559 research outputs found
Planetary research at Lowell Observatory
Scientific goals include a better determination of the basic physical characteristics of cometary nuclei, a more complete understanding of the complex processes in the comae, a survey of abundances and gas/dust ratios in a large number of comets, and measurement of primordial (12)C/(13)C and (14)N/(15)N ratios. The program also includes the observation of Pluto-Charon mutual eclipses to derive dimensions. Reduction and analysis of extensive narrowband photometry of Comet Halley from Cerro Tololo Inter-American Observatory, Perth Observatory, Lowell Observatory, and Mauna Kea Observatory were completed. It was shown that the 7.4-day periodicity in the activity of Comet Halley was present from late February through at least early June 1986, but there is no conclusive evidence of periodic variability in the preperihelion data. Greatly improved NH scalelengths and lifetimes were derived from the Halley data which lead to the conclusion that the abundance of NH in comets is much higher than previously believed. Simultaneous optical and thermal infrared observations were obtained of Comet P/Temple 2 using the MKO 2.2 m telescope and the NASA IRTF. Preliminary analysis of these observations shows that the comet's nucleus is highly elongated, very dark, and quite red
The Distance to the Coma Cluster from Surface Brightness Fluctuations
We report on the first determination of the distance to the Coma Cluster
based on surface brightness fluctuation (SBF) measurements obtained from Hubble
Space Telescope WFPC2 observations of the bright E0 galaxy NGC 4881 in the Coma
Cluster and ground-based observations of the standard E1 galaxy NGC 3379 in the
Leo-I group. Relative distances based on the I-band fluctuation magnitude,
I(SBF), are strongly dependent on metallicity and age of the stellar
population. However, the radial changes in the stellar populations of the two
giant ellipticals, NGC 3379 and NGC 4881, are well described by published Mg_2
gradients, and the ground-based measurements of I(SBF) at several radial points
in NGC 3379 are used to calibrate I(SBF) in terms of the Mg_2 index. The
distance to NGC 3379, assumed to be identical to the average SBF distance of
the Leo-I group, is combined with the new SBF measurements of NGC 4881 to
obtain a Coma Cluster distance of 102+-14 Mpc. Combining this distance with the
cosmic recession velocity of Coma (7186+-428 km/s), we find the Hubble constant
to be H_0 = 71+-11 km/s/Mpc.Comment: 12 pages, LaTex, includes aaspp4.sty and 3 eps figures. To appear in
ApJ Letter
Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
We present new (B,I) photometry for the globular cluster systems in eight
Brightest Cluster Galaxies (BCGs), obtained with the ACS/WFC camera on the
Hubble Space Telescope. In the very rich cluster systems that reside within
these giant galaxies, we find that all have strongly bimodal color
distributions All the BCGs show population gradients, with much higher relative
numbers of red clusters within 5 kpc of their centers, consistent with their
having formed at later times than the blue, metal-poor population. A striking
new feature of the color distributions emerging from our data is that for the
brightest clusters (M_I < -10.5) the color distribution becomes broad and less
obviously bimodal. we suggest that it may be a characteristic of many BCGs.
Furthermore, the blue (metal-poor) clusters become progressively redder with
increasing luminosity, following a mass/metallicity scaling relation Z ~
M^0.55. We argue that these GCS characteristics are consistent with a
hierarchical-merging formation picture in which the metal-poor clusters formed
in protogalactic clouds or dense starburst complexes with gas masses in the
range 10^7 - 10^10 M_Sun, but where the more massive clusters on average formed
in bigger clouds with deeper potential wells where more pre-enrichment could
occur.Comment: 48 pages, 24 Figures, PDF, Submitted to Astrophys.J. and refereed.
For complete pdf file with better figures, see:
http://physwww.mcmaster.ca/%7Eharris/Preprints.htm
Spatial and temporal distribution and nest site characteristics of feral honey bee (Hymenoptera: apidae) colonies in a coastal prairie landscape
We evaluated the distribution and abundance of feral honey bee, Apis mellifera L.,
colonies in a coastal prairie landscape by examining nest site characteristics, population trends, and
spatial and temporal patterns in cavity use. The colony densities of up to 12.5 colonies per km2 were
the highest reported in the literature for an area including both suitable and unsuitable patches of
nesting habitat. The measured cavity attributes were similar to those reported from other areas. The
time occupied and turnover indices provided useful information about cavity quality, although none
of the measured cavity attributes were correlated with these indices. Unmeasurable cavity characteristics,
such as cavity volume, may provide a better estimate of cavity quality. Spatial patterns existed
in cavity use by the feral colonies, with the colonies showing an aggregated pattern of distribution
throughout the study. Colony aggregations probably resulted from the distribution of resources,
especially cavities. Two years after the arrival of Africanized honey bees, cavities used by Africanized
and European colonies were aggregated in distribution. During what seemed to be a transition period,
both Africanized and European colonies were randomly distributed. After that time, European
colonies remained randomly distributed, whereas Africanized colonies were aggregated. Therefore,
the invasion of Africanized honey bees seemed to fragment the existing European population,
corresponding to a decrease in the overall number of European colonies in the study area
Long term preservation of DNA from honey bees (Apis mellifera) collected in aerial pitfall traps
This study examines the preservation of nuclear and mitochondrial DNA from honey bee (Apis mellifera L.) specimens which were first kept in propylene glycol-based antifreeze under various conditions, and then stored long-term, refrigerated in 95% ethanol. Two sets of bees were subjected to the propylene glycol treatment, then ethanol storage. One set consisted of bees captured in the field in propylene glycol-containing "aerial pitfall traps", where they remained for up to 21 days. A second set consisted of bees taken from a hive and kept in propylene glycol under various temperature and lighting conditions for up to 90 days. Both the field bees and laboratory bees were then stored long-term in ethanol before evaluation of the persistence of nuclear and mitochondrial DNA using the polymerase chain reaction. DNA integrity was preserved for both field and laboratory specimens. The results demonstrate that propylene glycol-captured, ethanol-preserved honey bees retain both nuclear and mitochondrial DNA after capture and long tern preservation. It is suggested that with little or no modification, the techniques described here might he applied to other studies involving trap-collected arthropod specimens
Two Clusters with Radio-quiet Cooling Cores
Radio lobes inflated by active galactic nuclei at the centers of clusters are
a promising candidate for halting condensation in clusters with short central
cooling times because they are common in such clusters. In order to test the
AGN-heating hypothesis, we obtained Chandra observations of two clusters with
short central cooling times yet no evidence for AGN activity: Abell 1650 and
Abell 2244. The cores of these clusters indeed appear systematically different
from cores with more prominent radio emission. They do not have significant
central temperature gradients, and their central entropy levels are markedly
higher than in clusters with stronger radio emission, corresponding to central
cooling times ~ 1 Gigayear. Also, there is no evidence for fossil X-ray
cavities produced by an earlier episode of AGN heating. We suggest that either
(1) the central gas has not yet cooled to the point at which feedback is
necessary to prevent it from condensing, possibly because it is conductively
stabilized, or (2) the gas experienced a major heating event Gyr in
the past and has not required feedback since then. The fact that these clusters
with no evident feedback have higher central entropy and therefore longer
central cooling times than clusters with obvious AGN feedback strongly suggests
that AGNs supply the feedback necessary to suppress condensation in clusters
with short central cooling times.Comment: ApJ Letter, in pres
Chandra and ROSAT observations of Abell 194: detection of an X-ray cavity and mapping the dynamics of the cluster
Based on Chandra and ROSAT observations, we investigated the nearby poor
cluster Abell 194, which hosts two luminous radio galaxies, NGC547 (3C 40B) and
NGC541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r~34
kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC547. The
estimated age of the cavity is t=7.9 x 10^7 years and the total work of the AGN
is 3.3 x 10^59 erg, hence the cavity power is P_cav=1.3 x 10^44 erg/s.
Furthermore, in the Chandra images of NGC545 and NGC541 we detected sharp
surface brightness edges, identified as merger cold fronts, and extended tails.
Using the pressure ratios between inside and outside the cold fronts we
estimated that the velocities of NGC545 and NGC541 correspond to Mach-numbers
of M=1.0^{+0.3}_{-0.5} and M=0.9^{+0.2}_{-0.5}, respectively. The low radial
velocities of these galaxies relative to the mean radial velocity of Abell 194
imply that their motion is oriented approximately in the plane of the sky.
Based on these and earlier observations, we concluded that NGC545 and NGC541
are falling through the cluster, whose center is NGC547, suggesting that Abell
194 is undergoing a significant cluster merger event. Additionally, we detected
20 bright X-ray sources around NGC547 and NGC541, a surprisingly large number,
since the predicted number of resolved LMXBs and CXB sources is 2.2 and 4.1,
respectively. To explain the nature of additional sources, different
possibilities were considered, none of which are satisfactory. We also studied
the origin of X-ray emission in Minkowski's Object, and concluded that it is
most likely dominated by the population of HMXBs rather than by hot diffuse
ISM. Moreover, in view of the galaxy dynamics in Abell 194, we explored the
possibility that the starburst in Minkowski's Object was triggered by its past
interaction with NGC541, and concluded that it may be a viable path.Comment: 12 pages, 7 figures, accepted for publication in Ap
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