Abstract
We extend results first announced by Franz et al., that identified vA 351 = H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance ...Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7 years, we establish a parallax, relative orbit, and mass fraction for two components, with a period,
and total mass 2.1
. With ground-based radial velocities from the McDonald Observatory Otto Struve 2.1 m Telescope Sandiford Spectrograph, and Center for Astrophysics Digital Speedometers, spanning 37 years, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (
days), having a mass ratio
/
= 0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher-mass component. The quadruple system consists of three M dwarfs (A, B, C) and one white dwarf (D). We determine individual M dwarf masses
= 0.53 ± 0.10
,
= 0.43 ± 0.04
, and
= 0.41 ± 0.04
. The white dwarf mass, 0.54 ± 0.04
, comes from cooling models, an assumed Hyades age of 670 Myr, and consistency with all previous and derived astrometric, photometric, and radial velocity results. Velocities from H
α
and He
i
emission lines confirm the BC period derived from absorption lines, with similar (He
i
) and higher (H
α
) velocity amplitudes. We ascribe the larger H
α
amplitude to emission from a region each component shadows from the other, depending on the line of sight.
We observed the 2017 July 17 stellar occultation of HD 168233 by the Kuiper Belt Object (486958) 2014 MU69, the close flyby target of the extended New Horizons mission. Rather than capture a solid ...body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for two HST orbits during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from ∼20000 km to ∼75000 km from the main body.
We observed the 2018 August 4 stellar occultation by the Kuiper Belt object (486958) 2014 MU69, the first close flyby target of the extended New Horizons mission. Rather than capture a solid-body ...occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for one HST orbit during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on τ of ∼0.02-0.08 for rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from ∼1660 to ∼57,700 km from the main body.
•We present new lightcurves for 19 jovian Trojans smaller than 30km in diameter.•∼40% of Trojans in this size range have rotation periods longer than 24h.•The YORP effect may be responsible for the ...slowly rotation of small Trojans.
Several lines of evidence support a common origin for, and possible hereditary link between, cometary nuclei and jovian Trojan asteroids. Due to their distance and low albedos, few comet-sized Trojans have been studied. We present new lightcurve information for 19 Trojans≲30km in diameter, more than doubling the number of objects in this size range for which some rotation information is known. The minimum densities for objects with complete lightcurves are estimated and are found to be comparable to those measured for cometary nuclei. A significant fraction (∼40%) of this observed small Trojan population rotates slowly (P>24h), with measured periods as long as 375h (Warner, B.D., Stephens, R.D. 2011. Minor Planet Bull. 38, 110–111). The excess of slow rotators may be due to the YORP effect. Results of the Kolmogorov–Smirnov test suggest that the distribution of Trojan rotation rates is dissimilar to those of Main Belt Asteroids of the same size. Concerted observations of a large number of Trojans could establish the spin barrier (Warner, B.D., Harris, A.W., Pravec, P. 2009. Icarus 202, 134–146), making it possible to estimate densities for objects near the critical period.
We report the discovery that the pre-main-sequence (PMS) object LkCa 3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close ...(~0".5) visual pair, with one component being a moderately eccentric 12.94 day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented by new near-infrared (NIR) spectroscopy shows both visual components to be double lined; the second one has a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and NIR flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we also detect the rotational signal of die primary in the 4.06 day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these consttaints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting that the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa 3 and the well-known quadruple PMS system GG Tau with the widely used models from the Lyon series for a mixing length parameter of alpha sub(ML) = 1.0 strongly favor the Dartmouth models.
We report on Keck Interferometer observations of the double-lined binary (B) component of the quadruple pre-main-sequence (PMS) system HD 98800. With these interferometric observations, combined with ...astrometric measurements made by the Hubble Space Telescope (HST) Fine Guidance Sensors (FGS) and published radial velocity observations, we have estimated preliminary visual and physical orbits of the HD 98800 B subsystem. Our orbit model calls for an inclination of 66.8 c 3.2 and allows us to infer the masses and luminosities of the individual components. In particular we find component masses of 0.699 c 0.064 and 0.582 c 0.051 M sub( )for the Ba (primary) and Bb (secondary) components, respectively. Spectral energy distribution (SED) modeling of the B subsystem suggests that the B circumstellar material is a source of extinction along the line of sight to the B components. This seems to corroborate a conjecture by Tokovinin that the B subsystem is viewed through circumbinary material, but it raises important questions about the morphology of that circumbinary material. Our modeling of the subsystem component SEDs finds temperatures and luminosities in agreement with previous studies, and coupled with the component mass estimates allows for comparison with PMS models in the low-mass regime with few empirical constraints. Solar abundance models seem to underpredict the inferred component temperatures and luminosities, while assuming slightly subsolar abundances brings the models and observations into better agreement. The current preliminary orbit does not yet place significant constraints on existing PMS stellar models, but prospects for additional observations improving the orbit model and component parameters are very good.
Abstract
We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the
New Horizons
extended mission. Three of the four efforts led to positive detections of the ...body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by the Stratospheric Observatory for Infrared Astronomy with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 August 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 ± 0.0005 hr. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the
New Horizons
flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
A photometric catalog, developed for the calibration of the Deep Ecliptic Survey, is presented. The catalog contains 213,272 unique sources that were measured in V and R filters and transformed to ...the Johnson-Cousins systems using the Landolt standard catalog. All of the sources lie within 6? of the ecliptic and cover all longitudes except for the densest stellar regions nearest the galactic center. Seventeen percent of the sources in the catalog are derived from three or more nights of observation. The catalog contains sources as faint as R ~19 but the largest fraction fall in the R ~15-16 (V ~16-17) mag range. All magnitude bins down to R = 19 have a significant fraction of objects with uncertainties <=0.1 mag.
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