Nearby young single black holes

We consider nearby young black holes formed after supernova explosions in close binaries whose secondary components are currently observed as the so-called runaway stars. Using data on runaway stars and making reasonable assumptions about the mechanisms of supernova explosion and binary breakup, we estimate the present positions of nearbyyoung black holes. For two objects, we obtained relatively small error regions (～50–100 deg²). The possibility of detecting these nearby young black holes is discussed.     

Cosmic ray acceleration in hypernova remnants expanding in wind bubbles of Wolf-Rayet progenitor stars

The determination of the origin of cosmic rays with observed energies in excess of 10¹⁷ eV that exceed the expected energies of cosmic rays accelerated by supernova remnants in the galaxy is a pressing problem in modern astrophysics. Hypernova remnants are one of the possible galactic sources of cosmic rays with energies of up to 10¹⁹ eV. Hypernovae constitute a class of extremely powerful supernova explosions, whose supposed progenitors are massive Wolf-Rayet stars. We analyze the special aspects of acceleration of cosmic rays in hypernova remnants that expand in wind bubbles of Wolf-Rayet progenitor stars. We show that these cosmic rays may attain maximum energies of 10¹⁸ eV even with a relatively conservative choice of acceleration parameters and account for tens of percent of the total cosmic ray flux observed in the vicinity of the earth in the energy range of 10¹⁶–10¹⁸ eV if the galactic hypernova explosion rate in the modern epoch reaches ? _S ～ 10^?4 year^?1.     

Chemical evolution of the galaxy during its contraction

Models for the chemical evolution of the galaxy are constructed in which the time evolution is imposed by the contraction rate of the galaxy and present observations of stellar metal abundances as a function of height above the galactic plane. Stars with massm?3.5m _⊙ do not contribute to the metal enrichment of the interstellar gas, and we argue that the interstellar metal abundance at this epoch should be fairly insensitive to the size of the mass fraction of the galaxy that condenses into such stars. The birth rate for stars more massive than 3.5m _⊙ is assumed proportional toV _gal ^?n , whereV _gal is the contracting volume of the main body of the galaxy. If a dynamic time-scale is adopted for the contraction of the galaxy, then the assumed power-law birth rate yields suitable chemical evolution models only if observed Population II metals are synthesized in stars more massive than about 8.5m _⊙. This mass range is consistent with the predictions of current stellar-evolution theory. Provided the birth function does include stars more massive than 8.5m _⊙, the relation between the value of the parametern in the birth rate and the observed chemical evolution rate is not particularly sensitive to the specific form adopted for the initial mass spectrum, or to the proportionality constant in the birth rate. We find (i)n?1.4, in general, and (ii)n is close to 1.4 if the contraction of the galaxy to a heighth=400 pc above the plane occurs at close to the free-fall rate. These results are independent of the form of the initial mass spectrum, providedS ³ is small. HereS is the total mass fraction of the galaxy that cycles through stars during its contraction. Numerical models, with an explicit initial mass spectrum, indicate that the same restrictions on the values ofn apply approximately whenS ³ is not small. To introduce low mass stars, we allow the birth rate for stars more massive than 3.5m _⊙ to level off at a time intervalt _L just before the contraction of the galaxy stops, while the total birth rate remains a simple power law. We find that reasonable models are obtained witht _L ?1.5×10⁷ yr if the galaxy contracts at a dynamic rate. However, aside from these restrictions on the values ofn andt _L , there is no uniquely favored model. For any suitable model, the supernova rate must be small enough so that shock waves from neighboring supernovae do not collide during the adiabatic expansion stage. Otherwise, the interstellar gas would not have time to cool, and its high temperature would tend to impede both star formation and the rapid contraction of the galaxy. The supernova rates in the numerical models given here are small enough to avoid this problem, but large enough to achieve a uniform metal abundance on a time scale short compared to the chemical-evolution time scale. At the epoch considered here, the interstellar metal abundance is approximately less than 0.4Z _⊙, and the models are assumed to apply before galactic-scale inhomogeneities, such as the galactic nucleus, become important. Therefore, the chemical mixing time scales imply that most Population II stars of the same age should have approximately the same initial metal abundance, unless the clustering of supernova explosions associated with massive Population II stars is significant. It is shown that collisions between shock waves from neighboring supernovae can produce local regions of significantly enhanced density. The peak bolometric luminosity of the galaxy during its contraction is similar to that predicted by Partridge and Peebles (1967a), but it occurs during the final stages of contraction to the disc. Numerical models give values between 13 and 34 yr^?1 for the average number of supernova explosions per year during this bright phase. The X-ray luminosity of the galaxy from these supernovae may be comparable to that of Seyfert galaxies.     

The origin of intergalactic thermonuclear supernovae

The population synthesis method is used to study the possibility of explaining the appreciable fraction of the intergalactic type-Ia supernovae (SN Ia), 20 ₋₁₅ ⁺¹² %, observed in galaxy clusters (Gal-Yam et al. 2003) when close white dwarf binaries merge in the cores of globular clusters. In a typical globular cluster, the number of merging double white dwarfs does not exceed ∼10⁻¹³ per year per average cluster star in the entire evolution time of the cluster, which is a factor of ∼3 higher than that in a Milky-Way-type spiral galaxy. From 5 to 30% of the merging white dwarfs are dynamically expelled from the cluster with barycenter velocities up to 150 km s⁻¹. SN Ia explosions during the mergers of double white dwarfs in dense star clusters may account for ∼1% of the total rate of thermonuclear supernovae in the central parts of galaxy clusters if the baryon mass fraction in such star clusters is ∼0.3%.     

Pulsar velocities

Radio pulsars have long been established as having high velocities that are probably produced in the violence of their formation in Supernovae (Gunn & Ostriker 1970; Lyne, Anderson & Salter 1982). Three recent developments have resulted in a reassessment of their velocities: the adoption of a new distance scale (Taylor & Cordes 1993), many new determinations of proper motion (Harrison, Lyne & Anderson 1993; Bailes et al. 1989; Fomalont et al. 1992) and the realisation (Harrison & Lyne 1993) that estimates of speeds derived from scintillation measurements were systematically low by about a factor of 2. Taking into account a strong selection effect that makes the observed velocities unrepresentative of those acquired at birth, it seems that the mean space velocity of pulsars at birth is 450 ± 90 km s^-1 (Lyne and Lorimer 1994), about a factor of 3 greater than earlier estimates. The general migration from the Galactic plane is consistent with birth in the supernova of massive Population I stars. An outstanding question is how such velocities are produced in the kinetics of supernova collapse. This large increase in birth velocity is likely to have a major impact upon our understanding of the retention of neutron stars in binary systems, globular clusters and the Galaxy as it exceeds or is comparable with all their escape velocities. The rapid spatial separation of fast and slow pulsars will have a profound effect upon calculations of the galactic population and birth rate, both of which have been underestimated in the past. Furthermore, the distribution of dead neutron stars will be more isotropic and may better match the distribution of the gamma-ray burst sources. A small number of pulsars are at a large distance from the Galactic plane, but moving towards it. The most likely origin of these objects lies in OB runaway stars.     

New observations of the pulsar wind nebula in the supernova remnant CTB 80

We investigated the kinematics of the pulsar wind nebula (PWN) in the old supernova remnant CTB 80 using the Fabry-Perot interferometer of the 6-m Special Astrophysical Observatory telescope. In addition to the previously known expansion of the system of bright filaments with a velocity of 100–200 km s^?1, we detected weak high-velocity features in the Hα line at least up to velocities of 400–450 km s^?1. We analyzed the morphology of the PWN in the Hα, [S II], and [O III] lines using HST archival data and discuss its nature. The shape of the central filamentary shell, which is determined by the emission in the [O III] line and in the radio continuum, is shown to be consistent with the bow-shock model for a significant (about 60°) inclination of the pulsar’s velocity vector to the plane of the sky. In this case, the space velocity of the pulsar is twice as high as its tangential velocity, i.e., it reaches ?500 km s^?1, and PSR B1951+32 is the first pulsar whose radial velocity about 40 km s^?1 has been estimated from PWN observations. The shell-like Hα-structures outside the bow shock front in the east and the west could be associated with both the pulsar’s jets and the pulsar wind breakthrough due to the layered structure of the extended CTB 80 shell.     

Structure and kinematics of the interstellar medium in the star-forming region in the BCD galaxy VII Zw 403 (UGC 6456)

The structure and kinematics of ionized supershells in the star-forming region in the BCD galaxy VII Zw 403 (UGC 6456) are analyzed using observations with the SCORPIO focal reducer on the 6-m Special Astrophysical Observatory telescope in three modes: direct imaging (in the Hα, [O III], and [S II] lines), long-slit spectroscopy, and spectroscopy with a scanning Fabry-Perot interferometer. In addition to the previously known bright H II regions and the faint giant ring that surrounds the entire starforming region, many new faint diffuse and arc structures have been detected. A fine structure of the giant ring has been revealed. We do not confirm the previously detected expansion of the bright shells around young stellar associations with a velocity of 50–70 km s^?1. We have estimated their expansion velocities to be no higher than 15–20 km s^?1; the corresponding kinematic age, no younger than 3–4 Myr, agrees well with the age of the compact OB associations associated with them. We correlate the faint extended filamentary and diffuse regions of ionized gas identified almost in the entire central region of the galaxy and the giant H II ring with the older (10 Myr) stellar population of the most recent starburst. Weak high-velocity [O III] and Hα line wings (up to 300 km s^?1 from the line center) have been detected in the brightest H II region. Such velocities have been observed in the galaxy for the first time. The previously published Hα luminosity measurements for the galaxy are refined.     

Broadband spectrum of the total X-ray emission from the galaxy M31

We present the results of measurements of the total X-ray flux from the Andromeda galaxy (M31) in the 3-100 keV band based on data from the RXTE/PCA, INTEGRAL/ISGRI, and SWIFT/BAT space experiments. We show that the total emission from the galaxy has a multicomponent spectrum whose main characteristics are specified by binaries emitting in the optically thick and optically thin regimes. The galaxy’s luminosity at energies 20–100 keV gives about 6% of its total luminosity in the 3–100 keV band. The emissivity of the stellar population in M31 is L _{2–20 keV} ～ 1.1 × 10²⁹ erg s^?1 M _⊙ ^?1 in the 2–20 keV band and L _{20–100 keV} ～ 8 × 10²⁷ erg s^?1 M _⊙ ^?1 in the 20–100 keV band. Since low-mass X-ray binaries at high luminosities pass into a soft state with a small fraction of hard X-ray emission, the detection of individual hard X-ray sources in M31 requires a sensitivity that is tens of times better (up to 10^?13 erg s^?1 cm^?2) than is needed to detect the total hard X-ray emission from the entire galaxy. Allowance for the contribution from the hard spectral component of the galaxy changes the galaxy’s effective Compton temperature approximately by a factor of 2, from ～1.1 to ～2.1 keV.     

The calibrated map of the HII region S237 in Hα emission

The difference of spatial distributions between the O-type stars, supernovae and red giant stars found by Riekeet al. (1980) in the nuclear region of M82 can be interpreted if the star formation has been triggered by shock waves expanding from the nucleus with velocities of 100 km s^–1 at 300 pc from the centre and if the explosions have recurrently occurred with time interval of about 2×10⁶ yr. The recurrent formation of such giant compressed gas layer makes the formation rate of massive stars efficient.     

Bulk motions of flat galaxies on 100-Mpc scales from new data

We use a new expanded and partially modified sample of 1501 thin edge-on spiral galaxies from the RFGC catalog to analyze the non-Hubble bulk motions of galaxies on the basis of a generalized multiparameter Tully-Fisher relation. The results obtained have confirmed and refined our previous conclusions (Parnovsky et al. 2001), in particular, the statistical significance of the quadrupole and octupole components of the galaxy bulk velocity field. The quadrupole component, which is probably produced by tidal forces from overdense regions, leads to a difference in the recession velocities of galaxies on scales of 8000–10000 km s^?1 up to 6% of their Hubble velocity. On Local Supercluster scales (3000 km s^?1), its contribution increases to about 20%. Including the octupole components in the model causes the dipole component to decrease to the 1σ level. In contrast, in the dipole model, the galaxy bulk velocity relative to the frame of reference of the cosmic microwave background is 310±75 km s^?1 toward the apex with l=311° and b=12°. We also consider a sample of 1493 galaxies that was drawn using a more stringent galaxy selection criterion. The difference between the results of our data analysis for this sample and for the sample of 1501 galaxies is primarily attributable to a decrease in the dipole velocity component (290±75 km s^?1 toward the apex with l=310° and b=12°) and a decrease in σ by about 2%.     

Testing the Distance Scale of the Gaia TGAS Catalogue by the Kinematic Method

We have studied the simultaneous and separate solutions of the basic kinematic equations obtained using the stellar velocities calculated on the basis of data from the Gaia TGAS and RAVE5 catalogues. By comparing the values of Ω'₀ found by separately analyzing only the line-of-sight velocities of stars and only their proper motions, we have determined the distance scale correction factor p to be close to unity, 0.97 ± 0.04. Based on the proper motions of stars from the Gaia TGAS catalogue with relative trigonometric parallax errors less than 10% (they are at a mean distance of 226 pc), we have found the components of the group velocity vector for the sample stars relative to the Sun (U, V,W)_⊙ = (9.28, 20.35, 7.36) ± (0.05, 0.07, 0.05) km s^?1, the angular velocity of Galactic rotation Ω⁰ = 27.24 ± 0.30 km s?1 kpc?1, and its first derivative Ω'₀ = ?3.77 ± 0.06 km s^?1 kpc^?2; here, the circular rotation velocity of the Sun around the Galactic center is V₀ = 218 ± 6 km s^?1 kpc (for the adopted distance R₀ = 8.0 ± 0.2 kpc), while the Oort constants are A = 15.07 ± 0.25 km s^?1 kpc^?1 and B = ?12.17 ± 0.39 km s^?1 kpc^?1, p = 0.98 ± 0.08. The kinematics of Gaia TGAS stars with parallax errors more than 10% has been studied by invoking the distances from a paper by Astraatmadja and Bailer-Jones that were corrected for the Lutz–Kelker bias. We show that the second derivative of the angular velocity of Galactic rotation Ω'₀ = 0.864 ± 0.021 km s^?1 kpc^?3 is well determined from stars at a mean distance of 537 pc. On the whole, we have found that the distances of stars from the Gaia TGAS catalogue calculated using their trigonometric parallaxes do not require any additional correction factor.     

Puzzling Origin of CEMP-r/s Stars: An Interpretation of Abundance and Enrichment of s- and r-Process Elements from Asymptotic Giant Branch Supernovae

CEMP-r/s stars at low metallicity are known as double-enhanced stars that show enhancements of both r-process and s-process elements. The chemical abundances of these very metal-poor stars provide us a lot of information for putting new restraints on models of neutron-capture processes. In this article, we put forward an accreted scenario in which the double enrichment of r-process and s-process elements is caused by a former intermediate-mass Asymptotic Giant Branch (AGB) companion in a detached binary system. As the AGB superwind is only present at the ultimate phase of AGB stars, there is thus a lot of potential that the degenerate-core mass of an intermediate-mass AGB star reaches the Chandrasekhar limit before the AGB superwind. In these circumstances, both s-process elements produced in the AGB shell and r-process elements synthesized in the subsequent explosion would be sprayed contemporaneously and accreted by its companion. Despite similarity to physical conditions of a core-collapse supernova, a major focus in this scenario is the degenerate C–O core surrounded by an envelope of a former intermediate-mass AGB donor that may collapse and explode. Due to the existence of an outer envelope, r-process nucleosynthesis is expected to occur. Hypothesizing the material-rich europium (Eu) accreted by the secondary via the wind from the supernova to be in proportion to the geometric fraction of the companion with respect to the exploding donor star, we find that the estimated yield of Eu (as representative of r-process elements) per AGB supernova event is about 1 × 10^?9 M _⊙ ～ 5 × 10^?9 M _⊙. Using the yields of Eu, the overabundance of r-process elements in CEMP-r/s stars can be accounted for. The calculated results show that the value of parameter f , standing for efficiency of wind pollution from the AGB supernova, will reach about 10⁴, which means that the enhanced factor is much larger than unity due to the impact of gravity of the donor and the result of the gravitational focusing effect of the companion.     

Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system

The Pulkovo Compilation of Radial Velocities (PCRV) has been made to study the stellar kinematics in the local spiral arm. The PCRV contains weighted mean absolute radial velocities for 35 495 Hipparcos stars of various spectral types and luminosity classes over the entire celestial sphere mainly within 500 pc of the Sun. The median accuracy of the radial velocities obtained is 0.7 km s^?1. Results from 203 publications were used in the catalogue. Four of them were used to improve the radial velocities of standard stars from the IAU list. The radial velocities of 155 standard stars turned out to be constant within 0.3 km s^?1. These stars were used to analyze 47 768 mean radial velocities for 37 200 stars from 12 major publications (～80% of all the data used). Zero-point discrepancies and systematic dependences on radial velocity, B-V color index, right ascension, and declination were found in radial velocity differences of the form “publication minus IAU list of standards.” These discrepancies and dependences were approximated and taken into account when calculating the weighted mean radial velocities. 1128 stars whose independent radial-velocity determinations were available at least in three of these publications and agreed within 3 km s^?1 were chosen as the work list of secondary standards. Radial-velocity differences of the form “publication minus list of secondary standards” were used by analogy to correct the zero points and systematic dependences in the radial velocities from 33 more publications (～ 13% of the data used). In addition, the radial velocities from 154 minor publications (～7% of the data used) pertaining to well-known instruments were used without any corrections.     

Oscillation structure of gamma-ray bursts and their possible origin

It is hypothesized that thermonuclear burning of the matter from the envelope of a massive compact star accreting onto a hot neutron star produced by spherically symmetric collapse of a stellar iron core can proceed in oscillation mode (much as is the case during thermal explosions of carbon-oxygen cores in lower mass stars). Local density oscillations near the neutron-star surface can generate shock waves; in these shocks, the electron-positron plasma is stratified from the remaining matter, and shells of an expanding relativistic fireball with an oscillation time scale in cosmological gamma-ray bursts (GRBs) of ～10^?2 s are formed. It is pointed out that the GRB progenitors can be nonrotating massive Wolf-Rayet (WR) stars whose collapse, according to observational data, can proceed without any substantial envelope ejection.     

Soft and supersoft X-ray sources in symbiotic stars

Assuming that soft X-ray sources in symbiotic stars result from strong thermonuclear runaways, and supersoft X-ray sources from weak thermonuclear runaways or steady hydrogen burning symbiotic stars, we investigate the Galactic soft and supersoft X-ray sources in symbiotic stars by means of population synthesis. The Galactic occurrence rates of soft X-ray sources and supersoft X-ray sources are from ～2 to 20 yr^?1, and ～2 to 17 yr^?1, respectively. The numbers of X-ray sources in symbiotic stars range from 2390 to 6120. We simulate the distribution of X-ray sources over orbital periods, masses and mass accretion rates of white dwarfs. The agreement with observations is reasonable.     

Peculiar motions of galaxy clusters and groups in the Hercules and Leo supercluster regions

We present the results of our study of the peculiar motions for 41 galaxy clusters and groups in the regions of the Hercules and Leo superclusters (0.027 < z < 0.045). For this purpose, based on SDSS (Data Release 8) data, we compiled a sample of early-type galaxies in the investigated clusters and groups, constructed their fundamental planes (FPs), and determined independent distances and peculiar velocities. The Hubble law between the radial velocities galaxy clusters and the distances derived from the FPs holds for the rich Hercules supercluster as a whole. At the same time, however, significant peculiar motions along the line of sight with rms deviations of 736 ± 50 and 584 ± 50 km s^?1 are observed within this supercluster and in its immediate neighborhood. In the poor Leo supercluster, the rms deviation is also large, 625 ± 70 km s^?1. Its Hubble diagram exhibits the approach of galaxy clusters and groups along the line of sight relative to the most massive cluster A1185. In the immediate neighborhood of the Leo supercluster (virtually in its field), the rms deviation of the peculiar velocities is minimal, 287 ± 60 km s^?1.     

Kinematics of the galaxy from OB stars with proper motions from the Gaia DR1 catalogue

We consider two samples of OB stars with different distance scales that we have studied previously. The first and second samples consist of massive spectroscopic binaries with photometric distances and distances determined from interstellar calcium lines, respectively. The OB stars are located at heliocentric distances up to 7 kpc. We have identified them with the Gaia DR1 catalogue. Using the proper motions taken from the Gaia DR1 catalogue is shown to reduce the random errors in the Galactic rotation parameters compared to the previously known results. By analyzing the proper motions and parallaxes of 208 OB stars from the Gaia DR1 catalogue with a relative parallax error of less than 200%, we have found the following kinematic parameters: (U, V)_⊙ = (8.67, 6.63)± (0.88, 0.98) km s^?1, Ω₀ = 27.35 ± 0.77 km s^?1 kpc^?1, Ω′₀ = ?4.13 ± 0.13 km s^?1 kpc^?2, and Ω″₀ = 0.672 ± 0.070 km s^?1 kpc^?3, the Oort constants are A = ?16.53 ± 0.52 km s^?1 kpc^?1 and B = 10.82 ± 0.93 km s^?1 kpc^?1, and the linear circular rotation velocity of the local standard of rest around the Galactic rotation axis is V ₀ = 219 ± 8 km s^?1 for the adopted R ₀ = 8.0 ± 0.2 kpc. Based on the same stars, we have derived the rotation parameters only from their line-of-sight velocities. By comparing the estimated values of Ω′₀, we have found the distance scale factor for the Gaia DR1 catalogue to be close to unity: 0.96. Based on 238 OB stars of the combined sample with photometric distances for the stars of the first sample and distances in the calcium distance scale for the stars of the second sample, line-of-sight velocities, and proper motions from the Gaia DR1 catalogue, we have found the following kinematic parameters: (U, V, W)_⊙ = (8.19, 9.28, 8.79)± (0.74, 0.92, 0.74) km s^?1, Ω₀ = 31.53 ± 0.54 km s^?1 kpc^?1, Ω′₀ = ?4.44 ± 0.12 km s^?1 kpc^?2, and Ω″₀ = 0.706 ± 0.100 km s^?1 kpc^?3; here, A = ?17.77 ± 0.46 km s^?1 kpc^?1, B = 13.76 ± 0.71 km s^?1 kpc^?1, and V ₀ = 252 ± 8 km s^?1.     

A runaway binary star escaping from the Θ<Superscript>1</Superscript> ori system

A runaway binary star escaping in runaway from the multiple system Θ¹ Ori C is studied. The radial velocities of both components are measured and radial velocity curves are constructed and solved for them. The physical parameters and chemical compositions of the stars are determined.     

A study of two a-stars that are escaping from the Θ1 Ori C system

Two A-stars that are moving in the opposite directions with respect to a system with radial velocities +100 and ?200 km/s were detected in the θ¹ Ori C system (HD 37022). These stars are considered to be escaping stars. An analysis of the high-quality spectra using the cross-correlation method allowed us to determine the physical characteristics of these stars: effective temperature, gravitational acceleration, relative and absolute luminosities, mass, chemical composition, and the locations of the stars on the Hertzsprung-Russell diagram.