A Semiempirical Determination of the Wind Velocity Structure for the Hybrid-Chromosphere Star alpha Trianguli Australis

Harper, G. M.; Wood, Brian E.; Linsky, Jeffrey L.; Bennett, P. D.; Ayres, Thomas R.; Brown, Alexander

doi:10.1086/176312

Cited by 32 publications

(32 citation statements)

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“…Pressures appear lower by an order of magnitude in a Aqr. The inferred pressures are consistent with previous upper limits for b Dra (Brown et al 1984) and lower limits (Harper et al 1995) for a TrA, and are in good agreement with the density derived from C ii diagnostics in a TrA (Hartmann et al 1985). It is also clear that processes must be considered that can weaken the diagnostic lines: interstellar extinction and wind absorption.…”

Section: Discussionsupporting

confidence: 89%

“…The ratio of the resonance line l1206.50 of Si iii ( ) to the intersystem transition at 1892.03 Å Harper et al (1995), for 0.05 6.7 ‫ע‬ 0.13 a Aqr from Hartmann et al (1985), and for b Dra 19.7 ‫ע‬ 3.8 from Brown et al (1984)-we find that the ratio (in units of ergs) l1892/l1206 has values ≈1.0-1.17 (a TrA), 0.35 (a Aqr), and 0.62 (b Dra). All of these values are at or below the lowdensity limit (1.18 for ; 0.9 for ) of the theo-…”

Section: Si III Diagnosticsmentioning

confidence: 99%

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[ITAL]ORFEUS[/ITAL] Observations of Luminous Cool Stars

Dupree¹,

Brickhouse²

1998

The Astrophysical Journal

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The ORFEUS telescope obtained far-ultraviolet spectra (ll912-1218) of three luminous cool stars: b Draconis (HD 159181) and two hybrid stars, a Aquarii (HD 209750) and a Trianguli Australis (HD 150798). Most striking is the detection of blueshifted O vi l1032, and C iii l977 emission relative to Si iii l1206, indicating outward motion, and the markedly narrow resonance line profiles of C iii and Si iii in the two hybrid objects as compared with the coronal star b Dra. The observed Doppler shifts suggest that a warm wind of at least K occurs 5 3 # 10 in the hybrid stars with outflows ∼100-200 km s ; narrow lines of C iii and Si iii are consistent with signatures Ϫ1 of wind absorption. The asymmetric profile of C iii in b Dra might also result from wind absorption, although the acceleration would have to begin at higher temperatures (T ∼ 70,000 K) in this coronal star as compared with the hybrids, since its chromospheric Mg ii profiles show no asymmetry due to wind absorption. Electron densities determined from C iii multiplets in b Dra and a TrA indicate values between 8.3 and 8.6 dex (cm Ϫ3 ), giving a pressure of ∼ cm Ϫ3 K, at K. Wind absorption and interstellar extinction must be 13 42 # 10 T ∼ 7 # 10 considered when applying emission-line diagnostics in this wavelength region.

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Section: Discussionsupporting

confidence: 89%

Section: Si III Diagnosticsmentioning

confidence: 99%

[ITAL]ORFEUS[/ITAL] Observations of Luminous Cool Stars

Dupree¹,

Brickhouse²

1998

The Astrophysical Journal

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“…The red giant wind is not a steady outward stream but an outflow consisting of many small-scale structures. Our simulations show that both hot plasma and cool chromospheric wind coexist in red giant stars, which is consistent with reported hybrid activities (Hartmann et al 1980, Harper et al 1995, Ayres et al 1998). …”

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confidence: 91%

Evolution of stellar winds from the Sun to red giants

Suzuki¹

2008

Proc. IAU

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Abstract. By performing global 1D MHD simulations, we investigate the heating and acceleration of solar and stellar winds in open magnetic field regions. Our simulation covers from photosphere to 20-60 stellar radii, and takes into account radiative cooling and thermal conduction. We do not adopt ad hoc heating function; heating is automatically calculated from the solutions of Riemann problem at the cell boundaries. In the solar wind case we impose transverse photospheric motions with velocity ∼1 km/s and period between 20 seconds and 30 minutes, which generate outgoing Alfvén waves. We have found that the dissipation of Alfvén waves through compressive wave generation by decay instability is quite effective owing to the density stratification, which leads to the sufficient heating and acceleration of the coronal plasma. Next, we study the evolution of stellar winds from main sequence to red giant phases. When the stellar radius becomes ∼10 times of the Sun, the steady hot corona with temperature 10 6 K, suddenly disappears. Instead, many hot and warm (10 5 −10 6 K) bubbles are formed in cool (T < 2 × 10 4 K) chromospheric winds because of the thermal instability of the radiative cooling function; the red giant wind is not a steady stream but structured outflow.

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“…Both of our targets have been observed with the HST , a TrA with both the GHRS (Harper et al 1995) and STIS, and HD 104237 with the GHRS (Brown et al 1997). A brief summary of each FUSE observation is given below, and a more detailed discussion of each data set will be presented in future papers.…”

Section: The Observationsmentioning

confidence: 88%

Identification of FeiiEmission Lines inFUSEStellar Spectra

Harper

Wilkinson

Brown

et al. 2001

ApJ

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We identify two complexes of Fe II emission lines in far-ultraviolet spectra of the stars a TrA and HD 104237. Using spectra from both the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space T elescope (HST ), we show that these emission lines, which represent the majority of previously unidentifed emission features in cool star spectra between 912 and 1180 are Ñuorescent decays in Fe II following excitation by H Lya. SpeciÐ-A , cally, following photoexcitation from the third term (4s a 4D) of Fe II, subsequent decays are observed to the two lowest terms (4s a 6D and 3d7 a 4F) which are observed near 1100 and 1135 respectively. A , Decays to higher terms, and hence longer wavelengths, also are clearly seen in the STIS spectra. Di †er-ences in the Ñuorescent Fe II spectra of a TrA and HD 104237 are tentatively identiÐed as resulting from di †erences in the intrinsic width of the density-weighted H Lya radiation Ðelds. The additional Fe II lines observed in a TrA result from a broadened H Lya proÐle. Two features near 1060 appear to be Ñuo-A rescent lines of Cr II, also excited by H Lya.

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A Semiempirical Determination of the Wind Velocity Structure for the Hybrid-Chromosphere Star alpha Trianguli Australis

Cited by 32 publications

References 0 publications

[ITAL]ORFEUS[/ITAL] Observations of Luminous Cool Stars

[ITAL]ORFEUS[/ITAL] Observations of Luminous Cool Stars

Evolution of stellar winds from the Sun to red giants

Identification of FeiiEmission Lines inFUSEStellar Spectra

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