A multiwavelength survey of NGC 6752: X-ray counterparts, two new dwarf novae and a core-collapsed radial profile

Thomson, Grace S.; Knigge, Christian; Dieball, A.; Maccarone, T. J.; Dolphin, Andrew E.; Zurek, David; Long, Knox S.; Shara, Michael M.; Sarajedini, Ata

doi:10.1111/j.1365-2966.2012.21104.x

Cited by 18 publications

(36 citation statements)

References 44 publications

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“…We could not find an optical counterpart in our reference image. Three more are Dwarf Novae (V25, V26, V27) discovered by Thomson et al (2012) of which V26 is the only object in which we could detect variability.…”

Section: Known Variablesmentioning

confidence: 93%

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs

Jaimes¹,

Bramich²,

Skottfelt³

et al. 2016

A&A

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Aims. We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution than has been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. Methods. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. Results. The light curves of 12 541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center.

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Section: Known Variablesmentioning

confidence: 93%

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs

Jaimes¹,

Bramich²,

Skottfelt³

et al. 2016

A&A

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show abstract

“…Table 1 summarizes the result of this counterpart search. Figure 7 shows finding charts for identifications that have changed or are new since the previous studies by Pooley et al (2002) and Thomson et al (2012).…”

Section: Chandra Source Identificationmentioning

confidence: 99%

“…They took this as evidence that NGC 6752 is experiencing a postcore-collapse bounce. Most recently, Thomson et al (2012) obtained surface-density profiles from HST ACS imaging, again finding that the profile is not well described by a single King model. They present a double-King-model fit and conclude that the cluster is either in a core-collapsed or postcore-collapse state.…”

Section: Introductionmentioning

confidence: 99%

Identification of Faint Chandra X-Ray Sources in the Core-collapsed Globular Cluster NGC 6752

Lugger

Cohn

Cool

et al. 2017

ApJ

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We have searched for optical identifications for 39 Chandra X-ray sources that lie within the 1. 9 half-mass radius of the nearby (d = 4.0 kpc), core-collapsed globular cluster, NGC 6752, using deep Hubble Space Telescope ACS/WFC imaging in B 435 , R 625 , and Hα. Photometry of these images allows us to classify candidate counterparts based primarily on color-magnitude and color-color diagram location. The color-color diagram is particularly useful for quantifying the Hα-line equivalent width. In addition to recovering 11 previously detected optical counterparts, we propose 20 new optical IDs. In total, there are 16 likely or less certain cataclysmic variables (CVs), nine likely or less certain chromospherically active binaries, three galaxies, and three active galactic nuclei (AGNs). The latter three sources, which had been identified as likely CVs by previous investigations, now appear to be extragalactic objects based on their proper motions. As we previously found for NGC 6397, the CV candidates in NGC 6752 fall into a bright group that is centrally concentrated relative to the turnoff-mass stars and a faint group that has a spatial distribution that is more similar to that of the turnoff-mass stars. This is consistent with an evolutionary scenario in which CVs are produced by dynamical interactions near the cluster center and diffuse to larger radius orbits as they age.

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“…In addition, there are 39 X-ray sources within the 1' 9" half-mass radius of NGC 6752, of which 16 are likely cataclysmic variables (CVs) and 3 are background AGN (Lugger et al (2017)). Three dwarf novae (CX1, CX4 and CX7) within this GC have been seen in outburst, over the last twenty years, using B band photometry and far UV/Hα observations (Kaluzny & Thompson (2009), Thomson et al (2012), Lugger et al (2017)). Some of these objects could be sources of gamma-ray emission, but the lack of gamma-ray variability on timescales of 6 months suggests this contribution is minor.…”

Section: Ngc 6752mentioning

confidence: 99%

Gamma-ray emission from high Galactic latitude globular clusters

Lloyd

Chadwick

Brown

2018

Monthly Notices of the Royal Astronomical Society

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We analyse 8 years of PASS 8 Fermi-LAT data, in the 60 MeV -300 GeV energy range, from 30 high Galactic latitude globular clusters. Six of these globular clusters are detected with a TS > 25, with NGC 6254 being detected as gamma-ray bright for the first time. The most significant detection is of the well-known globular cluster 47 Tuc, and we produce a refined spectral fit for this object with a log parabola model. NGC 6093, NGC 6752 and NGC 6254 are fitted with hard, flat power law models, NGC 7078 is best fitted with a soft power law and NGC 6218 is best fitted with a hard, broken power law. This variety of spectral models suggests that there is a variety of γ-ray source types within globular clusters, in addition to the traditional millisecond pulsar interpretation. We identify a correspondence between diffuse X-ray emission in globular cluster cores and gamma-ray emission. This connection suggests that gammaray emission in globular clusters could also arise from unresolved X-ray sources or a relativistic electron population, perhaps generated by the millisecond pulsars. X-ray observations of further gamma-ray bright globular clusters would allow a functional relationship to be determined between diffuse X-ray and gamma-ray emission.

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A multiwavelength survey of NGC 6752: X-ray counterparts, two new dwarf novae and a core-collapsed radial profile

Cited by 18 publications

References 44 publications

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs

Identification of Faint Chandra X-Ray Sources in the Core-collapsed Globular Cluster NGC 6752

Gamma-ray emission from high Galactic latitude globular clusters

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