Joanna Mikolajewska

GX 339-4: The Distance, state transitions, hysteresis and spectral correlations

We study X-ray and variability and distance of GX 339–4. We derive the distance of > 7 kpc, based on recent determination of the binary parameters. We study data from the ASM aboard Ginga, the BATSE aboard CGRO, and the ASM, PCA and HEXTE aboard RXTE. From 1987 to 2004, GX 339–4 underwent �15 outbursts and went through all known states of black-hole binaries. For the first time, we present the PCA data from the initial hard state of the outburst of 2004. We then study colourcolour and colour-flux correlations. In the hard state, there is a strong anticorrelation between the 1.5–5 and 3–12 keV spectral slopes, which we explain by thermal Comptonization of disc photons. There is also a softening of the spectrum above 3 keV with the increasing flux that becomes stronger with increasing energy up to �200 keV. This indicates an anticorrelation between the electron temperature and luminosity, explained by hot accretion models. In addition, we see a variable broad-band slope with a pivot at �200 keV. In the soft state, there is a high energy tail with varying amplitude beyond a strong and variable blackbody component. We confirm the presence of pronounced hysteresis, with the hard-to-soft state transitions occurring at much higher (and variable) luminosities than the soft-to-hard transitions. We fit the RXTE/ASM data with a model consisting of an outer accretion disc and a hot inner flow. State transitions are associated then with variations in the disc truncation radius, which we fit as � 6GM/c 2 in the soft state and several times that in the hard state. The disappearence of the inner disc takes place at a lower accretion rate than its initial appearance due to the dependence of the transitions on the source history. We provide further evidence against the X-ray emission in the hard state being nonthermal synchrotron, and explain the observed radio-X-ray correlation by the jet power being correlated with the accretion power.

GRS 1915+105: the distance, radiative processes and energy-dependent variability

We present an exhaustive analysis of five broad-band observations of GRS 1915+105 in two variability states, / and w, observed simultaneously by the Proportional Counter Array (PCA) and High-Energy X-ray Timing Experiment (HEXTE) detectors aboard the Rossi X-ray Timing Explorer, and the Oriented Scintillation Spectrometer Experiment (OSSE) detector aboard the Compton Gamma-ray Observatory. We find all the spectra well fitted by Comptonization of disc blackbody photons, with very strong evidence for the presence of a non-thermal electron component in the Comptonizing plasma. Both the energy and the power spectra in the X state are typical of the very high/intermediate state of black hole binaries. The spectrum of the ω state is characterized by a strong blackbody component Comptonized by thermal electrons and a weak non-thermal tail. We then calculate rms spectra (fractional variability as functions of energy) for the PCA data. We accurately model the rms spectra by coherent superposition of variability in the components implied by the spectral fits, namely a less variable blackbody and more variable Comptonization. The latter dominates at high energies, resulting in a flattening of the rms at high energies in most of the data. This is also the case for the spectra of the quasi-periodic oscillations present in the X state. Then, some of our data require a radial dependence of the rms of the disc blackbody. We also study the distance to the source, and find d ≃ 11 kpc as the most likely value, contrary to a recent claim of a much lower value.

IPHAS and the symbiotic stars I. Selection method and first discoveries

Context. The study of symbiotic stars is essential to understand important aspects of stellar evolution in interacting binaries. Their observed population in the Galaxy is however poorly known, and is one to three orders of magnitudes smaller than the predicted population size. Aims. IPHAS, the INT Photometric Ha survey of the Northern Galactic plane, gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume, and discover a significant number of new systems. Methods. A method of selecting candidate symbiotic stars by combining IPHAS and near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic binaries from normal stars and most of the other types of Ha emission line stars in the Galaxy. The only exception are T Tauri stars, which can however be recognized because of their concentration in star forming regions. Results. Using these selection criteria, we discuss the classification of a list of 4338 IPHAS stars with Ha in emission. 1500 to 2000 of them are likely to be Be stars. Among the remaining objects, 1183 fulfill our photometric constraints to be considered candidate symbiotic stars. The spectroscopic confirmation of three of these objects, which are the first new symbiotic stars discovered by IPHAS, proves the potential of the survey and selection method.

Evolution of the symbiotic binary system AG Dranconis

We present an analysis of new and archival photometric and spectroscopic observations of the symbiotic star AG Draconis. This binary has undergone several 1 - 3 mag optical and ultraviolet eruptions during the past 15 years. Our combination of optical and ultraviolet spectroscopic data allow a more complete analysis of this system than in previous papers. AG Dra is composed of a K-type bright giant M(sub g) approximately 1.5 solar mass) and a hot, compact star M(sub h approximatelly 0.4 - 0.6 solar mass) embedded in a dense, low metallicity nebula. The hot component undergoes occasional thermonuclear runaways that produce 2 - 3 mag optical/ultraviolet eruptions. During these eruptions, the hot component develops a low velocity wind that quenches x-ray emission from the underlying hot white dwarf. The photoionized nebula changes its volume by a factor of 5 throughout an eruptin cycle. The K bright giant occults low ionization emission lines during superior conjunctions at all outburst phases but does not occult high ionization lines in outburst (and perhaps quiescence). This geometry and the component masses suggest a system inclination of i approximately 30 deg - 45 deg.

Evolution of the symbiotic binary system AG Pegasi: the slowest classical nova eruption ever recorded

We present an analysis of new and existing photometric and spectroscopic observations of the ongoing eruption in the symbiotic star AG Pegasi, showing that this binary has evolved considerably since the turn of the century. Recent dramatic changes in both the UV continuum and the wind from the hot component allow a more detailed analysis than in previous papers. AG Peg is composed of a normal M3 giant and a hot, compact star embedded in a dense, ionized nebula. The hot component powers the activity observed in this system, including a dense wind and a photoionized region within the outer atmosphere of the red giant. The hot component contracted in radius at roughly constant luminosity from 1850 to 1985. Its bolometric luminosity declined by a factor of about 4 during the past 5 yr. Both the mass loss rate from the hot component and the emission activity decreased in step with the hot components total luminosity, while photospheric radiation from the red giant companion remained essentially constant.

Spectroscopic orbits and variations of RS Ophiuchi

The aims of our study are to improve the orbital elements of the giant and to derive the spectroscopic orbit for the white dwarf companion. Spectral variations related to the 2006 outburst are also studied. The spectroscopic orbits have been obtained by measuring the radial velocities of the cool component absorption lines and the broad Halpha emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. A new period of 453.6 days and a mass ratio, q=M_g/M_h=0.59 were determined. Assuming a massive white dwarf as the hot component, M_h= 1.2-1.4 M_{\odot}, the red giant mass is M_g= 0.68-0.80 M_{\odot} and the orbit inclination, i = 49-52^{\circ}. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the LiI doublet in RS Oph and its radial velocities fit very well the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 km/s and two other extended emission components at -200 and +150 km/s. These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane.

On the nature of the symbiotic binary CI Cygni

An analysis of ultraviolet and optical spectroscopy is presented for the symbiotic binary CI Cyg. This system contains an M5 II asymptotic branch giant Mg of about 1.5 solar mass, transfering material at a few times 0.00001 solar mass/yr into a large accretion disk surrounding a main-sequence star with Mh of about 0.5 solar mass. A boundary layer at the inner edge of the disk photoionizes a small nebula approximately confined to the Roche volume of the accreting star. An extended, more highly ionized region forms when material ejected from the disk interacts with the red giant wind. 115 refs.

Cyg X-3: A Galactic Double Black Hole or Black-hole-Neutron-star Progenitor

There are no known stellar-origin double black hole (BH-BH) or black-hole-neutron-star (BH-NS) systems. We argue that Cyg X-3 is a very likely BH-BH or BH-NS progenitor. This Galactic X-ray binary consists of a compact object, wind-fed by a Wolf-Rayet (W-R) type companion. Based on a comprehensive analysis of observational data, it was recently argued that Cyg X-3 harbors a 2-4.5 M ☉ black hole (BH) and a 7.5-14.2 M ☉ W-R companion. We find that the fate of such a binary leads to the prompt (lsim 1 Myr) formation of a close BH-BH system for the high end of the allowed W-R mass (M W-R gsim 13 M ☉). For the low- to mid-mass range of the W-R star (M W-R ~ 7-10 M ☉) Cyg X-3 is most likely (probability 70%) disrupted when W-R ends up as a supernova. However, with smaller probability, it may form a wide (15%) or a close (15%) BH-NS system. The advanced LIGO/VIRGO detection rate for mergers of BH-BH systems from the Cyg X-3 formation channel is ~10 yr–1, while it drops down to ~0.1 yr–1 for BH-NS systems. If Cyg X-3 in fact hosts a low-mass black hole and massive W-R star, it lends additional support for the existence of BH-BH/BH-NS systems.

On the nature of the symbiotic binary AX Persei

Photometric and spectroscopic observations of the symbiotic binary AX Persei are presented. This system contains a red giant that fills its tidal lobe and transfers material into an accretion disk surrounding a low-mass main-sequence star. The stellar masses - 1 solar mass for the red giant and about 0.4 solar mass for the companion - suggest AX Per is poised to enter a common envelope phase of evolution. The disk luminosity increases from L(disk) about 100 solar luminosity in quiescence to L(disk) about 5700 solar luminosity in outburst for a distance of d = 2.5 kpc. Except for visual maximum, high ionization permitted emission lines - such as He II - imply an EUV luminosity comparable to the disk luminosity. High-energy photons emitted by a hot boundary layer between the disk and central star ionize a surrounding nebula to produce this permitted line emission. High ionization forbidden lines form in an extended, shock-excited region well out of the binarys orbital plane and may be associated with mass loss from the disk.

On symbiotic stars and type Ia supernovae

We examine the possibility that symbiotic stars-wide binaries containing a red giant and a white dwarf-produce a significant fraction of Type Ia supernovae (SN Ia). These binaries probably cannot account for SN Ia events if the white dwarf mass must evolve to the Chandrasekhar limit during the expected lifetime of the red giant primary star. However, symbiotic binaries are good candidates for helium detonation supernovae in low-mass white dwarfs. If helium detonations can produce the majority of SN Ia events, then symbiotic stars might account for a large fraction of Type Ia supernovae