Star and protoplanetary disk properties in Orion's suburbs

Abstract

Context. Knowledge of the evolution of circumstellar accretion disks is pivotal to our understanding of star and planet formation; and yet despite intensive theoretical and observational studies, the disk dissipation process is not well understood. Infrared observations of large numbers of young stars, as performed by the Spitzer Space Telescope, may advance our knowledge of this inherently complex process. While infrared data reveal the evolutionary status of the disk, they hold little information on the properties of the central star and the accretion characteristics. Aims. Existing 2MASS and Spitzer archive data of the Lynds 1630N and 1641 clouds in the Orion GMC provide disk properties of a large number of young stars. We wish to complement these data with optical data that provide the physical stellar parameters and accretion characteristics. Methods. We performed a large optical spectroscopic and photometric survey of the aforementioned clouds. Spectral types, as well as accretion and outflow characteristics, are derived from our VLT/VIMOS spectra. Optical SDSS and CAHA/LAICA imaging was combined with 2MASS, Spitzer IRAC, and MIPS imaging to obtain spectral energy distributions from 0.4 to 24 μm. Reddened model atmospheres were fitted to the optical/NIR photometric data, keeping T eff fixed at the spectroscopic value. Mass and age estimates of individual objects were made through placement in the HR diagram and comparison to several sets of pre-main sequence evolutionary tracks. Results. We provide a catalog of 132 confirmed young stars in L1630N and 267 such objects in L1641. We identify 28 transition disk systems, 20 of which were previously unknown, as well as 42 new transition disk candidates for which we have broad-band photometry but no optical spectroscopy. We give mass and age estimates for the individual stars, as well as equivalent widths of optical emission lines, the extinction, and measures of the evolutionary state of the circumstellar dusty disk. We estimate mass accretion ratesṀ acc from the equivalent widths of the Hα, Hβ, and He I 5876 Å emission lines, and find a dependence ofṀ acc ∝ M α * , with α ∼ 3.1 in the subsolar mass range that we probe. An investigation of a large literature sample of mass accretion rate estimates yields a similar slope of α ∼ 2.8 in the subsolar regime, but a shallower slope of α ∼ 2.0 if the whole mass range of 0.04 M ≤ M * ≤ 5 M is included. The fraction of stars with transition disks that show significant accretion activity is relatively low compared to stars with still optically thick disks (26 ± 11% vs. 57 ± 6%, respectively). However, those transition disks that do show significant accretion have the same median accretion rate as normal optically thick disks of 3−4 × 10 −9 M yr −1 . Analyzing the age distribution of various populations, we find that the ages of the CTTSs and the WTTSs with disks are statistically indistinguishable, the WTTSs without disks are significantly older than the CTTSs, and the ages of the transition disks and the WTTSs wi...

POISSON project

“…Connelley & Greene (2010) suggest that this particular feature may be indicative of FU Orionis like stars, and might have a disc wind origin. According to Fang et al (2009), the optical Lines tracing the jet activity have also been identified in our sample, but with a detection rate lower than that of the accretion lines. Namely the [O i] line at 0.63 μm has been identified in 43% of the optical spectra, the [S ii] doublet at 0.68 μm in 36%, the [Fe ii] 1.64 μm and H 2 2.12 μm lines in 19% and 32% of the NIR spectra, respectively.…”

“…The IRAC images were performed in High-Dynamic Range mode with integration times of 0.4 and 10.4 s (Spitzer program ID 43), and have been presented in previous papers (Megeath et al 2005;Fang et al 2009). The MIPS images (Spitzer program ID 47) have effective integration times of 80, 40, and 8 s at 24, 70, and 160 μm, respectively, and have been presented by Fang et al (2009).…”

“…IRAC and MIPS 24 μm photometry for our targets was reported by Megeath et al (2005) and Fang et al (2009), and kindly provided by these authors.…”

“…For comparison, additional extinction estimates retrieved from the literature (Strom et al 1989;Fang et al 2009;Connelley & Greene 2010) are also reported in Col. 8 of Table 5.…”

Fossil magnetic field of accretion disks of young stars

“…We carry out calculations for stellar masses M = 0.5 − 2 M ⊙ and use observational correlations of stellar luminosity and accretion rate with stellar mass. Dimensionless accretion rate,ṁ = m 2 (Fang et al 2009). Accretion disk mass is calculated as…”