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Дата изменения: Wed Jul 1 20:35:22 1998 Дата индексирования: Sat Dec 22 16:57:22 2007 Кодировка: |
where
in units of ergs/cm2/sec/Å, where:
) is the average value of the surface brightness, I
, over the Npixs ¥Npix
pixels in the rectangle being integrated.
is as given above (i.e., the values in the _x2d or _sx2 image).
is the plate scale (in arcsec/pixel) in the dispersion direction as given in the SCALE_A1 header keyword.
¥m
by Npixs ¥ms region on the sky, where Npix
¥m
equals the width of the emission feature in the spectral direction.
converts between diffuse continuum source surface brightness and diffuse emission line surface brightness and is given in the CONT2EML header keyword; it is simply the slit width expressed in Angstroms. The solid angle of a pixel in arcsec2 (ms ¥m
) is given in the header keyword OMEGAPIX.
(h) is the wavelength-dependent correction for the extraction slit of height h to a slit of infinite height, which is obtained from the reference table specified by the keyword PCTAB. That is, to derive the flux from a point source, integrate the _x2d or _sx2 file over the default extraction slit height (from the PCTAB) and multiply the result by DIFF2PT. The default extraction slit height for first-order modes is at present 11 pixels for the MAMAs and 7 pixels for the CCD. If the desired extraction slit height differs from the default, the PCTAB has a set of wavelength-dependent corrections for selected alternative apertures that must also be applied. See STIS ISR 98-01 for further details. Of course, point source observers are better advised to use the x1d task to extract a one-dimensional spectrum from their long-slit first-order data, which will then apply the wavelength-dependent aperture throughput, the defined point source extraction aperture and calibration, as well as perform background subtraction.
where
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