F25LYA—FUV-MAMA, Lyman-α

Description

The F25LYA filter with the FUV-MAMA provides narrowband imaging of the HI 1216 Å Lyman-α line.

Recommended Uses

Lyman-α imaging. Differencing two images taken with 25MAMA and F25SRF2 is another option.

Special Considerations

Sensitivity is limited by geocoronal Lyman-α. Observers can limit the background (with some cost to the total amount of observing time per orbit) by using the DARKTIME special requirement.

Users may also want to consider whether the ACS SBC detector with the F122M filter might be a better choice for their observing program.

 

Pivot λ (Å)	FWHM (Å)	AB mag zero point	Speak	Bλ	R80 (arcsec)	Flux in central pixel
1242.8	141.2	19.470	8.76e+12	99.5	0.35	6%

Figure 14.88: F25LYA FUV-MAMA Integrated System Throughput and Redleak

Table 14.36: F25LYA FUV-MAMA Sensitivity & Throughput

λ	Sensitivity	% Throughput
1150.	5.06E11	0.02
1175.	3.42E12	0.13
1200.	7.42E12	0.27
1225.	8.15E12	0.29
1250.	5.62E12	0.20
1275.	3.40E12	0.12
1300.	2.05E12	0.07
1325.	1.27E12	0.04
1350.	8.13E11	0.03
1375.	5.62E11	0.02

Figure 14.89: Point Source S/N vs. flux for the F25LYA FUV-MAMA mode. Curves are labeled by required exposure time (seconds).

Figure 14.90: Extended Source S/N vs. flux for the F25LYA FUV-MAMA mode. Top curves are for an area of 0.2 arcsec2; bottom curves are for 1 arcsec2. Average sky assumed. Curves are labeled by required exposure time (seconds).

Table 14.37: Radial Profile for F25LYA*

Radius			Fraction of Energy Encircled
Pix	arcsec	intensity
1	0.024	2.440e-02	0.100
1.5	0.037	1.702e-02	0.174
2	0.049	1.199e-02	0.254
3	0.073	6.423e-03	0.387
4	0.098	3.326e-03	0.485
5	0.122	1.718e-03	0.549
10	0.245	3.888e-04	0.712
15	0.367	2.140e-04	0.816
20	0.490	1.044e-04	0.895
25	0.613	4.910e-05	0.943
30	0.735	1.741e-05	0.968
40	0.980	8.124e-06	0.994

* See STIS ISR 2003-01.

Figure 14.91: Point Source PSF for F25LYA FUV-MAMA, 7."5 square (at pixel 739, 368, log scaled, B-V=-0.04)

Figure 14.92: Point Source Encircled Energy for F25LYA FUV-MAMA

Figure 14.93: Point Source Intensity vs. Radius for F25LYA FUV-MAMA