On the Origin of Sub-subgiant Stars. I. Demographics

Geller, Aaron M.; Leiner, Emily; Bellini, Andrea; Gleisinger, Robert; Haggard, Daryl; Kamann, Sebastian; Leigh, Nathan W. C.; Sills, Alison; Watkins, Laura L.; Zurek, David

doi:10.3847/1538-4357/aa6af3

Cited by 67 publications

(82 citation statements)

References 117 publications

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“…We do not detect variability in the radial velocities of the fourth RS and it is not associated with an X-ray source. These correlations fit the general characteristics of SSG and RS as described in Geller et al (2017a). Orbital parameters for several SSG systems in NGC 3201, including the Hα emitters discovered here, are presented in Giesers et al (2019).…”

Section: Red Stragglers and Sub-subgiantssupporting

confidence: 78%

A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

Göttgens

Husser

Kamann

et al. 2019

A&A

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Aims. Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousands other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra, that means spectra that contain emission lines, we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. Methods. To detect emission lines in each spectrum, we model the expected shape of an emission line as a Gaussian curve. This template is used for matched filtering on the differences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of Hα emission are checked visually and cross-matched with published catalogues. Results. We find 156 stars with Hα emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detect Hα emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.

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Section: Red Stragglers and Sub-subgiantssupporting

confidence: 78%

A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

Göttgens

Husser

Kamann

et al. 2019

A&A

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“…5). Stars in this position ("red stragglers") are frequently associated with coronally active X-ray sources in open and globular clusters (Belloni et al 1998;Cool et al 2013;Geller et al 2017). Therefore, we think it very likely that CX1a is associated with this star, a cluster member.…”

Section: X-ray Point Source Cx1a: a Star In The Cluster?mentioning

confidence: 98%

The X-ray emissivity of low-density stellar populations

Heinke

Ivanov

Koch

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The dynamical production of low-mass X-ray binaries and brighter cataclysmic variables (CVs) in dense globular clusters is well-established. We investigate how the X-ray emissivity of fainter X-ray binaries (principally CVs and coronally active binaries) varies between different environments. We compile calculations (largely from the literature) of the X-ray emissivity of old stellar populations, including open and globular clusters and several galaxies. We investigate three literature claims of unusual X-ray sources in low-density stellar populations. We show that a suggested quiescent neutron star in the open cluster NGC 6819 is a foreground M dwarf. We show that the suggested diffuse X-ray emission from an old nova shell in the globular cluster NGC 6366 is actually a background galaxy cluster. And we show that a suggested population of quiescent X-ray binaries in the Sculptor Dwarf Galaxy is mostly (perhaps entirely) background galaxies. We find that above densities of 10 4 M /pc 3 , the X-ray emissivity of globular clusters increases, due to dynamical production of X-ray emitting systems. Below this density, globular clusters have lower X-ray emissivity than the other populations, and we do not see a strong dependence of X-ray emissivity due to density effects. We find significant correlations between X-ray emissivity and binary fraction, metallicity, and density. Sampling these fits via bootstrap techniques gives less significant correlations, but confirms the effect of metallicity on low-density populations, and that of density on the full globular cluster sample.

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“…The evolution of these stars cannot be explained by single star evolution. Geller et al (2017a) 49 17 163 02 49 15 143 03 44 15 143 04 36 12 114 Deep 16 4 160 194 63 723 ios explained in Leiner et al (2017) for SSG and RS are isolated binary evolution, the rapid stripping of a subgiant's envelope, or stellar collisions. So far, from observations and simulations, no channel can be excluded, but it seems that the binary channel is dominant in globular clusters (Geller et al 2017b).…”

Section: Sub-subgiant Starsmentioning

confidence: 99%

“…The four sub-subgiants in our sample could also be defined as red stragglers, since they are at the boundary of both definitions inGeller et al (2017a).…”

mentioning

confidence: 99%

A stellar census in globular clusters with MUSE: Binaries in NGC 3201

Giesers

Kamann

Dreizler

et al. 2019

A&A

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We utilize multi-epoch MUSE spectroscopy to study binary stars in the core of the Galactic globular cluster NGC 3201. Our sample consists of 3553 stars with 54 883 spectra in total comprising 3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in our sample has between 3 and 63 (with a median of 14) reliable radial velocity measurements within five years of observations. We introduce a statistical method to determine the probability of a star showing radial velocity variations based on the whole inhomogeneous radial velocity sample. Using HST photometry and an advanced dynamical MOCCA simulation of this specific cluster we overcome observational biases that previous spectroscopic studies had to deal with. This allows us to infer a binary frequency in the MUSE FoV and enables us to deduce the underlying true binary frequency of (6.75 ± 0.72) % in NGC 3201. The comparison of the MUSE observations with the MOCCA simulation suggests a significant fraction of primordial binaries. We can also confirm a radial increase of the binary fraction towards the cluster centre due to mass segregation. We discovered that in the core of NGC 3201 at least (57.5 ± 7.9) % of blue straggler stars are in a binary system. For the first time in a study of globular clusters, we were able to fit Keplerian orbits to a significant sample of 95 binaries. We present the binary system properties of eleven blue straggler stars and the connection to SX Phoenicis-type stars. We show evidence that two blue straggler formation scenarios, the mass transfer in binary (or triple) star systems and the coalescence due to binary-binary interactions, are present in our data. We also describe the binary and spectroscopic properties of four sub-subgiant (or red straggler) stars. Furthermore, we discovered two new black hole candidates with minimum masses (M sin i) of (7.68 ± 0.50) M , (4.4 ± 2.8) M , and refine the minimum mass estimate on the already published black hole to (4.53 ± 0.21) M . These black holes are consistent with an extensive black hole subsystem hosted by NGC 3201.

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On the Origin of Sub-subgiant Stars. I. Demographics

Cited by 67 publications

References 117 publications

A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

The X-ray emissivity of low-density stellar populations

A stellar census in globular clusters with MUSE: Binaries in NGC 3201

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