scholarly journals THERMAL MODIFICATION OF EUCALYPTUS WOOD AND USE FOR FLOORS OF LOW TRAFFIC ENVIRONMENTS

FLORESTA ◽  
2021 ◽  
Vol 51 (2) ◽  
pp. 457
Author(s):  
Claudio Gumane Francisco Juizo ◽  
Marcio Pereira Da Rocha ◽  
Ana Clara Moreira Morais ◽  
Carolina Nogueira Xavier ◽  
Mônica Bezerra De Oliveira ◽  
...  
Keyword(s):  
Mass Loss ◽  
Surface Hardness ◽  
Thermal Modification ◽  
High Mass ◽  
Concentrated Load ◽  
Ball Impact ◽  
Distributed Load ◽  
Eucalyptus Wood ◽  
High Mass Loss ◽  
Low Traffic

The aim of this work was to evaluate the effect of thermal modification on surface hardness and depressions by applying loads to obtain floors for low traffic environments. Four clones were used from which logs were obtained and split into boards dried in time, and grouped for testing in their natural condition (NT) and thermally modified at 200 degrees Celsius for four hours (T) in a schedule with a heating of 1 degree per minute, on electric oven. Then in the samples from each clone were evaluated the mass loss, specific gravity, lignin and holocelluloses content, Janka hardness, fall ball impact depressions, distributed load depressions, and concentrated load depressions using track equipment which transfer a load of 890N to the woods at a speed of 0.06 ms-1. In the results verified high mass loss in the E. grandis x E. urophylla clone from controlled polination. The lignin contents showed increases and holocelluloses contents showed significant decreases after thermal modification. There was a reduction in Janka hardness in the woods with the exception of E. urophylla clone which presented lower depressions in the fall ball test after thermal modification. Verified increasing in depressions in the concentrated and distributed load tests, after thermal modification. And the E. urophylla clone presented lower depressions after 25 and 50 passes respectively, being the most recommended for obtaining floors for saunas, garden decks, swimming pools as it does not require high loading requirements.

scholarly journals ISOCAM and DENIS Survey of 0.5 square degrees in the Bar of the LMC. Detection of the whole TP-AGB Star Population

1999 ◽  
Vol 191 ◽  
pp. 561-566
Author(s):  
C. Loup ◽  
E. Josselin ◽  
M.-R. Cioni ◽  
H.J. Habing ◽  
J.A.D.L. Blommaert ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Evolutionary Models ◽  
Agb Stars ◽  
Complete Sample ◽  
High Mass Loss ◽  
Low Mass ◽  
The One ◽  
Good Agreement ◽  
Loss Rates

We surveyed 0.5 square degrees in the Bar of the LMC with ISOCAM at 4.5 and 12 μm, and with DENIS in the I, J, and Ks bands. Our goal was to build a complete sample of Thermally-Pulsing AGB stars. Here we present the first analysis of 0.14 square degrees. In total we find about 300 TP-AGB stars. Among these TP-AGB stars, 9% are obscured AGB stars (high mass-loss rates); 9 of them were detected by IRAS, and only 1 was previously identified. Their luminosities range from 2 500 to 14 000 L⊙, with a distribution very similar to the one of optical TP-AGB stars (i.e. those with low mass-loss rates). Such a luminosity distribution, as well as the percentage of obscured stars among TP-AGB stars, is in very good agreement with the evolutionary models of Vassiliadis & Wood (1993) if most of the TP-AGB stars that we find have initial masses smaller than 1.5 to 2 M⊙.

scholarly journals Variable Winds in Early-B Hypergiants

1999 ◽  
Vol 169 ◽  
pp. 222-229
Author(s):  
Bernhard Wolf ◽  
Thomas Rivinius
Keyword(s):  
Mass Loss ◽  
Terminal Velocity ◽  
Spectral Lines ◽  
High Mass ◽  
High Dispersion ◽  
Echelle Spectrograph ◽  
Variability Pattern ◽  
Evolutionary Phase ◽  
High Mass Loss ◽  
Wind Velocities

AbstractEarly-B hypergiants belong to the most luminous stars in the Universe. They are characterized by high mass-loss rates (Ṁ ≈ 10−5Mʘyr−1) and low terminal wind velocities (v∞ʘ400 kms−1) implying very dense winds. They represent a short-lived evolutionary phase and are of particular interest for evolutionary theories of massive stars with mass loss. Due to their high luminosity they play a key role in connection with the “wind momentum - luminosity relation”. Among the main interesting characteristics of early-B hypergiants are the various kinds of photometric and spectroscopic variations. In several recent campaigns our group has performed extensive high dispersion spectroscopy of galactic early-B hypergiants with our fiber-fed echelle spectrograph FLASH/HEROS at the ESO-50 cm telescope. The main outcome was that their dense winds behave hydrodynamically differently to the less luminous supergiants of comparable spectral type. Outwardly accelerated propagating discrete absorption components of the P Cyg-type lines are the typical features rather than rotationally modulated line profile variations. These discrete absorptions could be traced in different spectral lines from photospheric velocities up to 75% of the terminal velocity. The stellar absorption lines show a pulsation-like radial velocity variability pattern lasting up to two weeks as the typical time scale. The radius variations connected with this pulsation-like motions are correlated with the emission height of the P Cyg-type profiles.

scholarly journals Observational connections between LBV’s and other stars, with emphasis on Wolf-Rayet stars

1989 ◽  
Vol 113 ◽  
pp. 229-240
Author(s):  
A. F. J. Moffat ◽  
L. Drissen ◽  
C. Robert
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Underlying Mechanism ◽  
High Mass ◽  
Strong Line ◽  
Essential Step ◽  
High Mass Loss ◽  
Loss Rates ◽  
R Domain

Abstract.We suggest that the LBV mechanism is an essential step to “force” massive stars (M(ZAMS) ≥ 40M⊙) to finally enter the Wolf-Rayet (W-R) domain in the Hertzsprung-Russel diagram (HRD). Just as massive supergiants showincreasingvariability as theyapproachthe Humphreys-Davidson (H-D)instability limit (horizontally in the HRD diagram), so the W-R stars showdecreasingvariability as theyrecede fromthe H-D limit (at first horizontally into the WNL domain, then, with their high mass loss rates, plunging irreversably downwards as ever hotter, smaller and fainter, strong-line W-R stars). Among the W-R stars, the luminous WNL subtypes (especially WN8) are the most variable, probably as a consequence of blob ejection in the wind. The underlying mechanism which triggers this ejection is possibly related to wind instabilities and may thus be quite different from the source of variability in luminous supergiants or LBV’s in quiescence, where photospheric effects dominate.

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 Luminous Blue Variables, cool hypergiants and some impostors in the H-R diagram

2003 ◽  
Vol 212 ◽  
pp. 38-46
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Surface Activity ◽  
Massive Star ◽  
Massive Stars ◽  
High Mass ◽  
Luminous Blue Variables ◽  
Star Evolution ◽  
High Mass Loss ◽  
Massive Star Evolution

Current observations of the S Dor/LBVs and candidates and the implications for their important role in massive star evolution are reviewed. Recent observations of the cool hypergiants are altering our ideas about their evolutionary state, their atmospheres and winds, and the possible mechanisms for their asymmetric high mass loss episodes which may involve surface activity and magnetic fields. Recent results for IRC+10420, ρ Cas and VY CMa are highlighted. S Dor/LBVs in eruption, and the cool hypergiants in their high mass loss phases with their optically thick winds are not what their apparent spectra and temperatures imply; they are then ‘impostors’ on the H-R diagram. The importance of the very most massive stars, like η Carinae and the ‘supernovae impostors’ are also discussed.

scholarly journals The O stars: optical review

1979 ◽  
Vol 83 ◽  
pp. 1-22
Author(s):  
J. B. Hutchings
Keyword(s):  
Neutron Star ◽  
Interstellar Medium ◽  
Mass Loss ◽  
Large Fraction ◽  
Significant Fraction ◽  
High Mass ◽  
X Ray ◽  
The Galaxy ◽  
High Mass Loss ◽  
Rough Outline

I would like to start with a quick overview of the O stars - their significance and role in the galaxy and in astrophysics - just to remind ourselves of why we are here and what we hope to talk about. In Table 1 I show a rough outline of the contribution of O stars to what happens in the galaxy as a whole. Because of their extreme luminosity, they contribute a large fraction of the radiation of the galaxy, while forming a very tiny group of objects and mass. Because of their short lifetime they are a population that has gone through 104 generations in the life of the galaxy. Their high mass loss rates may account for a large fraction of the new matter injected into the interstellar medium, and they probably power some significant fraction of the hard X-ray sources in the galaxy, by virtue of the fact that a companion can become a neutron star a) without disrupting the binary and b) while the companion is still a mass losing O star.

scholarly journals Close binary models for Luminous Blue Variable stars

1989 ◽  
Vol 113 ◽  
pp. 185-194
Author(s):  
J. S. Gallagher
Keyword(s):  
Mass Loss ◽  
Binary Stars ◽  
Mass Loss Rate ◽  
Variable Stars ◽  
High Mass ◽  
Close Binary ◽  
Close Binaries ◽  
System A ◽  
Close Binary Stars ◽  
High Mass Loss

AbstractThe evolution of massive close binary stars inevitably involves mass exchange between the two stellar components as well as mass loss from the system. A combination of these two processes could produce the stellar wind-modulated behavior seen in LB Vs. The possibility that LBVs are powered by accretion is examined, and does not appear to be a satisfactory general model. Instead, identification of LBVs with close binaries in high mass-loss rate or common envelope evolutionary phases shows promise.

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).

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