Related papers: Polars -- multisite emission -- multiwavelength ob…
During the low optical brightness states of AM Herculis systems (polars) when accretion has declined to a very low value, the underlying magnetic white dwarf photosphere can be modelled without the complication of thermal bremstrahlung and…
We present a magnetic stripping model for AM Her type objects. Our model is based on an equilibrium condition between ram pressure and magnetic pressure in a stiff dipolar magnetic field. We investigate the detailed geometry of the…
There are only a handful of known short-period pre-main sequence spectroscopic binaries with significant accretion rates (Class II sources). AK Sco stands out in this list because the system is composed of two equal mass F5 stars in a…
The radiation-dominated polar emitting region of an accreting X-ray pulsar is simulated numerically in the framework of a three-dimensional (geometrically two-dimensional) model. The radiative transfer within the emitting region and the…
In an accreting X-ray pulsar, a neutron star accretes matter from a stellar companion through an accretion disk. The high magnetic field of the rotating neutron star disrupts the inner edge of the disc, funneling the gas to flow onto the…
We present HST/ACS ultraviolet photometry of three quiescent black hole X-ray transients: X-ray Nova Muscae 1991 (GU Mus), GRO J0422+32 (V518 Per), and X-ray Nova Vel 1993 (MM Vel), and one neutron star system, Aql X-1. These are the first…
We model the multiwavelength properties of binaries accreting at super-critical rates with the aim to better understand the observational properties of Ultra-luminous X-ray Sources (ULXs). We calculate an extended grid of binary systems…
Giant planets generate accretion luminosity as they form. Much of this energy is radiated in strong H$\alpha$ line emission, which has motivated direct imaging surveys at optical wavelengths to search for accreting protoplanets. However,…
Accreting highly magnetized pulsars in binary systems are among the brightest X-ray emitters in our Galaxy. Although a number of high statistical quality broad-band (0.1-100 keV) X-ray observations are available, the spectral energy…
Observations of the ultraviolet continuum of the X-ray binary system Her X-1/HZ Herculis with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show quasiperiodic oscillations (QPOs) at frequencies of 8+/-2 and 43+/-2…
Context: The INTEGRAL hard X-ray observatory has revealed an emerging population of highly obscured X-ray binary systems through multi-wavelength observations. Previous studies have shown that many of these sources are high-mass X-ray…
We investigate the X-ray properties of the powerful radio galaxy Hercules A (3C 348) using ROSAT HRI, PSPC and ASCA observations. The ASCA data are well fit by a thermal plasma model with a temperature of about 4.3 keV and abundances 0.4…
Binarity is often invoked to explain peculiarities that can not be explained by the standard theory of stellar evolution. Detecting orbital motion via the Doppler effect is the best method to test binarity when direct imaging is not…
The study of X-ray pulsar accretion columns helps us characterize accretion physics in this extreme regime of strong gravity and strong magnetic fields. Previous observations of the X-ray pulsar Hercules X-1 revealed a highly broadened Fe K…
We present the results of recent multicolor photometric and high-resolution spectroscopic observations of the bright Be star Pi Aquarii. Observational data collected from the literature were used to study the star's variations over the last…
A fraction of the Ultra Luminous X-ray (ULX) sources are known to be accreting neutron stars as they show coherent X-ray pulsations with pulse periods ranging from ~1-30 seconds. While initially thought to host intermediate-mass black…
The near-star environment around young stars is very dynamic with winds, disks, and outflows. These processes are involved in star and planet formation, and influence the formation and habitability of planets around host stars. Even for the…
(Abridged:) We present the identification of optical counterparts to 23 Galactic Bulge Survey X-ray sources. We report their accurate coordinates and optical spectra acquired at the VLT and Magellan. All sources are classified as accreting…
We present results of the analysis of a sample of 22 stars of spectral types from O7 to B5 and luminosity classes I-V for which Spitzer/IRS spectra are available. The IRS spectra of these stars are examined for signs of excess infrared (IR)…
Structures of X-ray emitting magnetic polar regions on neutron stars in X-ray pulsars are studied in a range of the accretion rate, 10$^{17}$ g s$^{-1} \sim 10^{18}$ g s$^{-1}$. It is shown that a thin but tall, radiation energy dominated,…