Interstellar Na I Toward the Pleiades: Evidence for a Foreground Shock

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Session 62 -- Very Young Stars
Display presentation, Thursday, 9:20-4:00, Pauley Room

[62.02] Interstellar Na I Toward the Pleiades: Evidence for a Foreground Shock

R.E.White, W.B.Forrester, A.M.Gonnella (Smith C.)

We have obtained high signal-to-noise spectra of the NaI D-lines with spectral resolution 200,000 toward 36 stars in and near the Pleiades star cluster, using the Coude' Feed Telescope at Kitt Peak National Observatory. The line profiles show extraordinary variety, revealing kinematic and ionization differences along the lines of sight through and past the cluster. Some sight-lines appear to exhibit only a single velocity component at the ambient gas velocity [V(sun) = 16.5 km s$^{-1}$, V(LSR) = 7.5 km s$^{-1}$]. Sight-lines that penetrate the molecular cloud toward the back of the cluster as seen from the sun exhibit a velocity component that is redshifted by about 3 km s$^{-1}$ from the ambient gas velocity. According to White \& Bally (1993), this component represents gas deflected away from the sun by a shock as the cluster plows supersonically through the ambient interstellar medium. Their interpretation requires a corresponding foreground velocity component blueshifted by about 10 km s$^{-1}$. Although photoionization in the cluster vicinity makes the absorption by Na I very weak, the predicted shock component is clearly present on several lines of sight.


White, R. E., \& Bally, J. 1993, ApJ, 409, in press.

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