70 research outputs found
Stellar explosion in the weak field approximation of the Brans-Dicke theory
We treat a very crude model of an exploding star, in the weak field
approximation of the Brans-Dicke theory, in a scenario that resembles some
characteristics data of a Type Ia Supernova. The most noticeable feature, in
the electromagnetic component, is the relationship between the absolute
magnitude at maximum brightness of the star and the decline rate in one
magnitude from that maximum. This characteristic has become one of the most
accurate method to measure luminosity distances to objects at cosmological
distances. An interesting result is that the active mass associated with the
scalar field is totally radiated to infinity, representing a mass loss in the
ratio of the "tensor" component to the scalar component of 1 to ( is the Brans-Dicke parameter), in agreement with a general result
of Hawking. Then, this model shows explicitly, in a dynamical case, the
mechanism of radiation of scalar field, which is necessary to understand the
Hawking result.Comment: 11 pages, no figures. Published in Class. Quantum Gravity V22 (2005
A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representative of an
active mass-transferring system that is changing before our eyes and which may
be an example of the formation of a Wolf-Rayet star through tidal stripping.
Utilizing new and previously published spectra, we present examples of how a
number of illustrative absorption and emission features vary during the binary
orbit. We identify spectral features associated with each component, calculate
a new, double-lined spectroscopic binary orbit, and find masses of 7.1 +/- 1.2
M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the hidden massive
companion. Through tomographic reconstruction of the component spectra from the
composite spectra, we confirm the O9.7 Ibpe spectral class of the bright
supergiant and discover a B0.5 I spectrum associated with the hidden massive
companion; however, we suggest that the latter is actually the spectrum of the
photosphere of the accretion torus immediately surrounding the massive
companion. We describe the complex nature of the mass loss flows from the
system in the context of recent hydrodynamical models for beta Lyr, leading us
to conclude RY Scuti has matter leaving the system in two ways: 1) a bipolar
outflow from winds generated by the hidden massive companion, and 2) mass from
the bright O9.7 Ibpe supergiant flowing from the region near the L2 point to
fill out a large, dense circumbinary disk. This circumbinary disk (radius ~ 1
AU) may feed the surrounding double-toroidal nebula (radius ~ 2000 AU).Comment: 41 pages with 7 tables and 11 figures, accepted to Ap
The Stony Brook / SMARTS Atlas of mostly Southern Novae
We introduce the Stony Brook / SMARTS Atlas of (mostly) Southern Novae. This
atlas contains both spectra and photometry obtained since 2003. The data
archived in this atlas will facilitate systematic studies of the nova
phenomenon and correlative studies with other comprehensive data sets. It will
also enable detailed investigations of individual objects. In making the data
public we hope to engender more interest on the part of the community in the
physics of novae. The atlas is on-line at
\url{http://www.astro.sunysb.edu/fwalter/SMARTS/NovaAtlas/} .Comment: 11 figures; 5 table
Nova light curves from the Solar Mass Ejection Imager (SMEI) - II. The extended catalogue
We present the results from observing nine Galactic novae in eruption with the Solar Mass Ejection Imager (SMEI) between 2004 and 2009. While many of these novae reached peak magnitudes that were either at or approaching the detection limits of SMEI, we were still able to produce light curves that in many cases contained more data at and around the initial rise, peak, and decline than those found in other variable star catalogs. For each nova, we obtained a peak time, maximum magnitude, and for several an estimate of the decline time (t2). Interestingly, although of lower quality than those found in Hounsell et al. (2010a), two of the light curves may indicate the presence of a pre-maximum halt. In addition the high cadence of the SMEI instrument has allowed the detection of low amplitude variations in at least one of the nova light curves
Rate of Period Change as a Diagnostic of Cepheid Properties
Rate of period change for a Cepheid is shown to be a parameter that
is capable of indicating the instability strip crossing mode for individual
objects, and, in conjunction with light amplitude, likely location within the
instability strip. Observed rates of period change in over 200 Milky Way
Cepheids are demonstrated to be in general agreement with predictions from
stellar evolutionary models, although the sample also displays features that
are inconsistent with some published models and indicative of the importance of
additional factors not fully incorporated in models to date.Comment: Published in PASP (March 2006); TeX source & figures now provide
Elemental Abundances in the Ejecta of Old Classical Novae from Late-Epoch Spitzer Spectra
We present Spitzer Space Telescope mid-infrared IRS spectra, supplemented by
ground-based optical observations, of the classical novae V1974 Cyg, V382 Vel,
and V1494 Aql more than 11, 8, and 4 years after outburst respectively. The
spectra are dominated by forbidden emission from neon and oxygen, though in
some cases, there are weak signatures of magnesium, sulfur, and argon. We
investigate the geometry and distribution of the late time ejecta by
examination of the emission line profiles. Using nebular analysis in the low
density regime, we estimate lower limits on the abundances in these novae. In
V1974 Cyg and V382 Vel, our observations confirm the abundance estimates
presented by other authors and support the claims that these eruptions occurred
on ONe white dwarfs. We report the first detection of neon emission in V1494
Aql and show that the system most likely contains a CO white dwarf.Comment: 22 pages, 12 figure
UX Monocerotis as a W Serpentis binary
Using our new photometric and spectroscopic observations as well as all
available published data, we present a new interpretation of the properties of
the peculiar emission-line binary UX Mon. We conclude that this binary is in a
rare phase of fast mass transfer between the binary components prior to the
mass ratio reversal. We firmly establish that the orbital period is secularly
decreasing at a rate of seconds per year. From several lines
of reasoning, we show that the mass ratio of the component losing mass to the
mass-gaining component must be larger than 1 and find our most probable
value to be . The BINSYN suite of programs and the steepest
descent method were used to perform the final modeling. We modeled the star as
a W Ser star with a thick disk around its primary. Although the remaining
uncertainties in some of the basic physical elements describing the system in
our model are not negligible, the model is in fair agreement with available
observations. Only the nature of the light variations outside the primary
eclipse remains unexplained
New Baade-Wesselink distances and radii for four metal-rich Galactic Cepheids
We provided accurate estimates of distances, radii and iron abundances for
four metal-rich Cepheids, namely V340 Ara, UZ Sct, AV Sgr and VY Sgr. The main
aim of this investigation is to constrain their pulsation properties and their
location across the Galactic inner disk. We adopted new accurate NIR (J,H,K)
light curves and new radial velocity measurements for the target Cepheids to
determinate their distances and radii using the Baade-Wesselink technique. In
particular, we adopted the most recent calibration of the IR surface brightness
relation and of the projection factor. Moreover, we also provided accurate
measurements of the iron abundance of the target Cepheids. Current distance
estimates agree within one sigma with similar distances based either on
empirical or on theoretical NIR Period-Luminosity relations. However, the
uncertainties of the Baade-Wesselink distances are on average a factor of 3-4
smaller when compared with errors affecting other distance determinations. Mean
Baade-Wesselink radii also agree at one sigma level with Cepheid radii based
either on empirical or on theoretical Period-Radius relations. Iron abundances
are, within one sigma, similar to the iron contents provided by Andrievsky and
collaborators, thus confirming the super metal-rich nature of the target
Cepheids. We also found that the luminosity amplitudes of classical Cepheids,
at odds with RR Lyrae stars, do not show a clear correlation with the
metal-content. This circumstantial evidence appears to be the consequence of
the Hertzsprung progression together with the dependence of the topology of the
instability strip on metallicity, evolutionary effects and binaries.Comment: 9 pages, 7 figures, A&A accepte
Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling
We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5 yr. All four stars are found to be multiperiodic.
The strongest secondary mode with frequency f2 has an amplitude of a few mmag, 20–45 times lower than the main radial mode with frequency f1. The two oscillations have a period ratio of P2/P1 = 0.612–0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is non-radial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P2/P1 ∼ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f2 at ∼1/2f2 and at ∼3/2f2. This is a signature of period doubling of the secondary oscillation, and is the first detection of period doubling in RRc stars. The amplitudes and phases of f2 and its subharmonics are variable on a time-scale of 10–200 d. The dominant radial mode also shows variations on the same time-scale, but with much smaller amplitude. In three Kepler RRc stars we detect additional periodicities, with amplitudes below 1 mmag, that must correspond to non-radial g-modes. Such modes never before have been observed in RR Lyrae variables
Investigation of tumor hypoxia using a two-enzyme system for in vitro generation of oxygen deficiency
<p>Abstract</p> <p>Background</p> <p>Oxygen deficiency in tumor tissue is associated with a malign phenotype, characterized by high invasiveness, increased metastatic potential and poor prognosis. Hypoxia chambers are the established standard model for <it>in vitro </it>studies on tumor hypoxia. An enzymatic hypoxia system (GOX/CAT) based on the use of glucose oxidase (GOX) and catalase (CAT) that allows induction of stable hypoxia for <it>in vitro </it>approaches more rapidly and with less operating expense has been introduced recently. Aim of this work is to compare the enzymatic system with the established technique of hypoxia chamber in respect of gene expression, glucose metabolism and radioresistance, prior to its application for <it>in vitro </it>investigation of oxygen deficiency.</p> <p>Methods</p> <p>Human head and neck squamous cell carcinoma HNO97 cells were incubated under normoxic and hypoxic conditions using both hypoxia chamber and the enzymatic model. Gene expression was investigated using Agilent microarray chips and real time PCR analysis. <sup>14</sup>C-fluoro-deoxy-glucose uptake experiments were performed in order to evaluate cellular metabolism. Cell proliferation after photon irradiation was investigated for evaluation of radioresistance under normoxia and hypoxia using both a hypoxia chamber and the enzymatic system.</p> <p>Results</p> <p>The microarray analysis revealed a similar trend in the expression of known HIF-1 target genes between the two hypoxia systems for HNO97 cells. Quantitative RT-PCR demonstrated different kinetic patterns in the expression of carbonic anhydrase IX and lysyl oxidase, which might be due to the faster induction of hypoxia by the enzymatic system. <sup>14</sup>C-fluoro-deoxy-glucose uptake assays showed a higher glucose metabolism under hypoxic conditions, especially for the enzymatic system. Proliferation experiments after photon irradiation revealed increased survival rates for the enzymatic model compared to hypoxia chamber and normoxia, indicating enhanced resistance to irradiation. While the GOX/CAT system allows independent investigation of hypoxia and oxidative stress, care must be taken to prevent acidification during longer incubation.</p> <p>Conclusion</p> <p>The results of our study indicate that the enzymatic model can find application for <it>in vitro </it>investigation of tumor hypoxia, despite limitations that need to be considered in the experimental design.</p
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