# Presentation: 273335

## Departures from Spherical Symmetry in Mira Variables at PTI

**R. R. Thompson (JPL/U Wyoming)**
**M. J. Creech-Eakman (Caltech/JPL)**
**G. T. van Belle (JPL)**
***American Astronomical Society***
***Meeting 198, 4 June 2001***

## Abstract

**We report evidence of departures from spherical symmetry in a sub-sample of the Mira dataset taken with the Palomar Testbed Interferometer (PTI). The criteria for testing such departures is two-fold: first, that the visibility data using the N-S and N-W baselines be taken within 0.1 of a Mira's pulsation phase (to rule out dramatic size changes); and second, that extensive hour coverage be taken on a single baseline. **
**Of the 11 stars which meet this criteria, 9 show evidence of a departure from spherical symmetry when fit using a uniform elliptical disk model. It must be stressed that this "ellipticity" may only be apparent in nature, as atmospheric structures such as starspots, limb-darkening, binarity and non-radial pulsation induced outflows can influence apparent geometries of these stars. Axial ratios (2b/2a) for the model ellipses range between 0.60 and 0.90 for the eight stars. **
**We also report wideband (2.2 um) models of R Tri. These models - which rely upon Fast Fourier Transforms and Monte Carlo techniques - support a geometry of a slightly elliptical star with a circumstellar region of gas/dust in emission. **
***The work performed here was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.***

## The Palomar Testbed Interferometer

**Maximum projected baselines:   N-S 110m, N-W 85m**
**Resolution range 1.0 - 5.5 mas**
**40 cm collecting apertures, K ~ 5 fringe tracking,                            V ~ 12 angle tracking**
**Visibilities in H-band (4 chan) and K-band (5 chan)  R ~ 22 - 50**

## Miras as post-AGB stars

**Pulsation driven shockwaves.**
**Outer layers are convective to carry away energy production.**
**Outer layers lifted by shockwave(s).**
**Mass loss due to a superwind, creating circumstellar shells, dM/dt ~ 10**** -7 ****to 10**** -4 ****M****sol**** / yr**

## Mira Variables

**Pulsation periods: 120 - 500 days.**
**Short period (< 200 d), long period (> 400 d).**
**Classed with “long period variables” (LPV)**
******V****mag**** ~ 5 - 10, or 100 - 10,000 x brightness amplitude**
**T****eff**** ~ 2800 - 3500 K, but dust can make them appear cooler ( down to 1800K).**
**L / L****sol**** ~ 1000 - 10,000**
**R / R****sol**** ~ 100 - 800**
**Evidence for: jets, circumstellar shells, dusty regions.**
**Convective hot spots theorized.**
**Departures from spherically-symmetric geometry.**
**Chemical taxonomy: oxygen-rich (M), intermediate (S), carbon-rich (C). **

## Departures from Spherical Symmetry

**Asymptotic giant branch (AGB) and post-AGB stars are characterized by their extended atmospheres. As such, departures from spherical symmetry of these outer atmospheres may occur as a result of non-radial pulsation, stellar hotspots due to large-scale convection and asymmetric mass outflows. Spatially-resolved studies of  using various techniques depict evolved supergiants, semi-regular pulsators and Mira stars as having geometric asymmetries in their outer atmospheres.**
******Ori****	****	****mid-IR interferometry****	****(Weiner et al., 2000)**
**R Leo      ****	****near -IR aperture masking****	****(Tuthill et al., 1994)**
**R Leo, W Hya      ****	****FGS, HST****	****	****(Lattanzi et al., 1997)**
**R Aqr      ****	****mid-IR interferometry****	****(Tuthill et al., 2000)**
******Cet       ****	****direct imaging, HST****	****(Karovska et al., 1999)**
**R Cas      ****	****speckle masking****	****	****(Hofmann et al., 2000)**
**(7 Mira stars) ****	****near-IR interferometry****	****(Thompson et al., 2000)**

## Results from near-infrared long baseline interferometry

**Using two-baseline uniform disk angular sizes, or single baseline FFT fits to visibilities, we have detected departures from spherical symmetry in 9 Mira stars. Axial ratios (b/a) of simple uniform ellipse fits and corresponding position angles vary with wavelength. The following stars were tested.**
**V CVn  (M6e) ****	****	****R Gem (Se) ****	****	****RZ Peg (Ce)**
**R Boo (M4e) ****	****	****	****	****	****T Lyn (Ne)****	**
**R Del (M5e)**
**R Vir (M4e)**
**RS Her (M5e)**
**S Gem (M6e)**
**S Lac (M5e)**
**T And (M3e)**
**TU And (M5e)**
**X Del (M6e)**
**R Tri (M4e)**

## Axial Ratios and Postion Angles

**	****Phase****	****   2.0********m****	****   2.1********m****	****   2.2********m****	****    2.3********m****	****    2.4********m  **
**V CVn****	****     ?         ****	****0.76 (0.04)   0.92 (0.09)    0.86 (0.04)    0.87 (0.02)      -------****	****  ****	****(b/a)**
**                                   ****	*****219 (3)        241  (42)       241 (14)        230 (4)             -------******	******   ******	******PA (deg)***
**R Vir              0.96          --------          ****0.99 (0.02)    0.92 (0.05)     0.93 (0.08)****     0.78 (0.14)****	****(b/a)**
**  ****	****	*****-------  ******	******------            315 (9)           7 (51)******              318 (7)*****             ****	*****PA (deg)***
**RS Her****	****   0.90  ****	****-------****	****0.73 (0.12)****	****0.72 (0.16)****	****  0.78 (0.19)****	****     0.80 (0.09)****	****(b/a)**
***	******	******	******327 (4)******	******337 (10)******	******342 (34)******	******     328 (7)******	******	******PA (deg)***
**S Gem****	****  0.23****	****0.88 (0.02)****	****0.83 (0.04)****	****0.93 (0.01)****	**** 0.90 (0.02)****	****    0.86 (0.03)****	****(b/a)**
**	****	*****1 (9)******	******22 (6)******	******4 (7)******	******17 (3)******	******    21 (7)******	******	******PA (deg)***
**T And****	****  0.78****	****--------          ---------         0.92 (0.07)   0.94 (0.08)      ****0.99 (0.05)****	****(b/a)**
**                                         ****--------          ---------          *****335 (5)        344 (10)          ******327 (3)******                           PA (deg)***
**TU And ****	****  0.19****	****0.89 (0.20)****	****0.92 (0.09)****	****0.95 (0.06)****	****0.84 (0.06)****	****  ****0.96 (0.05)****	****	****(b/a)**
***	******	******340 (62)******	******347 (60)******	******13 (61)******	******27 (19)******	******  ******337 (40)******	******	******PA (deg)***
**X Del****	****  0.18****	****1.00 (0.02)****	****0.98 (0.02)****	****0.89 (0.02)****	****0.86 (0.03)****	****  0.86 (0.02)****	****	****(b/a)**
***	******	******  ******------******	******269 (4)******	******275 (16)******	******268 (12)******	******  270 (20)******	******	******PA (deg)*****     **
**R Gem           0.37     ****	****--------         ****0.96 (0.02)    0.96 (0.02)   0.95  (0.03)    0.96 (0.02)****       ****	****(b/a)**
**                                         *****-------- ******        8  (1)            36 (9)            1 (19)             18  (13)****** ******	******      ******	******PA (deg)***

## Time-dependent changes, R Del

**Uniform disk angular sizes from 2 baselines (NS, NW) show R Del maintaining axial ratios near 0.9 but whose position angles changed over the course of one pulsation cycle.**

## Time-dependent changes, R Boo

**Uniform disk angular sizes from 2 baselines (NS, NW) show R Boo changing from an ellipse just past maximum light, to a more spherical shape near phase 0.4 with non-static position angles.**

## The Enigmatic R Tri

**R Triangulum: oxygen-rich Mira, P = 266 d**
**Single baseline, extensive hour angle coverage between phases 0.84 and 0.95.**
**When data is fit to a uniformly-bright sphere (UD) : ********2**** ~ 300!**
**An “event” at phase 0.93??**

## Models tested on R Tri

**Using FFTs on calibrated wideband visibilities three models fit the dataset better than a uniform spherical or elliptical disk. Monte Carlo techniques were utilized.**
**In each case, a secondary structure brighter than the stellar atmosphere is found between PA 15 - 25 degrees.**