- 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.
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Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/90/2089
- Title:
- Stars of very low metal abundance. I
- Short Name:
- J/AJ/90/2089
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An objective-prism and a narrowband interference filter have been used in combination on the Curtis Schmidt telescope at CTIO to conduct a search for extremely metal-poor stars. The filter restricts the bandpass to the region around the H and K lines of CaII; the metal-poor candidates are those stars with weak or absent H and K. Slit spectra (1 A resolution) of some 450 candidates are used to measure equivalent widths of the CaII K line and Balmer features. A calibration of the K-line strength for giants in the metal-poor globular cluster NGC 6397 and field dwarfs and giants of known metallicity is used to identify survey candidates with metal abundance [Fe/H]<=-2.0; a list of 134 such stars is presented. UBV photometry is used to distinguish between two groups of metal-poor stars: a group with objects near the main-sequence turnoff, on the subgiant branch, and on the giant branch; and a second group with objects on the red horizontal branch (RHB) and asymptotic giant branch (AGB). The RHB-AGB stars exhibit the well-known weak G-band effect; three CH-strong objects are identified among the subgiants.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/663
- Title:
- Stellar density map of the Milky Way
- Short Name:
- J/ApJ/714/663
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We map the stellar structure of the Galactic thick disk and halo by applying color-magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75+/-0.07kpc and 4.1+/-0.4kpc, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A41
- Title:
- Stellar halo of NGC 5128 (Centaurus A)
- Short Name:
- J/A+A/657/A41
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The extended stellar halos of galaxies contain important clues for investigating their assembly history and evolution. We investigate the resolved stellar content and the extended halo of NGC 5128 as a function of galactocentric distance, and trace the halo outward to its currently detectable limits. We used Hubble Space Telescope images obtained with the WFPC2, ACS, and WFC3 cameras equipped with F606W and F814W filters to resolve individual red giant branch (RGB) stars in 28 independent pointings across the halo of NGC 5128. The stellar halo analysis for 14 of these pointings is presented here for the first time. Star counts from deep VI color-magnitude diagrams reaching at least 1.5mag below the tip of the RGB are used to derive the surface density distribution of the halo. The contamination by Milky Way stars is assessed with a new control field, with models, and by combining optical and near-IR photometry. We present a new calibration of the WFC3 F606W + F814W photometry to the ground-based VI photometric system. The photometry shows that the stellar halo of NGC 5128 is dominated by old RGB stars that are present in all fields. The V-band surface brightness of fields changes from 23 to 32mag/arcsec^2^ between the innermost field only 8.3kpc from the galaxy center to our outermost halo fields, which are located 140 kpc away from the center along the major axis and 92 kpc along the minor axis. Within the inner ~30kpc, we also find evidence for a 2-3Gyr old population traced by asymptotic giant branch stars that are brighter than the tip of the RGB. This population contributes only up to 10% in total stellar mass if it is 2Gyr old, but a larger fraction of 30-40% is required if its age is 3Gyr. The stellar surface density profile is well fit by a classic r^1/4^ curve or a simple power-law form ~r^-3.1^ over the full radial range, with no obvious break in the slope, but with large field-to-field scatter. The ellipticity measured from integrated-light photometry in the inner parts, e=(b/a)=0.77, flattens to e=0.54+/-0.02 beyond 30kpc. Considering the flattening of the outer halo, the projection of the elliptical isophote on the semimajor axis for our most distant field reaches nearly 30 effective radii.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/170
- Title:
- The SEGUE K giant survey. II. Distances of 6036 stars
- Short Name:
- J/ApJ/784/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an online catalog of distance determinations for 6036 K giants, most of which are members of the Milky Way's stellar halo. Their medium-resolution spectra from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration are used to derive metallicities and rough gravity estimates, along with radial velocities. Distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g-r)_0_ color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to properly propagate the errors in metallicities, magnitudes, and colors into distance uncertainties. We also fold in prior information about the giant-branch luminosity function and the different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays a small role in the distance estimates, but that neglecting the luminosity prior could lead to a systematic distance modulus bias of up to 0.25mag, compared to the case of using the luminosity prior. We find a median distance precision of 16%, with distance estimates most precise for the least metal-poor stars near the tip of the red giant branch. The precision and accuracy of our distance estimates are validated with observations of globular and open clusters. The stars in our catalog are up to 125kpc from the Galactic center, with 283 stars beyond 50kpc, forming the largest available spectroscopic sample of distant tracers in the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/PASP/102/1392
- Title:
- UBV photometry from HK survey. I
- Short Name:
- J/PASP/102/1392
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric photometry is presented for a sample of 139 halo stars drawn an extension of the HK (Ca II H & K lines) objective-prism survey of Beers, Preston and Shectmann (1988ApJS...67..461) to the Northern Galactic hemisphere. The candidates for which photometry is reported here were selected to span a wide range of types, but are dominated by stars classified as type AB, A, or "metal-poor" (MP).
- ID:
- ivo://CDS.VizieR/J/AJ/87/1515
- Title:
- UBV photometry of AB stars in halo
- Short Name:
- J/AJ/87/1515
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of photoelectric UBV photometry of 234 AB stars in the southern galactic halo are presented. The stars were chosen from the Curtis Schmidt objective-prism survey of Preston and Shectman and comprise a sample of halo objects selected without kinematic bias. The majority of the stars lie in the region of the (U-B, B-V) plane occupied by field and globular cluster blue horizontal-branch stars.
