2,840 research outputs found

    Aerothermochemical analysis of non-oscillatory and oscillatory characteristics of liquid bipropellant rocket motors - Wave model, droplet heating, and evaporation program computation Third quarterly report no. 65-1

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    Aerothermochemical analysis of nonoscillatory and oscillatory characteristics of liquid bipropellant rocket motors - wave model, droplet heating, and evaporation computer progra

    Steady state aerothermochemistry for liquid bipropellant rocket motors

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    Model and theoretical equations describing liquid propellant droplet ballistics and combustion gas behavior in bipropellant rocket motors - aerothermochemistr

    An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. III. Completing the sample

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    We present optical nuclear spectra for nine 3CR radio sources obtained with the Telescopio Nazionale Galileo, that complete our spectroscopic observations of the sample up to redshifts << 0.3. We measure emission line luminosities and ratios, and derive a spectroscopic classification for these sources.Comment: Accepted for publication in A&A. We provide as additional material two tables presenting the main data for the whole sample, combining the results presented here with those of Paper I and Paper I

    The Axis Ratio Distribution of Local and Distant Galaxies

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    Surface photometry from 16 HST/WFPC2 fields in the I(F814W) filter is used to derive the distribution of apparent axis ratios for galaxies in progressively fainter magnitude intervals for I<25. We assess the systematic and accidental errors in ellipticity measurements as a function of image resolution and signal-to-noise ratio, and statistically correct for the effect of cosmological surface brightness dimming on our isophotal measurements. The axis ratio distribution for the local galaxy population was computed using logR measurements for 1569 RC3 galaxies with Bt<13 mag. Nonparametric tests are used to show that our distant samples, in the redshift range 0.1<z<1.5, are not statistically different from the local sample. We present image montages of galaxies selected randomly from different axis ratio and apparent magnitude ranges and discuss the evolutionary consequences of the lack of a strong difference between the ellipticity distributions in near and far data sets.Comment: LaTex, 35 pages, 8 figures, accepted for Dec97 A

    Color--Luminosity Relations for the Resolved Hot Stellar Populations in the Centers of M 31 and M 32

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    We present Faint Object Camera (FOC) ultraviolet images of the central 14x14'' of Messier 31 and Messier 32. The hot stellar population detected in the composite UV spectra of these nearby galaxies is partially resolved into individual stars, and their individual colors and apparent magnitudes are measured. We detect 433 stars in M 31 and 138 stars in M 32, down to detection limits of m_F275W = 25.5 mag and m_F175W = 24.5 mag. We investigate the luminosity functions of the sources, their spatial distribution, their color-magnitude diagrams, and their total integrated far-UV flux. Although M 32 has a weaker UV upturn than M 31, the luminosity functions and color-magnitude diagrams of M 31 and M 32 are surprisingly similar, and are inconsistent with a majority contribution from any of the following: PAGB stars more massive than 0.56 Msun, main sequence stars, or blue stragglers. Both the the luminosity functions and color-magnitude diagrams are consistent with a dominant population of stars that have evolved from the extreme horizontal branch (EHB) along tracks with masses between 0.47 and 0.53 Msun. These stars are well below the detection limits of our images while on the zero-age EHB, but become detectable while in the more luminous (but shorter) AGB-Manque' and post-early asymptotic giant branch (PEAGB) phases. The FOC observations require that only a only a very small fraction of the main sequence population (2% in M 31 and 0.5% in M 32) in these two galaxies evolve though the EHB and post-EHB phases, with the remainder evolving through bright PAGB evolution that is so rapid that few if any stars are expected in the small field of view covered by the FOC.Comment: 35 pages, Latex. 19 figures. To appear in ApJ. Uses emulateapj.sty and apjfonts.sty (included). Color plates distributed seperatedly: fig1.jpg and fig2.jp

    M Dwarfs from Hubble Space Telescope Star Counts. IV

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    We study a sample of about 1400 disk M dwarfs that are found in 148 fields observed with the Wide Field Camera 2 (WFC2) on the Hubble Space Telescope and 162 fields observed with pre-repair Planetary Camera 1 (PC1), of which 95 of the WFC2 fields are newly analyzed. The method of maximum likelihood is applied to derive the luminosity function and the Galactic disk parameters. At first, we use a local color-magnitude relation and a locally determined mass-luminosity relation in our analysis. The results are consistent with those of previous work but with considerably reduced statistical errors. These small statistical errors motivate us to investigate the systematic uncertainties. Considering the metallicity gradient above the Galactic plane, we introduce a modified color-magnitude relation that is a function of Galactic height. The resultant M dwarf luminosity function has a shape similar to that derived using the local color-magnitude relation but with a higher peak value. The peak occurs at MV∌12M_V \sim 12 and the luminosity function drops sharply toward MV∌14M_V \sim 14. We then apply a height-dependent mass-luminosity function interpolated from theoretical models with different metallicities to calculate the mass function. Unlike the mass function obtained using local relations, which has a power-law index α=0.47\alpha = 0.47, the one derived from the height-dependent relations tends to be flat (α=−0.10\alpha = -0.10). The resultant local surface density of disk M dwarfs (12.2 +/- 1.6 M_sun pc^{-2}) is somewhat smaller than the one obtained using local relations (14.3 +/- 1.3 M_sun pc^{-2}). Our measurement favors a short disk scale length, H = 2.75 +/- 0.16 (statistical) +/- 0.25 (systematic) kpc.Comment: 20 pages, 10 ps figures, accepted for publication in Ap

    Hot Populations in M87 Globular Clusters

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    We have obtained HST/STIS far- and near-UV photometry of globular clusters in four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total of 66 globular clusters (GCs) in common with the deep HST optical-band study of Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the M87 GCs have UV/optical properties that are distinct from clusters in the Milky Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB populations than do Milky Way analogues. Cluster mass is probably not a factor in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun and overlap the local E galaxy sample in estimated Mg_2 line indices. Nonetheless, the clusters produce much more UV light at a given Mg_2, being up to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear to represent a transition between Milky Way-type clusters and E galaxies. The differences are in the correct sense if the clusters are significantly older than the E galaxies. Comparisons with Galactic open clusters indicate that the hot stars lie on the extreme horizontal branch, rather than being blue stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find that 43 of our UV detections have no optical-band counterparts. Most appear to be UV-bright background galaxies, seen through M87. Eleven NUV variable sources detected at only one epoch in the central field are probably classical novae. [Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ. Full resolution version available at http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd
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