17,748 research outputs found
Reference models for thermospheric NO
Nitric oxide has been measured with an ultraviolet spectrometer on the polar-orbiting satellite Solar Mesosphere Explorer (SME) for the period January 1982 to August 1986. The nitric oxide database contains densities at all latitudes sorted into 5 degree bins and at altitudes between 100 and 140 km sorted into 3.3 km-bins. The largest densities occur at latitudes in the auroral zones where the density varies as a function of geomagnetic activity. Variations of a factor of 10 occur between times of intense activity and quiet times. At low latitudes, the nitric oxide density at 110 km varies from a mean value of 3 times 10(exp 7) molecules per cubic cm in January 1982 to a mean value of 4 times 10(exp 6) molecules per cubic cm during solar minimum conditions in 1986. In addition, the low-latitude nitric oxide density varies plus or minus 50 percent with a period of 27 days during times of high solar activity
No Evidence for [O III] Variability in Mrk 142
Using archival data from the 2008 Lick AGN Monitoring Project, Zhang & Feng
(2016) claimed to find evidence for flux variations in the narrow [O III]
emission of the Seyfert 1 galaxy Mrk 142 over a two-month time span. If
correct, this would imply a surprisingly compact size for the narrow-line
region. We show that the claimed [O III] variations are merely the result of
random errors in the overall flux calibration of the spectra. The data do not
provide any support for the hypothesis that the [O III] flux was variable
during the 2008 monitoring period.Comment: Response to Zhang & Feng 2016, MNRAS Letters, 457, L64
(arXiv:1512.07673). Accepted for publication in MNRAS Letters. 5 pages, 2
figure
Iron Emission in the z=6.4 Quasar SDSS J114816.64+525150.3
We present near-infrared J and K-band spectra of the z = 6.4 quasar SDSS
J114816.64+525150.3 obtained with the NIRSPEC spectrograph at the Keck-II
telescope, covering the rest-frame spectral regions surrounding the C IV 1549
and Mg II 2800 emission lines. The iron emission blend at rest wavelength
2900-3000 A is clearly detected and its strength appears nearly
indistinguishable from that of typical quasars at lower redshifts. The Fe II /
Mg II ratio is also similar to values found for lower-redshift quasars,
demonstrating that there is no strong evolution in Fe/alpha broad-line emission
ratios even out to z=6.4. In the context of current models for iron enrichment
from Type Ia supernovae, this implies that the SN Ia progenitor stars formed at
z > 10. We apply the scaling relations of Vestergaard and of McLure & Jarvis to
estimate the black hole mass from the widths of the C IV and Mg II emission
lines and the ultraviolet continuum luminosity. The derived mass is in the
range (2-6)x10^9 solar masses, with an additional uncertainty of a factor of 3
due to the intrinsic scatter in the scaling relations. This result is in
agreement with the previous mass estimate of 3x10^9 solar masses by Willott,
McLure, & Jarvis, and supports their conclusion that the quasar is radiating
close to its Eddington luminosity.Comment: To appear in ApJ Letter
Intermediate-mass Black Holes in Galactic Nuclei
We present the first homogeneous sample of intermediate-mass black hole
candidates in active galactic nuclei. Starting with broad-line active nuclei
from the Sloan Digital Sky Survey, we use the linewidth-luminosity-mass scaling
relation to select a sample of 19 galaxies in the mass range M_BH ~ 8 x 10^4 -
10^6 solar masses. In contrast to the local active galaxy population, the host
galaxies are ~1 mag fainter than M* and thus are probably late-type systems.
The active nuclei are also faint, with M_g ~ -15 to -18 mag, while the
bolometric luminosities are close to the Eddington limit. The spectral
properties of the sample are compared to the related class of objects known as
narrow-line Seyfert 1 galaxies. We discuss the importance of our sample as
observational analogues of primordial black holes, contributors to the
integrated signal for future gravitational wave experiments, and as a valuable
tool in the calibration of the M-sigma relation.Comment: 4 pages, 4 figures. To appear in "The Interplay among Black Holes,
Stars and ISM in Galactic Nuclei," Proc. IAU 222 (Gramado, Brazil), eds Th.
Storchi Bergmann, L.C. Ho, H.R. Schmit
Stellar Velocity Dispersion and Black Hole Mass in the Blazar Markarian 501
The recently discovered correlation between black hole mass and stellar
velocity dispersion provides a new method to determine the masses of black
holes in active galaxies. We have obtained optical spectra of Markarian 501, a
nearby gamma-ray blazar with emission extending to TeV energies. The stellar
velocity dispersion of the host galaxy, measured from the calcium triplet lines
in a 2"x3.7" aperture, is 372 +/- 18 km/s. If Mrk 501 follows the M-sigma
correlation defined for local galaxies, then its central black hole has a mass
of (0.9-3.4)x10^9 solar masses. This is significantly larger than some previous
estimates for the central mass in Mrk 501 that have been based on models for
its nonthermal emission. The host galaxy luminosity implies a black hole of
6x10^8 solar masses, but this is not in severe conflict with the mass derived
from the M-sigma relation because the M_BH-L_bulge correlation has a large
intrinsic scatter. Using the emission-line luminosity to estimate the
bolometric luminosity of the central engine, we find that Mrk 501 radiates at
an extremely sub-Eddington level of L/L_Edd ~ 10^-4. Further applications of
the M-sigma relation to radio-loud active galactic nuclei may be useful for
interpreting unified models and understanding the relationship between radio
galaxies and BL Lac objects.Comment: To appear in ApJ Letters. 5 pages, 2 figure
A digitalized solar ultraviolet spectrum
Digitalized solar ultraviolet spectrum obtained in rocket experiments for use in analysis of upper atmosphere experiment
Model for Cumulative Solar Heavy Ion Energy and Linear Energy Transfer Spectra
A probabilistic model of cumulative solar heavy ion energy and LET spectra is developed for spacecraft design applications. Spectra are given as a function of confidence level, mission time period during solar maximum and shielding thickness. It is shown that long-term solar heavy ion fluxes exceed galactic cosmic ray fluxes during solar maximum for shielding levels of interest. Cumulative solar heavy ion fluences should therefore be accounted for in single event effects rate calculations and in the planning of space missions
Ultraviolet spectroscopy of planets
Spectroscopy of planetary ultraviolet radiation - Rayleigh scattering and electron excitatio
High-resolution observation of the Venus dayglow spectrum 1250-1430 angstroms
The spectrum of the dayglow of Venus between 1250 and 1430 A was measured in high resolution with the International Ultraviolet Explorer. Seven exposures which were made with the short wavelength camera in the high dispersion mode using the large aperture were combined to give a total exposure time of 309 min. The atomic oxygen lines at 1302.2, 1304.9, 1306.0, and 1355.6 A are present. In addition, the (14,3) and (14,4) bands of the carbon monoxide fourth positive system at 1317 and 1354 A respectively are identified. These bands are compared with synthetic spectra, showing the excitation mechanism to be fluorescent scattering of solar Lyman alpha radiation
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