A submillimetre search for cold extended debris disks in the $\mathsf{\beta}$ Pictoris moving group

Abstract

Context. Previous observations with the Infrared Astronomical Satellite and the Infrared Space Observatory, and ongoing observations with Spitzer and AKARI, have led to the discovery of over 200 debris disks, based on detected mid-and far infrared excess emission, indicating warm circumstellar dust. To constrain the properties of these systems, e.g., to more accurately determine the dust mass, temperature and radial extent, follow-up observations in the submillimetre wavelength region are needed. Aims. The β Pictoris moving group is a nearby stellar association of young (∼12 Myr) co-moving stars including the classical debris disk star β Pictoris. Due to their proximity and youth, they are excellent targets when searching for submillimetre emission from cold, extended, dust components produced by collisions in Kuiper-Belt-like disks. They also allow an age independent study of debris disk properties as a function of other stellar parameters. Methods. We observed 7 infrared-excess stars in the β Pictoris moving group with the LABOCA bolometer array, operating at a central wavelength of 870 μm at the 12-m submillimetre telescope APEX. The main emission at these wavelengths comes from large, cold dust grains, which constitute the main part of the total dust mass, and hence, for an optically thin case, make better estimates on the total dust mass than earlier infrared observations. Fitting the spectral energy distribution with combined optical and infrared photometry gives information on the temperature and radial extent of the disk. Results. From our sample, β Pic, HD 181327, and HD 172555 were detected with at least 3σ certainty, while all others are below 2σ and considered non-detections. The image of β Pic shows an offset flux density peak located near the south-west extension of the disk, similar to the one previously found by SCUBA at the JCMT. We present SED fits for detected sources and give an upper limit on the dust mass for undetected ones. Conclusions. We find a mean fractional dust luminosityf dust = 1.1 × 10 −3 at t ≈ 12 Myr, which together with recent data at 100 Myr suggests an f dust ∝ t −α decline of the emitting dust, with α > 0.8.

Kuiper belts around nearby stars

“…Resulting β parameters are all between 0.1 and 0.8, suggesting grains significantly larger than those in the ISM, in agreement with previous results for debris disks (e.g. Najita & Williams 2005;Nilsson et al 2009;Roccatagliata et al 2009). However, it should be noted that the presence of colder secondary dust components in addition to the fitted disk could be responsible for some abnormally low β values.…”

“…Due to the large age uncertainties (represented by horizontal error bars) we refrain from making a fit, and instead only display dashed lines showing the expected decline for three different values of α. We conclude that the temporal evolution of the fractional dust luminosity determined from our observations is in agreement with Nilsson et al (2009), and f dust could perhaps decline as fast as the t −2 found by Spangler et al (2001), although α < 0.8 can not be excluded due to large error bars and small stellar sample. This trend will be better constrained after the completion of the ongoing APEX/LABOCA Large Programme.…”

“…The fraction of detected debris disks in this first round of observations (45%) is considerably higher than that of previous submm surveys, e.g. that of nearby bright stars (9%, Holmes et al 2003), β Pictoris Moving Group (17%, Nilsson et al 2009;Liu et al 2004), FEPS nearby stars (3%, Carpenter et al 2005), nearby G stars (15%, Greaves et al 2005), and M dwarfs (6%, Lestrade et al 2006). This cannot only be explained by higher instrument sensitivity but is most likely due to a selection effect, having chosen an initial sample of stars with high far-IR excesses, and we are not expecting such a high detection rate from our ongoing Large Programme observations.…”

“…As all of the sources were relatively faint we used filtering and settings optimised for point source extraction, with full beam smoothing, resulting in clean maps with 27 effective resolution. Details of the data reduction procedure can be found in Kovács (2008) and are summarised in Nilsson et al (2009). The general reduction steps involve flux calibration (opacity correction and counts-to-Jy conversion), flagging of bad (unresponsive, very noisy, or those that were too fast or too slow) channels, correlated noise removal, despiking, data weighting, and map making.…”

An icy Kuiper belt around the young solar-type star HD 181327

“…6.1 for a discussion on the compatibility of the model to these observations). Therefore, the sub-mm regime is only represented by a measurement with the LABOCA bolometer array at the 12-m telescope APEX (Nilsson et al 2009, λ ∼ 870 μm), which thus represents a key piece of information. These archival data, together with our new observations, constitute the 49 measurements that are displayed in Fig.…”