The Earliest Phases of Star formation (EPoS)

Schmalzl, M.; Launhardt, R.; Stutz, Amelia M.; Linz, H.; Bourke, Tyler L.; Beuther, H.; Henning, Th.; Krause, O.; Nielbock, M.; Schmiedeke, A.

doi:10.1051/0004-6361/201322176

Cited by 15 publications

(56 citation statements)

References 73 publications

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“…The profile equations and iteration method are described in Sect. 3.3 (see also Nielbock et al 2012;Lippok et al 2013;Schmalzl et al 2014). The self-consistent radiative transfer, on the other hand, also uses pre-defined density profiles (e.g., from a physical model or here derived by the raytracing inversion technique), but involves a model of the ISRF Notes.…”

Section: General Strategymentioning

confidence: 99%

“…Consequently, the derivation of density profiles from dust emission data was often done with the simplifying assumption of isothermality (e.g., Ward-Thompson et al 1999;Kirk et al 2005;Launhardt 2005;Launhardt et al 2010) Final T maps (FITS format) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/cgi-bin/qcat?J/A+A/592/A61 or relied on weakly constrained model temperature profiles (e.g., Evans et al 2001;Zucconi et al 2001;Shirley et al 2005). Only more recently have some studies tried to constrain the temperature distribution of starless molecular cloud cores directly from observational data of the thermal dust continuum emission (e.g., Ward-Thompson et al 2002;Schnee & Goodman 2005;Stamatellos et al 2007;Stutz et al 2010;Nielbock et al 2012;Beuther et al 2012;Lippok et al 2013;Launhardt et al 2013;Pitann et al 2013;Schmalzl et al 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Using a robust temperature mapping algorithm that applies modified black-body fits to the dust emission spectra, we have already shown that these isolated cores are thermally dominated by heating from the interstellar radiation field (ISRF); they have warm (14−20 K) exteriors and cooler interiors (<11−14 K, Stutz et al 2010;Launhardt et al 2013). In addition, because of their isolation and simple structure, we were able to use a ray-tracing inversion technique to reconstruct the 3D temperature and density profiles of the globules (Nielbock et al 2012;Lippok et al 2013;Schmalzl et al 2014). We found that the temperature profiles of the starless cores drop to 7−13 K toward their centers, while their outer detectable rims are typically warmer by 5.5 ± 2.5 K.…”

Section: Introductionmentioning

confidence: 99%

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Earliest phases of star formation (EPoS)

Lippok

Launhardt

Henning

et al. 2016

A&A

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Context. Stars form by the gravitational collapse of cold and dense molecular cloud cores. Constraining the temperature and density structure of such cores is fundamental for understanding the initial conditions of star formation. We use Herschel observations of the thermal far-infrared (FIR) dust emission from nearby and isolated molecular cloud cores and combine them with ground-based submillimeter continuum data to derive observational constraints on their temperature and density structure. Aims. The aim of this study is to verify the validity of a ray-tracing inversion technique developed to derive the dust temperature and density structure of nearby and isolated starless cores directly from the dust emission maps and to test if the resulting temperature and density profiles are consistent with physical models. Methods. We have developed a ray-tracing inversion technique that can be used to derive the temperature and density structure of starless cores directly from the observed dust emission maps without the need to make assumptions about the physical conditions. Using this ray-tracing inversion technique, we derive the dust temperature and density structure of six isolated starless molecular cloud cores from dust emission maps in the wavelengths range 100 µm-1.2 mm. We then employ self-consistent radiative transfer modeling to the density profiles derived with the ray-tracing inversion method. In this model, the interstellar radiation field (ISRF) is the only heating source. The local strength of the ISRF as well as the total extinction provided by the outer envelope are treated as semi-free parameters which we scale within defined limits. The best-fit values of both parameters are derived by comparing the self-consistently calculated temperature profiles with those derived by the ray-tracing method. Results. We confirm earlier results and show that all starless cores are significantly colder inside than outside, with central core temperatures in the range 7.5−11.9 K and envelope temperatures that are 2.4−9.6 K higher. The core temperatures show a strong negative correlation with peak column density which suggests that the thermal structure of the cores is dominated by external heating from the ISRF and shielding by dusty envelopes. We find that temperature profiles derived with the ray-tracing inversion method can be well-reproduced with self-consistent radiative transfer models if the cores have geometry that is not too complex and good data coverage with spatially resolved maps at five or more wavelengths in range between 100 µm and 1.2 mm. We also confirm results from earlier studies that found that the usually adopted canonical value of the total strength of the ISRF in the solar neighbourhood is incompatible with the most widely used dust opacity models for dense cores. However, with the data available for this study, we cannot uniquely resolve the degeneracy between dust opacity law and strength of the ISRF.

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Section: General Strategymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Earliest phases of star formation (EPoS)

Lippok

Launhardt

Henning

et al. 2016

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“…(d) Slight differences to the values derived by Schmalzl et al (2013) and Nielbock et al (2012) can be accounted to the uncertainties discussed in Sect. 3.1.…”

Section: Chemical Modelingmentioning

confidence: 99%

“…We also developed a ray-tracing method to restore the full volume density and dust temperature structure of these cores. The results are presented in Nielbock et al (2012) for B 68, for CB 17 in Schmalzl et al (2013), and in this paper for the remaining five globules.…”

Section: Introductionmentioning

confidence: 99%

Gas-phase CO depletion and N₂H⁺abundances in starless cores

Lippok

Launhardt

Semenov

et al. 2013

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Context. In the dense and cold interiors of starless molecular cloud cores, a number of chemical processes allow for the formation of complex molecules and the deposition of ice layers on dust grains. Dust density and temperature maps of starless cores derived from Herschel continuum observations constrain the physical structure of the cloud cores better than ever before. We use these to model the temporal chemical evolution of starless cores. Aims. We derive molecular abundance profiles for a sample of starless cores. We then analyze these using chemical modeling based on dust temperature and hydrogen density maps derived from Herschel continuum observations. Methods. We observed the 12 CO (2-1), 13 CO (2-1), C 18 O (2-1) and N 2 H + (1-0) transitions towards seven isolated, nearby low-mass starless molecular cloud cores. Using far infrared (FIR) and submillimeter (submm) dust emission maps from the Herschel key program Earliest Phases of Star formation (EPoS) and by applying a ray-tracing technique, we derived the physical structure (density, dust temperature) of these cores. Based on these results we applied time-dependent chemical modeling of the molecular abundances. We modeled the molecular emission profiles with a line-radiative transfer code and compared them to the observed emission profiles. Results. CO is frozen onto the grains in the center of all cores in our sample. The level of CO depletion increases with hydrogen density and ranges from 46% up to more than 95% in the core centers of the three cores with the highest hydrogen density. The average hydrogen density at which 50% of CO is frozen onto the grains is 1.1 ± 0.4 × 10 5 cm −3 . At about this density, the cores typically have the highest relative abundance of N 2 H + . The cores with higher central densities show depletion of N 2 H + at levels of 13% to 55%. The chemical ages for the individual species are on average (2 ± 1) × 10 5 yr for 13 CO, (6 ± 3) × 10 4 yr for C 18 O, and (9 ± 2) × 10 4 yr for N 2 H + . Chemical modeling indirectly suggests that the gas and dust temperatures decouple in the envelopes and that the dust grains are not yet significantly coagulated. Conclusions. We observationally confirm chemical models of CO-freezeout and nitrogen chemistry. We find clear correlations between the hydrogen density and CO depletion and the emergence of N 2 H + . The chemical ages indicate a core lifetime of less than 1 Myr.

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Prestellar core modeling in the presence of a filament

Steinacker

Bacmann

Henning

et al. 2016

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Context. Lacking a paradigm for the onset of star formation, it is important to derive basic physical properties of prestellar cores and filaments like density and temperature structures. Aims. We aim to disentangle the spatial variation in density and temperature across the prestellar core L1689B, which is embedded in a filament. We want to determine the range of possible central densities and temperatures that are consistent with the continuum radiation data. Methods. We apply a new synergetic radiative transfer method: the derived 1D density profiles are both consistent with a cut through the Herschel PACS/SPIRE and JCMT SCUBA-2 continuum maps of L1689B and with a derived local interstellar radiation field. Choosing an appropriate cut along the filament major axis, we minimize the impact of the filament emission on the modeling. Results. For the bulk of the core (5000-20000 au) an isothermal sphere model with a temperature of around 10 K provides the best fits. We show that the power law index of the density profile, as well as the constant temperature can be derived directly from the radial surface brightness profiles. For the inner region (< 5000 au), we find a range of densities and temperatures that are consistent with the surface brightness profiles and the local interstellar radiation field. Based on our core models, we find that pixel-by-pixel single temperature spectral energy distribution fits are incapable of determining dense core properties. Conclusions. We conclude that, to derive physical core properties, it is important to avoid azimuthally-averaging core and filament. Correspondingly, derived core masses are too high since they include some mass of the filament, and might introduce errors when determining core mass functions. The forward radiative transfer methods also avoids the loss of information owing to smearing of all maps to the coarsest spatial resolution. We find the central core region to be colder and denser than estimated in recent inverse radiative transfer modeling, possibly indicating the start of star formation in L1689B.

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The Earliest Phases of Star formation (EPoS)

Cited by 15 publications

References 73 publications

Earliest phases of star formation (EPoS)

Earliest phases of star formation (EPoS)

Gas-phase CO depletion and N₂H⁺abundances in starless cores

Prestellar core modeling in the presence of a filament

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The Earliest Phases of Star formation (EPoS)

Cited by 15 publications

References 73 publications

Earliest phases of star formation (EPoS)

Earliest phases of star formation (EPoS)

Gas-phase CO depletion and N2H+abundances in starless cores

Prestellar core modeling in the presence of a filament

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Gas-phase CO depletion and N₂H⁺abundances in starless cores