scholarly journals Detection of Water Maser Emission from a Carbon Star V778 Cygni

1988 ◽  
Vol 108 ◽  
pp. 53-54
Author(s):  
Y. Nakada ◽  
H. Izumiura ◽  
T. Onaka ◽  
O. Hashimoto ◽  
N. Ukita ◽  
...  
Keyword(s):  
Carbon Star ◽  
Emission Feature ◽  
Circumstellar Envelopes ◽  
Gas Phase Chemistry ◽  
Evolved Stars ◽  
Molecular Lines ◽  
Circumstellar Shells ◽  
M Stars ◽  
Phase Chemistry ◽  
Water Maser

Infrared spectra of evolved stars are generally dominated by the radiation from their circumstellar shells. M stars are characterized by the 10 μm emission feature from silicate dust grains, while C stars by the 11 μm SiC band. However, some C stars have been found to show the 10 μm feature indicating the oxygen-rich property of their circumstellar dust (Willems and de Jong 1986, Little-Marenin 1986).In order to investigate the gas phase chemistry of the circumstellar envelopes around these peculiar objects, we have observed radio molecular lines of H2O, SiO, HCN, and CO towards three of them BM Gem (C5, 4J), V778 Cyg (C4, 5J), and EU And (C4, 4).

Mid-IR spectra of the M-type Mira variable R Tri observed with the Spitzer IRS

2020 ◽  
Vol 493 (1) ◽  
pp. 807-814
Author(s):  
Dana K Baylis-Aguirre ◽  
M J Creech-Eakman ◽  
Tina Güth
Keyword(s):  
Ir Spectra ◽  
Emission Feature ◽  
Absorption Feature ◽  
Cool Temperature ◽  
Circumstellar Envelopes ◽  
Mira Variables ◽  
Mira Variable ◽  
Molecular Lines ◽  
Infrared Spectrometer ◽  
Vibrational Bands

ABSTRACT We present analysis of mid-infrared (IR) spectra of the oxygen-rich Mira variable R Tri. The data were taken with the Spitzer Infrared Spectrometer (IRS) as part of a study tracking how Mira variables’ regular pulsations affect circumstellar envelopes. We detected strong emission lines at 13.87, 16.18, and 17.6 $\hbox{$\mu $m}$, and one strong absorption feature at 14.98 $\hbox{$\mu $m}$. The emission features at 13.87 and 16.18 $\hbox{$\mu $m}$ are excited vibrational bands of CO2, while the absorption feature is the fundamental ν2 band. The 17.6 $\hbox{$\mu $m}$ emission feature has a completely different character than the molecular lines and we report its identification as Fe i fluorescence. We used a two-slab model with the radiative transfer code radex to model the CO2 Q-branch bandheads. Our results indicate a slab of gas with T∼600 K located at ∼3–4 R*. The cool temperature discrepancy with the radius provides observational evidence for the previously theoretical ‘refrigeration zone’.

scholarly journals Physics and chemistry of UV illuminated gas: the Horsehead case

2012 ◽  
Vol 10 (H16) ◽  
pp. 593-593 ◽  
Author(s):  
V. Guzmán ◽  
J. Pety ◽  
P. Gratier ◽  
J. R. Goicoechea ◽  
M. Gerin ◽  
...  
Keyword(s):  
Gas Phase ◽  
Spatial Scales ◽  
Interesting Case ◽  
Gas Phase Chemistry ◽  
Physical Conditions ◽  
Neutral Gas ◽  
Molecular Lines ◽  
Phase Chemistry ◽  
Physical And Chemical ◽  
Complex Organic

AbstractMolecular lines are used to trace the physical conditions of the gas in different environments, from high-z galaxies to proto-planetary disks. To fully benefit from the diagnostic power of the molecular lines, the formation and destruction paths of the molecules must be quantitatively understood. This is challenging because the physical conditions are extreme and the dynamic plays an important role. In this context the PDR of the Horsehead mane is a particularly interesting case because the geometry is simple (almost 1D, viewed edge-on; Abergel et al.2003), the density profile is well constrained and we are making several efforts to constrain the thermal profile. The combination of small distance to Earth (at 400 pc, 1″ corresponds to 0.002 pc), low illumination (χ = 60) and high density (nH ~ 105 cm−3) implies that all the interesting physical and chemical processes can be probed in a field-of-view of less than 50″ (with typical spatial scales ranging between 1″ and 10″). Hence, the Horsehead PDR is a good source to benchmark the physics and chemistry of UV illuminated neutral gas.In our recent work on the ISM physics and chemistry in the Horsehead we have shown the importance of the interplay between the solid and gas phase chemistry in the formation of (complex) organic molecules, like H2CO, CH3OH and CH3CN, which reveal that photo-desorption of ices is an efficient mechanism to release molecules into the gas phase (Guzmán et al.2011, Gratier et al. in prep, Guzman et al. in prep)}. We have also provided new diagnostics of the UV illuminated matter. For example, we detected CF+ and resolved its hyperfine structure (Guzman et al.2012b). We propose that CF+, which is observable from the ground, can be used as a proxy of C+ (Guzman et al.2012). Finally, we reported the first detection of the small hydrocarbon C3H+, which sheds light on the formation pathways of other observed small hydrocarbons, like C3H and C3H2 ((Pety et al. 2012). Part of these results were possible thanks to a complete an unbiased line survey at 1, 2 and 3 mm performed with the IRAM-30m telescope (Horsehead WHISPER), where approximately 30 species (plus their isotopologues) are detected.

scholarly journals Molecular lines in the envelopes of evolved stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 169-170 ◽  
Author(s):  
Yong Zhang ◽  
Sun Kwok ◽  
Dinh-V- Trung
Keyword(s):  
Planetary Nebula ◽  
Central Star ◽  
Molecular Ions ◽  
Stellar Winds ◽  
X Rays ◽  
Circumstellar Envelopes ◽  
Chain Molecules ◽  
Evolved Stars ◽  
Physical Environments ◽  
Molecular Lines

AbstractWe report a spectral line survey of the circumstellar envelopes of evolved stars at millimeter wavelengths. The data allow us to investigate the chemical processes in different physical environments and evolutionary stages. A total of more than 500 emission features (mostly rotational transitions of molecules) are detected in the survey. Our observations show that the sources in different evolutionary stages have remarkably different chemical composition. As a star evolves from AGB stage to proto-planetary nebula, the abundances of Si-bearing molecules (SiO, SiCC, and SiS) decrease, while the abundances of some long-chain molecules, such as CH3CN, C4H, and HC3N, increase. After further evolution to planetary nebula, the abundances of neutral molecules dramatically decrease, and the emission from molecular ions becomes more intense. These differences can be attributed to the changes of the role that dust, stellar winds, shock waves, and UV/X-rays from the central star play in different evolutionary stages. These results will provide significant constraints on models of circumstellar chemistry.

scholarly journals What Species Remain to be Seen?

1992 ◽  
Vol 150 ◽  
pp. 181-186 ◽  
Author(s):  
B. E. Turner
Keyword(s):  
Gas Phase ◽  
Refractory Element ◽  
Circumstellar Envelopes ◽  
Neutral Species ◽  
Interstellar Clouds ◽  
Gas Phase Chemistry ◽  
Element Chemistry ◽  
Thermochemical Equilibrium ◽  
Phase Chemistry ◽  
Laboratory Synthesis

We review what species remain to be seen for several types of astrochemistry: Thermochemical Equilibrium (TE) in circumstellar envelopes (CSEs); photo- and ion-molecule chemistry in CSEs; ion-molecule chemistry in cold interstellar clouds; grain chemistry (passive, catalytic, disruptive); and shock chemistry. In CSEs, a rich Si gas-phase chemistry is now recognized, and two predicted species (SiN, SiH2) have been seen. Others are predicted. In the ISM, a global picture of refractory-element chemistry predicts that compounds of Mg, Na, Fe, and possibly Al occur with detectable gas-phase abundance. Predicted species require laboratory synthesis and spectroscopy. Reactions of hydrocarbon ions with neutral species dominate the formation of the families CnH, HCnN, H2Cn, and CnO in both interstellar (TMC-1) and circumstellar (IRC10216) cases, and readily explain the favored values of n in each case as well as predicting which higher-n species remain to be seen. Confirmation of H3O+ (interstellar) is discussed.

scholarly journals Circumstellar Dust around M, S and C Stars

2000 ◽  
Vol 177 ◽  
pp. 361-366
Author(s):  
Irene R. Little-Marenin
Keyword(s):  
Dust Emission ◽  
Emission Feature ◽  
Circumstellar Dust ◽  
Circumstellar Shells ◽  
M Stars

The circumstellar shells of M stars produce emission features due to amorphous silicates peaking around 10 and 18 μm, with additional emission at 11 μm due to crystalline olivine and at 13.1 μm (unknown carrier). C stars are associated with SiC dust emission at 11.2 μm with additional emission around 8.9 μm, whereas S stars have a relatively weak 10.5 μm emission feature which is due neither to silicates nor to SiC.

scholarly journals The Abundance of SiC2 in Carbon Star Envelopes

2017 ◽  
Vol 13 (S332) ◽  
pp. 261-269
Author(s):  
Sarah Massalkhi ◽  
M. Agúndez ◽  
J. Cernicharo ◽  
J. P. Fonfría ◽  
M. Santander-García
Keyword(s):  
Silicon Carbide ◽  
Gas Phase ◽  
Carbon Star ◽  
Active Role ◽  
Agb Stars ◽  
Dust Grains ◽  
Circumstellar Envelopes ◽  
Carbon Stars ◽  
Evolved Stars

AbstractSilicon carbide dust grains are ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. To date, only three molecules containing an Si–C bond have been identified to have significant abundances in C-rich AGB stars: SiC2, SiC, and Si2C. The ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars.

scholarly journals Polyynes and Polycyclic Aromatic Molecules in C-rich Circumstellar Envelopes

1994 ◽  
Vol 146 ◽  
pp. 134-148 ◽  
Author(s):  
Alain Omont
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Aromatic Molecules ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Polycyclic Aromatic ◽  
Circumstellar Shells ◽  
Evolution Stage ◽  
Circumstellar Environment

The aim of this review is to discuss our knowledge on molecules in the circumstellar environment of evolved stars. In particular the presence and the behaviour of various kinds of molecules with several or many carbon atoms, in relation to C-rich dust, is considered.Such objects include mainly: (i) circumstellar shells of AGB carbon stars, either visible (such as Y CVn) or infrared (such as IRC+10216 (CW Leo)); (ii) planetary nebulae (PNe, e.g. NGC 7027); (iii) pre-planetary nebulae (PPNe, also called post-AGB stars, such as CRL 2688 or the Red Rectangle), probably in an intermediate evolution stage between the two former classes. I will not discuss more peculiar classes, such as R CrB stars and novae, for which very little is known about the presence of such molecular species.

Shock-tube study of the decomposition of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1395-1426 ◽  
Author(s):  
Paul Sela ◽  
Sebastian Peukert ◽  
Jürgen Herzler ◽  
Christof Schulz ◽  
Mustapha Fikri
Keyword(s):  
Mass Spectrometry ◽  
Shock Tube ◽  
High Repetition Rate ◽  
Rate Coefficients ◽  
Gas Chromatography Mass Spectrometry ◽  
High Concentration ◽  
Gas Phase Chemistry ◽  
Reflected Shock ◽  
Flight Mass Spectrometry ◽  
Phase Chemistry

AbstractShock-tube experiments have been performed to investigate the thermal decomposition of octamethylcyclotetrasiloxane (D4, Si4O4C8H24) and hexamethylcyclotrisiloxane (D3, Si3O3C6H18) behind reflected shock waves by gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) in a temperature range of 1160–1600 K and a pressure range of 1.3–2.6 bar. The main observed stable products were methane (CH4), ethylene (C2H4), ethane (C2H6), acetylene (C2H2) and in the case of D4 pyrolysis, also D3 was measured as a product in high concentration. A kinetics sub-mechanism accounting for the D4 and D3 gas-phase chemistry was devised, which consists of 19 reactions and 15 Si-containing species. The D4/D3 submechanism was combined with the AramcoMech 2.0 (Li et al., Proc. Combust. Inst. 2017, 36, 403–411) to describe hydrocarbon chemistry. The unimolecular rate coefficients for D4 and D3 decomposition are represented by the Arrhenius expressions ktotal/D4(T) = 2.87 × 1013 exp(−273.2 kJ mol−1/RT) s−1 and ktotal/D3(T) = 9.19 × 1014 exp(−332.0 kJ mol−1/RT) s−1, respectively.

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