31 research outputs found
Mapping the stellar age of the Milky Way bulge with the VVV : II. Deep JK s catalog release based on PSF photometry
Context. The bulge represents the best compromise between old and massive Galactic components, and as such its study is a valuable opportunity to understand how the bulk of the Milky Way formed and evolved. In addition, being the only bulge in which we can individually resolve stars in all evolutionary sequences, the properties of its stellar content provide crucial insights into the formation of bulges. Aims. We are providing a detailed and comprehensive census of the Milky Way bulge stellar populations by producing deep and accurate photometric catalogs of the inner ∼300 deg 2 of the Galaxy. Methods. We performed DAOPHOT/ALLFRAME point spread function (PSF) fitting photometry of multi-epochs J and K s images provided by the VISTA Variables in the Vía Láctea (VVV) survey to obtain deep photometric catalogs. Artificial star experiments have been conducted on all images to properly assess the completeness and the accuracy of the photometric measurements. Results. We present a photometric database containing nearly 600 million stars across the bulge area surveyed by the VVV. Through the comparison of derived color-magnitude diagrams of selected fields representative of different levels of extinction and crowding, we show the quality, completeness and depth of the new catalogs. With the exception of the fields located along the plane, this new photometry samples stars down to ∼1-2 mag below the old main sequence turnoff with unprecedented accuracy. To demonstrate the tremendous potential inherent to this new dataset, we give a few examples of possible applications, including (i) star count studies through the dataset completeness map; (ii) surface brightness map; and (iii) cross-correlation with Gaia DR2. Conclusions. The database presented here represents an invaluable collection for the whole community, and we encourage its exploitation. The photometric catalogs including completeness information are publicly available through the ESO Science Archive as part of the MW-BULGE-PSPHOT release.Peer reviewedFinal Accepted Versio
Galactic Bulge Population II Cepheids in the VVV Survey: Period-Luminosity Relations and a Distance to the Galactic Center
We present the near-infrared observations of population II Cepheids in the
Galactic bulge from VVV survey. We identify 340 population II Cepheids in the
Galactic bulge from VVV survey based on their match with OGLE-III Catalogue.
The single-epoch and multi-epoch observations complement the
accurate periods and optical mean-magnitudes from OGLE. The sample
consisting of BL Herculis and W Virginis subtypes is used to derive
period-luminosity relations after correcting mean-magnitudes for the
extinction. Our -band period-luminosity relation, , is consistent with published work
for BL Herculis and W Virginis variables in the Large Magellanic Cloud. We
present a combined OGLE-III and VVV catalogue with periods, classification,
mean magnitudes and extinction for 264 Galactic bulge population II Cepheids
having good-quality -band light curves. The absolute magnitudes for
population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space
Telescope parallaxes, together with calibrated magnitudes for Large Magellanic
Cloud population II Cepheids, are used to obtain a distance to the Galactic
center, , which
changes by with different extinction laws. While noting the
limitation of small number statistics, we find that the present sample of
population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial
distribution, similar to metal-poor RR Lyrae variables. We do not find evidence
of the inclined bar as traced by the metal-rich red-clump stars. The number
density for population II Cepheids is more limited as compared to abundant RR
Lyraes but they are bright and exhibit a wide range in period that provides a
robust period-luminosity relation for an accurate estimate of the distance to
the Galactic center.Comment: 9 pages, 8 figures, Accepted for publication in A&
New variable stars in the Galactic Bulge: I. The bright regime
We report the detection of 1143 variable stars towards the Galactic bulge,
including 320 previously uncatalogued variables, using time-series photometry
extracted from data obtained with the VIMOS imager at the Very Large Telescope.
Observations of the Sagittarius Window Eclipsing Extrasolar Planet Search
(SWEEPS) field in the Galactic Bulge were taken over 2 years between March and
October at a cadence of 4 days, enabling the detection of variables with
periods up to 100 days. Many of these were already known, but we detected
a significant number of new variables, including 26 Cepheids, a further 18
Cepheid candidates, and many contact binaries. Here we publish the catalog of
the new variables, containing coordinates, mean magnitudes as well as periods
and classification; full light curves for these variables are also made
available electronically.Comment: 14 pages, 9 figures; submitted to MNRA
Mapping the stellar age of the Milky Way bulge with the VVV. I. The method
Recent observational programmes are providing a global view of the Milky Way
bulge that serves as template for detailed comparison with models and
extragalactic bulges. A number of surveys (i.e. VVV, GIBS, GES, ARGOS, BRAVA,
APOGEE) are producing comprehensive and detailed extinction, metallicity,
kinematics and stellar density maps of the Galactic bulge with unprecedented
accuracy. However, the still missing key ingredient is the distribution of
stellar ages across the bulge. To overcome this limitation, we aim to age-date
the stellar population in several bulge fields with the ultimate goal of
deriving an age map of the Bulge. This paper presents the methodology and the
first results obtained for a field along the Bulge minor axis, at .
We use a new PSF-fitting photometry of the VISTA Variables in the V\'{i}a
L\'{a}ctea (VVV) survey data to construct deep color-magnitude diagrams of the
bulge stellar population down to 2 mag below the Main Sequence turnoff.
We find the bulk of the bulge stellar population in the observed field along
the minor axis to be at least older than 7.5 Gyr. In particular, when
the metallicity distribution function spectroscopically derived by GIBS is
used, the best fit to the data is obtained with a combination of synthetic
populations with ages in between 7.5 Gyr and 11 Gyr. However, the
fraction of stars younger than 10 Gyr strongly depends upon the number
of Blue Straggler Stars present in the bulge. Simulations show that the
observed color-magnitude diagram of the bulge in the field along the minor axis
is incompatible with the presence of a conspicuous population of
intermediate-age/young (i.e. Gyr) stars.Comment: 14 pages, 7 figues, Accepted for publication on A&
The Star Formation History of Eridanus II: On the Role of Supernova Feedback in the Quenching of Ultrafaint Dwarf Galaxies
Eridanus II (EriII) is an ultra-faint dwarf (UFD) galaxy (M_V=-7.1) located
at a distance close to the Milky Way virial radius. Early shallow
color-magnitude diagrams (CMD) indicated that it possibly hosted an
intermediate-age or even young stellar population, which is unusual for a
galaxy of this mass. In this paper, we present new ACS/HST CMDs reaching the
oldest main sequence turnoff with excellent photometric precision, and derive a
precise star formation history (SFH) for this galaxy through CMD-fitting. This
SFH shows that the bulk of the stellar mass in Eri II formed in an extremely
short star formation burst at the earliest possible time. The derived star
formation rate profile has a width at half maximum of 500 Myr and reaches a
value compatible with null star formation 13 Gyr ago. However, tests with mock
stellar populations and with the CMD of the globular cluster M92 indicate that
the star formation period could be shorter than 100 Myr.
From the quantitative determination of the amount of mass turned into stars
in this early star formation burst (~2x10^5 Msun) we infer the number of SNe
events and the corresponding energy injected into the interstellar medium. For
reasonable estimates of the EriII virial mass and values of the coupling
efficiency of the SNe energy, we conclude that EriII could be quenched by SNe
feedback alone, thus casting doubts on the need to invoke cosmic reionization
as the preferred explanation for the early quenching of old UFD galaxies.Comment: 18 pages, 8 figures, ApJ, accepted Dec 29, 202
VVV WIN 1733−3349: a low extinction window to probe the far side of the Milky Way bulge
Windows of low extinction in the Milky Way (MW) have been used along the past decades for the study of the Galactic structure and the stellar population across the inner bulge and disc. Here, we report the analysis of another low extinction near-IR window discovered by the VISTA Variables in the Viá Láctea Survey (VVV). VVV WIN 1733-3349 is about half a degree in size and is conveniently located right in the MW plane, at Galactic coordinates (l, b) = (-5.2,-0.3). The mean extinction of VVV WIN 1733-3349 is = 0.61 ± 0.08 mag, which is much smaller than the extinction in the surrounding area. The excess in the star counts is consistent with the reduced extinction and complemented by studying the distribution of red clump (RC) stars. Thanks to the strategic low-latitude location of VVV WIN 1733-3349, we are able to interpret their RC density fluctuations with the expected overdensities due to the presence of the spiral arms beyond the bulge. In addition, we find a clear excess in the number of microlensing events within the window, which corroborates our interpretation that VVV WIN 1733-3349 is revealing the far side of the MW bulge. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Indexación. Scopu
MATERIALES ARQUEOLÓGICOS DESCUBIERTOS EN LAS EXCAVACIONES [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
VVVX-Gaia Discovery of a Low Luminosity Globular Cluster in the Milky Way Disk
© 2020 ESOMilky Way globular clusters (MW GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-IR images and photometry from the VISTA Variables in the Via L\'actea Extended Survey (VVVX) allow us to chart previously unexplored regions. Our long term aim is to complete the census of MW GCs. The immediate goals are to estimate the astrophysical parameters, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities and ages. We use the near-IR VVVX survey database, in combination with Gaia DR2 optical photometry, and with the Two Micron All Sky Survey (2MASS) photometry. We report the detection of a heretofore unknown Galactic Globular Cluster at RA = 14:09:00.0; DEC=-65:37:12 (J2000). We calculate a reddening of E(J-K_s)=(0.3 +/- 0.03) mag and an extinction of A_Ks=(0.15 +/- 0.01) mag for this new GC. Its distance modulus and corresponding distance were measured as (m-M)=(15.93 +/- 0.03) mag and D=(15.5 +/- 1.0) kpc, respectively. We estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding dex and t=(11.0 +/- 1.0) Gyr. The mean GC PMs from Gaia are mu_alpha^(star)=(-4.68 +/- 0.47) mas yr^(-1) and mu_delta=(-1.34 \pm 0.45) mas yr^(-1). The total luminosity of our cluster is estimated to be M_Ks=(-7.76 +/- 0.5) mag. We have found a new low-luminosity, old and metal-rich globular cluster, situated in the far side of the Galactic disk, at R_G=11.2 kpc from the Galactic centre, and at z=1.0 kpc below the plane. Interestingly, the location, metallicity and age of this globular cluster are coincident with the Monoceros Ring (MRi) structure.Peer reviewe