- ID:
- ivo://CDS.VizieR/J/ApJ/868/110
- Title:
- R-Process Alliance: 1st release in Galactic halo
- Short Name:
- J/ApJ/868/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the detailed abundances and r-process classifications of 125 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R~31500) with the 3.5m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from FeI lines, taking into account <3D> non-LTE corrections and using differential abundances with respect to a set of standards. Of the 125 new stars, 124 have [Fe/H]{<}-1.5, 105 have [Fe/H]{<}-2.0, and 4 have [Fe/H]{<}-3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3<=[Eu/Fe]<=+1.0 and [Ba/Eu]<0) and 4 new r-II stars (with [Eu/Fe]>+1.0). Nineteen stars are found to exhibit a "limited-r" signature ([Sr/Ba]>+0.5, [Ba/Eu]<0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, {alpha}, and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/750/76
- Title:
- r-process peaks elements in HD 160617
- Short Name:
- J/ApJ/750/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selenium may be surprising in light of predictions that the production of the lightest r-process elements generally should be decoupled from the heavier r-process elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/79
- Title:
- SDSS-DR8 BHB stars in the Milky Way's halo
- Short Name:
- J/ApJ/738/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative "close pair distribution" as a statistic in the four-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that are close in position on the sky tend to have more similar distances and radial velocities compared to a random sampling of these overall distributions. We make analogous mock observations of 11 numerical halo formation simulations, in which the stellar halo is entirely composed of disrupted satellite debris, and find a level of substructure comparable to that seen in the actually observed BHB star sample. This result quantitatively confirms the hierarchical build-up of the stellar halo through a signature in phase (position-velocity) space. In detail, the structure present in the BHB stars is somewhat less prominent than that seen in most simulated halos, quite possibly because BHB stars represent an older sub-population. BHB stars located beyond 20kpc from the Galactic center exhibit stronger substructure than at r_gc_<20kpc.
- ID:
- ivo://CDS.VizieR/J/AJ/162/125
- Title:
- Searching transiting planets around halo stars. I.
- Short Name:
- J/AJ/162/125
- Date:
- 21 Mar 2022 00:52:16
- Publisher:
- CDS
- Description:
- By measuring the elemental abundances of a star, we can gain insight into the composition of its initial gas cloud-the formation site of the star and its planets. Planet formation requires metals, the availability of which is determined by the elemental abundance. In the case where metals are extremely deficient, planet formation can be stifled. To investigate such a scenario requires a large sample of metal-poor stars and a search for planets therein. This paper focuses on the selection and validation of a halo star sample. We select ~17000 metal-poor halo stars based on their Galactic kinematics, and confirm their low metallicities ([Fe/H]<-0.5), using spectroscopy from the literature. Furthermore, we perform high-resolution spectroscopic observations using LBT/PEPSI and conduct detailed metallicity ([Fe/H]) analyses on a sample of 13 previously-known halo stars that also have hot kinematics. We can use the halo star sample presented here to measure the frequency of planets and to test planet formation in extremely metal-poor environments. The result of the planet search and its implications will be presented and discussed in a companion paper by Boley et al.
55. Spaghetti Survey
- ID:
- ivo://CDS.VizieR/J/AJ/120/2496
- Title:
- Spaghetti Survey
- Short Name:
- J/AJ/120/2496
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Spaghetti project is a pencil-beam photometric and spectroscopic survey designed to identify structure in the Galactic halo. Four-color stellar photometry in the modified Washington filter set is used to identify halo stars for spectroscopic observations. The filters include C, M, T2 and DDO51. The fields in the survey are chosen from high Galactic-latitude positions with low reddening and no stars as bright as SAO stars. Thus far we have imaged 134 fields covering a total area of 52deg^2^. These fields are listed in table1.dat. Due to weather, the only fully calibrated photometry was measured from images taken with the BTC ccd mosaic camera on the CTIO 4m telescope in April 1999. Table4.dat lists these stars from the 53 BTC fields, which covers a total area of 13 square degrees. These data include only those stars whose measurement errors are less than 0.04 in all four filters (32655 total stars). Photometric measurements of stars in the other fields will be published as soon as they can be fully calibrated. See <GCPD/48> for a short description of the Washington Photometric system.
- ID:
- ivo://CDS.VizieR/J/AJ/125/2502
- Title:
- Spectral indices of Galactic halo
- Short Name:
- J/AJ/125/2502
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our calibration of spectroscopic measures of luminosity and metallicity for halo giant candidates and give metallicities and distances for our first sample of spectroscopically confirmed giants. These giants have distances ranging from 15 to 83kpc. As surveys reach farther into the Galaxy's halo with K giant samples, identification of giants becomes more difficult. This is because the numbers of foreground halo K dwarfs rise for V magnitudes of 19-20, typical for halo giants at 100kpc. Our photometric survey uses the strength of the Mgb/H feature near 5170{AA} to weed K dwarfs out of the disk and thick disk, but we need spectroscopic measures of the strength of the Ca II K, Ca I {lambda}4227, and Mgb/H features to distinguish between the very metal-poor dwarfs and halo giants. Using a full error analysis of our spectroscopic measures, we show why a signal-to-noise ratio of ~15pixel^-1^ at Ca I {lambda}4227 and ~10 at Ca II K is needed for reliable luminosity discrimination. We use the Ca II K and Mgb features to measure metallicity in our halo giants, with typical errors (random plus systematic) of 0.3dex for [Fe/H] values from -0.8 to -3.0.
- ID:
- ivo://CDS.VizieR/J/AJ/103/267
- Title:
- Spectrocopy of hot stars in galactic halo
- Short Name:
- J/AJ/103/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper presents spectroscopy for 769 hot stars from the HK objective-prism/interference-filter survey of Beers et al. (1985), 193 of which have also available broadband UBV colors. When available, photometric information is used to obtain estimates of the surface temperature for degenerates and for O- and B-type subdwarfs, based on previously derived calibrations. Several extremely hot (T(eff) greater than 50,000 K) He-rich sdO stars are identified. Out of 769 stars in this sample, 551 are clearly identified on the basis of their Balmer line profiles as field horizontal-branch (FHB) or mid-to late-type A stars. The A stars exhibit rotation and line-of-sight dispersion consistent with membership in the galactic thick disk. The FHB stars exhibit kinematic properties which suggest a transition from thick disk to halo.
- ID:
- ivo://CDS.VizieR/V/65
- Title:
- Spectroscopically Selected Halo K Giants
- Short Name:
- V/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog results from a survey for distant Field K giants in the Galactic halo made for purposes of locating a chemically and kinematically unbiased sample out to about 25 kpc from the Sun. The motivation for the study and sample selection are outlined by Ratnatunga & Freeman (1985ApJ...291..260R), while details and analysis of the results will be found in Ratnatunga & Freeman (1989). Three high-galactic latitude fields each of 20 square degrees, designated by their Selected-Area identifications, include the following: SA 141 (l=240,b=-85); SA 189 (277, -50); and SA 127 (272, +38), and have the apparent magnitude range 13 < V < 16 and color range (B-V) > 0.9. Stars were selected from PDS photographic photometry of Schmidt plates (see Ratnatunga 1983, catalog II/121). K-giant selection used the Mgb+MgH feature at 5100A from digital image analysis of PDS scans of ESO 1-m Schmidt telescope objective-prism spectra with 450 A/mm at H-gamma resolution on IIIa-J plates exposed through a Schott GG475 filter. Luminosity confirmation, line-of-sight velocities, and metallicity were determined from 2-A resolution slit spectra taken with the 4-m Anglo- Australian and 1.9-m Mount Stromlo telescopes. Cross identifications exist for some stars in the SA 141 SGP field only.
- ID:
- ivo://CDS.VizieR/J/AJ/155/256
- Title:
- Spectroscopic validation of RAVE metal-poor stars
- Short Name:
- J/AJ/155/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a medium-resolution (R~2000) spectroscopic follow-up campaign of 1694 bright (V<13.5), very metal-poor star candidates from the RAdial Velocity Experiment (RAVE). Initial selection of the low-metallicity targets was based on the stellar parameters published in RAVE Data Releases 4 (Cat. III/272) and 5 (Cat. III/279). Follow up was accomplished with the Gemini-N and Gemini-S, the ESO/NTT, the KPNO/Mayall, and the SOAR telescopes. The wavelength coverage for most of the observed spectra allows for the determination of carbon and {alpha}-element abundances, which are crucial for considering the nature and frequency of the carbon-enhanced metal-poor (CEMP) stars in this sample. We find that 88% of the observed stars have [Fe/H]=< -1.0, 61% have [Fe/H]=< -2.0, and 3% have [Fe/H]=< -3.0 (with four stars at [Fe/H]=< -3.5). There are 306 CEMP star candidates in this sample, and we identify 169 CEMP Group I, 131 CEMP Group II, and 6 CEMP Group III stars from the A(C) versus [Fe/H] diagram. Inspection of the [{alpha}/C] abundance ratios reveals that five of the CEMP Group II stars can be classified as "mono-enriched second-generation" stars. Gaia DR1 matches were found for 734 stars, and we show that transverse velocities can be used as a confirmatory selection criteria for low-metallicity candidates. Selected stars from our validated list are being followed-up with high-resolution spectroscopy to reveal their full chemical-abundance patterns for further studies.
- ID:
- ivo://CDS.VizieR/J/ApJS/53/791
- Title:
- Spectroscopy of AB stars in halo
- Short Name:
- J/ApJS/53/791
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Reticon spectroscopy has been obtained for 224 high-latitude AB stars chosen from the Curtis Schmidt objective-prism survey of Preston and Schectamn. Additional spectra of radial velocity standards, globular cluster blue horizontal-branch and RR Lyrae stars, and Population I late B and early A stars have been obtained. Radial velocities have been determined for all the program objects by cross-correlating the spectra with those of radial velocities standards. The standard error in a single observation is 11km/s.
