87 research outputs found
Survey Simulations of a New Near-Earth Asteroid Detection System
We have carried out simulations to predict the performance of a new
space-based telescopic survey operating at thermal infrared wavelengths that
seeks to discover and characterize a large fraction of the potentially
hazardous near-Earth asteroid (NEA) population. Two potential architectures for
the survey were considered: one located at the Earth-Sun L1 Lagrange point, and
one in a Venus-trailing orbit. A sample cadence was formulated and tested,
allowing for the self-follow-up necessary for objects discovered in the daytime
sky on Earth. Synthetic populations of NEAs with sizes >=140 m in effective
spherical diameter were simulated using recent determinations of their physical
and orbital properties. Estimates of the instrumental sensitivity, integration
times, and slew speeds were included for both architectures assuming the
properties of new large-format 10 um detector arrays capable of operating at
~35 K. Our simulation included the creation of a preliminary version of a
moving object processing pipeline suitable for operating on the trial cadence.
We tested this pipeline on a simulated sky populated with astrophysical sources
such as stars and galaxies extrapolated from Spitzer and WISE data, the catalog
of known minor planets (including Main Belt asteroids, comets, Jovian Trojans,
etc.), and the synthetic NEA model. Trial orbits were computed for simulated
position-time pairs extracted from the synthetic surveys to verify that the
tested cadence would result in orbits suitable for recovering objects at a
later time. Our results indicate that the Earth-Sun L1 and Venus-trailing
surveys achieve similar levels of integral completeness for potentially
hazardous asteroids larger than 140 m; placing the telescope in an interior
orbit does not yield an improvement in discovery rates. This work serves as a
necessary first step for the detailed planning of a next-generation NEA survey.Comment: AJ accepted; corrected typ
Asteroseismology from space: The δ Scuti star θ^2 Tauri monitored by the WIRE satellite
The bright variable star θ^2 Tauâ was monitored with the star camera on the WideâField Infrared Explorer satellite. Twelve independent frequencies were detected down to the 0.5 mmag amplitude level. Their reality was investigated by searching for them using two different algorithms and by some internal checks: both procedures strengthened our confidence in the results. All the frequencies are in the range 10.8â14.6 cd^(-1). The histogram of the frequency spacings shows that 81% are below 1.8 cd^(-1); rotation may thus play a role in the mode excitation. The fundamental radial mode is not observed, although it is expected to occur in a region where the noise level is very low (55 Îźmag). The rms residual is about two times lower than that usually obtained from successful groundâbased multisite campaigns. The comparison of the results of previous campaigns with the new ones establishes the amplitude variability of some modes
Evolutionary model and oscillation frequencies for alpha Ursae Majoris: A comparison with observations
Inspired by the observations of low-amplitude oscillations of alpha Ursae Majoris A by Buzasi et al. using the WIRE satellite, a,grid of stellar evolutionary tracks has been constructed to derive physically consistent interior models for the nearby red giant. The pulsation properties of these models were then calculated and compared with the observations. It is found that, by adopting the correct metallicity and for a normal helium abundance, only models in the mass range of 4.0-4.5 M. fall within the observational error box for alpha UMa A. This mass range is compatible, within the uncertainties, with the mass derived from the astrometric mass function. Analysis of the pulsation spectra of the models indicates that the observed alpha UMa oscillations can be most simply interpreted as radial (i.e., l = 0) p-mode oscillations of low radial order n. The lowest frequencies observed by Buzasi et al. are compatible, within the observational errors, with model frequencies of radial orders n = 0, 1, and 2 for models in the mass range of 4.0-4.5 M.. The higher frequencies observed can also be tentatively interpreted as higher n-valued radial p-modes, if we allow that some n-values are not presently observed. The theoretical l = 1, 2, and 3 modes in the observed frequency range are g-modes with a mixed mode character, that is, with p-mode-like characteristics near the surface and g-mode-like characteristics in the interior The calculated radial p-mode frequencies are nearly equally spaced, separated by 2-3 mu HZ. The nonradial modes are very densely packed throughout the observed frequency range and, even if excited to significant amplitudes at the surface, are unlikely to be resolved by the present observations
Large-scale structure in a new deep IRAS galaxy redshift survey
We present here the first results from two recently completed, fully sampled redshift surveys comprising 3703 IRAS Faint Source Survey (FSS) galaxies. An unbiased counts-in-cells analysis finds a clustering strength in broad agreement with other recent redshift surveys and at odds with the standard cold dark matter model. We combine our data with those from the QDOT and 1.2 Jy surveys, producing a single estimate of the IRAS galaxy clustering strength. We compare the data with the power spectrum derived from a mixed dark matter universe. Direct comparison of the clustering strength seen in the IRAS samples with that seen in the APM-Stromlo survey suggests b_O/b_I=1.20+/-0.05 assuming a linear, scale independent biasing. We also perform a cell by cell comparison of our FSS-z sample with galaxies from the first CfA slice, testing the viability of a linear-biasing scheme linking the two. We are able to rule out models in which the FSS-z galaxies identically trace the CfA galaxies on scales 5-20h^{-1}Mpc. On scales of 5 and 10h^{-1}Mpc no linear-biasing model can be found relating the two samples. We argue that this result is expected since the CfA sample includes more elliptical galaxies which have different clustering properties from spirals. On scales of 20h^{-1}Mpc no linear-biasing model with b_O/b_I < 1.70 is acceptable. When comparing the FSS-z galaxies to the CfA spirals, however, the two populations trace the same structures within our uncertaintie
Preliminary Results from NEOWISE: An Enhancement to the Wide-field Infrared Survey Explorer for Solar System Science
The Wide-field Infrared Survey Explorer (WISE) has surveyed the entire sky at four infrared wavelengths with greatly improved sensitivity and spatial resolution compared to its predecessors, the Infrared Astronomical Satellite and the Cosmic Background Explorer. NASA's Planetary Science Division has funded an enhancement to the WISE data processing system called "NEOWISE" that allows detection and archiving of moving objects found in the WISE data. NEOWISE has mined the WISE images for a wide array of small bodies in our solar system, including near-Earth objects (NEOs), Main Belt asteroids, comets, Trojans, and Centaurs. By the end of survey operations in 2011 February, NEOWISE identified over 157,000 asteroids, including more than 500 NEOs and ~120 comets. The NEOWISE data set will enable a panoply of new scientific investigations
Large-scale structure in a new deep IRAS galaxy redshift survey
We present here the first results from two recently completed, fully sampled
redshift surveys comprising 3703 IRAS Faint Source Survey (FSS) galaxies. An
unbiased counts-in-cells analysis finds a clustering strength in broad
agreement with other recent redshift surveys and at odds with the standard cold
dark matter model. We combine our data with those from the QDOT and 1.2 Jy
surveys, producing a single estimate of the IRAS galaxy clustering strength. We
compare the data with the power spectrum derived from a mixed dark matter
universe. Direct comparison of the clustering strength seen in the IRAS samples
with that seen in the APM-Stromlo survey suggests b_O/b_I=1.20+/-0.05 assuming
a linear, scale independent biasing. We also perform a cell by cell comparison
of our FSS-z sample with galaxies from the first CfA slice, testing the
viability of a linear-biasing scheme linking the two. We are able to rule out
models in which the FSS-z galaxies identically trace the CfA galaxies on scales
5-20h^{-1}Mpc. On scales of 5 and 10h^{-1}Mpc no linear-biasing model can be
found relating the two samples. We argue that this result is expected since the
CfA sample includes more elliptical galaxies which have different clustering
properties from spirals. On scales of 20h^{-1}Mpc no linear-biasing model with
b_O/b_I < 1.70 is acceptable. When comparing the FSS-z galaxies to the CfA
spirals, however, the two populations trace the same structures within our
uncertainties.Comment: Also at ftp://artemis.ph.ic.ac.uk/pub/so/papers/lss_paper.uu; MNRAS
Accepted 1995 November 1
Asteroseismology from space: the Delta Scuti star Theta2 Tauri monitored by the WIRE satellite
The first intensive photometric time-series of a Delta Scuti star was
obtained from space. Theta2 Tau was monitored with the star camera on the
Wide-Field Infrared Explorer (WIRE) satellite. Twelve independent frequencies
were detected down to the 0.5 mmag amplitude level. Their reality was
investigated by searching for them using two different algorithms and by some
internal checks. All the frequencies are in the range 10.8-14.6 c\d. The
histogram of the frequency spacings shows that 81% are below 1.8 c\d; rotation
may thus play a role in the mode excitation. The fundamental radial mode is not
observed, although it is expected to occur in a region where the noise level is
very low (55 micromag). The rms residual is about two times lower than that
usually obtained from successful ground--based multisite campaigns. The
comparison of the results of previous campaigns with the new ones establishes
the amplitude variability of some modes.Comment: 7 pages (in A&A style), 7 eps figures. Accepted for A&A Main Journa
UV to IR SEDs of UV selected galaxies in the ELAIS fields: evolution of dust attenuation and star formation activity from z=0.7 to z=0.2
We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a
sample of intermediate redshift (0.2 < z < 0.7) UV-selected galaxies from the
ELAIS-N1 and ELAIS-N2 fields by fitting a multi-wavelength dataset to a library
of GRASIL templates. Star formation related properties of the galaxies are
derived from the library of models by using the Bayesian statistics. We find a
decreasing presence of galaxies with low attenuation and low total luminosity
as redshift decreases, which does not hold for high total luminosity galaxies.
In addition the dust attenuation of low mass galaxies increases as redshift
decreases, and this trend seems to disappear for galaxies with M* > 10^11
M_sun. This result is consistent with a mass dependent evolution of the dust to
gas ratio, which could be driven by a mass dependent efficiency of star
formation in star forming galaxies. The specific star formation rates (SSFR)
decrease with increasing stellar mass at all redshifts, and for a given stellar
mass the SSFR decreases with decreasing redshift. The differences in the slope
of the M*--SSFR relation found between this work and others at similar redshift
could be explained by the adopted selection criteria of the samples which, for
a UV selected sample, favours blue, star forming galaxies.Comment: 21 figures, accepted for publication in Ap
UV-optical colors as probes of early-type galaxy evolution
We have studied âź2100 early-type galaxies in the SDSS DR3 which have been detected by the GALEX Medium Imaging Survey (MIS), in the redshift range O <z <0.1.1. Combining GALEXUV photometry with corollary optical data from the SDSS, we find that, at a 95% confidence level, at least âź30% of galaxies in this sample have UV to optical colors consistent with some recent star formation within the last Gyr. In particular, galaxies with an NUV - r color less than 5.5 are very likely to have experienced such recent star formation, taking into account the possibility of a contribution to NUV flux from the UV upturn phenomenon. We find quantitative agreement between the observations and the predictions of a semianalytical ACDM hierarchical merger model and deduce that early-type galaxies in the redshift range 0 <z <0.11 have âź 1 % -3 % of their stellar mass in stars less than 1 Gyr old. The average age of this recently formed population is âź300-500 Myr. We also find that "monolithically" evolving galaxies, where recent star formation can be driven solely by recycled gas from stellar mass loss, cannot exhibit the blue colors (NUV - r <5.5) seen in a significant fraction (âź30%) of our observed sample.Peer reviewe
The effect of environment on the UV colour-magnitude relation of early-type galaxies
We use \textit{GALEX} (Galaxy Evolution Explorer) near-UV (NUV) photometry of
a sample of early-type galaxies selected in \textit{SDSS} (Sloan Digital Sky
Survey) to study the UV color-magnitude relation (CMR). color is an
excellent tracer of even small amounts (% mass fraction) of recent
(\la 1 Gyr) star formation and so the CMR allows us to study the
effect of environment on the recent star formation history. We analyze a
volume-limited sample of 839 visually-inspected early-type galaxies in the
redshift range brighter than of -21.5 with any
possible emission-line or radio-selected AGN removed to avoid contamination. We
find that contamination by AGN candidates and late-type interlopers highly bias
any study of recent star formation in early-type galaxies and that, after
removing those, our lower limit to the fraction of massive early-type galaxies
showing signs of recent star formation is roughly This suggests
that residual star formation is common even amongst the present day early-type
galaxy population.
We find that the fraction of UV-bright early-type galaxies is 25% higher in
low-density environments. However, the density effect is clear only in the
lowest density bin. The blue galaxy fraction for the subsample of the brightest
early-type galaxies however shows a very strong density dependence, in the
sense that the blue galaxy fraction is lower in a higher density region.Comment: Accepted for publication in ApJ, paper with high-resolution figures
can be downloaded at:
http://www-astro.physics.ox.ac.uk/~kevins/PAPERS/uv_environment.p
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