199 research outputs found
Highly Variable Extinction and Accretion in the Jet-driving Class I Type Young Star PTF 10nvg (V2492 Cyg, IRAS 20496+4354)
We report extensive new photometry and spectroscopy of the highly variable
young stellar object PTF 10nvg including optical and near-infrared time series
data as well as mid-infrared and millimeter data. Following the previously
reported 2010 rise, during 2011 and 2012 the source underwent additional
episodes of brightening and dimming events including prolonged faint states.
The observed high-amplitude variations are largely consistent with extinction
changes having a 220 day quasi-periodic signal. Spectral evolution includes not
only changes in the spectral slope but correlated variation in the prominence
of TiO/VO/CO bands and atomic line emission, as well as anticorrelated
variation in forbidden line emission which, along with H_2, dominates optical
and infrared spectra at faint epochs. Neutral and singly-ionized atomic species
are likely formed in an accretion flow and/or impact while the origin of
zero-velocity atomic LiI 6707 in emission is unknown. Forbidden lines,
including several rare species, exhibit blueshifted emission profiles and
likely arise from an outflow/jet. Several of these lines are also seen
spatially offset from the continuum source position, presumably in a shocked
region of an extended jet. CARMA maps resolve on larger scales a spatially
extended outflow in mm-wavelength CO. We attribute the observed photometric and
spectroscopic behavior in terms of occultation of the central star as well as
the bright inner disk and the accretion/outflow zones that renders shocked gas
in the inner part of the jet amenable to observation at the faint epochs. We
discuss PTF 10nvg as a source exhibiting both accretion-driven (perhaps
analogous to V1647 Ori) and extinction-driven (perhaps analogous to UX Ori or
GM Cep) high-amplitude variability phenomena.Comment: accepted to AJ - in press (74 pages
Discovery of a Transiting Adolescent Sub-Neptune Exoplanet with K2
The role of stellar age in the measured properties and occurrence rates of
exoplanets is not well understood. This is in part due to a paucity of known
young planets and the uncertainties in age-dating for most exoplanet host
stars. Exoplanets with well-constrained ages, particularly those which are
young, are useful as benchmarks for studies aiming to constrain the
evolutionary timescales relevant for planets. Such timescales may concern
orbital migration, gravitational contraction, or atmospheric photo-evaporation,
among other mechanisms. Here we report the discovery of an adolescent
transiting sub-Neptune from K2 photometry of the low-mass star K2-284. From
multiple age indicators we estimate the age of the star to be 120 Myr, with a
68% confidence interval of 100-760 Myr. The size of K2-284 b ( = 2.8
0.1 ) combined with its youth make it an intriguing case study for
photo-evaporation models, which predict enhanced atmospheric mass loss during
early evolutionary stages.Comment: Accepted to AJ, 36 pages, 17 figures, 5 table
SSAGES : Software Suite for Advanced General Ensemble Simulations
Molecular simulation has emerged as an essential tool for modern-day research, but obtaining proper results and making reliable conclusions from simulations requires adequate sampling of the system under consideration. To this end, a variety of methods exist in the literature that can enhance sampling considerably, and increasingly sophisticated, effective algorithms continue to be developed at a rapid pace. Implementation of these techniques, however, can be challenging for experts and non-experts alike. There is a clear need for software that provides rapid, reliable, and easy access to a wide range of advanced sampling methods and that facilitates implementation of new techniques as they emerge. Here we present SSAGES, a publicly available Software Suite for Advanced General Ensemble Simulations designed to interface with multiple widely used molecular dynamics simulations packages. SSAGES allows facile application of a variety of enhanced sampling techniquesâincluding adaptive biasing force, string methods, and forward flux samplingâthat extract meaningful free energy and transition path data from all-atom and coarse-grained simulations. A noteworthy feature of SSAGES is a user-friendly framework that facilitates further development and implementation of new methods and collective variables. In this work, the use of SSAGES is illustrated in the context of simple representative applications involving distinct methods and different collective variables that are available in the current release of the suite. The code may be found at: https://github.com/MICCoM/SSAGES-public
Non-O157 Shiga Toxinâproducing Escherichia coli Associated with Venison
News reports of âE. coli outbreaksâ usually refer to Shiga toxinâproducing E. coli O157. But there are other types of Shiga toxinâproducing E. coli, often called STEC,about which less is known. For these other types of STEC, what is the source? What are the risk factors? An outbreak among 29 high school students in Minnesota provided some answers. The source of this outbreak was a white-tailed deer that had been butchered and eaten at the school. The risk factors for infection were handling raw or eating undercooked venison. To prevent this type of STECinfection, people should handle and cook venison with the same caution recommended for other meats
Three small planets transiting the bright young field star K2-233
We report the detection of three small transiting planets around the young K3
dwarf K2-233 (2MASS J15215519-2013539) from observations during Campaign 15 of
the K2 mission. The star is relatively nearby ( = 69 pc) and bright ( =
10.7 mag, = 8.4 mag), making the planetary system an attractive target
for radial velocity follow-up and atmospheric characterization with the James
Webb Space Telescope. The inner two planets are hot super-Earths ( = 1.40
0.06 R, = 1.34 0.08 R), while the outer
planet is a warm sub-Neptune ( = 2.6 0.1 R). We estimate
the stellar age to be 360 Myr based on rotation, activity, and
kinematic indicators. The K2-233 system is particularly interesting given
recent evidence for inflated radii in planets around similarly-aged stars, a
trend potentially related to photo-evaporation, core-cooling, or both
mechanisms.Comment: Accepted to AJ. 15 pages, 6 figures, 3 table
Standard operating procedure for somatic variant refinement of sequencing data with paired tumor and normal samples
Seeing Through the Ring: Near-infrared Photometry of V582 Mon (KH 15D)
We examine the light and color evolution of the T Tauri binary KH 15D through photometry obtained at wavelengths between 0.55 and 8.0 ÎŒm. The data were collected with A Novel Dual Imaging CAMera (ANDICAM) on the 1.3 m SMARTS telescope at Cerro-Tololo Inter-American Observatory and with InfraRed Array Camera on the Spitzer Space Telescope. We show that the system's circumbinary ring, which acts as a screen that covers and uncovers different portions of the binary orbit as the ring precesses, has reached an orientation where the brighter component (star B) fully or nearly fully emerges during each orbital cycle. The fainter component (star A) remains fully occulted by the screen at all phases. The leading and trailing edges of the screen move across the sky at the same rate of ~15 m s^(â1), consistent with expectation for a ring with a radius and width of ~4 au and a precession period of ~6500 years. Light and color variations continue to indicate that the screen is sharp edged and opaque at VRIJH wavelengths. However, we find an increasing transparency of the ring edge at 2.2, 3.6, and 4.5 ÎŒm. Reddening seen at the beginning of the eclipse that occurred during the CSI 2264 campaign particularly suggests selective extinction by a population of large dust grains. Meanwhile, the gradual bluing observed while star B is setting is indicative of forward scattering effects at the edge of the ring. The spectral energy distribution of the system at its bright phase shows no evidence of infrared excess emission that can be attributed to radiation from the ring or other dust component out to 8 ÎŒm
An Asymmetric Eclipse Seen toward the Pre-main-sequence Binary System V928 Tau
K2 observations of the weak-lined T Tauri binary V928 Tau A and B show the detection of a single, asymmetric eclipse, which may be due to a previously unknown substellar companion eclipsing one component of the binary with an orbital period >66 days. Over an interval of about 9 hr, one component of the binary dims by around 60%, returning to its normal brightness about 5 hr later. From modeling of the eclipse shape, we find evidence that the eclipsing companion may be surrounded by a disk or a vast ring system. The modeled disk has a radius of 0.9923 ± 0.0005 R*, with an inclination of 56 78 ± 0 03, a tilt of 41 22 ± 0 05, an impact parameter of â0.2506 ± 0.0002 R*, and an opacity of 1.00. The occulting disk must also move at a transverse velocity of 6.637 ± 0.002 R* dayâ»Âč, which, depending on whether it orbits V928 Tau A or B, corresponds to approximately 73.53 or 69.26 km sâ»Âč. A search in ground-based archival data reveals additional dimming events, some of which suggest periodicity, but no unambiguous period associated with the eclipse observed by K2. We present a new epoch of astrometry that is used to further refine the orbit of the binary, presenting a new lower bound of 67 yr, and constraints on the possible orbital periods of the eclipsing companion. The binary is also separated by 18'' (~2250 au) from the lower-mass CFHT-BD-Tau 7, which is likely associated with V928 Tau A and B. We also present new high-dispersion optical spectroscopy that we use to characterize the unresolved stellar binary
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