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Space Telescope Imaging Spectrograph

ACTIVITY TITLE: MAMA Spectroscopic Throughputs



DESCRIPTION: This activity has two functions: Determination of the STIS sensitivity for the MAMA spectroscopic modes and a baseline measurement for standard focus monitoring at NUV wavelengths.

Confirmation of STIS sensitivity for MAMA spectroscopic modes: Obtain exposures in the FUV and NUV low-resolution, medium-resolution and echelle modes to determine the post-SM4 STIS spectroscopic sensitivity, (re)establish a baseline for contamination/ sensitivity monitoring, and evaluate changes in sensitivity since the STIS side-2 LVPS failure. To accomplish this, an external standard star is observed in each of the 2 low-resolution MAMA spectroscopic modes (G140L and G230L) at the nominal target position through the 52X2 slit. The sensitivity of the medium resolution long-slit modes (G140M and G230M) is checked at a total of three central wavelengths (1173A, 1567A, and 2818A). BD+28D4211 is observed using the echelle modes with the 2X2 slit at a total of 5 central wavelengths: E140M(1425A), E140H(1416A), E230M(1978A, 2707A), and E230H(2263A) to determine the spectroscopic throughput of these modes.

This activity resumes sensitivity monitoring of each MAMA spectroscopic mode to enable detection of any change due to contamination or other causes. Cycle 17 resumes the previously established duty cycle for monitoring the sensitivity of the UV channels. Calibration standards stars are observed once every 3 months for the low-resolution spectroscopic modes, yearly for each of the 2 medium-resolution modes, and once every 6 months for each of the 4 echelle modes. This activity uses the same calibration standards, AGK+81D266, GRW+70D5824, and BD+28D4211, that were used in previous HST Cycles to monitor the STIS sensitivity. Each target is specific to a particular mode.

Baseline measurement for focus monitoring a at NUV wavelengths: ACQ/PEAKs are performed using the CCD/G230LB mode with the 0.1X0.09 aperture. The target is stepped in a crossed linear pattern to enable measurement of the focus (PSF) in the cross-dispersion (spatial) direction as a function of UV wavelength. The focus is also monitored in imaging mode by observing an appropriate standard star with the F28X50OII filter and the CCD.


DEPENDENCIES: Execute after the CCD target acquisition activity (STIS-13) and the FUV (STIS-23) and NUV (STIS-24) MAMA Image Quality activities. This activity uses external UV targets and the FUV and NUV MAMA detectors. It should execute after the end of the BEA period.

DURATION: 4 orbits (external).


ANALYSES & EXPECTED RESULTS: This activity will provide a broad range of basic performance information. The absolute sensitivity of STIS will be measured for each FUV and NUV grating mode. Ratioing these results for each UV mode with the previous (Cycle 12) sensitivity will provide a measurement of the STIS environment over the past several years and establish the current baseline for contamination monitoring and trending instrument sensitivity. The UV is sensitive to contaminants. Wavelength dependent sensitivity corrections will be derived and implemented in the calibration pipeline and used to refine exposure time predictions (ETC updates). The spectroscopic focus and UV (OII) imaging focus will be monitored as part of a Cycle 17 trending program.

COMMENTS: This activity comprises the three visits of the nominal Cycle 17 MAMA Spectroscopic Sensitivity Monitoring program. It establishes the Spectroscopic Sensitivity Monitor baseline for the low-resolution, medium-resolution, and echelle modes. Prior to first-order medium-resolution spectral sensitivity observations, an image of the standard star is taken using the F28X50OII aperture with the CCD as part of an ongoing UV focus monitoring program.

This activity may be regarded as part of the Cycle 17 calibration program.

AUTHOR/telephone/email: Mary Elizabeth Kaiser/401-516-5088/

DATE: September 26, 2007