J/A+A/578/A131 Gas and dust in the star-forming region rho OphA (Liseau+, 2015)
Gas and dust in the star-forming region ρ Oph A.
The dust opacity exponent β and the gas-to-dust mass ratio g2d.
Liseau R., Larsson B., Lunttila T., Olberg M., Rydbeck G., Bergman P.,
Justtanont K., Olofsson G., de Vries B.L.
<Astron. Astrophys. 578, A131 (2015)>
=2015A&A...578A.131L 2015A&A...578A.131L
ADC_Keywords: Molecular clouds ; Interstellar medium ; Nebulae ; YSOs ;
Abundances ; Radio lines ; Spectroscopy ; Models
Keywords: ISM: general - ISM: individual objects: rho Oph A -
dust, extinction - ISM: abundances - stars: formation
Abstract:
Using mapping observations of the very dense rho Oph A core, we
examined standard 1D and non-standard 3D methods to analyse data of
far-infrared and submillimeter continuum radiation. The resulting dust
surface density distribution can be compared to that of the gas. The
latter was derived from the analysis of accompanying molecular line
emission, observed with Herschel from space and with APEX from the
ground. As a gas tracer we used N2H+, which is believed to be much
less sensitive to freeze-out than CO and its isotopologues. Radiative
transfer modelling of the N2H+(J=3-2) and (J=6-5) lines with their
hyperfine structure explicitly taken into account provides solutions
for the spatial distribution of the column density N(H2), hence the
surface density distribution of the gas. The gas-to-dust mass ratio is
varying across the map, with very low values in the central regions
around the core SM1. The global average, =88, is not far from the
canonical value of 100, however. In rho Oph A, the exponent beta of
the power-law description for the dust opacity exhibits a clear
dependence on time, with high values of 2 for the envelope-dominated
emission in starless Class-1 sources to low values close to 0 for the
disk-dominated emission in ClassIII objects. beta assumes intermediate
values for evolutionary classes in between. Since beta is primarily
controlled by grain size, grain growth mostly occurs in circumstellar
disks. The spatial segregation of gas and dust, seen in projection
toward the core centre, probably implies that, like C18O, also
N2H+ is frozen onto the grains.
Description:
The mapping of the N2H+ (3-2) line used SHeFI-APEX-2 and the Fast
Fourier Transform Spectrometer with 73.6kHz wide channels, resulting
in a velocity resolution of 0.082km/s per channel and a spectral
coverage corresponding to 200km/s. The N2H+ (6-5) map was obtained
with HIFI on Herschel. The continuum observations were carried out
with two bolometer multi-pixel cameras at APEX, viz. the Large Apex
Bolometer Camera LABOCA at 0.87mm (40'x40') and the Submillimetre
Array SABOCA at 0.35 mm wavelength (8'x8'). All our data are
retrievable from the ESO Science Archive APEX
http://archive.eso.org/wdb/wdb/eso/apex/form and the Herschel Science
Archive http://www.cosmos.esa.int/web/herschel/science-archive Fully
reduced and modeled data are found in the directory fits.
Objects:
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RA (2000) DE Designation(s)
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16 26 27.90 -24 23 57.00 rho Oph A (in L1688) = rho Oph A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 145 32 List of fits files
fits/* . 32 Individual fits files
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See also:
J/A+A/510/A98 : 12C18O(3-2) map of rho Oph A (Liseau+, 2010)
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 image center (J2000)
10- 18 F9.5 deg DEdeg ? Declination of image center (J2000)
20- 24 F5.2 arcsec/pix Scale [1/16]? Scale of the image
26- 29 I4 --- Nx [26/1454] Number of pixels along X-axis
31- 34 I4 --- Ny [27/1003] Number of pixels along Y-axis
36- 39 I4 --- Nz [127/2445]? Number of slices (for data cubes)
42- 48 F7.3 GHz f.max ? Lower value of frequency interval
54- 60 F7.3 GHz f.min ? Upper value of frequency interval
66- 72 F7.3 kHz df [76/500]? Spectal resolution
75- 79 I5 Kibyte size [20/21063] Size of the fits file
81-103 A23 --- FileName Name of the FITS file in subdirectory fits
105-108 A4 --- --- [Fig.]
109-110 I2 --- Fig [2/18] Figure number in the paper
112-145 A34 --- Title Title of the file
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Acknowledgements:
Rene Liseau, rene.liseau(at)chalmers.se
(End) Patricia Vannier [CDS] 13-Apr-2015