ISO observations of the radio-loud BALQSO 1556+3517

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To date, the quasar 1556+3517 is the only radio loud Broad Absorption Line QSO (BALQSO; Becker et al. 1997). This prompted narrow band filter imaging observations in the range 4-15 micron with the ISO satellite. The source is clearly detected in all filters and appears point-like and isolated at the resolution of ISO. The overall Spectral Energy Distribution (SED) in erg/s peaks at a rest wavelength > 6 micron and is reddened by 1.6 visual magnitudes. Correction for reddening brings 1556+3517 within 1.3 sigma from the log R = 1 dividing line between radio-loud and radio-quiet sources. The mid-IR luminosity integrated over the 1.8-6 micron rest wavelength range is 2 E+46 erg/s (Ho = 75 km/s/Mpc, qo = 0), which requires at least 4 solar masses of dust and 800 solar masses of associated gas. It is unlikely that such a large mass stems from the BAL wind itself.