The lithium abundances of planet-harbouring stars have been compared with the lithium abundances of open clusters and field stars. Young (chromospherically active) and subgiant stars have been eliminated from the comparison because they are at different stages of evolution and Li processing than the planet-harbouring stars, and hence have systematically higher Li abundances. The analysis showed that the Li abundances of the planet-harbouring stars are indistinguishable from those of non-planet-harbouring stars of the same age, temperature and composition. This conclusion is opposite to that arrived at by Gonzalez & Laws; it is believed that the field-star sample used by them contained too wide a range of ages, evolutionary types and temperatures to be accommodated by the model that they adopted to describe the dependence of Li on the parameters. The Li abundance does not appear set to provide key insights into the formation and evolution of planetary systems. 相似文献
We have used echelle spectra of resolving power 35 000 to derive chemical abundances and the 12C/13C ratio in the 1.9-d carbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparison star. We confirm that RT TrA is very metal-rich with [Fe/H]=+0.4. In addition, C and N are substantially in excess, and a small deficiency in O is present. We interpret these anomalies as resulting from the appearance on the stellar surface of material enriched in 12C by the 3- α process, followed by CNO cycling to convert 12C to 13C and 14N. In addition, some 16O has been processed to 14N. The partial processing of 16O to 14N indicates that substantial 17O may be present. Proton capture seems to have enhanced 23Na from the Ne isotopes. 相似文献
When the National Weather Service (NWS) issues a tornado warning, the alert is rapidly and widely disseminated to individuals in the general area of the warning. Historically, the assumption has been that a false-negative warning perception (i.e., when someone located within a warning polygon does not believe they have received a tornado warning) carries a higher cost than a false-positive warning perception (i.e., when someone located outside the warning area believes they have received a warning). While many studies investigate tornado warning false alarms (i.e., when the NWS issues a tornado warning, but a tornado does not actually occur), less work focuses on studying individuals outside of the warning polygon bounds who believe they received a warning (i.e., false-positive perceptions). This work attempts to quantify the occurrence of false-positive perceptions and possible factors associated with the rate of occurrence. Following two separate storm events, Oklahomans were asked whether they perceived a tornado warning. Their geolocated responses were then compared to issued warning polygons. Individuals closer to tornado warnings or within a different type of warning (e.g., a severe thunderstorm warning) are more likely to report a false-positive perception than those farther away or outside of other hazard warnings. Further work is needed to understand the rate of false-positive perceptions across different hazards and how this may influence warning response and trust in the National Weather Service.