Runaway OB Stars Research Articles

New runaway OB stars with HIPPARCOS

A Monte Carlo method for detection of runaway OB stars from observational data is proposed. 61 runaway OB star candidates have been detected by an analysis of Hipparcos proper motions. The peculiar tangential and total transverse velocities have been determined for these stars. A list of the detected runaway star candidates is presented. The evidence of a discrepancy between photometric and parallactic distances of runaway OB star candidates is presented.

The Ionized Gas in the Aftermath of a Starburst: The Case of NGC 1569

Results from multislit optical spectroscopy of 16 H II regions and deep Hα imaging of the amorphous galaxy NGC 1569 are presented. The extinction across the main body of the galaxy, as derived from the Balmer Hα/Hβ line ratio, indicates that most of the observed extinction is taking place in our own Galaxy; the latter amounts to (AV)local = 1.61 ± 0.09, while the extinction due to NGC 1569 is (AV)intrinsic = 0.65 ± 0.04. The electron temperature was measured in three H II regions using the [O III] λ4363 line. The O/H distribution shows no gradient along the main axis of the galaxy, which is consistent with the behavior observed in other low-mass galaxies. The average metal abundance is 12 + log O/H = 8.26, with little scatter, suggesting, on one hand, that mixing mechanisms are very efficient throughout the main body of the galaxy, or, on the other, that the most recent nucleosynthetic products are hiding in a hot coronal gas phase. Up to 20% ± 4% of the global Hα emission originates from the faint diffuse halo component surrounding the main body of NGC 1569. We explore the possibility that runaway OB stars that are due to cluster ejection and associated with the burst of supernovae which ended ~5 × 106 yr ago could be responsible for most of the ionization of the halo gas.

A Search for Pulsar Companions to OB Runaway Stars

view Abstract Citations (38) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Search for Pulsar Companions to OB Runaway Stars Sayer, R. W. ; Nice, D. J. ; Kaspi, V. M. Abstract We have searched for radio pulsar companions to 40 nearby OB runaway stars. Observations were made at 575 and 770 MHz with the NRAO 140 foot (43 m) telescope. The survey was sensitive to long- period pulsars with flux densities of 1 mJy or more. No pulsar companions to OB runaways were discovered. One previously unknown pulsar was discovered, PSR J2044 +4614, while observing toward target 0 star BD +45°3260. Follow-up timing observations of the pulsar measured its position to high precision, revealing a 9' separation between the pulsar and the target star, unequivocally indicating they are not associated. The pulsar is ordinary, except that its dispersion measure, 315 pc cm-3, is unusually high given its Galactic longitude, l = 85°. The nondetection of pulsars bound to target stars places an upper limit of 8% (95% confidence) for the fraction of runaway OB stars with pulsar companions detectable via pulsed radio emission by surveys such as ours. Assuming standard models for the pulsar beaming fraction and luminosity function, we conclude most OB runaways do not have pulsar companions. Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177063 Bibcode: 1996ApJ...461..357S Keywords: STARS: PULSARS: GENERAL; STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: PSR J2044+4614; STARS: BINARIES: GENERAL; STARS: EARLY-TYPE full text sources ADS | data products SIMBAD (43)

DO OB Runaway Stars Have Pulsar Companions?

We have conducted a VLA search for radio pulsars at the positions of 44 nearby OB runaway stars. The observations involved both searching images for point sources of continuum emission and a time series analysis. Our mean flux sensitivity to pulsars slower than 50 ms was 0.2 mJy. No new pulsars were found in the survey. The size of the survey, combined with the high sensitivity of the observations, sets a significant constraint on the probability, $f_p$, of a runaway OB star having an observable pulsar companion. We find $f_p \le 6.5$\% with 95\% confidence, if the general pulsar luminosity function is applicable to OB star pulsar companions. If a pulsar beaming fraction of \onethird is assumed, then we estimate that fewer than 20\% of runaway OB stars have neutron star companions, unless pulsed radio emission is frequently obscured by the OB stellar wind. Our result is consistent with the dynamical (or cluster) ejection model for the formation of OB runaways. The supernova ejection model is not ruled out, but is constrained by these observations to allow only a small binary survival fraction, which may be accommodated if neutron stars acquire significant natal kicks. According to Leonard, Hills and Dewey (1994), a 20\% survival fraction corresponds to a 3-d kick velocity of 420 km s$^{-1}$. This value is in close agreement with recent revisions of the pulsar velocity distribution.

Massive close binaries: Observational characteristics

Theoretically predicted evolutionary phases of massive close binaries are compared with the observations. For the evolution up to the High-Mass X-ray Binary (HMXB) phase there is fair agreement between theory and observation. Beyond the HMXB phase there is much uncertainty. Notably it is puzzling why we observe so few systems consisting of a helium star and a neutron star (Cygnus X-3 is the only one found so far), and why the incidence of double neutron stars is so low. A better understanding of Common Envelope evolution is required in order to answer these questions. The role of velocity kicks imparted to neutron stars during supernova collapse is discussed. Such kicks might cause many runaway OB stars to be single.

The implications of runaway OB stars for high-mass star formation

We use the properties of OB runaway stars and, assuming that they are ejected from their parent clusters by dynamical binary-binary interactions, deduce certain necessary characteristics of high-mass star formation. We deduce that massive stars form in small groups of binaries that are biased towards unit mass ratio, and that within these groups the IMF is severely under-represented in low-mass stars compared with the field star IMF

Supernovae in Binary Systems : Production of Run-Away Stars and Pulsars

AbstractThe effects of an instantaneous asymmetric supernova explosion in an eccentric binary system are analyzed, taking into account the mass loss out of the system, the influence of the impact of the supernova shell on the companion star and the extra “kick” velocity which a collapsed star might receive in an asymmetric supernova explosion. For a random orientat-ion in space of this asymmetric kick velocity, the survival probability and the runaway velocities are derived and their properties discussed for an explosion occurring at a given position in the initial keplerian orbit and the mean and extreme values of these quantities over one orbit are derived. As an example, the outcome of a possible supernova explosion in the ten best known WR+OB binaries is studied and a comparison is made with the observed run-away OB stars, radio pulsars and binary X-ray pulsars.

The velocity-mass correlation of the O-type stars - Model results

This paper presents new model results describing the evolution of massive close binaries from their initial ZAMS to post-supernova stages. Unlike the previous conservative study by Stone (Astrophys. J. 232, 520 (1979) (Paper II)), these results allow explicitly for mass loss from the binary system occurring during the core hydrogen- and helium-burning stages of the primary binary star as well as during the Roche lobe overflow. Because of uncertainties in these rates, model results are given for several reasonable choices for these rates. All of the models consistently predict an increasing relation between the peculiar space velocities and masses for runaway OB stars which agrees well with the observed correlations discussed in Stone (Astron. J. 86, 544 (1981) (Paper III)) and also predict a lower limit at Mroughly-equal11M/sub sun/ for the masses of runaway stars, in agreement with the observational limit found by A. Blaauw (Bull. Astron. Inst. Neth. 15, 265, 1961), both of which support the binary-supernova scenario described by van den Heuvel and Heise for the origin of runaway stars. These models also predict that the more massive O stars will produce correspondingly more massive compact remnants, and that most binaries experiencing supernova-induced kick velocities of magnitude V/submore » k/> or approx. =300 km s/sup -1/ will disrupt following the explosions. The best estimate for this velocity as established from pulsar observations is V/sub k/roughly-equal150 km s/sup -1/, in which case probably only 15% if these binaries will be disrupted by the supernova explosions, and therefore, almost all runaway stars should have either neutron star or black hole companions.« less

Asymmetric Supernova Explosions: The Missing Link between Wolf-Rayet Binaries, Run-Away OB Stars and Pulsars

The WR binary systems, consisting of a WR star and an O 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−1. 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−1 (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 and of the disrupted OB star 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.