Quote:
Originally Posted by Tim Thompson
[snip]
But in fact, all observations, especially in modern science, are subject to a limited amount of tweaking, because they are dependent on the model of the measuring device. You need to know the point spread function, the frequency response function, the sensitivity, & etc. for the measuring instrument (such as a CCD detector). It is common for scientists to publish observations, and later modify the observations with an improved model for their detectors (I have had to do that myself, as the point spread function for the IRAC instrument on the Spitzer Space Telescope is still not determined as well as we desire).
These tweaks to observations would appear insignificantly small to an outsider. But observers & experimentalists correctly feel responsible for producing observations which are as precise & accurate as they can be. And that level of precision is increasingly necessary to differentiate between competing theories & hypotheses.
[snip]
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It may be that the amount of work that goes into converting what comes from an instrument (in raw form) into a 'clean' observation is not widely understood. Nor the fact that there are, very often, changes that result from (sometimes much later) post-processing, as the performance of the instruments becomes better understood, etc.
To give some examples, similar to those in the quoted post, consider
the ST-ECF (my bold):
Quote:
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The ST-ECF consists of a small group of astronomers, software scientists and media specialists who support Hubble science in Europe and collaborate internationally on HST science, instrument, archive and outreach activities.
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And take just one example, from the Instrument science section,
Model Based Corrections to Data from Radiation Damaged Detectors (the link is to a PDF).
And SDSS; as an example, the most recent data-release (
DR6): "
Imaging caveats The following caveat is new to DR6 [...] The following caveat has been characterized quantitatively now [...] "
Finally, an example from
HIPPARCOS:
Improved Hipparcos Parallaxes of Coma Berenices and NGC 6231, a paper which references a bit of a controversy ("
a more consistent parallax of the Pleiades").
OK, so I can't resist this 2007 paper, especially in light of
this BAUT thread:
Cepheid parallaxes and the Hubble constant:
Quote:
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Revised Hipparcos parallaxes for classical Cepheids are analysed together with 10 Hubble Space Telescope (HST)-based parallaxes. In a reddening-free V, I relation we find that the coefficient of logP is the same within the uncertainties in our Galaxy as in the Large Magellanic Cloud (LMC), contrary to some previous suggestions. Cepheids in the inner region of NGC4258 with near solar metallicities confirm this result. We obtain a zero-point for the reddening-free relation and apply it to the Cepheids in galaxies used by Sandage et al. to calibrate the absolute magnitudes of Type Ia supernova (SNIa) and to derive the Hubble constant. We revise their result for H0 from 62 to 70 +/- 5kms-1Mpc-1. The Freedman et al. value is revised from 72 to 76 +/- 8kms-1Mpc-1. These results are insensitive to Cepheid metallicity corrections. The Cepheids in the inner region of NGC4258 yield a modulus of 29.22 +/- 0.03 (int.) compared with a maser-based modulus of 29.29 +/- 0.15. Distance moduli for the LMC, uncorrected for any metallicity effects, are 18.52 +/- 0.03 from a reddening-free relation in V, I; 18.47 +/- 0.03 from a period-luminosity relation at K; 18.45 +/- 0.04 from a period-luminosity-colour relation in J, K. Adopting a metallicity correction in V, I from Macri et al. leads to a true LMC modulus of 18.39 +/- 0.05.
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