143 research outputs found
Addressing the Crisis in Fundamental Physics
I present the case for fundamental physics experiments in space playing an
important role in addressing the current "dark energy'' crisis. If cosmological
observations continue to favor a value of the dark energy equation of state
parameter w=-1, with no change over cosmic time, then we will have difficulty
understanding this new fundamental physics. We will then face a very real risk
of stagnation unless we detect some other experimental anomaly. The advantages
of space-based experiments could prove invaluable in the search for the a more
complete understanding of dark energy. This talk was delivered at the start of
the Fundamental Physics Research in Space Workshop in May 2006.Comment: 11 pages, Opening talk presented at the 2006 Workshop on Fundamental
Physics in Space. Submitted to Int'l Journal of Modern Physics,
On the future of Gamma-Ray Burst Cosmology
With the understanding that the enigmatic Gamma-Ray Burts (GRBs) are beamed
explosions, and with the recently discovered ``Ghirlanda-relation'', the dream
of using GRBs as cosmological yardsticks may have come a few steps closer to
reality. Assuming the Ghirlanda-relation is real, we have investigated possible
constraints on cosmological parameters using a simulated future sample of a
large number of GRBs inspired by the ongoing SWIFT mission. Comparing with
constraints from a future sample of Type Ia supernovae, we find that GRBs are
not efficient in constraining the amount of dark energy or its equation of
state. The main reason for this is that very few bursts are available at low
redshifts.Comment: 5 pages, 2 figures, matches version accepted for publication in JCA
New UltraCool and Halo White Dwarf Candidates in SDSS Stripe 82
A 2.5 x 100 degree region along the celestial equator (Stripe 82) has been
imaged repeatedly from 1998 to 2005 by the Sloan Digital Sky Survey. A new
catalogue of ~4 million light-motion curves, together with over 200 derived
statistical quantities, for objects in Stripe 82 brighter than r~21.5 has been
constructed by combining these data by Bramich et al. (2007). This catalogue is
at present the deepest catalogue of its kind. Extracting the ~130000 objects
with highest signal-to-noise ratio proper motions, we build a reduced proper
motion diagram to illustrate the scientific promise of the catalogue. In this
diagram disk and halo subdwarfs are well-separated from the cool white dwarf
sequence. Our sample of 1049 cool white dwarf candidates includes at least 8
and possibly 21 new ultracool H-rich white dwarfs (T_eff < 4000K) and one new
ultracool He-rich white dwarf candidate identified from their SDSS optical and
UKIDSS infrared photometry. At least 10 new halo white dwarfs are also
identified from their kinematics.Comment: 10 pages, 5 figures, published in MNRAS, minor text changes, final
versio
23 High Redshift Supernovae from the IfA Deep Survey: Doubling the SN Sample at z>0.7
We present photometric and spectroscopic observations of 23 high redshift
supernovae spanning a range of z=0.34-1.03, 9 of which are unambiguously
classified as Type Ia. These supernovae were discovered during the IfA Deep
Survey, which began in September 2001 and observed a total of 2.5 square
degrees to a depth of approximately m=25-26 in RIZ over 9-17 visits, typically
every 1-3 weeks for nearly 5 months, with additional observations continuing
until April 2002. We give a brief description of the survey motivations,
observational strategy, and reduction process. This sample of 23 high-redshift
supernovae includes 15 at z>0.7, doubling the published number of objects at
these redshifts, and indicates that the evidence for acceleration of the
universe is not due to a systematic effect proportional to redshift. In
combination with the recent compilation of Tonry et al. (2003), we calculate
cosmological parameter density contours which are consistent with the flat
universe indicated by the CMB (Spergel et al. 2003). Adopting the constraint
that Omega_total = 1.0, we obtain best-fit values of (Omega_m,
Omega_Lambda)=(0.33, 0.67) using 22 SNe from this survey augmented by the
literature compilation. We show that using the empty-beam model for
gravitational lensing does not eliminate the need for Omega_Lambda > 0.
Experience from this survey indicates great potential for similar large-scale
surveys while also revealing the limitations of performing surveys for z>1 SNe
from the ground.Comment: 67 pages, 12 figures, 12 tables, accepted for publication in the
Astrophysical Journa
Probing for cosmological parameters with LAMOST measurement
In this paper we study the sensitivity of the Large Sky Area Multi-Object
Fiber Spectroscopic Telescope (LAMOST) project to the determination of
cosmological parameters, employing the Monte Carlo Markov Chains (MCMC) method.
For comparison, we first analyze the constraints on cosmological parameters
from current observational data, including WMAP, SDSS and SN Ia. We then
simulate the 3D matter power spectrum data expected from LAMOST, together with
the simulated CMB data for PLANCK and the SN Ia from 5-year Supernovae Legacy
Survey (SNLS). With the simulated data, we investigate the future improvement
on cosmological parameter constraints, emphasizing the role of LAMOST. Our
results show the potential of LAMOST in probing for the cosmological
parameters, especially in constraining the equation-of-state (EoS) of the dark
energy and the neutrino mass.Comment: 7 pages and 3 figures. Replaced with version accepted for publication
in JCA
Light and Motion in SDSS Stripe 82: The Catalogues
We present a new public archive of light-motion curves in Sloan Digital Sky
Survey (SDSS) Stripe 82, covering 99 deg in right ascension from RA = 20.7 h to
3.3 h and spanning 2.52 deg in declination from Dec = -1.26 to 1.26 deg, for a
total sky area of ~249 sq deg. Stripe 82 has been repeatedly monitored in the
u, g, r, i and z bands over a seven-year baseline. Objects are cross-matched
between runs, taking into account the effects of any proper motion. The
resulting catalogue contains almost 4 million light-motion curves of stellar
objects and galaxies. The photometry are recalibrated to correct for varying
photometric zeropoints, achieving ~20 mmag and ~30 mmag root-mean-square (RMS)
accuracy down to 18 mag in the g, r, i and z bands for point sources and
extended sources, respectively. The astrometry are recalibrated to correct for
inherent systematic errors in the SDSS astrometric solutions, achieving ~32 mas
and ~35 mas RMS accuracy down to 18 mag for point sources and extended sources,
respectively.
For each light-motion curve, 229 photometric and astrometric quantities are
derived and stored in a higher-level catalogue. On the photometric side, these
include mean exponential and PSF magnitudes along with uncertainties, RMS
scatter, chi^2 per degree of freedom, various magnitude distribution
percentiles, object type (stellar or galaxy), and eclipse, Stetson and Vidrih
variability indices. On the astrometric side, these quantities include mean
positions, proper motions as well as their uncertainties and chi^2 per degree
of freedom. The here presented light-motion curve catalogue is complete down to
r~21.5 and is at present the deepest large-area photometric and astrometric
variability catalogue available.Comment: MNRAS accepte
The SuperMACHO Microlensing Survey
We present the first results from our next-generation microlensing survey,
the SuperMACHO project. We are using the CTIO 4m Blanco telescope and the
MOSAIC imager to carry out a search for microlensing toward the Large
Magellanic Cloud (LMC). We plan to ascertain the nature of the population
responsible for the excess microlensing rate seen by the MACHO project. Our
observing strategy is optimized to measure the differential microlensing rate
across the face of the LMC. We find this derivative to be relatively
insensitive to the details of the LMC's internal structure but a strong
discriminant between Galactic halo and LMC self lensing. In December 2003 we
completed our third year of survey operations. 2003 also marked the first year
of real-time microlensing alerts and photometric and spectroscopic followup. We
have extracted several dozen microlensing candidates, and we present some
preliminary light curves and related information. Similar to the MACHO project,
we find SNe behind the LMC to be a significant contaminant - this background
has not been completely removed from our current single-color candidate sample.
Our follow-up strategy is optimized to discriminate between SNe and true
microlensing.Comment: To appear in Proceedings of IAU Symposium 225: Impact of
Gravitational Lensing on Cosmology, 6 page
Pushing the Boundaries of Conventional Core-Collapse Supernovae: The Extremely Energetic Supernova SN 2003ma
We report the discovery of a supernova (SN) with the highest apparent energy
output to date and conclude that it represents an extreme example of the Type
IIn subclass. The SN, which was discovered behind the Large Magellanic Cloud at
z = 0.289 by the SuperMACHO microlensing survey, peaked at M_R = -21.5 mag and
only declined by 2.9 mag over 4.7 years after the peak. Over this period, SN
2003ma had an integrated bolometric luminosity of 4 x 10^51 ergs, more than any
other SN to date. The radiated energy is close to the limit allowed by
conventional core-collapse explosions. Optical spectra reveal that SN 2003ma
has persistent single-peaked intermediate-width hydrogen lines, a signature of
interaction between the SN and a dense circumstellar medium. The light curves
show further evidence for circumstellar interaction, including a long plateau
with a shape very similar to the classic SN IIn 1988Z -- however, SN 2003ma is
ten times more luminous at all epochs. The fast velocity measured for the
intermediate-width H_alpha component (~6000 km/s) points towards an extremely
energetic explosion (> 10^52 ergs), which imparts a faster blast-wave speed to
the post-shock material and a higher luminosity from the interaction than is
observed in typical SNe IIn. Mid-infrared observations of SN 2003ma suggest an
infrared light echo is produced by normal interstellar dust at a distance ~0.5
pc from the SN.Comment: 21 pages, 15 figures, accepted for publication in Ap
Lightcurves of Type Ia Supernovae from Near the Time of Explosion
We present a set of 11 type Ia supernova (SN Ia) lightcurves with dense,
pre-maximum sampling. These supernovae (SNe), in galaxies behind the Large
Magellanic Cloud (LMC), were discovered by the SuperMACHO survey. The SNe span
a redshift range of z = 0.11 - 0.35. Our lightcurves contain some of the
earliest pre-maximum observations of SNe Ia to date. We also give a functional
model that describes the SN Ia lightcurve shape (in our VR-band). Our function
uses the "expanding fireball" model of Goldhaber et al. (1998) to describe the
rising lightcurve immediately after explosion but constrains it to smoothly
join the remainder of the lightcurve. We fit this model to a composite observed
VR-band lightcurve of three SNe between redshifts of 0.135 to 0.165. These SNe
have not been K-corrected or adjusted to account for reddening. In this
redshift range, the observed VR-band most closely matches the rest frame
V-band. Using the best fit to our functional description of the lightcurve, we
find the time between explosion and observed VR-band maximum to be
17.6+-1.3(stat)+-0.07(sys) rest-frame days for a SN Ia with a VR-band Delta
m_{-10} of 0.52mag. For the redshifts sampled, the observed VR-band
time-of-maximum brightness should be the same as the rest-frame V-band maximum
to within 1.1 rest-frame days.Comment: 35 pages, 18 figures, 15 tables; Higher quality PDF available at
http://ctiokw.ctio.noao.edu/~sm/sm/SNrise/index.html; AJ accepte
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