scholarly journals Pulsars in Globular Clusters

1996 ◽  
Vol 174 ◽  
pp. 181-182 ◽  
Author(s):  
S. R. Kulkarni ◽  
S. B. Anderson
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Massive Stars ◽  
Orbital Evolution ◽  
Precise Determination ◽  
Radio Pulsars ◽  
Dense Cores ◽  
Short Period ◽  
Low Mass ◽  
Low Magnetic Field

Since the discovery of the first globular cluster pulsar in M28 (Lyne et al. 1987) a total of 33 pulsars have been found to reside within 13 seperate clusters. Many (but not all) of the cluster pulsars have properties similar to the millisecond pulsars in the disk: short period, binarity and low magnetic field strength. The common understanding is that these pulsars are primordial neutron stars (i.e. the remnants of massive stars in clusters) which have been spun up by accretion of matter from a companion. Therefore, in this framework, the cluster pulsars are descendents of Low Mass X-ray Binaries (LMXBs) (Alpar et al. 1982). This hypothesis is by no means accepted by all workers (e.g. Michel 1987, Ray & Kluzniak 1990, Romani 1990, Bailyn & Grindlay 1993). These workers have argued that at least some (if not all) cluster pulsars could be formed by accretion induced collapse of massive white dwarfs. In either case, it is clear from the sensitivity limits of current cluster searches, and the luminosity of field pulsars, that there are currently O(103) extant radio pulsars in the Galactic globular cluster system.In this review, specifically targeted for astronomers working in the field of globular clusters, not pulsar astronomers, we argue that cluster pulsars have provided us with a new window into the population of long-dead massive stars and the physics of tidal capture. The precision with which pulsars can be timed has created new diagnostics: measurement of the mass distribution in the dense cores, measurement of orbital evolution on short timescales and precise determination of orbital characteristics. It is fair to say that all these diagnostics are unique, and not obtainable by other observations. Despite this, it is our assessment that the typical astronomer who works in the field of globular clusters is apparently unaware of these relevant contributions. Hopefully this review will bridge this gap. A complete copy of the review article may be found at http://astro.caltech.edu/~srk.

scholarly journals Massive star archeology in globular clusters

2014 ◽  
Vol 9 (S307) ◽  
pp. 96-97
Author(s):  
W. Chantereau ◽  
C. Charbonnel ◽  
G. Meynet
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Massive Star ◽  
Massive Stars ◽  
Hot Stars ◽  
Low Mass Stars ◽  
Multiple Populations ◽  
Long Time ◽  
Low Mass ◽  
The Universe

AbstractGlobular clusters are among the oldest structures in the Universe and they host today low-mass stars and no gas. However, there has been a time when they formed as gaseous objects hosting a large number of short-lived, massive stars. Many details on this early epoch have been depicted recently through unprecedented dissection of low-mass globular cluster stars via spectroscopy and photometry. In particular, multiple populations have been identified, which bear the nucleosynthetic fingerprints of the massive hot stars disappeared a long time ago. Here we discuss how massive star archeology can be done through the lense of these multiple populations.

scholarly journals The diverse origin of exoplanets' eccentricities & inclinations

2010 ◽  
Vol 6 (S276) ◽  
pp. 221-224
Author(s):  
Eric B. Ford
Keyword(s):  
Rotation Axis ◽  
Orbital Evolution ◽  
Giant Planets ◽  
Direct Imaging ◽  
Wide Binary ◽  
Hot Jupiters ◽  
Short Period ◽  
New Type ◽  
Low Mass ◽  
Diverse Origin

AbstractRadial velocity surveys have discovered over 400 exoplanets. While measuring eccentricities of low-mass planets remains a challenge, giant exoplanets display a broad range of orbital eccentricities. Recently, spectroscopic measurements during transit have demonstrated that the short-period giant planets (“hot-Jupiters”) also display a broad range of orbital inclinations (relative to the rotation axis of the host star). Both properties pose a challenge for simple disk migration models and suggest that late-stage orbital evolution can play an important role in determining the final architecture of planetary systems. One possible formation mechanism for the inclined hot-Jupiters is some form of eccentricity excitation (e.g., planet scattering, secular perturbations due to a distant planet or wide binary) followed tidal circularization. The planet scattering hypothesis also makes predictions for the population of planets at large separations. Recent discoveries of planets on wide orbits via direct imaging and highly anticipated results from upcoming direct imaging campaigns are poised to provide a new type of constraint on planet formation. This proceedings describes recent progress in understanding the formation of giant exoplanets.

scholarly journals CCD Observations of Variable Stars in Globular Clusters

1989 ◽  
Vol 111 ◽  
pp. 285-285
Author(s):  
H.A. Smith ◽  
J.R. Kuhn ◽  
J. Curtis
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Variable Stars ◽  
Michigan State University ◽  
State University ◽  
Ccd Photometry ◽  
Rr Lyrae ◽  
Short Period ◽  
Ccd Observations ◽  
Period Variable

AbstractBVR observations of the relatively metal-rich globular cluster NGC 6388 have been obtained with a CCD on the CTIO 0.9 m telescope. Eighteen possible short period variable stars have been discovered in or near the cluster. At least 10 of these are probable RR Lyrae members of NGC 6388. We confirm the finding of Hazen and Hesser that this cluster is one of the most metal-rich to contain a significant number of RR Lyraes. A program of CCD photometry of field and cluster variable stars has been initiated on the 0.6m telescope of the Michigan State University Observatory.

scholarly journals Core-hydrogen-burning RSGs in the early globular clusters

2015 ◽  
Vol 11 (A29B) ◽  
pp. 473-473
Author(s):  
Dorottya Szécsi ◽  
Jonathan Mackey ◽  
Norbert Langer
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Massive Stars ◽  
Shell Formation ◽  
Low Mass Stars ◽  
Hydrogen Burning ◽  
The Core ◽  
Anomalous Surface ◽  
Low Metallicity ◽  
Low Mass

AbstractThe first stellar generation in galactic globular clusters contained massive low-metallicity stars (Charbonnel et al. 2014). We modelled the evolution of this massive stellar population and found that such stars with masses 100-600 M⊙ evolve into cool RSGs (Szécsi et al. 2015). These RSGs spend not only the core-He-burning phase but even the last few 105 years of the core-H-burning phase on the SG branch. Due to the presence of hot massive stars in the cluster at the same time, we show that the RSG wind is trapped into photoionization confined shells (Mackey et al. 2014). We simulated the shell formation around such RSGs and find them to become gravitationally unstable (Szécsi et al. 2016). We propose a scenario in which these shells are responsible for the formation of the second generation low-mass stars in globular clusters with anomalous surface abundances.

scholarly journals Globular Clusters as Extragalactic Distance Indicators: Maximum Likelihood Methods

1988 ◽  
Vol 126 ◽  
pp. 617-618
Author(s):  
David A. Hanes ◽  
Donna G. Whittaker
Keyword(s):  
Maximum Likelihood ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Likelihood Estimation ◽  
Absolute Magnitude ◽  
Universal Constant ◽  
Precise Determination ◽  
Good Precision ◽  
Distance Information ◽  
Distance Indicators

We have explored the use of maximum likelihood estimation techniques in the use of globular cluster luminosity functions (LFs) as distance indicators. In particular, we have tested size-of-sample effects through the analysis of Monte Carlo simulations of LFs drawn from an assumed universal population like that characterizing the globular clusters in the Local Group. Our working assumption, following others before us, is that the underlying LF is adequately well described by a Gaussian normal in a number vs. absolute magnitude representation.For typically observable sample sizes in studies which are limited to the bright half of the LF, statistical limitations preclude a precise determination of the attributes which fully describe the LF, even in the absence of field object contamination. In particular, the intrinsic dispersion (the shape parameter of the LF) must be taken to be a universal constant, independent of galaxy type; only then may the turnover magnitude (which contains the distance information) be derived with good precision. Some data exist for nearby galaxies (including ellipticals) which permit an assessment of the universality of the intrinsic dispersion: they are not inconsistent with the hypothesis. However, it will be important to test this point in future as more data are secured.Real globular clusters in remote galaxies are unresolved, and the samples are contaminated with foreground field stars and remote background objects. This contamination necessitates corrections which are statistical in nature, applicable to binned LFs. Through numerical simulations, we have tested the limitations imposed by realistic numbers of field objects in globular cluster LFs in remote galaxies, testing for systematic biases and assessing the attainable precision in derived distance as a function of the sample size and the limiting magnitude.

scholarly journals Short Period Variables in the Magellanic Cloud Cluster NGC 1466

1973 ◽  
Vol 21 ◽  
pp. 113-119 ◽  
Author(s):  
M. V. Norris
Keyword(s):  
Globular Cluster ◽  
Metal Content ◽  
Globular Clusters ◽  
Magellanic Clouds ◽  
Horizontal Branch ◽  
A Value ◽  
Short Period ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Metal Abundance

NGC 1466 (α1950 = 3h44.m6, δ1950= -71°45’) is a globular cluster which appears to be situated between the two Magellanic Clouds. Previous estimates (Gascoigne, 1966) put it at roughly the same distance from us as the LMC, so it is regarded as a member of the Cloud system. It is globular in appearance, and its colour-magnitude diagram confirms this classification. It has a fairly well-developed horizontal branch, and was found by Wesselink (1970) to be quite rich in variables. The metallicity index, Q, (van den Bergh, 1967) has a value of -0.36 for NGC 1466 (Andrews and Lloyd Evans, 1971). This would rank it with M5 and NGC 6171 as a cluster of intermediate metal content. This comparison is consistent with the value of Δ V for the cluster, which, at 2.m6, is representative of the Δ V values of globular clusters of intermediate metal abundance in the Galaxy.

scholarly journals Theoretical Implications of the 47 Tuc Pulsars

2000 ◽  
Vol 177 ◽  
pp. 589-594
Author(s):  
Frederic A. Rasio
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Radio Pulsars ◽  
Formation And Evolution ◽  
Millisecond Radio

AbstractTwenty millisecond radio pulsars have now been observed in the globular cluster 47 Tuc. This is by far the largest sample of radio pulsars known in any globular cluster. These recent observations provide a unique opportunity to re-examine theoretically the formation and evolution of recycled pulsars in globular clusters.

scholarly journals The Globular Cluster Population of X-ray Binaries

1987 ◽  
Vol 125 ◽  
pp. 187-197 ◽  
Author(s):  
Frank Verbunt ◽  
Piet Hut
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Encounter Rate ◽  
Formation Mechanisms ◽  
Main Sequence Stars ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.

scholarly journals Supergiants and their shells in young globular clusters

2018 ◽  
Vol 612 ◽  
pp. A55 ◽  
Author(s):  
Dorottya Szécsi ◽  
Jonathan Mackey ◽  
Norbert Langer
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Second Generation ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Hydrogen Burning ◽  
Mass Budget ◽  
Low Metallicity ◽  
Low Mass ◽  
Galactic Globular Clusters

Context. Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars. Aims. We aim to present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster. Methods. Simulations of low-metallicity massive stars (Mi ~ 150−600 M⊙) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in young globular clusters. Under these conditions, photoionization-confined shells form around the supergiants. We have simulated such a shell, investigated its stability and analysed its composition. Results. We find that the shell is gravitationally unstable on a timescale that is shorter than the lifetime of the supergiant, and the Bonnor-Ebert mass of the overdense regions is low enough to allow star formation. Since the low-mass stellar generation formed in this shell is made up of the material lost from the supergiant, its composition necessarily reflects the composition of the supergiant wind. We show that the wind contains hot-hydrogen-burning products, and that the shell-stars therefore have very similar abundance anomalies that are observed in the second generation stars of globular clusters. Considering the mass-budget required for the second generation star-formation, we offer two solutions. Either a top-heavy initial mass function is needed with an index of −1.71 to −2.07. Alternatively, we suggest the shell-stars to have a truncated mass distribution, and solve the mass budget problem by justifiably accounting for only a fraction of the first generation. Conclusions. Star-forming shells around cool supergiants could form the second generation of low-mass stars in Galactic globular clusters. Even without forming a photoionizaton-confined shell, the cool supergiant stars predicted at low-metallicity could contribute to the pollution of the interstellar medium of the cluster from which the second generation was born. Thus, the cool supergiant stars should be regarded as important contributors to the evolution of globular clusters.

scholarly journals Observations of low mass companions to massive stars

2009 ◽  
Vol 5 (H15) ◽  
pp. 760-760
Author(s):  
H. Zinnecker
Keyword(s):  
Massive Stars ◽  
High Mass ◽  
Multiple Systems ◽  
X Ray ◽  
Ob Stars ◽  
Spectroscopic Monitoring ◽  
Short Period ◽  
Low Mass ◽  
X Ray Binaries

Massive stars are known to be multiple systems, often in tight, short-period OB stars binaries (SB1 and SB2, found by spectroscopic monitoring). However, little is known about low-mass companions to massive stars, such as A, F, and G stars with masses in the range of 1 to 3 solar masses. Yet systems of massive stars with wide low-mass companions (of the order of a few AU) must exist, for these are the progenitors of LMXB and HMXB (low-mass and high-mass X-ray binaries).

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