HST Call for Proposals and HST Primer for Cycle 24

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A.2 COS Examples

This section illustrates two examples of COS Phase I observations. Additional details are available in the COS Instrument Handbook.

A.2.1

Example 1: COS NUV Imaging and Spectroscopy in One Orbit

The COS NUV channel is used to observe an object at declination -10o. First, an image is taken, followed by obtaining a TIME-TAG spectrum with two exposures using different gratings. The specific observations, as requested by the user, are summarized in Table A.4.

•	Based on information in Table 6.1, there are 54 minutes of orbital visibility per orbit.

•	Overheads for the observations, documented in Chapter 6, are compiled in Table A.5.

Therefore, a preliminary observing strategy can be created by the user to fit the observations in one orbit, as shown in Table A.6. In this example, we assume that the coordinates of the object are known to an accuracy of 0.4 arcsec or better. See the COS Instrument Handbook for details.

Table A.4:

COS Example 1: Planned Exposures

Config	Mode	Spectral element	Number of exposures	Time per exposure (seconds)	Notes
COS/NUV	ACQ/IMAGE	MIRRORA	1	20	target acquisition
COS/NUV	TIME-TAG	G185M	1	1200	central wavelength 1850 å
COS/NUV	TIME-TAG	G225M	1	600	central wavelength 2250 å

Table A.5:

COS Example 1: Incurred Overheads

Overhead	Overhead time (minutes)	Notes	see Table
Guide star acquisition	6	First orbit in new visit	6.2
ACQ/IMAGE	3	Target acquisition	6.3
NUV spectroscopy	5	Single spectroscopic exposure	6.5

Table A.6:

COS Example 1: Orbit Planning

Activity	Duration (minutes)	Elapsed time (minutes)
Orbit 1
Guide star acquisition	6	6
ACQ/IMAGE	3	9
G185M Overhead	5	13
G185M Exp time	20	34
G225M Overhead	5	39
G225M Exp time	10	49
Unused	2	54

A.2.2

Example 2: COS NUV Imaging and FUV Spectroscopy in Two Orbits

The COS NUV channel is used to acquire the same object as in Example 1, in imaging mode, then uses the FUV channel to obtain a TIME-TAG spectrum with two exposures using the same grating and central wavelength. The planned exposures are summarized in Table A.7.

•	Based on information in Table 6.1, there are 54 minutes of orbital visibility time per orbit.

•	Overheads for the observations, documented in Chapter 6, are compiled in Table A.8.

Therefore, a preliminary observing strategy can be created by the user to fit the observations in two orbits, as shown in Table A.9. In this example, we assume that the coordinates of the object are known to an accuracy of 0.4 arcsec or better. See the COS Instrument Handbook for details.

Table A.7:

COS Example 2: Planned Exposures

Config	Mode	Spectral element	Number of exposures	Time per exposures (seconds)	Notes
COS/NUV	ACQ/IMAGE	MIRRORA	1	30	Target acquisition
COS/FUV	TIME-TAG	G160M	1	2100	Central wavelength 1600 å
COS/FUV	TIME-TAG	G160M	1	2700	Central wavelength 1600 å

Table A.8:

COS Example 2: Incurred Overheads

Overhead	Overhead time (minutes)	Notes	see Table
Guide star acquisition	6	First orbit in new visit	6.2
Guide star reacquisition	4	Per orbit after first orbit	6.2
ACQ/IMAGE	3	Target acquisition	6.3
FUV spectroscopy	5	First spectroscopic exposure in a series of identical exposures	6.5
FUV spectroscopy	2	Subsequent spectroscopic exposure in a series of identical exposures	6.5

Table A.9:

COS Example 2: Orbit Planning

Activity	Duration (minutes)	Elapsed time (minutes)
Orbit 1
Guide star acquisition	6	6
ACQ/IMAGE	3	9
G160M Overhead	5	14
G160M Exp time	35	49
Unused	5	54
Orbit 2
Guide star reacquisition	4	4
G160M Overhead	2	6
G160M Exp time	45	51
Unused	3	54