Full Aperture Complement

The STIS aperture wheel has 65 positions, several of which correspond to multiple slits or masks. Only a small fraction of the available-but-unsupported spectroscopic apertures are currently supported. Table 1.1 provides a complete list of STIS apertures for spectroscopy, together with comments regarding their characteristics or purposes. Schematics of three complex apertures are given in Figure 1.1, Figure 1.2 and Figure 1.3.

Table A1.1: STIS Spectroscopic Apertures. Supported apertures are in boldface.

Apertures	Comments
Apertures for First-Order Gratings
52X0.05 52X0.1 52X0.2 52X0.5 52X2	Long slits; length by width in arcseconds.
52X0.05E1 52X0.1E1 52X0.2E1 52X0.5E1 52X2E1	Long slits centered at 19.7 arcsec in +Y position. (Places compact target at row ~900 on the CCD to reduce CTE losses.)
52X0.05F1 52X0.05F2 52X0.1F1 52X0.1F2 52X0.2F1 52X0.2F2 52X0.5F1 52X0.5F2 52X2F1 52X2F2	Fiducial bars on the long slits which can be used for coronagraphic spectroscopy. Only the 52X0.2F1 is supported. All these fiducial bar slits are available-but-unsupported with the echelle gratings.
52X0.1B0.5 52X0.1B1.0 52X0.1B3.0	A long slit with 3 fiducial bars where width in arcsec is given by the third dimension. See Figure 1.1.
2X2 6X6	Square apertures of the given dimensions in arcsec.
25MAMA 50CCD	Supported full-field clear apertures.
F25QTZ F25SRF2 F28X50LP	Long-pass filters. F25QTZ and F25SRF2 are supported for G140L and G140M.
F28X50OII F28X50OIII	Narrow-band CCD filters.
F25ND3 F25ND5 F25NDQ1 F25NDQ2 F25NDQ3 F25NDQ4	Supported neutral-density filters for MAMA detectors.
F25MGII F25CN279 F25CIII F25CN182	Narrow-band filters with G230L and G230M. Only F25MGII is supported.
F25LYA	The F25LYA filter is available-but-unsupported with the G140L, G140M, E140H, and E140M gratings only.
31X0.05NDA 31X0.05NDB 31X0.05NDC	Neutral-density-filtered long slits of the given dimensions in arcsec, which may be used for bright objects or flat-field calibration. The dex ND factors are 0.4, 0.8 and 1.2, respectively.
36X0.05P45 36X0.05N45 36X0.6P45 36X0.6N45	Long slits of the given dimensions in arcsec which are inclined at ±45° to facilitate observations of moving targets at off-nominal rolls. See Figure 1.1.
Apertures for Echelle Gratings
0.1X0.03  0.1X0.06  0.1X0.09  0.1X0.2	The latter two are supported with E230H.
0.2X0.06  0.2X0.09 0.2X0.2  0.2X0.5	0.2X0.06 and 0.2X0.2 are supported with E230M and E140M, while 0.2X0.09 and 0.2X0.2 are with E230H and E140H.
0.3X0.06  0.3X0.09 0.3X0.2
0.5X0.5
1X0.06  1X0.2
2X2
6X0.06  6X0.2  6X0.5  6X6	The 6X0.2 long slit, of the given dimensions in arcsec, is supported with the echelles only.
52X0.05  52X0.1 52X0.2	Long slits for use with the echelles.
0.2X0.06FP   0.2X0.2FP	Masks with five apertures each of the given dimensions in arcsec, suffixed A through E, for reduction of fixed-pattern noise; see Figure 1.3. These apertures are supported with the echelles only.
0.2X0.05ND 0.3X0.05ND	Neutral-density-filtered slits for bright objects or flat fields. The dex ND factors are 2.0 and 3.0, respectively.
25MAMA	Supported full-field clear aperture.
F25QTZ  F25SRF2	Supported long-pass filters. Both are supported for E140H and E140M.
F25ND3  F25ND5 F25NDQ1  F25NDQ2 F25NDQ3  F25NDQ4	Supported neutral-density filters.
F25MGII  F25CN279 F25CIII  F25CN182	Narrow-band filters. F25MGII is supported for E230H and E230M.
36X0.05P45  36X0.05N45 36X0.6P45  36X0.6N45	Long slits of the given dimensions in arcsec which are inclined at ±45° to facilitate observations of moving targets at off-nominal rolls. See Figure 1.2.
Apertures for the Prism
52X0.05 52X0.1 52X0.2 52X0.5 52X2 52X0.2F1	Supported long slits. Long slit with fiducial bar.
25MAMA	Supported full-field clear aperture.
F25QTZ  F25SRF2	Supported long-pass filters.
F25ND3  F25ND5 F25NDQ1  F25NDQ2 F25NDQ3  F25NDQ4	Supported neutral-density filters.
F25MGII  F25CN279 F25CIII  F25CN182	Narrow-band filters. F25MGII is supported.

Figure A1.1: Schematic Showing the 52x 0.1" Long Slit with 3 Occulting Bars.

Figure A1.2: Schematic Showing the STIS 45° Slits Design. A second pair has the same morphology but widths of 0.6" (central) and 2.0" (peripheral).

Figure A1.3: Schematic Showing the Configuration of the Fixed-Pattern Slits. There are two sets with slit widths of 0.06" and 0.2", and lengths of 0.2" in both cases. Axis1 corresponds to the dispersion direction.  

The 45° slits ( Figure 1.2) are nominally inclined at plus or minus that angle with respect to the dispersion and normal long slit, in order to increase the scheduling flexibility for moving target observations with specified position angles. Otherwise, the HST roll angle constraints severely limit the windows for such observations. These slits have different widths in their central and outer segments, and there are two pairs with different dimensions.

The fixed-pattern slits ( Figure 1.3) comprise two masks with five apertures each, which are spaced to place the spectrum at different detector locations designed to optimize the reduction of fixed-pattern noise. The target is moved from one aperture to another, and the slit wheel is repositioned, with the intention that the spectrum shifts along the dispersion direction only.

It is not feasible to provide detailed transmission properties of all of the unsupported apertures at this time. They can in many cases be estimated from the data provided for similar supported apertures in Chapter 13, and from the imaging data in Table 14.37 on page 436.