5.3 Valid Exposure Times

The minimum COS exposure duration is 0.1 s (but FLASH=YES TIME-TAG exposures impose a longer minimum; see Section 5.7.1). The maximum is 6500 s. Between these extremes COS exposure times must be integer multiples of 0.1 s. If the observer specifies an exposure time that is not a multiple of 0.1 s, its value is rounded down to the next lower integer multiple of 0.1 s, (or set to 0.1 s if a smaller value is specified). Exposure times larger than about 3000 s are normally appropriate only for visits with the Continuous Viewing Zone (which is a special requirement that must be requested and justified in the Phase I proposal) because the visibility period of a typical orbit is ~50 minutes. See the HST Primer for information about HSTʹs orbit and visibility periods.

For TARGET=WAVE exposures, DEF (default) must be entered as the exposure time. The value appropriate for the optical configuration will be chosen from a table established at STScI for best performance. At present TARGET=WAVE flash durations are identical to those given in Table 5.2.

Table 5.2: TAGFLASH Exposure Durations.

Grating

Central Wavelength (Å)

Flash Duration (s)GratingCentral Wavelength (Å)Flash Duration (s)

G130M

1055

142

G225M (cont.)

2339

12

1096

 52

2357

12

1222

 52

2373

22

all others

 12

2390

 7

G160M

all

 12

2410

 7

G140L

all

  7

G285M

2617

12

G185M

1786

 12

2637

12

1817

 12

2657

 7

1835

 12

2676

22

1850

 22

2695

22

1864

 32

2709

12

1882

 17

2719

 7

1890

 12

2739

 7

1900

 22

2850

22

1913

 17

2952

 7

1921

 12

2979

17

1941

 12

2996

17

1953

 17

3018

22

1971

 17

3035

27

1986

 12

3057

32

2010

 12

3074

32

G225M

2186

  7

3094

32

2217

 12

G230L

2635

 7

2233

  7

2950

 7

2250

 22

3000

 7

2268

 12

3360

12

2283

 12

MIRRORA

...

7

2306

 12

MIRRORB

...

12

2325

 12