F25LYA - FUV-MAMA, Lyman-alpha

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

Pixels

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