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| Paper: |
How Could Precise Stellar Radial Velocities Help to Understand Field and Cluster-Member Flare Stars |
| Volume: |
185, Precise Stellar Radial Velocities, IAU Colloquium 170 |
| Page: |
218 |
| Authors: |
Szécsényi-Nagy, G. |
| Abstract: |
There are a lot of flare stars in the apparent fields of stellar aggregates. The regions most abundant in this species are that of the Orion nebula and of the Pleiades open cluster. Statistical investigation of the data collected during the past decades suggested that both of these young stellar systems may contain about a thousand (or even more) flare stars. Their number is inferior to the total of cluster member red dwarfs of course. This huge population of unexpected members inspired colleagues to give new estimates for the total mass of these systems and to try to determine the contribution of red dwarf stars to the total mass of the Galaxy. Everything seemed to be correct until very recently when a detailed and really deep proper motion survey of the Pleiades field provided a quite shocking result. It has been shown that a substantial part of the flare stars identified in the sky field of the Pleiades cluster can not be proper motion members of the system (Szecsenyi-Nagy et al., in press). The percentage of high probability members is about 45-50 while at least 40% of all flare stars catalogued and investigated are field stars, partly foreground but even more probably background stars. Since proper motion studies can only be done in the case of well (and for long) observed regions and we do not intend to wait half a century for second epoch plates, the combination of photometric and radial velocity data is suggested in order to get an instantaneous decision on the membership probabilities of these red dwarfs. It is quite well known that the radial velocities of the brighter members of the Pleiades do not deviate considerably from the mean radial velocity of the cluster itself. The scatter is in the order of magnitude of the accuracy of measurements, quite contrary to the proper motion values. That is why the precise stellar radial velocity measurement of late dwarfs is initiated in the fields of stellar aggregates abundant in flare stars. Although these objects are intrinsically faint, modern spectroscopic techniques and up-to-date photon detectors may provide the measurements necessary for the reliable membership classification of the flare-active red dwarfs. As a by-product the spectroscopic data may contribute to the better understanding and modelling of the stellar flare phenomenon too. |
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