196 research outputs found
Using globular clusters to test gravity in the weak acceleration regime:NGC 7099
No full textAims.A test of Newton's law of gravity in the low acceleration
regime using globular clusters is presented and new results for the core
collapsed globular cluster NGC 7099 given.
Methods.The run of the
gravitational potential as a function of distance is probed by studying
the velocity dispersion profile of the cluster, as derived from a set
of 125 radial velocities with accuracy better than 1 km s-1. The
velocity dispersion profile is traced up to ~18 pc from the
cluster center.
Results.The dispersion is found to be maximal at the
center, then decrease until pc from the center, well inside
the cluster tidal radius of 42 pc. After that the dispersion remains
basically constant with an average value of km s-1. Assuming
a total V mag of mag for NGC 7099, the acceleration at pc
from the center is cm s-2, where τ is the mass-to-light ratio. Thus, for \tau \la
2 typical of globular clusters, the flattening of the velocity
dispersion profile occurs for a value of the internal acceleration of
gravity that is fully consistent with cm s-2 observed in
galaxies.
Conclusions.This new result for NGC 7099 brings to 4 the clusters
with velocity dispersion profile probing acceleration below a0. All
four have been found to have a flat dispersion profile at large radii
where the acceleration is below a0, thereby mimicking elliptical galaxies
qualitatively and quantitatively. Whether this indicates a failure
of Newtonian dynamics in the low acceleration limit or some more
conventional dynamical effect (e.g., tidal heating) is still
unclear. However, the similarities emerging between very different
globular clusters, as well as between globular clusters and elliptical
galaxies, seem to favor the first of these two possibilities
Performance test torelli di razza Rendena: risultati del quarto e quinto ciclo di prova 1989 1990
No full textClinical associations between severity of impulsivity, psychiatric morbidity, dysfunctional defences and personality disorder: A comparative study with axis-I disorders
No full textObjective: Psychiatric morbidity, impulsive behaviour and use of dysfunctional and maladaptive defences are core features of personality disorder (PD). This study aims to evaluate the significance of the strength of the association between these three core dimensions and PD. Method: Using a cross-sectional design, a sample of co-morbid Axis-I &-II disorders, and a sample of Axis-I disorders with no co-morbid PD were recruited at three general psychiatric mental health resource centres and then compared. PD as dependent variable was analysed both as a categorical and as a dimensional entity using the Structured Clinical Interview for DSM-IV. The Symptoms Checklist 90-R general severity index (GSI), the Barratt Impulsivity Scale (BIS) and the Defense Style Questionnaire (DSQ) were used to measure severity of psychiatric morbidity, impulsivity and defensive style, respectively. Results: BIS was a highly significant predictor of categorical PD (β = .13, SE = .03, p < .001), but not GSI and DSQ. BIS and GSI significantly predicted PD as a dimensional construct (β = 0.32, SE = .08, t = 4.05, p < 0.001; and β = 5.04, SE = 1.54, t = 3.28, p = 0.002, respectively). The diagnostic efficiency statistics found that BIS had greater sensitivity (.82) and specificity (.79), and overall predictive power (.87) of correctly identifying true positive and true negative PD diagnosis compared to the other two measures. Conclusions: BIS may be used in routine clinical practice as a screening measure to identify the presence of PD in complex presentations
The 's' process nucleosynthesis in low mass stars and the neutron source (C-13)(alpha, n)(O-16)
No full textThe heavy element synthesis induced by the large neutron fluxes released
by the reaction (C13)(alpha, n)(O-16) in low mass planetary nebulas
progenitors experiencing thermal pulses is examined. The mechanism of
semiconvection proposed by Iben and Renzini (1982) for the formation of
the initial (C-13) is assumed to be effective. A new reaction network
has been created, incorporating updated values for the cross-sections of
alpha-, p- and n-captures on 350 nuclei and including 80 branching
points along the neutron capture path. As a preliminary investigation 14
thermal pulses were followed. The results of the computations and their
relevance in explaining the formation of the heavy n-rich elements are
briefly discussed
First Results from the X-Ray and Optical Survey of the Chandra Deep Field South
No full textWe present our first results from 120 ks of X-ray observations obtained with the Advanced CCD Imaging Spectrometer on the Chandra X-Ray Observatory. The field of the two combined exposures is 0.096 deg(2) and the detection limit is to a S/N of 2 (corresponding to similar to7 net counts). We reach a flux of 2 x 10(-16) erg s(-1) cm(-2) in the 0.5-2 keV soft band and 2 x 10(-15) erg s(-1) cm(-2) in the 2-10 keV hard band. Our combined sample has 144 soft sources and 91 hard sources, for a total of 159 sources. Fifteen sources are detected only in the hard band, and 68 only in the soft band. For the optical identification, we carried out a survey in V RI with the FORS-1 imaging spectrometer on the Antu telescope (UT-1 at VLT) complete to R less than or equal to 26. This data set was complemented with data from the ESO Imaging Survey (EIS) in the UBJK bands and the ESO Wide Field Imager Survey (WFI) in the B band. The positional accuracy of the X-ray detections is of the order of 1" in the central 6'. Optical identifications are found for similar or equal to 90% of the sources. Optical spectra have been obtained for 12 objects. We obtain the cumulative spectra of the faint and bright X-ray sources in the sample and also the hardness ratios of individual sources. A power-law Dt in the range 2-10 keV using the Galactic value of N-H similar or equal to 8 x 10(19) cm(-2) yields a photon index of Gamma = 1.70 +/- 0.12 and 1.35 +/- 0.20 (errors at 90% confidence level) for the bright and faint samples, respectively, showing a flattening of the spectrum at lower fluxes. Hardness ratio is given as a function of X-ray flux and confirms this result. The spectrum of our sources is approaching the spectrum of the X-ray background (XRB) in the hard band, which has an effective Gamma = 1.4. Correlation function analysis for the angular distribution of the sources indicates that they are significantly clustered on scales as large as 100". The scale dependence of the correlation function is a power law with index gamma similar to 2, consistent with that of the galaxy distribution in the local universe. Consequently, the discrete sources detected by deep Chandra-pointed observations can be used as powerful tracers of the large-scale structure at high redshift. We discuss the log N- log S relationship and the discrete source contribution to the integrated X-ray sky flux. In the soft band, the sources detected in the field at fluxes below 10(-15) erg s(-1) cm(-2) contribute (4.0 +/- 0.3) x 10(-12) erg cm(-2) s(-1) deg(-2) to the total XRB. The flux resolved in the hard band down to the flux limit of 2 x 10(-15) erg s(-1) cm(-2) contributes (1.05 +/- 0.2) x 10(-11) erg cm(-2) s(-1) deg(-2). Once the contribution from the bright counts resolved by ASCA is included, the total resolved XRB amounts to 1.3 x 10(-11) erg cm(-2) s(-1) deg(-2), which is 60%-80% of the total measured background. This result confirms that the XRB is due to the integrated contribution of discrete sources, but shows that there is still a relevant fraction (at least 20%) of the hard XRB to be resolved at fluxes below 10(-15) erg s(-1) cm(-2). We discuss the X-ray flux versus R magnitude relation for the identified sources. We find that similar or equal to 10% of the sources in our sample are not immediately identifiable at R > 26. For these sources, S-x/S-opt whereas most of the ROSAT and Chandra sources have S-x/S-opt <10. We have also found a population of objects with unusually low S-x/S-opt that are identified as galaxies. The R-K versus R color diagram shows that the Chandra sources continue the trend seen by ROSAT. For our 12 spectroscopically studied objects with redshifts, we observe four QSOs, five Seyfert 2 galaxies, one elliptical, and two interacting galaxies. We compare L-x versus z obtained with these measurements and show that Chandra is achieving the predicted sensitivity
IRAS and near infrared observations of peculiar nebulosities
No full textThe authors used the IRAS survey to search for IR emission from 95
peculiar nebulosities with CO emission. Fifty-two IRAS sources are
associated with them. The authors discuss the nature of the sources on
the basis of their IRAS color-color diagram and of near-IR observations
Evidence of thin dust shells in some RS CVn stars
No full textUBVRIJHK light curves of four active RS CVn binaries, together with
coordinated spectrophotometric observations in the range 1.4-2.5
microns, are presented. From the reconstruction of the whole spectral
distributions (from U to K), the presence of spot-related photospheric
perturbations and IR excesses is inferred. These excesses cannot be
simply explained by a combination of stellar spectra (even changing the
accepted spectral types). Analysis shows that thermal radiation from a
thin dust shell surrounding the system may explain the data
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