- ID:
- ivo://CDS.VizieR/J/AJ/119/1824
- Title:
- Caby photometry of {Omega} Centauri
- Short Name:
- J/AJ/119/1824
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new measurements of the metallicity of 131 RR Lyrae stars in the globular cluster {omega} Centauri, using the hk index of the Caby photometric system. The hk method has distinct advantages over {delta}S and other techniques in determining the metallicity of RR Lyrae stars and has allowed us to obtain the most complete and homogeneous metallicity data to date for the RR Lyrae stars in this cluster. For RR Lyrae stars in common with the {delta}S observations of Butler, Dickens, & Epps (1978ApJ...225..148B) and Gratton, Tornambe, & Ortolani (1986A&A...169..111G), we have found that our metallicities, [Fe/H]_hk_, deviate systematically from their {delta}S metallicity, while our [Fe/H]_hk_ for well-observed, field RR_ab_ stars are consistent with previous spectroscopic measurements.
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- ID:
- ivo://CDS.VizieR/J/AJ/109/2828
- Title:
- CaII H and K filter photometry II.
- Short Name:
- J/AJ/109/2828
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog of 1990 stars on the Caby system is presented. The sample includes stars covering an extensive range in spectral type, luminosity class, and metallicity, as well as apparent magnitude. The hk indices are on the standard system defined in Anthony-Twarog et al. (1991AJ....101.1902A), while the V and (b-y) indices have been transformed to the system of Olsen (1993A&AS..102...89O), superseding the values in the original catalog of standard stars.
- ID:
- ivo://CDS.VizieR/J/AJ/116/1922
- Title:
- CaII H and K filter photometry III.
- Short Name:
- J/AJ/116/1922
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New photometry on the uvby Ca system is presented for over 300 stars. When combined with previous data, the sample is used to calibrate the metallicity dependence of the hk index for cooler, evolved stars. The metallicity scale is based upon the standardized merger of spectroscopic abundances from 38 studies since 1983, providing an overlap of 122 evolved stars with the photometric catalog. The hk index produces reliable abundances for stars in the [Fe/H] range from -0.8 to -3.4, losing sensitivity among cooler stars due to saturation effects at higher [Fe/H], as expected.
- ID:
- ivo://CDS.VizieR/III/159A
- Title:
- Ca II H and K Measurements Made at MWO
- Short Name:
- III/159A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during the years 1966-1983. These results are derived from 65,263 individual observations of 1296 stars. For each star, for each observing season, the maximum, minimum, mean, and variation of the instrumental H and K index "S" are given, as well as a measurement of the accuracy of observation. A total of 3110 seasonal summaries are reported. These observations were obtained with two instruments, HKP-1 and HKP-2. The HKP-2 instrument is a four-channel chopping spectrometer which records counts in 1.09{AA} FWHM triangular bandpasses centered in the H and K lines as well as in two 20{AA} reference bandpasses centered on 3901.067 and 4001.067{AA}. The stellar activity is expressed by the index S defined as S = {alpha} (Nh+Nk)/(Nr+Nv) where Nh and Nk are the counts (corrected from background) in the H and K lines, Nr and Nv those in the reference continuum bandpasses, and {alpha} is a constant of proportionality used to correct for night-to-night instrumental variations. Higher values of S generally correspond to higher levels of chromospehric activities. Factors which effect the ability to detect stellar activity variations and accurately measure their amplitudes such as the accuracy of the H and K measurements and scattered light contamination are discussed. Relations are given which facilitate intercomparison of "S" values with residual intensities from ordinary spectrophotometry, and for converting measurements to absolute fluxes.
- ID:
- ivo://CDS.VizieR/J/AJ/136/1039
- Title:
- CaII index of SMC red giant branch stars
- Short Name:
- J/AJ/136/1039
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant branch stars in 13 fields distributed in different positions in the Small Magellanic Cloud, ranging from ~1{deg} to ~4{deg} from its center. In the innermost fields, the average metallicity is [Fe/H]~-1. This value decreases when we move away toward outermost regions. This is the first detection of a spectroscopic metallicity gradient in this galaxy. We show that the metallicity gradient is related to an age gradient, in the sense that more metal-rich stars, which are also younger, are concentrated in the central regions of the galaxy.
- ID:
- ivo://CDS.VizieR/J/PASP/111/335
- Title:
- CaII-M_v_ Correlation (Wilson-Bappu Effect)
- Short Name:
- J/PASP/111/335
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hipparcos parallaxes were used to derive absolute visual magnitudes of G, K, and M stars with Ca II emission line widths previously measured by O.C. Wilson. A linear relationship similar to the one derived originally by Wilson & Bappu and improved by Lutz & Kelker was found from M_v_=+7 to -2. For stars brighter than M_v_=-2 a substantial number of stars show Ca II emission lines that are broader than expected from the linear fit. Most of those stars are bright giants and supergiants of type G.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A76
- Title:
- CaII triplet equivalent widths in 30 globulars
- Short Name:
- J/A+A/563/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- When they are established with sufficient precision, the ages, metallicities and kinematics of Galactic globular clusters (GGCs) can shed much light on the dynamical and chemical evolution of the Galactic halo and bulge. While the most fundamental way of determining GC abundances is by mean high-resolution spectroscopy, in practice this method is limited to only the brighter stars in the nearest and less reddened objects. This restriction has, over the years, led to the development of a large number of techniques that measure the overall abundance indirectly from parameters that correlate with overall metallicity. One of the most efficient methods is measuring of the equivalent width (EW) of the calcium II triplet (CaT) at {lambda}~~8500{AA} in red giants, which are corrected for the luminosity and temperature effects using the V magnitude differences from the horizontal branch (HB). We establish a similar method in the near-infrared (NIR), by combining the power of the differential magnitudes technique with the advantages of NIR photometry to minimize differential reddening effects. We used the Ks magnitude difference between the star and the reddest part of the HB (RHB) or of the red clump (RC) to generate reduced equivalent widths (rEW) from the previously presented datasets. Then we calibrated these rEW against three previously reported different metallicity scales; one of which we corrected using high-resolution spectroscopic metallicities.
- ID:
- ivo://CDS.VizieR/J/AJ/135/836
- Title:
- Calcium triplet index in LMC stars
- Short Name:
- J/AJ/135/836
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared CaII triplet (CaT) spectroscopy has been used to derive stellar metallicities for individual stars in four Large Magellanic Cloud fields situated at galactocentric distances of 3{deg}, 5{deg}, 6{deg}, and 8{deg} to the north of the bar. The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age-metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age-metallicity relationships (AMRs) for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk AMR is similar to that for clusters. However, the lack of objects with ages between 3 and 10Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the AMR of the bar. Simple chemical evolution models have been used to reproduce the observed AMRs with the purpose of investigating which mechanism has participated in the evolution of the disk and bar.
- ID:
- ivo://CDS.VizieR/J/PASP/120/1128
- Title:
- Calibrated griz magnitudes of Tycho stars
- Short Name:
- J/PASP/120/1128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometric calibration at an accuracy of ~5% in an arbitrary celestial location is frequently needed. However, existing all-sky astronomical catalogue do not reach this accuracy, and time consuming photometric calibration procedures are required. I fitted the Hipparcos B_T_, and V_T_ magnitudes, along with the 2MASS J, H, and K magnitudes of Tycho-2 catalog-stars with stellar spectral templates. From the best fit spectral template derived for each star, I calculated its synthetic SDSS griz magnitudes, and constructed an all-sky catalog of griz magnitudes of bright stars (V<12). Testing this method on SDSS photometric telescope observations, I find that the photometric accuracy, for a single star, is usually about 0.12, 0.12, 0.10 and 0.08 mag (1sigma), for the g, r, i, and z-bands, respectively. However, by using ~10 such stars, the typical errors per calibrated field (systematic + statistical) can be reduced to about 0.04, 0.03, 0.02, and 0.02 mag, in the g, r, i, and z-bands, respectively. Therefore, in cases for which several calibration stars can be observed in the field of view of an instrument, it is possible to photometrically calibrate the image.
- ID:
- ivo://CDS.VizieR/J/A+A/608/L8
- Title:
- Calibration of G passband for Gaia DR1
- Short Name:
- J/A+A/608/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On September 2016 the first data from Gaia were released (DR1). The first release included photometry for over 109 sources in the very broad G system. To test the correspondence between G magnitudes in DR1 and the synthetic equivalents derived using spectral energy distributions from observed and model spectrophotometry. To correct the G passband curve and to measure the zero point in the Vega system. Methods. I have computed the synthetic G and Tycho-2 BTVT photometry for a sample of stars using the Next Generation Spectral Library (NGSL) and the Hubble Space Telescope (HST) CALSPEC spectroscopic standards. I have found that the nominal G passband curve is too blue for the DR1 photometry, as shown by the presence of a color with an exponent of 0.783 eliminates the color term. The corrected passband has a Vega zero point of 0.070+/-0.004 magnitudes.
