498 research outputs found
The Orbit and Occultations of KH 15D
The unusual flux variations of the pre-main-sequence binary star KH 15D have
been attributed to occultations by a circumbinary disk. We test whether or not
this theory is compatible with newly available data, including recent radial
velocity measurements, CCD photometry over the past decade, and photographic
photometry over the past 50 years. We find the model to be successful, after
two refinements: a more realistic motion of the occulting feature, and a halo
around each star that probably represents scattering by the disk. The occulting
feature is exceptionally sharp-edged, raising the possibility that the dust in
the disk has settled into a thin layer, and providing a tool for fine-scale
mapping of the immediate environment of a T Tauri star. However, the window of
opportunity is closing, as the currently visible star may be hidden at all
orbital phases by as early as 2008.Comment: To appear in ApJ [16 pages, 13 figures
Recommended from our members
Individualized decision aid for diverse women with lupus nephritis (IDEA-WON): A randomized controlled trial.
BackgroundTreatment decision-making regarding immunosuppressive therapy is challenging for individuals with lupus. We assessed the effectiveness of a decision aid for immunosuppressive therapy in lupus nephritis.Methods and findingsIn a United States multicenter, open-label, randomized controlled trial (RCT), adult women with lupus nephritis, mostly from racial/ethnic minority backgrounds with low socioeconomic status (SES), seen in in- or outpatient settings, were randomized to an individualized, culturally tailored, computerized decision aid versus American College of Rheumatology (ACR) lupus pamphlet (1:1 ratio), using computer-generated randomization. We hypothesized that the co-primary outcomes of decisional conflict and informed choice regarding immunosuppressive medications would improve more in the decision aid group. Of 301 randomized women, 298 were analyzed; 47% were African-American, 26% Hispanic, and 15% white. Mean age (standard deviation [SD]) was 37 (12) years, 57% had annual income of <$40,000, and 36% had a high school education or less. Compared with the provision of the ACR lupus pamphlet (n = 147), participants randomized to the decision aid (n = 151) had (1) a clinically meaningful and statistically significant reduction in decisional conflict, 21.8 (standard error [SE], 2.5) versus 12.7 (SE, 2.0; p = 0.005) and (2) no difference in informed choice in the main analysis, 41% versus 31% (p = 0.08), but clinically meaningful and statistically significant difference in sensitivity analysis (net values for immunosuppressives positive [in favor] versus negative [against]), 50% versus 35% (p = 0.006). Unresolved decisional conflict was lower in the decision aid versus pamphlet groups, 22% versus 44% (p < 0.001). Significantly more patients in the decision aid versus pamphlet group rated information to be excellent for understanding lupus nephritis (49% versus 33%), risk factors (43% versus 27%), medication options (50% versus 33%; p †0.003 for all); and the ease of use of materials was higher in the decision aid versus pamphlet groups (51% versus 38%; p = 0.006). Key study limitations were the exclusion of men, short follow-up, and the lack of clinical outcomes, including medication adherence.ConclusionsAn individualized decision aid was more effective than usual care in reducing decisional conflict for choice of immunosuppressive medications in women with lupus nephritis.Trial registrationClinicaltrials.gov, NCT02319525
TESS Discovery of an ultra-short-period planet around the nearby M dwarf LHS 3844
Data from the newly-commissioned \textit{Transiting Exoplanet Survey
Satellite} (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf
located 15 pc away. The planet has a radius of and
orbits the star every 11 hours. Although the existence of an atmosphere around
such a strongly irradiated planet is questionable, the star is bright enough
(, ) for this possibility to be investigated with transit and
occultation spectroscopy. The star's brightness and the planet's short period
will also facilitate the measurement of the planet's mass through Doppler
spectroscopy.Comment: 10 pages, 4 figures. Submitted to ApJ Letters. This letter makes use
of the TESS Alert data, which is currently in a beta test phase, using data
from the pipelines at the TESS Science Office and at the TESS Science
Processing Operations Cente
Three red suns in the sky: A transiting, terrestrial planet in a triple M-dwarf system at 6.9 pc
We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of , an orbital period of days, and an equilibrium temperature of K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3Ï upper mass limit of 8.4 on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co-planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.Accepted manuscrip
The Aligned Orbit of the Eccentric Warm Jupiter K2-232b
Measuring the obliquity distribution of stars hosting warm Jupiters may help us to understand the formation of close-orbiting gas giants. Few such measurements have been performed due to practical difficulties in scheduling observations of the relatively infrequent and long-duration transits of warm Jupiters. Here, we report a measurement of the Rossiter-McLaughlin effect for K2-232 b, a warm Jupiter on an 11.17 day orbit with an eccentricity of 0.26. The data were obtained with the Automated Planet Finder during two separate transits. The planet's orbit appears to be well aligned with the spin axis of the host star, with a projected spin-orbit angle of λ = -11.°1 ± 6.°6. Combined with the other available data, we find that high obliquities are almost exclusively associated with planets that either have an orbital separation greater than 10 stellar radii or orbit stars with effective temperatures hotter than 6000 K. This pattern suggests that the obliquities of the closest-orbiting giant planets around cooler stars have been damped by tidal effects
TOI 540 b: A Planet Smaller than Earth Orbiting a Nearby Rapidly Rotating Low-mass Star
We present the discovery of TOI 540 b, a hot planet slightly smaller than
Earth orbiting the low-mass star 2MASS J05051443-4756154. The planet has an
orbital period of days ( 170 ms) and a radius of , and is likely terrestrial based on the observed
mass-radius distribution of small exoplanets at similar insolations. The star
is 14.008 pc away and we estimate its mass and radius to be and , respectively. The
star is distinctive in its very short rotational period of hours and correspondingly small Rossby number of 0.007 as
well as its high X-ray-to-bolometric luminosity ratio of based on a serendipitous XMM-Newton detection during a slew operation.
This is consistent with the X-ray emission being observed at a maximum value of
as predicted for the most rapidly rotating M
dwarfs. TOI 540 b may be an alluring target to study atmospheric erosion due to
the strong stellar X-ray emission. It is also among the most accessible targets
for transmission and emission spectroscopy and eclipse photometry with JWST,
and may permit Doppler tomography with high-resolution spectroscopy during
transit. This discovery is based on precise photometric data from TESS and
ground-based follow-up observations by the MEarth team.Comment: 18 pages, 7 figures. Accepted for publication in The Astronomical
Journa
The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey
This document is the Accepted Manuscript version of the following article: R. Paul Butler, et al, The LCES HIRES/Keck Precision Radial Velocity Exoplanet Survey, The Astronomical Journal, Vol 153 (5), 19 pp., published 13 April 2017. The Version of Record is available online at doi: https://doi.org/10.3847/1538-3881/aa66ca. Paper data available at: http://home.dtm.ciw.edu/ebps/data/. © 2017. The American Astronomical Society. All rights reserved.We describe a 20-year survey carried out by the Lick-Carnegie Exoplanet Survey Team (LCES), using precision radial velocities from HIRES on the Keck-I telescope to find and characterize extrasolar planetary systems orbiting nearby F, G, K, and M dwarf stars. We provide here 60,949 precision radial velocities for 1,624 stars contained in that survey. We tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices. These signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in Keplerian motion about the host star. Of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as "significant" signals that require confirmation by additional data before rising to classification as planet candidates. Of particular interest is our detection of a candidate planet with a minimum mass of 3.9 Earth masses and an orbital period of 9.9 days orbiting Lalande 21185, the fourth-closest main sequence star to the Sun. For each of our exoplanetary candidate signals, we provide the period and semi-amplitude of the Keplerian orbital fit, and a likelihood ratio estimate of its statistical significance. We also tabulate 18 Keplerian-like signals that we classify as likely arising from stellar activity.Peer reviewedFinal Accepted Versio
The current management of acute uncomplicated appendicitis: should there be a change in paradigm? A systematic review of the literatures and analysis of treatment performance
TESS Reveals HD 118203 b to be a Transiting Planet
The exoplanet HD 118203 b, orbiting a bright (V = 8.05) host star, was discovered using the radial velocity method by da Silva et al., but was not previously known to transit. Transiting Exoplanet Survey Satellite (TESS) photometry has revealed that this planet transits its host star. Nine planetary transits were observed by TESS, allowing us to measure the radius of the planet to be 1.136^(+0.029)_(-0.028) R_J, and to calculate the planet mass to be 2.166^(+0.074)_(-0.079) M_J. The host star is slightly evolved with an effective temperature of T_(eff) = 5683^(+84)_(-85) K and a surface gravity of log g = 3.889^(+0.017)_(-0.018). With an orbital period of 6.134985^(+0.000029_(-0.000030) days and an eccentricity of 0.314 ± 0.017, the planet occupies a transitional regime between circularized hot Jupiters and more dynamically active planets at longer orbital periods. The host star is among the 10 brightest known to have transiting giant planets, providing opportunities for both planetary atmospheric and asteroseismic studies
- âŠ