1,076 research outputs found
The Circumstellar Extinction of Planetary Nebulae
We analyze the dependence of circumstellar extinction on core mass for the
brightest planetary nebulae (PNe) in the Magellanic Clouds and M31. We show
that in all three galaxies, a statistically significant correlation exists
between the two quantities, such that high core mass objects have greater
extinction. We model this behavior, and show that the relation is a simple
consequence of the greater mass loss and faster evolution times of high mass
stars. The relation is important because it provides a natural explanation for
the invariance of the [O III] 5007 planetary nebula luminosity function (PNLF)
with population age: bright Population I PNe are extinguished below the cutoff
of the PNLF. It also explains the counter-intuitive observation that
intrinsically luminous Population I PNe often appear fainter than PNe from
older, low-mass progenitors.Comment: 12 pages, 2 figures, accepted for ApJ, April 10, 199
HIV Vulnerability in Out-of-School Adolescents and Youth in Yunnan, China
This study investigated multiple aspects of vulnerability to HIV in out-of-school adolescents and youth in Yunnan Province, a high HIV risk region in China. The findings show that socially disadvantaged adolescents and youth were overrepresented in the out-of-school young people in Yunnan. The out-of-school young people in Yunnan exhibited 1) limited knowledge about HIV transmission and prevention, 2) a high prevalence of unprotected sexual activity, 3) high exposure to illicit drugs and alcohol use and a high prevalence of drug use in themselves, and 4) limited access to health services. There is an indication of higher exposure to risk behaviours in the younger age group. The study population used multiple media, particularly television, internet and radio, to obtain information about HIV transmission and pre- vention, particularly in the younger age group. These media may be an effective way of reaching this population in fu- ture HIV education and prevention programs in the region
A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
We present UBVRI photometry obtained from Mosaic images of M31 and M33 using
the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq
degrees of M33, chosen so as to include all of the regions currently active in
forming massive stars. The catalog contains 371,781 and 146,622 stars in M31
and M33, respectively, where every star has a counterpart (at least) in B, V,
and R. We compare our photometry to previous studies. We provide cross
references to the stars confirmed as members by spectroscopy, and compare the
location of these to the complete set in color-magnitude diagrams. While
follow-up spectroscopy is needed for many projects, we demonstrate the success
of our photometry in being able to distinguish M31/M33 members from foreground
Galactic stars. We also present the results of newly obtained spectroscopy,
which identifies 34 newly confirmed members, including B-A supergiants, the
earliest O star known in M31, and two new Luminous Blue Variable candidates
whose spectra are similar to that of P Cygni.Comment: Accepted by the Astronomical Journal. A version with higher
resolution figures can be found at:
http://www.lowell.edu/users/massey/M3133.pdf.g
AAOmega radial velocities rule out current membership of the planetary nebula NGC 2438 in the open cluster M46
We present new radial velocity measurements of 586 stars in a one-degree
field centered on the open cluster M46, and the planetary nebula NGC 2438
located within a nuclear radius of the cluster. The data are based on
medium-resolution optical and near-infrared spectra taken with the AAOmega
spectrograph on the Anglo-Australian Telescope. We find a velocity difference
of about 30 km/s between the cluster and the nebula, thus removing all
ambiguities about the cluster membership of the planetary nebula caused by
contradicting results in the literature. The line-of-sight velocity dispersion
of the cluster is 3.9+/-0.3 km/s, likely to be affected by a significant
population of binary stars.Comment: 6 pages + 5 figures, accepted for publication in MNRA
Stochastic evolution of cosmological parameters in the early universe
We develop a stochastic formulation of cosmology in the early universe, after
considering the scatter in the redshift-apparent magnitude diagram in the early
epochs as an observational evidence for the non-deterministic evolution of
early universe. We consider the stochastic evolution of density parameter in
the early universe after the inflationary phase qualitatively, under the
assumption of fluctuating factor in the equation of state, in the
Fokker-Planck formalism. Since the scale factor for the universe depends on the
energy density, from the coupled Friedmann equations we calculated the two
variable probability distribution function assuming a flat space geometry.Comment: 10 page
Planetary Nebulae as standard candles XI. Application to Spiral Galaxies
We report the results of an [O III] lambda 5007 survey for planetary nebulae
(PN) in three spiral galaxies: M101 (NGC 5457), M51 (NGC 5194/5195) and M96
(NGC 3368). By comparing on-band/off-band [O III] lambda 5007 images with
images taken in H-alpha and broadband R, we identify 65, 64 and 74 PN
candidates in each galaxy, respectively. From these data, an adopted M31
distance of 770 kpc, and the empirical planetary nebula luminosity function
(PNLF), we derive distances to M101, M51, and M96 of 7.7 +/- 0.5, 8.4 +/- 0.6,
and 9.6 +/- 0.6 Mpc. These observations demonstrate that the PNLF technique can
be successfully applied to late-type galaxies, and provide an important overlap
between the Population I and Population II distance scales. We also discuss
some special problems associated with using the PNLF in spiral galaxies,
including the effects of dust and the possible presence of [O III] bright
supernova remnants.Comment: 38 pages, TeX, with tables included but not figures. Uses epsf.tex
and kpnobasic.tex. To be published in the Astophysical Journal. Full paper is
available at http://www.astro.psu.edu/users/johnf/Text/research.htm
Intracluster Planetary Nebulae in the Virgo Cluster I. Initial Results
We report the initial results of a survey for intracluster planetary nebulae
in the Virgo Cluster. In two 16' x 16' fields, we identify 69 and 16
intracluster planetary nebula candidates, respectively. In a third 16' x 16'
field near the central elliptical galaxy M87, we detect 75 planetary nebula
candidates, of which a substantial fraction are intracluster in nature. By
examining the number of the planetaries detected in each field and the shape of
the planetary nebula luminosity function, we show that 1) the intracluster
starlight of Virgo is distributed non-uniformly, and varies between subclumps A
and B, 2) the Virgo Cluster core extends ~3 Mpc in front of M87, and thus is
elongated along the line-of-sight, and 3) a minimum of 22% of Virgo's stellar
luminosity resides between the galaxies in our fields, and that the true number
may be considerably larger. We also use our planetary nebula data to argue that
the intracluster stars in Virgo are likely derived from a population that is of
moderate age and metallicity.Comment: 20 pages, 3 figures, accepted for publication in the Astrophysical
Journal. Paper is also available at
http://www.astro.psu.edu/users/johnf/Text/research.htm
Energy Deposition and Excitation of Wakefield in Case of 100keV/u Ion Beam Passing through a Plasma Target
Recently our team investigated the energy deposition
and excitation of wakefield in case of
hundreds keV proton/helium ion beams passing
a gas-discharged plasma target..
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