Access to Astronomical Catalogues

J/PASP/120/1128     Calibrated griz magnitudes of Tycho star        (Ofek, 2008)
Calibrated griz magnitudes of Tycho stars: All-sky photometric calibration
using bright stars
     Ofek E.O.
    <Publ. Astron. Soc. Pac. 120, 1128 (2008)>
    =2008PASP..120.1128O
ADC_Keywords: Infrared sources; Photometry, infrared ; Photometry, SDSS


Abstract:
    Photometric calibration at an accuracy of ∼5% in an arbitrary
    celestial location is frequently needed. However, existing all-sky
    astronomical catalogue do not reach this accuracy, and time consuming
    photometric calibration procedures are required. I fitted the
    Hipparcos BT, and VT magnitudes, along with the 2MASS J, H, and K
    magnitudes of Tycho-2 catalog-stars with stellar spectral templates.
    From the best fit spectral template derived for each star, I
    calculated its synthetic SDSS griz magnitudes, and constructed an
    all-sky catalog of griz magnitudes of bright stars (V<12). Testing
    this method on SDSS photometric telescope observations, I find that
    the photometric accuracy, for a single star, is usually about 0.12,
    0.12, 0.10 and 0.08 mag (1sigma), for the g, r, i, and z-bands,
    respectively. However, by using ∼10 such stars, the typical errors per
    calibrated field (systematic + statistical) can be reduced to about
    0.04, 0.03, 0.02, and 0.02 mag, in the g, r, i, and z-bands,
    respectively. Therefore, in cases for which several calibration stars
    can be observed in the field of view of an instrument, it is possible
    to photometrically calibrate the image.

Description:
    The catalog was constructed from the stars with BT<13mag and
    VT<12mag in the Tycho-2 catalog (Hog et al. 2000, Cat. I/259),
    cross-correlated with the 2MASS catalog (Cutri et al. 2003, 
    Cat. II/246). The BTVTJHK magnitudes were fitted with the
    131 spectral templates of Pickes 1998 (Cat. J/PASP/110/863).

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
catalog.dat      175  1560980   Catalog


See also:
     I/259 : The Tycho-2 Catalogue (Hog+ 2000)
    II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
 J/PASP/110/863 : A Stellar Spectral Flux Library: 1150 - 25000 A (Pickles 1998)


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

   Bytes Format Units   Label     Explanations

   2- 12  F11.7 deg     RAdeg     Right Ascension J2000.0
  15- 25  F11.7 deg     DEdeg     Declination J2000.0
      29  I1    ---     ok        [0,1] Flag indicating a good standard (1)
  33- 37  F5.2  mag     BTmag     BT magnitude
  39- 42  F4.2  mag     e_BTmag   BT magnitude error
  44- 48  F5.2  mag     VTmag     VT magnitude
  50- 53  F4.2  mag     e_VTmag   VT magnitude error
  56- 60  F5.2  mag     Jmag      ?=- J magnitude
  61- 65  F5.2  mag     e_Jmag    ?=- J magnitude error (2)
  67- 71  F5.2  mag     Hmag      ?=- H magnitude
  72- 76  F5.2  mag     e_Hmag    ?=- H magnitude error (2)
  78- 82  F5.2  mag     Kmag      ?=- K magnitude
  83- 87  F5.2  mag     e_Kmag    ?=- K magnitude error (2)
  93-100  A8    ---     rmsTem    Best rms-fit spectral template (3)
 102-106  F5.2  mag     minRMS    ?=- the rms for the best rms-fit template
 108-112  F5.2  mag     gmag      ?=- rms-fit g-band magnitude
                                      (0.06 magnitude already added)
 114-118  F5.2  mag     rmag      ?=- rms-fit r-band magnitude
                                      (0.04 magnitude already added)
 120-124  F5.2  mag     imag      ?=- rms-fit i-band magnitude
                                      (0.03 magnitude already added)
 126-130  F5.2  mag     zmag      ?=- rms-fit z-band magnitude
                                      (0.03 magnitude already added)
 136-143  A8    ---     chiTem    Best χ^2^-fit spectral template (3)
 144-151  F8.2  ---     minChi    ?=- the χ2 for the best 
                                      χ2-fit template (dof=4)
 153-157  F5.2  mag     2gmag     ?=- χ2-fit g-band magnitude
                                      (0.07 magnitude already added)
 159-163  F5.2  mag     2rmag     ?=- χ2-fit r-band magnitude
                                      (0.04 magnitude already added)
 165-169  F5.2  mag     2imag     ?=- χ2-fit i-band magnitude
                                      (0.04 magnitude already added)
 171-175  F5.2  mag     2zmag     ?=- χ2-fit z-band magnitude
                                      (0.03 magnitude already added)

Note (1): Value 1 for a good standard, i.e.,
     J>6 & H>6 & K>6 & err(BT)<0.15 & err(VT)<0.15 & minRMS<0.15.
Note (2): 10.00 indicates no error value.

Note (3): Template names adopted from the stellar spectra catalog of
     Pickles (1998PASP..110..863P, Cat. J/PASP/110/863)


Acknowledgements:
    Eran O. Ofek, eran(at)astro.caltech.edu
(End)                                     Patricia Vannier [CDS]     19-Aug-2008