Red Giant Mass Loss Research Articles

The Active Chromospheres of Lithium-rich Red Giant Stars* * Based on observations obtained with the Hobby–Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

We have gathered near-infrared zyJ-band high-resolution spectra of nearly 300 field red giant stars with known lithium abundances in order to survey their He i λ10830 absorption strengths. This transition is an indicator of chromospheric activity and/or mass loss in red giants. The majority of stars in our sample reside in the red clump or red horizontal branch based on their V − J, M V color–magnitude diagram, and Gaia T eff and log(g) values. Most of our target stars are Li-poor in the sense of having normally low Li abundances, defined here as log ϵ(Li) < 1.25. Over 90% of these Li-poor stars have weak λ10830 features. However, more than half of the 83 Li-rich stars (log ϵ(Li) > 1.25) have strong λ10830 absorptions. These large λ10830 lines signal excess chromospheric activity in Li-rich stars; there is almost no indication of significant mass loss. The Li-rich giants may also have a higher binary fraction than Li-poor stars, based on their astrometric data. It appears likely that both residence on the horizontal branch and present or past binary interaction play roles in the significant Li–He connection established in this survey.

SIMULATIONS OF THE SYMBIOTIC RECURRENT NOVA V407 CYG. I. ACCRETION AND SHOCK EVOLUTIONS

The shock interaction and evolution of nova ejecta with a wind from a red giant star in a symbiotic binary system are investigated via three-dimensional hydrodynamics simulations. We specifically model the March 2010 outburst of the symbiotic recurrent nova V407~Cygni from the quiescent phase to its eruption phase. The circumstellar density enhancement due to wind-white dwarf interaction is studied in detail. It is found that the density-enhancement efficiency depends on the ratio of the orbital speed to the red giant wind speed. Unlike another recurrent nova, RS~Ophiuchi, we do not observe a strong disk-like density enhancement, but instead observe an aspherical density distribution with $\sim 20\%$ higher density in the equatorial plane than at the poles. To model the 2010 outburst, we consider several physical parameters, including the red giant mass loss rate, nova eruption energy, and ejecta mass. A detailed study of the shock interaction and evolution reveals that the interaction of shocks with the red giant wind generates strong Rayleigh-Taylor instabilities. In addition, the presence of the companion and circumstellar density enhancement greatly alter the shock evolution during the nova phase. The ejecta speed after sweeping out most of the circumstellar medium decreases to $\sim 100-300$ km-s$^{-1}$, depending on model, which is consistent with the observed extended redward emission in [N~II] lines in April 2011.

Mass Loss from Evolved Stars in Elliptical Galaxies

Most of the X-ray emitting gas in early-type galaxies probably originates from red giant mass loss and here we model the interaction between this stellar mass loss and the hot ambient medium. Using two-dimensional hydrodynamic simulations, we adopt a temperature for the ambient medium of 3E6 K along with a range of ambient densities and stellar velocities. When the stellar velocity is supersonic relative to the ambient medium, a bow shock occurs, along with a shock driven into the stellar ejecta, which heats only a fraction of the gas. Behind the bow shock, a cool wake develops but the fast flow of the hot medium causes Kelvin-Helmholtz instabilities to grow and these fingers are shocked and heated (without radiative cooling). Along with the mixing of this wake material with the hot medium, most of the stellar ejecta is heated to approximately the temperature of the hot ambient medium within 2 pc of the star. With the addition of radiative cooling, some wake material remains cool (< 1E5 K), accounting for up to 25% of the stellar mass loss. Less cooled gas survives when the ambient density is lower or when the stellar velocity is higher than in our reference case. These results suggest that some cooled gas should be present in the inner part of early-type galaxies that have a hot ambient medium. These calculations may explain the observed distributed optical emission line gas as well as the presence of dust in early-type galaxies.

The contribution of halo red giant mass loss to the high-velocity gas falling onto the Milky Way disk

The origin of gas falling from the halo toward the disk of the Milky Way is still largely unclear. Here the amount of gas shed by the (older) halo red giants is estimated. The distribution of red giants (RGs) in the halo is not known but that of a subset of stars in the post RG phase, the sdB stars of the horizontal-branch (HB), is. Using the mid-plane density and z-distribution of sdB stars, the ratio of sdB stars to all HB stars, and the RG mass loss, the infall due to total mass lost by all halo RG stars at kpc is calculated. For the extended halo component kpc-2 yr-1 while the thick disk component RGs contribute kpc-2 yr-1, each with an uncertainty of a factor 4. The total rate of infall due to RG mass-loss is kpc-2 yr-1, a sizeable fraction of the equally uncertain observed rate of infall of material. Since most of the RG stars in the extended halo are old, their mass loss is predominantly metal-poor, while that of the disk RGs is more metal-rich. The galactic fountain flow provides additional metal-rich infall and small galaxies being accreted contribute to the infall of gas as well.

Onset of Shear Instability in Rotating Red Giants

We incorporate into an evolutionary code a unified treatment of turbulent transport due to convective and shear instabilities in a rotating star. The effects of composition gradients are included in a consistent way. We use the code to follow the evolution of rotating stars from the pre-main sequence to near the tip of the red giant branch. We find that at a certain stage in the red giant evolution of a 1 M☉ star, when the convectively unstable region occupies an extensive outer envelope, shear instability sets in in a zone just below the H-burning shell. However, at a later time, shear instability also develops in a second (outer) region that lies between the H-burning shell and the convective envelope. The onset of the outer region of shear instability coincides closely in time with a well-defined feature of red giant evolution: the "bump" (so-called because of its effect on the luminosity function of clusters). This evolutionary bump has recently been identified as a significant empirical marker among red giants: cool massive winds have been found to set in abruptly after the star evolves through the bump. The results we report in the present paper suggest that the onset of mass loss in red giants may be correlated with the onset of an outer region of shear instability inside the star. We offer some speculations concerning the possible physics of such a correlation.

Onset of Mass Loss in Red Giants: Association with an Evolutionary Event

Stencel & Mullan used asymmetries in the Mg II k emission profile to determine the location of a velocity dividing line (VDL) in the H-R diagram. Stars to the right of (and above) the VDL were observed to have asymmetries that are consistent with the presence of cool massive winds. Stars to the left of (and below) the VDL showed no evidence for winds. We show that the VDL lies close to a certain event of stellar evolution on the red giant branch (RGB). The event occurs when the hydrogen-burning shell evolves outward through a discontinuity in molecular weight. In some low-mass stars, this event causes a kink in the evolutionary track of an individual low-mass star. In a cluster, the combined effects of such kinks create a bump in the luminosity function. Our result suggests that evolution through the kink (or bump) on the RGB is associated with the onset of a cool massive wind. Theoretical possibilities to explain this association will be explored in a subsequent paper.

A CORAVEL radial-velocity monitoring of S stars: Symbiotic activity vs. orbital separation. III.

Orbital elements are presented for the Tc-poor S stars HR 363 (= HD 7351) and HD 191226. With an or- bital period of 4592 d (=12.6 y), HR 363 has the longest period known among S stars, and yet it is a strong X-ray source. Its X-ray flux is similar to that of HD 35155, an S star with one of the shortest orbital periods (640 d). This surprising result is put in perspective with other diagnos- tics of binary interaction observed in binary S stars. They reveal that there is no correlation between the level of bi- nary interaction and the orbital period. All these activity diagnostics moreover exhibit a strong time-variability. In the well-documented case of HR 1105, this time-variability appears to be a combination of orbital modulation and secular variation. A stream of gas from the red-giant wind, which is heated when funneled through the inner Lagrangian point, has been proposed as the source of the hard photons (Shcherbakov & Tuominen 1992). Dierent viewing angles of the stream during the orbital cycle ac- count for the orbital modulation, whereas long-term fluc- tuations of the mass-loss rate account for the secular vari- ations. Little dependence to the orbital separation is ex- pected for this kind of activity. If such streams are causing the activity observed in the other binary S stars as well, it would provide a natural explanation for the absence of correlation between orbital periods and activity levels, since the red-giant mass loss rate would be the dominant factor. The existence of such funneled streams is moreover predicted by smooth particle hydrodynamics simulations of mass transfer in detached binary systems.

Illumination in Symbiotic Binary Stars: Non‐LTE Photoionization Models. II. Wind Case

We describe a non-LTE photoionization code to calculate the wind structure and emergent spectrum of a red giant wind illuminated by the hot component of a symbiotic binary system. We consider spherically symmetric winds with several different velocity and temperature laws and derive predicted line fluxes as a function of the red giant mass loss rate, \mdot. Our models generally match observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8} \msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant wind as viewed from the hot component is a crucial parameter in these models. Winds with cross-sections of 2--3 red giant radii reproduce the observed fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models favor winds with acceleration regions that either lie far from the red giant photosphere or extend for 2--3 red giant radii.

Red Giant Mass Loss and Planetary Nebula Formation

It is generally believed that red giant mass loss plays some role in the formation of planetary nebulae (PNe), but the connection is not clearly understood. To investigate this issue we have undertaken an extensive search for molecular gas in PNe, which is likely to be remnant material of the red giant wind not yet ionized by the central star. The search has been carried out with the NRAO 12 m telescope in the 1.3 mm line of 00 which is widely observable in the molecular winds of red giants.

Pulsations Grain Condensation and Mass Loss in Long-Period Variable Stars

The role of pulsations on the rate of dust condensation and associated mass loss in red giants is discussed. Pulsations result in an increase of the atmospheric scale height which can enhance mass loss by several orders of magnitude. We stress that such effects should be included in attempts to model this mass loss mechanism.

Mass loss in red giants and supergiants

The circumstellar envelopes surrounding late-type giants and supergiants were studied using high resolution, photoelectric scans of strong optical resonance lines. A method for extracting the circumstellar from the stellar components of the lines allowed a quantitative determination of the physical conditions in the envelopes and the rates of mass loss at various positions in the red giant region of the HR diagram. The observed strengthening of the circumstellar spectrum with increasing luminosity and later spectral type is probably caused by an increase in the mass of the envelopes. The mass loss rate for individual stars is proportional to the visual luminosity; high rates for the supergiants suggest that mass loss is important in their evolution. The bulk of the mass return to the interstellar medium in the red giant region comes from the normal giants, at a rate comparable to that of planetary nebulae.

Mass loss in red giants and supergiants

view Abstract Citations (11) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass loss in the red giants and supergiants. Sanner, F. Abstract The circumstellar envelopes surrounding 13 late-type giants and supergiants have been studied using a homogeneous collection of high-resolution, photoelectric scans of strong optical resonance lines. Various properties of the envelopes, including the mass loss rate, dilution factor, hydrogen density, and degree of ionization, have been determined quantitatively. Publication: The Astrophysical Journal Pub Date: February 1976 DOI: 10.1086/182050 Bibcode: 1976ApJ...204L..41S Keywords: Giant Stars; Late Stars; Mass Transfer; Stellar Envelopes; Stellar Spectrophotometry; Supergiant Stars; Graphs (Charts); M Stars; Mass Flow Rate; Optical Resonance; Photoelectric Emission; Stellar Luminosity; Astrophysics full text sources ADS | data products SIMBAD (12)

Radiation pressure on grains as a mechanism for mass loss in red giants

Radiation pressure on grains as a mechanism for mass loss in red giants

The Solar Wind – an Example of a Cosmical Plasma and a Stellar Wind

When Parker developed the theory of the solar wind, he suggested that other stars might also be surrounded by an expanding atmosphere. This suggestion has been worked out by Deutsch (1958, 1960, 1961, 1969) and by Weymann (1960, 1963), who discussed coronal evaporation as a possible mechanism for mass loss in red giants and used hydrodynamical equations for describing the phenomena. During the last few years detailed observations of the solar wind have been made, and the theoretical approach has also been further developed. Both might help us in our understanding of problems of a quasi-stationary mass loss of stars. But besides its relevance for the study of other stellar winds, the solar wind is important, as it is the best observed cosmical plasma available for guidance in the study of other cosmical, collisionless plasmas. What makes the interplanetary plasma so important is that beyond several solar radii from the Sun there are no collisions among the gas particles (one solar radius [R⊙] is 7.0 × 1010 cm; 1 AU is 215 R⊙). Only near the Sun the collision rate is sufficiently high to maintain isotropy of the thermal particle motions and to produce ordinary fluid behavior. At larger distances from the Sun the fluid behavior is maintained by irregularities in weak magnetic fields and by micro-instabilities in the plasma.

Coronal Evaporation as a Possible Mechanism for Mass Loss in Red Giants.

view Abstract Citations (55) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Coronal Evaporation as a Possible Mechanism for Mass Loss in Red Giants. Weymann, Ray Abstract The consequences ot the possible existence of a corona of a red giant are investigated from a hydrodynamic p ] of view, under the assumption that depdsition 6f mechanical energy is confined to a narrow layer just above the surface of the star. Because of tbe energy losses due to radiation, steady sub- sonic flows do not exist, and only under special circumstances can hydrostatic solutions exist. In contrast, steady supersonic flows can exist, and tbe mass loss accompanying them would be significant from an eyolutionary point of view. However, investigation of the observational consequences of such fl6ws rules them `out because of the expected presence of lines displaced toward much higher velocities ihan those actually observed. Other possible models for mass .ejection are briefly discussed. Publication: The Astrophysical Journal Pub Date: September 1960 DOI: 10.1086/146937 Bibcode: 1960ApJ...132..380W full text sources ADS |

Mass loss in red giants

On high-dispersion spectrograms of some luminous M giants, the zero-volt lines of all abundant atoms and ions are double. (Fig. 1 (a), Pl. I, p. 112). This spectroscopic peculiarity was discovered by W. S. Adams and Miss MacCormack (1935), who wrote that “a possible explanation of the origin of the abnormal lines…… may be an envelope of gas surrounding the stars and expanding with a moderate velocity”. Recently it was found that some of the abnormal lines which occur in the M 5 II star α Herculis can also be seen in the spectrum of its visual companion, a giant G-type star. In this system, it is clear that the Adams-MacCormack model is correct: both stars are enveloped in gas that has been ejected from the M star (Fig. 2). Moreover, the circumstellar envelope of α Herculis must measure at least 2000 astronomical units in diameter, and in it the gas velocity exceeds the velocity of escape. The M star is clearly losing mass to the interstellar medium at a rate that has been estimated to be a about 10−7 solar masses per year.