1,516 research outputs found
Interferometry of chemically peculiar stars: theoretical predictions vs. modern observing facilities
By means of numerical experiments we explore the application of
interferometry to the detection and characterization of abundance spots in
chemically peculiar (CP) stars using the brightest star eps~Uma as a case
study. We find that the best spectral regions to search for spots and stellar
rotation signatures are in the visual domain. The spots can clearly be detected
already at a first visibility lobe and their signatures can be uniquely
disentangled from that of rotation. The spots and rotation signatures can also
be detected in NIR at low spectral resolution but baselines longer than 180~m
are needed for all potential CP candidates. According to our simulations, an
instrument like VEGA (or its successor e.g., FRIEND) should be able to detect,
in the visual, the effect of spots and spots+rotation, provided that the
instrument is able to measure , and/or closure phase. In
infrared, an instrument like AMBER but with longer baselines than the ones
available so far would be able to measure rotation and spots. Our study
provides necessary details about strategies of spot detection and the
requirements for modern and planned interferometric facilities essential for CP
star research.Comment: Accepted by NMRAS, 18 pages, 11 figures, 2 table
Modelling the atmosphere of the carbon-rich Mira RU Vir
Context. We study the atmosphere of the carbon-rich Mira RU Vir using the
mid-infrared high spatial resolution interferometric observations from
VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the
carbon-rich Mira RU Vir, with state of the art models, in this way deepening
the knowledge of the dynamic processes at work in carbon-rich Miras. Methods.
We compare spectro-photometric and interferometric measurements of this
carbon-rich Mira AGB star, with the predictions of different kinds of modelling
approaches (hydrostatic model atmospheres plus MOD-More Of Dusty,
self-consistent dynamic model atmospheres). A geometric model fitting tool is
used for a first interpretation of the interferometric data. Results. The
results show that a joint use of different kind of observations (photometry,
spectroscopy, interferometry) is essential to shed light on the structure of
the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit well
the ISO spectrum in the wavelength range {\lambda} = [2.9, 25.0] {\mu}m.
Nevertheless, a discrepancy is noticeable both in the SED (visible), and in the
visibilities (shape and level). A possible explanation are intra-/inter-cycle
variations in the dynamic model atmospheres as well as in the observations. The
presence of a companion star and/or a disk or a decrease of mass loss within
the last few hundred years cannot be excluded but are considered unlikely.Comment: 15 pages. Accepted in A&
The complex environment of the bright carbon star TX Psc as probed by spectro-astrometry
Context: Stars on the asymptotic giant branch (AGB) show broad evidence of
inhomogeneous atmospheres and circumstellar envelopes. These have been studied
by a variety of methods on various angular scales. In this paper we explore the
envelope of the well-studied carbon star TX Psc by the technique of
spectro-astrometry. Aims: We explore the potential of this method for detecting
asymmetries around AGB stars. Methods:We obtained CRIRES observations of
several CO v=1 lines near 4.6 m and HCN lines near 3 m in
2010 and 2013. These were then searched for spectro-astrometric signatures. For
the interpretation of the results, we used simple simulated observations.
Results: Several lines show significant photocentre shifts with a clear
dependence on position angle. In all cases, tilde-shaped signatures are found
where the positive and negative shifts (at PA 0deg) are associated with blue
and weaker red components of the lines. The shifts can be modelled with a
bright blob 70 mas to 210 mas south of the star with a flux of several percent
of the photospheric flux. We estimate a lower limit of the blob temperature of
1000 K. The blob may be related to a mass ejection as found for AGB stars or
red supergiants. We also consider the scenario of a companion object.
Conclusions: Although there is clear spectro-astrometric evidence of a rather
prominent structure near TX Psc, it does not seem to relate to the other
evidence of asymmetries, so no definite explanation can be given. Our data thus
underline the very complex structure of the environment of this star, but
further observations that sample the angular scales out to a few hundred
milli-arcseconds are needed to get a clearer picture
The MIPSGAL View of Supernova Remnants in the Galactic Plane
We report the detection of Galactic supernova remnants (SNRs) in the mid-infrared (at 24 and 70 Όm), in the coordinate ranges 10° < l < 65° and 285° < l < 350°, |b| < 1°, using MIPS aboard the Spitzer Space Telescope. We search for infrared counterparts to SNRs in Green's catalog and identify 39 out of 121, i.e., a detection rate of about 32%. Such a relatively low detection fraction is mainly due to confusion with nearby foreground/background sources and diffuse emission. The SNRs in our sample show a linear trend in [F_8/F_(24)] versus [F_(70)/F_(24)]. We compare their infrared fluxes with their corresponding radio flux at 1.4 GHz and find that most remnants have a ratio of 70 Όm to 1.4 GHz which is similar to those found in previous studies of SNRs (with the exception of a few that have ratios closer to those of H II regions). Furthermore, we retrieve a slope close to unity when correlating infrared (24 and 70 Όm) with 1.4 GHz emission. Our survey is more successful in detecting remnants with bright X-ray emission, which we find is well correlated with the 24 Όm morphology. Moreover, by comparing the power emitted in the X-ray, infrared, and radio, we conclude that the energy released in the infrared is comparable to the cooling in the X-ray range
Analysis of the thin layer of Galactic warm ionized gas in the range 20 < l < 30 deg, -1.5 < b < +1.5 deg
We present an analysis of the thin layer of Galactic warm ionized gas at an
angular resolution ~ 10'. This is carried out using radio continuum data at 1.4
GHz, 2.7 GHz and 5 GHz in the coordinate region 20 < l < 30 deg, -1.5 < b <
+1.5 deg. For this purpose, we evaluate the zero level of the 2.7 and 5 GHz
surveys using auxiliary data at 2.3 GHz and 408 MHz. The derived zero level
corrections are T_{zero}(2.7 GHz)=0.15 +/- 0.06 K and T_{zero}(5 GHz)=0.1 +/-
0.05 K. We separate the thermal (free-free) and non-thermal (synchrotron)
component by means of a spectral analysis performed adopting an antenna
temperature spectral index -2.1 for the free-free emission, a realistic spatial
distribution of indices for the synchrotron radiation and by fitting,
pixel-by-pixel, the Galactic spectral index. We find that at 5 GHz, for |b| = 0
deg, the fraction of thermal emission reaches a maximum value of 82%, while at
1.4 GHz, the corresponding value is 68%. In addition, for the thermal emission,
the analysis indicates a dominant contribution of the diffuse component
relative to the source component associated with discrete HII regions.Comment: 9 pages, 9 figures, accepted to MNRA
Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis
Supported Co catalysts were prepared for sodium borohydride and ammonia borane hydrolysis by magnetron sputtering for the first time under different conditions. Ni foam was selected as support. Deposition conditions (time, pressure, and power) were varied to improve catalytic activity. A decrease in deposition power from 200 to 50 W, leads to a decrease in crystallite and column size and a higher activity of catalysts. The increase in deposition pressure from 1.5 Ă 10â2 to 4.5 Ă 10â2 mbar produces same effect but in this case the enhancement in activity is higher because amorphous materials were obtained. The highest activity for SB hydrolysis was 2650 ml minâ1 gcatâ1 for the 50 W Co 4.5 (4 h) sample (Ea = 60 ± 2 kJ molâ1). For AB hydrolysis activity for the 50 W Co 3.2 (4 h) sample was similar. Durability of the thin films was tested for both reactions upon cycling (14 cycles). Diluted acid washing was effective to recover the activity for sodium borohydride reaction but not for ammonia borane hydrolysis. The strong CoâNH3 interactions explain the non-efficiency of the acid washing
Evaluation of Psychometric and Linguistic Properties of the Italian Adolescent Pain Assessment Scales: A Systematic Review
Introduction: Adolescentsâ pain experiences
are complex and multidimensional, and evaluating
pain only from a sensory and affective
point of view may be in many instances limiting
and inadequate; this is the reason why it is
of paramount importance to identify the tools
which can better assess the pain experienced by
young patients. A person-oriented approach is
highly encouraged, as it may better investigate
the cognitive and behavioral development typical
of this age group. The aim of this review
paper is to describe the available tools which are
able to adequately assess pain intensity in adolescents,
in particular those validated in Italian.
Methods: We conducted a systematic review
using four databases: CINAHL, PsycINFO,
PubMed and Cochrane, and selected all the
articles published between January 1970 and
November 2017. We selected all the papers
reporting the validation process of pain assessment
tools specifically tailored for adolescent
patients (age range 10â18 years) and based on
psychometric and linguistic parameters, and
focused especially on the tools available in
Italian and able to measure acute and chronic
pain.
Results: The results of our investigation have
revealed the existence of 40 eligible tools, 17 of
which are monodimensional and the remaining
23 multidimensional, more specifically tailored
to assess both acute and chronic pain. Some of
the instruments (26) were self-reports while
others were classified as behavioral (13) and/or
mixed. Only one tool turned out to be suitable
for fragile adolescents, while six adopted a
person-oriented approach that better emphasized
the cognitive and behavioral process typical
of the adolescent population. None of them
has ever been validated in Italian.
Conclusion: Valid and reliable psychometric
tools specifically organized to provide a cultural
and linguistic evaluation of the patient are
indeed the most recommended instruments to
assess the intensity of the pain experienced by
the patient, as they may provide useful information to implement a health policy
aimed at identifying the best assistance
programs
- âŠ