1,010 research outputs found
The "red shelf" of the Hb line in the Seyfert 1 galaxies RXS J01177+3637 and HS 0328+05
A few Seyfert 1s have a Hb profile with a red wing usually called the "red
shelf". The most popular interpretation of this feature is that it is due to
broad redshifted lines of Hb and [OIII]4959,5007; we have observed two Seyfert
1s displaying a "red shelf" and showed that in these two objects the main
contributor is most probably the HeI 4922,5016 lines having the velocity and
width of the broad Hb component. There is no evidence for the presence of a
broad redshifted component of Hb or [OIII] in any of these two objects.Comment: LaTeX file (uses AA vers. 5.1 class, enclosed), 8 pages, 9 figures.
Accepted for publication in Astronomy & Astrophysics. Also available at
http://www.obs-hp.fr/www/preprints.htm
Miscellaneous observations of active galactic nuclei. II
We observed 37 AGN candidates and classified them on the basis of their
spectroscopic properties; three are confirmed QSOs, one is a BL Lac object,
nine are Seyfert 1 galaxies, four Seyfert 2s, while twenty are HII regions.Comment: LaTeX 2e, 15 pages (4 tables and 9 .eps figures included in text).
Uses L-AA 3.0, epsf.tex and psfig.sty (not included). Accepted to appear in
A&
A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies
We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1
galaxies (NLS1s) or known to have a broad Balmer component narrower than 2000
km/s. Out of these, 19 turned out to have been spectroscopically misidentified
in previous studies; only 64 of the selected objects are genuine NLS1s. We have
spectroscopically observed 59 of them and tried to characterize their Narrow
and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with
Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components
are well fitted by a single Lorentzian profile. This has consequences
concerning their FWHMs and line ratios: when the broad Balmer components are
fitted with a Lorentzian, most narrow line regions have line ratios typical of
Seyfert 2s while, when a Gaussian profile isused for fitting the broad Balmer
components, the line ratios are widely scattered in the usual diagnostic
diagrams (Veilleux & Osterbrock 1987). We find that, in general, the [O III]
lines have a relatively narrow Gaussian profile (~ 200-500 km/s FWHM) with
often, in addition, a second broad (~ 500-1800 km/s FWHM), blueshifted Gaussian
component. We do not confirm that the [O III] lines are weak in NLS1s. As
previously suggested, there is a continuous transition of all properties
between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit
of 2000 km/s used to separate the two species is arbitrary; R_4570, the ratio
of the Fe II to the H_beta fluxes, could be a physically more meaningful
parameter to distinguish them. (abridged abstract)Comment: LaTeX file, 24 pages, 15 figures, uses the new A&A macro (enclosed:
aa5.cls). Figs. 1-5 and 7 are bitmapped; non-bitmapped, high quality figures
are included in the .ps and .pdf versions of the paper, available at
http://www.obs-hp.fr/www/preprints.html. Accepted for publication in
Astronomy & Astrophysic
Empirical Uncertainty Estimators for Astrometry from Digital Databases
In order to understand the positional uncertainties of arbitrary objects in
several of the current major databases containing astrometric information, a
sample of extragalactic radio sources with precise positions in the
International Celestial Reference Frame (ICRF) is compared with the available
positions of their optical counterparts. The discrepancies between the radio
and various optical positions are used to derive empirical uncertainty
estimators for the USNO-A2.0, USNO-A1.0, Guide Star Selection System (GSSS)
images, and the first and second Digitized Sky Surveys (DSS-I and DSS-II). In
addition, an estimate of the uncertainty when the USNO-A2.0 catalog is
transferred to different image data is provided. These optical astrometric
frame uncertainties can in some cases be the dominant error term when
cross-identifying sources at different wavelengths.Comment: 12 pages including 2 figures and 1 table. Accepted for publication in
The Astronomical Journal, October 1999. Values in Table 1 for DSS I corrected
99-07-1
Quasars in the 2MASS Second Incremental Data Release
Using the 2MASS Second Incremental Data Release, we have searched for near
infrared counterparts to 13214 quasars from the Veron-Cetty & Veron(2000)
catalog. We have detected counterparts within 4 arcsec for 2277 of the
approximately 6320 quasars within the area covered by the 2MASS Second
Incremental Data Release. Only 1.6% of these are expected to be chance
coincidences. Though this sample is heterogeneous, we find that known
radio-loud quasars are more likely to have large near-infrared-to-optical
luminosity ratios than radio-quiet quasars are, at a statistically significant
level. This is consistent with dust-reddened quasars being more common in
radio-selected samples than in optically-selected samples, due to stronger
selection effects against dust-reddened quasars in the latter. We also find a
statistically significant dearth of optically luminous quasars with large
near-infrared-to-optical luminosity ratios. This can be explained in a dust
obscuration model but not in a model where synchrotron emission extends from
the radio into the near-infrared and creates such large ratios. We also find
that selection of quasar candidates from the B-J/J-K color-color diagram,
modelled on the V-J/J-K selection method of Warren, Hewett & Foltz (2000), is
likely to be more sensitive to dust-obscured quasars than selection using only
infrared-infrared colors.Comment: To be published in May issue of Astronomical Journal (26 pages, 8
figures, 2 tables) Replaced Figure 6 and
Fabry Perot Halpha Observations of the Barred Spiral NGC 3367
We report the gross properties of the velocity field of the barred spiral
galaxy NGC 3367. The following values were found: inclination with respect to
the plane of the sky, i=30 deg; position angle (PA) of receding semi major axis
PA=51 and systemic velocity V(sys)=3032 km/s. Large velocity dispersion are
observed of upt o 120 km/s in the nuclear region, of up to 70 km/s near the
eastern bright sources just beyond the edge of the stellar bar where three
spiral arms seem to start and in the western bright sources at about 10 kpc.
Deviations from normal circular velocities are observed from all the disk but
mainly from the semi circle formed by the string of south western Halpha
sources. An estimate of the dynamical mass is M(dyn)=2x10^11 Msolar.Comment: Accepted to be published in May 2001 issue in the A.J. 19 pages, 7
figure
Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I.Observational Results
We present optical spectra and emission-line ratios of 12 Narrow-Line Seyfert
1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A
common feature in the EUV continuum of active galactic nuclei is the big blue
bump (BBB), generally associated with thermal accretion disk emission. While
Galactic absorption prevents direct access to the EUV range, it can be mapped
by measuring the strength of a variety of forbidden optical emission lines that
respond to different EUV continuum regions. We find that narrow emission-line
ratios involving [OII]3727, Hbeta, [OIII]5007, [OI]6300, Halpha,[NII]6583, and
[SII]6716,6731 indicate no significant difference between NLS1s and Broad-Line
Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy
distributions of their ionizing EUV - soft X-ray continua are similar. The
relative strength of important forbidden high ionization lines like [NeV]3426
compared to HeII4686 and the relative strength of [FeX]6374 appear to show the
same range as in BLS1 galaxies. However, a trend of weaker
F([OI]6300)/F(Halpha) emission-line ratios is indicated for NLS1s compared to
BLS1s. To recover the broad emission-line profiles we used Gaussian components.
This approach indicates that the broad Hbeta profile can be well described with
a broad component (FWHM = 3275 +- 800 km/s) and an intermediate broad component
(FWHM = 1200 +- 300 km/s). The width of the broad component is in the typical
range of normal BLS1s. The emission-line flux that is associated with the broad
component in these NLS1s amounts to at least 60% of the total flux. Thus it
dominates the total line flux, similar to BLS1 galaxies.Comment: 34 pages, 9 figures. accepted for publication in the
Astrophys.Journa
Spectroscopy and 3D imaging of the Crab nebula
Spectroscopy of the Crab nebula along different slit directions reveals the 3
dimensional structure of the optical nebula. On the basis of the linear radial
expansion result first discovered by Trimble (1968), we make a 3D model of the
optical emission. Results from a limited number of slit directions suggest that
optical lines originate from a complicated array of wisps that are located in a
rather thin shell, pierced by a jet. The jet is certainly not prominent in
optical emission lines, but the direction of the piercing is consistent with
the direction of the X-ray and radio jet. The shell's effective radius is ~ 79
seconds of arc, its thickness about a third of the radius and it is moving out
with an average velocity 1160 km/s.Comment: 21 pages, 14 figures, submitted to ApJ, 3D movie of the Crab nebula
available at http://www.fiz.uni-lj.si/~vidrih
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