Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars

By F. V. D. van der Tak, E. V. van Dishoeck, N. Evans II, G. Blake. 2000

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The physical structure of the envelopes around a sample of 14 massive young stars is investigated using maps and spectra in submillimeter continuum and lines of C17O, CS, C34S, and H2CO. Nine of the sources are highly embedded luminous (103-105 L☉) young stellar objects that are bright near-infrared sources but weak in radio continuum; the other objects are similar but not bright in the near-infrared and contain "hot-core"-type objects and/or ultracompact H II regions. The data are used to constrain the temperature and density structure of the circumstellar envelopes on 102-105 AU scales, to investigate the relation between the different objects, and to search for evolutionary effects. The total column densities and the temperature profiles are obtained by fitting self-consistent dust models to submillimeter photometry. The calculated temperatures range from 300 to 1000 K at ~102 AU and from 10 to 30 K at ~105 AU from the star. Visual extinctions are a few hundred to a few thousand magnitudes, assuming a grain opacity at 1300 μm of ≈1 cm-2 g-1 of dust, as derived earlier for one of our sources. The mid-infrared data are consistent with a 30% decrease of the opacity at higher temperatures, caused by the evaporation of the ice mantles. The CS, C34S, and H2CO data as well as the submillimeter dust emission maps indicate density gradients n ∝ r-α. Assuming a constant CS abundance throughout the envelope, values of α = 1.0-1.5 are found, which is significantly flatter than the α = 2.0 ± 0.3 generally found for low-mass objects. This flattening may indicate that in massive young stellar objects, nonthermal pressure is more important for the support against gravitational collapse, while thermal pressure dominates for low-mass sources. We find α = 2 for two hot-core-type sources but regard this as an upper limit since, in these objects, the CS abundance may be enhanced in the warm gas close to the star. The assumption of spherical symmetry is tested by modeling infrared absorption line data of 13CO, CS emission-line profiles and near-infrared continuum. There is a distinct, but small deviation from spherical symmetry: the data are consistent with a decrease of the optical depth by a factor of ≈3 in the central ≲10''. The homogeneity of the envelopes is verified by the good agreement of the total masses in the power-law models with the virial masses. Modeling of C17O emission shows that ≈40%-90% of the CO is frozen out onto the dust. The CO abundances show a clear correlation with temperature, as expected if the abundance is controlled by freeze-out and thermal desorption. The CS abundance is 3 × 10-9 on average, ranging from (4-8) × 10-10 in the cold source GL 7009S to (1-2) × 10-8 in the two hot-core-type sources. Dense outflowing gas is seen in the CS and H2CO line wings; the predominance of blueshifted emission suggests the presence of dense, optically thick material within 10'' of the center. Interferometric continuum observations at 1300-3500 μm show compact emission, probably from a 0.″3 diameter, optically thick dust component, such as a dense shell or a disk. The emission is a factor of 10-100 stronger than expected for the envelopes seen in the single-dish data, so that this component may be opaque enough to explain the asymmetric CS and H2CO line profiles. The evolution of the sources is traced by the overall temperature (measured by the far-infrared color), which increases systematically with the decreasing ratio of envelope mass to stellar mass. The observed anticorrelation of near-infrared and radio continuum emission suggests that the erosion of the envelope proceeds from the inside out. Conventional tracers of the evolution of low-mass objects do not change much over this narrow age range.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/30c8e1c7abe1b485d92c6a4c1f5ff58ba852eb50

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Citations in the corpus

The Physical Conditions for Massive Star Formation: Dust Continuum Maps and Modeling (2002, methodology): “Fitting the beam profiles with a Gaussian, we find that the FWHM is at least 1400, which is significantly different from the beam size reported in previous studies using SHARC at 350 lm (1000, van der Tak et al. 2000; 1100, Hunter et al. 2000).”
The Formation of Massive Stars from Turbulent Cores (2002, background): “According to van der Tak et al. (2000), the clumps in which high-mass cores are embedded have values of kρ ranging from 1 to 2, centered around 1.5.1 Beuther et al. (2002) find kρ ≃ 1.6± 0.5 for their sample of massive star-forming regions, while Mueller et al. (2002b) find kρ ≃ 1.8± 0.4 for a…”
A CS J = 5 → 4 Mapping Survey Toward High-Mass Star-forming Cores Associated with Water Masers (2003, methodology): “Previous studies (e.g., van der Tak et al. 2000, Hatchell et al. 2000, Beuther et al. 2002) and our modeling of the dust continuum emission (Mueller et al. 2002b) indicate that the distribution of density is well fitted by a power law, n(r) ∝ r−p.”
Physical structure and CO abundance of low-mass protostellar envelopes (2002, background): “Van der Tak et al. (2000b) likewise found a trend of increasing CO abundance with massweighted temperature for a sample of high-mass YSOs and suggested that this trend was due to freeze-out of CO in the cold objects.”
Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A Grid of 200,000 YSO Model SEDs (2006, background): “…(though see Allen et al. (2003) for a discussion of magnetic braking), and observations of radial intensity profiles are consistent with free-fall collapse (Chandler & Richer 2000; van der Tak et al. 2000; Beuther et al. 2002; Mueller et al. 2002; Young et al. 2003; Hatchell & van der Tak 2003).”
Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results (2010, background): “2011 PASP, 123:138–170 such as CO (Jørgensen et al. 2002), CH3OH (e.g., van der Tak et al. 2000a; Maret et al. 2005; Kristensen et al. 2010a), and H2CO (e.g., van Dishoeck et al. 1995; Ceccarelli et al. 2000b; Schöier et al. 2002; Maret et al. 2005; Jørgensen et al. 2005b) and confirmed by…”
Observations of the Icy Universe (2015, background): “Models show that envelope heating and dispersal occur at the same time (van der Tak et al., 2000).”
Molecular inventories and chemical evolution of low-mass protostellar envelopes (2003, methodology): “Our CS abundances are also similar to those inferred for a sample of high-mass protostars by van der Tak et al. (2000) using a similar analysis.”
Testing grain-surface chemistry in massive hot-core regions (2007, methodology): “The CH3OH rotation diagram for some sources like W 33A appears to consist of two temperature components as seen previously by van der Tak et al. (2000) (Fig.”
FRAGMENTATION AT THE EARLIEST PHASE OF MASSIVE STAR FORMATION (2009, background): “The density profiles in both P1 and P2 cores are consistent with a power-law relation r−b with b between 1.5 and 2, similar to those found in hot molecular cores (van der Tak et al. 2000).”
A computer program for fast non-LTE analysis of interstellar line spectra With diagnostic plots to interpret observed line intensity ratios (2007, methodology): “See for example Van der Tak et al. (2000b), Schöier et al. (2002), and Leurini et al. (2004) for details of such calculations.”
HERSCHEL SURVEY OF GALACTIC OH+, H2O+, AND H3O+: PROBING THE MOLECULAR HYDROGEN FRACTION AND COSMIC-RAY IONIZATION RATE (2014, background): “90−00.26) has a systemic velocity of about 37 km s−1 as measured from various emission lines (e.g. van der Tak et al. 2000; Wienen et al. 2012; San José-Garćıa et al. 2013).”
ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks (2004, background): “…are well correlated with increased gas/solid ratios derived from ISO (van Dishoeck & Helmich 1996, Boonman & van Dishoeck 2003, see §9.2) and submillimeter data (van der Tak et al. 2000a) as well as increased dust color temperatures derived from the 45/100 µm ISO flux ratios (Boogert et al. 2000a).”
A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE (2013, methodology): “Out of the sources observed by both Pulliam et al. (2012) and van der Tak et al. (2000), the only source present in both datasets is W3 IRS5.”
Tracing the Mass during Low-Mass Star Formation. II. Modeling the Submillimeter Emission from Preprotostellar Cores (2000, methodology): “OH5 opacities have been successful at reproducing the SED of both high mass (van der Tak et al. 2000) and low mass star forming cores (Paper II).”
Cosmic-ray ionization of molecular clouds (2009, unknown): “…× 10−17 c W3 IRS5 2.3 × 1023 b 6.4 × 10−17 c S 140 1.4 × 1023 b 8.5 × 10−17 c DR21(OH) 1.1 × 1023 e 3.1 × 10−18 e a From de Boisanger et al. (1996). b CO column density and CO/H2 ratio from van der Tak et al. (2000). c CR rate from van der Tak & van Dishoeck (2000). d From Doty et al. (2002). e…”
Chemistry as a probe of the structures and evolution of massive star-forming regions (2002, methodology): “This inner radius was chosen not only for consistency with the observations of van der Tak et al. (2000), but also as extrapolation of a density power law further into the interior of the envelope leads to column densities inconsistent with observations (see Sect.”
Does IRAS 16293–2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment (2002, methodology): “Van der Tak et al. (2000b) used a similar approach for the case of massive protostars.”
THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS (2011, background): “There is thus no evidence that variations in pure CO2 fractions can be explained by variable envelope sizes (toward high-mass protostars, envelope temperatures and sizes anti-correlate, see van der Tak et al. 2000).”