6,817 research outputs found
The optical-ultraviolet continuum of Seyfert 2 galaxies
This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting
the single galaxies in the sample of Heckman et al. (1995) with composite
models (shock+ photoionization from the active center), we show that five main
components characterize the SED of the continuum. Shocks play an important role
since they produce a high temperature zone where soft X-rays are emitted.
We show that in the optical-UV range, the slope of the NLR emission
reproduces the observed values, and may be the main component of the
featureless continuum. The presence of star forming regions cannot be excluded
in the circumnuclear region of various Seyfert galaxies. An attempt is made to
find their fingerprints in the observed AGN spectra. Finally, it is
demonstrated that multi-cloud models are necessary to interpret the spectra of
single objects, even in the global investigation of a sample of galaxies.Comment: 26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To
appear in "The Astrophysical Journal
Implosion-driven shock tube
Detonation wave striking PETN explosive shell producing implosion or implosion wave in shock tub
Pulse rates recorded by digital film positioner
System converts detector pulse rates to photographs of binary scale indicator lights on continuously moving film. The system then scans the film and transfers the data to computer-compatible magnetic tape
Period-magnitude relations for M giants in Baade's Window NGC6522
A large and complete sample of stars with K < 9.75 in the NGC6522 Baade's
Window is examined using light curves from MACHO and IJK from DENIS. All 4 of
the sequences ABCD in the K vs logP diagram of the LMC are seen in the Bulge.
The Bulge sequences however show some differences from the Magellanic Clouds.
The sequences may be useful as distance indicators. A new diagram of the
frequency of late-type variables is presented. The catalogued SR variables of
the solar nbd are found to be a subset of the total of SRs, biased towards
large amplitude.Comment: 11 pages 11 fig
Mid-IR period-magnitude relations for AGB stars
Asymptotic Giant Branch variables are found to obey period-luminosity
relations in the mid-IR similar to those seen at K_S (2.14 microns), even at 24
microns where emission from circumstellar dust is expected to be dominant.
Their loci in the M, logP diagrams are essentially the same for the LMC and for
NGC6522 in spite of different ages and metallicities. There is no systematic
trend of slope with wavelength. The offsets of the apparent magnitude vs. logP
relations imply a difference between the two fields of 3.8 in distance modulus.
The colours of the variables confirm that a principal period with log P > 1.75
is a necessary condition for detectable mass-loss. At the longest observed
wavelength, 24 microns, many semi-regular variables have dust shells comparable
in luminosity to those around Miras. There is a clear bifurcation in LMC
colour-magnitude diagrams involving 24 micron magnitudes.Comment: 5 pages, 4 figure
Long-term IR Photometry of Seyferts
Long-term (up to 10000d) monitoring has been undertaken for 41 Seyferts in
the near-IR (JHKL). All but 2 showed variability, with K ampl in the range <0.1
to > 1.1 mags. The timescale for detectable change is from about one week to a
few years. A simple cross-correlation study shows evidence for delays of up to
several hundred days between the variations seen at the shortest wavelengths
and the longest in many galaxies. In particular, the data for F9 now extend to
twice the interval covered earlier and the delay between its UV and IR outputs
persists. An analysis of the fluxes shows that, for any given galaxy, the
colours of the variable component are usually independent of the level of
activity. The state of activity can be parameterized. Taken over the whole
sample, the colours of the variable components fall within moderately narrowly
defined ranges. In particular, the H-K colour is appropriate to a black body of
temperature 1600K. The H-K excess for a heavily reddened nucleus can be
determined and used to find E_{B-V}, which can be compared to the values found
from the visible region broad line fluxes. Using flux-flux diagrams, the flux
within the aperture from the underlying galaxy can often be determined without
the need for model surface brightness profiles. In many galaxies it is apparent
that here must be an additional constant contribution from warm dust.Comment: Better quality available from ftp://ftp.saao.ac.za/pub/isg/seyf.pd
Photometric Variability Among the Brightest Asymptotic Giant Branch Stars Near the Center of M32
Deep K' images with 0.1 arcsec angular resolution, obtained with ALTAIR+NIRI
on Gemini North, are used to investigate photometric variablity among the
brightest asymptotic giant branch (AGB) stars in the central regions of M32.
Based on a comparison with brightnesses obtained from the K-band data discussed
by Davidge et al. (2000, ApJ, 545, L89), it is concluded that (1) at least 60%
of bright AGB stars near the center of M32 are photometrically variable, and
(2) the amplitudes of the light variations are similar to those of long period
variables in the Galactic bulge. We do not find evidence for a population of
large amplitude variables, like those detected by IRAS in the Galactic bulge.
The technique discussed here may prove useful for conducting an initial
reconnaisance of photometric variability among AGB stars in spheroids in the
Virgo cluster and beyond, where the required long exposure times may restrict
observations to only a few epochs.Comment: 8 pages of text, 3 postscript figures. ApJ (letters) in pres
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