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Search Results: 1 - 10 of 216143 matches for " Andrew P. Odell "
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Period variation in BW Vulpeculae redux
Andrew P. Odell
Physics , 2012, DOI: 10.1051/0004-6361/201219418
Abstract: For the past 25 years, BW Vulpeculae has been the topic of period analyses centered on a secular period change with a periodic variation superposed, presumed to be due to light time effects in a binary system. According to this paradigm, one would expect what seems like a period increase of about 0.5 s during or soon after the year 2001. I have continued photometric monitoring through the year 2012, adding 35 new timings of maximum and minimum light. This expected change in period did not occur, which rules out that interpretation of the period variation. As of 2012, the observed timings are about two hours early compared to those predicted by the quadratic ephemeris, but are very close to those predicted by the linear ephemeris. In fact, the period has remained constant for the last 32 years, indicating that the previous epochs of constant period are almost certainly the correct interpretation, though the cause of the period changes is still not clear. Continued photometric monitoring of BW Vul leads to the conclusion that the period changes are abrupt, followed by epochs of constant period lasting between 12 and at least 32 years.
A New Look at Open Cluster NGC 6520
Andrew P. Odell
Physics , 2013, DOI: 10.1088/0004-6256/147/1/7
Abstract: We use CCD and photoelectric photometry with Stromgren filters along with medium resolution spectra to investigate NGC 6520, an open cluster very nearly in the direction of the galactic center. We find an age of 60 Myr, a distance of 2 kpc, and an average reddening E(b-y) = 0.295, but which increases toward the south. The average heliocentric radial velocity of the B stars is -29 km/sec, while the velocity of the nearby Barnard 86 is about 0 (heliocentric, -11 km/sec compared to the LSR). This velocity difference amounts to about 1.8 kpc since the cluster formed, implying that it is extremely doubtful NGC 6520 is related to Barnard 86.
Karl Rakos - Obituary
Andrew P. Odell
Physics , 2012,
Abstract: Professor Dr. Karl Dragutin Rakos passed away on October 31, 2011 one day before his 86th birthday. With that the Vienna astronomical community lost a valued researcher, university teacher and co-founder of modern astrophysical research at the Institut f\"ur Astronomie of the University of Vienna.
The Butcher-Oemler Effect in Abell 2317
Karl D. Rakos,Andrew P. Odell,James M. Schombert
Physics , 1997, DOI: 10.1086/304858
Abstract: This paper presents deep narrow band photometry of the cluster A2317 (z=0.211) carried out using KPNO 4 m and Steward 2.3 m telescopes. Using rest frame Stromgren photometry, it is determined that A2317 has an unusually high fraction of blue galaxies (the Butcher-Oemler effect) for its redshift (f_B=0.35). We demonstrate that the ratio of blue to red galaxies has a strong dependence on absolute magnitude such that blue galaxies dominate the top of the luminosity function. Spectrophotometric classification shows that a majority of the red galaxies are E/S0's, with a small number of reddened starburst galaxies. Butcher-Oemler galaxies are shown to be galaxies with star formation rates typical of late-type spirals and irregular. Starburst systems were typically found to be on the lower end of the cluster luminosity function. In addition, blue galaxies are preferentially found in the outer edges of the cluster, whereas the red galaxies are concentrated in the cluster core.
Cluster Populations in A115 and A2283
Karl D. Rakos,James M. Schombert,Andrew P. Odell,Susanna Steindling
Physics , 2000, DOI: 10.1086/309344
Abstract: This paper presents four color narrow-band photometry of clusters A115 ($z=0.191$) and A2283 ($z=0.182$) in order to follow the star formation history of various galaxy types. Although located at similar redshifts, the two clusters display very different fractions of blue galaxies (i.e. the Butcher-Oemler effect, $f_B = 0.13$ for A115, $f_B = 0.30$ for A2283). A system of photometric classification is applied to the cluster members that divides the cluster population into four classes based on their recent levels of star formation. It is shown that the blue population of each cluster is primarily composed of normal starforming (SFR $< 1 M_{\sun}$ yrs$^{-1}$) galaxies at the high luminosity end, but with an increasing contribution from a dwarf starburst population below $M_{5500}= -20$. This dwarf starburst population appears to be the same population of low mass galaxies identified in recent HST imaging (Koo et al 1997), possible progenitors to present-day cluster dwarf ellipticals, irregulars and BCD's. Deviations in the color-magnitude relationship for the red galaxies in each cluster suggest that a population of blue S0's is evolving into present-day S0 colors at this epoch. The radial distribution of the blue population supports the prediction of galaxy harassment mechanisms for tidally induced star formation operating on an infalling set of gas-rich galaxies.
Ages and Metallicities of Cluster Galaxies in A779 using Modified Str?mgren Photometry
Yuvraj Harsha Sreedhar,Andrew P. Odell,Karl D. Rakos,Gerhard Hensler,Werner W. Zeilinger
Physics , 2012,
Abstract: In the quest for the formation and evolution of galaxy clusters, Rakos and co-workers introduced a spectrophotometric method using the modified Str\"omgren photometry. But with the considerable debate toward the project's abilities, we re-introduce the system after a thorough testing of repeatability of colors and reproducibility of the ages and metallicities for six common galaxies in the three A779 data sets. A fair agreement has been found between the modified Str\"omgren and Str\"omgren filter systems to produce similar colors (with the precision of 0.09 mag in (uz-vz), 0.02 mag in (bz-yz), and 0.03 mag in (vz-vz)), ages and metallicities (with the uncertainty of 0.36 Gyr and 0.04 dex from the PCA and 0.44 Gyr and 0.2 dex using the GALEV models). We infer that the technique is able to relieve the age-metallicity degeneracy by separating the age effects from the metallicity effects, but still unable to completely break. We further extend this paper to re-study the evolution of galaxies in the low mass, dynamically poor A779 cluster by correlating the luminosity (mass), density, radial distance with the estimated age, metallicity, and the star formation history. Our results distinctly show the bimodality of the young, low-mass, metal-poor population with the mean age of 6.7 Gyr (\pm 0.5 Gyr) and the old, high-mass, metal-rich galaxies with the mean age of 9 Gyr (\pm 0.5 Gyr). The method also observes the color evolution of the blue cluster galaxies to red, and the downsizing phenomenon. Our analysis shows that the modified Str\"omgren photometry is very well suited for studying low- and intermediate-z clusters, as it is capable of observing deeper with better spatial resolution at spectroscopic redshift limits, and the narrowband filters estimate the age and metallicity with lesser uncertainties compared to other methods that study stellar population scenarios.
New light curves and ephemeris for the close eclipsing binary V963 PER
Andrew P. Odell,Patrick Wils,Clarissa Dirks,Blythe Guvenen,Jo C. O'Malley,Antonio S. Villarreal,Rita M. Weinzettle
Physics , 2011,
Abstract: We have obtained CCD photometry in 2010-11 of V963 Per (=GSC3355 0394), which is a recently identified close binary star with unequal eclipse depths. The seven new eclipse timings yield an improved ephemeris, but we caution that secondary eclipse can be affected by variation of the light curve. This variation seems to be on a monthly timescale at the few percent level.
On Weakly Null FDD's in Banach Spaces
Edward Odell,Haskell P. Rosenthal,Thomas Schlumprecht
Mathematics , 1992,
Abstract: In this paper we show that every sequence (F_n) of finite dimensional subspaces of a real or complex Banach space with increasing dimensions can be ``refined'' to yield an F.D.D. (G_n), still having increasing dimensions, so that either every bounded sequence (x_n), with x_n in G_n for n in N, is weakly null, or every normalized sequence (x_n), with x_n in G_n for n in N, is equivalent to the unit vector basis of l_1. Crucial to the proof are two stabilization results concerning Lipschitz functions on finite dimensional normed spaces. These results also lead to other applications. We show, for example, that every infinite dimensional Banach space X contains an F.D.D. (F_n), with lim_{n to infty} dim (F_n)=infty, so that all normalized sequences (x_n), with x_n in F_n, n in N, have the same spreading model over X. This spreading model must necessarily be 1-unconditional over X.
On certain classes of Baire-1 functions with applications to Banach space theory
Richard Haydon,Edward Odell,Haskell P. Rosenthal
Mathematics , 1991,
Abstract: Certain subclasses of $B_1(K)$, the Baire-1 functions on a compact metric space $K$, are defined and characterized. Some applications to Banach spaces are given.
Low back pain status in elite and semi-elite Australian football codes: a cross-sectional survey of football (soccer), Australian-Rules, rugby league, rugby union and non-athletic controls
Wayne Hoskins, Henry Pollard, Chris Daff, Andrew Odell, Peter Garbutt, Andrew McHardy, Kate Hardy, George Dragasevic
BMC Musculoskeletal Disorders , 2011, DOI: 10.1186/1471-2474-12-158
Abstract: The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2474/12/158/prepub
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