Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...296..771m&link_type=abstract
Astronomy and Astrophysics, v.296, p.771
Astronomy and Astrophysics
Astrophysics
71
Stars: Fundamental Parameters, Infrared: Stars, Stars: General, Stars: Atmospheres, Techniques: Photometric
Scientific paper
Absolute flux calibrations are crucial in astrophysics. Our purpose in this paper is to constrain as much as possible the uncertainties on the visible and near infrared stellar absolute monochromatic fluxes and to fix their intrinsic values with a high level of confidence, from a careful examination of the available calibrations. Taking into account the reliability of the different kinds of terrestrial reference sources, among which blackbodies are more fundamental and more reliable than Tu lamps, we are able to constrain the visible monochromatic flux f_5556_ of the reference star Vega within the standard error +/-0.7%, the internal consitency being +/-0.4%. A likely systematic error due to the Tu lamp used in 1969 at the Palomar Observatory lead us to discard the low value obtained there. There are strong reason to retain f_5556_(α Lyr)=3.46x10^-11^W/m^2^/nm, which corresponds to f_5500_(αLyr)=3.56+/-0.01x10^-11^W/m^2^/nm^ and to f_5500_(V =0.0)=3.66+/-0.01x10^-11^W/m^2^/nm for a Vega like star. The near infrared Vega flux calibrations relying on model atmospheres contain a systematic error caused by the near infrared excess of the star relative to the models. Then giving the proper weight to the non model dependent calibrations, we derive the most reliable values at the moment for the absolute monochromatic fluxes corresponding to the effective wavelengths of the filters J, H, K and L in the Johnson photometric system. The internal accuracy for each of them is within 2%, which is better than the flux measurement uncertainty, estimated to 2% or 3%. The best representative Planck function of these calibrations is used to derive the IR ESO system calibration. The fluxes corresponding to the four ESO filters are obtained within 2%, instead of the previous 4%, and they are about 1% higher than those given earlier. In the visible as well as in the infrared domains, more direct absolute flux calibrations would be useful.
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