APEX telescope efficiencies

The table is adapted from A&A 454, L13-L16 (2006). Beam sizes (θ_mb) have been determined by deconvolving planet scans. The listed efficiencies are forward efficiency (η_f), aperture efficiency (η_a), main beam efficiency (η_mb), and Moon efficiency (η_M). The uncertainties of the listed efficiencies are expected to be 5-10%.

The Kelvin to Jansky conversion factor for the APEX antenna is given by 24.4/η_a Jy/K. Hence, for the aperture efficiencies in the table above we obtain the following Kelvin to Jansky conversion factors. Also added below are the estimates for the frequency bands of coming receivers.

Instrument	Frequency [GHz]	Kelvin to Jansky conversion [Jy/K]	ηmb	Comment
APEX-1	230	39	0.75	Estimated from the Ruze formula
APEX-2	352	41	0.73
APEX-3/FLASH-I	464	48	0.60
CHAMP+-I	650	53	0.56	Estimated from the Ruze formula. See also note below.
FLASH-II/CHAMP+-II	812	70	0.43	See note below
APEX-T2	1300	(120)	(0.25)	Estimated from the Ruze formula

Note 1: Efficiency measurements listed in this page can be used as a reference but are a bit outdated. A new toolbox is under development and updated values will be provided soon in this page.

Note 2: The CHAMP+ efficiencies vary from year to year and in order to get the most accurate number please refer to the CHAMP+ web pages at MPIfR

According to the Ruze formula the aperture efficiency, η_a, will degrade with shorter wavelength, λ, as

η_a (λ) = η_a (∞) exp(-16π²σ²/λ²)

where σ is the antenna surface RMS value (i.e. describing small scale deviations from a perfect surface). The estimates of the values at 1300 GHz should be considered highly uncertain. No effects due to error beams, blockage, spillover, etc have been taken into account.