B68 – The HERSCHEL viewDust temperatures and densities

Markus Nielbock (MPIA)(Herschel PACS ICC)

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, in prep.; see also poster A05)

• 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, in press; see poster A07)

Barnard 68

B68

B71

B69B70

B73

B74

B72

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

Continuum data

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 (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

Core collision scenario

Burkert & Alves (2009)

B68

B71

B69

Alves et al. (2001)

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

• exploit public Herschel data covering larger environment of B68

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