Debris Disks in the Upper Scorpius Ob Association

Abstract

We present MIPS 24 μm and 70 μm photometry for 205 members of the Upper Scorpius OB Association. These data are combined with published MIPS photometry for 15 additional association members to assess the frequency of circumstellar disks around 5 Myr old stars with spectral types between B0 and M5. Twelve stars have a detectable 70 μm excess, each of which also has a detectable 24 μm excess. A total of 54 stars are identified with a 24 μm excess more than 32% above the stellar photosphere. The MIPS observations reveal 19 excess sources-8 A/F/G stars and 11 K/M stars-that were not previously identified with an 8 μm or 16 μm excess. The lack of short-wavelength emission and the weak 24 μm excess suggests that these sources are debris systems or the remnants of optically thick primordial disks with inner holes. Despite the wide range of luminosities of the stars hosting apparent debris systems, the excess characteristics are consistent with all stars having dust at similar orbital radii after factoring in variations in the radiation blowout particle size with spectral type. The results for Upper Sco are compared to similar photometric surveys from the literature to re-evaluate the evolution of debris emission. After considering the completeness limits of published surveys and the effects of stellar evolution on the debris luminosity, we find that the magnitude of the 24 μm excess around F-type stars increases between ages of 5 and 17 Myr as found by previous studies, but at 2.6σ confidence. For B7-A9 and G0-K5 stars, any variations in the observed 24 μm excess emission over this age range are significant at less than 2σ confidence.

ASPITZERMIPS STUDY OF 2.5-2.0M☉STARS IN SCORPIUS-CENTAURUS

“…We expect that 2.5 M stars will appear as B9.5 through B9 members of US, UCL, and LCC and that 2.0 M stars will appear as A9 through A0 members of US and as A7 through A0 members of UCL and LCC (Table 4). For US, we infer a disk fraction of 6/16 (38 +13 −10 %) for 2.5 M stars and 7/20 (35 +12 −9 %) for 2.0 M stars from the Oudmaijer et al (1992) IRAS 25 μm survey and the Carpenter et al (2009) MIPS 24 μm survey. We note that two of the excess systems around A-type stars, discovered by Oudmaijer et al (1992), are "primordial" based on the presence of Hα emission: HIP 79476/HD 145718 and HIP 81624/HD 150193 .…”

“…Since the US disk fractions are similar to the UCL and LCC disk fractions (both including and excluding primordial systems), we do not believe that there is strong evidence for a change in the disk fractions between ages ∼11 Myr and ∼15-20 Myr for 2.0-2.5 M stars. The MIPS 24 μm observations in our survey can be combined with those from other surveys Carpenter et al 2009;Su et al 2006;Oudmaijer et al 1992) to determine whether ScoCen disks exhibit mass-dependent evolution. We find that the disk fractions for 2.0-2.5 M stars are somewhat smaller than those measured for 1.0-1.5 M stars (∼33%) and that the disk fraction for higher mass stars (>3 M ) is substantially smaller, 4/57 (7% +5 −2 %) with Be stars forming the majority of high-mass systems with 24 μm and/or 70 μm excess.…”

“…Their statistical analysis also indicated a peak in 24 μm excess emission at 10-15 Myr, followed by a decline up to 1 Gyr. More recently, Carpenter et al (2009) observed 62 B-and A-type members of the ∼11 Myr Upper Sco Subgroup. They found that an increase in 24 μm excess emission for stars with ages between 5 and 17 Myr was statistically insignificant (<2σ ).…”

Rocky Planet Formation: Quick and Neat

“…In a sample of 27 K-type pre-main sequence stars with masses of 0.8-1.3 M , most of the excess sources (7/9) have IR colors consistent with primordial disks (Carpenter et al 2006(Carpenter et al , 2009a. Although two additional stars have 24 µm excesses consistent with debris disks, both have cool dust (T d 200 K).…”

The Greater Taurus–Auriga Ecosystem. I. There is a Distributed Older Population

“…Finally, the disk should eventually be dispersed by photoevaporation or outflows, or incorporated into planetary companions. The dispersal timescale is observationally demonstrated to lengthen with decreasing stellar mass (e.g., Carpenter et al 2006Carpenter et al , 2009. There should also be a dependence on the initial disk mass (which stochastically results from the initial specific angular momentum of the envelope).…”