Quality Control and
Data Processing

The QC group processes a stream of science-grade data products for selected VLT instruments. They are created using certified pipelines and certified master calibrations. Find an overview of the current streams here.

The NACO pipeline is designed to reduce some types of the raw science data. Please, be aware that the adopted reduction strategy may not be suitable for some particular scientific purposes. The following types of the NACO raw science data are NOT supported by the pipeline (situation for P86and later). Not all of the science modes have been used after 2015-01 (after the detector upgrade). Science raw frame screen shots shown in the following pages are from observations earlier than 2015-01 (before the detector upgrade):

The following types of NACO raw science data are supported by the pipeline:

Frame Type	DPR.TYPE	DPR.TECH
SCIENCE_IMG	OBJECT	IMAGE,JITTER
SCIENCE_IMG	SKY	IMAGE,JITTER
SCIENCE_SPEC	OBJECT	SPECTRUM,JITTER
SCIENCE_SPEC	SKY	SPECTRUM,JITTER

The following types of the NACO raw science data are NOT supported by the pipeline (situation for P86and later). Not all of the science modes have been used after 2015-01 (after the detector upgrade). Science raw frame screen shots shown in the following pages are from observations earlier than 2015-01 (before the detector upgrade):

specle imaging cube mode

Frame Type SCIENCE_IMG_CUBE
DPR.TYPE OBJECT; SKY
DPR.TECH IMAGE,JITTER,NOAO,CUBE; IMAGE,JITTER,NOAO,CUBE,PT

description: This open-loop imaging mode with NAOS-CONICA has been offered since P86 (October 2010). Associated with detector windowing and fast readouts (cube mode) it allows the user to apply various speckle interferometry techniques. For further details please consult the NACO User Manual.

This mode is offered in service but is not supported by the pipeline. User has to provide his/her own photometric standard(s) as the standard calibration plan does not include this mode and photometric precision is subject to the technique used.

imaging SDI/SDI+

Frame Type SCIENCE_SDI
DPR.TYPE OBJECT; SKY
DPR.TECH IMAGE,DIFFERENTIAL,JITTER; IMAGE,DIFFERENTIAL,JITTER,CUBE; IMAGE,DIFFERENTIAL,JITTER,PT; IMAGE,DIFFERENTIAL,JITTER,CUBE,PT

description: The SDI+, or SDI, mode of NACO consists of four images through three narrow band filters which are simultaneously recorded on the detector. Two images are taken outside the ~ 1.6 um methane feature (at 1.575 um and 1.600 um) and two images taken inside the feature (both at 1.625 um). All filters have a FWHM of 25 nm. The plate scale of the SDI+ camera is 17.32 mas/pixel. This mode was designed to detect methane rich objects near very bright stars.

This is an example of the SDI+ lamp flat raw frame. The transmitted wavelengths are 1.6 um (top left), 1.575 um (top right), and 1.625 um (bottom left and right). Note that the vertical misalignment of the mask varies with time and cannot be corrected for.

In P82, the SDI+ permanently replaced the "old SDI", now decommissioned.

This mode is offered in service and visitor mode. It is not supported by the pipeline. calibrations:The calibration plan includes

• standard detector darks with readout mode and DIT matching the one used for science;
• standard lamp and/or sky flat fields as well as internal lamp flat field with the SDI+ mask in (not supported by the pipeline);
• nightly zero points;

coronography

Frame Type SCIENCE_CORONOGRAPHY
DPR.TYPE OBJECT; SKY
DPR.TECH CORONOGRAPHY,JITTER; CORONOGRAPHY,JITTER,PT; CORONOGRAPHY,JITTER,CUBE; CORONOGRAPHY,JITTER,CUBE,PT

description: The coronographic observations are obtained using the Lyot-type coronograph with a circular focal plane mask and undersized pupil plane mask inserted in the optical axis. Five masks are available: two opaque masks with diameter 0.7 arcsec (INS.OPTI1.NAME=C_0.7) and 1.4 arcsec (INS.OPTI1.NAME=C_1.4), a semi-transparent mask with diameter 0.7 arsec (INS.OPTI1.NAME=C_0.7_sep_10), and two four quadrant phase masks, one optimized for K-band (INS.OPTI1.NAME=4QPM_K) and the other in H-band (INS.OPTI1.NAME=4QPM_H). The coronographic observations can be also obtained in the pupil tracking (PT) and/or cube (CUBE) modes. For more information regarding coronography, available masks and their characteristics consult the NACO User Manual In addition (as of P86), a new Apodizing Phase Plate (APP) (see APP coronography) has been installed in the pupil plane and is operated at 4.05 um (NB and IB filters) just like direct imaging.

	This is an example of the coronographic observation using the C_0.7 mask. The mask's diameter is 0.7 arcsec, it is 100% opaque held in place by wires.
	This is an example of the coronographic sky observation using the 4QPM_K mask. This 4 quadrant phase mask is optimized for a wavelength of 2.18 um. It's FOV is 13 x 13 '' and the diameter is that of the central Lyot spot.

This is an example of the coronographic sky observation using the semi-transparent, C_0.7_sep_10 mask, with camera S27. The semi-transparent mask is placed on the transparent plate. It's transmissivity is measured to about 3.5x10(-3).

This mode is offered in service and visitor mode. It is not supported by the pipeline. calibrations:The calibration plan includes

• standard detector darks with readout mode and DIT matching the one used for science;
• standard lamp and/or sky flat fields without the focal plane mask; users are offered possibility to design the night time flat fields for the C_0.7_sep_10 and 4QPMs masks to avoid problems with instrument flexure;
• nightly zero points;

APP coronography

Frame Type SCIENCE_CORONOGRAPHY
DPR.TYPE OBJECT; SKY
DPR.TECH IMAGE,JITTER,APP,CUBE; IMAGE,JITTER,APP,CUBE,PT; SPECTRUM,NODDING,APP

description: A new coronographic Apodizing Phase Plate (APP) has been offerend since P86. It is mounted in the OPTI3 wheel (INS.OPTI3.NAME=APP_coro) and designed to work in the 3-5 um range. It is offered to work with the filters NB_4.05 and Lprime. The IB_4.05 filtered showed problems and is now decommissioned.

Since no occulting mask is present in the focal plane, it works like simple, direct Lprime imaging. This new observing mode is suitable for searches of faint companion as it provides higher contrast at small angular separation - from 0.2 to 0.7 arcsec from the main star on one side. It can be combined with cube mode and pupil tracking. For more information regarding APP coronography consult the NACO User Manual

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This is an example of the APP coronographic observation in filter NB_4.05. The picture is just a small snapshot of the upper central area of the detector region.

This mode is offered in visitor mode. It is not supported by the pipeline. calibrations:The calibration plan includes

• standard detector darks with readout mode and DIT matching the one used for science;
• standard sky flat fields without the focal plane mask;
• sky flat with APP mask in the focal plane (DPR.TECH=IMAGE,APP);
• nightly zero points - optional;

SDI4

Frame Type SCIENCE_SDI
DPR.TYPE OBJECT; SKY
DPR.TECH SDI4; SDI4,PT; SDI4,CUBE; SDI4,CUBE,PT

description: The SDI4 has been offered since P81 (April 2008). It is a combination of the SDI+ (see imaging, SDI/SDI+) and the 4 quadrant phase mask (coronography), optimized for the H-band. The purpose of this mode is to achieve high contrast and improve detectability of faint sub-stellar companions near bright stars, ideally down to massive extra solar giant planets, by reducing the photon noise at small angular separation. For further details consult the NACO User Manual.

This is an example of the SDI4 science observations. Note the characteristic 4 quadrant pattern of the SDI+ field-of-view each superposed with the 4QPM_H mask.

Prism Spectroscopy

Frame Type SCIENCE_SPEC
DPR.TYPE OBJECT; SKY
DPR.TECH SPECTRUM,JITTER
SEQ.SPECMODE L27_P1; S13_P1; S27_P1

description: The NACO prism spectroscopy has been re-introduced since P86. There are three spectroscopic modes with the prism - L27 P1, S13 P1, and S27_P1. The spectral resolution varies from about 40 in the J-band to 250 in the M-band. The spectral traces of prism spectra are quite complex. In general, the trace can be fitted with the 4th order Legendre polynomial, but the coefficients of the polynomial depend on the location of the spectra on the array. For further details regarding the characteristics of the modes consult the NACO User Manual.

Example of the stellar spectrum with the L27_P1 mode. The spectrum extends from 0.85 um on the top to 5.5 um near the bottom. Note striking changes in brightness along the wavelength direction.

Polarimetry

Frame Type SCIENCE_POLARIMETRY
DPR.TYPE OBJECT; SKY
DPR.TECH POLARIMETRY,WOLLASTON,JITTER; POLARIMETRY,WOLLASTON,CHOPPING

also wire grid polarimetry; has been discontinued since P82:

DPR.TECH POLARIMETRY,WIRE_GRID; POLARIMETRY,WIRE_GRID,JITTER; POLARIMETRY,WIRE_GRID,CHOPPING

description: CONICA is equipped with a MgF2 Wollaston prism, used for imaging polarimetry, as well as a turntable half-wave plate. The Wollaston prism is located in the OPTI4 filter wheel (INS.OPTI4.NAME=Wollaston_00). Since the J-band filter is in the same wheel, J-band polarimetric observations are not possible. Also, the half-wave plate is installed in the CONICA's entrance wheel, where the calibration mirror is situated. Thus, internal calibrations with the half-wave plate cannot be done.

Wire grid polarimetry and the Wollaston_45 are no longer available (as of P82).

The Wollaston splits the incoming light into ordinary and extraordinary beams. An image taken with the Wollaston prism will contain two images of every object. To avoid sources overlapping a special mask consisting of alternating opaque and transmitting stripes is inserted in the optical path.

For more information regarding polarimetric mode of NACO consult the NACO User Manual and the instrument web pages.

	An example of the polarimetric observation with filter H and camera S27
	Polarimetric observations with filter Ks and camera S13. No Mprime observations are offered with polarimetry.

SAM

Frame Type SCIENCE_SAM
DPR.TYPE OBJECT; SKY
DPR.TECH IMAGE,JITTER,SAM; IMAGE,JITTER,SAM,PT; IMAGE,JITTER,SAM,CUBE,PT
INS.OPTI3.NAME 18Holes; 7Holes; 9Holes; BB_9holes

description: The Sparse Aperture interferometric Masks (SAM) mode was commissioned in March 2008 and offered to the public as of P82. The purpose of this mode is to obtain the very highest angular resolution at the diffraction limit. Four masks were manufactured to fit NACO specification - 18Holes, 7Holes, 9Holes, and BB_9holes. They were installed in the OPTI3 filter wheel of CONICA. For detailed description of the masks see the NACO SAM web pages. Sparse Aperture Masking is useful for very narrow fields of view (the outer limit is set by the resolution of the shortest baseline in the mask). Its supertiority over conventional full-pupil imaging applies only to typically several resolution elements of the PSF core. In the infrared, this typically means that SAM is useful for objects where the entire field of interest lies within several hundred milli-arcsecs from a bright star. (Although there may be ways to mosaic larger fields together, these have never been successfully demonstrated). In general, the more holes in the mask, the smaller the holes must be (to preserve non-redundancy) and consequently the less light is passed by the mask. To choose which masks is appropriate for scientific applications consult the NACO User Manual. To take a full advantage of the SAM technique it was estimated that for NACO the useful magnitude limit could be as faint as 10-12 mag.

In observations, the dominating source of background noise is turbulent atmosphere. Rapid readout of the detector array tends to freeze the motion of the interference fringes, reducing the impact of turbulances on the measured coherence of the incoming wavefront. Thus, preferably the SAM observations are taken in the cube mode, where the Double_ReadResetRead/HighDensity (DCR/HD) readout detector mode is used. Also, given the very small useful science field-of-view, only selected window of the array is read (e.g. 256 x 258 pixels), which further speeds up the read out time.

In addition, SAM must be combined with pupil tracking mode because the occultation of one of the mask holes by the telescope spiders would compromise the calibration properties of the experiment.

	The NACO image of the pupil showing the telescope spiders.
	An example of the SAM observations with the 7Holes mask. The frame is windowed to 256 x 258 pixels.

SAM Pol

Frame Type SCIENCE_SAMPOL
DPR.TYPE OBJECT; SKY
DPR.TECH IMAGE,JITTER,SAMPOL; IMAGE,JITTER,SAMPOL,PT; IMAGE,JITTER,SAMPOL,CUBE,PT
INS.OPTI3.NAME 18Holes; 7Holes; 9Holes; BB_9holes

description: The simultaneous use of the Wollaston together with the SAM masks (see sparse aperture interferometric masks section) presents a unique opportunity with CONICA to examine systems where there may be polarization signals at very high spatial resolutions. The SAMPol, new observing mode of NACO was offered in P86.

It is similar to SAM and uses pupil tracking and cube modes (cube mode section).

SAMPol is offered with all filters except J and Mprime.

Note that SAMPol does not use the Polarimetry Mask, usually needed in classic polarimetry (see polarimetry) to cover the overlapping parts of the beams, because SAM/SAMPol are only used for single-object targets and there should never be the possibility for confusion between overlapping fields that the mask is intended to avoid.

For more information consult the NACO User Manual and the instrument web pages.

An example of the SAMPol observations with filter NB_1.64, 9Holes mask. The data were taken in the pupil tracking, cube mode.

SAMPol is offered only in the visitor mode. It is not supported by the pipeline. calibrations:The calibration plan includes

• standard detector darks with readout mode and DIT matching the one used for science;
• standard sky (twilight) and/or internal flat fields without the mask;

CUBE MODE

Frame Type SCIENCE_IMG
DPR.TYPE OBJECT; SKY
DPR.TECH IMAGE,JITTER,CUBE; IMAGE,JITTER,CUBE,PT; IMAGE,JITTER,APP,CUBE; IMAGE,JITTER,APP,CUBE,PT; IMAGE,DIFFERENTIAL,JITTER,CUBE; IMAGE,DIFFERENTIAL,JITTER,CUBE,PT; SDI4,CUBE; SDI4,CUBE,PT; CORONOGRAPHY,JITTER,CUBE; CORONOGRAPHY,JITTER,CUBE,PT; IMAGE,JITTER,SAM,CUBE,PT; IMAGE,JITTER,SAMPOL,CUBE,PT

description: The cube mode is the mode in which every single DIT frame is saved. Thus, one cube (each "fits" file) includes NDIT frames (e.g. NAXIS3=11). This mode is particularly interesting for lucky-imaging type of observations, where one wants to select the best frames out of a set before co-adding them. The mode can be used for time resolved applications, provided one selects detector setups that do not lose frames and no single DIT frame time stamping is needed.

The size of each cube is limited by the maximum file size accepted by current version of Linux, 512 MB. Therefore, given a certain detector window, this fixes the maximum number of planes that can be saved in a cube (i.e. NDIT).

Cube mode is offered in combination with 5 different window sizes. Note that since windowing is done on chip (i.e. hardware windowing), NY=NX+2. Another feature of hardware windowing is that one cannot choose the position of the window within the full frame array: each window is centered on pixel (512,512), and the STARTX and STARTY parameters are fixed by the chosen window size.

In terms of data format, cubes are 3-D FITS files (i.e. NAXIS=3), a cube plus the same 3 FITS extensions. The size of the third axis (NAXIS3) is equal to NDIT+1: NDIT is the number of saved DIT frames, and the additional frame at the end of the cube is the combined image, i.e. the frame obtained as a sum of all DIT planes divided by NDIT. This last plane in the cube is the equivalent 2-D image one would obtain in single frame mode. The combined image is used for sanity check and quality control at the observatory. Users are cautioned to use only the first NDIT frames of each cube for their data reduction. Note also that the first frame in the cube may suffer from some reset anomaly and should probably be discarded. Cubes have NAXIS2=NAXIS1+2 as a rule. For example, if one windows the array to half its size and takes NDIT=200, the size of the cube will be (NAXIS1,NAXIS2,NAXIS3)=(512,514,201). The FITS extensions remain unchanged.

For more information regarding cube mode, available windows, the minimum DIT and the maximum NDIT for various readout and detector modes consult the NACO User Manual and the instrument web pages.

calibrations:The calibration plan includes

• standard (non-cube) detector darks with readout mode and DIT matching the one used for science;
• standard (non-cube) sky (twilight) and internal flat fields;
• standard (non-cube) nightly zero points;