- ID:
- ivo://CDS.VizieR/J/MNRAS/443/2492
- Title:
- {Delta}a observations of 3 globular clusters
- Short Name:
- J/MNRAS/443/2492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of {Delta}a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow-band system measures the flux distribution in the region from 4900 to 5600{AA} in order to find any peculiarities around 5200{AA}. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present {Delta}a photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3{sigma} detection limit of each globular cluster, about 3 percent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.
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- ID:
- ivo://CDS.VizieR/J/A+A/564/A42
- Title:
- {Delta}a-photometry in 10 open clusters
- Short Name:
- J/A+A/564/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detection of magnetic chemically peculiar (CP2) stars in open clusters of the Milky Way can be used to study the influence of different galactic environments on the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Furthermore it is still unknown if the CP2 phenomenon evolves, i.e. does the strength of the peculiarity feature at 5200{AA} increase or decrease with age. Methods. We have observed ten young to intermediate age open clusters in the {Delta}a photometric system.
- ID:
- ivo://CDS.VizieR/J/A+A/441/631
- Title:
- {Delta}a photometry of CP stars
- Short Name:
- J/A+A/441/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have summarized all {Delta}a measurements for galactic field stars (1474 objects) from the literature published over more than two decades. These measurements were, for the first time, compiled and homogeneously analyzed. The {Delta}a intermediate band photometric system samples the depth of the 5200{AA} flux depression by comparing the flux at the center with the adjacent regions with bandwidths of 110{AA} to 230{AA}. Because it was slightly modified over the last three decades, we checked for systematic trends for the different measurements but found no correlations whatsoever. The {Delta}a photometric system is most suitable to detecting magnetic chemically peculiar (CP) stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. Furthermore, the groups of (metal-weak) lambda Bootis, as well as classical Be/shell stars, can be successfully investigated. In addition, we also analyzed the behaviour of supergiants (luminosity class I and II). On the basis of apparent normal type objects, the correlation of the 3sigma significance limit and the percentage of positive detection for all groups was derived.
- ID:
- ivo://CDS.VizieR/J/A+AS/130/455
- Title:
- Delta-a photometry of southern B & A bright stars
- Short Name:
- J/A+AS/130/455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 2 lists the HR and HD numbers, the run in which the observations were obtained (sometimes several observations per run and/or on several runs, a, Delta a absolute and expressed in units of the average standard deviation of normal stars from the normality line, b-y and its dereddened quantity (b-y)_0, m_1, the spectral types from the BS Catalogue and the Michigan spectral survey (where available), then a column which indicates whether the object was used for the construction of the normality line (N) or entered the group of double stars (D), and finally the peculiarity group to which the star belongs (Preston's CP1-4, {lambda} Boo, {delta} Del, emission line objects E, supergiants SG and a Barium star Ba). For a description of the {DELTA}a photometric system, see e.g. <GCPD/75>
- ID:
- ivo://CDS.VizieR/J/A+A/597/A73
- Title:
- delta Cep HARPS-N radial velocities
- Short Name:
- J/A+A/597/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The projection factor p is the key quantity used in the Baade-Wesselink (BW) method for distance determination; it converts radial velocities into pulsation velocities. Several methods are used to determine p, such as geometrical and hydrodynamical models or the inverse BW approach when the distance is known. We analyze new HARPS-N spectra of delta Cep to measure its cycle-averaged atmospheric velocity gradient in order to better constrain the projection factor. We first apply the inverse BW method to derive p directly from observations. The projection factor can be divided into three subconcepts: (1) a geometrical effect (p_0_), (2) the velocity gradient within the atmosphere (f_grad_), and (3) the relative motion of the optical pulsating photosphere with respect to the corresponding mass elements (f_o_-g). We then measure the fgrad value of delta Cep for the first time. When the HARPS-N mean cross-correlated line-profiles are fitted with a Gaussian profile, the projection factor is p_cc-g_=1.239+/-0.034(stat.)+/-0.023 (syst.). When we consider the different amplitudes of the radial velocity curves that are associated with 17 selected spectral lines, we measure projection factors ranging from 1.273 to 1.329. We find a relation between fgrad and the line depth measured when the Cepheid is at minimum radius. This relation is consistent with that obtained from our best hydrodynamical model of delta Cep and with our projection factor decomposition. Using the observational values of p and f_grad_ found for the 17 spectral lines, we derive a semi-theoretical value of f_o-g_. We alternatively obtain f_o-g_=0.975+/-0.002 or 1.006+/-0.002 assuming models using radiative transfer in plane-parallel or spherically symmetric geometries, respectively. The new HARPS-N observations of delta Cep are consistent with our decomposition of the projection factor. The next step will be to measure p0 directly from the next generation of visible interferometers. With these values in hand, it will be possible to derive fo-g directly from observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/144
- Title:
- {delta} Cephei new spectroscopic observations
- Short Name:
- J/ApJ/804/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical Cepheid variable stars are crucial calibrators of the cosmic distance scale thanks to a relation between their pulsation periods and luminosities. Their archetype, {delta} Cephei, is an important calibrator for this relation. In this paper, we show that {delta}Cephei is a spectroscopic binary based on newly obtained high-precision radial velocities. We combine these new data with literature data to determine the orbit, which has period 2201 days, semi-amplitude 1.5km/s, and high eccentricity (e=0.647). We re-analyze Hipparcos intermediate astrometric data to measure {delta} Cephei's parallax (varpri=4.09+/-0.16mas) and find tentative evidence for an orbital signature, although we cannot claim detection. We estimate that Gaia will fully determine the astrometric orbit. Using the available information from spectroscopy, velocimetry, astrometry, and Geneva stellar evolution models (M_{delta}Cep_~5.0-5.25M_{sun}_), we constrain the companion mass to within 0.2M_{sun}_<M_2_<1.2. We discuss the potential of ongoing and previous interactions between the companion and {delta} Cephei near pericenter passage, informing reported observations of circumstellar material and bow shock. The orbit may have undergone significant changes due to a Kozai-Lidov mechanism driven by the outer (visual and astrometric) companion HD213307. Our discovery of {delta} Cephei's nature as a spectroscopic binary exposes a hidden companion and reveals a rich and dynamical history of the archetype of classical Cepheid variables.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A45
- Title:
- delta Cep VEGA/CHARA observing log
- Short Name:
- J/A+A/593/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The B-W method is used to determine the distance of Cepheids and consists in combining the angular size variations of the star, as derived from infrared surface-brightness relations or interferometry, with its linear size variation, as deduced from visible spectroscopy using the projection factor. The underlying assumption is that the photospheres probed in the infrared and in the visible are located at the same layer in the star whatever the pulsation phase. While many Cepheids have been intensively observed by infrared beam combiners, only a few have been observed in the visible. This paper is part of a project to observe Cepheids in the visible with interferometry as a counterpart to infrared observations already in hand. Methods. Observations of Delta Cep itself were secured with the VEGA/CHARA instrument over the full pulsation cycle of the star. These visible interferometric data are consistent in first approximation with a quasi-hydrostatic model of pulsation surrounded by a static circumstellar environment (CSE) with a size of {theta}_CSE_=8.9+/-3.0mas and a relative flux contribution of f_CSE_=0.07+/-0.01. A model of visible nebula (a background source filling the field of view of the interferometer) with the same relative flux contribution is also consistent with our data at small spatial frequencies. However, in both cases, we find discrepancies in the squared visibilities at high spatial frequencies (maximum 2{sigma}) with two different regimes over the pulsation cycle of the star, {phi}=0.0-0.8 and {phi}=0.8-1.0. We provide several hypotheses to explain these discrepancies, but more observations and theoretical investigations are necessary before a firm conclusion can be drawn. For the first time we have been able to detect in the visible domain a resolved structure around delta Cep. We have also shown that a simple model cannot explain the observations, and more work will be necessary in the future, both on observations and modelling.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/134
- Title:
- delta Orionis Aa. III. Radial velocities
- Short Name:
- J/ApJ/809/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system {delta} Ori A, consisting of a binary O9.5II+early-B (Aa1 and Aa2) with P=5.7days, and a more distant tertiary (O9IV P>400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
- ID:
- ivo://CDS.VizieR/J/A+AS/106/21
- Title:
- Delta Sct stars: a new revised list
- Short Name:
- J/A+AS/106/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An extensive and up to date list of delta Sct stars is presented. This catalogue is intended to be a comprehensive review of observational characteristics of all the delta Sct stars known until now, including stars contained in earlier catalogues together with other new discovered variables, covering information published until November 1993. Global information in the form of histograms and diagrams are also shown.
- ID:
- ivo://CDS.VizieR/J/A+AS/129/9
- Title:
- Delta Sct stars in Praesepe
- Short Name:
- J/A+AS/129/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric photometry of seven Delta Scuti stars in Praesepe was secured. Three of them were observed simultaneously at observatories located at different longitudes. Period analysis has been carried out for each star with different computing packages and the results compared to those in the literature. Their physical characteristics have been determined from the Stromgren photometry and theoretical and empirical calibrations.