529 research outputs found
Detection of a Hot Binary Companion of Carinae
We report the detection of a hot companion of Carinae using high
resolution spectra (905 - 1180 \AA) obtained with the Far Ultraviolet
Spectroscopic Explorer (\fuse) satellite. Observations were obtained at two
epochs of the 2024-day orbit: 2003 June during ingress to the 2003.5 X-ray
eclipse and 2004 April several months after egress. These data show that
essentially all the far-UV flux from \etacar shortward of \lya disappeared at
least two days before the start of the X-ray eclipse (2003 June 29), implying
that the hot companion, \etaB, was also eclipsed by the dense wind or extended
atmosphere of \etaA. Analysis of the far-UV spectrum shows that \etaB is a
luminous hot star. The \nii \wll1084-1086 emission feature suggests that it may
be nitrogen-rich. The observed far-UV flux levels and spectral features,
combined with the timing of their disappearance, is consistent with \etacar\
being a massive binary system
Cepheid Masses: FUSE Observations of S Mus
S Mus is the Cepheid with the hottest known companion. The large ultraviolet
flux means that it is the only Cepheid companion for which the velocity
amplitude could be measured with the echelle mode of the HST GHRS.
Unfortunately, the high temperature is difficult to constrain at wavelengths
longer than 1200 \AA because of the degeneracy between temperature and
reddening. We have obtained a FUSE spectrum in order to improve the
determination of the temperature of the companion. Two regions which are
temperature sensitive near 16,000 K but relatively unaffected by H
absorption (940 \AA, and the Ly wings) have been identified. By
comparing FUSE spectra of S Mus B with spectra of standard stars, we have
determined a temperature of 17,000 500 K. The resultant Cepheid mass is
6.0 0.4 M. This mass is consistent with main sequence
evolutionary tracks with a moderate amount of convective overshoot.Comment: accepted to Ap
Optimality Properties of a Proposed Precursor to the Genetic Code
We calculate the optimality of a doublet precursor to the canonical genetic
code with respect to mitigating the effects of point mutations and compare our
results to corresponding ones for the canonical genetic code. We find that the
proposed precursor has much less optimality than that of the canonical code.
Our results render unlikely the notion that the doublet precursor was an
intermediate state in the evolution of the canonical genetic code. These
findings support the notion that code optimality reflects evolutionary
dynamics, and that if such a doublet code originally had a biochemical
significance, it arose before the emergence of translation
Properties and Spatial Distribution of Dust Emission in the Crab Nebula
The nature and quantity of dust produced in supernovae (SNe) is still poorly understood. Recent IR observations of freshly-formed dust in supernova remnants (SNRs) have yielded significantly lower dust masses than predicted by theoretical models and observations high-redshift galaxies. The Crab Nebula's pulsar wind is thought to be sweeping up freshly-formed SN dust along with the SN ejecta. The evidence for this dust was found in the form of an IR bump in the integrated spectrum of the Crab and in extinction against the synchrotron nebula that revealed the presence of dust in the filament cores. We present the first spatially-resolved emission spectra of dust in the Crab Nebula acquired with the Spitzer Space Telescope. The IR spectra are dominated by synchrotron emission and show forbidden line emission from both sides of the expanding nebula, including emission from [S III], [Si II], [Ne II], [Ne III], [Ne V], [Ar III], [Ar V], [Fe II], and [Ni II]. We extrapolated a synchrotron spectral data cube from the Spitzer 3.6 and 4.5 micron images, and subtracted this contribution from our 15-40 micron spectral data to produce a map of the residual continuum emission from dust. The emission appears to be concentrated along the ejecta filaments and is well described by astronomical silicates at an average temperature of 65 K. The estimated mass of dust in the Crab Nebula is 0.008 solar masses
Serodiagnosis of infectious mononucleosis by using recombinant Epstein-Barr virus antigens and enzyme-linked immunosorbent assay technology
Four recombinant, diagnostically useful Epstein-Barr virus (EBV) proteins representative of the viral capsid antigen (p150), diffuse early antigen (p54), the major DNA-binding protein (p138), and the EBV nuclear antigen (p72) (W. Hinderer, H. Nebel-Schickel, H.H. Sonneborn, M. Motz, R. KĂĽhbeck, and H. Wolf, J. Exp. Clin. Cancer Res. 7[Suppl.]:132, 1988) were used to set up individual enzyme-linked immunosorbent assays (ELISAs) for the qualitative and quantitative detection of immunoglobulin M (IgM) and IgG antibodies. In direct comparison with results obtained by standard immunofluorescence or immunoperoxidase assays, it was then shown that the recombinant EBV ELISAs provide the means for specific and sensitive serodiagnosis of infectious mononucleosis (IM) caused by EBV. The most useful markers in sera from such patients proved to be IgM antibodies against p54, p138, and p150. Additional positive markers for recent or ongoing IM apparently were IgG antibodies against p54 and p138. In contrast, anti-p72 IgG had a high preference for sera from healthy blood donors and, therefore, can be considered indicative of past exposure to the virus. Altogether, the individual ELISAs proved to be as specific and at least as sensitive for the diagnosis of IM as the currently available standard techniques are. Moreover, our findings suggest that, by combining individual test antigens, a workable ELISA system consisting of three assays (IgM against p54, p138, and p150; IgG against p54 and p138; and IgG against p72) can be established for the standardized rapid diagnosis of acute EBV infections
Physical Conditions in Circumstellar Gas surrounding SN 1987A 12 Years After Outburst
Two-dimensional spectra of Supernova 1987A were obtained on 1998 November
14-15 (4282 days after outburst) with the Space Telescope Imaging Spectrograph
(STIS) on board the Hubble Space Telescope (HST). The slit sampled portions of
the inner circumstellar ring at the east and west ansae as well as small
sections of both the northern and southern outer rings. The temperature and
density at these locations are estimated by nebular analysis of [N II], [O
III], and [S II] emission line ratios, and with time-dependent
photoionization/recombination models. The results from these two methods are
mutually consistent. The electron density in the inner ring is ~ 4000 cm-3 for
S II, with progressively lower densities for N II and O III. The electron
temperatures determined from [N II] and [O III] line ratios are ~11,000 K and
\~22,000 K, respectively. These results are consistent with evolutionary trends
in the circumstellar gas from similar measurements at earlier epochs. We find
that emission lines from the outer rings come from gas of lower density (n_e
\la 2000 cm-3) than that which emits the same line in the inner ring. The N/O
ratio appears to be the same in all three rings. Our results also suggest that
the CNO abundances in the northern outer ring are the same as in the inner
ring, contrary to earlier results of Panagia et al. (1996). Physical conditions
in the southern outer ring are less certain because of poorer signal-to-noise
data. The STIS spectra also reveal a weak Ha emission redshifted by ~100 km s-1
at p.a. 103\arcdeg that coincides with the recently discovered new regions that
are brightening (Lawrence et al. 2000). This indicates that the shock
interaction in the SE section of the inner ring commenced over a year before it
became apparent in HST images.Comment: 25 pages, 6 figures, to appear in December 1, 2000 Astrophysical
Journa
Observations and simulations of nova Vul 1984 no. 2: A nova with ejecta rich in oxygen, neon, and magnesium
Nova Vul 1984 no. 2 was observed with IUE from Dec. 1984 through Nov. 1987. The spectra are characterized by strong lines from Mg, Ne, C, Si, O, N, and other elements. Data obtained in the ultraviolet, infrared, and optical show that this nova is ejecting material rich in oxygen, neon, and magnesium
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