arXiv:astro-ph/0106222v1 13 Jun 2001 9918)cnanms ftekonnab tr ( (Luyten nearby the catalogue known the and (NLTT) of 1979) Tenths most contain (Luyten Two 1979-1980) catalogue Luyten (LHS) New Second Half planets. Earth-like also but Jupiter-class nearby ( very on stars sys- concentrate plan- will planetary DARWIN) extrasolar TPF, for of in- (SIM, detection search ets the for the for for missions points Future initial as very tems. starting well the the as function, main function of the mass stellar (Henry observation of the undetected detailed of one far vestigations the is so 10 stars But are at nearby 1997). that stars infer all al. can of et one of 30% Stars statistics about Nearby the pc neigh- From of solar incomplete. Catalogue the very the of still content is stellar bourhood the on knowledge Our Introduction 1. o srnm,Hiebr,jitywt h pns Nation Max-Planck-Institute Spanish the Astronomy the for with by Comission jointly operated Heidelberg, Astronomy, Alto, for Calar Centre, edopitrqet to requests offprint Send ⋆ wl eisre yhn later) hand by inserted be (will Astrophysics & Astronomy erhfrnab tr mn rprmto tr eetdb selected stars motion proper among stars nearby for Search ihpoe oinctlge,eg h Luyten the e.g. catalogues, motion proper High iiigatooe,Gra-pns Astronomical German-Spanish astronomer, Visiting h eutn pcrsoi itneetmt rmcompar ( from motion estimate proper distance large its spectroscopic and resulting 2090 The LHS of spectrum resolution ( n ihrltvl rgtifae antds( magnitudes infrared bright relatively with and tr:lwms,bondwarfs brown mass, low stars: words. Key bouemgiue fM. wrsi 6 is dwarfs M6.5 of magnitudes absolute w ieeteoh n nte2ASdt ae nypoe mo proper Only base. data 2MASS the in and epochs different two only Abstract. accepted ; Received 3 2 1 < d > µ e-mail: M¨onchhofstraße 12-14, Rechen-Institut, Astronomisches e-mail: Tautenb D–07778 Tautenburg, Th¨uringer Landessternwarte srpyiaice ntttPtdm ndrSenat 1 Sternwarte der e-mail: An Potsdam, Institut Astrophysikalisches .Dsoeyo H 00a pcrsoi itneof distance spectroscopic at 2090 LHS of Discovery I. d 0p)i re ob bet eelntonly not reveal to able be to order in pc) 10 .8ace/r rmteNT aaou Lye 1979-1980) (Luyten catalogue NLTT the from arcsec/yr) 0.18 c nodrt n ery(i.e. nearby find to order In pc. 6 = [email protected] [email protected] [email protected] epeettedsoeyo rvosyukonvr nearby very unknown previously a of discovery the present We srmtyadclsilmcais srmty–astronom – mechanics: celestial and astrometry .D Scholz R.-D. : aucitno. manuscript pia-oifae photometry optical-to-infrared .D Scholz R.-D. . 0 ± 1 .Meusinger H. , 1 < d . casmn nucranyi bouemgiueof magnitude absolute in uncertainty an assuming pc 1 K < d 5p)rddaf,w eietfidhg rprmto stars motion proper high re-identified we dwarfs, red pc) 25 s al < 0 eeslce o olwu pcrsoy h low- The spectroscopy. follow-up for selected were 10) ntytpbihd l tr ihn1 cd aeproper have do CNS4 pc current limit. below 10 that the within motion above stars In proper motions all arcsec/yr. a published) 0.18 yet with of (not dwarf limit M CNS3, NLTT the one the in only contained arcsec/yr. less pc is Stars 0.5 10 distances than there within Nearby larger stars with of 280 motions the (1991) proper Catalogue Among have Jahreiß the pc & 5 in than Gliese stars of 58 (CNS3) All pc). 25 r k a oee ytePlmrOsraoySky Observatory these Palomar and 50s, the the in the by starting observations of covered (POSS) north- Survey magnitude was The sky. limiting sky southern lower the ern in the catalogues motion is proper stars nearby of 1997; Reid & Gizis 2001). 1997; al. al et et (Henry Jahreiß on going LHS still the is among stars stars nearby observations. of al. discovery follow-up et the Nevertheless, photometric (Jahreiß and pc 25 spectroscopic within in lie ex- to can The 40% one 2001). stars about NLTT find red dis- to and their pect faint determine the to Among order tances. in further investigated been –92 edleg Germany Heidelberg, D–69120 n h infrared the ing ,D142Ptdm Germany Potsdam, D–14482 6, 2 h aoiyo the of majority The n esnfrteicmltns ftecatalogue the of incompleteness the for reason One r,Germany urg, .9ace/r lsiyti tra nM. dwarf. M6.5 an as this classify arcsec/yr) 0.79 ,⋆ n .Jahreiß H. and , insaswt large with stars tion ∼ cldt ae uvy tr:lt-ye– late-type stars: – surveys base: data ical notclDgtzdSySre aafor data Survey Sky Digitized optical in 50LSsasrcie uhmr attention more much received stars LHS 3500 JHK tr-LS29 tadsac of distance a at 2090 LHS - star s antdso H 00with 2090 LHS of magnitudes 3 ∼ 00 LTsashv o yet not have stars NLTT 60000 R d − K ∼ s oorindex colour pc 6 ± . mag. 0.4 y 2 R.-D. Scholz et al.: Search for nearby stars among stars. I. Discovery of LHS 2090 at d ∼6 pc

Schmidt plates constitute the first of Luyten’s data base allows an all-sky search with the input of target high proper motion star surveys (e.g. Luyten 1979). lists or by pre-defined search parameters. Nevertheless, few faint high proper motion stars can be We have cross-identified NLTT stars in a region cover- found from second epoch POSS observations (Monet et al. ing about 50% of the northern sky (07h <α< 19h,δ> 0◦) 2000). South of δ = −30◦, which is the POSS survey limit with the 2MASS data base. Only bright 2MASS sources in the southern sky, only recently deep high proper motion (Ks < 10) identified with faint (Luyten’s R> 14.5) NLTT surveys have been started using Schmidt plates (Scholz stars within a search radius of 60 arcsec were further inves- et al. 2000; Ruiz et al. 2001). New high proper motion tigated. All identifications were checked with two epochs stars as bright as the active M5 star APMPM J0237-5928 of DSS images. In addition to the optical magnitude esti- (R = 13.4, spectroscopic distance: 12 pc) discovered by mates given in the proper motion catalogue, we also ex- Scholz et al. (1999) can be found in that region. tracted the R magnitudes from the A2.0 catalogue (Monet There are several attempts to detect nearby stars ne- et al. 1998). The DSS1 images usually had the same epoch glecting the proper motion information during the first as the A2.0 catalogue, whereas the DSS2 images had an steps of the search. One possibility is to search for ex- epoch close to that of the 2MASS data. tremely red faint objects, i.e. very late-type M dwarfs and LHS 2090 turned out as a candidate nearby star in our the new class of L dwarfs obtained in the Two Micron All first sample of about 50 stars selected for follow-up clas- Sky Survey (2MASS) (Reid et al. 2000; Gizis et al. 2000) sification spectroscopy. With Ks =8.4 and R − Ks =6.4 and in the DEep Near-Infrared Survey (DENIS) (Delfosse (USNO-2MASS), LHS 2090 was one of the most promis- et al. 2001). Another way to detect missing nearby M ing objects in the list of candidates. The whole sample of dwarfs consists in the subsequent observation of X-ray about 35 objects which was successfully observed spectro- sources in order to identify young M dwarfs with small scopically, will be subject of a forthcoming paper. space motions not present in proper motion catalogues (Fleming 1998). But all new nearby stars found in these 3. Former information on LHS 2090 surveys turned out to be high proper motion stars, at least in those cases when distances of less than about 15 pc were LHS 2090 was detected by Willem Luyten within the scope measured. of his proper motion survey with the 48-inch Schmidt tele- As a logical consequence, we have started a search for scope and got the detection designation LP368-128. Its the missing stars in the solar neighbourhood by combining refined (LHS) proper motion is 0.785′′ in 216.3◦. Willem the proper motion catalogues with near-infrared and op- Luyten’s estimates of its red and photographic magni- tical sky surveys. The 2MASS data base (2nd incremental tudes are R = 15.5 and mpg = 17.4, respectively. Luyten release public data base) and the A2.0 catalogue (Monet hoped that the mean error of the magnitudes are not et al. 1998) can well be used for that purpose. The proper larger than ±0.6 mag though errors of even 1.5 do oc- motion stars, however, have to be re-identified in digitized cur (Luyten 1964). Having this in mind Luyten’s magni- sky survey (DSS) images at two different epochs. tudes are in good agreement with the USNO-A2.0 values R = 14.8 and B = 17.7, which are also measurements of 2. Combining proper motion and photometry the POSS-I O and E plates. A finding chart of LHS 2090 was published in the LHS Atlas (Luyten & Albers 1979). Samples of very red (optical-to-infrared colour) point Luyten attributed a spectral class “m” to this object. sources in the 2MASS or DENIS survey may contain com- Since Luyten’s publication, no additional information on pact extragalactic sources, distant red giants, nearby red LHS2090 became available unless the most recent as- dwarfs and very nearby asteroids. If the source is relatively trometric and photometric measurements in USNO-A2.0 faint in the optical (R > 10) and shows a proper motion and 2MASS (09h00m23s.59, +21◦50′05′′. 5 (J2000 at 2MASS of the order of 0.1 to 10 arcsec/yr (with Barnards’s star epoch 1998.44)). It was too faint to enter the photometric still being the record holder in stellar proper motions), it surveys of LHS stars carried out by Eggen or Weis. must be a dwarf. For a red giant with that faint , the proper motion would transform to a very 4. Spectroscopic distance estimate of LHS 2090 large space velocity (> 1000 km/s), which is much larger than the Galactic escape speed (cf. Leonard & Tremaine Spectroscopic follow-up observations were carried out with 1990; Meillon et al. 1997). CAFOS, the focal reducer and faint objects spectrograph In a previous paper (Jahreiß et al. 2001) we selected at the 2.2m Calar Alto telescope. The grism B-400 was red NLTT stars (Luyten’s spectral classes “m” and “m+”) used yielding 9.6A˚ per pixel on the SITe1d CCD and a as candidates of nearby stars and obtained more accurate wavelength coverage from 4000A˚ to 8000A.˚ A slit width of positions and photographic photometry from the APM 1 arcsec was used, corresponding to a spectral resolution sky catalogues (Irwin et al. 1994). However, the optical of 18A.˚ The exposure time was 60 seconds for LHS 2090 colours of these late-type star candidates show only a weak and 120 seconds for the bright comparison star GJ 1111 correlation with spectral subclass (Scholz et al. 2000). (observed during twilight). As already mentioned in Jahreiß et al. (2001), optical- The spectra were calibrated by standard procedures to-infrared colours are a much better choice. The 2MASS within the MIDAS package for bias-subtraction, flat- R.-D. Scholz et al.: Search for nearby stars among proper motion stars. I. Discovery of LHS 2090 at d ∼6pc 3

Alto, Spain, This research has made use of the SIMBAD database and the VizieR Catalogue Service, Strasbourg, of the STScI Digitized Sky Survey and of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation. We would like to thank Darja Golikowa for her help with the re-identification of high proper motion stars in DSS images and their cross-correlation with USNO A2.0 and 2MASS data. RDS gratefully acknowledges financial support from the Deutsches Zentrum f¨ur Luft- und Raumfahrt (DLR) (F¨order- kennzeichen 50 OI 0001). We thank the referee, John Gizis, for his prompt report.

References Fig. 1. Spectrum of LHS 2090 in comparison to that of Delfosse X., Forveille T., Martin E.L. et al. 2001, A&A, 366, the well known M6.5 star GJ 1111. Both spectra were L13 taken with the 2.2m telescope at Calar Alto. The spectra Fleming T.A. 1998, ApJ, 504, 461 are nearly identical, and we adopted the spectral type of Gizis J.E., Reid I.N. 1997, PASP, 109, 849 M6.5 for LHS 2090. Gizis J.E., Monet D.G., Reid I.N., Kirkpatrick J.D., Liebert J., Williams R.J. 2000, AJ, 120, 1085 fielding and wavelength calibration using Ne-Ar lamp Gliese W., Jahreiß H. 1991, Preliminary Version of the Third spectra. For relative flux calibration we have used spec- Catalogue of Nearby Stars, computer-readable version on tra of secondary spectrophotometric standard stars from ADC Selected Astronomical Catalogs Vol.1 - CD-ROM Henry T.J., Ianna P.A., Kirkpatrick J.D., Jahreiß H. 1997, AJ, Oke & Gunn (1983). 114, 388 The low-resolution spectrum of LHS 2090 is nearly Irwin M.J., Maddox S.J., McMahon R.G. 1994, Spectrum No. identical to that of the known M6.5 dwarf GJ 1111 (see 2, 14-16 Figure 1). With that spectral type and taking the mean Jahreiß H., Scholz R.-D., Meusinger H., Lehmann I. 2001, absolute magnitudes of M6.5 dwarfs MJ = 10.51,MH = A&A, 370, 967

9.94,MKs = 9.60 given in Kirkpatrick & McCarthy Kirkpatrick J.D., McCarthy D.W. 1994, AJ, 107, 333 (1994), we obtained spectroscopic distance estimates dJ = Leonard P.J.T., Tremaine S. 1990, ApJ, 353, 486

6.06 pc, dH = 6.07 pc, dKs = 5.83 pc, respectively. A Luyten W.J. 1964, Proper motion survey with the 48 inch conservative assumtion of ±0.4 mag accuracy in absolute Schmidt telescope. Vol II The North Pole. University of magnitude yields 6.0 ± 1.1 pc. Minnesota, Minneapolis Luyten W.J. 1979, LHS Catalogue. Second Edition. University of Minnesota, Minneapolis 5. Conclusions Luyten W.J. 1979-1980, New Luyten Catalogue of Stars with Proper Motions Larger than Two Tenths of an Arcsecond, 1. After the recent discovery of DENIS-P J104817.7- University of Minnesota, Minneapolis, computer-readable 395606.1 (Delfosse et al. 2001), an M9 dwarf at only version on ADC Selected Astronomical Catalogs Vol.1 - 4 pc spectroscopic distance from the , we have CD-ROM found another very nearby star, LHS 2090, at 6 pc. Luyten W.J., Albers H. 1979, LHS atlas. An atlas of iden- 2. Despite its large proper motion (µ =0.785 arcsec/yr), tification charts for LHS stars. University of Minnesota, LHS 2090 had not been further investigated up to now. Minneapolis 3. The low-dispersion spectrum of LHS 2090 closely re- Meillon L., Crifo F., Gomez A., Udry S., Mayor M. 1997, in sembles that of the M6.5 star GJ 1111. We conclude Battrick B. (ed.), Hipparcos Venice’97, ESA-SP 402, p. 591 therefore that LHS 2090 is of spectral type M6.5 as Monet D., Bird A., Canzian B. et al. 1998, USNO-A V2.0, A Catalog of Astrometric Standards, U.S. Naval well. Hence the distance estimate based on the 2MASS Observatory Flagstaff Station (USNOFS) and Universities JHKs magnitudes yields d = 6 pc. Trigonometric par- Space Research Association (USRA) stationed at USNOFS allax determination and investigation of a possible bi- Monet D.G., Fisher M.D., Liebert J., Canzian B., Harris H.C., narity of LHS 2090 is needed for confirmation. Reid I.N. 2000, AJ, 120, 1541 4. The combination of high proper motion star data with Oke J.B., Gunn J.E. 1983, ApJ, 266, 713 infrared sky surveys such as the 2MASS survey is Reid I.N., Kirkpatrick J.D., Gizis J.E., Dahn C.C., Monet a very effective tool for finding previously unknown D.G., Williams R.J., Liebert J., Burgasser, A.J. 2000, AJ, nearby red dwarfs. 119, 369 Ruiz M.T., Wischnjewsky M., Rojo P.M., Gonzalez L.E. 2001, Acknowledgements. The spectroscopic confirmation of nearby ApJSS, 133, 119 star candidates is based on observations made with the 2.2 m Scholz R.-D., Irwin M., Schweitzer A., Ibata R. 1999, A&A, telescope of the German-Spanish Astronomical Centre, Calar 345, L55 4 R.-D. Scholz et al.: Search for nearby stars among proper motion stars. I. Discovery of LHS 2090 at d ∼6 pc

Scholz R.-D., Irwin M., Ibata R., Jahreiß H., Malkov O.Yu. 2000, A&A, 353, 958