We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), the U.S. Naval Observatory (18), the New Technology Telescope (14), and the United ...Kingdom Infrared Telescope (9). To complete the 20 pc census of ≥T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150 K wide Teff bins covering the range 300-1050 K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20 pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in Teff. The best fit of these predictions to our L, T, and Y observations is a simple power-law model with 0.6 (where ), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350 K. We also find that the low-mass cutoff to formation, if one exists, is lower than ∼5 MJup, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.
The sensitivities of radial velocity (RV) surveys for exoplanet detection are extending to increasingly longer orbital periods, where companions with periods of several years are now being regularly ...discovered. Companions with orbital periods that exceed the duration of the survey manifest in the data as an incomplete orbit or linear trend, a feature that can either present as the sole detectable companion to the host star, or as an additional signal overlain on the signatures of previously discovered companion(s). A diagnostic that can confirm or constrain scenarios in which the trend is caused by an unseen stellar rather than planetary companion is the use of high-contrast imaging observations. Here, we present RV data from the Anglo-Australian Planet Search (AAPS) for 20 stars that show evidence of orbiting companions. Of these, six companions have resolved orbits, with three that lie in the planetary regime. Two of these (HD 92987b and HD 221420b) are new discoveries. Follow-up observations using the Differential Speckle Survey Instrument (DSSI) on the Gemini South telescope revealed that 5 of the 20 monitored companions are likely stellar in nature. We use the sensitivity of the AAPS and DSSI data to place constraints on the mass of the companions for the remaining systems. Our analysis shows that a planetary-mass companion provides the most likely self-consistent explanation of the data for many of the remaining systems.
While following up L dwarf candidates selected photometrically from the Two Micron All Sky Survey, we uncovered an unusual object designated 2MASS J01415823-4633574. Its optical spectrum exhibits ...very strong bands of vanadium oxide but abnormally weak absorptions by titanium oxide, potassium, and sodium. Morphologically, such spectroscopic characteristics fall intermediate between old field early-L dwarfs log(g) - 5 and very late M giants log(g) - 0, leading us to favor low gravity as the explanation for the unique spectral signatures of this L dwarf. Such a low gravity can be explained only if this L dwarf is much lower in mass than a typical old field L dwarf of similar temperature and is still contracting to its final radius. These conditions imply a very young age. Further evidence of youth is found in the near-infrared spectrum, including a triangular-shaped H-band continuum, reminiscent of young brown dwarf candidates discovered in the Orion Nebula Cluster. Using the above information along with comparisons to brown dwarf atmospheric and interior models, our current best estimate is that this L dwarf has an age of 1-50 Myr and a mass of 6-25M sub(J). Although the lack of a lithium detection (pseudo-equivalent width <1 AA) might appear to contradict other evidence of youth, we suggest that lithium becomes weaker at lower gravity like all other alkali lines and thus needs to be carefully considered before being used as a diagnostic of age or mass for objects in this regime. The location of 2MASS 0141-4633 on the sky coupled with a distance estimate of 635 pc and the above age estimate suggests that this object may be a brown dwarf member of either the 30 Myr old Tucana/Horologium association or the 612 Myr old b Pic moving group. Distance as determined through trigonometric parallax (underway) and a measure of the total space motion are needed to test this hypothesis.
Abstract
Gliese 86 is a nearby K dwarf hosting a giant planet on a ≈16 day orbit and an outer white dwarf companion on a ≈century-long orbit. In this study we combine radial velocity data (including ...new measurements spanning more than a decade) with high angular resolution imaging and absolute astrometry from Hipparcos and Gaia to measure the current orbits and masses of both companions. We then simulate the evolution of the Gl 86 system to constrain its primordial orbit when both stars were on the main sequence; the closest approach between the two stars was then about 9 au. Such a close separation limited the size of the protoplanetary disk of Gl 86 A and dynamically hindered the formation of the giant planet around it. Our measurements of Gl 86 B and Gl 86 Ab’s orbits reveal Gl 86 as a system in which giant planet formation took place in a disk truncated at ≈2 au. Such a disk would be just big enough to harbor the dust mass and total mass needed to assemble Gl 86 Ab’s core and envelope, assuming a high disk accretion rate and a low viscosity. Inefficient accretion of the disk onto Gl 86 Ab, however, would require a disk massive enough to approach the Toomre stability limit at its outer truncation radius. The orbital architecture of the Gl 86 system shows that giant planets can form even in severely truncated disks and provides an important benchmark for planet formation theory.
ABSTRACT
An unprecedented number of exoplanets are being discovered by the Transiting Exoplanet Survey Satellite (TESS). Determining the orbital parameters of these exoplanets, and especially their ...mass and radius, will depend heavily upon the measured physical characteristics of their host stars. We have cross-matched spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the TESS Input Catalog and Gaia Data Release 2, to create a curated, self-consistent catalogue of physical and chemical properties for 47 285 stars. Using these data, we have derived isochrone masses and radii that are precise to within 5 per cent. We have revised the parameters of three confirmed, and twelve candidate, TESS planetary systems. These results cast doubt on whether CTOI-20125677 is indeed a planetary system, since the revised planetary radii are now comparable to stellar sizes. Our GALAH–TESS catalogue contains abundances for up to 23 elements. We have specifically analysed the molar ratios for C/O, Mg/Si, Fe/Si, and Fe/Mg, to assist in determining the composition and structure of planets with Rp < 4R⊕. From these ratios, 36 per cent fall within 2$\sigma$ sigma of the Sun/Earth values, suggesting that these stars may host rocky exoplanets with geological compositions similar to planets found within our own Solar system.
GNOSIS is a prototype astrophotonic instrument that utilizes "OH suppression fibers" consisting of fiber Bragg gratings and photonic lanterns to suppress the 103 brightest atmospheric emission ...doublets between 1.47 and 1.7 mu m. GNOSIS was commissioned at the 3.9 m Anglo-Australian Telescope with the IRIS2 spectrograph to demonstrate the potential of OH suppression fibers, but may be potentially used with any telescope and spectrograph combination. We present the instrument design and report the results of laboratory and on-sky tests from commissioning. While these tests demonstrated high throughput ( approximately 60%) and excellent suppression of the skylines by the OH suppression fibers, surprisingly GNOSIS produced no significant reduction in the interline background and the sensitivity of GNOSIS+IRIS2 is about the same as IRIS2. OH suppression fibers could potentially impact ground-based astronomy at the level of adaptive optics or greater.
Solar-like Oscillations in α Centauri B Kjeldsen, Hans; Bedding, Timothy R; Butler, R. Paul ...
The Astrophysical journal,
12/2005, Letnik:
635, Številka:
2
Journal Article
The measured proper motion of Fornax, expressed in the equatorial coordinate system, is (ma,md) = (47.6 ± 4.6, - 36.0 ± 4.1) mas century-1. This proper motion is a weighted mean of four independent ...measurements for three distinct fields. Each measurement uses a quasi-stellar object as a reference point. Removing the contribution of the motion of the Sun and of the local standard of rest to the measured proper motion produces a Galactic rest-frame proper motion of (m,m) = (24.4 ± 4.6, - 14.3 ± 4.1) mas century-1. The implied space velocity with respect to the Galactic center has a radial component of Vr = -31.8 ± 1.7 km s-1 and a tangential component of Vt = 196 ± 29 km s-1. Integrating the motion of Fornax in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 118 (66, 137) and 152 (144, 242) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.13 (0.1,0.38), and the orbital period is 3.2 (2.5, 4.6) Gyr. The orbit is retrograde and inclined by 101° (94°, 107°) to the Galactic plane. Fornax could be a member of a proposed 'stream' of galaxies and globular clusters; however, the membership of another proposed galaxy in the stream, Sculptor, has been previously ruled out. Fornax is in the Kroupa-Theis-Boily plane, which contains 11 of the Galactic satellite galaxies, but its orbit will take it out of that plane.
We analyze our recently published velocity measurements of alpha Cen A. After adjusting the weights on a night-by-night basis in order to optimize the window function to minimize sidelobes, we ...extract 42 oscillation frequencies with l = 0-3 and measure the large and small frequency separations. We give fitted relations to these frequencies that can be compared with theoretical models and conclude that the observed scatter about these fits is due to the finite lifetimes of the oscillation modes. We estimate the mode lifetimes to be 1-2 days, substantially shorter than in the Sun.
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