47 research outputs found
Applications of thermal energy storage in the cement industry
In the manufacture of cement, literally trillions of Btu's are rejected to the environment each year. The purpose of this feasibility study program was to determine whether thermal energy storage could be used to conserve or allow alternative uses of this rejected energy. This study identifies and quantifies the sources of rejected energy in the cement manufacturing process, established use of this energy, investigates various storage system concepts, and selects energy conservation systems for further study. Thermal performance and economic analyses are performed on candidate storage systems for four typical cement plants representing various methods of manufacturing cement. Through the use of thermal energy storage in conjunction with waste heat electric power generation units, an estimated 2.4 x 10 to the 13th power Btu/year, or an equivalent on investment of the proposed systems are an incentive for further development
Discovery, classification, and scientific exploration of transient events from the Catalina Real-time Transient Survey
Exploration of the time domain - variable and transient objects and phenomena
- is rapidly becoming a vibrant research frontier, touching on essentially
every field of astronomy and astrophysics, from the Solar system to cosmology.
Time domain astronomy is being enabled by the advent of the new generation of
synoptic sky surveys that cover large areas on the sky repeatedly, and
generating massive data streams. Their scientific exploration poses many
challenges, driven mainly by the need for a real-time discovery,
classification, and follow-up of the interesting events. Here we describe the
Catalina Real-Time Transient Survey (CRTS), that discovers and publishes
transient events at optical wavelengths in real time, thus benefiting the
entire community. We describe some of the scientific results to date, and then
focus on the challenges of the automated classification and prioritization of
transient events. CRTS represents a scientific and a technological testbed and
precursor for the larger surveys in the future, including the Large Synoptic
Survey Telescope (LSST) and the Square Kilometer Array (SKA).Comment: 22 pages, 12 figures, invited review for the Bulletin of Astronomical
Society of Indi
The Discovery and Nature of Optical Transient CSS100217:102913+404220
We report on the discovery and observations of the extremely luminous optical
transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic
observations show this transient was coincident with a galaxy at redshift
z=0.147, and reached an apparent magnitude of V ~ 16.3. After correcting for
foreground Galactic extinction we determine the absolute magnitude to be M_V
=-22.7 approximately 45 days after maximum light. Based on our unfiltered
optical photometry the peak optical emission was L = 1.3 x 10^45 erg s^-1, and
over a period of 287 rest-frame days had an integrated bolometric luminosity of
1.2 x 10^52 erg. Analysis of the pre-outburst SDSS spectrum of the source shows
features consistent with a Narrow-line Seyfert1 (NLS1) galaxy. High-resolution
HST and Keck followup observations show the event occurred within 150pc of
nucleus of the galaxy, suggesting a possible link to the active nuclear region.
However, the rapid outburst along with photometric and spectroscopic evolution
are much more consistent with a luminous supernova. Line diagnostics suggest
that the host galaxy is undergoing significant star formation. We use extensive
follow-up of the event along with archival CSS and SDSS data to investigate the
three most likely sources of such an event; 1) an extremely luminous supernova;
2) the tidal disruption of a star by the massive nuclear black hole; 3)
variability of the central AGN. We find that CSS100217 was likely an extremely
luminous type IIn supernova that occurred within range of the narrow-line
region of an AGN. We discuss how similar events may have been missed in past
supernova surveys because of confusion with AGN activity.Comment: submitted to Ap
SDWFS-MT-1: A Self-Obscured Luminous Supernova at z~0.2
We report the discovery of a six-month-long mid-infrared transient,
SDWFS-MT-1 (aka SN 2007va), in the Spitzer Deep, Wide-Field Survey of the NOAO
Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low
luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8)
irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2
in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least
10^51 ergs. The optical emission was likely fainter than the mid-infrared,
although our constraints on the optical emission are poor because the transient
peaked when the source was "behind" the Sun. The Spitzer data are consistent
with emission by a modified black body with a temperature of ~1350 K. We rule
out a number of scenarios for the origin of the transient such as a Galactic
star, AGN activity, GRB, tidal disruption of a star by a black hole and
gravitational lensing. The most plausible scenario is a supernova exploding
inside a massive, optically thick circumstellar medium, composed of multiple
shells of previously ejected material. If the proposed scenario is correct,
then a significant fraction (~10%) of the most luminous supernova may be
self-enshrouded by dust not only before but also after the supernova occurs.
The spectral energy distribution of the progenitor of such a supernova would be
a slightly cooler version of eta Carina, peaking at 20-30 microns.Comment: 26 pages, 5 figures, 1 table, accepted for publication in Ap
Supernova 2007bi as a pair-instability explosion
Stars with initial masses 10 M_{solar} < M_{initial} < 100 M_{solar} fuse
progressively heavier elements in their centres, up to inert iron. The core
then gravitationally collapses to a neutron star or a black hole, leading to an
explosion -- an iron-core-collapse supernova (SN). In contrast, extremely
massive stars (M_{initial} > 140 M_{solar}), if such exist, have oxygen cores
which exceed M_{core} = 50 M_{solar}. There, high temperatures are reached at
relatively low densities. Conversion of energetic, pressure-supporting photons
into electron-positron pairs occurs prior to oxygen ignition, and leads to a
violent contraction that triggers a catastrophic nuclear explosion. Tremendous
energies (>~ 10^{52} erg) are released, completely unbinding the star in a
pair-instability SN (PISN), with no compact remnant. Transitional objects with
100 M_{solar} < M_{initial} < 140 M_{solar}, which end up as iron-core-collapse
supernovae following violent mass ejections, perhaps due to short instances of
the pair instability, may have been identified. However, genuine PISNe, perhaps
common in the early Universe, have not been observed to date. Here, we present
our discovery of SN 2007bi, a luminous, slowly evolving supernova located
within a dwarf galaxy (~1% the size of the Milky Way). We measure the exploding
core mass to be likely ~100 M_{solar}, in which case theory unambiguously
predicts a PISN outcome. We show that >3 M_{solar} of radioactive 56Ni were
synthesized, and that our observations are well fit by PISN models. A PISN
explosion in the local Universe indicates that nearby dwarf galaxies probably
host extremely massive stars, above the apparent Galactic limit, perhaps
resulting from star formation processes similar to those that created the first
stars in the Universe.Comment: Accepted version of the paper appearing in Nature, 462, 624 (2009),
including all supplementary informatio
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
We report the results of long observing campaigns on two novalike variables:
V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra,
complex line profiles signifying mass loss at particular orbital phases, and
similar orbital periods (respectively 0.12433 and 0.12056 d). They are
well-credentialed members of the SW Sex class of cataclysmic variables. Their
light curves are also quite complex. V442 Oph shows periodic signals with
periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar
signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long
periods respectively as a "negative superhump" and the wobble period of the
accretion disk. The superhump could then possibly arise from the heating of the
secondary (and structures fixed in the orbital frame) by inner-disk radiation,
which reaches the secondary relatively unimpeded since the disk is not
coplanar.
At higher frequencies, both stars show another type of variability:
quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying
these strong signals of low stability may be weak signals of higher stability.
Similar QPOs, and negative superhumps, are quite common features in SW Sex
stars. Both can in principle be explained by ascribing strong magnetism to the
white dwarf member of the binary; and we suggest that SW Sex stars are
borderline AM Herculis binaries, usually drowned by a high accretion rate. This
would provide an ancestor channel for AM Hers, whose origin is still
mysterious.Comment: PDF, 41 pages, 4 tables, 16 figures; accepted, in press, to appear
December 2002, PASP; more info at http://cba.phys.columbia.edu
SN 2008jb: A "Lost" Core-Collapse Supernova in a Star-Forming Dwarf Galaxy at ~10 Mpc
We present the discovery and follow-up observations of SN 2008jb, a
core-collapse supernova in the dwarf irregular galaxy ESO 302-14 at 9.6 Mpc.
This transient was missed by galaxy-targeted surveys and was only found in
archival optical images obtained by CRTS and ASAS. It was detected shortly
after explosion and reached a bright optical maximum, Vmax = 13.6 mag (M_Vmax ~
-16.5). The shape of the light curve shows a plateau of 100 days, followed by a
drop of 1.4 mag in V-band to a decline with the approximate Co 56 decay slope,
consistent with 0.04 Msun of Ni 56 synthesized in the explosion. A spectrum
obtained 2 years after explosion shows a broad, boxy Halpha emission line,
which is unusual for type IIP supernovae. We detect the supernova in archival
Spitzer and WISE images obtained 8-14 months after explosion, which show clear
signs of warm dust emission. The dwarf irregular host galaxy has a low
gas-phase oxygen abundance, 12 + log(O/H) = 8.2 (~1/5 Solar), similar to those
of the SMC and the hosts of long gamma-ray bursts and luminous core-collapse
supernovae. We study the host environment using GALEX FUV, R-band, and Halpha
images and find that the supernova occurred in a large star-formation complex.
The morphology of the Halpha emission appears as a large shell (R = 350 pc)
surrounding the FUV and optical emission. We estimate an age of ~9 Myr and a
total mass of ~2 x 10^5 Msun for the star-formation complex. These properties
are consistent with the expanding Halpha supershells observed in well-studied
nearby dwarf galaxies, which are tell-tale signs of feedback from the
cumulative effect of massive star winds and supernovae. The age estimated for
the star-forming region suggests a relatively high-mass progenitor star with
initial mass of ~20 Msun. We discuss the implications of these findings in the
study of core-collapse supernova progenitors. (Abridged)Comment: 41 pages, 10 figures, accepted in ApJ; small changes, conclusions
unchange
The 2001 Superoutburst of WZ Sagittae
We report the results of a worldwide campaign to observe WZ Sagittae during
its 2001 superoutburst. After a 23-year slumber at V=15.5, the star rose within
2 days to a peak brightness of 8.2, and showed a main eruption lasting 25 days.
The return to quiescence was punctuated by 12 small eruptions, of ~1 mag
amplitude and 2 day recurrence time; these "echo outbursts" are of uncertain
origin, but somewhat resemble the normal outbursts of dwarf novae. After 52
days, the star began a slow decline to quiescence.
Periodic waves in the light curve closely followed the pattern seen in the
1978 superoutburst: a strong orbital signal dominated the first 12 days,
followed by a powerful /common superhump/ at 0.05721(5) d, 0.92(8)% longer than
P_orb. The latter endured for at least 90 days, although probably mutating into
a "late" superhump with a slightly longer mean period [0.05736(5) d]. The
superhump appeared to follow familiar rules for such phenomena in dwarf novae,
with components given by linear combinations of two basic frequencies: the
orbital frequency omega_o and an unseen low frequency Omega, believed to
represent the accretion disk's apsidal precession. Long time series reveal an
intricate fine structure, with ~20 incommensurate frequencies. Essentially all
components occurred at a frequency n(omega_o)-m(Omega), with m=1, ..., n. But
during its first week, the common superhump showed primary components at n
(omega_o)-Omega, for n=1, 2, 3, 4, 5, 6, 7, 8, 9 (i.e., m=1 consistently); a
month later, the dominant power shifted to components with m=n-1. This may
arise from a shift in the disk's spiral-arm pattern, likely to be the
underlying cause of superhumps.
The great majority of frequency components ... . (etc., abstract continues)Comment: PDF, 54 pages, 4 tables, 21 figures, 1 appendix; accepted, in press,
to appear July 2002, PASP; more info at http://cba.phys.columbia.edu
OSIRIS-REx Contamination Control Strategy and Implementation
OSIRIS-REx will return pristine samples of carbonaceous asteroid Bennu. This manuscript describes how pristine was defined based on expectations of Bennu and on a realistic understanding of what is achievable with a constrained schedule and budget, and how that definition flowed to requirements and implementation. To return a pristine sample, the OSIRIS-REx spacecraft sampling hardware was maintained at Level 100 A/2 and less than 180 nanograms per square centimeter of amino acids and hydrazine on the sampler head through precision cleaning, control of materials, and vigilance. Contamination is further characterized via witness material exposed to the spacecraft assembly and testing environment as well as in space. This characterization provided knowledge of the expected background and will be used in conjunction with archived spacecraft components for comparison with the samples when they are delivered to Earth for analysis. Most of all, the cleanliness of the OSIRIS-REx spacecraft was achieved through communication between scientists, engineers, managers, and technicians
The Catalina Surveys Periodic Variable Star Catalog
We present ~47,000 periodic variables found during the analysis of 5.4
million variable star candidates within a 20,000 square degree region covered
by the Catalina Surveys Data Release-1 (CSDR1). Combining these variables with
type-ab RR Lyrae from our previous work, we produce an on-line catalog
containing periods, amplitudes, and classifications for ~61,000 periodic
variables. By cross-matching these variables with those from prior surveys, we
find that > 90% of the ~8,000 known periodic variables in the survey region are
recovered. For these sources we find excellent agreement between our catalog
and prior values of luminosity, period and amplitude, as well as
classification.
We investigate the rate of confusion between objects classified as contact
binaries and type-c RR Lyrae (RRc's) based on periods, colours, amplitudes,
metalicities, radial velocities and surface gravities. We find that no more
than few percent of these variables in these classes are misidentified. By
deriving distances for this clean sample of ~5,500 RRc's, we trace the path of
the Sagittarius tidal streams within the Galactic halo. Selecting 146
outer-halo RRc's with SDSS radial velocities, we confirm the presence of a
coherent halo structure that is inconsistent with current N-body simulations of
the Sagittarius tidal stream. We also find numerous long-period variables that
are very likely associated within the Sagittarius tidal streams system.
Based on the examination of 31,000 contact binary light curves we find
evidence for two subgroups exhibiting irregular lightcurves. One subgroup
presents significant variations in mean brightness that are likely due to
chromospheric activity. The other subgroup shows stable modulations over more
than a thousand days and thereby provides evidence that the O'Connell effect is
not due to stellar spots.Comment: Accepted ApJS, 43 pages, 9 tables, 44 figures (some at reduced
resolution