40,042 research outputs found
A high excitation HII region in the faint dwarf elliptical galaxy A0951+68
We present the results of BVRI imaging and optical spectroscopy of the dwarf
galaxy A0951+68. The images reveal that, although this galaxy is classified as
a dwarf elliptical, it has some properties that are similar to dwarf irregular
galaxies. It contains two bright knots of emission, one of which is red and
unresolved and the other blue and resolved. The blue knot also shows a high
excitation emission line spectrum. The observed line ratios indicate that this
is an HII region, although with some line ratios that are border-line with
those in AGN. The emission line luminosity is consistent with ionisation by a
single, very luminous O star, or several smaller O stars, but the extended blue
light in the knot shows that this has occurred as part of a substantial recent
star formation event. We find that the metal abundance, while low compared to
typical large galaxies, actually seems to be high for such a low luminosity
dwarf. The position of A0951 in the literature is incorrect and we provide the
correct value.Comment: 8 pages, Latex, 4 encapsulated postscript figures included, 1
separate JPEG figure; to be published in Monthly Notice
On the dust tori in Palomar-Green quasars
The dust clouds in the torus of the quasar are irradiated by the central
source, and the clouds at the inner radius of the torus re-radiate mostly in
the near-infrared (NIR) wavebands. The ratio of the near-infrared luminosity to
the bolometric luminosity L_NIR/L_bol can therefore reflect the torus geometry
to some extent. We find a significant correlation between the ratio of the
near-infrared luminosity to the bolometric luminosity L_NIR/L_bol and the
central black hole mass M_bh for the Palomar-Green(PG) quasars, whereas no
correlation is found between the Eddington ratio L_bol/L_Edd and the ratio
L_NIR/L_bol. Similar correlations are found for the mid-infrared and
far-infrared cases. It may imply that the torus geometry, i.e., the solid angle
subtended by the dust torus as seen from the central source, does not evolve
with the accretion rate. The correlation of the solid angle subtended by the
torus with the central black hole mass M_bh implies that the formation of the
dust torus is likely regulated by the central black hole mass. We find that the
torus thickness H increases with quasar bolometric luminosities, which is
different from the constant torus thickness H with luminosity assumed in the
receding torus model. The mean covering factor of the dust clouds at the inner
radius of the torus derived from the IR emission data is ~0.39 for PG quasars.
The average relative thickness H/R of the tori in the PG quasars derived from
the ratios of the infrared to bolometric luminosities is ~0.9. We suggest that
the further IR observations on a larger quasar sample including more fainter
quasars by the Spitzer Space Telescope will help understand the physics of the
dust tori in quasars.Comment: The incorrect V-magnitude used for 1351+640 is fixed, the main
conclusions are not changed, accepted for publication in Ap
The Apollo 17 mare basalts: Serenely sampling Taurus-Littrow
As we are all aware, the Apollo 17 mission marked the final manned lunar landing of the Apollo program. The lunar module (LM) landed approximately 0.7 km due east of Camelot Crater in the Taurus-Littrow region on the southwestern edge of Mare Serenitatis. Three extravehicular activities (EVA's) were performed, the first concentrating around the LM and including station 1 approximately 1.1 km south-southeast of the LM at the northwestern edge of Steno Crater. The second traversed approximately 8 km west of the LM to include stations 2, 3, 4, and 5, and the third EVA traversed approximately 4.5 km to the northwest of the LM to include stations 6, 7, 8, and 9. This final manned mission returned the largest quantity of lunar rock samples, 110.5 kg/243.7 lb, and included soils, breccias, highland samples, and mare basalts. This abstract concentrates upon the Apollo 17 mare basalt samples
Using Apollo 17 high-Ti mare basalts as windows to the lunar mantle
The Apollo 17 high-Ti mare basalts are derived from source regions containing plagioclase that was not retained in the residue. Ilmenite appears to remain as a residual phase, but plagioclase is exhausted. The open-system behavior of the type B2 basalts results in slightly higher Yb/Hf and La/Sm ratios. The nature of the added component is not clear, but may be a KREEP derivative or residue. The recognition of plagioclase in the source(s) of these basalts suggests that the location of the source region(s) would be more likely to be less than 150 km (i.e., closer to the plagioclase-rich crust), which would allow incorporation of plagioclase into the source through incomplete separation of crustal feldspar
Wanted: Lunar detectives to unravel the mysteries of the Moon! Crime to be solved: Mass extinctions on the Moon by meteorite impact!
The criteria and clues for identifying meteorite contamination are outlined to aid in the quest for more knowledge regarding the evolution of the Moon and the early Earth. The Warren and Wasson seven criteria for establishing the pristine nature of highland rocks are presented. Other topics covered include iron/nickel metals, monomict nature, and lunar glasses. The major conclusion is that pristinity should not be the primary consideration in the study of lunar rocks. The most important criterion to establish is whether or not the lunar sample contains more than one lunar rock type. Even if a sample is non-pristine, as long as only one lunar rock type is present, petrogenetic interpretation can still be carried out
Home monitoring of foot skin temperatures to prevent ulceration
OBJECTIVE - To evaluate the effectiveness of at-home infrared temperature monitoring as a preventative tool in individuals at high risk for diabetes-related lower-extremity ulceration and amputation. RESEARCH DESIGN AND METHODS - Eighty-five patients who fit diabetic foot risk category 2 or 3 (neuropathy and foot deformity or previous history of ulceration or partial foot amputation) were randomized into a standard therapy group (n = 41) or an enhanced therapy group (n = 44). Standard therapy consisted of therapeutic footwear, diabetic foot education, and regular foot evaluation by a podiatrist. Enhanced therapy included the addition of a handheld infrared skin thermometer to measure temperatures on the sole of the foot in the morning and evening. Elevated temperatures (>4°F compared with the opposite foot) were considered to be "at risk" of ulceration due to inflammation at the site of measurement. When foot temperatures were elevated, subjects were instructed to reduce their activity and contact the study nurse. Study subjects were followed for 6 months. RESULTS - The enhanced therapy group had significantly fewer diabetic foot complications (enhanced therapy group 2% vs. standard therapy group 20%, P = 0.01, odds ratio 10.3, 95% CI 1.2-85.3). There were seven ulcers and two Charcot fractures among standard therapy patients and one ulcer in the enhanced therapy group. CONCLUSIONS - These results suggest that at-home patient self-monitoring with daily foot temperatures may be an effective adjunctive tool to prevent foot complications in individuals at high risk for lower-extremity ulceration and amputation
Optical and X-ray Variability in The Least Luminous AGN, NGC4395
We report the detection of optical and X-ray variability in the least
luminous known Seyfert galaxy, NGC4395. The featureless continuum changed by a
factor of 2 in 6 months, which is typical of more luminous AGN. The largest
variation was seen at shorter wavelengths, so that the spectrum becomes
`harder' during higher activity states. In a one week optical broad band
monitoring program, a 20% change was seen between successive nights. In a 1
month period the spectral shape changed from a power law with spectral index
alpha ~0 (characteristic of quasars) to a spectral index alpha ~2 (as observed
in other dwarf AGN). ROSAT HRI and PSPC archive data show a variable X-ray
source coincident with the galactic nucleus. A change in X-ray flux by a factor
\~2 in 15 days has been observed. When compared with more luminous AGN, NGC4395
appears to be very X-ray quiet. The hardness ratio obtained from the PSPC data
suggests that the spectrum could be absorbed. We also report the discovery of
weak CaIIK absorption, suggesting the presence of a young stellar cluster
providing of the order of 10% of the blue light. Using HST UV archive data,
together with the optical and X-ray observations, we examine the spectral
energy distribution for NGC4395 and discuss the physical conditions implied by
the nuclear activity under the standard AGN model. The observations can be
explained by either an accreting massive black hole emitting at about 10^(-3)
L_(Edd) or by a single old compact SNR with an age of 50 to 500 yr generated by
a small nuclear starburst.Comment: 19 pages, 9 figures, to appear in MNRA
- …