A modern single-channel photometer

Next, consider a more modern photometer that uses pulse-counting. It has a ``neutral'' filter in addition to standard uvby filters. The ``neutral'' filter is in series with the passband filters, and is used to determine the dead-time correction. The positions of these two filter mechanisms are recorded as two adjacent digits in the data, so we can treat them as a single filter code; the second digit is 1 when the ``neutral'' filter is in the beam.

There is also a shutter whose position is encoded separately in the data stream: 0 means open, 1 means shut. This can be treated as a second logical filter mechanism.

The photomultiplier in this modern instrument is in a thermoelectrically cooled chamber, regulated to run at $0^{\circ}$ C (273 K). Table I.14 shows what we get.

Again, there is only one detector, so we need not include the NDETUSED column.

 

Table: Instrument table file for a two-channel photometer

Descriptor values:

NFILTCAR = 2

NDETS = 2

FILTSTAT = MEASURED

FILTCAT = ' ' (blank string)

CONDITION = AVERAGE

Passband sub-table

NBAND	BAND	FILTCODE_1	FILTCODE_2	REDLEAK	NDETUSED
---	--	-----	-----	----	----
1	U	1	any	BLOCKED	1
2	B	2	any	BLOCKED	1
3	V	3	any	ABSENT	1
4	R	any	1	BLOCKED	2
5	I	any	2	ABSENT	2
6	DARK1	0	any		1
7	DARK2	any	0		2

Detector sub-table

NDET	DET	SNUMBER	MODE	COOLING
--	--	----	--	----
1	PMT	S-13	CI	MEASURED
2	PMT	GAAS	CI	DRYICE