3 research outputs found
AT2019wxt: An ultra-stripped supernova candidate discovered in electromagnetic follow-up of a gravitational wave trigger
We present optical, radio and X-ray observations of a rapidly-evolving
transient AT2019wxt (PS19hgw), discovered during the search for an
electromagnetic (EM) counterpart to the gravitational-wave (GW) trigger
S191213g (LIGO Scientific Collaboration & Virgo Collaboration 2019a). Although
S191213g was not confirmed as a significant GW event in the off-line analysis
of LIGO-Virgo data, AT2019wxt remained an interesting transient due its
peculiar nature. The optical/NIR light curve of AT2019wxt displayed a
double-peaked structure evolving rapidly in a manner analogous to currently
know ultra-stripped supernovae (USSNe) candidates. This double-peaked structure
suggests presence of an extended envelope around the progenitor, best modelled
with two-components: i) early-time shock-cooling emission and ii) late-time
radioactive Ni decay. We constrain the ejecta mass of AT2019wxt at
which indicates a significantly stripped
progenitor that was possibly in a binary system. We also followed-up AT2019wxt
with long-term Chandra and Jansky Very Large Array observations spanning
260 days. We detected no definitive counterparts at the location of
AT2019wxt in these long-term X-ray and radio observational campaigns. We
establish the X-ray upper limit at erg cm s
and detect an excess radio emission from the region of AT2019wxt. However,
there is little evidence for SN1993J- or GW170817-like variability of the radio
flux over the course of our observations. A substantial host galaxy
contribution to the measured radio flux is likely. The discovery and early-time
peak capture of AT2019wxt in optical/NIR observation during EMGW follow-up
observations highlights the need of dedicated early, multi-band photometric
observations to identify USSNe.Comment: 20 pages, 14 figures, Submitted to Ap
Updated Planetary Mass Constraints of the Young V1298 Tau System Using MAROON-X
The early K-type T-Tauri star, V1298 Tau (, ) hosts four transiting planets with radii ranging
from . The three inner planets have orbital periods of
while the outer planet's period is poorly constrained by
single transits observed with \emph{K2} and \emph{TESS}. Planets b, c, and d
are proto-sub-Neptunes that may be undergoing significant mass loss. Depending
on the stellar activity and planet masses, they are expected to evolve into
super-Earths/sub-Neptunes that bound the radius valley. Here we present results
of a joint transit and radial velocity (RV) modelling analysis, which includes
recently obtained \emph{TESS} photometry and MAROON-X RV measurements. Assuming
circular orbits, we obtain a low-significance () RV detection
of planet c implying a mass of and a
conservative upper limit of . For planets b and d, we
derive upper limits of and . For planet e, plausible discrete periods of are ruled out at a level while seven solutions with
are consistent with the most probable
solution within . Adopting the most
probable solution yields a RV detection with mass a of
. Comparing the updated mass and radius constraints
with planetary evolution and interior structure models shows that planets b, d,
and e are consistent with predictions for young gas-rich planets and that
planet c is consistent with having a water-rich core with a substantial
( by mass) H envelope.Comment: 18 pages, 13 figures, accepted for publication in A
A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
Close-in giant exoplanets with temperatures greater than 2,000 K (''ultra-hot
Jupiters'') have been the subject of extensive efforts to determine their
atmospheric properties using thermal emission measurements from the Hubble and
Spitzer Space Telescopes. However, previous studies have yielded inconsistent
results because the small sizes of the spectral features and the limited
information content of the data resulted in high sensitivity to the varying
assumptions made in the treatment of instrument systematics and the atmospheric
retrieval analysis. Here we present a dayside thermal emission spectrum of the
ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on JWST. The
data span 0.85 to 2.85 m in wavelength at an average resolving power of
400 and exhibit minimal systematics. The spectrum shows three water emission
features (at 6 confidence) and evidence for optical opacity,
possibly due to H, TiO, and VO (combined significance of 3.8).
Models that fit the data require a thermal inversion, molecular dissociation as
predicted by chemical equilibrium, a solar heavy element abundance
(''metallicity'', M/H = 1.03 solar), and a
carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside
brightness temperature map, which shows a peak in temperature near the
sub-stellar point that decreases steeply and symmetrically with longitude
toward the terminators.Comment: JWST ERS bright star observations. Uploaded to inform JWST Cycle 2
proposals. Manuscript under review. 50 pages, 14 figures, 2 table