The Dust Cloud around the White Dwarf G29-38

Abstract

We present new observations of the white dwarf G29-38 with the camera (4.5 and 8 mm), photometer (24 mm), and spectrograph (5.5-14 mm) of the Spitzer Space Telescope. This star has an exceptionally large infrared excess, amounting to 3% of the bolometric luminosity. The spectral energy distribution (SED) has a continuum peak around 4.5 mm and a 9-11 mm emission feature 1.25 times brighter than the continuum. A mixture of amorphous olivine and a small amount of forsterite in an emitting region 1-5 from the star can reproduce the shape of the 9-11 mm R , feature. The SED also appears to require amorphous carbon to explain the hot continuum. Our new measurements support the idea that a relatively recent disruption of a comet or asteroid created the cloud.

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

“…The collective properties of all published (N ∼ 250 as of this writing), metal-polluted white dwarfs support the accretion of planetary debris for the population at large Farihi et al 2010a;Zuckerman et al 2003), including even those stars that do not exhibit detectable infrared excesses (Rocchetto et al 2014). These findings imply that at least 30% (Koester (Farihi et al 2008;Reach et al 2005). Also listed are 3σ upper limits from MIPS 70 µm photometry (Jura et al 2009b), and the similar PACS and ALMA limits reported here.…”

“…All dusty white dwarfs observed with IRS on Spitzer exhibit strong silicate emission features consistent with olivines, (Jura et al 2009a;Reach et al 2009;Lisse et al 2008;Reach et al 2005), and which are also seen in the infrared spectra of evolved solids associated with planet formation (Lisse et al 2008).…”

Circumstellar debris and pollution at white dwarf stars

“…First are the strong silicate emission features (Reach et al, 2005a;Jura et al, 2007b). In fact, the emission observed at GD 362 is among the strongest silicate features seen towards any mature star (compare e.g.…”

“…Within the first two cycles of Spitzer observations, the only two known white dwarfs with circumstellar dust (G29-38 and GD 362 4 ) were observed with all three cryogenic instruments (Reach et al, 2005a;Jura et al, 2007b). The Infrared Array Camera (IRAC; Fazio et al 2004) obtained photometry at 3.6, 4.5, 5.7, and 7.9 µm, the Infrared Spectrograph (IRS; Houck et al 2004) acquired R ∼ 100 spectra between 5 and 15 µm, and the Multi-band Imaging Photometer for Spitzer (MIPS; Rieke et al 2004) measured fluxes at 24 µm for the two earliest examples shown in Figure 3, and later for a number of similar white dwarf targets prior to the loss of cryogen in 2009.…”

“…While models indicate dusty stars such as Vega harbor substantial planetary material consistent with orbital regions analogous to the Kuiper Belt, those same (blackbody) models would place 1000 K dust orbiting these two white dwarfs within 0.7 R (roughly 50 stellar radii). The next wave of disks discovered and characterized photometrically by Spitzer strongly suggested that a lack of cool material was a hallmark of Figure 3: The first two dusty and metal-enriched white dwarfs observed with all three cryogenic instruments aboard Spitzer (Reach et al, 2005a;Jura et al, 2007b). Colored error bars represent photometric data: GALEX far-and nearultraviolet (purple); optical UBV RI or ugriz (blue); near-infrared JHK (green); IRAC 3 − 8 µm (orange); N-band, IRS 16 µm, and MIPS 24 µm (red).…”