75 research outputs found
Stellar populations in the surrounding field of the LMC clusters NGC 2154 and NGC 1898
In this paper we present a study and comparison of the star formation rates
(SFR) in the fields around NGC 1898 and NGC 2154, two intermediate-age star
clusters located in very different regions of the Large Magellanic Cloud. We
also present a photometric study of NGC 1898, and of seven minor clusters which
happen to fall in the field of NGC 1898, for which basic parameters were so far
unknown. We do not focus on NGC 2154, because this cluster was already
investigated in Baume et al. 2007, using the same theoretical tools. The ages
of the clusters were derived by means of the isochrone fitting method on their
color-magnitude diagrams. Two distinct populations of clusters were
found: one cluster (NGC 2154) has a mean age of 1.7 Gyr, with indication of
extended star formation over roughly a 1 Gyr period, while all the others have
ages between 100 and 200 Myr. The SFRs of the adjacent fields were inferred
using the downhill-simplex algorithm. Both SFRs show enhancements at 200, 400,
800 Myr, and at 1, 6, and 8 Gyr. These bursts in the SFR are probably the
result of dynamical interactions between the Magellanic Clouds (MCs), and of
the MCs with the Milky Way.Comment: 10 pages, 11 eps figures, in press in MNRAS. For a version including
references contact the author
The VMC survey - XIV : First results on the look-back time star formation rate tomography of the Small Magellanic Cloud
Date of Acceptance: 20/01/2015We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJKs filters, covering 14 deg2 (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour-magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68 per cent confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39°, although deviations of up to ±3 kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age-metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2 Gyr and the peak of star formation in the SMC Bar at ~40 Myr. We clearly detect periods of enhanced star formation at 1.5 and 5 Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1 Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages.Peer reviewe
The mass-loss, expansion velocities, and dust production rates of carbon stars in the Magellanic Clouds
The properties of carbon stars in the Magellanic Clouds (MCs) and their total dust production rates are predicted by fitting their spectral energy distributions (SED) over pre-computed grids of spectra reprocessed by dust. The grids are calculated as a function of the
stellar parameters by consistently following the growth for several dust species in their circumstellar envelopes, coupled with a stationary wind. Dust radiative transfer is computed taking as input the results of the dust growth calculations. The optical constants for amorphous carbon are selected in order to reproduce different observations in the
infrared and optical bands of Gaia Data Release 2. We find a tail of extreme mass-losing carbon stars in the Large Magellanic Cloud (LMC) with low gas-to-dust ratios that is not present in the Small Magellanic Cloud (SMC). Typical gas-to-dust ratios are around 700 for the extreme stars, but they can be down to similar to 160-200 and similar to 100 for
a few sources in the SMC and in the LMC, respectively. The total dust production rate for the carbon star population is similar to 1.77 +/- 0.45 x 10(-5) M-circle dot yr(-1), for the LMC, and similar to 2.52 +/- 0.96 x 10(-6) M-circle dot yr(-1), for the SMC. The extreme carbon stars
observed with the Atacama Large Millimeter Array and their wind speed are studied in detail. For the most dust-obscured star in this sample the estimated mass-loss rate is similar to 6.3 x 10(-5) M-circle dot yr(-1). The grids of spectra are available at:(1) and included in the
SED-fitting python package for fitting evolved stars.(2
An update on methods for Sarcopenia Diagnosis: From bench to bedside
Sarcopenia has been recognized as an age-related syndrome characterized by low muscle mass, low muscle strength, and low physical performance that is associated with increased likelihood of adverse outcomes including falls, fractures, hospitalization, frailty and mortality. Therefore, it is necessary to identify the condition early for applying intervention and prevention of the disastrous consequences of sarcopenia if left untreated. Clinical definition and diagnostic criteria for sarcopenia have been developed in the last years and different tools have been proposed for screening subjects with sarcopenia, evaluating the muscle mass, the muscle strength and the physical performance. In this review we analyzed the diagnostic criteria of sarcopenia and examined the current assessment tools used for the diagnosis and screening of sarcopenia
The VMC Survey. V. First results for Classical Cepheids
The VISTA Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting deep
Ks-band time-series photometry of the pulsating variable stars hosted by the
system formed by the two Magellanic Clouds (MCs) and the "bridge" connecting
them. In this paper we present the first results for Classical Cepheids, from
the VMC observations of two fields in the Large Magellanic Cloud (LMC). The VMC
Ks-band light curves of the Cepheids are well sampled (12-epochs) and of
excellent precision. We were able to measure for the first time the Ks
magnitude of the faintest Classical Cepheids in the LMC (Ks\sim17.5 mag), which
are mostly pulsating in the First Overtone (FO) mode, and to obtain FO
Period-Luminosity (PL), Period-Wesenheit (PW), and Period-Luminosity-Color
(PLC) relations, spanning the full period range from 0.25 to 6 day. Since the
longest period Cepheid in our dataset has a variability period of 23 day, we
have complemented our sample with literature data for brighter F Cepheids. On
this basis we have built a PL relation in the Ks band that, for the first time,
includes short period pulsators, and spans the whole range from 1.6 to 100 days
in period. We also provide the first ever empirical PW and PLC relations using
the (V-Ks) color and time-series Ks photometry. The very small dispersion
(\sim0.07 mag) of these relations makes them very well suited to study the
three-dimensional (3D) geometry of the Magellanic system. The use of "direct"
(parallax- and Baade-Wesselink- based) distance measurements to both Galactic
and LMC Cepheids, allowed us to calibrate the zero points of the PL, PW, and
PLC relations obtained in this paper, and in turn to estimate an absolute
distance modulus of (m-M)0=18.46\pm0.03 for the LMC. This result is in
agreement with most of the latest literature determinations based on Classical
Cepheids.Comment: 12 pages, 7 figures: MNRAS in pres
Asymptotic Giant Branch Stars in the Sculptor Dwarf Spheroidal Galaxy
JHK_S photometry is presented for a 35 arcmin square field centred on the
Sculptor dwarf spheroidal galaxy. With the aid of published kinematic data
definite galaxy members are identified and the width in J-K of the
colour-magnitude diagram is shown to be consistent with an old population of
stars with a large range in metal abundance. We identify two Asymptotic Giant
Branch variables, both carbon Miras, with periods of 189 and 554 days,
respectively, and discuss their ages, metallicities and mass loss as well as
their positions in the Mira period-luminosity diagram. There is evidence for a
general period-age relation for Local Group Miras. The mass-loss rate for the
554-day variable, MAG29, appears to be consistent with that found for Miras of
comparable period in other Local Group galaxies.Comment: accepted for publication in MNRA
The VMC survey - XI : Radial Stellar Population Gradients in the Galactic Globular Cluster 47 Tucanae
Copyright American Astronomical SocietyWe present a deep near-infrared color-magnitude diagram of the Galactic globular cluster 47 Tucanae, obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA) as part of the VISTA near-infrared Y, J, Ks survey of the Magellanic System (VMC). The cluster stars comprising both the subgiant and red giant branches exhibit apparent, continuous variations in color-magnitude space as a function of radius. Subgiant branch stars at larger radii are systematically brighter than their counterparts closer to the cluster core; similarly, red-giant-branch stars in the cluster's periphery are bluer than their more centrally located cousins. The observations can very well be described by adopting an age spread of ~0.5 Gyr as well as radial gradients in both the cluster's helium abundance (Y) and metallicity (Z), which change gradually from (Y = 0.28, Z = 0.005) in the cluster core to (Y = 0.25, Z = 0.003) in its periphery. We conclude that the cluster's inner regions host a significant fraction of second-generation stars, which decreases with increasing radius; the stellar population in the 47 Tuc periphery is well approximated by a simple stellar population.Peer reviewe
The VMC Survey - VI. Quasars behind the Magellanic system
The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for different types of studies. We have searched
for criteria to identify candidate QSOs using observations from the VISTA
survey of the Magellanic Clouds system (VMC) that provides photometry in the
YJKs bands and 12 epochs in the Ks band. The (Y-J) versus (J-Ks) diagram has
been used to distinguish QSO candidates from Milky Way stars and stars of the
Magellanic Clouds. Then, the slope of variation in the Ks band has been used to
identify a sample of high confidence candidates. These criteria were developed
based on the properties of 117 known QSOs presently observed by the VMC survey.
VMC YJKs magnitudes and Ks light-curves of known QSOs behind the Magellanic
system are presented. About 75% of them show a slope of variation in Ks>10^-4
mag/day and the shape of the light-curve is in general irregular and without
any clear periodicity. The number of QSO candidates found in tiles including
the South Ecliptic Pole and the 30 Doradus regions is 22 and 26, respectively,
with a ~20% contamination by young stellar objects, planetary nebulae, stars
and normal galaxies. By extrapolating the number of QSO candidates to the
entire VMC survey area we expect to find about 1200 QSOs behind the LMC, 400
behind the SMC, 200 behind the Bridge and 30 behind the Stream areas, but not
all will be suitable for astrometry. Further, the Ks band light-curves can help
support investigations of the mechanism responsible for the variations.Comment: 17 pages, 15 figures, replaced with accepted version by Astronomy &
Astrophysic
- …