1,953 research outputs found
A PSF-based approach to Kepler/K2 data. I. Variability within the K2 Campaign 0 star clusters M 35 and NGC 2158
Kepler and K2 data analysis reported in the literature is mostly based on
aperture photometry. Because of Kepler's large, undersampled pixels and the
presence of nearby sources, aperture photometry is not always the ideal way to
obtain high-precision photometry and, because of this, the data set has not
been fully exploited so far. We present a new method that builds on our
experience with undersampled HST images. The method involves a point-spread
function (PSF) neighbour-subtraction and was specifically developed to exploit
the huge potential offered by the K2 "super-stamps" covering the core of dense
star clusters. Our test-bed targets were the NGC 2158 and M 35 regions observed
during the K2 Campaign 0. We present our PSF modeling and demonstrate that, by
using a high-angular-resolution input star list from the Asiago Schmidt
telescope as the basis for PSF neighbour subtraction, we are able to reach
magnitudes as faint as Kp~24 with a photometric precision of 10% over 6.5
hours, even in the densest regions. At the bright end, our photometric
precision reaches ~30 parts-per-million. Our method leads to a considerable
level of improvement at the faint magnitudes (Kp>15.5) with respect to the
classical aperture photometry. This improvement is more significant in crowded
regions. We also extracted raw light curves of ~60,000 stars and detrended them
for systematic effects induced by spacecraft motion and other artifacts that
harms K2 photometric precision. We present a list of 2133 variables.Comment: 27 pages (included appendix), 2 tables, 25 figures (5 in low
resolution). Accepted for publication in MNRAS on November 05, 2015. Online
materials will be available on the Journal website soo
The helium spread in the Globular cluster 47 Tuc
Spectroscopy has shown the presence of the CN band dicothomy and the Na-O
anticorrelations for 50--70% of the investigated samples in the cluster 47 Tuc,
otherwise considered a "normal" prototype of high metallicity clusters from the
photometric analysis. Very recently, the re-analysis of a large number of
archival HST data of the cluster core has been able to put into evidence the
presence of structures in the Sub Giant Branch: it has a brighter component
with a spread in magnitude by 0.06 mag and a second one, made of about
10% of stars, a little fainter (by 0.05 mag). These data also show that
the Main Sequence of the cluster has an intrinsic spread in color which, if
interpreted as due to a small spread in helium abundance, suggests
Y0.027. In this work we examine in detail whether the Horizontal
Branch morphology and the Sub Giant structure provide further independent
indications that a real --although very small-helium spread is present in the
cluster. We re--analyze the HST archival data for the Horizontal Branch of 47
Tuc, obtaining a sample of 500 stars with very small photometric errors,
and build population synthesis based on new models to show that its particular
morphology can be better explained by taking into account a spread in helium
abundance of 2% in mass. The same variation in helium is able to explain the
spread in luminosity of the Sub Giant Branch, while a small part of the second
generation is characterized by a small C+N+O increase and provides an
explanation for the fainter Sub Giant Branch. We conclude that three
photometric features concur to form the paradigm that a small but real helium
spread is present in a cluster that has no spectacular evidence for multiple
populations like those shown by other massive clusters.Comment: Accepted for publication in the MNRAS on 2010 June 8. Received 2010
May 19; in original form 2010 February 9. 7 pages and 3 figures. No table
Observing multiple stellar populations with FORS2@VLT - Main sequence photometry in outer regions of NGC 6752, NGC 6397, and NGC 6121 (M 4)
We present the photometric analysis of the external regions of three Galactic
Globular Clusters: NGC 6121, NGC 6397 and NGC 6752. The main goal is the
characterization of the multiple stellar populations along the main sequence
(MS) and the study of the radial trend of the different populations hosted by
the target clusters. The data have been collected using FORS2 mounted at the
ESO/VLT@UT1 telescope in UBVI filters. From these data sets we extracted
high-accuracy photometry and constructed color-magnitude diagrams. We exploit
appropriate combination of colors and magnitudes which are powerful tools to
identify multiple stellar populations, like B versus U-B and V versus
c_{U,B,I}=(U-B)-(B-I) CMDs. We confirm previous findings of a split MS in NGC
6752 and NGC 6121. Apart from the extreme case of omega Centauri, this is the
first detection of multiple MS from ground-based photometry. For NGC 6752 and
NGC 6121 we compare the number ratio of the blue MS to the red MS in the
cluster outskirts with the fraction of first and second generation stars
measured in the central regions. There is no evidence for significant radial
trend. The MS of NGC 6397 is consistent with a simple stellar population. We
propose that the lack of multiple sequences is due both to observational errors
and to the limited sensitivity of U,B,V,I photometry to multiple stellar
populations in metal-poor GCs. Finally, we compute the helium abundance for the
stellar populations hosted by NGC 6121 and NGC 6752, finding a mild (Delta Y ~
0.02) difference between stars in the two sequences.Comment: 16 pages, 5 tables, 17 figures, accepted for pubblication in A&
The helium content of globular clusters: NGC6121 (M4)
He has been proposed as a key element to interpret the observed multiple MS,
SGB, and RGB, as well as the complex horizontal branch (HB) morphology. Stars
belonging to the bluer part of the HB, are thought to be more He rich (\Delta
Y=0.03 or more) and more Na-rich/O-poor than those located in the redder part.
This hypothesis was only partially confirmed in NGC 6752, where stars of the
redder zero-age HB showed a He content of Y=0.25+-0.01, fully compatible with
the primordial He content of the Universe, and were all Na-poor/O-rich. Here we
study hot blue HB (BHB) stars in the GC NGC 6121 (M4) to measure their He plus
O/Na content. We observed 6 BHB stars using the UVES@VLT2 spectroscopic
facility. In addition to He, O, Na, and Fe abundances were estimated. Stars
turned out to be all Na-rich and O-poor and to have a homogeneous enhanced He
content with a mean value of Y=0.29+-0.01(random)+-0.01(systematic). The high
He content of blue HB stars in M4 is also confirmed by the fact that they are
brighter than red HB stars (RHB). Theoretical models suggest the BHB stars are
He-enhanced by \Delta Y=0.02-0.03 with respect to the RHB stars. The whole
sample of stars has a metallicity of [Fe/H]=-1.06+-0.02 (internal error). This
is a rare direct measurement of the (primordial) He abundance for stars
belonging to the Na-rich/O-poor population of GC stars in a temperature regime
where the He content is not altered by sedimentation or extreme mixing as
suggested for the hottest, late helium flash HB stars. Our results support
theoretical predictions that the Na-rich/O-poor population is also more He-rich
than the Na-poor/O-rich generation and that a leading contender for the 2^{nd}
parameter is the He abundance.Comment: 18 pages, 8 figures, accepted for publication on Ap
A hot horizontal branch star with a close K-type main-sequence companion
Dynamical interactions in binary systems are thought to play a major role in
the formation of extreme horizontal branch stars (EHBs) in the Galactic field.
However, it is still unclear if the same mechanisms are at work in globular
clusters, where EHBs are predominantly single stars. Here we report on the
discovery of a unique close binary system (period ~1.61 days) in the globular
cluster NGC6752, comprising an EHB and a main-sequence companion of 0.63+-0.05
Msun. Such a system has no counterpart among nearly two hundred known EHB
binaries in the Galactic field. Its discovery suggests that either field
studies are incomplete, missing this type of systems possibly because of
selection effects, or that a particular EHB formation mechanism is active in
clusters but not in the field
Flutuação populacional de NoctuÃdeos determinada pela captura com armadilhas luminosas na região norte de Londrina, Paraná.
Objetivo: analisar a composição das espécies e a flutuação da população durante o ano, no distrito da Warta, norte da cidade de Londrina, PR, por meio da captura de armadilhas ?Luiz de Queiróz
Preservação em longo prazo do fungo entomapatogênico de lepidópteros, Nomuraea rileyi a -20°C.
Hubble Space Telescope Observations of an Outer Field in Omega Centauri: A Definitive Helium Abundance
We revisit the problem of the split main sequence (MS) of the globular
cluster omega Centauri, and report the results of two-epoch Hubble Space
Telescope observations of an outer field, for which proper motions give us a
pure sample of cluster members, and an improved separation of the two branches
of the main sequence. Using a new set of stellar models covering a grid of
values of helium and metallicity, we find that the best possible estimate of
the helium abundance of the bluer branch of the MS is Y = 0.39 +/- 0.02. For
the cluster center we apply new techniques to old observations: we use indices
of photometric quality to select a high-quality sample of stars, which we also
correct for differential reddening. We then superpose the color-magnitude
diagram of the outer field on that of the cluster center, and suggest a
connection of the bluer branch of the MS with one of the more prominent among
the many sequences in the subgiant region. We also report a group of undoubted
cluster members that are well to the red of the lower MS.Comment: 26 pages, 10 figures (4 in low resolution. AJ accepted on March 21,
201
Variable stars in one open cluster within the Kepler/K2-Campaign-5 field: M 67 (NGC 2682)
In this paper we continue the release of high-level data products from the
multiyear photometric survey collected at the 67/92 cm Schmidt Telescope in
Asiago. The primary goal of the survey is to discover and to characterise
variable objects and exoplanetary transits in four fields containing five
nearby open clusters spanning a broad range of ages. This second paper releases
a photometric catalogue, in five photometric bands, of the Solar-age,
Solar-metallicity open cluster M 67 (NGC 2682). Proper motions are derived
comparing the positions observed in 2013 at the Asiago's Schmidt Telescope with
those extracted from [email protected] MPG/ESO images in 2000. We also analyse the
variable sources within M 67. We detected 68 variables, 43 of which are new
detection. Variable periods and proper-motion memberships of a large majority
of sources in our catalogue are improved with respect to previous releases. The
entire catalogue will be available in electronic format. Besides the general
interest on an improved catalogue, this work will be particularly useful
because of: (1) the imminent release of Kepler/K2 Campaign-5 data of this
cluster, for which our catalogue will provide an excellent, high spatial
resolution input list, and (2) characterisation of the M 67 stars which are
targets of intense HARPS and HARPS-N radial-velocity surveys for planet search.Comment: 8 pages, 6 figures (2 at low resolution), 2 tables. Accepted for
publication in MNRAS on October 17, 2015. Electronic materials available at
the url http://groups.dfa.unipd.it/ESPG/M67.html , and later on the Journal
and at the CD
Multiple stellar populations in three rich Large Magellanic Cloud star clusters
We present deep colour-magnitude diagrams for three rich intermediate-age
star clusters in the Large Magellanic Cloud, constructed from archival ACS
F435W and F814W imaging. All three clusters exhibit clear evidence for peculiar
main-sequence turn-offs. NGC 1846 and 1806 each possess two distinct turn-off
branches, while the turn-off for NGC 1783 shows a much larger spread in colour
than can be explained by the photometric uncertainties. We demonstrate that
although all three clusters contain significant populations of unresolved
binary stars, these cannot be the underlying cause of the observed turn-off
morphologies. The simplest explanation is that each cluster is composed of at
least two different stellar populations with very similar metal abundances but
ages separated by up to ~300 Myr. The origin of these unusual properties
remains unidentified; however, the fact that at least three massive clusters
containing multiple stellar populations are now known in the LMC suggests a
potentially significant formation channel.Comment: To appear in ApJ Letters, replaced with accepted versio
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