Calibration Behavior as a Function of Sky Background

Objective

The purpose of this task is to begin to measure the dependence latent image behavior, responsivity, and linearity has on sky background levels.

Description

This task measures a number of calibration stars in photometry mode. The task comes in two flavors: the early version (campaign E) is short and ideally would observe 4 24µm standards on high backgrounds. The stars available for the August 23 launch date are overwhelmingly on low backgrounds, however, so only low-background stars have been selected. If new high-background stars become available, those should be used, instead. These data will be used as an initial check of linearity on high backgrounds and for an assessment of latent image recovery on high backgrounds. In the later version (campaign R) of the test, the stars are only oberved with the Ge:Ga arrays and are selected to cover a moderate range of fluxes on medium and high backgrounds. No calibration problems that depend on background are expected on the Si:As array, so it is not necessary to include that array in this later version of the task. Extensive calibration at low background will be done in the routine calibration tasks (mips-92[0,2,4]) and in mips-400, so it is only necessary to concentrate on medium and high background here.

The observations mimic the routine standard-star observations: 2 cycles of small-field photometry on the 24µm array, 3 cycles of small-field photometry on the 70µm array and 2 cycles of superresolution observations on the 160µm array. The choice of integration times is dictated by the same considerations used in mips-400 - see that task cookbook for more details. The stars are listed below. The stars have been selected to cover a wide flux range within the dynamic range of the detector and, as far as possible, to lie in a similar region of sky to minimize the number of large spacecraft slews required.

Si:As Candidate Stars
ID	type	RA	DEC	Band	flux	bkgd.	visibility
		(2000)	(2000)	(µm)	(mJy)	(MJy/sr)
HD028471	G5V	04:25:09.2	-64:04:49	24	21	15.6	2003/08/24-2006/05/01
HD41371	K0III	06:00:07.7	-64:18:36	24	98	15.5	2003/08/24-2006/05/01
HD42701	K3III	06:06:50.5	-67:17:00	24	283	15.5	2003/08/24-2006/05/01
HD53501	K3III	06:59:50.5	-67:54:59	24	1178	15.7	2003/08/24-2006/05/01

Ge:Ga Candidate Stars
		(2000)	(2000)	(um)	(mJy)	MJy/sr
ID	type	RA	DEC	Band	flux	bkgd.	visibility
HD209952	B7IV	22:08:14.0	-46:57:40	70	110	7.3	2003/10/02-2003/11/22
HD53501	K3III	06:59:50.5	-67:54:59	70	140	6.0	2003/08/24-2006/05/01
HD002151	G2IV	00:25:45.1	-77:15:15	70	240	5.2	2003/08/24-2003/11/17
HD39425	K2III	05:50:57.6	-35:46:06	70	540	5.3	2003/08/31-2004/04/12
HD51799	M1III	06:56:16.0	-48:43:16	70	630	5.4	2003/09/23-2004/05/29
HD198542	M0III	20:51:49.3	-26:55:09	70	830	15.0	2003/10/01-2003/11/12
HD211416	K3III	22:18:30.1	-60:15:35	70	1200	6.0	2003/09/16-2003/11/17
HD39425	K2III	05:50:57.6	-35:46:06	160	100	6.2	2003/08/31-2004/04/12
HD51799	M1III	06:56:16.0	-48:43:16	160	120	9.6	2003/09/23-2004/05/29
HD50310	K1III	06:49:56.2	-50:36:52	160	130	12.1	2003/09/17-2004/06/02
HD197989	K0III	20:46:12.7	33:58:13	160	160	44.3	2003/10/03-2003/12/09
HD198542	M0III	20:51:49.3	-26:55:09	160	160	12.7	2003/10/01-2003/11/12
HD211416	K3III	22:18:30.1	-60:15:35	160	220	5.2	2003/09/16-2003/11/17
HD189319	M0III	19:58:45.4	19:29:32	160	230	43.4	2003/09/21-2003/11/15
HD186791	K3II	19:46:15.6	10:36:48	160	290	56.9	2003/09/19-2003/11/07
HD24512	M2III	03:47:14.3	-74:14:20	160	440	15.4	2003/08/24-2003/12/19
HD048915	A0V	06:45:08.9	-16:42:58	160	530	60.4	2003/09/25-2003/11/20
HD164058	K5III	17:56:36.4	51:29:20	160	600	7.7	2003/08/24-2003/11/10
HD045348	F0II	06:23:57.1	-52:41:44	160	610	11.3	2003/08/24-2004/05/31
HD131873	K4III	14:50:42.3	74:09:20	160	610	4.6	2003/09/27-2004/06/10

Scheduling Notes

• The 160µm and 70µm observations are deliberately targeted as separate AORs, even when the same target will be observed in both bands. The Ge:Ga part of this task should be scheduled such that the 160µm observations are obtained first. Since our ground testing indicates that the 160µm array requires more frequent anneals than the 70µm array, a single anneal done before execution of this task should be sufficient for the full run of the task.
• An attempt has been made to optimze the AOR order by minimizing the total distance the spacecraft must slew. Executing the AORs in the order listed in the AOR files is recommended, unless a better optimization is found.
• These notes are duplicated in comments in the AOR files.

Data Collected

This task will collect 12-30 images of each star in each band. The data will all be collected in photometry mode and the reduction will be identical for each star. The campaign E version of the task requires 30 minutes to execute while the campagn R version of the task requires 4.8 hours to execute.

Data Reformatting Requirements

Array Data Desired:

Si:As array in campaign E

Ge:Ga arrays in campaign R

Data Reformatting Option:

• NORMAL
  1 FITS file per AOR per array.

Special Instructions:

Task Dependencies

• mips-100: 24µm first light - ensures we can do simple photometry
• mips-922: 70µm flux standards - ensures we can do simple photometry
• mips-924: 160µm flux standards - ensures we can do simple photometry

Calibration Dependencies

• darks (all arrays)
• 24µm flats
• 24µm linearity correction
• 70 and 160µm wide-field illumination corrections
• electronic linearity correction (all arrays)

Output and Deliverable Products

• reduced data
• report on effects of varying background levels

Data Analysis

The data will be reduced as for the other calibration standards, by running them through the DAT and extracting fluxes with IDP3 (see the routine calibration task cookbooks, MIPS-920, 922, and 924, for more detail). The data should be grouped by background level, and several tests can then be made with the data:

Software Requirements

• MIPS DAT
• IDP3

Actions Following Analysis

• make report available to IT/IST

Failure Modes and Responses

If this task fails outright to collect any data, it should obviously be repeated. If it collects data, but there are not enough suitable stars to gauge the effects of background, the task should be repeated with additional stars and backgrounds.

Additional Notes

The Ge:Ga part of this task should be repeated peroidically throughout the first 6 months of the mission, using different stars as they become available.