Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21542417c&link_type=abstract
American Astronomical Society, AAS Meeting #215, #424.17; Bulletin of the American Astronomical Society, Vol. 42, p.333
Astronomy and Astrophysics
Astronomy
1
Scientific paper
Since the study by Porto de Mello & da Silva(1997,ApJ,482) the nearby 5.5-mag G2V star 18 Scorpii has been considered one of the best solar twins, being a near-perfect match to our Sun in all physical characteristics(Teff, R, log(g), MV, metallicity, luminosity, and chromospheric CaII H&K emissions). Also, 18 Sco has a rotation period of PRot=22.7±0.5 days(Petit et al. 2008), which is very close to that of the Sun. In addition, ongoing CaII H&K observations carried out at Lowell Observatory indicate a possible 7-11yr. activity cycle. However, until our X-ray observations with XMM-Newton in Aug 2005, 18 Sco had never been observed in this spectral region. The analysis of these measurements yield an X-ray luminosity and coronal plasma temperature of LX=8±1.5ergs/s and TCorona 1.5-2 MK. These data were taken near mid-cycle and match very closely with those of the Sun(LX 6-30ergs/s TCorona 2 MK). In addition to these measures, interferometric angular diameter measures with the Palomar Testbed Interferometer yield a stellar diameter of 0.975±0.162 R/RSun. Fitting the star's observed properties to current evolution models indicates a mass of M=0.98±0.05 MSun and an age of 4-5 Gyr. This age estimate (4.4±0.4 Gyr) is in excellent agreement with an age inferred from age-rotation-activity relations from the Sun in Time project. These observations demonstrate that 18 Sco is a bonafide solar twin out through the X-ray portion of the spectrum. Such a distinction makes is a very important star to use as a proxy "Night Time” Sun for standardization purposes, an excellent candidate for asteroseismic studies, and as a target for searches for life-bearing terrestrial planets.
This research is supported by grants from NASA/FUSE, NSF/RUI and by the Villanova University Research for Undergraduates Award Program, which we gratefully acknowledge.
Coughlin Jared
DePasquale Joseph
DeWarf Laurence
Engle Scott G.
Guinan Edward F.
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