Philip A. Ianna

THE SOLAR NEIGHBORHOOD. XVII. PARALLAX RESULTS FROM THE CTIOPI 0.9 m PROGRAM: 20 NEW MEMBERS OF THE RECONS 10 PARSEC SAMPLE

Astrometric measurements for 25 red dwarf systems are presented, including the first definitive trigonometric parallaxes for 20 systems within 10 pc of the Sun, the horizon of the RECONS sample. The three nearest systems that had no previous trigonometric parallaxes (other than perhaps rough preliminary efforts) are SO 0253+1652 (3.84 ± 0.04 pc, the 23rd nearest system), SCR 1845-6357 AB (3.85 ± 0.02 pc, 24th nearest), and LHS 1723 (5.32 ± 0.04 pc, 56th nearest). In total, seven of the systems reported here rank among the nearest 100 stellar systems. Supporting photometric and spectroscopic observations have been made to provide full characterization of the systems, including complete VRIJHKs photometry and spectral types. A study of the variability of 27 targets reveals six obvious variable stars, including GJ 1207, for which we observed a flare event in the V band that caused it to brighten by 1.7 mag. Improved parallaxes for GJ 54 AB and GJ 1061, both important members of the 10 pc sample, are also reported. Definitive parallaxes for GJ 1001 A, GJ 633, and GJ 2130 ABC, all of which have been reported to be within 10 pc, indicate that they are beyond 10 pc. From the analysis of systems with (previously) high trigonometric parallax errors, we conclude that parallaxes with errors in excess of 10 mas are insufficiently reliable for inclusion in the RECONS sample. The cumulative total of new additions to the 10 pc sample since 2000 is now 34 systems: 28 by the RECONS team and six by other groups. This total represents a net increase of 16% in the number of stellar systems reliably known to be nearer than 10 pc.

The Optical Mass-Luminosity Relation at the End of the Main Sequence (0.08-0.20 M☉)*

The empirical mass-luminosity relation at M is presented for stars with masses 0.08-0.20 M☉ based upon new observations made with Fine Guidance Sensor 3 on the Hubble Space Telescope. The targets are nearby, red dwarf multiple systems in which the magnitude differences are typically measured to ±0.1 mag or better. The M values are generated using the best available parallaxes and are also accurate to ±0.1 mag, because the errors in the magnitude differences are the dominant error source. In several cases this is the first time the observed sub-arcsecond multiples have been resolved at optical wavelengths. The mass-luminosity relation defined by these data reaches to M=18.5 and provides a powerful empirical test for discriminating the lowest mass stars from high-mass brown dwarfs at wavelengths shorter than 1 μm.

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.

The Solar Neighborhood. XIII. Parallax Results from the CTIOPI 0.9 Meter Program: Stars with μ ≥ 10 yr−1 (MOTION Sample)

We present the first set of definitive trigonometric parallaxes and proper motions from the Cerro Tololo Inter-American Observatory Parallax Investigation. Full astrometric reductions for the program are discussed, including methods of reference star selection, differential color refraction corrections, and conversion of relative to absolute parallax. Using data acquired at the 0.9 m telescope at CTIO, full astrometric solutions and VRIJHKs photometry are presented for 36 red and white dwarf stellar systems with proper motions faster than 10 yr-1. Of these, 33 systems have their first ever trigonometric parallaxes, which comprise 41% of MOTION systems (those reported to have proper motions greater than 10 yr-1) south of δ = 0° that have no parallaxes. Four of the systems are new members of the RECONS 10 pc sample for which the first accurate trigonometric parallaxes are published here: DENIS J1048-3956 (4.04 ± 0.03 pc), GJ 1128 (LHS 271, 6.53 ± 0.10 pc), GJ 1068 (LHS 22, 6.97 ± 0.09 pc), and GJ 1123 (LHS 263, 9.02 ± 0.16 pc). In addition, two red subdwarf–white dwarf pairs, LHS 193AB and LHS 300AB, are identified. The white dwarf secondaries fall in a previously uncharted region of the H-R diagram.

THE SOLAR NEIGHBORHOOD. XXI. PARALLAX RESULTS FROM THE CTIOPI 0.9 m PROGRAM: 20 NEW MEMBERS OF THE 25 PARSEC WHITE DWARF SAMPLE

We present accurate trigonometric parallaxes for 20 new members of the 25 pc white dwarf (WD) sample as part of the Discovery and Evalution of Nearby Stellar Embers (DENSE) project.7 http://www.DenseProject.com Previously, there were a total of 112 WD systems with trigonometric parallaxes placing them within 25 pc and of these, 99 have trigonometric parallaxes known to better than 10%. Thus, the 20 new members presented in this work represent a 20% increase in the number of WDs accurately known to be within 25 pc. In addition, we present updated parallaxes for seven known WDs within 10 pc that have been observed as part of the Astrometric Search for Planets Encircling Nearby Stars initiative to monitor nearby southern red dwarfs and WDs for astrometric perturbations from unseen companions. Including a few WD companions and WDs beyond 25 pc, we present a total of 33 trigonometric parallaxes. We perform atmospheric modeling for WDs to determine physical parameters (i.e., T eff, log g, mass, and WD age). Finally, a new ZZ Ceti pulsating WD was identified and revised constraints are placed on two mixed H/He atmosphere cool WDs that display continuum absorption in the near-infrared.

The Solar Neighborhood. XIV. Parallaxes from the Cerro Tololo Inter-American Observatory Parallax Investigation—First Results from the 1.5 m Telescope Program

Trigonometric parallaxes, proper motions, and VJ(RI)KC photometry are presented for 31 stars targeted by the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), a program of wide scope aimed at discovering and characterizing nearby stars. The data given are the first that have been obtained with the CTIO 1.5 m telescope, targeting a fainter subset of the CTIOPI input list. We present the first trigonometric parallaxes for 21 systems, of which one is within 10 pc (LP 647-013 at 9:59 � 0:22 pc) and six are between 10 and 25 pc. Concurrently with our Cerro Tololo 0.9 m program, we have determined parallaxes for DEN 1048� 3956 and LTT 6933 that place them at 4:00 � 0:03 and 16:24 � 0:43 pc from the Sun, respectively. We also present an improved parallax for the important nearby triple system GJ 2005ABC, placing it at 7:72 � 0:15 pc from the Sun. The remaining seven parallaxes are for calibration stars, whose values indicate that our results agree well with other parallax determinations. We present color-magnitude and color-color diagrams that, in combination with theoretical isochrones from the literature and other derived properties of the observed sample, have aided the identification of the general nature of each of our targets. We have in this way discovered five new subdwarfs and several very low mass stars, a few of which may be brown dwarfs.

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. XVI. PARALLAXES FROM CTIOPI: FINAL RESULTS FROM THE 1.5 m TELESCOPE PROGRAM

Trigonometric parallaxes, proper motions and VJ(RI)KC photometry are given for 25 stars (of which one is a zero-parallax control field) targeted by the Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI), a widely scoped program aimed at discovering and characterizing nearby stars. The trigonometric parallaxes and proper motions presented are the last that were obtained with the CTIO 1.5 m telescope, which targeted the fainter subset of the CTIOPI input list. First trigonometric parallaxes are given for 22 systems, of which one is within 10 pc (DENIS 0255-4700), and 10 of which are between 10 and 25 pc. At a distance of 4.97 ± 0.10 pc, and with a spectral type of L7.5 V, DENIS 0255-4700 is now the closest known L dwarf. In addition, with MV = 24.44, it is the faintest dwarf with a measured absolute visual magnitude. We present preliminary trigonometric parallaxes for five additional systems worthy of follow-up, and VRIJHKS photometry and photometric distance estimates for four of them. We also give photometry and distance estimates for 21 other promising targets in our input list for which definitive trigonometric parallaxes were not possible; 13 are likely to be closer than 25 pc. We also present color-magnitude and color-color diagrams, which, in combination with theoretical isochrones from the literature, tangential velocities, and MR and MJ, have aided to identify the general nature of each of our targets. We have in this way discovered one new (spectroscopically confirmed) subdwarf and two suspected extreme subdwarfs that could be among the most extreme cases of these objects. We have also identified several very low mass stars, a few of which could be brown dwarfs. This concludes the CTIOPI 1.5 m program, from which we have derived a total of 69 trigonometric parallaxes (55 definitive, 6 preliminary, and 8 calibration).

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