J/A+A/558/A58 NGC 1333-IRAS 4A C18O, NO and O2 spectra (Yildiz+, 2013)
Deep observations of O2 toward a low-mass protostar with Herschel-HIFI.
Yildiz U.A., Acharyya K., Goldsmith P.F., van Dishoeck E.F., Melnick G.,
Snell R., Liseau R., Chen J.-H., Pagani L., Bergin E., Caselli P.,
Herbst E., Kristensen L.E., Visser R., Lis D.C., Gerin M.
<Astron. Astrophys. 558, A58 (2013)>
=2013A&A...558A..58Y 2013A&A...558A..58Y
ADC_Keywords: YSOs ; Millimetric/submm sources ; Spectroscopy
Keywords: astrochemistry - stars: formation - ISM: abundances - ISM: molecules -
ISM: individual objects: NGC 1333 IRAS 4A
Abstract:
According to traditional gas-phase chemical models, O2 should be
abundant in molecular clouds, but until recently, attempts to detect
interstellar O2 line emission with ground- and space-based
observatories have failed.
Following the multi-line detections of O2 with low abundances in the
Orion and rho Oph A molecular clouds with Herschel, it is important to
investigate other environments, and we here quantify the O2
abundance near a solar-mass protostar.
Observations of molecular oxygen, O2, at 487GHz toward a deeply
embedded low-mass Class 0 protostar, NGC 1333-IRAS 4A, are presented,
using the Heterodyne Instrument for the Far Infrared (HIFI) on the
Herschel Space Observatory. Complementary data of the chemically
related NO and CO molecules are obtained as well. The high spectral
resolution data are analysed using radiative transfer models to infer
column densities and abundances, and are tested directly against full
gas-grain chemical models.
The deep HIFI spectrum fails to show O2 at the velocity of the dense
protostellar envelope, implying one of the lowest abundance upper
limits of O2/H2 at <6x10-3 (3 sigma). The O2/CO abundance
ratio is less than 0.005. However, a tentative (4.5 sigma) detection
of O2 is seen at the velocity of the surrounding NGC1333 molecular
cloud, shifted by 1km/s relative to the protostar. For the
protostellar envelope, pure gas-phase models and gas-grain chemical
models require a long pre-collapse phase (∼0.7-1x106-years), during
which atomic and molecular oxygen are frozen out onto dust grains and
fully converted to H2O, to avoid overproduction of O2 in the dense
envelope. The same model also reproduces the limits on the chemically
related NO molecule if hydrogenation of NO on the grains to more
complex molecules such as NH2OH, found in recent laboratory
experiments, is included. The tentative detection of O2 in the
surrounding cloud is consistent with a low-density PDR model with
small changes in reaction rates.
The low O2 abundance in the collapsing envelope around a low-mass
protostar suggests that the gas and ice entering protoplanetary disks
is very poor in O2.
Description:
Files contain the observations of O2, C18O 1-0, C18O 3-2,
C18O 5-4, and NO toward NGC 1333 IRAS 4A low mass protostar. C18O
1-0 and 3-2 observations conducted in mapping mode, therefore they
were convolved to 44-arcsec beam in order to compare with the
Herschel-HIFI observations of molecular oxygen.
Objects:
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RA (2000) DE Designation(s)
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03 29 10.5 +31 13 30.9 NGC 1333 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 152 5 List of FITS spectrum
fits/* . 5 Individual FITS spectra
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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- 24 I5 --- Nx [261/10764] Number of lines
26- 37 E12.6 Hz Freql Lower value of frequency interval
39- 49 E11.6 Hz Frequ Upper value of frequency interval
51- 56 I6 Hz dFreq Resolution on Frequency
58- 68 A11 --- Line Line observed
70- 76 F7.3 GHz Freq Rest frequency of line
78-119 A42 --- Title Title of the file
121-152 A32 --- FileName Name of FITS file in subdirectory fits
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Acknowledgements:
Umut Yildiz, yildiz(at)strw.leidenuniv.nl
(Current: Umut.Yildiz(at)jpl.nasa.gov)
(End) U. Yildiz [Leiden Obs., NASA/JPL-Caltech], P. Vannier [CDS] 07-Oct-2013