- ID:
- ivo://CDS.VizieR/J/A+A/628/A132
- Title:
- IK Tau and HIP 20188 visible polarimetric imaging
- Short Name:
- J/A+A/628/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present visible polarimetric imaging observations of the oxygen-rich AGB star IK Tau obtained with SPHERE-ZIMPOL (phase 0.27) as well as interferometric observations with AMBER. The polarimetric imaging capabilities of SPHERE-ZIMPOL have allowed us to spatially resolve clumpy dust clouds at 20-50mas from the central star, which corresponds to 2-5R* when combined with a central star's angular diameter of 20.7+/-1.53 mas measured with AMBER. The diffuse, asymmetric dust emission extends out to ~73R*. We find that the TiO emission extends to 150 mas (15R*). The AMBER data in the CO lines also suggest a molecular outer atmosphere extending to ~1.5R*. The results of our 2-D Monte Carlo radiative transfer modelling of dust clumps suggest that the polarized intensity and degree of linear polarization can be reasonably explained by small-sized (0.1{mu}m) grains of Al_2_O_3, MgSiO_3, or Mg_2_SiO_4 in an optically thin shell ({tau}_550 nm=0.5+/-0.1) with an inner boundary radius of 3.5*. IK Tau's mass-loss rate is 20 to 50 times higher than the previously studied AGB stars W Hya, R Dor, and o Cet. Nevertheless, our observations of IK Tau revealed that clumpy dust formation occurs close to the star as seen in those low mass-rate AGB stars.
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- ID:
- ivo://CDS.VizieR/J/PAZh/38/183
- Title:
- IRAS 19336-0400 UBV light curves
- Short Name:
- J/PAZh/38/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photoelectric and spectral observations of a hot candidate proto-planetary nebula early B-type supergiant with emission lines in spectrum-IRAS 19336-0400. The light and color curves display fast irregular brightness variations with maximum amplitudes {Detla}V=0.30m, {Detla}B=0.35m, {Detla}U=0.40m and color-brightness correlations. By the variability characteristics IRAS 19336-0400 appears similar to other hot proto-planetary nebulae
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/631
- Title:
- IR photometry of LMC O-rich evolved stars
- Short Name:
- J/MNRAS/440/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to determine the composition of the dust in the circumstellar envelopes of oxygen-rich asymptotic giant branch (AGB) stars, we have computed a grid of MODUST radiative-transfer models for a range of dust compositions, mass-loss rates, dust-shell inner radii and stellar parameters. We compare the resulting colours with the observed oxygen-rich AGB stars from the SAGE-Spec Large Magellanic Cloud (LMC) sample, finding good overall agreement for stars with a mid-infrared excess. We use these models to fit a sample of 37 O-rich AGB stars in the LMC with optically thin circumstellar envelopes, for which 5-35{mu}m Spitzer infrared spectrograph (IRS) spectra and broad-band photometry from the optical to the mid-infrared are available. From the modelling, we find mass-loss rates in the range ~8x10^-8^-5x10^-6^M_{sun}_/yr, and we show that a grain mixture consisting primarily of amorphous silicates, with contributions from amorphous alumina and metallic iron, provides a good fit to the observed spectra. Furthermore, we show from dust models that the AKARI [11]-[15] versus [3.2]-[7] colour-colour diagram is able to determine the fractional abundance of alumina in O-rich AGB stars.
- ID:
- ivo://CDS.VizieR/J/A+AS/146/437
- Title:
- IR spectra of oxygen-rich evolved stars
- Short Name:
- J/A+AS/146/437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed the 8-13.5{mu}m UKIRT CGS3 spectra of 142 M-type stars including 80 oxygen-rich AGB stars and 62 red supergiants, with a view to understanding the differences and similarities between the dust features of these stars. We have classified the spectra into groups according to the observed appearance of the infrared features.
- ID:
- ivo://CDS.VizieR/J/AJ/162/187
- Title:
- IRTF spectral indices for giant stars
- Short Name:
- J/AJ/162/187
- Date:
- 15 Mar 2022
- Publisher:
- CDS
- Description:
- We present infrared spectral indices (1.0-2.3{mu}m) of Galactic late-type giants and red supergiants (RSGs). We used existing and new spectra obtained at resolution power R=2000 with SpeX on the IRTF telescope. While a large CO equivalent width (EW), at 2.29{mu}m ([CO,2.29]>~45{AA}) is a typical signature of RSGs later than spectral type M0, [CO] of K-type RSGs and giants are similar. In the [CO,2.29] versus [MgI,1.71] diagram, RSGs of all spectral types can be distinguished from red giants because the MgI line weakens with increasing temperature and decreasing gravity. We find several lines that vary with luminosity, but not temperature: SiI (1.59{mu}m), Sr (1.033{mu}m), Fe+Cr+Si+CN (1.16{mu}m), Fe+Ti (1.185{mu}m), Fe+Ti (1.196{mu}m), Ti+Ca (1.28{mu}m), and Mn (1.29{mu}m). Good markers of CN enhancement are the Fe+Si+CN line at 1.087{mu}m and CN line at 1.093{mu}m. Using these lines, at the resolution of SpeX, it is possible to separate RSGs and giants. Contaminant O-rich Mira and S-type AGBs are recognized by strong molecular features due to water vapor features, TiO band heads, and/or ZrO absorption. Among the 42 candidate RSGs that we observed, all but one were found to be late types. Twenty-one have EWs consistent with those of RSGs, 16 with those of O-rich Mira AGBs, and one with an S-type AGB. These infrared results open new, unexplored, potential for searches at low resolution of RSGs in the highly obscured innermost regions of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJS/119/83
- Title:
- IUE sample of binaries with hot component
- Short Name:
- J/ApJS/119/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained or retrieved IUE spectra for over 100 middle- and late-type giant and supergiant stars whose spectra indicate the presence of a hot component earlier than type F2. The hot companions are classified accurately by temperature class from their far-UV spectra. The interstellar extinction of each system and the relative luminosities of the components are derived from analysis of the UV and optical fluxes, using a grid of UV intrinsic colors for hot dwarfs. We find that there is fair agreement in general between current UV spectral classification and ground-based hot component types, in spite of the difficulties of assigning the latter. There are a few cases in which the cool component optical classifications disagree considerably with the temperature classes inferred from our analysis of UV and optical photometry. The extinction parameter agrees moderately well with other determinations of B-V color excess. Many systems are worthy of further study especially to establish their spectroscopic orbits. Further work is planned to estimate luminosities of the cool components from the data herein; in many cases, these luminosities' accuracies should be comparable to or exceed those of the Hipparcos parallaxes.
- ID:
- ivo://CDS.VizieR/J/PAZh/36/144
- Title:
- JHKLM photometry of 3 RV Tau supergiants
- Short Name:
- J/PAZh/36/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed our long-term (1995-2008) JHKLM photometry for three variable RV Tau supergiants. It follows from this analysis that: the amplitude of the JHK brightness variations is approximately the same, 0.9-1mag, for the three stars; a negative linear trend is noticeable in the variations of the mean J brightness for AC Her; and the mean J brightness of R Sct and V Vul remained constant. The observed J brightness fluctuations in the supergiants are shown to be consistent either only with the temperature pulsations (AC Her and V Vul) or with the temperature and radial pulsations (R Sct).
- ID:
- ivo://CDS.VizieR/J/A+A/568/L13
- Title:
- K-band spectrum of the very massive star W49nr1
- Short Name:
- J/A+A/568/L13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Very massive stars (M>100M_{sun}_) are very rare objects, but have a strong influence on their environment. The formation of this kind of objects is of prime importance in star formation, but observationally still poorly constrained. We report on the identification of a very massive star in the central cluster of the star-forming region W49. We investigate near-infrared K-band spectroscopic observations of W49 from VLT/ISAAC together with JHK images obtained with NTT/SOFI and LBT/LUCI. We derive a spectral type of W49nr1, the brightest star in the dense core of the central cluster of W49.
- ID:
- ivo://CDS.VizieR/J/AJ/158/20
- Title:
- K-M stars of class I candidate RSGs in Gaia DR2
- Short Name:
- J/AJ/158/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate individual distances and luminosities of a sample of 889 nearby candidate red supergiants (RSGs) with reliable parallaxes ({omega}/{sigma}_{omega}_>4 and RUWE<2.7) from Gaia Data Release 2 (DR2, Cat. I/345). The sample was extracted from the historical compilation of spectroscopically derived spectral types by Skiff (Cat. B/mk), and consists of K-M stars that are listed with class I at least once. The sample includes well-known RSGs from Humphreys (1978ApJS...38..309H), Elias et al. (1985ApJS...57...91E), Jura & Kleinmann (1990ApJS...73..769J), and Levesque et al. (2005ApJ...628..973L). Infrared and optical measurements from the Two Micron All Sky Survey, Catalog of Infrared Observations (CIO), Midcourse Space Experiment, Wide-field Infrared Survey Explorer, MIPSGAL, Galactic Legacy Infrared Midplane Extraordinaire (GLIMPSE), and The Naval Observatory Merged Astrometric Dataset catalogs allow us to estimate the stellar bolometric magnitudes. We analyze the stars in the luminosity versus effective temperature plane and confirm that 43 sources are highly probably RSGs with M_bol_< -7.1 mag. Of the stars in the sample, 43% have masses >7 M_{sun}_. Another ~30% of the sample consists of giant stars.
- ID:
- ivo://CDS.VizieR/J/A+A/513/A53
- Title:
- LABOCA 870um images of evolved stars
- Short Name:
- J/A+A/513/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During their evolution, Asymptotic Giant Branch (AGB) stars experience a high mass-loss which leads to the formation of a circumstellar envelope (CSE) of dust and gas. The mass loss process is the most important phenomenon during this evolutionary stage. In order to understand it, it is important to study the physical parameters of the CSE. The emission of the CSE in the (sub)millimetre range is dominated by the dust continuum. This means that (sub)millimetre observations are a key tool in tracing the dust and improving our knowledge of the mass-loss process. We analysed new sub-millimetre observations of 9 evolved stars in order to constrain the CSE physical parameters. The data were taken by the new APEX bolometer LABoCa. The fluxes at 870 um are derived and the extended emission is investigated. We computed the spectral energy distribution (SEDs) with the 1D radiative transfer code DUSTY, which we compared to literature data. Grain properties were calculated with both a spherical grains distribution and a continuous distribution of ellipsoids (CDE), and a comparison between the two is drawn. Synthetic surface brightness maps were derived from the modelling and were compared to the LABoCa brightness maps. We detected the presence of extended emission around four stars. Physical parameters of the circumstellar envelope were derived from SED modelling, like the dust chemical composition, the dust condensation temperature and the total mass of the envelope.
