Modeling the NIR-silhouette massive disk candidate in M 17

Abstract

Aims. The physical properties of the massive disk candidate in the star-forming region M 17 are analyzed. Methods. Making use of the rare configuration in which the gas and dust structure is seen in silhouette against the background radiation at λ = 2.2 µm, we determine the column density distribution from a high-resolution NAOS/CONICA image. The influence of scattered light on the mass determination is analyzed using 3D radiative transfer calculations. Further upper flux limits derived from observations with the Spitzer telescope at MIR wavelengths are used together with the NACO image to estimate the flux from the central object. For a range of stellar radii, stellar surface temperatures, and dust grain sizes, we apply three different models to account for the observed fluxes. The stability of the disk against self-gravitational forces is analyzed calculating the ratio of the gravitational acceleration by the central object and the disk, and the deviations from a Keplerian profile. Results. We find that the column density is consistent with a central source surrounded by a rotationally symmetric distribution of gas and dust. The extent of the symmetric disk part is about 3000 AU, with a warped point-symmetrical extension beyond that radius, and therefore larger than any circumstellar disk yet detected. The modeling yields a radial density powerlaw exponent of −1.1 indicating a flat radial density distribution, and a large e-folding scale height ratio H/R of about 0.5. The mass of the entire disk estimated from the column density is discussed depending on the assumed distance and the dust model and ranges between 0.02 and 5 M . We conclude that unless a star is located close to the disk in the foreground, scattered light will have little influence on the mass determination. We present a Spitzer image taken at λ = 7.8 µm with the disk seen in emission and identify polycyclic aromatic hydrocarbon (PAH) emission on the disk surface excited by the nearby massive stars as a possible source. Our 3D radiative transfer calculations for the scattered light image of the central source through an edge-on disk indicate that the elliptical shape seen in the NACO image does not require the assumption of a binary system and that it is consistent with a single object. We derive stellar main sequence masses of several M , 50 M , or 10 M , depending on our assumptions that the extinction of the stellar flux is dominated (i) by the outer disk, (ii) by an inner disk comparable to the disks around intermediate-mass stars, or (iii) by an inner disk with dominating hot dust emission. We find that even for a star-disk mass ratio of 1, only the outer parts of the circumstellar disk may be influenced by self-gravity effects due to the large e-folding scale height ratio.

HK-band imaging polarimetry and radiative transfer modeling of the massive young stellar object CRL 2136

“…Previous observations of massive stars reported disk mass ranges of < ∼ 0.1 M to ∼1 M ; e.g. Ori IRc2; Plambeck et al (1995); Blake et al (1996), Cep A; Patel et al (2005), and M 17; Steinacker et al (2006). These results might have implications for the evolutionary stage of the system, although some of these differences could be due to the use of different methods to estimate the disk parameters (e.g.…”

“…Preibisch et al 2003;Alvarez et al 2004;Weigelt et al 2006;Kraus et al 2006) and radio interferometry (e.g. Menten & van der Tak 2004;Patel et al 2005;Steinacker et al 2006). Furthermore, the circumstellar environment of young stellar objects (YSOs) is also known to be a molecule-forming region.…”

Benchmark problems for continuum radiative transfer

“…Recent studies of circumstellar discs are based on detailed comparisons of high-quality data sets, combining various kinds of observation (SED, multiple wavelength scattered light images, polarisation map, infrared or millimetre visibilities) to the predictions of RT codes (e.g. Wood et al 2002;Watson & Stapelfeldt 2004;Wolf et al 2003;D'Alessio et al 2006;Steinacker et al 2006;Doucet et al 2007;Fitzgerald et al 2007;Pontoppidan et al 2007;Pinte et al 2007Pinte et al , 2008aGlauser et al 2008;Tannirkulam et al 2008). Such studies will become more and more common with the advent of new instruments like VLT/SPHERE, Gemini/GPI, JWST, Herschel and ALMA, and validating the accuracy of RT codes is of particular importance.…”

A massive protostellar core with an infalling envelope

“…Recently, significant observational evidence has been found that the accretion scenario is also valid in the regime of high-mass star formation (Beltrán et al 2006;Beuther et al 2006;Beuther & Steinacker 2007;Puga et al 2006;Keto & Wood 2006;Steinacker et al 2006). This poses the question of whether the initial conditions under which massive stars form are also comparable to low-mass star birth, i.e.…”