124 research outputs found
Variable stars in the VVV globular clusters
Indexación: Scopus.The VVV survey observed some of the most crowded and most obscured regions in the inner Milky Way during the last years. A significant sample of the less known globular clusters in our galaxy lie there. Combining the high-resolution, wide-field, near infrared capabilities of the survey camera, the use of 5 different filters, and multi-epoch observations, we are able to overcome many of the previous challenges that prevented a proper study of these objects. Particularly, the identification of the RR Lyrae stars in these globular clusters is proving to be a fundamental tool to establish accurately their distances and reddenings, and to infer information about the Oosterhoff dichotomy that Galactic globular clusters seem to follow. © The Authors, published by EDP Sciences, 2017.https://www.epj-conferences.org/articles/epjconf/pdf/2017/21/epjconf_puls2017_01022.pd
The WFCAM Multi-wavelength Variable Star Catalog
Stellar variability in the near-infrared (NIR) remains largely unexplored.
The exploitation of public science archives with data-mining methods offers a
perspective for the time-domain exploration of the NIR sky. We perform a
comprehensive search for stellar variability using the optical-NIR multi-band
photometric data in the public Calibration Database of the WFCAM Science
Archive (WSA), with the aim of contributing to the general census of variable
stars, and to extend the current scarce inventory of accurate NIR light curves
for a number of variable star classes. We introduce new variability indices
designed for multi-band data with correlated sampling, and apply them for
pre-selecting variable star candidates, i.e., light curves that are dominated
by correlated variations, from noise-dominated ones. Pre-selection criteria are
established by robust numerical tests for evaluating the response of
variability indices to colored noise characteristic to the data. We find 275
periodic variable stars and an additional 44 objects with suspected variability
with uncertain periods or apparently aperiodic variation. Only 44 of these
objects had been previously known, including 11 RR~Lyrae stars in the outskirts
of the globular cluster M3 (NGC~5272). We provide a preliminary classification
of the new variable stars that have well-measured light curves, but the
variability types of a large number of objects remain ambiguous. We classify
most of the new variables as contact binary stars, but we also find several
pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are
likely Cepheids. We also identify 32 highly reddened variable objects close to
previously known dark nebulae, suggesting that these are embedded young stellar
objects. We publish our results and all light-curve data as the WFCAM Variable
Star Catalog.Comment: 21 pages, 11 figure
The VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulge
Solid insight into the physics of the inner Milky Way is key to understanding
our Galaxy's evolution, but extreme dust obscuration has historically hindered
efforts to map the area along the Galactic mid-plane. New comprehensive
near-infrared time-series photometry from the VVV Survey has revealed 35
classical Cepheids, tracing a previously unobserved component of the inner
Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic
mid-plane, traversing across the bulge. The discovered period (age) spread of
these classical Cepheids implies a continuous supply of newly formed stars in
the central region of the Galaxy over the last 100 million years.Comment: Accepted for publication in The Astrophysical Journal Letters.
Near-IR finding charts of the Cepheids are available at the following URL:
http://www.astro.puc.cl/~idekany/pub/inner_disk_ceph_fc.pn
Blazhko modulation in the infrared
We present first direct evidence of modulation in the -band of
Blazhko-type RR Lyrae stars that are identified by their secular modulations in
the I-band data of OGLE-IV. A method has been developed to decompose the
-band light variation into two parts originating from the temperature and
the radius changes using synthetic data of atmosphere-model grids. The
amplitudes of the temperature and the radius variations derived from the method
for non-Blazhko RRab stars are in very good agreement with the results of the
Baade-Wesselink analysis of RRab stars in the M3 globular cluster confirming
the applicability and correctness of the method. It has been found that the
Blazhko modulation is primarily driven by the change in the temperature
variation. The radius variation plays a marginal part, moreover it has an
opposite sign as if the Blazhko effect was caused by the radii variations. This
result reinforces the previous finding based on the Baade-Wesselink analysis of
M3 (NGC 5272) RR Lyrae, that significant modulation of the radius variations
can only be detected in radial-velocity measurements, which relies on spectral
lines that form in the uppermost atmospheric layers. Our result gives the first
insight into the energetics and dynamics of the Blazhko phenomenon, hence it
puts strong constraints on its possible physical explanations.Comment: 16 pages, accepted for publication in MNRA
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