646 research outputs found
Variable stars in the Fornax dSph Galaxy. II. Pulsating stars below the horizontal branch
We have carried out an intensive survey of the northern region of the Fornax
dwarf spheroidal galaxy with the aim of detecting the galaxy's short--period
pulsating stars (P<0.25 days). Observations collected over three consecutive
nights with the Wide Field Imager of the 2.2m MPI telescope at ESO allowed us
to detect 85 high-amplitude (0.20-1.00 mag in B-light) variable stars with
periods in the range from 0.046 to 0.126 days, similar to SX Phoenicis stars in
Galactic metal-poor stellar populations. The plots of the observed periods vs.
the B and V magnitudes show a dispersion largely exceeding the observational
errors. To disentangle the matter, we separated the first-overtone from the
fundamental-mode pulsators and tentatively identified a group of subluminous
variables, about 0.35 mag fainter than the others. Their nature as either
metal-poor intermediate-age stars or stars formed by the merging of close
binary systems is discussed. The rich sample of the Fornax variables also led
us to reconstruct the Period-Luminosity relation for short-period pulsating
stars. An excellent linear fit, M(V)=-1.83(+/-0.08)-3.65(+/-0.07) log P(fund),
was obtained using 153 Delta Scuti and SX Phoenicis stars in a number of
different stellar systems.Comment: 11 pages plus 1 on-line figure and 1 on-line table; accepted for
publication in ApJ. Part of this work has been the subject of the Laurea
thesis of LDA. His supervisor and our colleague, Prof. Laura E. Pasinetti,
suddendly passed away on September 13, 2006. Several astronomers have been
trained under her tutelage and we gratefully honor her memor
Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the delta Scuti stars rho Pup and DX Cet
High-resolution spectroscopy is a powerful tool to study the dynamical
structure of pulsating stars atmosphere. We aim at comparing the line asymmetry
and velocity of the two delta Sct stars rho Pup and DX Cet with previous
spectroscopic data obtained on classical Cepheids and beta Cep stars. We
obtained, analysed and discuss HARPS high-resolution spectra of rho Pup and DX
Cet. We derived the same physical quantities as used in previous studies, which
are the first-moment radial velocities and the bi-Gaussian spectral line
asymmetries. The identification of f=7.098 (1/d) as a fundamental radial mode
and the very accurate Hipparcos parallax promote rho Pup as the best standard
candle to test the period-luminosity relations of delta Sct stars. The action
of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle
variations in the radial velocity measurements of rho Pup. Using the
spectral-line asymmetry method, we also found the centre-of-mass velocities of
rho Pup and DX Cet, V_gamma = 47.49 +/- 0.07 km/s and V_gamma = 25.75 +/- 0.06
km/s, respectively. By comparing our results with previous HARPS observations
of classical Cepheids and beta Cep stars, we confirm the linear relation
between the atmospheric velocity gradient and the amplitude of the radial
velocity curve, but only for amplitudes larger than 22.5 km/s. For lower values
of the velocity amplitude (i.e., < 22.5 km/s), our data on rho Pup seem to
indicate that the velocity gradient is null, but this result needs to be
confirmed with additional data. We derived the Baade-Wesselink projection
factor p = 1.36 +/- 0.02 for rho Pup and p = 1.39 +/- 0.02 for DX Cet. We
successfully extended the period-projection factor relation from classical
Cepheids to delta Scuti stars.Comment: Accepted for publication in A&A (in press
Geodetic monitoring in Nepal: preliminary results from Gorkha earthquake (25 April 2015)
The Himalaya arc is one of the most complex and tectonically active areas in the world, a very long (2500km) plate boundary capable of catastrophic earthquakes up to 8 Mw (Rajendran and Rajendran, 2011). Segments of the complex fault system, that accomodate the deformation between Asia and India, lie in correspondence of densely populated cities (i.e. 7.8 Mw on 25 April 2015). A good monitoring system, composed of seismographs and a geodetic network, is the indispensable scientific base to assess and mitigate the risk in this area and to get a better understanding of the dynamics of those geodynamic processes. In this contribution we present the preliminary data and analysis from two GNSS stations located in Nepal, one near to the Everest Pyramid (EvK2CNR), the other one near to the Nagarkot city. Both the antennas seem to have sensed and measured the deformation due to the last catastrophic quake occurred on 25 April 2015. The GNSS time series in the Nagarkot station showed an abrupt change in the displacement, that could be the effect of the near field deformation associated to the quake. A forward model approach, using the Okada model (1985), has been used to verify the compatibility of the observed field to the modeled deformation. The other station that is farther from the fault seems to have recorded a transient deformation. We further analyze the noise level of the station and possible atmospheric induced signals.
Using the Okada model to simulate different displacement scenarios due to different earthquake parameters, we are able to assess the sensitivity of the network and efficiently program the installation of further stations
First steps towards a landslide inventory map of the Central Karakoram National Park
The northeastern part of Pakistan is known to be a region of extremes, where the highest reliefs and the longest glaciers of the world may be found. In this environment, through the multidisciplinary Social, Economic and Environmental Development (SEED) Project the knowledge of the sustainable exploitation possibilities of the Central Karakoram National Park area (CKNP) will be improved. One of this project's objectives is the analysis of the geological hazards giving as output a landslide inventory and a susceptibility map, utilizable as functional tools for a future sustainable territorial planning. The Bagrot Valley, chosen as test site, was partially field surveyed and part of the landslide-prone areas preliminarily identified through DEM analysis, GIS techniques and Analytical Hierarchy Process (AHP) methodology, were later validated on the field. ASTER DEM was used as the basis of morphometric analysis
YY CMi: contact or near contact system?
New V photoelectric observations of the eclipsing system YY CMi, obtained at
La Silla, Chile, and Merate Observatory, Italy, are presented. New times of
minima and ephemeris based on our observations are also given. The V light
curve was analysed by using the WD code to derive the geometrical and physical
parameters of the system. Since no spectroscopic mass ratio is available, the
q-search method was applied to yield the preliminary range of the mass ratio in
order to search for the final solution. First the unspotted solution was
carried out by using the unperturbed parts of the light curve and applying the
DC program of the WD code. The solution was performed by assuming contact (mode
3) and semi-detached (mode 4) configuration, since no classification of the
system is possible from the shape of the light curve. The solution in mode 4
does not lead to an acceptable model, since the secondary was found to be
slightly overcontact. Therefore the contact solution was finally adopted.
Moreover the light curve peculiarities (Max II fainter than Max I and excess of
light around the phase 0.32) were explained by assuming a cool and a hot spot
on the surface of the secondary (cooler) component. The degree of contact is
very small (f about 3%) and the thermal contactis poor (T1-T2) about 650 K.
These results together with the high photometric mass ratio q about 0.89
indicate that YY CMi is very probably a system at the beginning or the end of
the contact phase.Comment: 7 pages, 7 ps figures. Accepted for Astronomy and Astrophysics,
Supplement Serie
Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the delta Scuti stars AI Vel and beta Cas
Aims. The Baade-Wesselink method of distance determination is based on the
oscillations of pulsating stars. The key parameter of this method is the
projection factor used to convert the radial velocity into the pulsation
velocity. Our analysis was aimed at deriving for the first time the projection
factor of delta Scuti stars, using high-resolution spectra of the
high-amplitude pulsator AI Vel and of the fast rotator beta Cas. Methods. The
geometric component of the projection factor (i.e. p0) was calculated using a
limb-darkening model of the intensity distribution for AI Vel, and a
fast-rotator model for beta Cas. Then, using SOPHIE/OHP data for beta Cas and
HARPS/ESO data for AI Vel, we compared the radial velocity curves of several
spectral lines forming at different levels in the atmosphere and derived the
velocity gradient associated to the spectral-line-forming regions in the
atmosphere of the star. This velocity gradient was used to derive a dynamical
projection factor p. Results. We find a flat velocity gradient for both stars
and finally p = p0 = 1.44 for AI Vel and p = p0 = 1.41 for beta Cas. By
comparing Cepheids and delta Scuti stars, these results bring valuable insights
into the dynamical structure of pulsating star atmospheres. They suggest that
the period-projection factor relation derived for Cepheids is also applicable
to delta Scuti stars pulsating in a dominant radial mode
A survey of lineage-specific genes in Triticeae reveals de novo gene evolution from genomic raw material
Diploid plant genomes typically contain ~35,000 genes, almost all belonging to highly conserved gene families. Only a small fraction are lineage-specific, which are found in only one or few closely related species. Little is known about how genes arise de novo in plant genomes and how often this occurs; however, they are believed to be important for plants diversification and adaptation. We developed a pipeline to identify lineage-specific genes in Triticeae, using newly available genome assemblies of wheat, barley, and rye. Applying a set of stringent criteria, we identified 5942 candidate Triticeae-specific genes (TSGs), of which 2337 were validated as protein-coding genes in wheat. Differential gene expression analyses revealed that stress-induced wheat TSGs are strongly enriched in putative secreted proteins. Some were previously described to be involved in Triticeae non-host resistance and cold response. Additionally, we show that 1079 TSGs have sequence homology to transposable elements (TEs), ~68% of them deriving from regulatory non-coding regions of Gypsy retrotransposons. Most importantly, we demonstrate that these TSGs are enriched in transmembrane domains and are among the most highly expressed wheat genes overall. To summarize, we conclude that de novo gene formation is relatively rare and that Triticeae probably possess ~779 lineage-specific genes per haploid genome. TSGs, which respond to pathogen and environmental stresses, may be interesting candidates for future targeted resistance breeding in Triticeae. Finally, we propose that non-coding regions of TEs might provide important genetic raw material for the functional innovation of TM domains and the evolution of novel secreted proteins
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