22 research outputs found
Variable Intrinsic Absorption in Mrk 279
We examine the variability in the intrinsic absorption in the Seyfert 1
galaxy Mrk 279 using three epochs of observations from the Far Ultraviolet
Spectroscopic Explorer (FUSE) and two epochs of observations with the Space
Telescope Imaging Spectrograph on the Hubble Space Telescope. Rather than
finding simple photoionization responses of the absorbing gas to changes in the
underlying continuum, the observed changes in the absorption profiles can be
understood more clearly if the effective covering fraction of the gas in all
emission components, continuum and broad and intermediate velocity width
emission lines, is accounted for. While we do not uniquely solve for all of
these separate covering fractions and the ionic column densities using the
spectral data, we examine the parameter space using previously well-constrained
solutions for continuum and single emission component covering fractions.
Assuming full coverage of the continuum, we find that of the two velocity
components of the Mrk 279 absorption most likely associated with its outflow,
one likely has zero coverage of the intermediate line region while the other
does not. For each component, however, the broad line region is more fully
covered than the intermediate line region. Changes in the O VI column densities
are unconstrained due to saturation, but we show that small changes in the
nonsaturated C IV and N V column densities are consistent with the outflow gas
having zero or partial covering of the intermediate line region and an
ionization parameter changing from ~0.01 to ~0.1 from 2002 to 2003 as the UV
continuum flux increased by a factor of ~8. The absence of a change in the C
III absorbing column density is attributed to this species arising outside the
Mrk 279 outflow.Comment: 36 pages, 18 figures, accepted to Ap
Intrinsic Absorption in the Spectrum of NGC 7469: Simultaneous Chandra, FUSE, and STIS Observations
We present simultaneous X-ray, far-ultraviolet, and near-ultraviolet spectra
of the Seyfert 1 galaxy NGC 7469 obtained with the Chandra X-Ray Observatory,
the Far Ultraviolet Spectroscopic Explorer, and the Space Telescope Imaging
Spectrograph on the Hubble Space Telescope. Previous non-simultaneous
observations of this galaxy found two distinct UV absorption components, at
-560 and -1900 km/s, with the former as the likely counterpart of the X-ray
absorber. We confirm these two absorption components in our new UV
observations, in which we detect prominent O VI, Ly alpha, N V, and C IV
absorption. In our Chandra spectrum we detect O VIII emission, but no
significant O VIII or O VII absorption. We also detect a prominent Fe K alpha
emission line in the Chandra spectrum, as well as absorption due to
hydrogen-like and helium-like neon, magnesium, and silicon at velocities
consistent with the -560 km/s UV absorber. The FUSE and STIS data reveal that
the H I and C IV column densities in this UV- and X-ray- absorbing component
have increased over time, as the UV continuum flux decreased. We use measured H
I, N V, C IV, and O VI column densities to model the photoionization state of
both absorbers self-consistently. We confirm the general physical picture of
the outflow in which the low velocity component is a highly ionized, high
density absorber with a total column density of 10^20 cm^-2, located near the
broad emission line region, although due to measurable columns of N V and C IV,
we assign it a somewhat smaller ionization parameter than found previously,
U~1. The high velocity UV component is of lower density, log N=18.6, and likely
resides farther from the central engine as we find its ionization parameter to
be U=0.08.Comment: Minor correction to abstract; STScI eprint #1683; 50 pages, incl. 19
figures, 4 tables; Accepted to Ap
Distance to the RR Lyrae Star V716 Monocerotis
We present high quality BVRI CCD photometry of the variable star V716
Monocerotis (= NSV 03775). We confirm it to be an RR Lyrae star of variability
type ab (i.e. a fundamental mode pulsator), and determine its metallicity
([Fe/H] = -1.33 +/- 0.25), luminosity (Mv = 0.80 +/- 0.06), and foreground
reddening (E(B-V) = 0.05-0.17) from the Fourier components of its light curve.
These parameters indicate a distance of 4.1 +/- 0.3 kpc, placing V716 Mon near
the plane of the Galaxy well outside the solar circle. This research was
conducted as part of the 1999 Research Experiences for Undergraduates (REU) and
Practicas de Investigacion en Astronomia (PIA) Programs at Cerro Tololo
Inter-American Observatory (CTIO).Comment: 9 pages including 2 figures and 2 tables; accepted by PAS
Quasars and the Big Blue Bump
We investigate the ultraviolet-to-optical spectral energy distributions
(SEDs) of 17 active galactic nuclei (AGNs) using quasi-simultaneous
spectrophotometry spanning 900-9000 Angstrom (rest frame). We employ data from
the Far Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope
(HST), and the 2.1-meter telescope at Kitt Peak National Observatory (KPNO).
Taking advantage of the short-wavelength coverage, we are able to study the
so-called "big blue bump," the region where the energy output peaks, in detail.
Most objects exhibit a spectral break around 1100 Angstrom. Although this
result is formally associated with large uncertainty for some objects, there is
strong evidence in the data that the far-ultraviolet spectral region is below
the extrapolation of the near-ultraviolet-optical slope, indicating a spectral
break around 1100 Angstrom. We compare the behavior of our sample to those of
non-LTE thin-disk models covering a range in black-hole mass, Eddington ratio,
disk inclination, and other parameters. The distribution of ultraviolet-optical
spectral indices redward of the break, and far-ultraviolet indices shortward of
the break, are in rough agreement with the models. However, we do not see a
correlation between the far-ultraviolet spectral index and the black hole mass,
as seen in some accretion disk models. We argue that the observed spectral
break is intrinsic to AGNs, although intrinsic reddening as well as
Comptonization can strongly affect the far-ultraviolet spectral index. We make
our data available online in digital format.Comment: 32 pages (10pt), 12 figures. Accepted for publication in Ap
X-ray/UV Observing Campaign on the Mrk 279 AGN Outflow: A Global Fitting Analysis of the UV Absorption
We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy
Mrk 279 based on simultaneous long observations with the Hubble Space Telescope
(41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the
line-of-sight covering factors and ionic column densities, we separately fit
two groups of absorption lines: the Lyman series and the CNO lithium-like
doublets. For the CNO doublets we assume that all three ions share the same
covering factors. The fitting method applied here overcomes some limitations of
the traditional method using individual doublet pairs; it allows for the
treatment of more complex, physically realistic scenarios for the
absorption-emission geometry and eliminates systematic errors that we show are
introduced by spectral noise. We derive velocity-dependent solutions based on
two models of geometrical covering -- a single covering factor for all
background emission sources, and separate covering factors for the continuum
and emission lines. Although both models give good statistical fits to the
observed absorption, we favor the model with two covering factors because: (a)
the best-fit covering factors for both emission sources are similar for the
independent Lyman series and CNO doublet fits; (b) the fits are consistent with
full coverage of the continuum source and partial coverage of the emission
lines by the absorbers, as expected from the relative sizes of the nuclear
emission components; and (c) it provides a natural explanation for variability
in the Ly absorption detected in an earlier epoch. We also explore
physical and geometrical constraints on the outflow from these results.Comment: 17 pages, 15 figures (9 color), emulateapj, accepted for publication
in The Astrophysical Journa