Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary Nebula

SBS 1150+599A is a blue stellar object at high galactic latitude discovered in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are presented, demonstrating that it is very likely to be an old planetary nebula in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the diameter of the nebula to be 9.2", comparable to that estimated from spectra by Tovmassian et al. Lower limits to the central star temperature were derived using the Zanstra hydrogen and helium methods to determine that the star's effective temperature must be > 68,000K and that the nebula is optically thin. New spectra from the MMT and FLWO telescopes are presented, revealing the presence of strong [Ne V] lambda 3425, indicating that the central star temperature must be > 100,000K. With the revised diameter, new central star temperature, and an improved central star luminosity, we can constrain photoionization models for the nebula significantly better than before. Because the emission-line data set is sparse, the models are still not conclusive. Nevertheless, we confirm that this nebula is an extremely metal-poor planetary nebula, having a value for O/H that is less than 1/100 solar, and possibly as low as 1/500 solar.Comment: 19 pages, 6 figures. Accepted for publication in the Astronomical Journa

Many-worlds interpretation of quantum theory and mesoscopic anthropic principle

We suggest to combine the Anthropic Principle with Many-Worlds Interpretation of Quantum Theory. Realizing the multiplicity of worlds it provides an opportunity of explanation of some important events which are assumed to be extremely improbable. The Mesoscopic Anthropic Principle suggested here is aimed to explain appearance of such events which are necessary for emergence of Life and Mind. It is complementary to Cosmological Anthropic Principle explaining the fine tuning of fundamental constants. We briefly discuss various possible applications of Mesoscopic Anthropic Principle including the Solar Eclipses and assembling of complex molecules. Besides, we address the problem of Time's Arrow in the framework of Many-World Interpretation. We suggest the recipe for disentangling of quantities defined by fundamental physical laws and by an anthropic selection.Comment: 11 page

Multi-wavelength study of a new Galactic SNR G332.5-5.6

We present compelling evidence for confirmation of a Galactic supernova remnant (SNR) candidate, G332.5-5.6, based initially on identification of new, filamentary, optical emission line nebulosity seen in the arcsecond resolution images from the AAO/UKST HAlpha survey. The extant radio observations and X-ray data which we have independently re-reduced, together with new optical spectroscopy of the large-scale fragmented nebulosity, confirms the identification. Optical spectra, taken across five different, widely separated nebula regions of the remnant as seen on the HAlpha images, show average ratios of [NII]/HAlpha =2.42, [SII]/HAlpha = 2.10, and [SII] 6717/6731 = 1.23, as well as strong [OI] 6300, 6364A and [OII] 3727A emission. These ratios are firmly within those typical of SNRs. Here, we also present the radio-continuum detection of the SNR at 20/13cm from observations with the Australia Telescope Compact Array (ATCA). Radio emission is also seen at 4850 MHz, in the PMN survey (Griffith and Wright 1993) and at 843 MHz from the SUMSS survey (Bock, Large and Sadler 1999). We estimate an angular diameter of ~30 arcmin and obtain an average radio spectral index of alpha = -0.6 +- 0.1 which indicates the non-thermal nature of G332.5-5.6. Fresh analysis of existing ROSAT X-ray data in the vicinity also confirms the existence of the SNR. The distance to G332.5-5.6 has been independently estimated by Reynoso and Green (2007) as 3.4 kpc based on measurements of the HI lambda21 cm line seen in absorption against the continuum emission. Our cruder estimates via assumptions on the height of the dust layer (3.1 kpc) and using the Sigma-D relation (4 kpc) are in good agreement.Comment: 14 pages, 18 figures. Accepted for publishing in the MNRA

105110^{51} Ergs: The Evolution of Shell Supernova Remnants

This paper reports on a workshop hosted by the University of Minnesota, March 23-26, 1997. It addressed fundamental dynamical issues associated with the evolution of shell supernova remnants and the relationships between supernova remnants and their environments. The workshop considered, in addition to classical shell SNRs, dynamical issues involving X-ray filled composite remnants and pulsar driven shells, such as that in the Crab Nebula. Approximately 75 participants with wide ranging interests attended the workshop. An even larger community helped through extensive on-line debates prior to the meeting. Each of the several sessions, organized mostly around chronological labels, also addressed some underlying, general physical themes: How are SNR dynamics and structures modified by the character of the CSM and the ISM and vice versa? How are magnetic fields generated in SNRs and how do magnetic fields influence SNRs? Where and how are cosmic-rays (electrons and ions) produced in SNRs and how does their presence influence or reveal SNR dynamics? How does SNR blast energy partition into various components over time and what controls conversion between components? In lieu of a proceedings volume, we present here a synopsis of the workshop in the form of brief summaries of the workshop sessions. The sharpest impressions from the workshop were the crucial and under-appreciated roles that environments have on SNR appearance and dynamics and the critical need for broad-based studies to understand these beautiful, but enigmatic objects. \\Comment: 54 pages text, no figures, Latex (aasms4.sty). submitted to the PAS

Pulsar PSR B0656+14, the Monogem Ring, and the Origin of the `Knee' in the Primary Cosmic Ray Spectrum

The Monogem ring is a bright, diffuse, 25-degree-diameter supernova remnant easily visible in soft X-ray images of the sky. Projected within the ring is a young radio pulsar, PSR B0656+14. An association between the remnant and pulsar has been considered, but was seemingly ruled out by the direction and magnitude of the pulsar proper motion and by a distance estimate that placed the pulsar twice as far from Earth as the remnant. Here we show that in fact the pulsar was born very close to the center of the expanding remnant, both in distance and projection. The inferred pulsar and remnant ages are in good agreement. The conclusion that the pulsar and remnant were born in the same supernova explosion is nearly inescapable. The remnant distance and age are in remarkable concordance with the predictions of a model for the primary cosmic ray energy spectrum in which the `knee' feature is produced by a single dominant source.Comment: 4 pages, to appear in the Astrophys. J. Lett. Full size color figure can be found at http://www.thorsett.org/researc

Evolution of the Ionizing Background and the Epoch of Reionization from the Spectra of z~6 Quasars

We study the process of cosmic reionization and estimate the ionizing background in the IGM using the Lyman series absorption in the spectra of the four quasars at 5.7<z<6.3 discovered by the SDSS. We derive the evolution of the ionizing background at high redshifts, using both semi-analytic techniques and cosmological simulations to model the density fluctuations in the IGM. The existence of the complete Ly alpha Gunn-Peterson trough in the spectrum of the z=6.28 quasar SDSS 1030+0524 indicates a photoionization rate Gamma_{-12} at z~6 lower than 0.08, at least a factor of 6 smaller than the value at z~3. The Ly beta and Ly gamma Gunn-Peterson troughs give an even stronger limit Gamma_{-12}<0.02 due to their smaller oscillator strengths, indicating that the ionizing background in the IGM at z~6 is more than 20 times lower than that at z~3. Meanwhile, the volume-averaged neutral hydrogen fraction increases from 10^{-5} at z~3 to >10^{-3} at z~6. At this redshift, the mass-averaged neutral hydrogen fraction is larger than 1%; the mildly overdense regions (delta > 3) are still mostly neutral and the comoving mean free path of ionizing photons is shorter than 8 Mpc. Comparison with simulations of cosmological reionization shows that the observed properties of the IGM at z~6 are typical of those in the era at the end of the overlap stage of reionization when the individual HII regions merge. Thus, z~6 marks the end of the reionization epoch. The redshift of reionization constrains the small scale power of the mass density fluctuations and the star forming efficiency of the first generation of objects.Comment: AJ accepted, 27 pages; minor change

Search for Pairs of Isolated Radio Pulsars - Components in Disrupted Binary Systems

We have developed a method for analyzing the kinematic association of isolated relativistic objects - possible remnants of disrupted close binary systems. We investigate pairs of fairly young radio pulsars with known proper motions and estimated distances (dispersion measures) that are spaced no more than 2-3 kpc apart. Using a specified radial velocity distribution for these objects, we have constructed 100-300 thousand trajectories of their possible motion in the Galactic gravitational field on a time scale of several million years. The probabilities of their close encounters at epochs consistent with the age of the younger pulsar in the pair are analyzed. When these probabilities exceed considerably their reference values obtained by assuming a purely random encounter between the pulsars under consideration, we conclude that the objects may have been gravitationally bound in the past. As a result, we have detected six pulsar pairs (J0543+2329/J0528+2200, J1453-6413/J1430-6623, J2354+6155/J2321+6024, J1915+1009/J1909+1102, J1832-0827/J1836-1008, and J1917+1353/J1926+1648) that are companions in disrupted binary systems with a high probability. Estimates of their kinematic ages and velocities at binary disruption and at the present epoch are provided

CMB Anisotropy Induced by a Moving Straight Cosmic String

We showed that the part of strings could be detected by optical method is only 20% from the total available amount of such objects, therefore the gravitational lensing method has to be "completed" by CMB one. We found the general structure of the CMB anisotropy generated by a cosmic string for simple model of straight string moving with constant velocity. For strings with deficit angle 1-2 arcsec the amplitude of generated anisotropy has to be 15-30 muK (the corresponding string linear density is (G mu) ~ 10^{-7} and energy is GUT one, 10^{15} GeV). To use both radio and optical methods the deficit angle has to be from 0.1 arcsec to 5-6 arcsec. If cosmic string can be detected by optical method, the length of corresponding brightness spot of anisotropy has to be no less than 100 degrees.Comment: 6 pages, 1 Postscript figure, will be published in proceedings of QUARKS-2008, 15th International Seminar on High Energy Physics, Sergiev Posad, Russia, 23-29 May, 200

Tight Cosmological Constraints from the Angular-Size/Redshift Relation for Ultra-Compact Radio Sources

Some years ago (Jackson and Dodgson 1997) analysis of the angular-size/redshift relationship for ultra-compact radio sources indicted that for spatially flat universes the best choice of cosmological parameters was Omega_m=0.2 and Omega_Lambda=0.8. Here I present an astrophysical model of these sources, based upon the idea that for those with redshift z>0.5 each measured angular size corresponds to a single compact component which is moving relativistically towards the observer; this model gives a reasonable account of their behaviour as standard measuring rods. A new analysis of the original data set (Gurvits 1994), taking into account possible selection effects which bias against large objects, gives Omega_m=0.24+0.09/-0.07 for flat universes. The data points match the corresponding theoretical curve very accurately out to z~3, and there is clear and sustained indication of the switch from acceleration to deceleration, which occurs at z=0.85.Comment: 21 pages, 7 figures, published versio

Hubble Space Telescope imaging of a peculiar stellar complex in NGC 6946

The stellar populations in a stellar complex in NGC 6946 are analyzed on images taken with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The complex is peculiar by its very high density of stars and clusters and semicircular shape. Its physical dimensions are about the same as for the local Gould Belt, but the stellar density is 1 - 2 orders of magnitude higher. In addition to an extremely luminous, 15 Myr old cluster discussed in an earlier paper, accounting for about 17% of the integrated V-band light, we identify 18 stellar clusters within the complex with luminosities similar to the brightest open clusters in the Milky Way. The color-magnitude diagram of individual stars in the complex shows a paucity of red supergiants compared to model predictions in the 10-20 Myr age range for a uniform star formation rate. We thus find tentative evidence for a gap in the dispersed star formation history, with a concentration of star formation into a young globular cluster during this gap. Confirmation of this result must, however, await a better understanding of the late evolution of stars in the corresponding mass range (> 12 Msun). A reddening map based on individual reddenings for 373 early-type stars is presented, showing significant variations in the absorption across the complex. These may be responsible for some of the arc-like structures previously identified on ground-based images. We finally discuss various formation scenarios for the complex and the star clusters within it.Comment: 51 pages, including 19 figures and 4 tables. Accepted for publication in Ap