A Test of Possible NICMOS Non-linearity
Observations of standard stars with NICMOS grism (G096), when compared with the same standards taken by STIS (G750L), show a disagreement over the wavelength range 0.8 to 1 micron. Further comparison with ACS F850LP data confirms thisnon-linearity to be due to NICMOS in the sense that fainter stars in NICMOS appear too faint relative to a brighter normalisation. We investigate this over a wide magnitude range by compiling samples of stars (over the range 8 < J < 17) and galaxies (spanning the range 17 < J < 25), with available data with both NICMOS (F110W and F160W) and ground-based JHbands. We find no difference between the NICMOS F160W and ground-based H-band magnitudes. However, in the case of NICMOS F110W and J-band filters, allowing for differences in the filter response functions, we find a trend at the bright-end (J < 17), confirming a non-linearity but smaller than that was seen in Bohlin effect by a factor of 2-3. No significant slope is seen at the faint-end. This non-linearity is interpreted as being due to trapping and the difference in exposure times between the bright and faint objects (Riess 2005). We conclude that most of the observations will not be strongly affected by this effect as the source count rates are sufficiently high so that the fraction of charge lost to traps is negligible. The most affected observations are for faint sources with relatively short exposures.
INSTRUMENT SCIENCE REPORT
This report gives a description of the IDL software developed to generate the latest geometric correction models and describes the process of using the specific routines to generate geometric correction models.
Characterization and gene cloning of a maltotriose-forming exo-amylase from Kitasatospora sp. MK-1785
A maltotriose-forming amylase (G3Amy) from Kitasatospora sp. MK-1785 was successfully isolated from a soil sample by inhibiting typical extracellular α-amylases using a proteinaceous α-amylase inhibitor. G3Amy was purified from the MK-1785 culture supernatant and characterized. G3Amy produced maltotriose as the principal product from starch and was categorized as an exo-α-amylase. G3Amy could also transfer maltotriose to phenolic and alcoholic compounds. Therefore, G3Amy can be useful for not only maltotriose manufacture but also maltooligosaccharide-glycoside synthesis. Further, the G3Amy gene was cloned and expressed in Escherichia coli cells. Analysis of its deduced amino acid sequence revealed that G3Amy consisted of an N-terminal GH13 catalytic domain and two C-terminal repeat starch-binding domains belonging to CBM20. It is suggested that natural G3Amy was subjected to proteolysis at N-terminal region of the anterior CBM20 in the C-terminal region. As with natural G3Amy, recombinant G3Amy could produce and transfer maltotriose from starch.