- ID:
- ivo://CDS.VizieR/II/43
- Title:
- K-line photometry of Southern A stars
- Short Name:
- II/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The photoelectric measurements of the strength of the Calcium K-line has been extended by 223 stars of predominantly southern or equatorial declinations which are well distributed in right ascension. This has expanded the existent list to 369 field stars for which a k-index is available, including many more Am stars. All available k-index data for field stars are presented here.
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- ID:
- ivo://CDS.VizieR/II/44
- Title:
- K-Line photometry of stars in Population I clusters
- Short Name:
- II/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric photometry of the K-line of calcium has been performed for the A stars of five open clusters (Hyades, Pleiades, IC 2391, IC 2602, and NGC 6475) and one association (Orion). All observations were carried out simultaneously with the field stars measurements in Paper II (II/43), with the 16-inch (40cm) and 36-inch (91cm) telescopes of the Cerro Tololo Inter-American Observatory, between May 1969 and January 1970.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A73
- Title:
- Light curve of V945 Cen in Geneva photometry
- Short Name:
- J/A+A/520/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A detailed analysis of multicolour Geneva photometry and high-resolution echelle spectroscopy of the B8.5V star V945 Cen (HD 112409, V=5.2mag) whose short-term periodic variability was first detected from the HIPPARCOS data, led to the finding that the object is an ellipsoidal variable and a close double-lined spectroscopic binary with a 0.6496d orbital period and a circular orbit. The components have spectral types B7 and B8.5 and are both main-sequence objects. The system is detached but close to a contact configuration and is observed at an inclination of ~23-24{deg}. A notable finding is that the optical spectrum also contains a third system of spectral lines corresponding to a late B spectral type that remained stationary during the 5 days of spectral observations. From several independent lines of reasoning, we tentatively conclude that the third spectrum belongs to a real third body in the system. However, the possibility that it instead originates in circumbinary gas cannot be excluded completely, and additional spectral and interferometric observations are required to help us determine its origin conclusively.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A95
- Title:
- Light curves of NGC 6910 pulsating stars
- Short Name:
- J/A+A/632/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this study is to obtain the age of the open cluster NGC 6910 by means of ensemble asteroseismology of the early-type pulsating members, to derive their stellar parameters, and to classify the excited modes. We used time-series analysis, performed photometric and spectroscopic mode identification, and calculated grids of evolutionary and seismic models to apply the procedure of ensemble asteroseismology for nine pulsating members of NGC 6910. With two iterations of the procedure of ensemble asteroseismology we derived an age of 10.6^+0.9^_-0.8_Myr for NGC 6910. We also identified the degree l for 8 of 37 modes detected in these stars and classified all modes in terms of p, g, and mixed-mode pulsations. Of the nine pulsating stars examined in the paper, eight are {beta} Cep stars, including three that are hybrid {beta} Cep and slowly pulsating B-type (SPB) pulsators, and one is an SPB star. Interestingly, the least massive {beta} Cep star, NGC 6910-38, has a mass of about 5.6 solar masses. The present theory does not predict unstable p modes in B-type stars with such a low mass. The g modes with relatively high frequencies (>3.5d^-1^), observed in three members of the cluster, are also stable according to seismic modelling. Both findings pose a challenge for theoretical calculations and prompt a revision of the opacities. The procedure of ensemble asteroseismology was found to be successful for NGC 6910 and {chi} Per on the basis of pulsating B-type stars and can therefore be applied to other young open clusters that are rich in such stars.
- ID:
- ivo://CDS.VizieR/J/A+A/299/557
- Title:
- Light variations on Beta Pic
- Short Name:
- J/A+A/299/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed {beta} Pictoris photometric measurements obtained from La Silla by the Geneva Observatory from 1975 to 1992. These data show evidence of variations in the brightness of the star, with no color dependency. Here, we demonstrate that the light variations are present on long as well as on short time scales. On a long time scale, we show that the apparent magnitude of {beta} Pictoris decreased by 0.011+/-0.004mag from 1979 to 1982. Moreover, when we consider all the measurements, the chance that there is no variation at all can be estimated to be less than 10^-4^. On short time scales there is a peculiar feature observed during about 30 days; the variations may be as high as 0.04mag magnitude. A maximum entropy reconstruction of the photometric data is tentatively proposed and some physical interpretations are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/499/967
- Title:
- Long-term monitoring of {gamma} Dor stars
- Short Name:
- J/A+A/499/967
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- gamma Dor stars are excellent targets for asteroseismology since the gravity modes present in these stars probe the deep stellar interiors. Mode identification will improve the knowledge of these stars considerably. A selected group of gamma Dor stars and some candidates were observed with the Mercator telescope to find and/or confirm the periodicities in the light variations and to derive reliable amplitude ratios in different pass bands. A frequency analysis was performed on all new data obtained in the Geneva photometric system. In order to have more reliable and accurate frequencies, the new data were combined with similar data from the literature and with Hipparcos observations. A set of frequencies that minimized the residuals in a harmonic fit was searched for while allowing means and amplitudes to vary from one observation set to another.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/2033
- Title:
- Lyman-break galaxies (LBG) in the HUDF
- Short Name:
- J/ApJ/703/2033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 407 z~3 Lyman break galaxies (LBGs) to a limiting isophotal u-band magnitude of 27.6mag in the Hubble Ultra Deep Field. The LBGs are selected using a combination of photometric redshifts and the u-band drop-out technique enabled by the introduction of an extremely deep u-band image obtained with the Keck I telescope and the blue channel of the Low Resolution Imaging Spectrometer. The Keck u-band image, totaling 9hr of integration time, has a 1{sigma} depth of 30.7mag/arcsec^2^, making it one of the most sensitive u-band images ever obtained. The u-band image also substantially improves the accuracy of photometric redshift measurements of ~50% of the z~3 LBGs, significantly reducing the traditional degeneracy of colors between z~3 and z~0.2 galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/9
- Title:
- Machine-learning investigation of the open cluster M67
- Short Name:
- J/ApJ/869/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we use a machine-learning method, random forest (RF), to identify reliable members of the old (4Gyr) open cluster M67 based on the high-precision astrometry and photometry taken from the second Gaia data release (Gaia-DR2). The RF method is used to calculate membership probabilities of 71117 stars within 2.5{deg} of the cluster center in an 11-dimensional parameter space, the photometric data are also taken into account. Based on the RF membership probabilities, we obtain 1502 likely cluster members (>=0.6), 1361 of which are high-probability cluster members (>=0.8). Based on high-probability memberships with high-precision astrometric data, the mean parallax (distance) and proper-motion of the cluster are determined to be 1.1327+/-0.0018mas (883+/-1pc) and (<{mu}_{alpha}_cos{delta}>,<{mu}_{delta}_>)=(-10.9378+/-0.0078,-2.9465 +/-0.0074)mas/yr, respectively. We find the cluster to have a mean radial velocity of +34.06+/-0.09km/s, using 74 high-probability cluster members with precise radial-velocity measures. We investigate the spatial structure of the cluster, the core and limiting radius are determined to be 4.80'+/-0.11' (~1.23+/-0.03pc) and 61.98'+/-1.50' (~15.92+/-0.39pc), respectively. Our results reveal that an escaped member with high membership probability (~0.91) is located at a distance of 77' (~20pc) from the cluster center. Furthermore, our results reveal that at least 26.4% of the main-sequence stars in M67 are binary stars. We confirm that significant mass segregation has taken place within M67.
- ID:
- ivo://CDS.VizieR/J/MNRAS/469/3042
- Title:
- Metallicities in the Geneva photometric system
- Short Name:
- J/MNRAS/469/3042
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the most homogeneous Geneva seven-colour photometric system to derive new metallicity calibrations for early A- to K-type stars that cover both, dwarf stars and giants. The calibrations are based on several spectroscopic data sets that were merged to a common scale, and we applied them to open cluster data to obtain an additional proof of the metallicity scale and accuracy. In total, metallicities of 54 open clusters are presented. The accuracy of the calibrations for single stars is in general below 0.1dex, but for the open cluster sample with mean values based on several stars we find a much better precision, a scatter as low as about 0.03dex. Furthermore, we combine the new results with another comprehensive photometric data set to present a catalogue of mean metallicities for more than 3000 F- and G-type dwarf stars with sigma about 0.06dex. The list was extended by more than 1200 hotter stars up to about 8500K (or spectral type A3) by taking advantage of their almost reddening free characteristic in the new Geneva metallicity calibrations. These two large samples are well suited as primary or secondary calibrators of other data, and we already identified about 20 spectroscopic data sets that show offsets up to about 0.4dex.
- ID:
- ivo://CDS.VizieR/J/A+AS/130/223
- Title:
- Multiplicity among peculiar A stars I.
- Short Name:
- J/A+AS/130/223
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial velocities measured with the Coravel scanner are used to determine the orbits of two Ap stars and of two Am stars. The Ap stars HD 8441 appears to be a triple system (though of SB1 type), while improved orbital elements and masses are given for the classical Ap star beta CrB. Both Am stars HD 43478 and HD 93961 are SB2 binaries, and the fundamental elements of the former can be known thanks to its eclipsing nature.
