7,168 research outputs found
Using Optical and Near-IR Photometry to Test MACHO Lens Candidates
We obtained new VLT/ISAAC H-band observations for five MACHO LMC source stars
and adjacent LMC field regions. After combining our near-IR photometry with
HST/PC BVRI optical photometry, we compared the MACHO objects to the adjacent
field stars in a variety of color-magnitude and color-color diagrams. These
diagnostic diagrams were chosen to be sensitive to our hypothesis that at least
some of the MACHO lenses were foreground Galactic disk or thick disk M dwarfs.
For the five lensed objects we studied, our hypothesis could be ruled out for
main sequence lens masses >= 0.1 Mo for distances out to 4 kpc. On the other
hand, the fact that LMC-MACHO-5, an object not in our study, has been recently
found to have just such a foreground lens, highlights that the remainder of the
LMC MACHO objects should be searched for the signature of their lenses using
our photometric technique, or via near-IR spectroscopy. We also constructed
diagnostic color-color diagrams sensitive to determining reddening for the
individual MACHO source stars and found that these five objects did not show
evidence for significant additional reddening. At least these five MACHO
objects are thus also inconsistent with the LMC self-lensing hypothesis.Comment: 28 pages, 8 figures, ApJ, accepted for Oct 1 issu
The Luminosity Function of Magnitude and Proper-Motion Selected Samples. The case of White-Dwarfs
The luminosity function of white dwarfs is a powerful tool for studies of the
evolution and formation of the Milky Way. The (theoretical) white dwarf cooling
sequence provides a useful indicator of the evolutionary time scales involved
in the chronometry and star formation history of the galactic disk, therefore,
intrinsically faint (& old) white dwarfs in the immediate solar neighborhood
can be used to determine an upper limit for the age of the galactic disk.
In this paper we examine the faint-end () behavior of the disk
white dwarf luminosity function using the method, but fully
including the effects of realistic observational errors in the derived
luminosity function. We employ a Monte Carlo approach to produce many different
realizations of the luminosity function from a given data set with
pre-specified and reasonable errors in apparent magnitude, proper-motions,
parallaxes and bolometric corrections. These realizations allow us to compute
both a mean and an expected range in the luminosity function that is compatible
with the observational errors.
We find that current state-of-the art observational errors, mostly in the
bolometric corrections and trigonometric parallaxes, play a major role in
obliterating (real or artificial) small scale fluctuations in the luminosity
function. We also find that a better estimator of the true luminosity function
seems to be the median over simulations, rather than the mean. When using the
latter, an age for the disk of 10 Gyr or older can not be ruled out from the
sample of Leggett, Ruiz, and Bergeron (1998).Comment: Manuscript AAS Latex macro v4.0, 33 pages, 13 postscript figures
(Color in figs. 9 and 12). Accepted for publication in The Astrophysical
Journal. Replaced by two-column version & indication of acceptance by the Ap
Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax Measurements
A photometric and spectroscopic analysis of 152 cool white dwarf stars is
presented. The discovery of 7 new DA white dwarfs, 2 new DQ white dwarfs, 1 new
magnetic white dwarf, and 3 weak magnetic white dwarf candidates, is reported,
as well as 19 known or suspected double degenerates. The photometric energy
distributions, the Halpha line profiles, and the trigonometric parallax
measurements are combined and compared to model atmosphere calculations to
determine the effective temperature and the radius of each object, and also to
constrain the atmospheric composition. New evolutionary sequences with C/O
cores with thin and thick hydrogen layers are used to derive masses and ages.
We confirm the existence of a range in Teff between 5000 and 6000K where almost
all white dwarfs have H-rich atmospheres. There is little evidence for mixed
H/He dwarfs, with the exception of 2 He-rich DA stars, and 5 C2H white dwarfs
which possibly have mixed H/He/C atmospheres. The DQ sequence terminates near
6500K, below which they are believed to turn into C2H stars. True DC stars
slightly above this temperature are found to exhibit H-like energy
distributions despite the lack of Halpha absorption. Attempts to interpret the
chemical evolution show the problem to be complex. Convective mixing is
necessary to account for the non-DA to DA ratio as a function of temperature.
The presence of helium in cool DA stars, the existence of the non-DA gap, and
the peculiar DC stars are also explained in terms of convective mixing,
although our understanding of how this mechanism works needs to be revised. The
oldest object in our sample is about 7.9 Gyr or 9.7 Gyr old depending on
whether thin or thick hydrogen layer models are used. The mean mass of our
sample is 0.65 +/- 0.20 Msun.Comment: Accepted by ApJ Suppl (~April 2001); 79 pages incl. 25 figure
The Chemical Composition of the Small Magellanic Cloud H II Region NGC 346 and the Primordial Helium Abundance
Spectrophotometry in the 3400-7400 range is presented for 13 areas of the
brightest H II region in the SMC: NGC 346. The observations were obtained at
CTIO with the 4-m telescope. Based on these observations its chemical
composition is derived. The helium and oxygen abundances by mass are given by:
Y(SMC)=0.2405+-0.0018 and O(SMC)=0.00171+-0.00025. From models and observations
of irregular and blue compact galaxies it is found that dY/dO=3.5+-0.9 and
consequently that the primordial helium abundance by mass is given by:
Yp=0.2345+-0.0026 (1-sigma). This result is compared with values derived from
Big Bang nucleosynthesis, and with other determinations of Yp.Comment: 32 pages + 5 figures Referee Revised Versio
How stable are visions for protected area management? Stakeholder perspectives before and during a pandemic
Envisioning processes enable protected area managers to chart a course for future management to reach desired goals, but unexpected changes that could affect future visions are not usually considered. The global COVID-19 pandemic provided an opportunity to explore changes in stakeholder visions, the values that underpin the visions, and their perceptions of landscape changes and the underlying drivers (e.g. climate change, mass tourism and demographic trends). Through a mixed-methods approach in this post-evaluation study, we gathered comparative data on these issues from stakeholders in the Sierra de Guadarrama National Park, Spain, between July 2019 (pre-pandemic) and October 2020 (mid-pandemic). Our qualitative analysis demonstrates that pre-pandemic, differences in visions for protected area management were largely spurred by different perceptions of drivers of change, rather than differences in values or perceived landscape changes, which were similar across different vision themes. One year later, in the midst of the COVID-19 pandemic, the majority of stakeholders reported that their values, visions and perceptions of drivers did not change despite this large-scale disturbance. Of the 20%-30% of stakeholders that did report changes, visions generally shifted towards greater prioritization of biodiversity and nature conservation as a result of heightened perceptions of the impacts of drivers of change associated with an increase in the numbers of park visitors. These drivers included mass tourism, mountain recreation, lack of environmental awareness, and change in values and traditions. Our findings reinforce the importance of adaptive and inclusive management of protected areas, including enhancing transparency and communications regarding factors driving change in the landscape, and integration of local and traditional knowledge and stakeholder perceptions of changes and drivers. Furthermore, management plans integrating stakeholder values have the potential to stay relevant even in the face of wildcard events such as a pandemic. To enhance the relevancy of visions and scenarios in conservation and land-use planning, scenario planning methodologies should more strongly consider different potential disturbances and how drivers of change in the near and far future can be affected by wildcard events such as a pandemic. A free Plain Language Summary can be found within the Supporting Information of this article.Peer reviewe
The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine
We have investigated the S0 â S1 UV vibronic spectrum and time-resolved S1 state dynamics of
jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization,
UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond timeresolved
pump/delayed ionization measurements. The experimental study is complemented with
spin-component-scaled second-order coupled-cluster and multistate complete active space second
order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cmâ1
about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional
transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation
and out-of-plane distortions upon 1ÏÏâ excitation predicted by the calculations. The methyl torsion
and ÎœâČ1 (butterfly) vibrations are strongly coupled, in the S1 state. The S0 â S1 vibronic spectrum
breaks off at a vibrational excess energy Eexc ⌠500 cmâ1, indicating that a barrier in front of the
ethylene-type S1 S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cmâ1.
The S1 S0 internal conversion rate constant increases from kIC = 2 · 109 sâ1 near the S1(v = 0)
level to 1 · 1011 sâ1 at Eexc = 516 cmâ1. The 1ÏÏâ state of 1MCyt also relaxes into the lower-lying
triplet T1 (3ÏÏâ) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value
is 2.4 cmâ1. The ISC rate constant is 10â100 times lower than kIC; it increases from kISC = 2 · 108 sâ1
near S1(v = 0) to kISC = 2 · 109 sâ1 at Eexc = 516 cmâ1. The T1 state energy is determined from the
onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cmâ1. The T2 (3nÏâ)
state lies >1500 cmâ1 above S1(v = 0), so S1 T2 ISC cannot occur, despite the large SOC
parameter of 10.6 cmâ1. An upper limit to the adiabatic ionization energy of 1MCyt is determined
as 8.41 ± 0.02 eV. Compared to cytosine, methyl substitution at N1 lowers the adiabatic ionization
energy by â„0.32 eV and leads to a much higher density of vibronic bands in the S0 â S1 spectrum.
The effect of methylation on the radiationless decay to S0 and ISC to T1 is small, as shown by
the similar break-off of the spectrum and the similar computed mechanismsThis research has been supported by the Schweiz. Nationalfonds (Grant Nos. 121993 and 132540), the AgĂšncia de GestiĂł dâAjuts Universitaris i de Recerca (AGAUR) from Catalonia (Spain) (Grant No. 2014SGR1202), the Ministerio de EconomĂa y Competividad (MINECO) from Spain (Grant No. CTQ2015-69363-P), and the National Natural Science Foundation of China (Grant No. 21303007
Antiproliferative activity of flavonoids from croton Sphaerogynus baill. (euphorbiaceae)
Croton sphaerogynus is a shrub from the Atlantic Rain Forest in southeastern Brazil. A lyophilized crude EtOH extract from leaves of C. sphaerogynus, obtained by maceration at room temperature (seven days), was suspended in methanol and partitioned with hexane. The purified MeOH phase was fractionated over Sephadex LH-20 yielding five fractions (F1-F5) containing flavonoids, as characterized by HPLC-DAD and HPLC-MS analyses. The antiproliferative activity of the crude EtOH extract, MeOH and hexane phases, and fractions F1-F5 was evaluated on in vitro cell lines NCI-H460 (nonsmall cell lung), MCF-7 (breast cancer), and U251 (glioma). The MeOH phase showed activity (mean log GI(50) 0.54) higher than the hexane phase and EtOH extract (mean log GI(50) 1.13 and 1.19, resp.). F1 exhibited activity against NCI-H460 (nonsmall cell lung) (GI(50) 1.2 mu g/mL), which could be accounted for the presence of flavonoids and/or diterpenes. F4 showed moderate activity (mean log GI(50) 1.05), while F5 showed weak activity (mean log GI(50) 1.36). It is suggested that the antiproliferative activity of the crude EtOH extract and MeOH phase is accounted for a synergistic combination of flavonoids and diterpenes2015COORDENAĂĂO DE APERFEIĂOAMENTO DE PESSOAL DE NĂVEL SUPERIOR - CAPESFUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO - FAPESPsem informação2012/10079-
Antiproliferative Activity Of Flavonoids From Croton Sphaerogynus Baill. (euphorbiaceae).
Croton sphaerogynus is a shrub from the Atlantic Rain Forest in southeastern Brazil. A lyophilized crude EtOH extract from leaves of C. sphaerogynus, obtained by maceration at room temperature (seven days), was suspended in methanol and partitioned with hexane. The purified MeOH phase was fractionated over Sephadex LH-20 yielding five fractions (F1-F5) containing flavonoids, as characterized by HPLC-DAD and HPLC-MS analyses. The antiproliferative activity of the crude EtOH extract, MeOH and hexane phases, and fractions F1-F5 was evaluated on in vitro cell lines NCI-H460 (nonsmall cell lung), MCF-7 (breast cancer), and U251 (glioma). The MeOH phase showed activity (mean logâGI50 0.54) higher than the hexane phase and EtOH extract (mean logâGI50 1.13 and 1.19, resp.). F1 exhibited activity against NCI-H460 (nonsmall cell lung) (GI50 1.2âÎŒg/mL), which could be accounted for the presence of flavonoids and/or diterpenes. F4 showed moderate activity (mean logâGI50 1.05), while F5 showed weak activity (mean logâGI50 1.36). It is suggested that the antiproliferative activity of the crude EtOH extract and MeOH phase is accounted for a synergistic combination of flavonoids and diterpenes.201521280
Constituents and antiproliferative activity of extracts from leaves of croton macrobothrys
Croton macrobothrys Baill, Euphorbiaceae, is a tree from the Atlantic Forest in Southern Brazil, used in traditional medicine and popularly known as "dragon's blood" and "pau-sangue". Leaf n-hexane, dichloromethane and methanol extracts were analyzed by GC/MS and evaluated for their in vitro antiproliferative activity on cell lines 786-0 (kidney), HT-29 (colon), K562 (leukemia), NCI-ADR/RES (drug resistant ovary), NCI-H460 (lung), MCF-7 (mammary), PC-3 (prostate), OVCAR-3 (ovary), U251 (glioma) and UACC-62 (melanoma). The dicloromethane extract exhibited activity against all cell lines at the concentration 25 ”g/mL, in particular on cell lines NCI-H460 (GI50 0.33 ÎŒg/mL) and K5662 (GI50 0.91 ÎŒg/mL). Relevant constituents in dichloromethane extract are the alkaloids corydine and salutaridine, as well as the diterpenes geranylgeraniol and crotonin-derived clerodanes216972977CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO - CNPQCOORDENAĂĂO DE APERFEIĂOAMENTO DE PESSOAL DE NĂVEL SUPERIOR - CAPESFUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO - FAPESPSem informaçãoSem informação08/10595-3; 08/09942-
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