The Solar Neighborhood. XXII. Parallax Results from the CTIOPI 0.9m Program: Trigonometric Parallaxes of 64 Nearby Systems with 0\farcs5 ≤μ≤ 1\farcs0 yr −1 (SLOWMO sample)
Adric R. Riedel, John P. Subasavage, Charlie T. Finch, Wei Chun Jao, Todd J. Henry, Jennifer G. Winters, Misty A. Brown, Philip A. Ianna, Edgardo Costa, Rene A. Mendez
aa r X i v : . [ a s t r o - ph . S R ] A ug submitted to the Astronomical Journal
15 JUNE 2010
The Solar Neighborhood. XXII. Parallax Results from theCTIOPI 0.9m Program: Trigonometric Parallaxes of 64 NearbySystems with 0 . ′′ ≤ µ ≤ . ′′ − (SLOWMO sample) Adric R. Riedel Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302-4106 [email protected]
John P. Subasavage Cerro Tololo Inter-american Observatory, La Serena, Chile [email protected]
Charlie T. Finch Astrometry Department, U.S. Naval Observatory, Washington DC 20392 [email protected]
Wei Chun Jao , Todd J. Henry , Jennifer G. Winters , Misty A. Brown Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302-4106 [email protected], [email protected], [email protected],[email protected]
Philip A. Ianna Department of Astronomy, University of Virginia, Charlottesville, VA 22904 [email protected]
Edgardo Costa , Rene A. Mendez Departamento de Astronomia, Universidad de Chile, Santiago, Chile [email protected], [email protected]
ABSTRACT
We present trigonometric parallaxes of 64 stellar systems with proper motionsbetween 0 . ′′ − and 1 . ′′ − from the ongoing RECONS (Research ConsortiumOn Nearby Stars) parallax program at CTIO (the Cerro Tololo InteramericanObservatory). All of the systems are south of DEC = +30, and 58 had noprevious trigonometric parallaxes. In addition to parallaxes for the systems,we present proper motions, Johnson-Kron-Cousins V RI photometry, variabilitymeasurements, and spectral types. Nine of the systems are multiple; we presentresults for their components, three of which are new astrometric detections. Ofthe 64 systems, 56 are within 25 parsecs of the Sun and 52 of those are in thesouthern hemisphere, comprising 5.7% of the total number of known southern 25parsec systems.
1. Introduction
One of the most important products of nearby star research will be a volume-limitedsample of nearby stars. All-inclusive volume-limited samples of stars will allow us to answerlarge numbers of questions about the formation, kinematics, stellar mass fraction, and metal-licity distributions of stars and (if representative) the galaxy itself. Due to the faintness ofthe M dwarfs that make up at least
72% of all nearby stars, surveys aiming at completenessare easiest carried out near the Sun. Large numbers of potential nearby stars have beenfound in ongoing series of proper motion surveys, most notably (among others too numer-ous to mention here) the surveys of Luyten (Luyten 1979), Giclas (Giclas 1958), Pokorny(Pokorny et al. 2003), ourselves (Subasavage et al. 2005), and Lepine (L´epine 2005). Variousother surveys (for instance, Reyl´e & Robin 2004; Reid et al. 2008; Jahreiß et al. 2008) havefollowed up on those discoveries with spectroscopy and photometry to determine distancesand spectral properties of these systems, although a great many still remain uninvestigated.For our purposes, however, we need accurate distances to prove membership, obtain accurateluminosities, and good kinematics.While there are many methods used to determine stellar distances, the most accuratemethod remains the trigonometric parallax. It does not rely on any prior knowledge aboutthe star (as photometric and spectroscopic “parallaxes” do), nor does it require a cluster Visiting Astronomer, Cerro Tololo Inter-american Observatory. CTIO is operated by AURA, Inc. undercontract to the National Science Foundation.
Hipparcos mission (Perryman et al. 1997). TheYPC is a compilation of 15994 parallax measurements for 8112 stars from various observato-ries, representing ground-based parallax efforts prior to 1995 for stars as faint as V = 21 . Hipparcos mission’s catalog(van Leeuwen 2007) contains 117955 stellar parallaxes, generally with errors less than 1 masfor stars brighter than V = 8. These compendia have already enabled statistical studiesof stellar formation, evolution, composition, kinematics, and populations, making detailedlarge-scale surveys like the Geneva-Copenhagen Survey (Holmberg et al. 2009) of F and Gdwarfs, for example, finally possible.Despite the size of its catalog, Hipparcos did not find the complete population of nearbystars. The faint magnitude limit of
Hipparcos was V ∼
13, with a completeness limit of V ∼ . Hipparcos , but intrinsically faint stars such as M dwarfs, cool subdwarfs,and white dwarfs largely remain the purview of the YPC, or of new ground-based effortssuch as the one discussed here. A truly inclusive, volume-limited survey of all types of starson the scale of the Geneva-Copenhagen survey is still not possible — large numbers of starsin the solar neighborhood are still unconfirmed, large numbers of M dwarfs are still missingfrom nearby star lists. The mission of RECONS (Research Consortium On Nearby Stars) is to understand thesolar neighborhood, including the discovery, confirmation, and characterization of nearbystars and their environments. RECONS has been operating a trigonometric parallax pro-gram called CTIOPI (Cerro Tololo Interamerican Observatory Parallax Investigation) at theCTIO 0.9m telescope since 1999 with a primary goal of pushing the parallax-verified solarneighborhood sample — systems within 25 pc, with a concentration on those within 10 pc —toward completion. This is the fifth paper of results from the ongoing program at the 0.9m,following Jao et al. (2005), Henry et al. (2006), Gizis et al. (2007), and Subasavage et al. . ′′ − and1 . ′′ − , our “SLOWMO” sample. Of the 64 systems, 56 are within 25 pc of the Sun, andall are south of DEC= +30. In addition to the parallaxes, we provide new measurementsof proper motions, Johnson-Kron-Cousins V RI photometry, variability, spectral types, andastrometric measurements of multiple systems.
2. The Sample
Completing the stellar census within 25 pc is a daunting task. If we assume the currentcensus of systems within 5 pc is accurate (50 systems, see Henry et al. (2006) for the mostrecent additions within five pc) and representative of the stellar space density of the solarneighborhood, we expect 6250 star systems within 25 pc. The most complete parallax-selected list of objects remains the NStars Database, which includes only 2011 systemswithin 25 pc (Henry et al. 2002), indicating that the sample is only 32% complete. Clearly,much more work is needed to achieve a truly comprehensive volume-limited sample of space;only then will we truly be able to characterize the compositional nature of the Galaxy. Eventhe Gaia mission, with a limiting magnitude of V = 20, will not reach the end of the mainsequence past ten parsecs.The 64 systems discussed in this paper are listed in Tables 1 and 2. They were se-lected for the CTIOPI program for a variety of reasons: either their high proper motionmade them targets for M. Brown’s masters thesis on SLOWMO systems, their estimateddistances suggested they might be within 10 parsecs, or they had YPC parallaxes withlarge errors that placed the system within 10 parsecs. The systems themselves are all fromLuyten (1979), Luyten (1957), Wroblewski & Torres (1991), Wroblewski & Torres (1994),Scholz et al. (2000), and a private communications with Scholz (1999) for APMPM J2127-3844. Most of them were investigated for companions in Jao et al. (2003). All of the systemshave proper motions of 0 . ′′ . ′′ − , have red dwarf primaries with V = 10.35–19.17 andhave spectral types M1.0V to M6.0V. Seven of the systems presented here have known orsuspected companions; we confirm six of them and present individual parallax measurementsfor components of three. We have also discovered evidence of multiplicity for a further threesystems and suspect additional components in five more systems; thus 14% (9 out of 64) of µ ≥ . ′′ − (Jao et al. 2005) (our MOTION sample), red dwarfs within10 pc (Henry et al. 2006), and white dwarfs within 25 pc (Subasavage et al. 2009) from theCTIOPI 0.9m program, and mixed samples from our 1.5m program (Costa et al. 2005, 2006).
3. Observations3.1. Astrometric and Photometric Observations
All astrometric and photometric observations were carried out at the CTIO 0.9m tele-scope, initially (1999-2003) under the aegis of the NOAO (National Optical Astronomy Ob-servatory) Surveys Program, and later (2003-present) via the SMARTS (Small and ModerateAperture Research Telescope System) Consortium. The observations presented in this paperwere obtained between 1999 and 2009 utilizing the center 1024x1024 pixels of the 0.9m tele-scope’s Tek 2048x2046 CCD and CTIO’s V J , R KC , and I KC (hereafter without subscripts) filters. Additional details of the observing protocol can be found in Jao et al. (2005).Four significant instrumental events in the course of the CTIOPI program have affecteddata published in this paper: • In February 2005, the Tektronix V filter (hereafter “old V ”) used by CTIOPIcracked and was replaced by the almost-photometrically identical (transmission prop-erties and bandwidth) Tektronix V filter (hereafter “new V ”). With four years ofnew V data, we are able to make some comparisons between the two:As reported in Subasavage et al. (2009), the new V filter is photometrically consis-tent with the old V filter to within reported CTIOPI accuracies (0.03 mag, Henry et al.2004), although we find our V filter photometry is only accurate to 0.05 mag in thisdataset.Also as reported in Subasavage et al. (2009), some new V filter data cause a few-mas offset in the RA axis astrometric residuals. This is endemic to the new V filteritself and is not the result of changing filters; recent data taken with the old V filtershow no such behavior in the residuals when added to older data. Parallax results using Subscripts: “J” indicates Johnson, and “KC” indicates Kron-Cousins. The central wavelengths for V J , R KC , and I KC are 5475, 6425, and 8075 ˚A, respectively. V filter data are slightly but non-systematically displaced relative to resultsusing only old V data, which were found to be consistent with YPC and Hipparcos parallaxes in Jao et al. (2005). Part of the error appears to depend on the filter itself,the rest appears to depend on coverage: tests were only conducted on stars with largedatasets before and after the V filter replacement. Those stars tend to have bettercoverage of the parallax ellipse in old V (earlier) than in new V (later, when theirparallaxes were well determined and they became lower priority targets). Even so,the new V parallax is usually within 2- σ of the old V measurement, and mixed V parallaxes are always within 2- σ . All parallaxes in this paper using new V filter dataare noted in Table 1. • In April 2005, the Telescope Control System (TCS) on the 0.9m was completely re-placed and refurbished, yielding improved pointing and tracking. No astrometric effectshave been detected in datasets spanning the TCS upgrade. • On 7 March 2009, a power outage damaged the gain = 1 circuitry for the CCD,and CTIOPI began using gain = 2. The differences between the two gains are purelyelectrical, and tests confirm that the switch does not affect our astrometry, as expected. • In July 2009, the old V filter was returned to service. Extensive tests showed thehairline crack near the edge does not affect data acquired on the central quarter of theCCD as used in CTIOPI. Furthermore, testing many stellar fields indicated no adverseeffects on the astrometry when reducing data with and without recent data in the old V filter. Recent old V filter data have been used in this paper’s astrometric reductionsof LHS 1050, LHS 1561, LHS 3443, LHS 4009AB, and LHS 4016. We carried out spectroscopic observations at two telescopes to determine the spectraltypes of 25 of the objects listed in Table 2. From 2003–2006, we used the CTIO 1.5m, theR-C Spectrograph with a Loral 1200 ×
800 CCD, and the 32/I grating to obtain spectracovering 6000–9500˚A at a resolution of 8.6˚A. For WT 244 and GJ 438, we used the CTIO4m, the R-C spectrograph with a Loral 3X ×
1K CCD, and the 181 grating to obtainspectra covering 5500–10000˚A at a resolution of 5.7˚A. Further details concerning the 1.5mspectroscopy program and associated data reduction can be found in Henry et al. (2004),while details of the 4m spectroscopy program can be found in Henry et al. (2002). 7 –
4. Results4.1. Astrometry — Parallaxes and Proper Motions
Parallaxes and proper motions of 64 stellar systems are presented in Table 1. Nine ofour systems have multiple parallax measurements, from YPC, our CTIOPI 1.5m program, ormultiple components published in this paper. For these cases, we present weighted averagesystem parallaxes in Table 3.All parallax data were analyzed with the custom IRAF/IDL pipeline used in CTIOPIpublications since 2005, using an iterative Gaussfit program described in Jao et al. (2005).Starting in 2007, the reduction methodology was changed by the implementation of a newSExtractor centroiding algorithm, described in Subasavage et al. (2009).As always, CTIOPI parallaxes must meet several criteria before they are deemed fit topublish. First, to ensure good coverage of the parallax ellipse, there is an informal limitof 30 frames each in the ‘morning’ and ‘evening’ halves of the ellipse with a goal of having20 usable frames each; the number of frames used in the final reductions ranged from 45(LHS 2899) to 137 (LHS 1630AB). Second, the system must be followed for about two yearsto decouple the star’s motion into parallax and proper motion; the coverage in this papervaries from 1.99 years (LHS 2335) to 10.15 years (LHS 4009AB). Third, CTIOPI targets areexpected to have parallax errors less than 3 mas before publishing. The smallest parallaxerror we are publishing here is 0.63 mas (GJ 1157) and the largest is 2.57 mas (LHS 1050and LHS 2122), while the median error on these parallaxes is 1.37 mas.Our parallaxes are derived by measuring the motion of the target star (pi star) relativeto background reference stars, and then correcting the parallactic motion to an absolutereference frame with
V RI band photometric distance estimates to the reference star ensemble(not to be confused with our
V RIJ HK distance estimates for red dwarfs, discussed in § V RI bands to smooth over atmospheric effects and consequently improve centroids. We have alsore-observed several systems (e.g. LHS 1561, LHS 3909, and LHS 3443) after a multi-yearhiatus to improve proper motions and possibly reveal long-period perturbations (see § Seven of our systems contain known multiples: LHS 1630AB, LHS 1749AB, LHS 1955AB,LHS 2567/2568, LHS 3001/3002, LHS 3739/3738AB, and LHS 4009AB. We have resolvedorbital motion above the 3- σ level (angular motion or changes in separation) for five of thosesystems, as described in Table 4. Apart from LHS 1955AB, all values published in Table 4are derived from at least three frames on the nights listed.The components of LHS 1630AB, LHS 1749AB and LHS 1955AB are close enough thattheir PSFs (point spread functions) overlap. In the case of LHS 1630AB the B componentwas never fully resolved, but it does appear as an elongation to the PSF. LHS 1749ABwas only resolved on 15 frames from four nights. LHS 1955AB was only resolved on sevenframes from five nights using restricted centroiding parameters that enabled the separationof blended sources; the two frames from the earliest night and the one frame from the latestnight are used to derive the results in Table 4.Errors presented in Table 4 include both measurement and systematic errors. Thesystematic errors were computed from the nights of data measured for Table 4, with theexception of the three frames used for LHS 1955AB. All frames from a single visit (onenight of observations on one system) were compared to the 2MASS All-Sky Point SourceCatalog using imwcs ; the standard deviations of the plate scales and rotations per-visitwere then averaged across all visits to get a more representative error. Systematics for theCTIO 0.9m on those frames give a 0.015% error in the plate scale (and therefore separations),and a 0.0083 degree error in the rotation (and therefore position angles). In all cases, themeasurement errors dominate the systematic errors. Three of the systems discussed here — LHS 1582AB, LHS 2071AB, and LHS 3738AB— have been found to be previously undetected astrometric binaries, as shown in Figures2, 3, and 4, respectively. For comparison, three additional stars — LHS 2021, LHS 3739and LHS 4009AB — are shown in Figures 5, 4 and 6. LHS 2021 and LHS 3739 appear tobe single stars while LHS 4009AB is a known close binary that also appears single in ourdata. We re-observed LHS 4009AB several years after the parallax was finished to searchfor long-term perturbations; none was found. All five systems are discussed in detail in § § The variability values in Table 2 are calculated according to the methodology of Honeycutt(1992) with additional details given in Henry et al. (2006). In Table 2 we list the level ofvariability in magnitudes (Column 8) of each target star in its parallax filter (Column 7).The number of nights on which each star was observed (Column 9) and the number of frames(Column 10) used for the variability study are also given.Although many M dwarfs are minutely variable, none of the stars in this sample havebeen found to vary by more than 2% in the frame series available. The single exception isLHS 1749AB at 0.028 mag. In this case, the variability is likely due to the B component ata separation of 3 ′′ falling within the relative photometry aperture, and variations in seeingaffecting the extracted fluxes. V RI magnitudes are listed in Table 2, along with extracted
J HK s magnitudes fromthe Two Micron All Sky Survey Catalog of Point Sources (Skrutskie et al. 2006). The errorson the V RI magnitudes are less than 0.05 mag for V , and 0.03 mag for R and I , withfew exceptions, most notably the faint stars LHS 2021 and LHS 3002. All photometricobservations were reduced via a custom IRAF pipeline and transformed onto a the Johnson-Kron-Cousins system through the use of photometric standards from Landolt (1992), Landolt(2007) and Graham (1982), as described in Henry et al. (2006). For purposes of initial target selection as well as for additional analysis once trigonomet-ric distances are determined, we used our CCD photometry combined with 2MASS
J HK photometry to calculate the photometric distances listed in Table 2 (Columns 16 and 17).The fourth-order polynomial fits for twelve color-absolute magnitude relations, the processby which the relations were determined, and the calculation of internal and external errorsare described in detail in Henry et al. (2004). Our quoted photometric distances have in-ternal errors (defined as the standard deviation of the distances estimated from the twelverelations) below 10% and an additional external systematic error of 15.3%. The distributionof internal errors is shown in Figure 7; the average error is 3.9%, which is much smaller thanthe external errors. The errors listed for the photometric distances given in Table 2 includeboth internal and external errors. 11 –Because the fits used for the photometric distance estimates are derived using mainsequence stars, the estimates are only accurate when the objects are single, main-sequence,M dwarfs. For the most part, these systems are indeed single, and 54 of the 64 systems (84%)fall within the 2- σ range when their combined internal and external errors are considered,as shown in Figure 8. Stars above the 2- σ line in Figure 8 are likely to be underluminoussubdwarfs, while those below the 2- σ line are presumably overluminous multiples. There areno subdwarfs in this sample, (although LHS 1050, LHS 1807, and LHS 3739/3738AB may beslightly metal-poor) but there are several known close multiples with combined photometry,either previously known (LHS 1630AB, LHS 1955AB, LHS 4009AB), or discovered by us(LHS 1582AB, LHS 2071AB, LHS 3738AB). There is considerable scatter in M V along themain sequence, visible in Figure 9, with up to two full magnitudes of spread for early to midM dwarfs. An equal magnitude binary will have a distance estimated to be 41% closer viaphotometry than is determined trigonometrically, but given the spread in M V in the mainsequence, only further work will confirm or refute the multiplicity of suspected targets. Spectral types are given in Table 2, and come from five sources that can be arranged intotwo broad groups. One group is from RECONS spectroscopy, detailed in Kirkpatrick et al.(1991), Henry et al. (1994), and Henry et al. (2002). RECONS spectroscopy was used todetermine the spectral types of all stars not taken from literature, and by Kirkpatrick et al.(1995) to classify LHS 1807.The remaining spectral types are from the Palomar/Michigan State University NearbyStar Spectroscopic Survey (PMSU) (Reid et al. 1995; Hawley et al. 1996) and related paperReid et al. (2007), all of which use the same weighted spectral indicies method linked to thespectral standards in Kirkpatrick et al. (1991). Where RECONS classifications were doneover a range of 6000–9000˚A with an effective resolution of 5.7–8.6˚A depending on the setup( §
5. Systems Worthy of NoteLHS 1050:
A 1.3- σ underluminous single-star system (11.7 ± ± ± ± LHS 1561:
The most overluminous system in the sample, it has a 4.4- σ distancemismatch (29.2 ± ± σ , which is oftena sign of unresolved orbital motion. LHS 1582AB:
A new astrometric binary with a 6.4 yr period and an 18 mas photocen-tric semi-major axis (see Figure 2). It has a 2.7- σ distance mismatch (21.1 ± ± LHS 1630AB:
We confirm the Adaptive Optics companion reported in Beuzit et al.(2004) seen on 18 September 2002 with a separation of 0 . ′′
61 at a position angle of 72 deg.The B component is visible in I band photometry frames as of 2007, as shown in Figure10. The system has a 2.8- σ distance mismatch (17.8 ± ± LHS 1749AB:
A close visual binary discovered by Jao et al. (2003) with a separationof 2 . ′′ ± ± ∼ V than A, as shown in Figure 11. LHS 1749Bis separable from A on 15 parallax frames; the resulting relative parallax result is 43.17 ± ± LHS 1807:
A 1.5- σ underluminous system (14.1 ± ± LHS 1955AB:
A close visual binary listed in Luyten (1979) with a 0 . ′′ σ overluminosity (13.5 ± ± ∼ R than A, and separable from A on only sevenframes over five nights using special SExtractor settings. Using those frames, we can obtaina relative parallax for B: 73.65 ± ± ± ± ∼
80 yr. All results for B are questionable dueto severe PSF contamination.
LHS 2010:
This system has a 3.0- σ distance mismatch (13.7 ± ± LHS 2021:
Contains the lowest luminosity star in our sample: V = 19.17, spectraltype M6.0V (despite unusually red colors), which can be seen in the lower right of Figure9. This paper’s distance (15.7 ± ± LHS 2071AB:
A new astrometric binary with P > σ overluminosity(15.0 ± ± LHS 5156:
The final parallax is entirely based on new V filter data due to insufficientold V coverage. Our reduction does not show the characteristic new V wobble ( § σ . GJ 438:
The hottest and most luminous star in the sample, as can be seen in Figure 9.The YPC distance (8.4 ± ± LHS 2520:
The third-most overluminous system in this sample; it has a 3.2- σ distancemismatch (12.8 ± ± LHS 2567/2568:
A visual binary with a separation of 8 . ′′ σ distance mismatch (21.4 ± ± σ (20.6 ± ± σ due to orbital motion presented in Table 4. A weightedsystem parallax is given in Table 3. LHS 3001/3002:
A visual binary with a separation of 12 . ′′ σ due to orbitalmotion presented in Table 4. A weighted system parallax is given in Table 3. LHS 3080:
The second-most overluminous system in this sample. It has a 3.2- σ dis-tance mismatch system (28.2 ± ± LHS 3197:
We have used an average correction to absolute parallax (1.50 ± ′ and a center only 22 ′ away at a positionangle of 43 deg. GJ 633:
The published YPC distance (9.6 ± ± ± § ′′ away that contaminated the previous result. The system is still not in theRECONS 10 parsec sample. A weighted mean system parallax (this new result and YPC)is given in Table 3. WT 562:
Unrelated to the system SCR 1826-6542 (Finch et al. 2007), 5 . ′ µ = 0 . ′′
611 yr − at 180.9 deg while SCR 1826-6542 has µ = 0 . ′′
311 yr − at 178.9 deg.Early results also suggest SCR 1826-6542 is several parsecs closer. LHS 3739/3738AB:
A heirarchical triple system consisting of a new astrometric bi-nary, LHS 3738AB, which is itself the B component of a known visual binary with LHS 3739.The system is the most underluminous in our sample. Using identical reference fields and 15 –frames (see Figure 4), LHS 3739 has no signs of perturbation and is 1.6- σ under luminous(19.6 ± ± σ (19.7 ± ± . ′′ σ . This orbital motion is detectedand presented in Table 4. A weighted system parallax is given in Table 3.The LHS 3738AB new astrometric binary has a 5.8 year period and a 27 mas photocen-tric semi-major axis (see Figure 4), and has been resolved by Gemini North. A preliminaryorbit is given in Table 5 and was removed from the data before fitting the final parallax.Further results will be published in a later paper. LHS 4009AB:
We do not confirm the companion from Montagnier et al. (2006) re-solved with adaptive optics on 14 October 2005 with a separation of 0 . ′′
07 at a position angleof 250 deg, and ∆ K = 0 .
15 in what Montagnier et al. (2006) claim is a three year orbit.The system has a 1.9- σ distance mismatch (12.5 ± ± R . LHS 4016:
The system has a 2.0- σ distance mismatch (24.2 ± ± V filter was not used prevents any definite determination.
6. Discussion
As shown in Figure 1, our parallax errors compare favorably to the errors from otherground-based parallax efforts, as summarized in YPC. Our increased accuracy can be at-tributed to our use of CCD images for our astrometry, while most of the YPC parallaxeswere measured from photographic plates.In Figure 13 we plot the distribution of tangential velocities listed in Column 15 ofTable 1. Most of the stars have v tan = 25–100 km sec − , as expected for disk red dwarfs(Mihalas & Binney 1981). The single star with v tan = 126 km sec − is LTT 5066, which at 46pc is the furthest star discussed in this paper; by photometry and spectroscopy it is a dwarf,not a subdwarf. Our sample is kinematically biased, requiring stars to have 0 . ′′ ≤ µ ≤ . ′′ − . As such, the nearest star, LHS 5156, must have a tangential velocity between 25 and50 km sec − , while our farthest star, LTT 5066, could not be in our proper motion regime ifit were moving any slower than 110 km sec − .The 56 systems within 25 pc described here constitute 2.7% of all systems now confirmedby parallax to be in the 25 pc sample (5.7% of systems in the southern hemisphere), accordingto the statistics from the NStars Database (Henry et al. 2002), using 2011 previously knownsystems as a baseline. Including parallax results from the entire CTIOPI program, we haveadded 155 new systems (a 7.7% increase) to the all-sky 25 pc sample. Of those 25 pcsystems, 142 are in the southern hemisphere, a net increase of 16.6% in the south alone. Weare currently observing roughly a hundred additional systems that may prove to be within25 pc, and continue to add more as observing time and stamina permit. Nonetheless, wedo not anticipate completing the census of all systems in the solar neighborhood throughCTIOPI alone, which means that ground-based sky survey efforts such as Pan-STARRS (ThePanoramic Survey Telescope & Rapid Response System), SkyMapper, LSST (the LargeSynoptic Survey Telescope), and space-based missions like Gaia, will undoubtedly revealmany more of the Sun’s neighbors.
7. Acknowledgements
The RECONS effort is supported primarily by the National Science Foundation throughgrants AST 05-07711 and AST 09-08402, as well as through NASA’s
Space InterferometryMission . Observations were initially made possible by NOAO’s Survey Program and havecontinued via the SMARTS Consortium. This research has made use of results from theNStars Project, NASA’s Astrophysics Data System Bibliographic Services, the SIMBAD andVizieR databases operated at CDS, Strasbourg, France, the SuperCOSMOS Sky Survey, andthe 2MASS database.The authors also wish to thank Mr. Sergio Dieterich for the Gemini observations andreductions; Dr. Brian Mason for supplying the orbit-fitting code; and the staff of the CerroTololo Inter-american Observatory, particularly Edgardo Cosgrove, Arturo Gomez, AlbertoMiranda, and Joselino Vasquez for their help over the years. The authors also wish to thankDr. Hugh Harris and Dr. Jennifer Bartlett for their constructive comments. 17 –
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This preprint was prepared with the AAS L A TEX macros v5.2.
20 – N u m be r o f pa r a ll a x e s Fig. 1.— Parallax errors for systems in this paper (black), and previous CTIOPI parallaxpapers (gray) are shown versus previous ground-based parallaxes from YPC (white, extendsoff this graph). Our improved precision is due to our CCD-based astrometry while the bulkof previous work was done with photographic plates. A few systems in this paper are also inYPC (see Table 3). The enormous spike at 15 mas is a result of the methods used in YPCto assign errors to parallaxes published without error. 21 –Fig. 2.— Plots of the nightly means of our astrometric residuals in RA and DEC for LHS1582AB after solving for parallax and proper motion. A perturbation with a ∼ ∼ K =0.1 and an orbital period ∼ N u m be r o f s t a r s Fig. 7.— The internal photometry distance errors are shown without the 15.3% externalsystematic error. The average error is 3.9%, indicating that the distance estimates areremarkably consistent for this sample. 25 – P ho t o m e t r i c ( CCD ) e s t i m a t e ( p c )
32% (2- σ ) error32% + 41% (binary) LHS 3739 (A)LHS 1050LHS 1351LHS 1807LHS 2520 LHS 1955ABLHS 4009ABLHS 1630ABLHS 1582ABLHS 2567 (A)LHS 4016LHS 1561LHS 3080
Fig. 8.— Photometric distance estimates compared to trigonometric parallax distances,identical distances are plotted with a dotted line. Dashed lines display the average 2- σ errorof our photometric distance estimates. Beyond the solid line, even an equal-luminosity bi-nary cannot fully account for the mismatch between trigonometric and photometric distanceestimates. LHS 2567/2568 are plotted with squares, LHS 3001 (the nearer one by trigono-metric parallax)/3002 with diamonds, and LHS 3739/3738AB with triangles. LTT 5066 at46 pc is not plotted. 26 – M v average error M1 M3 M5 M7
LHS 1749ABLHS 4016LHS 1630ABLHS 1561LHS 2010LHS 2122LHS 2567 (A)LHS 2520LHS 3080LHS 1955ABLHS 1582ABLHS 2071ABLHS 4009ABGJ 438 LHS 1050LHS 1807LHS 3739 (A) LHS 3002 (B)LHS 2021
Fig. 9.— All 67 system components with parallaxes reported here are plotted as large solidpoints on an observational HR diagram. Small points represent stars in the RECONS 10pc sample. LHS 2567/2568 are enclosed with squares, LHS 3001/3002 with diamonds, andLHS 3739/3738AB with triangles. 27 –Fig. 10.— Contour plots of LHS 1630AB (left) and example single star Ref I filter. LHS 1630B was firstreported by Beuzit et al. (2004) at separation 0 . ′′
61, angle 72 deg in 2002. Grid markings are5 pixels (2 . ′′ V filter on 2003 October 09. The B componentis obvious in the image but difficult to separate cleanly on most frames. The four years ofavailable data suggest slight orbital motion. Grid markings are 5 pixels (2.05 ′′ ). 28 –Fig. 12.— Contour plots of LHS 1955AB for three nights in the R filter. LHS 1955B isoccasionally visible as a saddle point or even a peak (middle frame). The motion seen heresuggests an ∼
80 yr orbit. Grid markings are 5 pixels (2.05 ′′ ). N u m be r o f S ys t e m s Fig. 13.— Tangential velocity distribution for our systems. The fastest moving star is alsoour most distant, LTT 5066.able 1. Astrometric Results
R.A. Decl. π (rel) π (corr) π (abs) µ P.A. V tan
Name (J2000.0) a Filter N sea b N frm Coverage b Years b N ref (mas) (mas) (mas) (mas yr − ) (deg) (km s − ) Notes(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)LHS 1050 00 15 49.25 +13 33 22.3 V
7s 60 1999.71–2009.75 10.03 7 84.46 ± ± ± ± ± c LHS 1351 02 11 18.06 -63 13 41.0 V ± ± ± ± ± R
5s 58 1999.71–2003.86 4.15 5 64.09 ± ± ± ± ± V
5s 70 1999.71–2005.00 5.29 9 66.32 ± ± ± ± ± R
9s 70 2000.87–2009.63 8.76 6 45.50 ± ± ± ± ± c d LHS 1630AB 04 07 20.50 -24 29 13.7 V
10s 137 1999.71–2009.03 9.32 5 54.44 ± ± ± ± ± c e LHS 1748 05 15 46.72 -31 17 45.3 V
5c 58 2000.88–2005.14 4.26 9 41.76 ± ± ± ± ± V
5s 91 2000.88–2005.05 4.17 6 44.93 ± ± ± ± ± c g LHS 1767 05 31 04.33 -30 11 44.8 V
5c 57 2003.96–2007.99 4.03 10 64.53 ± ± ± ± ± e WT 178 05 37 39.77 -61 54 43.8 R ± ± ± ± ± V
5c 76 2000.14–2005.05 4.91 8 47.63 ± ± ± ± ± R ± ± ± ± ± c GJ 1088 06 10 52.89 -43 24 17.8 V
5s 51 2000.88–2005.06 4.18 6 85.44 ± ± ± ± ± V
3c 93 2000.88–2003.14 2.26 9 60.91 ± ± ± ± ± R
5c 83 2000.94–2009.32 8.38 10 72.76 ± ± ± ± ± c g LHS 2010 08 27 11.83 -44 59 21.1 V
4c 85 2001.14–2004.18 3.03 9 71.33 ± ± ± ± ± c LHS 2021 08 30 32.57 +09 47 15.5 I ± ± ± ± ± c LHS 2071AB 08 55 20.25 -23 52 15.0 R
7s 69 2000.07–2009.30 9.23 11 66.16 ± ± ± ± ± c d LHS 2106 09 07 02.75 -22 08 50.1 R
5s 56 2000.06–2006.04 5.97 7 65.12 ± ± ± ± ± R ± ± ± ± ± V ± ± ± ± ± c f WT 244 09 44 23.73 -73 58 38.3 I ± ± ± ± ± R
8s 66 2001.15–2009.25 8.10 9 53.03 ± ± ± ± ± V
3c 56 2001.14–2003.14 1.99 8 49.58 ± ± ± ± ± V
5s 70 2001.15–2005.14 3.99 5 51.74 ± ± ± ± ± R ± ± ± ± ± V ± ± ± ± ± c e LHS 2520 12 10 05.59 -15 04 16.9 V
4s 56 2000.07–2004.43 4.37 7 77.11 ± ± ± ± ± V
5s 61 2001.14–2005.14 3.99 7 61.00 ± ± ± ± ± R
7s 58 2000.07–2009.03 8.96 7 45.54 ± ± ± ± ± c ALHS 2568 12 29 54.66 -05 27 20.6 R
7s 58 2000.07–2009.03 8.96 7 47.29 ± ± ± ± ± c BLHS 2718 13 20 03.86 -35 24 44.1 V
5s 62 2001.15–2005.14 3.99 11 72.05 ± ± ± ± ± R
5s 56 2001.15–2005.09 3.94 12 70.32 ± ± ± ± ± Table 1—Continued
R.A. Decl. π (rel) π (corr) π (abs) µ P.A. V tan
Name (J2000.0) a Filter N sea b N frm Coverage b Years b N ref (mas) (mas) (mas) (mas yr − ) (deg) (km s − ) Notes(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)LHS 2836 13 59 10.45 -19 50 03.4 V ± ± ± ± ± V
5s 45 2000.14–2005.14 4.99 8 74.00 ± ± ± ± ± I
5s 78 2000.58–2009.25 8.67 9 56.36 ± ± ± ± ± c ALHS 3002 14 56 27.79 +17 55 08.9 I
5s 78 2000.58–2009.25 8.67 9 54.83 ± ± ± ± ± c BLHS 3167 16 13 05.93 -70 09 08.0 R
6s 85 2000.57–2009.32 8.75 10 58.22 ± ± ± ± ± V
5s 53 2000.58–2004.45 3.87 10 52.03 ± ± ± ± ± R ± ± h ± ± ± c LHS 3218 16 35 24.64 -27 18 54.7 R
6s 77 2000.23–2009.32 9.09 8 51.31 ± ± ± ± ± V ± ± ± ± ± c e LHS 3295 17 29 27.34 -80 08 57.4 V
5s 68 2000.57–2004.25 3.68 8 78.20 ± ± ± ± ± I ± ± ± ± ± c LHS 3413 18 49 51.21 -57 26 48.6 R
5s 69 2000.57–2009.32 8.75 9 81.13 ± ± ± ± ± V
5s 69 2000.58–2009.75 9.17 8 47.44 ± ± ± ± ± V
8s 68 2000.58–2009.32 8.75 9 93.12 ± ± ± ± ± e APMPM J2127-3844 21 27 04.58 -38 44 50.8 R
4s 58 1999.62–2004.73 5.11 8 48.76 ± ± ± ± ± V ± ± ± ± ± V ± ± ± ± ± R
9s 113 1999.64–2009.65 10.01 10 49.60 ± ± ± ± ± c BC d LHS 3739 21 58 50.19 -32 28 17.8 R
9s 113 1999.64–2009.65 10.01 10 49.70 ± ± ± ± ± c AWT 870 22 06 40.68 -44 58 07.4 R
6s 70 2000.41–2005.90 5.48 7 55.41 ± ± ± ± ± R ± ± ± ± ± R
4c 62 2000.58–2005.80 5.23 10 45.38 ± ± ± ± ± R
6s 83 1999.62–2009.78 10.15 7 79.38 ± ± ± ± ± c LHS 4016 23 48 36.06 -27 39 38.9 V
6s 68 2000.87–2009.75 8.87 6 40.75 ± ± ± ± ± c LHS 4021 23 50 31.64 -09 33 32.6 V ± ± ± ± ± V ± ± ± ± ± e Beyond 25 pcLHS 1561 03 34 39.63 -04 50 33.3 V
6c 61 2000.07–2009.99 9.93 9 33.19 ± ± ± ± ± c LHS 1656 04 18 51.03 -57 14 01.1 I ± ± ± ± ± R ± ± ± ± ± R
6c 66 2000.58–2009.57 8.99 9 34.73 ± ± ± ± ± c LHS 3147 16 02 23.57 -25 05 57.3 R ± ± ± ± ± V
4c 74 2000.58–2003.30 2.72 10 37.20 ± ± ± ± ± Table 1—Continued
R.A. Decl. π (rel) π (corr) π (abs) µ P.A. V tan
Name (J2000.0) a Filter N sea b N frm Coverage b Years b N ref (mas) (mas) (mas) (mas yr − ) (deg) (km s − ) Notes(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)LHS 3484 19 47 04.49 -71 05 33.1 R
7s 65 2000.58–2009.32 8.75 8 37.51 ± ± ± ± ± R
5s 61 1999.62–2004.45 4.82 7 35.90 ± ± ± ± ± a coordinates are epoch and equinox 2000.0; each target’s coordinates were extracted from 2MASS and then transformed to epoch 2000.0 using the propermotions and position angles listed here. b ‘Coverage’ and ‘Years’ run from the first to last data point; ‘Seasons’ counts observing semesters where a dataset was taken, and denotes if coverage was‘c’ontinuous (more than one night of data in all seasons) or ‘s’cattered. Coverage extended by a single frame is denoted with a + in the Seasons column. c System has notes in § d The astrometric perturbation was removed from the final parallax fit. e Astrometric results use new V filter data. f Astrometric results use new V filter data only . g Parallax measured for the A component alone. h Generic correction to absolute adopted; field is reddened by a nebula. able 2. Photometric Results
Alternate No. of abs. σ No. of rel. No. of
J H K spectral phot No. ofName Name V J R KC I KC Nights π filter a (mag) Nights Frames (2MASS) (2MASS) (2MASS) type ref dist Relations Notes(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18)LHS 1050 GJ 12 12.62 11.46 10.04 3 V .011 12 60 8.62 8.07 7.81 M3.0V ..... 15.17 ± V .010 12 68 8.54 7.98 7.73 M2.5V Haw96 b ± R .015 11 58 9.06 8.52 8.17 M4.0V Rei95 c ± V .018 15 70 8.63 8.02 7.75 M3.5V Rei95 12.42 ± R .019 19 70 9.80 9.18 8.85 M4.5V Rei95 13.27 ± V .015 22 137 8.24 7.68 7.44 M3.5VJ ..... 11.72 ± a LHS 1748 L 521-2 12.08 11.06 9.83 2 V .017 11 58 8.59 7.99 7.73 M2.5V Haw96 19.91 ± V .028 16 91 8.21 7.62 7.36 M2.0V Haw96 16.44 ± V .012 13 57 9.05 8.49 8.19 M3.0V ..... 17.31 ± a WT 178 14.81 13.47 11.77 3 R .014 16 68 10.14 9.53 9.23 M4.5V Rei07 d ± V .010 17 76 9.74 9.16 8.87 M3.5V ..... 19.08 ± R .008 12 66 9.22 8.67 8.37 M3.0V Kir95 e ± V .016 13 51 8.17 7.58 7.31 M3.5V ..... 11.02 ± V .010 16 93 8.55 8.04 7.76 M3.5V Haw96 15.84 ± R .011 15 83 8.31 7.69 7.35 M4.0V Rei95 8.56 ± V .011 14 85 7.75 7.15 6.87 M3.5V Haw96 8.91 ± I .016 15 54 11.89 11.17 10.76 M6.0V ..... 14.42 ± R .016 16 69 9.11 8.54 8.20 M4.0VJ ..... 10.77 ± R .014 12 56 9.53 9.00 8.65 M4.5V Rei95 14.47 ± R .015 11 64 8.47 7.83 7.55 M3.5V Haw96 11.86 ± V .010 14 60 8.62 8.10 7.77 M4.5V ..... 9.62 ± a WT 244 15.17 13.80 12.02 3 I .010 14 64 10.23 9.71 9.38 M4.5V ..... 17.13 ± R .020 15 66 9.42 8.87 8.61 M3.5V Rei95 20.27 ± V .010 9 56 8.36 7.76 7.47 M2.5V Haw96 16.62 ± V .014 12 70 9.17 8.59 8.32 M3.0V Rei95 19.89 ± R .014 14 64 9.44 8.86 8.54 M3.0V Haw96 17.40 ± V .008 14 92 7.14 6.58 6.32 M1.0V ..... 12.63 ± a LHS 2520 LP 734-32 12.09 10.88 9.30 3 V .014 10 56 7.77 7.14 6.86 M3.5V Rei95 7.59 ± V .010 13 61 9.17 8.63 8.36 M4.0V Haw96 14.98 ± R .015 12 58 8.82 8.27 7.96 M3.5V Rei95 13.55 ± R .013 12 58 9.79 9.24 8.92 M3.5V Rei95 18.99 ± V .012 12 62 8.83 8.25 7.98 M3.0V Haw96 16.04 ± R .012 9 56 8.66 8.07 7.78 M3.5V Rei95 12.59 ± Table 2—Continued
Alternate No. of abs. σ No. of rel. No. of
J H K spectral phot No. ofName Name V J R KC I KC Nights π filter a (mag) Nights Frames (2MASS) (2MASS) (2MASS) type ref dist Relations Notes(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18)LHS 2836 L 763-63 12.88 11.60 9.90 3 V .013 22 108 8.33 7.76 7.44 M4.0V ..... 8.86 ± V .016 12 45 8.95 8.39 8.09 M3.5V Rei95 15.40 ± I .013 17 78 10.74 10.15 9.85 M4.5V Rei95 19.74 ± I .012 17 78 11.98 11.30 10.92 M6 V Rei95 17.47 ± R .014 17 85 9.26 8.74 8.39 M4.0V ..... 14.73 ± V .011 10 53 8.92 8.36 8.11 M3.5V Rei95 17.31 ± R .011 14 51 9.55 9.00 8.68 M4.5V ..... 14.13 ± R .016 18 77 9.78 9.27 9.00 M4.0V Rei95 20.86 ± V .011 20 100 8.89 8.31 8.05 M2.5V ..... 19.47 ± a LHS 3295 L 21-3 12.18 11.02 9.53 2 V .007 14 68 8.09 7.52 7.30 M3.0V ..... 11.32 ± I .010 18 80 10.35 9.81 9.45 M4.5V ..... 16.96 ± R .017 13 69 8.32 7.70 7.46 M3.5V Haw96 9.85 ± V .009 14 69 8.47 7.92 7.66 M2.0V Haw96 14.98 ± V .014 14 68 7.69 7.12 6.83 M2.5V Haw96 10.83 ± a APMPM J2127-3844 14.60 13.31 11.66 2 R .015 12 58 10.03 9.56 9.28 M4.0V ..... 21.41 ± V .015 17 74 9.46 8.83 8.53 M4.0V ..... 13.11 ± V .012 14 70 8.74 8.12 7.89 M2.0V Haw96 17.23 ± R .010 24 113 10.65 10.09 9.76 M4.5V Haw96 18.50 ± R .010 24 113 10.39 9.83 9.56 M3.5V Haw96 27.56 ± R .015 15 70 9.76 9.18 8.89 M4.0V ..... 15.99 ± R .012 12 55 9.06 8.48 8.22 M3.0V Rei95 19.45 ± R .008 12 62 9.53 8.97 8.71 M3.5V Haw96 21.89 ± R .017 17 83 9.21 8.61 8.31 M4.5VJ ..... 9.21 ± V .016 16 68 8.58 8.02 7.74 M2.5V Rei95 17.20 ± V .017 15 60 8.94 8.39 8.04 M4.0V Rei95 11.84 ± V .011 16 59 8.59 7.98 7.74 M3.5V ..... 12.24 ± a Beyond 25 pcLHS 1561 G 77-64 13.07 11.84 10.30 4 V .010 13 61 8.83 8.27 7.93 M3.5V Rei95 13.49 ± I .009 13 51 9.52 8.94 8.65 M2.5V ..... 25.68 ± R .010 16 69 10.48 9.96 9.70 M3.0V ..... 44.38 ± R .012 17 66 9.67 9.11 8.82 M4.0V ..... 15.73 ± R .012 18 72 9.28 8.69 8.41 M3.5V Rei95 20.74 ± V .008 13 74 8.59 8.00 7.77 M2.5V Haw96 20.36 ± able 2—Continued Alternate No. of abs. σ No. of rel. No. of
J H K spectral phot No. ofName Name V J R KC I KC Nights π filter a (mag) Nights Frames (2MASS) (2MASS) (2MASS) type ref dist Relations Notes(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18)LHS 3484 L 79-24 13.88 12.70 11.19 2 R .008 14 65 9.79 9.22 8.98 M3.5V Haw96 24.66 ± R .009 11 61 10.18 9.67 9.41 M3.5V ..... 29.54 ± a Astrometric results and relative photometry use new V filter data. b Hawley et al. (1996) c Reid et al. (1995) d Reid et al. (2007) (luminosity class inferred from the paper, where giants were simply discarded) e Kirkpatrick et al. (1995)
35 –Table 3. Combined system parallaxes π π
Weighted π Name (mas) source Name (mas) source (mas)(1) (2) (3) (4) (5) (6) (7)LHS 1050 85.85 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
36 –Table 4. Multiple System Parameters
Binary UT Date Sep. PA Period ∆Name (mas) (deg) (years) mag
Notes1 2 3 4 5 6 7LHS 1582AB - 18.4 ± a - 6.35 ± > ± ± > V ∼ b ± ± ± ± ∼
80 ∆ R ∼ b c LHS 2071AB - 21.2 ± a - 16.46 ± ± ± > V =1.142009 JAN 13 8062.2 ± ± ± ± > V =2.962009 MAR 31 12702.6 ± ± ± ± >
10 ∆ V =1.06 (wide)2009 AUG 27 113115.6 ± ± ± a - 5.85 ± a Photocentric semimajor axis b Estimate from relative photometry from relative parallax reduction c Based on two and one frames, respectively; uses different centroiding parameters.
Table 5. Preliminary Orbital Elements
P a a i Long. Nodes (Ω) T Long. Periastron ( ω )Designation (yr) (arcsec) (deg) (deg) (yr) e (deg)1 2 3 4 5 6 7 8LHS 1582AB 6.4 ± ± ± ± ± ± ± ± b ± ± ± ± ± ± ± ± ± ± ± ± ± a Photocentric semimajor axis b Highly uncertain
37 –Table 6. Comparison of spectral types37 –Table 6. Comparison of spectral types