Work based on MUSE observations should cite the paper Bacon et al., SPIE 7735, 7 (2010).
MUSE, the Multi-Unit Spectroscopic Explorer, is an Integral Field Spectrograph located at the Nasmyth B focus of Yepun, the VLT UT4 telescope. It has a modular structure composed of 24 identical IFU modules that together sample, in Wide Field Mode (WFM), a near-contiguous 1 squared arcmin field of view. Spectrally the instrument samples almost the full optical domain with a mean resolution of 3000. Spatially, the instrument samples the sky with 0.2 arcseconds spatial pixels in the currently offered Wide Field Mode with natural seeing (WFM-noAO).
In the future, MUSE will utilise the VLT Adaptive Optics Facility (AOF) via the GALACSI Adaptive Optics system. It will then offer, in addition, an AO-corrected 1'x1' field of view with 0.2 arcseconds sampling (WFM-AO) or a 7.5x7.5 arcsec2 field of view sampled at 0.025"/pixel (NFM-AO).
- Formation of galaxies
- Nearby galaxies
- Stars and resolved stellar populations
- Solar system
MUSE in a nutshell
The table below gives the basic parameters of the instrument.
|Number of IFU modules||24|
480-930 nm (nominal)
465-930 nm (extended)
|Detectors||24 x 4k x 4k MIT/LL CCD|
|AO type||Ground Layer, 4x(5-10 W) lasers|
||14 % (480 nm) 35 % (750 nm) 14 % (930 nm)|
Wide Field Mode (Currently offered)
|Field of view||59.9"x 60.0"
|Spatial Sampling||0.2" /pixel
|Spatial resolution (FWHM)||0.3"-- 0.4"
|Resolving power||1770 (480 nm) -- 3590 (930 nm)|
(1 hr, airmass=1.0, seeing 0.8"@V)
VAB = 22.64 mag (550 nm)
IAB= 22.28 mag (784.9 nm)
Wide Field Mode with AO (Not currently offered)
|Gain in ensquared energy within one pixel with respect to seeing||2|
|Condition of operation with AO||70th percentile|
|Sky coverage with AO||70% at Galactic Pole|
Narrow Field Mode (Not offered yet. To be offered with GALACSI)
|Field of view||7.42" x 7.43"|
|Spatial Sampling||0.025" / pixel|
|Spatial resolution(FWHM)||0.03" -- 0.05"|
|Resolving power||1740 (480 nm) -- 3450 (930 nm)|
|Predicted limiting flux in 1 hr||2.3 10-18 erg s-1 cm-2|
|Predicted limiting magnitude in 1 hr||RAB = 22.3 mag|
|Predicted limiting surface brightness in 1 hr||RAB = 17.3 mag arcsec-2|
These are the main performed as part of the standard calibration plan.
|Calibration||No. of exposures (per mode)||Frequency||Phase||Purpose|
|Bias||11||Daily||Day||Master bias, bias characteristics|
Master dark, dark current
|Geometrical calibration: Multi-Pinhole mask with arc lamps
||80||Monthly||Day||Relative location of the slices|
|Flat-field with continuum lamp||11||Daily||Day||Illumination correction, Tracing solution, Background light, Instrument throughput.|
Arc lamp exposures
|5 per lamp (a)||Daily||Day||Wavelength solution, Dispersion characteristics|
|Flat-field with sky||>3||Weekly||Twilight||Large scale illumination correction|
|Flat-field with continuum lamp||n (b)||hourly during the night
|Attached Flat-field with continuum lamp||n||On request||Night||
Attached arc lamp exposures
|n||On request||Night||High-precision wavelength solution|
||(c)||Night||Absolute flux calibration. Optional: Telluric correction|
|Telluric star||n||On request||Night||Telluric correction|
(a) The default is to obtain five exposure per lamp for each of the Ne, Xe, and HgCd lamps. Every 90 days we take 15 frames per lamp to obtain the Line Spread Function (LSF).
(b) These single flat fields are taken automatically at hourly intervals during the night or when the change in temperature is above 0.3 degrees.
(c) During clear or photometric nights in which MUSE science OBs are executed.
The table below gives the instrumental overheads that can be used for the proposal preparation phase.
|Interactive acquisition loop
|Slow guiding loop closure
|Detector readout + file merging
|Telescope offset < 2'||15|
|SGS loop closure for large ofsets||90|
||Attached flat (5 flats)
|Attached arcs (3 calibrations, 1 per lamp)
180s + 112s/exposure
(1 per lamp)
Examples of overhead computation
Example 1. Not using SGS
Ttotal = 360s (preset) + Tacq + 120s (acquisition, 1 iteration) + N*(15s+UIT+80s)
with Tacq the acquisition integration time, and UIT the integration time of each of the N exposures.
Example 2. using the SGS with small telescope offsets and no PA offsets
Ttotal = 360s (preset) + Tacq + 120s (acquisition, 1 iteration) + 90s (SGS loop closure) +N*(15s+UIT+80s+15s (telescope offset) )
Example 3. using the SGS with large telescope offsets and PA offsets
In that case we are assuming that the SGS has to close the loop after each offset/rotation because it has lost the current guide stars.
Ttotal = 360s (preset) + Tacq + 120s (acquisition, 1 iteration) + 90s (SGS loop closure) +N*(15s+UIT+80s+15s (telescope offset) + 20s (PA rotation) + 90s (SGS loop closure))
MUSE Science show case 1: Kapteyn's Star
First light image of a M1 red dwarf of 9th magnitude, in the constellation of Pictor, named after the dutch astronomer Jacobus Kapteyn who discover it in 1898.