Introduction
The SOAR Adaptive Module (SAM) is a laser-assisted adaptive optics instrument at the 4.1-m SOAR telescope. By compensating selectively low-altitude turbulence, it improves resolution at visible wavelengths. The instrument contains a 4Kx4K CCD imager covering the 3-arcmin square field. The paper describing the instrument is Tokovinin et al. (2016). [1]
Images as sharp as 0.3′′ have been obtained under favorable conditions of weak high-altitude turbulence which happen ~50% of the scheduled SAM nights. Under such conditions, the typical FWHM resolution delivered by SAM is 0.4′′ in the I band and 0.5′′ in the V band. The compensation quality is uniform over the field (FWHM variation of few percent). On nights with strong high turbulence (which does not necessarily mean poor seeing), SAM brings only a marginal resolution gain in closed loop and delivers V -band FWHM between 0.6′′ and 1′′.
The first paper using SAM commissioning data on the globular cluster NGC 6496 was published by Fraga et al. (2013, [2] AJ, 145, 165) [2]. It demonstrates that the photometric precision and limiting magnitude in crowded stellar fields are improved by using the SAM AO system and that good-quality photometry can be derived from the SAMI images.
In the figure 1 from Fraga et al. 2013 shown above, we show the full-frame image of NGC 6496 in the I-band taken with the SAM Imager (SAMI; north is up, east to the left). The enlarged fragments of 15 × 12 arcsecond size compare closed-loop (upper) and open-loop (lower) images taken with the same exposure time of 120 s and displayed on the same intensity scale, at the center and near the edge of the field.
SAM in Numbers [3]
Documentation for the SAM User
Documentation for the SAM Operator (SAM Support Scientist)
SAMI has one filter wheel with 7 positions for 3 inch square filters. We have acquired two new broadband filter sets for exclusive use with SAMI: a Kron-Cousins BVRI set and a SDSS griz set. We also have new Ha, NI, [NII] and [SII] narrow band filters, in addition to several redshifted Ha filters designed for the Fabry-Perot module (more details in this link [16]). The table below shows the updated list of available filters, with the vendor-supplied transmission curves.
Filter Name | Filter Set | Central wavelength (Å) | FWHM Width (Å) | Transmission Curve |
---|---|---|---|---|
SAMI-B | K-C | 4400 | 1000 | Plot [17] |
SAMI-V | K-C | 5500 | 800 | Plot [18] |
SAMI-R | K-C | 6550 | 1800 | Plot [19] |
SAMI-I | K-C | 7800 | 1050 | Plot [20] |
SAMI-g | SDSS | 4750 | 735 | Plot [21] |
SAMI-r | SDSS | 6250 | 735 | Plot [22] |
SAMI-i | SDSS | 7750 | 765 | Plot [23] |
SAMI-z | SDSS | 9500 | 2328 | Plot [24] |
SAMI-Ha | Narrow | 6563 | 75 | Plot [25] |
SAMI-[NI] | Narrow | 5180 | 55 | |
SAMI-[NII]6583 | Narrow | 6583 | 18 | Plot [26] |
SAMI-[SII] | Narrow | 6724 | 75 | Plot [27] |
SAMI-[SII]6738 | Narrow | 6738 | 27 | Plot [28] |
BTFI_5021/17 | Narrow | 5030.9 | 16.5 | |
BTFI_6569/20 | BTFI | 6569.2 | 18.6 | |
BTFI_6579/20 | BTFI | 6578.8 | 19.9 | |
BTFI_6600/20 | BTFI | 6600.5 | 19.3 | |
BTFI_6745/38 | BTFI | 6745 | 38.5 |
SAM compensates partially turbulence in the atmospheric ground layer and in the telescope dome. The delivered image quality (DIQ) approaches the free-atmosphere seeing produced by turbulence above ~0.5km. When the free atmosphere is calm, SAM provides an appreciable gain in the DIQ, but when the total seeing is dominated by the free atmosphere, the gain from using SAM can be marginal and the DIQ can be mediocre. This is illustrated by the two figures below.
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Left plot: on February 26, 2013, the free atmosphere (red line) was calm, the DIQ in the I band (blue dots) was between 0.3 and 0.4 arcsec FWHM - much better than the site seeing (black line). Right plot: one month before that, on January 29, 2013, the seeing was less stable and often dominated by the free atmosphere. In these conditions the DIQ could be worse than 1 arcsecond, and the resolution gain provided by SAM was variable. Note that the site seeing was similar on both nights. The performance of SAM depends on the free-atmosphere seeing , not on the total seeing!
Turbulence compensation in SAM is partial, better at longer wavelengths. The DIQ of SAM depends on the wavelength stronger than the natural seeing. The plot above shows the median DIQ for a good night of March 6, 2012, in closed (compensated) and open (uncompensated) loop. Yet another consequence of partial compensation is that the point-spread function is more "peaked" compared to the natural seeing. It can be modeled by a Moffat function with beta~2. With such PSF, the encircled energy is improved, but not as much as the FWHM resolution.
The plots below show FWHM resolution as function of the star position in the field. The data were obtained on a good night of March 3/4, 2013 in the I band, when SAM provided a very good resolution. The uniformity over the field is excellent. However, some degradation towards the field border is seen in the left plot. It is produced by partially compensated turbulrnce at low altitude.
This material is based on the SAM Commissioning report [29].
Focus depth w.r.t. flange surface: 150mm
OAP parameters:
Focal length 810mm
Off-axis distance 213.277mm
Diameter 175mm
Deformable mirror BIM-60
Number of electrodes: 60
Pupil diameter: 50mm, incidence angle: 12.5deg
Min. curvature radius (400V on all electrodes): 16.7m
Tip-Tilt guiders
Patrol field: 100x100mm (5x5 arcmin)
Probe field of view: 3x3arcsec
Total mass at installation (3-Aug-2009) ~300kg
Offset towards SOAR w.r.t. the ISB hole: 67.5m
Aperture diameter 4.10m
Plate scale 0.330mm/arcsec or 3.025arcsec/mm
M1 curvature radius at vertex: -13.50970m
M1 conic constant: -1.002667
M2 curvature radius: -2.03265m
M1-M2 distance: 5.83922m
M2-M3 distance: 4.98922m
M3 to focus: 4250.0m
Effective focal length: 68.175m (F/16.63)
Focal surface radius: 0.9656m (convex outside)
Central obscuration: 0.228 (diameter 936.5mm)
Wavelength 355nm
Nominal power 10W
Nominal pulse frequency 10kHz, pulse length 34ns
Laser head size: 813x127x86mm, mass: 14.5kg
Typical power consumption: 400W laser, 700W chiller
Power supply size: 427x364x76mm, mass: 8.4kg
Chiller size: 533x440x264mm, mass 55kg
Pixel size 10 micron or 15.23mas
Format 658(H)x496(V) or 6.58x4.96mm or 10.0x7.55arcsec
Pixel size 15micron or 45.5mas
4Kx4K (3x3 arcmin on the sky)
Filters: TBD
Back to SAM webpage [30]
Last change: Dec-23-2014, César Briceño
Send comments to: Andrei Tokovinin [31]
Instrument support scientists
Andrei Tokovinin (atokovinin@ctio.noao.edu [31])
Cesar Briceno (cbriceno@ctio.noao.edu [32])
Bruno Quint (bquint@ctio.noao.edu [33])
Engineering support
Manuel Martinez (mmartinez@ctio.noao.edu [34]) - electronics, motion control software
Rolando Cantarutti (rcantarutti@ctio.noao.edu [35]) - real-time and instrument control software, HRCAM
Omar Estay (oestay@ctio.noao.edu [36]) - SAMI software
Roberto Tighe (rtighe@ctio.noao.edu [37]) - optics
Links
[1] http://adsabs.harvard.edu/abs/2016PASP..128l5003T
[2] http://adsabs.harvard.edu/abs/2013AJ....145..165F
[3] http://www.ctio.noao.edu/soar/content/sam-numbers
[4] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/sami-manual.pdf
[5] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/sami-sw.pdf
[6] http://www.ctio.noao.edu/soar/content/filters-sami
[7] http://www.ctio.noao.edu/soar/content/soar-staff
[8] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/guide.pdf
[9] https://www.space-track.org/auth/login
[10] http://www.ctio.noao.edu/soar/content/sam-computers
[11] http://www.ctio.noao.edu/soar/sites/default/files/documents/Instruments/SAM/LCH_Scripts.pdf
[12] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/ICsoft-UserManual-3.7.0-291113.pdf
[13] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/aom-sw.pdf
[14] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/SLCH-UserManual.pdf
[15] http://www.ctio.noao.edu/soar/content/instrument-documentation-0
[16] http://www.ctio.noao.edu/soar/content/filters-sam-fp
[17] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/Kron-Cousins_B.jpg
[18] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/Kron-Cousins_V.jpg
[19] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/Kron-Cousins_R.jpg
[20] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/Kron-Cousins_I.jpg
[21] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SDSS_g.jpg
[22] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SDSS_r.jpg
[23] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SDSS_i.jpg
[24] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SDSS_z.jpg
[25] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SAMI_filt_Ha_curve.png
[26] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SAMI_filt_NII_Narrow_curve.jpg
[27] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SAMI_filt_SII_curve.png
[28] http://www.ctio.noao.edu/soar/sites/default/files/SAM/SAMI_Filters/SAMI_filt_SII_narrow_curve.png
[29] http://www.ctio.noao.edu/soar/sites/default/files/SAM/archive/samrep.pdf
[30] http://www.ctio.noao.edu/soar/content/soar-adaptive-optics-module-sam
[31] mailto:atokovinin@ctio.noao.edu
[32] mailto:cbriceno@ctio.noao.edu
[33] mailto:bquint@ctio.noao.edu
[34] mailto:mmartinez@ctio.noao.edu
[35] mailto:rcantarutti@ctio.noao.edu
[36] mailto:oestay@ctio.noao.edu
[37] mailto:rtighe@ctio.noao.edu