Since 1967 32 fields in the Milky Way were observed for variable stars. * New variable stars in Cygnus (1982IBVS.2157....1D) [8/65] Survey of an area of 20{deg}x15{deg} centered at 20h50m, +45{deg} in Cygnus. This area has been followed photographically in two colours during the period 1967 to 1981. As a rule one observation per summer was obtained. * New variable stars in Cassiopeia (1986IBVS.2878....1D) [66/105] Survey in an area 20{deg}x15{deg} centered at 1h06m, +60{deg}01'. Seventeen plate pairs exposed in the period 1967 to 1981 were collected and treated in the same way as described in the previous report. These observations provide approximate B and V magnitudes. In addition, six exposures were obtained in the period August 8 to September 23, 1985 on Technical Pan film. * New variable stars in Cygnus, Lyra and Vulpecula (1993IBVS.3855....1D) [106/185] Area of 20{deg}x15{deg} centred at 19h46m +30{deg}. * New variable stars in Cygnus, Lacerta and Andromeda (1996IBVS.4329....1D) [186/220] Area of 20{deg}x15{deg} centered at 20h40m, +45{deg} (1950). * New variable stars in the northern Milky Way (1997IBVS.4458....1D) [221/280] Area of 20{deg}x15{deg} centered at 22h42m, +60{deg} (1950) * New variable stars in the northern Milky Way (1998IBVS.4642....1D) [281/315] Results of a variable-star search in the 20{deg}x15{deg} area centered at 20h18m, +60{deg} (1950). * New variable stars in Andromeda and Cassiopeia (1999IBVS.4734....1D [316/341] Results of a variable-star search in the 20{deg}x15{deg} area centered at 0h30m, +45{deg} (1950). * New variable stars in Lyra and Cygnus (2000IBVS.4898....1D) [342/366] Results of a variable-star search in the 20{deg}x15{deg} area centered at 19h00m/+45{deg} (1950). * New variable stars along the northern Milky way (2001IBVS.5181....1D) [367/420] Results of a variable-star search in the 20{deg}x15{deg} area centered at 21h22m/+{deg} (1950).
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.
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.
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.
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.
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.
Nearly 1000 nights of high-precision photometry of the delta Scuti variable 4 CVn were obtained from 1966 to 2012. These data led to the discovery of 64+ frequencies of pulsation together with systematic changes in amplitudes and small period changes on a timescale of decades. This paper presents the previously unpublished data.
About 766 {delta} Scuti stars were observed by LAMOST by 2017 June 16. Stellar atmospheric parameters of 525 variables were determined, while spectral types were obtained for all samples. In the paper, those spectroscopic data are catalogued. We detect a group of 131 unusual and cool variable stars (UCVs) that are distinguished from the normal {delta} Scuti stars (NDSTs). On the H-R diagram and the logg-T diagram, the UCVs are far beyond the red edge of pulsational instability trip. Their effective temperatures are lower than 6700K with periods in the range from 0.09 to 0.22d. NDSTs have metallicity close to that of the Sun as expected, while UCVs are slightly metal poor than NDSTs. The two peaks on the distributions of the period and stellar atmospheric parameters are all caused by the existence of UCVs. When those UCVs are excluded, it is discovered that the effective temperature, the gravitational acceleration, and the metallicity all are correlated with the pulsating period for NDSTs and their physical properties and evolutionary states are discussed. Detection of those UCVs indicates that about 25 per cent of the known {delta} Scuti stars may be misclassified. However, if some of them are confirmed to be pulsating stars, they will be a new-type pulsator and their investigations will shed light on theoretical instability domains and on the theories of interacting between the pulsation and the convection of solar-type stars. Meanwhile, 88 {delta} Scuti stars are detected to be the candidates of binary or multiple systems.
Projected rotational velocities and effective temperatures for 68 delta Sct stars as well as 41 non-variable stars of similar spectral type and luminosity are presented here. The observations were performed between 1990 and 1994 at two different observatories: the Observatorio del Roque de los Muchachos (La Palma, Spain) and the McDonald Observatory (Texas, USA).
An extensive and up-dated list of {delta} Sct stars is presented here. More than 500 papers, published during the last few years, have been revised and 341 new variables have been added to our last list, six years ago. This catalogue is intended to be a comprehensive review on the 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 January 2000. In summary, 636 variables, 1149 references and 182 individual notes are presented in this new list.
