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We present the results of the first observations, taken with FLAMES duringScience Verification, of red giant branch (RGB) stars in the globular clusterNGC 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) withGIRAFFE in MEDUSA mode, monitoring ~ 3 mag down from the RGB tip. Spectra weretaken of the Halpha, Na I D and Ca II H and K lines. This is by far the largestand most complete collection of such data in globular cluster giants, both forthe number of stars observed within one cluster, and for monitoring all themost important optical diagnostics of chromospheric activity/massmotions.Evidence of mass motions in the atmospheres was searched from asymmetryin the profiles and coreshifts of the Halpha, Na I D and Ca II K lines, as wellas from Halpha emission wings. We have set the detection thresholds for theonset of Halpha emission, negative Na D_2 coreshifts and negative K_3coreshifts at log L/Lsun ~ 2.5, 2.9 and 2.8, respectively. These limits aresignificantly fainter than the results found by nearly all previous studies.Also the fraction of stars where these features have been detected has beenincreased significantly with respect to the previous studies. Our observationsconfirm the widespread presence of chromospheres among globular cluster giants,as it was found among Population I red giants. Some of the above diagnosticssuggest clearly the presence of outward mass motions in the atmosphere ofseveral stars.Comment: 21 pages, 11 figures, in press in Astronomy & Astrophysic

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