scholarly journals The 8-22μm Excess in Carbon Stars From IRAS LRS Spectra

1989 ◽  
Vol 106 ◽  
pp. 402-402
Author(s):  
S. J. Little ◽  
I. R. Little-Marenin
Keyword(s):  
Dust Emission ◽  
Unknown Origin ◽  
Carbon Star ◽  
Variable Stars ◽  
Emission Feature ◽  
Absorption Feature ◽  
Carbon Stars ◽  
Mira Variables ◽  
Period Variable ◽  
Ir Emission

We have measured the excess IR emission from carbon mira and SR variable stars from IRAS LRS spectra. The 8-22μm excess is defined as the ratio of flux above a 2500K energy distribution fit to the LRS spectrum at about 8μm. The carbon star LRS spectra show both emission and absorption features, which are incorporated into our 8-22pm excess. The most prominent feature in carbon stars is the 11.2μm SiC dust emission feature extending from 10μm to 13.8 μm. We observe another emission feature of unknown origin which peaks between 8.4-8.7μm. The SiC emission feature is occasionally blended on the red side by an absorption feature (attributed to gaseous HCN + C2H2) which extends from about 12-16μm. Many of the spectra appear to turn down at the 8μm end due (?) to an HCN + C2H2 absorption feature located at 7.1μm. Carbon stars do not generally show as large an excess as the M mira variables do. The figure below shows our measured excesses for both carbon miras and carbon semi-regular variables. There appears to be little correlation of excess with period, however the mira variables show about twice the range of variation of excess that the semi-regular variables do. We find little correlation between our measured 8-22μm excess and the excesses of Jura (Ap. J., 303, 327, 1986) based on the ratio of 12μm flux to 2μm flux. Our data do support hi s conclusion that longer period variable stars show larger average excesses, but this is only true for mira variables in our analysis.

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 Unidentified Species in Envelopes around Carbon Stars

2013 ◽  
Vol 9 (S297) ◽  
pp. 219-222
Author(s):  
B. W. Jiang ◽  
A. Li ◽  
K. Zhang ◽  
J. M. Liu ◽  
J. Gao ◽  
...  
Keyword(s):  
Ir Spectra ◽  
Emission Spectrum ◽  
Single Photon ◽  
Dust Emission ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Carbon Stars ◽  
Unidentified Species ◽  
Ir Emission

AbstractThe infrared (IR) spectra of many evolved carbon-rich stars exhibit two prominent dust emission features peaking around 21μm and 30μm, with the former exclusively seen in proto-planetary nebulae (PPNe), while the latter seen in a much wider range of objects, including AGB stars, PPNe and planetary nebulae (PNe). The 30μm feature is seen in all the 21μm sources, but no correlation is found between these two features. Over a dozen carrier candidates have been proposed for the 21μm feature, but none of them has been widely accepted and the nature of the 21μm feature remains a mystery. The carrier of the 30μm feature also remains unidentified. MgS dust, once widely accepted as a valid carrier, was ruled out because of the sulfur budget problem. In this work we examine nano-sized FeO dust as a carrier for the 21μm feature. We calculate the IR emission spectrum of FeO nanodust which undergoes single-photon heating in PPNe. It is found that the 21μm feature emitted by FeO nanodust is too broad to explain the observed feature. For the 30μm feature, we argue that graphite could be a viable carrier. Graphite, provided its d.c. conductivity σd.c. exceeds ~100ohm−1cm−1, exhibits a pronounced band at 30μm.

scholarly journals Observations and Models for Red Giants with Unusual Dust

1989 ◽  
Vol 106 ◽  
pp. 367-367
Author(s):  
Ian Griffin ◽  
C.J. Skinner ◽  
B.R. Whitmore
Keyword(s):  
Service Time ◽  
Dust Emission ◽  
Red Giants ◽  
Carbon Stars ◽  
Near Ir ◽  
Medium Resolution ◽  
Silicate Feature ◽  
L Band ◽  
M Stars ◽  
Selection Of

We present near IR (H, K and L band) medium resolution (ƛ/Δƛ ∼ 600) spectra for a selection of 9 red giants which have previously been shown to exhibit anomalous dust emission as characterised by their IRAS LRS spectra. The objects observed (during UKIRT and AAT service time) include Carbon stars whose LRS spectra show the 9.7μm silicate feature and also M stars whose LRS spectra display an 11.3μm feature similar to that usually associated with emission from SiC dust grains.

scholarly journals Measurements of the 3.3 μm Diffuse Galactic Emission Feature with AROME

1990 ◽  
Vol 139 ◽  
pp. 212-213
Author(s):  
M. Giard ◽  
F. Pajot ◽  
J. M. Lamarre ◽  
G. Serra
Keyword(s):  
Surface Brightness ◽  
Galactic Plane ◽  
Elevation Angle ◽  
Emission Feature ◽  
Field Of View ◽  
Interstellar Matter ◽  
Galactic Emission ◽  
Polycyclic Aromatic ◽  
Hydrocarbon Molecules ◽  
Ir Emission

AROME∗ is a balloon-borne experiment which was built to carry out measurements of IR emission features in the diffuse galactic flux. The field of view is 0.5° and surface brightness gradients are detected through azimuthal scanning at a constant elevation angle. The detection of a feature is done by comparison of the fluxes measured in narrow and wide photometric bands centered on the feature's wavelength. Two flights have been performed (August 1987, October 1988), which detected a 3.3 μm feature in the direction of the galactic plane −6° < b < 6°, 60° > l > −50°. Since this feature is characteristic of aromatic C-H bonds, we assigned it to the emission of transiently heated polycyclic aromatic hydrocarbon molecules (PAHs). With this assumption, AROME measurements show that PAHs are an ubiquitous component of the interstellar matter which contain about 10% of the available cosmic carbon.

scholarly journals Lithium Observations in the Sun

1968 ◽  
Vol 1 ◽  
pp. 243-246
Author(s):  
Edith A. Müller
Keyword(s):  
Unknown Origin ◽  
Absorption Feature ◽  
The Sun ◽  
Degree Of Ionization ◽  
Lithium Abundance ◽  
Resonance Doublet ◽  
Lower Temperature ◽  
Central Depth ◽  
The Continuum

The determination of the lithium abundance in the solar atmosphere is essentially based on the LiI resonance doublet at λ 6707·761 and 6707·912 Å. These two lines form a very faint absorption feature, the central depth of the stronger component being of the order of 1% of the continuum. The violet component, which is also the stronger of the two, occurs near the red wing of a faint solar line of unknown origin, and the lines appear to be blended with other faint lines including possibly the doublet of the Li6 isotope (the isotopic shift being 0·160 Å). No other line of LiI has been detected in the Fraunhofer spectum of the undisturbed solar disk. This is nothing surprising, because practically all lithium is expected to be ionized in the photosphere on account of its low ionization potential (Xion = 5·37 e.v.). In sunspot spectra the lower temperature reduces the degree of ionization of lithium and causes a strengthening of the LiI lines. In fact, the LiI resonance lines which appear as a very faint absorption feature on disk spectra are about 50 times stronger in spot spectra. Furthermore, the very weak feature at λ 6103·6 Å was identified by Dubov (1964) and by Schmahl and Schröter (1965) as due to the 2s 2S–3d 2D transition of LiI. Both the resonance doublet and the faint feature at 6103·6 Å have been used by the above-mentioned authors to derive the lithium abundance in spots.

scholarly journals A Gas and Dust Rich Giant Elliptical Galaxy

2005 ◽  
Vol 13 ◽  
pp. 872-874
Author(s):  
O. Krause ◽  
U. Lisenfeld ◽  
U. Klaas ◽  
D. Lemke ◽  
M. Haas ◽  
...  
Keyword(s):  
Elliptical Galaxy ◽  
Dust Emission ◽  
Optical Spectra ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Bolometric Luminosity ◽  
Thermal Radio ◽  
Visual Extinction ◽  
Dust Mass ◽  
Ir Emission

AbstractThe bolometric luminosity of LFIR = 2×1012 L⊙ makes ISOSS J 15079+7247 one of the most luminous and unusual galaxies detected by the 170 μm ISOPHOT Serendipity Survey (ISOSS). The detection of CO (1-0) emission identifies a giant elliptical galaxy at redshift z = 0.2136 as the counterpart of the FIR source. The derived high gas mass of 3 × 1010 M⊙ favours the picture that the dust emission is associated with this elliptical galaxy. The ultraluminous IR emission can be explained by a hidden starburst in the center of the elliptical. This is supported by the strength of non-thermal radio continuum emission. The huge dust mass of 5×108 M⊙ corresponds to a visual extinction of AV ~ 1000 mag, being consistent with the non-detection of any signatures of a strong starburst in ISOSS J 15079+7247 in optical spectra.

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