J/A+A/606/A121 NGC1333 IRAS 4A ALMA and PdBI maps (Lopez-Sepulcre+, 2017)
Complex organics in IRAS 4A revisited with ALMA:
Striking contrast between two neighbouring protostellar cores.
Lopez-Sepulcre A., Sakai N., Neri R., Imai M., Oya Y., Ceccarelli C.,
Higuchi A., Aikawa Y., Bottinelli S., Caux E., Hirota T., Kahane C.,
Lefloch B., Vastel C., Watanabe Y., Yamamoto S.
<Astron. Astrophys. 606, A121 (2017)>
=2017A&A...606A.121L 2017A&A...606A.121L (SIMBAD/NED BibCode)
ADC_Keywords: Infrared sources ; Radio lines
Keywords: astrochemistry - stars: formation - ISM: abundances -
ISM: individual objects: NGC1333 IRAS 4A
Abstract:
Hot corinos are extremely rich in complex organic molecules (COMs).
Accurate abundance measurements of COMs in such objects are crucial to
constrain astrochemical models. In the particular case of close binary
systems this can only be achieved through high angular resolution
imaging.
We aim to perform an interferometric study of multiple COMs in NGC1333
IRAS 4A, which is a protostellar binary hosting hot corino activity,
at an angular resolution that is sufficient to distinguish easily the
emission from the two cores separated by 1.8".
We used the Atacama Large (sub-)Millimeter Array (ALMA) in its 1.2mm
band and the IRAM Plateau de Bure Interferometer (PdBI) at 2.7mm to
image, with an angular resolution of 0.5" (120au) and 1" (235au),
respectively, the emission from 11 different organic molecules in
IRAS 4A. This allowed us to clearly disentangle A1 and A2, the two
protostellar cores. For the first time, we were able to derive the
column densities and fractional abundances simultaneously for the two
objects, allowing us to analyse the chemical differences between them.
Molecular emission from organic molecules is concentrated exclusively
in A2, while A1 appears completely devoid of COMs or even simpler
organic molecules, such as HNCO, even though A1 is the strongest
continuum emitter. The protostellar core A2 displays typical hot
corino abundances and its deconvolved size is 70au. In contrast, the
upper limits we placed on COM abundances for A1 are extremely low,
lying about one order of magnitude below prestellar values. The
difference in the amount of COMs present in A1 and A2 ranges between
one and two orders of magnitude. Our results suggest that the optical
depth of dust emission at these wavelengths is unlikely to be
sufficiently high to completely hide a hot corino in A1 similar in size
to that in A2. Thus, the significant contrast in molecular richness
found between the two sources is most probably real. We estimate that
the size of a hypothetical hot corino in A1 should be less than 12 au.
Our results favour a scenario in which the protostar in A2 is either
more massive and/or subject to a higher accretion rate than A1, as a
result of inhomogeneous fragmentation of the parental molecular clump.
This naturally explains the smaller current envelope mass in A2 with
respect to A1 along with its molecular richness. The extremely low
abundances of organic molecules in A1 with respect to those in A2
demonstrate that the dense inner regions of a young protostellar core
lacking hot corino activity may be poorer in COMs than the outer
protostellar envelope.
Description:
The Atacama Large (sub-)Millimeter Array (ALMA) was used on 14 June
2014, in its Cycle 2 operations, to observe IRAS 4A in Band 6
(∼250GHz). A total of 35 antennas of the 12m array were used with a
minimum and maximum baseline length of 18m and 784m, respectively.
The phase centre of the observation was
RA=03:29:10.51, DE=+31:13:31.3 (J2000) and the total integration
time onsource was 26-min.
The PdBI was used on 29 January 2005 in its A configuration to observe
IRAS 4A at 2.7mm. The baselines ranged from 32 to 400m.
The phase centre of the observations was
RA=03:29:10.30, DE=+31:13:31.0 (J2000).
Objects:
------------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------------
03 29 10.49 +31 13 30.8 IRAS 4A = [JCC87] IRAS 4A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 116 18 List of fits maps
fits/* . 18 Individual fits maps
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See also:
J/A+A/558/A58 : NGC 1333-IRAS 4A C18O, NO and O2 spectra (Yildiz+, 2013)
J/A+A/568/A125 : NGC 1333 IRAS 4A H2O observations (Santangelo+, 2014)
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- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 31 I2 mJy/beam.km/s RMS ? Root mean square (RMS) noise level
33- 36 F4.2 arcsec Beam1 ? Beam size
37 A1 --- --- [x]
38- 41 F4.2 arcsec Beam2 ? Beam size
43- 46 I4 deg PA []? Position angle
48- 51 I4 Kibyte size Size of FITS file
53- 64 A12 --- FileName Name of FITS file, in subdirectory fits
66-116 A51 --- Title Title of the FITS file
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Acknowledgements:
Ana Lopez-Sepulcre, lopez(at)iram.fr
(End) Patricia Vannier [CDS] 13-Jul-2017