A dusty component to the gaseous debris disk around the white dwarf SDSS J1228+1040

We present Infrared Spectrometer And Array Camera (ISAAC) spectroscopy and ISAAC, UKIDSS, and Spitzer Space Telescope broadband photometry of SDSS J1228+1040 - a white dwarf for which evidence of a gaseous metal-rich circumstellar disk has previously been found from optical emission lines. The data show a clear excess in the near- and mid-infrared (IR), providing compelling evidence for the presence of dust in addition to the previously identified gaseous debris disk around the star. The IR excess can be modeled in terms of an optically thick but geometrically thin disk. We find that the inner disk temperatures must be relatively high (∼1700 K) in order to fit the spectral energy distribution in the near-IR. These data provide the first evidence for the coexistence of both gas and dust in a disk around a white dwarf, and show that their presence is possible even around moderately hot (∼22,000 K) stars.