J/A+A/647/A109 NIR observations of LDN1512 (Saajasto+, 2021)
Multi-wavelength observations and modelling of a quiescent cloud LDN1512.
Saajasto M., Juvela M., Lefevre C., Pagani L., Ysard N.
<Astron. Astrophys. 647, A109 (2021)>
=2021A&A...647A.109S 2021A&A...647A.109S (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular clouds
Keywords: ISM: clouds - stars: formation - radiative transfer - scattering -
radiation mechanisms: thermal
Abstract:
Light scattering at near-infrared wavelengths has been used to study
the optical properties of the interstellar dust grains, but these
studies are limited by the assumptions on the strength of the
radiation field. On the other hand, thermal dust emission can be used
to constrain the properties of the radiation field, although this is
hampered by uncertainty about the dust emissivity.
Combining light scattering and emission studies allows us to probe the
properties of the dust grains in detail. We wish to study if current
dust models allow us to model a molecular cloud simultaneously in the
near infrared (NIR) and far infrared (FIR) wavelengths and compare the
results with observations. Our aim is to place constraints on the
properties of the dust grains and the strength of the radiation field.
We present computations of dust emission and scattered light of a
quiescent molecular cloud LDN1512. We use NIR observations covering
the J, H, and Ks bands, and FIR observations between 250 and 500 micron
from Herschel space telescope. We construct radiative transfer models
for LDN1512 that include an anisotropic radiation field and a
three-dimensional cloud model.
We are able to reproduce the observed FIR observations, with a
radiation field derived from the DIRBE observations, with all of the
tested dust models. However, with the same density distribution and
the assumed radiation field, the models fail to reproduce the observed
NIR scattering in all cases except for models that take into account
dust evolution via coagulation and mantle formation. The intensity
from the diffuse interstellar medium (ISM) like, dust models can be
increased to match the observed one by reducing the derived density,
increasing the intensity of the background sky and the strength of the
radiation field between factors from 2 to 3. We find that the column
densities derived from our radiative transfer modelling can differ by
a factor of up to two, compared to the column densities derived from
the observations with modified blackbody fits. The discrepancy in the
column densities is likely caused because of temperature difference
between a modified blackbody fit and the real spectra.The difference
between the fitted temperature and the true temperature could be as
high as ΔT=±1.5K.
We show that the observed dust emission can be reproduced with several
different assumptions about the properties of the dust grains.
However, in order to reproduce the observed scattered surface
brightness dust evolution must be taken into account.
Description:
This catalogue contains the near infrared observations of a cloud
LDN1512. The observations cover the the wide filters J (1.25 micron),
H (1.6 micron), and Ks (2.15 micron) and are taken with the WIRCAM
instrument on the CFHT. The observations were carried out using the
Sky-Target-Sky (STS) dithering mode, to subtract the atmospheric
IR-emission and to preserve any extended scattered light from the
source. The seeing conditions during the observations were good, with
typical values less than 1 arcsec. Data reduction was performed at the
TERAPIX center using a specific reduction method to recover the
extended emission.
Objects:
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RA (2000) DE Designation(s)
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05 04 09.7 +32 43 09 LDN1512 = LDN 1512
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 94 3 List of NIR fits images
fits/* . 3 Individual NIR fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 F3.1 arcsec/pix scale Scale of the image
24- 27 I4 --- Nx Number of pixels along X-axis
29- 32 I4 --- Ny Number of pixels along Y-axis
34- 39 I6 Kibyte size Size of FITS file
41- 53 A13 --- FileName Name of FITS file, in subdirectory fits
55- 94 A40 --- Title Title of the FITS file
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Acknowledgements:
Mika Saajasto, mika.saajasto(at)helsinki.fi
(End) M. Saajasto [Univ. of Helsinki, Finland], P. Vannier [CDS] 05-Feb-2021