IK Tauri Research Articles

High-level Ab Initio Studies of the Spectroscopic Properties of Triatomic [Al, S, O]x (x = 0, +1) and Its Potential for Detection in Space

Abstract Highly reliable molecular properties have been computed for the [Al, S, O] x (x = 0, +1) molecular system. Spectroscopic parameters are predicted from analysis of each isomer’s 3D potential energy surface calculated using the explicitly correlated multireference configuration interaction method, including the Davidson correction (MRCI-F12+Q). These parameters provide an accurate prediction of spectroscopic data that can be used in laboratory and observational studies of these molecules. Linear-SAlO is expected to have a large permanent dipole moment suitable for detection in the circumstellar envelopes of large, evolved, oxygen-rich stars such as VY Canis Majoris, IK Tauri, and R Doradus. Frequencies are provided for rotational transitions originating from the most highly populated rotational state based on a Boltzmann distribution. Additionally, both linear isomers exhibit a flat potential along the bending angle and are predicted to have very low bending mode frequencies (<200 cm−1), complicating the spectra of these molecules.

Exploring the innermost dust formation region of the oxygen-rich AGB star IK Tauri with VLT/SPHERE-ZIMPOL and VLTI/AMBER

Context. Low- and intermediate-mass stars on the asymptotic giant branch (AGB) are known to be prevalent dust providers to galaxies, replenishing the surrounding medium with molecules and dust grains. However, the mechanisms responsible for the formation and acceleration of dust in the cool extended atmospheres of AGB stars are still open to debate. Aims. We present visible polarimetric imaging observations of the oxygen-rich AGB star IK Tau obtained with the high-resolution polarimetric imager VLT/SPHERE-ZIMPOL at post-maximum light (phase 0.27) as well as high-spectral resolution long-baseline interferometric observations with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). We aim to spatially resolve the dust and molecule formation regions, and to investigate their physical and chemical properties within a few stellar radii of IK Tau. Methods. IK Tau was observed with VLT/SPHERE-ZIMPOL at three wavelengths in the pseudo-continuum (645, 748, and 820 nm), in the Hα line at 656.3 nm, and in the TiO band at 717 nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 μm with a spectral resolution of 12 000. Results. The excellent polarimetric imaging capabilities of SPHERE-ZIMPOL have allowed us to spatially resolve clumpy dust clouds at 20–50 mas from the central star, which corresponds to 2–5 R⋆ when combined with a central star’s angular diameter of 20.7 ± 1.53 mas measured with VLTI/AMBER. The diffuse, asymmetric dust emission extends out to ~73 R⋆. We find that the TiO emission extends to 150 mas (15 R⋆). The AMBER data in the individual CO lines also suggest a molecular outer atmosphere extending to ~1.5 R⋆. The results of our 2D Monte Carlo radiative transfer modelling of dust clumps suggest that the polarized intensity and degree of linear polarization can be reasonably explained by small-sized (0.1 μm) grains of Al2O3, MgSiO3, or Mg2SiO4 in an optically thin shell (τ550 nm = 0.5 ± 0.1) with an inner and outer boundary radius of 3.5 R⋆ and ≳25 R⋆, respectively. The observed clumpy structures can be reproduced by a density enhancement of a factor of 3.0 ± 0.5. However, the model still predicts the total intensity profiles to be too narrow compared to the observed data, which may be due to the TiO emission and/or grains other than homogeneous, filled spheres. Conclusions. IK Tau’s mass-loss rate is 20–50 times higher than the previously studied AGB stars W Hya, R Dor, and o Cet. Nevertheless, our observations of IK Tau revealed that clumpy dust formation occurs close to the star as seen in those low mass-rate AGB stars.

Interferometric observations of SiO thermal emission in the inner wind of M-type AGB stars IK Tauri and IRC+10011.

Asymptotic giant branch (AGB) stars go through a process of strong mass loss that involves pulsations of the atmosphere, which extends to a region in which the conditions are adequate for dust grains to form. Radiation pressure acts on these grains which, coupled to the gas, drive a massive outflow. The details of this process are not clear, including which molecules are involved in the condensation of dust grains. We seek to study the role of the SiO molecule in the process of dust formation and mass loss in M-type AGB stars. Using the IRAM NOEMA interferometer we observed the 28SiO and 29SiO J = 3 - 2, v = 0 emission from the inner circumstellar envelope of the evolved stars IK Tau and IRC+10011. We computed azimuthally averaged emission profiles to compare the observations to models using a molecular excitation and ray-tracing code for SiO thermal emission. We observe circular symmetry in the emission distribution. We also find that the source diameter varies only marginally with radial velocity, which is not the expected behaviour for envelopes expanding at an almost constant velocity. The adopted density, velocity, and abundance laws, together with the mass-loss rate, which best fit the observations, give us information concerning the chemical behaviour of the SiO molecule and its role in the dust formation process. The results indicate that there is a strong coupling between the depletion of gas-phase SiO and gas acceleration in the inner envelope. This could be explained by the condensation of SiO into dust grains.

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

During their asymptotic giant branch, evolution low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the high-resolution HIFI spectrometer onboard Herschel. We report on the first detection of H_2^{16}O and the rarer isotopologues H_2^{17}O and H_2^{18}O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6x10^{-5}, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H_2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.

SiO MASERS IN ASYMMETRIC MIRAS. III. IK TAURI

This is the third paper in a series of multi-epoch observations at 7 mm wavelength of the SiO masers in several asymptotic giant branch stars from a sample of Mira variable stars showing evidence of asymmetric structure in the infrared. These stars have been observed interferometrically in the infrared by Infrared Optical Telescope Array and with Very Long Baseline Array measurements of the SiO masers. In this paper, we present the observations of IK Tauri (IK Tau). There is a persistent elliptical distribution of the masers around the star {approx}40 x {approx}30 mas in size with a major axis at position angle {approx}30 deg. The SiO masers in the circumstellar envelope exhibit large-scale systematic motions which reverse direction on timescales of a decade, roughly the interval between the ejections of dust shells. The orientations on the sky of the apparent rotation-like bulk motion and of the major axis of the maser ellipse differ by 37 deg. (2.5{sigma}) making any relationship uncertain. The systemic velocity of IK Tau is estimated to be 33.3 {+-} 1.0 km s{sup -1}. A comparison is made with the model calculations of Gray et al. which predict some but not all observed features.

Variable Asymmetry of the Circumstellar Envelope in IK Tauri Traced by SiO Maser Emission

Abstract We observed the SiO ($v=1$ and $v=2$, $J=$ 1-0) maser emissions toward the Mira variable IK Tauri (IK Tau, NML Tau, IRC$+$10050) over nine epochs from 2003 November to 2005 April using the VLBI Exploration of Radio Astrometry (VERA) telescope array. We found that the SiO maser distributions around IK Tau are highly variable, depending on the stellar pulsation phase. The velocity structures were complex and also time-variable, and are inconsistent with a simply rotating shell that was suggested by previous observations. Based on fittings of the SiO maser distributions to elliptical ring models, we found that the ring size seems to vary in correlation with the pulsation phase, as previously found for TX Cam. Comparisons of the $v=1$ and $v=2$ maser distributions reveal that 42-50% of the maser pairs have a positional offset less than 0.5mas, suggesting that the maser pumping in these spots is likely to be dominated by line overlapping or collisional pumping, rather than pure radiative pumping. In order to model the velocity structure of the spoke-like features observed in IK Tau, we propose a ballistic-orbit model, in which a gas clump ejected from the stellar surface moves radially outward with a gravitational deceleration, and argue that the stellar mass can be deduced from that model.

Oxygen-rich Mass Loss with a Pinch of Salt: NaCl in the Circumstellar Gas of IK Tauri and VY Canis Majoris

The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau)—the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H2, of in VY CMa and in IK Tau, with source 9 9 f ∼ 5 # 10 f ∼ 4 # 10 sizes of 0.5 and 0.3, respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where , although it appears to condense out earlier in the O-rich case. Chemical 9 f ∼ (0.2–2) # 10 equilibrium calculations indicate that NaCl is the major carrier of sodium at K for oxygen-rich stars, with T ∼ 1100 predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells. Subject headings: astrochemistry — radio lines: stars — stars: chemically peculiar —

Axial Symmetry and Rotation in the SiO Maser Shell of IK Tauri

We observed v = 1, J = 1-0 43 GHz SiO maser emission toward the Mira variable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 × 32 mas with an axial ratio of 1.8 : 1. The major axis of this elliptical distribution is oriented at a position angle of ~59°. The line-of-sight velocity structure of the SiO masers has an apparent axis of symmetry consistent with the elongation axis of the maser distribution. Relative to the assumed stellar velocity of 35 km s-1, the blue- and redshifted masers were found to lie to the northwest and southeast of this symmetry axis, respectively. This velocity structure suggests a northwest-southeast (NW-SE) rotation of the SiO maser shell with an equatorial velocity, which we determine to be ~3.6 km s-1. Such a NW-SE rotation is in agreement with a circumstellar envelope geometry invoked to explain previous H2O and OH maser observations. In this geometry, H2O and OH masers are preferentially created in a region of enhanced density along the NE-SW equator orthogonal to the rotation/polar axis suggested by the SiO maser velocities.

Multiple Dust Shells and Motions around IK Tauri as Seen by Infrared Interferometry

A visibility curve of IK Tau has been measured with the ISI, an 11 μm stellar interferometer, over a period of several years. Time variations in 11 μm flux were also measured. The results indicate an approximately periodic distribution of dust shells around the star, with shells separated by 200-250 mas and a diameter of about 200 mas for the innermost shell. Some shell motion has been detected, and if velocities are the same as those measured for CO gas and OH masers, the motion implies that the distance to IK Tau is about 265 pc and that shells have been emitted at times separated by about 12 yr, which is considerably longer than the star's luminosity period of 470 days.

Detection of Ammonia Emission toward Oxygen-rich Evolved Stars

view Abstract Citations (27) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Ammonia Emission toward Oxygen-rich Evolved Stars Menten, Karl M. ; Alcolea, Javier Abstract Using the Effelsberg 100 m telescope, we have discovered emission in the (J, K) = (1, 1) and (2, 2) inversion transitions of ammonia (NH3) toward the circumstellar envelopes of the Mira variable 1K Tau and the OH/IR hypergiant IRC +10420. Modeling our spectra, we find that [NH3/H2] abundance ratios of a few times 10-6 are required to explain the observational results. These values are of the same order as the ammonia abundances previously inferred from infrared absorption measurements toward oxygen-rich evolved stars. The high NH3 abundances implied by our observations present a challenge to models of circumstellar chemistry, which fall short of reproducing the observed values by several orders of magnitude. We also present high-quality spectra of the NH3 (1, 1), (2, 2), and (3, 3) lines toward the peculiar bipolar nebula OH 231.8+4.2, which is the only oxygen-rich (post-)AGB object with previously detected NH3 radio emission. Toward this source the (1, 1) profile looks strikingly different from the profiles of the (2, 2) and (3, 3) lines, which resemble each other closely. Similar to many millimeter-wavelength lines from other molecules, the NH3 (1, 1) line shows high-velocity emission. In contrast, the (2, 2) and (3, 3) lines have narrow line profiles that are quite different from profiles observed in spectra from any other molecule and arise from a warm (Tkin > 50 K) region close to the central star. The high-velocity material dominating the (1, 1) spectrum is emitted from a cooler (≲20 K), more extended region. Publication: The Astrophysical Journal Pub Date: July 1995 DOI: 10.1086/175971 Bibcode: 1995ApJ...448..416M Keywords: STARS: CIRCUMSTELLAR MATTER; STARS: INDIVIDUAL ALPHANUMERIC: IRC +10420; STARS: INDIVIDUAL CONSTELLATION NAME: IK TAURI; STARS: LATE-TYPE; STARS: VARIABLES: OTHER LONG-PERIOD VARIABLES full text sources ADS | data products SIMBAD (5)

On estimating the intrinsic properties of Miras from observational data

view Abstract Citations (38) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On estimating the intrinsic properties of Miras from observational data. Cahn, J. H. ; Wyatt, S. P. Abstract Some consequences of the Wood-Cahn (1977) model of late stellar evolution, including mass loss via stellar winds, are examined. Broad features of the model are summarized, and equations and numerical data are outlined for the task of relating the model predictions to available observational data for Mira variables. It is found that: (1) approximate lines of constant mean spectral type at maximum light (Sp(max)) can be estimated in the Mira zone of the (M, log L) diagram; (2) these lines are roughly parallel to lines of constant temperature; (3) the lines of Sp(max) are tilted with respect to lines of constant period, so that an approximate present-day mass and mean bolometric luminosity can be assigned to a given Mira if the star's period and Sp(max) are known; the star's main-sequence mass and age can be estimated from the evolutionary equation governing its track across the (M, log L) plane; and (5) the boundaries of the Mira zone and the present location of a star within that zone permit one to estimate an approximate time scale for the star's evolution through the Mira phase and to tell whether it will go through a planetary-nebula stage before becoming a white dwarf. The results are applied to Mira itself, IK Tauri, and the post-Mira planetary nebula NGC 7027. Publication: The Astrophysical Journal Pub Date: April 1978 DOI: 10.1086/156014 Bibcode: 1978ApJ...221..163C Keywords: M Stars; Stellar Evolution; Stellar Mass Ejection; Stellar Models; Variable Stars; Binary Stars; Bolometers; Mira Variables; Stellar Spectrophotometry; Stellar Winds; Astrophysics; Evolution:Mira Variables; Stellar Evolution: Models full text sources ADS |

The period and spectral range of IK Tau.

view Abstract Citations (39) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The period and spectral range of IK Tauri. Wing, R. F. ; Lockwood, G. W. Abstract The mean period of 1K Tauri, a very cool Mira variable, has been found to be 470 j 5 days on the basis of 8 years of photometric observations in the 1- region. Its mean amplitude of 2.7 mag in 1(104) is the largest known among Miras. The spectral type consistently reaches M10 at minimum light and has not been observed earlier than M8.1 at maximum. It is pointed out that, in the case of a Mira variable observed in only two consecutive cycles, a better estimate of the mean period can be obtained from the interval between successive maxima than from the interval between recurrences of the same magnitude. Subject headings: infrared sources - long-period variables - spectral classification - stars, individual Publication: The Astrophysical Journal Pub Date: September 1973 DOI: 10.1086/152376 Bibcode: 1973ApJ...184..873W full text sources ADS | data products SIMBAD (6)