854 research outputs found
ALFA & 3D: integral field spectroscopy with adaptive optics
One of the most important techniques for astrophysics with adaptive optics is
the ability to do spectroscopy at diffraction limited scales. The extreme
difficulty of positioning a faint target accurately on a very narrow slit can
be avoided by using an integral field unit, which provides the added benefit of
full spatial coverage. During 1998, working with ALFA and the 3D integral field
spectrometer, we demonstrated the validity of this technique by extracting and
distinguishing spectra from binary stars separated by only 0.26". The
combination of ALFA & 3D is also ideally suited to imaging distant galaxies or
the nuclei of nearby ones, as its field of view can be changed between
1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution
we present new results both on galactic targets, namely young stellar objects,
as well as extra-galactic objects including a Seyfert and a starburst nucleus.Comment: SPIE meeting 4007 on Adaptive Optical Systems Technology, March 200
Experimental philosophy leading to a small scale digital data base of the conterminous United States for designing experiments with remotely sensed data
Research using satellite remotely sensed data, even within any single scientific discipline, often lacked a unifying principle or strategy with which to plan or integrate studies conducted over an area so large that exhaustive examination is infeasible, e.g., the U.S.A. However, such a series of studies would seem to be at the heart of what makes satellite remote sensing unique, that is the ability to select for study from among remotely sensed data sets distributed widely over the U.S., over time, where the resources do not exist to examine all of them. Using this philosophical underpinning and the concept of a unifying principle, an operational procedure for developing a sampling strategy and formal testable hypotheses was constructed. The procedure is applicable across disciplines, when the investigator restates the research question in symbolic form, i.e., quantifies it. The procedure is set within the statistical framework of general linear models. The dependent variable is any arbitrary function of remotely sensed data and the independent variables are values or levels of factors which represent regional climatic conditions and/or properties of the Earth's surface. These factors are operationally defined as maps from the U.S. National Atlas (U.S.G.S., 1970). Eighty-five maps from the National Atlas, representing climatic and surface attributes, were automated by point counting at an effective resolution of one observation every 17.6 km (11 miles) yielding 22,505 observations per map. The maps were registered to one another in a two step procedure producing a coarse, then fine scale registration. After registration, the maps were iteratively checked for errors using manual and automated procedures. The error free maps were annotated with identification and legend information and then stored as card images, one map to a file. A sampling design will be accomplished through a regionalization analysis of the National Atlas data base (presently being conducted). From this analysis a map of homogeneous regions of the U.S.A. will be created and samples (LANDSAT scenes) assigned by region
Stellar Dynamics and the implications on the merger evolution in NGC6240
We report near-infrared integral field spectroscopy of the luminous merging
galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by
1.6arcsec are the central parts of inclined, rotating disk galaxies with equal
mass bulges. The dynamical masses of the nuclei are much larger than the
stellar mass derived from the K-band light, implying that the progenitor
galaxies were galaxies with massive bulges. The K-band light is dominated by
red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years
ago, possibly by the most recent perigalactic approach. Strong feedback effects
of a superwind and supernovae are responsible for a short duration burst
(~5x10^6 years) which is already decaying. The two galaxies form a
prograde-retrograde rotating system and from the stellar velocity field it
seems that one of the two interacting galaxies is subject to a prograde
encounter. Between the stellar nuclei is a prominent peak of molecular gas
(H_2, CO). The stellar velocity dispersion peaks there indicating that the gas
has formed a local, self-gravitating concentration decoupled from the stellar
gravitational potential. NGC 6240 has previously been reported to fit the
paradigm of an elliptical galaxy formed through the merger of two galaxies.
This was based on the near-infrared light distribution which follows a
r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far
not relaxed, rotation plays an important role, as does self-gravitating gas,
and the near-infrared light is dominated by young stars.Comment: 34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the
Astrophysical Journal, revised versio
Haemophilus influenzae type b and Streptococcus pneumoniae as causes of pneumonia among children in Beijing, China.
To determine if Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae could be identified more often from the nasopharynx of patients with pneumonia than from control patients, we obtained nasopharyngeal swab specimens from 96 patients with chest x-ray-confirmed pneumonia and 214 age-matched control patients with diarrhea or dermatitis from the outpatient department at Beijing Children's Hospital. Pneumonia patients were more likely to be colonized with Hib and S. pneumoniae than control patients, even after the data were adjusted for possible confounding factors such as day-care attendance, the presence of other children in the household, and recent antibiotic use. In China, where blood cultures from pneumonia patients are rarely positive, the results of these nasopharyngeal cultures provide supporting evidence for the role of Hib and S. pneumoniae as causes of childhood pneumonia
NICMOS Imaging of Infrared-Luminous Galaxies
We present near-infrared images obtained with the HST NICMOS camera for a
sample of 9 luminous (LIGs: L_IR (8-1000 microns) >~ 10^11 L_sun) and 15
ultra-luminous (ULIGS: L_IR >~ 10^12 L_sun) infrared galaxies. The sample
includes representative systems classified as warm (f_25/f_60 > 0.2) and cold
(f_25/f_60 <~ 0.2) based on the mid-infrared colors and systems with nuclear
emission lines classified as HII (i.e. starburst), QSO, Seyfert and LINER. The
morphologies of the sample galaxies are diverse and provide further support for
the idea that they are created by the collision or interactions of spiral
galaxies. Although no new nuclei are seen in the NICMOS images, the NICMOS
images do reveal new spiral structures, bridges, and circumnuclear star
clusters...Comment: LaTex, 27 pages with 14 gif and 4 jpg figures, AJ, in press, contour
figures of the NICMOS images can be viewed at
http://nedwww.ipac.caltech.edu/level5/Scoville/frames.htm
Discovery of a nuclear gas bar feeding the active nucleus in Circinus
We report the discovery of gas inflow motions towards the active nucleus of
the Circinus galaxy caused by the non-axisymmetric potential of a nuclear gas
bar. Evidence for dust associated with the bar comes from the HST/NICMOS H-K
color map, whereas the streaming motions along the gas bar are seen in the
velocity field of the H2 S(1)(1-0) emission line. The gas bar is about 100 pc
long with a visual extinction in excess of 10 mag. Indication for the gaseous
nature of this bar comes from the lack of a stellar counterpart even in the K
band where the extinction is greatly reduced.
We also use the NICMOS emission line images (Pa-alpha, [SiVI], and [FeII]) to
study the innermost region of the ionization cones and the nuclear star forming
activity. We discuss the possible relationship of these components with the
gaseous bar.Comment: 14 pages, 7 figures (3 color plates), accepted for publication in Ap
The Stellar Cusp Around the Supermassive Black Hole in the Galactic Center
We analyze deep near-IR adaptive optics imaging as well as new proper motion
data of the nuclear star cluster of the Milky Way. The surface density
distribution of faint stars peaks within 0.2" of the black hole candidate
SgrA*. The radial density distribution of this stellar 'cusp' follows a power
law of exponent 1.3-1.4. The K-band luminosity function of the overall nuclear
stellar cluster (within 9" of SgrA*) resembles that of the large scale,
Galactic bulge, but shows an excess of stars at K<14.
We find that most of the massive early type stars at distances 1-10" from
SgrA* are located in two rotating and geometrically thin disks. These disks are
inclined at large angles and counter-rotate with respect to each other. Their
stellar content is essentially the same, indicating that they formed at the
same time.
The star closest to SgrA* in 2002, S2, exhibits a 3.8 micron excess. We
propose that the mid-IR emission either comes from the accretion flow around
the black hole itself, or from dust in the accretion flow that is heated by the
ultra-violet emission of S2.Comment: 59 pages, 18 figure
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