arXiv.org > astro-ph

Astrophysics

astro-ph new abstracts, Fri, 19 May 06 00:00:15 GMT
0605429 -- 0605469 received

astro-ph/0605429 [abs, ps, pdf, other] :

Title: Transient pulsed radio emission from a magnetar
Authors: Fernando Camilo (1), Scott Ransom (2), Jules Halpern (1), John Reynolds (3), David Helfand (1), Neil Zimmerman (1), John Sarkissian (3) ((1) Columbia, (2) NRAO, (3) ATNF)
Comments: 6 pages, 2 figures. Submitted to Nature

Anomalous X-ray pulsars (AXPs) are neutron stars whose properties are best explained by the magnetar model. Their very large X-ray luminosities exceed those available from braking of the stellar rotation by magnetic torque, and are generated instead by decay of ultra-strong magnetic fields. The ubiquitous radio pulsars, which are powered by rotational energy loss, display no magnetar-like X-ray activity and have enduring radio emission, while magnetars have lacked any radio emission. XTE J1810-197 was identified as a transient AXP in early 2003 when its X-ray luminosity increased by a factor of ~100 compared to the quiescent level, and X-ray pulsations were observed with period 5.54s. The detection from XTE J1810-197 of a point-like radio source of unknown origin one year after the X-ray outburst further distinguishes it from all other magnetars. Here we show that XTE J1810-197 emits remarkable radio pulsations. These are sharply modulated at the rotation period with peak flux density >1Jy and are highly linearly polarised, conclusively establishing the first detection of magnetospheric radio emission from a magnetar. In contrast to ordinary pulsars, there is no evidence of radio activity prior to the 2003 X-ray outburst, and the intrinsic flux varies on short timescales with an approximately flat spectrum such that, at >20GHz, XTE J1810-197 is currently the brightest neutron star known. This discovery provides a unique opportunity to probe in detail the dynamic magnetosphere of a neutron star with extreme properties.

 

astro-ph/0605430 [abs, ps, pdf, other] :

Title: The Hubble diagram extended to z>>1: the gamma-ray properties of GRBs confirm the Lambda-CDM model
Authors: C. Firmani (1,2), V. Avila-Reese (2), G. Ghisellini (1), G. Ghirlanda (1) ((1) Osserv. Astron. di Brera, Italy; (2) Instituto de Astronomia, U.N.A.M., Mexico)
Comments: 5 pages, 4 figures included. Submitted to MNRAS Letters

Tight constraints on cosmological parameters can be obtained with standard candles spanning a range of redshifts as large as possible. We propose to treat SN Ia and long Gamma-Ray Bursts (GRBs) as a single class of candles. Taking advantage of the recent release of the Supernova Legacy Survey and {\it the recent finding of a tight correlation among the energetics and other prompt gamma-ray emission properties of GRBs}, we are able to standardize the luminosities/energetics of both classes of objects. In this way we can jointly use GRB and SNIa as cosmological probes to constrain Omega_m and Omega_L and the Dark Energy equation of state parameters through the same Bayesian method that we have, so far, applied to GRBs alone. Despite the large disparity in number (115 SNIa versus 19 GRBs) we show that the constraints on Omega_m and Omega_L are greatly improved by the inclusion of GRBs. More importantly, the result of the combined sample is in excellent agreement with the Lambda-CDM concordance cosmological model and does not require an evolving equation of state for the Dark Energy.

 

astro-ph/0605431 [abs, ps, pdf, other] :

Title: Are GRB 980425 and GRB 031203 real outliers or twins of GRB 060218?
Authors: G.Ghisellini, G.Ghirlanda, S.Mereghetti, Z.Bosnjak, F.Tavecchio, C.Firmani
Comments: submitted to MNRAS

GRB 980425 and GRB 031203 are apparently two outliers with respect to the correlation between the isotropic equivalent energy E_iso emitted in the prompt radiation phase and the peak frequency E_peak of the spectrum in a vF(v) representation (the so-called Amati relation). We discuss if these two bursts are really different from the others or if their location in the E_iso-E_peak plane is the result of other effects, such as viewing them off-axis, or through a scattering screen, or a misinterpretation of their spectral properties. The latter case seems particularly interesting after GRB 060218, that, unlike GRB 031203 and GRB 980425, had a prompt emission detected both in hard and soft X-rays which lasted ~2800 seconds. This allowed to determine its E_peak and total emitted energy. Although it shares with GRB 031203 the total energetics, it is not an outlier with respect to the Amati correlation. We then investigate if a hard-to-soft spectral evolution in GRB 031203 and GRB 980425, consistent with all the observed properties, can give rise to a time integrated spectrum with an E_peak consistent with the Amati relation.

 

astro-ph/0605432 [abs, ps, pdf, other] :

Title: No Astrophysical Dyadospheres
Authors: Don N. Page
Comments: 64 pages, LaTeX

It is shown how pair production itself would prevent the astrophysical formation of dyadospheres, hypothetical regions where the electric field exceeds the critical value for rapid Schwinger pair production. Pair production is a self-regulating process that would discharge a growing electric field, in the example of a hypothetical collapsing charged stellar core, before it reached 6% of the minimum dyadosphere value, keeping the pair production rate more than 26 orders of magnitude below the dyadosphere value, and keeping the efficiency below 0.0002(M/M_sun)^{1/2}.

 

astro-ph/0605433 [abs, ps, pdf, other] :

Title: Differential Radial Velocities and Stellar Parameters of Nearby Young Stars
Authors: Diane Paulson, Sylvana Yelda
Comments: Accepted for publication in the PASP

Radial velocity searches for substellar mass companions have focused primarily on stars older than 1 Gyr. Increased levels of stellar activity in young stars hinders the detection of solar system analogs and therefore there has been a prejudice against inclusion of young stars in radial velocity surveys until recently. Adaptive optics surveys of young stars have given us insight into the multiplicity of young stars but only for massive, distant companions. Understanding the limit of the radial velocity technique, restricted to high-mass, close-orbiting planets and brown dwarfs, we began a survey of young stars of various ages. While the number of stars needed to carry out full analysis of the problems of planetary and brown dwarf population and evolution is large, the beginning of such a sample is included here. We report on 61 young stars ranging in age from beta Pic association (~12 Myr) to the Ursa Majoris association (~300 Myr). This initial search resulted in no stars showing evidence for companions greater than ~1-2 M_Jup in short period orbits at the 3 sigma-level. Additionally, we present derived stellar parameters, as most have unpublished values. The chemical homogeneity of a cluster, and presumably of an association, may help to constrain true membership. As such, we present [Fe/H] abundances for the stars in our sample.

 

astro-ph/0605434 [abs, ps, pdf, other] :

Title: Dyadospheres Don't Form
Authors: Don N. Page
Comments: 11 pages, LaTeX, submitted for the proceedings of the VII Asia-Pacific International Conference on Gravitation and Astrophysics (ICGA7), 2005 November 23-26, National Central University, Jhongli, Taiwan, Republic of China

Pair production itself prevents the development of dyadospheres, hypothetical macroscopic regions where the electric field exceeds the critical Schwinger value. Pair production is a self-regulating process that would discharge a growing electric field, in the example of a hypothetical collapsing charged stellar core, before it reached 6% of the minimum dyadosphere value, keeping the pair production rate more than 26 orders of magnitude below the dyadosphere value.

 

astro-ph/0605435 [abs, ps, pdf, other] :

Title: The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
Authors: F. Heitsch (1), A.D. Slyz (2), J.E.G. Devriendt (2), L.W. Hartmann (1), A. Burkert (3) ((1) Dept. of Astronomy, U Michigan, (2) CRAL, Observatoire de Lyon, (3) University Observatory Munich)
Comments: 15 pages, 20 figures, accepted by ApJ

Molecular Cloud Complexes (MCCs) are highly structured and ``turbulent''. Observational evidence suggests that MCCs are dynamically dominated systems, rather than quasi-equilibrium entities. The observed structure is more likely a consequence of the formation process rather than something that is imprinted after the formation of the MCC. Converging flows provide a natural mechanism to generate MCC structure. We present a detailed numerical analysis of this scenario. Our study addresses the evolution of a MCC from its birth in colliding atomic hydrogen flows up until the point when H$_2$ may begin to form. A combination of dynamical and thermal instabilities breaks up coherent flows efficiently, seeding the small-scale non-linear density perturbations necessary for local gravitational collapse and thus allowing (close to) instantaneous star formation. Many observed properties of MCCs come as a natural consequence of this formation scenario. Since converging flows are omnipresent in the ISM, we discuss the general applicability of this mechanism, from local star formation regions to galaxy mergers.

 

astro-ph/0605436 [abs, ps, pdf, other] :

Title: A simple model for the size-evolution of elliptical galaxies
Authors: Sadegh Khochfar, Joseph Silk
Comments: 4 pages, submitted to ApJ Letters

We use semi-analytical modelling of galaxy formation to predict the redshift-size-evolution of elliptical galaxies. Using a simple model in which relative sizes of elliptical galaxies of a given mass correlate with the fraction of stars formed in a star burst during a major merger event, we are able to reproduce the observed size redshif t evolution. The size evolution is a result of the amount of cold gas available during the major merger. Mergers at high redshifts are gas-rich and produce ellipticals with smaller sizes. In particular we find a power-law relation between the sizes at different redshifts, with the power-law index giving a measure of the relative amount of dissipation during the mergers that lead to the formation of an elliptical. The size evolution is found to be stronger for more massive galaxies as they involve more gas at high redshifts when they form compared to less massive ellipticals. Local ellipticals more massive than $5 \times 10^{11}$ M$_{\odot}$ will be approximately 4 times larger than their counterparts at $z=2$. Our results indicate that the scatter in the size of similar massive present day elliptical galaxies is a result of their formation epoch, with smaller ellipticals being formed earlier.

 

astro-ph/0605437 [abs, ps, pdf, other] :

Title: First Detection of HCO+ Emission at High Redshift
Authors: Dominik A. Riechers (1), Fabian Walter (1), Christopher L. Carilli (2), Axel Weiss (3), Frank Bertoldi (4), Karl M. Menten (3), Kirsten K. Knudsen (1), Pierre Cox (5)- ((1)-MPIA Heidelberg, Germany; (2)-NRAO Socorro, USA; (3)-MPIfR Bonn, Germany; (4)-AIfA Bonn, Germany; (5)-IRAM Grenoble, France)
Comments: 5 pages, 3 figures, ApJL, in press (accepted May 17, 2006)

We report the detection of HCO+(1-0) emission towards the Cloverleaf quasar (z=2.56) through observations with the Very Large Array. This is the first detection of ionized molecular gas emission at high redshift (z>2). HCO+ emission is a star formation indicator similar to HCN, tracing dense molecular hydrogen gas (n(H_2) ~= 10^5 cm^{-3}) within star-forming molecular clouds. We derive a lensing-corrected HCO+ line luminosity of L'(HCO+) = 3.5 x 10^9 K km/s pc^2. Combining our new results with CO and HCN measurements from the literature, we find a HCO+/CO luminosity ratio of 0.08 and a HCO+/HCN luminosity ratio of 0.8. These ratios fall within the scatter of the same relationships found for low-z star-forming galaxies. However, a HCO+/HCN luminosity ratio close to unity would not be expected for the Cloverleaf if the recently suggested relation between this ratio and the far-infrared luminosity were to hold. We conclude that a ratio between HCO+ and HCN luminosity close to 1 is likely due to the fact that the emission from both lines is optically thick and thermalized and emerges from dense regions of similar volumes. The CO, HCN and HCO+ luminosities suggest that the Cloverleaf is a composite AGN--starburst system, in agreement with the previous finding that about 20% of the total infrared luminosity in this system results from dust heated by star formation rather than heating by the AGN. We conclude that HCO+ is potentially a good tracer for dense molecular gas at high redshift.

 

astro-ph/0605438 [abs, ps, pdf, other] :

Title: Penetrating the Deep Cover of Compton Thick Active Galactic Nuclei
Authors: N. A. Levenson, T. M. Heckman, J. H. Krolik, K. A. Weaver, P. T. Zycki
Comments: To appear in ApJ, September 1, 2006

We analyze observations obtained with the Chandra X-ray Observatory of bright Compton thick active galactic nuclei (AGNs), those with column densities in excess of 1.5 x 10^{24} cm^{-2} along the lines of sight. We therefore view the powerful central engines only indirectly, even at X-ray energies. Using high spatial resolution and considering only galaxies that do not contain circumnuclear starbursts, we reveal the variety of emission AGNs alone may produce. Approximately 1% of the continuum's intrinsic flux is detected in reflection in each case. The only hard X-ray feature is the prominent Fe K alpha fluorescence line, with equivalent width greater than 1 keV in all sources. The Fe line luminosity provides the best X-ray indicator of the unseen intrinsic AGN luminosity. In detail, the morphologies of the extended soft X-ray emission and optical line emission are similar, and line emission dominates the soft X-ray spectra. Thus, we attribute the soft X-ray emission to material that the central engines photoionize. Because the resulting spectra are complex and do not reveal the AGNs directly, crude analysis techniques such as hardness ratios would mis-classify these galaxies as hosts of intrinsically weak, unabsorbed AGNs and would fail to identify the luminous, absorbed nuclei that are present. We demonstrate that a three-band X-ray diagnostic can correctly classify Compton thick AGNs, even when significant soft X-ray line emission is present. The active nuclei produce most of the galaxies' total observed emission over a broad spectral range, and much of their light emerges at far-infrared wavelengths. Stellar contamination of the infrared emission can be severe, however, making long-wavelength data alone unreliable indicators of the buried AGN luminosity.

 

astro-ph/0605439 [abs, ps, pdf, other] :

Title: The 21cm Signature of the First Stars
Authors: Xuelei Chen, Jordi Miralda-Escude
Comments: 18 2col pages including 14 figures, submitted to ApJ

We predict the 21-cm signature of the first metal-free stars. The soft X-rays emitted by these stars penetrate the atomic medium around their host halos, generating Lyman alpha photons that couple the spin and kinetic temperatures. These creates a region we call the Lyman alpha sphere, visible in 21-cm against the CMB, which is much larger than the HII region produced by the same star. The spin and kinetic temperatures are strongly coupled before the X-rays can substantially heat the medium, implying that a strong 21-cm absorption signal from the adiabatically cooled gas in Hubble expansion around the star is expected when the medium has not been heated previously. A central region of emission from the gas heated by the soft X-rays is also present although with a weaker signal than the absorption. The Lyman alpha sphere is a universal signature that should be observed around any first star illuminating its vicinity for the first time. The 21-cm radial profile of the Lyman alpha sphere can be calculated as a function of the luminosity, spectrum and age of the star. For a star of a few hundred solar masses and zero metallicity (as expected for the first stars), the physical radius of the Lyman alpha sphere can reach tens of kiloparsecs. The first metal-free stars should be strongly clustered because of high cosmic biasing; this implies that the regions producing a 21-cm absorption signal may contain more than one star and will generally be irregular and not spherical, because of the complex distribution of the gas. We discuss the feasiblity of detecting these Lyman alpha spheres, which would be present at redshifts $z\sim 30$ in the Cold Dark Matter model. Their observation would represent a direct proof of the detection of a first star.

 

astro-ph/0605440 [abs, ps, pdf, other] :

Title: Effects of primordial helicity on CMB
Authors: Tina Kahniashvili (1,2) ((1)Kansas State University (USA), (2) Center for Plasma Astrophysics (Georgia))
Comments: for Proceedings of CMB Workshop at Irvine, March 2006

I present here a brief overview of the effects caused by parity violating cosmological sources (such as magnetic or kinetic helicity) on the CMB fluctuations. I discuss also primordial helicity induced relic gravitational waves. All these effects can serve as cosmological tests for primordial helicity detection.

 

astro-ph/0605441 [abs, ps, pdf, other] :

Title: The peculiar sdB NGC6121-V46: A low-mass double degenerate ellipsoidal variable in a globular cluster
Authors: S. J. O'Toole, R. Napiwotzki, U. Heber, H. Drechsel, S. Frandsen, F. Grundahl, H. Bruntt

The variable sdB known as V46 in the globular cluster M4 has remained enigmatic since its discovery almost 10 years ago. We present here radial velocity measurements obtained from medium-resolution VLT/FORS2 spectra that show variations at twice the period of the luminosity changes. This implies that the system is an ellipsoidal variable. Unlike the other sdB binaries of this nature, the fundamental parameters of this star we derive suggest that it lies below the Zero Age Extreme Horizontal Branch. From the cluster distance and the gravity we determine the mass of V46 to be ~0.19Msun. This is too low to sustain core helium burning. From the mass function we derive a lower limit for the companion of only 0.26Msun. We discuss the star's origin in the context of close binary evolution in the field and globular clusters.

 

astro-ph/0605442 [abs, ps, pdf, other] :

Title: Noncommutative KKLMMT Model
Authors: Qing-Guo Huang
Comments: 9 pages, 2 figures

In the noncommutative space-time the fine tuning in KKLMMT model can be significantly released and a nice running of spectral index fitting the WMAP three year data can be achieved. The fitting results show that the noncommutative mass scale is roughly $5\times 10^{14}$ Gev. The string mass scale is higher than the noncommutative scale unless the string coupling is smaller than $10^{-10}$.

 

astro-ph/0605443 [abs, ps, pdf, other] :

Title: The Nainital-Cape Survey -- II:Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results
Authors: Santosh Joshi (1,2), D. L. Mary (2,3), Peter Martinez (4), D. W. Kurtz (5) V. Girish (6), S. Seetha (7), Ram Sagar (2), B. N. Ashoka (7) ((1) Inter-University Centre for Astronomy and Astrophysics (IUCAA) Ganeshkhind, Pune, India, (2) Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital, India, (3) Astronomisches Rechen-Institut am Zentrum fuer Astronomie, Moenchhofstrasse, Heidelberg, Germany, (4) South African Astronomical Observatory (SAAO), South Africa, (5) Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK, (6) Tata Institute of Fundamental Research (TIFR), Homi Bhabha Road, Mumbai, India, (7) ISRO Satellite Center, Airport Road, Bangalore, India)
Comments: 14 pages, 13 figures, Accepted for publication in A&A

To search photometric variability in chemically peculiar A type stars in the northern hemisphere. High-speed photometric observations of Ap and Am star candidates have been carried out from ARIES (Manora Peak, Nainital) using a three-channel fast photometer attached to the ARIES 104-cm Sampurnanand telescope. This paper presents three new variables: HD 113878, HD 118660 and HD 207561. During the time span of the survey (1999 December to 2004 January) pulsations of the $\delta$ Sct type were also found for the two evolved Am stars HD 102480 and HD 98851, as reported in Joshi et al. (2002, 2003). Additionally, we present 140 null results of the survey for this time span. The star HD 113878 pulsates with a period of 2.31 hr, which is typical of $\delta$ Sct stars. HD 118660 exhibits multi-periodic variability with a prominent period of nearly 1 hr. These periods need to be investigated and make HD 118660 a particularly interesting target for further observations. For HD 207561, a star classified as Am, a probable pulsation with a period of 6 min was found in the light curves obtained on two consecutive nights. Both HD 102480 and HD 98851 exhibit unusual alternating high and low amplitude maxima, with a period ratio of 2:1. The analysis of the null results confirms the photometric quality of the Nainital

 

astro-ph/0605444 [abs, ps, pdf, other] :

Title: Small-scale magnetic buoyancy and magnetic pumping effects in a turbulent convection
Authors: I. Rogachevskii, N. Kleeorin
Comments: 13 pages, 4 figure, REVTEX4, Geophysical and Astrophysical Fluid Dynamics, in press

We determine the nonlinear drift velocities of the mean magnetic field and nonlinear turbulent magnetic diffusion in a turbulent convection. We show that the nonlinear drift velocities are caused by the three kinds of the inhomogeneities, i.e., inhomogeneous turbulence; the nonuniform fluid density and the nonuniform turbulent heat flux. The inhomogeneous turbulence results in the well-known turbulent diamagnetic and paramagnetic velocities. The nonlinear drift velocities of the mean magnetic field cause the small-scale magnetic buoyancy and magnetic pumping effects in the turbulent convection. These phenomena are different from the large-scale magnetic buoyancy and magnetic pumping effects which are due to the effect of the mean magnetic field on the large-scale density stratified fluid flow. The small-scale magnetic buoyancy and magnetic pumping can be stronger than these large-scale effects when the mean magnetic field is smaller than the equipartition field. We discuss the small-scale magnetic buoyancy and magnetic pumping effects in the context of the solar and stellar turbulent convection. We demonstrate also that the nonlinear turbulent magnetic diffusion in the turbulent convection is anisotropic even for a weak mean magnetic field. In particular, it is enhanced in the radial direction. The magnetic fluctuations due to the small-scale dynamo increase the turbulent magnetic diffusion of the toroidal component of the mean magnetic field, while they do not affect the turbulent magnetic diffusion of the poloidal field.

 

astro-ph/0605445 [abs, ps, pdf, other] :

Title: The X-ray afterglow flat segment in short GRB 051221A: Energy injection from a millisecond magnetar?
Authors: Yizhong Fan, Dong Xu
Comments: 4 pages including 1 figure

In GRB 051221A, an X-ray afterglow flat segment lasting $\sim 10^4$ seconds represents the first clear case of strong energy injection in the external shock of a short GRB afterglow. In this work, we show that a millisecond pulsar with dipole magnetic field $\sim 10^{14}$ Gauss could well account for that energy injection. The good quality X-ray flat segment thus suggests that the central engine of this short burst may be a millisecond magnetar.

 

astro-ph/0605446 [abs, ps, pdf, other] :

Title: On the validity of the 630 nm Fe I nm lines for the magnetometry of the internetwork quiet Sun
Authors: M. J. Martinez Gonzalez, M. Collados, B. Ruiz Cobo
Comments: Accepted for publication in A&A

The purpose of this work is to analyze the reliability of the magnetic field strengths inferred from the 630 nm pair of Fe I lines at internetwork quiet Sun regions. Some numerical experiments have been performed that demonstrate the inability of these lines to recover the magnetic field strength in such low flux solar regions. It is shown how different model atmospheres, with magnetic field strengths ranging from few hundred Gauss to kiloGauss, give rise to Stokes profiles that can not be distinguished. The reasons for this degeneracy are discussed.

 

astro-ph/0605447 [abs, ps, pdf, other] :

Title: UCDs - a mixed bag of objects
Authors: Michael Hilker (AIfA, Bonn)
Comments: 8 pages, 3 figures, invited review for "Globular Clusters - Guides to Galaxies", Concepcion, Chile, March 6th-10th, 2006, eds. T. Richtler & S. Larsen (Springer)

The name "Ultra-Compact Dwarf Galaxy" (UCD) was invented for a new type of astronomical object that has been discovered in cores of nearby galaxy clusters a decade ago. UCDs resemble globular clusters, but are up to 100 times more massive and slightly more extended. Their luminosities are comparable to those of nuclei of the most massive dwarf ellipticals or late-type spirals. Various formation scenarios have been brought forward to explain the origin and evolution of UCDs. Two of them seem to be most promising: first, UCDs might be the remnant nuclei of galaxies that have been disrupted in the cluster environment. Second, UCDs might have formed from the agglomeration of many young, massive star clusters that were created during ancient merger events. In this contribution, I review the discovery history of UCDs, summarize their observational properties in the fundamental plane of stellar systems and discuss the implications for the different formation scenarios based on our current knowledge about these enigmatic objects.

 

astro-ph/0605448 [abs, ps, pdf, other] :

Title: Optical spectroscopy of BL Lacertae objects. Broad lines, companion galaxies and redshift lower limits
Authors: B. Sbarufatti (1), R. Falomo (2), A. Treves (1), J. Kotilainen (3). (1: Universita` dell'Insubria, Como, Italy, 2: INAF - Osservatorio Astronomico di Padova, Italy; 3: Tuorla Observatory, Piikkioo, Finland)
Comments: Accepted for publication on Astronomy & Astrophysics, 15 pages, 8 figures

Aims: We present optical spectroscopy of a sample of BL Lac objects, to determine their redshift, to study their broad emission line properties and to characterize their close environment. Methods: Twelve objects were observed using the ESO 3.6m and the NOT 2.5m telescopes, obtaining spectra for the BL Lacs and for nearby sources. Results: For seven objects, nuclear emission lines and/or absorption lines from the host galaxy were detected. In all the four cases where absorption lines were revealed, the host galaxy has been resolved with HST or ground-based imaging. The broad H_alpha luminosities (or their upper limits) of the BL Lacs are similar to those of radio-loud quasars. For two BL Lacs, spectroscopy of close companions indicates that they are at the redshift of the BL Lacs, and therefore physically associated and likely interacting. Five BL Lacs have a featureless spectrum. In these cases, we apply a new technique to derive lower limits for their redshift. which are consistent with lower limits deduced from imaging.

 

astro-ph/0605449 [abs, ps, pdf, other] :

Title: Magnetars as cooling neutron stars with internal heating
Authors: A.D. Kaminker (1), D.G. Yakovlev (1), A.Y. Potekhin (1), N. Shibazaki (2), P.S. Shternin (1), O.Y. Gnedin (3) ((1) Ioffe Inst., (2) Rikkyo Univ., (3) Ohio State Univ.)
Comments: 8 pages, 5 figures, submitted to MNRAS

We study thermal structure and evolution of magnetars as cooling neutron stars with a phenomenological heat source in a spherical internal layer. We explore the location of this layer as well as the heating rate that could explain high observable thermal luminosities of magnetars and would be consistent with the energy budget of neutron stars. We conclude that the heat source should be located in an outer magnetar's crust, at densities rho < 5e11 g/cm^3, and should have the heat intensity of the order of 1e20 erg/s/cm^3. Otherwise the heat energy is mainly emitted by neutrinos and cannot warm up the surface.

 

astro-ph/0605450 [abs, ps, pdf, other] :

Title: Crossing the phantom divide without phantom matter
Authors: Luis P. Chimento, Ruth Lazkoz, Roy Maartens, Israel Quiros
Comments: 5 pages, 5 figures, revtex4

A class of braneworld models can lead to phantom-like acceleration of the late universe, but without the need for any phantom matter. In the simplest models, the universe contains only cold dark matter and a cosmological constant. We generalize these models by introducing a quintessence field. The new feature in our models is that quintessence leads to a crossing of the phantom divide, $w=-1$. This is a purely gravitational effect, and there is no phantom instability. Furthermore, the Hubble parameter is always decreasing, and there is no big rip singularity in the future.

 

astro-ph/0605451 [abs, ps, pdf, other] :

Title: The messy environment of Mrk 6
Authors: N.J. Schurch, R.E. Griffiths, R.S. Warwick
Comments: 11 pages, 8 figures. Accepted for publication by MNRAS 05/2006

In recent years it has become clear that understanding the absorption present in AGN is essential given its bearing on unification models. We present the most recent XMM-Newton observation of Mrk 6, with the goal of understanding the nature and origin of the complex absorption intrinsic to this source. X-ray spectral fitting shows that a simple warm absorption model provides an equally good statistical representation of the CCD data as a partial covering model. Furthermore, once the RGS data are included in the spectral fitting, the simple warm absorber model provides a very good fit to the data, without increasing the complexity of the model, in contrast with the partial covering model which requires the addition of either a low metalicity (<0.03 solar) thermal plasma or low temperature blackbody emission in order to provide a similar quality fit. The warm absorber is also a considerably more natural way to explain the variability observed in the X-ray absorbing column density between the previous XMM-Newton observation and this one, requiring only a second, higher column density, higher ionisation, absorber to be present during the previous XMM-Newton observation. In comparison, the partial covering models which requires moving, clumpy, material relatively close to the source that result in two distinct lines of sight, with separate absorbing columns that each vary considerably without any associated change in their covering fractions, in order to explain the observed variability. We associate the warm absorber either with an accretion disk wind with densities of ~10^9 /cm^3, or with an ionised `skin' or atmosphere of the molecular torus with densities of ~10^3 - 10^5 /cm^3.

 

astro-ph/0605452 [abs, ps, pdf, other] :

Title: Hubble Space Telescope Observations of Star Clusters in M101
Authors: P. Barmby (CfA), K.D. Kuntz (JHU/GSFC), J.P. Huchra (CfA), J.P. Brodie (UCO/Lick)
Comments: AJ in press; 22 pages including 9 figures. See this http URL for PR image using these data

Hubble Space Telescope Advanced Camera for Surveys (ACS) images are used to identify and study star cluster candidates in the nearby spiral galaxy M101. About 3000 round, slightly-resolved cluster candidates are identified in 10 ACS pointings covering an area of 106 arcmin^2. The cluster candidates' color and size distributions are consistent with those of star clusters in other nearby spirals. The majority of the M101 candidates are blue and more likely to be associated with the galaxy's spiral arms, implying that they are young. The galaxy-luminosity-normalized number of `young massive clusters' in M101 is similar to that found in other spirals, as is the cluster density at a fiducial absolute magnitude. We confirm a previous finding that M101 has a large number of faint, red star clusters: if these are old globular clusters then this galaxy has a very large globular cluster population. More plausible is that the faint red clusters are reddened young clusters; their colors and luminosities are also consistent with this explanation.

 

astro-ph/0605453 [abs, ps, pdf, other] :

Title: Quasars and Galaxy Clusters Paired Across NGC 4410
Authors: H. Arp, E.M. Burbidge, D. Carosati
Comments: criticisms appended at end

The aim is to investigate the region of the sky around NGC4410/Mrk1325 for objects which are physically associated with this active, double nucleus galaxy. We use archived data to study the placement, brightness, X-ray properties and redshifts of objects within 60' of the bright, central galaxy. It is found that pairs of quasars are aligned across NGC 4410 which, if ejected from it, have equal and opposite ejection velocities and fall very close to the quantized Karlsson redshift peaks for quasars. X-ray sources and Abell galaxy clusters at higher redshifts appear elongated along directions away from NGC4410.

 

astro-ph/0605454 [abs, ps, pdf, other] :

Title: The evolutionary state of the southern dense core Cha-MMS1
Authors: A. Belloche, B. Parise, F.F.S. van der Tak, P. Schilke, S. Leurini, R. Guesten, L.-A. Nyman
Comments: Accepted by Astronomy & Astrophysics as a letter, to appear in the special issue on the APEX first results

Aims: Our goal is to set constraints on the evolutionary state of the dense core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: We analyze molecular line observations carried out with the new submillimeter telescope APEX. We look for outflow signatures around the dense core and probe its chemical structure, which we compare to predictions of models of gas-phase chemistry. We also use the public database of the Spitzer Space Telescope (SST) to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F, which are at the same distance. Results: We measure a large deuterium fractionation for N2H+ (11 +/- 3 %), intermediate between the prestellar core L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+ (2.5 +/- 0.9 %), which is probably the result of depletion removing HCO+ from the high-density inner region. Our CO(3-2) map reveals the presence of a bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not find evidence for an outflow powered by Cha-MMS1. We also report the detection of Cha-MMS1 at 24, 70 and 160 microns by the instrument MIPS of the SST, at a level nearly an order of magnitude lower than IRAM 04191 and L1521F. Conclusions: Cha-MMS1 appears to have already formed a compact object, either the first hydrostatic core at the very end of the prestellar phase, or an extremely young protostar that has not yet powered any outflow, at the very beginning of the Class 0 accretion phase.

 

astro-ph/0605455 [abs, ps, pdf, other] :

Title: Rates and properties of type Ia supernovae as a function of mass and star-formation in their host galaxies
Authors: M. Sullivan, D. Le Borgne, C. J. Pritchet, A. Hodsman, J. D. Neill, D. A Howell, R. G Carlberg, P. Astier, E. Aubourg, D. Balam, S. Basa, A. Conley, S. Fabbro, D. Fouchez, J. Guy, I. Hook, R. Pain, N. Palanque-Delabrouille, K. Perrett, N. Regnault, J. Rich, R. Taillet, S. Baumont, J. Bronder, R. S. Ellis, M. Filiol, V. Lusset, S. Perlmutter, P. Ripoche, C. Tao
Comments: Accepted for publication in ApJ

(ABRIDGED) We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar populations, with observed rates that depend on the stellar mass and mean star-formation rates (SFRs) of their host galaxies. Models where the SN Ia rate depends solely on host galaxy stellar mass are ruled out with 99% confidence. Our analysis is based on 100 spectroscopically-confirmed SNe Ia, plus 24 photometrically-classified events, all from the Supernova Legacy Survey (SNLS) and distributed over 0.2<z<0.75. Using multi-band photometry, we estimate stellar masses and SFRs for the SN Ia host galaxies by fitting their broad-band spectral energy distributions with the galaxy spectral synthesis code, PEGASE.2. We show that the SN Ia rate per unit mass is proportional to the specific SFR of the parent galaxies -- more vigorously star-forming galaxies host more SNe Ia per unit stellar mass, broadly equivalent to the trend of increasing SN Ia rate in later-type galaxies seen in the local universe. Following earlier suggestions for a simple "two-component" model approximating the SN Ia rate, we find bivariate linear dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of the host systems. We also demonstrate a dependence of distant SN Ia light-curve shapes on star-formation in the host galaxy, similar to trends observed locally. Passive galaxies, with no star-formation, preferentially host faster-declining/dimmer SNe Ia, while slower-declining/brighter events are only found in systems with ongoing star-formation. We model the light-curve width distribution in star-forming galaxies as the sum of a young component, and an old component taken from the distribution in non-star-forming galaxies.

 

astro-ph/0605456 [abs, ps, pdf, other] :

Title: Off-axis emission from relativistic plasma flows
Authors: E.V. Derishev (1), F.A. Aharonian (2), Vl.V. Kocharovsky (1) ((1) Institute of Applied Physics, Nizhny Novgorod, Russia, (2) Max-Planck-Institut fuer Kernphysik, Heidelberg, Germany)
Comments: Submitted to the Astrophysical Journal

We show that there is no universal law describing how the spectra and luminosity of synchrotron and inverse Compton radiation from relativistic jets change with increasing observation angle. Instead, the physics of particle acceleration leaves pronounced imprints in the observed spectra and allows for a freedom in numerous modifications of them. The impact of these effects is the largest for high-energy radiation and depends on the details of particle acceleration mechanism(s), what can be used to discriminate between different models. Generally, the beam patterns of relativistic jets in GeV-TeV spectral domain are much wider than the inverse Lorentz factor. The off-axis emission in this energy range appear to be brighter, have much harder spectra and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone.
The implications include the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars, and the prediction of GeV-TeV afterglow from transient jet sources, such as Gamma-Ray Bursts. We also discuss the phenomenon of beam-pattern broadening in application to neutrino emission.

 

astro-ph/0605457 [abs, ps, pdf, other] :

Title: Resonant Relaxation near the Massive Black Hole in the Galactic Center
Authors: Clovis Hopman, Tal Alexander (Weizmann)
Comments: Proceedings of the Galactic Center Workshop 2006

The coherent torques between stars on orbits near massive black holes (MBHs) lead to resonant angular momentum relaxation. Due to the fact that orbits are Keplerian to good approximation, the torques efficiently change the magnitude of the angular momenta and rotate the orbital inclinations. As a result the stars are rapidly randomized. The galactic MBH is a good system for the observational study of resonant relaxation. The age of the young B-stars at a distance of $\sim0.01 pc$ from the MBH is comparable to the resonant relaxation time, implying that resonant relaxation may have played an important role in their dynamical structure. In contrast, the O-stars in the stellar disks at $\sim0.1 pc$ are younger than the resonant relaxation time, as required by their dynamical coherence. Resonant relaxation dynamics dominates the event rate of gravitational wave (GW) emission from inspiraling stars into MBHs of masses comparable to the Galactic MBH. Resonant relaxation leads to rates $\lesssim 10$ times higher than those predicted by 2-body relaxation, which would improve the prospects of detecting these events by future GW detectors, such as LISA.

 

astro-ph/0605458 [abs, ps, pdf, other] :

Title: Properties of Post-AGB stars
Authors: P. Garcia-Lario
Comments: 8 pages, 4 figures, invited review to appear in Proc. IAU Symp. 234, Planetary Nebulae in Our Galaxy and Beyond (3-7 Apr 2006), eds. M.J. Barlow & R.H. Mendez (Cambridge Univ. Press)

A review is presented of the most relevant results obtained in the last few years on this rare class of astronomical sources. Multi-wavelength analysis of an increasing number of post-AGB stars reveal that they constitute a more inhomogeneous population of stars than previously thought. The new data available allow us to study these sources with unprecedent spatial resolution and to extend our spectroscopic knowledge in a systematic way to the infrared for the first time, where crucial information is contained on the chemical composition of the gas and dust in their circumstellar shells. The overall infrared properties derived from ISO and Spitzer data can be used to trace the mass loss history and the chemical evolution of the ejected material. The new results impose severe observational constraints to the current nucleosynthesis models and suggest that the evolution is mainly determined not only by the initial mass but also by the metallicity of the progenitor star. Post-AGB samples are likely to grow in the near future with the advent of new data from space facilities like Spitzer or Akari. Studies of post-AGB stars in the galactic halo, the Magellanic Clouds and other galaxies of the Local Group will certainly improve our knowledge on the evolutionary connections between AGB stars and PNe.

 

astro-ph/0605459 [abs, ps, pdf, other] :

Title: Microquasar hadronic jets at very high-energy gamma-rays
Authors: Bosch-Ramon, V., Aharonian, F. A., Paredes, J. M
Comments: 4 pages, 2 figures, 1 Table. Proceedings of the Cherenkov 2005 Conference, 27-29 April 2005 - Ecole Polytechnique, Palaiseau, France; edited by B. Degrange, G. Fontaine

Microquasars (MQs) present emission over the whole spectrum, from radio wavelengths to gamma-rays. The microquasar spectral energy distribution is very complex, being a signature of the different physical processes that generate the radiation emitted by these objects. In this work, we estimate the amount of broad-band emission produced by relativistic protons, released from the jet of a MQ, interacting with high density regions of the ISM. We show that a two components source, the microquasar itself and the region of interaction between the jets and the ISM, could be unveiled by the new instruments at high-energy and very high-energy gamma-rays.

 

astro-ph/0605460 [abs, ps, pdf, other] :

Title: Deep spectroscopy of 9C J1503+4528: a very young CSS radio source at z=0.521
Authors: K.J. Inskip, D. Lee, Garret Cotter, T.J. Pearson, A.C.S. Readhead, R.C. Bolton, C. Chandler, G. Pooley, J.M. Riley, E.M. Waldram
Comments: Accepted for publication in MNRAS. 13 pages, 13 figures (3 in colour), 2 tables

9C J1503+4528 is a very young CSS radio galaxy, with an age of order 10^4 years. This source is therefore an ideal laboratory for the study ofthe intrinsic host galaxy/IGM properties, interactions between the radio source and surrounding ISM, links between star formation and AGN activity and the radio source triggering mechanism. Here we present the results of a spectroscopic analysis of this source, considering each of these aspects of radio source physics.
We find that shock ionization by the young radio source is important in the central regions of the galaxy on scales similar to that of the radio source itself, whilst evidence for an AGN ionization cone is observed at greater distances. Line and continuum features require the presence of a young stellar population, the best-fit model for which implies an age of 5x10^6 years, significantly older than the radio source.
Most interestingly, the relative sizes of radio source and extended emission line region suggest that both AGN and radio source are triggered at approximately the same time.
If both the triggering of the radio source activity and the formation of the young stellar population had the same underlying cause, this source provides a sequence for the events surrounding the triggering process. We propose that the AGN activity in 9C J1503+4528 was causedby a relatively minor interaction, and that a super-massive black hole powering the radio jets must have been in place before the AGN was triggered.

 

astro-ph/0605461 [abs, ps, pdf, other] :

Title: Elastic or magnetic? A toy model for global magnetar oscillations with implications for QPOs during flares
Authors: Kostas Glampedakis, Lars Samuelsson, Nils Andersson
Comments: 5 pages, 2 eps figures, submitted to MNRAS Letters

We use a simple toy-model to discuss global MHD modes of a neutron star, taking into account the magnetic coupling between the elastic crust and the fluid core. Our results suggest that the notion of pure torsional crust modes is not useful for the coupled system, all modes excite Alfven waves in the core. However, we also show that the modes that are most likely to be excited by a fractured crust, eg. during a magnetar flare, are such that the crust and the core oscillate in concert. For our simple model, the frequencies of these modes are similar to the ``pure crustal'' frequencies. In addition, our model provides a natural explanation for the presence of lower frequency ($< 30$~Hz) QPOs seen in the December 2004 giant flare of SGR 1806-20.

 

astro-ph/0605462 [abs, ps, pdf, other] :

Title: The Compton-Getting effect on ultra-high energy cosmic rays of cosmological origin
Authors: M. Kachelriess, P.D. Serpico
Comments: 4 pages, no figure

Deviations from isotropy have been a key tool to identify the origin and the primary type of cosmic rays at low energies. We suggest that the Compton-Getting effect can play a similar role at ultra-high energies: If at these energies the cosmic ray flux is dominated by sources at cosmological distances, then the movement of the Sun relative to the cosmic microwave background frame induces a dipole anisotropy at the 0.6% level. The energy dependence and the orientation of this anisotropy provide important information about the transition between galactic and extragalactic cosmic rays, the charge of the cosmic ray primaries, the galactic magnetic field and, at the highest energies, the energy-loss horizon of cosmic rays. A 3-sigma detection of this effect requires around 10^6 events in the considered energy range and is thus challenging but not impossible with present detectors. As a corollary we note that the Compton-Getting effect allows one also to constrain the fraction of the diffuse gamma-ray background emitted by sources at cosmological distance, with promising detection possibilities for the GLAST satellite.

 

astro-ph/0605463 [abs, ps, pdf, other] :

Title: A 0.8-2.4 microns spectral atlas of Active Galactic Nuclei
Authors: R. Riffel A. Rodriguez-Ardila M. G. Pastoriza
Comments: 39 pages, 17 figures, accepted for publication in Astronomy and Astrophysics (15/05/2006)

Aims: Present a near-infrared spectral atlas of 47 active galactic nuclei (AGN), of all degrees of activity, in the wavelength interval of 0.8-2.4 microns, including the fluxes of the observed emission lines. Analyze the espectroscopic properties of the continuum and emission line spectra of the sources.
Methods: In order to exclude aperture and seeing effects we use near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8-2.4 microns), taking simultaneously the JHK-bands spectra.
Results: We present the most extensive NIR spectral atlas of AGN made up to date aimed at creating a suitable database to study the continuum and line emission properties of these objects in a region full of interesting features. Overall we conclude that the shape of the continuum of QSOs and Seyfert 1's are similar, being essentially flat in H and K band, in the J band, a strong variation is found. In Seyfert 2 galaxies, the continuum smoothly decreases from 1.2 microns redwards in almost all sources. In J, it smoothly rises bluewards in some sources while in others a small decreased is observed. The spectra are dominated by strong emission features of H I, He I, He II, [S III] and conspicuous forbidden lines of low and high ionization species. Molecular lines of H2 are common features to most objects. The absence of O I and Fe II lines in Seyfert 2 galaxies give observational support to the fact that these lines are formated in the outermost portion of the broad line region. [P II] and coronal lines are detected in all degrees of activity. The [Fe II] 12570A/16436\A line ratio becomes as a reliable reddening indicator for Seyfert galaxies.

 

astro-ph/0605464 [abs, ps, pdf, other] :

Title: Mid-Infrared Spectroscopy of Disks around Classical T Tauri Stars
Authors: W. J. Forrest, B. Sargent, E. Furlan, P. D'Alessio, N. Calvet, L. Hartmann, K. I. Uchida, J. D. Green, D. M. Watson, C. H. Chen, F. Markwick-Kemper, L. D. Keller, G. C. Sloan, T. L. Herter, B. R. Brandl, J. R. Houck, D. J. Barry, P. Hall, P. W. Morris, J. Najita, P. C. Myers
Comments: AASTEX, 10 pages text, 2 figures, 1 table, published September 2004 in The Astrophysical Journal Supplement Series
Journal-ref: The Astrophysical Journal Supplement Series, 2004, vol. 154, p. 443

We present the first Spitzer Infrared Spectrograph (IRS; The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation funded by NASA through the Jet Propulsion Laboratory and the Ames Research Center.) observations of the disks around classical T Tauri stars: spectra in the 5.2-30 micron range of six stars. The spectra are dominated by emission features from amorphous silicate dust, and a continuous component from 5 to 8 microns that in most cases comprises an excess above the photosphere throughout our spectral range. There is considerable variation in the silicate feature/continuum ratio, which implies variations of inclination, disk flaring, and stellar mass accretion rate. In most of our stars, structure in the silicate feature suggests the presence of a crystalline component. In one, CoKu Tau/4, no excess above the photosphere appears at wavelengths shortward of the silicate features, similar to 10 Myr old TW Hya, Hen 3-600, and HR 4796A. This indicates the optically thick inner disk is largely absent. The silicate emission features with peaks at 9.7 and 18 microns indicate small dust grains are present. The extremely low 10-20 micron color temperature of the dust excess, 135 K, indicates these grains are located more than 10 AU from the star. These features are suggestive of gravitational influence by planets or close stellar companions and grain growth in the region within 10 AU of the star, somewhat surprising for a star this young (1 Myr).

 

astro-ph/0605465 [abs, ps, pdf, other] :

Title: Reionization from cosmic string loops
Authors: Ken D. Olum, Alexander Vilenkin
Comments: 7 pp., RevTeX, no figures

Loops formed from a cosmic string network at early times would act as seeds for early formation of halos, which would form galaxies and lead to early reionization. With reasonable guesses about astrophysical and string parameters, the cosmic string scale $G\mu$ must be no more than about $3\times 10^{-8}$ to avoid conflict with the reionization redshift found by WMAP. The bound is much stronger for superstring models with a small string reconnection probability. For values near the bound, cosmic string loops may explain the discrepancy between the WMAP value and theoretical expectations.

 

astro-ph/0605466 [abs, ps, pdf, other] :

Title: Leptonic emission from microquasar jets: from radio to very high-energy gamma-rays
Authors: Bosch-Ramon, V., Paredes, J. M., Romero, G. E
Comments: 2 pages, 1 figure. Proceedings of the conference: "International Astronomical Union Symposium No. 230: Populations of High Energy Sources in Galaxies". Edited by Evert J.A. Meurs & Giuseppina Fabbiano

Microquasars are sources of very high-energy gamma-rays and, very probably, high-energy gamma-ray emitters. We propose a model for a jet that can allow to give accurate observational predictions for jet emission at different energies and provide with physical information of the object using multiwavelength data.

 

astro-ph/0605467 [abs, ps, pdf, other] :

Title: Elementary Physics in the Cellular Automaton Universe
Authors: Robert L. kurucz (Harvard-Smithsonian Center for Astrophysics)
Comments: 13 pages

General relativity is a mathematical model that uses sophisticated geometry to describe simple physics. It agrees with experiment in the few tests that can be made, but the whole edifice is not physics. Instead of using observations to test that model, I derive a simple empirical model of elementary physics and cosmology from the observations. The observations imply that the universe is a finite cellular automaton; that there is no curved space; that fundamental particles are massless; that "massy" particles, including electrons, are composed of fundamental particles; that gravitational mass is inertial mass; that black holes are made from neutrons compressed into bosons; that the universe was produced from cold compressed particles, not radiation; and that the universe is not expanding.

 

astro-ph/0605468 [abs, ps, pdf, other] :

Title: {Millimeter Multiplicity in NGC 6334 I and I(N)
Authors: T.R. Hunter, C.L. Brogan, S.T. Megeath, K.M. Menten, H. Beuther, S. Thorwirth
Comments: 6 pages, 3 figures, to appear in The Astrophysical Journal

Using the Submillimeter Array (SMA), we have imaged the 1.3 millimeter continuum emission at the center of the massive star-forming regions NGC 6334 I and I(N). In both regions, the SMA observations resolve the emission into multiple millimeter sources, with most of the sources clustered into areas only 10,000 AU in diameter. Toward NGC 6334 I, we find four compact sources: the two brightest (I-SMA1 and I-SMA2) are associated with previously-known ammonia cores; I-SMA3 is coincident with the peak of the compact HII region (NGC 6334 F); and I-SMA4 is a newly-discovered object. While I-SMA3 exhibits a mixture of free-free and dust emission, the rest of the objects are dust cores. Toward NGC 6334 I(N), seven compact dust cores are found, one of which is associated with a faint centimeter source. With the exception of I-SMA3, none of the millimeter sources have infrared counterparts in Spitzer Space Telescope 3-8 micron images. Using a simple physical model for the dust continuum emission, the estimated mass of interstellar material toward each of these compact objects is in the range of 3 to 66 solar masses. The total mass in the compact objects appears to be similar in I and I(N). The small size of these groups of sources suggest that these objects are proto-Trapezia forming in the centers of clusters of low to intermediate-mass stars.

 

astro-ph/0605469 [abs, ps, pdf, other] :

Title: Radiatively-Driven Cosmology in the Cellular Automaton Universe
Authors: Robert L. Kurucz (Harvard-Smithsonian Center for Astrophysics)
Comments: 13 pages, 17 pages of color figures, fig 3 in a jpeg file, others in one postscript file

This is an updated version of my paper "An outline of radiatively-driven cosmology" (Kurucz 2000). Here the Big Bang universe is replaced by a finite cellular automaton universe with no expansion (Kurucz 2006). The Big Bang is replaced by many little bangs spread throughout the universe that interact to produce the initial perturbations that form Population III stars, globular clusters, and galaxies, but no large-scale structure. These perturbations evolve into the universe as we now observe it. Evolution during the first billion years is controlled by radiation. Globular clusters are formed by radiatively-driven implosions, galaxies are formed by radiatively-triggered gravitational collapse of systems of globular clusters, and voids and the microwave background are formed by radiatively-driven expansion. After this period most of the strong radiation sources are exhausted and the universe relaxes into gravitational old age as we know it. To relieve the boredom we present the results of gedanken experiments (Kurucz 1992) in a traditional, linear, chronological sequence in the hope of stimulating research on the many topics considered.