Mid-infrared interferometry of the Mira star RR Sco with the VLTI/MIDI instrument collaborators: Keiichi Ohnaka, MPIfR Keiichi Ohnaka, MPIfR Karl-Heinz Hofmann, MPIfR Karl-Heinz Hofmann, MPIfR Dieter Schertl, MPIfR Dieter Schertl, MPIfR Gerd Weigelt, MPIfR Gerd Weigelt, MPIfR Thomas Preibisch, MPIfR Thomas Preibisch, MPIfR Christoph Leinert, MPIA Christoph Leinert, MPIA Rainer Koehler, MPIA Rainer Koehler, MPIA Markus Wittkowski, ESO Markus Wittkowski, ESO Markus Schoeller, ESO Markus Schoeller, ESO Andrea Richichi, ESO Andrea Richichi, ESO Francesco Paresce, ESO Francesco Paresce, ESO Science Demonstration Time (SDT) team (Malbet et al.) Science Demonstration Time (SDT) team (Malbet et al.) Thomas Driebe, MPIfR

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Outline The MIDI instrument at the VLTI Motivation The Mira star RR Sco VLTI observations of RR Sco Modeling Summary and conclusions

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco The VLTI located at Cerro Paranal in Chile and operated by ESO operating since Mar unit telescopes (UTs) with 8.2m mirrors and AO 3 movable auxillary telescopes (ATs) with 1.8m mirrors (2 nd AT should arrive in July) 30 stations with baselines ranging from 8 to 200m instruments: - VINCI - MIDI - AMBER

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco The 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 substraction  limiting magnitude: - N = 3.25 m (2 Jy) with prism - N = 1.5 m (10 Jy) with grism spatial resolution 20 B=100 m picture taken from MIDI homepage: see also :

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco The MIDI instrument warm optics cold optics (two radiation shields) 30/70 photometric beam splitter ZnSe plate with 50/50 coating for beam com- bination filters and dispersing elements 240 x 320 pixel detector

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Motivation increase of the apparent diameter from the near-infrared toward longer wavelengths seems to be a common phenomenon in M giants and supergiants: % diameter increase from K to L’ band in M-type Miras and semiregular M giants ( Menneson et al ) - 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 ) 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 K - hydrogen molecule number densities ~ cm -3

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Motivation 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

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco The Mira star RR Sco oxygen-rich Mira variable (C/O < 1) spectral type M6II-IIIe-M9 pulsation period days ( Kholopov et al ) distance: 320 +/- 120 pc ( Knapp et al ) V = 6 m m ; K = -0.5 m m ( Whitelock et al ) IRAS:  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 ?

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco MIDI observations of RR Sco - Overview 7 observations of RR Sco on June 14 th, 15 th, and 16 th 2003 as part of the Science Demonstration Time program variability phase 0.6 spectral resolution  30 (prism) baseline UT1-UT3 (102m) projected baseline: m observables: 2 interferometric and 2 photometric signals  raw visibility = modulus of the Fourier transform of the object’s intensity distribution  mid-infrared spectrum (  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)

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco MIDI observations of RR Sco – Visibilities (I) no asymmetry detected

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco MIDI observations of RR Sco – Visibilities (II) next step: next step: visibility fit for each spectral channel with visibility fit for each spectral channel with uniform disk model uniform disk model

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco MIDI observations of RR Sco – diameter =  m: d = 18 mas =  m: d = 18 mas > 10  m: d = mas > 10  m: d = mas

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco MIDI observations of RR Sco - Spectrum calibration using HD : MIDI spectrum + absolutely calibrated spectrum from Cohen et al. (1999) comparison with IRAS LRS (  ~0.1 dex difference)

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco VINCI observations of RR Sco 5 K-band visibility measurements on July 10 th and 11 th 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 fiber optics beam combiner based on the FLUOR instrument concept - K band (  m) d K = /- 0.5 mas  d K = ½ * d N  d K = ½ * d N

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Modeling – 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

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Modeling – Basic assumptions central star  blackbody with T = 3000 K, radius R circumstellar warm molecular layer: - H 2 O + SiO - extends from R to R mol - constant temperature and density input parameters: - R mol and T mol - column densities of H 2 O 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 )

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Modeling – warm H 2 O + SiO layer T = 1600 K, R = 2.2 R N = 3 * 10 cm N = 1 * 10 cm  (N band) fair agreement for  10  m H O SiO mol 2

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Modeling – 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 (Al 2 O 3 ) (motivated by study of Lorenz-Martins & Pompeia 2000) - 1/r 2 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)

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Modeling – warm H 2 O + SiO layer + dust shell T = 1600 K, R = 2.2 R N = 3 * 10 cm N = 1 * 10 cm T dust,in = 1000 K, R dust,in = 7.5 R 20% silicate, 80% corundum   m  ;  visual  H O SiO mol 2

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Modeling – Intensity profiles and visibilities in addition: K-band diameter prediction based on our best-fit model (including CO absorption): d K = 11.6 mas  in agreement with VINCI data flux contribution from dust shell: ~ 8.3  m  m

21/06/ Cambridge Workshop on Cool Stars - MIDI observations of RR Sco Summary and conclusions 7 observations of the Mira star RR Sco with the VLTI/MIDI instrument in June 2003 (SDT program) d = 18 mas between 8 and 10  m; d = mas between 10 and 13  m visibilities and diameters between 8 and 13  m  d = 18 mas between 8 and 10  m; d = mas between 10 and 13  m calibrated mid-infrared spectrum in agreement with IRAS LRS d K = /- 0.5 mas 5 VLTI/VINCI observations of RR Sco: d K = /- 0.5 mas opt. thick warm molecular layer (H 2 O + SiO), R mol = 2.2 R + opt. thin dust shell (20 % silicates + 80 % corundum), R in = R modeling: opt. thick warm molecular layer (H 2 O + SiO), R mol = 2.2 R + opt. thin dust shell (20 % silicates + 80 % corundum), R in = 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