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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 (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) ------------------------------------------- 05 29 00.9 -04 41 33 S Ori = HD 36090 ------------------------------------------- File Summary:
FileName Lrecl Records Explanations
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
Byte-by-byte Description of file: tablea1.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: tablea[234].dat
Bytes Format Units Label Explanations
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
Note (1): Two maser transitions were observed: v=1,J=1-0 (43.1GHz) and v=2,J=1-0 (42.8GHz)
Acknowledgements: M. Wittkowski, mwittkow(at)eso.org
(End) Markus Wittkowski [ESO], Patricia Vannier [CDS] 10-May-2007
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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