- ID:
- ivo://CDS.VizieR/J/ApJ/898/150
- Title:
- High-res. MIKE obs. of metal-poor stars
- Short Name:
- J/ApJ/898/150
- Date:
- 21 Mar 2022 08:50:22
- Publisher:
- CDS
- Description:
- Extensive progress has recently been made in our understanding of heavy-element production via the r-process in the universe, specifically with the first observed neutron star binary merger (NSBM) event associated with the gravitational-wave signal detected by LIGO, GW170817. The chemical abundance patterns of metal-poor r-process-enhanced stars provide key evidence for the dominant site(s) of the r-process and whether NSBMs are sufficiently frequent or prolific r-process sources to be responsible for the majority of r-process material in the universe. We present atmospheric stellar parameters (using a nonlocal thermodynamic equilibrium analysis) and abundances from a detailed analysis of 141 metal-poor stars carried out as part of the R-Process Alliance (RPA) effort. We obtained high-resolution "snapshot" spectroscopy of the stars using the MIKE spectrograph on the 6.5m Magellan Clay telescope at Las Campanas Observatory in Chile. We find 10 new highly enhanced r-II (with [Eu/Fe]>+1.0), 62 new moderately enhanced r-I (+0.3<[Eu/Fe]<~+1.0), and 17 new limited-r ([Eu/Fe]<+0.3) stars. Among those, we find 17 new carbon-enhanced metal-poor (CEMP) stars, of which five are CEMP-no. We also identify one new s-process-enhanced ([Ba/Eu]>+0.5) and five new r/s (0.0<[Ba/Eu]<+0.5) stars. In the process, we discover a new ultra-metal-poor (UMP) star at [Fe/H]=-4.02. One of the r-II stars shows a deficit in {alpha} and Fe-peak elements, typical of dwarf galaxy stars. Our search for r-process-enhanced stars by RPA efforts has already roughly doubled the known r-process sample.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/211/28
- Title:
- High resolution EUV spectrum of N_2_
- Short Name:
- J/ApJS/211/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed high-resolution (FWHM=0.2{AA}) extreme-ultraviolet (EUV, 800-1350{AA}) laboratory emission spectra of molecular nitrogen excited by an electron impact at 20 and 100eV under (mostly) optically thin, single-scattering experimental conditions. A total of 491 emission features were observed from N_2_ electronic-vibrational transitions and atomic N I and N II multiplets and their emission cross sections were measured. Molecular emission was observed at vibrationally excited ground-state levels as high as v"=17, from the a^1^{Pi}_g_, b^1^{Pi}_u_, and b'^1^{Sigma}_u_^+^ excited valence states and the Rydberg series c'_n+1_^1^{Sigma}_u_^+^, c_n_^1^{Pi}_u_, and o_n_^1^{Pi}_u_ for n between 3 and 9. The frequently blended molecular emission bands were disentangled with the aid of a sophisticated and predictive quantum-mechanical model of excited states that includes the strong coupling between valence and Rydberg electronic states and the effects of predissociation. Improved model parameters describing electronic transition moments were obtained from the experiment and allowed for a reliable prediction of the vibrationally summed electronic emission cross section, including an extrapolation to unobserved emission bands and those that are optically thick in the experimental spectra. Vibrationally dependent electronic excitation functions were inferred from a comparison of emission features following 20 and 100eV electron-impact collisional excitation. The electron-impact-induced fluorescence measurements are compared with Cassini Ultraviolet Imaging Spectrograph observations of emissions from Titan's upper atmosphere.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/67
- Title:
- High-resolution FIR spectrum of anti-vinyl alcohol
- Short Name:
- J/ApJ/847/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a detailed analysis of the high-resolution far-infrared spectrum of anti-vinyl alcohol, which has been previously identified toward Sagittarius B2(N). The {nu}_15_ OH torsional fundamental investigated here is more than 200cm^-1^ removed from the next nearest vibration, making it practically unperturbed and ideal to help refine the ground state rotational constants that were previously determined from 25 microwave lines. We assigned 1335 lines within the {nu}_15_ fundamental centered at 261.5512cm^-1^, with J and K_a_ ranges of 1-59 and 0-16, respectively. The microwave and far-infrared line positions were fit with Watson-type A- and S-reduced Hamiltonians, with the inclusion of quartic and select sextic distortion terms. This resulted in a significant refinement of the ground state constants, in addition to the determination of the {nu}_15_=1 state constants for the first time. The spectroscopic parameters are in good agreement with the results from anharmonic coupled-cluster calculations, and should be useful in searches for rotationally and/or vibrationally warm anti-vinyl alcohol in interstellar molecular clouds.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/105
- Title:
- High-resolution GC abundances. II.
- Short Name:
- J/ApJ/834/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present abundances of globular clusters (GCs) in the Milky Way and Fornax from integrated-light (IL) spectra. Our goal is to evaluate the consistency of the IL analysis relative to standard abundance analysis for individual stars in those same clusters. This sample includes an updated analysis of seven clusters from our previous publications and results for five new clusters that expand the metallicity range over which our technique has been tested. We find that the [Fe/H] measured from IL spectra agrees to ~0.1dex for GCs with metallicities as high as [Fe/H]=-0.3, but the abundances measured for more metal-rich clusters may be underestimated. In addition we systematically evaluate the accuracy of abundance ratios, [X/Fe], for Na I, Mg I, Al I, Si I, Ca I, Ti I, Ti II, Sc II, V I, Cr I, Mn I, Co I, Ni I, Cu I, Y II, Zr I, Ba II, La II, Nd II, and Eu II. The elements for which the IL analysis gives results that are most similar to analysis of individual stellar spectra are Fe I, Ca I, Si I, Ni I, and Ba II. The elements that show the greatest differences include Mg I and Zr I. Some elements show good agreement only over a limited range in metallicity. More stellar abundance data in these clusters would enable more complete evaluation of the IL results for other important elements.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A78
- Title:
- High-resolution IR airglow spectrum
- Short Name:
- J/A+A/555/A78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A flux-calibrated high-resolution spectrum of the airglow emission is a practical {lambda}-calibration reference for astronomical spectral observations. It is also useful for constraining the molecular parameters of the OH molecule and the physical conditions in the upper mesosphere. We used the data collected during the first technical commissioning of the GIANO spectrograph at the Telescopio Nazionale Galileo (TNG). The high-resolution (R>~50000) spectrum simultaneously covers the 0.95-2.4 micron wavelength range. Relative flux calibration is achieved by the simultaneous observation of a spectrophotometric standard star. We derived a list of improved positions and intensities of OH infrared lines. The list includes {Lambda}-split doublets, many of which are spectrally resolved. Compared with previous works, the new results correct errors in the wavelengths of the Q-branch transitions. The relative fluxes of OH lines from different vibrational bands show remarkable deviations from theoretical predictions: the {DELTA} v=3,4 lines are a factor of 2 and 4 brighter than expected. We also found evidence of a significant fraction (1-4%) of OH molecules with non-thermal population of high-J levels. Finally, we list wavelengths and fluxes of 153 lines not attributable to OH. Most of these can be associated with O_2_, while 37 lines in the H band are not identified. The O_2_ and unidentified lines in the H band account for ~=5% of the total airglow flux in this band.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/40
- Title:
- High resolution NIR RVs of K2-M4 low-mass stars
- Short Name:
- J/ApJ/822/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2-M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (~25-150Myr) moving groups, the young field star {epsilon} Eridani, and 18 nearby (<25pc) low-mass stars and achieved typical single-measurement precisions of 8-15m/s with a long-term stability of 15-50m/s over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ~25-50m/s at ~2.3125{mu}m, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ876bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD160934AB and GJ725AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3{sigma}-5{sigma}. Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of <~5m/s in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/40
- Title:
- High-resolution NIR spectra of local giants
- Short Name:
- J/ApJ/817/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 705 local giant stars observed using the New Mexico State University 1m telescope with the Sloan Digital Sky Survey-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph, for which we estimate stellar ages and the local star formation history (SFH). The high-resolution (R~22500), near infrared (1.51-1.7{mu}m) APOGEE spectra provide measurements of stellar atmospheric parameters (temperature, surface gravity, [M/H], and [{alpha}/M]). Due to the smaller uncertainties in surface gravity possible with high-resolution spectra and accurate Hipparcos distance measurements, we are able to calculate the stellar masses to within 30%. For giants, the relatively rapid evolution up the red giant branch allows the age to be constrained by the mass. We examine methods of estimating age using both the mass-age relation directly and a Bayesian isochrone matching of measured parameters, assuming a constant SFH. To improve the SFH prior, we use a hierarchical modeling approach to constrain the parameters of the model SFH using the age probability distribution functions of the data. The results of an {alpha}-dependent Gaussian SFH model show a clear age-[{alpha}/M] relation at all ages. Using this SFH model as the prior for an empirical Bayesian analysis, we determine ages for individual stars. The resulting age-metallicity relation is flat, with a slight decrease in [M/H] at the oldest ages and a ~0.5 dex spread in metallicity across most ages. For stars with ages <~1Gyr we find a smaller spread, consistent with radial migration having a smaller effect on these young stars than on the older stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/120
- Title:
- High-resolution obs. of CO isotopologues in YSOs
- Short Name:
- J/ApJ/813/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study reports an unusual heterogeneity in [^12^C^16^O]/[^13^C^16^O] abundance ratios of carbon monoxide observed in the gas phase toward seven ~solar-mass young stellar objects (YSOs) and three dense foreground clouds in the nearby star-forming regions, Ophiuchus, Corona Australis, Orion, and Vela, and an isolated core, L43. Robust isotope ratios were derived using infrared absorption spectroscopy of the 4.7{mu}m fundamental and 2.3{mu}m overtone rovibrational bands of CO at very high spectral resolution ({lambda}/{Delta}{lambda}~95000), observed with the Cryogenic Infrared Echelle Spectrograph (CRIRES) on the Very Large Telescope. We find [^12^C^16^O]/[^13^C^16^O] values ranging from ~85 to 165, significantly higher than those of the local interstellar medium (ISM) (~65-69). These observations are evidence for isotopic heterogeneity in carbon reservoirs in solar-type YSO environments, and encourage the need for refined galactic chemical evolution models to explain the ^12^C/^13^C discrepancy between the solar system and local ISM. The oxygen isotope ratios are consistent with isotopologue-specific photodissociation by CO self-shielding toward the disks, VV CrA N and HL Tau, further substantiating models predicting CO self-shielding on disk surfaces. However, we find that CO self-shielding is an unlikely general explanation for the high [^12^C^16^O]/[^13^C^16^O] ratios observed in this study. Comparison of the solid CO against gas-phase [^12^C^16^O]/[^13^C^16^O] suggests that interactions between CO ice and gas reservoirs need to be further investigated as at least a partial explanation for the unusually high [^12^C^16^O]/[^13^C^16^O] observed.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/112
- Title:
- High-resolution spectra of * bet CMi
- Short Name:
- J/ApJ/836/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The late-type Be star {beta} CMi is remarkably stable compared to other Be stars that have been studied. This has led to a realistic model of the outflowing Be disk by Klement+ (2015A&A...584A..85K). These results showed that the disk is likely truncated at a finite radius from the star, which Klement et al. suggest is evidence for an unseen binary companion in orbit. Here we report on an analysis of the Ritter Observatory spectroscopic archive of {beta} CMi to search for evidence of the elusive companion. We detect periodic Doppler shifts in the wings of the H{alpha} line with a period of 170 days and an amplitude of 2.25km/s, consistent with a low-mass binary companion (M~0.42M_{sun}_). We then compared small changes in the violet-to-red peak height changes (V/R) with the orbital motion. We find weak evidence that it does follow the orbital motion, as suggested by recent Be binary models by Panoglou et al. Our results, which are similar to those for several other Be stars, suggest that {beta} CMi may be a product of binary evolution where Roche lobe overflow has spun up the current Be star, likely leaving a hot subdwarf or white dwarf in orbit around the star. Unfortunately, no direct sign of this companion star is found in the very limited archive of International Ultraviolet Explorer spectra.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/23
- Title:
- High-resolution spectra of 9 RGB stars in NGC6681
- Short Name:
- J/ApJ/846/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain high-resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5+/-3.7km/s and find a mean [Fe/H]=-1.63+/-0.07dex and [{alpha}/Fe]=0.42+/-0.11dex. Additionally, we confirm the existence of a Na-O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini+ (2007AJ....133.1658S) and Piotto+ (2015AJ....149...91P) we are able to identify these two populations as discrete sequences in the cluster CMD. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences in these populations, these results do help put constraints on possible polluter candidates.
