The formation of ultra-compact X-ray binaries (UCXBs) has not been well understood. Previous works show that ultra-short orbital periods (< 1 hr) may be reached through mass transfer driven by magnetic braking in normal low/intermediate-mass X-ray binaries (L/IMXBs) only for an extremely small range of initial binary parameters, which makes it difficult to account for the rather large populatio...

In an effort to understand the correlation between X-ray emission and present star formation rate (SFR), we obtained XMM-Newton data to estimate the X-ray luminosities of a sample of actively starforming HII galaxies. The obtained X-ray luminosities are compared to other well known tracers of star formation activity such as the far infrared and the ultraviolet luminosities. We also compare the ...

We present a broadband power spectral density function (PSD) measured from extensive RXTE monitoring data of the low-luminosity AGN NGC 4258, which has an accurate, maser-determined black hole mass of (3.9± 0.1)× 10 M⊙. We constrain the PSD break time-scale to be greater than 4.5 d at >90% confidence, which appears to rule out the possibility that NGC 4258 is an analogue of black hole X-ray bin...

We have observed the old open clusters M 67 and NGC 188 with the ROSAT PSPC. In M 67 we detect a variety of X-ray sources. The X-ray emission by a cataclysmic variable, a single hot white dwarf, two contact binaries, and some RS CVn systems is as expected. The X-ray emission by two binaries located below the subgiant branch in the Hertzsprung Russell diagram of the cluster, by a circular binary...

Observations of galactic and extra-galactic globular clusters have shown that on average metal-rich clusters are ∼ 3 times as likely to contain a bright X-ray source than their metal-poor counterparts. We propose that this can be explained by taking into account the difference in the stellar structure of main sequence donors with masses between ∼ 0.85M⊙ and ∼ 1.25M⊙ at different metallicities. ...

The relativistic precession model for quasi periodic oscillations, QPOs, in low mass X-ray binaries is reviewed. The behaviour of three simultaneous types of QPOs is well matched in terms of the fundamental frequencies for geodesic motion in the strong field of the accreting compact object for reasonable star masses and spin frequencies. The model ascribes the higher frequency kHz QPOs, the low...