Further evidence of mass loss from globular cluster stars

Mallia, E. A.; Pagel, B. E. J.

doi:10.1093/mnras/184.1.55p

Cited by 19 publications

(11 citation statements)

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“…It follows from data in Table 3 of the cited paper that the velocity difference between the absorption core and the emission peaks does not significantly change from star to star, being about 50 km s −1 . The mass loss rate was determined in the model of stellar wind, like in the studies by Cohen (1976) and by Mallia & Pagel (1978). Our Table 1 shows that the velocity difference between the core and the emission peaks for K 413 is in agreement with the general pattern of the Cacciari & Freeman (1983) survey.…”

Section: The Spectral Features Of K 413supporting

confidence: 76%

“…Such profiles were first found in the spectra of four globular cluster stars by Cohen (1976) using photographic echelle spectra recorded with a two-stage image tube. Then Mallia & Pagel (1978) raised the number of Hα-emission stars to 12 with the RGO spectrograph and a photon counter. Recording spectra with a diode array at a three times poorer resolution compared to our resolution, Cacciari & Freeman (1983) surveyed spectra of bright stars in 12 globular clusters.…”

Section: The Spectral Features Of K 413mentioning

confidence: 99%

“…Low optical thickness follows also from the fact that no contribution from the envelope is observed for other strong lines of the photospheric spectrum (with the exception of the sodium resonance doublet). Mass loss rate estimates from Cacciari & Freeman (1983), Cohen (1976), Mallia & Pagel (1978) were essential for the problem of consistency of evolutionary computations of the RGB, HB, and AGB stages. It was noticed already in the first observations that the intensity ratio of the short-wave and long-wave residuals of the emission component differed from star to star and varied in time for each star.…”

Section: The Spectral Features Of K 413mentioning

confidence: 99%

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K 413, a star near the AGB in the globular cluster M 12

Клочкова

Samus

2001

A&A

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Abstract. CCD spectra obtained with the echelle spectrometer of the 6-meter telescope were used to determine, by the model atmospheres method, the fundamental parameters (T eff = 4800 K, log g = 0. The spectrum of K 413 shows, for the Hα line, an variable absorption and emission profile. From its high luminosity and chemical abundance anomalies, we can suppose that K 413 is in an evolutionary stage after the AGB. In the spectrum, we find absorption details that can be identified with diffuse interstellar bands displaced by 16 km s −1 to longer wavelengths relative to the star's velocity.

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Section: The Spectral Features Of K 413supporting

confidence: 76%

Section: The Spectral Features Of K 413mentioning

confidence: 99%

Section: The Spectral Features Of K 413mentioning

confidence: 99%

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K 413, a star near the AGB in the globular cluster M 12

Клочкова

Samus

2001

A&A

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“…The pioneering investigations of the Hα line profile in globular cluster red giants (Cohen 1976(Cohen , 1978(Cohen , 1979(Cohen , 1980(Cohen , 1981Mallia & Pagel 1978;Peterson 1981Peterson , 1982Cacciari & Freeman 1983;Gratton et al 1984) detected asymmetric and variable Hα emission wings along the brightest part of the RGB, which were generally interpreted as evidence of an extended atmosphere until Dupree et al (1984) showed that they could instead be signatures of a static stellar chromosphere.…”

Section: Diagnostics Of Velocity Fieldsmentioning

confidence: 99%

Modelling chromospheric line profiles as diagnostics of velocity fields inω Centauri red giant stars

Vieytes

Mauas

Cacciari

et al. 2010

A&A

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Context. Mass loss of ∼0.1−0.3 M from Population II red giant stars (RGB) is a requirement of stellar evolution theory in order to account for several observational evidences in globular clusters. Aims. The aim of this study is to detect the presence of outward velocity fields, which are indicative of mass outflow, in six luminous red giant stars of the stellar cluster ω Cen. Methods. We compare synthetic line profiles computed using relevant model chromospheres to observed profiles of the Hα and Ca II K lines. The spectra were taken with UVES (R = 45 000) and the stars were selected so that three of them belong to the metalrich population and three to the metal-poor population, and sample as far down as 1 to 2.5 mag fainter than the respective RGB tips. Results. We do indeed reveal the presence of low-velocity outward motions in four of our six targets, without any apparent correlation with astrophysical parameters.Conclusions. This provides direct evidence that outward velocity fields and mass motions exist in RGB stars as much as 2.5 mag fainter than the tip. On the assumption that the mass outflow may eventually lead to mass loss from the star, we estimate mass-loss rates of some 10 −9 −10 −10 M yr −1 that are compatible with the stellar evolution requirements. These rates seem to be correlated with luminosity rather than metallicity.

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“…Metal-poor giants brighter than log (L/L ) $ 2:5 in both the halo field and globular clusters frequently exhibit emission in one or both of the wings of the H absorption line (e.g., Cohen 1976;Mallia & Pagel 1978;Cacciari & Freeman 1983;Gratton et al 1984;Smith & Dupree 1988;Bates et al 1993;Kemp & Bates 1995). Lyons et al (1996) conclude that %80% of a total of 68 stars from five globular clusters with log (L/L ) > 2:7 exhibit H emission.…”

Section: Introductionmentioning

confidence: 99%

Hubble Space TelescopeObservations of Chromospheres in Metal-Deficient Field Giants

Dupree

Smith

2007

Astron J

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Hubble Space Telescope high-resolution spectra of metal-deficient field giants more than double the stars in previous studies, span $3 mag on the red giant branch, and sample an abundance range ½Fe/H ¼ À1 to À3. These stars, in spite of their age and low metallicity, possess chromospheric fluxes of Mg ii (k2800) that are within a factor of 4 of Population I stars, and they give signs of a dependence on the metal abundance at the lowest metallicities. The Mg ii k line widths depend on luminosity and correlate with metallicity. Line profile asymmetries reveal outflows that occur at lower luminosities (M V ¼ À0:8) than detected in Ca K and H lines in metal-poor giants, suggesting mass outflow occurs over a larger span of the red giant branch than previously thought and confirming that the Mg ii lines are good wind diagnostics. These results do not support a magnetically dominated chromosphere, but they appear more consistent with some sort of hydrodynamic or acoustic heating of the outer atmospheres.

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Further evidence of mass loss from globular cluster stars

Cited by 19 publications

References 0 publications

K 413, a star near the AGB in the globular cluster M 12

K 413, a star near the AGB in the globular cluster M 12

Modelling chromospheric line profiles as diagnostics of velocity fields inω Centauri red giant stars

Hubble Space TelescopeObservations of Chromospheres in Metal-Deficient Field Giants

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