scholarly journals ALMA observations of the “fresh” carbon-rich AGB star TX Piscium

2019 ◽  
Vol 621 ◽  
pp. A50 ◽  
Author(s):  
M. Brunner ◽  
M. Mecina ◽  
M. Maercker ◽  
E. A. Dorfi ◽  
F. Kerschbaum ◽  
...  
Keyword(s):  
High Resolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Dust Emission ◽  
Asymptotic Giant Branch ◽  
Circumstellar Envelope ◽  
Spherically Symmetric ◽  
Stellar Rotation ◽  
Brown Dwarf ◽  
Rotation Rates

Aims. The carbon-rich asymptotic giant branch (AGB) star TX Piscium (TX Psc) has been observed multiple times during multiple epochs and at different wavelengths and resolutions, showing a complex molecular CO line profile and a ring-like structure in thermal dust emission. We investigate the molecular counterpart in high resolution, aiming to resolve the ring-like structure and identify its origin. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) observations have been carried out to map the circumstellar envelope (CSE) of TX Psc in CO(2–1) emission and investigate the counterpart to the ring-like dust structure. Results. We report the detection of a thin, irregular, and elliptical detached molecular shell around TX Psc, which coincides with the dust emission. This is the first discovery of a non-spherically symmetric detached shell, raising questions about the shaping of detached shells. Conclusions. We investigate possible shaping mechanisms for elliptical detached shells and find that in the case of TX Psc, stellar rotation of 2 km s−1 can lead to a non-uniform mass-loss rate and velocity distribution from stellar pole to equator, recreating the elliptical CSE. We discuss the possible scenarios for increased stellar momentum, enabling the rotation rates needed to reproduce the ellipticity of our observations, and come to the conclusion that momentum transfer of an orbiting object with the mass of a brown dwarf would be sufficient.

scholarly journals How to disentangle geometry and mass-loss rate from AGB-star spectral energy distributions

2020 ◽  
Vol 642 ◽  
pp. A142 ◽  
Author(s):  
J. Wiegert ◽  
M. A. T. Groenewegen ◽  
A. Jorissen ◽  
L. Decin ◽  
T. Danilovich
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Spectral Energy ◽  
High Angular Resolution ◽  
Circumstellar Envelope ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
The Impact

Context. High-angular-resolution observations of asymptotic giant branch (AGB) stars often reveal non-spherical morphologies for the gas and dust envelopes. Aims. We aim to make a pilot study to quantify the impact of different geometries (spherically symmetric, spiral-shaped, and disc-shaped) of the dust component of AGB envelopes on spectral energy distributions (SEDs), mass estimates, and subsequent mass-loss rate (MLR) estimates. We also estimate the error made on the MLR if the SED is fitted by an inappropriate geometrical model. Methods. We use the three-dimensional Monte-Carlo-based radiative-transfer code RADMC-3D to simulate emission from dusty envelopes with different geometries (but fixed spatial extension). We compare these predictions with each other, and with the SED of the AGB star EP Aqr that we use as a benchmark since its envelope is disc-like and known to harbour spiral arms, as seen in CO. Results. The SEDs involving the most massive envelopes are those for which the different geometries have the largest impact, primarily on the silicate features at 10 and 18 μm. These different shapes originate from large differences in optical depths. Massive spirals and discs appear akin to black bodies. Optically thick edge-on spirals and discs (with dust masses of 10−4 and 10−5 M⊙) exhibit black-body SEDs that appear cooler than those from face-on structures and spheres of the same mass, while optically thick face-on distributions appear as warmer emission. We find that our more realistic models, combined spherical and spiral distributions, are 0.1 to 0.5 times less massive than spheres with similar SEDs. More extreme, less realistic scenarios give that spirals and discs are 0.01 to 0.05 times less massive than corresponding spheres. This means that adopting the wrong geometry for an AGB circumstellar envelope may result in a MLR that is incorrect by as much as one to two orders of magnitude when derived from SED fitting.

scholarly journals The Rotational Velocity of Helium-rich Pre-White Dwarfs

2004 ◽  
Vol 215 ◽  
pp. 573-574 ◽  
Author(s):  
Thomas Rauch ◽  
Sebastian Köper ◽  
Stefan Dreizler ◽  
Klaus Werner ◽  
Ulrich Heber ◽  
...  
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
White Dwarfs ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Rotational Velocity ◽  
Line Profiles ◽  
Line Broadening ◽  
Stellar Rotation ◽  
Upper Limits

Previous investigations on hydrogen-rich white dwarfs generally yield only very small rotational velocities (v sin i). We have analyzed line profiles in high-resolution optical spectra of eight hydrogen-deficient (pre-) white dwarfs and find deviations from the dominant Stark line broadening in five cases which, interpreted as an effect of stellar rotation, indicate projected rotational velocities of 40 – 70 km s–1. For the three least luminous stars upper limits of v sin i = 15 – 25 km s–1 could be derived only. The resulting velocities correlate with luminosity and mass. However, since the mass-loss rate is correlated to the luminosity of a star, the observed line profiles may be affected by a stellar wind as well. In the case of RX J2117.1+3412, this would solve discrepancies to results of pulsational modeling (v sin i ≈ 0).

scholarly journals Ionisation fractions and mass-loss in O stars

1987 ◽  
Vol 122 ◽  
pp. 449-450
Author(s):  
Raman K. Prinja ◽  
Ian D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Column Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Stellar Radius ◽  
Left Part ◽  
Hr Diagram

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.

scholarly journals The runaway supergiant HD 188209 (O9.5Iab): a binary or a pulsating star?

1999 ◽  
Vol 193 ◽  
pp. 69-70
Author(s):  
Garik Israelian ◽  
Artemio Herrero ◽  
E. Santolaya-Rey ◽  
A. Kaufer ◽  
F. Musaev ◽  
...  
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Mass Loss ◽  
Radial Velocity ◽  
Loss Rate ◽  
State Of The Art ◽  
Mass Loss Rate ◽  
Fundamental Parameters ◽  
Binary Nature ◽  
Period 2

We report radial velocity studies of photospheric absorption lines from spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations with a quasi-period ∼ 2 days have been detected in high-resolution echelle spectra and most probably indicate that the supergiant is pulsating. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile have been observed. The fundamental parameters of the star have been derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, these last including the mass-loss rate. The binary nature of this star is not suggested either from Hipparcos photometry or from radial-velocity curves.

scholarly journals The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr

2019 ◽  
Vol 484 (2) ◽  
pp. 1865-1888 ◽  
Author(s):  
D T Hoai ◽  
P T Nhung ◽  
P Tuan-Anh ◽  
P Darriulat ◽  
P N Diep ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Equatorial Region ◽  
Data Cube ◽  
Asymptotic Giant Branch ◽  
Expansion Velocity ◽  
Circumstellar Envelope ◽  
Low Velocity ◽  
Loss Mechanism ◽  
Asymptotic Giant Branch Star

ABSTRACT ALMA observations of CO(1–0) and CO(2–1) emissions of the circumstellar envelope of EP Aqr, an oxygen-rich asymptotic giant branch star, are reported. A thorough analysis of their properties is presented using an original method based on the separation of the data cube into a low-velocity component associated with an equatorial outflow and a faster component associated with a bipolar outflow. A number of important and new results are obtained concerning the distribution in space of the effective emissivity, the temperature, the density, and the flux of matter. A mass-loss rate of (1.6 ± 0.4)×10−7 solar masses per year is measured. The main parameters defining the morphology and kinematics of the envelope are evaluated and uncertainties inherent to de-projection are critically discussed. Detailed properties of the equatorial region of the envelope are presented including a measurement of the line width and a precise description of the observed inhomogeneity of both morphology and kinematics. In particular, in addition to the presence of a previously observed spiral enhancement of the morphology at very small Doppler velocities, a similarly significant but uncorrelated circular enhancement of the expansion velocity is revealed, both close to the limit of sensitivity. The results of the analysis place significant constraints on the parameters of models proposing descriptions of the mass-loss mechanism, but cannot choose among them with confidence.

scholarly journals Red Giant Stars: Comparison of Observations and Theory

1984 ◽  
Vol 108 ◽  
pp. 195-206
Author(s):  
Jeremy Mould
Keyword(s):  
Mass Loss ◽  
Parameter Space ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Carbon Stars ◽  
Giant Stars ◽  
Theoretical Investigations ◽  
Red Giant

Recent observations in both the field and the clusters of the Magellanic Clouds suggest a higher mass loss rate during or at the end of the asymptotic giant branch phase than previously supposed. Recent theoretical investigations offer an explanation for the frequency of carbon stars in the Clouds, but a rich parameter space remains to be explored, before detailed agreement can be expected.

scholarly journals Warm CO in evolved stars from the THROES catalogue

2019 ◽  
Vol 622 ◽  
pp. A123 ◽  
Author(s):  
J. M. da Silva Santos ◽  
J. Ramos-Medina ◽  
C. Sánchez Contreras ◽  
P. García-Lario
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Strong Line ◽  
Order Estimate ◽  
Evolved Stars ◽  
Flux Variability ◽  
The Impact ◽  
Loss Rates

Context. This is the second paper of a series making use of Herschel/PACS spectroscopy of evolved stars in the THROES catalogue to study the inner warm regions of their circumstellar envelopes (CSEs). Aims. We analyse the CO emission spectra, including a large number of high-J CO lines (from J = 14–13 to J = 45–44, ν = 0), as a proxy for the warm molecular gas in the CSEs of a sample of bright carbon-rich stars spanning different evolutionary stages from the asymptotic giant branch to the young planetary nebulae phase. Methods. We used the rotational diagram (RD) technique to derive rotational temperatures (Trot) and masses (MH2) of the envelope layers where the CO transitions observed with PACS arise. Additionally, we obtained a first order estimate of the mass-loss rates and assessed the impact of the opacity correction for a range of envelope characteristic radii. We used multi-epoch spectra for the well-studied C-rich envelope IRC+10216 to investigate the impact of CO flux variability on the values of Trot and MH2. Results. The sensitivity of PACS allowed for the study of higher rotational numbers than before indicating the presence of a significant amount of warmer gas (∼200 − 900 K) that is not traceable with lower J CO observations at submillimetre/millimetre wavelengths. The masses are in the range MH2 ∼ 10−2 − 10−5 M⊙, anticorrelated with temperature. For some strong CO emitters we infer a double temperature (warm T¯rot ∼ 400 K and hot T¯rot ∼ 820 K) component. From the analysis of IRC+10216, we corroborate that the effect of line variability is perceptible on the Trot of the hot component only, and certainly insignificant on MH2 and, hence, the mass-loss rate. The agreement between our mass-loss rates and the literature across the sample is good. Therefore, the parameters derived from the RD are robust even when strong line flux variability occurs, and the major source of uncertainty in the estimate of the mass-loss rate is the size of the CO-emitting volume.

scholarly journals Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Doradus

2018 ◽  
Vol 609 ◽  
pp. A63 ◽  
Author(s):  
M. Van de Sande ◽  
L. Decin ◽  
R. Lombaert ◽  
T. Khouri ◽  
A. de Koter ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Gaussian Profile ◽  
Macro Scale ◽  
Abundance Profile ◽  
Envelope Model

Context. The stellar outflows of low- to intermediate-mass stars are characterised by a rich chemistry. Condensation of molecular gas species into dust grains is a key component in a chain of physical processes that leads to the onset of a stellar wind. In order to improve our understanding of the coupling between the micro-scale chemistry and macro-scale dynamics, we need to retrieve the abundance of molecules throughout the outflow. Aims. Our aim is to determine the radial abundance profile of SiO and HCN throughout the stellar outflow of R Dor, an oxygen-rich AGB star with a low mass-loss rate. SiO is thought to play an essential role in the dust-formation process of oxygen-rich AGB stars. The presence of HCN in an oxygen-rich environment is thought to be due to non-equilibrium chemistry in the inner wind. Methods. We analysed molecular transitions of CO, SiO, and HCN measured with the APEX telescope and all three instruments on the Herschel Space Observatory, together with data available in the literature. Photometric data and the infrared spectrum measured by ISO-SWS were used to constrain the dust component of the outflow. Using both continuum and line radiative transfer methods, a physical envelope model of both gas and dust was established. We performed an analysis of the SiO and HCN molecular transitions in order to calculate their abundances. Results. We have obtained an envelope model that describes the dust and the gas in the outflow, and determined the abundance of SiO and HCN throughout the region of the stellar outflow probed by our molecular data. For SiO, we find that the initial abundance lies between 5.5 × 10-5 and 6.0 × 10-5 with respect to H2. The abundance profile is constant up to 60 ± 10 R∗, after which it declines following a Gaussian profile with an e-folding radius of 3.5 ± 0.5 × 1013 cm or 1.4 ± 0.2 R∗. For HCN, we find an initial abundance of 5.0 × 10-7 with respect to H2. The Gaussian profile that describes the decline starts at the stellar surface and has an e-folding radius re of 1.85 ± 0.05 × 1015 cm or 74 ± 2 R∗. Conclusions. We cannot unambiguously identify the mechanism by which SiO is destroyed at 60 ± 10 R∗. The initial abundances found are higher than previously determined (except for one previous study on SiO), which might be due to the inclusion of higher-J transitions. The difference in abundance for SiO and HCN compared to high mass-loss rate Mira star IK Tau might be due to different pulsation characteristics of the central star and/or a difference in dust condensation physics.

scholarly journals An ALMA view of SO and SO2 around oxygen-rich AGB stars

2020 ◽  
Vol 494 (1) ◽  
pp. 1323-1347 ◽  
Author(s):  
T Danilovich ◽  
A M S Richards ◽  
L Decin ◽  
M Van de Sande ◽  
C A Gottlieb
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Energy Levels ◽  
High Mass ◽  
High Angular Resolution ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Abundance Distribution ◽  
High Mass Loss

ABSTRACT We present and analyse SO and SO2, recently observed with high angular resolution and sensitivity in a spectral line survey with ALMA, for two oxygen-rich AGB stars: the low mass-loss rate R Dor and high mass-loss rate IK Tau. We analyse 8 lines of SO detected towards both stars, 78 lines of SO2 detected towards R Dor, and 52 lines of SO2 detected towards IK Tau. We detect several lines of 34SO, 33SO, and 34SO2 towards both stars, and tentatively S18O towards R Dor, and hence derive isotopic ratios for these species. The spatially resolved observations show us that the two sulphur oxides are co-located towards R Dor and trace out the same wind structures in the circumstellar envelope. Much of the emission is well reproduced with a Gaussian abundance distribution spatially centred on the star. Emission from the higher energy levels of SO and SO2 towards R Dor provides evidence in support of a rotating inner region of gas identified in earlier work. The new observations allow us to refine the abundance distribution of SO in IK Tau derived from prior observations with single antennas, and confirm that the distribution is shell like with the peak in the fractional abundance not centred on the star. The confirmation of different types of SO abundance distributions will help fine-tune chemical models and allows for an additional method to discriminate between low and high mass-loss rates for oxygen-rich AGB stars.

scholarly journals Stellar Pulsation: (I) Analysis of Stability of Envelope

1993 ◽  
Vol 134 ◽  
pp. 167-168
Author(s):  
Yu Zhi-Yao
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Life Time ◽  
Circumstellar Envelope ◽  
Constant Mass ◽  
Mira Variable ◽  
Stellar Pulsation ◽  
Analysis Of Stability

AbstractThe life-time of the star on AGB is approximately 6 × 104 yr. We divide it into front half and back half of AGB (including to optical Mira variable and OH/IR star) according to their evolution character. The observations show that the star has non-pulsation, but constant mass loss rate (~ 5 × 10−7M⊙ yr−1) on front half of AGB. Its circumstellar envelope is formed. When the star has pulsation on back half of AGB, its mass loss rate is relative with time, and increases gradually. In this time the star is on the stage of optical Mira variable. When the mass loss rate reaches the value of ~ 3 × 10−6M⊙ yr−1, the star evoluted from the stage of optical variable into the stage of radio bright OH/IR star. On the end of AGB the mass loss rate reaches ~10−4M⊙ yr−1. (Band and Habing 1983, Hermen and Habing 1985).

Sign in / Sign up

Export Citation Format

Share Document