- ID:
- ivo://CDS.VizieR/J/A+A/489/1271
- Title:
- CO and OH abundances of 23 K-M giants
- Short Name:
- J/A+A/489/1271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the high resolution infrared spectra observed with the Fourier Transform Spectrometer (FTS) at the 4m telescope of the Kitt Peak National Observatory (KPNO), ro-vibrational lines of ^12^C^16^O, ^13^C^16^O, ^12^C^17^O, and ^16^OH were measured. Some details of the observed spectra including the resolution, S/N ratio, and data of observation are given in table2. The spectroscopic and equivalent width data are given in table3 for 23 red giant stars. The resulting data are used to investigate the nature of the infrared spectra of K-M giant stars. It is found that only the weak lines (log(W/nu)<-4.75) carry the information on the photosphere and hence can be used to extract the nature of the photosphere such as the stellar abundances. The intermediate-strength (-4.75<log(W/nu)<-4.40) as well as the strong (log(W/nu)>-4.4) lines are badly disturbed by the lines of non-photospheric origin. In other words, most lines dominating the infrared spectra, except for the weak lines, are actually hybrid of at least two different kinds of lines originating in the photosphere and in an extra molecular layers outside of photosphere. The nature of the extra layers is not known well, but it may be related to the molecular envelope producing H_2_O lines, not only in late M but also in early M giants as well. Also, the intermediate-strength lines include those with LEP as high as 2eV and hence the extra molecular layer should be quite warm. For the reason outlined above, we determine C, O, and their isotopic abundances using only the weak lines, but we listed the measured data not only of the weak lines but also of the stronger lines as well in table3, with the hope that these data can be of some use to clarify the nature of the warm extra molecular layers.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/469/3802
- Title:
- Compact binary systems around Kepler red giants
- Short Name:
- J/MNRAS/469/3802
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of 168 oscillating red giants from NASA's Kepler mission that exhibit anomalous peaks in their Fourier amplitude spectra. These peaks result from ellipsoidal variations that are indicative of binary star systems, at frequencies such that the orbit of any stellar companion would be within the convective envelope of the red giant. Alternatively, the observed phenomenon may be due to a close binary orbiting a red giant in a triple system, or chance alignments of foreground or background binary systems contaminating the target pixel aperture. We identify 87 stars in the sample as chance alignments using a combination of pixel Fourier analysis and difference imaging. We find that in the remaining 81 cases, the anomalous peaks are indistinguishable from the target star to within 4 arcsec, suggesting a physical association. We examine a GALAXIA model of the Kepler field of view to estimate background star counts and find that it is highly unlikely that all targets can be explained by chance alignments. From this, we conclude that these stars may comprise a population of physically associated systems.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A24
- Title:
- Cool carbon stars in the halo and Fornax dSph
- Short Name:
- J/A+A/562/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show H{alpha} in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars.
- ID:
- ivo://CDS.VizieR/J/AJ/142/103
- Title:
- Cool evolved stars in SAGE-SMC and SAGE-LMC
- Short Name:
- J/AJ/142/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC", or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160um). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ~20% of the global SMC flux (extended + point-source) at 3.6um, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/597/323
- Title:
- Cool stars at the Galactic Center
- Short Name:
- J/ApJ/597/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {lambda}/{Delta}{lambda}=550-1200 near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~5pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the H-R diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1592
- Title:
- Cool stars in galactic clusters
- Short Name:
- J/MNRAS/403/1592
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated the relevant trend of the bolometric correction (BC) at the cool-temperature regime of red giant stars and its possible dependence on stellar metallicity. Our analysis relies on a wide sample of optical-infrared spectroscopic observations, along the 3500{AA}=>2.5um wavelength range, for a grid of 92 red giant stars in five (three globular + two open) Galactic clusters, along the full metallicity range covered by the bulk of the stars, -2.2<=[Fe/H]<=+0.4.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A119
- Title:
- CoRoT red giants abundances
- Short Name:
- J/A+A/564/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained as part of the ground-based follow-up campaigns for 19 targets holding great asteroseismic potential. These data are used to accurately estimate in a self-consistent manner their fundamental parameters and the abundances of 16 chemical species. Some powerful probes of mixing are investigated (the Li and CNO abundances, as well as the carbon isotopic ratio in a few cases). The information provided by the spectroscopic and seismic data is combined to provide more accurate physical parameters and abundances. The stars in our sample follow the general trends between various abundance ratios and the metallicity observed in stars of the Galactic disk. After allowance is made for the chemical evolution of the interstellar medium, the observational signature of internal mixing phenomena is revealed through the detection at the stellar surface of the products of the CN and, in the case of the most massive stars, NeNa cycles. Together with the asteroseismic constraints, these data will pave the way for a detailed theoretical investigation of the physical processes responsible for the transport of chemical elements in evolved, low- and intermediate-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A1
- Title:
- Coupling factors of 5166 KIC
- Short Name:
- J/A+A/600/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The power of asteroseismology relies on the capability of global oscillations to infer the stellar structure. For evolved stars, we benefit from unique information directly carried out by mixed modes that probe their radiative cores. This third article of the series devoted to mixed modes in red giants focuses on their coupling factors, which have remained largely unexploited up to now. With the measurement of coupling factors, we intend to give physical constraints on the regions surrounding the radiative core and the hydrogen-burning shell of subgiants and red giants. A new method for measuring the coupling factor of mixed modes was implemented, which was derived from the method recently implemented for measuring period spacings. This new method was automated so that it could be applied to a large sample of stars. Coupling factors of mixed modes were measured for thousands of red giants. They show specific variation with mass and evolutionary stage. Weak coupling is observed for the most evolved stars on the red giant branch only; large coupling factors are measured at the transition between subgiants and red giants as well as in the red clump. The measurement of coupling factors in dipole mixed modes provides a new insight into the inner interior structure of evolved stars. While the large frequency separation and the asymptotic period spacings probe the envelope and core, respectively, the coupling factor is directly sensitive to the intermediate region in between and helps determine its extent. Observationally, the determination of the coupling factor is a prior to precise fits of the mixed-mode pattern and can now be used to address further properties of the mixed-mode pattern, such as the signature of buoyancy glitches and core rotation.
- ID:
- ivo://CDS.VizieR/J/ApJS/237/18
- Title:
- Cr, Co, and Ni abundances for metal-poor red giants
- Short Name:
- J/ApJS/237/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of the abundances of chromium, cobalt, and nickel in 4113 red giants, including 2277 stars in globular clusters (GCs), 1820 stars in the Milky Way's dwarf satellite galaxies, and 16 field stars. We measured the abundances from mostly archival Keck/DEIMOS medium-resolution spectroscopy with a resolving power of R~6500 and a wavelength range of approximately 6500-9000{AA}. The abundances were determined by fitting spectral regions that contain absorption lines of the elements under consideration. We used estimates of temperature, surface gravity, and metallicity that we previously determined from the same spectra. We estimated systematic error by examining the dispersion of abundances within mono- metallic GCs. The median uncertainties for [Cr/Fe], [Co/Fe], and [Ni/Fe] are 0.20, 0.20, and 0.13, respectively. Finally, we validated our estimations of uncertainty through duplicate measurements, and we evaluated the accuracy and precision of our measurements through comparison to high-resolution spectroscopic measurements of the same stars.
- ID:
- ivo://CDS.VizieR/J/A+A/382/184
- Title:
- Crystalline silicates around evolved stars
- Short Name:
- J/A+A/382/184
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper in a series of three where we present the first comprehensive inventory of solid state emission bands observed in a sample of 17 oxygen-rich circumstellar dust shells surrounding evolved stars. The data were taken with the Short and Long Wavelength Spectrographs on board of the Infrared Space Observatory (ISO) and cover the 2.4 to 195{mu}m wavelength range. The spectra show the presence of broad 10 and 18{mu}m bands that can be attributed to amorphous silicates. In addition, at least 49 narrow bands are found whose position and width indicate they can be attributed to crystalline silicates. Almost all of these bands were not known before ISO.
