Sub-millimeter Atmospheric Opacity Over “El Leoncito” Site

Ground-based radio telescopes observing at millimeter/submillimeter wavelengths need information on atmospheric attenuation to recover the corrected brightness temperature of astrophysical objects. To determine the zenital opacity, several methods have been used. In comparison with other techniques, the solar brightness method allows determining the atmospheric opacity up to high values and only depends on estimating, as accurately as possible, the product P = ηT
_Θ
where η is the beam efficiency and T
_Θ
is the Sun brightness temperature at the observation frequencies. Although T
_Θ
and η are not known individually, we assume that P must be constant. In this work, we reported the measured the zenith opacity at 212 GHz, τ
₂₁₂
, and 405 GHz, τ405 using the solar brightness method, over "El Leoncito" site (2550 m altitude above sea level) for the period 20062014. We found a linear correlation between τ
₂₁₂
and τ
₄₀₅
with R = 0.90, the resulting relation τ
₄₀₅
= 0.07+6.90 τ
₂₁₂
, allows to estimate the opacity at 405 GHz. Our result also shows that the ration of opacities (τ
₄₀₅
/τ
₂₁₂
) is ≈ 7, which indicates an excellent agreement with the value of model prediction (≈ 7). As expected, a clear seasonal pattern of opacity measurements is observed along the years. Finally, we also confirm that there is a significance correlation between the opacities obtained and the precipitable water vapor content (PWV) over "El Leoncito" site, between 2011 and 2014.