64 research outputs found
A Rich Cluster of Galaxies Near the Quasar B2 1335+28 at z=1.1: Color Distribution and Star-Formation Properties
We previously reported a significant clustering of red galaxies (R-K=3.5--6)
around the radio-loud quasar B2 1335+28 at z=1.086. In this paper, we establish
the existence of a rich cluster at the quasar redshift, and study the
properties of the cluster galaxies through further detailed analysis of the
photometric data. The color distribution of the galaxies in the cluster is
quite broad and the fraction of blue galaxies (\sim 70%) is much larger than in
intermediate-redshift clusters. Using evolutionary synthesis models, we show
that this color distribution can be explained by galaxies with various amounts
of star-formation activity mixed with the old stellar populations. Notably,
there are about a dozen galaxies which show very red optical-NIR colors but
also show significant UV excess with respect to passive-evolution models. They
can be interpreted as old early-type galaxies with a small amount of star
formation. The fact that the UV-excess red galaxies are more abundant than the
quiescent red ones suggests that a large fraction of old galaxies in this
cluster are still forming stars to some extent. However, a sequence of
quiescent red galaxies is clearly identified on the R-K versus K
color-magnitude (C-M) diagram. The slope and zero point of their C-M relation
appear to be consistent with those expected for the precursors of the C-M
relation of present-day cluster ellipticals when observed at z=1.1. We estimate
the Abell richness class of the cluster to be R \sim 1. New X-ray data
presented here place an upper limit of L_x < 2 10^{44} erg s^{-1} for the
cluster luminosity. Inspections of the wider optical images reveal some lumpy
structure, suggesting that the whole system is still dynamically young.Comment: 54 pages including 13 Postscript figures, 1 jpg figure, and 1 table,
uses aasms4.sty and epsf.sty. Accepted for publication in ApJ: Replaced as
the older verison was missed to include the figure 2c, 2d, and figure
Asiago eclipsing binaries program. I. V432 Aur
The orbit and physical parameters of the previously unsolved eclipsing binary
V432 Aur, discovered by Hipparcos, have been derived with errors better than 1%
from extensive Echelle spectroscopy and B, V photometry. Synthetic spectral
analysis of both components has been performed, yielding T_eff and log g in
close agreement with the orbital solution, a metallicity [Z/Z_sun]=-0.60 and
rotational synchronization for both components. Direct comparison on the
theoretical L, T_eff plane with the Padova evolutionary tracks and isochrones
for the masses of the two components (1.22 and 1.08 M_sun) provides a perfect
match and a 3.75 Gyr age. The more massive and cooler component is approaching
the base of the giant branch and displays a probable pulsation activity with an
amplitude of Delta V = 0.075 mag and Delta rad.vel. = 1.5 km/sec. With a T_eff
= 6080 K it falls to the red of the nearby instability strip populated by delta
Sct and gamma Dor types of pulsating variables. Orbital modeling reveals a
large and bright surface spot on it. The pulsations activity and the large
spot(s) suggest the presence of macro-turbulent motions in its atmosphere. They
reflect in a line broadening that at cursory inspection could be taken as
indication of a rotation faster than synchronization, something obviously odd
for an old, expanding star.Comment: A&A, 11 pages, accepted Jan 7, 200
MOA-2009-BLG-387Lb: A massive planet orbiting an M dwarf
We report the discovery of a planet with a high planet-to-star mass ratio in
the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations
over a 12-day interval, one of the longest for any planetary event. The host is
an M dwarf, with a mass in the range 0.07 M_sun < M_host < 0.49M_sun at 90%
confidence. The planet-star mass ratio q = 0.0132 +- 0.003 has been measured
extremely well, so at the best-estimated host mass, the planet mass is m_p =
2.6 Jupiter masses for the median host mass, M = 0.19 M_sun. The host mass is
determined from two "higher order" microlensing parameters. One of these, the
angular Einstein radius \theta_E = 0.31 +- 0.03 mas, is very well measured, but
the other (the microlens parallax \pi_E, which is due to the Earth's orbital
motion) is highly degenate with the orbital motion of the planet. We
statistically resolve the degeneracy between Earth and planet orbital effects
by imposing priors from a Galactic model that specifies the positions and
velocities of lenses and sources and a Kepler model of orbits. The 90%
confidence intervals for the distance, semi-major axis, and period of the
planet are 3.5 kpc < D_L < 7.9 kpc, 1.1 AU < a < 2.7AU, and 3.8 yr < P < 7.6
yr, respectively.Comment: 20 pages including 8 figures. A&A 529 102 (2011
The Spectral Energy Distribution of Fermi bright blazars
(Abridged) We have conducted a detailed investigation of the broad-band
spectral properties of the \gamma-ray selected blazars of the Fermi LAT Bright
AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray
spectra with Swift, radio, infra-red, optical and other hard X-ray/gamma-ray
data, collected within three months of the LBAS data taking period, we were
able to assemble high-quality and quasi-simultaneous Spectral Energy
Distributions (SED) for 48 LBAS blazars.The SED of these gamma-ray sources is
similar to that of blazars discovered at other wavelengths, clearly showing, in
the usual Log - Log F representation, the typical broad-band
spectral signatures normally attributed to a combination of low-energy
synchrotron radiation followed by inverse Compton emission of one or more
components. We have used these SEDs to characterize the peak intensity of both
the low and the high-energy components. The results have been used to derive
empirical relationships that estimate the position of the two peaks from the
broad-band colors (i.e. the radio to optical and optical to X-ray spectral
slopes) and from the gamma-ray spectral index. Our data show that the
synchrotron peak frequency is positioned between 10 and
10 Hz in broad-lined FSRQs and between and Hz in
featureless BL Lacertae objects.We find that the gamma-ray spectral slope is
strongly correlated with the synchrotron peak energy and with the X-ray
spectral index, as expected at first order in synchrotron - inverse Compton
scenarios. However, simple homogeneous, one-zone, Synchrotron Self Compton
(SSC) models cannot explain most of our SEDs, especially in the case of FSRQs
and low energy peaked (LBL) BL Lacs. (...)Comment: 85 pages, 38 figures, submitted to Ap
8--13 um spectroscopy of YSOs: Evolution of the silicate feature
In order to investigate possible connections between dust processing and disk
properties, 8--13 um spectra of 34 young stars, with a range of circumstellar
environments and spectral types A to M, were obtained using the Long Wavelength
Spectrometer at the W. M. Keck Observatory. The broad 9.7 um amorphous silicate
feature which dominates this wavelength regime evolves from absorption in
young, embedded sources, to emission in optically revealed stars, and to
complete absence in older debris disk systems for both low- and
intermediate-mass stars. The peak wavelength and FWHM are centered about 9.7
and ~2.3 um, corresponding to amorphous olivine, with a larger spread in FWHM
for embedded sources and in peak wavelength for disks. In a few of our objects
that have been previously identified as class I low-mass YSOs, the observed
silicate feature is complex, with absorption near 9.5 um and emission peaking
around 10 um. Although most of the emission spectra show broad classical
features attributed to amorphous silicates, variations in the shape/strength
may be linked to dust processing, including grain growth and/or silicate
crystallization. We study quantitatively the evidence for evolutionary trends
in the 8--13 um spectra through a variety of spectral shape diagnostics. Based
on the lack of correlation between these diagnostics and broad-band infrared
luminosity characteristics for silicate emission sources, we conclude that
although spectral signatures of dust processing are present, they can not be
connected clearly to disk evolutionary stage (for optically thick disks) or
optical depth (for optically thin disks). The diagnostics of silicate
absorption features (other than the central wavelength of the feature),
however, are tightly correlated with optical depth.Comment: 27 pages, 13 figures, accepted for publication by ApJ, formatted with
emulateapj using revtex4 v4.
A very young star forming region detected by the ISOPHOT Serendipity Survey
We present a multi-wavelength study of the star forming region ISOSS J
20298+3559, which was identified by a cross-correlation of cold compact sources
from the 170 micron ISOPHOT Serendipity Survey (ISOSS) database coinciding with
objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J
20298+3559 is associated with a massive dark cloud complex (M ~ 760
M) and located in the Cygnus X giant molecular cloud. We derive a
distance of 1800 pc on the basis of optical extinction data. The low average
dust temperature (T ~ 16 K) and large mass (M ~ 120 M) of the dense
inner part of the cloud, which has not been dispersed, indicates a recent begin
of star formation. The youth of the region is supported by the early
evolutionary stage of several pre- and protostellar objects discovered across
the regio n: I) Two candidate Class 0 objects with masses of 8 and 3.5
M, II) a gravitationally bound, cold (T ~ 12 K) and dense (n(H)
\~ 2 x 10 cm) cloud core with a mass of 50 M and III) a
Herbig B2 star with a mass of 6.5 M and a bolometric luminosity of
2200 L, showing evidence for ongoing accretion and a stellar age of
less than 40000 years. The dereddened SED of the Herbig star is well reproduced
by an accretion disc + star model. The externally heated cold cloud core is a
good candidate for a massive pre-protostellar object. The star formation
efficiency in the central cloud region is about 14 %.Comment: 14 pages, 14 figures, 7 tables. Accepted for publication in Astronomy
& Astrophysic
Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71. I. Simultaneous broadband observations during November 2003
Some intra-day variable, compact extra-galactic radio sources show brightness
temperatures severely exceeding 10^{12} K, the limit set by catastrophic
inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation.
The violation of the IC limit, possible under non-stationary conditions, would
lead to IC avalanches in the soft-gamma-ray energy band during transient
periods. For the first time, broadband signatures of possible IC catastrophes
were searched for in S5 0716+71. A multifrequency observing campaign targetting
S5 0716+71 was carried out in November 2003 under the framework of the European
Network for the Investigation of Galactic nuclei through Multifrequency
Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope
(WEBT), involving a pointing by the soft-gamma-ray satellite INTEGRAL, optical,
near-infrared, sub-millimeter, millimeter, radio, and Very Long Baseline Array
(VLBA) monitoring. S5 0716+71 was very bright at radio frequencies and in a
rather faint optical state during the INTEGRAL pointing; significant inter-day
and low intra-day variability was recorded in the radio regime, while typical
fast variability features were observed in the optical band. No correlation was
found between the radio and optical emission. The source was not detected by
INTEGRAL, neither by the X-ray monitor JEM-X nor by the gamma-ray imager ISGRI,
but upper limits to the source emission in the 3-200 keV energy band were
estimated. A brightness temperature Tb>2.1x10^{14} K was inferred from the
radio variability, but no corresponding signatures of IC avalanches were
recorded at higher energies. The absence of IC-catastrophe signatures provides
either a lower limit delta>8 to the Doppler factor affecting the radio emission
or strong constraints for modelling of the Compton catastrophes in S5 0716+71.Comment: 15 pages, 3 EPS figures, 3 tables, to appear in A&
The comet Halley dust and gas environment
Quantitative descriptions of environments near the nucleus of comet P /Halley have been developed to support spacecraft and mission design for the flyby encounters in March, 1986. To summarize these models as they exist just before the encounters, we review the relevant data from prior Halley apparitions and from recent cometary research. Orbital elements, visual magnitudes, and parameter values and analysis for the nucleus, gas and dust are combined to predict Halley's position, production rates, gas and dust distributions, and electromagnetic radiation field for the current perihelion passage. The predicted numerical results have been useful for estimating likely spacecraft effects, such as impact damage and attitude perturbation. Sample applications are cited, including design of a dust shield for spacecraft structure, and threshold and dynamic range selection for flight experiments. We expect that the comet's activity may be more irregular than these smoothly varying models predict, and that comparison with the flyby data will be instructive.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43774/1/11214_2004_Article_BF00175326.pd
Optimierung des Duesenauftragsverfahrens - Messtechnische Erfassung des Strichbildes beim Auftrag der Streichfarbe mittels Freistrahlduese Abschlussbericht
SIGLEAvailable from TIB Hannover: F04B554 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekArbeitsgemeinschaft Industrieller Forschungsvereinigungen 'Otto von Guericke' e.V. (AIF), Koeln (Germany)DEGerman
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