- ID:
- ivo://CDS.VizieR/J/A+A/440/111
- Title:
- Spectra of SMC star clusters
- Short Name:
- J/A+A/440/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present flux-calibrated integrated spectra in the range 360-680nm for 18 concentrated SMC clusters. The objects are part of a systematic spectroscopic survey of SMC star clusters which is being undertaken at Complejo Astronomico El Leoncito (CASLEO) in San Juan (Argentina) and Cerro Tololo Inter-American Observatory (CTIO, Chile).
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Search Results
- ID:
- ivo://CDS.VizieR/J/AN/320/105
- Title:
- Spectrophotometry of 26 supergiants in the LMC
- Short Name:
- J/AN/320/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New spectrophotometric data for 3 galactic and 23 LMC F to G supergiants are presented. The wavelength range of the spectra is 3400 to 6400{AA}, the resolution about 10{AA}. The mean transformational error of the fluxes is 0.03mag. The S/N ratio is about 100 and 30 for galactic and LMC stars, respectively. Details about the reduction one may found in Oestreicher & Schmidt-Kaler (1998MNRAS.299..625O) and Malyuto et al. (1997MNRAS.286..500M). The fluxes are given in magnitudes according to the system of Hayes & Latham (1975ApJ...197..593H). For each star an ASCII file is given with the name of the first identifier. In the first column the wavelength, in the second column the flux is given.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/57
- Title:
- Spectroscopic HR diagram of OB stars in the SMC
- Short Name:
- J/ApJ/868/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive stellar atmosphere analysis of 329 O- and B-type stars in the Small Magellanic Cloud (SMC) from the RIOTS4 survey. Using spectroscopically derived effective temperature Teff and surface gravities, we find that classical Be stars appear misplaced to low Teff and high luminosity in the spectroscopic Hertzsprung-Russell diagram (sHRD). Together with the most luminous stars in our sample, the stellar masses derived from the sHRD for these objects are systematically larger than those obtained from the conventional Hertzsprung-Russell diagram. This suggests that the well-known, spectroscopic mass-discrepancy problem may be linked to the fact that both groups of stars have outer envelopes that are nearly gravitationally unbound. The non-emission-line stars in our sample mainly appear on the main sequence, allowing a first estimate of the terminal-age main sequence (TAMS) in the SMC, which matches the predicted TAMS between 12 and 40M_{sun}_ at SMC metallicity. We further find a large underabundance of stars above ~25M_{sun}_ near the zero-age main sequence, reminiscent of such earlier findings in the Milky Way and Large Magellanic Cloud.
- ID:
- ivo://CDS.VizieR/J/AJ/144/88
- Title:
- Spectroscopy of 6 LMC RR Lyrae and 3 SMC RR Lyrae
- Short Name:
- J/AJ/144/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5m Magellan telescopes, we obtain medium resolution (R~2000-6000) spectra of six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars were chosen because their previously determined photometric metallicities were among the lowest metallicities found for stars belonging to the old populations in the Magellanic Clouds. We find the spectroscopic metallicities of these stars to be as low as [Fe/H]_spec_=-2.7dex, the lowest metallicity yet measured for any star in the Magellanic Clouds. We confirm that for metal-poor stars, the photometric metallicities from the Fourier decomposition of the light curves are systematically too high compared to their spectroscopic counterparts. However, for even more metal-poor stars below [Fe/H]_phot_<-2.8dex this trend is reversed and the spectroscopic metallicities are systematically higher than the photometric estimates. We are able to determine abundance ratios for 10 chemical elements (Fe, Na, Mg, Al, Ca, Sc, Ti, Cr, Sr, and Ba), which extend the abundance measurements of chemical elements for RR Lyrae stars in the Clouds beyond [Fe/H] for the first time. For the overall [{alpha}/Fe] ratio, we obtain an overabundance of 0.36dex, which is in very good agreement with results from metal-poor stars in the Milky Way halo as well as from the metal-poor tail in dwarf spheroidal galaxies. Comparing the abundances with those of the stars in the Milky Way halo we find that the abundance ratios of stars of both populations are consistent with another. Therefore, we conclude that from a chemical point of view early contributions from Magellanic-type galaxies to the formation of the Galactic halo as claimed in cosmological models are plausible.
- ID:
- ivo://CDS.VizieR/J/AJ/129/1465
- Title:
- Spectroscopy of red giants in the LMC bar
- Short Name:
- J/AJ/129/1465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report metallicities and radial velocities derived from spectra at the near-infrared calcium triplet for 373 red giants in a 200arcmin^2^ area at the optical center of the LMC bar. These are the first spectroscopic abundance measurements of intermediate-age and old field stars in the high surface brightness heart of the LMC. The metallicity distribution is sharply peaked at the median value [Fe/H]=-0.40, with a small tail of stars extending down to [Fe/H]<=-2.1; 10% of the red giants are observed to have [Fe/H]<=-0.7.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/124
- Title:
- Spectroscopy on LMC clusters
- Short Name:
- J/ApJ/749/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of an ongoing program to measure detailed chemical abundances in nearby galaxies, we use a sample of young- to intermediate-age clusters in the Large Magellanic Cloud with ages of 10Myr-2Gyr to evaluate the effect of isochrone parameters, specifically core convective overshooting, on Fe abundance results from high-resolution, integrated light spectroscopy. In this work we also obtain fiducial Fe abundances from high-resolution spectroscopy of the cluster individual member stars. We compare the Fe abundance results for the individual stars to the results from isochrones and integrated light spectroscopy to determine whether isochrones with convective overshooting should be used in our integrated light analysis of young- to intermediate-age (10Myr-3Gyr) star clusters. We find that when using the isochrones from the Teramo group, we obtain more accurate results for young- and intermediate-age clusters over the entire age range when using isochrones without convective overshooting. While convective overshooting is not the only uncertain aspect of stellar evolution, it is one of the most readily parameterized ingredients in stellar evolution models, and thus important to evaluate for the specific models used in our integrated light analysis. This work demonstrates that our method for integrated light spectroscopy of star clusters can provide unique tests for future constraints on stellar evolution models of young- and intermediate-age clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/49
- Title:
- Spitzer/IRAC observations of SMC Cepheids
- Short Name:
- J/ApJ/816/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using Spitzer observations of classical Cepheids we have measured the true average distance modulus of the Small Magellanic Cloud (SMC) to be 18.96+/-0.01_stat_+/-0.03_sys_mag (corresponding to 62+/-0.3kpc), which is 0.48+/-0.01mag more distant than the LMC. This is in agreement with previous results from Cepheid observations, as well as with measurements from other indicators such as RR Lyrae stars and the tip of the red giant branch. Utilizing the properties of the mid-infrared Leavitt Law we measured precise distances to individual Cepheids in the SMC, and have confirmed that the galaxy is tilted and elongated such that its eastern side is up to 20kpc closer than its western side. This is in agreement with the results from red clump stars and dynamical simulations of the Magellanic Clouds and Stream.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A92
- Title:
- Spitzer/IRS analysis of the 30-micron sources
- Short Name:
- J/A+A/626/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis and comparison of the 30{mu}m dust features seen in the Spitzer Space Telescope spectra of 207 carbon-rich asymptotic giant branch (AGB) stars, post-AGB objects, and planetary nebulae (PNe) located in the Milky Way, the Magellanic Clouds (MCs), or the Sagittarius dwarf spheroidal galaxy (Sgr dSph), which are characterised by different average metallicities. We investigated whether the formation of the 30{mu}m feature carrier may be a function of the metallicity. Through this study we expect to better understand the late stages of stellar evolution of carbon-rich stars in these galaxies. Our analysis uses the "Manchester method" as a basis for estimating the temperature of dust for the carbon-rich AGB stars and the PNe in our sample. For post-AGB objects we changed the wavelength ranges used for temperature estimation, because of the presence of the 21{mu}m feature on the short wavelength edge of the 30{mu}m feature. We used a black-body function with a single temperature deduced from the Manchester method or its modification to approximate the continuum under the 30{mu}m feature. We find that the strength of the 30{mu}m feature increases until dust temperature drops below 400K. Below this temperature, the large loss of mass and probably the self-absorption effect reduces the strength of the feature. During the post-AGB phase, when the intense mass-loss has terminated, the optical depth of the circumstellar envelope is smaller, and the 30{um}m feature becomes visible again, showing variety of values for post-AGB objects and PNe, and being comparable with the strengths of AGB stars. In addition, the AGB stars and post-AGB objects show similar values of central wavelengths - usually between 28.5 and 29.5{mu}m. However, in case of PNe the shift of the central wavelength towards longer wavelengths is visible. The normalised median profiles for AGB stars look uniformly for various ranges of dust temperature, and different galaxies. We analysed the profiles of post-AGB objects and PNe only within one dust temperature range (below 200K), and they were also similar in different galaxies. In the spectra of 17 PNe and five post-AGB objects we found the broad 16-24{mu}m feature. Two objects among the PNe group are the new detections: SMP LMC 51, and SMP LMC 79, whereas in the case of post-AGBs the new detections are: IRAS 05370-7019, IRAS 05537-7015, and IRAS 21546+4721. In addition, in the spectra of nine PNe we found the new detections of 16-18{mu}m feature. We also find that the Galactic post-AGB object IRAS 11339-6004 has a 21{mu}m emission. Finally, we have produced online catalogues of photometric data and Spitzer IRS spectra for all objects that show the 30{mu}m feature. These resources are available online for use by the community. The most important conclusion of our work is the fact that the formation of the 30{mu}m feature is affected by metallicity. Specifically that, as opposed to more metal-poor samples of AGB stars in the MCs, the feature is seen at lower mass-loss rates, higher temperatures, and has seen to be more prominent in Galactic carbon stars. The averaged feature (profile) in the AGB, post-AGB objects, and PNe seems unaffected by metallicity at least between a fifth and solar metallicity, but in the case of PNe it is shifted to significantly longer wavelengths.
- ID:
- ivo://CDS.VizieR/J/ApJ/826/44
- Title:
- Spitzer/IRS obs. of Magellanic carbon stars
- Short Name:
- J/ApJ/826/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C_2_H_2_ at 7.5{mu}m. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.
- ID:
- ivo://CDS.VizieR/J/ApJ/743/76
- Title:
- Spitzer photometry of LMC Cepheids
- Short Name:
- J/ApJ/743/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Carnegie Hubble Program is designed to improve the extragalactic distance scale using data from the post-cryogenic era of Spitzer. The ultimate goal is a determination of the Hubble constant to an accuracy of 2%. This paper is the first in a series on the Cepheid population of the Large Magellanic Cloud, and focusses on the period-luminosity (PL) relations (Leavitt laws) that will be used, in conjunction with observations of Milky Way Cepheids, to set the slope and zero point of the Cepheid distance scale in the mid-infrared. To this end, we have obtained uniformly sampled light curves for 85 LMC Cepheids, having periods between 6 and 140 days. PL and period-color relations are presented in the 3.6um and 4.5um bands. We demonstrate that the 3.6um band is a superb distance indicator. The cyclical variation of the [3.6]-[4.5] color has been measured for the first time. We attribute the amplitude and phase of the color curves to the dissociation and recombination of CO molecules in the Cepheid's atmosphere. The CO affects only the 4.5um flux making it a potential metallicity indicator.
