722 research outputs found
On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg II k
line at 2796.34 A. The work is based on a selection of 230 stars observed by
both the IUE and HIPPARCOS satellites, covering a wide range of spectral type
and absolute visual magnitudes. The Wilson-Bappu relationship here provided is
considered to represent an improvement over previous recent results for the
considerably larger data sample used as well as for a proper consideration of
the measurement errors. No evidence has been found for a possible dependence of
the WB effect on stellar metallicity and effective temperature.Comment: 8 pages, 8 figures Accepted for publication on A&
Novel spectral-timing methods for X-ray binary variability studies
This work explores the connection between the spectral properties of the X-ray emission produced by black hole X-ray binaries (BHXRBs) and the variability properties of these sources that are embedded in lightcurves. While BHXRBs are mostly studied using âstatic observablesâ such as the average energy spectrum, a variability timescale-resolved study (in terms of Fourier-frequencies) provides a much stronger and more reliable tool for understanding the intricate physics and geometrical properties of accretion flows around stellar-mass black holes.In the present Thesis, we first show how the geometrical properties of the accretion disc can be mapped by combining spectra and frequency-resolved time-lags. A time-scale-dependent reflection model is developed in terms of Fourier-frequencies and compared to observational hard-state data of GX 339â4 obtainedwithXMM-Newton. Secondly, we explore the variability properties of the accretion disc in SWIFT J1753.5â0127 using a combination of novel spectraltiming methods and the soft X-ray coverage of XMM-Newton. Finally, we show the development of a novel technique for fitting correlated signals in the Fourier domain as a function of energy and Fourier-frequency that can prove particularly useful with high signal-to-noise datasets fromfuture X-ray missions
A study of the Mg II 2796.34 A emission line in late--type normal, and RS CVn stars
We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars
and make a comparison with the normal stars studied in a previous paper (Paper
I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS
parallaxes and observed at high resolution with IUE. We confirm that RS CVn
stars tend to possess wider Mg II lines than normal stars having the same
absolute visual magnitude. However, we could not find any correlation between
the logarithmic line width log Wo and the absolute visual magnitude Mv (the
Wilson--Bappu relationship) for these active stars, contrary to the case of
normal stars addressed in Paper I. On the contrary, we find that a strong
correlation exists in the (Mv, log L) plane (L is the absolute flux in the
line). In this plane, normal and RS CVn stars are distributed along two nearly
parallel straight lines with RS CVn stars being systematically brighter by
about 1 dex. Such a diagram provides an interesting tool to discriminate active
from normal stars. We finally analyse the distribution of RS CVn and of normal
stars in the (log L, log Wo) plane, and find a strong linear correlation for
normal stars, which can be used for distance determinations.Comment: 10 pages, 7 figures, latex, to be published in A&
Interpreting historic and cultural landscapes. Potential and risks in Geographical information Systems building for knowledge and management
The paper discusses potentials and limits of Geographical Information Systems in supporting the territorialization of multidisciplinary landscape analysis for the management of a World Heritage Site on the basis of several studies carried out about cultural landscapes in a spatial-planning perspective (Landscape Atlases, Regional Landscape Plans,âŠ)
On behalf of the Italian Ministry of Cultural Heritage, a multidisciplinary team of experts in historic features, built heritage and landscape studies has developed the analysis on the UNESCO serial Site âResidences of the Royal House of Savoyâ to identify a strategic vision for the management of this complex system (12 properties, 7,000 hectares).
Applying a landscape approach has implied:
âą developing a set of sectoral analysis sound from a disciplinary point of view but suitable to a direct comparison with existing lists of assets, which derive from several regulative and planning instruments;
âą extending expert analysis beyond the administrative boundaries of the WHL (property and buffer zone) to highlight fundamental relationships between the protected area and its territorial surroundings.
The GIS must offer a response by:
âą returning expertsâ multidisciplinary analysis without losing the additional interpretative level arising from a holistic view.
âą highlighting landscape historic, scenic and environmental relations trespassing traditional WHL properties facilitating connections with broader land management.
The discussion concerns the methodological approach proposed for a GIS responding to landscape-oriented research calling for the legibility/consultation of the single mapped features within the complex system in which each one finds its proper meaning.
Examples concerning multiple landscape relations between WHL Site and its landscape are given as well as issues concerning their geographical representation.
Final considerations will stress both the benefits and the risks of the coexistence of different data collections (strictly descriptive or management-oriented) within the same web-GIS, potentially leading to ambiguity. The proposed method is addressed to all cases of protected sites management plans encompassing cultural landscapes
I Quaderni di Careggi- Fifth issue- Landscape Observatories
Having regard to Recommendation CM/Rec (2008)3 on the Guidelines for the implementation of the
European Landscape Convention, âlandscape observatories, centers and institutesâ are one of the main instruments for the implementation of landscape policies (II.3.3). They facilitate the collection and exchange of information and study protocols between states and local communities.
This issue of the Quaderni di Careggi presents an international overview of the activities of landscape observatories, a reflection on their mission and effectiveness with regard to the ELC objectives, and a reflection on the relationships between the different subjects, thanks to the participation of institutional bodies, public officials as well as researchers and representatives of civil society. It reflects part of the scientific contributions which will be presented during the V Careggi Seminar (Florence, 27-28th June 2013)
Landscape Observatories in Europe from the ELC Recommendations to Local Initiatives. Rationale and Issues of the Seminar
Having regard to Recommendation CM/Rec (2008)3 on the Guidelines for the implementation of the
European Landscape Convention, âlandscape observatories, centers and institutesâ are one of the main instruments for the implementation of landscape policies (II.3.3). They facilitate the collection and exchange of information and study protocols between states and local communities.
This issue of the Quaderni di Careggi presents an international overview of the activities of landscape observatories, a reflection on their mission and effectiveness with regard to the ELC objectives, and a reflection on the relationships between the different subjects, thanks to the participation of institutional bodies, public officials as well as researchers and representatives of civil society. It reflects part of the scientific contributions which will be presented during the V Careggi Seminar (Florence, 27-28th June 2013
The evolution of ultraviolet emission lines from the circumstellar material surrounding SN 1987A
The presence of narrow high-temperature emission lines from nitrogen-rich gas
close to SN 1987A has been the principal observational constraint on the evolu-
tionary status of the supernova's progenitor. A new analysis of the complete
five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A
(1987.2--1992.3) provide fluxes for the N V 1240, N IV] 1486, He II 1640, OIII]
1665, NIII] 1751, and CIII] 1908 lines with significantly reduced random and
systematic errors and reveals significant short-term fluctuations in the light
curves. The N V, N IV] and N III] lines turn on sequentially over 15 to 20 days
and show a progression from high to low ionization potential, implying an ioni-
zation gradient in the emitting region. The line emission turns on suddenly at
83+/-4 days after the explosion, as defined by N IV]. The N III] line reaches
peak luminosity at 399+/-15 days. A ring radius of (6.24+/-0.20)E{17} cm and
inclination of 41.0+/-3.9 is derived from these times, assuming a circular
ring. The probable role of resonant scattering in the N V light curve
introduces systematic errors that leads us to exclude this line from the timing
analysis. A new nebular analysis yields improved CNO abundance ratios
N/C=6.1+/-1.1 and N/O=1.7+/-0.5, confirming the nitrogen enrichment found in
our previous paper. From the late-time behavior of the light curves we find
that the emission origi- nates from progressively lower density gas. We
estimate the emitting mass near maximum (roughly 400 days) to be roughly
4.7E{-2} solar masses, assuming a filling factor of unity and an electron
density of 2.6E4 cm^{-3}. These results are discussed in the context of current
models for the emission and hydrodynamics of the ring.Comment: 38 pages, AASTeX v.4.0, 13 Postscript figures; ApJ, in pres
A study of the expanding envelope of Nova V1974 Cyg 1992 based on IUE high resolution spectroscopy
We have carried out a detailed analysis of the IUE archival high resolution
spectra of the classical nova V1974 Cyg 1992. In addition to the P Cygni and
emission lines, two shortward shifted absorption systems are present. Evidence
is given that these absorptions originate in two separate expanding shells,
outside the wind layers where the emission lines are formed. The outer main
shell, containing most of the matter ejected at outburst, produces the
so-called ``principal absorption line system'', and the inner faster moving
second shell produces the so-called ``diffuse--enhanced absorption line
system''. The outflow velocity of the two shells increases exponentially with
time reaching a value of about 1750 km/s and 2900 km/s, respectively. We
suggest that the acceleration of the shells is the result of increasing
line-radiation pressure due to the UV-brightening of the star as the effective
radius decreases. Around day 60 the second shell has overtaken the slower
moving principal system shell, and merged with it. This explains: the sudden
disappearance of the diffuse line system near that date, the upward jump of 240
km/s in velocity of the principal system and the first detection of hard X-ray
emission on day 63. This velocity jump indicates that the main shell is about 4
times more massive than the second shell. The deceleration suffered by the
diffuse-enhanced system after the shock provides a shock temperature of about
1.6 KeV, in fairly good agreement with the temperature of the observed hard
X-ray emission.Comment: 19 pages, 11 figure
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