35 research outputs found
Research on the Problem of High-Precision Deployment for Large-Aperture Space-Based Science Instruments
The present paper summarizes results from an ongoing research program conducted jointly by the University of Colorado and NASA Langley Research Center since 1994. This program has resulted in general guidelines for the design of high-precision deployment mechanisms, and tests of prototype deployable structures incorporating these mechanisms have shown microdynamically stable behavior (i.e., dimensional stability to parts per million). These advancements have resulted from the identification of numerous heretofore unknown microdynamic and micromechanical response phenomena, and the development of new test techniques and instrumentation systems to interrogate these phenomena. In addition, recent tests have begun to interrogate nanomechanical response of materials and joints and have been used to develop an understanding of nonlinear nanodynamic behavior in microdynamically stable structures. The ultimate goal of these efforts is to enable nano-precision active control of micro-precision deployable structures (i.e., active control to a resolution of parts per billion)
Examining the Properties of Low-Luminosity Hosts of Type Ia Supernovae from ASAS-SN
We present a spectroscopic analysis of 44 low-luminosity host galaxies of
Type Ia supernovae (SNe Ia) detected by the All-Sky Automated Survey for
Supernovae (ASAS-SN), using the emission lines to measure metallicities and
star formation rates. We find that although the star formation activity of our
sample is representative of general galaxies, there is some evidence that the
lowest-mass SN Ia host galaxies (log()) in our sample have
high metallicities compared to general galaxies of similar masses. We also
identify a subset of 5 galaxies with particularly high metallicities. This
highlights the need for spectroscopic analysis of more low-luminosity, low-mass
SN Ia host galaxies to test the robustness of these conclusions and their
potential impact on our understanding of SN Ia progenitors.Comment: 13 pages, 7 figures, 2 tables. Submitted to ApJ. Full versions of the
tables in the paper are available in machine-readable format as ancillary
file
ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003
We present the discovery that ASASSN-14ko is a periodically flaring AGN at
the center of the galaxy ESO 253-G003. At the time of its discovery by the
All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a
supernova close to the nucleus. The subsequent six years of V- and g-band
ASAS-SN observations reveal that ASASSN-14ko has nuclear flares occurring at
regular intervals. The seventeen observed outbursts show evidence of a
decreasing period over time, with a mean period of days
and a period derivative of . The most recent
outburst in May 2020, which took place as predicted, exhibited spectroscopic
changes during the rise and a had a UV bright, blackbody spectral energy
distribution similar to tidal disruption events (TDEs). The X-ray flux
decreased by a factor of 4 at the beginning of the outburst and then returned
to its quiescent flux after ~8 days. TESS observed an outburst during Sectors
4-6, revealing a rise time of days in the optical and a decline
that is best fit with an exponential model. We discuss several possible
scenarios to explain ASASSN-14ko's periodic outbursts, but currently favor a
repeated partial TDE. The next outbursts should peak in the optical on UT
2020-09-7.41.1 and UT 2020-12-26.51.4.Comment: 26 pages, 15 figures, 7 tables. Will be submitted to ApJ. The latest
flare is currently ongoing, as we predicte
Discovery and Follow-up of ASASSN-19dj: An X-ray and UV Luminous TDE in an Extreme Post-Starburst Galaxy
We present observations of ASASSN-19dj, a nearby tidal disruption event (TDE)
discovered in the post-starburst galaxy KUG 0810+227 by the All-Sky Automated
Survey for Supernovae (ASAS-SN) at a distance of d 98 Mpc. We observed
ASASSN-19dj from 21 to 392 days relative to peak UV/optical emission using
high-cadence, multi-wavelength spectroscopy and photometry. From the ASAS-SN
-band data, we determine that the TDE began to brighten on 2019 February 6.8
and for the first 25 days the rise was consistent with a flux
power-law. ASASSN-19dj peaked in the UV/optical on 2019 March 6.5 (MJD =
58548.5) at a bolometric luminosity of . Initially remaining roughly constant in X-rays and slowly fading
in the UV/optical, the X-ray flux increased by over an order of magnitude
225 days after peak, resulting from the expansion of the X-ray emitting
surface. The late-time X-ray emission is well-fit by a blackbody with an
effective radius of and a temperature of
. Analysis of Catalina Real-Time Transient
Survey images reveals a nuclear outburst roughly 14.5 years earlier with a
smooth decline and a luminosity of erg
s, although the nature of the flare is unknown. ASASSN-19dj occurred in
the most extreme post-starburst galaxy yet to host a TDE, with Lick
H = \AA.Comment: 25 pages, 14 figures. Will be submitted to MNRAS. For a short video
description please see https://youtu.be/WjTZwO7vcF
Fast and Not-so-Furious: Case Study of the Fast and Faint Type IIb SN 2021bxu
We present photometric and spectroscopic observations and analysis of
SN~2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova
(SN). SN~2021bxu is unique, showing a large initial decline in brightness
followed by a short plateau phase. With
during the plateau, it is at the lower end of the luminosity distribution of
stripped-envelope supernovae (SE-SNe) and shows a distinct 10 day plateau
not caused by H- or He-recombination. SN~2021bxu shows line velocities which
are at least slower than typical SE-SNe. It is
photometrically and spectroscopically similar to Type IIb SNe during the
photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find
that the bolometric light curve is best described by a composite model of shock
interaction between the ejecta and an envelope of extended material, combined
with a typical SN~IIb powered by the radioactive decay of Ni. The
best-fit parameters for SN~2021bxu include a Ni mass of , an ejecta mass of
, and an ejecta
kinetic energy of . From the fits to the properties of the extended material of
Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing
envelope mass. SN~2021bxu has on the low end compared to
SE-SNe and Ca-rich SNe in the literature, demonstrating that SN~2021bxu-like
events are rare explosions in extreme areas of parameter space. The progenitor
of SN~2021bxu is likely a low mass He star with an extended envelope.Comment: 18 pages, 15 figures, submitted to MNRA
SN 2022crv: IIb, Or Not IIb: That is the Question
We present optical and near-infrared observations of SN~2022crv, a stripped
envelope supernova in NGC~3054, discovered within 12 hrs of explosion by the
Distance Less Than 40 Mpc Survey. We suggest SN~2022crv is a transitional
object on the continuum between SNe Ib and SNe IIb. A high-velocity hydrogen
feature (20,000 -- 16,000 ) was conspicuous in
SN~2022crv at early phases, and then quickly disappeared around maximum light.
By comparing with hydrodynamic modeling, we find that a hydrogen envelope of
\msun{} can reproduce the behaviour of the hydrogen feature
observed in SN~2022crv. The early light curve of SN~2022crv did not show
envelope cooling emission, implying that SN~2022crv had a compact progenitor
with extremely low amount of hydrogen. The analysis of the nebular spectra
shows that SN~2022crv is consistent with the explosion of a He star with a
final mass of 4.5 -- 5.6 \msun{} that has evolved from a 16 -- 22
\msun{} zero-age main sequence star in a binary system with about 1.0 -- 1.7
\msun{} of oxygen finally synthesized in the core. The high metallicity at the
supernova site indicates that the progenitor experienced a strong stellar wind
mass loss. In order to retain a small amount of residual hydrogen at such a
high metallicity, the initial orbital separation of the binary system is likely
larger than 1000~. The near-infrared spectra of SN~2022crv
show a unique absorption feature on the blue side of He I line at
1.005~m. This is the first time that such a feature has been
observed in a Type Ib/IIb, and could be due to \ion{Sr}{2}. Further detailed
modelling on SN~2022crv can shed light on the progenitor and the origin of the
mysterious absorption feature in the near infrared.Comment: 33 pages, 23 figures, submitted to Ap
Strong Carbon Features and a Red Early Color in the Underluminous Type Ia SN 2022xkq
We present optical, infrared, ultraviolet, and radio observations of SN
2022xkq, an underluminous fast-declining type Ia supernova (SN Ia) in NGC 1784
( Mpc), from to 180 days after explosion. The
high-cadence observations of SN 2022xkq, a photometrically transitional and
spectroscopically 91bg-like SN Ia, cover the first days and weeks following
explosion which are critical to distinguishing between explosion scenarios. The
early light curve of SN 2022xkq has a red early color and exhibits a flux
excess which is more prominent in redder bands; this is the first time such a
feature has been seen in a transitional/91bg-like SN Ia. We also present 92
optical and 19 near-infrared (NIR) spectra, beginning 0.4 days after explosion
in the optical and 2.6 days after explosion in the NIR. SN 2022xkq exhibits a
long-lived C I 1.0693 m feature which persists until 5 days post-maximum.
We also detect C II 6580 in the pre-maximum optical spectra. These
lines are evidence for unburnt carbon that is difficult to reconcile with the
double detonation of a sub-Chandrasekhar mass white dwarf. No existing
explosion model can fully explain the photometric and spectroscopic dataset of
SN 2022xkq, but the considerable breadth of the observations is ideal for
furthering our understanding of the processes which produce faint SNe Ia.Comment: 38 pages, 16 figures, accepted for publication in ApJ, the figure 15
input models and synthetic spectra are now available at
https://zenodo.org/record/837925
Research On The Problem Of High-Precision Deployment For Large-Aperture Space-Based Science Instruments
The present paper summarizes results from an ongoing research program conducted jointly by the University of Colorado and NASA Langley Research Center since 1994. This program has resulted in general guidelines for the design of high-precision deployment mechanisms, and tests of prototype deployable structures incorporating these mechanisms have shown microdynamically stable behavior (i.e., dimensional stability to parts per million). These advancements have resulted from the identification of numerous heretofore unknown microdynamic and micromechanical response phenomena, and the development of new test techniques and instrumentation systems to interrogate these phenomena. In addition, recent tests have begun to interrogate nanomechanical response of materials and joints and have been used to develop an understanding of nonlinear nanodynamic behavior in microdynamically stable structures. The ultimate goal of these efforts is to enable nano-precision active control of micro-precisio..