Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.5101g&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #51.01; Bulletin of the American Astronomical Society, Vol. 24, p.1205
Other
6
Scientific paper
ROSAT X-ray observations of the young solar-type star, HD 129333 (G0 V; mv =~ +7.5; tau =~ 70 Myr) and the old solar-type star beta Hydri (G2 IV; mv = +2.80; tau =~ 9 Gyr) are discussed. HD 129333 represents the ZAMS Sun, 4.5 Gyr ago when it was rotating about 10 times faster than today and had correspondingly much greater levels of chromospheric and coronal activity. In contrast, beta Hydri represents the future Sun near the end of its hydrogen-core burning stage, when it should be rotating more slowly and should have lower levels of activity. The ROSAT observations of the young sun HD 129333 show it to be a relatively strong source of coronal X-rays with an Lx(0.1-2.0 keV) =~ 1-2 times 10(30) ergs s(-1) . The best fit to the X-ray energy distribution indicates a two-temperature component corona with T1 = 2 times 10(6) K and T2 = 10 times 10(6) K. The high levels of coronal emission found for HD 129333 are consistent with its rapid rotation (Prot =~ 2.8d) and the strong chromospheric and TR emissions seen in the IUE data. This study indicates that the early ZAMS Sun was an intense X-ray source about a thousand times stronger than the present Sun. The high levels of X-ray and UV emissions implied for the early Sun could have had a significant impact on the evolution and chemistry of the primordial atmospheres of the solar system planets -- including that of the Earth. As discussed by Dravins and collaborators (1992), beta Hydri is an older Sun with a rotation period of =~ 45(d) and with chromospheric emissions which are about half those of the present Sun. ROSAT observations of beta Hydri indicate a cooler, less luminous corona with T =~ 1.5 times 10(6) K and Lx =~ 1 times 10(27) ergs s(-1) . The ROSAT and IUE data and the available ground-based photometry will be discussed together with observations of other solar-type stars with intermediate ages. More ROSAT data is expected to be collected on beta Hydri, and these results will be presented if available. This research is supported by NASA grants NAG 5-1662, NAG 5-1703, and NAG 5-382. Photometry for these stars is being carried out with the Four College Consortium 0.8m APT which is supported under NSF grant AST-8616362.
Dorren David J.
Guinan Edward F.
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