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

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 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

The Neighbourhood of B68 with Herschel

(Public) data of P. André’s Herschel KP “Gould’s Belt Survey”

PACS 70 µm PACS 100 µm PACS 160 µm

SPIRE 250 µm SPIRE 350 µm SPIRE 500 µm

~50’