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B68 – The HERSCHEL view Dust temperatures and densities
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Transcript of B68 – The HERSCHEL view Dust temperatures and densities
B68 – The HERSCHEL viewDust temperatures and densities
Markus Nielbock
Ralf Launhardt, Jürgen Steinacker, Amy Stutz, Zoltan Balog, Henrik Beuther, Jeroen Bouwman, Thomas Henning, Pierre Hily-Blant, Jouni Kainulainen, Oliver Krause, Hendrik Linz, Nils Lippok, Sarah Ragan, Christophe Risacher, Anika Schmiedeke
EPoS – The Earliest Phases of Star formation• Herschel guaranteed time key programme (PI: O. Krause, MPIA)
• to investigate well studied cloud cores across the entire mass range
• to determine the dust temperature and density distribution of 12 near and isolatedlow-mass cores (Launhardt et al. 2012, submitted)
• used PACS and SPIRE bolometers at 100, 160, 250, 350, and 500 µm
• added ground-based (sub)mm and NIR extinction data
• this talk: results of the starless core B68 (Nielbock et al. 2012, A&A, 547, A11)
Barnard 68• starless core
• distance: 150 pc
• mass: 3 M
• size: 0.2 pc (40 000 AU)
• pre-stellar?
• possibly on the verge of collapseAlves et al. (2001)
Bonnor-Ebert fit
NIR extinction
Ray-Tracing Modelling Results• simple SED fitting affected by LoS temperature averaging
• employed 3D ray-tracing SED fitting (outside in)
• assumed functional relationship for mean radial density profile parameterisation
(Plummer-like, e.g. Whitworth & Ward-Thompson 2001)
•externally heated
Tdust = 8 – 17 (20) K nH = (3.4 0.04) x 105 cm-3
Ray-Tracing Modelling Results• radial distribution of temperature and densities
• flat central distributions
• steep slope in transition region
Þ nH ~ r-3.5
Þ filamentary origin? (Ostriker 1964)
• strong spatial variations r > 1’
Þ spheroid assumption invalid there• density drops to a flat distribution of
the ambient tenous medium
Anisotropic irradiation
• peculiar crescent-shaped morphology of FIR emission does not follow density
• connected to (very uncertain) temperature gradient to SE?
• can be explained with irradiation by anisotropic external irradiation field
• 3D rad. transfer modellingcan reproduce shapequalitatively
• B68 40 pc above gal. plane
• B2IV star Oph nearby
Summary and conclusions
• observed the starless core B68 with the Herschel Space Telescope
• resolved the distribution of the dust temperature and density
• negative temperature gradient from up to 20 K at the outskirts to 8 K in the core centre
• central density agrees with NIR extinction mapping results of Alves et al. (2001)
• steep slope of mean radial density profile nH ~ r-3.5 between r = 1’ and 3’
• contradicts SIS predictions, but agrees with filamentary origin or/and external pressure
• peculiar FIR morphology consistent with anisotropic radiation field
• ground-based CO observations are qualitatively consistent with core collision scenario
Next steps:
• full 3D radiative transfer modelling
• investigate origin of irradiation by studying scattered light
• exploit public Herschel data covering larger environment of B68