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2.
O. Hashimoto H. Izumiura D. J. M. Kester Tj. R. Bontekoe 《Astrophysics and Space Science》1995,224(1-2):477-478
Extended emission components are clearly found in the IRAS scan data of optically visible oxygen-rich AGB stars which show no 10µm silicate band feature in the IRAS LRS spectra but a strong infrared excess in the IRAS photometric data. It is most likely that these stars really have their circumstellar dust envelopes, which are detached from the central stars, indicating a halting of mass loss for a significant period. 相似文献
3.
The spectral signatures of circumstellar dust shells (CS) of late-type stars cannot be tied in a simple manner to their optical spectral features. The spectral indices of featureless low-resolution spectrometer (LRS) spectra of K and early-M (M0-M5) stars are consistent with that of the Rayleigh-Jeans law and those of late-M (M6 and later) stars tend to have lower values showing CS radiation. There is no correlation observed between the optical sub-type and the 10 m emission strength for M stars. The absence of a simple relationship is also evident for C stars where the temperature and abundance indices show no correlation with the 11 m emission strength. The sample is confined to the IRC stars identified with accurate spectra observed by the LRS of IRAS. The IRC stars are the whole sky survey done with the 2 m band, where late-type stars are bright and interstellar extinction is one-tenth of the visual colour band. 相似文献
4.
IRAS low-resolution spectra for 17 sources are presented in this paper. Together with the carbon star catalog, information
from recent literatures, the ISO observation and the IRAS two-color diagram, it is found that among them 5 sources are new
silicate carbon stars, 5 sources are candidates of silicate carbon stars and other 7 sources are probable candidates of silicate
carbon stars. Some discussions are made for their infrared properties. 相似文献
5.
Observations of 5 stellar sources with unusual characteristics of IRAS Low Resolution Spectra were made with the SWS on ISO.
Observed stars are 4 late-type stars with silicate bands and one planetary nebula. Their IRAS LRS contain somewhat unusual
features in respect of the 10/18 μm intensity ratio or narrow emission feature from unknown molecular bands. Some narrow unusual
features are confirmed by ISO SWS01 spectra but the broad features were turned out to be false.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
We collected 55 galactic extreme carbon stars from the published literature in this paper. Observational data from IRAS, 2MASS
and ISO were analyzed. The results show that the infrared properties of extreme carbon stars are quite different to those
for ordinary visual carbon stars. It is shown from IRAS and 2MASS photometric data that extreme carbon stars have much redder
infrared colors not only in the far infrared, but also in the near infrared, hence they have much thicker ciucumstellar envelopes
and mass loss. It is also indicated from IRAS Low-Resolution Spectra (LRS) and ISO Short Wavelength Spectra (SWS) that they
have much redder infrared spectra from 2 μm to 45 μm. The above results are believed to be the signature of undergoing the
last stages of AGB evolution for extreme carbon stars. 相似文献
7.
Robert E. Stencel 《Astrophysics and Space Science》1995,224(1-2):563-564
Since the publication of our correlation (1990 Ap.J. 350, L45) suggesting a temporal relationship among: (a) shapes of 10 micron silicates seen in IRAS Low Resolution Spectra (LRS); (b) IRAS broad band colors; (c) light curve asymmetries, and (d) the types of masers associated with various Mira variable stars, the question has arisen whether the implied chronology refelcts the interval between thermal pulses, or the more lengthy ascent of the AGB. There is evidence in favor of the former interpretation. A strong implication of this idea is that variability among pre-silicate spectra should be significant. Several examples of this have been found in the extended LRS database, and are presented. Finally, plans are presented to continue monitoring of selected variables in the 10 micron region, to verify the variability suggested in the limited phase coverage provided in the LRS database. Monitoring will include use of our facilities at the Mt.Evans-Womble Observatory — highest in the world at 4313 meters altitude. 相似文献
8.
From the LRS spectra of almost 2000 IRAS sources showing the 1612 MHz OH emission we found 9 candidates for OH/IR stars with SiC features in their envelopes. Further study indicates that 6 of these are definitely or very probably carbon star with the 11.3 μm SiC emission feature in addition of being OH/IR stars showing the 1612 MHz OH maser emission. 相似文献
9.
IRAS 17213-3841作为富碳星列于新版碳星星表中．然而该星的IRAS低分辨率光谱显示富氧的硅酸盐发射特征；光谱观测结果表明，该星是一个接近零龄主序的，光谱型为O9／B0的早型发射线星，而不是碳星，因此应从碳星星表中剔除．此外，将它证认为碳星的近红外-IRAS双色图方法并不是一个完全可靠的方法，用这一方法来证认碳星必须十分小心． 相似文献
10.
IRAS low-resolution spectra are presented for 36 HAEBE stars. It is found that silicate dust is common material in the circumstellar
disks or/and shells of HAEBE stars. It is also found that the PAH feature often appears as well. In addition, the correlation
between the dust features and spectral type, and infrared excesses can be found for most HAEBE stars.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
H. J. Walker 《Astrophysics and Space Science》1994,217(1-2):139-140
The IRAS Low Resolution Spectrometer (LRS) covered the spectral region from 7µm to 23µm, and an Atlas was produced containing 5425 spectra. Most of the spectra were associated with evolved stars, including over 3000 spectra from the dust shells around O-rich stars. When Artificial Intelligence techniques were applied to the dataset, a new classification was derived. A scheme with 77 classes, grouped into 9 metaclasses, resulted, and for those types of spectra which were well represented in the initial dataset (i.e. the evolved stars) a very subtle classification was derived, often using line shapes, relative line strengths, or the presence of additional weak features. 相似文献
12.
Massimo Marengo &#;eljko Ivezi&#; Gillian R. Knapp 《Monthly notices of the Royal Astronomical Society》2001,324(4):1117-1130
We analyse the differences in infrared circumstellar dust emission between oxygen-rich Mira and non-Mira stars, and find that they are statistically significant. In particular, we find that these stars segregate in the K–[12] versus [12]–[25] colour–colour diagram, and have distinct properties of the IRAS LRS spectra, including the peak position of the silicate emission feature. We show that the infrared emission from the majority of non-Mira stars cannot be explained within the context of standard steady-state outflow models.
The models can be altered to fit the data for non-Mira stars by postulating non-standard optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300–400 K) than typical silicate grain condensation temperatures (800–1000 K) . We argue that the latter is more probable and provide detailed model fits to the IRAS LRS spectra for 342 stars. These fits imply that two-thirds of non-Mira stars and one-third of Mira stars do not have hot dust (>500 K) in their envelopes.
The absence of hot dust can be interpreted as a recent (∼100 yr) decrease in the mass-loss rate. The distribution of best-fitting model parameters agrees with this interpretation and strongly suggests that the mass loss resumes on similar time-scales. Such a possibility appears to be supported by a number of spatially resolved observations (e.g. recent Hubble Space Telescope images of the multiple shells in the Egg Nebula) and is consistent with new dynamical models for mass loss on the asymptotic giant branch. 相似文献
The models can be altered to fit the data for non-Mira stars by postulating non-standard optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300–400 K) than typical silicate grain condensation temperatures (800–1000 K) . We argue that the latter is more probable and provide detailed model fits to the IRAS LRS spectra for 342 stars. These fits imply that two-thirds of non-Mira stars and one-third of Mira stars do not have hot dust (>500 K) in their envelopes.
The absence of hot dust can be interpreted as a recent (∼100 yr) decrease in the mass-loss rate. The distribution of best-fitting model parameters agrees with this interpretation and strongly suggests that the mass loss resumes on similar time-scales. Such a possibility appears to be supported by a number of spatially resolved observations (e.g. recent Hubble Space Telescope images of the multiple shells in the Egg Nebula) and is consistent with new dynamical models for mass loss on the asymptotic giant branch. 相似文献
13.
R. J. Sylvester 《Monthly notices of the Royal Astronomical Society》1999,309(1):180-188
New mid-infrared spectra are presented of a number of oxygen-rich evolved stars which have IRAS LRS (Low Resolution Spectrometer) spectra that were classified as showing SiC emission. Two of the sources, IRC−20445 and IRC−20461, show the unidentified infrared (UIR) bands superposed on silicate emission features. Both objects have been classified as M supergiants. Several other sources show three-component spectra, with peaks at 10, 11 and 13 μm. The 13-μm source FI Lyr shows a narrow emission feature at 19 μm. Emission by oxide grains may be responsible for the 11-, 13- and 19-μm features. One object, IRC−20455, shows a self-absorbed silicate feature. There is no clear evidence for SiC emission in any of the spectra: the LRS spectra were erroneously classified as showing SiC emission because of the relatively strong 11-μm emission. 相似文献
14.
在具有低分辨率光谱资料的IRAS点源的光学证认中,我们发现,IRAS 19213+1723很可能是一个新的致密的HII区,这之后在南部西班牙Calar Alto天文台所作的光谱观测等资料肯定了我们上述的推想。 相似文献
15.
Parag Seal 《Astrophysics and Space Science》1995,234(2):223-232
Far infrared IRAS measurements and near infrared observational data of nineteen faint symbiotic stars are presented in this paper. From their flux distributions and the near infrared and far infrared colours an attempt is made to study the type of these stars. The colour temperature, dust temperature and mass-loss rates are estimated from the far infrared flux ratios and compared to those of known S and D type symbiotic stars. Probably nine of them are S type, two of them are D type and three of them are D type symbiotic stars. But it is difficult to suggest the type of five stars from the information available. 相似文献
16.
A. Roman-Lopes Z. Abraham R. Ortiz A. Rodriguez-Ardila 《Monthly notices of the Royal Astronomical Society》2009,394(1):467-478
K -band spectra of young stellar candidates in four Southern hemisphere clusters have been obtained with the Gemini Near-Infrared Spectrograph in Gemini South. The clusters are associated with IRAS sources that have colours characteristic of ultracompact H ii regions. Spectral types were obtained by comparison of the observed spectra with those of a near-infrared (NIR) library; the results include the spectral classification of nine massive stars and seven objects confirmed as background late-type stars. Two of the studied sources have K -band spectra compatible with those characteristic of very hot stars, as inferred from the presence of C iv , N iii and N v emission lines at 2.078, 2.116 and 2.100 μm, respectively. One of them, I16177_IRS1, has a K -band spectrum similar to that of Cyg OB2 7, an O3If* supergiant star. The nebular K -band spectrum of the associated Ultra-Compact (UC) H ii region shows the s-process [Kr iii ] and [Se iv ] high excitation emission lines, previously identified only in planetary nebula. One young stellar object was found in each cluster, associated with either the main IRAS source or a nearby resolved Midecourse Space eXperiment ( MSX ) component, confirming the results obtained from previous NIR photometric surveys. The distances to the stars were derived from their spectral types and previously determined JHK magnitudes; they agree well with the values obtained from the kinematic method, except in the case of IRAS 15408−5356 , for which the spectroscopic distance is about a factor of 2 smaller than the kinematic value. 相似文献
17.
给出２６ 个金牛Ｔ 型星的ＩＲＡＳ低分辨率红外光谱．根据这些光谱讨论了它们有关的性质和所处环境．分析发现硅酸盐尘埃在金牛Ｔ 型星拱星壳层中是常见的物质 相似文献
18.
M. Marengo M. Busso L. Origlia P. Persi M. Ferrari-Toniolo G. Silvestro M. Tapia 《Astrophysics and Space Science》1995,224(1-2):511-512
We observed 17 AGB and post-AGB circumstellar envelopes wuth the midinfrared camera TIRCAM. The collected photometry is compared with the IRAS LRS spectra and a two color diagram for the chemical classification of the dust is developed. 相似文献
19.
M. Kun † J. Vinkó ‡ L. Szabados 《Monthly notices of the Royal Astronomical Society》2000,319(3):777-790
In order to reveal the star-forming history of the molecular cloud complex we studied the intermediate mass stellar population in the Cepheus Flare region. (Paper I dealt with the distance and the young stellar object candidates of the region.) Correlating the IRAS Point Source Catalogue and Faint Source Catalogue positions with those of 1214 B8–A8 and 1760 F0–F5 type stars brighter than and classified during an objective prism survey, we identified 19 stars showing far-infrared excess emission in the Cepheus Flare region. In addition to the 16 stars whose counterparts are given in the IRAS catalogues, we found three more stars with infrared excess not recognized before. In order to identify the young medium-mass stars associated with the Cepheus Flare molecular clouds we observed the optical spectra of the IR-excess stars, and using published optical photometry and the IRAS data we examined their spectral energy distributions (SEDs) and IRAS two-colour diagram. The observations resulted in the discovery of a new Herbig Ae/Be star, BD +68°1118, coinciding with IRAS 21169+6842. More evolved HAe/Be stars may be SAO 19953, BD +67°1314 and BD +69°1231, whose H α lines showed weak emission components. Possible β Pictoris- or Vega-type stars may be HD 203854, HD 212826 and HD 216486, whereas the far-infrared fluxes at the positions of BD +72°1018, HD 210806 and HD 217903 can be attributed to the heating of the interstellar environment. We used distances and radial velocities of the stars derived from the spectroscopy and published optical photometry as indicators of their relations to the clouds. Information on the environment of the observed stars deduced from the diffuse interstellar band at λ 6613 is briefly discussed. 相似文献
20.
Roger J. Sylvester Vincent Mannings 《Monthly notices of the Royal Astronomical Society》2000,313(1):73-86
Photometric observations at optical and near-infrared wavelengths are presented for members of a new sample of candidate Vega-like systems, or main sequence stars with excess infrared emission due to circumstellar dust. The observations are combined with IRAS fluxes to define the spectral energy distributions of the sources. Most of the sources show only photospheric emission at near-IR wavelengths, indicating a lack of hot (∼1000 K) dust. Mid-infrared spectra are presented for four sources from the sample. One of them, HD 150193, shows strong silicate emission, while another, HD 176363, was not detected. The spectra of two stars from our previous sample of Vega-like sources both show UIR-band emission, attributed to hydrocarbon materials. Detailed comparisons of the optical and IRAS positions suggest that in some cases the IRAS source is not physically associated with the visible star. Alternative associations are suggested for several of these sources. Fractional excess luminosities are derived from the observed spectral energy distributions. The values found are comparable to those measured previously for other Vega-like sources. 相似文献