DEIMOS Exposure Recipes

S. M. Faber, A. C. Phillips, G. D. Wirth
Version 2.0, December 2002

Definitions
Direct-imaging recipes
Spectroscopic recipes
Direct imaging flat fields
Spectroscopic flat fields
FCS exposure times
- Direct imaging
- Spectroscopy
TV exposures

Definitions

Standard Slitmasks

GOH-foo mask: Grid of holes mask; for direct-imaging focusing
LOSH3 mask: Line-of-slitlets-and-holes; 4.5 arcmin from center of telescope focal plane; slitwidth = 0.5 arcsec; for spectroscopic focusing
GOSpH3 mask: Grid-of-holes for spectroscopy; small holes distributed in two dimensions over the slitmask; for spectroscopic focusing

Complete list of standard slitmasks

Internal lamps

Qz - Quartz iodide continuum
Ne - Neon
Cd - Cadmium
Ar - Argon
Kr - Krypton
Xe - Xenon
Zn - Zinc
Hg - Mercury
NAKX - Ne, Ar, Kr, Xe
NHCXZ - Ne, Hg, Cd, Xe, Zn

Order-blocking filters

One of these, or a broadband filter, must be in place at all times in order for the camera to be able to focus on the CCD mosaic.

BAL12 (clear)
GG400
GG455
GG495
OG550

Complete list of order-blocking filters

Direct-imaging recipes

Through-focus series using GOH-X mask with internal lamps

Filter	Lamp	Time [sec]	Peak flux [DN]
B	Qz	4	40,000
V	Ne	10	30,000
R	Hg	2	30,000
I	Ne	2	40,000
Z	Ne	4	35,000

Through-focus series using GOH-X mask using dome lamps

Filter	Lamp	Time [sec]	Peak flux [DN]
B	FLSPECTR	10	12,000
V	FLSPECTR	3	30,000
V	Dome fluor	1	25,000
R	FLSPECTR	1	30,000
	FLIMAGIN	20	8,000
	Dome fluor	1	?
I	FLSPECTR	---	too bright
I	FLIMAGIN	10	8,000
Z	FLSPECTR	1	50,000
Z	FLIMAGIN	10	10,000

Through-focus series using GOH-X mask and night sky

Filter	Time [sec]	Peak flux [DN]
B	200	70
V	200	100
R	100	200
I	100	1000
Z	100	800

Direct images of slitmasks using internal lamps

Filter	Lamp	Time [sec]	Peak flux [DN]
R	Xe	2	10,000
OG550	Zn	1	30,000

Spectroscopic recipes

Through-focus series using GOSPH-3 mask with internal lamps

Also good for wavelength calibration. Note: be sure to let Cd, Zn, and Hg warm up for at least 3 minutes!

Grating	Filter	Central Wavelength	Lamps	Time [sec]
830G	OG550	7500 A	NAKX	1
1200G	OG550	8000 A	NAKX	1
600	GG455	7000 A	NHCXZ	2
600	GG455	7000 A	Xe	100
600	GG400	6500 A	NHCXZ	2
600	BAL12	6500 A	XeKrAr	100
900	BAL12	6600 A	NHCXZ	2
900	BAL12	6600 A	Xe	100
900	GG400	5600 A	NHCXZ	2
900	GG400	5600 A	XeKrAr	100

Blue lines below 5500 A:

Kr: 7 lines, 4273-4502 A, few hundred counts in 20 sec
Cd: 3 lines, 4660-5085 A, few thousand counts in 2 sec; medium Ar
Hg: 2 lines, 4046-4358 A, few thousand counts in 2 sec; strong Ar
Xe: 11 lines, 4736-5695 A, few thousand counts in 100 sec
Ar: 7 lines, 4158-4510 A, ~100 counts in 20 sec
Zn: 3 lines, 4680-5181 A, few thousand counts in 2 sec; weak Ar
Ne: 1 line, ~4900 A, few thousand counts in 20 sec

Note: Kr is deleted from short-exposure blue recipes because it crowds the red spectrum at low dispersion. Ar is deleted because it is already in the Hg lamp.

Through-focus series using GOSPH-3 mask using dome fluorescents

Note: dome spectrum is rich only beyond 6400 A.

Grating	Filter	Central Wavelength	Time [sec]	Comments
830G	OG550	7500 A	25
1200G	OG550	8000 A	50
600	GG495	7500 A	7	To avoid sat blue Hg lines
600	GG455	7000 A	7	"
900	BAL12	6000 A	9	"
900	OG550	7200 A	20

Exact times and counts depend on when taken. The following data are for a series of 5 exposures each taken at sunset in two gratings. The series started 4 minutes after sunset and was taken in the order shown. Spectral twilight flats should really start 15 minutes BEFORE sunset (note: special Director's permission is needed to open that early).

Grating	Filter	Central Wavelength	Time [sec]	Avg signal [DN]
830G	OG550	7900	30	20,000
120G	OG550	8300	100	5,000

Typical night-sky spectral intensities

Grating	Typical OH-line peak intensity	Typical continuum level between OH lines
1200G	0.01 e/sec/px	1.0 e/sec/px
830G	0.015 e/sec/px	1.5 e/sec/px

Direct imaging flat fields

Broadband dome flats

Filter	Lamp	Time [sec]	Peak flux [DN]
B	FLSPECTR+FLIMAGIN	3	21,000
V	FLIMAGIN	11	19,000
R	FLIMAGIN	10	30,000
I	FLIMAGIN	7	40,000
Z	FLIMAGIN	10	32,000

Broadband twilight flats

Filter	Time	Peak counts
B	2	20,000
V	2	20,000
R	6	20,000
I	10	20,000
Z	10	20,000

Exact times and counts depend on when taken.
These data are for a series of 10 exposures taken at dawn starting with Z and ending with B, two flats in each filter.
The series ended 15 min before sunrise.

Typical sky counts in a dark-sky broadband exposure

Filter	Sky flux [DN/s]
B	TBD
V	TBD
R	TBD
I	TBD
Z	TBD

Spectroscopic flat fields

Internal spectroscopic flats using Qz lamp

Grating	Filter	Central wavelength [A]	Time [sec]	Peak flux [DN]	Slitwidth [arcsec]
830G	OG550	7500	15	45,000	0.75
1200G	OG550	8000	12	40,000	1.00
600	GG455	7500	6	40,000	1.00
600	GG400	6500	TBD	TBD	TBD
900	BAL12	6600	TBD	TBD	TBD
900	BAL12	5600	10	42000 (red) 2,000 (blue)	0.50

Need 10 of these to get good S/N in blue.

Dome spectral flats

Grating	Filter	Central wavelength [A]	Time [sec]	Peak counts
830G	OG550	7500	100	30,000
1200G	OG550	7800	150	25,000
600	GG495	7500	TBD	TBD
600	GG455	7000	90	30,000
600	GG400	6500	TBD	TBD
900	BAL12	6600	TBD	TBD
900	BAL12	5600	TBD	TBD

Use 1.00 arcsec slitwidth with FLSPECTR lamp.
Note: the dome spectral lamp on Keck II is too faint; CARA should install a brighter lamp if possible.

Archival slitless dome spectral flats

Grating	Filter	Central wavelength [A]	Time [sec]	Peak flux [DN]
830G	OG550	8000	15	40,000
830G	BAL12/GG400	7000	15	40,000
1200G	OG550	7750	20	45,000
1200G	BAL12/GG400	6600	20	45,000

To measure for px-px variations and condensation monitoring.
Use FLIMAGIN.
Take three exposures at each tilt and add together.

Archival GRATEFOP exposures

Iillumination comes from positioning LED on grating transport stage. Shines light directly through camera, illuminating bubbles in coupling fluid and other defects. Recipe:

Spectroscopic mode, to get image of whole detector
BAL12 or other blue cuton filter; focus the CCD for filter used (precaution, probably does not matter)
Slider 3 (tilt and grating do not matter)
Hatch closed
modify -s deimot GRATEFOP=on
Take 3×10 sec exposures
modify -s deimot GRATEFOP=off

Slitless standard star spectra

Good for stars in range 10.5-11.5 V mag.
Use 50s exposure time for all gratings, tilts, and filters.

FCS exposure times

The FCS lamps are a bit too bright and need adjustment. The following are the data for the current brightnesses (2002 December) before adjustment.

Direct imaging

Filter	Lamp	Time [sec]	Peak flux [DN]
B	LED	1	50,000
V	Cu1	1	50,000
R	LED	1	Slightly saturated
I	Cu1	1	Heavily saturated
Z	Cu1	1	10,000

Spectroscopy

Use the CuAr lamps for all gratings.
Exposures are 10 sec below 5500 A and 1-5 sec beyond this.
Peak counts in the blue are a few hundred.
Peak counts in the red are a few×10,000.

TV exposures

Broadband TV dome flats

Filter	Time [sec]	Peak flux [DN]
Filter	Time [sec]	Mirror	Slitmask
B	20	7,000	1,000
V	20	13,000	2,000
R	5	17,000	4,000
I	2	16,000	4,000
R1	10	16,000	5,000
R2	10	20,000	1,000
Clear	1	14,000	4,000

TV through-focus using dome fluorescents

Exposure times are 1 msec for all filters, except for ND2, which is 300 msec.
The dome fluorescents are probably too bright for the Clear filter.
Lots of scattered light in the ND2 exposure.

TV through-focus using dome FLSPECTR lamps

Filter	Light source	Exposure time [msec]	Comments
B	FLSPECTR	2000
V	FLSPECTR	500
I	FLSPECTR	1000
R	FLSPECTR	300
R1	FLSPECTR	1500
R2	FLSPECTR	?
ND2	Internal Ne	10000	FLSPECTR too faint
Clear	FLSPECTR	100

TV through-focus using internal lamps

Try to use Qz whenever possible, as illumination is better.

Filter	Light source	Exposure time [msec]	Comments
B	Qz	500	Lots of scattered light
V	Qz	150
I	Ar	50	Ar illumination unven. Try using Qz next time
R	Qz	1	Really that short? Compare V.
R1	Qz	1	"
R2	Qz	1	"
ND2	Qz	200	Big reflection off focal plane
Clear	Ne	1

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Last modified: Wed Dec 15 22:11:13 HST 2004

S. M. Faber, A. C. Phillips, G. D. Wirth Version 2.0, December 2002

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