- ID:
- ivo://CDS.VizieR/J/AJ/134/1298
- Title:
- CaII equivalent widths in 29 Galactic clusters
- Short Name:
- J/AJ/134/1298
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From observations of almost 500 red giant branch stars in 29 Galactic open and globular clusters, we have investigated the behavior of the infrared Ca II triplet (8498, 8542, and 8662{AA}) in the age range 13Gyr<=age<=0.25Gyr and the metallicity range -2.2<=[Fe/H]<=+0.47. These are the widest ranges of ages and metallicities in which the behavior of the Ca II triplet lines has been investigated in a homogeneous way. We report the first empirical study of the variation of the Ca II triplet lines' strength, for given metallicities, with respect to luminosity.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/426/1591
- Title:
- CaII equivalent widths of dM1 stars
- Short Name:
- J/MNRAS/426/1591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 187 high-resolution spectra for 62 different M1 dwarfs from observations obtained with the FIbre-fed Echelle Spectrograph (FIES) on the Nordic Optical Telescope (NOT) and from observations with the Fibre-fed Extended Range Echelle Spectrograph (FEROS) from the European Southern Observatory (ESO) data base. We also compiled other measurements available in the literature.
- 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/A+A/493/1099
- Title:
- CaII HK emission in rapidly rotating stars
- Short Name:
- J/A+A/493/1099
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of chromospheric CaII H&K activity for 481 solar-like stars. To determine the activity we used the Mount Wilson method and a newly developed method which allows to also measure CaII H&K emission features in very rapidly rotating stars. The new technique determines the activity by comparing the line shapes from known inactive slowly rotating template stars that have been artificially broadened to spectra of rapid rotators. We have analyzed solar-like stars ranging from T_eff}=5000 to 7800K with rotational velocities up to 190km/s in our sample of FOCES and FEROS spectra. The effects of the rotational broadening on the two methods have been quantified. Our method has proven to produce consistent results where S-Index values are available and offers the possibility to measure the chromospheric activity at the onset of the solar-like dynamo.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A82
- Title:
- CaIIHK emission in stars with close-in planets
- Short Name:
- J/A+A/540/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The planet-star interaction is manifested in many ways. It has been found that a close-in exoplanet causes small but measurable variability in the cores of a few lines in the spectra of several stars, which corresponds to the orbital period of the exoplanet. Stars with and without exoplanets may have different properties. The main goal of our study is to search for the influence that exoplanets might have on atmospheres of their host stars. Unlike the previous studies, we do not study changes in the spectrum of a host star or differences between stars with and without exoplanets. We aim to study a large number of stars with exoplanets and the current level of their chromospheric activity and to look for a possible correlation with the exoplanetary properties.
- ID:
- ivo://CDS.VizieR/J/A+AS/146/103
- Title:
- CaII H&K to CaII IRT echelle spectra
- Short Name:
- J/A+AS/146/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the third paper of a series aimed at studying the chromosphere of active binary systems using the information provided for several optical spectroscopic features. High resolution echelle spectra including all the optical chromospheric activity indicators from the CaII H&K to CaII IRT lines are analysed here for 16 systems. The chromospheric contribution in these lines has been determined using the spectral subtraction technique. Very broad wings have been found in the subtracted H{alpha} profile of the very active star HU Vir. These profiles are well matched using a two-component Gaussian fit (narrow and broad) and the broad component can be interpreted as arising from microflaring. Red-shifted absorption features in the H{alpha} line have been detected in several systems and excess emission in the blue wing of FG UMa was also detected. These features indicate that several dynamical processes, or a combination of them, may be involved. Using the E_H{alpha}_/E_H{beta}_ ratio as a diagnostic we have detected prominence-like extended material viewed off the limb in many stars of the sample, and prominences viewed against the disk at some orbital phases in the dwarfs OU Gem and BF Lyn. The He I D_3_ line has been detected as an absorption feature in mainly all the giants of the sample. Total filling-in of the He I D_3_, probably due to microflaring activity, is observed in HU Vir. Self-absorption with red asymmetry is detected in the CaII H&K lines of the giants 12 Cam, FG UMa and BM CVn. All the stars analysed show clear filled-in CaII IRT lines or even notable emission reversal. The small values of the E_8542_/E_8498_ ratio we have found indicate CaII IRT emission arises from plage-like regions. Orbital phase modulation of the chromospheric emission has been detected in some systems, in the case of HU Vir evidence of an active longitude area has been found.
- 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/MNRAS/327/918
- Title:
- CaII in extragalactic red giants
- Short Name:
- J/MNRAS/327/918
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic abundance determinations for stars spanning a Hubble time in age are necessary in order to determine unambiguously the evolutionary histories of galaxies. Using FORS1 in multi-object spectroscopy mode on ANTU (UT1) at the ESO VLT on Paranal, we have obtained near-infrared spectra from which we have measured the equivalent widths of the two strongest Ca II triplet lines to determine metal abundances for a sample of red giant branch stars, selected from ESO NTT optical (I, V-I) photometry of three nearby Local Group galaxies: the Sculptor dwarf spheroidal, the Fornax dwarf spheroidal and the dwarf irregular NGC 6822. The summed equivalent width of the two strongest lines in the Ca II triplet absorption-line feature, centred at 8500{AA}, can be readily converted into an [Fe/H] abundance using the previously established calibrations by Armandroff & Da Costa (1991AJ....101.1329A) and Rutledge, Hesser & Stetson (1997, Cat. <J/PASP/109/883>). We have measured metallicities for 37 stars in Sculptor, 32 stars in Fornax and 23 stars in NGC 6822, yielding more precise estimates of the metallicity distribution functions for these galaxies than it is possible to obtain photometrically. In the case of NGC 6822, this is the first direct measurement of the abundances of the intermediate-age and old stellar populations. We find metallicity spreads in each galaxy which are broadly consistent with the photometric width of the red giant branch, although the abundances of individual stars do not always appear to correspond to their colour. This is almost certainly predominantly due to a highly variable star formation rate with time in these galaxies, which results in a non-uniform, non-globular-cluster-like evolution of the Ca/Fe ratio.
