- ID:
- ivo://CDS.VizieR/J/AJ/150/123
- Title:
- Catalog of 316 K giant candidates
- Short Name:
- J/AJ/150/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared (IR) excesses around K-type red giants (RGs) have previously been discovered using Infrared Astronomy Satellite (IRAS) data, and past studies have suggested a link between RGs with overabundant Li and IR excesses, implying the ejection of circumstellar shells or disks. We revisit the question of IR excesses around RGs using higher spatial resolution IR data, primarily from the Wide-field Infrared Survey Explorer. Our goal was to elucidate the link between three unusual RG properties: fast rotation, enriched Li, and IR excess. Our sample of RGs includes those with previous IR detections, a sample with well-defined rotation and Li abundance measurements with no previous IR measurements, and a large sample of RGs asserted to be Li-rich in the literature; we have 316 targets thought to be K giants, about 40% of which we take to be Li-rich. In 24 cases with previous detections of IR excess at low spatial resolution, we believe that source confusion is playing a role, in that either (a) the source that is bright in the optical is not responsible for the IR flux, or (b) there is more than one source responsible for the IR flux as measured in IRAS. We looked for IR excesses in the remaining sources, identifying 28 that have significant IR excesses by ~20{mu}m (with possible excesses for 2 additional sources). There appears to be an intriguing correlation in that the largest IR excesses are all in Li-rich K giants, though very few Li-rich K giants have IR excesses (large or small). These largest IR excesses also tend to be found in the fastest rotators. There is no correlation of IR excess with the carbon isotopic ratio, ^12^C/^13^C. IR excesses by 20{mu}m, though relatively rare, are at least twice as common among our sample of Li-rich K giants. If dust shell production is a common by-product of Li enrichment mechanisms, these observations suggest that the IR excess stage is very short-lived, which is supported by theoretical calculations. Conversely, the Li-enrichment mechanism may only occasionally produce dust, and an additional parameter (e.g., rotation) may control whether or not a shell is ejected.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/715/1094
- Title:
- Census of self-obscured massive stars
- Short Name:
- J/ApJ/715/1094
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new link in the causal mapping between massive stars and potentially fatal explosive transients opened with the 2008 discovery of the dust-obscured progenitors of the luminous outbursts in NGC 6946 and NGC 300. Here, we carry out a systematic mid-IR photometric search for massive, luminous, and self-obscured stars in four nearby galaxies: M33, NGC 300, M81, and NGC 6946. For detection, we use only the 3.6um and 4.5um IRAC bands, as these can still be used for multi-epoch Spitzer surveys of nearby galaxies (<~10Mpc). We combine familiar point-spread function and aperture photometry with an innovative application of image subtraction to catalog the self-obscured massive stars in these galaxies. In particular, we verify that stars analogous to the progenitors of the NGC 6946 (SN 2008S) and NGC 300 transients are truly rare in all four galaxies: their number may be as low as ~1 per galaxy at any given moment. This result empirically supports the idea that the dust-enshrouded phase is a very short lived phenomenon in the lives of many massive stars and that these objects constitute a natural extension of the asymptotic giant branch sequence. We also provide mid-IR catalogs of sources in NGC 300, M81, and NGC 6946.
- ID:
- ivo://CDS.VizieR/J/A+A/566/L10
- Title:
- Cepheid radial velocity amplitude modulations
- Short Name:
- J/A+A/566/L10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical Cepheids are crucial calibrators of the extragalactic distance scale. The Baade-Wesselink technique can be used to calibrate Cepheid distances using Cepheids in the Galaxy and the Magellanic Clouds. To report the discovery of modulations in radial velocity (RV) curves of four Galactic classical Cepheids and to investigate their impact as a systematic uncertainty for Baade-Wesselink distances. Highly precise Doppler measurements were obtained using the Coralie high-resolution spectrograph since 2011. Particular care was taken to sample all phase points in order to very accurately trace the RV curve during multiple epochs and to search for differences in linear radius variations derived from observations obtained at different epochs. Different timescales are sampled, ranging from cycle-to-cycle to months and years. The unprecedented combination of excellent phase coverage obtained during multiple epochs and high precision enabled the discovery of significant modulation in the RV curves of the short-period s-Cepheids QZ Normae and V335 Puppis, as well as the long-period fundamental mode Cepheids l Carinae and RS Puppis. The modulations manifest as shape and amplitude variations that vary smoothly over timescales of years for short-period Cepheids, and from one pulsation cycle to the next in the long-period Cepheids. The order of magnitude of the effect ranges from several hundred m/s to a few km/s. The resulting difference among linear radius variations derived using data from different epochs can lead to systematic errors of up to 15% for Baade-Wesselink-type distances, if the employed angular and linear radius variations are not determined contemporaneously. The different nature of the Cepheids exhibiting modulation in their RV curves suggests that this phenomenon is common. The observational baseline is not yet sufficient to conclude whether these modulations are periodic. In order to ensure the accuracy of Baade-Wesselink distances, angular and linear radius variations should always be determined contemporaneously.
- ID:
- ivo://CDS.VizieR/J/AZh/88/284
- Title:
- Chemical abundance of Hercules moving group
- Short Name:
- J/AZh/88/284
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a comparative analysis of the kinematics, ages, and elemental abundances for 17 red giants in the Hercules moving group are presented. Model atmospheres are used to determine the parameters of the stellar atmospheres and the abundances of about 20 elements. The masses and ages of the stars are estimated, and the components of their Galactic velocities and the elements of their Galactic orbits are calculated. Our analysis demonstrates that the Hercules stream is a heterogeneous group of objects from the thin and thick disks.
- ID:
- ivo://CDS.VizieR/J/ApJ/775/L27
- Title:
- Chemical abundances in a metal-poor RGB star
- Short Name:
- J/ApJ/775/L27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundances for 27 elements ranging from oxygen to erbium in the metal-poor ([Fe/H]=-1.67) bulge red giant branch star 2MASS 18174532-3353235. The results are based on equivalent width and spectrum synthesis analyses of a high-resolution (R~30000) spectrum obtained with the Magellan-MIKE spectrograph. While the light (Z<~30) element abundance patterns match those of similar metallicity bulge and halo stars, the strongly enhanced heavy element abundances are more similar to "r-II" halo stars (e.g., CS 22892-052) typically found at [Fe/H]<~-2.5. We find that the heaviest elements (Z>=56) closely follow the scaled-solar r-process abundance pattern. We do not find evidence supporting significant s-process contributions; however, the intermediate mass elements (e.g., Y and Zr) appear to have been produced through a different process than the heaviest elements. The light and heavy element abundance patterns of 2MASS 18174532-3353235 are in good agreement with the more metal-poor r-process enhanced stars CS 22892-052 and BD +17{deg}3248. 2MASS 18174532-3353235 also shares many chemical characteristics with the similar metallicity but comparatively {alpha}-poor Ursa Minor dwarf galaxy giant COS 82. Interestingly, the Mo and Ru abundances of 2MASS 18174532-3353235 are also strongly enhanced and follow a similar trend recently found to be common in moderately metal-poor main-sequence turn-off halo stars.
- ID:
- ivo://CDS.VizieR/J/AJ/161/183
- Title:
- Chemical abundances in 52 M-giant stars
- Short Name:
- J/AJ/161/183
- Date:
- 18 Jan 2022
- Publisher:
- CDS
- Description:
- We measured ^35^Cl abundances in 52-M giants with metallicities in the range -0.5<[Fe/H]<0.12. Abundances and atmospheric parameters were derived using infrared spectra from CSHELL on the NASA Infrared Telescope Facility and from optical echelle spectra. We measured Cl abundances by fitting a H^35^Cl molecular feature at 3.6985{mu}m with synthetic spectra. We also measured the abundances of O, Ca, Ti, and Fe using atomic absorption lines. We find that the [Cl/Fe] ratio for our stars agrees with chemical evolution models of Cl, and the [Cl/Ca] ratio is broadly consistent with the solar ratio over our metallicity range. Both indicate that Cl is primarily made in core-collapse supernovae with some contributions from Type Ia supernovae. We suggest that other potential nucleosynthesis processes, such as the {nu}-process, are not significant producers of Cl. Finally, we also find our Cl abundances are consistent with HII and planetary nebular abundances at a given oxygen abundance, although there is scatter in the data.
- ID:
- ivo://CDS.VizieR/J/ApJ/824/5
- Title:
- Chemical abundances in NGC 5024 (M53)
- Short Name:
- J/ApJ/824/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Fe, Ca, Ti, Ni, Ba, Na, and O abundances for a sample of 53 red giant branch stars in the globular cluster (GC) NGC 5024 (M53). The abundances were measured from high signal-to-noise medium resolution spectra collected with the Hydra multi-object spectrograph on the Wisconsin-Indiana-Yale-NOAO 3.5m telescope. M53 is of interest because previous studies based on the morphology of the cluster's horizontal branch suggested that it might be composed primarily of first generation (FG) stars and differ from the majority of other GCs with multiple populations, which have been found to be dominated by the second generation (SG) stars. Our sample has an average [Fe/H]=-2.07 with a standard deviation of 0.07dex. This value is consistent with previously published results. The alpha-element abundances in our sample are also consistent with the trends seen in Milky Way halo stars at similar metallicities, with enhanced [Ca/Fe] and [Ti/Fe] relative to solar. We find that the Na-O anti-correlation in M53 is not as extended as other GCs with similar masses and metallicities. The ratio of SG to the total number of stars in our sample is approximately 0.27 and the SG generation is more centrally concentrated. These findings further support that M53 might be a mostly FG cluster and could give further insight into how GCs formed the light element abundance patterns we observe in them today.
- ID:
- ivo://CDS.VizieR/J/A+A/360/509
- Title:
- Chemical abundances in 7 red giants
- Short Name:
- J/A+A/360/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances of about fifteen elements from oxygen to europium are measured in seven red giants of the two open clusters NGC 2360 and NGC 2447. The effective temperatures of the giants are determined spectroscopically by taking advantage of their known masses (~2M_{sun}_ in NGC 2360 and ~3M_{sun}_ in NGC 2447) and bolometric magnitudes. The average iron abundances we obtain for the two clusters are [Fe/H]=0.07 for NGC 2360 and [Fe/H]=0.03 for NGC 2447.
- ID:
- ivo://CDS.VizieR/J/AJ/160/181
- Title:
- Chemical abundances in red giants with Magellan
- Short Name:
- J/AJ/160/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution Magellan/MIKE spectroscopy of 42 red giant stars in seven stellar streams confirmed by the Southern Stellar Stream Spectroscopic Survey (S5): ATLAS, Aliqa Uma, Chenab, Elqui, Indus, Jhelum, and Phoenix. Abundances of 30 elements have been derived from over 10000 individual line measurements or upper limits using photometric stellar parameters and a standard LTE analysis. This is currently the most extensive set of element abundances for stars in stellar streams. Three streams (ATLAS, Aliqa Uma, and Phoenix) are disrupted metal-poor globular clusters, although only weak evidence is seen for the light-element anticorrelations commonly observed in globular clusters. Four streams (Chenab, Elqui, Indus, and Jhelum) are disrupted dwarf galaxies, and their stars display abundance signatures that suggest progenitors with stellar masses ranging from 106 to 107M{sun}. Extensive description is provided for the analysis methods, including the derivation of a new method for including the effect of stellar parameter correlations on each star's abundance and uncertainty. This paper includes data gathered with the 6.5m Magellan Telescopes located at Las Campanas Observatory, Chile.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A146
- Title:
- Chemical abundances of 8 metal-poor stars
- Short Name:
- J/A+A/562/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine chemical compositions of six red giant stars in the Bootes I dwarf spheroidal galaxy, based on the high-resolution spectra obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of 12 elements, including C, Na, alpha, Fe-peak, and neutron capture elements, were determined for the sample stars. The abundance results were compared to those in field Milky Way halo stars previously obtained using an abundance analysis technique similar to the present study. We confirm the low metallicity of Boo-094 ([Fe/H]=-3.4). Except for this star, the abundance ratios ([X/Fe]) of elements lighter than zinc are generally homogeneous with small scatter around the mean values in the metallicities spanned by the other five stars (-2.7<[Fe/H]<-1.8). Specifically, all of the sample stars with [Fe/H]>-2.7 show no significant enhancement of carbon. The [Mg/Fe] and [Ca/Fe] ratios are almost constant with a modest decreasing trend with increasing [Fe/H] and are slightly lower than the field halo stars. The [Sr/Fe] and [Sr/Ba] ratios also tend to be lower in the Bootes I stars than in the halo stars. Our results of small scatter in the [X/Fe] ratios for elements lighter than zinc suggest that these abundances were homogeneous among the ejecta of prior generation(s) of stars in this galaxy.
