Search

Start Over Subject optical astronomy Capability Type Simple Cone Search
541. Chemical abundances in 43 metal-poor stars
ID:
ivo://CDS.VizieR/J/A+A/440/321
Title:
Chemical abundances in 43 metal-poor stars
Short Name:
J/A+A/440/321
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni and Ba for 43 metal-poor field stars in the solar neighbourhood, most of them subgiants or turn-off-point stars, with iron abundances [Fe/H] ranging from -0.4 to -3.0. About half of this sample has not been analysed spectroscopically in detail before. Effective temperatures were estimated from uvby photometry, and surface gravities primarily from Hipparcos parallaxes. The analysis is differential relative to the Sun, and carried out with plane-parallel MARCS models. Various sources of error are discussed and found to contribute a total error of about 0.1-0.2dex for most elements, while relative abundances, such as [Ca/Fe], are most probably more accurate. For the oxygen abundances, determined in an NLTE analysis of the 7774{AA} triplet lines, the errors may be somewhat larger.
542. Chemical abundances in 52 M-giant 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.
543. Chemical abundances in NGC 5024 (M53)
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.
544. Chemical abundances in red giants with Magellan
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.
545. Chemical abundances of 3 stars in Grus II galaxy
ID:
ivo://CDS.VizieR/J/ApJ/897/183
Title:
Chemical abundances of 3 stars in Grus II galaxy
Short Name:
J/ApJ/897/183
Date:
15 Mar 2022 04:18:06
Publisher:
CDS
Description:
We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy GrusII. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass (>=20M{sun}) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of GrusII could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high- mass stars, thus the possible top-heavy initial mass function of GrusII would increase the likelihood of any of these events occurring. The time delay between the {alpha} and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in GrusII.
546. Chemical composition of halo and disk stars
ID:
ivo://CDS.VizieR/J/A+A/326/751
Title:
Chemical composition of halo and disk stars
Short Name:
J/A+A/326/751
Date:
21 Oct 2021
Publisher:
CDS
Description:
Table A1 lists the Stromgren photometry together with color excesses, E(b-y), photometric metallicities, [Fe/H] , calculated from the calibrations of Schuster & Nissen (1989A&A...221...65S), and absolute magnitudes, M(V), and distances derived with the equations of Nissen & Schuster (1991A&A...251..457N) using the photometric metallicities. Table A2 contains coordinates, proper motions and radial velocities for the program stars as well as distances calculated from the calibrations Nissen & Schuster (1991A&A...251..457N) using the spectroscopic metallicities scaled to our photometric [Fe/H] system. Table A3 gives a list of the 209 spectral lines, which were analyzed, arranged element by element. The table contains the wavelength, the excitation potential of the lower level corresponding to the line, the gf-value, the enhancement factor of the classical van der Waals damping constant, the statistical weight of the upper level, and the equivalent widths measured for the two "standard" stars, HD 22879 and HD 76932. Table A4 contains the measured equivalent widths for all program stars. Table A5 gives abundance ratios and kinematical as well as orbital parameters for the program stars. First are given the data for the 16 disk stars, then follows the 14 halo stars.
547. Chemically peculiar stars in the LMC
ID:
ivo://CDS.VizieR/J/A+A/459/871
Title:
Chemically peculiar stars in the LMC
Short Name:
J/A+A/459/871
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high precision photometric Delta a observations of 417 objects in NGC 2136/7 and its surrounding field, of which five turned out to be bona fide magnetic CP stars. In addition, we discovered two Be/Ae stars. This intermediate band photometric system samples the depth of the 520nm flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 11nm to 23nm. The Delta a photometric system is most suitable for detecting CP2 stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. From our investigations of NGC 1711, NGC 1866, NGC 2136/7, their surroundings, and one independent field of the LMC population, we derive an occurrence of classical chemically peculiar stars of 2.2(6)% in the LMC, which is only half the value found in the Milky Way. The mass and age distribution of the photometrically detected CP stars is not different from that of similar objects in galactic open clusters.
548. Cheshire Cat galaxies: redshifts and magnitudes
ID:
ivo://CDS.VizieR/J/ApJ/806/268
Title:
Cheshire Cat galaxies: redshifts and magnitudes
Short Name:
J/ApJ/806/268
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Cheshire Cat is a relatively poor group of galaxies dominated by two luminous elliptical galaxies surrounded by at least four arcs from gravitationally lensed background galaxies that give the system a humorous appearance. Our combined optical/X-ray study of this system reveals that it is experiencing a line of sight merger between two groups with a roughly equal mass ratio with a relative velocity of ~1350 km/s. One group was most likely a low-mass fossil group, while the other group would have almost fit the classical definition of a fossil group. The collision manifests itself in a bimodal galaxy velocity distribution, an elevated central X-ray temperature and luminosity indicative of a shock, and gravitational arc centers that do not coincide with either large elliptical galaxy. One of the luminous elliptical galaxies has a double nucleus embedded off-center in the stellar halo. The luminous ellipticals should merge in less than a Gyr, after which observers will see a massive 1.2-1.5x10^14^ M_{sun}_ fossil group with an M_r_=-24.0 brightest group galaxy at its center. Thus, the Cheshire Cat offers us the first opportunity to study a fossil group progenitor. We discuss the limitations of the classical definition of a fossil group in terms of magnitude gaps between the member galaxies. We also suggest that if the merging of fossil (or near-fossil) groups is a common avenue for creating present-day fossil groups, the time lag between the final galactic merging of the system and the onset of cooling in the shock-heated core could account for the observed lack of well-developed cool cores in some fossil groups.
549. CH(G) index of SDSS evolved stars
ID:
ivo://CDS.VizieR/J/ApJ/765/156
Title:
CH(G) index of SDSS evolved stars
Short Name:
J/ApJ/765/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have measured the CH G band (CH(G)) index for evolved stars in the globular cluster M3 based on the Sloan Digital Sky Survey (SDSS) spectroscopic survey. It is found that there is a useful way to select red giant branch (RGB) stars from the contamination of other evolved stars such as asymptotic giant branch (AGB) and red horizontal branch (RHB) stars by using the CH(G) index versus (g-r)_0_ diagram if the metallicity is known from the spectra. When this diagram is applied to field giant stars with similar metallicity, we establish a calibration of CH(G)=1.625(g-r)_0_-1.174(g-r)^2^_0_-0.934. This method is confirmed by stars with [Fe/H]~-2.3 where spectra of member stars in globular clusters M15 and M92 are available in the SDSS database. We thus extend this kind of calibration to every individual metallicity bin ranging from [Fe/H]~-3.0 to [Fe/H]~0.0 by using field red giant stars with 0.4<=(g-r)_0_<=1.0. The metallicity-dependent calibrations give CH(G)=1.625(g-r)_0_-1.174(g-r)^2^_0_+0.060[Fe/H]-0.830 for -3.0<[Fe/H]<=-1.2 and CH(G)=0.953(g-r)_0_-0.655(g-r)^2^_0_+0.060[Fe/H]-0.650 for -1.2<[Fe/H]<0.0. The calibrations are valid for the SDSS spectroscopic data set, and they cannot be applied blindly to other data sets. With the two calibrations, a significant number of the contaminating stars (AGB and RHB stars) were excluded and thus a clear sample of red giant stars is obtained by selecting stars within +/-0.05mag of the calibration. The sample is published online and it is expected that this large and clean sample of RGB stars will provide new information on the formation and evolution of the Galaxy.
550. Chinese Small Telescope ARray (CSTAR)
ID:
ivo://CDS.VizieR/J/PASP/122/347
Title:
Chinese Small Telescope ARray (CSTAR)
Short Name:
J/PASP/122/347
Date:
21 Oct 2021
Publisher:
CDS
Description:
In 2008 January the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with a different filter (g,r,i, and open) and has a 4.5{deg}x4.5{deg} field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every ~30s throughout the year whenever it is dark. During 2008, CSTAR 1 performed almost flawlessly, acquiring more than 0.3 million -band images for a total integration time of 1728hr during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to magnitude could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the south celestial pole (Dec=-90{deg}), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts, and minor planets.