Publications Ofthe Astronomical Society Ofthe Pacific 99:490-496, June 1987

Publications ofthe Astronomical Society ofthe Pacific 99:490-496, June 1987

RADIAL VELOCITIES OF M DWARF STARS

GEOFFREY W. MARCY,* VICTORIA LINDSAY,* AND KAREN WILSON Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132 Received 1987 February 26, revised 1987 March 28

ABSTRACT Radial velocities for 72 M dwarfs have been obtained having internal errors of about 0.1 km s1 and external errors of about 0.4 km s_1. Multiple velocity measurements of ten dMe stars have yielded a set of six which have no stellar companions, providing confirmation that the dMe phenomenon can occur in single stars. These single dMe stars have low space motions indicative of relative youth. Four stars from the entire survey were found to have double-line spectra and two were found to be single-line spectroscopic binaries of low amplitude. The zero point of the velocity scale is found to agree well with that of O. C. Wilson (1967) and differences are noted among other radial-velocity studies. Most of the stars in this study have velocities sufficiently well determined to constitute potential radial-velocity standards. Key words: K-M dwarfs-radial velocities

I. Introduction atic difference between their velocities and O. C. 1 Accurate measurements of radial velocities for M Wilson's of —1.7 km s , a discrepancy not explainable by dwarfs are used to address a number of astrophysical the random errors of the two studies. problems such as the age dependence of the kinematics of Thus, it is not known at present which zero point is to the Galaxy (cf. Mayor 1974; Wielen 1974), the existence of be preferred. Here we present velocities of 72 M dwarfs which are internally consistent to better than 0.1 km s-1 substellar companions (Marcy et al. 1986), and the nature of magnetic/chromospheric activity (Bopp and Meredith and which are anchored to an absolute velocity scale 1986; Young, Sadjadi, and Harlan 1987). The most widely determined by high-resolution spectra of a subsample of used set of M-dwarf velocities has been that established the same stars. by O. C. Wilson (1967), both because of the large size of II. Observations the sample and because individual absorption lines were During a two-year period from June 1983 to June 1985, measured, yielding a well-defined zero point. The inter- 1 a major program was carried out at the 100-inch (2.5 m) nal errors in Wilson s study were about 2 km s and the velocities were systematically different from those in the telescope of the Mount Wilson Observatory to obtain 1 highly accurate radial velocities of relatively faint stars. General Catalogue (Wilson 1953) by only 0.5 km s . Recently, Young et al. (1987) have similarly obtained The primary goal of the project was the detection of velocities with an accuracy of 1 to 2 km s1 for 48 M dwarfs single-line spectroscopic binaries of extremely low ampli- in the solar neighborhood. tude. While this principal aim continues (now at Lick Cross-correlation methods, both analogue and digital Observatory), the data in hand permit determination of (Griffin 1967; Simkin 1974), are particularly well suited to absolute velocities for many of the program stars. A sam- M dwarfs owing to their rather complicated spectra and ple of M dwarfs was chosen from the list of Joy and Abt their relative faintness. Cross-correlation velocities have (1974) with the following selection criteria: spectral type been recently obtained for a large number of M dwarfs by later than dM2 (though a few bright dMO stars were Stauffer and Hartmann (1986) and by Bopp and Meredith included), accessibility by the Mount Wilson 100-inch (1986). All of these measurements have quoted internal telescope (dec. < 50°), brighter than V = 11.5, and void of errors of about 1 km s1. Difficulties arise, however, in companions within 10 arc sec. The final sample is not the determination of the zero points of each velocity complete but contains 80% of all of the single M dwarfs system. This problem stems primarily from the lack of later than dM2 and brighter than V = 10.5 that are listed velocity standards, especially for M dwarfs later than Ml. in the Gliese catalogue (Gliese 1969). The coudé spectrograph of the Mount Wilson 100-inch For example, Stauffer and Hartmann (1986) find a system- telescope was used with the 114-inch (2.9 m) camera and a new grating (graciously loaned by the Jet Propulsion Lab- * Guest Observer, Lick Observatory. oratories) to yield a reciprocal dispersion of 1.0 A mm-1.

490 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System M DWARF STARS 491

The intensified Reticon detector (Shectman 1981) was velocities obtained on that night. Typically, 20 stars are employed because it produces essentially no noise itself observed per night, so that this nightly correction should and is therefore ideal for the anticipated low signal-to- have an error of about a/V2Ö, where σ is the internal noise applications. This setup yields a pixel spacing of error. Tests of repeatability during a night show that σ is about 0.010 A corresponding to 500 m s1 at λ = 6000 Α. about 150 m s-1, yielding nightly systematic errors of less Several significant structural modifications were made to than about 40 m s1. In effect, the program stars them- the spectrograph to ensure stability of the optics during selves provide the nightly reference velocity scale (with a the course of a night. Careful steps were taken to ensure zero point to be discussed below) and stars found to be that both the optical axis and/-ratio of the telescope were variable are not used as references. matched by those of all calibration sources. All observa- The determination of the zero point of the velocity scale tions were made within three hours of the meridian. has been carried out with extremely high-resolution spec- As the major source of error was anticipated to be the tra of a subset of the program stars, enabling measure- nonuniform illumination of the slit (cf. Griffin and Griffin ment of individual absorption lines. The spectra were 1973), the slit width was chosen to be 0.35 arc sec. This, of obtained with the echelle spectrograph and image-tube course, did not eliminate that source of error. Indeed, scanner located at the coudé focus of the Lick Observa- experience showed that the poorest velocities occurred tory 120-inch (3-m) telescope (Soderblom 1982; Robinson on nights of sub-arc-second seeing, a common problem at and Wampler 1972). The spectrograph was used in single- Mount Wilson. pass mode and was fed with the 0.6-m coudé auxiliary The observing procedure involves obtaining a spec- telescope. The spectra cover 13 angstroms with a recipro- trum of the comparison source, a thorium hollow-cathode cal dispersion of 0.4 A mnT1 and are centered at λ6496, a lamp, both before and after each stellar spectrum. The region containing four deep, narrow, and relatively un- typical exposure time for a star with V = 11 is 30 minutes. blended lines. The spectra were reduced using the stan- These comparison spectra are used to monitor the zero dard reduction package written by M. Hartoog. point of the wavelength scale during the night. At the The four lines used are; X6493.782 (Cal), λ6494.985 beginning and end of each night long exposures are made (Fei), X6498.943 (Fei), and X6499.650 (Caí). These of the thorium source to determine the shape of the adopted wavelengths were taken from Kurucz and dispersion function in detail. Peytremann (1975) and are systematically different from Data reduction involves correcting the raw spectra for those given by Moore, Minnaert, and Houtgast (1966) by varying pixel sensitivity and the determination of a wave- an amount (latter — former) = 0.0043 A, implying a possi- length scale using a fifth-order Legendre polynomial fit to ble systematic error in the final stellar velocities of 0.20 the thorium lines. All spectra (stellar and "book-end" km s1. Velocities were obtained by determining the first thoriums) are rebinned in wavelength, and the small moment of each absorption line. Of the four lines wavelength drifts of the book-end comparison spectra are X6498.943 became unusable in some of the fainter and determined. These drifts are used to correct the zero later-type M dwarfs and was rejected. point of the wavelength scale of the stellar spectra. The In Table I we identify (by Gliese number) the M dwarfs observed drift per hour, typically less than 100 m s-1, is observed with the echelle. In the second column is given effectively removed with this procedure. the spectral type from Joy and Abt (1974), in the third The Doppler shift of each stellar spectrum is now deter- column is given the UT date of observation, and in the mined relative to a template which is a composite of 12 fourth column is shown the uncertainty in the mean stars in the sample and is designed to be representative of velocity of the four absorption lines used in the determi- the range of M dwarf subclasses among program stars. nation. This uncertainty typically lies between 0.2 km s-1 The resulting cross-correlation function is fit to a parabola and 0.6 km s_1 and reflects not only random errors owing near the peak, yielding the velocity of the program star to photon statistics but also effects due to blends which relative to the template. Much of the cross-correlation analysis was built upon existing routines kindly provided TABLE I by Alan Dressier. Radial Velocities from Lick Echelle Experience has shown that the resulting velocities con- -1 -1 tain small systematic errors from night to night amounting Gliese sp UT Date omean(kms ) Velocity (kms ) to several hundred m s-1 (owing probably to small 411 M2 7 June 0.53 " 85-45 820B M0 7 June 0.19 - 64.05 changes in the optical system). We have attempted to 699 m4.5 8 June 0.83 -110.9^ 752A M3 8 June 0.64 + 36.67 remove this effect by determining the difference in veloc- 880 M2.5 8 June 0.67 " 28.02 15A M2.5 9 June 0.4l + 11.91 ity between the long-term average of each star and the 380 M0 9 June 0.12 - 25-17 388 M3.5 9 June 0-37 + 12.43 velocity obtained on the night under consideration. The 411 M2 9 June 0.42 - 84.37 820B MO 9 June 0.35 " 64.29 average of these differences for all stars observed on a 908 M2.5 9 June 0.64 - 70.09 given night is then applied as a correction to all of the

cause the first moment of the rest wavelength of each line variations. As Ν is typically about 10, one expects internal to differ systematically from its laboratory wavelength. errors of about 0.07 km s_1 for the velocities in Table 11. However, it is noteworthy that the brightest two stars The systematic errors are larger and have several listed in Table I (Gis. nos. 820B and 380) have uncertain- sources. The echelle velocities provided a zero-point cor- ties in the mean velocity of the lines of less than 0.35 km rection which is uncertain due both to uncertain wave- s_1. Thus it appears that any systematic errors due to lengths of the absorption lines (a 0.2 km s-1 effect) and to blends must be less than 0.35 km s-1, unless all four lines the random errors associated with each echelle measure- are systematically shifted by blends in the same direction, ment. The latter is computed to be 0.1 km s-1, the by roughly the same amount. weighted error in the mean of all the echelle velocities. One anticipated source of error is that due to changes in Errors will also occur if the location of the cross-correla- the spectrograph, especially the illumination of optics by tion peak is spectral-type dependent, such as would occur the thorium lamp, which will cause spurious systematic if line blends in the spectrum of the program star were, by Doppler shifts from night to night. The collimation of the chance, systematically redward or blueward of the lines in thorium lamp was set carefully on the first of the three the template spectrum. It is worthy of note that all veloc- nights and observations of 61 Cygni A were made on each ities derived with either analogue or digital cross-correla- night to correct for spectrograph changes. The resulting tion schemes are subject to this spectral-type dependent corrections to the velocities were: —0.12 km s1 and effect. This problem is especially severe in late Κ and M +0.58 km s-1 on nights two and three, respectively. The stars because of the introduction of molecular vibration- final, corrected velocities for all stars observed with the rotation bands which are invariably asymmetric. We have Lick echelle are shown in the fifth column of Table I. greatly reduced this effect by using a template which is These Lick echelle velocities provide a set of M-dwarf representative of the spectral types in the sample. standards with which to determine an additive correction Nonetheless, we have searched for such an effect by to all of the Mount Wilson velocities, the correction being taking the difference between the cross-correlation veloc- required because of the unknown velocity of the cross- ities in Table II and the velocities in Table I (derived from correlation template. The correction was computed by individual absorption lines) as a function of spectral type. determining the average difference between the Lick A weighted least-squares analysis of the velocity differ- velocities and the raw Mount Wilson velocities for all stars ences (Table I — Table II) versus spectral type yields a in common. A weighting scheme based on the uncertain- negligible slope, i.e., no spectral-type effect is found. As a ties in the mean of the four absorption lines in the Lick worst case we have taken the 1 σ value for the slope over -1 determination was adopted. For amean <0.2 km s , the the range of spectral types in this study, thereby yielding _1 weight given was 3; for 0.2 < amean <0.4 the weight was 2; the maximum allowable systematic effect: 0.4 km s . and for amean >0.4 the weight was 1. This procedure It is worth recalling that while the zero point of the resulted in a correction of 5.452 km s~l to the raw Mount present velocities is tied to measurements of individual Wilson velocities and was fairly independent of the absorption lines, each line employed actually carries in- weighting scheme. The final, fully corrected velocities for formation about some characteristic optical depth. Tur- all M dwarfs in the sample are given in Table II. The bulent flows may be correlated with temperature in such second column shows the number of observations, the a way as to induce systematic velocities of the gas in the third column shows the standard deviation of the veloc- line-forming region relative to the center of a mass of the ities, and the fourth column contains the final velocities. star (cf. Dravins 1985). The effect may be as large as The fifth column contains notes regarding the possible several tenths of a kilometer per second and may depend presence of companions or other comments of interest. on spot cycle and stellar age. Also note that the gravita- tional redshift for M dwarfs is about 1/2 km s_1; no correc- ΠΙ. Discussion tion for this has been made here. A. On the Integrity of the Velocities It is useful to compare the present velocities with those As there are currently no bona-fide radial-velocity stan- previously published. The differences between the dards for M dwarfs, it is valuable to carry out an indepen- present velocities and those of Wilson (1967) for the 24 -1 dent assessment of the uncertainties in the present mea- stars in common yield < Vpresent — ν\ν> = —0.4 km s , a surements. The internal uncertainties can be determined statistically insignificant difference. For the 43 stars in from the scatter of measurements about the mean for each common with Stauffer and Hartmann's study (1986) one _1 star. All velocities in Table II represent the average of Ν finds < Vpresent — VSH> = +1.3 km s . For the seven stars observations, each of which has an error of about 0.23 km in common with Bopp and Meredith's study (1986) one 1 1 s" , based on the average rms scatter (excluding known finds < Vpresent — VBM > = +2.4 km s . The latter two velocity variables). Thus, the internal error of each aver- studies are based on cross-correlation approaches and age velocity is estimated to be 0.23 km s" VVÑ and may seem to suffer from inaccurate zero-point determinations. be less if some of the average rms scatter is due to real In the case of Bopp and Meredith the few "standard stars"

TABLE II cu Summary of All Velocities in Survey

Gliese Ν Veloci ty Notes obs . {kms" ( km s -1 ) 14 13 Ο.32 + 3.32 Companion (Lip'c't, Borg'n 1978) 15A 10 0.23 + 11.97 GX And 15B 7 0.16 + 10.98 26 7 19 - 0.28 Wolf IO56 33 6 15 - 9.73 astrometric comp. {Borgman 1985) 70 8 23 - 26.04 87 10 0.28 - 2.77 107B 12 Ο.25 + 25.98 109 8 0.22 + 30.34 lines broad, VX Ari 173 14 Ο.29 - 7.02 176 14 0.21 + 25.97 179 3 O.I6 - 9.10 Ross 401 205 16 Ο.23 + 8.52 206 1 double lines, V998 213 4 O.I7 +105.35 Ross 47 229 14 0.22 + 4.59 251 13 0. 19 + 22.72 Wolf 294 268 2 possible double lines, Ross 986 273 16 Ο.27 + 18.10 285 9 0.22 + 26.59 YZ CMi 289 2 O.O5 + 48.45 broad lines 353 16 0.24 + 19.95 361 12 Ο.27 + 11.49 Ross 85 369 15 Ο.29 + 62.16 380 20 0.28 - 25.29 388 17 0.20 + 12.36 AD Leo 393 14 Ο.25 + 8.36 402 1 - I.09 411 19 0.16 - 84.74 Lalande 2II85, HD 95735 412A 14 0.22 + 68.94 4i4a 13 0.18 - 15.72 4i4b 12 0.26 - 15.19 436 10 O.I3 + 9.65 Ross 905 447 7 0.26 - 31.31 Ross 128 459.3 10 Ο.25 - 0.66 461 10 O.I9 + 3.97 464 9 0.20 + 6.81 480 8 0.24 - 4.28 486 1 + 19.20 507.1 19 0.28 - 11.69 Ross IOO7 521 19 Ο.38 - 65.18 526 18 O.I5 + 15.69 552 7 0.26 + 7 . 60 569 12 0.28 - 7.17 57OB 16 3.49 + 33.54 lines possibly double 570.2 6 0.48 + 7.74 Ross 53 581 7 0.26 - 9.42 623 22 1.40 - 27.52 smooth vel. variations 638 20 Ο.23 - 31.10 649 16 0.18 + 4.32 654 14 Ο.19 + 34.60 694 6 0.21 - 14.02 699 22 0.24 -110.86 Barnard's Star 701 15 O.3O + 32.47 72OA 10 0.12 - 31.12 735 4 double lines 745A 8 0.28 + 32.22 Ross 73O 745B 5 Ο.34 + 31.90 752A 14 0.18 + 35.82 806 6 0 . 4l" - 24.03 σ = O.I7 with 1 point removed 82OA 19 0.22 - 64.97 61 Cyg A 82OB 24 O.I3 - 63.89 61 Cyg Β 829 3 lines possibly double, Ross 775 849 5 Ο.25 - 15.39 851 11 Ο.29 - 51.37 Ross 271 863 7 0.14 - 6.40 873 9 0.24 + Ο.47 EV Lac 875.1 1 - 1.59 GT Peg 876 9 Ο.29 - 1.84 880 13 0.21 - 27.35 905 1 - 77.58 poor quality spectrum 908 9 O.I3 - 71.20

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 494 MARCY, LINDSAY, AND WILSON employed have velocities accurate only to one or two km masses. Indeed, such a close, low-mass companion would s1, and indeed the authors point out that systematic not be able to retain its hydrogen-helium envelope owing errors may be in the range of 1-2 km sIn the case of to the heating from the outside by the nearby M dwarf. Stauifer and Hartmann's thorough M-dwarf study, two Thus, with only metals remaining, the putative compan- templates were used: G1526 and HD 3765. They assumed ion would have so little mass as to be ineffective in tidally a velocity for G1526 of +14.1 km sbut three other feeding angular momentum into the rotation of the dMe independent measurements for G1526 are significantly star. larger: The General Catalogue (Wilson 1953) gives 15.2 Therefore, the six dMe stars described above consti- km s"1, Wilson (1967) gives 15.6 km s-1, and the present tute the members of a set of astrophysically single stars. study gives 15.69 km s~1. Their other template, HD 3765, That is, there is little possibility (save for extreme values is K2 V and thus may cause the spectral-type-dependent of inclination) that there exists near any of these stars a systematic errors mentioned above. For the study of companion which could affect the properties of the star Young et al. (1987) we find < Vpresent — VySH> = +2.5 km itself, most notably its angular momentum. These six s_1, based on 21 stars in common. This difference is based dMe stars have Gliese numbers: 15B, 179, 285, 388, 569, on a preliminary preprint kindly provided by A. Young. and 873. Knowledge of their rotation periods and ages Finally, it may be pointed out that the velocities pre- would permit testing of the hypothesis noted above. Two sented here carry internal and external errors comparable possible avenues of approach would be to monitor the to the best stellar velocities published to date for any set of strength of Ha or Ca π H and Κ with a time resolution stars, for example, those of Batten et al. (1983) or Mayor under 12 hours to search for periodicity. It may also be and Maurice (1985). Thus the stars in the present sample possible to measure Li differentially in these stars, using 1 which have standard deviations of under 0.3 km s" repre- nonactive dM stars as references, and thereby obtain sent potential radial-velocity standard stars. Indeed, they measures of relative age. (Li X6707 in K5 Pleiades dwarfs probably represent the best radial velocities currently (cf. Butler et al. 1987) has an easily measurable equivalent available for any M dwarfs. As the duration of observa- width of about 0.1 A.) Spectroscopic measurements of tions was only about two years, one cannot rule out the rotational velocities would seem to be difficult since the possibility of long time-scale velocity variations. small radii of M dwarfs yield relatively low equatorial B. On the dMe Phenomenon velocities even for periods as short as five days. Also, the A growing body of evidence suggests that the Ha emis- current inability to model dM spectra, along with the sion and photometric variations seen in some dwarf M- possibility that dMe spectral lines may be intrinsically type stars occur when the rotation period is below about broader than those of dM stars (owing to plage regions), five days, presumably owing to the onset of magnetic makes differential υ sin i measurements especially chal- dynamo processes not yet understood (cf. Bopp and lenging. Meredith 1986; Young et al. 1987). Since rotation rate is One age indicator for these single dMe stars can be known to decline with age, one might expect that a given extracted from their space motions. Their average space dMe star is either relatively young or is tidally coupled to velocity, relative to the Sun, is found to be 25.4 km s-1 a companion having orbital period less than five days. The which can be compared with that of other stellar types in precision of the velocities reported here permits further the solar neighborhood: 43 km s-1 for all dM stars in the examination of the above hypothesis. solar neighborhood, 24 km s-1 for A5 dwarfs, and 15 km Our initial sample of M dwarfs contains ten dMe stars, s"1 for BO dwarfs (Mihalas and Binney 1981). Thus these none of which was known to have a close companion when few single dMe stars appear to be considerably younger the sample was chosen. Three of them (G1206, G1268, and than the general population of dM stars, in accord with G1735) were found to have double-lined spectra. (Stauffer the evidence that the incidence of dMe stars is high in and Hartmann (1986) and Young et al. (1987) also note young clusters (Kraft and Greenstein 1967). probable duplicity of G1206 and G1735.) The presence of C. Notes on Individual Stars double lines in an M-dwarf star implies that the orbital period is less than about two years. Further spectroscopic Astrometry of Gliese 806 by Lippincott (1979) has indi- observations would be useful to determine whether the cated the presence of a companion having a mass of about orbital period is less than five days. 20 ïïîjup. The reported period is 6.3 yr, the semimajor axis Of the remaining seven dMe stars, six were repeatedly of the primary about the center of mass is 0.145 AU, the observed and none showed velocity variations above the eccentricity is 0.5, and the inclination is 78°. Thus the noise of 0.2 km s~l. One can easily show that the maxi- expected radial-velocity amplitude is mum possible mass for a companion having an orbital Κ = 2 ttö (1 — e)~m sin HP = 0.776 km s-1 . period of less than five days consistent with these nonde- 1 tections is 0.7 S)îjup/sin i. Thus, if short-period compan- (Full range is 1.55 km s .) From the orbital elements, ions exist near these dMe stars they must have planetary one can show that the maximum radial velocity should

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System M DWARF STARS 495 have occurred at about 1983.6 and minimum should be at evidence of variations above a conservative cutoff of 0.5 1987.0 (assuming ω = 189° according to the revised or- km sLastly, in addition to the three dMe stars men- bital elements kindly provided by Elliot Borgman). Since tioned above, G1829 also showed evidence of double the velocity observations started at 1983.6 and ended at lines, making it a probable double-line spectroscopic bi- 1985.5, one would expect that the observed velocities of nary. Gliese 806 would decrease monotonically. The six individual velocity measurements for Gliese 806 given in IV. Summary Table III have an insufficient time baseline (only 30% of a We have attempted to acquire for dwarf M stars a set of period) to determine conclusively whether or not the radial-velocity measurements which are more accurate velocity decline is occurring as predicted. Clearly, how- than those previously published. The velocities were de- ever, the measured velocities do not show a convincing termined by digital cross correlation with a template trend of any sort. representative of the program stars, and the zero point Two stars in our sample show definite velocity varia- was established by measurements of individual absorp- tions, namely, G1570B and G1623, as evidenced by their tion lines from high-resolution echelle spectra. The inter- large standard deviations. The sets of velocities for both nal precision of the listed velocities is estimated to be 0.1 stars display low amplitude and periodic variations, in- km s1 based on the observed scatter. The systematic dicative of low-mass companions. However, for neither errors, including uncertainties in wavelengths of the ab- case is there a sufficiently long data string to accurately sorption lines, random errors in the echelle measure- determine orbital elements. For G1623 an astrometric ments, and spectral-type-dependent cross-correlation er- detection of a companion has been made (Lippincott and rors, are all less than 0.4 km s_1. The final velocities differ Borgman 1978) which, when coupled with the radial-ve- systematically from those of O. C. Wilson (1967) by only locity data, will permit an unambiguous determination of 0.4 km s"1, a discrepancy which is statistically insignifi- companion mass. For G1570B the absorption lines occa- cant. The present velocities appear to be considerably sionally appear broad and perhaps double. more precise than any previously published for M dwarfs Several other stars of note should be mentioned. Bopp and indeed are comparable in quality to those currently and Espenak have noted unusual photometric behavior of used as radial-velocity "standard stars" for other spectral G1176 which could be explained if there were a cooler types. secondary with starspots. However, the present radial- A set of astrophysically single dMe stars has been estab- velocity measurements of G1176 exhibit a standard devia- lished and they appear to have low space motions, consis- tion of only 0.21 km s1, making the presence of a stellar tent with relative youth. Î'our of the 72 stars in the survey companion unlikely. Young et al. (1987) found a larger- turned out to be double-line spectroscopic binaries, and than-average scatter in radial-velocity measurements of two were found to be single-line binaries. Monitoring the G1873 (EV Lacertae). But the standard deviation found velocities of the remaining single stars will permit detec- here for nine measurements made during two years was tion of substellar companions, down to a mass of ten 0.24 km s_1, consistent with no variations. Similarly, Jupiter masses, if they exist within several AU from the there are several stars in the sample for which Gliese star. (1969) reports that large velocity variations were claimed We are indebted to Tony Misch for invaluable technical in the past (e.g., G1880 reported to show a range of 33 km help at Mount Wilson Observatory, to James Frazer and s"1). However, with the exception of G1570B and G1623 Howard Lanning for help in data acquisition, to Kenneth mentioned above, none of the stars in the sample shows Clardy and Christopher Hodges for help in data reduction, and to Douglas K. Duncan for helping to adjust the TABLE m high-resolution spectrograph at Mount Wilson Observa- tory. We thank Lick Observatory for generous allocations Velocities of Gliese 806 of telescope time. We are also grateful to the National Science Foundation (AST 86-03979) for support of this Date (U.T.) Velocity (kms -1 ■ research. REFERENCES 1983 Aug 01 -24 . 12 Batten, A. H., Harris, H. C., McClure, R. D., and Scarfe, C. D. 1983, 1983 Sep 12 -23.90 Pub. Dom. Αρ. Obs., 16, 143. 1984 May 26 -24.40 Bopp, Β. W., and Meredith, R. 1986, Pub. A.S.P., 98, 772. 1984 Jul 30 -23.28 Butler, R. P., Cohen, R. D., Duncan, D. K., and Marcy, G. W. 1987, 1984 Dec 31 -24.30 Ap. /., in press. -24 . 16 Dravins, D. 1985, inlAU Colloquium 88, Stellar Radial Velocities, ed. 1985 Jun 26 A. G. D. Phillip and D. W. Latham (Schenectady: L. Davis Press), p. 311.

Gliese, W. 1969, Catalogue of Nearby Stars, Astronomischen Rechen- Davis Press), p. 299. Institut Heidelberg, No. 22. Mihalis, D., and Binney, J. 1981, Galactic Astronomy (San Francisco: Griffin, R. F. 1967, Ap.J., 148, 465. W. H. Freeman), p. 423. Griffin, R. F., and Griffin, R. E. 1973, M.N.R.A.S., 162, 243. Moore, G. E., Minnaert, M. G. J., and Houtgast, J. 1966, The Solar Joy, A. H., and Abt, H. A. 1974, Ap.J. Suppl, 28, 1. Spectrum 2935 A to 8770 A, Natl. Bur. Standards Mono., No. 61. Kraft, R., and Greenstein, J. 1967. in Low Luminosity Stars, ed. S. Robinson, L. B., and Wampler, E. J. 1972, Pub. A.S.P., 84, 161. Kumar (London; Gordon and Breach), p. 65. Shectman, S. 1981, Carnegie Institution of Washington Year Book, Kurucz, R. L., and Peytremann, E. 1975, Smithsonian Astrophysical 1980, p. 4586. Observatory Special Report No. 362. Simkin, S. M. 1974, Asir. Αρ., 31, 129. Lippincott, S. L. 1979, Pub. A.S.P., 91, 784. Soderblom, D. R. 1982, Ap. /., 263, 239. Lippincott, S. L., and Borgman, E. R. 1978, Pub. A.S.P., 90, 226. Stauffer, J. R., and Hartmann, L. 1986, Ap. J. Suppl., 61, 531. Marcy, G. W., Lindsay, V., Bergengren, J., and Moore, D. 1986, in Young, Α., Sadjadi, 8., and Harlan, Ε. 1987, Αρ. J., 314, 272. Proceedings of the Workshop on the Astrophysics of Brown Dwarfs, Wielen, R. 1974, in Highlights of Astronomy, Vol. 3. XVth General ed. M. Kafatos (London: Gambridge University Press), p. 50. Assembly of the A.A.U., ed. G. Gontopouls (Dordrecht: Reidel). Mayor, M. 1974, Asir. Αρ., 32, 321. Wilson, O. G. 1967, A.J., 72, 905. Mayor, M., and Maurice, E. 1985, in/AC/ Colloquium88, Stellar Radial Wilson, R. E. 1953, General Catalogue of Stellar Radial Velocities Velocities, ed. A. G. D. Philip and D. W. Latham (Schenectady: L. (Washington, DC: Garnegie Institution of Washington).