scholarly journals Results and Future Uses of Heterodyne Spatial Interferometry at 11 Microns

1979 ◽  
Vol 50 ◽  
pp. 16-1-16-14 ◽  
Author(s):  
Edmund C. Sutton
Keyword(s):  
Spatial Distribution ◽  
Circumstellar Dust ◽  
Dust Grains ◽  
Heterodyne Interferometry ◽  
Dust Shells ◽  
Future Developments ◽  
Mira Variables ◽  
Infrared Stars

AbstractHeterodyne spatial interferometry at a wavelength of 11 microns has been used to examine properties of circumstellar dust shells. Among the objects which have been observed are several M-type supergiants and Mira variables as well as several peculiar infrared stars. These measurements provide information on the temperature and spatial distribution of dust grains. Possible future developments in heterodyne interferometry include longer baselines for higher resolution and the use of larger telescopes for greater sensitivity.

scholarly journals Long Baseline Interferometric Observations of Circumstellar Dust Shells at 11 Microns

1994 ◽  
Vol 158 ◽  
pp. 383-386
Author(s):  
W.C. Danchi ◽  
L. Greenhill ◽  
M. Bester ◽  
C.G. Degiacomi ◽  
C.H. Townes ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Radiative Transfer ◽  
Circumstellar Dust ◽  
Dust Formation ◽  
Late Type ◽  
Dust Shells ◽  
Long Baseline ◽  
Higher Temperature ◽  
Single Baseline ◽  
Radiative Transfer Modeling

The spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) located at Mt. Wilson. Currently operating with a single baseline as a heterodyne interferometer at 11.15 μm, the ISI has obtained visibility curves of these stars. Radiative transfer modeling of the visibility curves has yielded estimates of the inner radii of the dust shells, the optical depth at 11 μm, and the temperature of the dust at the inner radii. For stars in which the dust is resolved, estimates of the stellar diameter and temperature can also be made. Broadly speaking two classes of stars have been found. One class has inner radii of their dust shells very close to the photospheres of the stars themselves (3–5 stellar radii) and at a higher temperature (~ 1200 K) than previously measured. This class includes VY CMa, NML Tau, IRC +10216, and o Ceti. For the latter two the visibility curves change with the luminosity phase of the star and new dust appears to form at still smaller radii during minimum luminosity. The second class of stars has dust shells with substantially larger inner radii and very little dust close to the stars, and includes α Ori, α Sco, α Her, R Leo, and χ Cyg. This indicates sporadic production of dust and no dust formation within the last several decades.

scholarly journals Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells

2020 ◽  
Vol 644 ◽  
pp. A139
Author(s):  
Hans-Peter Gail ◽  
Akemi Tamanai ◽  
Annemarie Pucci ◽  
Ralf Dohmen
Keyword(s):  
Infrared Emission ◽  
Dust Particles ◽  
Circumstellar Dust ◽  
Expansion Velocity ◽  
Condensation Temperature ◽  
Dust Formation ◽  
Dust Grains ◽  
Dust Shell ◽  
Dust Shells ◽  
Stellar Outflows

Aims. We study the growth of dust in oxygen-rich stellar outflows in order to find out to which extent dust growth models can quantitatively reconcile with the quantities and nature of dust as derived from observations of the infrared emission from circumstellar dust shells. Methods. We use a set of nine well-observed massive supergiants with optically thin dust shells as testbeds because of the relatively simple properties of the outflows from massive supergiants, contrary to the case of AGB stars. Models of the infrared emission from their circumstellar dust shells are compared to their observed infrared spectra to derive the essential parameters that rule dust formation in the extended envelope of these stars. The results are compared with a model for silicate dust condensation. Results. For all objects, the infrared emission in the studied wavelength range, between 6 and 25 μm, can be reproduced rather well by a mixture of non-stoichiometric iron-bearing silicates, alumina, and metallic iron dust particles. For three objects (μ Cep, RW Cyg, and RS Per), the observed spectra can be sufficiently well reproduced by a stationary and (essentially) spherically symmetric outflow in the instantaneous condensation approximation. For these objects, the temperature at the onset of massive silicate dust growth is of the order of 920 K and the corresponding outflow velocity of the order of the sound velocity. This condensation temperature is only somewhat below the vapourisation temperature of the silicate dust and suggests that the silicate dust grows on the corundum dust grains that formed well inside of the silicate dust shell at a much higher temperature. The low expansion velocity at the inner edge of the silicate dust shell further suggests that, for these supergiants, the region inside the silicate dust shell has an only subsonic average expansion velocity, though a high degree of supersonic turbulence is indicated by the widths of spectral lines. Conclusions. Our results suggest that for the two major problems of dust formation in stellar outflows, that is (i) formation of seed nuclei and (ii) their growth to macroscopic dust grains, we are gradually coming close to a quantitative understanding of the second item.

scholarly journals An Infrared Colour Discriminator for Giant and Supergiant Optical M Stars

1995 ◽  
Vol 148 ◽  
pp. 307-310
Author(s):  
Moedji Raharto
Keyword(s):  
Spectral Type ◽  
Point Sources ◽  
Circumstellar Dust ◽  
Evolutionary Stage ◽  
Colour Properties ◽  
Early Type ◽  
Dust Shells ◽  
Mira Variables ◽  
Colour Distribution ◽  
M Stars

AbstractAn infrared colour - MK spectral type diagram of optical M giants, M Miras and M supergiants is presented. The area in the diagram with m12 − m25 > 0.70 and MK spectral type earlier than M4 is occupied by early type optical M supergiants. The region of spectral type later than M4 is occupied by optical late M giants (Mira variables) and late M supergiants. The area in the diagram with a colour range of 0.15 < m12 − m25 < 0.70 is occupied by optical giants (Mira Variables) and supergiants (M supergiants with blue companions and probably some M supergiants in the evolutionary stage pre or post M supergiants with large infrared excesses). Finally, the area in the diagram with m12 − m25 < 0.15 is clearly occupied by M giants without circumstellar dust shells. The colour distribution of the M giants, M supergiants and M Miras in the colour - spectral type diagram suggests that we can use the colour properties as search criteria for (i) early M supergiants with colours of m12 − m25 > 0.70, (ii) late M supergiants with colours of m12 − m25 > 0.70, (iii) M giants with m12 − m25 < 0.15, (iv) Mira candidates using IRAS point sources which are also identified as optical M stars.

scholarly journals Identifying circumstellar dust around oxygen-rich mira variables with maser emission via continuum elimination

2021 ◽  
Author(s):  
◽  
Lisa Shepard
Keyword(s):  
Major Effect ◽  
Peak Position ◽  
Asymptotic Giant Branch ◽  
Correct Identification ◽  
Spectral Features ◽  
Agb Stars ◽  
Dust Grains ◽  
Maser Emission ◽  
Dust Shells ◽  
Mira Variables

Stars between about 0.8 and 8 times the mass of the Sun will eventually evolve, becoming asymptotic giant branch (AGB) stars, where they pulsate and eject mass from their atmospheres, forming dust shells in the space around them. Evolved low- and intermediate-mass stars with carbon-to-oxygen ratios (C/O) below unity are known as oxygen-rich stars. O-rich stars are surrounded by dust shells containing mineral species dominated by silicate dust grains. In this dissertation, I examine whether dust grains around evolved, oxygen-rich AGB stars have any correlation with maser emission, and to understand the connection, if any, between specific types of maser emission and dust spectral features. I have investigated several methods of continuum elimination using spectroscopy data for the archetypal dusty AGB star, Mira. I have investigated the ~10[mu]m and ~18[mu]m spectral features in the continuum-eliminated spectrum including peak position, barycenter, and full width half maxima (FWHM). The positions and widthved spectral features were compared with those seen in laboratory spectra. I then looked for a correlation between maser emission and dust spectral features in a sample of Mira variables. The types of masers have been identified, and peak positions, barycenter positions, and FWHM have been measured for the sample spectra. The results show that the method of continuum elimination matters for correct identification of dust minerals, while varying the temperature and precise continuum shapes do not have a major effect on the positions of spectral features. Observed astronomical silicate features are complex and indicate the need for different compositions of minerals. Finally, there does not appear to be a correlation between the presence of a maser and dust spectral features based on the information available for analysis.

scholarly journals Gaia DR2 data and the evolutionary status of eight high-velocity hot post-AGB candidates

2020 ◽  
Vol 72 (6) ◽  
Author(s):  
Mudumba Parthasarathy ◽  
Tadafumi Matsuno ◽  
Wako Aoki
Keyword(s):  
Effective Temperature ◽  
High Velocity ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Agb Stars ◽  
Horizontal Branch ◽  
Dust Shells ◽  
The Past ◽  
Gaia Dr2 ◽  
Branch Star

Abstract From Gaia DR2 data of eight high-velocity hot post-AGB candidates, LS 3593, LSE 148, LS 5107, HD 172324, HD 214539, LS IV −12 111, LS III +52 24, and LS 3099, we found that six of them have accurate parallaxes which made it possible to derive their distances, absolute visual magnitudes (MV) and luminosity (log L/L⊙). All the stars except LS 5107 have an accurate effective temperature (Teff) in the literature. Some of these stars are metal poor, and some of them do not have circumstellar dust shells. In the past, the distances of some stars were estimated to be 6 kpc, which we find to be incorrect. The accurate Gaia DR2 parallaxes show that they are relatively nearby, post-AGB stars. When compared with post-AGB evolutionary tracks we find their initial masses to be in the range 1 M⊙ to 2 M⊙. We find the luminosity of LSE 148 to be significantly lower than that of post-AGB stars, suggesting that this is a post-horizontal-branch star or post-early-AGB star. LS 3593 and LS 5107 are new high-velocity hot post-AGB stars from Gaia DR2.

scholarly journals Discovery of Infrared Stars in Globular Clusters in the Magellanic Clouds and Their Light Variations

1998 ◽  
Vol 11 (1) ◽  
pp. 395-395
Author(s):  
S. Nishida ◽  
T. Tanabé ◽  
S. Matsumoto ◽  
T. Onaka ◽  
Y. Nakada ◽  
...  
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Main Sequence ◽  
Near Infrared ◽  
Magellanic Clouds ◽  
Infrared Light ◽  
Agb Stars ◽  
Dust Shells ◽  
Infrared Stars ◽  
Infrared Survey

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively. The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.

Spatial Distribution of Dust Grains within HiiRegions

2002 ◽  
Vol 570 (2) ◽  
pp. 688-696 ◽  
Author(s):  
Akio K. Inoue
Keyword(s):  
Spatial Distribution ◽  
Dust Grains

scholarly journals Dust formation in oxygen-rich circumstellar shells around long–period variables

1999 ◽  
Vol 191 ◽  
pp. 233-238 ◽  
Author(s):  
Kyung Sook Jeong ◽  
Jan Martin Winters ◽  
Erwin Sedlmayr
Keyword(s):  
Variable Star ◽  
Chemical Species ◽  
Circumstellar Dust ◽  
Agb Stars ◽  
Fluid Element ◽  
Dust Grains ◽  
Promising Candidate ◽  
Long Period ◽  
Period Variable ◽  
Circumstellar Shells

We present the first steps of our work aimed at a consistent time-dependent modeling of oxygen–rich circumstellar dust shells (CDS) around pulsating AGB stars. The nature of the most likely nucleation seeds is investigated for this situation and we find that TiO2 is a most promising candidate to serve as the primary condensate, forming already at temperatures well above 1 000 K. These nuclei evolve to macroscopic dust grains by heterogeneous growth processes involving several chemical species. We investigate the varying chemical composition of the resulting dust grains as they evolve as a function of time in a fluid element moving through the CDS of an oxygen–rich long-period variable star (LPV).

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