Northern Sky Narrowband Survey: Instruments
A survey of the northern sky, focusing on emission lines Hα (656.3 nm), [OIII] (500.7 nm), and [SII] (671.7 nm and 673.0 nm), but also collecting continuum data, started at the end of 2018. The entire northern hemisphere down to a declination of -16° is being surveyed.This page gives an overview of the instruments. Results of the survey can be found in the sections data releases and Images.
Instruments
Below are two tables. The first describes the different instruments, and the second lists how many of the instruments from the first table were active during each period. The column angular resolution in the first table contains the FWHM of a point source.| Instrument index | Emission line, FWHM Bandwidth / Passband / Filter | Field of view | Aperture | Focal length | Angular resolution | Comment |
|---|---|---|---|---|---|---|
| 1 | 656.3 nm (Hα, emission line of HII), 3.5 nm | 7.6° × 5.8° | 5 cm | 135 mm | 9″ | Panasonic MN34230 sensor |
| 2 | Bayer CFA + Light pollution filter | f15.5° × 10.3° | 7 cm | 135 mm | 17″ | DSLR camera |
| 3 | 656.3 nm (Hα, emission line of HII), 3.5 nm | 7.6° × 5.8° | 6 cm | 135 mm | 9″ | Panasonic MN34230 sensor |
| 4 | 656.3 nm, 35 nm | 7.6° × 5.8° | 5 cm | 135 mm | 9″ | Panasonic MN34230 sensor. See below. |
| 5a | 410 nm to 550 nm (SDSS G') | 6.8° × 4.5° | 10 cm | 300 mm | 7″ | Sony IMX455 sensor |
| 5b | 555 nm to 650 nm (SDSS R' + 400 nm to 650 nm bandpass) | 6.8° × 4.5° | 10 cm | 300 mm | 7″ | Sony IMX455 sensor, Hα is blocked |
| 5c | 695 nm to 845 nm (SDSS I') | 6.8° × 4.5° | 10 cm | 300 mm | 7″ | Sony IMX455 sensor |
| 6a | 505.7 nm (emission line of OIII), 4 nm | 10° × 6.8° | 6 cm | 135 mm | 10″ | Sony IMX571 sensor |
| 6b | 671.7 nm and 673.0 nm (emission lines of SII), 4 nm | 10° × 6.8° | 6 cm | 135 mm | 10″ | Sony IMX571 sensor |
| Instrument index: | 1 | 2 | 3 | 4 | 5a | 5b | 5c | 6a | 6b |
|---|---|---|---|---|---|---|---|---|---|
| Nov 2018 to Apr 2020 | 4 | 2 | |||||||
| Apr 2020 to Jul 2020 | 1 | 2 | 3 | ||||||
| Jul 2020 to Jan 2022 | 2 | 3 | 1 | ||||||
| Jan 2022 to Sep 2022 | 2 | 3 | 1 | 1 | 1 | 1 | |||
| Sep 2022 to Dec 2023 | 3 | 1 | 1 | 1 | 1 | ||||
| Dec 2022 to Apr 2023 | 3 | 1 | 1 | 1 | 1 | 1 | 1 | ||
| Apr 2023 to Jan 2024 | 3 | 1 | 1 | 1 | 1 | 2 | 3 | ||
| Jan 2024 to Sep 2024 | 3 | 1 | 1 | 1 | 1 | 3 | 3 | ||
| Since Sep 2024 | 4 | 1 | 1 | 1 | 3 | 3 |
On the 135 mm lenses, the filters are front-mounted, so the aperture is determined by the filter size. Since the transmission wavelength of the (interference) filters depends on the incident angle, the usable field of view is limited by the passband width. This limitation applies to the narrowband cameras, and the field of view was chosen such that the maximum transmission drop at the emission lines across the field of view is about 5%. The continuum cameras can use the full lens-constrained field of view.
Instrument 4 was intended for precise continuum subtraction using data captured in parallel with the other Hα cameras and a wider bandpass filter centered on the Hα line. This approach proved unsuitable due to reflection artifacts. Furthermore, geocoronal emissions and a small bias drift of the cameras made it impossible to avoid background estimation and the associated limitations. Thus, data from this instrument is not used, and the filter was replaced with a normal H&\alpha; filter in September 2024.
Images of the instruments
Since 2022, the instruments are arranged in two arrays. Photos of them can be found below. Click on the images for higher resolution versions.
![Array of the Northern Sky Narrowband Survey containing [OIII] and [SII] instruments](sw2-1.jpg)
![Array of the Northern Sky Narrowband Survey containing [OIII] and [SII] instruments](sw2-2.jpg)
