Individual files can be fetched (via http) from here
or via ftp from: ftp://cdsarc.u-strasbg.fr/pub/cats/VIII/54

The catalogue can be queried from: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=VIII/54

This standardized document follows the rules of the Standard Description for Astronomical Catalogues. For those having to work on this catalogue using FORTRAN programs, this ReadMe file can be transformed into a f77-compliant program which reads the files making up this catalogue, in two versions: either a f77 program loading whole files into arrays, or a f77-program reading each data file line by line.

VIII/54  Atlas of Galactic Neutral Hydrogen  (Hartmann+, 1997)
================================================================================
Atlas of Galactic Neutral Hydrogen
    Hartmann D., Burton W.B.
   <Cambridge University Press (1997)>
   =1997agnh.book.....H
================================================================================
ADC_Keywords: H I data; Interstellar medium; Surveys; Radio sources; Atlases

Keywords: Galaxy: structure - ISM: clouds - ISM: general -
          ISM: kinematics and dynamics - surveys

Description:
    The Leiden/Dwingeloo HI survey mapped the 21-cm spectral line emission
    over the entire sky  above declinations  of -30  degrees using  a grid
    spacing of ~  0.5 degree and a velocity sampling of ~  1.03 km/s.  The
    useful velocity  (V_lsr)  range is from -450  to +400 km/s.  The Atlas
    presents calibrated spectra in units of brightness temperature.  Using
    interpolation and averaging,  the authors have placed their data on an
    evenly-spaced  grid   in  Galactic  coordinates   (l,b).   A  detailed
    discussion of the instrument and calibration procedures is provided in
    the published Atlas.

    The average sensitivity level of the survey is 0.07 K (1-sigma,  rms).
    This sensitivity level  depends  critically  on  the  success  of  the
    stray-radiation  correction  as   discussed   in   Hartmann   et   al.
    (1996A&AS..119..115H). In that discussion, several caveats are offered
    regarding the removal of stray radiation, in particular that component
    which might be due to reflection from the ground.  Some instances have
    been found where there are residuals which are clearly larger than the
    mean accuracy quoted as representative of the Leiden/Dwingeloo survey.
    Users of the data are reminded that the stray-radiation correction was
    applied  conservatively,  ensuring that no overestimate was calculated
    and  removed,  thereby  yielding  spurious  negative  intensities.   A
    specific example of remaining spurious emission is evident towards the
    North Galactic Pole, a direction notoriously difficult to observe. All
    spectra taken towards b=+90 degrees should,  of course,  be identical,
    no matter the longitude or  the  orientation  of  the  telescope  with
    respect to the ground or to the meridian.  Because the sky was sampled
    in 5x5 degree boxes,   a spectrum  was recorded  at b=+90  degrees for
    every  Nx5 degrees (N=0..72)  in longitude.   The spectra in the final
    dataset  were interpolated between  these measured spectra  to yield a
    0.5x0.5 degree  grid.  So,  only  every 10th spectrum  at this extreme
    latitude corresponds to an observed spectrum. Comparing all spectra at
    b=+90  reveals differences which are larger than expected.  The origin
    of this discrepancy is currently unknown.

    There   is  also  an  instrumental  effect  which  reveals  itself  as
    correlated noise,  showing a pattern which alternates sign at adjacent
    channels  when the very lowest levels of intensity are examined.  This
    effect  is due  to an  offset in  the DAS  autocorrelator used  as the
    backend in the Leiden/Dwingeloo survey.  The presence of this artifact
    becomes noticeable only after averaging 50 or more spectra. Although a
    Hanning convolution of the data would eliminate this effect,  it would
    also degrade the velocity resolution;   as  the  correlated  noise  is
    noticeable only at very low levels (about 15 mK),  well below the mean
    rms  sensitivity of the survey itself,   the original spectra have not
    been Hanning smoothed.  Excepted are those spectra which suffered from
    sinc  interference.  These spectra were Hanning smoothed to enable the
    elimination of the interference spike.

    Dr.   Lloyd Higgs has compared the HI  spectra made with the DRAO 26-m
    telescope  in support of the Canadian Galactic Plane Survey with those
    of the Leiden Dwingeloo Survey, and has pointed out what are evidently
    calibration problems in a small number of isolated LDS spectra. Either
    Hartmann, Burton, or Higgs could provide additional information.

    The  Leiden/Dwingeloo HI survey  is intended primarily  for studies of
    the interstellar gas associated  with  our  own  Galaxy.   There  are,
    however, a small number of spectra in which 'contaminating' signatures
    from  known external galaxies  are present.  Detections  of roughly 50
    such external galaxies were made;  refer to table 4 of the Atlas for a
    list.

    The HI  spectra from the  Leiden/Dwingeloo survey are  archived as 721
    files.  Each file is  in  FITS  image  format,   and  maps  the  21-cm
    brightness  temperature  at   a  fixed   Galactic  longitude   for  an
    evenly-spaced  rectangular  grid  of  (Galactic  latitude,   velocity)
    points.  There is one FITS file  for  every  0.5  degree  in  Galactic
    longitude in the "fits" subdirectory.

    In addition to the 721 (b,v) FITS files, there is an (l,b)  FITS image
    named  TOTAL_HI.FIT,  which contains the integrated intensity map over
    the velocity range -450 km/s <= V_lsr <= +400 km/s.  The map units are
    in [K.km/s]  and the  FITS  header  contains  comments  regarding  the
    conversion to column densities.

    Included as a  visual aid is  the GIF image  file total_hi.gif,  which
    depicts the velocity-integrated map.

    The data were  originally distributed  on a  CD-ROM enclosed  with the
    Atlas  of Galactic Neutral  Hydrogen (reference given  above).  The CD
    also contains animations of velocity slices through the data cube.

File Summary:

       FileName      Lrecl  Records   Explanations

× ReadMe            80        .   This file
× total_hi.gif   140194        1   761 x 361 GIF image of velocity integrated map
× total_hi.fit    2880      363   Velocity integrated map for whole sky
× maps.dat          23      721   Summary of latitude-velocity maps
× fits/*             0      721   Latitude-velocity maps for 0.5°-step longitude


Byte-by-byte Description of file: maps.dat

   Bytes Format Units   Label     Explanations

   1-  5  F5.1  deg     GLON      [0,360] Longitude of map
   7- 13  F7.2  m/s     DVel      Velocity increment per pixel
  15- 23  A9    ---     FITSfile  Name of FITS file in subdirectory "fits"


Acknowledgements:
    Thanks to  the authors and  Cambridge University Press  for making the
    data available for public distribution.  The Leiden-Dwingeloo Galactic
    H I survey  project was  supported by  the Netherlands  Foundation for
    Research   in  Astronomy  (NFRA)   with  financial  backing  from  the
    Netherlands Organization for Scientific Research (NWO).

References:
  Dap Hartmann, Kalberla P.M.W, Burton W.B. & Mebold U.:
              1996 A&AS 119, 115  =1996A&AS..119..115H
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(End)                             J. Weiland [ADF/ADC]               19-Apr-1999