160,741 research outputs found
Possible detection of phase changes from the non-transiting planet HD 46375b by CoRoT
The present work deals with the detection of phase changes in an exoplanetary
system. HD 46375 is a solar analog known to host a non-transiting Saturn-mass
exoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for
34 days during the fall of 2008. We attempt to identify at optical wavelengths,
the changing phases of the planet as it orbits its star. We then try to improve
the star model by means of a seismic analysis of the same light curve and the
use of ground-based spectropolarimetric observations. The data analysis relies
on the Fourier spectrum and the folding of the time series. We find evidence of
a sinusoidal signal compatible in terms of both amplitude and phase with light
reflected by the planet. Its relative amplitude is Delta Fp/F* = [13.0, 26.8]
ppm, implying an albedo A=[0.16, 0.33] or a dayside visible brightness
temperature Tb ~ [1880,2030] K by assuming a radius R=1.1 R_Jup and an
inclination i=45 deg. Its orbital phase differs from that of the
radial-velocity signal by at most 2 sigma_RV. However, the tiny planetary
signal is strongly blended by another signal, which we attribute to a telluric
signal with a 1 day period. We show that this signal is suppressed, but not
eliminated, when using the time series for HD 46179 from the same CoRoT run as
a reference. This detection of reflected light from a non-transiting planet
should be confirmable with a longer CoRoT observation of the same field. In any
case, it demonstrates that non-transiting planets can be characterized using
ultra-precise photometric lightcurves with present-day observations by CoRoT
and Kepler. The combined detection of solar-type oscillations on the same
targets (Gaulme et al. 2010a) highlights the overlap between exoplanetary
science and asteroseismology and shows the high potential of a mission such as
Plato.Comment: 4 pages, 6 figure
NICMOS Imaging of a Damped Lyman-alpha Absorber at z=1.89 toward LBQS 1210+1731 : Constraints on Size and Star Formation Rate
We report results of a high-resolution imaging search (in rest frame
H- and optical continuum) for the galaxy associated with the damped
Lyman- (DLA) absorber at toward the quasar
LBQS 1210+1731, using HST/NICMOS. After PSF subtraction, a feature is seen in
both the broad-band and narrow-band images, at a projected separation of
0.25\arcsec from the quasar. If associated with the DLA, the object would be
kpc in size with a flux of Jy in
the F160W filter, implying a luminosity at {\AA} in
the rest frame of L at ,
for . However, no significant H- emission is seen,
suggesting a low star formation rate (SFR) (3 upper limit of 4.0
M yr), or very high dust obscuration.
Alternatively, the object may be associated with the host galaxy of the quasar.
H-band images obtained with the NICMOS camera 2 coronagraph show a much fainter
structure kpc in size and containing four knots of
continuum emission, located 0.7\arcsec away from the quasar. We have probed
regions far closer to the quasar sight-line than in most previous studies of
high-redshift intervening DLAs. The two objects we report mark the closest
detected high-redshift DLA candidates yet to any quasar sight line. If the
features in our images are associated with the DLA, they suggest faint,
compact, somewhat clumpy objects rather than large, well-formed proto-galactic
disks or spheroids.Comment: 52 pages of text, 19 figures, To be published in Astrophysical
Journal (accepted Dec. 8, 1999
Dark-ages reionization & galaxy formation simulation IV: UV luminosity functions of high-redshift galaxies
In this paper we present calculations of the UV luminosity function from the
Dark-ages Reionization And Galaxy-formation Observables from Numerical
Simulations (DRAGONS) project, which combines N-body, semi-analytic and
semi-numerical modelling designed to study galaxy formation during the Epoch of
Reionization. Using galaxy formation physics including supernova feedback, the
model naturally reproduces the UV LFs for high-redshift star-forming galaxies
from through to . We investigate the luminosity--star
formation rate (SFR) relation, finding that variable SFR histories of galaxies
result in a scatter around the median relation of -- dex depending on
UV luminosity. We find close agreement between the model and observationally
derived SFR functions. We use our calculated luminosities to investigate the
luminosity function below current detection limits, and the ionizing photon
budget for reionization. We predict that the slope of the UV LF remains steep
below current detection limits and becomes flat at
. We find that () per cent of the total
UV flux at () has been detected above an observational limit of
, and that galaxies fainter than
are the main source of ionizing photons for
reionization. We investigate the luminosity--stellar mass relation, and find a
correlation for galaxies with that has the form
, in good agreement with observations, but
which flattens for fainter galaxies. We determine the luminosity--halo mass
relation to be , finding that
galaxies with reside in host dark matter haloes of
at , and that this mass decreases
towards high redshift.Comment: 17 pages, 14 figures, Accepted for publication in MNRA
The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field Method
Recently, we have developed and calibrated the Synthetic Field Method (SFM)
to derive the total extinction through disk galaxies. The method is based on
the number counts and colors of distant background field galaxies that can be
seen through the foreground object, and has been successfully applied to NGC
4536 and NGC 3664, two late-type galaxies located, respectively, at 16 and 11
Mpc. Here, we study the applicability of the SFM to HST images of galaxies in
the Local Group, and show that background galaxies cannot be easily identified
through these nearby objects, even with the best resolution available today. In
the case of M 31, each pixel in the HST images contains 50 to 100 stars, and
the background galaxies cannot be seen because of the intrinsic granularity due
to strong surface brightness fluctuations. In the LMC, on the other hand, there
is only about one star every six linear pixels, and the lack of detectable
background galaxies results from a ``secondary'' granularity, introduced by
structure in the wings of the point spread function. The success of the SFM in
NGC 4536 and NGC 3664 is a natural consequence of the reduction of the
intensity of surface brightness fluctuations with distance. When the dominant
confusion factor is structure in the PSF wings, as is the case of HST images of
the LMC, and would happen in M 31 images obtained with a 10-m diffraction-
limited optical telescope, it becomes in principle possible to improve the
detectability of background galaxies by subtracting the stars in the foreground
object. However, a much better characterization of optical PSFs than is
currently available would be required for an adequate subtraction of the wings.
Given the importance of determining the dust content of Local Group galaxies,
efforts should be made in that direction.Comment: 45 pages, 10 Postscript figure
The Photometry of Undersampled Point Spread Functions
An undersampled point spread function may interact with the microstructure of
a solid-state detector such that the total flux detected can depend sensitively
on where the PSF center falls within a pixel. Such intra-pixel sensitivity
variations will not be corrected by flat field calibration and may limit the
accuracy of stellar photometry conducted with undersampled images, as are
typical for Hubble Space Telescope observations. The total flux in a stellar
image can vary by up to 0.03 mag in F555W WFC images depending on how it is
sampled, for example. For NIC3, these variations are especially strong, up to
0.39 mag, strongly limiting its use for stellar photometry. Intra-pixel
sensitivity variations can be corrected for, however, by constructing a
well-sampled PSF from a dithered data set. The reconstructed PSF is the
convolution of the optical PSF with the pixel response. It can be evaluated at
any desired fractional pixel location to generate a table of photometric
corrections as a function of relative PSF centroid. A caveat is that the
centroid of an undersampled PSF can also be affected by the pixel response
function, thus sophisticated centroiding methods, such as cross-correlating the
observed PSF with its fully-sampled counterpart, are required to derive the
proper photometric correction.Comment: 20 pages, 14 postscript figures, submitted to the PAS
Ultra-high energy cosmic rays from Quark Novae
We explore acceleration of ions in the Quark Nova (QN) scenario, where a
neutron star experiences an explosive phase transition into a quark star (born
in the propeller regime). In this picture, two cosmic ray components are
isolated: one related to the randomized pulsar wind and the other to the
propelled wind, both boosted by the ultra-relativistic Quark Nova shock. The
latter component acquires energies while
the former, boosted pulsar wind, achieves ultra-high energies
eV. The composition is dominated by ions present in the pulsar wind in the
energy range above eV, while at energies below eV the
propelled ejecta, consisting of the fall-back neutron star crust material from
the explosion, is the dominant one. Added to these two components, the
propeller injects relativistic particles with Lorentz factors , later to be accelerated by galactic supernova shocks. The
QN model appears to be able to account for the extragalactic cosmic rays above
the ankle and to contribute a few percent of the galactic cosmic rays below the
ankle. We predict few hundred ultra-high energy cosmic ray events above
eV for the Pierre Auger detector per distant QN, while some thousands
are predicted for the proposed EUSO and OWL detectors.Comment: 20 pages, 1 figure. Major revisions in the text. Accepted for
publication in the Astrophysical Journa
Science for gifted children in grade four.
Thesis (Ed.M.)--Boston Universit
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