2,519 research outputs found
Eclipsing Binaries in the OGLE Variable Star Catalogs.V. Long-Period Beta Lyrae-type Systems in the Small Magellanic Cloud and the PLC-beta Relation
Thirty eight long-period (P>10 days), apparently contact binary stars
discovered by the OGLE-II project in the SMC appear to be Beta Lyrae-type
systems with ellipsoidal variations of the cool components dominating over
eclipse effects in the systemic light variations and in the total luminosity. A
new period-luminosity- color (PLC) relation has been established for these
systems; we call it the PLC-beta relation, to distinguish it from the Cepheid
relation. Two versions of the PLC-beta relation - based on the (B-V)0 or (V-I)0
color indices - have been calibrated for 33 systems with (V-I)0>0.25 spanning
the orbital period range of 11 to 181 days. The relations can provide
maximum-light, absolute-magnitude estimates accurate to epsilon-M_V~0.35 mag.
within the approximate range -3<M_V<+1. In terms of their number in the SMC,
the long-period Beta Lyrae-type binaries are about 50 times less common than
the Cepheids. Nevertheless, their large luminosities coupled with continuous
light variations make these binaries very easy to spot in nearby galaxies, so
that the PLC-beta relation can offer an auxiliary and entirely independent
method of distance determination to nearby stellar systems rich in massive
stars. The sample of the long-period Beta Lyrae systems in the SMC analyzed in
this paper is currently the best defined and uniform known sequence of such
binaries.Comment: submitted for publication in Astronomical Journal; 8 PS figures, 2
table
Millimetre-VLBI Monitoring of AGN with Sub-milliarcsecond Resolution
Global millimetre VLBI allows detailed studies of the most central jet
regions of AGN with unprecedent spatial resolution of a few 100-1000
Schwartzschild radii to be made. Study of these regions will help to answer the
question how the highly relativistic AGN jets are launched and collimated.
Since the early 1990s, bright mm-sources have been observed with global 3 mm
VLBI. Here we present new images from an ongoing systematic analysis of the
available observations. In particular, we focus on the structure and structural
evolution of the best observed AGN jets, taking 3C 454.3 as a characteristic
example. This core-dominated and highly variable quasar shows a complex
morphology with individual jet components accelerating superluminally towards
the outer structure. We briefly discuss the X-ray properties of 3C 454.3 and
present its radio- to X-ray large-scale brightness distribution.Comment: 4 pages, 4 figures, Proceedings of the 7th EVN Symposium held in
Toledo, Spain in October 2004, needs evn2004.cl
The Low CO Content of the Extremely Metal Poor Galaxy I Zw 18
We present sensitive molecular line observations of the metal-poor blue
compact dwarf I Zw 18 obtained with the IRAM Plateau de Bure interferometer.
These data constrain the CO J=1-0 luminosity within our 300 pc (FWHM) beam to
be L_CO < 1 \times 10^5 K km s^-1 pc^2 (I_CO < 1 K km s^-1), an order of
magnitude lower than previous limits. Although I Zw 18 is starbursting, it has
a CO luminosity similar to or less than nearby low-mass irregulars (e.g. NGC
1569, the SMC, and NGC 6822). There is less CO in I Zw 18 relative to its
B-band luminosity, HI mass, or star formation rate than in spiral or dwarf
starburst galaxies (including the nearby dwarf starburst IC 10). Comparing the
star formation rate to our CO upper limit reveals that unless molecular gas
forms stars much more efficiently in I Zw 18 than in our own galaxy, it must
have a very low CO-to-H_2 ratio, \sim 10^-2 times the Galactic value. We detect
3mm continuum emission, presumably due to thermal dust and free-free emission,
towards the radio peak.Comment: 5 pages in emulateapj style, accepted by the Astrophysical Journa
Preemption in the Rehnquist and Roberts Courts: An Empirical Analysis
This article presents an empirical analysis of the Rehnquist Courtâs and the Roberts Courtâs decisions on the federal (statutory) preemption of state law. In addition to raw outcomes for or against preemption, we examine cases by subject-matter, level of judicial consensus, tort versus regulatory preemption, party constellation, and origin in state or federal court. We present additional data and analysis on the role of state amici and of the U.S. Solicitor General in preemption cases, and we examine individual justicesâ voting records. Among our findings, one stands out: over time and especially under the Roberts Court, lawyerly preemption questions have assumed a distinctly ideological flavor. Preemption cases are much more likely to be contested than they were in earlier decades; and in those cases, once-rare judicial bloc voting has become common
Interferometric Observations of Powerful CO Emission from the three Submillimeter Galaxies at z=2.30, 2.51 and 3.35
We report IRAM Plateau de Bure, millimeter interferometry of three z=~2.4 to
3.4, SCUBA deep field galaxies. Our CO line observations confirm the rest-frame
UV/optical redshifts, thus more than doubling the number of confirmed,
published redshifts of the faint submillimeter population and proving their
high-z nature. In all three sources our measurements of the intrinsic gas and
dynamical mass are large (1e10 to 1e11 Msun). In at least two cases the data
show that the submillimeter sources are part of an interacting system. Together
with recent information gathered in the X-ray, optical and radio bands our
observations support the interpretation that the submm-population consists of
gas rich (gas to dynamical mass ratio ~0.5) and massive, composite
starburst/AGN systems, which are undergoing a major burst of star formation and
are evolving into m*-galaxies.Comment: only minor modifications to comply with the ApJL edition rule
Lens magnification by CL0024+1654 in the U and R band
[ABRIDGED] We estimate the total mass distribution of the galaxy cluster
CL0024+1654 from the measured source depletion due to lens magnification in the
R band. Within a radius of 0.54Mpc/h, a total projected mass of
(8.1+/-3.2)*10^14 M_sol/h (EdS) is measured, which corresponds to a mass-
to-light ratio of M/L(B)=470+/-180. We compute the luminosity function of
CL0024+1654 in order to estimate contamination of the background source counts
from cluster galaxies. Three different magnification-based reconstruction
methods are employed using both local and non-local techniques. We have
modified the standard single power-law slope number count theory to incorporate
a break and applied this to our observations. Fitting analytical magnification
profiles of different cluster models to the observed number counts, we find
that the cluster is best described either by a NFW model with scale radius
r_s=334+/-191 kpc/h and normalisation kappa_s=0.23+/-0.08 or a power-law
profile with slope xi=0.61+/-0.11, central surface mass density
kappa_0=1.52+/-0.20 and assuming a core radius of r_core=35 kpc/h. The NFW
model predicts that the cumulative projected mass contained within a radius R
scales as M(<R)=2.9*10^14*(R/1')^[1.3-0.5lg (R/1')] M_sol/h. Finally, we have
exploited the fact that flux magnification effectively enables us to probe
deeper than the physical limiting magnitude of our observations in searching
for a change of slope in the U band number counts. We rule out both a total
flattening of the counts with a break up to U_AB<=26.6 and a change of slope,
reported by some studies, from dlog N/dm=0.4->0.15 up to U_AB<=26.4 with 95%
confidence.Comment: 19 pages, 12 figures, submitted to A&A. New version includes more
robust U band break analysis and contamination estimates, plus new plot
Chemically Distinct Nuclei and Outflowing Shocked Molecular Gas in Arp 220
We present the results of interferometric spectral line observations of Arp
220 at 3.5mm and 1.2mm from the Plateau de Bure Interferometer (PdBI), imaging
the two nuclear disks in HCN and , HCO and , and HNC as well as SiO and , HCN, and SO. The gas traced by SiO
has a complex and extended kinematic signature including a prominent P Cygni
profile, almost identical to previous observations of HCO. Spatial
offsets north and south of the continuum centre in the emission and
absorption of the SiO P Cygni profile in the western nucleus (WN)
imply a bipolar outflow, delineating the northern and southern edges of its
disk and suggesting a disk radius of pc, consistent with that found by
ALMA observations of Arp 220. We address the blending of SiO and
HCO by considering two limiting cases with regards to the
HCO emission throughout our analysis. Large velocity gradient (LVG)
modelling is used to constrain the physical conditions of the gas and to infer
abundance ratios in the two nuclei. Our most conservative lower limit on the
[HCN]/[HCO] abundance ratio is 11 in the WN, cf. 0.10 in the
eastern nucleus (EN). Comparing these ratios to the literature we argue on
chemical grounds for an energetically significant AGN in the WN driving either
X-ray or shock chemistry, and a dominant starburst in the EN.Comment: 28 pages, 17 figures, accepted to Ap
Low and intermediate-mass close binary evolution and the initial - final mass relation
Using Eggleton's stellar evolution code, we carry out 150 runs of Pop I
binary evolution calculations, with the initial primary mass between 1 and 8
solar masses the initial mass ratio between 1.1 and 4, and the onset of Roche
lobe overflow (RLOF) at an early, middle, or late Hertzsprung-gap stage. We
assume that RLOF is conservative in the calculations, and find that the remnant
mass of the primary may change by more than 40 per cent over the range of
initial mass ratio or orbital period, for a given primary mass. This is
contrary to the often-held belief that the remnant mass depends only on the
progenitor mass if mass transfer begins in the Hertzsprung gap. We fit a
formula, with an error less than 3.6 per cent, for the remnant (white dwarf)
mass as a function of the initial mass of the primary, the initial mass ratio,
and the radius of the primary at the onset of RLOF. We also find that a
carbon-oxygen white dwarf with mass as low as 0.33 solar masses may be formed
if the primary's initial mass is around 2.5 solar masses.Comment: 7 pages for main text, 11 pages for appendix (table A1), 12 figure
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