2,899 research outputs found
Classical Cepheids, what else?
We present new and independent estimates of the distances to the Magellanic
Clouds (MCs) using near-infrared (NIR) and optical--NIR period--Wesenheit (PW)
relations. The slopes of the PW relations are, within the dispersion, linear
over the entire period range and independent of metal content. The absolute
zero points were fixed using Galactic Cepheids with distances based on the
infrared surface-brightness method. The true distance modulus we found for the
Large Magellanic Cloud--- mag---and the
Small Magellanic Cloud--- mag---agree quite
well with similar distance determinations based on robust distance indicators.
We also briefly discuss the evolutionary and pulsation properties of MC
Cepheids
Galactic Cepheids with Spitzer: I. Leavitt Law and Colors
Classical Cepheid variable stars have been important indicators of
extragalactic distance and Galactic evolution for over a century. The Spitzer
Space Telescope has opened the possibility of extending the study of Cepheids
into the mid- and far-infrared, where interstellar extinction is reduced. We
have obtained photometry from images of a sample of Galactic Cepheids with the
IRAC and MIPS instruments on Spitzer. Here we present the first mid-infrared
period-luminosity relations for Classical Cepheids in the Galaxy, and the first
ever Cepheid period-luminosity relations at 24 and 70 um. We compare these
relations with theoretical predictions, and with period-luminosity relations
obtained in recent studies of the Large Magellanic Cloud. We find a significant
period-color relation for the [3.6]-[8.0] IRAC color. Other mid-infrared colors
for both Cepheids and non-variable supergiants are strongly affected by
variable molecular spectral features, in particular deep CO absorption bands.
We do not find strong evidence for mid-infrared excess caused by warm (~500 K)
circumstellar dust. We discuss the possibility that recent detections with
near-infrared interferometers of circumstellar shells around delta Cep, l Car,
Polaris, Y Oph and RS Pup may be a signature of shocked gas emission in a
dust-poor wind associated to pulsation-driven mass loss.Comment: Accepted by The Astrophysical Journal on Nov 11, 200
New Evidence for Mass Loss from delta Cephei from HI 21-cm Line Observations
Recently published Spitzer observations of the classical Cepheid archetype
delta Cephei revealed an extended dusty nebula surrounding this star and its
hot companion. The infrared emission resembles a bow shock aligned with the
direction of space motion of the star, indicating that delta Cep is undergoing
mass-loss through a stellar wind. Here we report HI 21-cm line observations
with the VLA to search for neutral atomic hydrogen associated with this wind.
Our VLA data reveal a spatially extended HI nebula (~13' or 1 pc across)
surrounding the position of delta Cep. The nebula has a head-tail morphology,
consistent with circumstellar ejecta shaped by the interaction between a
stellar wind and the ISM. We directly measure a mass of circumstellar hydrogen
M_HI\approx0.07M_odot, although the total HI mass may be larger. The HI data
imply a stellar wind with an outflow velocity V_o=35.6\pm1.2 km/s and a
mass-loss rate of M_dot=(1.0\pm0.8)x10**-6 M_dot/yr. We have computed
theoretical evolutionary tracks that include mass loss across the instability
strip and show that a mass-loss rate of this magnitude, sustained over the
preceding Cepheid lifetime of delta Cep, could be sufficient to resolve a
significant fraction of the discrepancy between the pulsation and evolutionary
masses for this star. (abridged)Comment: ApJ, in press (January 1, 2012). Version with full resolution figures
available at
http://www.haystack.mit.edu/hay/staff/lmatthew/matthews_deltaCep.pd
Superconductivity in a Molecular Metal Cluster Compound
Compelling evidence for band-type conductivity and even bulk
superconductivity below K has been found in
Ga-NMR experiments in crystalline ordered, giant Ga
cluster-compounds. This material appears to represent the first realization of
a theoretical model proposed by Friedel in 1992 for superconductivity in
ordered arrays of weakly coupled, identical metal nanoparticles.Comment: 5 pages, 4 figure
Theoretical fits of the \delta Cephei light, radius and radial velocity curves
We present a theoretical investigation of the light, radius and radial
velocity variations of the prototype Cephei. We find that the best fit
model accounts for luminosity and velocity amplitudes with an accuracy better
than , and for the radius amplitude with an accuracy of .
The chemical composition of this model suggests a decrease in both helium (0.26
vs 0.28) and metal (0.01 vs 0.02) content in the solar neighborhood. Moreover,
distance determinations based on the fit of light curves agree at the
level with the trigonometric parallax measured by the Hubble Space
Telescope (HST). On the other hand, distance determinations based on angular
diameter variations, that are independent of interstellar extinction and of the
-factor value, indicate an increase of the order of 5% in the HST parallax.Comment: accepted for publication on ApJ Letter
SYNTHESIS OF 1-BENZOYL-3-PHENYL-1H-PYRAZOLE-4-CARBALDEHYDE AND EVALUATION OF THEIR ANTIOXIDANT AND ANTI-INFLAMMATORY ACTIVITY
Objective: The main objective of this study is to synthesize a series of 1-Benzoyl-3-phenyl-1H-pyrazole-4-carbaldehyde (4a-e) derivatives and evaluation of the synthesized compounds for their antioxidant and anti-inflammatory activity.
Methods: A series of substituted acetophenones are condensed with hydrazides to the corresponding hydrazones which are subsequently cyclized by using vilsmier-Haack reaction to give final series of 1-Benzoyl-3-phenyl-1H-pyrazole-4-carbaldehyde (4a-e) derivatives respectively. All newly synthesized compounds were characterized on the basis of infrared, proton nuclear magnetic resonance and mass spectral data and screened for their antioxidant and anti-inflammatory activities.
Results: In view of the significant biological activity profile of Pyrazole, the synthesized compounds (4a-e) were evaluated for their antioxidant potency by DPPH, Nitric oxide, Hydroxyl radical scavenging, and Hydrogen Peroxide method. Compounds 4c and 4e showed potent antioxidant activity then standard. Synthesized compounds were also screened for anti-inflammatory activity. Among all the molecules 4c, 4e, and 4d showed significant activity as compared to standard drug diclofenac sodium.
Conclusion: in this study, we synthesized 1-Benzoyl-3-phenyl-1H-pyrazole-4-carbaldehyde (4a-e) derivatives. Further, these derivatives showed significant antioxidant and anti-inflammatory activity. Among them, two molecules 4c and 4e have shown near action to the standard
Massive stellar systems: observational challenges and perspectives in the E-ELT era
We introduce the empirical framework concerning optical and near-infrared (NIR) photometry of crowded stellar fields. In particular, we address the impact that linear detectors and analytical PSF played in improving the accuracy and the precision of multi-band color-magnitude diagrams (CMDs). We focus our attention on recent findings based on deep NIR images collected with Adaptive Optics (AO) systems at the 8-10m class telescopes and discuss pros and cons of the different approaches. We also discuss the estimate of the absolute age of globular clusters using a well defined knee along the lower main sequence. We mention the role which the current AO-assisted instruments will have in addressing longstanding astrophysical problems of the Galactic center. Finally, we outline the role of first generation of E-ELT instruments upon photometry and spectroscopy of crowded stellar fields
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