Wra 751 is a Luminous Blue Variable that lately exhibits strong changes in light and colour. We summarize the available photometry of Wra 751, present new photometric observations, and discuss these data with special attention on the systematic differences between the various data sources. In addition, we establish an empirical relationship between b-y and B-V for this class of stars. Wra 751 is a strong-active member of the S Dor class exhibiting very-long term S Doradus phases with an amplitude of about two magnitudes in V and a cycle length of several decades. The associated B-V colour-index amplitude is about 0.4mag. At this moment this LBV, which is the reddest member of the class, goes through the bright (and red) stage of a long-term S Dor cycle. The S Dor behaviour of this system shows some resemblance to the temporal characteristics of the Galactic LBV AG Car: time scales and amplitudes of light and colour variability are very similar.
The aim of this work was to perform a multiphase spectroscopic study of W Vir which represents stars of the class of Population II cepheids, in order to trace the behaviour of emission features in different lines, and to use the data to describe the dynamical processes in the atmosphere of this star associated with the shock wave propagation.
Photographic magnitudes are presented for the irregular variable WW Vulpeculae. They were derived from Argelander brightness estimates carried out on N=2774 plates of the Harvard College Observatory Plate Collection. The data set covers the period 1898 to 1966.
We have detected 300 X-ray sources within the half-mass radius (2.79') of the globular cluster 47 Tucanae in a deep (281ks) Chandra exposure. We perform photometry and simple spectral fitting for our detected sources and construct luminosity functions, X-ray color-magnitude, and color-color diagrams. Eighty-seven X-ray sources show variability on timescales from hours to years. Thirty-one of the new X-ray sources are identified with chromospherically active binaries from the catalogs of Albrow and coworkers (2001, Cat. <J/ApJ/559/1060>). We estimate that the total number of neutron stars in 47 Tuc is of order 300, reducing the discrepancy between theoretical neutron star retention rates and observed neutron star populations in globular clusters. Comprehensive tables of source properties and simple spectral fits are provided electronically.
X-ray bursts have recently been discovered in the Cepheids {delta}Cep and {beta}Dor modulated by the pulsation cycle. We have obtained an observation of the Cepheid {eta}Aql with the XMM-Newton satellite at the phase of maximum radius; the phase at which there is a burst of X-rays in {delta}Cep. No X-rays were seen from the Cepheid {eta}Aql at this phase, and the implications for Cepheid upper atmospheres are discussed. We have also used the combination of X-ray sources, as well as Gaia and 2MASS data, to search for a possible grouping around the young intermediate mass Cepheid. No indication of such a group was found.
We have studied the rapid X-ray time variability in 149 pointed observations with the Rossi X-Ray Timing Explorer (RXTE)'s Proportional Counter Array of the atoll source 4U 1636-53 in the banana state and, for the first time with RXTE, in the island state. We compare the frequencies of the variability components of 4U 1636-53 with those in other atoll and Z sources and find that 4U 1636-53 follows the universal scheme of correlations previously found for other atoll sources at (sometimes much) lower luminosities. Our results on the hectohertz QPO suggest that the mechanism that sets its frequency differs from that for the other components, while the amplitude-setting mechanism is common. A previously proposed interpretation of the narrow low-frequency QPO frequencies in different sources in terms of harmonic mode switching is not supported by our data or by previous data on other sources, and the frequency range that this QPO covers is found to be unrelated to spin, angular momentum, or luminosity.
We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ~376.75 deg^2^ at RA~150{deg} and DE~27{deg} down to a magnitude limit of i~19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. (2009, J/MNRAS/398/1757) and Sesar et al. (2010, J/ApJ/708/717) RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.
We present a thorough analysis of multicolour CCD observations of two modulated RRab-type variables, XY And and UZ Vir. These Blazhko stars show relatively simple light-curve modulation with the usual multiplet structures in their Fourier spectra. One additional, independent frequency with linear-combination terms of the pulsation frequency is also detected in the residual spectrum of each of the two stars. The amplitude and phase relations of the triplet components are studied in detail. Most of the epoch-independent phase differences show a slight, systematic colour dependence. However, these trends have opposite signs in the two stars. The mean values of the global physical parameters and their changes with the Blazhko phase are determined, utilizing the inverse photometric method (IPM). The modulation properties and the IPM results are compared for the two variables. The pulsation period of XY And is the shortest when its pulsation amplitude is the highest, while UZ Vir has the longest pulsation period at this phase of the modulation. Despite this contrasting behaviour, the phase relations of the variations in their mean physical parameters are similar. These results do not agree with the predictions of the Blazhko model of Stothers.
The weekly averaged near-infrared fluxes for 2652 stars were extracted from the cold and warm era all-sky maps of the Diffuse Infrared Background Experiment (DIRBE). Since the DIRBE program only archived the individual Calibrated Infrared Observations for the 10 month cold era mission, the weekly averaged fluxes were all that were available for the warm era. The steps required to extract stellar fluxes are described as are the adjustments that were necessary to correct the results for several systematic effects. The observations are at a cadence of once a week for 3.6 years (~1300 days), providing continuous sampling on variable stars that span the entire period for the longest fundamental pulsators. The stars are divided into three categories: those with large amplitude of variability, smaller amplitude variables, and sources whose near-infrared brightness do not vary according to our classification criteria. We show examples of the results and the value of the added baseline in determining the phase lag between the visible and infrared.
