DOCSLIB.ORG

Radio Pulsars Around Intermediate-Mass Black Holes in Superstellar Clusters A

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Radio Pulsars Around Intermediate-Mass Black Holes in Superstellar Clusters � A Mon. Not. R. Astron. Soc. 364, 344–352 (2005) doi:10.1111/j.1365-2966.2005.09568.x Radio pulsars around intermediate-mass black holes in superstellar clusters A. Patruno,1,2 M. Colpi,2 A. Faulkner3 and A. Possenti4 1Astronomical Institute ‘A. Pannekoek’, University of Amsterdam, Kruislaan 403, 1098 SJ, the Netherlands 2Dipartimento di Fisica G. Occhialini, Universitadi` Milano Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy 3University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire 4INAF, Osservatorio Astronomico di Cagliari, Poggio dei Pini, Strada 54, Capoterra, Italy Downloaded from https://academic.oup.com/mnras/article/364/1/344/1153149 by guest on 30 September 2021 Accepted 2005 August 27. Received 2005 August 25; in original form 2005 July 8 ABSTRACT We study accretion in binaries hosting an intermediate-mass black hole (IMBH) of ∼1000 M, and a donor star more massive than 15 M. These systems experience an active X-ray phase characterized by luminosities varying over a wide interval, from <1036 erg s−1 up to a few 1040 erg s−1 typical of the ultraluminous X-ray sources (ULXs). Roche lobe overflow on the zero-age main sequence and donor masses above 20 M can maintain a long-lived accretion phase at the level required to feed a ULX source. In wide systems, wind transfer rates are magnified by the focusing action of the IMBH yielding wind luminosities 1038 erg s−1. These high-mass IMBH binaries can be identified as progenitors of IMBH–radio pulsar (PSR) binaries. We find that the formation of an IMBH–PSR binary does not necessarily require the transit through a ULX phase, but that a ULX can highlight a system that will evolve into an IMBH–PSR, if the mass of the donor star is constrained to lie within 15–30 M.Weshow that binary evolution delivers the pre-exploding helium core in an orbit such that after explosion, the neutron star has a very high probability to remain bound to the IMBH, at distances of 1– 10 au. The detection of an IMBH–PSR binary in the Milky Way has suffered, so far, from the same small number of statistics limit affecting the population of ULXs in our Galaxy. Ongoing deeper surveys or next-generation radio telescopes such as the Square Kilometre Array will have an improved chance to unveil such intriguing systems. The timing analysis of a pulsar orbiting around an IMBH would weigh the black hole in the still uncharted interval of mass around 1000 M. Keywords: accretion, accretion discs – black hole physics – X-rays: binaries – X-rays: galaxies. 2004; Zampieri et al. 2004), the properties of the optical and radio 1 INTRODUCTION counterparts (Kaaret et al. 2004; Liu, Bregman & Seitzer 2004; Recent high-resolution X-ray imaging and spectroscopic studies Zampieri et al. 2004; K¨ording,Colbert & Falcke 2005; Miller, with Chandra and XMM have led to the discovery of a large sample Mushotzky & Neff 2005; Soria et al. 2005) and the timing behaviour of a new class of compact sources with luminosities in the inter- of at least one source in the starburst galaxy M82 (Strohmayer & val between 3 × 1039 and 1041 erg s−1, which are in excess of the Mushotzky 2003; Fiorito & Titarchuk 2004) support this view. The Eddington limit of a stellar-mass black hole of 20 M (Fabbiano IMBH hypothesis however does not represent the only possibil- 1989; see Mushotzky 2004, for a critical review). These sources ity to explain the emission of ULXs, because mechanical beaming can find a simple interpretation in the hypothesis that intermediate- working in a thick disc around a conventional stellar-mass black mass black holes (IMBHs) exist with mass 102–104 M accreting hole, or Doppler boosting from a jet in a microblazar could pro- from a companion star in binary systems (Fabbiano 1989; Miller duce the same range of observed luminosities (King et al. 2001; & Colbert 2004; Mushotzky 2004). The detection of a cool-disc K¨ording, Falcke & Markoff 2002; Kaaret et al. 2003; Mushotzky thermal spectral component in a number of ultraluminous X-ray 2004). Moreover, in recent work, Rappaport, Podsiadlowski sources (ULXs; Miller et al. 2003; Cropper et al. 2004; Dewangan &Pfahl (2005) use binary evolution calculations to show how the et al. 2004; Kaaret, Ward & Zezas 2004; Miller, Fabian & Miller largest part of the ULX population may be explained with a stellar- mass black hole emitting at a super Eddington rate of ∼10 without E-mail: [email protected] the requirement of an IMBH (see also Podsiadlowski, Rappaport & C 2005 The Authors. Journal compilation C 2005 RAS Radio pulsars around IMBHs 345 Han 2003 and Pfahl, Podsiadlowski & Rappaport 2005 for an ex- hosted in the core of our Galaxy (Pfahl & Loeb 2004). Thus, the issue tended study on the evolution of stellar-mass black hole binaries). of pulsars around black holes is becoming of paramount importance. This is also in agreement with another study of King & Dehnen In this paper we assume the hypothesis of the formation of IMBHs (2005) where the authors claim that the luminosities of a large sam- in young dense star clusters, and we start our evolution study just ple of ULXs could be explained using helium enriched matter and after the formation/capture of a high-mass star around the IMBH, mechanical beaming with a stellar-mass black hole. However, all the which could be the progenitor of an IMBH–PSR system. In this alternatives to the IMBH hypothesis meet with strong difficulties framework, Hopman, Portegies Zwart & Alexander (2004) consid- when the luminosity of a ULX is in excess of ∼1040 erg s−1, be- ered the possibility that a passing star is tidally captured by the cause, in this case, beaming under rather extreme conditions should IMBH in a stable, close, not plunging orbit. Mass transfer may ini- be at work to match with the observations, or super Eddington fac- tiate, after circularization, while the star is on the main sequence or tors greater than ∼10 could be difficult to achieve. On the other evolving away from it. Dynamical capture of a massive star by an hand, although the hypothesis of an IMBH explains naturally many IMBH is a further possibility, as shown by Baumgardt et al. (2004). of the observational clues, it clashes with the problem of provid- In an exchange interaction of a binary star, the IMBH can acquire Downloaded from https://academic.oup.com/mnras/article/364/1/344/1153149 by guest on 30 September 2021 ing a viable mechanism of formation. Until now, two possibilities a companion, likely a massive star, given that the IMBH forms in have been proposed: the formation of an IMBH through runaway a mass-segregated environment, where stellar encounters play an collisions among massive stars undergoing fast dynamical segrega- important role. tion, in the core of a dense super star cluster (see G¨urkan,Freitag & The observational appearance of binaries hosting an IMBH has Rasio 2004; Portegies Zwart et al. 2004a), or the wandering of an only been partly explored, and mainly in the context of ULXs. IMBH, relic of a zero metallicity Population III star (Abel, Bryan & Portegies Zwart et al. (2004b) studied the evolution of an IMBH Norman 2000). In the first case, the giant star that forms in the core of 1000 M accreting from a donor star of mass between 5 and of the dense star cluster, collapses into an IMBH. This can occur in 15 M (see also Kalogera et al. 2004 for another binary evolu- a star-forming region, and the result is based on very large detailed tionary study). Typically, light donors (5M)donot transfer N-body simulations (Portegies Zwart et al. 2004a). The case of a mass at a sufficiently sustained rate to produce sources as bright as wandering IMBH relic of the early assembly of haloes in a currently ULXs; only the high-mass stars (10 M)onthe main sequence star-forming galaxy is uncertain, in particular the capture of gas or or beyond can provide luminosities in excess of 1040 erg s−1. Thus, of a star to ignite accretion (Volonteri & Perna 2005). IMBHs cannot easily be identified on the basis of their X-ray activ- In order to solve the controversy on the real existence of IMBHs ity; they can display a rather wide range of luminosities, depending in ULXs, the only secure route would be the determination of the on the mass of the donor star, and on the mass transfer mechanism, optical mass function, similar to the procedure for the stellar-mass as will be shown in this paper. Only when they outshine as bright black holes in the Milky Way (Orosz et al. 2002). This is difficult ULXs can they become visible over the stellar-mass black holes. however, because ULXs are distant sources hosted in external (star- In this paper we address a number of issues, under the hypothesis burst) galaxies for which the optical identification of the companion that an X-ray and/or a ULX phase precedes that in which the system is troublesome, and even in the lucky circumstance of good identi- appears as an IMBH-PSR binary. fication (see Kaaret et al. 2004; Liu et al. 2004; Miller et al. 2004; (i) What are the characteristics of the X-ray phase and of mass Soria et al. 2005; Zampieri et al. 2004) the optical spectrum is too transfer when considering massive donors around an IMBH? noisy to allow a mass estimate of the black hole. (ii) Is the formation of a radio pulsar likely? In this paper we propose an alternative way to discover and weigh (iii) What is the probability that an asymmetric kick, imparted to a IMBH: it uses the detection of a young radio pulsar (PSR) around the neutron star at birth, will unbind the system? an IMBH.
Load more

Recommended publications
  • Exploring Pulsars
    High-energy astrophysics Explore the PUL SAR menagerie Astronomers are discovering many strange properties of compact stellar objects called pulsars. Here’s how they fit together. by Victoria M. Kaspi f you browse through an astronomy book published 25 years ago, you’d likely assume that astronomers understood extremely dense objects called neutron stars fairly well. The spectacular Crab Nebula’s central body has been a “poster child” for these objects for years. This specific neutron star is a pulsar that I rotates roughly 30 times per second, emitting regular appar- ent pulsations in Earth’s direction through a sort of “light- house” effect as the star rotates. While these textbook descriptions aren’t incorrect, research over roughly the past decade has shown that the picture they portray is fundamentally incomplete. Astrono- mers know that the simple scenario where neutron stars are all born “Crab-like” is not true. Experts in the field could not have imagined the variety of neutron stars they’ve recently observed. We’ve found that bizarre objects repre- sent a significant fraction of the neutron star population. With names like magnetars, anomalous X-ray pulsars, soft gamma repeaters, rotating radio transients, and compact Long the pulsar poster child, central objects, these bodies bear properties radically differ- the Crab Nebula’s central object is a fast-spinning neutron star ent from those of the Crab pulsar. Just how large a fraction that emits jets of radiation at its they represent is still hotly debated, but it’s at least 10 per- magnetic axis. Astronomers cent and maybe even the majority.
    [Show full text]
  • Brochure Pulsar Multifunction Spectroscopy Service Complete Cased Hole Formation Evaluation and Reservoir Saturation Monitoring from A
    Pulsar Multifunction spectroscopy service Introducing environment-independent, stand-alone cased hole formation evaluation and saturation monitoring 1 APPLICATIONS FEATURES AND BENEFITS ■ Stand-alone formation evaluation for diagnosis of bypassed ■ Environment-independent reservoir saturation monitoring ■ High-performance pulsed neutron generator (PNG) hydrocarbons, depleted reservoirs, and gas zones in any formation water salinity ● Optimized pulsing scheme with multiple square and short ● Differentiation of gas-filled porosity from very low porosity ● Production fluid profile determination for any well pulses for clean separation in measuring both inelastic and formations by using neutron porosity and fast neutron cross inclination: horizontal, deviated, and vertical capture gamma rays 8 section (FNXS) measurements ● Detection of water entry and flow behind casing ● High neutron output of 3.5 × 10 neutron/s for greater ■ measurement precision Petrophysical evaluation with greater accuracy by accounting ● Gravel-pack quality determination by using for grain density and mineral properties in neutron porosity elemental spectroscopy ■ State-of-the-art detectors ■ Total organic carbon (TOC) quantified as the difference ■ Metals for mining exploration ● Near and far detectors: cerium-doped lanthanum bromide between the measured total carbon and inorganic carbon ■ High-resolution determination of reservoir quality (RQ) (LaBr3:Ce) ■ Oil volume from TOC and completion quality (CQ) for formation evaluation ● Deep detector: yttrium aluminum perovskite
    [Show full text]
  • Pos(INTEGRAL 2010)091
    A candidate former companion star to the Magnetar CXOU J164710.2-455216 in the massive Galactic cluster Westerlund 1 PoS(INTEGRAL 2010)091 P.J. Kavanagh 1 School of Physical Sciences and NCPST, Dublin City University Glasnevin, Dublin 9, Ireland E-mail: [email protected] E.J.A. Meurs School of Cosmic Physics, DIAS, and School of Physical Sciences, DCU Glasnevin, Dublin 9, Ireland E-mail: [email protected] L. Norci School of Physical Sciences and NCPST, Dublin City University Glasnevin, Dublin 9, Ireland E-mail: [email protected] Besides carrying the distinction of being the most massive young star cluster in our Galaxy, Westerlund 1 contains the notable Magnetar CXOU J164710.2-455216. While this is the only collapsed stellar remnant known for this cluster, a further ~10² Supernovae may have occurred on the basis of the cluster Initial Mass Function, possibly all leaving Black Holes. We identify a candidate former companion to the Magnetar in view of its high proper motion directed away from the Magnetar region, viz. the Luminous Blue Variable W243. We discuss the properties of W243 and how they pertain to the former Magnetar companion hypothesis. Binary evolution arguments are employed to derive a progenitor mass for the Magnetar of 24-25 M Sun , just within the progenitor mass range for Neutron Star birth. We also draw attention to another candidate to be member of a former massive binary. 8th INTEGRAL Workshop “The Restless Gamma-ray Universe” Dublin, Ireland September 27-30, 2010 1 Speaker Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
    [Show full text]
  • Central Engines and Environment of Superluminous Supernovae
    Central Engines and Environment of Superluminous Supernovae Blinnikov S.I.1;2;3 1 NIC Kurchatov Inst. ITEP, Moscow 2 SAI, MSU, Moscow 3 Kavli IPMU, Kashiwa with E.Sorokina, K.Nomoto, P. Baklanov, A.Tolstov, E.Kozyreva, M.Potashov, et al. Schloss Ringberg, 26 July 2017 First Superluminous Supernova (SLSN) is discovered in 2006 -21 1994I 1997ef 1998bw -21 -20 56 2002ap Co to 2003jd 56 2007bg -19 Fe 2007bi -20 -18 -19 -17 -16 -18 Absolute magnitude -15 -17 -14 -13 -16 0 50 100 150 200 250 300 350 -20 0 20 40 60 Epoch (days) Superluminous SN of type II Superluminous SN of type I SN2006gy used to be the most luminous SN in 2006, but not now. Now many SNe are discovered even more luminous. The number of Superluminous Supernovae (SLSNe) discovered is growing. The models explaining those events with the minimum energy budget involve multiple ejections of mass in presupernova stars. Mass loss and build-up of envelopes around massive stars are generic features of stellar evolution. Normally, those envelopes are rather diluted, and they do not change significantly the light produced in the majority of supernovae. 2 SLSNe are not equal to Hypernovae Hypernovae are not extremely luminous, but they have high kinetic energy of explosion. Afterglow of GRB130702A with bumps interpreted as a hypernova. Alina Volnova, et al. 2017. Multicolour modelling of SN 2013dx associated with GRB130702A. MNRAS 467, 3500. 3 Our models of LC with STELLA E ≈ 35 foe. First year light ∼ 0:03 foe while for SLSNe it is an order of magnitude larger.
    [Show full text]
  • Pulsars and Supernova Remnants
    1604–2004: SUPERNOVAE AS COSMOLOGICAL LIGHTHOUSES ASP Conference Series, Vol. 342, 2005 M. Turatto, S. Benetti, L. Zampieri, and W. Shea Pulsars and Supernova Remnants Roger A. Chevalier Dept. of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903, USA Abstract. Massive star supernovae can be divided into four categories de- pending on the amount of mass loss from the progenitor star and the star’s ra- dius. Various aspects of the immediate aftermath of the supernova are expected to develop in different ways depending on the supernova category: mixing in the supernova, fallback on the central compact object, expansion of any pul- sar wind nebula, interaction with circumstellar matter, and photoionization by shock breakout radiation. Models for observed young pulsar wind nebulae ex- panding into supernova ejecta indicate initial pulsar periods of 10 − 100 ms and approximate equipartition between particle and magnetic energies. Considering both pulsar nebulae and circumstellar interaction, the observed properties of young supernova remnants allow many of them to be placed in one of the super- nova categories; the major categories are represented. The pulsar properties do not appear to be related to the supernova category. 1. Introduction The association of SN 1054 with the Crab Nebula and its central pulsar can be understood in the context of the formation of the neutron star in the core collapse and the production of a bubble of relativistic particles and magnetic fields at the center of an expanding supernova. Although the finding of more young pulsars and their wind nebulae initially proceeded slowly, there has recently been a rapid set of discoveries of more such pulsars and nebulae (Camilo 2004).
    [Show full text]
  • Astrophysics VLT/UVES Spectroscopy of Wray 977, the Hypergiant
    UvA-DARE (Digital Academic Repository) VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2 Kaper, L.; van der Meer, A.; Najarro, F. DOI 10.1051/0004-6361:20065393 Publication date 2006 Document Version Final published version Published in Astronomy & Astrophysics Link to publication Citation for published version (APA): Kaper, L., van der Meer, A., & Najarro, F. (2006). VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2. Astronomy & Astrophysics, 457(2), 595- 610. https://doi.org/10.1051/0004-6361:20065393 General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:02 Oct 2021 A&A 457, 595–610 (2006) Astronomy DOI: 10.1051/0004-6361:20065393 & c ESO 2006 Astrophysics VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301−2 L.
    [Show full text]
  • (NASA/Chandra X-Ray Image) Type Ia Supernova Remnant – Thermonuclear Explosion of a White Dwarf
    Stellar Evolution Card Set Description and Links 1. Tycho’s SNR (NASA/Chandra X-ray image) Type Ia supernova remnant – thermonuclear explosion of a white dwarf http://chandra.harvard.edu/photo/2011/tycho2/ 2. Protostar formation (NASA/JPL/Caltech/Spitzer/R. Hurt illustration) A young star/protostar forming within a cloud of gas and dust http://www.spitzer.caltech.edu/images/1852-ssc2007-14d-Planet-Forming-Disk- Around-a-Baby-Star 3. The Crab Nebula (NASA/Chandra X-ray/Hubble optical/Spitzer IR composite image) A type II supernova remnant with a millisecond pulsar stellar core http://chandra.harvard.edu/photo/2009/crab/ 4. Cygnus X-1 (NASA/Chandra/M Weiss illustration) A stellar mass black hole in an X-ray binary system with a main sequence companion star http://chandra.harvard.edu/photo/2011/cygx1/ 5. White dwarf with red giant companion star (ESO/M. Kornmesser illustration/video) A white dwarf accreting material from a red giant companion could result in a Type Ia supernova http://www.eso.org/public/videos/eso0943b/ 6. Eight Burst Nebula (NASA/Hubble optical image) A planetary nebula with a white dwarf and companion star binary system in its center http://apod.nasa.gov/apod/ap150607.html 7. The Carina Nebula star-formation complex (NASA/Hubble optical image) A massive and active star formation region with newly forming protostars and stars http://www.spacetelescope.org/images/heic0707b/ 8. NGC 6826 (Chandra X-ray/Hubble optical composite image) A planetary nebula with a white dwarf stellar core in its center http://chandra.harvard.edu/photo/2012/pne/ 9.
    [Show full text]
  • Stellar Evolution
    AccessScience from McGraw-Hill Education Page 1 of 19 www.accessscience.com Stellar evolution Contributed by: James B. Kaler Publication year: 2014 The large-scale, systematic, and irreversible changes over time of the structure and composition of a star. Types of stars Dozens of different types of stars populate the Milky Way Galaxy. The most common are main-sequence dwarfs like the Sun that fuse hydrogen into helium within their cores (the core of the Sun occupies about half its mass). Dwarfs run the full gamut of stellar masses, from perhaps as much as 200 solar masses (200 M,⊙) down to the minimum of 0.075 solar mass (beneath which the full proton-proton chain does not operate). They occupy the spectral sequence from class O (maximum effective temperature nearly 50,000 K or 90,000◦F, maximum luminosity 5 × 10,6 solar), through classes B, A, F, G, K, and M, to the new class L (2400 K or 3860◦F and under, typical luminosity below 10,−4 solar). Within the main sequence, they break into two broad groups, those under 1.3 solar masses (class F5), whose luminosities derive from the proton-proton chain, and higher-mass stars that are supported principally by the carbon cycle. Below the end of the main sequence (masses less than 0.075 M,⊙) lie the brown dwarfs that occupy half of class L and all of class T (the latter under 1400 K or 2060◦F). These shine both from gravitational energy and from fusion of their natural deuterium. Their low-mass limit is unknown.
    [Show full text]
  • Neutron Stars to Open Their Heavy Hearts
    NEWS IN FOCUS it arrives at the International Space Station, INSIDE A NEUTON STA NASA’s Neutron Star Interior Composition A NASA mission will use X-ray spectroscopy to gather clues about the interior of neutron Explorer (NICER), a washing-machine-sized stars — the Universe’s densest forms of matter. box, will use X-rays coming from hotspots at the spinning stars’ poles to calculate the size of the stars. Outer crust Size matters, because a bigger star suggests Atomic nuclei, free electrons a stiff core that is relatively able to withstand Inner crust gravity’s compression, which means that it is Heavier atomic nuclei, free probably tightly packed with neutrons jostling neutrons and electrons against each other at higher pressure than that SVS FROM NASA GODDARD SOURCE: ADAPTED Outer core in atomic nuclei. A smaller, more compact Quantum liquid where star, meanwhile, would mean a soft interior, neutrons, protons and electrons exist in a soup in which neutrons could be dissolved in a sea of their constituent quarks. Other, more exotic proposals include the core being made of Inner core ‘hyperons’, which incorporate heavier ‘strange’ Unknown ultra-dense matter. ? Neutrons and protons may quarks within them. remain as particles, break down NICER will pinpoint the stars’ radii by into their constituent quarks, or even become ‘hyperons’. studying how their huge gravitational fields bend the light they emit. Seen from the space station, the light is fainter when the beam points away, but remains visible because the star’s gravitational field diverts some of the light back this way. The extent to which the light dims when the beam faces away tells astrono- Atmosphere mers about this field, and consequently the Hydrogen, helium, carbon star’s mass-to-radius ratio.
    [Show full text]
  • Super Stellar Clusters with a Bimodal Hydrodynamic Solution: an Approximate Analytic Approach
    A&A 471, 579–583 (2007) Astronomy DOI: 10.1051/0004-6361:20077282 & c ESO 2007 Astrophysics Super stellar clusters with a bimodal hydrodynamic solution: an approximate analytic approach R. Wünsch1, S. Silich2, J. Palouš1, and G. Tenorio-Tagle2 1 Astronomical Institute, Academy of Sciences of the Czech Republic, v.v.i., Bocníˇ II 1401, 141 31 Prague, Czech Republic e-mail: [email protected] 2 Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, Mexico Received 12 February 2007 / Accepted 22 May 2007 ABSTRACT Aims. We look for a simple analytic model to distinguish between stellar clusters undergoing a bimodal hydrodynamic solution from those able to drive only a stationary wind. Clusters in the bimodal regime undergo strong radiative cooling within their densest inner regions, which results in the accumulation of the matter injected by supernovae and stellar winds and eventually in the formation of further stellar generations, while their outer regions sustain a stationary wind. Methods. The analytic formulae are derived from the basic hydrodynamic equations. Our main assumption, that the density at the star cluster surface scales almost linearly with that at the stagnation radius, is based on results from semi-analytic and full numerical calculations. Results. The analytic formulation allows for the determination of the threshold mechanical luminosity that separates clusters evolving in either of the two solutions. It is possible to fix the stagnation radius by simple analytic expressions and thus to determine the fractions of the deposited matter that clusters evolving in the bimodal regime blow out as a wind or recycle into further stellar generations.
    [Show full text]
  • Asymmetric Supernova Explosions : the Missing Link Between Wolf-Rayet Binaries, Run-Away Ob Stars and Pulsars
    ASYMMETRIC SUPERNOVA EXPLOSIONS : THE MISSING LINK BETWEEN WOLF-RAYET BINARIES, RUN-AWAY OB STARS AND PULSARS Jean-Pierre De Cuyper Astrofysisch Instituut, Vrije Universiteit Brussel, Belgium. The WR binary systems, consisting of a WR star and an 0 or B star companion, are supposed to be the progenitors of the massive X-ray binaries. The missing link is generally accepted to be the SN explosion of the WR star which leaves a pulsar remnant. As most pulsars originate from single stars, observations of their proper motions indicate that they receive at their birth a "kick" velocity of about 100 km s We assume this velocity to be due to the asymmetry of the SN explosion. This asymmetry, together with the loss of the SN shell and its impact on the OB star, may cause to disrupt the remaining system. For the ten best known WR binaries we evaluated the survival probability P after an instantaneous SN explosion, leaving a 1.5 M collapsar with a random orientated kick velocity of 75 kms (case a) and 150 kms_1 (case b) respectively. The influence of the impact is found to be marginal. The run-away velocity of the remaining system v and of the disrupted OB star v are comparable and of the same order of magnitude, but smaller than the initial orbital velocity of the OB companion; which decreases for increasing values of the initial orbital period. They are found to be independent of the kick velocity. Systems with an initial period of less than a few weeks stay together for case a and have .
    [Show full text]
  • Pennsylvania Science Olympiad Southeast Regional Tournament 2013 Astronomy C Division Exam March 4, 2013
    PENNSYLVANIA SCIENCE OLYMPIAD SOUTHEAST REGIONAL TOURNAMENT 2013 ASTRONOMY C DIVISION EXAM MARCH 4, 2013 SCHOOL:________________________________________ TEAM NUMBER:_________________ INSTRUCTIONS: 1. Turn in all exam materials at the end of this event. Missing exam materials will result in immediate disqualification of the team in question. There is an exam packet as well as a blank answer sheet. 2. You may separate the exam pages. You may write in the exam. 3. Only the answers provided on the answer page will be considered. Do not write outside the designated spaces for each answer. 4. Include school name and school code number at the bottom of the answer sheet. Indicate the names of the participants legibly at the bottom of the answer sheet. Be prepared to display your wristband to the supervisor when asked. 5. Each question is worth one point. Tiebreaker questions are indicated with a (T#) in which the number indicates the order of consultation in the event of a tie. Tiebreaker questions count toward the overall raw score, and are only used as tiebreakers when there is a tie. In such cases, (T1) will be examined first, then (T2), and so on until the tie is broken. There are 12 tiebreakers. 6. When the time is up, the time is up. Continuing to write after the time is up risks immediate disqualification. 7. In the BONUS box on the answer sheet, name the gentleman depicted on the cover for a bonus point. 8. As per the 2013 Division C Rules Manual, each team is permitted to bring “either two laptop computers OR two 3-ring binders of any size, or one binder and one laptop” and programmable calculators.
    [Show full text]