J/A+A/545/A56 Mid-infrared diameter of 4 AGBs (Zhao-Geisler+, 2012)
Dust and molecular shells in asymptotic giant branch stars. Mid-infrared
interferometric observations of R Aql, R Aqr, R Hya, W Hya and V Hya.
Zhao-Geisler R., Quirrenbach A., Koehler R., Lopez B.
<Astron. Astrophys. 545, A56 (2012)>
=2012A&A...545A..56Z 2012A&A...545A..56Z
ADC_Keywords: Stars, giant; Infrared sources; Interferometry; Stars, diameters
Keywords: stars: AGB and post-AGB - circumstellar matter -
infrared: stars - stars: mass loss
Abstract:
Asymptotic giant branch (AGB) stars are one of the largest
distributors of dust into the interstellar medium. However, the wind
formation mechanism and dust condensation sequence leading to the
observed high mass-loss rates have not yet been constrained well
observationally, in particular for oxygen-rich AGB stars.
The immediate objective in this work is to identify molecules and dust
species which are present in the layers above the photosphere, and
which have emission and absorption features in the mid-infrared (IR),
causing the diameter to vary across the N- band, and are potentially
relevant for the wind formation.
Mid-IR (8-13 micron) interferometric data of four oxygen-rich AGB
stars (R Aql, R Aqr, R Hya, and W Hya) and one carbon-rich AGB star
(V Hya) were obtained with MIDI/VLTI between April 2007 and September
2009. The spectrally dispersed visibility data are analyzed by fitting
a circular fully limb-darkened disk (FDD).
The FDD diameter as function of wavelength is similar for all
oxygen-rich stars. The apparent size is almost constant between 8 and
10 micron and gradually increases at wavelengths longer than 10
micron. The apparent FDD diameter in the carbon-rich star V Hya
essentially decreases from 8 to 12 micron. The FDD diameters are about
2.2 times larger than the photospheric diameters estimated from K-band
observations found in the literature. The silicate dust shells of R
Aql, R Hya and W Hya are located fairly far away from the star, while
the silicate dust shell of R Aqr and the amorphous carbon (AMC) and
SiC dust shell of V Hya are found to be closer to the star at around 8
photospheric radii. Phase-to-phase variations of the diameters of the
oxygen-rich stars could be measured and are on the order of 15% but
with large uncertainties.
From a comparison of the diameter trend with the trends in RR Sco and
S Ori it can be concluded that in oxygen-rich stars the overall larger
diameter originates from a warm molecular layer of H2O, and the
gradual increase longward of 10 micron can be most likely attributed
to the contribution of a close Al2O3 dust shell. The chromatic trend
of the Gaussian FWHM in V Hya can be explained with the presence of
AMC and SiC dust. The observations suggest that the formation of
amorphous Al2O3 in oxygen-rich stars occurs mainly around or after
visual minimum. However, no firm conclusions can be drawn concerning
the mass-loss mechanism. Future modeling with hydrostatic and
self-consistent dynamical stellar atmospheric models will be required
for a more certain understanding.
Description:
The files contain the calibrated visibilities of all USED observations
listed in the observation log (32, 26, 64 and 48 for R Aql, R Aqr, R
Hya and V Hya, respectively) as function of wavelength (8-12 micron),
cf. Table C.2 (appendix C) in the online version. Data are ordered by
time and are obtained with MIDI and reduced/calibrated with MIA/EWS.
Objects:
---------------------------------------------------------------
RA (2000) DE Designation(s) (files)
---------------------------------------------------------------
19 06 22.25 +08 13 48.0 R Aql = HD 177940 (dataraql.dat)
23 43 49.46 -15 17 04.1 R Aqr = HD 222800 (dataraqr.dat)
13 29 42.78 -23 16 52.8 R Hya = HD 117287 (datarhya.dat)
10 51 37.26 -21 15 00.3 V Hya = BD-20 3283 (datavhya.dat)
---------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
dataraql.dat 490 71 Calibrated visibilities of R Aql
dataraqr.dat 400 71 Calibrated visibilities of R Aqr
datarhya.dat 967 71 Calibrated visibilities of R Hya
datavhya.dat 730 71 Calibrated visibilities of V Hya
tablec2.dat 99 214 Detailed observation logs of R Aql, R Aqr,
R Hya, and V Hya
--------------------------------------------------------------------------------
See also:
J/A+A/530/A120 : Mid-infrared diameter of W Hya (Zhao-Geisler+, 2011)
Byte-by-byte Description of file: data*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.7 um lambda Wavelength
12- 22 F11.8 --- V01 [0/1] Calibrated visibility # 1 (1)
27- 38 F12.9 --- V02 [0/1] Calibrated visibility # 2 (1)
42- 53 F12.9 --- V03 [0/1] Calibrated visibility # 3 (1)
57- 68 F12.9 --- V04 [0/1] Calibrated visibility # 4 (1)
72- 83 F12.9 --- V05 [0/1] Calibrated visibility # 5 (1)
87- 98 F12.9 --- V06 [0/1] Calibrated visibility # 6 (1)
102-113 F12.9 --- V07 [0/1] Calibrated visibility # 7 (1)
117-128 F12.9 --- V08 [0/1] Calibrated visibility # 8 (1)
132-143 F12.9 --- V09 [0/1] Calibrated visibility # 9 (1)
147-158 F12.9 --- V10 [0/1] Calibrated visibility # 10 (1)
162-173 F12.9 --- V11 [0/1] Calibrated visibility # 11 (1)
177-189 F13.10 --- V12 [0/1] Calibrated visibility # 12 (1)
192-204 F13.10 --- V13 [0/1] Calibrated visibility # 13 (1)
207-219 F13.10 --- V14 [0/1] Calibrated visibility # 14 (1)
222-233 F12.9 --- V15 [0/1] Calibrated visibility # 15 (1)
237-248 F12.9 --- V16 [0/1] Calibrated visibility # 16 (1)
252-264 F13.10 --- V17 [0/1] Calibrated visibility # 17 (1)
267-278 F12.9 --- V18 [0/1] Calibrated visibility # 18 (1)
282-293 F12.9 --- V19 [0/1] Calibrated visibility # 19 (1)
297-308 F12.9 --- V20 [0/1] Calibrated visibility # 20 (1)
312-323 F12.9 --- V21 [0/1] Calibrated visibility # 21 (1)
327-338 F12.9 --- V22 [0/1] Calibrated visibility # 22 (1)
342-353 F12.9 --- V23 [0/1] Calibrated visibility # 23 (1)
357-368 F12.9 --- V24 [0/1] Calibrated visibility # 24 (1)
372-383 F12.9 --- V25 [0/1] Calibrated visibility # 25 (1)
387-398 F12.9 --- V26 [0/1] Calibrated visibility # 26 (1)
402-413 F12.9 --- V27 [0/1]? Calibrated visibility # 27 (1)
417-429 F13.10 --- V28 [0/1]? Calibrated visibility # 28 (1)
432-443 F12.9 --- V29 [0/1]? Calibrated visibility # 29 (1)
447-458 F12.9 --- V30 [0/1]? Calibrated visibility # 30 (1)
462-474 F13.10 --- V31 [0/1]? Calibrated visibility # 31 (1)
477-489 F13.10 --- V32 [0/1]? Calibrated visibility # 32 (1)
492-503 F12.9 --- V33 [0/1]? Calibrated visibility # 33 (1)
507-518 F12.9 --- V34 [0/1]? Calibrated visibility # 34 (1)
522-534 F13.10 --- V35 [0/1]? Calibrated visibility # 35 (1)
537-548 F12.9 --- V36 [0/1]? Calibrated visibility # 36 (1)
552-563 F12.9 --- V37 [0/1]? Calibrated visibility # 37 (1)
567-578 F12.9 --- V38 [0/1]? Calibrated visibility # 38 (1)
582-595 F14.11 --- V39 [0/1]? Calibrated visibility # 39 (1)
597-608 F12.9 --- V40 [0/1]? Calibrated visibility # 40 (1)
612-625 F14.11 --- V41 [0/1]? Calibrated visibility # 41 (1)
627-638 F12.9 --- V42 [0/1]? Calibrated visibility # 42 (1)
642-653 F12.9 --- V43 [0/1]? Calibrated visibility # 43 (1)
657-668 F12.9 --- V44 [0/1]? Calibrated visibility # 44 (1)
672-683 F12.9 --- V45 [0/1]? Calibrated visibility # 45 (1)
687-698 F12.9 --- V46 [0/1]? Calibrated visibility # 46 (1)
702-713 F12.9 --- V47 [0/1]? Calibrated visibility # 47 (1)
717-728 F12.9 --- V48 [0/1]? Calibrated visibility # 48 (1)
732-743 F12.9 --- V49 [0/1]? Calibrated visibility # 49 (1)
747-758 F12.9 --- V50 [0/1]? Calibrated visibility # 50 (1)
762-773 F12.9 --- V51 [0/1]? Calibrated visibility # 51 (1)
777-789 F13.10 --- V52 [0/1]? Calibrated visibility # 52 (1)
792-804 F13.10 --- V53 [0/1]? Calibrated visibility # 53 (1)
807-819 F13.10 --- V54 [0/1]? Calibrated visibility # 54 (1)
822-833 F12.9 --- V55 [0/1]? Calibrated visibility # 55 (1)
837-848 F12.9 --- V56 [0/1]? Calibrated visibility # 56 (1)
852-863 F12.9 --- V57 [0/1]? Calibrated visibility # 57 (1)
867-878 F12.9 --- V58 [0/1]? Calibrated visibility # 58 (1)
882-894 F13.10 --- V59 [0/1]? Calibrated visibility # 59 (1)
897-910 F14.11 --- V60 [0/1]? Calibrated visibility # 60 (1)
912-925 F14.11 --- V61 [0/1]? Calibrated visibility # 61 (1)
927-939 F13.10 --- V62 [0/1]? Calibrated visibility # 62 (1)
942-953 F12.9 --- V63 [0/1]? Calibrated visibility # 63 (1)
957-967 F11.8 --- V64 [0/1]? Calibrated visibility # 64 (1)
-------------------------------------------------------------------------------
Note (1): Dates and observations explained in tablec2.dat.
-------------------------------------------------------------------------------
Byte-by-byte Description of file: tablec2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Star Star name
7- 9 A3 --- Obs Observation number VNN
11- 20 A10 "YYYY-MM-DD" Obs.Date Observation date
22- 33 A12 "h:m:s" Obs.Time Observation time
35- 37 A3 --- P Semester of proposal
39- 40 A2 --- AT AT station (1)
42- 46 A5 --- Disp Dispersive element (GRISM or PRISM)
48- 53 A6 --- Cal Calibrator used out of those available
55- 59 F5.2 m B Projected baseline length
61- 66 F6.2 deg PA [-17/131] Position angle of the projected
baseline on the sky
68- 71 F4.2 --- Phase Visual light phase
73- 77 F5.2 deg H Elevation
79- 86 A8 --- QF Quality flag showing if that observation is
used for the model fitting or not
88- 99 A12 --- FileName Name of the file with corresponding
visibilities
--------------------------------------------------------------------------------
Note (1): AT stations codes as follows:
----------------------------------------------------------------------
Name AT stations Ground length Ground PA Resolution (at 10um)
(m) (°) mas
----------------------------------------------------------------------
A = E0-G0 16.006 71.020 128
B = G0-H0 31.998 70.998 64
B* = A0-D0 32.011 71.014 64
C = E0-H0 48.004 71.005 42
D = D0-H0 64.005 71.012 32
E = D0-G1 71.557 134.443 28
F = H0-G1 71.555 7.576 28
----------------------------------------------------------------------
--------------------------------------------------------------------------------
Acknowledgements:
Ronny Zhao-Geisler, rgeisler(at)lsw.uni-heidelberg.de
(End) Patricia Vannier [CDS] 03-Jul-2012