Jennifer G. Winters

THE SOLAR NEIGHBORHOOD. XXXIII. PARALLAX RESULTS FROM THE CTIOPI 0.9 m PROGRAM: TRIGONOMETRIC PARALLAXES OF NEARBY LOW-MASS ACTIVE AND YOUNG SYSTEMS

We present basic observational data and association membership analysis for 45 young and active low-mass stellar systems from the ongoing RECONS photometry and astrometry program at the Cerro Tololo Inter-American Observatory. Most of these systems have saturated X-ray emission (log(Lx/Lbol) > -3.5) based on X-ray fluxes from the ROSAT All-Sky Survey, and many are significantly more luminous than main-sequence stars of comparable color. We present parallaxes and proper motions, Johnson-Kron-Cousins VRI photometry, and multiplicity observations from the CTIOPI program on the CTIO 0.9m telescope. To this we add low-resolution optical spectroscopy and line measurements from the CTIO 1.5m telescope, and interferometric binary measurements from the Hubble Space Telescope Fine Guidance Sensors. We also incorporate data from published sources: JHKs photometry from the 2MASS point source catalog; X-ray data from the ROSAT All-Sky Survey; and radial velocities from literature sources. Within the sample of 45 systems, we identify 21 candidate low-mass pre-main-sequence members of nearby associations, including members of beta Pictoris, TW Hydrae, Argus, AB Doradus, two ambiguous 30 Myr old systems, and one object that may be a member of the Ursa Major moving group. Of the 21 candidate young systems, 14 are newly identified as a result of this work, and six of those are within 25 parsecs of the Sun.

A temperate rocky super-Earth transiting a nearby cool star

M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

THE SOLAR NEIGHBORHOOD. XXX. FOMALHAUT C

LP 876-10 is a nearby active M4 dwarf in Aquarius at a distance of 7.6 pc. The star is a new addition to the 10 pc census, with a parallax measured via the REsearch Consortium On Nearby Stars (RECONS) astrometric survey on the Small and Moderate Aperture Research Telescope System’s 0.9 m telescope. We demonstrate that the astrometry, radial velocity, and photometric data for LP 876-10 are consistent with the star being a third bound stellar component to the Fomalhaut multiple system, despite the star lying nearly 6 ◦ away from Fomalhaut A in the sky. The three-dimensional separation of LP 876-10 from Fomalhaut is only 0.77 ± 0.01 pc, and 0.987 ± 0.006 pc from TW PsA (Fomalhaut B), well within the estimated tidal radius of the Fomalhaut system (1.9 pc). LP 87610 shares the motion of Fomalhaut within ∼ 1k m s −1 , and we estimate an interloper probability of ∼10 −5 . Neither our echelle spectroscopy nor astrometry are able to confirm the close companion to LP 876-10 reported in the Washington Double Star Catalog (WSI 138). We argue that the Castor Moving Group to which the Fomalhaut system purportedly belongs, is likely to be a dynamical stream, and hence membership to the group does not provide useful age constraints for group members. LP 876-10 (Fomalhaut C) has now risen from obscurity to become a rare example of a field M dwarf with well-constrained age (440 ± 40 Myr) and metallicity. Besides harboring a debris disk system and candidate planet, Fomalhaut now has two of the widest known stellar companions.

The Solar Neighborhood. XXXII. The Hydrogen Burning Limit

We construct a Hertzsprung-Russell diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4. We report newly observed VRI photometry for all 63 objects and new trigonometric parallaxes for 37 objects. The remaining 26 objects have trigonometric parallaxes from the literature. We combine our optical photometry and trigonometric parallaxes with 2MASS and WISE photometry and employ a novel spectral energy distribution fitting algorithm to determine effective temperatures, bolometric luminosities, and radii. Our uncertainties range from ~20?K to ~150?K in temperature, ~0.01 to ~0.06 in log (L/L ?) and ~3% to ~10% in radius. We check our methodology by comparing our calculated radii to radii directly measured via long baseline optical interferometry. We find evidence for the local minimum in the radius-temperature and radius-luminosity trends that signals the end of the stellar main sequence and the start of the brown dwarf sequence at T eff ~ 2075 K, log (L/L ?) ~ ?3.9, and (R/R ?) ~ 0.086. The existence of this local minimum is predicted by evolutionary models, but at temperatures ~400?K cooler. The minimum radius happens near the locus of 2MASS?J0523?1403, an L2.5 dwarf with V ? K = 9.42. We make qualitative arguments as to why the effects of the recent revision in solar abundances accounts for the discrepancy between our findings and the evolutionary models. We also report new color-absolute magnitude relations for optical and infrared colors which are useful for estimating photometric distances. We study the optical variability of all 63 targets and find an overall variability fraction of 36% at a threshold of 15?mmag in the I band, which is in agreement with previous studies.

THE SOLAR NEIGHBORHOOD. XXII. PARALLAX RESULTS FROM THE CTIOPI 0.9 m PROGRAM: TRIGONOMETRIC PARALLAXES OF 64 NEARBY SYSTEMS WITH 0.″5 ⩽μ⩽ 1.″0 yr–1 (SLOWMO SAMPLE)

We present trigonometric parallaxes of 64 stellar systems with proper motions between 05 yr?1 and 10 yr?1 from the ongoing Research Consortium On Nearby Stars parallax program at the Cerro Tololo Inter-American Observatory. All of the systems are south of decl. =+30, and 58 had no previous trigonometric parallaxes. In addition to parallaxes for the systems, we present proper motions, Johnson-Kron-Cousins VRI photometry, variability measurements, and spectral types. Nine of the systems are multiple; we present results for their components, three of which are new astrometric detections. Of the 64 systems, 56 are within 25?pc of the Sun and 52 of those are in the southern hemisphere, comprising 5.7% of the total number of known southern 25?pc systems.

THE SOLAR NEIGHBORHOOD. XXIV. PARALLAX RESULTS FROM THE CTIOPI 0.9 m PROGRAM: STARS WITH μ ⩾ 1.″0 yr–1 (MOTION SAMPLE) AND SUBDWARFS

We present 41 trigonometric parallaxes of 37 stellar systems, most of which have proper motions greater than 1. �� 0y r −1 . These are the first trigonometric parallaxes for 24 systems. Overall, there are 15 red dwarf systems and 22 red subdwarf systems in the sample. Five of the systems are multiples with directly detected companions, and we have discovered perturbations caused by unseen companions in two additional cases, the dwarf LHS 501 and the subdwarf LHS 440. The latter system may eventually provide important dynamical mass points on the subdwarf mass‐luminosity relation. Two additional stars of note are LHS 272, the third closest M-type subdwarf at a distance of only 13.6 pc, and LHS 2734 AB, a high-velocity subdwarf binary with Vtan > 700 km s −1 , which likely exceeds

The solar neighborhood. XXXV. Distances to 1404 M dwarf systems within 25 PC in the southern sky

We present trigonometric, photometric, and photographic distances to 1748 southern (d  ⩽ 0 ) M dwarf systems with  ⩾ μ 01 8 · yr �1 , of which 1404 are believed to lie within 25 pc of the Sun. The stars have ⩽⩽ V 6.67 21.38 J and ⩽⩽ VK 3.50 ( ) 9.27 Js , covering the entire M dwarf spectral sequence from M0.0 V through M9.5 V. This sample therefore provides a comprehensive snapshot of our current knowledge of the southern sky for the nearest M dwarfs that dominate the stellar population of the Galaxy. Roughly one-third of the 1748 systems, each of which has an M dwarf primary, have published high quality parallaxes, including 179 from the REsearch Consortium On Nearby Stars astrometry program. For the remaining systems, we offer photometric distance estimates that have well-calibrated errors. The bulk of these (∼700) are based on new V RI J KC KC photometry acquired at the CTIO/ SMARTS 0.9 m telescope, while the remaining 500 primaries have photographic plate distance estimates calculated using SuperCOSMOS B RI JF 59 IVN photometry. Confirmed and candidate subdwarfs in the sample have been identified, and a census of companions is included.

The solar neighborhood. XXXIV. a search for planets orbiting nearby M dwarfs using astrometry

Astrometric measurements are presented for seven nearby stars with previously detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ 1214) and one K dwarf (BD

The Solar Neighborhood. XXIII. CCD Photometric Distance Estimates of SCR Targets—77 M Dwarf Systems within 25 pc

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THE SOLAR NEIGHBORHOOD. XXXI. DISCOVERY OF AN UNUSUAL RED+WHITE DWARF BINARY AT ∼25 pc VIA ASTROMETRY AND UV IMAGING

10 3166). Measurements are also presented for six additional nearby M dwarfs without known planets, but which are more favorable to astrometric detections of low mass companions, as well as three binary systems for which we provide astrometric orbit solutions. Observations have baselines of three to thirteen years, and were made as part of the RECONS long-term astrometry and photometry program at the CTIO/SMARTS 0.9m telescope. We provide trigonometric parallaxes and proper motions for all 16 systems, and perform an extensive analysis of the astrometric residuals to determine the minimum detectable companion mass for the 12 M dwarfs not having close stellar secondaries. For the six M dwarfs with known planets, we are not sensitive to planets, but can rule out the presence of all but the least massive brown dwarfs at periods of 2 - 12 years. For the six more astrometrically favorable M dwarfs, we conclude that none have brown dwarf companions, and are sensitive to companions with masses as low as 1