4,103 research outputs found
WSRT and VLA Observations of the 6 cm and 2 cm lines of H2CO in the direction of W 58 C1(ON3) and W 58 C2
Absorption in the J{K-K+} = 2{11}-2{12} transition of formaldehyde at 2 cm
towards the ultracompact HII regions C1 and C2 of W 58 has been observed with
the VLA with an angular resolution of ~0.2'' and a velocity resolution of ~1
km/s. The high resolution continuum image of C1 (ON 3) shows a partial shell
which opens to the NE. Strong H2CO absorption is observed against W 58 C1. The
highest optical depth (tau > 2) occurs in the SW portion of C1 near the edge of
the shell, close to the continuum peak. The absorption is weaker towards the
nearby, more diffuse compact HII region C2, tau<~0.3. The H2CO velocity (-21.2
km/s) towards C1 is constant and agrees with the velocity of CO emission,
mainline OH masers, and the H76 alpha recombination line, but differs from the
velocity of the 1720 MHz OH maser emission (~-13 km/s). Observations of the
absorption in the J{K-K+} = 1{10}-1{11} transition of formaldehyde at 6 cm
towards W 58 C1 and C2 carried out earlier with the WSRT at lower resolution
(~4''x7'') show comparable optical depths and velocities to those observed at 2
cm. Based on the mean optical depth profiles at 6 cm and 2 cm, the volume
density of molecular hydrogen n(H2) and the formaldehyde column density N(H2CO)
were determined. The n(H2) is ~6E4 /cm**3 towards C1. N(H2CO) for C1 is ~8E14
/cm**2 while that towards C2 is ~8E13 /cm**2.Comment: AJ in press Jan 2001, 14 pages plus 6 figures (but Fig. 1 has 4
separate parts, a through d). Data are available at
http://adil.ncsa.uiuc.edu/document/00.HD.0
Selected Factors Associated with Age-specific Net Migration for South Dakota, 1970-1980
A study of South Dakota net migration was conducted to (1) determine the extent of age-specific migration from 1970-80; (2) compare current age-specific migration patterns with the previous decade; and (3) determine selected socio-demographic factors associated with the 1970-80 migration for the 20-29 age group. The unit of analysis was county. Multiple regression was used, and Lee’s model provided the theoretical framework. Analysis of Objective One revealed that: from 1970 to 1980, (1) South Dakota experienced total ne out-migration of 26,384 persons; (2) twelve five-year age categories experienced net out-migration; (3) the 20-29 age group accounted for 73 percent of the total net out-migrants; and (4) women out-migrated in larger numbers and at slightly later ages than men. Analysis of objective Two showed that: (1) South Dakota experienced net out-migration for both 1960s and 1970s; (2) net out-migration during the 1970s was less than the 1960s; (3) more age categories experienced net out-migration in the 1960s than in the 1970s; and (4) the 20-29 age group accounted for 40 percent of the total net out-migration in the 1960s, but for 73 percent of the total in the 1970s. Analysis of Objective Three revealed five socio-demographic factors accounted for 79 percent of the observed variation in the age 20-29 net migration in the state, including the rate of migration for the 20-29 age group in the 1960s, three employment characteristics, and median income level. For counties experiencing net in-migration for the 20-29 age group during the 1970s, median education levels accounted for 70 percent of the variation in the age 20-29 migration. Counties experiencing net out-migration for the 20-29 age group during the 1970s, median education levels accounted for 70 percent of the observed variation in the age 20-29 migration. Counties experiencing net out-migration for the 20-29 age group show that 78 percent of the observed variation in migration for that age group was accounted for by the age 20-29 migration rate in the 1960s, family status scores, median income levels, manufacturing employment rates, health status scores and housing availability
Application of Reliability and System Safety Analytical Techniques to a Civic Need
Many billions of tax payer dollars have been spent on aerospace programs. In order to continue further expenditures for the exploration of space, the American people demand a payoff which is beneficial to the average citizen. This paper will outline one such spin-off ; VIZ, the application of reliability and system safety analytical techniques to a civic need
Factors Associated with Population Changes in Rural South Dakota Communities
Students of demography have long been aware that populations change over time: they are dynamic. The determination and explanation of population change forms the central focus of population analysis, and the question arises as to what factors best explain observed variations in population changes occurring in South Dakota rural towns. Consequently, this study investigates the following problem. What is the association between selected demographic, geographic, economic, and social factors and the population changes that transpired from 1960 to 1970 in South Dakota incorporated places classified as rural in both 1960 and 1970? Specifically, the study attempts to determine: 1. What changes in population occurred from 1960 to 1970 in South Dakota small towns. 2. How these population changes varied by small town when controlled for selected variables. 3. What factors help explain the observed variations in population change reported for the towns under study. The possibility of a declining population concerns numerous groups. Local businessmen fear the loss of potential consumers, farmers fear the loss of marketing and trading facilities, and community leaders fear waning support or loyalty. Conventional agencies are faced with a declining tax base and continued expenditures for schools, roads, and other services: and the entire population of the community is threatened with the loss not only of individuals but also of facilities such as hospitals, churches, and schools
Radio Variability of Sagittarius A* - A 106 Day Cycle
We report the presence of a 106-day cycle in the radio variability of Sgr A*
based on an analysis of data observed with the Very Large Array (VLA) over the
past 20 years. The pulsed signal is most clearly seen at 1.3 cm with a ratio of
cycle frequency to frequency width f/Delta_f= 2.2+/-0.3. The periodic signal is
also clearly observed at 2 cm. At 3.6 cm the detection of a periodic signal is
marginal. No significant periodicity is detected at both 6 and 20 cm. Since the
sampling function is irregular we performed a number of tests to insure that
the observed periodicity is not the result of noise. Similar results were found
for a maximum entropy method and periodogram with CLEAN method. The probability
of false detection for several different noise distributions is less than 5%
based on Monte Carlo tests. The radio properties of the pulsed component at 1.3
cm are spectral index alpha ~ 1.0+/- 0.1 (for S nu^alpha), amplitude Delta
S=0.42 +/- 0.04 Jy and characteristic time scale Delta t_FWHM ~ 25 +/- 5 days.
The lack of VLBI detection of a secondary component suggests that the
variability occurs within Sgr A* on a scale of ~5 AU, suggesting an instability
of the accretion disk.Comment: 14 Pages, 3 figures. ApJ Lett 2000 accepte
The neutral gas in the environs of the Geminga gamma-ray pulsar
We present a high-resolution (24 arcsec) study of the HI interstellar gas
distribution around the radio-quiet neutron star Geminga. Based on Very Large
Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field
around Geminga. These observations have revealed the presence of a neutral gas
shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which
surrounds Geminga at a radial velocity compatible with the kinematical distance
of the neutron star. In addition, morphological agreement is observed between
the internal face of the HI shell and the brightest structure of Geminga's tail
observed in X-rays.We explore the possibility that this morphological agreement
is the result of a physical association.Comment: One tarfile including a Latex file (7 pages) and two figures. Paper
accepted for publication in Advances in Space Research; typos corrected;
changes in section Results and Discussion after referee's suggestions. S.
Johnston's affilation correcte
GMRT and VLA observations at 49cm and 20cm of the HII region near l=24.4d, b=0.1d
We report multifrequency radio continuum and hydrogen radio recombination
line observations of HII regions near l=24.8d b=0.1d using the Giant Metrewave
Radio Telescope (GMRT) at 1.28 GHz (n=172), 0.61 GHz (n=220) and the Very Large
Array (VLA) at 1.42 GHz (n=166). The region consists of a large number of
resolved HII regions and a few compact HII regions as seen in our continuum
maps, many of which have associated infrared (IR) point sources. The largest
HII region at l=24.83d and b=0.1d is a few arcmins in size and has a shell-type
morphology. It is a massive HII region enclosing ~ 550 solar mass with a linear
size of 7 pc and an rms electron density of ~ 110 cm^-3 at a kinematic distance
of 6 kpc. The required ionization can be provided by a single star of spectral
type O5.5.
We also report detection of hydrogen recombination lines from the HII region
at l=24.83d and b=0.1d at all observed frequencies near Vlsr=100 km/s. We model
the observed integrated line flux density as arising in the diffuse HII region
and find that the best fitting model has an electron density comparable to that
derived from the continuum. We also report detection of hydrogen recombination
lines from two other HII regions in the field.Comment: 14 pages, 8 Figures. Uses JAA style file. Accepted for publication in
Journal of Astrophysics and Astronomy. High resolution figures (fig 1a, fig
1b and fig 2b) can be downloaded from http://www.ncra.tifr.res.in/~ngk/G2
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