Search results for "stars [X rays]"
showing 7 items of 7 documents
All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO O2 data
2019
We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast-spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. We employ three different semi-coherent methods ($\textit{FrequencyHough}$, $\textit{SkyHough}$, and $\textit{Time-Domain $\mathcal{F}$-statistic}$) to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from $-1\times10^{-8}$ to $2\times10^{-9}$ Hz/s. None of these searches has found clear evidence for a CW signal, so we present upper limits on the gravitational-wave strain amplitude $h_0$ (the …
The spin and orbit of the newly discovered pulsar IGR J17480-2446
2011
We present an analysis of the spin and orbital properties of the newly discovered accreting pulsar IGR J17480-2446, located in the globular cluster Terzan 5. Considering the pulses detected by the Rossi X-ray Timing Explorer at a period of 90.539645(2) ms, we derive a solution for the 21.27454(8) hr binary system. The binary mass function is estimated to be 0.021275(5) Msun, indicating a companion star with a mass larger than 0.4 Msun. The X-ray pulsar spins up while accreting at a rate of between 1.2 and 1.7E-12 Hz/s, in agreement with the accretion of disc matter angular momentum given the observed luminosity. We also report the detection of pulsations at the spin period of the source dur…
Multi-wavelength diagnostics of accretion in an X-ray selected sample of CTTSs
2010
High resolution X-ray spectroscopy has revealed soft X-rays from high density plasma in Classical T-Tauri stars (CTTSs), probably arising from the accretion shock region. However, the mass accretion rates derived from the X-ray observations are consistently lower than those derived from UV/optical/NIR studies. We aim to test the hypothesis that the high density soft X-ray emission is from accretion by analysing optical accretion tracers from an X-ray selected sample of CTTSs in a homogeneous manner. We analyse optical spectra of a sample of CTTSs and calculate the accretion rates based on measuring optical emission lines. These are then compared to the accretion rates derived from the X-ray…
Modeling accretion shocks on CTTSs and their X-ray emission
2009
Recent high spectral resolution X-ray observations of some CTTSs show the presence of high density plasma (ne=10^{11}-10^{13} cm^{-3}) at temperature T=2-3 MK. This plasma is likely heated up by an accretion shock on the star surface. We investigate this issue by an accurate modelling of the impact of an accretion stream onto the stellar chromosphere. Specifically, we present a large set of 1D hydrodynamical simulations aimed at investigating the physical properties of the system as a function of the density, and the velocity of the accretion stream and of the abundances of the heavy elements. We also synthesize the plasma X-ray emission from the simulations results, in order to link the ob…
Modeling the X-ray emission from jets observed with Chandra
2009
The Second APOKASC Catalog: The Empirical Approach
2018
We present a catalog of stellar properties for a large sample of 6676 evolved stars with APOGEE spectroscopic parameters and \textit{Kepler} asteroseismic data analyzed using five independent techniques. Our data includes evolutionary state, surface gravity, mean density, mass, radius, age, and the spectroscopic and asteroseismic measurements used to derive them. We employ a new empirical approach for combining asteroseismic measurements from different methods, calibrating the inferred stellar parameters, and estimating uncertainties. With high statistical significance, we find that asteroseismic parameters inferred from the different pipelines have systematic offsets that are not removed b…
Observatory science with eXTP
2019
Disponible preprint en: arXiv:1812.04023v1 [astro-ph.HE] [v1] Mon, 10 Dec 2018 19:00:52 UTC (4,376 KB)