mid-infrared interferometry of the mira star rr sco with the vlti/midi instrument collaborators:...

Mid-infrared interferometry of the Mira Mid-infrared interferometry of the Mira star RR Sco with the VLTI/MIDI instrumentstar RR Sco with the VLTI/MIDI instrument

collaborators:collaborators:

Keiichi Ohnaka, Keiichi Ohnaka, MPIfRMPIfR

Karl-Heinz Hofmann, Karl-Heinz Hofmann, MPIfRMPIfR

Dieter Schertl, MPIfRDieter Schertl, MPIfR

Gerd Weigelt, MPIfRGerd Weigelt, MPIfR

Thomas Preibisch, Thomas Preibisch, MPIfRMPIfR

Christoph Leinert, Christoph Leinert, MPIAMPIA

Rainer Koehler, MPIARainer Koehler, MPIA

Markus Wittkowski, Markus Wittkowski, ESOESO

Markus Schoeller, Markus Schoeller, ESOESO

Andrea Richichi, ESOAndrea Richichi, ESO

Francesco Paresce, Francesco Paresce, ESOESO

Science DemonstrationScience Demonstration Time (SDT) team Time (SDT) team (Malbet et al.) (Malbet et al.)

Thomas Driebe, MPIfR

April 18, 2023 213. Cambridge Workshop on Cool Stars - MIDI observations of RR Sco

OutlineOutline

The MIDI instrument at the VLTIThe MIDI instrument at the VLTI

MotivationMotivation

The Mira star RR ScoThe Mira star RR Sco

VLTI observations of RR ScoVLTI observations of RR Sco

ModelingModeling

Summary and conclusionsSummary and conclusions


The VLTIThe VLTI

located at Cerro Paranal in Chile and operated by ESO operating since Mar

2001 4 unit telescopes (UTs)

with 8.2m mirrors and AO 3 movable auxillary

telescopes (ATs) with 1.8m mirrors (2nd AT should arrive in July) 30 stations with

baselines ranging from 8 to 200m instruments:

- VINCI - MIDI - AMBER

www.eso.org/projects/vlti


The MIDI instrumentThe MIDI instrument

Mid-infrared Interferometric Instrument 2-telescope beam combiner consortium of institutes in

Germany, Netherlands, and France (P.I. Ch. Leinert, MPIA) first fringes in Dec 2002 operates in the N band

between 8 and 13 m spectrally dispersed fringes:

- prism ( - grism (chopping for background

substractionlimiting magnitude:

- N = 3.25m (2 Jy) with prism - N = 1.5m (10 Jy) with grism spatial resolution 20 mas @

B=100 m

picture taken from MIDI homepage: www.mpia-hd.mpg.de/MIDI see also : www.eso.org/instruments/midi



increase of the apparent diameter from the near-infrared toward longer wavelengths seems to be a common phenomenon in M giants and supergiants: - 20 ... 100 % diameter increase from K to L’ band in M-type Miras and semiregular M giants (Menneson et al. 2002) - diameter increase by a factor of 2 (Miras) and 1.3 (supergiants) from the K band to the 11 m region (Weiner et al. 2000, 2003a, 2003b) possible explanation:

- opt. thin gaseous layer extending to ~ 3 stellar radii (Menneson et al. 2002) - warm water vapor envelope extending to ~ 2 stellar radii (Perrin et al. 2004)

detailed analyses of ISO/SWS spectra of Miras and semiregular M giants revealed the existence of a warm, dense molecular layer close to the star (Tsuji et al. 1997, Yamamura et al. 1999, Cami et al. 2000, Matsuura et al. 2002): - radial extension typically a few stellar radii - temperature of 1000 ... 2000 K - hydrogen molecule number densities ~ 1012 cm-3



basic idea for this study:

- mid-infrared spectro-interferometric observations with VLTI/MIDI might give further observational evidence for the existence of such a warm molecular layer - wavelength dependence of the apparent diameter across the N band provides important constraint for models of the circumstellar environment including such a molecular layer and/or a dust shell


The Mira star RR ScoThe Mira star RR Sco

oxygen-rich Mira variable (C/O < 1) spectral type M6II-IIIe-M9 pulsation period 281.4 days (Kholopov et al. 1988) distance: 320 +/- 120 pc (Knapp et al. 2003) V = 6m ... 12m ; K = -0.5m ... 0.0m (Whitelock et al. 2000) IRAS: 188.7 Jy @ 12 m IRAS LRS: weak dust feature

appropriate coordinates brightness (V, N) expected size no GTO target spectrum: weak dust

feature study of warm molecular layer

Why RR Sco ?Why RR Sco ?


MIDI observations of RR Sco - OverviewMIDI observations of RR Sco - Overview

7 observations of RR Sco on June 14th, 15th , and 16th 2003 as part of the Science Demonstration Time program variability phase 0.6 spectral resolution 30 (prism) baseline UT1-UT3 (102m) projected baseline: 74 ... 102m observables: 2 interferometric and 2 photometric

signals raw visibility = modulus of the Fourier transform of the object’s intensity distribution mid-infrared spectrum (8 ... 13 m) 23 observations of 7 different calibrator stars data reduction using power spectrum analysis as

described in Leinert et al. (2004, A&A in press)


MIDI observations of RR Sco – MIDI observations of RR Sco – Visibilities (I)Visibilities (I)

no asymmetry detectedno asymmetry detected


MIDI observations of RR Sco – MIDI observations of RR Sco – Visibilities (II)Visibilities (II)

next step:next step: visibility fit for visibility fit for each spectral each spectral channel with channel with uniform disk uniform disk model model


MIDI observations of RR Sco – diameterMIDI observations of RR Sco – diameter

= 7.5 ... = 7.5 ... 10 10 m:m: d = 18 mas d = 18 mas > 10 > 10 m:m:

d = 18 ... 24 d = 18 ... 24 masmas


MIDI observations of RR Sco - MIDI observations of RR Sco - SpectrumSpectrum

calibration using HD 151680: MIDI spectrum + absolutely calibrated spectrum from Cohen et al. (1999) comparison with

IRAS LRS ( ~0.1 dex difference)


VINCI observations of RR ScoVINCI observations of RR Sco

5 K-band visibility measurements on July 10th and 11th 2003 using VLTI/VINCI: - 40cm siderostats - stations E0 and G0 16m baseline - data reduction SW from Kervella et al. (2004) VLTI/VINCI:

- ESO commissioning instrument - in operation between Mar 2001 and Jan 2004 - fiber optics beam combiner based on the FLUOR instrument concept - K band (m)

ddKK = 10.2 +/- 0.5 mas = 10.2 +/- 0.5 mas ddK K = ½ * d= ½ * dNN


Modeling – The goalModeling – The goal

find a model (as simple as possible) which ... - can explain the wavelength dependence of the diameter of RR Sco inside the N band as measured with MIDI - is consistent with the observed mid-infrared spectrum of RR Sco - can explain the diameter increase of RR Sco from the K band to the N band - can be applied to other Mira stars and supergiants to explain the observed wavelength dependence of the diameter from the K band to the L and N bands


Modeling – Basic assumptionsModeling – Basic assumptions

central star blackbody with T = 3000 K, radius R circumstellar warm molecular layer:

- H2O + SiO - extends from R to Rmol

- constant temperature and density input parameters:

- Rmol and Tmol

- column densities of H2O and SiO R = 4.5 mas (based on VINCI measurement and

conversion factor adopted from Woodruff et al. 2004) details on the model scheme and application to Ori and

Her Ohnaka (2004a, A&A 421, 1149) application to Mira stars (2 layer model) Ohnaka

(2004b, A&A accepted)


Modeling – warm HModeling – warm H22O + SiO layerO + SiO layer

T = 1600 K, R = 2.2 R N = 3 * 10 cm N = 1 * 10 cm (N band) fair agreement for

10 m

21

21

-2

-2H O

SiO

mol mol

2


Modeling – ImprovementsModeling – Improvements

idea: introducing a dust shell which might account for the observed diameter increase for 10 m dust shell properties:

- mixture of silicates and corundum (Al2O3) (motivated by study of Lorenz-Martins & Pompeia 2000) - 1/r2 density distribution - single-sized grains with a = 0.1 m - outer dust shell radius is at 100 R - temperature distribution from thermal balance in opt. thin limit (see Ohnaka et al. 2001) additional input parameters:

- temperature at the inner dust shell boundary - optical depth of the dust shell - dust composition (relative contributions)


Modeling – warm HModeling – warm H22O + SiO layer + O + SiO layer + dust shelldust shell

T = 1600 K, R = 2.2 R N = 3 * 10 cm N = 1 * 10 cm Tdust,in = 1000 K, Rdust,in =

7.5 R 20% silicate, 80%

corundum m; visual

21

21

-2

-2H O

SiO

mol mol

2


Modeling – Intensity profiles and Modeling – Intensity profiles and visibilitiesvisibilities

in addition:KK-band -band diameterdiameterprediction basedon our best-fitmodel (includingCO absorption):ddKK = 11.6 = 11.6 masmas in agreementwith VINCI data

flux contributionfrom dust shell:~ 5%@ 8.3 m~40%@12.06 m


Summary and conclusionsSummary and conclusions

7 observations of the Mira star RR Sco with the VLTI/MIDI instrument in June 2003 (SDT program) visibilities and diameters between 8 and 13 m

d = 18 mas between 8 and 10 d = 18 mas between 8 and 10 m; d = 18 ... 24 mas between 10 m; d = 18 ... 24 mas between 10 and 13 and 13 mm calibrated mid-infrared spectrum in agreement with IRAS LRS 5 VLTI/VINCI observations of RR Sco: ddKK = 10.2 +/- 0.5 mas = 10.2 +/- 0.5 mas modeling: opt. thick warm molecular layer (Hopt. thick warm molecular layer (H22O + SiO), RO + SiO), Rmolmol = =

2.2 R2.2 R + opt. thin dust shell (20 % silicates + 80 % + opt. thin dust shell (20 % silicates + 80 % corundum), Rcorundum), Rinin = 7...8 R = 7...8 R model can explain the diameter increase from the K band to the

N band as well as the wavelength dependence of the diameter across the N band modeling supports the existence of an extended molecular layer

in late M giants mid-infrared spectro-interferometry is well suited to probe this

warm molecular layer and the circumstellar environment around late-type giants in future: - observations of other Miras, non-Miras, supergiants using

MIDI and AMBER - improved modeling with atmosphere models from Bessel, Scholz & Wood (1996) - follow-up observations of RR Sco

mid-infrared interferometry of the mira star rr sco with the vlti/midi instrument collaborators:...

Documents

mpifr slide

vinci midi

midi homepage

mpifr thomas preibisch

mpifr christoph leinert

mpifr gerd weigelt

eso markus wittkowski

eso markus schoeller