94 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
Submillimeter observing conditions on Cerro Chajnantor
Consistently superb observing conditions are crucial for achieving the scientific objectives of a ground based telescope. For observations at submillimeter wavelengths, choosing a site with very little atmospheric water vapor is paramount. In northern Chile, the high Andes near San Pedro de Atacama are among the highest and driest places on Earth. At the 5000 m Chajnantor plateau, long term measurements have demonstrated observing conditions are excellent for submillimeter astronomy. Even better conditions prevail on higher mountain peaks in the vicinity. For the CCAT, we have selected a candidate site at 5612 m near the summit of Cerro Chajnantor. Radiosonde measurements, meteorological data, and measurements of the 350 Consistently superb observing conditions are crucial for achieving the scientific objectives of a ground based telescope. For observations at submillimeter wavelengths, choosing a site with very little atmospheric water vapor is paramount. In northern Chile, the high Andes near San Pedro de Atacama are among the highest and driest places on Earth. At the 5000 m Chajnantor plateau, long term measurements have demonstrated observing conditions are excellent for submillimeter astronomy. Even better conditions prevail on higher mountain peaks in the vicinity. For the CCAT, we have selected a candidate site at 5612 m near the summit of Cerro Chajnantor. Radiosonde measurements, meteorological data, and measurements of the 350 μm transparency all indicate submillimeter observing conditions are consistently better at the CCAT site than at the plateau. transparency all indicate submillimeter observing conditions are consistently better at the CCAT site than at the plateau
First Science Results From SOFIA/FORCAST: Super-Resolution Imaging of the S140 Cluster at 37\micron
We present 37\micron\ imaging of the S140 complex of infrared sources
centered on IRS1 made with the FORCAST camera on SOFIA. These observations are
the longest wavelength imaging to resolve clearly the three main sources seen
at shorter wavelengths, IRS 1, 2 and 3, and are nearly at the diffraction limit
of the 2.5-m telescope. We also obtained a small number of images at 11 and
31\micron\ that are useful for flux measurement. Our images cover the area of
several strong sub-mm sources seen in the area -- SMM 1, 2, and 3 -- that are
not coincident with any mid-infrared sources and are not visible in our longer
wavelength imaging either. Our new observations confirm previous estimates of
the relative dust optical depth and source luminosity for the components in
this likely cluster of early B stars. We also investigate the use of
super-resolution to go beyond the basic diffraction limit in imaging on SOFIA
and find that the van Cittert algorithm, together with the "multi-resolution"
technique, provides excellent results
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
TEDI: the TripleSpec Exoplanet Discovery Instrument
The TEDI (TripleSpec - Exoplanet Discovery Instrument) will be the first
instrument fielded specifically for finding low-mass stellar companions. The
instrument is a near infra-red interferometric spectrometer used as a radial
velocimeter. TEDI joins Externally Dispersed Interferometery (EDI) with an
efficient, medium-resolution, near IR (0.9 - 2.4 micron) echelle spectrometer,
TripleSpec, at the Palomar 200" telescope. We describe the instrument and its
radial velocimetry demonstration program to observe cool stars.Comment: 6 Pages, To Appear in SPIE Volume 6693, Techniques and
Instrumentation for Detection of Exoplanets II
Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. I. Physical Conditions in the X-ray Absorbers
We present a detailed analysis of the intrinsic X-ray absorption in the
Seyfert 1 galaxy NGC 4151 using Chandra/HETGS data obtained 2002 May, as part
of a program which included simultaneous UV spectra using HST/STIS and FUSE.
NGC 4151 was in a relatively low flux state during the observations reported
here, although roughly 2.5 times as bright in the 2 --10 keV band as during a
Chandra observation in 2000. The soft X-ray band was dominated by emission
lines, which show no discernible variation in flux between the two
observations. The 2002 data show the presence of a very highly ionized
absorber, in the form of H-like and He-like Mg, Si, and S lines, as well as
lower ionization gas via the presence of inner-shell absorption lines from
lower-ionization species of these elements. The former is too highly ionized to
be radiatively accelerated in a sub-Eddington source such as NGC 4151. We find
that the lower ionization gas had a column density a factor of ~ 3 higher
during the 2000 observation. If due to bulk motion, we estimate that this
component must have a velocity of more than 1250 km/sec transverse to our
line-of-sight. We suggest that these results are consistent with a
magneto-hydrodynamic flow.Comment: 42 pages, 14 figures. Accepted for publication in The Astrophysical
Journa
Observations of the Crab Nebula and its pulsar in the far-ultraviolet and in the optical
We present HST/STIS far-UV observations of the Crab nebula and its pulsar.
Broad, blueshifted absorption arising in the nebula is seen in C IV 1550,
reaching about 2500 km/s. This can be interpreted as evidence for a fast outer
shell, and we adopt a spherically symmetric model to constrain the properties
of this. We find that the density appears to decrease outward in the shell. A
lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy
of 1.5EE{49} ergs. A massive 10^{51} erg shell cannot be excluded, but is less
likely if the density profile is much steeper than R^{-4} and the velocity is
<6000 km/s. The observations cover the region 1140-1720 A. With the time-tag
mode of the spectrograph we obtain the pulse profile. It is similar to that in
the near-UV, although the primary peak is marginally narrower. Together with
the near-UV data, and new optical data from NOT, our spectrum of the pulsar
covers the entire region from 1140-9250 A. Dereddening the spectrum gives a
flat spectrum for E(B-V)=0.52, R=3.1. This dereddened spectrum of the Crab
pulsar can be fitted by a power law with spectral index alpha_{\nu} = 0.11 +/-
0.04. The main uncertainty is the amount and characteristics of the interstel-
lar reddening, and we have investigated the dependence of \alpha_{\nu} on
E(B-V) and R. In the extended emission covered by our 25" x 0.5" slit in the
far-UV, we detect C IV 1550 and He II 1640 emission lines from the Crab nebula.
Several interstellar absorption lines are detected toward the pulsar. The Ly
alpha absorption indicates a column density of 3.0+/-0.5\EE{21} cm^{-2} of
neutral hydrogen, which agrees well with our estimate of E(B-V)=0.52 mag. Other
lines show no evidence of severe depletion of metals in atomic gas.Comment: 18 pages emulateapj style, including 10 figures. ApJ, accepte
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