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Distance Estimates (distance + estimate)

Distribution by Scientific Domains

Physics and Astronomy	70%

Selected Abstracts

Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
A. Rebassa-Mansergas
ABSTRACT We present a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available. We detect significant radial velocity variations in 18 WDMS, identifying them as post-common-envelope binaries (PCEBs) or strong PCEB candidates. Strict upper limits to the orbital periods are calculated, ranging from 0.43 to 7880 d. Given the sparse temporal sampling and relatively low spectral resolution of the SDSS spectra, our results imply a PCEB fraction of ,15 per cent among the WDMS in the SDSS data base. Using a spectral decomposition/fitting technique we determined the white dwarf effective temperatures and surface gravities, masses and secondary star spectral types for all WDMS in our sample. Two independent distance estimates are obtained from the flux-scaling factors between the WDMS spectra, and the white dwarf models and main-sequence star templates, respectively. Approximately one-third of the systems in our sample show a significant discrepancy between the two distance estimates. In the majority of discrepant cases, the distance estimate based on the secondary star is too large. A possible explanation for this behaviour is that the secondary star spectral types that we determined from the SDSS spectra are systematically too early by one to two spectral classes. This behaviour could be explained by stellar activity, if covering a significant fraction of the star by cool dark spots will raise the temperature of the interspot regions. Finally, we discuss the selection effects of the WDMS sample provided by the SDSS project. [source]

G315.1+2.7: a new Galactic supernova remnant from the AAO/UKST H, survey

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
M. Stupar
ABSTRACT New narrow-band H, imaging and subsequent optical spectra confirm G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a bona fide Galactic SNR. Present observations are based on independent discovery of filamentary optical emission nebulosity on images of the Anglo-Australian Observatory/United Kingdom Schmidt Telescope H, survey of the southern Galactic plane which were found to coincide with existing multifrequency radio detections. Separate medium- and high-dispersion spectra were taken across two locations of this 11-arcmin north,south (NS) aligned optical filament. The resulting spectral signatures were found to strongly confirm the SNR identification based on standard emission-line ratio discriminators which characterize emission from shock-heated gas. The average observed ratios of S ii/H,= 1.13, N ii/H,= 1.43 and S ii 6717/6731 = 1.46, together with the simultaneous detection of [O ii] 3727, [O iii] 5007 and [O i] 6300 Å, all point to a SNR origin of the observed optical emission. There is also an excellent positional coincidence between the new H, filament and the north-east radio arc of G315.1+2.7 seen at several frequencies. Careful scrutiny of the low-resolution but high-sensitivity Southern H, Sky Survey Atlas also revealed a low-level but distinct optical emission arc. This arc precisely correlates with the large, 2.5°, NS angular extent of the proposed new SNR also seen as a fractured structure in the extant radio data. G315.1+2.7 was detected previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified associated radio emission at 843 MHz from the now publicly available Sydney University Molonglo Sky Survey. On the basis of optical imaging and spectra and radio observations at five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large projected angular extent of the new remnant, together with the distance estimate of ,1.7 kpc and diameter of ,80 pc, make G315.1+2.7 one of the largest remnants known. [source]

On the distance to the Ophiuchus star-forming region

ASTRONOMISCHE NACHRICHTEN, Issue 1 2008
E.E. Mamajek
Abstract The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ,300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ,40% (,120,165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star-forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ,11 pc of the centroid of the ,5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ,1 km s,1 in each vector component. Both Oph and Upper Sco have negligible motion (<1 km s,1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Analysis of two Chinese yak (Bos grunniens) populations using bovine microsatellite primers

JOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 4 2003
Wang Minqiang
Summary Two Chinese domestic yak populations representing the Plateau type and the Huanhu Alpine type were analysed with 12 bovine microsatellite primers. All primer pairs functioned in the yak genome and polymorphism was found at all loci. The allele size ranges and frequencies of the two yak populations were similar and there was considerable overlap with the allele size ranges observed in cattle. Data for European cattle breeds was obtained from the Cattle Diversity Database (CaDBase) to interpret the heterozygosity and genetic distance estimates in yak populations. Heterozygosity estimated for the two yak populations was comparable with that of European cattle while Nei's Genetic Distance DA between the two yak populations was less than distances between the most closely related German cattle breeds. Bovine microsatellite primers proved to be a valuable tool for characterization of yak populations. Zusammenfassung Untersuchungen von zwei chinesischen Yak (Bos grunniens) Herden mittels Primersequenzen von Rindermikrosatelliten Primersequenzen von Rindermikrosatelliten wurden verwendet, um zwei chinesische Yak-Herden zu analysieren, eine vom Plateau-Typ und eine andere vom Huanhu-Bergtyp. Alle 12 Primerpaare führten zu polymorphen Amplifikationsprodukten mit den DNA-Proben der Yaks. Der Allelgrößenbereich und die Allelfrequenzen aller 12 Marker waren in den beiden Yak-Herden sehr ähnlich. Zum Vergleich wurden Typisierungsergebnisse der 12 Mikrosatellitengenorte von 15 europäischen Rinderassen aus der Rinderdiversitätsdatenbank CaDBase entnommen. Ein großer Teil der Yak-Allele hatte die gleiche Größe wie beim Rind und auch der geschätzte Heterozygotiegrad der beiden Yak-Populationen war vergleichbar mit dem durchschnittlichen Heterozygotiegrad der 15 Rinderrassen. Die genetische Distanz (Nei's DA) zwischen beiden Yak-Herden wurde jedoch geringer geschätzt als zwischen zwei Paaren eng verwandter Rinderrassen. Die Ergebnisse zeigen, dass Sequenzinformationen von Rindermikrosatellitenprimern für die Charakterisierung von Yak-Populationen auf der molekularen Ebene nützlich sein können. [source]

Phylogenetic position of Salmo(Platysalmo)platycephalus Behnke 1968 from south-central Turkey, evidenced by genetic data

JOURNAL OF FISH BIOLOGY, Issue 4 2004
S. Su
To determine whether the current classification of the flathead trout Salmo (Platysalmo) platycephalus, endemic to the upper reaches of the Zamanti River system, Turkey, based solely on morphology, is in congruence with molecular phylogeny, the nucleotide sequence variation in mitochondrial (control region and cytochrome b gene) and nuclear (internal transcribed spacer of rRNA genes) DNA for the flathead trout and various representatives of the genus Salmo was studied. On the basis of pair-wise genetic distance estimates, the highest differences were found to exist between the flathead trout and S. salar, S. ohridana and S. obtusirostris, whereas the differences between the flathead trout and S. trutta were minimal. All the analyses performed firmly positioned the flathead trout within the Adriatic phylogeographic lineage of S. trutta; however, the exact position of the flathead trout within the Adriatic cluster was irresolvable. Accordingly, classifying the flathead trout as a subgenus of Salmo is unjustifiable and its reclassification in a lower taxonomic category is suggested by the present study. [source]

Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopy

Further analysis of the population history of ancient Egyptians

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009
Michael A. Schillaci
Abstract The origins of state formation in ancient Egypt have been the focus of recent research utilizing biological data to test hypotheses regarding in situ development of local groups, or large-scale in-migration, possibly by an invading army. The primary goal of the present research is to further test these hypotheses. Our secondary goal is to compare different distance measures and assess how they might affect interpretation of population history. We analyze craniodental nonmetric data using several different measures of biological distance, as well as a method for estimating group diversity using multidimensional scaling of distance estimates. Patterns of biological variation and population relationships were interpreted in temporal and geographic contexts. The results of our analyses suggest that the formation of the ancient Egyptian state likely included a substantial in situ process, with some level of contribution by outside migrants probable. The higher level of population structure in Lower Egypt, relative to Upper Egypt, suggests that such influence and migration by outsiders may not have been widespread geographically. These findings support, but serve to refine further those obtained by the second author in a previous study. Moreover, our comparison of distance measures indicates that the choice of measure can influence identification and interpretation of the microevolutionary processes shaping population history, despite being strongly correlated with one another. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source]