J/A+A/470/191 Mid-IR and radio interferometry of S Ori (Wittkowski+, 2007)
The Mira variable S Orionis: relationships between the photosphere, molecular
layer, dust shell, and SiO maser shell at 4 epochs.
Wittkowski M., Boboltz D.A., Ohnaka K., Driebe T., Scholz M.
<Astron. Astrophys. 470, 191 (2007)>
=2007A&A...470..191W 2007A&A...470..191W (SIMBAD/NED BibCode)
ADC_Keywords: Interferometry ; Masers ; Spectra, infrared
Keywords: techniques: interferometric - masers - stars: AGB and post-AGB -
stars: atmospheres - stars: mass-loss - stars: individual: S Orionis
Abstract:
We present the first multi-epoch study that includes concurrent
mid-infrared and radio interferometry of an oxygen-rich Mira star. We
obtained mid-infrared interferometry of S Ori with VLTI/MIDI at four
epochs in December 2004, February/March 2005, November 2005, and
December 2005. We concurrently observed v=1, J=1-0 (43.1GHz) and v=2,
J=1-0 (42.8GHz) SiO maser emission toward S Ori with the VLBA in
January, February, and November 2005. The MIDI data are analyzed using
self-excited dynamic model atmospheres including molecular layers,
complemented by a radiative transfer model of the circumstellar dust
shell. The VLBA data are reduced to the spatial structure and
kinematics of the maser spots. The modeling of our MIDI data results
in phase-dependent continuum photospheric angular diameters of
9.0±0.3mas (phase 0.42), 7.9±0.1mas (0.55), 9.7±0.1mas (1.16),
and 9.5±0.4mas (1.27). The dust shell can best be modeled with Al2O3
grains alone using phase-dependent inner boundary radii between 1.8
and 2.4 photospheric radii. The dust shell appears to be more compact
with larger optical depth near visual minimum (tauV∼2.5), and more
extended with lower optical depth after visual maximum (tauV∼1.5).
The ratios of the 43.1GHz/42.8GHz SiO maser ring radii to the
photospheric radii are 2.2±0.3/2.1±0.2 (phase 0.44),
2.4±0.3/2.3±0.4 (0.55), and 2.1±0.3/1.9±0.2 (1.15). The maser
spots mark the region of the molecular atmospheric layers shortly
outward of the steepest decrease of the mid-infrared model intensity
profile. Their velocity structure indicates a radial gas expansion. S
Ori shows significant phase-dependences of photospheric radii and dust
shell parameters. Al2O3 dust grains and SiO maser spots form at
relatively small radii of ∼1.8-2.4 photospheric radii. Our results
suggest increased mass-loss and dust formation close to the surface
near minimum visual phase, when Al2O3 dust grains are co-located with
the molecular gas and the SiO maser shells, and a more expanded dust
shell after visual maximum. Silicon does not appear to be bound in
dust, as our data shows no sign of silicate grains.
Description:
We present the calibrated MIDI data and the characteristics of the
43.1GHz and 42.8GHz SiO maser components. Table A1 contains the
calibrated MIDI visibility and flux data. It lists for each epoch of
observation and each spectral channel with central wavelength lambda
the uv coordinates in 1/arcsec, the visibility amplitude V with the
corresponding error, as well as the total flux fnu in Jansky with
its error. Tables A2-A4 list for VLBA epochs A, B, C, respectively,
the characteristics of the individual maser components. Listed are the
maser transition (v=1, J=1-0, 43.1GHz or v=2, J=1-0, 42.8GHz), the
line-of-sight velocity vLSR in km/s, the flux Snu in Jansky/beam
with its error, and the offset coordinates relative to a reference
position with their errors in milli-arcseconds.
Objects:
-------------------------------------------
RA (2000) DE Designation(s)
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05 29 00.9 -04 41 33 S Ori = HD 36090
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 68 214 Calibrated MIDI visibility and flux data from 4
epochs
tablea2.dat 48 61 SiO maser characteristics derived from the
epoch A (2005 Jan. 17) VLBA data
tablea3.dat 48 62 SiO maser characteristics derived from the
epoch B (2005 Feb. 28) VLBA data
tablea4.dat 48 97 SiO maser characteristics derived from the
epoch C (2005 Nov. 05) VLBA data
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1 A1 --- Epoch [A-D] Epoch of observation
3- 12 A10 "YYYY-MM-DD" Obs.date Date of observation
14- 18 A5 "h:m" Obs.time Time of observation (UT)
20- 28 E9.3 m lambda Central Wavelength
30- 35 F6.3 1/arcsec u Spatial frequency u
37- 43 F7.3 1/arcsec v Spatial frequency v
45- 49 F5.3 --- Vamp Visibility Amplitude V
51- 55 F5.3 --- e_Vamp Error of Vamp
57- 62 F6.2 Jy fnu Total flux at lambda
64- 68 F5.2 Jy e_fnu Error of fnu
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Byte-by-byte Description of file: tablea[234].dat
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Bytes Format Units Label Explanations
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1- 3 A3 -- v [v=12] Maser transition (1)
5- 8 F4.1 km/s vLSR LSR velocity
10- 14 F5.3 Jy Snu Flux (in Jy/beam)
16- 20 F5.3 Jy e_Snu Error of Snu (in Jy/beam)
22- 28 F7.3 mas oRA Offset in Right ascension
30- 34 F5.3 mas e_oRA Error of ORA
36- 42 F7.3 mas oDE Offset in Declination
44- 48 F5.3 mas e_oDE Error of ODE
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Note (1): Two maser transitions were observed:
v=1,J=1-0 (43.1GHz) and v=2,J=1-0 (42.8GHz)
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Acknowledgements:
M. Wittkowski, mwittkow(at)eso.org
(End) Markus Wittkowski [ESO], Patricia Vannier [CDS] 10-May-2007