226 research outputs found
Mineral Concentration of Herbage from Three Paulownia Species Used for Goat Browse
Goats naturally prefer a high proportion of browse in their diets. Therefore, research was initiated to investigate various silvo-pastoral production systems. In May 1997, six Paulownia treatments were planted in a randomized complete block experiment with six replications. Trees were between 6 and 12 cm in height at planting. Treatments included: P. fortunei seedlings, P. tomentosa seedlings, P. elongata seedlings, and three P. elongata clones. Each 4-m wide plot contained a single row of 12 trees with an intra-row spacing of 1 m. Leaf samples were analyzed from all six replications to determine mineral concentration in October 1997, and June and August 1998. Ca and P concentrations varied widely, and the Ca:P ratio exceeded the desired 2:1 with a range from 2.7:1 to 10.1:1. In October 1997, concentrations of Ca were similar in leaf laminae and petioles (1.26%), whereas P concentrations were twice as high in laminae (0.19%) as in petioles (0.09%). In October 1997, laminae from seedlings contained greater concentrations of Ca, Fe, and Zn than did laminae from clones, whereas the opposite was true for every element, with the exception of Fe, in June 1998. By August 1998, these differences had disappeared. Regardless of sampling date and leaf part, concentrations of Ca, Mg, K, Fe, Mn and Zn were sufficient to fulfill goat nutritional requirements, whereas P concentrations were too low. Goats readily browsed Paulownia laminae and no clear preference trends were observed between treatments
Preliminary Parallaxes of 40 L and T Dwarfs from the U.S. Naval Observatory Infrared Astrometry Program
We present preliminary trigonometric parallaxes and proper motions for 22 L
dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager. Relative to
absolute parallax corrections are made by employing 2MASS and/or SDSS
photometry for reference frame stars. We combine USNO infrared and optical
parallaxes with the best available CIT system photometry to determine M_J, M_H,
and M_K values for 37 L dwarfs between spectral types L0 to L8 and 19 T dwarfs
between spectral types T0.5 and T8 and present selected absolute magnitude
versus spectral type and color diagrams, based on these results. Luminosities
and temperatures are estimated for these objects. Of special interest are the
distances of several objects which are at or near the L-T dwarf boundary so
that this important transition can be better understood. The previously
reported early-mid T dwarf luminosity excess is clearly confirmed and found to
be present at J, H, and K. The large number of objects that populate this
luminosity excess region indicates that it cannot be due entirely to selection
effects. The T dwarf sequence is extended to M_J~16.9 by 2MASS J041519-0935
which, at d = 5.74 pc, is found to be the least luminous [log(L/L_sun)=-5.58]
and coldest (T_eff~760 K) brown dwarf known. Combining results from this paper
with earlier USNO CCD results we find that, in contrast to the L dwarfs, there
are no examples of low velocity (V_tan < 20 km/s) T dwarfs. We briefly discuss
future directions for the USNO infrared astrometry program.Comment: 73 pages, 9 figures, 9 tables, accepted for publication in The
Astronomical Journa
The Discovery of an Embedded Cluster of High-Mass Stars Near SGR 1900+14
Deep I-band imaging to approximately I = 26.5 of the soft gamma-ray repeater
SGR 1900+14 region has revealed a compact cluster of massive stars located only
a few arcseconds from the fading radio source thought to be the location of the
SGR (Frail, Kulkarni, & Bloom 1999). This cluster was previously hidden in the
glare of the pair of M5 supergiant stars (whose light was removed by PSF
subtraction) proposed by Vrba et al. (1996) as likely associated with the SGR
1900+14. The cluster has at least 13 members within a cluster radius of
approximately 0.6 pc, based on an estimated distance of 12-15 kpc. It is
remarkably similar to a cluster found associated with SGR 1806-20 (Fuchs et al.
1999). That similar clusters have now been found at or near the positions of
the two best-studied SGRs suggests that young neutron stars, thought to be
responsible for the SGR phenomenon, have their origins in proximate compact
clusters of massive stars.Comment: 5 pages, 3 figures, accepted Astrophysical Journal Letter
Goats to Control the Encroachment of Undesirable Brush and Woody Species in Cattle Pastures
Field studies were initiated in an abandoned, overgrown 8.4 ha orchard left untouched for 15 years to evaluate the effectiveness of using goats (Capra hircus hircus) to manage undesirable vegetation. Goats alone (G: 30 does/ha) or cattle (Bos taurus) with goats (GC:17 does/ha and 3 steers/ha) were mob-grazed twice a year during four grazing seasons. Multiflora rose (Rosa multiflora Thunb.) canopy area decreased from 12 to 2.5 m2 in grazed pastures and multiflora rose live canes were 100% in the control, 0% in G, and only 8% in GC at the completion of the study. Following two years of rest, cattle alone (C: 6 steers) or goats + cattle (GC: 9 goats and 6 steers) were rotationally grazed on the same site. Over four grazing seasons, brambles (Rubus spp.) and honeysuckle (Locifera japonica) vines were practically eliminated from grazed pastures. Multiflora rose bushes grew to a height of 1.8 m in C, but were kept low (avg .6 m) in GC (P \u3c 0.01). Similarly, multiflora rose canopy area was well controlled in GC (avg .5 m2), but increased to 7 m2 in C (P \u3c 0.03). Black locust (Robinia pseudoacacia L.) trees were browsed by goats and cattle and were practically eliminated from grazed pastures. Integrating goats into mountain grazing systems is a useful and environmentally-friendly management tool to keep these pastures in production
Parallax and Luminosity Measurements of an L Subdwarf
We present the first parallax and luminosity measurements for an L subdwarf,
the sdL7 2MASS J05325346+8246465. Observations conducted over three years by
the USNO infrared astrometry program yield an astrometric distance of
26.7+/-1.2 pc and a proper motion of 2.6241+/-0.0018"/yr. Combined with
broadband spectral and photometric measurements, we determine a luminosity of
log(Lbol/Lsun) = -4.24+/-0.06 and Teff = 1730+/-90 K (the latter assuming an
age of 5-10 Gyr), comparable to mid-type L field dwarfs. Comparison of the
luminosity of 2MASS J05325346+8246465 to theoretical evolutionary models
indicates that its mass is just below the sustained hydrogen burning limit, and
is therefore a brown dwarf. Its kinematics indicate a ~110 Myr, retrograde
Galactic orbit which is both eccentric (3 <~ R <~ 8.5 kpc) and extends well
away from the plane (Delta_Z = +/-2 kpc), consistent with membership in the
inner halo population. The relatively bright J-band magnitude of 2MASS
J05325346+8246465 implies significantly reduced opacity in the 1.2 micron
region, consistent with inhibited condensate formation as previously proposed.
Its as yet unknown subsolar metallicity remains the primary limitation in
constraining its mass; determination of both parameters would provide a
powerful test of interior and evolutionary models for low-mass stars and brown
dwarfs.Comment: Accepted to ApJ 10 September 2007; 13 pages, 5 figures, 3 tables,
formatted in emulateapj styl
ASCA Discovery of an X-ray Pulsar in the Error Box of SGR1900+14
We present a 2 - 10 keV ASCA observation of the field around the soft gamma
repeater SGR1900+14. One quiescent X-ray source was detected in this
observation, and it was in the SGR error box. In 2 - 10 keV X-rays, its
spectrum may be fit by a power law with index -2.2, and its unabsorbed flux is
9.6 x 10^-12 erg cm^-2 s^-1. We also find a clear 5.16 s period. The properties
of the three well-studied soft gamma repeaters are remarkably similar to one
another, and provide evidence that all of them are associated with young,
strongly magnetized neutron stars in supernova remnants.Comment: Accepted for publication in the Astrophysical Journal Letter
Infrared Excess in the Be Star Delta Scorpii
We present infrared photometric observations of the Be binary system delta
Scorpii obtained in 2006. The J,H and K magnitudes are the same within the
errors compared to observations taken 10 months earlier. We derive the infrared
excess from the observation and compare this to the color excess predicted by a
radiative equilibrium model of the primary star and its circumstellar disk. We
use a non-LTE computational code to model the gaseous envelope concentrated in
the star's equatorial plane and calculate the expected spectral energy
distribution and Halpha emission profile of the star with its circumstellar
disk. Using the observed infrared excess of delta Sco, as well as Halpha
spectroscopy bracketing the IR observations in time, we place constraints on
the radial density distribution in the circumstellar disk. Because the disk
exhibits variability in its density distribution, this work will be helpful in
understanding its dynamics.Comment: 12 pages, 14 figures, to be published in PASP May 200
The Near-Infared Survey of the N49 Region around the Soft Gamma Repeater SGR 0526-66
We report the results of a deep near-infrared survey with the Very Large Telescope/Infrared Spectrometer and Array Camera of the environment of the supernova remnant N49 in the Large Magellanic Cloud, which contains the soft gamma repeater SGR 0526-66. Two of the four confirmed SGRs are potentially associated with compact stellar clusters. We thus searched for a similar association of SGR 0526-66 and imaged a young stellar cluster at a projected distance of ∼30 pc from the SGR. This constitutes the third cluster–SGR link and lends support to scenarios in which SGR progenitors originate in young dusty clusters. If confirmed, the cluster-SGR association constrains the age and thus the initial mass of SGR progenitor
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