295 research outputs found
Segmenting the Visitor Market by the Timing of Their Activity Decisions
The purpose of this study was to describe visitors to a Florida county and determine if a CVB\u27s promotional campaign strategies conformed with visitors\u27 need for information. The research focused on the timing of visitors\u27 activity decisions to assess whether promotional efforts were being channeled in ways that conformed to the timing of visitors\u27 information needs and decision making. Responses from 546 completed surveys revealed that 71.5% of the respondents decided which recreational activities they would engage in prior to leaving home; 3.7% made that decision en route to the county; and 24. 9% after arriving in the county. Further analysis revealed that respondents who made their activity decisions after arriving in the county were typically a part of the long haul market, stayed significantly longer than the other counterparts, and spent, on average, nearly twice as much as those that made their activity decisions prior to leaving home. Implications for marketers are discussed
The Joint Efficient Dark-energy Investigation (JEDI): Measuring the cosmic expansion history from type Ia supernovae
JEDI (Joint Efficient Dark-energy Investigation) is a candidate
implementation of the NASA-DOE Joint Dark Energy Mission (JDEM). JEDI will
probe dark energy in three independent methods: (1) type Ia supernovae, (2)
baryon acoustic oscillations, and (3) weak gravitational lensing. In an
accompanying paper, an overall summary of the JEDI mission is given. In this
paper, we present further details of the supernova component of JEDI. To derive
model-independent constraints on dark energy, it is important to precisely
measure the cosmic expansion history, H(z), in continuous redshift bins from z
\~ 0-2 (the redshift range in which dark energy is important). SNe Ia at z > 1
are not readily accessible from the ground because the bulk of their light has
shifted into the near-infrared where the sky background is overwhelming; hence
a space mission is required to probe dark energy using SNe. Because of its
unique near-infrared wavelength coverage (0.8-4.2 microns), JEDI has the
advantage of observing SNe Ia in the rest frame J band for the entire redshift
range of 0 < z < 2, where they are less affected by dust, and appear to be
nearly perfect standard candles. During the first year of JEDI operations,
spectra and light curves will be obtained for ~4,000 SNe Ia at z < 2. The
resulting constraints on dark energy are discussed, with special emphasis on
the improved precision afforded by the rest frame near-infrared data.Comment: 8 pages, accepted for publication in SPIE proceeding
SN 1987A's Circumstellar Envelope, II: Kinematics of the Three Rings and the Diffuse Nebula
We present several different measurements of the velocities of structures
within the circumstellar envelope of SN 1987A, including the inner, equatorial
ring (ER), outer rings (ORs), and the diffuse nebulosity at radii < 5 pc, based
on CTIO 4m and HST data. A comparison of STIS and WFPC2 [N II]6583 loci for the
rings show that the ER is expanding in radius at 10.5+-0.3 km/s, with the
northern OR expanding along the line of sight at about 26 km/s, and for the
southern OR, about 23 km/s. Similar results are found with CTIO 4m data.
Accounting for inclination, the best fit to all data show both ORs with an
expansion from the SN of 26 km/s. The ratio of the ER to OR velocities is
nearly equal to the ratio of ER to OR radii, so the rings are roughly
homologous, all having kinematic ages corresponding to about 20,000 yr before
the SN explosion. This makes previously reported, large compositional
differences between the ER and ORs difficult to understand. Additionally, a
grid of longslit 4m/echelle spectra centered on the SN shows two velocity
components over a region roughly coextensive with the outer circumstellar
envelope extending about 5 pc (20 arcsec) from the SN. One component is
blueshifted and the other redshifted from the SN centroid by about 10 km/s
each. These features may represent a bipolar flow expanding from the SN, in
which the ORs are propelled 10-15 km/s faster than that of the surrounding
envelope into which they propogate. The kinematic timescale for the entire
nebula is at least about 350,000 yr. The kinematics of these various structures
constrain possible models for the evolution of the progenitor and its formation
of a mass loss nebula.Comment: 25 pages AASTeX text plus 12 figures. ApJ, in pres
QSOs and Absorption Line Systems Surrounding the Hubble Deep Field
We have imaged a 45x45 sq. arcmin. area centered on the Hubble Deep Field
(HDF) in UBVRI passbands, down to respective limiting magnitudes of
approximately 21.5, 22.5, 22.2, 22.2, and 21.2. The principal goals of the
survey are to identify QSOs and to map structure traced by luminous galaxies
and QSO absorption line systems in a wide volume containing the HDF. We have
selected QSO candidates from color space, and identified 4 QSOs and 2 narrow
emission-line galaxies (NELGs) which have not previously been discovered,
bringing the total number of known QSOs in the area to 19. The bright z=1.305
QSO only 12 arcmin. away from the HDF raises the northern HDF to nearly the
same status as the HDF-S, which was selected to be proximate to a bright QSO.
About half of the QSO candidates remain for spectroscopic verification.
Absorption line spectroscopy has been obtained for 3 bright QSOs in the field,
using the Keck 10m, ARC 3.5m, and MDM 2.4m telescopes. Five heavy-element
absorption line systems have been identified, 4 of which overlap the
well-explored redshift range covered by deep galaxy redshift surveys towards
the HDF. The two absorbers at z=0.5565 and z=0.5621 occur at the same redshift
as the second most populated redshift peak in the galaxy distribution, but each
is more than 7Mpc/h (comoving, Omega_M=1, Omega_L=0) away from the HDF line of
sight in the transverse dimension. This supports more indirect evidence that
the galaxy redshift peaks are contained within large sheet-like structures
which traverse the HDF, and may be precursors to large-scale ``pancake''
structures seen in the present-day galaxy distribution.Comment: 36 pages, including 9 figures and 8 tables. Accepted for publication
in the Astronomical Journa
Survey for Transiting Extrasolar Planets in Stellar Systems: III. A Limit on the Fraction of Stars with Planets in the Open Cluster NGC 1245
We analyze a 19-night photometric search for transiting extrasolar planets in
the open cluster NGC 1245. An automated transit search algorithm with
quantitative selection criteria finds six transit candidates; none are bona
fide planetary transits. We characterize the survey detection probability via
Monte Carlo injection and recovery of realistic limb-darkened transits. We use
this to derive upper limits on the fraction of cluster members with close-in
Jupiter-radii, RJ, companions. We carefully analyze the random and systematic
errors of the calculation. For similar photometric noise and weather properties
as this survey, observing NGC 1245 twice as long results in a tighter
constraint on "Hot Jupiter", HJ, companions than observing an additional
cluster of similar richness as NGC 1245 for the same length of time as this
survey. This survey observed ~870 cluster members. If 1% of stars have 1.5 RJ
HJ companions, we expect to detect one planet for every 5000 dwarf stars
observed for a month. To reach a ~2% upper limit on the fraction of stars with
1.5 RJ HJ companions, we conclude a total sample size of ~7400 dwarf stars
observed for at least a month will be needed. Results for 1.0 RJ companions,
without substantial improvement in the photometric precision, will require a
small factor larger sample size.Comment: 24 pages, 15 figures, submitted A
Probing the time dependence of dark energy
A new method to investigate a possible time-dependence of the dark energy
equation of state is proposed. We apply this methodology to two of the most
recent data sets of type Ia supernova (Union2 and SDSS) and the baryon acoustic
oscillation peak at . For some combinations of these data, we show
that there is a clear departure from the standard CDM model at
intermediary redshifts, although a non-evolving dark energy component () cannot be ruled out by these data. The approach developed here may be
useful to probe a possible evolving dark energy component when applied to
upcoming observational data.Comment: 6 pages, 3 figures, LaTe
The remnant of SN1987A revealed at (sub-)mm wavelengths
Context: Supernova 1987A (SN1987A) exploded in the Large Magellanic Cloud
(LMC). Its proximity and rapid evolution makes it a unique case study of the
early phases in the development of a supernova remnant. One particular aspect
of interest is the possible formation of dust in SN1987A, as SNe could
contribute significantly to the dust seen at high redshifts. Aims: We explore
the properties of SN1987A and its circumburst medium as seen at mm and sub-mm
wavelengths, bridging the gap between extant radio and infrared (IR)
observations of respectively the synchrotron and dust emission. Methods:
SN1987A was observed with the Australia Telescope Compact Array (ATCA) at 3.2
mm in July 2005, and with the Atacama Pathfinder EXperiment (APEX) at 0.87 mm
in May 2007. We present the images and brightness measurements of SN1987A at
these wavelengths for the first time. Results: SN1987A is detected as an
unresolved point source of 11.2 +/- 2.0 mJy at 3.2 mm (5" beam) and 21 +/- 4
mJy at 0.87 mm (18" beam). These flux densities are in perfect agreement with
extrapolations of the powerlaw radio spectrum and modified-blackbody dust
emission, respectively. This places limits on the presence of free-free
emission, which is similar to the expected free-free emission from the ionized
ejecta from SN1987A. Adjacent, fainter emission is observed at 0.87 mm
extending ~0.5' towards the south-west. This could be the impact of the
supernova progenitor's wind when it was still a red supergiant upon a dense
medium. Conclusions: We have established a continuous spectral energy
distribution for the emission from SN1987A and its immediate surroundings,
linking the IR and radio data. This places limits on the contribution from
ionized plasma. Our sub-mm image reveals complexity in the distribution of cold
dust surrounding SN1987A, but leaves room for freshly synthesized dust in the
SN ejecta.Comment: Accepted for publication in Astronomy and Astrophysics Letters on 28
April 2011. A better quality figure 1 can be had from
http://www.astro.keele.ac.uk/~jacco/research/SN1987A087mm.ep
Towards an explanation for the 30 Dor (LMC) Honeycomb nebula - the impact of recent observations and spectral analysis
The unique Honeycomb nebula, most likely a peculiar supernova remnant, lies
in 30 Doradus in the Large Magellanic Cloud. Due to its proximity to SN1987A,
it has been serendipitously and intentionally observed at many wavelengths.
Here, an optical spectral analysis of forbidden line ratios is performed in
order to compare the Honeycomb high-speed gas with supernova remnants in the
Galaxy and the LMC, with galactic Wolf-Rayet nebulae and with the optical line
emission from the interaction zone of the SS433 microquasar and W50 supernova
remnant system. An empirical spatiokinematic model of the images and spectra
for the Honeycomb reveals that its striking appearance is most likely due to a
fortuitous viewing angle. The Honeycomb nebula is more extended in soft X-ray
emission and could in fact be a small part of the edge of a giant LMC shell
revealed for the first time in this short wavelength domain. It is also
suggested that a previously unnoticed region of optical emission may in fact be
an extension of the Honeycomb around the edge of this giant shell. A secondary
supernova explosion in the edge of a giant shell is considered for the creation
of the Honeycomb nebula. A microquasar origin of the Honeycomb nebula as
opposed to a simple supernova origin is also evaluated.Comment: 12 pages, 9 figures, accepted for publication in MNRA
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