# VISTA Filter Set

Z | Y | J | H | K_{s} | 1.18μm | |
---|---|---|---|---|---|---|

Central Wavelength (μm) | 0.877 |
1.020 |
1.252 |
1.645 |
2.147 |
1.191 |

Width (μm) | 0.097 | 0.093 | 0.172 |
0.291 |
0.309 |
0.011 |

Effective Wavelegth (μm) | 0.878 |
1.021 |
1.254 |
1.646 |
2.149 |
1.191 |

Vega to AB | 0.502 | 0.600 | 0.916 | 1.366 | 1.827 | 0.853 |

NB. the previous Vega to AB conversions (v1.3) for Z,Y,J,H,Ks were: 0.524, 0.618, 0.937, 1.384, 1.839

A sample detector QE curve is shown superposed in purple. The narrow grey curve in the J-band is the NB118 filter. Filter transmission tables and the QE curve are available in the ESO VISTA instrument pages.

Central wavelengths and widths defined using the half-max transmission points. Note that the central wavelength defined this way agrees with the weighted centre-of-gravity to within +/- 0.001. Effects of the detector QE curve were not included in these estimates.

The formula for Effective Wavelength is taken from equation 3 in Fukugita et al. (1996) and does incorporate the QE curve.

For the calculation of AB magnitude we follow Hewett et al. 2006, using the Bohlin & Gilliand 2004 spectrum of Vega (and assuming it is zero magnitude in all filters). For each filter we find the constant flux value (*f*_{nu}) which gives the same integrated flux in the filter bandpass as Vega (filter transmission*QE). The definition of the AB magnitude system then follows from AB_{nu}=-2.5 log *f*_{nu} - 48.60 (where *f*_{nu} is in units of ergs/s/cm^{2}/Hz).

Note that VISTA uses a Ks passband similar to 2MASS, unlike WFCAM which uses K. For comparison (and using the same code) the WFCAM values for ZYJHK are : 0.529, 0.633, 0.937, 1.376, 1.897 : all within a few % of the VISTA corrections except for K (as expected given the differences with K_{s}). These values are within a few parts per thousand of the independently computed values in Hewett et al. (2006).