464,931 research outputs found
Sky coverage modeling for the whole sky for laser guide star multiconjugate adaptive optics
The scientific productivity of laser guide star adaptive optics systems strongly depends on the sky coverage, which describes the probability of finding natural guide stars for the tip/tilt wavefront sensor(s) to achieve a certain performance. Knowledge of the sky coverage is also important for astronomers planning their observations. In this paper, we present an efficient method to compute the sky coverage for the laser guide star multiconjugate adaptive optics system, the Narrow Field Infrared Adaptive Optics System (NFIRAOS), being designed for the Thirty Meter Telescope project. We show that NFIRAOS can achieve more than 70% sky coverage over most of the accessible sky with the requirement of 191 nm total rms wavefront
A simple model to interpret the ultraviolet, optical and infrared SEDs of galaxies
We present a simple, largely empirical but physically motivated model, which
is designed to interpret consistently multi-wavelength observations from large
samples of galaxies in terms of physical parameters, such as star formation
rate, stellar mass and dust content. Our model is both simple and versatile
enough to allow the derivation of statistical constraints on the star formation
histories and dust contents of large samples of galaxies using a wide range of
ultraviolet, optical and infrared observations. We illustrate this by deriving
median-likelihood estimates of a set of physical parameters describing the
stellar and dust contents of local star-forming galaxies from the Spitzer
Infrared Nearby Galaxy Sample (SINGS) and from a newly-matched sample of SDSS
galaxies observed with GALEX, 2MASS, and IRAS. The model reproduces well the
observed spectral energy distributions of these galaxies across the entire
wavelength range from the far-ultraviolet to the far-infrared. We find
important correlations between the physical parameters of galaxies which are
useful to investigate the star formation activity and dust properties of
galaxies. Our model can be straightforwardly applied to interpret observed
ultraviolet-to-infrared spectral energy distributions (SEDs) from any galaxy
sample.Comment: 4 pages, 3 figures, to appear in the Conference Proceedings of IAU
Symposium No. 262: Stellar Populations - Planning for the Next Decade, G.
Bruzual & S. Charlot ed
Extending Target Tracking Capabilities through Trajectory and Momentum Setpoint Optimization
Terrestrial target tracking is performed by many communications and Earth observation missions to track groundfixed targets. Previous Space Flight Laboratory (SFL) missions have demonstrated target tracking with high pointing accuracy, enabled by the use of an on-board star tracker. The allowable target tracking trajectories for these missions is constrained by the need to point the star tracker away from the Sun and Earth, which often means operating with a restricted envelope of allowable targets. An additional issue affecting target tracking missions is the stictioninduced jitter associated with reaction wheel zero speed crossings. This paper presents the development of 3TECS, a software platform with the dual purpose of performing trajectory optimization to achieve minimum energy slews under star tracker exclusion constraints, and momentum setpoint optimization for reaction wheel zero-crossing placement. It is shown that, for SFLâs DAUNTLESS-class spacecraft, the trajectory planning results in the ability to track any target visible below the horizon with greater than 98:7% star tracker availability, across a wide range of orbits. Additionally, we show that the momentum setpoint planning provides low-jitter payload operation windows of greater than 160 s in duration. This is in contrast to the existing solution that can result in zero-crossing jitter directly coinciding with key payload operations
Spectral Evolution Models for the Next Decade
Spectral evolution models are a widely used tool for determining the stellar
content of galaxies. I provide a review of the latest developments in stellar
atmosphere and evolution models, with an emphasis on massive stars. In contrast
to the situation for low- and intermediate mass stars, the current main
challenge for spectral synthesis models are the uncertainties and rapid
revision of current stellar evolution models. Spectral libraries, in particular
those drawn from theoretical model atmospheres for hot stars, are relatively
mature and can complement empirical templates for larger parameter space
coverage. I introduce a new ultraviolet spectral library based on theoretical
radiation-hydrodynamic atmospheres for hot massive stars. Application of this
library to star-forming galaxies at high redshift, i.e., Lyman-break galaxies,
will provide new insights into the abundances, initial mass function and ages
of stars in the very early universe.Comment: 8 pages, to appear in IAU Symp. 262, Stellar Populations - Planning
for the Next Decade, eds. G. Bruzual & S. Charlo
Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA
© 2020, The Author(s). We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron starâblack hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. During O3, the median localization volume (90% credible region) is expected to be on the order of 105,106,107Mpc3 for binary neutron star, neutron starâblack hole, and binary black hole systems, respectively. The localization volume in O4 is expected to be about a factor two smaller than in O3. We predict a detection count of 1-1+12(10-10+52) for binary neutron star mergers, of 0-0+19(1-1+91) for neutron starâblack hole mergers, and 17-11+22(79-44+89) for binary black hole mergers in a one-calendar-year observing run of the HLV network during O3 (HLVK network during O4). We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers
Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA
We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron starâblack hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. During O3, the median localization volume (90% credible region) is expected to be on the order of 105,106,107Mpc3 for binary neutron star, neutron starâblack hole, and binary black hole systems, respectively. The localization volume in O4 is expected to be about a factor two smaller than in O3. We predict a detection count of 1-1+12(10-10+52) for binary neutron star mergers, of 0-0+19(1-1+91) for neutron starâblack hole mergers, and 17-11+22(79-44+89) for binary black hole mergers in a one-calendar-year observing run of the HLV network during O3 (HLVK network during O4). We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers. © 2020, The Author(s)
Multiplicity of young brown dwarfs in Cha I
How frequent are brown dwarf binaries? Do brown dwarfs have planets? Are
current theoretical pre-main-sequence evolutionary tracks valid down to the
substellar regime? - Any detection of a companion to a brown dwarf takes us one
step forward towards answering these basic questions of star formation.
We report here on a search for spectroscopic and visual companions to young
brown dwarfs in the Cha I star forming cloud.
Based on spectra taken with UVES at the VLT, we found significant radial
velocity (RV) variations for five bona-fide and candidate brown dwarfs in Cha
I. They can be caused by either a (substellar or planetary) companion or
stellar activity. A companion causing the detected RV variations would have
about a few Jupiter masses. We are planning further UVES observations in order
to explore the nature of the detected RV variations. We also found that the RV
dispersion is only ~ 2km/s indicating that there is probably no run-away brown
dwarf among them.
Additionally a search for companions by direct imaging with the HST and SOFI
(NTT) has yielded to the detection of a few companion candidates in larger
orbits.Comment: Conference proceeding "Origins of stars and planets: The VLT view",
ESO, Garching, April 24-27 200
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