Long period variables and mass loss in the globular clusters NGC 362 and NGC 2808

Lebzelter, T.; Wood, P. R.

doi:10.1051/0004-6361/201016319

Cited by 13 publications

(18 citation statements)

References 68 publications

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“…Studies have shown that the amplitudes of Mira pulsations do not exceed 30 km s −1 (e.g. Hinkle 1978;Hinkle et al 1982;Hinkle et al 1997;Lebzelter et al 2000;Lebzelter et al 2005;Lebzelter & Wood 2011). Our stars show velocities faster than this limit.…”

Section: Atmospheric Active Starsmentioning

confidence: 67%

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High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

Lützgendorf

Gualandris

Kissler-Patig

et al. 2012

A&A

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Context. We report the detection of five high-velocity stars in the core of the globular cluster NGC 2808. The stars lie on the red giant branch and show total velocities between 40 and 45 km s −1 . For a core velocity dispersion σ c = 13.4 km s −1 , this corresponds to up to 3.4σ c . These velocities are close to the estimated escape velocity (∼50 km s −1 ) and suggest an ejection from the core. Two of these stars have been confirmed in our recent integral field spectroscopy data and we will discuss them in more detail here. These two red giants are located at a projected distance of ∼0.3 pc from the center. According to their positions on the color magnitude diagram, both stars are cluster members. Aims. We investigate several possible origins for the high velocities of the stars and conceivable ejection mechanisms. Since the velocities are close to the escape velocity, it is not obvious whether the stars are bound or unbound to the cluster. We therefore consider both cases in our analysis. Methods. We perform numerical simulations of three-body dynamical encounters between binaries and single stars and compare the resulting velocity distributions of escapers with the velocities of our stars. If the stars are bound, the encounters must have taken place when the stars were still on the main sequence. We compare the predictions for a single dynamical encounter with a compact object with those of a sequence of two-body encounters due to relaxation. If the stars are unbound, the encounter must have taken place recently, when the stars were already in the giant phase. Results. After including binary fractions and black-hole retention fractions, projection effects, and detection probabilities from Monte-Carlo simulations, we estimate the expected numbers of detections for all the different scenarios. Based on these numbers, we conclude that the most likely scenario is that the stars are bound and were accelerated by a single encounter between a binary of main-sequence stars and a ∼10 M black hole. Finally, we discuss the origin of previously discovered fast stars in globular clusters, and conclude that the case of NGC 2808 is most likely a representative case for most other detections of fast stars in globular clusters. We show that with the present analysis we are able to explain high-velocity stars in the clusters M3 and 47 Tucanae with simple dynamical encounters.

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Section: Atmospheric Active Starsmentioning

confidence: 67%

“…However, an explanation could be that these stars have radial velocities of about 20 km s −1 on top of their Mira pulsations. Lebzelter & Wood (2011) recently investigated the long period variables of NGC 2808. Unfortunately, they had to exclude the inner regions of the cluster due to crowding.…”

Section: Atmospheric Active Starsmentioning

confidence: 99%

High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

Lützgendorf

Gualandris

Kissler-Patig

et al. 2012

A&A

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“…This effect is most noticeable in spectral features such as the TiO bands which are predominantly formed in the coolest, brightest giants. We were able to trace a one percent difference between our two R7000 observations of NGC 2808 (observed 159 days apart) to three known (Lebzelter & Wood 2011) long period variables in our field-of-view.…”

Section: Fe5335 Fe5270mentioning

confidence: 82%

The WAGGS project – I. The WiFeS Atlas of Galactic Globular cluster Spectra

Usher

Pastorello

Bellstedt

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present the WiFeS Atlas of Galactic Globular cluster Spectra, a library of integrated spectra of Milky Way and Local Group globular clusters. We used the WiFeS integral field spectrograph on the Australian National University 2.3 m telescope to observe the central regions of 64 Milky Way globular clusters and 22 globular clusters hosted by the Milky Way's low mass satellite galaxies. The spectra have wider wavelength coverage (3300Å to 9050Å) and higher spectral resolution (R = 6800) than existing spectral libraries of Milky Way globular clusters. By including Large and Small Magellanic Cloud star clusters, we extend the coverage of parameter space of existing libraries towards young and intermediate ages. While testing stellar population synthesis models and analysis techniques is the main aim of this library, the observations may also further our understanding of the stellar populations of Local Group globular clusters and make possible the direct comparison of extragalactic globular cluster integrated light observations with well understood globular clusters in the Milky Way. The integrated spectra are publicly available via the project website.

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“…Most of the mass loss occurs on the AGB, except for the lower-mass stars where mass loss on the RGB is substantial in a relative sense, of the order 0.25 M in total (McDonald et al 2009(McDonald et al , 2011Lebzelter and Wood 2011).…”

Section: The Total Mass Lost By An Agb Starmentioning

confidence: 99%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

471

376

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As low-and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newlyformed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angularresolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their windforming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angularresolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building B Susanne Höfner

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Long period variables and mass loss in the globular clusters NGC 362 and NGC 2808

Cited by 13 publications

References 68 publications

High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

High-velocity stars in the cores of globular clusters: the illustrative case of NGC 2808

The WAGGS project – I. The WiFeS Atlas of Galactic Globular cluster Spectra

Mass loss of stars on the asymptotic giant branch

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