48 research outputs found
Discovery of a New WZ Sagittae Type Cataclysmic Variable in the Kepler/K2 Data
We identify a new, bright transient in the Kepler/K2 Campaign 11 field. Its
light curve rises over seven magnitudes in a day and then declines three
magnitudes over a month before quickly fading another two magnitudes. The
transient was still detectable at the end of the campaign. The light curve is
consistent with a WZ~Sge type dwarf nova outburst. Early superhumps with a
period of 82 minutes are seen in the first 10 days and suggest that this is the
orbital period of the binary which is typical for the WZ~Sge class. Strong
superhump oscillations develop ten days after peak brightness with periods
ranging between 83 and 84 minutes. At 25 days after the peak brightness a bump
in the light curve appears to signal a subtle rebrightening phase implying that
this was an unusual type-A outburst. This is the only WZ~Sge type system
observed by Kepler/K2 during an outburst. The early rise of this outburst is
well-fit with a broken power law. In first 10 hours the system brightened
linearly and then transitioned to a steep rise with a power law index of 4.8.
Looking at archival Kepler/K2 data and new TESS observations, a linear rise in
the first several hours at the initiation of a superoutburst appears to be
common in SU~UMa stars.Comment: 11 pages, 14 figures, 2 tables, accepted to appear in the Monthly
Notices of the Royal Astronomical Societ
K2: Background Survey - The search for undiscovered transients in Kepler/K2 data
The K2 mission of the Kepler Space Telescope offers a unique possibility to examine sources of both Galactic and extragalactic origin with high-cadence photometry. Alongside the multitude of supernovae and quasars detected within targeted galaxies, it is likely that Kepler has serendipitously observed many transients throughout K2. Such events will likely have occurred in background pixels, coincidentally surrounding science targets. Analysing the background pixels presents the possibility to conduct a high-cadence survey with areas of a few square degrees per campaign. We demonstrate the capacity to independently recover key K2 transients such as KSN 2015K and SN 2018oh. With this survey, we expect to detect numerous transients and determine the first comprehensive rates for transients with lifetimes of <1 d.This research was supported by an Australian Government
Research Training Program (RTP) Scholarship and utilizes data
collected by the K2 missio
The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses
We present spatially and spectrally resolved Atacama Large
Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the
pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of
the CO and CO =2-1 transitions permits a measurement of
the total stellar mass in this system, , and the
circum-triple disk inclination, . Optical spectra spanning
a 35 year period were used to derive new radial velocities and, coupled with a
spectroscopic disentangling technique, revealed that the A and B components of
GW Ori form a double-lined spectroscopic binary with a day
period; a tertiary companion orbits that inner pair with a day
period. Combining the results from the ALMA data and the optical spectra with
three epochs of astrometry in the literature, we constrain the individual
stellar masses in the system (,
, ) and
find strong evidence that at least one (and likely both) stellar orbital planes
are misaligned with the disk plane by as much as . A -band light
curve spanning 30 years reveals several new 30 day eclipse events
0.1-0.7~mag in depth and a 0.2 mag sinusoidal oscillation that is clearly
phased with the AB-C orbital period. Taken together, these features suggest
that the A-B pair may be partially obscured by material in the inner disk as
the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude
that stellar evolutionary models are consistent with our measurements of the
masses and basic photospheric properties if the GW Ori system is 1 Myr
old.Comment: 26 pages, 15 figures, accepted to Ap
Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed
to locate quasars during the epoch of reionization. In this paper we present
the discovery of the first four CFHQS quasars at redshift greater than 6,
including the most distant known quasar, CFHQS J2329-0301 at z=6.43. We
describe the observational method used to identify the quasars and present
optical, infrared, and millimeter photometry and optical and near-infrared
spectroscopy. We investigate the dust properties of these quasars finding an
unusual dust extinction curve for one quasar and a high far-infrared luminosity
due to dust emission for another. The mean millimeter continuum flux for CFHQS
quasars is substantially lower than that for SDSS quasars at the same redshift,
likely due to a correlation with quasar UV luminosity. For two quasars with
sufficiently high signal-to-noise optical spectra, we use the spectra to
investigate the ionization state of hydrogen at z>5. For CFHQS J1509-1749 at
z=6.12, we find significant evolution (beyond a simple extrapolation of lower
redshift data) in the Gunn-Peterson optical depth at z>5.4. The line-of-sight
to this quasar has one of the highest known optical depths at z~5.8. An
analysis of the sizes of the highly-ionized near-zones in the spectra of two
quasars at z=6.12 and z=6.43 suggest the IGM surrounding these quasars was
substantially ionized before these quasars turned on. Together, these
observations point towards an extended reionization process, but we caution
that cosmic variance is still a major limitation in z>6 quasar observations.Comment: 15 pages, 9 figures, AJ, in press, minor changes to previous versio
A Large and Variable Leading Tail of Helium in a Hot Saturn Undergoing Runaway Inflation
Atmospheric escape shapes the fate of exoplanets, with statistical evidence
for transformative mass loss imprinted across the mass-radius-insolation
distribution. Here we present transit spectroscopy of the highly irradiated,
low-gravity, inflated hot Saturn HAT-P-67 b. The Habitable Zone Planet Finder
(HPF) spectra show a detection of up to 10% absorption depth of the 10833
Angstrom Helium triplet. The 13.8 hours of on-sky integration time over 39
nights sample the entire planet orbit, uncovering excess Helium absorption
preceding the transit by up to 130 planetary radii in a large leading tail.
This configuration can be understood as the escaping material overflowing its
small Roche lobe and advecting most of the gas into the stellar -- and not
planetary -- rest frame, consistent with the Doppler velocity structure seen in
the Helium line profiles. The prominent leading tail serves as direct evidence
for dayside mass loss with a strong day-/night- side asymmetry. We see some
transit-to-transit variability in the line profile, consistent with the
interplay of stellar and planetary winds. We employ 1D Parker wind models to
estimate the mass loss rate, finding values on the order of
g/s, with large uncertainties owing to the unknown XUV flux of the F host star.
The large mass loss in HAT-P-67 b represents a valuable example of an inflated
hot Saturn, a class of planets recently identified to be rare as their
atmospheres are predicted to evaporate quickly. We contrast two physical
mechanisms for runaway evaporation: Ohmic dissipation and XUV irradiation,
slightly favoring the latter.Comment: Submitted to The Astronomical Journa
The architecture of the GW Ori Young triple-star system and its disk : dynamical masses, mutual inclinations, and recurrent eclipses
We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the pre-main-sequence hierarchical triple-star system GW Ori. A forward modeling of the 13CO and C18O J = 2-1 transitions permits a measurement of the total stellar mass in this system, 5.29+/- 0.09 Mâ , and the circumtriple disk inclination, 137 o. 6+/- 2 o. 0. Optical spectra spanning a 35 yr period were used to derive new radial velocities and, coupled with a spectroscopic disentangling technique, revealed that the A and B components of GW Ori form a double-lined spectroscopic binary with a period of 241.50 ± 0.05 days; a tertiary companion orbits that inner pair with a period of 4218 ± 50 days. Combining the results from the ALMA data and the optical spectra with three epochs of astrometry in the literature, we constrain the individual stellar masses in the system (MA â 2.7 Mâ , MB â 1.7 Mâ , MC â 0.9 Mâ) and find strong evidence that at least one of the stellar orbital planes (and likely both) is misaligned with the disk plane by as much as 45°. A V-band light curve spanning 30 yr reveals several new âŒ30-day eclipse events 0.1-0.7 mag in depth and a 0.2 mag sinusoidal oscillation that is clearly phased with the AB-C orbital period. Taken together, these features suggest that the A-B pair may be partially obscured by material in the inner disk as the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude that stellar evolutionary models are consistent with our measurements of the masses and basic photospheric properties if the GW Ori system is âŒ1 Myr old.Peer reviewe
The igrins yso survey. i. stellar parameters of pre-main-sequence stars in taurus- auriga
We present fundamental parameters for 110 canonical K- and M-type (1.3-0.13Me) Taurus-Auriga young stellar objects (YSOs). The analysis produces a simultaneous determination of effective temperature (Teff), surface gravity (log g), magnetic-field strength (B), and projected rotational velocity (v sin i). Our method employed synthetic spectra and high-resolution (R ⌠45,000) near-infrared spectra taken with the Immersion GRating INfrared Spectrometer (IGRINS) to fit specific K-band spectral regions most sensitive to those parameters. The use of these high-resolution spectra reduces the influence of distance uncertainties, reddening, and non-photospheric continuum emission on the parameter determinations. The median total (fit + systematic) uncertainties were 170 K, 0.28 dex, 0.60 kG, 2.5 km s-1 for Teff, log g, B, and v sin i, respectively. We determined B for 41 Taurus YSOs (upper limits for the remainder) and find systematic offsets (lower Teff, higher log g and v sin i) in parameters when B is measurable but not considered in the fit. The average log g for the Class II and Class III objects differs by 0.23 ± 0.05 dex, which is consistent with Class III objects being the more evolved members of the star-forming region. However, the dispersion in log g is greater than the uncertainties, which highlights how the YSO classification correlates with age (log g), yet there are exceptionally young (lower log g) Class III YSOs and relatively old (higher log g) Class II YSOs with unexplained evolutionary histories. The spectra from this work are provided in an online repository along with TW Hydrae Association comparison objects and the model grid used in our analysis