<i>Hubble Space Telescope</i>Observations of Chromospheres in Metal-Deficient Field Giants

Dupree, A. K.; Li, Timothy Q.; Smith, Graeme H.

doi:10.1086/520925

Cited by 20 publications

(22 citation statements)

References 81 publications

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“…Mass flows can produce asymmetric profiles of Hα and Na D, as well as emission asymmetries and velocity shifts in the reversed absorption core of Ca ii and Mg ii. These features have been measured in red giants in many globular clusters (Cacciari et al 2004;McDonald & van Loon 2007;Mészáros et al 2008Mészáros et al , 2009b and in metal-poor field stars (Smith & Dupree 1988;Dupree & Smith 1995;Dupree et al 2007). However, the velocities inferred from the optical profiles are generally less than the escape velocity from the star, and cannot truly be identified as stellar winds.…”

Section: Spectroscopic Diagnostics Of Windsmentioning

confidence: 79%

“…There are no X-ray sources at the positions of the two stars with strongest He absorption in the HEASARC Archives (http://heasarc.gsfc.nasa.gov), indicating that X-ray illumination does not appear to be present to strengthen the line. The RHB star, BD +17 • 3248, has a chromosphere as documented also by the presence of Mg ii ultraviolet emission (Dupree et al 2007). (Dupree et al 1992a;Smith et al 2004) have been added to this figure (see Table 3 The star HD 195636 displays an exceptionally strong He line.…”

Section: Equivalent Widthsmentioning

confidence: 99%

“…Three of the target stars (BD +17 • 3248, HD 122956, and HD 126587) have high resolution Hubble Space Telescope spectra available of the Mg ii line at λ2800 (Dupree et al 2007). Asymmetries of the line emissions indicate motions in the chromosphere, and these were found in stars brighter than M V = −0.8.…”

Section: Line Profilesmentioning

confidence: 99%

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Fast Winds and Mass Loss From Metal-Poor Field Giants

Dupree

Smith

Strader

2009

The Astronomical Journal

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Echelle spectra of the infrared He i λ10830 line were obtained with NIRSPEC on the Keck 2 telescope for 41 metal-deficient field giant stars including those on the red giant branch (RGB), asymptotic giant branch (AGB), and red horizontal branch (RHB). The presence of this He i line is ubiquitous in stars with T eff 4500 K and M V fainter than −1.5, and reveals the dynamics of the atmosphere. The line strength increases with effective temperature for T eff 5300 K in RHB stars. In AGB and RGB stars, the line strength increases with luminosity. Fast outflows ( 60 km s −1 ) are detected from the majority of the stars and about 40% of the outflows have sufficient speed as to allow escape of material from the star as well as from a globular cluster. Outflow speeds and line strengths do not depend on metallicity for our sample ([Fe/H]= −0.7 to −3.0), suggesting the driving mechanism for these winds derives from magnetic and/or hydrodynamic processes. Gas outflows are present in every luminous giant, but are not detected in all stars of lower luminosity indicating possible variability. Mass loss rates ranging from ∼3 × 10 −10 to ∼6 × 10 −8 M yr −1 estimated from the Sobolev approximation for line formation represent values with evolutionary significance for red giants and RHB stars. We estimate that 0.2 M will be lost on the RGB, and the torque of this wind can account for observations of slowly rotating RHB stars in the field. About 0.1-0.2 M will be lost on the RHB itself. This first empirical determination of mass loss on the RHB may contribute to the appearance of extended horizontal branches in globular clusters. The spectra appear to resolve the problem of missing intracluster material in globular clusters. Opportunities exist for "wind smothering" of dwarf stars by winds from the evolved population, possibly leading to surface pollution in regions of high stellar density.

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Section: Spectroscopic Diagnostics Of Windsmentioning

confidence: 79%

Section: Equivalent Widthsmentioning

confidence: 99%

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Fast Winds and Mass Loss From Metal-Poor Field Giants

Dupree

Smith

Strader

2009

The Astronomical Journal

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“…Low-mass stars in galactic globular clusters lose ∼20% of their mass during the ascent of the first red giant branch (RGB; Dupree et al 2007;Origlia et al 2007;McDonald & van Loon 2007), offering a partial explanation for the blue extent of the core-helium-burning horizontal branch (Rood 1973). It has been argued recently that in the old (8 Gyr), supersolar-metallicity ( ), massive open cluster NGC 6791, at least Z Ӎ 0.05 40% of RGB stars experience higher rates of mass loss; this would lead to their departure from the RGB before the helium flash, resulting in undermassive helium white dwarfs (Castellani & Castellani 1993;Hansen 2005;Kalirai et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Spitzer Space Telescope Evidence in NGC 6791: No Super Mass Loss at Supersolar Metallicity to Explain Helium White Dwarfs?

Loon

Boyer

McDonald

2008

ApJ

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We use archival Spitzer Space Telescope photometry of the old, supersolar-metallicity, massive open cluster NGC 6791 to look for evidence of enhanced mass loss, which has been postulated to explain the optical luminosity function and low white dwarf masses in this benchmark cluster. We find a conspicuous lack of evidence for prolificacy of circumstellar dust production that would have been expected to accompany such mass loss. We also construct the optical and infrared luminosity functions, and demonstrate that these fully agree with theoretical expectations. We thus conclude that there is no evidence for the mass loss of supersolar metallicity red giants to be sufficiently high that they can avoid the helium flash at the tip of the red giant branch.

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“…Earlier studies by Schrijver (1987) and Rutten et al (1991) have not identified a metallicity effect on chromospheric emission, particularly Ca II and Mg II, especially in main-sequence stars. On the other hand, more recent observations by the Hubble Space Telescope concerning chromospheric Mg II fluxes given by Dupree, Li & Smith (2007) indicate signs of dependence on metallicity at the lowest metallicities, although these results were obtained for giants rather than dwarfs.…”

Section: Comparison To Observational Datamentioning

confidence: 76%

Longitudinal magnetic tube wave fluxes in stars of low metallicity

Fawzy

2010

Monthly Notices of the Royal Astronomical Society

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A modified theory of turbulence generation is combined with the magnetohydrodynamic equations to numerically compute the wave energies generated at the base of magnetic flux tubes for stars with effective temperatures ranging from Teff= 3000 to 7000 K, gravity log g= 4.44 and with different metal abundances: solar, 0.1, 0.01 and 0.001 of solar metallicity. The results show that the effect of metallicity is very important for cool stars (Teff < 5500 K). The current numerical approach allows for non‐linear waves with large amplitudes and thus the obtained results for time‐averaged wave energy fluxes are higher than those obtained by the analytical approach. For hot stars the effect is negligible. The computed energy fluxes are essential for constructing theoretical models of the magnetic chromosphere of low‐metallicity stars. The maximum obtained wave energy flux for low‐metallicity stars is about 7.3 × 108 erg cm−2 s−1.

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Hubble Space TelescopeObservations of Chromospheres in Metal-Deficient Field Giants

Cited by 20 publications

References 81 publications

Fast Winds and Mass Loss From Metal-Poor Field Giants

Fast Winds and Mass Loss From Metal-Poor Field Giants

Spitzer Space Telescope Evidence in NGC 6791: No Super Mass Loss at Supersolar Metallicity to Explain Helium White Dwarfs?

Longitudinal magnetic tube wave fluxes in stars of low metallicity

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