitted with a synthetic elliptical galaxy template based on an
evolved stellar population (age ~2.6 Gyr). The SED of the host is difficult to
reproduce with non-evolving metallicity templates. In contrast, if the short
GRB host galaxy metallicity enrichment is considered, the synthetic templates
fit the observed SED satisfactorily. The internal host extinction is low (A_v
\~< 0.4 mag) so it cannot explain the faintness of the afterglow. This short
GRB host galaxy is more massive (~5x10^10 Mo) and luminous (~1.1 L*) than most
of the long-duration GRB hosts. A statistical comparison based on the ages of
short- and long-duration GRB host galaxies strongly suggests that
short-duration GRB hosts contain, on average, older progenitors. These findings
support a different origin for short- and long-duration GRBs.Comment: A&A in pres
Wide Field Photometry of the Galactic Globular Cluster M22
We present wide field photometry of the Galactic Globular Cluster M~22 in the
B, V and I passbands for more than 186,000 stars. The study is complemented by
the photometry in two narrowband filters centered on H and the
adjacent continuum, and by infrared J, H and K magnitudes derived from the 2
MASS survey for 2000 stars. Profiting from this huge database, we
completely characterized the evolved stellar sequences of the cluster by
determining a variety of photometric parameters, including new photometric
estimates of the mean metallicity, reddening and distance to the cluster. In
particular, from our multi-wavelength analysis, we re-examined the
long-standing metallicity spread problem in M~22. According to our dataset, we
conclude that most of the observed width of the red giant branch must be due to
differential reddening, which amounts to a maximum of , although the presence of a small metallicity spread cannot
be completely ruled out. More specifically, the maximum metallicity spread
allowed by our data is of the order of [Fe/H] dex,
i.e., not much more than what allowed by the photometric errors. Finally, we
identified most of the known variable stars and peculiar objects in our field
of view. In particular, we find additional evidence supporting previous optical
identifications of the central star of the Planetary Nebula IRAS 18333-2357,
which is associated with M~22.Comment: 15 pages, 16 figures, accepted for publication in MNRA
Photometric and Spectroscopic study of a highly reddened type Ia supernova SN 2003hx in NGC 2076
We present CCD photometry and optical spectra of the type Ia
supernova SN 2003hx which appeared in the galaxy NGC 2076, obtained till
146 days after the epoch of band maximum. The supernova reached at maximum
brightness in band on JD 245 2893 1.0 with an apparent magnitude of
14.92 0.01 mag which was estimated by making template fits to the light
curves. SN 2003hx is an example of a highly reddened supernova with =
0.56 0.23. We estimate = 1.97 0.54 which indicates the small
size of dust particles as compared to their galactic counterparts. The
luminosity decline rate is = 1.17 0.12 mag and the
absolute band magnitude obtained from the luminosity versus decline rate
relation (Phillips et al. 1999) is = -19.20 0.18 mag. The
peak bolometric luminosity indicates that 0.66 mass of
Ni was ejected by the supernova. The spectral evolution indicates the supernova
to be a normal type Ia event.Comment: 16 pages, 21 figures, 5 tables, Accepted for publication in MNRA
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