INGRID's filters and pupil stops

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INGRID's filters and pupil stops

The light path of INGRID passes through (i) a pupil stop wheel and (ii) two filter wheels. The two filter wheels are identical in design, but the first is dedicated to broad band filters, and the second to narrow band filters. For an overview of the mechanical system click here. For more details see the following sections:

Observing configurations
Changing filters and pupil stops
Current configuration of filters and pupil stops in INGRID
Filter properties
Pupil stop properties

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Observing configurations

For the afternoon setup and science observations with INGRID, the following configurations are recommended:

Configuration name		Pupil stop wheel	Filter wheel 1	Filter wheel 2
GUI	Command line	Pupil stop wheel	Filter wheel 1	Filter wheel 2
Dark	dark	blank	blank1	blank1
Simplex-J-Barr	simplex-j-barr	clear	j-barr	clear
Simplex-H-Barr	simplex-h-barr	clear	h-barr	clear
Simplex-Ks-Barr	simplex-ks-barr	clear	ks-barr	clear
Z	z	naomi-clr	z	clear
J-Barr	j-barr	naomi-clr	j-barr	clear
H-Barr	h-barr	naomi-clr	h-barr	clear
Ks-Barr	ks-barr	naomi-obs	ks-barr	clear
Jcont	jcont	naomi-clr	j-barr	jcont
Pab	pab	naomi-clr	j-barr	pab
Hcont	hcont	naomi-clr	h-barr	hcont
Fe2	fe2	naomi-clr	h-barr	fe2
H2v1-0	h2v1-0	naomi-obs	ks-barr	h2v1-0
Brg	brg	naomi-obs	ks-barr	brg
H2v2-1	h2v2-1	naomi-obs	ks-barr	h2v2-1
Kcont	kcont	naomi-obs	ks-barr	kcont
J	j	naomi-clr	j	clear
H	h	naomi-clr	h	clear
Ks	ks	naomi-obs	ks	clear
K	k	naomi-obs	k	clear

These configurations may be invoked using (i) the 'Configuration Tool' section of the INGRID GUI or (ii) the following command line syntax:

SYS> filter ingrid <configuration name>

Both the command line and the GUI will move the filter wheels and pupil stop wheel to the appropriate positions, ensuring that the latter is always repositioned last. (This is because the three wheels are mounted on the same rotational shaft and so the movement of one wheel can slightly influence the position of another one.)

Changing filters and pupil stops

The filter and pupil stop wheels can be controlled individually using either the command line or the 'Mechanism Control' section of the INGRID GUI. Note that while individual control is useful for engineering purposes, the use of the configurations outlined in the previous section is strongly recommend for observing.

The command line syntax for the filter and pupil wheel movements is:

SYS> fwheel1 ingrid <filter name> or <position>

SYS> fwheel2 ingrid <filter name> or <position>

SYS> pstop ingrid <pupil stop name> or <position>

The current options for <filter name> and <pupil stop name> are given in the following section. Note that replacing the name/position by datum will allow one to datum the mechanism.

When moving filters and pupil wheels individually, make sure that the pupil stop is the last mechanism to be moved.

Current configuration of filters and pupil stops in INGRID

Position	Pupil stop wheel	Filter wheel 1	Filter wheel 2
1	ker	clear	brg
2	clear	j-barr	h2v1-0
3	kel	h-barr	fe2
4	naomi-obs	ks-barr	hcont
5	naomi-clr	z	pab
6	fmask	j	jcont
7	blank	h	clear
8	cass-j	k	blank1
9	cass-s	ks	blank2
10	osca-obs	blank1	kcont
11	osca-clr	blank2	h2v2-1

Note that blank indicates that an "aluminium blank" is in the light path (useful for dark frames) while clear means that there is nothing in the light path. See below for more details about the other pupil stops and filters.

Filter properties

The filters have thicknesses of less than 6mm and diameters of 38mm (±0.1mm). They are all angled at 5° to the optical beam to reduce ghosting and are all specified for adaptive optics observations except for the Z filter. The two tables below show the set of filters currently available for INGRID. Note that the J-Barr filter has not been included as it has not been scanned; it is expected to have similar properties to those of the J filter.

All filters were purchased in collaboration with the Gemini filter buying consortium (headed by Alan Tokunaga); more details can be found here. The transmission curves have been measured at room temperature and at 0° angle with respect to the incident light. The central wavelengths of the narrow band filters are sensitive to both temperature and the angle of incidence, so transmission curves have also been estimated at values appropriate for INGRID (ie. 5° incidence and T=77K). See here for more details.

Graphical overview of INGRID broad band filter transmissions
Graphical overview of INGRID K-band filter transmissions

INGRID broad band filters (Filter Wheel 1)

Filter name	CWL (µm)	FWHM (µm)	50% transmission (T) cut (µm)		Peak T (%)	Transmission (warm)
Filter name	CWL (µm)	FWHM (µm)	On	Off		Curve	Data
Z	1.033	0.073	0.996	1.069	88	Curve
J	1.250	0.160	1.170	1.330	90	Curve
H	1.635	0.290	1.490	1.780	87	Curve
H-Barr	1.635	0.290	1.490	1.780	97	Curve
Ks	2.150	0.310	1.990	2.300	95	Curve
Ks-Barr	2.150	0.320	1.990	2.310	89	Curve
K	2.200	0.335	2.028	2.364	95	Curve

INGRID narrow band filters (Filter Wheel 2)

Filter name	CWL (µm)	FWHM (µm)	Peak T (%)	Transmission			CWL drift (nm / K)	Emission line (µm)
				Curve	Data
				Curve	Warm	Cold
J-continuum	1.209	0.018	63	Curve			0.0318	-
Pa-beta	1.283	0.020	71	Curve			0.0255	1.2818
H-continuum	1.573	0.024	74	Curve			0.0311	-
[Fe II]	1.642	0.024	74	Curve			0.0311	1.6436
H2 v=1-0	2.121	0.032	72	Curve			0.0396	2.121
Br-gamma	2.170	0.032	69	Curve			0.0732	2.1655
H2 v=2-1	2.246	0.034	56	Curve			0.0439	2.247
K-continuum	2.270	0.033	70	Curve			0.0756	-

The last column of the above table gives the wavelength of the rest-frame emission line associated with each filter. Please note that the Br-gamma filter is redshifted by ~4nm with respect to the rest-frame wavelength of the corresponding emission line.

Pupil stop properties

INGRID pupil stops

Pupil stop	Inner diameter (mm)	Outer Diameter (mm)	Comments
ker	-	-	Knife edge right
kel	-	-	Knife edge left
naomi-obs	1.76	3.895
naomi-clr	-	3.895
fmask			Focus mask
cass-j	7.36	23.92
cass-s	6.82	25.25
osca-obs	1.377	3.22
osca-clr	-	3.22

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Last Updated: 20 February 2009
Ian Skillen, wji@ing.iac.es