5,304 research outputs found
CORN (\u3cem\u3eZea mays\u3c/em\u3e L.) YIELD RESPONSE TO DEFOLIATION AT DIFFERENT ROW WIDTHS
Corn (Zea mays L.) defoliation experiments have been conducted for more than 120 years. However, there is limited data on the effect of row width on defoliation in modern hybrids. A two-year experiment was conducted in Lexington, Kentucky with two hybrids (113 relative maturity (RM) and 120 RM), two row widths (38 and 76 cm) and a combination of defoliation timings and severities: 0% defoliation (control), V7-100%, V14-50%, V14-100%, R2-50% and R2-100%. No yield difference among hybrids was observed in 2012. Yields were 26% greater in 38-cm rows than 76-cm rows in 2012. For 2013, corn yield for 38-cm was 10% greater, but hybrid, row width and defoliation interacted. Lowest yields were caused by V14-100% followed by R2-100%. Defoliations of V14-50% and R2-50% reduced yields in some cases. Complete defoliations at V7 did not reduce yields in most comparisons. Light interception below 80% during the critical period was enough to attain maximum yields in defoliated plants. Kernel number and kernel weight were most reduced by V14-100% and R2-100% defoliations, respectively. There is a potential for narrow rows to reduce grain yield losses after a defoliation event, when compared with wide rows
The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. II. Sensitivity of the survey and an Atlas of Synthetic Dwarf Galaxies
SECCO is a survey devoted to the search for stellar counterparts within Ultra
Compact High Velocity Clouds. In this contribution we present the results of a
set of simulations aimed at the quantitative estimate of the sensitivity of the
survey as a function of the total luminosity, size and distance of the stellar
systems we are looking for. For all our synthetic galaxies we assumed an
exponential surface brightness profile and an old and metal-poor population.
The synthetic galaxies are simulated both on the images and on the photometric
catalogs, taking into account all the observational effects. In the fields
where the available observational material is of the top quality we detect
synthetic galaxies as >=5 sigma over-densities of resolved stars down to
muV,h=30.0 mag/arcsec2, for D<=1.5 Mpc, and down to muV,h~29.5 mag/arcsec2, for
D<=2.5 Mpc. In the field with the worst observational material of the whole
survey we detect synthetic galaxies with muV,h<=28.8 mag/arcsec2 out to D<=1.0
Mpc, and those with muV,h<=27.5 mag/arcsec2 out to D<=2.5 Mpc. Dwarf galaxies
with MV=-10, with sizes in the range spanned by known dwarfs, are detected by
visual inspection of the images up to D=5 Mpc independently of the image
quality. In the best quality images dwarfs are partially resolved into stars up
to D=3.0 Mpc, and completely unresolved at D=5 Mpc. As an independent test of
the sensitivity of our images to low surface brightness galaxies we report on
the detection of several dwarf spheroidal galaxies probably located in the
Virgo cluster with MV<=-8.0 and muV,h<=26.8 mag/arcsec2. The nature of the
previously discovered SECCO 1 stellar system, also likely located in the Virgo
cluster, is re-discussed in comparison with these dwarfs. While specific for
the SECCO survey, our study may also provide general guidelines for detection
of faint stellar systems with 8m class telescopes.Comment: accepted for publication on A&
HII regions within a compact high velocity cloud. A nearly star-less dwarf galaxy?
Within the SECCO survey we identified a candidate stellar counterpart to the
Ultra Compact High Velocity Cloud (UCHVC) HVC274.68+74.70-123, that was
suggested by Adams et al. (2013) as a possible mini-halo within the Local Group
of galaxies. The spectroscopic follow-up of the brightest sources within the
candidate reveals the presence of two HII regions whose radial velocity is
compatible with physical association with the UVHVC. The available data does
not allow us to give a definite answer on the nature of the newly identified
system. A few alternative hypotheses are discussed. However, the most likely
possibility is that we have found a new faint dwarf galaxy residing in the
Virgo cluster of galaxies, which we name SECCO-1. Independently of its actual
distance, SECCO-1 displays a ratio of neutral hydrogen mass to V luminosity of
M_{HI}/L_V>= 20, by far the largest among local dwarfs. Hence, it appears as a
nearly star-less galaxy and it may be an example of the missing links between
normal dwarfs and the dark mini halos that are predicted to exist in large
numbers according to the currently accepted cosmological model.Comment: Accepted for publication in ApJ Letters. Pdflatex, emulateapj.cls. 6
pages, 3 figures, 2 table
Multi-Element Abundance Measurements from Medium-Resolution Spectra. III. Metallicity Distributions of Milky Way Dwarf Satellite Galaxies
We present metallicity distribution functions (MDFs) for the central regions
of eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II,
Sculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the
published catalog of abundance measurements from the previous paper in this
series. The measurements are based on spectral synthesis of iron absorption
lines. For each MDF, we determine maximum likelihood fits for Leaky Box,
Pre-Enriched, and Extra Gas (wherein the gas supply available for star
formation increases before it decreases to zero) analytic models of chemical
evolution. Although the models are too simplistic to describe any MDF in
detail, a Leaky Box starting from zero metallicity gas fits none of the
galaxies except Canes Venatici I well. The MDFs of some galaxies, particularly
the more luminous ones, strongly prefer the Extra Gas Model to the other
models. Only for Canes Venatici I does the Pre-Enriched Model fit significantly
better than the Extra Gas Model. The best-fit effective yields of the less
luminous half of our galaxy sample do not exceed 0.02 Z_sun, indicating that
gas outflow is important in the chemical evolution of the less luminous
galaxies. We surmise that the ratio of the importance of gas infall to gas
outflow increases with galaxy luminosity. Strong correlations of average [Fe/H]
and metallicity spread with luminosity support this hypothesis.Comment: 17 pages, 5 figures; accepted for publication in ApJ; minor
corrections in v3; corrected typographical errors in Tables 1 and 3 in v
Horizontal flows concurrent with an X2.2 flare in active region NOAA 11158
Horizontal proper motions were measured with local correlation tracking (LCT)
techniques in active region NOAA 11158 on 2011 February 15 at a time when a
major (X2.2) solar flare occurred. The measurements are based on continuum
images and magnetograms of the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory. The observed shear flows along the polarity
inversion line were rather weak (a few 100 m/s). The counter-streaming region
shifted toward the north after the flare. A small circular area with flow
speeds of up to 1.2 km/s appeared after the flare near a region of rapid
penumbral decay. The LCT signal in this region was provided by small-scale
photospheric brigthenings, which were associated with fast traveling moving
magnetic features. Umbral strengthening and rapid penumbral decay was observed
after the flare. Both phenomena were closely tied to kernels of white-light
flare emission. The white-light flare only lasted for about 15 min and peaked 4
min earlier than the X-ray flux. In comparison to other major flares, the X2.2
flare in active region NOAA 11158 only produced diminutive photospheric
signatures.Comment: 6 pages, 4 figures, accepted for publication in Astronomische
Nachrichten/A
The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. I. Photos of ghosts
We present an imaging survey aimed at searching for the stellar counterparts
of recently discovered ultra-compact high-velocity HI clouds (UCHVC). Adams et
al. (2013) proposed these clouds to be candidate mini-haloes in the Local Group
and/or its surroundings, within a distance range of 0.25-2.0 Mpc. Using the
Large Binocular Telescope we obtain wide-field (~ 23' X 23') g- and r-band
images of the twenty-five most promising and most compact clouds among the
fifty-nine identified by Adams et al. Careful visual inspection of all the
images does not reveal any stellar counterpart even slightly resembling LeoP,
the only local dwarf galaxy that was found as a counterpart to a previously
detected high velocity cloud. Only a possible distant (D>3.0 Mpc) counterpart
to HVC274.68+74.70-123 has been identified on our images. The point source
photometry in the central 17.3' X 7.7' chips reaches r<= 26.5, and is expected
to contain most of the stellar counterparts to the UCHVCs. However, no obvious
stellar over-density is detected in any of our fields, in marked contrast to
our comparison LeoP field in which the dwarf galaxy is detected at a >30 sigma
significance level. Only HVC352.45+59.06+263 may be associated with a weak
over-density, whose nature cannot be ascertained with our data. Sensitivity
tests shows that our survey would have detected any dwarf galaxy dominated by
an old stellar population, with an integrated absolute magnitude M_V<= -8.0, a
half-light radius r_h<= 300 pc, and lying within 1.5 Mpc from us, thereby
confirming that it is unlikely that the observed UCHVCs are associated with
stellar counterparts typical of known Local Group dwarf galaxies.Comment: Accepted for publication by A&A. PdfLaTex. 24 pages, 27 figures.
Minor changes; A&A language editin
The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies
We present a large sample of fully self-consistent hydrodynamical
Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It
has enabled us to identify the key physical parameters and mechanisms at the
origin of the observed variety in the Local Group dSph properties. The initial
total mass (gas + dark matter) of these galaxies is the main driver of their
evolution. Star formation (SF) occurs in series of short bursts. In massive
systems, the very short intervals between the SF peaks mimic a continuous star
formation rate, while less massive systems exhibit well separated SF bursts, as
identified observationally. The delay between the SF events is controlled by
the gas cooling time dependence on galaxy mass. The observed global scaling
relations, luminosity-mass and luminosity-metallicity, are reproduced with low
scatter. We take advantage of the unprecedentedly large sample size and data
homogeneity of the ESO Large Programme DART, and add to it a few independent
studies, to constrain the star formation history of five Milky Way dSphs,
Sextans, LeoII, Carina, Sculptor and Fornax. For the first time, [Mg/Fe] vs
[Fe/H] diagrams derived from high-resolution spectroscopy of hundreds of
individual stars are confronted with model predictions. We find that the
diversity in dSph properties may well result from intrinsic evolution. We note,
however, that the presence of gas in the final state of our simulations, of the
order of what is observed in dwarf irregulars, calls for removal by external
processes.Comment: 21 Pages, 19 figures ; Accepted for publication in A&A. Higher
resolution version may be downloaded here :
http://obswww.unige.ch/~revaz/publications/aa2009_1173
5-dimensional Quantum Gravity Effects in Exclusive Double Diffractive Events
The experimentally measurable effects related to extra dimensional gravity in
a RS-type brane world are estimated. Two options of the RS framework (namely,
with small and large curvature) are considered. It is shown that both can be
detected by the joint experiment of the CMS and TOTEM Collaborations at the
LHC.Comment: 11 pages, 6 figures, 4 tables, acknowledgments are adde
A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
[abridged] We present the results of a spectroscopic survey of the recently
discovered faint Milky Way satellites Boo, UMaI, UMaII and Wil1. Using the
DEIMOS spectrograph on Keck, we have obtained samples that contain from 15 to
85 probable members of these satellites for which we derive radial velocities
precise to a few km/s down to i~21-22. About half of these stars are observed
with a high enough S/N to estimate their metallicity to within \pm0.2 dex. From
this dataset, we show that UMaII is the only object that does not show a clear
radial velocity peak. However, the measured systemic radial velocity
(v_r=115\pm5 km/s) is in good agreement with recent simulations in which this
object is the progenitor of the recently discovered Orphan Stream. The three
other satellites show velocity dispersions that make them highly dark-matter
dominated systems. In particular the Willman 1 object is not a globular cluster
given its metallicity scatter over -2.0<[Fe/H]<-1.0 and is therefore almost
certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity
dispersion of only 4.3_{-1.3}^{+2.3} km/s around a systemic velocity of
-12.3\pm2.3 km/s which implies a mass-to-light ratio of ~700 and a total mass
of ~5x10^5 Msun for this satellite, making it the least massive satellite
galaxy known to date. Such a low mass could mean that the 10^7 Msun limit that
had until now never been crossed for Milky Way and Andromeda satellite galaxies
may only be an observational limit and that fainter, less massive systems exist
within the Local Group. However, more modeling and an extended search for
potential extra-tidal stars are required to rule out the possibility that these
systems have not been significantly heated by tidal interaction.Comment: 24 pages, 11 figures, MNRAS accepte
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