On the nature and mass loss of Bulge OH/IR stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 353-354
Author(s):  
Joris A. D. L. Blommaert ◽  
Martin A. T. Groenewegen ◽  
Kay Justtanont ◽  
L. Decin
Keyword(s):  
Mass Loss ◽  
Total Mass ◽  
Photometric Data ◽  
Galactic Latitude ◽  
Agb Stars ◽  
High Galactic Latitude ◽  
Total Mass Loss ◽  
Successful Search ◽  
Ir Stars ◽  
Transfer Modelling

AbstractWe report on the successful search for CO (2-1) and (3-2) emission associated with OH/IR stars in the Galactic Bulge. We observed a sample of eight extremely red AGB stars with the APEX telescope and detected seven. The sources were selected at sufficient high Galactic latitude to avoid interference by interstellar CO, which hampered previous studies of inner galaxy stars. We also collected photometric data and Spitzer IRS spectroscopy to construct the SEDs, which were analysed through radiative transfer modelling. We derived variability periods of our stars from the VVV and WISE surveys. Through dynamical modelling we then retrieve the total mass loss rates (MLR) and the gas-to-dust ratios. The luminosities range between approximately 4,000 and 5,500 L⊙ and periods are below 700 days. The total MLR ranges between 10−5 and 10−4 M⊙ yr−1. The results are presented in Blommaert et al. 2018 and summarized below.

scholarly journals Possible Proto-Planetary Nebulae

1989 ◽  
Vol 106 ◽  
pp. 384-390
Author(s):  
M. Parthasarathy
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Planetary Nebulae ◽  
Evolutionary Stage ◽  
Galactic Latitude ◽  
Agb Stars ◽  
Recent Past ◽  
High Galactic Latitude ◽  
Dust Shells

AbstractIRAS data for high-galactic-latitude F supergiants, a few luminous F-G stars, and a few peculiar (forbidden) emission-line stars reveal they have dust shells with characteristics similar to those observed in planetary nebulae. The objects described here appear to have experienced severe mass loss in the recent past on the AGB. These stars are most likely post-AGB stars or evolving from the tip of AGB towards the left in the H-R diagram and may be described as possible proto-planetary nebulae. From the IRAS data we find ten additional possible proto-planetary nebulae. From the IRAS data of HD 56126, -53° 5072, HD 168625 and -59° 6723 the luminosities, temperatures and masses of the dust shells are derived. HD 56126 (F5I), HD 168625 (B8Iae), and -59° 6723 (B8Iae) appear to be in an evolutionary stage (post-AGB) similar to that of HD 161796 and HR 4049.

Leaching of Am-241 from a Radioactive Waste Glass Corroded in the Presence of Stainless Steel Corrosion Products and/or Bentonite

1987 ◽  
Vol 112 ◽  
Author(s):  
Masaki Tsukamoto ◽  
Inga-Kari Björner ◽  
Hilbert Christensen ◽  
Hans-Peter Hermansson ◽  
Lars Werme
Keyword(s):  
Stainless Steel ◽  
Radioactive Waste ◽  
Mass Loss ◽  
Total Mass ◽  
Corrosion Behaviour ◽  
Steel Corrosion ◽  
Waste Glass ◽  
Corrosion Products ◽  
Total Mass Loss ◽  
Elemental Mass

AbstractThe release of Am-241 during corrosion of the radioactive waste glass, JSS-A, has been studied in the presence of corrosion products and/or uncom-pacted bentonite. The corrosion behaviour of Am-241 has been analyzed using gamma spectrometry. Adsorption of Am-241 on bentonite is observed in all cases. The contents of Am-241 in centrifuged leachates are in most cases less than 1/100 of total values. The normalized elemental mass loss of Am increases initially with corrosion time, and the values in the presence of bentonite and corrosion products are larger than those in the presence of bentonite alone. This tendency is in agreement with results previously found for other elements. The release of Am is low, only about 10–20 % of the corresponding total mass loss.

Dose-Rate Dependence of Radiation Damage in Polymers

1998 ◽  
Vol 4 (S2) ◽  
pp. 800-801
Author(s):  
R.F. Egerton ◽  
I. Rauf
Keyword(s):  
Energy Loss ◽  
Mass Loss ◽  
Dose Rate ◽  
Radiation Damage ◽  
Total Mass ◽  
Room Temperature ◽  
Low Loss ◽  
Total Mass Loss ◽  
Diffraction Patterns ◽  
Accumulated Dose

Three aspects of radiation damage are of concern to electron microscopists: changes in crystallographic or molecular structure, mass loss and change in chemical composition. Structural change can be monitored from the fading of diffraction patterns or from loss of fine structure in an energy-loss spectrum. Total mass loss, in the form of a reduction in inelastic-scattering power, can be observed from the low-loss spectrum. Mass loss can also be monitored from energy-loss ionization edges, with the advantage that the loss of particular elements can be studied separately. It is possible to assign a characteristic dose De for the disappearance of a particular element.At room temperature, the amount of damage usually depends on the accumulated dose (exposure) but not on the dose rate (current density). However, cooling the specimen tends to reduce mass loss, probably because of the reduced diffusion coefficients.

scholarly journals Wintertime storage of water in buried supraglacial lakes across the Greenland Ice Sheet

2014 ◽  
Vol 8 (4) ◽  
pp. 3999-4031 ◽  
Author(s):  
L. S. Koenig ◽  
D. J. Lampkin ◽  
L. N. Montgomery ◽  
S. L. Hamilton ◽  
J. B. Turrin ◽  
...  
Keyword(s):  
Mass Loss ◽  
Total Mass ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Subsurface Water ◽  
Blue Color ◽  
Total Mass Loss ◽  
Supraglacial Lakes ◽  
Hydrologic System ◽  
Surface Melt

Abstract. Surface melt over the Greenland Ice Sheet (GrIS) is increasing and estimated to account for half or more of the total mass loss. Little, however, is known about the hydrologic pathways that route surface melt within the ice sheet. In this study, we present over-winter storage of water in buried supraglacial lakes as one hydrologic pathway for surface melt, referred to as buried lakes. Airborne radar echograms are used to detect the buried lakes that are distributed extensively around the margin of the GrIS. The subsurface water can persist through multiple winters and is, on average, ~4.2 + 0.4 m below the surface. The few buried lakes that are visible at the surface of the GrIS have a~unique visible signature associated with a darker blue color where subsurface water is located. The volume of retained water in the buried lakes is likely insignificant compared to the total mass loss from the GrIS but the water will have important implications locally for the development of the englacial hydrologic network, ice temperature profiles and glacial dynamics. The buried lakes represent a small but year-round source of meltwater in the GrIS hydrologic system.

scholarly journals Obscured AGB Stars in the LMC

1995 ◽  
Vol 155 ◽  
pp. 427-428 ◽  
Author(s):  
Albert Zijlstra ◽  
Cecile Loup ◽  
Rens Waters ◽  
Patricia Whitelock ◽  
Francois Guglielmo
Keyword(s):  
Mass Loss ◽  
Agb Stars ◽  
Ir Stars ◽  
The Galaxy ◽  
Loss Rates

AbstractWe have carried out a search for obscured AGB stars in the LMC, observing fields in the vicinity of faint IRAS sources. About 25 heavily reddened AGB stars were found, with bolometric magnitudes close to the classical AGB limit of Mbol = −7.1. 10−µm. photometry for 5 sources show that these are oxygen-rich; they are similar to the Galactic OH/IR stars. Mass-loss rates vary between 5×10−4 and 2×10−6 M⊙ yr−1. We find no evidence that the mass-loss rates vary with luminosity. Neither do the mass-loss rates differ in a clear systematic way between the SMC and the LMC. The expansion velocities appear to be slightly lower in the LMC than in the Galaxy. All of the luminous stars for which periods are available have luminosities significantly above the period-luminosity relation derived for optical LMC Miras.

scholarly journals Wintertime storage of water in buried supraglacial lakes across the Greenland Ice Sheet

2015 ◽  
Vol 9 (4) ◽  
pp. 1333-1342 ◽  
Author(s):  
L. S. Koenig ◽  
D. J. Lampkin ◽  
L. N. Montgomery ◽  
S. L. Hamilton ◽  
J. B. Turrin ◽  
...  
Keyword(s):  
Mass Loss ◽  
Total Mass ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Expression ◽  
Subsurface Water ◽  
Blue Color ◽  
Total Mass Loss ◽  
Supraglacial Lakes ◽  
Hydrologic System

Abstract. Increased surface melt over the Greenland Ice Sheet (GrIS) is now estimated to account for half or more of the ice sheet's total mass loss. Here, we show that some meltwater is stored, over winter, in buried supraglacial lakes. We use airborne radar from Operation IceBridge between 2009 and 2012 to detect buried supraglacial lakes, and we find that they were distributed extensively around the GrIS margin through that period. Buried supraglacial lakes can persist through multiple winters and are, on average, ~ 1.9 + 0.2 m below the surface. Most buried supraglacial lakes exist with no surface expression of their occurrence in visible imagery. The few buried supraglacial lakes that do exhibit surface expression have a unique visible signature associated with a darker blue color where subsurface water is located. The volume of retained water in the buried supraglacial lakes is likely insignificant compared to the total mass loss from the GrIS, but the water may have important implications locally for the development of the englacial hydrologic system and ice temperatures. Buried supraglacial lakes represent a small but year-round source of meltwater in the GrIS hydrologic system.

scholarly journals Probing chemical processes in AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 201-206 ◽  
Author(s):  
Fredrik L. Schöier ◽  
Hans Olofsson
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Line Emission ◽  
Chemical Processes ◽  
Agb Stars ◽  
Molecular Line ◽  
Large Sample ◽  
Preliminary Results ◽  
Transfer Modelling ◽  
Non Equilibrium

AbstractWe are conducting multi-transition observations of circumstellar line emission from common molecules such as HCN, SiO, CS, SiS and CN for a large sample of AGB stars with varying photospheric C/O-ratios and mass-loss charachteristics. Our recently published results for SiO and SiS clearly show that major constraints on the relative roles of non-equilibrium chemistry, dust condensation, and photodissociation can be obtained from the study of circumstellar molecular line emission. Presented here are also preliminary results based on detailed radiative transfer modelling of HCN line emission.

scholarly journals The Evolution of AGB Stars

1992 ◽  
Vol 9 ◽  
pp. 617-619 ◽  
Author(s):  
P.R. Wood ◽  
E. Vassiliadis
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Stellar Evolution ◽  
Large Mass ◽  
Dual Process ◽  
Radial Pulsation ◽  
Agb Stars ◽  
Carbon Stars ◽  
Ir Stars ◽  
Loss Rates

Computations of AGB stellar evolution which include the effects of mass loss are still relatively rare. However, in order to relate numbers of Mira variables, OH/IR stars and carbon stars to associated stellar populations, it is necessary to understand evolutionary timescales on the AGB.The dominant factors controlling very late AGB evolution are shell flashes and mass loss, and some quantitative estimate of the latter is needed for stellar evolution calculations. The favoured mechanism for the production of the large mass loss rates observed in late AGB stars such as OH/IR stars and dust-enshrouded carbon stars, which have mass loss rates up to a few times 10−5 M⊙ yr−1 (see van der Veen and Rugers 1989 for a compilation), is a dual process involving the lévitation of matter above the photosphere by large-amplitude radial pulsation followed by the formation of grains on which radiation pressure acts to drive the circumstellar material away from the star (Castor 1981; Holzer and MacGregor 1985; Hearn 1990). The studies by Wood (1979) and Bowen (1988) show that, by themselves, neither pulsation nor radiation pressure acting on grains can produce the very large mass loss rates from AGB stars.

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