[ITAL]Chandra[/ITAL] Exposes the Core-collapsed Globular Cluster NGC 6397

Grindlay, Jonathan E.; Heinke, C. O.; Edmonds, P. D.; Murray, Stephen S.; Cool, A. M.

doi:10.1086/338499

Cited by 143 publications

(192 citation statements)

References 18 publications

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“…The low luminosity and relatively hard X-ray spectrum of W29 are similar to those of U12 (the X-ray counterpart of NGC 6397A; Grindlay et al 2001b) and 47 Tuc J, both eclipsing MSP binaries (see Grindlay et al 2002). The X-ray spectrum of W29 can be best fit with a power law (photon index = 1:8 AE 0:6 when fixing N H to the nominal cluster value; 2 ¼ 1:55), and the luminosity in the 0.5-2.5 keV band is 7:8 Â 10 30 ergs s À1 .…”

Section: W29 and Chandra-hst Astrometrymentioning

confidence: 64%

A Millisecond Pulsar Optical Counterpart with Large‐Amplitude Variability in the Globular Cluster 47 Tucanae

Edmonds

Gilliland

Camilo

et al. 2002

ApJ

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Using extensive Hubble Space Telescope imaging, combined with Chandra X-ray and Parkes radio data, we have detected the optical binary companion to a second millisecond pulsar (MSP) in the globular cluster 47 Tucanae. This faint (V ¼ 22:3) blue (VÀI = 0.7) star shows a large-amplitude (60%-70%) sinusoidal variation in both V and I. The period (3.19066 hr) and phase of the variation match those of the MSP 47 Tuc W (which does not have an accurate radio timing position) to within 0.5 s and 1.2 minutes, respectively, well within the 1 errors. The phase dependence of the intensity and color implies that heating of a tidally locked companion causes the observed variations. The eclipsing nature of this MSP in the radio, combined with the relatively large companion mass (greater than 0.13 M ) and the companion's position in the color-magnitude diagram, suggests that the companion is a main-sequence star, a rare circumstance for an MSP companion. This system is likely to have had a complex evolution and represents an interesting case study in MSP irradiation of a close companion. We present evidence for another optical variable with similar properties to the companion of 47 Tuc W. This variable also may be an MSP companion, although no radio counterpart has yet been detected.

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Section: W29 and Chandra-hst Astrometrymentioning

confidence: 64%

A Millisecond Pulsar Optical Counterpart with Large‐Amplitude Variability in the Globular Cluster 47 Tucanae

Edmonds

Gilliland

Camilo

et al. 2002

ApJ

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“…The post-recycling exchange of a fresh main-sequence star into this binary is also consistent with the data and furthermore consistent with our picture of the dynamically evolving binary population in the NGC 6397 core. Additional evidence in support of such a picture for the core of NGC 6397 is presented by Grindlay et al (2001b), who find that another of the BY Dra candidates discovered by TGE01 may actually be a multiply exchanged millisecond pulsar (based on the X-ray properties).…”

Section: An Evolving Populationmentioning

confidence: 91%

“…Of particular importance is the primordial binary star population (Heggie 1975;Hut et al 1992), which provides a crucial internal energy source for the cluster by virtue of inelastic scattering encounters. Some of the more dramatic products of these encounters include recycled pulsars (Rappaport, Putney, & Verbunt 1989;Phinney 1996), low-mass X-ray binaries (Verbunt & Johnston 1996), cataclysmic variables (CVs; Di Stefano & Rappaport 1994;Cool et al 1995;Grindlay et al 2001aGrindlay et al , 2001b, and blue stragglers (Sigurdsson, Davies, & Bolte 1994;Lombardi, Rasio, & Shapiro 1996). Cool et al (1998, hereafter CGC98) and Edmonds et al (1999, hereafter EGC99) have reported the detection of a new stellar population near the center of the core-collapsed globular cluster NGC 6397.…”

Section: Introductionmentioning

confidence: 99%

Helium Core White Dwarfs in Globular Clusters

Hansen

Kalogera

Rasio

2003

ApJ

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We examine the theoretical implications of a population of low-mass helium core white dwarfs in globular clusters. In particular, we focus on the observed population in the core of NGC 6397, where several low-mass white dwarf candidates have been identified as '' nonflickerers '' by Cool and collaborators. Age and mass estimates from cooling models, combined with dynamical and evolutionary considerations, lead us to infer that the dark binary companions are C/O white dwarfs rather than neutron stars. Furthermore, we find that the progenitor binaries very likely underwent an exchange interaction within the last 10 9 yr. We examine the prospects for detecting a similar population in other globular clusters, with particular attention to the case of 47 Tuc.

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“…However, the epoch in between our fourth and fifth epoch is not covered by the NUV observations, so we cannot tell whether the sources were indeed brighter in between the fourth and fifth epoch or not. Shara et al (2005) suggested that the CVs U17 (CV3 in Shara et al 2005, Grindlay et al 2001b) and U19 (CV2) underwent DN eruptions. U17 (CV3) was seen to brighten in optical WFPC2 data, but not in the STIS FUV data available at that time.…”

Section: Nuv Variabilitymentioning

confidence: 99%

“…Chandra X-ray observations have been carried out by Grindlay et al (2001a) and Bogdanov et al (2010), detecting 79 X-ray sources within the half-mass radius of this cluster. Shara et al (2005) used WFPC2 and STIS UV imaging and detected dwarf nova (DN) eruptions in two CVs that had previously been suggested to be magnetic systems (Grindlay et al 2001b) and which are usually not expected to show DN eruptions. Shara et al (2005) suggested that these two systems might be intermediate polars that occasionally undergo DN eruptions, which might explain the scarcity of DNs in GCs.…”

mentioning

confidence: 99%

Far-ultraviolet observation of the globular cluster NGC 6397

Dieball

Rasekh

Knigge

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present an observational far-UV (FUV) and near-UV (NUV) study of the core region of the globular cluster NGC 6397. The observations were obtained with the Space Telescope Imaging Spectrograph (STIS, FUV), and the Wide Field Camera 3 (WFC3, NUV) on board the Hubble Space Telescope. Here, we focus on the UV bright stellar populations such as blue stragglers (BSs), white dwarfs (WDs) and cataclysmic variables (CVs). We present the first FUV − NUV color-magnitude diagram (CMD) for this cluster. To support our classification of the stellar populations, we compare our FUV − NUV CMD with optical data from the ACS Survey of Galactic Globular Clusters. The FUV − NUV CMD indicates 16 sources located in the WD area, and ten BSs within the 25 ′′ × 25 ′′ of the STIS FUV data. Eighteen Chandra X-ray sources are located within the FUV field of view. Thirteen of those have a NUV counterpart, of which nine sources also have a FUV counterpart. Out of those, five sources are previously suggested CVs, and indeed all five are located in the WD/CV region in our FUV − NUV CMD. Another CV only has a FUV but no NUV counterpart. We also detect a NUV (but no FUV) counterpart to the MSP located in the core of this cluster. The NUV lightcurves of the CVs and MSP show flickering behaviour typical of CVs. We found that the BSs and CVs are the most centrally concentrated population. This might be an effect of mass segregation or indicate the preferred birth place of BSs and CVs via dynamical interactions in the dense core region of GCs. HB stars are the least centrally concentrated population and absent in the innermost area of the core.

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[ITAL]Chandra[/ITAL] Exposes the Core-collapsed Globular Cluster NGC 6397

Cited by 143 publications

References 18 publications

A Millisecond Pulsar Optical Counterpart with Large‐Amplitude Variability in the Globular Cluster 47 Tucanae

A Millisecond Pulsar Optical Counterpart with Large‐Amplitude Variability in the Globular Cluster 47 Tucanae

Helium Core White Dwarfs in Globular Clusters

Far-ultraviolet observation of the globular cluster NGC 6397

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