ALMA and Herschel observations of the prototype dusty and polluted white dwarf G29-38

Abstract

ALMA Cycle 0 and Herschel¹ PACS observations are reported for the prototype, nearest, and brightest example of a dusty and polluted white dwarf, G29-38. These long-wavelength programmes attempted to detect an outlying, parent population of bodies at 1-100 au, from which originates the disrupted planetesimal debris that is observed within 0.01 au and which exhibits L_IR/L_* = 0.039. No associated emission sources were detected in any of the data down to L_IR/L_* ∼ 10^-4, generally ruling out cold dust masses greater than 10²⁴-10²⁵ g for reasonable grain sizes and properties in orbital regions corresponding to evolved versions of both asteroid and Kuiper belt analogues. Overall, these null detections are consistent with models of long-term collisional evolution in planetesimal discs, and the source regions for the disrupted parent bodies at stars like G29-38 may only be salient in exceptional circumstances, such as a recent instability. A larger sample of polluted white dwarfs, targeted with the full ALMA array, has the potential to unambiguously identify the parent source(s) of their planetary debris.