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The Tucana/Horologium, Columba, AB Doradus, and Argus Associations: New Members and Dusty Debris Disks
We propose 35 star systems within ~70 pc of Earth as newly identifiedmembers of nearby young stellar kinematic groups; these identificationsinclude the first A- and late-B-type members of the AB Doradus movinggroup and field Argus Association. All but one of the 35 systems containa bright solar- or earlier-type star that should make an excellenttarget for the next generation of adaptive optics (AO) imaging systemson large telescopes. AO imaging has revealed four massive planets inorbit around the ? Boo star HR 8799. Initially, the planets wereof uncertain mass due in large part to the uncertain age of the star. Wefind that HR 8799 is a likely member of the ~30 Myr old ColumbaAssociation, implying planet masses ~6 times that of Jupiter. Weconsider Spitzer Space Telescope MIPS photometry of stars in the ~30 Myrold Tucana/Horologium and Columba Associations, the ~40 Myr old fieldArgus Association, and the ~70 Myr old AB Doradus moving group. Thepercentage of stars in these young stellar groups that display excessemission above the stellar photosphere at 24 and 70 ?mwavelengths—indicative of the presence of a dusty debrisdisk—is compared with corresponding percentages for members of 11open clusters and stellar associations with ages between 8 and 750 Myr,thus elucidating the decay of debris disks with time.
| RACE-OC project: Rotation and variability of young stellar associations within 100 pc
Context. Examining the angular momentum of stars and its interplay withtheir magnetic fields represent a promising way to probe the stellarinternal structure and evolution of low-mass stars. Aims: Weattempt to determine the rotational and magnetic-related activityproperties of stars at different stages of evolution.We focused ourattention primarily on members of clusters and young stellarassociations of known ages. In this study, our targets are 6 young loosestellar associations within 100 pc and with ages in the range 8-70 Myr:TW Hydrae (~8 Myr), ? Pictoris (~10 Myr), Tucana/Horologium,Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additionalrotational data for ? Persei and the Pleiades from the literatureare also considered. Methods: Rotational periods of starsexhibiting rotational modulation due to photospheric magnetic activity(i.e., starspots) were determined by applying the Lomb-Scargleperiodogram technique to photometric time-series data obtained by theAll Sky Automated Survey (ASAS). The magnetic activity level was derivedfrom the amplitude of the V lightcurves. The statistical significance ofthe rotational evolution at different ages was inferred by applying atwo-sided Kolmogorov-Smirnov test to subsequent age-bins. Results: We detected the rotational modulation and measured the rotationperiods of 93 stars for the first time, and confirmed the periods of 41stars already known from the literature. For an additional 10 stars, werevised the period determinations by other authors. The sample wasaugmented with periods of 21 additional stars retrieved from theliterature. In this way, for the first time we were able to determinethe largest set of rotation periods at ages of ~8, ~10 and ~30 Myr, aswell as increase by 150% the number of known periodic members of AB Dor. Conclusions: The analysis of the rotation periods in youngstellar associations, supplemented by Orion Nebula Cluster (ONC) and NGC2264 data from the literature, has allowed us to find that in the0.6-1.2 M? range the most significant variations in therotation period distribution are the spin-up between 9 and 30 Myr andthe spin-down between 70 and 110 Myr. Variations of between 30 and 70Myr are rather doubtful, despite the median period indicating asignificant spin-up. The photospheric activity level is found to becorrelated with rotation at ages greater than ~70 Myr and to show someadditional age dependence besides that related to rotation and mass.Tables 1.1-1.7 and Figs. 1.1-1.22 are only available in electronic format http://www.aanda.orgBased on theAll Sky Automated Survey photometric data.
| Search for associations containing young stars (SACY). III. Ages and Li abundances
Context: Our study is a follow-up of the SACY project, an extended highspectral resolution survey of more than two thousand opticalcounterparts to X-ray sources in the southern hemisphere targeted tosearch for young nearby association. Nine associations have either beennewly identified, or have had their member list revised. Groupsbelonging to the Sco-Cen-Oph complex are not considered in the presentstudy. Aims: These nine associations, with ages of between about 6Myr and 70 Myr, form an excellent sample to study the Li depletion inthe pre-main sequence (PMS) evolution. In the present paper, weinvestigate the use of Li abundances as an independent clock toconstrain the PMS evolution. Methods: Using our measurements ofthe equivalent widths of the Li resonance line and assuming fixedmetallicities and microturbulence, we calculated the LTE Li abundancesfor 376 members of various young associations. In addition, weconsidered the effects of their projected stellar rotation.Results: We present the Li depletion as a function of age in the firsthundred million years for the first time for the most extended sample ofLi abundances in young stellar associations. Conclusions: A clearLi depletion can be measured in the temperature range from 5000 K to3500 K for the age span covered by the nine associations studied in thispaper. The age sequence based on the Li-clock agrees well with theisochronal ages, the ?Cha association being the only possibleexception. The lithium depletion patterns for the associations presentedhere resemble those of the young open clusters with similar ages,strengthening the notion that the members proposed for these loose youngassociations have indeed a common physical origin. The observed scatterin the Li abundances hampers the use of Li in determining reliable agesfor individual stars. For velocities above 20 km s-1,rotation seems to play an important role in inhibiting the Li depletion.Based on observations collected at the ESO - La Silla and at theLNA-OPD.Tables [see full textsee full text]-[see full textsee full text] areonly available in electronic form at http://www.aanda.org
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| Lithium Depletion of Nearby Young Stellar Associations
We estimate cluster ages from lithium depletion in fivepre-main-sequence groups found within 100 pc of the Sun: the TW Hydraeassociation, η Chamaeleontis cluster, β Pictoris moving group,Tucanae-Horologium association, and AB Doradus moving group. Wedetermine surface gravities, effective temperatures, and lithiumabundances for over 900 spectra through least-squares fitting tomodel-atmosphere spectra. For each group, we compare the dependence oflithium abundance on temperature with isochrones from pre-main-sequenceevolutionary tracks to obtain model-dependent ages. We find that theη Cha cluster and the TW Hydrae association are the youngest, withages of 12+/-6 Myr and 12+/-8 Myr, respectively, followed by the βPic moving group at 21+/-9 Myr, the Tucanae-Horologium association at27+/-11 Myr, and the AB Dor moving group at an age of at least 45 Myr(whereby we can only set a lower limit, since the models-unlike realstars-do not show much lithium depletion beyond this age). Here theordering is robust, but the precise ages depend on our choice of bothatmospheric and evolutionary models. As a result, while our ages areconsistent with estimates based on Hertzsprung-Russell isochrone fittingand dynamical expansion, they are not yet more precise. Our observationsdo show that with improved models, much stronger constraints should befeasible, as the intrinsic uncertainties, as measured from the scatterbetween measurements from different spectra of the same star, are verylow: around 10 K in effective temperature, 0.05 dex in surface gravity,and 0.03 dex in lithium abundance.
| M dwarfs: effective temperatures, radii and metallicities
We empirically determine effective temperatures and bolometricluminosities for a large sample of nearby M dwarfs, for which highaccuracy optical and infrared photometry is available. We introduce anew technique which exploits the flux ratio in different bands as aproxy of both effective temperature and metallicity. Our temperaturescale for late-type dwarfs extends well below 3000K (almost to the browndwarf limit) and is supported by interferometric angular diametermeasurements above 3000K. Our metallicities are in excellent agreement(usually within 0.2dex) with recent determinations via independenttechniques. A subsample of cool M dwarfs with metallicity estimatesbased on hotter Hipparcos common proper motion companions indicates ourmetallicities are also reliable below 3000K, a temperature rangeunexplored until now. The high quality of our data allows us to identifya striking feature in the bolometric luminosity versus temperatureplane, around the transition from K to M dwarfs. We have compared oursample of stars with theoretical models and conclude that thistransition is due to an increase in the radii of the M dwarfs, a featurewhich is not reproduced by theoretical models.
| On the kinematic evolution of young local associations and the Scorpius-Centaurus complex
Context: Over the last decade, several groups of young (mainly low-mass)stars have been discovered in the solar neighbourhood (closer than ~100pc), thanks to cross-correlation between X-ray, optical spectroscopy andkinematic data. These young local associations - including an importantfraction whose members are Hipparcos stars - offer insights into thestar formation process in low-density environments, shed light on thesubstellar domain, and could have played an important role in the recenthistory of the local interstellar medium. Aims: To study the kinematicevolution of young local associations and their relation to other youngstellar groups and structures in the local interstellar medium, thuscasting new light on recent star formation processes in the solarneighbourhood. Methods: We compiled the data published in theliterature for young local associations. Using a realistic Galacticpotential we integrated the orbits for these associations and theSco-Cen complex back in time. Results: Combining these data with thespatial structure of the Local Bubble and the spiral structure of theGalaxy, we propose a recent history of star formation in the solarneighbourhood. We suggest that both the Sco-Cen complex and young localassociations originated as a result of the impact of the inner spiralarm shock wave against a giant molecular cloud. The core of the giantmolecular cloud formed the Sco-Cen complex, and some small cloudlets ina halo around the giant molecular cloud formed young local associationsseveral million years later. We also propose a supernova in young localassociations a few million years ago as the most likely candidate tohave reheated the Local Bubble to its present temperature.
| SIM PlanetQuest Key Project Precursor Observations to Detect Gas Giant Planets around Young Stars
We present a review of precursor observing programs for the SIMPlanetQuest Key Project devoted to detecting Jupiter-mass planets aroundyoung stars. In order to ensure that the stars in the sample are free ofvarious sources of astrometric noise that might impede the detection ofplanets, we have initiated programs to collect photometry, high-contrastimages, interferometric data, and radial velocities for stars in boththe northern and southern hemispheres. We have completed a high-contrastimaging survey of target stars in Taurus and the Pleiades and found nodefinitive common proper motion companions within 1" (140 AU) of the SIMtargets. Our radial velocity surveys have shown that many of the targetstars in Sco-Cen are fast rotators, and a few stars in Taurus and thePleiades may have substellar companions. Interferometric data of a fewstars in Taurus show no signs of stellar or substellar companions withseparations of 5-50 mas. The photometric survey suggests thatapproximately half of the stars initially selected for this program arevariable to a degree (1 σ > 0.1 mag) that would degrade theastrometric accuracy achievable for that star. While the precursorprograms are still a work in progress, we provide a comprehensive listof all targets and rank them according to their viability as a result ofthe observations taken to date. The observable that removes by far themost targets from the SIM young stellar object (YSO) program isphotometric variability.
| Rotation and Activity of Pre-Main-Sequence Stars
We present a study of rotation (vsini) and chromospheric activity(Hα equivalent width) based on an extensive set of high-resolutionoptical spectra obtained with the MIKE instrument on the 6.5 m MagellanClay telescope. Our targets are 74 F-M dwarfs in four young stellarassociations, spanning ages from 6 to 30 Myr. By comparing Hα EWsin our sample to results in the literature, we see a clear evolutionarysequence: Chromospheric activity declines steadily from the T Tauriphase to the main sequence. Using activity as an age indicator, we finda plausible age range for the Tuc-Hor association of 10-40 Myr. Between5 and 30 Myr, we do not see evidence for rotational braking in the totalsample, and thus angular momentum is conserved, in contrast to youngerstars. This difference indicates a change in the rotational regulationat ~5-10 Myr, possibly because disk braking cannot operate longer thantypical disk lifetimes, allowing the objects to spin up. Therotation-activity relation is flat in our sample; in contrast tomain-sequence stars, there is no linear correlation for slow rotators.We argue that this is because young stars generate their magnetic fieldsin a fundamentally different way from main-sequence stars, and not justthe result of a saturated solar-type dynamo. By comparing our rotationalvelocities with published rotation periods for a subset of stars, wedetermine ages of 13+7-6 and9+8-2 Myr for the η Cha and TWA associations,respectively, consistent with previous estimates. Thus we conclude thatstellar radii from evolutionary models by Baraffe et al. (1998) are inagreement with the observed radii to within +/-15%.
| Search for associations containing young stars (SACY). I. Sample and searching method
We report results from a high-resolution optical spectroscopic surveyaimed to search for nearby young associations and young stars amongoptical counterparts of ROSAT All-Sky Survey X-ray sources in theSouthern Hemisphere. We selected 1953 late-type (B-V~≥~0.6),potentially young, optical counterparts out of a total of 9574 1RXSsources for follow-up observations. At least one high-resolutionspectrum was obtained for each of 1511 targets. This paper is the firstin a series presenting the results of the SACY survey. Here we describeour sample and our observations. We describe a convergence method in the(UVW) velocity space to find associations. As an example, we discuss thevalidity of this method in the framework of the β Pic Association.
| Accretion Disks around Young Stars: Lifetimes, Disk Locking, and Variability
We report the findings of a comprehensive study of disk accretion andrelated phenomena in four of the nearest young stellar associationsspanning 6-30 million years in age, an epoch that may coincide with thelate stages of planet formation. We have obtained ~650 multiepochhigh-resolution optical spectra of 100 low-mass stars that are likelymembers of the η Chamaeleontis (~6 Myr), TW Hydrae (~8 Myr), βPictoris (~12 Myr), and Tucanae-Horologium (~30 Myr) groups. Our datawere collected over 12 nights between 2004 December and 2005 July on theMagellan Clay 6.5 m telescope. Based on Hα line profiles, alongwith a variety of other emission lines, we find clear evidence ofongoing accretion in 3 out of 11 η Cha stars and 2 out of 32 TWHydrae members. None of the 57 β Pic or Tuc-Hor members showsmeasurable signs of accretion. Together, these results imply significantevolution of the disk-accretion process within the first several Myr ofa low-mass star's life. While a few disks can continue to accrete for upto ~10 Myr, our findings suggest that disks accreting for beyond thattimescale are rather rare. This result provides an indirect constrainton the timescale for gas dissipation in inner disks and, in turn, ongas-giant planet formation. All accretors in our sample are slowrotators, whereas nonaccretors cover a large range in rotationalvelocities. This may hint at rotational braking by disks at ages up to~8 Myr. Our multiepoch spectra confirm that emission-line variability iscommon even in somewhat older T Tauri stars, among which accretors tendto show particularly strong variations. Thus, our results indicate thataccretion and wind activity undergo significant and sustained variationsthroughout the lifetime of accretion disks.
| On the Rotation of Post-T Tauri Stars in Associations
Nearby associations or moving groups of post-T Tauri stars with agesbetween ~10 and 30 Myr are excellent objects for the study of theinitial spin-up phase during the pre-main-sequence evolution. Anempirical approach is adopted here for the first time with these starsto infer their rotations, properties, and relations to X-ray emission.Three nearby associations with distances less than 100 pc areconsidered: the TW Hydrae association (TWA) with an age of 8 Myr, theβ Pictoris moving group (BPMG) with an age of 12 Myr, and acombination of Tucana and Horologium associations (Tuc/HorA; 30 Myr).Two low- and high-rotation modes are considered for each association,with stellar masses of0.1Msolar<=M<1.5Msolar and1.5Msolar<=M<=2.6Msolar, respectively.Because no observed rotational periods are known for these stars, we usea mathematical tool to infer representative equatorial rotationvelocities v0(eq) from the observed distribution of projectedrotational velocities (vsini). This is done for each mode and for eachassociation. A spin-up is found for the high-rotation mode, whereas inthe low-rotation mode the v0(eq) do not increasesignificantly. This insufficient increase of v0(eq) isprobably the cause of a decrease of the total mean specific angularmomentum for the low-mass stars between 8 and 30 Myr. However, for thehigh-mass stars, where a sufficient spin-up is present, the specificangular momentum is practically conserved in this same time interval. Atwo-dimensional (mass and vsini) K-S statistical test yields resultscompatible with a spin-up scenario. By supposing that the distributionof the masses of these three associations follows a universal massfunction, we estimate the number of members of these associations thatremain to be detected. The analysis of rotational and stellar massesusing the luminosity X-ray indicators LX andLX/Lb present similar properties, as does thedependence on stellar mass and rotation, at least for the youngerassociations TWA and BPMG, to those obtained for T Tauri stars in theOrion Nebula Cluster (1 Myr). A strong desaturation effect appears at~30 Myr, the age of Tuc/HorA, measured essentially by the early-G andlate-F type stars. This effect seems to be provoked by the minimumconfiguration of the stellar convection layers, attained for the firsttime for the higher mass stars at ~30 Myr. The desaturation appears tobe independent of rotation at this stage.
| Young Stars Near the Sun
Until the late 1990s the rich Hyades and the sparse UMa clusters werethe only coeval, comoving concentrations of stars known within 60 pc ofEarth. Both are hundreds of millions of years old. Then beginning in thelate 1990s the TW Hydrae Association, the Tucana/Horologium Association,the Pictoris Moving Group, and the AB Doradus Moving Group wereidentified within 60 pc of Earth, and the Chamaeleontis cluster wasfound at 97 pc. These young groups (ages 8 50 Myr), along with othernearby, young stars, will enable imaging and spectroscopic studies ofthe origin and early evolution of planetary systems.
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| Tucana Association
Among star clusters, only the sparse Ursa Major nucleus is closer toEarth than the recently identified Tucana association. Based on newphotometric VRI magnitudes, we construct a color-magnitude diagramcomposed of likely and possible Tucana members. The implied age of theTucana association stars, <~40 Myr, is consistent with the agedetermined from a previous analysis by Stelzer & Neuhäuser ofthe X-ray luminosities of plausible association members. Based primarilyon space motions and X-ray fluxes, we identify potential new members ofthe Tucana association not considered in earlier studies. Torres andcoworkers recently identified a group of post-T Tauri stars, theHorologium association, which is located near the Tucana association inright ascension and declination. Because the Horologium stars have thesame space motions, age, distance from Earth, volume density, and rangeof spectral types as Tucana stars, we suggest that, rather than beingcharacterized as a separate group, it would be appropriate andeconomical to subsume the Horologium association stars into the Tucanastream.
| X-ray emission from young stars in the Tucanae association
We report on X-ray emission from members of the recently discoveredTucanae association, a group of stars with youth signatures and similarspace motion. The Tucanae association is the nearest known region ofrecent star formation ( ~ 45 pc) far from molecular clouds(\cite{Zuckerman00.1}). We have made use of the ROSAT Data Archive andsearched for X-rays from Tucanae stars in both ROSAT All-Sky Survey(RASS) and pointed observations. While the RASS provides completecoverage of the sky, only three potential Tucanae members have beenobserved during PSPC pointings. All three stars have been detected. Forthe RASS the percentage of detections is 59%. The comparison of theX-ray luminosity function of Tucanae to that of other star formingregions may provide clues to the uncertain age of the association. Wefind that the distribution of X-ray luminosities is very similar to theones derived for the TW Hya association, the Taurus-Auriga T TauriStars, and the IC 2602 cluster, but significantly brighter than theluminosity distribution of the Pleiades. We conclude that the stars inTucanae are most likely young, on the order of 10-30 Myr. Strongvariability of most stars emerges from the X-ray lightcurves whereseveral flares and irregular variations are observed.
| Identification of a Nearby Stellar Association in theHipparcos Catalog: Implications for Recent, Local Star Formation
The TW Hydrae Association (~55 pc from Earth) is the nearest knownregion of recent star formation. Based primarily on the Hipparcoscatalog, we have identified a group of nine or 10 comoving star systemsat a common distance (~45 pc) from Earth that appear to compriseanother, somewhat older association (``the Tucanae Association'').Together with ages and motions recently determined for some nearby fieldstars, the existence of the Tucanae and TW Hydrae Associations suggeststhat the Sun is now close to a region that was the site of substantialstar formation only 10-50 Myr ago. The TW Hydrae Association representsa final chapter in the local star formation history.
| New light on faint stars. I - The luminosity function in the solar neighbourhood
From photoelectric photometry of red dwarf stars identified in anobjective prism survey, a magnitude-limited complete sample has beendefined. Applying photometric parallaxes, calibrated for theKron-Cousins system by observations of trigonometric parallax stars,this sample is used to determine the space densities of stars withabsolute magnitudes between + 7 and + 12. The resultant luminosityfunction is consistent with the Luyten and Wielen functions for thesolar neighbourhood. An analysis of the stellar kinematics shows littlesignificant evidence of a substantial local population of low spacemotion M-dwarfs.
| Photometry of Southern Hemisphere red dwarf stars
Results are presented for a photometric investigation of aspectroscopically selected sample of red dwarf stars in the SouthernHemisphere. Absolute magnitudes and distances for the stars areestimated from broadband red colors. Three stars which may besubluminous are identified, as are several stars which may be within 25pc. The tangential velocity and velocity dispersion of the sample aresimilar to values found in other studies of nearby late-type stars.
| The space density and kinematics of dwarf M stars
The results of an objective-prism survey for dwarf stars, K7 and later,are presented. One hundred twenty-one red sensitive plates covering 1720sq. degrees of the southern sky were obtained with the Curtis Schmidttelescope at C.T.I.O. The resulting luminosity function rises from log N+ 10 = 7.9 at MV = 8 to about 8.7 at MV = 11 and12. About 75% of the dwarfs in this survey are identified with BPMstars, but inserting the proper motions given into the equations of themethod of mean absolute magnitudes yields values of MB aboutthree magnitudes brighter than the spectral types would indicate. Thatthe method of mean absolute magnitudes appears to be calibrated on starsof higher than average proper motion lends credence to the luminosityfunction result. A galactic mass density is found for the dwarfsconsidered.
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