4,690 research outputs found
Bulge RR Lyrae stars in the VVV tile
The VISTA Variables in the V\'ia L\'actea (VVV) Survey is one of the six ESO
public surveys currently ongoing at the VISTA telescope on Cerro Paranal,
Chile. VVV uses near-IR () filters that at present provide
photometry to a depth of mag in up to 36 epochs spanning
over four years, and aim at discovering more than 10 variable sources as
well as trace the structure of the Galactic bulge and part of the southern
disk. A variability search was performed to find RR Lyrae variable stars. The
low stellar density of the VVV tile , which is centered at
() (), makes it suitable to search for
variable stars. Previous studies have identified some RR Lyrae stars using
optical bands that served to test our search procedure. The main goal is to
measure the reddening, interstellar extinction, and distances of the RR Lyrae
stars and to study their distribution on the Milky Way bulge. A total of 1.5 sq
deg were analyzed, and we found 39 RR Lyrae stars, 27 of which belong to the
ab-type and 12 to the c-type. Our analysis recovers all the previously
identified RR Lyrae variables in the field and discovers 29 new RR Lyrae stars.
The reddening and extinction toward all the RRab stars in this tile were
derived, and distance estimations were obtained through the period--luminosity
relation. Despite the limited amount of RR Lyrae stars studied, our results are
consistent with a spheroidal or central distribution around and
kpc. for either the Cardelli or Nishiyama extinction law.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Variable stars in the globular cluster M28 (NGC 6626)
We present a new search for variable stars in the Galactic globular cluster
M28 (NGC 6626). The search is based on a series of BVI images obtained with the
SMARTS Consortium's 1.3m telescope at Cerro Tololo Inter-American Observatory,
Chile. The search was carried out using the ISIS v2.2 image subtraction
package. We find a total of 25 variable stars in the field of the cluster, 9
being new discoveries. Of the newly found variables, 1 is an ab-type RR Lyrae
star, 6 are c-type RR Lyrae, and 2 are long-period/semi-regular variables. V22,
previously classified as a type II Cepheid, appears as a bona-fide RRc in our
data. In turn, V20, previously classified as an ab-type RR Lyrae, could not be
properly phased with any reasonable period. The properties of the ab-type RR
Lyrae stars in M28 appear most consistent with an Oosterhoff-intermediate
classification, which is unusual for bona-fide Galactic globulars clusters.
However, the cluster's c-type variables do not clearly support such an
Oosterhoff type, and a hybrid Oosterhoff I/II system is accordingly another
possibility, thus raising the intriguing possibility of multiple populations
being present in M28. Coordinates, periods, and light curves in differential
fluxes are provided for all the detected variables.Comment: A&A, in pres
The VVV Survey RR Lyrae Population in the Galactic Center Region
Indexación: Scopus.We gratefully acknowledge the use of data from the ESO Public Survey program ID 179.B-2002 taken with the VISTA telescope, and data products from the Cambridge Astronomical Survey Unit (CASU). Support for the authors is provided by the BASAL Center for Astrophysics and Associated Technologies (CATA) through grant PFB-06, and the Ministry for the Economy, Development, and Tourism, Programa Iniciativa Cientifica Milenio through grant IC120009, awarded to the Millennium Institute of Astrophysics (MAS). D.M. and M.Z. acknowledge support from FONDECYT Regular grants No. 1170121, and 1150345, respectively. P.H. acknowledges financial support from FONDECYT regular grant 1170305. F.G. acknowledge support from CONICYT-PCHA Doctorado Nacional 2017-21171485 and Proyecto Fondecyt Regular 1150345. J.A.-G. acknowledges support by FONDECYT Iniciacion 11150916. D.M. is also grateful for the hospitality of the Vatican Observatory. This research made use of Astropy, a community-developed core Python package for astronomy; Scikit-learn, NumPy, and matplotlib, a Python library for publication-quality graphics; and Aladin Sky Atlas, developed at CDS, Strasbourg Observatory, France, and TOPCAT.Deep near-IR images from the VISTA Variables in the V a L ctea (VVV) Survey were used to search for RR Lyrae stars within 100 arcmin from the Galactic Center. A large sample of 960 RR Lyrae of type ab (RRab) stars were discovered. A catalog is presented featuring the positions, magnitudes, colors, periods, and amplitudes for the sample, in addition to estimated reddenings, distances, and metallicities, and measured individual relative proper motions. We use the reddening-corrected Wesenheit magnitudes, defined as WKs Ks 0.428 J Ks = - ( - ), in order to isolate bona fide RRL belonging to the Galaxy Center, finding that 30 RRab are foreground/background objects. We measure a range of extinctions from AKs 0.19 = to 1.75 mag for the RRab in this region, finding that large extinction is the main cause of the sample incompleteness. The mean period is P =0.5446±0.0025 days, yielding a mean metallicity of [Fe/H] =-1.30±0.01 (ς = 0.33) dex for the RRab sample in the Galactic Center region. The median distance for the sample is D =8.05±0.02 kpc. We measure the RRab surface density using the less reddened region sampled here, finding a density of 1000 RRab/sq deg at a projected Galactocentric distance RG =1.6 deg. Under simple assumptions, this implies a large total mass (M>109Me) for the old and metal-poor population contained inside RG. We also measure accurate relative proper motions, from which we derive tangential velocity dispersions of ςVl =125.0 and ςVb =124.1 km s-1 along the Galactic longitude and latitude coordinates, respectively. The fact that these quantities are similar indicate that the bulk rotation of the RRab population is negligible, and implies that this population is supported by velocity dispersion. In summary, there are two main conclusions of this study. First, the population as a whole is no different from the outer bulge RRab, predominantly a metal-poor component that is shifted with respect to the Oosterhoff type I population defined by the globular clusters in the halo. Second, the RRab sample, as representative of the old and metal-poor stellar population in the region, has high velocity dispersions and zero rotation, suggesting a formation via dissipational collapse. ©2018. The American Astronomical Society. All rights reserved.https://iopscience.iop.org/article/10.3847/1538-4357/aacf9
New type II Cepheids from VVV data towards the Galactic center
The Galactic center (GC) is the densest region of the Milky Way. Variability
surveys towards the GC potentially provide the largest number of variable stars
per square degree within the Galaxy. However, high stellar density is also a
drawback due to blending. Moreover, the GC is affected by extreme reddening,
therefore near infrared observations are needed. We plan to detect new variable
stars towards the GC, focusing on type II Cepheids (T2Cs) which have the
advantage of being brighter than RR Lyrae stars. We perform parallel
Lomb-Scargle and Generalized Lomb-Scargle periodogram analysis of the
-band time series of the VISTA variables in the Via Lactea survey, to
detect periodicities. We employ statistical parameters to clean our sample. We
take account of periods, light amplitudes, distances, and proper motions to
provide a classification of the candidate variables. We detected 1,019 periodic
variable stars, of which 164 are T2Cs, 210 are Miras and 3 are classical
Cepheids. We also found the first anomalous Cepheid in this region. We compare
their photometric properties with overlapping catalogs and discuss their
properties on the color-magnitude and Bailey diagrams. We present the most
extensive catalog of T2Cs in the GC region to date. Offsets in E() and
in the reddening law cause very large (1-2 kpc) uncertainties on
distances in this region. We provide a catalog which will be the starting point
for future spectroscopic surveys in the innermost regions of the Galaxy.Comment: A&A, accepte
Proper motions in the VVV Survey: Results for more than 15 million stars across NGC 6544
Context: In the last six years, the VVV survey mapped 562 sq. deg. across the
bulge and southern disk of the Galaxy. However, a detailed study of these
regions, which includes globular clusters (GCs) and thousands of open
clusters is by no means an easy challenge. High differential reddening and
severe crowding along the line of sight makes highly hamper to reliably
distinguish stars belonging to different populations and/or systems. Aims: The
aim of this study is to separate stars that likely belong to the Galactic GC
NGC 6544 from its surrounding field by means of proper motion (PM) techniques.
Methods: This work was based upon a new astrometric reduction method optimized
for images of the VVV survey. Results: Photometry over the six years baseline
of the survey allowed us to obtain a mean precision of mas/yr, in
each PM coordinate, for stars with Ks < 15 mag. In the area studied here,
cluster stars separate very well from field stars, down to the main sequence
turnoff and below, allowing us to derive for the first time the absolute PM of
NGC 6544. Isochrone fitting on the clean and differential reddening corrected
cluster color magnitude diagram yields an age of 11-13 Gyr, and
metallicity [Fe/H] = -1.5 dex, in agreement with previous studies restricted to
the cluster core. We were able to derive the cluster orbit assuming an
axisymmetric model of the Galaxy and conclude that NGC 6544 is likely a halo
GC. We have not detected tidal tail signatures associated to the cluster, but a
remarkable elongation in the galactic center direction has been found. The
precision achieved in the PM determination also allows us to separate bulge
stars from foreground disk stars, enabling the kinematical selection of bona
fide bulge stars across the whole survey area. Our results show that VVV data
is perfectly suitable for this kind of analysis.Comment: 13 pages, 12 figures, accepted in A&
SW @ SPAIN
Executive Summary: This report provides information about the current state of the art in Semantic Web research in Spain. The contents of this report are mainly based on the information that was gathered during the workshop "Ontologías y Web Semántica 2005", which was held in Santiago de Compostela in November 2005, and the contributions that members from most of the research groups working in Semantic-Webrelated areas in Spain have provided. The field of Semantic Web is quite widespread in Spain, with important groups developing methods, techniques and tools to support different areas: Ontological Engineering, semantic extraction and annotation from heterogeneous sources, semantic search engines, personalisation and Semantic Web Services
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