225 research outputs found
Infrared ground-based astronomy with the Hughes 256 X 256 PtSi array
It is shown that large format PtSi Schottky diode infrared arrays, the Hughes 256 X 256 hybrid Schottky array in particular, are competitive alternatives to the smaller format photovoltaic arrays for ground-based astronomy. The modest quantum efficiency of the PtSi compared to the photovoltaic devices is more than compensated for by the larger format. The use of hybrid technology yields effective fill factors of nearly 100 percent, and the low dark current, noise, excellent imaging characteristics, cost, and solid nitrogen operating temperature add to the effectiveness of this array for ground-based imaging. In addition to discussing the characteristics of this array, researchers present laboratory test data and astronomical results achieved at Kitt Peak
Recommended from our members
A qualitative, cross cultural examination of attitudes and behaviour in relation to cooking habits in France and Britain
Food campaigners, policy makers, journalists and academics continue to debate an alleged decline in home cooking, a corresponding increase in individualised eating habits and the impact of such trends upon public health. The focus of this research was to examine and compare current domestic food practices in Britain with those of another country, namely France. In-depth interviews with 27 members of the public drawn from both countries enabled the researchers to explore people’s actual cooking practices in the home. Analysis of the data revealed that respondents from both countries often lacked time to cook and increasingly relied on a mix of both raw and convenience-type foods to varying degrees. A range of cooking skills was employed in the home, although confidence in relation to cooking was more varied with the French respondents who demonstrated a greater willingness to ‘cook from scratch’. There was some evidence of men on both sides of The Channel engaging with cooking in the home although this often formed part of a leisure activity undertaken at weekends and for special occasions
Extragalactic infrared spectroscopy
The spectra of galaxies in the near infrared atmospheric transmission windows are explored. Emission lines were detected due to molecular hydrogen, atomic hydrogen recombination lines, a line attributed to FEII, and a broad CO absorption feature. Lines due to H2 and FEII are especially strong in interacting and merging galaxies, but they were also detected in Seyferts and normal spirals. These lines appear to be shock excited. Multi-aperture measurements show that they emanate from regions as large as 15 kpc. It is argued that starbursts provide the most plausible and consistent model for the excitation of these lines, but the changes of relative line intensity of various species with aperture suggest that other excitation mechanisms are also operating in the outer regions of these galaxies
The Optical/Near-IR Colors of Broad Absorption Line Quasars, Including the Candidate Radio-Loud BAL Quasar 1556+3517
A candidate radio-loud broad absorption line quasar (RLBAL) has been reported
by Becker et al. (1997). We present JHK observations of this object and three
other radio-detected BALs taken with the new Michigan-Dartmouth-MIT/Ohio
State/Aladdin IR Camera (MOSAIC) on the KPNO 4-meter. The candidate RLBAL
1556+3517 has B-K=6.63, redder than all but one or two known z>1 quasars. This
strongly suggests the observed continuum of this quasar is reddened by dust.
Even when this extreme reddening is taken into account 1556+3517 is still
probably radio-loud, although near-IR spectroscopy to measure its Balmer
decrement will be needed to verify this. In addition, since it is a
flat-spectrum object, VLBI observations to determine the extent (if any) to
which beaming affects our estimate of its radio luminosity will be needed
before 1556+3517 can be unequivocally declared a radio-loud BAL. We also use
our data and data from the literature to show that optically selected BALs as a
class have B-K colors consistent with the observed distribution for optically
selected quasars as a whole. Thus there is currently no evidence that the
tendency of optically selected BALs to be preferentially radio-intermediate
(Hooper, Francis, & Impey 1993) is due to extinction artificially lowering
estimated BAL optical luminosities. However, as most quasar surveys, both radio
and optical, would be insensitive to a population of reddened radio-quiet BALs,
the existence of a large population of reddened BALs similar to 1556+3517
cannot yet be ruled out.Comment: Accepted to ApJ Letters; 10 pages including 1 figure and 2 tables.
This version somewhat revised from initial submission, with a better figur
An analysis of likes and dislikes for history and geography of 3360 sixth grade children
Thesis (Ed.M.)--Boston Universit
Accretion Disk Evolution With Wind Infall I. General Solution and Application to Sgr A*
The evolution of an accretion disk can be influenced significantly by the
deposition of mass and angular momentum by an infalling Bondi-Hoyle wind. Such
a mass influx impacts the long-term behavior of the disk by providing
additional sources of viscosity and heating. In this paper, we derive and solve
the disk equations when these effects are taken into account. We present a
survey of models with various wind configurations and demonstrate that the disk
spectrum may then differ substantially from that of a standard alpha-disk. In
particular, it is likely that a wind-fed disk has a significant infrared bump
due to the deposition of energy in its outer region. We apply some of the
results of our calculations to the Galactic Center black hole candidate Sgr A*
and show that if a fossil disk is present in this source, it must have a very
low viscosity parameter (alpha<10^-4) and the Bondi-Hoyle wind must be
accreting with a very high specific angular momentum to prevent it from
circularizing in the inner disk region where its impact would be most
noticeable.Comment: accepted for The Astrophysical Journal, AAS LaTex, 20 pages, also
available at http://www.astro.umd.edu/~hfalcke/publications.html#wintercep
NH3 in the Central 10 pc of the Galaxy I: General Morphology and Kinematic Connections Between the CND and GMCs
New VLA images of NH3 (1,1), (2,2), and (3,3) emission in the central 10
parsecs of the Galaxy trace filamentary streams of gas, several of which appear
to feed the circumnuclear disk (CND). The NH3 images have a spatial resolution
of 16.5''x14.5'' and have better spatial sampling than previous NH3
observations. The images show the ``southern streamer,'' ``50 km/s cloud,'' and
new features including a ``western streamer'', 6 parsecs in length, and a
``northern ridge'' which connects to the CND. NH3(3,3) emission is very similar
to 1.2 mm dust emission indicating that NH3 traces column density well. Ratios
of the NH3(2,2) to (1,1) line intensities give an estimate of the temperature
of the gas and indicate high temperatures close to the nucleus and CND. The new
data cover a velocity range of 270 km/s, including all velocities observed in
the CND, with a resolution of 9.8 km/s. Previous NH3 observations with higher
resolution did not cover the entire range of velocities seen in the CND. The
large-scale kinematics of the CND do not resemble a coherent ring or disk. We
see evidence for a high velocity cloud within a projected distance of 50'' (2
pc) which is only seen in NH3(3,3) and is likely to be hot. Comparison to 6 cm
continuum emission reveals that much of the NH3 emission traces the outer edges
of Sgr A East and was probably pushed outward by this expanding shell. The
connection between the northern ridge (which appears to be swept up by Sgr A
East) and the CND indicates that Sgr A East and the CND are in close proximity
to each other. Kinematic evidence for these connections is presented in this
paper, while the full kinematic analysis of the central 10 pc will be presented
in Paper II.Comment: 16 pages (containing 6 figures), 8 additional JPEG figures. Accepted
for publication in ApJ. For full resolution images, see
http://cfa-www.harvard.edu/~rmcgary/SGRA/nh3_figures.htm
Spitzer IRAC Observations of Star Formation in N159 in the LMC
We present observations of the giant HII region complex N159 in the LMC using
IRAC on the {\it Spitzer Space Telescope}. One of the two objects previously
identified as protostars in N159 has an SED consistent with classification as a
Class I young stellar object (YSO) and the other is probably a Class I YSO as
well, making these two stars the youngest stars known outside the Milky Way. We
identify two other sources that may also be Class I YSOs. One component,
N159AN, is completely hidden at optical wavelengths, but is very prominent in
the infrared. The integrated luminosity of the entire complex is L L, consistent with the observed radio emission assuming a
normal Galactic initial mass function (IMF). There is no evidence for a red
supergiant population indicative of an older burst of star formation. The N159
complex is 50 pc in diameter, larger in physical size than typical HII regions
in the Milky Way with comparable luminosity. We argue that all of the
individual components are related in their star formation history. The
morphology of the region is consistent with a wind blown bubble $\approx
1-2Myr-old that has initiated star formation now taking place at the rim. Other
than its large physical size, star formation in N159 appears to be
indistinguishable from star formation in the Milky Way.Comment: 14 figure
Infalling Gas Towards the Galactic Center
VLA maps of ammonia emission were made for the Galactic Center region. The
NH3(1,1) and NH3(2,2) transitions were observed in three 2' x 2' fields
covering Sgr A* and the region 3' immediately south of it. In the central 3
parsecs surrounding Sgr A* we find emission which appears to be associated with
the circumnuclear disk (CND), both morphologically and kinematically. This
central emission is connected to a long, narrow 2 pc x 10 pc streamer of clumpy
molecular gas located towards the south, which appears to be carrying gas from
the nearby 20 km/s giant molecular cloud (GMC) to the circumnuclear region. We
find a velocity gradient along the streamer, with progressively higher
velocities as the gas approaches Sgr A*. The streamer stops at the location of
the CND, where the line width of the NH3 emission increases dramatically. This
may be the kinematic signature of accretion onto the CND. The ratio of the
NH3(2,2)/NH3(1,1) emission indicates that the gas is heated at the northern tip
of the streamer, located inside the eastern edge of the CND. The morphology,
kinematics and temperature gradients of the gas all indicate that the southern
streamer is located at the Galactic Center and is interacting with the
circumnuclear region.Comment: 11 pages, 10 figures, accepted by The Astrophysical Journal (figure 1
contours have been corrected
- …