102 research outputs found
Faint, Large-scale H-Alpha Filaments in the Milky Way
During the initial data reduction of the Wisconsin H-Alpha Mapper (WHAM)
H-Alpha Sky Survey, we have discovered several very long (~30--80 deg)
filaments superimposed on the diffuse H-Alpha background. These features have
no clear correspondence to the other phases of the interstellar medium revealed
by 21 cm, X-ray, IR, or radio continuum surveys, and they have no readily
identifiable origin or source of ionization. In this letter, the data for two
of these faint (I_{H-Alpha} = 0.5--1.5 R) structures are presented. The first
is an 80 deg-long, 2 deg-wide arch that extends nearly perpendicular to the
Galactic plane at l = 225 deg and attains a maximum latitude of +51 deg near l
= 240 deg. Where this feature appears to meet the Galactic plane near l = 225
deg, it is directly above the H II region surrounding CMa R1/OB1. A second
filament consists of a ~25--30 deg-long arc spanning l = 210--240 deg at b =
+30 deg to +40 deg. Both features have measurable velocity trends with
position. However, they have rather constant intensities along their entire
lengths, ranging from 0.5--1.5 R (EM = 1--3 cm^{-6} pc) with no obvious trends.Comment: 9 pages, 3 figures; Figure 1 is full color PostScript. Accepted for
publication by ApJ Letters. More information on the WHAM project can be found
at http://www.astro.wisc.edu/wham
Radial Velocities of Six OB Stars
We present new results from a radial velocity study of six bright OB stars
with little or no prior measurements. One of these, HD 45314, may be a
long-period binary, but the velocity variations of this Be star may be related
to changes in its circumstellar disk. Significant velocity variations were also
found for HD 60848 (possibly related to nonradial pulsations) and HD 61827
(related to wind variations). The other three targets, HD 46150, HD 54879, and
HD 206183, are constant velocity objects, but we note that HD 54879 has
H emission that may originate from a binary companion. We illustrate
the average red spectrum of each target.Comment: Accepted for publication in PASP July 2007 issu
New Methods for Determining the Ages of PMS Stars
We present three new methods for determining the age of groups of
pre-main-sequence stars. The first, creating empirical isochrones allows us to
create a robust age ordering, but not to derive actual ages. The second, using
the width of the gap in colour-magnitude space between the pre-main-sequence
and main-sequence (the radiative convective gap) has promise as a distance and
extinction independent measure of age, but is as yet uncalibrated. Finally we
discuss tau-squared fitting of the main sequence as the stars approach the
terminus of the main sequence. This method suggests that there is a factor two
difference between these "nuclear" ages, and more conventional
pre-main-sequence contraction ages.Comment: 6 pages, 3 figure
The r-Process Enriched Low Metallicity Giant HD 115444
New high resolution, very high signal-to-noise spectra of ultra-metal-poor
(UMP) giant stars HD 115444 and HD 122563 have been gathered with the
High-Resolution Echelle Spectrometer of the McDonald Observatory 2.7m
Telescope. With these spectra, line identification and model atmosphere
analyses have been conducted, emphasizing the neutron-capture elements. Twenty
elements with Z > 30 have been identified in the spectrum of HD 115444. This
star is known to have overabundances of the neutron-capture elements, but it
has lacked a detailed analysis necessary to compare with nucleosynthesis
predictions. The new study features a line-by-line differential abundance
comparison of HD 115444 with the bright, well-studied halo giant HD 122563. For
HD 115444, the overall metallicity is [Fe/H]~ -3.0. The abundances of the light
and iron-peak elements generally show the same pattern as other UMP stars (e.g.
overdeficiencies of manganese and chromium, overabundances of cobalt), but the
differential analysis indicates several nucleosynthesis signatures that are
unique to each star.Comment: To Appear in the Astrophysical Journa
Optical Light Curve of the Type Ia Supernova 1998bu in M96 and the Supernova Calibration of the Hubble Constant
We present the UBVRI light curves of the Type Ia supernova SN 1998bu which
appeared in the nearby galaxy M96 (NGC 3368). M96 is a spiral galaxy in the Leo
I group which has a Cepheid-based distance. Our photometry allows us to
calculate the absolute magnitude and reddening of this supernova. These data,
when combined with measurements of the four other well-observed supernovae with
Cepheid based distances, allow us to calculate the Hubble constant with respect
to the Hubble flow defined by the distant Calan/Tololo Type Ia sample. We find
a Hubble constant of 64.0 +/- 2.2(internal) +/- 3.5(external) km/s/Mpc,
consistent with most previous estimates based on Type Ia supernovae. We note
that the two well-observed Type Ia supernovae in Fornax, if placed at the
Cepheid distance to the possible Fornax spiral NGC 1365, are apparently too
faint with respect to the Calan/Tololo sample calibrated with the five Type Ia
supernovae with Cepheid distances to the host galaxies.Comment: AAS LaTeX, 20 pages, 4 figures, 6 tables, accepted for publication in
the Astronomical Journal. Figure 1 (finding chart) not include
The Chemical Composition and Age of the Metal-Poor Halo Star BD +17^\circ 3248
We have combined new high-resolution spectra obtained with the Hubble Space
Telescope (HST) and ground-based facilities to make a comprehensive new
abundance analysis of the metal-poor, halo star BD +17^\circ 3248. We have
detected the third r-process peak elements osmium, platinum, and (for the first
time in a metal-poor star) gold, elements whose abundances can only be reliably
determined using HST. Our observations illustrate a pattern seen in other
similar halo stars with the abundances of the heavier neutron-capture elements,
including the third r-process peak elements, consistent with a scaled solar
system r-process distribution. The abundances of the lighter neutron-capture
elements, including germanium and silver, fall below that same scaled solar
r-process curve, a result similar to that seen in the ultra-metal-poor star CS
22892--052. A single site with two regimes or sets of conditions, or perhaps
two different sites for the lighter and heavier neutron-capture elements, might
explain the abundance pattern seen in this star. In addition we have derived a
reliable abundance for the radioactive element thorium. We tentatively identify
U II at 3859 A in the spectrum of BD +17^\circ 3248, which makes this the
second detection of uranium in a very metal-poor halo star. Our combined
observations cover the widest range in proton number (from germanium to
uranium) thus far of neutron-capture elements in metal-poor Galactic halo
stars. Employing the thorium and uranium abundances in comparison with each
other and with several stable elements, we determine an average
cosmochronological age for BD +17^\circ 3248 of 13.8 +/- 4 Gyr, consistent with
that found for other similar metal-poor halo stars.Comment: 58 pages, 4 tables, 11 figures; To appear in ApJ Typo correcte
Differential inflammasome activation predisposes to acute-on-chronic liver failure in human and experimental cirrhosis with and without previous decompensation
OBJECTIVE Systemic inflammation predisposes acutely
decompensated (AD) cirrhosis to the development of
acute-on-chronic liver failure (ACLF). Supportive treatment
can improve AD patients, becoming recompensated. Little is
known about the outcome of patients recompensated after
AD. We hypothesise that different inflammasome activation
is involved in ACL F development in compensated and
recompensated patients.
DESIGN 249 patients with cirrhosis, divided into
compensated and recompensated (previous AD), were
followed prospectively for fatal ACL F development. Two
external cohorts (n=327) (recompensation, AD and ACL F)
were included. Inflammasome-driving interleukins (ILs),
IL-1α (caspase-4/11-dependent) and IL-1β (caspase-1-
dependent), were measured. In rats, bile duct ligationinduced cirrhosis and lipopolysaccharide exposition were
used to induce AD and subsequent recompensation.
IL-1α and IL-1β levels and upstream/downstream gene
expression were measured.
RESULTS Patients developing ACL F showed higher
baseline levels of ILs. Recompensated patients and
patients with detectable ILs had higher rates of ACL F
development than compensated patients. Baseline
CLIF-C (European Foundation for the study of chronic
liver failure consortium) AD, albumin and IL-1α
were independent predictors of ACL F development
in compensated and CLIF-C AD and IL-1β in
recompensated patients. Compensated rats showed
higher IL-1α gene expression and recompensated rats
higher IL-1β levels with higher hepatic gene expression.
Higher IL-1β detection rates in recompensated patients
developing ACL F and higher IL-1α and IL-1β detection
rates in patients with ACL F were confirmed in the two
external cohorts.
CONCLUSION Previous AD is an important risk factor
for fatal ACL F development and possibly linked with
inflammasome activation. Animal models confirmed
the results showing a link between ACL F development
and IL-1α in compensated cirrhosis and IL-1β in
recompensated cirrhosi
The Distances to Open Clusters from Main-Sequence Fitting. IV. Galactic Cepheids, the LMC, and the Local Distance Scale
We derive the basic properties of seven Galactic open clusters containing
Cepheids and construct their period-luminosity (P-L) relations. For our cluster
main-sequence fitting we extend previous Hyades-based empirical
color-temperature corrections to hotter stars using the Pleiades as a template.
We use BVI_{C}JHK_{s} data to test the reddening law, and include metallicity
effects to perform a more comprehensive study for our clusters than prior
efforts. The ratio of total to selective extinction R_V that we derive is
consistent with expectations. Assuming the LMC P-L slopes, we find =
-3.93 +/- 0.07 (statistical) +/- 0.14 (systematic) for 10-day period Cepheids,
which is generally fainter than those in previous studies. Our results are
consistent with recent HST and Hipparcos parallax studies when using the
Wesenheit magnitudes W(VI). Uncertainties in reddening and metallicity are the
major remaining sources of error in the V-band P-L relation, but a higher
precision could be obtained with deeper optical and near-infrared cluster
photometry. We derive distances to NGC4258, the LMC, and M33 of (m - M)_0 =
29.28 +/- 0.10, 18.34 +/- 0.06, and 24.55 +/- 0.28, respectively, with an
additional systematic error of 0.16 mag in the P-L relations. The distance to
NGC4258 is in good agreement with the geometric distance derived from water
masers [\Delta (m - M)_0 = 0.01 +/- 0.24]; our value for M33 is less consistent
with the distance from an eclipsing binary [\Delta (m - M)_0 = 0.37 +/- 0.34];
our LMC distance is moderately shorter than the adopted distance in the HST Key
Project, which formally implies an increase in the Hubble constant of 7% +/-
8%.Comment: 28 pages, 21 figures; accepted for publication in the Ap
Relation between the luminosity of young stellar objects and their circumstellar environment
We present a new model-independent method of comparison of NIR visibility
data of YSOs. The method is based on scaling the measured baseline with the
YSO's distance and luminosity, which removes the dependence of visibility on
these two variables. We use this method to compare all available NIR visibility
data and demonstrate that it distinguishes YSOs of luminosity >1000L_sun
(low-L) from YSOs of <1000L_sun (high-L). This confirms earlier suggestions,
based on fits of image models to the visibility data, for the difference
between the NIR sizes of these two luminosity groups. When plotted against the
``scaled'' baseline, the visibility creates the following data clusters: low-L
Herbig Ae/Be stars, T Tauri stars, and high-L Herbig Be stars. The T Tau
cluster is similar to the low-L Herbig Ae/Be cluster, which has ~7 times
smaller ``scaled'' baselines than the high-L Herbig Be cluster. We model the
shape and size of clusters with different image models and find that low-L
Herbig stars are the best explained by the uniform brightness ring and the halo
model, T Tauri stars with the halo model, and high-L Herbig stars with the
accretion disk model. However, the plausibility of each model is not well
established. Therefore, we try to build a descriptive model of the
circumstellar environment consistent with various observed properties of YSOs.
We argue that low-L YSOs have optically thick disks with the optically thin
inner dust sublimation cavity and an optically thin dusty outflow above the
inner disk regions. High-L YSOs have optically thick accretion disks with high
accretion rates enabling gas to dominate the NIR emission over dust. Although
observations would favor such a description of YSOs, the required dust
distribution is not supported by our current understanding of dust dynamics.Comment: 20 pages, 12 figures, Accepted for publication in the Astrophysical
Journa
Why are the K dwarfs in the Pleiades so Blue?
The K dwarfs in the Pleiades fall nearly one half magnitude below a main
sequence isochrone when plotted in a color-magnitude diagram utilizing V
magnitude as the luminosity index and B-V as the color index. This peculiarity
has been known for forty years but has gone unexplained and mostly ignored.
When compared to Praesepe members, the Pleiades K dwarfs again are subluminous
(or blue) in a color-magnitude diagram using B-V as the color index. However,
using V-I as the color index, stars in the two clusters are coincident to M_V ~
10; using V-K as the color index, Pleiades late K and M stars fall above the
main sequence locus defined by Praesepe members. We believe that the anomalous
spectral energy distributions for the Pleiades K dwarfs, as compared to older
clusters, are a consequence of rapid stellar rotation and may be primarily due
to spottedness. If so, the required areal filling factor for the cool component
has to be very large (=> 50%). Weak-lined T Tauri stars have similar color
anomalies, and we suspect this is a common feature of all very young K dwarfs
(sp. type > K3). The peculiar spectral energy distribution needs to be
considered in deriving accurate pre-main sequence isochrone-fitting ages for
clusters like the Pleiades since the age derived will depend on the temperature
index used.Comment: 41 pages, 15 figures, AASTeX5.0. Accepted 05 May 2003; Scheduled for
publication in the Astronomical Journal (August 2003
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