Search results for "LUMINOSITY"
showing 10 items of 560 documents
X-ray detection of the substellar twin 2MASS J11011926-7732383 AB
2007
2MASS J11011926-7732383 AB (hereafter 2M1101AB), located in the Cha I star forming region, is a rare wide-separation brown dwarf binary. XMM-Newton and Chandra observations of 2M1101AB have allowed us to examine the influence of physical parameters (mass, bolometric luminosity and effective temperature) on X-ray emission from a coeval pair of substellar objects. The spatial resolution of XMM-Newton is not sufficient to separate contributions from the two components in the binary. The X-ray source detected with XMM-Newton has a column density compatible with the infrared extinction of component A. On the other hand, the binary is resolved with Chandra, and the bulk of the X-ray emission is c…
Systematic Redshift of the Fe III UV Lines in Quasars. Measuring Supermassive Black Hole Masses under the Gravitational Redshift Hypothesis
2018
We find that the Fe III$\lambda\lambda$2039-2113 spectral feature in quasars appears systematically redshifted by amounts accountable under the hypothesis of gravitational redshift induced by the central supermassive black hole. Our analysis of 27 composite spectra from the BOSS survey indicates that the redshift and the broadening of the lines in the Fe III$\lambda\lambda$2039-2113 blend roughly follow the expected correlation in the weak limit of Schwarzschild geometry for virialized kinematics. Assuming that the Fe III UV redshift provides a measure of $M_{BH}\over R$ (${\Delta \lambda\over \lambda}\simeq{3\over2}{G\over c^2} {M_{BH}\over R}$) and using different estimates of the emittin…
Dust Envelope in Young Supernova Remnants
1974
As stated by Hoyle and Wickramasinghe (1970), hereafter referred to as HW, a significant fraction of the mass ejected by exploding supernovae may condense into solid particles during the expansion phase following explosion. Hence, observable effects on supernova light curves are to be expected.
X-ray variability of Pleiades late-type stars as observed with the ROSAT-PSPC
2003
We present a comprehensive analysis of X-ray variability of the late-type (dF7-dM) Pleiades stars, detected in all ROSAT-PSPC observations; X-ray variations on short (hours) and medium (months) time scales have been explored. We have grouped the stars in two samples: 89 observations of 42 distinct dF7-dK2 stars and 108 observations of 61 dK3-dM stars. The Kolmogorov-Smirnov test applied on all X-ray photon time series show that the percentage of cases of significant vari- ability is quite similar on both samples, suggesting that the presence of variability does not depend on mass for the time scales and mass range explored. The comparison between the Time X-ray Amplitude Distribution functi…
Measurement of top quark pair differential cross sections in the dilepton channel in pp collisions at s=7 and 8 TeV with ATLAS
2016
Measurements of normalized differential cross-sections of top quark pair ($t\bar t$) production are presented as a function of the mass, the transverse momentum and the rapidity of the $t\bar t$ system in proton-proton collisions at center-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at 7 TeV and 20.2 fb$^{-1}$ at 8 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Events with top quark pair signatures are selected in the dilepton final state, requiring exactly two charged leptons and at least two jets with at least one of the jets identified as likely to contain a $b$-hadron. The measured distributi…
Measurement of spin correlation in ttbar production using a matrix element approach
2011
correlation, assuming that the spin of the top quark is either correlated with the spin of the anti-top quark as predicted by the standard model or is uncorrelated. For the first time we use a matrix-element-based approach to study ttbar spin correlation. We use {ttbar -> W+bW-bbar ->l+nubl-nub} final states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96 TeV, where l denotes an electron or a muon. The data correspond to an integrated luminosity of 5.4 fb-1 and were collected with the dzero detector at the Fermilab Tevatron collider. The result agrees with the standard model prediction. We exclude the hypothesis that the spins of the ttbar are uncorrelated at the …
Precise measurement of the top quark mass in the dilepton channel at D0
2011
We measure the top quark mass (mt) in ppbar collisions at a center of mass energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat) +- 2.4(syst) GeV, which is in agreement with the current world average mt = 173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.
The BeppoSAX 0.1–18 keV spectrum of the bright atoll source GX 9+1: an indication of the source distance
2005
We report the results of a long, 350 ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12-18 keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color-color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of ~1.4 ¿ 1022 cm-2, fits the spectra in the energy range 1-18 keV well; however, below 1 keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12-18 keV energy range, is well fitted by the model above, if we use an equivalent hydrog…
High X-Ray Luminosity from Dynamo Stars
1981
In the present work we intend to show that a stellar dynamo mechanism can produce high X-ray luminosities and also give account for modulation periods of the order thousand seconds or larger.
Models and Astrophysical Parameters of High Mass X-ray Binaries
1996
The objective of this work is the High Mass X-ray Binaries. These systems consist of a neutron star orbiting around a star of spectral type OB. According to the luminosity class of the optical companion they split into Supergiant X-ray binaries and Be/X-ray systems. In both systems the high energy radiation is due to the accretion phenomenum, but in the first case the accreted metter comes from the strong stellar wind of the primary and in the second case it comes from the circumstellar envelope surrounding the Be star equator. In this work I concentrate on the optical and infrared bands of the electromagnetic spectrum although a discussion of the X-ray characteristics for some systems is a…