J/A+A/670/A12 Integrated spectra and moment 0 maps of LkCa 15 (Sturm+, 2023)
Disentangling protoplanetary disk gas mass and carbon depletion through combined
atomic and molecular tracers.
Sturm J.A., Booth A.S., McClure M.K., Leemker M., van Dishoeck E.F.
<Astron. Astrophys. 670, A12 (2023)>
=2023A&A...670A..12S 2023A&A...670A..12S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Spectroscopy ; Spectra, radio
Keywords: protoplanetary disks - astrochemistry -
planets and satellites: formation
Abstract:
The total disk gas mass and elemental C, N, and O composition of
protoplanetary disks are crucial ingredients for improving our
understanding of planetary formation. Measuring the gas mass is
complicated, since H2 cannot be detected in the cold bulk of the
disk and the elemental abundances with respect to hydrogen are
degenerate with gas mass in all disk models.
We aim to determine the gas mass and elemental abundances ratios C/H
and O/H in the transition disk around LkCa 15, one of the few disks
for which HD data are available, in combination with as many chemical
tracers as possible.
We present new NOrthern Extended Millimeter Array observations of CO,
13CO, C18O, and optically thin C17O J=2-1 lines, along with high
angular-resolution Atacama Large Millimeter Array millimeter continuum
and CO data to construct a representative model of LkCa 15. Using a
grid of 60 azimuthally symmetric thermo-chemical DALI disk models, we
translated the observed fluxes to elemental abundances and constrained
the best-fitting parameter space of the disk gas mass.
The transitions that constrain the gas mass and carbon abundance the
most are C17O J=2-1, N2H+ J=3-2 and HD J=1-0. Using these three
molecules, we find that the gas mass in the LkCa 15 disk is
Mg=0.01+0.01-0.004M☉, which is a factor of 6 lower than
previous estimations. This value is consistent with cosmic ray
ionization rates between 10-16-10-18s-1, where 10-18s-1
is a lower limit based on the HD upper limit. The carbon abundance is
C/H=(3±1.5)x10-5, implying a moderate depletion of elemental
carbon by a factor of 3-9. All other analyzed transitions also agree
with these numbers, within a modeling uncertainty of a factor of 2.
Using the resolved C2H image we find a C/O ratio of ∼1, which is
consistent with literature values of H2O depletion in this disk. The
absence of severe carbon depletion in the LkCa 15 disk is consistent
with the young age of the disk, but stands in contrast to the higher
levels of depletion seen in older cold transition disks.
Combining optically thin CO isotopologue lines with N2H+ is
promising with regard to breaking the degeneracy between gas mass and
CO abundance. The moderate level of depletion for this source with a
cold, but young disk, suggests that long carbon transformation
timescales contribute to the evolutionary trend seen in the level of
carbon depletion among disk populations, rather than evolving
temperature effects and presence of dust traps alone. HD observations
remain important for determining the disk's gas mass.
Description:
Fig. 1, integrated NOEMA spectra and moment 0 maps of LkCa 15. For
13CO 2-1, C18O 2-1 and C17O 2-1 the spectra is given as function
of relative velocity. The spectrum of CN 2-1 is given as function of
frequency corrected for the source velocity. Moment 0 maps in
Jy/beam*km/s are given for each of the aforementioned emission lines
Objects:
---------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------
04 39 17.79 +22 21 03.3 LkCa 15 = V* V1079 Tau
---------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
cospect.dat 39 100 Integrated CO isotopologue spectra as function
cnspect.dat 20 600 Integrated CN spectrum as function of frequency
list.dat 119 4 List of fits images
fits/* . 4 Individual fits images
--------------------------------------------------------------------------------
See also:
J/A+A/639/A121 : LkCa15 & 2MASS J16100501-2132318 ALMa images (Facchini+, 2020)
Byte-by-byte Description of file: cospect.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 km/s Vlsr Velocity relative to source
12- 19 F8.5 Jy Fnu13CO Flux density 13CO (2-1)
22- 29 F8.5 Jy FnuC18O Flux density C18O (2-1)
32- 39 F8.5 Jy FnuC17O Flux density C17O (2-1)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: cnspect.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.6 GHz Freq Frequency, corrected for source velocity
12- 20 F9.6 Jy FnuCN Flux density CN (2-1)
--------------------------------------------------------------------------------
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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 53 A26 "datime" Obs.date Observation date
55- 61 F7.3 GHz Freq Observed frequency
63- 65 I3 Kibyte size Size of FITS file
67- 80 A14 --- FileName Name of FITS file, in subdirectory fits
82-119 A38 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Ardjan Sturm, sturm(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 19-Jan-2023