We have measured the periods and light curves of 148 RR Lyrae variables from V=13.5 to 19.7 from the first 100 deg 2 of the QUEST RR Lyrae survey. Approximately 55% of these stars belong to the clump of stars detected earlier by the Sloan Digital Sky Survey. According to our measurements, this feature has ∼10 times the background density of halo stars, spans at least 37.5 • by 3.5 • in α and δ (≥ 30 by ≥ 3kpc), lies ∼ 50 kpc from the Sun, and has a depth along the line of sight of ∼ 5 kpc (1σ). These properties are consistent with the recent models that suggest it is a tidal stream from the Sgr dSph galaxy. The mean period of the type ab variables, 0.58 d , is also consistent. In addition, we have found two smaller over-densities in the halo, one of which may be related to the globular cluster Pal 5.
With the 1 m Schmidt telescope of the Llano del Hato Observatory and the QUEST CCD camera, 380 deg 2 of the sky have been surveyed for RR Lyrae variables in a band 2 .3 wide in declination (centered at = À1) and covering right ascensions from 4C1 to 6C1 and from 8C0 to 17C0. The bright limit (due to CCD saturation) and the faint limit are V $13.5 and $19.7, respectively, which correspond to $4 and $60 kpc from the Sun. We present a catalog of the positions, amplitudes, mean magnitudes, periods, and light curves of the 498 RR Lyrae variables that have been identified in this region of the sky. The majority of these stars (86%) are new discoveries. The completeness of the survey has been estimated from simulations that model the periods and light curves of real RR Lyrae variables and take into account the pattern of epochs of observation. While the completeness of the survey varies with apparent magnitude and with position, almost everywhere in the surveyed region it is quite high (>80%) for the type ab RR Lyrae variables and between 30% and 90% for the lowamplitude type c variables.
Context. Determining the parameters of massive stars is crucial to understand many processes in galaxies and the Universe, since these objects are important sources of ionization, chemical enrichment and momentum. 10m class telescopes enable us to perform detailed quantitative spectroscopic analyses of massive stars in other galaxies, sampling areas of different metallicity. Relating the stars to their environment is crucial to understand the physical processes ruling their formation and evolution. Aims. In preparation for the new instrumentation planned for the Gran Telescopio CANARIAS (GTC), our goal is to build a list of massive star candidates in the metal-poor irregular galaxy IC 1613. The catalogue must have very high astrometric accuracy, suitable for the current generation of multi-object spectrographs. A census of OB associations in this galaxy is also needed, to provide important additional information about the age and environment of the candidate OB stars. Methods. From observations taken with the Wide Field Camera (WFC) at the Isaac Newton Telescope (INT), we have built an astrometric and photometric catalogue of stars in IC 1613. Candidate blue massive stars are preselected by their colors. A friendsof-friends algorithm is developed to find their clustering in the galaxy. While a common physical origin for all the members of the associations cannot be ensured, this is a necessary first step to place candidate OB stars in a population context. Results. We have produced a deep catalogue of targets in IC 1613 that covers a large field of view. To achieve high astrometric accuracy, a new astrometric procedure was developed for the INT-WFC data. We also built a catalogue of OB associations in IC 1613 and found that they concentrate in the central regions, especially in the H ii bubbles. The study of extinction confirms that it is patchy, with local values of color-excess above the foreground value.
We analyze the dependence of the membership probabilities obtained from kinematical variables on the radius of the field of view around open clusters (the sampling radius, R s ). From simulated data, we show that optimal discrimination between cluster members and non-members is achieved when the sampling radius is very close to the cluster radius. At higher R s values, more field stars tend to be erroneously assigned as cluster members. From real data of two open clusters (NGC 2323 and NGC 2311), we infer that the number of identified cluster members always increases with increasing R s . However, there is a threshold value R s,opt above which the identified cluster members are severely contaminated by field stars and the effectiveness of membership determination is relatively small. This optimal sampling radius is 14 arcmin for NGC 2323 and 13 arcmin for NGC 2311. We discuss the reasons for this behavior and the relationship between cluster radius and optimal sampling radius. We suggest that, independently of the method used to estimate membership probabilities, several tests using different sampling radius should be performed to evaluate possible biases.
Context. The planetary system WASP-33 is an interesting target because of the discovery of a transiting planet, the misalignment of the stellar rotation axis and the planet orbit, the possible existence of an additional planet in the system, and the presence of δ Scuti pulsations in the hosting star. Its study promises in particular to help us understand the origin and evolution of giant planets orbiting very close to a star. Aims. We analyse high spatial resolution imaging with an adaptive optics system on the W.M. 10 m-Keck II telescope to investigate the prediction of an additional planet, and any other objects, and constrain the possible formation scenarios of the system. Methods. In November 2010, we recorded high spatial resolution images from 1 to 2.5 μm using the W.M. 10 m-Keck II telescope and its adaptive optics system, obtaining broad (Jc, Hc, and Kc) and narrow-band (FeII) images of the system. After data reduction, the contrast and angular resolution provided by this instrument allowed us to constrain the multiplicity of this system and detect one potential companion. Results. We present the discovery of a new object at a distance of 1.961 ± 0.003 from the WASP-33, at a position angle of 276.32 ± 0.24 deg. It might be either a dwarf star or brown dwarf, or an extragalactic object. In the case of a galactic object and assuming the same distance from the Sun, it would be 227 AU from the central star. We find no evidence of any additional objects. This constrains the possible constituents of the system, depending on its age and the constituent masses. Conclusions. We find a potential companion object to WASP-33. We need to confirm the gravitational link, but this object could influence the evolution of the planetary system depending on its orbital eccentricity. We exclude the existence of any additional objects. For example, objects of 0.8 M at projected physical distances greater than [2, 5] AU, objects of 0.3 M at projected physical distances greater than [11, 18] AU, or objects of 0.072 M at projected physical distances greater than [18, 75] AU, depending on the age of the system.
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