scholarly journals Dust Formation and the Doubly-Periodic Variable Stars

1995 ◽  
Vol 155 ◽  
pp. 196-197
Author(s):  
T. Lloyd Evans
Keyword(s):  
Dust Cloud ◽  
Variable Stars ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Dust Formation ◽  
Circumstellar Envelope ◽  
Pulsation Period ◽  
Deep Minimum ◽  
Resonance Emission ◽  
Semiregular Variable

AbstractThe doubly-periodic semiregular variable V Hydrae became redder and developed resonance emission lines and bands during the 1992-94 deep minimum, which therefore resulted from the production of a circumstellar dust cloud. This removes the need to postulate a secondary pulsation period, ten times as long as the main pulsation period, in the stellar as opposed to circumstellar envelope.

scholarly journals Imaging Ejecta from the Final Flash Star V605 Aql

2002 ◽  
Vol 187 ◽  
pp. 187-192
Author(s):  
Kenneth Hinkle ◽  
Richard Joyce ◽  
Steven Ridgway ◽  
Laird Close ◽  
Thomas Lebzelter ◽  
...  
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Dust Cloud ◽  
Optical Emission ◽  
Stellar Mass ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Dust Formation ◽  
Loss Process ◽  
Infrared Continuum

AbstractThe cloud of ejecta resulting from a final helium shell flash in V605 Aql has been imaged in both optical emission lines and infrared continuum. The obscuring circumstellar dust cloud, whose effects were first seen in 1923, is shown to be bipolar, suggesting dust formation takes place in a disk surrounding this star. The ongoing stellar mass loss in V605 Aql is part of the final flash episode, which has been ongoing since 1919. The pre-final flash planetary nebula, A58, is nearly circular. This implies that significant changes in the mass loss process occur between the AGB and final flash stages.

scholarly journals ALMA spectrum of the extreme OH/IR star OH 26.5+0.6

2018 ◽  
Vol 14 (S343) ◽  
pp. 436-437
Author(s):  
K. Justtanont ◽  
S. Muller ◽  
M. J. Barlow ◽  
D. Engels ◽  
D. A. García-Hernández ◽  
...  
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Gas Phase ◽  
Chemical Processes ◽  
Emission Lines ◽  
High Mass ◽  
Dust Formation ◽  
Circumstellar Envelope ◽  
High Mass Loss

AbstractWe present ALMA band 7 data of the extreme OH/IR star, OH 26.5+0.6. In addition to lines of CO and its isotopologues, the circumstellar envelope also exhibits a number of emission lines due to metal-containing molecules, e.g., NaCl and KCl. A lack of C18O is expected, but a non-detection of C17O is puzzling given the strengths of H217O in Herschel spectra of the star. However, a line associated with Si17O is detected. We also report a tentative detection of a gas-phase emission line of MgS. The ALMA spectrum of this object reveals intriguing features which may be used to investigate chemical processes and dust formation during a high mass-loss phase.

scholarly journals Observations of Mass Loss and Circumstellar Matter around Cool Carbon Stars

2000 ◽  
Vol 177 ◽  
pp. 367-375 ◽  
Author(s):  
T. Lloyd Evans
Keyword(s):  
Circumstellar Matter ◽  
Dust Formation ◽  
Infrared Photometry ◽  
Carbon Stars ◽  
Absorption Bands ◽  
Long Period ◽  
Resonance Emission ◽  
Long Period Variables ◽  
Circumstellar Gas ◽  
Semiregular Variable

Spectroscopy and infrared photometry of carbon stars show three distinct forms of circumstellar matter. IRAS 12311-3509 probably has an edge-on disk and the spectrum is dominated by resonance emission from atoms and molecules in the vicinity. The long-period variables V Hya and R Lep are undergoing deep fadings, apparently caused by dust formation around the star, while variable emission from circumstellar gas is seen. The semiregular variable T Mus showed absorption bands from very cool material during an unusual episode in 1994.

scholarly journals Variable dust emission by WC type Wolf–Rayet stars observed in the NEOWISE-R survey

2019 ◽  
Vol 488 (1) ◽  
pp. 1282-1300 ◽  
Author(s):  
P M Williams
Keyword(s):  
Dust Emission ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Dust Formation ◽  
Energy Distributions ◽  
Optical Photometry ◽  
The Galaxy ◽  
Infrared Spectral

ABSTRACT Photometry at 3.4 and 4.6 ${\mu m}$ of 128 Population I WC type Wolf–Rayet stars in the Galaxy and 12 in the Large Magellanic Cloud (LMC) observed in the WISE NEOWISE-R survey was searched for evidence of circumstellar dust emission and its variation. Infrared spectral energy distributions (SEDs) were assembled, making use of archival r, i, Z, and Y photometry to determine reddening and stellar wind levels for the WC stars found in recent IR surveys and lacking optical photometry. From their SEDs, 10 apparently non-variable stars were newly identified as dust makers, including three, WR 102-22, WR 110-10, and WR 124-10, having subtype earlier than WC8–9, the first such stars to show this phenomenon. The 11 stars found to show variable dust emission include six new episodic dust makers, WR 47c, WR 75-11, WR 91-1, WR 122-14, and WR 125-1 in the Galaxy and HD 38030 in the LMC. Of previously known dust makers, NEOWISE-R photometry of WR 19 captured its rise to maximum in 2018 confirming the 10.1-yr period, that of WR 125 the beginning of a new episode of dust formation suggesting a period near 28.3 yr. while that of HD 36402 covered almost a whole period and forced revision of it to 5.1 yr.

scholarly journals The Connection with B[e] stars

2000 ◽  
Vol 175 ◽  
pp. 26-36 ◽  
Author(s):  
Franz-Josef Zickgraf
Keyword(s):  
Common Property ◽  
Main Sequence ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Circumstellar Envelopes ◽  
Early Type Stars ◽  
Uniform Group

AbstractThe characteristics of the various types of B[e] stars are discussed and compared with those of classical Be stars. Both groups of stars are characterized by the presence of emission lines in their spectra, in particular of hydrogen. However, there are also significant differences between these classes. Classical Be stars lack hot circumstellar dust and strong forbidden low-excitation emission lines, which are typical characteristics produced by B[e]-type stars. While classical Be stars are a rather uniform group of early-type stars, B[e]-type stars form a quite heterogeneous group, very often of poorly known evolutionary status, comprising such diverse types of objects as near main-sequence objects, evolved lowmass proto-planetray nebulae and massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars sometimes find their way into the group of B[e] stars. However, despite these dissimilarities classical Be stars and B[e]-type stars, share a common property, namely the nonsphericity of their circumstellar envelopes.

scholarly journals Semiregular Variable Stars

Astrophysics ◽  
2019 ◽  
Vol 62 (4) ◽  
pp. 556-572 ◽  
Author(s):  
L. S. Kudashkina
Keyword(s):  
Variable Stars ◽  
Semiregular Variable Stars ◽  
Semiregular Variable

scholarly journals Observations of Long Period Variable Stars

1989 ◽  
Vol 106 ◽  
pp. 241-257
Author(s):  
T. Lloyd Evans
Keyword(s):  
Chemical Composition ◽  
Stellar Population ◽  
Variable Stars ◽  
Circumstellar Dust ◽  
Stellar Systems ◽  
Intrinsic Properties ◽  
Long Period ◽  
Large Samples ◽  
Period Variable ◽  
Infrared Wavelengths

The study of long period variable stars has been transformed in recent years by two observational developments. Large samples of stars have been observed at infrared wavelengths, providing knowledge of the intrinsic properties of the star as well as of circumstellar dust shells, and these observations have been extended to the variables in well defined stellar systems to allow their properties to be studied in relation to the stellar population to which they belong. Spectroscopic determinations of chemical composition have also provided several crucial insights.

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 Oh Observations Near the Reflection Nebulae Ngc 2068 and Ngc 2071

1974 ◽  
Vol 60 ◽  
pp. 301-302
Author(s):  
L. E. B. Johansson ◽  
B. Höglund ◽  
A. Winnberg ◽  
Nguyen-Q-Rieu ◽  
W. M. Goss
Keyword(s):  
Dust Cloud ◽  
T Tauri Stars ◽  
Emission Lines ◽  
Class I ◽  
Reflection Nebula ◽  
Cosmic Background ◽  
T Tauri ◽  
Reflection Nebulae

Narrow OH emission lines at 1667 MHz, apparently from a Class I source, have been observed near the reflection nebula NGC 2071. The region contains many T Tauri stars. OH emission corresponding to the dust cloud north and east of NGC 2024 is also seen. At 1720 MHz the dust cloud component appears in absorption; presumably the isotropic 2.7 K cosmic background is being absorbed.

Slow variability and circumstellar shells of red variable stars

1987 ◽  
Vol 122 ◽  
pp. 541-542
Author(s):  
T. Lloyd Evans
Keyword(s):  
Variable Stars ◽  
Circumstellar Dust ◽  
Infrared Photometry ◽  
Constant Ratio ◽  
Giant Stars ◽  
Long Period ◽  
Period Variations ◽  
Cyclic Variations ◽  
Circumstellar Shells ◽  
The Mean

Infrared photometry shows that while all RV Tauri stars have circumstellar dust shells, the RVb stars with slow cyclic variations in mean light as well as the 30–100 day variations common to all RV stars have more hot dust close to the star (Lloyd Evans 1985). Many M giant stars which are variables of semiregular type also show long-period variations in the mean light (O'Connell 1933; Payne-Gaposchkin 1954), with a roughly constant ratio between the two periods. Payne-Gaposchkin (1954) found P2/P1 ~9.4 for red variables of type M and P2/P1 ~19.4 for stars of type F-K, most of which are FV Tauri stars. Re-analysis using the more extensive data available now indicates P2/P1 ~10 for the M giants and P2/P1 ~15 for the FV Tauri stars. The nature of the long-period variability is unknown (Wood 1975).

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