Hubble Space Telescope Primer for Cycle 11

A.2 FGS

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Suppose that you wish to use the FGS to observe a binary star named Binary01, as well as five reference stars ref1,......,ref5. All stars are in the same FGS field of view, and can therefore be observed in one and the same visit (see Section 6.2.3). Stars ref4 and ref5 have magnitude V=14.6, and all the other targets have 13.0<V<14.0. The targets have a declination of +42 degrees, so that there are 54 minutes of visibility time per orbit (see Table 6.1). To enable the removal of drift and jitter in the post observation analysis of the data, the binary is observed in POS mode three times and the reference stars are each observed twice. Your desired exposures are listed in Table A.4, and the associated overheads are listed in Table A.5. In Table A.6 you can see how this fits into a total of 1 orbit.

Table A.4: (Continued)FGS Example: Planned Exposures

Config	Mode	Spectral Element	Number of Exp	Time per Exp [m]	Notes
FGS	POS	F583W	8	0.2	2 exposures of target Binary01, and 2 exposures for each of the targets ref1, ref2 and ref3
FGS	POS	F583W	4	0.7	2 exposures for each of the targets ref4 and ref5
FGS	TRANS	F583W	1	13.3	20 scans of 40 sec each (see Table 6.8) for Binary01

 
Table A.5: FGS Example: Incurred Overheads

Overhead	Overhead Time [m]	Notes	see Table
Guide star acquisition	6	First orbit in new visit	6.2
POS	1	per exposure, V<14	6.6
POS	2	per exposure, 14<V<15	6.6
TRANS	1	per target	6.6
TRANS	0.2	per scan	6.6
Instrument Setup	4	once every orbit	6.7
Instrument Shutdown	3	once every orbit	6.7

 
Table A.6: FGS Example: Orbit Planning

Activity	Duration [m]	Elapsed Time [m]
Orbit 1
Guide star acquisition	6	6
Instrument Setup	4	10
Binary01/POS mode Exp Time	0.2	10.2
Binary01/POS mode Overhead	1	11.2
ref1/POS mode Exp Time	0.2	11.4
ref1/POS mode Overhead	1	12.4
ref2/POS mode Exp Time	0.2	12.6
ref2/POS mode Overhead	1	13.6
ref3/POS mode Exp Time	0.2	13.8
ref3/POS mode Overhead	1	14.8
ref4/POS mode Exp Time	0.7	15.5
ref4/POS mode Overhead	2	17.5
ref5/POS mode Exp Time	0.7	18.2
ref5/POS mode Overhead	2	20.2
Binary01/POS mode Exp Time	0.2	20.4
Binary01/POS mode Overhead	1	21.4
ref1/POS mode Exp Time	0.2	21.6
ref1/POS mode Overhead	1	22.6
ref2/POS mode Exp Time	0.2	22.8
ref2/POS mode Overhead	1	23.8
ref3/POS mode Exp Time	0.2	24.0
ref3/POS mode Overhead	1	25.0
ref4/POS mode Exp Time	0.7	25.7
ref4/POS mode Overhead	2	27.7
ref5/POS mode Exp Time	0.7	28.4
ref5/POS mode Overhead	2	30.4
Binary01/POS mode Exp Time	0.2	30.6
Binary01/POS mode Overhead	1	31.6
Binary01/TRANS mode Exp Time	13.2	44.8
Binary01/TRANS mode Overhead	1+(20x0.2)	49.8
Instrument Shutdown	3	52.8
Unused	1.2	54.0