Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...473..539b&link_type=abstract
Astrophysical Journal v.473, p.539
Astronomy and Astrophysics
Astrophysics
20
Scientific paper
The VLA was used to observe a quiet region of the Sun on 1992 September 23 at 1.3 and 2 cm. Unlike previous interferometric microwave observations of the quiet Sun, we have used the total power data to calibrate the brightness temperature distribution in an absolute sense. We find a good correlation between the time-averaged 1.3 and 2 cm brightness distributions, and, in agreement with past studies at 3.6 and 6 cm, we find that both the 1.3 and 2 cm brightness distributions are closely correlated with the network magnetic field. The mean brightness at 1.3 and 2 cm was 10,400±1230 K and 12890±1415 K, respectively. The width of the σ1.3 cm brightness distribution function is σ1.3 = 270 K, while that at 2 cm is σ2 = 460 K.
We have examined the time variability of the 1.3 and 2 cm emission on a timescale of 2 hr. The correlation between the 1.3 and 2 cm brightness distributions is maintained, as is the correlation with the underlying magnetic field. However, considerable variability in the details of the brightness distribution is evident during the course of the day.
We compare our mean brightness measurements with those of Zirin, Baumert, & Hurford and compare the ensemble of observations with semi-empirical models of the chromosphere and transition region. The MCO model proposed by Avrett, which is in agreement with carbon monoxide observations, yields a microwave brightness temperature spectrum that is in excellent agreement with the microwave observations of Zirin et al. and those reported in this paper. The need for a model that reconciles all chromospheric observations optical, UV, infrared, and radio remains however. Inhomogeneous and/or dynamic chromospheric models are likely required.
Bastian Tim S.
Dulk George A.
Leblanc Yolanda
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