518 research outputs found
The Massive Disk Around OH 231.8+4.2
We have obtained 11.7 micron and 17.9 micron images at the Keck I telescope
of the circumstellar dust emission from OH 231.8+4.2, an evolved mass-losing
red giant with a well studied bipolar outflow. We detect both a central
unresolved point source and extended emission which is aligned with the bipolar
outflow seen on larger scales. We find that the unresolved central source can
be explained by an opaque, flared disk with an outer radius near 300 AU and an
outer temperature of about 130 K. One possible model to explain this flaring is
that the material in the disk is orbiting the central star and not simply
undergoing a radial expansion.Comment: ApJ, in pres
Investigation of Kepler Objects of Interest Stellar Parameters from Observed Transit Durations
The Kepler mission discovery of candidate transiting exoplanets (KOIs)
enables a plethora of ensemble analysis of the architecture and properties of
exoplanetary systems. We compare the observed transit durations of KOIs to a
synthetic distribution generated from the known eccentricities of radial
velocity (RV) discovered exoplanets. We find that the Kepler and RV
distributions differ at a statistically significant level. We identify three
related systematic trends that are likely due to errors in stellar radii, which
in turn affect the inferred exoplanet radii and the distribution thereof, and
prevent a valid analysis of the underlying ensemble eccentricity distribution.
First, 15% of KOIs have transit durations >20% longer than the transit duration
expected for an edge-on circular orbit, including 92 KOIs with transit
durations >50% longer, when only a handful of such systems are expected.
Second, the median transit duration is too long by up to ~25%. Random errors of
<50% in the stellar radius are not adequate to account for these two trends,
and they are present for all spectral types in the Kepler sample. We identify
that incorrect estimates of stellar metallicity and extinction could account
for these anomalies, rather than astrophysical effects such as eccentric
exoplanets improbably transiting near apastron. Third, we find that the median
transit duration is correlated with stellar radius, when no such trend is
expected. All three effects are still present, although less pronounced, when
considering only multiple transiting KOI systems which are thought to have a
low false positive rate. Improved stellar parameters for KOIs are necessary for
the validity of future ensemble tests of exoplanetary systems found by Kepler.Comment: PASP, in pres
A Spitzer Study of Debris Disks in the Young Nearby Cluster NGC 2232: Icy Planets Are Common around ~1.5-3 M☉ Stars
We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify one A-type star, HD 45435, that has definite excess emission at 4.5-24 μm indicative of debris from terrestrial planet formation. We also identify 2-4 late-type stars with possible 8 μm excesses and 8 early-type stars with definite 24 μm excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears to be correlated with 24 μm excess, a result that would be expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters. The frequency of debris disks around A-type stars appears to increase from ~25% at 5 Myr to ~50%-60% at 20-25 Myr. Older A-type stars have smaller debris disk frequencies: ~20% at 50-100 Myr. For these ages, the typical level of debris emission increases from 5 to 20 Myr and then declines. Because 24 μm dust emission probes icy planet formation around A-type stars, our results suggest that the frequency of icy planet formation is ηi ≳ 0.5-0.6. Thus, most A-type stars (≈1.5-3 M☉) produce icy planets
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Astro2020 Science White Paper Community Endorsement of the National Academies “Exoplanet Science Strategy” and “Astrobiology Strategy for the Search for Life in the Universe” Reports
The National Academies “Exoplanet Science Strategy” (ESS) and “Astrobiology Strategy for the Search for Life in the Universe” (AbS) reports present timely and consensus assessments of the current status, priorities and recommendations of the exoplanet and astrobiology science communities. We are signing our support for the findings and recommendations contained in the ESS and AbS as representing our consensus input to the Astrophysics 2020 decadal survey
A Young Planetary-Mass Object in the ρ Oph Cloud Core
We report the discovery of a young planetary-mass brown dwarf in the ρ Oph cloud core. The object was identified as such with the aid of a 1.5-2.4 μm low-resolution spectrum obtained using the NIRC instrument on the Keck I telescope. Based on the COND model, the observed spectrum is consistent with a reddened (A_V ~ 15-16) brown dwarf whose effective temperature is in the range 1200-1800 K. For an assumed age of 1 Myr, comparison with isochrones further constrains the temperature to ~1400 K and suggests a mass of ~2-3 Jupiter masses. The inferred temperature is suggestive of an early T spectral type, which is supported by spectral morphology consistent with weak methane absorption. Based on its inferred distance (~100 pc) and the presence of overlying visual absorption, it is very likely to be a ρ Oph cluster member. In addition, given the estimated spectral type, it may be the youngest and least massive T dwarf found so far. Its existence suggests that the initial mass function for the ρ Oph star-forming region extends well into the planetary-mass regime
The Peculiar Periodic YSO WL 4 in ρ Ophiuchus
We present the discovery of 130.87 day periodic near-infrared flux variability for the Class II T Tauri star WL 4 (= 2MASS J16271848-2429059, ISO-Oph 128). Our data are from the 2MASS Calibration Point Source Working Database, and constitute 1580 observations in J, H and K_s of a field in ρ Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve for WL 4 with eclipse amplitudes of ~0.4 mag lasting more than one-quarter the period, and color variations in J-H and H-K_s, of ~0.1 mag. The long period cannot be explained by stellar rotation. We propose that WL 4 is a triple YSO system, with an inner binary orbital period of 130.87 days. We posulate that we are observing each component of the inner binary alternately being eclipsed by a circum-binary disk with respect to our line of sight. This system will be useful in investigating terrestrial zone YSO disk properties and dynamics at ~1 Myr
Near-Infrared Variability in the 2MASS Calibration Fields: A Search for Planetary Transit Candidates
The 2MASS photometric calibration observations cover ~6 square degrees on the
sky in 35 "calibration fields" each sampled in nominal photometric conditions
between 562 and 3692 times during the four years of the 2MASS mission. We
compile a catalog of variables from the calibration observations to search for
M dwarfs transited by extra-solar planets. We present our methods for measuring
periodic and non-periodic flux variability. From 7554 sources with apparent Ks
magnitudes between 5.6 and 16.1, we identify 247 variables, including
extragalactic variables and 23 periodic variables. We have discovered three M
dwarf eclipsing systems, including two candidates for transiting extrasolar
planets.Comment: The Astrophysical Journal Supplement, in press; figures compresse
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