THE KECK APERTURE MASKING EXPERIMENT: SPECTRO-INTERFEROMETRY OF THREE MIRA VARIABLES FROM 1.1 TO 3.8 μm

We present results from a spectro-interferometric study of the Miras o Cet, R Leo, and W Hya obtained with the Keck Aperture Masking Experiment from 1998 September to 2002 July. The spectrally dispersed visibility data permit fitting with circularly symmetric brightness profiles such as a simple uniform disk (UD). The stellar angular diameter obtained over up to ~ 450 spectral channels spanning the region 1.1-3.8 μm is presented. Use of a simple UD brightness model facilitates comparison between epochs and with existing data and theoretical models. Strong size variations with wavelength were recorded for all stars, probing zones of H2O, CO, OH, and dust formation. Comparison with contemporaneous spectra extracted from our data shows a strong anticorrelation between the observed angular diameter and flux. These variations consolidate the notion of a complex stellar atmosphere consisting of molecular shells with time-dependent densities and temperatures. Our findings are compared with existing data and pulsation models. The models were found to reproduce the functional form of the wavelength versus angular diameter curve well, although some departures are noted in the 2.8-3.5 μm range.

[1]  William C. Danchi,et al.  First Surface-resolved Results with the Infrared Optical Telescope Array Imaging Interferometer: Detection of Asymmetries in Asymptotic Giant Branch Stars , 2006 .

[2]  W. C. Danchi,et al.  Diffraction-limited Near-IR Imaging at Keck Reveals Asymmetric, Time-variable Nebula around Carbon Star CIT 6 , 2000, astro-ph/0008487.

[3]  Donald M. A. Wilson,et al.  Cyclic variations in the angular diameter of χ Cygni , 2000 .

[4]  F. V. Leeuwen,et al.  Hipparcos, the New Reduction of the Raw Data , 2007 .

[5]  W. C. Danchi,et al.  The Keck Aperture Masking Experiment: Multiwavelength Observations of Six Mira Variables , 2007, 0709.3878.

[6]  C. Townes,et al.  Characteristics of dust shells around 13 late-type stars. , 1994 .

[7]  J. G. Robertson,et al.  Multiwavelength diameters of nearby Miras and semiregular variables , 2004 .

[8]  P. Wood,et al.  Optical and near-IR spectra of O-rich Mira variables: A comparison between models and observations , 2003, astro-ph/0309689.

[9]  S. D. Price,et al.  The Infrared Spectral Classification of Oxygen-rich Dust Shells , 1998 .

[10]  H. M. Dyck,et al.  Angular Size Measurements of 18 Mira Variable Stars at 2.2 ( , 1996 .

[11]  Bump Cepheids in the Magellanic Clouds: Metallicities, the Distances to the LMC and SMC, and the Pulsation-Evolution Mass Discrepancy , 2006, astro-ph/0601225.

[12]  F. Millour,et al.  J, H, K spectro-interferometry of the Mira variable S Orionis , 2008, 0801.0594.

[13]  M. Scholz,et al.  Observable effects of dust formation in dynamic atmospheres of M-type Mira variables , 2006, astro-ph/0601383.

[14]  Peter G. Tuthill,et al.  New diameter measurements of 10 Mira Variables: implications for effective temperatures, atmospheric structure and pulsation modes , 1995 .

[15]  G. Gatewood.  AN ASTROMETRIC STUDY OF THE MIRA VARIABLE R LEONIS AND THE OCCULTATION BINARY 19 LEONIS , 1992 .

[16]  Wesley A. Traub,et al.  Interferometry for Optical Astronomy II , 2003 .

[17]  F. P. Schloerb,et al.  High-resolution imaging of dust shells by using Keck aperture masking and the IOTA interferometer , 2004 .

[18]  F. P. Schloerb,et al.  First Surface-resolved Results with the IOTA Imaging Interferometer: Detection of Asymmetries in AGB stars , 2006 .

[19]  David Mozurkewich,et al.  Angular Diameters of Stars from the Mark III Optical Interferometer , 2003 .

[20]  P. Tuthill,et al.  Michelson Interferometry with the Keck I Telescope , 2000 .

[21]  J. G. Robertson,et al.  Wavelength dependence of angular diameters of M giants: an observational perspective , 1999 .

[22]  W. C. Danchi,et al.  Imaging the Disk around the Luminous Young Star LkHα 101 with Infrared Interferometry , 2002 .

[23]  T. Dumm,et al.  Stellar radii of M giants , 1998 .

[24]  Astrophysics,et al.  The K-band intensity profile of R Leonis probed by VLTI/VINCI ⋆ , 2004, astro-ph/0411133.

[25]  P. Tuthill,et al.  Pulsation of M-type Mira variables with moderately different mass: search for observable mass effects , 2004, astro-ph/0408540.

[26]  M. Schoeller,et al.  Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models , 2002 .

[27]  A. Lançon,et al.  The structure of H2O shells in Mira atmospheres Correlation with disk brightness distributions and a spectrophotometric signature , 2003 .

[28]  F. V. Leeuwen,et al.  AGB variables and the Mira period–luminosity relation , 2008, 0801.4465.

[29]  W. C. Danchi,et al.  Near- and mid-infrared subarcsecond structure of the dusty symbiotic star R Aquarii , 2000 .

[30]  William C. Danchi,et al.  Near-Infrared Interferometric Images of the Hot Inner Disk surrounding the Massive Young Star MWC 349A , 2001 .

[31]  M. Ireland,et al.  On the observability of geometric pulsation of M-type Mira variables , 2004 .

[32]  K. Ohnaka.  Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared , 2004, astro-ph/0406675.

[33]  G. Neugebauer,et al.  THE FIRST DIFFRACTION-LIMITED IMAGES FROM THE W. M. KECK TELESCOPE , 1996 .

[34]  G. Weigelt,et al.  Bispectrum speckle interferometry of the Red Rectangle: Diffraction-limited near-infrared images reconstructed from Keck telescope speckle data , 2002 .

[35]  Michael Scholz,et al.  Mira science with interferometry: a review , 2003, SPIE Astronomical Telescopes + Instrumentation.

[36]  Peter Tuthill,et al.  Pinwheels in the Quintuplet Cluster , 2006, Science.

[37]  Astrophysics,et al.  Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared , 2004, astro-ph/0404248.

[38]  G. V. van Belle,et al.  Multiepoch Interferometric Study of Mira Variables. I. Narrowband Diameters of RZ Pegasi and S Lacertae , 2002 .