510 research outputs found
Low-Mass Eclipsing Binaries in the Initial Kepler Data Release
We identify 231 objects in the newly released Cycle 0 dataset from the Kepler
Mission as double-eclipse, detached eclipsing binary systems with Teff < 5500 K
and orbital periods shorter than ~32 days. We model each light curve using the
JKTEBOP code with a genetic algorithm to obtain precise values for each system.
We identify 95 new systems with both components below 1.0 M_sun and eclipses of
at least 0.1 magnitudes, suitable for ground-based follow-up. Of these, 14 have
periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29
have periods greater than 10.0 days. This new sample of main-sequence,
low-mass, double-eclipse, detached eclipsing binary candidates more than
doubles the number of previously known systems, and extends the sample into the
completely heretofore unexplored P > 10.0 day period regime. We find
preliminary evidence from these systems that the radii of low-mass stars in
binary systems decrease with period. This supports the theory that binary
spin-up is the primary cause of inflated radii in low-mass binary systems,
although a full analysis of each system with radial-velocity and multi-color
light curves is needed to fully explore this hypothesis. As well, we present 7
new transiting planet candidates that do not appear among the recently released
list of 706 candidates by the Kepler team, nor in the Kepler False Positive
Catalog, along with several other new and interesting systems. We also present
novel techniques for the identification, period analysis, and modeling of
eclipsing binaries.Comment: 22 pages in emulateapj format. 9 figures, 4 tables, 2 appendices.
Accepted to AJ. Includes a significant addition of new material since last
arXiv submission and an updated method for estimating masses and radi
Estudio del proceso de cambio conceptual y la construcción del modelo científico precursor de ser vivo en niños de pre-escolar
La presente investigación estudia el cambio conceptual y la construcción de modelos científicos precursores en un contexto socioconstructivista con niños pequeños, utilizando una metodología cualitativa. Se analizan los cambios epistemológicos y ontológicos en las concepciones de los niños acerca de los seres vivos y cómo una estrategia didáctica basada en la construcción de un modelo científico precursor basado en propiedades biológicas los promueven. Los cambios en la comprensión de los niños fueron significativos en las dimensiones ontológicas y epistemológicas, presentando diferentes patones. Los segundos proporcionaron una mejor coherencia explicativa en su sistema conceptual contribuyendo, de esta forma, a los cambios ontológicos y promoviendo, a su vez, la construcción del modelo científico precursor de ser vivo
GJ 3236: a new bright, very low-mass eclipsing binary system discovered by the MEarth observatory
We report the detection of eclipses in GJ 3236, a bright (I = 11.6) very low
mass binary system with an orbital period of 0.77 days. Analysis of light- and
radial velocity curves of the system yielded component masses of 0.38 +/- 0.02
and 0.28 +/- 0.02 Msol. The central values for the stellar radii are larger
than the theoretical models predict for these masses, in agreement with the
results for existing eclipsing binaries, although the present 5% observational
uncertainties limit the significance of the larger radii to approximately 1
sigma. Degeneracies in the light curve models resulting from the unknown
configuration of surface spots on the components of GJ 3236 currently dominate
the uncertainties in the radii, and could be reduced by obtaining precise,
multi-band photometry covering the full orbital period. The system appears to
be tidally synchronized and shows signs of high activity levels as expected for
such a short orbital period, evidenced by strong Halpha emission lines in the
spectra of both components. These observations probe an important region of
mass-radius parameter space around the predicted transition to fully-convective
stellar interiors, where there are a limited number of precise measurements
available in the literature.Comment: 14 pages, 5 figures, 10 tables, emulateapj format. Accepted for
publication in Ap
Thirty New Low-Mass Spectroscopic Binaries
As part of our search for young M dwarfs within 25 pc, we acquired
high-resolution spectra of 185 low-mass stars compiled by the NStars project
that have strong X-ray emission. By cross-correlating these spectra with radial
velocity standard stars, we are sensitive to finding multi-lined spectroscopic
binaries. We find a low-mass spectroscopic binary fraction of 16% consisting of
27 SB2s, 2 SB3s and 1 SB4, increasing the number of known low-mass SBs by 50%
and proving that strong X-ray emission is an extremely efficient way to find
M-dwarf SBs. WASP photometry of 23 of these systems revealed two low-mass EBs,
bringing the count of known M dwarf EBs to 15. BD -22 5866, the SB4, is fully
described in Shkolnik et al. 2008 and CCDM J04404+3127 B consists of a two
mid-M stars orbiting each other every 2.048 days. WASP also provided rotation
periods for 12 systems, and in the cases where the synchronization time scales
are short, we used P_rot to determine the true orbital parameters. For those
with no P_rot, we use differential radial velocities to set upper limits on
orbital periods and semi-major axes. More than half of our sample has
near-equal-mass components (q > 0.8). This is expected since our sample is
biased towards tight orbits where saturated X-ray emission is due to tidal
spin-up rather than stellar youth. Increasing the samples of M dwarf SBs and
EBs is extremely valuable in setting constraints on current theories of stellar
multiplicity and evolution scenarios for low-mass multiple systems.Comment: Accepted to Ap
Prokaryotic picoplankton distribution within the oxygen minimum zone of the central Mexican Pacific across environmental gradients
O picophytoplankton marinho tornou-se uma questão importante para compreender a ecologia global das formas fototróficas, devido à sua ampla distribuição e contribuição para a biomassa e a produtividade. Estudamos os pigmentos de abundância, distribuição e assinatura do picofitoplâncton procarionte Prochlorococcus e Synechococcus durante um cruzeiro oceanográfico no Pacífico central mexicano, uma zona mínima de oxigênio relativamente poco conhecida (OMZ) e o efeito de três gradientes ambientais. As abundâncias de Prochlorococcus e Synechococcus foram comparáveis às encontradas em outras áreas tropicais (0.17 to 30.37 X 104 células mL1, e 0.9 to 30.97 X 104 células mL-1, respectivamente). As abundâncias de Prochlorococcus atingiram o maior número em águas mais profundas, coincidindo frequentemente com a segunda intensidade de fluorescência in situ profunda (e clorofila a), em estações oceânicas, abaixo da nitratoclina, enquanto as abundâncias de Synechococcus foram maiores nas águas de subsuperficie e sua concentração máxima geralmente coincidiu com os máximos de subsuperficie de fluorescência in situ, com abundâncias ligeiramente mais altas nas estações costeiras. As análises estatísticas suportam significativamente esses resultados. A distribuição da divinil-clorofila a foi errática ao longo da coluna de água e coincidiu ocasionalmente com os máximos de fluorescência in situ profundos, enquanto que a distribuição da zeaxantina seguiu geralmente a da clorofila a e as abundâncias de Synechococcus e atingiu o pico. Estes resultados são semelhantes aos encontrados anteriormente na área de estudo e em zonas mais temperadas, e também à tendência geral na OMZ, mas confirmam que a clorofila profunda a maxima é atribuída a altas densidades de Prochlorococcus. Além disso, encontramos a abundância e distribuição de Prochlorococcus e Synechococcus fortemente conduzida pelos gradientes ambientais observados.Marine picophytoplankton has become an important issue to understand the global ecology of phototrophic forms, due to its wide distribution and contribution to biomass and productivity. We studied the abundance, distribution and signature pigments of the prokaryote picophytoplankters Prochlorococcus and Synechococcus during an oceanographic cruise (26 April to 7 May, 2011) in the central Mexican Pacific, a relatively poorlyknown oxygen minimum zone (OMZ), and the effect of three environmental gradients. Prochlorococcus and Synechococcus abundances were comparable with those found in other tropical areas (0.17 to 30.37 X 104 cells mL-1, and 0.9 to 30.97 X 104 cells mL-1, respectively). Prochlorococcus abundances reached highest numbers in deeper waters, often coinciding with the second deep in situ fluorescence (and chlorophyll α) maxima, at oceanic stations, below the nitratecline, whereas Synechococcus abundances were higher at subsurface waters and its concentration maxima usually coincided with the subsurface in situ fluorescence maxima, with slightly higher abundances in coastal stations. Statistical analyses support significantly these results. Distribution of divinyl-chlorophyll α was erratic along the water column and occasionally coincided with the deep in situ fluorescence maxima, whereas the distribution of zeaxanthin usually followed that of chlorophyll α and the abundances of Synechococcus, and peaked together. These results are similar to those previously found in the study area and in more temperate zones, and also to the general trend in OMZ, but confirm that the second deep chlorophyll α maxima are attributed to high Prochlorococcus densities. We additionally found the abundance and distribution of Prochlorococcus and Synechococcus strongly driven by the environmental gradients observed
The Clusters AgeS Experiment (CASE). IV. Analysis of the Eclipsing Binary V69 in the Globular Cluster 47 Tuc
We use photometric and spectroscopic observations of the eclipsing binary
V69-47 Tuc to derive the masses, radii, and luminosities of the component
stars. Based on measured systemic velocity, distance, and proper motion, the
system is a member of the globular cluster 47 Tuc. The system has an orbital
period of 29.5 d and the orbit is slightly eccentric with e=0.056. We obtain
Mp=0.8762 +- 0.0048 M(Sun), Rp=1.3148 +-0.0051 R(Sun), Lp=1.94 +- 0.21 L(Sun)
for the primary and Ms=0.8588 +- 0.0060 M(Sun), Rs=1.1616 +- 0.0062 R(Sun),
Ls=1.53 +- 0.17 L(Sun) for the secondary. These components of V69 are the first
Population II stars with masses and radii derived directly and with an accuracy
of better than 1%. We measure an apparent distance modulus of (m-M)v=13.35 +-
0.08 to V69. We compare the absolute parameters of V69 with five sets of
stellar evolution models and estimate the age of V69 using mass-luminosity-age,
mass-radius-age, and turnoff mass - age relations. The masses, radii, and
luminosities of the component stars are determined well enough that the
measurement of ages is dominated by systematic differences between the
evolutionary models, in particular, the adopted helium abundance. By comparing
the observations to Dartmouth model isochrones we estimate the age of V69 to be
11.25 +- 0.21(random) +- 0.85(systematic) Gyr assuming [Fe/H]=-0.70,
[alpha/Fe]=0.4, and Y=0.255. The determination of the distance to V69, and
hence to 47Tuc, can be further improved when infrared eclipse photometry is
obtained for the variable.Comment: 49 pages, 15 figures, submitted to A
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