Contents of: aliases/./H/Hipparcos/epophot/ReadMe

The following document lists the file H/Hipparcos/epophot/ReadMe from catalogue aliases.
A plain copy of the file (without headers/trailers) may be downloaded.

I/239/epophot      Tycho/Hipparcos Epoch Photometry Data

    The Hipparcos and Tycho Catalogues (ESA 1997) are accessible as
    Catalog <I/239> ( at,
    or can directly be queried by VizieR from   or mirrors

    Transit data related to Tycho Catalogue objects considered to be of
    greatest astrophysical value constitute the Tycho Epoch Photometry
    Annex A, and is included in the CD-ROMs version of the Hiparcos
    catalogue; it concerns 34446 objects. Epoch photometry for 481553
    objects originally constitutes the Tycho Epoch Photometry Annex B;
    however the data related to some of the zones could not be recovered,
    but the majority of the lost data could be reconstructed and are
    marked as 'b' in the status of Tycho Epoch Photometry.

    The results of the individual transits stored in a 2-level directory
    tree, the first level being made of the 2 leftmost digits of the TYC1
    number (the leftmost of the 3 numbers making up the TYC designation).
    The Epoch Photometry data for all stars sharing the same TYC1 number
    are stored in a file, with a blank line is inserted between two
    objects; these files have been compressed with the gzip utility, but
    the starting byte of each individual file is reported in index files.

    Each object contained in the Epoch Photometry Annex consists in a
    1-line header, followed by the individual transit records. The record
    structure is described in section 2.6 of the first volume of the
    Hipparcos catalogue (pp. 229-235), and summarized below in the 
    "Header Records" section and "Individual transit records" section.

    It should be noted that the mean magnitudes reported in the header
    records (and also in the Tycho catalogue) have been computed with
    de-censoring methods -- i.e. absence of detections have been taken
    into account. The result is that the mean magnitudes are generally
    fainter than what can be derived from an arithmetic mean of the
    individual magnitudes.

    Transit data related to Hipparcos objects are stored in the
    hip_epo.dat file of the CD-ROM version of the Hipparcos catalogue, 
    and described in section 2.5 (pages 217-225) of volume 1. 
    The transit data are stored also as a header records described in the
    "Hipparcos Header Records" section below, followed by transit records
    described in the "Hipparcos Transit Records" section.

File Summary:
 FileName      Lrecl  Records   Explanations
README            80        .   This file
tyc_epo.dat       14   524423   The status of Tycho Epoch Photometry

See also:
    I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)

Byte-by-byte Description of file: tyc_epo.dat
  Bytes Format Units   Label     Explanations
  1- 12  A12   ---     TYC       Tycho star name
     14  A1    ---    morePhoto *[ABbc-] Availability of Tycho Epoch Photometry
Note on morePhoto: the statuses are:
   A : Best part of Tycho Epoch Photometry
   B : Less reliable Tycho Epoch Photometry
   b : indicates a class 'B' which was reconstructed in 2001 for some missing
       stars; the reconstruction did not give exactly the same result.
   c : star announced without Epoch Photometry, but a photometry could be
       derived in 2001.
   - : indicates a class 'B' for which the Epoch Photometry could not be

Header Records:
   Bytes Format Units  Label    Explanations
   1-  4  I4    ---    TYC1     TYC1-3 number
   6- 10  I5    ---    TYC2     TYC1-3
      12  I1    ---    TYC3     TYC1-3
  14- 16  I3    ---    Ntr      Number of transit records
  18- 20  I3    ---    Nb       Number of transits measured in the B_T_ band
  22- 27  F6.3  mag    BTmag    ? Mean BT magnitude (median or de-censored mean)
  29- 33  F5.3  mag    e_BTmag  ? Mean error on BTmag
  35- 40  F6.3  mag    BTmax    ? BTmag at maximum (15th percentile)
  42- 47  F6.3  mag    BTmin    ? BTmag at minimum (85th percentile)
  49- 51  I3    ---    Nv       Number of transits measured in the V_T_ band
  53- 58  F6.3  mag    VTmag    ? Mean VT magnitude (median or de-censored mean)
  60- 64  F5.3  mag    e_VTmag  ? Mean error on VTmag
  66- 71  F6.3  mag    VTmax    ? VTmag at maximum (15th percentile)
  73- 78  F6.3  mag    VTmin    ? VTmag at minimum (85th percentile)
  80- 81  I2    ---    Flag1    [0,63]? Duplicity/variability flag (1)
  83- 84  I2    ---    Flag2    [0,7] Status (2)
Note (1): Flag made of 6 bits:
   0 = approximate magnitude (from Tycho field T36)
   1 = Variable or suspected from GCVS or NSV catalogues (from Tycho field T47)
   2 = Variable or suspected from Tycho analysis (from Tycho field T48)
   3 = close pair, known from Hipparcos or Tycho (from Tycho field T2)
   4 = double or suspected, unresolved by Tycho (from Tycho field T49)
   5 = Variable or suspected from Hipparcos analysis (from Hipparcos field H6)

Note (2): Flag made of 3 bits:
   0 = standard star for photometric calibration in normal processing
   1 = standard star for photometric calibration in reprocessing
   2 = photometric reduction used instrument parameters from reprocessing
   The value of this flag is set to 3 (bits 0 and 1 set) for reconstructed
   photometry (stars having the 'b' or 'c' status in the morePhoto column
   of the tyc_epo.dat file). In this case, the values of Flag1, and of
   the magnitudes, are blank.

Individual transit records:
  Bytes Format Units  Label    Explanations
  1- 10  F10.5 d   JD-2440000 *Observation epoch (barycentric Julian date) (TT1)
 12- 17  F6.3  mag    BTmag    ? Transit calibrated magnitude for B_T_     (TT2)
 19- 23  F5.3  mag    e_BTmag  ? Standard error on BTmag                   (TT3)
 25- 30  F6.2  ct     BTbg     Background counts per sample (1/600s)       (TT4)
 32- 37  F6.3  mag    VTmag    ? Transit calibrated magnitude for V_T_     (TT5)
 39- 43  F5.3  mag    e_VTmag  ? Standard error on VTmag                   (TT6)
 45- 50  F6.2  ct     VTbg     Background counts per sample (1/600s)       (TT7)
 52- 58  F7.1  arcsec z       *Position at which the star transitted       (TT8)
 60- 64  F5.1  deg    PAz     *Position angle of the slit normal           (TT9)
 66- 70  I5    mas    Du       ? Astrometric residual of the transit      (TT10)
 72- 75  I4    mas    e_Du     ? Expected standard error on Du            (TT11)
 77- 81  F5.1  ---    F2      *? Goodness of fit                          (TT12)
 83- 84  I2    ---    Tflg    *[0,31] Transit flags                       (TT13)
Note on JD-2440000: for reconstructed transits (stars having the 'b' 
    or 'c' status in the morePhoto column of the tyc_epo.dat file), 4
    decimals only are supplied; 5 decimals are supplied for the other
    transit times.

Note on z, PAz:
    location of the transit on the star mapper slits. The position angle
    of the slit normal is reckoned positive in the direction of motion of
    the star in the field of view.

Note on F2: values exceeding +2.5 to +3 indicate a bad fit to the data.

Note on Tflg: the transit flag is made of 5 fits:
    0 = magnitude not measured in B_T_
    1 = magnitude not measured in V_T_
    2 = transit rejected in astrometry and de-censoring
    3 = transit on the vertical(0)/inclined(1) slit
    4 = transit in following(0)/preceding(1) field
    Therefore, transits having the rightmost bit set (i.e. Tflg&1 != 0)
    have blank BTmag and e_BTmag columns; 
    similarly, transits having (Tflg&2 != 0) have blank VTmag and e_BTmag.

Hipparcos Header Records:
   Bytes Format Units   Label     Explanations
   1-  6  I6    ---     HIP       Hipparcos number
       8  A1    ---     m_HIP     Component flag, similar to column H48 (1)
  10- 15  F6.3  mag     V-I       Color index used for photometric reductions
  17- 19  I3    ---     Ntr       Number of total transits
  21- 23  I3    ---     Nh        Number of photometrically accepted transits
  29- 35  F7.4  mag     Hpmag     Median Hipparcos magnitude
  37- 42  F6.4  mag     e_Hpmag   Standard error on Hpmag
  44- 48  F5.2  mag     Hpmax     5th percentile (max) Hipparcos magnitude
  50- 54  F5.2  mag     Hpmin     95th percentile (min) Hipparcos magnitude
  57- 67  F11.7 d       Per       ? Variability period
  69- 77  F9.4  d       T0        ? Reference epoch (BJD-2440000)
      79  A1    ---     VType     Variability type, from Hipparcos H52 field (2)
      81  A1    ---     Flg1      Variability Annex flag (from H53)
      83  A1    ---     Flg2      [ABC] Existing Light curve (from H54)
Note (1): indicates the component to which the photometry refers:
     A to Z : the letter indicates the specified component measured
     * : combined Hpmag of a double system, corrected for attenuation
     - : combined Hpmag of a multiple system, not corrected for attenuation

Note (2): the type is defined as:
     C : no variability detected ("constant")
     D : duplicity-induced variability
     M : possibly micro-variable (amplitude < 0.03mag)
     P : periodic variable
     R : V-I colour index was revised due to variability analysis
     U : unsolved variable which does not fall in the other categories

Hipparcos Transit Records:
  Bytes Format Units  Label    Explanations
  1- 10  F10.5 d   JD-2440000  Observation epoch (barycentric Julian date) (HT1)
 12- 18  F7.4  mag    Hpmag    Transit calibrated Hp magnitude             (HT2)
 20- 24  F5.3  mag    e_Hpmag  Standard error on Hpmag                     (HT3)
 26- 28  I3    ---    Tflg    *[0,511] Quality flag                        (HT4)
Note on Tflg: the transit flag is made of 9 fits:
    0 = NDAC only
    1 = FAST only
    2 = (not used)
    3 = Very high background estimate (threshold 70 Hz)
    4 = Possible interfering object in either field of view
    5 = FAST quality flag set
    6 = Perturbed for other identified reasons
    7 = Observation during Sun-pointing mode
    8 = Significant difference between FAST and NDAC data
(End)                                     Francois Ochsenbein [CDS]  2002-May-09

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