62 research outputs found
AIMP optical aspect coverage - Three dimensional approximation
Approximate method for determining duration of coverage of sunlit earth by anchored IMP optical aspect syste
Detecting 'Temperate' Jupiters: the prospects of searching for transiting gas giants in Habitable Zones
Wide-field photometric surveys in search of transiting extrasolar planets are now numerous and have met with some success in finding hot Jupiters. These transiting planets have very short periods and very small semimajor axes, facilitating their discovery in such surveys. Transiting planets with longer periods present more of a challenge, since they transit their parent stars less frequently. This paper investigates the effects of observing windows on detecting transiting planets by calculating the fraction of planets with a given period that have zero, one (single), two (double), or ≥3 (multiple) transits occurring while observations are being taken. We also investigate the effects of collaboration by performing the same calculations with combined observing times from two wide-field transit survey groups. For a representative field of the 2004 observing season, both XO and SuperWASP experienced an increase in single and double transit events by up to 20–40 per cent for planets with periods 14 < P < 150 d when collaborating by sharing data. For the XO Project using its data alone, between 20–40 per cent of planets with periods 14–150 d should have been observed at least once. For the SuperWASP Project, 50–90 per cent of planets with periods between 14–150 d should have been observed at least once. If XO and SuperWASP combine their observations, 50–100 per cent of planets with periods less than 20 d should be observed three or more times. We find that in general wide-field transit surveys have selected appropriate observing strategies to observe a significant fraction of transiting giant planets with semimajor axes larger than the hot Jupiter regime. The actual number of intermediate-period transiting planets that are detected depends upon their true semimajor axis distribution and the signal-to-noise ratio of the data. We therefore conclude that the investment of resources needed to investigate more sophisticated photometry calibrations or examine single and double transit events from wide-field surveys might be a worthwhile endeavour. The collaboration of different transit surveys by combining photometric data can greatly increase the number of transits observed for all semimajor axes. In addition, the increased number of data points can improve the signal-to-noise ratio of binned data, increasing the chances of detecting transiting extrasolar planets
Dust Streamers in the Virgo Galaxy M86 from Ram Pressure Stripping of its Companion VCC 882
The giant elliptical galaxy M86 in Virgo has a ~28 kpc long dust trail inside
its optical halo that points toward the nucleated dwarf elliptical galaxy, VCC
882. The trail seems to be stripped material from the dwarf. Extinction
measurements suggest that the ratio of the total gas mass in the trail to the
blue luminosity of the dwarf is about unity, which is comparable to such ratios
in dwarf irregular galaxies. The ram pressure experienced by the dwarf galaxy
in the hot gaseous halo of M86 was comparable to the internal gravitational
binding energy density of the presumed former gas disk in VCC 882. Published
numerical models of this case are consistent with the overall trail-like
morphology observed here. Three concentrations in the trail may be evidence for
the predicted periodicity of the mass loss. The evaporation time of the trail
is comparable to the trail age obtained from the relative speed of the galaxies
and the trail length. Thus the trail could be continuously formed from stripped
replenished gas if the VCC 882 orbit is bound. However, the high gas mass and
the low expected replenishment rate suggest that this is only the first
stripping event. Implications for the origin of nucleated dwarf ellipticals are
briefly discussed.Comment: 22 pages, 7 figures, Astronomical Journal, August 2000, in pres
Detecting "Temperate" Jupiters: The Prospects of Searching for Transiting Gas Giants in Habitability Zones
This paper investigates the effects of observing windows on detecting
transiting planets by calculating the fraction of planets with a given period
that have zero, one (single), two (double), or 3 (multiple) transits
occurring while observations are being taken. We also investigate the effects
of collaboration by performing the same calculations with combined observing
times from two wide-field transit survey groups. For a representative field of
the 2004 observing season, both XO and SuperWASP experienced an increase in
single and double transit events by up to 20-40% for planets with periods 14 <
P < 150 days when collaborating by sharing data. For the XO Project using its
data alone, between 20-40% of planets with periods 14-150 days should have been
observed at least once. For the SuperWASP Project, 50-90% of planets with
periods between 14-150 days should have been observed at least once. If XO and
SuperWASP combined their observations, 50-100% of planets with periods less
than 20 days should be observed three or more times. We find that in general
wide-field transit surveys have selected appropriate observing strategies to
observe a significant fraction of transiting giant planets with semimajor axes
larger than the Hot Jupiter regime. The actual number of intermediate-period
transiting planets that are detected depends upon their true semimajor axis
distribution and the signal-to-noise of the data.Comment: 14 pages, 12 figures, 4 tables, accepted to MNRA
A large atomic hydrogen shell in the outer Galaxy: SNR or stellar wind bubble?
We report the detection of a ring like HI structure toward l=90.0, b=2.8 with
a velocity of v_LSR=-99 km/s. This velocity implies a distance of d=13 kpc,
corresponding to a Galactocentric radius of R_gal=15 kpc. The l-v_LSR diagram
implies an expansion velocity of v_exp ~ 15 km/s for the shell. The structure
has an oblate, irregular shell-like appearance which surrounds weak infrared
emission as seen in the 60 micrometer IRAS data. At a distance of 13 kpc the
size of the object is about 110 x 220 pc and placed 500 pc above the Galactic
plane with a mass of 1e5 solar mass. An expanding shell with such a high mass
and diameter cannot be explained by a single supernova explosion or by a single
stellar wind bubble. We interpret the structure as a relic of a distant stellar
activity region powered by the joint action of strong stellar winds from early
type stars and supernova explosions.Comment: Accepted for publication by The Astrophysical Journal, 5 Pages, 4
Figure
An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey, using
both ground-based and Hubble Space Telescope images, of a complete sample of
nearby barred S0--Sa galaxies in the field, with a particular emphasis on
identifying and measuring central structures within the bars: secondary bars,
inner disks, nuclear rings and spirals, and off-plane dust. A discussion of the
frequency and statistical properties of the various types of inner structures
has already been published. Here, we present the data for the individual
galaxies and measurements of their bars and inner structures. We set out the
methods we use to find and measure these structures, and how we discriminate
between them. In particular, we discuss some of the deficiencies of ellipse
fitting of the isophotes, which by itself cannot always distinguish between
bars, rings, spirals, and dust, and which can produce erroneous measurements of
bar sizes and orientations.Comment: LaTeX, 66 pages (including 42 figures, 36 in color). To appear in The
Astrophysical Journal Supplement. Full-resolution and text-only versions
available at http://www.iac.es/galeria/erwin/research
Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR
We present a study of -ray emission from the core-collapse supernova
remnant Cas~A in the energy range from 0.1GeV to 10TeV. We used 65 hours of
VERITAS data to cover 200 GeV - 10 TeV, and 10.8 years of \textit{Fermi}-LAT
data to cover 0.1-500 GeV. The spectral analysis of \textit{Fermi}-LAT data
shows a significant spectral curvature around GeV that is
consistent with the expected spectrum from pion decay. Above this energy, the
joint spectrum from \textit{Fermi}-LAT and VERITAS deviates significantly from
a simple power-law, and is best described by a power-law with spectral index of
with a cut-off energy of TeV. These
results, along with radio, X-ray and -ray data, are interpreted in the
context of leptonic and hadronic models. Assuming a one-zone model, we exclude
a purely leptonic scenario and conclude that proton acceleration up to at least
6 TeV is required to explain the observed -ray spectrum. From modeling
of the entire multi-wavelength spectrum, a minimum magnetic field inside the
remnant of is deduced.Comment: 33 pages, 9 Figures, 6 Table
Dust Properties of NGC4753
We report BVR surface photometry of a lenticular galaxy, NGC4753 with
prominent dust lanes. We have used the multicolor broadband photometry to study
dust-extinction as a function of wavelength and derived the extinction curve.
We find the extinction curve of NGC 4753 to be similar to the Galactic
extinction curve in the visible region which implies that the sizes of dust
grains responsible for optical extinction are similar to those in our Galaxy.
We derive dust mass from optical extinction as well as from the far infrared
fluxes observed with IRAS. The ratio of the two dust masses,
, is 2.28 for NGC 4753, which is
significantly lower than the value of 8.4 \pm 1.3 found previously for a large
sample of elliptical galaxies. The total mass of the observed dust within
NGC4753 is about a factor of 10 higher than the mass of dust expected from loss
of mass from red giant stars and destruction by sputtering and grain-grain
collisions in low velocity shocks, and sputtering in supernova driven blast
waves. We find evidence for the coexistence of dust and H emitting gas
within NGC4753. The current star formation rate of NGC4753, averaged over past
, is estimated to be less than 0.21M_{\sun}yr^{-1}. A
substantial amount of dust within NGC4753 exists in the form of cirrus.Comment: 15 pages, 8 jpeg figures, 5 tables in one file, AASTEX style,
Accepted for publication in the Astronomical Journal, 1999 Augus
Ages for exoplanet host stars
Age is an important characteristic of a planetary system, but also one that
is difficult to determine. Assuming that the host star and the planets are
formed at the same time, the challenge is to determine the stellar age.
Asteroseismology provides precise age determination, but in many cases the
required detailed pulsation observations are not available. Here we concentrate
on other techniques, which may have broader applicability but also serious
limitations. Further development of this area requires improvements in our
understanding of the evolution of stars and their age-dependent
characteristics, combined with observations that allow reliable calibration of
the various techniques.Comment: To appear in "Handbook of Exoplanets", eds. Deeg, H.J. & Belmonte,
J.A, Springer (2018
The SAURON project. II. Sample and early results
Early results are reported from the SAURON survey of the kinematics and
stellar populations of a representative sample of nearby E, S0 and Sa galaxies.
The survey is aimed at determining the intrinsic shape of the galaxies, their
orbital structure, the mass-to-light ratio as a function of radius, the age and
metallicity of the stellar populations, and the frequency of kinematically
decoupled cores and nuclear black holes. The construction of the representative
sample is described, and its properties are illustrated. A comparison with
long-slit spectroscopic data establishes that the SAURON measurements are
comparable to, or better than, the highest-quality determinations. Comparisons
are presented for NGC 3384 and NGC 4365 where stellar velocities and velocity
dispersions are determined to a precision of 6 km/s, and the h3 and h4
parameters of the line-of-sight velocity distribution to a precision of better
than 0.02. Extraction of accurate gas emission-line intensities, velocities and
line widths from the datacubes is illustrated for NGC 5813. Comparisons with
published line-strengths for NGC 3384 and NGC 5813 reveal uncertainties of <
0.1 A on the measurements of the Hbeta, Mgb and Fe5270 indices. Integral-field
mapping uniquely connects measurements of the kinematics and stellar
populations to the galaxy morphology. The maps presented here illustrate the
rich stellar kinematics, gaseous kinematics, and line-strength distributions of
early-type galaxies. The results include the discovery of a thin, edge-on, disk
in NGC 3623, confirm the axisymmetric shape of the central region of M32,
illustrate the LINER nucleus and surrounding counter-rotating star-forming ring
in NGC 7742, and suggest a uniform stellar population in the decoupled core
galaxy NGC 5813.Comment: 20 pages, 17 figures. To be published in MNRAS. Version with full
resolution images available at
http://www.strw.leidenuniv.nl/~dynamics/Instruments/Sauron/pub_list.htm
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