EDP Sciences
Free access
Volume 413, Number 1, January I 2004
Page(s) 343 - 362
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20031508

A&A 413, 343-362 (2004)
DOI: 10.1051/0004-6361:20031508

Mass motions and chromospheres of RGB stars in the globular cluster NGC 2808

C. Cacciari1, A. Bragaglia1, E. Rossetti1, F. Fusi Pecci1, G. Mulas2, E. Carretta3, R. G. Gratton3, Y. Momany4 and L. Pasquini5

1  INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, 40126 Bologna, Italy
    e-mail: cacciari@bo.astro.it; angela@bo.astro.it; emanuel@bo.astro.it; flavio@bo.astro.it
2  INAF-Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
    e-mail: gmulas@ca.astro.it
3  INAF-Osservatorio Astronomico di Padova, vicolo Osservatorio 5, 35122 Padova, Italy
    e-mail: carretta@pd.astro.it; gratton@pd.astro.it
4  Università di Padova, Dip. di Astronomia, vicolo Osservatorio 2, 35122 Padova, Italy
    e-mail: momany@pd.astro.it
5  European Southern Observatory, Karl-Schwarzschild-Str. 2, 85749 Garching b. München, Germany
    e-mail: lpasquin@eso.org

(Received 19 June 2003 / Accepted 22 September 2003 )

We present the results of the first observations, taken with FLAMES during Science Verification, of red giant branch (RGB) stars in the globular cluster NGC 2808. A total of 137 stars was observed, of which 20 at high resolution ( R= 47 000) with UVES and the others at lower resolution ( R= 19 000-29 000) with GIRAFFE in MEDUSA mode, monitoring ~3 mag down from the RGB tip. Spectra were taken of the H $\alpha$, Na I D and Ca II H and K lines. This is by far the largest and most complete collection of such data in globular cluster giants, both for the number of stars observed within one cluster, and for monitoring all the most important optical diagnostics of chromospheric activity/mass motions. Evidence of mass motions in the atmospheres was searched from asymmetry in the profiles and coreshifts of the H $\alpha$, Na I D and Ca II K lines, as well as from H $\alpha$ emission wings. We have set the detection thresholds for the onset of H $\alpha$ emission, negative Na  D2 coreshifts and negative  K3 coreshifts at  $\log L/L_{\odot}\sim$ 2.5, 2.9 and 2.8, respectively. These limits are significantly fainter than the results found by nearly all previous studies. Also the fraction of stars where these features have been detected has been increased significantly with respect to the previous studies. Our observations confirm the widespread presence of chromospheres among globular cluster giants, as it was found among Population I red giants. Some of the above diagnostics suggest clearly the presence of outward mass motions in the atmosphere of several stars.

Key words: line: profiles -- globular clusters: individual: NGC 2808 -- stars: atmospheres -- stars: mass loss -- stars: Population II -- techniques: spectroscopic

Offprint request: C. Cacciari, cacciari@bo.astro.it

SIMBAD Objects

© ESO 2004