J/A+A/632/A19 IRAM intensity maps of 3 low-mass protostars (Taquet+ 2019)
Interferometric observations of warm deuterated methanol in the inner regions
of low-mass protostars.
Taquet V., Bianchi E., Codella C., Persson M.V., Ceccarelli C., Cabrit S.,
Jorgensen J.K., Kahane C., Lopez-Sepulcre A., Neri R.
<Astron. Astrophys. 632, A19 (2019)>
=2019A&A...632A..19T 2019A&A...632A..19T (SIMBAD/NED BibCode)
ADC_Keywords: Protostars ; Abundances ; Interferometry ; Radio lines ;
Infrared sources
Keywords: astrochemistry - molecular processes - ISM: abundances -
ISM: molecules - submillimeter: ISM - stars: formation
Abstract:
Methanol is a key species in astrochemistry since it is the most
abundant organic molecule in the interstellar medium and is thought to
be the mother molecule of many complex organic species. Estimating the
deuteration of methanol around young protostars is of crucial
importance because it highly depends on its formation mechanisms and
the physical conditions during its moment of formation. We analyse
several dozens of transitions from deuterated methanol isotopologues
coming from various existing observational datasets obtained with the
IRAM-PdBI and ALMA sub-mm interferometers to estimate the methanol
deuteration surrounding three low-mass protostars on Solar System
scales. A population diagram analysis allows us to derive a
[CH2DOH]/[CH3OH] abundance ratio of 3-6% and a [CH3OD]/[CH3OH]
ratio of 0.4-1.6% in the warm inner (<100-200AU) protostellar
regions. These values are typically ten times lower than those derived
with previous single-dish observations towards these sources but they
are one to two orders of magnitude higher than the methanol
deuteration measured in massive hot cores. Dust temperature maps
obtained from Herschel and Planck observations show that massive hot
cores are located in warmer molecular clouds than low-mass sources,
with temperature differences of about 10K. The comparison of our
measured values with the predictions of the gas-grain astrochemical
model GRAINOBLE shows that such a temperature difference is sufficient
to explain the different deuteration observed in low- to high-mass
sources. This suggests that the physical conditions of the molecular
cloud at the origin of the protostars mostly govern the present
observed deuteration of methanol and, therefore, of more complex
organic molecules. Finally, the methanol deuteration measured towards
young solar-type protostars on Solar System scales seems to be higher
by a factor of about 5 than the upper limit in methanol deuteration
estimated in comet Hale-Bopp. If this result is confirmed by
subsequent observations of other comets, this would imply that an
important reprocessing of the organic material likely occurred in the
solar nebula during the formation of the Solar System.
Description:
The two low-mass Class 0 protostars IRAS 2A and IRAS 4A located in the
NGC 1333 cloud at 299±14pc (Zucker et al. 2018ApJ...869...83Z 2018ApJ...869...83Z) were
observed with the IRAM PdBI at 143, 165, and 225 GHz. Observations at
143 and 165GHz were carried out on 2010 July 20, July 21, August 1,
August 3, November 24, and 2011 March 10, in the C and D
configurations of the array. Observations at 225GHz were performed on
2011 November 27 and 28, on 2012 March 12, 15, 21, and 27, and on 2012
April, 2 in the B and C configurations of the array.
Integrated intensity maps of the CH2DOH, CH3OD, CHD2OH, and
CH2DCN transitions targeted towards NGC1333-IRAS2A, -IRAS4A, and
HH212 used to determine the deuterium fractionation of methanol and
methyl cyanide.
Objects:
--------------------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------------------
03 28 55.55 +31 14 36.7 NGC1333-IRAS2A = [JCC87] IRAS 2A
03 29 10.49 +31 13 30.8 NGC1333-IRAS4A = [JCC87] IRAS 4A
05 43 51.41 -01 02 53.2 HH 212 = [CAZ2013] HH 212 MMS
--------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 138 104 List of fits maps
fits/* . 104 Individual fits maps
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
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- 33 I4 Kibyte size Size of FITS file
35- 75 A41 --- FileName Name of FITS file, in subdirectory fits
77-138 A62 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Vianney Taquet, vianney.taquet(at)gmail.com
(End) Patricia Vannier [CDS] 18-Oct-2019