74 research outputs found
The VVV-SkZ pipeline: an automatic PSF-fitting photometric pipeline for the VVV survey
We present the VVV-SkZ_pipeline, a DAOPHOT-based photometric pipeline,
created to perform PSF-fitting photometry of "VISTA Variables in the V\'ia
L\'actea" (VVV) ESO Public Survey data. The pipeline replaces the user avoiding
repetitive interaction in all the operations, retaining all of the benefits of
the power and accuracy of the DAOPHOT suite. The pipeline provides an
astrometrized photometric catalog reliable up to more than 2 magnitudes
brighter than the saturation limit, where other techniques fail. It also
produces deeper and more accurate photometry. These achievements allow the
VVV-SkZ_pipeline to produce data well anchored to the selected standard
photometric system and analyze important phenomena (i.e. TRGB, RGB slope, HB
morphology, RR Lyrae), that other methods are not able to manage.Comment: Accepted by RevMexAA for vol. 49, n.2, October 201
A multi-wavelength view on the dusty Wolf-Rayet star WR 48a
We present results from the first attempts to derive various physical
characteristics of the dusty Wolf-Rayet star WR 48a based on a multi-wavelength
view of its observational properties. This is done on the basis of new optical
and near-infrared spectral observations and on data from various archives in
the optical, radio and X-rays. The optical spectrum of WR 48a is acceptably
well represented by a sum of two spectra: of a WR star of the WC8 type and of a
WR star of the WN8h type. The strength of the interstellar absorption features
in the optical spectra of WR 48a and the near-by stars D2-3 and D2-7 (both
members of the open cluster Danks 2) indicates that WR 48a is located at a
distance of ~4 kpc from us. WR 48a is very likely a thermal radio source and
for such a case and smooth (no clumps) wind its radio emission suggests a
relatively high mass-loss rate of this dusty WR star (dM/dt = a few x 10^(-4)
solar masses per year). Long timescale (years) variability of WR 48a is
established in the optical, radio and X-rays. Colliding stellar winds likely
play a very important role in the physics of this object. However, some
LBV-like (luminous blue variable) activity could not be excluded as well.Comment: Accepted for publication in MNRAS; 16 pages, 16 figures, 6 table
Open cluster candidates in the VVVX area: VVVX CL 076 and CL 077
We are reporting some basic parameters of two newly discovered clusters, VVVX CL 076 and CL 077, recently discovered in the galactic disk area covered by the VISTA Variables in the Via Lactea eXtended (VVVX) ESO Public Survey. The preliminary analysis shows that both clusters are young and relatively close to the Sun.Peer reviewedFinal Published versio
On the neutral gas distribution and kinematics in the dwarf irregular galaxy IC 1613
We study the neutral hydrogen distribution and kinematics in the Local Group
dwarf irregular galaxy IC 1613 and compare them with the ionized gas
distribution and stellar content of the galaxy. We discuss several mechanisms
which may be responsible for the origin of the observed complicated HI
morphology and compare parameters of the most prominent kpc-scale HI structure
with the multiple SNe scenario.
The observations were performed with the Vary Large Array of NRAO with a
linear resolution ~23 pc at the adopted distance of 725 kpc and the spectral
channel width of 2.57 km/s. The numerical calculations have been provided with
our 2.5D Lagrangian scheme based on the thin layer approximation.
We found that the ISM of the galaxy is highly inhomogeneous and identified a
number of intermediate-scale (200 pc - 300 pc in diameter) HI arcs and shells
having expansion velocities of 10 to 20 km/s. Besides these shells, several
giant holes and arc-shaped structures have been revealed, whose radii exceed
several hundred parsecs. We found that parameters of the most prominent (M_HI =
2.8 x 10^7 Msol) kpc-scale structure and the level of the detected star
formation activity are inconsistent with the multiple SNe hypothesis.Comment: 10 pages, 4 figures, accepted for publication in the Astronomy and
Astrophysic
Kinematic Evidence for an Old Stellar Halo in the Large Magellanic Cloud
The oldest and most metal-poor Milky Way stars form a kinematically hot halo,
which motivates the two major formation scenarios for our galaxy: extended
hierarchical accretion and rapid collapse. RR Lyrae stars are excellent tracers
of old and metal-poor populations. We measure the kinematics of 43 RR Lyrae
stars in the inner regions of the nearby Large Magellanic Cloud (LMC) galaxy.
The velocity dispersion, \sigma_{true}=53\pm10 km/s, indicates that a
kinematically hot metal-poor old halo also exists in the LMC. This suggests
that our galaxy and smaller late-type galaxies like the LMC have similar early
formation histories.Comment: 8 pages, 2 figures; to be published in Science on Sept. 12, 200
An Automated tool to detect variable sources in the Vista Variables in the VĂa Láctea Survey. The VVV Variables (V^4) catalog of tiles d001 and d002
27 pages, 19 figuresTime-varying phenomena are one of the most substantial sources of astrophysical information, and their study has led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search for and analyze variable sources in the near-infrared K s band using the data from the VISTA Variables in the VĂa Láctea (VVV) ESO Public Large Survey. This process relies on the characterization of variable sources using different variability indices calculated from time series generated with point-spread function (PSF) photometry of sources under analysis. In particular, we used two main indices, the total amplitude and the eta index η, to identify variable sources. Once the variable objects are identified, periods are determined with generalized Lomb-Scargle periodograms and the information potential metric. Variability classes are assigned according to a compromise between comparisons with VVV templates and the period of the variability. The automated tool is applied on VVV tiles d001 and d002 and led to the discovery of 200 variable sources. We detected 70 irregular variable sources and 130 periodic ones. In addition, nine open-cluster candidates projected in the region are analyzed, and the infrared variable candidates found around these clusters are further scrutinized by cross-matching their locations against emission star candidates from VPHAS+ survey H α color cuts.Peer reviewedFinal Accepted Versio
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