scholarly journals Widespread HCN maser emission in carbon-rich evolved stars

2018 ◽  
Vol 613 ◽  
pp. A49 ◽  
Author(s):  
K. M. Menten ◽  
F. Wyrowski ◽  
D. Keller ◽  
T. Kamiński
Keyword(s):  
Mass Loss ◽  
Excited States ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Velocity Range ◽  
Vibrationally Excited ◽  
Maser Emission ◽  
Evolved Stars ◽  
Maser Line ◽  
Maser Action

Context. HCN is a major constituent of the circumstellar envelopes of carbon-rich evolved stars, and rotational lines from within its vibrationally excited states probe parts of these regions closest to the stellar surface. A number of such lines are known to show maser action. Historically, in one of them, the 177 GHz J = 2 → 1 line in the l-doubled bending mode has been found to show relatively strong maser action, with results only published for a single object, the archetypical high-mass loss asymptotic giant branch (AGB) star IRC+10216. Aims. To examine how common 177 GHz HCN maser emission is, we conducted an exploratory survey for this line toward a select sample of carbon-rich asymptotic giant branch stars that are observable from the southern hemisphere. Methods. We used the Atacama Pathfinder Experiment 12 meter submillimeter Telescope (APEX) equipped with a new receiver to simultaneously observe three J = 2 → 1 HCN rotational transitions, the (0, 11c, 0) and (0, 11d, 0) l-doublet components, and the line from the (0,0,0) ground state. Results. The (0, 11c, 0) maser line is detected toward 11 of 13 observed sources, which all show emission in the (0,0,0) transition. In most of the sources, the peak intensity of the (0, 11c, 0) line rivals that of the (0,0,0) line; in two sources, it is even stronger. Except for the object with the highest mass-loss rate, IRC+10216, the (0, 11c, 0) line covers a smaller velocity range than the (0,0,0) line. The (0, 11d, 0) line, which is detected in four of the sources, is much weaker than the other two lines and covers a velocity range that is smaller yet, again except for IRC+10216. Compared to its first detection in 1989, the profile of the (0, 11c, 0) line observed toward IRC+10216 looks very different, and we also appear to see variability in the (0,0,0) line profile (at a much lower degree). Our limited information on temporal variabilitydisfavors a strong correlation of maser and stellar continuum flux. Conclusions. Maser emission in the 177 GHz J = 2 → 1 (0, 11c, 0) line of HCN appears to be common in carbon-rich AGB stars. Like for other vibrationally excited HCN lines, our observations indicate that the origin of these lines is in the acceleration zone of the stellar outflow in which dust is forming. For all the stars toward which we detect the maser line, the number of photons available at 7 and 14 μm, corresponding to transitions to vibrationally excited states possibly involved in its pumping, is found to be far greater than that of the maser photons, which makes radiative pumping feasible. Other findings point to a collisional pumping scheme, however.

Millimetre Observations of Evolved Stars

1996 ◽  
Vol 13 (2) ◽  
pp. 185-186
Author(s):  
Jessica M. Chapman
Keyword(s):  
Mass Loss ◽  
Stellar Atmosphere ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
High Mass Loss ◽  
Transfer Momentum

Radio emission at centimetre and millimetre wavelengths provides a powerful tool for studying the circumstellar envelopes of evolved stars. These include stars on the asymptotic giant branch (AGB), post-AGB stars and a small number of massive M-type supergiant stars. The AGB stars and M-type supergiants are characterised by extremely high mass-loss rates. The mass loss in such an evolved star is driven by radiation pressure acting on grains which form in the outer stellar atmosphere. The grains are accelerated outwards and transfer momentum to the gas through grain–gas collisions. The outflowing dust and gas thus form an expanding circumstellar envelope through which matter flows from the star to the interstellar medium, at a typical velocity of 15 km s−1. For a recent review of circumstellar mass loss see Chapman, Habing & Killeen (1995).

scholarly journals Warm CO in evolved stars from the THROES catalogue

2018 ◽  
Vol 618 ◽  
pp. A171 ◽  
Author(s):  
J. Ramos-Medina ◽  
C. Sánchez Contreras ◽  
P. García-Lario ◽  
J. M. da Silva Santos
Keyword(s):  
Mass Loss ◽  
Total Mass ◽  
Loss Rate ◽  
Rotational Temperature ◽  
Mass Loss Rate ◽  
Radial Profile ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Physical Parameters ◽  
Evolved Stars

In this work (Paper I), we analyse Herschel-PACS spectroscopy for a subsample of 23 O-rich and 3 S-type evolved stars, in different evolutionary stages from the asymptotic giant branch (AGB) to the planetary nebula (PN) phase, from the THROES catalogue. (C-rich targets are separately studied in Paper II). The broad spectral range covered by PACS (∼55–210 μm) includes a large number of high-J CO lines, from J = 14 − 13 to J = 45 − 44 (v = 0), that allow us to study the warm inner layers of the circumstellar envelopes (CSEs) of these objects, at typical distances from the star of ≈1014–1015 cm and ≈1016 cm for AGBs and post-AGB-PNe, respectively. We have generated CO rotational diagrams for each object to derive the rotational temperature, total mass within the CO-emitting region and average mass-loss rate during the ejection of these layers. We present first order estimations of these basic physical parameters using a large number of high-J CO rotational lines, with upper-level energies from Eup ∼ 580 to 5000 K, for a relatively big set of evolved low-to-intermediate mass stars in different AGB-to-PN evolutionary stages. We derive rotational temperatures ranging from Trot ∼ 200 to 700 K, with typical values around 500 K for AGBs and systematically lower, ∼200 K, for objects in more advanced evolutionary stages (post-AGBs and PNe). Our values of Trot are one order or magnitude higher than the temperatures of the outer CSE layers derived from low-J CO line studies. The total mass of the inner CSE regions where the PACS CO lines arise is found to range from MH2 ∼ 10−6 to ≈10−2 M⊙, which is expected to represent a small fraction of the total CSE mass. The mass-loss rates estimated are in the range Ṁ ∼ 10−7 − 10−4 M⊙yr−1, in agreement (within uncertainties) with values found in the literature. We find a clear anticorrelation between MH2 and Ṁ vs. Trot that probably results from a combination of most efficient line cooling and higher line opacities in high mass-loss rate objects. For some strong CO emitters in our sample, a double temperature (hot and warm) component is inferred. The temperatures of the warm and hot components are ∼400–500 K and ∼600–900 K, respectively. The mass of the warm component (∼10−5–8 × 10−2 M⊙) is always larger than that of the hot component, by a factor of between two and ten. The warm-to-hot MH2 and Trot ratios in our sample are correlated and are consistent with an average temperature radial profile of ∝ r−0.5 ± 0.1, that is, slightly shallower than in the outer envelope layers, in agreement with recent studies.

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 Wind morphology around cool evolved stars in binaries

2020 ◽  
Vol 637 ◽  
pp. A91 ◽  
Author(s):  
I. El Mellah ◽  
J. Bolte ◽  
L. Decin ◽  
W. Homan ◽  
R. Keppens
Keyword(s):  
Mass Loss ◽  
Adaptive Mesh Refinement ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Large Fraction ◽  
Orbital Plane ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Evolved Stars

Context. The late evolutionary phase of low- and intermediate-mass stars is strongly constrained by their mass-loss rate, which is orders of magnitude higher than during the main sequence. The wind surrounding these cool expanded stars frequently shows nonspherical symmetry, which is thought to be due to an unseen companion orbiting the donor star. The imprints left in the outflow carry information about the companion and also the launching mechanism of these dust-driven winds. Aims. We study the morphology of the circumbinary envelope and identify the conditions of formation of a wind-captured disk around the companion. Long-term orbital changes induced by mass loss and mass transfer to the secondary are also investigated. We pay particular attention to oxygen-rich, that is slowly accelerating, outflows in order to look for systematic differences between the dynamics of the wind around carbon and oxygen-rich asymptotic giant branch (AGB) stars. Methods. We present a model based on a parametrized wind acceleration and a reduced number of dimensionless parameters to connect the wind morphology to the properties of the underlying binary system. Thanks to the high performance code MPI-AMRVAC, we ran an extensive set of 72 three-dimensional hydrodynamics simulations of a progressively accelerating wind propagating in the Roche potential of a mass-losing evolved star in orbit with a main sequence companion. The highly adaptive mesh refinement that we used, enabled us to resolve the flow structure both in the immediate vicinity of the secondary, where bow shocks, outflows, and wind-captured disks form, and up to 40 orbital separations, where spiral arms, arcs, and equatorial density enhancements develop. Results. When the companion is deeply engulfed in the wind, the lower terminal wind speeds and more progressive wind acceleration around oxygen-rich AGB stars make them more prone than carbon-rich AGB stars to display more disturbed outflows, a disk-like structure around the companion, and a wind concentrated in the orbital plane. In these configurations, a large fraction of the wind is captured by the companion, which leads to a significant shrinking of the orbit over the mass-loss timescale, if the donor star is at least a few times more massive than its companion. In the other cases, an increase of the orbital separation is to be expected, though at a rate lower than the mass-loss rate of the donor star. Provided the companion has a mass of at least a tenth of the mass of the donor star, it can compress the wind in the orbital plane up to large distances. Conclusions. The grid of models that we computed covers a wide scope of configurations: We vary the terminal wind speed relative to the orbital speed, the extension of the dust condensation region around the cool evolved star relative to the orbital separation, and the mass ratio, and we consider a carbon-rich and an oxygen-rich donor star. It provides a convenient frame of reference to interpret high-resolution maps of the outflows surrounding cool evolved stars.

scholarly journals SiO Masers in the Star Forming Regions W51 IRS2 and Sgr B2 MD5

1987 ◽  
Vol 115 ◽  
pp. 178-178
Author(s):  
N. Ukita ◽  
T. Hasegawa ◽  
N. Kaifu ◽  
K.-I. Morita ◽  
S. Okumura ◽  
...  
Keyword(s):  
Star Formation ◽  
Excited States ◽  
Line Intensity ◽  
Massive Star ◽  
Massive Star Formation ◽  
Vibrationally Excited ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
Upper Limit

The maser emission of the J = 1-0 lines of SiO in vibrationally excited states has been detected in two regions of massive star formation, W51 IRS2 and Sgr B2 MD5. The SiO masers apparently coincide with strong H2O masers in each source within the uncertainties of < 5″. Their velocity ranges fall within those of the nearest H2O masers (Figure 1). In W51 IRS2 the maser emission is observed only in the v = 2 state, and the upper limit of the v = 1 line (3σ) is 1/15th of the v = 2 line intensity. The v = 1 emission found in Sgr B2 MD5 is five times stronger than the marginally detected v = 2 emission (Figure 2). Their luminosities are comparable to those from the corresponding maser in Orion.

scholarly journals Chemical Peculiarities, Mass Loss, and Final Evolution of AGB Stars in the Magellanic Clouds

1988 ◽  
Vol 108 ◽  
pp. 31-37
Author(s):  
P.R. Wood
Keyword(s):  
Mass Loss ◽  
Great Majority ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Long Period ◽  
Evolved Stars ◽  
The Galaxy ◽  
Shed Light ◽  
Final Evolution

The Magellanic Clouds are sufficiently close that evolved stars which exhibit chemical peculiarities and the effects of mass loss can be readily observed. Such objects include carbon stars, S stars, long-period variables, OH/IR stars and planetary nebulae. Because of the relatively well-known distances of the Magellanic Clouds, the intrinsic luminosities of these objects can be accurately determined, in contrast to the situation in the Galaxy where the great majority of asymptotic giant branch (AGB) stars occur in the field population. In this review, observations of AGB stars in the Magellanic Clouds will be discussed with particular reference to those features which can shed light on mass loss and chemical peculiarities resulting from stellar evolution.

scholarly journals The first water fountain in a planetary nebula

2012 ◽  
Vol 8 (S287) ◽  
pp. 230-234
Author(s):  
Olga Suárez ◽  
José Francisco Gómez ◽  
Philippe Bendjoya ◽  
Luis. F. Miranda ◽  
Martín. A. Guerrero ◽  
...  
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Survival Times ◽  
Jet Formation ◽  
Evolved Stars ◽  
Water Masers ◽  
First Time ◽  
Water Maser

AbstractWater fountains are evolved stars showing water masers with velocity spanning more than ~100 km/s. They usually appear at the end of the Asymptotic Giant Branch (AGB) phase or at the beginning of the post-AGB phase, and their masers trace the first manifestation of axisymmetric collimated mass-loss. For the first time, masers with water fountain characteristics have been detected towards a PN (IRAS 15103–5754), which might require a revision of the current theories about jet formation and survival times. IRAS 15103-5754 was observed using the ATCA interferometer at 22 GHz (both continuum and water maser). The main results of these observations are summarized here. The evolutionary classification of this object is also discussed.

Isotopic SiO Maser Emission from the BAaDE Survey

2017 ◽  
Vol 13 (S336) ◽  
pp. 49-52
Author(s):  
M. J Claussen ◽  
M. R. Morris ◽  
Y. M. Pihlström ◽  
L. O. Sjouwerman ◽  
Keyword(s):  
Excited States ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Large Array ◽  
Line Profiles ◽  
Galactic Bulge ◽  
Late Type ◽  
Vibrationally Excited ◽  
Maser Emission ◽  
Very Large Array

AbstractThe Bulge Asymmetries and Dynamical Evolution (BAaDE) project aims to map the positions and velocities of up to ~20,000 late-type stars with SiO maser emission along the full Galactic plane, with a large concentration in the Galactic Bulge and inner Galaxy. Both J = 1 → 0 and J = 2 → 1 transitions using the Very Large Array (VLA) and the Atacama Large Millimeter Array (ALMA) are being observed. In the VLA observing setup, in addition to the 28SiO, v = 1 and v = 2J = 1 → 0 maser transitions, the bandwidth was wide enough to include the J = 1 → 0 transitions of the rare isotopologues of the SiO molecule in both the ground and vibrationally excited states: 29SiO, v = 0, 30SiO, v = 0, 29SiO, v = 1, and 29SiO, v = 2. Approximately 10% of the initial ~3500 targets of the project show maser emission from at least one of these lines. Some of these stars (with isotopic maser emission) show high radial velocities which implies that they are indeed in the Galactic Bulge or inner Galaxy (i.e. not foreground objects). We present line profiles, refined detection statistics, and the implications of the detection of the isotopic maser emission on pumping schemes that have been previously presented.

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