Low cost equipment for astronomical spectroscopy

The purpose of this paper is to show how we can obtain spectra for different astronomical objects using low coat equipment. Where a high-efficiency diffraction grating named “The Star Analyzer” was used by the International Astronomical Center (IAC) in Abu Dhabi, UAE to get the spectrum of different astronomical objects. Balmer series was readily visible when observing an “A” type star. TiO absorptions lines were distinguished by observing an “M” type star. Methane absorption lines were visible by observing Uranus and Neptune. Whereas HI and HeI emission lines were detected by observing a blue hypergiant. In addition, C2 Swan band absorption lines were identified by observing a red giant carbon star. This type of observation is very interesting for public outreach as well as university students, because it shows astrophysical principles for public and students practically and by using low cost equipment.

AGB Winds with Gas-Dust Drift in Stellar Evolution Codes

A significant fraction of new metals produced in stars enter the interstellar medium in the form of dust grains. Including dust and wind formation in stellar evolution models of late-stage low- and intermediate-mass stars provides a way to quantify their contribution to the cosmic dust component. In doing so, a correct physical description of dust formation is of course required, but also a reliable prescription for the mass-loss rate. Here, we present an improved model of dust-driven winds to be used in stellar evolution codes and insights from recent detailed numerical simulations of carbon-star winds including drift (decoupling of dust and gas). We also discuss future directions for further improvement.

Are extreme asymptotic giant branch stars post-common envelope binaries?

ABSTRACT Modelling dust formation in single stars evolving through the carbon-star stage of the asymptotic giant branch (AGB) reproduces well the mid-infrared colours and magnitudes of most of the C-rich sources in the Large Magellanic Cloud (LMC), apart from a small subset of extremely red objects (EROs). An analysis of the spectral energy distributions of EROs suggests the presence of large quantities of dust, which demand gas densities in the outflow significantly higher than expected from theoretical modelling. We propose that binary interaction mechanisms that involve common envelope (CE) evolution could be a possible explanation for these peculiar stars; the CE phase is favoured by the rapid growth of the stellar radius occurring after C/O overcomes unity. Our modelling of the dust provides results consistent with the observations for mass-loss rates $\dot{M} \sim 5\times 10^{-4}\,{\rm M}_{\odot }$ yr−1, a lower limit to the rapid loss of the envelope experienced in the CE phase. We propose that EROs could possibly hide binaries with orbital periods of about days and are likely to be responsible for a large fraction of the dust production rate in galaxies.

Gas and dust from metal-rich AGB stars

Context. Stars evolving through the asymptotic giant branch (AGB) phase provide significant feedback to their host system, which is both gas enriched in nuclear-burning products, and dust formed in their winds, which they eject into the interstellar medium. Therefore, AGB stars are an essential ingredient for the chemical evolution of the Milky Way and other galaxies. Aims. We study AGB models with super-solar metallicities to complete our vast database, so far extending from metal-poor to solar-chemical compositions. We provide chemical yields for masses in the range 1−8 M⊙ and metallicities Z = 0.03 and Z = 0.04. We also study dust production in this metallicity domain. Methods. We calculated the evolutionary sequences from the pre-main sequence through the whole AGB phase. We followed the variation of the surface chemical composition to calculate the chemical yields of the various species and model dust formation in the winds to determine the dust production rate and the total dust mass produced by each star during the AGB phase. Results. The physical and chemical evolution of the star is sensitive to the initial mass: M > 3 M⊙ stars experience hot bottom burning, whereas the surface chemistry of the lower mass counterparts is altered only by third dredge-up. The carbon-star phase is reached by 2.5−3.5 M⊙ stars of metallicity Z = 0.03, whereas all the Z = 0.04 stars (except the 2.5 M⊙) remain O-rich for the whole AGB phase. Most of the dust produced by metal-rich AGBs is in the form of silicate particles. The total mass of dust produced increases with the mass of the star, reaching ∼0.012 M⊙ for 8 M⊙ stars.

Rings and arcs around evolved stars – II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009, and NGC 7027

ABSTRACT We present a detailed comparative study of the arcs and fragmented ring-like features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using high-quality multi-epoch HST images. This comparison allows us to investigate the connection and possible evolution between the regular patterns surrounding AGB stars and the irregular concentric patterns around PNe. The radial proper motion of these features, ≃15 km s−1, are found to be consistent with the AGB wind and their linear sizes and interlapse times (500–1900 yr) also agree with those found around AGB stars, suggesting a common origin. We find evidence using radiative-hydrodynamic simulations that regular patterns produced at the end of the AGB phase become highly distorted by their interactions with the expanding PN and the anisotropic illumination and ionization patterns caused by shadow instabilities. These processes will disrupt the regular (mostly spiral) patterns around AGB stars, plausibly becoming the arcs and fragmented rings observed in the haloes of PNe.

Properties of carbon stars in the solar neighbourhood based on Gaia DR2 astrometry

Context. Stars evolving along the asymptotic giant branch (AGB) can become carbon rich in the final part of their evolution. The detailed description of their spectra has led to the definition of several spectral types: N, SC, J, and R. To date, differences among them have been partially established only on the basis of their chemical properties. Aims. An accurate determination of the luminosity function (LF) and kinematics together with their chemical properties is extremely important for testing the reliability of theoretical models and establishing on a solid basis the stellar population membership of the different carbon star types. Methods. Using Gaia Data Release 2 (Gaia DR2) astrometry, we determine the LF and kinematic properties of a sample of 210 carbon stars with different spectral types in the solar neighbourhood with measured parallaxes better than 20%. Their spatial distribution and velocity components are also derived. Furthermore, the use of the infrared Wesenheit function allows us to identify the different spectral types in a Gaia-2MASS diagram. Results. We find that the combined LF of N- and SC-type stars are consistent with a Gaussian distribution peaking at Mbol ∼ −5.2 mag. The resulting LF, however, shows two tails at lower and higher luminosities more extended than those previously found, indicating that AGB carbon stars with solar metallicity may reach Mbol ∼ −6.0 mag. This contrasts with the narrower LF derived in Galactic carbon Miras from previous studies. We find that J-type stars are about half a magnitude fainter on average than N- and SC-type stars, while R-hot stars are half a magnitude brighter than previously found, although fainter in any case by several magnitudes than other carbon types. Part of these differences are due to systematically lower parallaxes measured by Gaia DR2 with respect to HIPPARCOS values, in particular for sources with parallax ϖ < 1 mas. The Galactic spatial distribution and velocity components of the N-, SC-, and J-type stars are very similar, while about 30% of the R-hot stars in the sample are located at distances greater than ∼500 pc from the Galactic plane, and show a significant drift with respect to the local standard of rest. Conclusions. The LF derived for N- and SC-type in the solar neighbourhood fully agrees with the expected luminosity of stars of 1.5−3 M⊙ on the AGB. On a theoretical basis, the existence of an extended low-luminosity tail would require a contribution of extrinsic low-mass carbon stars, while the high-luminosity tail would imply that stars with mass values up to ∼5 M⊙ may become carbon stars on the AGB. J-type stars differ significantly not only in their chemical composition with respect to the N- and SC-types, but also in their LF, which reinforces the idea that these carbon stars belong to a different type whose origin is still unknown. The derived luminosities of R-hot stars means that it is unlikely that these stars are in the red-clump, as previously claimed. On the other hand, the derived spatial distribution and kinematic properties, together with their metallicity values, indicate that most of the N-, SC-, and J-type stars belong to the thin disc population, while a significant fraction of R-hot stars show characteristics compatible with the thick disc.

Carbon stars as standard candles: I. The luminosity function of carbon stars in the Magellanic Clouds

ABSTRACT Our goal in this paper is to derive a carbon-star luminosity function that will eventually be used to determine distances to galaxies at 50–60 Mpc and hence yield a value of the Hubble constant. Cool N-type carbon stars exhibit redder near-infrared colours than oxygen-rich stars. Using Two Micron All Sky Survey near-infrared photometry and the Gaia Data Release 2, we identify carbon stars in the Magellanic Clouds (MC) and the Milky Way (MW). Carbon stars in the MC appear as a distinct horizontal feature in the near-infrared ((J − Ks)0, MJ) colour–magnitude diagram. We build a colour selection (1.4 &lt; (J − Ks)0 &lt; 2) and derive the luminosity function of the colour-selected carbon stars. We find the median absolute magnitude and the dispersion, in the J band, for the Large and the Small Magellanic Clouds (LMC/SMC) to be, respectively, ($\bar{M_J} = -6.284~\pm ~0.004$ and σ = 0.352 ± 0.005) and ($\bar{M_J} = -6.160~\pm ~0.015$ and σ = 0.365 ± 0.014). The difference between the MC may be explained by the lower metallicity of the SMC, but in any case it provides limits on the type of galaxy whose distance can be determined with this technique. To account for metallicity effects, we developed a composite magnitude, named C, for which the error-weighted mean C magnitude of the MC are equal. Thanks to the next generation of telescopes (JWST, ELT, and TMT), carbon stars could be detected in MC-type galaxies at distances out to 50–60 Mpc. The final goal is to eventually try and improve the measurement of the Hubble constant while exploring the current tensions related to its value.

A SkyMapper view of the Large Magellanic Cloud: the dynamics of stellar populations

ABSTRACT We present the first SkyMapper stellar population analysis of the Large Magellanic Cloud (hereafter LMC), including the identification of 3578 candidate Carbon Stars through their extremely red g − r colours. Coupled with Gaia astrometry, we analyse the distribution and kinematics of this Carbon Star population, finding the LMC to be centred at (RA, Dec.) = (80.90° ± 0.29, −68.74° ± 0.12), with a bulk proper motion of $(\mu _{\alpha },\mu _{\delta }) = (1.878\pm 0.007,0.293\pm 0.018) \, \mathrm{mas \, yr^{-1}}$ and a disc inclination of i = 25.6° ± 1.1 at position angle θ = 135.6° ± 3.3°. We complement this study with the identification and analysis of additional stellar populations, finding that the dynamical centre for red giant branch stars is similar to that seen for the Carbon Stars, whereas for young stars the dynamical centre is significantly offset from the older populations. This potentially indicates that the young stars were formed as a consequence of a strong tidal interaction, probably with the Small Magellanic Cloud. In terms of internal dynamics, the tangential velocity profile increases linearly within $\sim \!3\ \, \mathrm{kpc}$, after which it maintains an approximately constant value of $V_{\mathrm{ rot}} = 83.6\pm 1.7 \, \mathrm{km \, s^{-1}}$ until $\sim \!7 \, \mathrm{kpc}$. With an asymmetric drift correction, we estimate the mass within $7\, \mathrm{kpc}$ to be $M_{\rm LMC}(\lt 7\, \mathrm{kpc}) = (2.5\pm 0.1)\times 10^{10}{\rm \, {\rm M}_{\odot }}$ and within the tidal radius ($\sim\! 30\ \, \mathrm{kpc}$) to be $M_{\rm LMC}(\lt 30\, \mathrm{kpc}) = (1.06 \pm 0.32)\times 10^{11}\ {\rm \, {\rm M}_{\odot }}$, consistent with other recent measurements.