J/A+A/631/A69 Bright C2H emission in Lupus disks (Miotello+ 2019)
Bright C2H emission in protoplanetary disks in Lupus:
high volatile C/O>1 ratios.
Miotello A., Facchini S., van Dishoeck E.F., Cazzoletti P., Testi L.,
Williams J.P., Ansdell M., van Terwisga S., van der Marel N
<Astron. Astrophys. 631, A69 (2019)>
=2019A&A...631A..69M 2019A&A...631A..69M (SIMBAD/NED BibCode)
ADC_Keywords: Millimetric/submm sources
Keywords: protoplanetary discs - astrochemistry - methods: observational -
submillimeter: planetary systems - ISM: molecules - radiative transfer
Abstract:
Recent ALMA surveys in different star-forming regions have shown that
CO emission in protoplanetary disks is much fainter than expected.
Accordingly, CO-based gas masses and gas/dust ratios are orders of
magnitude lower than previously thought. This may be explained either
as fast gas dispersal, or as chemical evolution and locking up of
volatiles in larger bodies leading to the low observed CO fluxes. The
latter processes lead to enhanced C/O ratios in the gas, which may be
reflected in enhanced abundances of carbon-bearing molecules like
C2H. The goal of this work is to employ C2H observations to
understand whether low CO fluxes are caused by volatile depletion, or
by fast gas dissipation. We present ALMA Cycle 4 C2H (N=3-2,
J=7/2-5/2, F=4-3 and F=3-2) observations of a subsample of nine
sources in the Lupus star-forming region. The integrated C2H emission
is determined and compared to previous CO isotopologue observations
and physical-chemical model predictions. Seven out of nine disks are
detected in C2H, whose line emission is almost as bright as ^{13}CO.
All detections are significantly brighter than the typical sensitivity
of the observations, hinting at a bimodal distribution of the C2H
line intensities. This conclusion is strengthened when our
observations are compared with additional C2H observations of other
disks. When compared with physical-chemical models run with DALI, the
observed C2H fluxes can be reproduced only if some level of volatile
carbon and oxygen depletion is allowed and [C]/[O]>1 in the gas.
Models with reduced gas/dust ratios near unity fail instead to
reproduce the observed C2H line luminosity. A steeper than linear
correlation between C2H and CN emission line is found for the Lupus
disks. This is linked to the fact that C2H emission lines are
affected more strongly by [C]/[O] variations than CN lines. Ring-like
structures are detected both in C2H and in continuum emission but, as
for CN, they do not seem to be connected. Sz 71 shows ring shaped
emission in both C2H and CN with the location of the peak intensity
coinciding, within our 30 au resolution. Our new ALMA C2H
observations favour volatile carbon and oxygen depletion rather than
fast gas dispersal to explain the faint CO observations for most of
the disks. This result has implications for disk-evolution and
planet-formation theories, as disk gas masses may be larger than
expected if CO is considered to be the main carbon carrier in the gas
phase.
Description:
We present our ALMA Cycle 4 (ID: 2016.1.00459.S ; PI: Miotello) C2H
observations of 9 sources in the Lupus star-forming region. Six
sources, J16011549-4152351, J16070854-3914075, MY Lup, Sz 114, Sz 71
and Sz 98, were observed on 2017 July 12 with 49 antennas (16.7-2700m
baselines) using J1517-2422 and J1610-3958 as calibrators. Four
targets, J16070384-3911113, J16090141- 3925119, Sz 129 and Sz 68, were
observed on 2017 July 15 with 42 antennas (18.6-1500 m baselines)
using J1427-4206 and J1610-3958 as calibrators. The spectral window
was centred on 262.006 GHz to target the C2H (N=3-2, J=7/2-5/2,
F=4-3 and F=3-2) line.
Objects:
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RA (2000) DE Designation(s)
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16 08 22.5 -39 04 46 Sz 98 = SSTc2d J160822.5-390446
15 46 44.7 -34 30 35 Sz 71 = V* GW Lup
16 07 08.6 -39 14 08 J16070854-3914075 = SSTc2d J160708.6-391408
16 09 01.8 -39 05 12 Sz 114 = SSTc2d J160901.8-390512
16 00 44.5 -41 55 31 MY Lup = SSTc2d J160044.5-415531
16 09 01.4 -39 25 12 J16090141-3925119 = SSTc2d J160901.4-392512
15 59 16.5 -41 57 10 Sz 129 = SSTc2d J155916.5-415710
16 07 03.8 -39 11 12 J16070384-3911113 = SSTc2d J160703.9-391112
15 45 12.9 -34 17 31 Sz 68 = SSTc2d J154512.9-341731
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 170 9 List of fits datacubes
fits/* . 9 Individual fits datacubes
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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- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 32 I3 --- Nz Number of pixels along Z-axis
34- 59 A26 "datime" Obs.date Observation date
61- 71 E11.6 Hz bFREQ Lower value of frequency interval
73- 83 E11.6 Hz BFREQ Upper value of frequency interval
85- 90 I6 Hz dFREQ Frequency resolution
92- 99 F8.4 km/s bVel Lower value of velocity interval
101-107 F7.4 km/s BVel Upper value of velocity interval
109-111 F3.1 km/s dVel [1.0] Velocity resolution
113-117 A5 --- Mol [C2H] Molecule name
119-124 I6 Kibyte size Size of FITS file
126-137 A12 --- FileName Name of FITS file, in subdirectory fits
139-170 A32 --- Title Title of the FITS file
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Acknowledgements:
Anna Miotello, amiotell(at)eso.org
(End) Patricia Vannier [CDS] 26-Sep-2019