On this page, we list the main changes that affected the instrument and its current status.

  • Starting in Period 100, we are changing the nighttime calibration plan. The Observatory will supply telluric standard stars only for cases where the requested S/N of the science spectrum in a single OB is 10 or below.  For all other cases, if the user requires telluric standard star, observations they must be accounted for in their time request at Phase 1. Users are encouraged to use the molecfit tool, which allows to fit and correct the telluric lines. However, observations of telluric standard stars may be required in some cases  (large number of intrinsic features, little or no continuum, low S/N). Users need to consider the following cases:

1. The requested S/N of the science spectrum in a single OB is >10: no observatory provided telluric standard star. Users that require a telluric need to submit them in a concatenation. The corresponding execution time must be taken into account at Phase 1.

2. The requested S/N of the science spectrum in a single OB is <10: The user has to explicitly state in the README file that they require a telluric standard star, which then will be provided by the observatory. 

  • February 2017: VIS readout noise has been recovered. (The increased readout was due to a grounding connection.)
  • January 2017: After X-shooter was remounted following the last mirror recoating, the readout noise is much higher in the VIS arm. All observations since 2016-12-20 are affected. Unfortunately, we have not yet identified the cause. The readout noise increased by 20-70% depending on the readout mode used, see http://www.eso.org/observing/dfo/quality/XSHOOTER/reports/HEALTH/trend_report_BIAS_VIS_ron_raw_HC.html
  • December 2016: The use of the MASTER RESPONSE function for the UVB-arm introduces a spectral artefact at λ=365nm, approximately the Balmer discontinuity, in the reduced spectra for data obtained since April 2015. The phase3 science archive contained affected data in 2015-2016. 
  • August 2015 Spectro-astrometry technique performed with XSHOOTER: Whelan et al. 2015, 579, A48.
  • August 2015: A document about the historical wavelength shift between the arms has been released. It presents their origin and the corrective actions that were performed. It is available from the manuals page.
  • Two mapping templates (slit and IFU modes) are offered since P96. They facilitate mapping observations and the data reduction with the REFLEX workflow.
  • In April 2015, a new pipeline version will be released. It corrects several bugs in the wavelength calibration due to non optimal correction of the flexures leading to offsets of a few km/s. There are still small residuals in the radial velocity depending on the position in the slit, which need to be fully characterized.
  • In P96, the ETC will take into account the difference between image quality and seeing.
  • Due to a software issue, the target centering was inaccurate in the y direction by 0.25" for g_prime and U band filter acquisitions between Dec 2013 and 2 Sep 2014.  The centering was possibly not optimum at some point between 2008 and 2013 for all filters with a shift of 0.17".
  • In Period 94, XSHOOTER is offered again at UT2. The instrument will be dismounted from UT3 early September 2014. The re-commissiong of the instrument on UT2 is scheduled for mid-October 2014. X-shooter will be operational starting on October 16.
  • Some tests were performed of a diaphragm mode that allows to observe very bright objects by diaphragming the entrance of the instrument. A small report is available here and some reduced data obtained during the technical night are available there
  • Since an upgrade of the VLT SW in January 2014, the quality of the aquisition images is suboptimal (higher bias and noise level). The imaging mode is not affected. 
  • Oct 2013: XSHOOTER is now installed at UT3. The efficiency of the telescope + instrument is better by 5-10% in all arms compared to UT2.
  • In P93, a light imaging mode performed with the fourth channel (A&G camera) will be offered.
  • No Large Programs are accepted from P93 onwards to allow for an eventual intervention to repair the ADC drives.
  • In P92, XSHOOTER will be moved from the UT2 to the UT3 Cassegrain focus.
  • The XSHOOTER pipeline version 2.2.0 has been released and its REFLEX 2.4 support as well. You may want to find it here.
  • In P91, the policy regarding the telluric standard stars observations will be modified (see User manual).
  • IMPORTANT: ADCs problems Due to mechanical problems with the ADC (atmospheric dispersion corrector) drives, the ADCs were disabled on August 1st 2012. During the previous months the ADCs for the UVB and VIS arms have been first occasionally and then increasingly failing. Incorrect position of ADCs leads to slit losses worse than if they are not used. An intervention to fix this problem is under evaluation. To minimize the slit losses, we advise to prepare observations as follows:
    1) Put the slit at parallactic angle (default value 9999), if possible.
    2) Observe the target close to the meridian, at low airmass. The mimimum airmass of your target will depend on its declination. As a reference a plot of the airmass vs. target declination corresponding to observing +/-2h from the meridian is shown on the VIMOS Phase 2 web page: VIMOS visibilities
  • The XSHOOTER pipeline version 1.4.5 has been released and its first REFLEX support as well: here.
  • A document describing the NIR readout mode, its regimes, and the impacts is available here.
  • In July 2011 the NIR slits wheel was replaced by a new one with two new slits of 0.6" and 0.9" with a K-band blocking filter allowing observations not dominated by the thermal background in J and H bands (background reduced by factors 3 to 4). Measurements show that the readout noise is the new limiting factor for these two slits. The 1.5" slit was removed. In addition, the TCCD performance was improved allowing a reduced pick-up noise.
  • New templates are available for P88 (spectrophotometric observations in nodding mode, additional AFC during an OB).
  • An oscillation of the dichroic absorption band in the UVB and VIS arms was reported. The last UVB arm order and the first four orders of the VIS arm suffer from this oscillation. More information on the Known Problems webpage: (see here)
  • October 2010: the pattern problem in the VIS arm has been fixed for both readout modes and the readout noise is constant.
  • There is a meeting devoted to the 1st year of XSHOOTER science (October 19-22, 2010): website
  • May 2010: XSHOOTER pipeline, current version 1.2.2: here. First public release of XSHOOTER pipeline, v1.0.0.
  • Feb 2010: The ESO Archive Group has prepared the XSHOOTER instrument specific query form: here.
  • New SM operation requirements/constraints might be implemented each new period. Please, always check the User Manual and the instrument specific phase 2 requirements or phase 2 news.


  • In Nov 2008 and Jan 2009 the UVB and VIS arms have been commissioned at the UT3 Cassegrain focus (see Messenger 134, 12 ).
  • The NIR arm has been commissioned in March 2009.
  • XSHOOTER commissioning data (Nov 2008, Jan 2009, Mar 2009 and May 2009) are public: here.
  • Paranalization data (29 May to 1 Jun 2009) are public: here.
  • XSHOOTER science verification (SV) data (Aug and Sep 2009) are public: here.

News about Science Data Product Forum

We would like to draw your attention to the existence of the Science Data Products internet forum which can be found at: http://www.eso.org/sci/data-processing/forum.html