509 research outputs found
X-ray monitoring of classical novae in the central region of M31. III. Autumn and winter 2009/10, 2010/11 and 2011/12
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray
sources (SSSs) in the central region of our neighbouring galaxy M31. We
performed a dedicated monitoring of the M31 central region, aimed to detect SSS
counterparts of CNe, with XMM-Newton and Chandra between Nov and Mar of the
years 2009/10, 2010/11 and 2011/12. In total we detected 24 novae in X-rays.
Seven of these sources were known from previous observations, including the M31
nova with the longest SSS phase, M31N~1996-08b, which was found to fade below
our X-ray detection limit 13.8 yr after outburst. Of the new discoveries
several novae exhibit significant variability in their short-term X-ray light
curves with one object showing a suspected period of about 1.3 h. We studied
the SSS state of the most recent outburst of a recurrent nova which had
previously shown the shortest time ever observed between two outbursts (about 5
yr). The total number of M31 novae with X-ray counterpart was increased to 79
and we subjected this extended catalogue to detailed statistical studies. Four
previously indicated correlations between optical and X-ray parameters could be
confirmed and improved. We found indications that the multi-dimensional
parameter space of nova properties might be dominated by a single physical
parameter. We discuss evidence for a different X-ray behaviour of novae in the
M31 bulge and disk. Exploration of the multi-wavelength parameter space of
optical and X-ray measurements is shown to be a powerful tool for examining
properties of extragalactic nova populations. While there are hints that the
different stellar populations of M31 (bulge vs disk) produce dissimilar nova
outbursts, there is also growing evidence that the overall behaviour of an
average nova might be understood in surprisingly simple terms.Comment: 39 pages (half of them for 9 tables), 14 figures, accepted for
publication in A&A; updated after language editing stag
The ages of very cool hydrogen-rich white dwarfs
The evolution of white dwarfs is essentially a cooling process that depends
primarily on the energy stored in their degenerate cores and on the
transparency of their envelopes. In this paper we compute accurate cooling
sequences for carbon-oxygen white dwarfs with hydrogen dominated atmospheres
for the full range of masses of interest. For this purpose we use the most
accurate available physical inputs for both the equation of state and opacities
of the envelope and for the thermodynamic quantities of the degenerate core. We
also investigate the role of the latent heat in the computed cooling sequences.
We present separately cooling sequences in which the effects of phase
separation of the carbon-oxygen binary mixture upon crystallization have been
neglected, and the delay introduced in the cooling times when this mechanism is
properly taken into account, in order to compare our results with other
published cooling sequences which do not include a treatment of this
phenomenon. We find that the cooling ages of very cool white dwarfs with pure
hydrogen atmospheres have been systematically underestimated by roughly 1.5 Gyr
at log(L/Lo)=-4.5 for an otherwise typical 0.6 Mo white dwarf, when phase
separation is neglected. If phase separation of the binary mixture is included
then the cooling ages are further increased by roughly 10%. Cooling tracks and
cooling isochrones in several color-magnitude diagrams are presented as well.Comment: 8 Pages; ApJ, accepted for publicatio
Recent discoveries of supersoft X-ray sources in M 31
Classical novae (CNe) have recently been reported to represent the major
class of supersoft X-ray sources (SSSs) in the central area of our neighbouring
galaxy M 31. This paper presents a review of results from recent X-ray
observations of M 31 with XMM-Newton and Chandra. We carried out a dedicated
optical and X-ray monitoring program of CNe and SSSs in the central area of M
31. We discovered the first SSSs in M 31 globular clusters (GCs) and their
connection to the very first discovered CN in a M 31 GC. This result may have
an impact on the CN rate in GCs. Furthermore, in our optical and X-ray
monitoring data we discovered the CN M31N 2007-11a, which shows a very short
SSS phase of 29 - 52 days. Short SSS states (durations < 100 days) of CNe
indicate massive white dwarfs (WDs) that are candidate progenitors of
supernovae type Ia. In the case of M31N 2007-11a, the optical and X-ray light
curves suggest a binary containing a WD with M_WD > 1.0 M_sun. Finally, we
present the discovery of the SSS counterpart of the CN M31N 2006-04a. The X-ray
light curve of M31N 2006-04a shows short-time variability, which might indicate
an orbital period of about 2 hours.Comment: 4 pages, 1 figure; Proc. of workshop "Supersoft X-ray Sources - New
Developments", ESAC, May 2009; accepted for publication in Astronomische
Nachrichte
The 21Na(p,gamma)22Mg Reaction and Oxygen-Neon Novae
The 21Na(p,gamma)22Mg reaction is expected to play an important role in the
nucleosynthesis of 22Na in Oxygen-Neon novae. The decay of 22Na leads to the
emission of a characteristic 1.275 MeV gamma-ray line. This report provides the
first direct measurement of the rate of this reaction using a radioactive 21Na
beam, and discusses its astrophysical implications. The energy of the important
state was measured to be E= 205.7 0.5 keV with a resonance
strength meV.Comment: Accepted for publication in Physical Review Letter
Caracterización fisicoquímica de mieles monoflorales de Euphorbia resinifera
The physicochemical characteristics of Euphorbia resinifera honey were studied. Considering the low
water content, the majority of the honeys presented a proper maturity. The values of acidity
revealed the absence of inappropriate fermentation, while the low values of hydroxymethylfurfural
(0.4–16.48 mg/kg) were suitable for of unprocessed honeys. The average values for electrical
conductivity and ashes were 451 µS/cm and 1.6 g/kg, respectively. As for the mineral content, the
K was the most abundant element; Ca, Na, Mg, P, S, and Si are all present in differing quantities in
the honeys. On the other hand, Principal Components Analysis (PCA) and Stepwise Discriminant
Analysis (SDA) were applied to distinguish between three related Euphorbia honey types. PCA
showed that the cumulative variance of the two first factors explained approximately 53%. The
results of SDA showed that variables with a higher discriminant power were K, C*ab and a*, and
100% of the samples were properly classified in their corresponding class.Los parámetros fisicoquímicos de 29 de mieles monoflorales de Euphorbia resinifera fueron estudiadas.
24 parámetros, incluyendo humedad, pH, acidez (libre, lactónica y total), HMF, cenizas, conductividad
eléctrica, monosacáridos (glucosa y fructosa), contenido mineral y parámetros cromáticos fueron
analizados. Desde el punto de vista de su calidad las mieles fueron acordes con la legislación
Europea en cuanto a contenido en agua, acidez y HMF. Los valores de cenizas y conductividad
eléctrica fueron 1,6 g/kg y 451 μS/cm, respectivamente. El contenido en minerales mostró que el K es
el elemento más abundante; mientras que Ca, Na, Mg, P, S y Si se presentaron en contenidos
intermedios. En cuanto a los valores de los parámetros del color fueron típicos de mieles ámbar
claras. Se ha realizado un análisis estadístico multivariante a los datos obtenidos para diferenciar tres
especies de mieles de Euphorbia. El análisis discriminante permite diferencia las mieles por su origen
botánico siendo el contenido en K, C*ab y la variable cromática a* las variables con mayor poder
discriminate, siendo el 100% de las muestras clasificadas correctamente en su grupo
Collimation and asymmetry of the hot blast wave from the recurrent nova V745 Scorpii
The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was
observed on February 22 and 23 by the Chandra X-ray Observatory Transmission
Grating Spectrometers. By that time the supersoft source phase had already
ended and Chandra spectra are consistent with emission from a hot, shock-heated
circumstellar medium with temperatures exceeding 10^7K. X-ray line profiles are
more sharply peaked than expected for a spherically-symmetric blast wave, with
a full width at zero intensity of approximately 2400 km/s, a full width at half
maximum of 1200 +/- 30 km/s and an average net blueshift of 165 +/- 10 km/s.
The red wings of lines are increasingly absorbed toward longer wavelengths by
material within the remnant. We conclude that the blast wave was sculpted by an
aspherical circumstellar medium in which an equatorial density enhancement
plays a role, as in earlier symbiotic nova explosions. Expansion of the
dominant X-ray emitting material is aligned close to the plane of the sky and
most consistent with an orbit seen close to face-on. Comparison of an
analytical blast wave model with the X-ray spectra, Swift observations and
near-infrared line widths indicates the explosion energy was approximately
10^43 erg, and confirms an ejected mass of approximately 10^-7 Msun. The total
mass lost is an order of magnitude lower than the accreted mass required to
have initiated the explosion, indicating the white dwarf is gaining mass and is
a supernova Type 1a progenitor candidate.Comment: To appear in the Astrophysical Journa
Spanish facilities and fisrst results in measuring thermodynamic temperature using the radiance method
Newport Pagnell, Buckinghamshire, May 18-19 2015; https://royalsociety.org/science-events-and-lectures/2015/05/new-kelvin/Currently, the dissemination of the kelvin, according to the International Temperature Scale (ITS-90), at high temperatures is realised at the Centro Español de Metrología (CEM) by using the fixed points of Ag and Cu and a standard radiation thermometer. Recently, absolute radiometry has been proposed by the CCT Working Group 5 [1] to be included in future revisions of the Mise-en-Practique for the kelvin (MeP-K). The Centro Español de Metrologia (CEM) in collaboration with the Instituto de Óptica of the Consejo Superior de Investigaciones Científicas (IO-CSIC) has been working in the following lines linked to this new alternative to disseminate the kelvin:
¿ Absolute calibration, i.e., calibration in terms of the thermodynamic temperature, of commercial radiation thermometers, by using a facility based on a monochromator and a high stability lamp [2]. At present, the uncertainties of these measurements, obtained with a KE-LP2 radiation thermometer, are about the ones obtained with the ITS-90 method, i. e. from 0,3 K to 1,1 K (from 1084,62 °C to 2474 °C, k = 2). Some improvements in the facilities described in [2] have been implemented in order to reduce uncertainty.
¿ Development of a filter radiometer to measure the thermodynamic temperature. It has been designed by CEM based in NPL previous work [3]. This filter radiometer can be calibrated with a laser based experimental setup, which improves the above measurement uncertainty [4]: from 0,2 K to 0,7 K (from 1084,62 °C to 2474 °C, k = 2). Because of some problems with the radiometer stability at 2500 °C, some changes in the design have been done.
The facilities used in [2] and [4] are currently been developed at CEM site as the transportation of the instruments for calibration has caused significant drifts. A complete description of IO-CSIC and new CEM facilities will be presented, together with the results obtained on the determination of the WP1 InK cells thermodynamic temperatures by using both, a radiation thermometer with an absolute calibration, and a filter radiometer.Peer Reviewe
Color influences sensory perception and liking of orange juice
Background: This study assesses the effect of slight hue variations in orange juice (reddish to greenish) on perceived flavour intensity, sweetness, and sourness, and on expected and actual liking. A commercial orange juice (COJ) was selected as a control, and colour-modified orange juices were prepared by adding red or green food dyes (ROJ and GOJ) that did not alter the flavour of the juice. A series of paired comparison tests were performed by 30 naive panellists to determine the influence of orange juice colour on flavour intensity, sweetness, and sourness. Then, 100 orange juice consumers were asked to rate expected liking of orange juice samples initially by visual evaluation and subsequently for actual liking upon consumption, using a labelled affective magnitude scale.
Results: Results of pair comparison tests indicated that colour changes did not affect flavour intensity and sweetness, but the greenish hue (GOJ) significantly increased the perceived sourness. Results of the consumers’ study indicated significant differences in expected liking between the orange juice samples, with ROJ having the highest expected liking. However, scores of actual liking after consumption were not significantly different. COJ and GOJ showed a significant increase in actual liking compared to expected liking.
Conclusions: This study shed light on how slight variations in orange juice hue (reddish to greenish hues) affect the perceived flavour intensity, sweetness, and sourness, and the expected and actual liking of orange juice
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