GHRS Observations of Cool, Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of alpha Orionis (M2 Iab)

Details GHRS Observations of Cool, Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of alpha Orionis (M2 Iab) GHRS Observations of Cool, Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of alpha Orionis (M2 Iab)

Apr 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...479..970c&link_type=abstract

Astrophysical Journal v.479, p.970

Astronomy and Astrophysics

Astronomy

29

Stars: Chromospheres, Ultraviolet: Stars, Stars: Individual Constellation Name: Alpha Orionis, Stars: Late-Type, Turbulence

Scientific paper

We present the results of a Goddard High Resolution Spectrograph (GHRS) study of flow and turbulent velocities in the outer atmosphere of the M2 Iab supergiant alpha Ori. Ions with observed chromospheric emission features include C I, C II, Si I, Si II, O I, Co II, Al II, Mg II, Cr II, Fe I, and Fe II, while the photospheric absorption spectrum is dominated by Fe I. The widths of optically thin lines of C II], Si II], Co II, and Fe II indicate an average chromospheric turbulent velocity (Doppler FWHM) in the range of 31--35 km s-1, which is substantially above the expected chromospheric sound velocity. The shape of the C II] profiles indicates that this turbulence is probably anisotropically distributed, with velocities preferentially directed along and/or perpendicular to the radial direction. The radial velocity of near-UV Fe I photospheric absorption lines averaged 18 km s-1, somewhat smaller than the systemic RV of alpha Ori itself (21 km s-1) and significantly smaller than the RV of the optical Fe I lines (23 km s-1) at the time of the HST observations. The various components of the chromospheric emission lines had radial velocities in the range 7--36 km s-1. The emission wings for most of the ionic species averaged ~20 km s-1, i.e., they were nominally at rest with regard to the star. The central absorption features in these lines, however, showed lower velocities, averaging ~16 km s-1. The radial velocity of the central reversals in the stronger lines was also found to be correlated with the opacity of the lines, changing from ~20 km s-1 for the lower opacity lines to ~14 km s-1 for the higher opacity lines. This implies that we are directly viewing the acceleration of the stellar wind in the chromosphere from rest to about 7 km s-1. Contrary to the results reported earlier by Carpenter (1984) on the basis of IUE data, there is no indication of a deceleration of the wind at large distances from the star.

Affiliated with

Also associated with

No associations

Rating

GHRS Observations of Cool, Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of alpha Orionis (M2 Iab) does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with GHRS Observations of Cool, Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of alpha Orionis (M2 Iab), we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and GHRS Observations of Cool, Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of alpha Orionis (M2 Iab) will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1316801