- ID:
- ivo://CDS.VizieR/J/A+A/569/A43
- Title:
- HE 2252-4225 abundance analysis
- Short Name:
- J/A+A/569/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of the r-process enhanced stars are important for better understanding the nature and origin of the r-process. We present a detailed abundance analysis of a very metal-poor giant star discovered in the HERES project, HE 2252-4225, which exhibits overabundances of the r-process elements, with [r/Fe]=+0.80. We determined the stellar atmosphere parameters, Teff=4710K, logg=1.65, and [Fe/H]=-2.63, and chemical abundances by analysing the high-quality VLT/UVES spectra. The surface gravity was calculated from the non-local thermodynamic equilibrium (NLTE) ionisation balance between FeI and FeII. Accurate abundances for a total of 38 elements, including 22 neutron-capture elements beyond Sr and up to Th, were determined in HE 2252-4225. For every chemical species, the dispersion in the single line measurements around the mean does not exceed 0.12dex. This object is deficient in carbon, as expected for a giant star with Teff<4800K. The stellar Na-Zn abundances are well fitted by the yields of a single supernova of 14.4M_{sun}_. For the neutron-capture elements in the Sr-Ru, Ba-Yb, and Os-Ir regions, the abundance pattern of HE 2252-4225 is in excellent agreement with the average abundance pattern of the strongly r-process enhanced stars CS 22892-052, CS 31082-001, HE 1219-0312, and HE 1523-091. This suggests a common origin of the first, second, and third r-process peak elements in HE 2252-4225 in the classical r-process. We tested the solar r-process pattern based on the most recent s-process calculations of Bisterzo, Travaglio, Gallino, Wiescher, and Kappeler and found that elements in the range from Ba to Ir match it very well. No firm conclusion can be drawn about the relationship between the first neutron-capture peak elements, Sr to Ru, in HE 2252-4225 and the solar r-process, due to the uncertainty in the solar r-process. The investigated star has an anomalously high Th/Eu abundance ratio, so that radioactive dating results in a stellar age of {tau}=1.5+/-1.5Gyr that is not expected for a very metal-poor halo star.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/516/A46
- Title:
- HE 2327-5642 abundance analysis
- Short Name:
- J/A+A/516/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis of a strongly r-process enhanced giant star discovered in the HERES project, HE 2327-5642, for which [Fe/H]=-2.78, [r/Fe]=+0.99 [r = elements from r-process]. We determined the stellar parameters and element abundances by analyzing the high-quality VLT/UVES spectra. The surface gravity was calculated from the non-local thermodynamic equilibrium (NLTE) ionization balance between FeI, and FeII, and CaI and CaII.
- ID:
- ivo://CDS.VizieR/J/ApJ/786/14
- Title:
- He abundances in M30 and NGC 6397
- Short Name:
- J/ApJ/786/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the helium abundance of the two metal-poor clusters M30 and NGC 6397. Helium estimates have been obtained by using the high-resolution spectrograph FLAMES at the European Southern Observatory Very Large Telescope and by measuring the He I line at 4471 {AA} in 24 and 35 horizontal branch (HB) stars in M30 and NGC 6397, respectively. This sample represents the largest data set of He abundances collected so far in metal-poor clusters. The He mass fraction turns out to be Y=0.252+/-0.003 ({sigma}=0.021) for M30 and Y=0.241+/-0.004 ({sigma}=0.023) for NGC 6397. These values are fully compatible with the cosmological abundance, thus suggesting that the HB stars are not strongly enriched in He. The small spread of the Y distributions are compatible with those expected from the observed main sequence splitting. Finally, we find a hint of a weak anticorrelation between Y and [O/Fe] in NGC 6397 in agreement with the prediction that O-poor stars are formed by (He-enriched) gas polluted by the products of hot proton-capture reactions.
- ID:
- ivo://CDS.VizieR/J/MNRAS/404/253
- Title:
- Heavy element abundances in HD 209621
- Short Name:
- J/MNRAS/404/253
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution spectra obtained from the Subaru Telescope High Dispersion Spectrograph have been used to update the stellar atmospheric parameters and metallicity of the star HD 209621. We have derived a metallicity of [Fe/H]=-1.93 for this star, and have found a large enhancement of carbon and of heavy elements, with respect to iron. Updates on the elemental abundances of four s-process elements (Y, Ce, Pr, Nd) along with the first estimates of abundances for a number of other heavy elements (Sr, Zr, Ba, La, Sm, Eu, Er, Pb) are reported.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/172
- Title:
- HeCS-red: Hectospec surveys of redMaPPer clusters
- Short Name:
- J/ApJ/862/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use dense redshift surveys to explore the properties of galaxy clusters selected from the redMaPPer catalog. Our new survey, Hectospec Cluster Survey of red-sequence-selected clusters (HeCS-red), includes 10589 new or remeasured redshifts from MMT/Hectospec observations of 27 redMaPPer clusters at redshifts z=0.08-0.25 with large estimated richnesses (richness estimate {lambda}>64). Our spectra confirm that each candidate cluster corresponds to a large overdensity in redshift space. The redMaPPer photometric redshifts have a slight bias toward higher redshifts. We measure the relation between velocity dispersion {sigma}p and {lambda}. The relation shows intrinsic scatter of 24% (and a range of 2x) in velocity dispersion at fixed richness. We extend our analysis to HeCS-red-ext, a sample that includes several clusters selected by X-ray flux or Sunyaev-Zeldovich signal. The heterogeneous sample of 121 clusters in HeCS-red-ext shows similar intrinsic scatter in the {sigma}p-{lambda} relation as the HeCS-red sample, but the range of {sigma}p at fixed richness increases to 3x. We evaluate the membership probability estimates Pmem for individual galaxies provided by redMaPPer. The spectroscopic membership fraction is larger than Pmem for 0.05<=P_mem_<=0.7; conversely, the spectroscopic membership fraction is smaller than P_mem_ at P_mem_>=0.8. We compare spectroscopic richness estimates with redMaPPer richness estimates and find good agreement on average, but a range of a factor of two in spectroscopic richness at fixed redMaPPer richness. Overall, within the high-richness and low-redshift cut of our sample, spectroscopically estimated parameters such as velocity dispersion correlate well with photometric richness estimates, although the relations contain substantial scatter.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/25
- Title:
- Hectochelle spectroscopy for 776 Kepler stars
- Short Name:
- J/ApJ/838/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The occurrence rate of hot Jupiters from the Kepler transit survey is roughly half that of radial velocity surveys targeting solar neighborhood stars. One hypothesis to explain this difference is that the two surveys target stars with different stellar metallicity distributions. To test this hypothesis, we measure the metallicity distribution of the Kepler targets using the Hectochelle multi-fiber, high-resolution spectrograph. Limiting our spectroscopic analysis to 610 dwarf stars in our sample with logg>3.5, we measure a metallicity distribution characterized by a mean of [M/H]_mean_=-0.045+/-0.009, in agreement with previous studies of the Kepler field target stars. In comparison, the metallicity distribution of the California Planet Search radial velocity sample has a mean of [M/H]_CPS,mean_=-0.005+/-0.006, and the samples come from different parent populations according to a Kolmogorov-Smirnov test. We refit the exponential relation between the fraction of stars hosting a close-in giant planet and the host star metallicity using a sample of dwarf stars from the California Planet Search with updated metallicities. The best-fit relation tells us that the difference in metallicity between the two samples is insufficient to explain the discrepant hot Jupiter occurrence rates; the metallicity difference would need to be ~0.2-0.3dex for perfect agreement. We also show that (sub)giant contamination in the Kepler sample cannot reconcile the two occurrence calculations. We conclude that other factors, such as binary contamination and imperfect stellar properties, must also be at play.
- ID:
- ivo://CDS.VizieR/J/ApJ/767/15
- Title:
- Hectospec Cluster Survey (HeCS)
- Short Name:
- J/ApJ/767/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The infall regions of galaxy clusters represent the largest gravitationally bound structures in a {Lambda}CDM universe. Measuring cluster mass profiles into the infall regions provides an estimate of the ultimate mass of these halos. We use the caustic technique to measure cluster mass profiles from galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey 58 clusters selected by X-ray flux at 0.1<z<0.3. The survey includes 22680 unique MMT/Hectospec redshifts for individual galaxies; 10145 of these galaxies are cluster members. For each cluster, we acquired high signal-to-noise spectra for ~200 cluster members and a comparable number of foreground/background galaxies. The cluster members trace out infall patterns around the clusters. The members define a very narrow red sequence. We demonstrate that the determination of velocity dispersion is insensitive to the inclusion of bluer members (a small fraction of the cluster population). We apply the caustic technique to define membership and estimate the mass profiles to large radii. The ultimate halo mass of clusters (the mass that remains bound in the far future of a {Lambda}CDM universe) is on average (1.99+/-0.11)M_200_, a new observational cosmological test in essential agreement with simulations. Summed profiles binned in M_200_ and in L_X_demonstrate that the predicted Navarro-Frenk-White form of the density profile is a remarkably good representation of the data in agreement with weak lensing results extending to large radius. The concentration of these summed profiles is also consistent with theoretical predictions.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/63
- Title:
- Hectospec survey of SZ clusters (HeCS-SZ)
- Short Name:
- J/ApJ/819/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We estimate cluster masses and velocity dispersions for 123 clusters from optical spectroscopy to compare the Sunyaev-Zeldovich (SZ) mass proxy and dynamical masses. Our new survey, HeCS-SZ (Hectospec Cluster Survey of SZ-selected clusters), includes 7721 new or remeasured redshifts from MMT/Hectospec observations of 21 SZ-selected clusters at redshifts z=0.05-0.20. We supplement the Hectospec data with spectra from the Sloan Digital Sky Survey (SDSS) and cluster data from the Cluster Infall Regions in SDSS project and the Hectospec Cluster Survey, our Hectospec survey of clusters selected by X-ray flux. We measure the scaling relation between velocity dispersion and SZ mass estimates from the integrated Compton parameter for an SZ-complete sample of 83 clusters. The observed relation agrees very well with a simple virial scaling from mass (based on SZ) to velocity dispersion. The SZ mass estimates (calibrated with hydrostatic X-ray mass estimates) are not significantly biased compared to dynamical mass estimates under the assumption of small velocity bias of galaxies compared to dark matter particles. Significant mass bias in SZ mass estimates could relieve tension between cosmological results from Planck SZ cluster counts and Planck CMB data. In principle, SZ mass bias and velocity bias of galaxies could conspire to yield good agreement, but the required velocity bias is {sigma}_galaxy_~0.77{sigma}_DM_, outside the range of recent models of velocity bias in the literature. More likely, SZ mass bias and velocity bias are both small, and the tension between SZ cluster counts and CMB data requires another explanation.
- ID:
- ivo://CDS.VizieR/J/A+A/441/685
- Title:
- HeI & HeII radial velocities of Sk 160/SMC X-1
- Short Name:
- J/A+A/441/685
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new optical spectroscopy of the eclipsing binary pulsar Sk 160/SMC X-1. From the He I absorption lines, taking heating corrections into account, we determine the radial velocity semi-amplitude of Sk 160 to be 21/8+/-1.8km/s. Assuming Sk 160 fills its Roche-lobe, the inclination angle of the system is i=65.3+/-1.3{deg} and in this case we obtain upper limits for the mass of the neutron star as Mx=1.21+/-0.10M_{sun}_ and for Sk 160 as Mo=16.6+/-0.4M_{sun}.
- ID:
- ivo://CDS.VizieR/J/AJ/158/192
- Title:
- He II emission from Wolf-Rayet stars in MW & LMC
- Short Name:
- J/AJ/158/192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We calibrated a technique to measure dust attenuation in star-forming galaxies. The technique utilizes the stellar-wind lines in Wolf-Rayet stars, which are widely observed in galaxy spectra. The He II 1640 and 4686 features are recombination lines whose ratio is largely determined by atomic physics. Therefore they can serve as a stellar dust probe in the same way as the Balmer lines are used as a nebular probe. We measured the strength of the He II 1640 line in 97 Wolf-Rayet stars in the Galaxy and the Large Magellanic Cloud. The reddening corrected fluxes follow a tight correlation with a fixed ratio of 7.76 for the He II 1640 to 4686 line ratio. Dust attenuation decreases this ratio. We provide a relation between the stellar E(B-V) and the observed line ratio for several attenuation laws. Combining this technique with the use of the nebular Balmer decrement allows the determination of the stellar and nebular dust attenuation in galaxies and can probe its effects at different stellar age and mass regimes, independently of the initial mass function and the star formation history. We derived the dust reddening from the He II line fluxes and compared it to the reddening from the Balmer decrement and from the slope of the ultraviolet continuum in two star-forming galaxies. The three methods result in dust attenuations which agree to within the errors. Future application of this technique permits studies of the stellar dust attenuation compared to the nebular attenuation in a representative galaxy sample.
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