J/A+A/675/A139 CI 609um and CII 158um spectra of IRC +10216 (Jeste+, 2023)
[C I] and [C II] emission in the circumstellar envelope of IRC +10216.
I. Observational data and NLTE modelling of the [C I] emission.
Jeste M., Wiesemeyer H., Menten K.M., Wyrowski F.
<Astron. Astrophys. 675, A139 (2023)>
=2023A&A...675A.139J 2023A&A...675A.139J (SIMBAD/NED BibCode)
ADC_Keywords: Stars, carbon; Spectroscopy
Keywords: stars: AGB and post-AGB - stars: carbon - circumstellar matter
Abstract:
The envelopes of evolved late-type stars on the asymptotic giant
branch are characterised by a complex chemistry that is close to
thermochemical equilibrium near the stellar surface; however, in the
outer envelope, it is dominated by radical reactions, assisted by a
photo-chemistry driven by the interstellar radiation field.
The study at hand aims to describe the distribution of atomic carbon,
C0, throughout the envelope, in support of an improved understanding
of its photo-chemistry. Additionally, we also briefly discuss the
observation of [CII] emission towards the star.
We obtain spectra of the [CI] 3P1-3P0 fine structure line (at
492.160700GHz) at projected distances of up to 78 arcsec from the
star. The line profiles are characterised by both direct fitting of
Gaussian components, and by modelling the observed line of the [CI]
triplet. We also report the detection of the 2P3/2-2P1/2 line (at
1900.5369 GHz) from the C+ fine structure singlet at the central
position and its non-detection at 32 arcsec from the star.
The overall picture of the [CI] emission from IRC +10216 agrees with
more limited previous studies. The satisfying agreement between the
observed and modelled line profiles, with emission at the systemic
velocity appearing beyond one beam (13 arcsec HPBW) from the star,
rules out that the C0 is located in a thin shell. Given that the
bond energy of CO falls only 0.1eV below the ionisation threshold of
C0, the absence of observable [CII] emission from sightlines beyond
a projected distance of ∼1017cm (≳20-30arcsec) from the
star (adopting a distance of 130 pc) does not contradict a scenario
where the majority of C0 is located between that of CO and C+, as
expected for an external far-ultraviolet radiation field. This
conjecture is also corroborated by a model in which the C0 shell is
located farther outside, failing to reproduce the [CI] line profiles
at intermediate sky-plane distances from the star. Comparing a
photo-chemical model adopted from literature with the simplifying
assumption of a constant C0 abundance with respect to the H2
density (with the 1/r2 fall-off of a mass-conserving expansion
flow), we constrain the inner boundary of the [CI] emitting shell,
located at ∼1016cm from the star.
Description:
The [CI] observations were performed at the APEX submm telescope
between 2021 November 15 and 30. The [CII] data were collected on
several SOFIA flights spanning a time interval of 882 days.
Objects:
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RA (2000) DE Designation(s)
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09 47 57.40 +13 16 43.5 IRC +10216 = 2MASS J09475740+1316435
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See also:
J/A+A/317/503 : Photometric + visibility data of IRC +10 216
(Groenewegen 1997)
J/A+A/330/676 : IRC+10216 Silicon and sulfur chemistry (Willacy+ 1998)
J/A+AS/142/181 : 2mm molecular line survey of IRC+10 216 (Cernicharo+, 2000)
J/ApJS/177/275 : 1.3 and 2mm survey of IRC+10216 (He+, 2008)
J/ApJS/190/348 : 1mm spectral survey of IRC+10216 + VY CMa (Tenenbaum+, 2010)
J/ApJS/193/17 : Spectral-line survey of IRC+10216 at 293-355GHz
(Patel+, 2011)
J/A+A/545/A12 : Chemistry of IRC+10216 inner wind modelled
(Cherchneff, 2012)
J/ApJ/806/L3 : Disilicon carbide (SiCSi) discovery in CW Leo
(Cernicharo+, 2015)
J/A+A/574/A56 : IRC +10216 17.8GHz-26.3GHz spectrum (Gong+, 2015)
J/A+A/606/A74 : IRC +10216 13.3GHz-18.5GHz spectrum (Zhang+, 2017)
J/A+A/601/A4 : IRC+10216 carbon chains mapped with ALMA (Agundez+, 2017)
J/A+A/618/A4 : IRC+10216 as a spectroscopic laboratory (Cernicharo+, 2018)
J/MNRAS/489/3492 : IRC+10216 + omi Cet SCUBA-2 light curves
(Dharmawardena+, 2019)
J/A+A/658/A39 : 31.0-50.3 GHz observations of IRC+10216 (Pardo+, 2022)
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 51 1 *Input parameters for the RATRAN model of
the [CI] emission
table2.dat 85 16 *Parameters deduced from direct fits to the
observed spectra
list.dat 134 2 List of fits files
listsp.dat 71 38 List of spectra
fits/* . 2 Fits tables with spectra
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Note on table1.dat: The [CI] abundance profile is taken from Fig. 3 of Reach
et al. (2022ApJ...926...69R 2022ApJ...926...69R). A second model uses a constant abundance
(with respect to hydrogen nuclei) of n(C0)/n(H)=4x105 and
rin=4x1016cm. We note that D is the distance to the source, rin and
rout are the inner and outer radius of the shell, respectively, vexp
is the expansion velocity, and Delta v is the line width (1/e half-width).
The power-law indices for the fall-off of density and kinetic temperature
(gas and dust temperature are assumed to be equal) with distance from the
star are ∼2 and ∼0.50, respectively. For comparison, the temperature
power-law index for purely adiabatic cooling at a constant expansion
velocity would be ∼4/3 (Crosas & Menten, 1997ApJ...483..913C 1997ApJ...483..913C).
Notes on table2.dat: The table summarises the physical parameters constrained
at different offsets from the star. Subset 1 refers to the blue-shifted peak
and subset 2 refers to the red-shifted peak. The parameters obtained for
offsets away from the central position were calculated by fitting the Gauss
method. We note that V is the LSR velocity, Integral(TMB dV) is the
calculated integrated intensity, Delta V refers to the line width calculated
from the Gauss method, and finally Tpeak is the peak temperature of the
fitted line.
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 F5.1 pc D Distance to observer
7- 13 E7.1 Msun/yr Mdot Mass loss rate
15- 21 E7.1 cm rin Inner radius
23- 29 E7.1 cm rout Outer radius
31- 37 E7.1 cm-3 nH2(rin) H2 number density at inner radius
39- 42 F4.0 K Trin Gas temperature at inner radius
44- 47 F4.1 km/s vexp Expansion velocity
49- 51 F3.1 km/s Deltav 1/e line half-width
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 F5.1 arcsec oRA Right-ascension offset x cos(DE)
7- 11 F5.1 arcsec oDE Declination offset
13- 18 F6.2 km/s v1 LSR velocity at blue-shifted peak
20- 23 F4.2 km/s e_v1 Error on v1
25- 28 F4.2 K.km/s lineArea1 Line area below blue-shifted component
30- 33 F4.2 K.km/s e_lineArea1 Error on lineArea1
35- 39 F5.2 km/s Deltav1 Width (FWHM) of blue-shifted component
41- 43 F3.1 km/s e_Deltav1 Error on delta_v1
45- 48 F4.2 K Tpeak1 Line peak (Tmb) of blue-shifted peak
50- 55 F6.2 km/s v2 LSR velocity at red-shifted peak
57- 60 F4.2 km/s e_v2 Error on v2
62- 65 F4.2 K.km/s lineArea2 Line area below red-shifted component
67- 70 F4.2 K.km/s e_lineArea2 Error on lineArea2
72- 76 F5.2 km/s Deltav2 Width (FWHM) of red-shifted component
78- 80 F3.1 km/s e_Deltav2 Error on delta_v2
82- 85 F4.2 K Tpeak2 Line peak (Tmb) of red-shifted peak
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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- 43 A19 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss)
45- 54 F10.5 GHz bFreq Lower value of frequency interval
56- 65 F10.5 GHz BFreq Upper value of frequency interval
67- 76 F10.2 Hz dFreq Frequency resolution
78- 80 I3 Kibyte size Size of FITS file
82-106 A25 --- FileName Name of FITS file, in subdirectory fits
108-134 A27 --- Title Title of the FITS file
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Byte-by-byte Description of file: listsp.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Line number within the file
4- 15 A12 --- Ident Identifier (1)
17- 42 A26 --- FileName Name of the fits table with spectra
in subdirectory fits
44- 71 A28 --- Title Title of the fits file
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Note (1): Identifiers are SCAN number for ci-609micron-irc10216.fit and
TELESCOP name for cii-irc10216.fit
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Acknowledgements:
Manali Jeste, mjeste(at)mpifr.de
Helmut Wiesemeyer, hwiese(at)mpifr.de
(End) Patricia Vannier [CDS] 21-Jun-2023