The mid-infrared extinction law in the darkest cores of the Pipe Nebula

Author(s)

J. Ascenso, C. J. Lada, J. Alves, C. G. Román-Zúñiga, M. Lombardi

Abstract

Context. The properties of dust grains, in particular their size

distribution, are expected to differ from the interstellar medium to the

high-density regions within molecular clouds. Aims: We measure

the mid-infrared extinction law produced by dense material in molecular

cloud cores. Since the extinction at these wavelengths is caused by

dust, the extinction law in cores should depart from what is found in

low-density environments if the dust grains have different properties.

Methods: We used the unbiased LINES method to measure the slope

of the reddening vectors in color-color diagrams. We derived the

mid-infrared extinction law toward the dense cores B59 and FeSt 1-457 in

the Pipe Nebula over a range of visual extinction between 10 and 50 mag,

using a combination of Spitzer/IRAC and ESO NTT/VLT data.

Results: The mid-infrared extinction law in both cores departs

significantly from a power law between 3.6 and 8 μm, suggesting that

these cores contain dust with a considerable fraction of large dust

grains. We find no evidence of any dependence in the extinction law with

column density up to 50 mag of visual extinction in these cores, and no

evidence of any variation between our result and those for other clouds

at lower column densities reported elsewhere in the literature. This

suggests either that large grains are present even in low column density

regions or that the existing dust models need to be revised at

mid-infrared wavelengths. We find a small but significant difference in

the extinction law of the two cores, which we tentatively associate with

the onset of star formation in B59.

Based on observations made with ESO Telescopes at the La Silla Paranal

Observatory under program IDs 62.I-0866, 65.I-0083, 67.C-0514, and

069.C-0426.

Organisation(s)

Department of Astrophysics

External organisation(s)

Harvard-Smithsonian Center for Astrophysics, Universidad Nacional Autonoma de Mexico, European Southern Observatory (Germany), Università degli Studi di Milano-Bicocca

Journal

Astronomy & Astrophysics

Volume

549

No. of pages

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/201220658

Publication date

01-2013

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics, 103003 Astronomy

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/the-midinfrared-extinction-law-in-the-darkest-cores-of-the-pipe-nebula(8262fc01-0257-4158-a80f-3d30147657ef).html