Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.9202p&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #92.02; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
3
Scientific paper
NGC 7027 is the planetary nebula with the highest flux density in the radio spectrum, and is widely used as a flux density calibrator. We present the results of 23 years of precise monitoring of its flux density, using the VLA, at seven frequency bands between 1.4 and 43 GHz.
At 1.4 GHz, we find the flux density is uniformly increasing at a rate of 0.24 percent/year. This directly measures the expansion of the nebula. The expansion parallax gives a distance of 800 pc. The optically thin flux density is decreasing at a rate of 0.15 percent/year. This is attributed to a decreasing number of ionizing photons as the star increases in temperature. Based on Rauch models, the temperature increase is found to be 280 +/25 K/year, assuming constant luminosity. This increase is very sensitive to stellar mass -we determine a value of 0.675 +/.002 solar masses. This is the first measurement of the remnant mass of a carbon star.
Perley Richard A.
van Hoof Peter
Zijlstra Albert A.
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