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Register a new userA K-band spectral mini-survey of Galactic B[e] stars
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We present a mini-survey of Galactic B[e] stars mainly undertaken with the Large Binocular Telescope (LBT). B[e] stars show morphological features with hydrogen emission lines and an infrared excess, attributed to warm circumstellar dust. In general, these features are assumed to arise from dense, non-spherical, disk-forming circumstellar material in which molecules and dust can condensate. Due to the lack of reliable luminosities, the class of Galactic B[e] stars contains stars at very different stellar evolutionary phases like Herbig AeBe, supergiants or planetary nebulae. We took near-infrared long-slit K-band spectra for a sample of Galactic B[e] stars with the LBT-Luci I. Prominent spectral features, such as the Brackett gamma line and CO band heads are identified in the spectra. The analysis shows that the stars can be characterized as evolved objects. Among others we find one LBV candidate (MWC314), one supergiant B[e] candidate with 13CO (MWC137) and in two cases (MWC623 and AS 381) indications for the existence of a late-type binary companion, complementary to previous studies. For MWC84, IR spectra were taken at different epochs with LBT-Luci I and the GNIRS spectrograph at the Gemini North telescope. The new data show the disappearance of the circumstellar CO emission around this star, previously detectable over decades. Also no signs of a recent prominent eruption leading to the formation of new CO disk emission are found during 2010 and 2013.
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Massive evolved stars in transition phases, such as Luminous Blue Variables (LBVs), B[e] Supergiants (B[e]SGs), and Yellow Hypergiants (YHGs), are not well understood, and yet crucial steps in determining accurate stellar and galactic evolution models. The circumstellar environments of these stars reveal their mass-loss history, identifying clues to both their individual evolutionary status and the connection between objects of different phases. Here we present a survey of 25 such evolved massive stars (16 B[e]SGs, 6 LBVs, 2 YHGs, and 1 Peculiar Oe star), observed in the K-band with the Spectrograph for INtegral Field Observation in the Near-Infrared (SINFONI; R = 4500) on the ESO VLT UT4 8 m telescope. The sample can be split into two categories based on spectral morphology: one group includes all of the B[e]SGs, the Peculiar Oe star, and two of the LBVs, while the other includes the YHGs and the rest of the LBVs. The difference in LBV spectral appearance is due to some objects being in a quiescent phase and some objects being in an active or outburst phase. CO emission features are found in 13 of our targets, with first time detections for MWC 137, LHA 120-S 35, and LHA 115-S 65. From model fits to the CO band heads, the emitting regions appear to be detached from the stellar surface. Each star with ^12CO features also shows ^13CO emission, signaling an evolved nature. Based on the level of ^13C enrichment, we conclude that many of the B[e]SGs are likely in a pre-Red Supergiant phase of their evolution. There appears to be a lower luminosity limit of log L/L_solar = 5.0 below which CO is not detected. The lack of CO features in several high luminosity B[e]SGs and variability in others suggests that they may in fact be LBV candidates, strengthening the connection between these two very similar transition phases.
We analyse medium-resolution spectra (Rsim 18000) of 19 late type dwarfs in order to determine vsini-s using synthetic rather than observational template spectra. For this purpose observational data around 2.2 $mu$m of stars with spectral classes from G8V to M9.5V were modelled. We find that the Na I (2.2062 and 2.2090 $mu$m) and $^{12}$CO 2-0 band features are modelled well enough to use for vsini determination without the need for a suitable observational template spectra. Within the limit of the resolution of our spectra, we use synthetic spectra templates to derive vsini values consistent with those derived in the optical regime using observed templates. We quantify the errors in our vsini determination due to incorrect choice of model parameters Teff, log $g$, $v_{rm micro}$, [Fe/H] or FWHM and show that they are typically less than 10 per cent. We note that the spectral resolution of our data(sim 16 km/s) limited this study to relatively fast rotators and that resolutions of 60000 will required to access most late-type dwarfs.
We analyse spectroscopic observations of the B[e] star HD 50138 (MWC 158, V743 Mon, or IRAS 06491-0654), a member of the FS CMa group, obtained over the last twenty years. Four different epochs are identified in the observational data, where the variability of the spectral features is substantially different. Additionally, two long periods of (3 000 +/- 500) and (5 000 +/- 1000) days are found in the variations of the equivalent widths of the H alpha and [OI] 6300 A lines and radial velocities of the H alpha line violet peak. Modest signatures of a regular period of ~34 days in the radial velocities of the H alpha red peak and H beta central depression are found in the season 2013/2014. The H alpha V/R changes indicate a periodicity of ~50 days. The correlations between individual spectral features significantly restricts the model of the object and suggest that it is most likely a binary system with a highly distorted disc with spiral arms around the primary component. At the same time, no obvious signs of the secondary component has been found in the objects spectrum.
We investigate the possible role of line-driven winds in the circumstellar envelope in B[e] stars, mainly the role of the $Omega$-slow wind solution, which is characterized by a slower terminal velocity and higher mass-loss rate, in comparison with the standard (m-CAK) wind solution. In this work, we assume two scenarios: 1) a spherically symmetric star and 2) a scenario that considers the oblate shape, considering only the oblate correction factor. For certain values of the line force parameters (according to previous works), we obtain in both scenarios a density contrast $gtrsim10^{2}$ between equatorial and polar densities, characterized for a fast polar wind and a slow and denser wind when the $Omega$-slow wind solution is obtained. All this properties are enhanced when the oblate correction factor is included in our calculations.
Infra-Red(IR) astronomical databases, namely, IRAS, 2MASS, WISE, and Spitzer, are used to analyze photometric data of 126 carbon stars whose spectra are visible in the First Byurakan Survey low-resolution spectral plates. Among these, six new objects, recently confirmed on the digitized FBS plates, are included. For three of them, moderate-resolution CCD optical spectra are also presented. In this work several IR color-color diagrams are studied. Early and late-type C stars are separated in the JHK Near-Infra-Red(NIR) color-color plots, as well as in the WISE W3-W4 versus W1-W2 diagram. Late N-type Asymptotic Giant Branch stars are redder in W1-W2, while early-types(CH and R giants) are redder in W3-W4 as expected. Objects with W2-W3 > 1.0 mag. show double-peaked spectral energy distribution, indicating the existence of the circumstellar envelopes around them. 26 N-type stars have IRAS Point Source Catalog(PSC) associations. For FBS 1812+455 IRAS Low-Resolution Spectra in the wavelength range 7.7 - 22.6micron and Spitzer Space Telescope Spectra in the range 5 - 38micro are presented clearly showing absorption features of C2H2(acetylene) molecule at 7.5 and 13.7micron , and the SiC(silicone carbide) emission at 11.3micron. The mass-loss rates for eight Mira-type variables are derived from the K-[12] color and from the pulsation periods. The reddest object among the targets is N-type C star FBS 2213+421, which belong to the group of the cold post-AGB R Coronae Borealis(R CrB) variables.
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