J/A+A/556/L1 ALMA observations of 12CO/13CO around R Scl (Vlemmings+, 2013)
ALMA observations of the variable 12CO/13CO ratio around the asymptotic giant
branch star R Sculptoris.
Vlemmings W.H.T., Maercker M., Lindqvist M., Mohamed S., Olofsson H.,
Ramstedt S., Brunner M., Groenewegen M.A.T., Kerschbaum F., Wittkowski M.
<Astron. Astrophys. 556, L1 (2013)>
=2013A&A...556L...1V 2013A&A...556L...1V
ADC_Keywords: Stars, giant ; Abundances ; Spectra, millimetric/submm
Keywords: Stars: abundances - Stars: AGB - Stars: carbon -
Stars: circumstellar matter
Abstract:
The detached-shell source R Scl, displaying CO emission from recent
mass loss, in a binary-induced spiral structure as well as in a clumpy
shell produced during a thermal pulse, provides a unique laboratory
for studying the differences in CO isotope abundances throughout its
recent evolution. We observed both the 12CO(J=3-2) and the
13CO(J=3-2) line using ALMA. We find significant variations in the
12CO/13CO intensity ratios and consequently in the abundance
ratios. The average CO isotope abundance ratio is at least a factor
three lower in the shell (∼19) than that in the present-day (≲300yr)
mass loss (>60). Additionally, variations in the ratio of more than an
order of magnitude are found in the shell itself. We attribute these
variations to the competition between selective dissociation and
isotope fractionation in the shell, of which large parts cannot be
warmer than ∼35K. However, we also find that the 12CO/13CO ratio
in the present-day mass loss is significantly higher than the
12C/13C ratio determined in the stellar photosphere from molecular
tracers (∼19). The origin of this discrepancy is still unclear, but we
speculate that it is due to an embedded source of UV-radiation that is
primarily photo-dissociating 13CO. This radiation source could be
the hitherto hidden companion. Alternatively, the UV-radiation could
originate from an active chromosphere of R Scl itself. Our results
indicate that caution should be taken when directly relating the
12CO/13CO intensity and 12C/13C abundance ratios for specific
asymptotic giant branch stars, in particular binaries or stars that
display signs of chromospheric stellar activity.
Description:
The fits files contain ALMA cycle 0 image cubes of the 12CO(J=3-2)
and 13CO(J=3-2) molecular line transition of the carbon AGB star
R Scl. The data has been smoothed to 3km/s for a direct comparison of
both transitions.
The 12CO(J=3-2) and 13CO(J=3-2) emission lines of R Scl were
observed using ALMA Band 7 (275-373GHz) on October 3-4 and 18-19 2011
during the ALMA cycle 0 observing program.
Objects:
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RA (2000) DE Designation(s)
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01 26 58.09 -32 32 35.4 R Sculptoris = V* R Scl
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fits.dat 100 2 FITS file designation in fits directory
fits/* . 2 12CO and 13CO FITS files (image cubes)
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See also:
J/AJ/143/36 : A catalog of Galactic infrared carbon stars (Chen+, 2012)
J/ApJS/190/203 : 3.6 years of DIRBE NIR stellar light curves (Price+, 2010)
J/A+A/429/235 : Effective temperatures of 119 C-rich giants (Bergeat+, 2005)
J/A+A/390/967 : Carbon-rich giants in the HR diagram (Bergeat+, 2002)
J/A+A/374/968 : Photometric & kinematic properties of LPVs (Mennessier+, 2001)
J/A+A/285/247 : Molecules in O- and C-rich envelopes (Bujarrabal+ 1994)
J/A+AS/102/361 : Li abundances in galactic C-stars (Boffin+ 1993)
J/A+AS/99/291 : CO & HCN observations of circumstellar envelopes (Loup+ 1993)
Byte-by-byte Description of file: fits.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- 22 F3.1 arcsec/pix scale [0.3] Scale of the image
24- 26 I3 pix Nx [432] Number of pixels along X-axis
27 A1 --- --- [x]
29- 31 I3 pix Ny [432] Number of pixels along Y-axis
32 A1 --- --- [x]
34- 35 I2 pix Nz [25] Number of channels
37- 43 F7.3 GHz RFreq [330/346] Rest frequency
45- 51 F7.3 GHz Freq1 Lower value of the frequency
53- 59 F7.3 GHz Freq2 Upper value of the frequency
61- 64 F4.2 MHz dFreq Resolution (step) in the frequency
66- 81 A16 --- FileName Name of FITS file in subdirectory fits
83-100 A18 --- Line Title of the FITS cube
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Acknowledgements:
Wouter Vlemmings: wouter.vlemmings(at)chalmers.se
(End) Wouter Vlemmings [Chalmers Univ.], Emmanuelle Perret [CDS] 03-Jul-2013