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FAQ

Imaging Bright Object Protection Limit

A few important points to note.

  • Limits are given as V magnitudes, ergs sec-1 cm-2 Å-1, ergs sec-1 cm-2 Å-1 arcsec-2.
  • The limits were derived assuming zero slit loss.
  • The imaging table includes a single point source limit. No single source in the field of view can exceed this limit.
  • The limits in the tables assume zero extinction. If your source, when corrected for Galactic extinction, does not exceed the absolute limits, then you will be allowed to observe your source.
  • The imaging table also includes an integrated magnitude limit. Remember that the global limit of 200,000 counts sec-1 applies to all sources imaged onto the MAMA detector. The integrated magnitude limit gives the total magnitude from all stars (or galaxies, or diffuse objects) of spectral type O which can appear in the MAMA field of view. Initial screening of all MAMA imaging observations will be done assuming all stars are O stars, however, ultimately for the final decision, the colors of the stars are taken into account whenever such information is available (see IHB Chapter 7).
  • Be aware of the additional limitations that exist for crowded fields and slightly-resolved stellar clusters (see IHB Section 7.7.3).

Table 14.40: MAMA Bright-Object limits (V magnitudes and cgs units). V magnitudes include NO additional safety factor to account for extrapolation uncertainties from the optical to the UV spectral range.
 
FUV-MAMA
NUV-MAMA
Spectral Type
25MAMA
F25SRF2
F25QTZ
F25LYA
25MAMA
F25SRF2
F25QTZ
F25CN182
F25CIII
F25CN270
F25MGII
Flat, point source1
9.6 × 10-15
1.7 × 10-14
5.1 × 10-14
4.5 × 10-13
2.1 × 10-15
2.4 × 10-15
2.5 × 10-15
2.5 × 10-14
1.9 × 10-13
1.6 × 10-14
8.5 × 10-14
Flat, extended, peak2
4.0 × 10-12
7.5 × 10-12
2.1 × 10-11
1.9 × 10-10
9.0 × 10-13
1.0 × 10-12
1.0 × 10-12
1.0 × 10-11
8.0 × 10-11
7.0 × 10-12
3.5 × 10-11
O5 V3
19.1
18.3
16.8
15.2
19.2
19.0
18.8
16.8
14.6
16.2
14.2
O7 V
18.9
18.1
16.6
15.0
19.1
18.9
18.7
16.7
14.5
16.1
14.2
O9 V
18.7
17.9
16.4
14.7
18.9
18.7
18.6
16.6
14.4
16.0
14.1
B0 V
18.6
17.8
16.3
14.6
18.8
18.7
18.5
16.5
14.3
16.0
14.0
B1 V
18.3
17.4
16.0
14.3
18.6
18.4
18.2
16.2
14.0
15.8
13.8
B3 V
17.4
16.7
15.3
13.3
17.9
17.8
17.7
15.5
13.3
15.3
13.4
B5 V
16.7
16.1
14.8
12.3
17.5
17.3
17.2
15.1
12.9
14.9
13.0
B8 V
15.5
15.1
13.8
10.6
16.7
16.6
16.5
14.3
12.1
14.2
12.3
A1 V
13.3
13.0
12.3
7.2
15.6
15.5
15.5
13.1
11.0
13.3
11.5
A3 V
12.1
11.9
11.5
5.4
15.4
15.3
15.2
12.8
10.8
13.1
11.3
A5 V
10.7
10.6
10.4
3.4
15.1
15.0
15.0
12.4
10.4
12.9
11.1
F0 V
8.5
8.3
8.3
0.9
14.6
14.5
14.4
11.5
9.4
12.5
10.7
F2 V
7.7
7.5
7.4
0.0
14.3
14.2
14.2
11.1
8.9
12.3
10.6
F5 V
5.8
5.7
5.6
-2.0
13.9
13.8
13.8
10.3
8.0
12.0
10.3
F8 V
4.7
4.6
4.5
<-2.0
13.7
13.6
13.5
9.8
7.4
11.7
10.1
G2 V4
4.8
3.9
3.6
1.4
12.9
12.8
12.8
8.7
6.5
11.1
9.7
G8 V5
4.2
3.3
3.0
0.8
12.5
12.4
12.4
8.1
6.0
10.7
9.4
K2 V6
5.7
3.9
3.2
2.6
11.8
11.7
11.7
7.2
5.6
9.9
9.2
KM III7
4.2
3.6
2.5
1.1
11.5
11.4
11.4
6.9
5.6
9.5
8.9
Integrated V magnitude8
13.4
12.6
11.2
9.6
13.5
13.3
13.1
11.2
8.9
10.5
8.5
Flat, extended, all detector9
7.2 × 10-15
1.4 × 10-14
4.1 × 10-14
3.6 × 10-13
1.7 × 10-15
1.9 × 10-15
2.0 × 10-15
2.0 × 10-14
1.5 × 10-13
1.3 × 10-14
6.7 × 10-14
1Maximum allowed flux for a point source in erg s-1 cm-2 Å-1.
2Maximum peak allowed flux for an extended source in erg s-1 cm-2 Å-1 arcsec-2.
3V magnitude limit for unreddened single stars. O5 V through F8 V are based on Kurucz models.
4The magnitudes listed for G2 V are for the Solar template in the STIS ETC.
5The magnitudes listed for G8 V are from IUE data for the star Tau Ceti.
6The magnitudes listed for K2 V are from IUE data for the star Epsilon Eri.
7The magnitudes listed for KM III are from IUE data for 9 stars of these types.
8Maximum integrated V magnitude for stars in the field assuming all are of O5 V spectral type.
9Maximum allowed flux for an extended source which covers the full detector in erg s-1 cm-2 Å-1 arcsec-2

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