E. Nihal Ercan

Migration of giant planets in planetesimal discs

Planets orbiting a planetesimal circumstellar disc can migrate inward from their initial positions because of dynamical friction between planets and planetesimals. The migration rate depends on the disc mass and on its time evolution. Planets that are embedded in long-lived planetesimal discs, having total mass of 10 −4 0.01M⊙, can migrate inward a large distance and can survive only if the inner disc is truncated or because of tidal interaction with the star. In this case the semi-major axis, a, of the planetary orbit is less than 0.1AU. Orbits with larger a are obtained for smaller value of the disc mass or for a rapid evolution (depletion) of the disc. This model may explain several of the orbital features of the giant planets that were discovered in last years orbiting nearby stars as well as the metallicity enhancement found in several stars associated with short-period planets.

Uniform Contribution of Supernova Explosions to the Chemical Enrichment of Abell 3112 out to R[subscript 200]

The spatial distribution of the metals residing in the intra-cluster medium (ICM) of galaxy clusters records all the information on a clusters nucleosynthesis and chemical enrichment history. We present measurements from a total of 1.2 Ms Suzaku XIS and 72 ks Chandra observations of the cool-core galaxy cluster Abell 3112 out its virial radius (~ 1470 kpc). We find that the ratio of the observed supernova type Ia explosions to the total supernova explosions has a uniform distribution at a level of 12-16% out to the clusters virial radius. The observed fraction of type Ia supernova explosions is in agreement with the corresponding fraction found in our Galaxy and the chemical enrichment of our Galaxy. The non-varying supernova enrichment suggests that the ICM in cluster outskirts was enriched by metals at an early stage before the cluster itself was formed during the period of intense star formation activity. Additionally, we find that the 2D delayed detonation model CDDT produces significantly worse fits to the X-ray spectra compared to simple 1D W7 models. This is due to the relative overestimate of Si, and underestimate of Mg, in these models with respect to the measured abundances.

X-RAY SPECTRAL ANALYSIS OF SU UMa TYPE DWARF NOVAE OBSERVED WITH ROSAT

X-ray spectral parameters were determined for eight SU UMa type Dwarf Novae observed with the ROSAT PSPC. The raw data were fitted with various spectral models and the best fit spectral models are found to be that of Raymond–Smith and Thermal Bremsstrahlung. The best fit temperatures were estimated to be between kT ~ 1.1-1.8 keV while the Column Densities were found to be between NH ~ 2.4×1020-4.1×1020cm-2. The estimated 0.1-2.4 keV fluxes were in the range of log FX=-13 to -11 ergs cm-2 s-1. FX/FUV and FX/Fopt rates were calculated to be between ~0.09 and ~0.37. This shows that most of the energy is radiated in the Optical and Ultraviolet band from the accretion disk in the quiescent state. Many of the SU UMa type Dwarf Novae show an Ultraviolet lag in their outburst spectrum, the Coronal Siphon Flow Model of Meyer and Meyer-Hofmeister may explain this phenomenon. This model proposes a corona at the boundary layer of a system when it is a quiescent state and suggests that some parts of the X-rays come from the corona. For these reasons, the equations of this model were applied to the results of the spectral analysis. Using this model, the mass accretion rates, the mass evaporation rates, and the radii of the coronas were calculated to be ~10-12.3-10-11.3 M⊙yr-1, ~10-6.5-10-5.5g cm-2s-1 and ~109.1-109.9cm, respectively. The pressures in the coronas were less than ~1200 g cm-2s-1 for (z) up to ~10×109cm. The obtained values suggest that the Corona model can indeed operate in SU UMa type Dwarf Novae.

1E 1207.4–5209-LIKE RADIO-QUIET NEUTRON STARS

In this work, the results of X-ray spectral analysis of radio-quiet X-ray pulsar 1E 1207.4–5209 and RX J0002+6246, RX J0822–4300, CXOU J185238.6+00402, which have the same observational characteristics as 1E 1207.4–5209, are represented based on XMM-Newton satellite observations. These four neutron stars with common physical properties may have similar physical evolution. It is shown that all of them have Pure blackbody spectra (two-blackbody fits in three cases) without a power law component. No pulsar wind nebula has been observed around any one of them, which strongly shows that they have low rotational energy loss despite their small ages. All of these neutron stars are physically connected to shell-type supernova remnants which are younger than (1–2) × 104yr. None of these sources has been detected to emit at radiofrequencies. These common spectral properties (and possibly common timing characteristics) of these neutron stars are examined. Their possible evolution is discussed based on a model represented in Ref. 1. As a result, it is quite possible that these objects form a new class of neutron stars quite different than the other types.

PLANETARY MIGRATION IN EVOLVING PLANETESIMAL DISKS

In the current paper, we further improved the model for the migration of planets introduced and extended to time-dependent planetesimal accretion disks by Del Popolo. In the current study, the assumption of Del Popolo, that the surface density in planetesimals is proportional to that of gas, is relaxed. In order to obtain the evolution of planetesimal density, we use a method developed by Stepinski and Valageas which is able to simultaneously follow the evolution of gas and solid particles for up to 107 years. Then, the disk model is coupled to migration model introduced by Del Popolo in order to obtain the migration rate of the planet in the planetesimal. We find that the properties of solids known to exist in protoplanetary systems, together with reasonable density profiles for the disk, lead to a characteristic radius in the range 0.03–0.2 AU for the final semi-major axis of the giant planet.Hence our model can explain the properties of discovered extrasolar giant planets.

XMM-Newton Observations of the Toothbrush and Sausage Clusters

Galaxy clusters are the largest gravitationally-bound objects in the universe. The member galaxies are embedded in a hot X-ray emitting Intra Cluster Medium (ICM) that has been enriched with metals produced by supernovae over the last billion years. Here we present new results from XMM-Newton archival observations of the merging clusters 1RXSJ0603.3+4213 and CIZA J2242.8+5301. These two clusters, also known as the Toothbrush and Sausage clusters, respectively, show a large radio relic associated with a merger shock North of their respective core [4,5].

Structural formation of the universe: As observed by X-ray satellites

Most celestial bodies emit their energy in the 0.5–5 keV range, thus the universe is very bright in X-rays. The Earths atmosphere protects life on earth from being burned out by the high energy UV and X-ray, while blocking the precious information from the universe. Therefore, the X-ray satellites should be placed either at high altitudes in order to have a clear vision of stars, galaxies and unveil the cosmic mystery. According to structural formation hierarchy of the universe, stars form galaxies and galaxies form clusters. Galaxy clusters are the largest gravitational entities of the universe, and yet one of the brightest X-ray sources in the universe. In this paper, we review the large-scale structural formation of the universe based on the analysis results of our TÜBİTAK scientific research project on clusters of galaxies with X-ray data, which is obtained from the scientific satellites facing outer space such as NASAs Chandra, ESAs XMM-Newton and ISAS/JAXAs Suzaku.

DYNAMICAL EVOLUTION OF CLUSTERS OF GALAXIES: THE EFFECT OF HIGH-VELOCITY SUBSTRUCTURE CLUMPS

In the Cold Dark Matter (hereafter CDM) scenario even isolated density peaks contain a high fraction of small scale clumps having velocities larger than the average escape velocity from the structure. These clumps populate protoclusters, especially in the peripheral regions, r≥Rf (where Rf is the filtering scale). During the cluster collapse and the subsequent secondary infall, collapsing or infalling clumps (having v vesc. We study the interaction between these two kinds of clumps by means of the impulse approximation1 and we find that the collapse of bound clumps is accelerated with respect to the homogeneous case (Gunn and Gotts model, Ref. 2). The acceleration of the collapse increases with decreasing height of the peak, ν. We finally compare the acceleration produced by this effect to the slowing down effect produced by the gravitational interaction of the quadrupole moment of the system with the tidal field of the matter of the neighboring proto-clusters studied by Del Popolo and Gambera.3 We find that the magnitude of the slowing down effect is larger than the acceleration produced by the effect studied in this paper, only in the outskirts of the cluster. We want to stress that the one which we study in this paper is also present in an isolated protocluster, being produced by the interaction of the collapsing clumps with the unbound substructure internal to the collapsing clumps itself while that studied in Ref. 3 is produced by substructure external to the density peak.