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Lithium Abundance in Solar-type Stars with Low Chromospheric Activity: Application to the Search for Maunder Minimum Analogs
We use measurements of lithium abundance to examine the evolutionaryhistory of stars frequently believed to be in a Maunder minimum (MM)state due to their low chromospheric activity. In a sample whosemain-sequence membership has been verified using Hipparcos parallaxdata, we find that stars with very low chromospheric activity logR'HK <= –5.0 have substantially depleted lithiumcompared with the full sample, with half of these lithium abundanceslying more than one standard deviation below the sample mean for theirrange of color index. One interpretation is that these stars are nearthe end of their main-sequence lifetime, and therefore their lowactivity does not necessarily signify a transient MM state in asolar-age star. Conversely, using information in published activity timeseries for some stars, and combined lithium and activity measurementsfrom the Ursa Major moving group and M67, we find limited evidence thata low-activity star having lithium abundance in the normal range for itscolor index may be a viable MM candidate. Thus, lithium abundance, whichcan be readily observed or even retrieved from some of the spectroscopicdata collected by recent planet-search surveys, may have value forexpanding and refining the program star lists for long-term MM searches.Finally, we find that the use of Hipparcos parallax data to ascertainmain-sequence membership sharpens the distinction in sample-mean lithiumabundance between stars with planet detections and comparison stars.
| Photoelectric observations of lunar occultations. XII
Occultation observations of 414 events observed between 6 July 1979 and4 September 1980 with the 0.76-m telescope of McDonald Observatory arereported. Timings and data on double stars are given. Angular diameterinformation in six cases is included. The stars concerned with their runnumbers are: SAO 161754 (5270); 94027 (Alpha Tau) (5319, 5381, 5454);159370 (Gamma Lib) (5325, 5571); 162413 (43 Sgr) (5332); 97472 (3 Cnc)(5414); and 93955 (Theta Tau) (5445).
| Lunar occultation summary. III
Observations of 242 photoelectric lunar occultation events studied atErwin W. Fick Observatory are reported. Approximately one-fourth ofthese are reappearances. From each observation are estimated the minimummagnitude differences between the observed object and possibleundetected companions. Occultation observations are given of 23 starsbrighter than 6th mag, including Alpha Vir, Beta-1 Sco, Mu Gem, Xi-2Sgr, Zeta Tau, Lambda Gem, and Beta Cap.
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Osservazione e dati astrometrici
| Costellazione: | Sagittario |
| Ascensione retta: | 19h21m08.81s |
| Declinazione: | -18°31'05.1" |
| Magnitudine apparente: | 8.239 |
| Distanza: | 628.931 parsec |
| Moto proprio RA: | -7 |
| Moto proprio Dec: | -17.4 |
| B-T magnitude: | 9.441 |
| V-T magnitude: | 8.339 |
Cataloghi e designazioni:
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