DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. V. Variables in the Field M31F

We undertook a long term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder -- M31 and M33 -- using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between September 1996 and October 1997 we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, fifth in the series, we present the catalog of variable stars found in the field M31F [(\alpha,\delta)= (10.\arcdeg10, 40.\arcdeg72), J2000.0]. We have found 64 variable stars: 4 eclipsing binaries, 52 Cepheids and 8 other periodic, possible long period or non-periodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.Comment: submitted to the Astronomical Journal, 31 pages, 18 figures; paper and data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/ and through WWW at http://cfa-www.harvard.edu/~kstanek/DIRECT

Supersoft X-Ray Sources in M31

The nearby Andromeda galaxy (M31) has been observed with the ROSAT PSPC in a mosaic of 6 pointings with 25 ksec each. In the paper describing the results on the total sample of detected sources, Supper et al. (1996) also report the positions for 15 supersoft X-ray sources and the blackbody fit results for the brightest of these sources. We report here in more detail on the X-ray spectral characteristics of all these 15 supersoft X-ray sources. Optical multi-colour photometric data obtained in 1990 at the Michigan- Dartmouth-MIT Observatory at Kitt Peak were used originally in the selection process of the supersoft sources, and are the basis for the finding charts given here for most selected X-ray sources.Comment: 8 pages postscript incl. figures, Proc. of Workshop on Supersoft X-Ray Sources, to appear in Lecture Notes in Physics vol. 472 (1996

Product Life Cycles and Innovation in the US Seed Corn Industry

The purpose of this study is to evaluate potential changes in the length of product life cycles in the US seed corn industry. We use the observed survival time on the market for hybrids sold during 1997-2009 to conduct a survival analysis. Our empirical results show that the average lifetimes of conventional and biotech corn hybrids have decreased over the last twelve years at similar rates and that the rate of decline in the life cycle length increased since 2004. We also find that the shorter product life cycles are closely linked to the accelerated levels of biotech product innovation in the US seed corn industry observed over the period of the analysis.Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

Product Life Cycles and Innovation in the US Seed Corn Industry

The purpose of this study is to evaluate potential changes in the length of product life cycles in the US seed corn industry. We use the observed survival time on the market for hybrids sold during 1997-2009 to conduct a survival analysis. Our empirical results show that the expected lifetimes for corn hybrids with single biotech traits are 5-15% longer than for hybrids with multiple (stacked) traits, and the expected lifetimes for conventional corn are 13-17% longer than stacked hybrids. Also, the product life cycles for all types of hybrids have decreased over the past twelve years (especially after 2004), but the rate of decline is roughly similar across hybrid types. Based on this evidence, we conclude that the shorter product life cycles are closely linked to the accelerated levels of biotech product innovation in the US seed corn industry over the period of analysis.accelerated failure time, biotechnology, product life cycle, survival analysis, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies, Research Methods/ Statistical Methods, Risk and Uncertainty,

DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. III. Variables in the Field M31C

We undertook a long term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder -- M31 and M33 -- using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between September 1996 and October 1997 we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, third in the series, we present the catalog of variable stars, most of them newly detected, found in the field M31C [(alpha,delta)=(11.10, 41.42) deg, J2000.0}]. We have found 115 variable stars: 12 eclipsing binaries, 35 Cepheids and 68 other periodic, possible long period or non-periodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.Comment: submitted to the Astronomical Journal, 39 pages, 27 figures; paper and data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/ and through WWW at http://cfa-www.harvard.edu/~kstanek/DIRECT

The Stellar Population of the M31 Spiral Arm Around OB Association A24

A study of the stellar population of the M31 spiral arm around OB association A24 was carried out based on the photometric data obtained from deep V and JHK imaging. The luminosity function was obtained for -7 <~ Mbol <~ -3.5 by applying the extinction correction corresponding to Av=1 and the bolometric correction BC(K) as an empirical function of (J-K)o. In comparing the observed color-luminosity diagrams with semitheoretical isochrones modified for the dust-shell effects, we found the young population of t <~ 30 Myr with supergiants of Mbol <~ -5, the bulk of the intermediate-age population of t ~ 0.2 - 2.5 Gyr with bright asymptotic giant branch (AGB) stars of -5 <~ Mbol <~ -4, and old populations of t ~> 3 Gyr with AGB and red giant branch (RGB) stars of Mbol ~> -4. The average star formation rate was estimated to be ~1.8x10^4 M_o/Myr and ~0.7x10^4 M_o/Myr per deprojected disk area of 1 kpc^2 from the number density of B0 V stars around Mv=-4.0 (age ~10 Myr) and the number density of bright AGB stars around Mbol = -4.3 (age ~1 Gyr), respectively. A study of the local variation in the V and the J and H luminosity functions revealed a kind of anticorrelation between the population of the young component and that of the intermediate-age component when subdomains of ~100 pc scales were concerned. This finding suggests that the disk domain around the A24 area experienced a series of star formation episodes alternatively among different subdomains with a timescale of a few spiral passage periods. Brief discussions are given about the interstellar extinction and about the lifetimes of bright AGB stars and the highly red objects (HROs) in the same area.Comment: 27 pages, 11 figures, accepted: ApJ, July 1, 199

The DIRECT project: Catalogs of stellar objects in nearby galaxies. II. Eastern arm and NGC 206 in M31

DIRECT is a project to directly obtain the distances to two important galaxies in the cosmological distance ladder, M31 and M33, using detached eclipsing binaries and Cepheids. As part of our search for these variables, we have obtained photometry and positions for thousands of stellar objects within the monitored fields, covering an area of 557.8 arcmin^2. In this research note we present the equatorial coordinates and BVI photometry for 26712 stars in the M31 galaxy, along the eastern arm and in the vicinity of the star forming region NGC206.Comment: 2 LaTeX pages, 2 Postscript figures, submitted to Astronomy & Astrophysic

Nature of the supercritical mesophase

It has been reported that at temperatures above the critical there is no “continuity of liquid and gas”, as originally hypothesized by van der Waals [1]. Rather, both gas and liquid phases, with characteristic properties as such, extend to supercritical temperatures [2]-[4]. Each phase is bounded by the locus of a percolation transition, i.e. a higher-order thermodynamic phase change associated with percolation of gas clusters in a large void, or liquid interstitial vacancies in a large cluster. Between these two-phase bounds, it is reported there exists a mesophase that resembles an otherwise homogeneous dispersion of gas micro-bubbles in liquid (foam) and a dispersion of liquid micro-droplets in gas (mist). Such a colloidal-like state of a pure one-component fluid represents a hitherto unchartered equilibrium state of matter besides pure solid, liquid or gas. Here we provide compelling evidence, from molecular dynamics (MD) simulations, for the existence of this supercritical mesophase and its colloidal nature. We report preliminary results of computer simulations for a model fluid using a simplistic representation of atoms or molecules, i.e. a hard-core repulsion with an attraction so short that the atoms are referred to as “adhesive spheres”. Molecular clusters, and hence percolation transitions, are unambiguously defined. Graphics of color-coded clusters show colloidal characteristics of the supercritical mesophase. We append this Letter to Natural Science with a debate on the scientific merits of its content courtesy of correspondence with Nature (Appendix)info:eu-repo/semantics/publishedVersio

Four Brown Dwarfs in the Taurus Star-Forming Region

We have identified four brown dwarfs in the Taurus star-forming region. They were first selected from $R$ and $I$ CCD photometry of 2.29 square degrees obtained at the Canada-France-Hawaii Telescope. Subsequently, they were recovered in the 2MASS second incremental data release point source catalog. Low-resolution optical spectra obtained at the William Herschel telescope allow us to derive spectral types in the range M7--M9. One of the brown dwarfs has very strong H$\alpha$ emission (EW=-340 \AA). It also displays Br$\gamma$ emission in an infrared spectrum obtained with IRCS on the Subaru telescope, suggesting that it is accreting matter from a disk. The \ion{K}{1} resonance doublet and the \ion{Na}{1} subordinate doublet at 818.3 and 819.5 nm in these Taurus objects are weaker than in field dwarfs of similar spectral type, consistent with low surface gravities as expected for young brown dwarfs. Two of the objects are cooler and fainter than GG Tau Bb, the lowest mass known member of the Taurus association. We estimate masses of only 0.03 M$_\odot$ for them. The spatial distribution of brown dwarfs in Taurus hints to a possible anticorrelation between the density of stars and the density of brown dwarfs.Comment: ApJ Letters (in press