2001A&A...366..636B


C.D.S. - SIMBAD4 rel 1.7 - 2020.10.24CEST17:12:04

2001A&A...366..636B - Astronomy and Astrophysics, volume 366, 636-650 (2001/2-1)

Quantification of molecular cloud structure using the Δ-variance.

BENSCH F., STUTZKI J. and OSSENKOPF V.

Abstract (from CDS):

We present a detailed study of the Δ-variance as a method to quantify molecular cloud structure. The Δ-variance was introduced by Stutzki et al. (1998A&A...336..697S) to analyze the drift behaviour of scalar functions and is used to characterize the spatial structure of observed molecular cloud images. For fractional Brownian motion structures (fBm-fractals), characterized by a power law power spectrum and random phases, the Δ-variance allows to determine the power spectral index β. We present algorithms to determine the Δ-variance for discretely sampled maps and study the influence of white noise, beam smoothing and the finite spatial extent of the maps. We find that for images with β>3, edge effects can bias the structure parameters when determined by means of a Fourier transform analysis. In contrast, the Δ-variance provides a reliable estimate for the spectral index β, if determined in the spatial domain. The effects of noise and beam smoothing are analytically represented in a leading order approximation. This allows to use the Δ-variance of observed maps even at scales where the influence of both effects becomes significant, allowing to derive the spectral index β over a wider range and thus more reliably than possible otherwise. The Δ-variance is applied to velocity integrated spectral line maps of several clouds observed in rotational transitions of 12CO and 13CO. We find that the spatial structure of the emission is well characterized by a power law power spectrum in all cases. For linear scales larger than ∼0.5pc the spectral index is remarkably uniform for the different clouds and transitions observed (2.5≤β≤2.8). Significantly larger values (βγ3) are found for observations made with higher linear resolution toward the molecular cloud Mcld 123.5+24.9 in the Polaris Flare, indicating a smoother spatial structure of the emission at small scales (<0.5pc).

Abstract Copyright:

Journal keyword(s): interstellar medium (ISM): clouds - ISM: structure - ISM: individual objects: polaris flare - turbulence - methods: data analysis

Simbad objects: 11

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Number of rows : 11

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME Polaris Cirrus Cloud MoC 01 52 29.6 +87 40 31           ~ 71 0
2 NGC 1333 OpC 03 29 11 +31 18.6           ~ 1231 1
3 NAME Perseus Cloud SFR 03 35.0 +31 13           ~ 1086 0
4 M 42 HII 05 35 17.3 -05 23 28           ~ 3751 0
5 NAME Ori A MoC 05 38 -07.1           ~ 2697 0
6 NAME Flame Nebula HII 05 41 42.7 -01 54 44           ~ 692 1
7 NAME Ori B MoC 05 41 43.0 -01 54 44           ~ 1181 0
8 NAME Mon R2 HII 06 07 46.6 -06 22 59           ~ 655 2
9 NAME Mon I MoC 06 35 +10.1           ~ 218 0
10 NGC 2264 OpC 06 40 58 +09 53.7     3.9     ~ 1602 1
11 NAME Polaris Flare MoC 11 00 14.8 +86 10 52           ~ 162 1

    Equat.    Gal    SGal    Ecl

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2020.10.24-17:12:04

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