A near-infrared survey of IRAS sources in the South Galactic Cap

The paper describes the JHK colours of late-type stars which were investigated as part of a survey of South Galactic Cap (b < -30°) IRAS sources selected on the basis of their 12/25µm flux ratios as high mass-loss candidates. Near-infrared two-colour diagrams provide an effective technique for distinguishing between various groups of late-type stars. Such diagrams are also useful in indicating which stars are likely to be peculiar and worthy of more detailed study. The late-type stars isolated by this survey comprise: 61 Mira variables (3 of which are carbon stars with very thick shells), 3 young stellar objects, 4 interacting binaries, 2 semi-regular carbon variables and 154 oxygen-rich giants.     

An infrared study of Herbig Ae/Be stars

The IRAS and 2MASS associations for 206 HAEBE stars are identified in this paper. From the color-color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material. It is also found that the IR excesses at IRAS region for few HAEBE stars and the near-IR excesses for some HAEBE stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, the evolution scenario (from embedded HAEBE stars to β Pictoris-like main-sequence stars) from Malfait et al. (1998) has been checked, our result does not support this evolution scenario.This publication makes use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, founded by the National Aeronautics and Space Administration and the National Science Foundation of the United States.     

Millimeter polarimetry of star-forming regions: magnetic field structure around low-mass stars

We have measured polarization of the 1.1 mm and 0.8 mm continuum emission for 3 pre-T Tauri stars and 2 T Tauri stars. Positive detections were made for NGC 1333 IRAS 4 and IRAS 16293-2422, while L1551 IRS 5 and HL Tau were only marginally detected. For GG Tau we measured a 2 upper limit of 3%. The polarization is interpreted in terms of thermal emission by magnetically aligned dust grains in circumstellar disks or envelopes. We have found a definite geometrical relation between the polarization and other circumstellar structure.     

Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

We look for high‐amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS‐3 Photometric V ‐band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5° centred on the bright star Alnilam (ε Ori) in the centre of the Orion Belt. We identify 32 highly variable stars, of which 16 had not been reported to vary before. They are mostly variable young stars and candidates (16) and background giants (8), but there are also field cataclysmic variables, contact binaries, and eclipsing binary candidates. Of the young stars, which typically are active Herbig Ae/Be and T Tauri stars with Hα emission and infrared flux excess, we discover four new variables and confirm the variability status of another two. Some of them belong to the well known σ Orionis cluster. Besides, six of the eight giants are new variables, and three are new periodic variables (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Statistical results from a jcmt survey of MM and sub-MM emission in herbig ae/be stars

We have detected 1.1 mm continuum emission from 24 of 53 Herbig Ae/Be stars surveyed with the JCMT. Survival analysis shows that 1.1 mm luminosity is correlated with bolometric luminosity and with IRAS 25µm luminosity. For those stars that were also detected at 0.45 or 0.8 mm we find a typical flux dependence of the form S _#x03BD; ³, which is steeper than that of most classical T Tauri stars.     

Infrared study of the extreme carbon stars based on IRAS, 2MASS and ISO data

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.     

Sio observations of mass-losing AGB stars

We have observed the first overtone rotation-vibration absorption bands of SiO near = 4µm for a sample of 23 oxygen-rich Mira and Semiregular variables using the ESO NTT and IRSPEC. We discuss the strength of the SiO absorption in terms of the near infrared, IRAS and pulsational properties of the stars. Especially among the Miras there are big differences in the strength of the SiO bands between individual objects, which are probably due to pulsational variability.This work is supported by the Austrian Science Fund Project P9638-AST.     

Rapidly oscillating M giant stars?

The Hipparcos mission discovered a few dozen M giant stars with periods P shorter than 10 d. Similar stars may be found in other large data bases of new variables (e.g., OGLE). The three possible sources of the magnitude variations – pulsation, starspots and ellipsoidal deformation – are discussed in general terms. The parallaxes and V − I colour indices are used to calculate radii and temperatures for all M giant variables with P <100 d. Masses are estimated from the positions of the stars in a Hertzsprung–Russell (HR) diagram, using evolutionary tracks. Using these data, it is shown that starspots can be ruled out as a variability mechanism in almost all cases, and ellipsoidal variations in about half of the stars. Pulsation in very high-overtone modes appears to be the only viable explanation for the stars with P <10 d. Many of the stars may be multiperiodic. IRAS data are used to deduce information about reddening and circumstellar dust. The apparently low level of mass-loss, as well as the kinematics and the spatial distribution of the stars, indicates that they are from a relatively young (i.e., thin disc) giant star population.     

Star formation in the Cepheus Flare region – II. A-type stars associated with IRAS sources

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.     

Infrared study of infrared carbon stars based on 2MASS,IRAS and ISO SWS data

For this paper, we collected all infrared carbon stars (IRCSs) known so far from the literature and identified the 2MASS counterparts of all IRCSs. Using 2MASS, IRAS and ISO SWS data, we investigate the infrared properties of IRCSs. We find that the infrared colors and temperatures of IRCSs—not only in the IRAS region but also in the near infrared—are between those for visual carbon stars and extreme carbon stars. The results in this paper strongly support the suggestion that the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars is the evolutionary sequence in the AGB phase for carbon-rich stars. In addition, using the ISO SWS data, we find that an evolutionary sequence also exists within the IRCS stage.     

Molecular abundances in carbon-rich circumstellar envelopes

Millimetre observations of three southern carbon stars, IRAS 07454-7112, IRAS 15082-4808 and IRAS 15194-5115 detected 14 molecular species and some of their isotopomers. The¹²C/¹³C ratio was found to vary between sources.     

100-yr mass-loss modulations on the asymptotic giant branch

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.     

Extended dust shells around carbon stars resolved by “HIRAS”

We have examined forty-two carbon stars which show excess emission at 60 and/or 100µm by applying maximum-entropy image reconstruction techniques to the IRAS 60µm survey data. Thirteen stars are found to be extended in the reconstructed images. Four of them show a detached ring centered on the stellar position. In particular, U Ant may have a double detached dust shell. The implications of our results are discussed concerning the variation of mass loss on the AGB evolution.     

Infrared Study of T Tauri Stars Based on IRAS and 2MASS Observations

The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented.     

The stellar composition of the star formation region CMa R1 – I. Results from new photometric and spectroscopic classifications

A new photometric and spectroscopic survey of the star formation region (SFR) CMa R1 is described. In a sample of 165 stars brighter than 13th mag, 88 stars were found to be probable members of the SFR. They are defined as early-type stars with E ( B − V )0.16 mag, which corresponds to a distance of about 1 kpc. 74 of the probable members are B stars. 19 stars are possibly associated with an IRAS point source. We derive a most probable distance of 1050±150 pc to the association. It appears that about 80 candidate members are pre-main-sequence stars with ages lower than 6 million years, while the main sequence extends over 6.0–7.6 mag, which is consistent with star formation starting about 8 million years ago and continuing until at least half a million years ago. Two bright B stars in the association (GU CMa and FZ CMa) seem to be much older and probably do not originate from the same star formation episode. The star formation efficiency appears to increase roughly monotonically with time up to half a million years ago. From our data, we conclude that only a minor fraction of the stars has been created through the scenario suggested by Herbst & Assousa, in which the members of CMa R1 form by compression of ambient material by a supernova shock wave. An extensive search for candidate members with H α emission did not reveal new Herbig Ae/Be candidates, so that the number of stars in this class seems to be limited to four: Z CMa, LkH α 218, LkH α 220 and possibly HD 53367.     

X-ray emission as a tracer of circumstellar matter around herbig ae/be stars

We have detected X-ray emission (1 keV) from young intermediate-mass stars (Herbig Ae/Be stars). Since these stars are not supposed to produce intrinsic X-ray emission (no convection, no coronae), we believe that our results suggest that the X-ray emission actually traces the shock interaction of the Ae/Be star stellar winds with remnant circumstellar matter left over from the star formation process, the presence of which is also indicated by far-infrared (IRAS) and submm/mm continuum data.     

Optical properties of the carbon dust grains in the envelopes around asymptotic giant branch stars

We have investigated the optical properties of the carbon dust grains in the envelopes around carbon-rich asymptotic giant branch stars, paying close attention to the infrared observations of the stars and the laboratory-measured optical data of the candidate dust grain materials. We have compared the radiative transfer model results with the observed spectral energy distributions of the stars including IRAS Point Source Catalog and IRAS Low Resolution Spectrograph data. We have deduced an opacity function of amorphous carbon dust grains from model fitting with infrared carbon stars. From the opacity function, we have derived the optical constants of the AMC grains. The optical constants satisfy the Kramers–Kronig relation and produce the opacity function that fits the observations of infrared carbon stars better than previous works in the wide wavelength range 1–1000 μm. We have used simple mixtures of the AMC and silicon carbide grains for modelling. We have compared the contributions that AMC and SiC grains make to the opacity for the cases of simple mixtures of them and spherical core–mantle type grains consisting of a SiC core and an AMC mantle .     

The infrared properties of barium stars

The infrared properties of barium stars are studied using published data in the K band and from IRAS . At 12 and 25 μm the emission from barium stars shows no excess over photospheric emission. Thus the claim made by Hakkila that some barium stars show evidence of the presence of warm (∼300  K ) circumstellar material is not supported. The 60-μm properties of barium stars are studied using survival analysis methods, and it is found that very few (3.7 ± 2.6 per cent) barium stars exhibit far-infrared excesses. Furthermore, it is found that the incidence of excess emission at 60 μm is lower in barium stars than for normal G and K giants. This may indicate that the mass-transfer event that is assumed to have taken place in barium stars has removed any cool circumstellar material that may have existed in these systems. Alternatively, it is suggested that the incidence of infrared excesses in normal G and K giants may have been over-estimated as a result of not fully accounting for foreground contamination by interstellar cirrus.     

First Byurakan Spectral Sky Survey. Stars of Late-Spectral Types. XIV. Zone +13° ≤ δ ≤ +33°

We present the fourteenth list of faint late M and carbon type stars detected on the plates of the First Byurakan Spectral Sky Survey in the zone +13° +33° covering about 4736 sq. degrees. From 260 stars, 118 are newly detected objects: they are 19 carbon stars, 5 carbon star candidates, and 94 M-type stars. Among 118 detected objects 73( 57 PSC + 16 FSC ) are unclassified IRAS sources. Accurate positions, spectral classes, red magnitudes, color indices, and near-infrared J, H and K photometry are given, using several astronomical databases. Finding charts from DSS are given for the most interesting objects.     

IRAS 17213-3841:晚型富碳星还是早型发射线星?

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．