STANDARD STAR NEWSLETTER #29 Ascii Version CONTENTS: Editorial p. 1 Note from the Working Group Chair, Chris Corballyp. 2 Some comments by the President of Commission 45, Tom Lloyd Evans p. 3 Announcements (SOFA) p. 4 Reports of Meetings at the IAU (JD13, Ultra--Cool Dwarfs) p. 5 Abstracts of Papers (Burnashev, Knyazeva, Stetson, Walborn) p. 8 Contributions (Radial Velocities of IAU Standard Stars, Colin Scarfe) p. 10 From the editor Our thanks and appreciation go to Chris Corbally who served as the editor of this Newsletter for nine years (a total of 12 issues). The past 12 issues have all been full of interesting notes and abstracts, and this one -- my first -- is no different, thanks to a number of contributors. The IAU General Assembly took place in August in Manchester, England. Associated with the General Assembly were a number of important meetings of relevance to this newsletter. Chris Corbally, in his new role as Chair reports on the meeting of the Working Group of Standard Stars (WGSS), and contributes a few comments as well. Tom Lloyd Evans, the new President of Commission 45 shares some thoughts on the work of that Commission, as well as a report on Joint Discussion 13, Hipparcos and the Luminosity Calibration of the Nearer Stars . Hugh Jones and Iain Steele report on the Ultra Cool Dwarfs meeting. Even though these last two reports contain some material not directly related to the subject of Standard Stars, I am happy to include summaries of these two very interesting and relevant meetings, and I think you will agree they are valuable and worthwhile contributions when you read them. You will find a description of the Standard Stars Working Group on the Web via: http://clavius.as.arizona.edu/ssn/ The SSN's homepage will also give you access to previous issues and links to other astronomical newsletters. With many thanks to our contributors, R.O.G. A Note From the Chair International Astronomical Union Working Group on Standard Stars (WGSS) You will see from reading between the lines of the report below that the Working Group on Standard Stars had a lively and productive meeting during the Manchester General Assembly. Thank you to those who came and to those who contributed by e--mail prior to the meeting! It is also clear from the report that the WGSS continues to have ``coordination" as its main task. We need to pool our collective wisdom in producing and making available lists of revised standards, settling criteria and/or methods, and agreeing on nomenclature. This coordination is achieved largely through this Newsletter and the follow--up by individuals in the appropriate Commissions, though occasionally a meeting helps significantly. So, I am sure you join me in welcoming Richard Gray to the essential role of Standard Star Newsletter editor. Equally, we sincerely thank Robert Garrison for chairing the WG and keeping its task focussed over the last nine years. Chris Corbally ccorbally@as.arizona.edu Report on the Meeting of the WGSS IAU Working Group on Standard Stars Report on meeting at IAU--GA XXIV, 11 August 2000 The meeting opened under the outgoing chairmanship of R. Garrison. C. Corbally was elected as the new chairman of the working group (WGSS) and the appointment of R. Gray as newsletter editor was approved by those present (17). Garrison defined the ongoing tasks of the WGSS as promoting and communicating work on standard stars, and its organizing structure as the chairman and editor. These definitions were accepted as both still relevant and workable. The meeting then turned to science matters. C. Scarfe outlined his comparison of DAO measures of IAU radial--velocity standards with those from CfA, and he showed that now there was virtually no difference, whatever the color of the star (Editor's note: See Colin Scarfe's contribution beginning on page 10 of this newletter ). S. Adelman pointed out how Hipparcos photometry was most useful in picking out the non--variable stars which might be used as standards. He is preparing a list of these. D. Crawford described the plan for photometric monitoring of standards by automated telescopes. The appeal by W. Buscombe (not present) for a clear identification of standards in the SIMBAD database was recognized as important. Garrison said that he had found the SIMBAD team very receptive to any tables of standards that he had submitted. P. Harmanec's (not present) request for a uniform set of solar values was also recognized. Garrison noted that a meeting in Flagstaff had settled on 18 Sco as the best solar analog. E. Griffin communicated the Spectroscopic Virtual Observatory's plans for a database of spectra of standard stars (at an R of about 30,000). R. Viotti and M. Meyer (both not present) had called for settling the spectral classification criteria out to the thermal IR. This provoked considerable discussion on the task of classifying in the near--IR (Garrison), on the need for a set of specifically IR standards (E. Milone), and on establishing faint standards, suitable for telescopes of 6--m aperture and greater (Mayer and Garrison). Such topics could well form part of a JD during the next IAU--GA. T. Hawarden warned that a set of photometric filters in the IR was in danger of being called the ``MK system". The prospect of confusion with the long--established spectral classification system was greeted with alarm by those present, and alternate names were suggested. In particular, it was urged that the naming of the new IR system should be submitted to the acronym clearing house which is under Commission 5. This discussion highlighted the need for liaison between the WGSS and Commission 5, and indeed the WGSS's necessary role in keeping communication about standards open between its sponsoring Commissions, namely 25, 29, 30, and 45. Chris Corbally ccorbally@as.arizona.edu Comment Excerpts from Comments by the President of Commission 45 IAU General Assembly Thomas Lloyd Evans STELLAR CLASSIFICATION There is probably a tendency among astronomers at large to think of stellar and especially spectral classification as a closed subject in which no more research is required. We of course know better, but it is a fact that few astronomers have moved into the field in recent years. We heard at the GA and other recent meetings of very ambitious projects which would generate huge catalogues of stars. Most of these will be stars of known type but there will be a minority of "exotic" objects such as turned up among optically--identified IRAS sources. These new surveys will penetrate into distant regions where the predominant stellar population, though similar to that of the solar neighbourhood, differs systematically in chemical composition and perhaps in other properties. Stars of the Central Bulge of the Galaxy and in globular star clusters represent the extremes in this respect, and classical stellar classification has not been very much used in their study. Rather, each such population has been treated as a special case using whichever observational and analytical techniques are in current use. New techniques such as CCD detectors for spectroscopy inevitably dictate changes, in this particular case a shift to longer wavelengths. Techniques of analysis need to be able to treat chemical composition, at least as a single parameter ``metal abundance", as a separate quantity from luminosity class. No one who has worked with low resolution spectra of globular cluster stars can feel entirely happy that we already have the situation under control. We saw at JD13 some indications of the way things may go. Notably there were encouraging signs that the doubts about how to use HIPPARCOS data to provide reliable luminosity calibrations of the MK classes are coming to an end. There was some new thinking on the physical meaning of the luminosity classes defined by some of our traditional parameters. We should soon have a more realistic idea of the calibration and the inherent limitations of the various techniques. The massive new surveys will necessarily rely on automated methods of mass classification, whether spectroscopic or photometric, to handle the large numbers of objects involved. This will set new challenges to the stellar classification community. Also, astronomers at large will want to see the physical basis for the classification criteria. Early work gave some plausible answers, but there is scope for new thinking, whether about the basics we take for granted or the exotic objects which present as special cases. STANDARD STARS AND OUR WEBSITE Given the perception that stellar classification is a well understood technique, it happens that we are sometimes asked by people in other fields whether we can classify a star for them, or to advise them on a choice of standard stars which they might use themselves. I wonder whether we might consider posting some useful references (for techniques and lists of standard stars), or even the list of fundamental standards, on our website? There is a link, via the Standard Star Newsletter site, to the Standard Objects for Astronomy site which does give a substantial list of useful references, but it is not as complete as one might wish. A more restricted -- say, to MK standard stars -- but more complete list would be very useful. Perhaps Chris or Richard Gray, the new editor of the Standard Star Newsletter, would like to comment. Announcements New hosts for SOFA The astronomy Internet site SOFA (``Standard Objects For Astronomy'') (see SSN No. 27, October 1999) has its new hosts. Initially created by Dr Patrice Corporon, it is now co--maintained by Shashikiran Ganesh (Astronomy & Astrophysics Division of the Physical Research Laboratory, Ahmedabad, India) and Anatoly Miroshnichenko (Department of Physics & Astronomy of the University of Toledo, USA). SOFA will be mirrored at sites in India and the USA at: http://www.prl.ernet.in/~shashi/SOFA/index.html and http://sofa.astro.utoledo.edu/SOFA The site contains links to various sources of standard objects for different astronomical techniques (photometry, spectroscopy, polarimetry, etc.) as well as references to useful catalogs and publications. Corrections, additions and further suggestions regarding SOFA's development are welcomed at the following email addresses: shashi@prl.ernet.in (Shashikiran Ganesh) anatoly@physics.utoledo.edu (Anatoly Miroshnichenko). Reports of Meetings at the IAU General Assembly Joint Discussion 13: HIPPARCOS and the Luminosity Calibration of the Nearer Stars T. Lloyd Evans South African Astronomical Observatory, P. O. Box 9, Observatory 7935, South Africa tle@canopus.saao.ac.za This Joint Discussion, organised by IAU Commission 45 and held with the participation of Commissions 8, 24, 26, 27, 29, 35 and 37, took place on 15 August at GA 24 in Manchester. There were eleven invited papers and thirty--one posters, several of which were described briefly by their authors during the discussions. The invited papers will be published in Highlights of Astronomy. The account here covers only a few points which caught my attention. The impetus for this Joint Discussion arose in part from contact with Philip Keenan, who aged over 90 was still undertaking important work on spectral classification and sought to harmonise the luminosity system with HIPPARCOS parallaxes. Robert Wing, a long--time colleague, presented a tribute to him. The first essential in making use of the HIPPARCOS data is that any sources of error must be understood and allowed for. Floor van Leeuwen addressed the quality assessment of the data with particular reference to concerns about systematic error in the parallaxes of star clusters. He concluded that there are no systematic or correlated errors beyond an angular scale of 1.2 deg in the HIPPARCOS parallaxes and that no ground--based and model--independent value of the parallax of the Pleiades differs significantly from the HIPPARCOS value. Anthony Brown concluded that main sequence fitting gives no reason to doubt the HIPPARCOS distances to open clusters, and also that the data for the nearer OB associations support the Mermilliod rather than the Schmidt--Kaler calibration of the main sequence for B stars. Frederic Arenou, with Xavier Luri, discussed the various types of bias and the statistical methods required to avoid them. Yveline Lebreton considered the problem from the theoretical point of view, with reference to physical parameters and the models required to relate them to the observations of colour and magnitude especially. Bob Garrison compared the absolute magnitudes of stars as obtained from previous luminosity classifications and from the use of HIPPARCOS parallaxes. A poster by Richard Gray reported that, for late--A to early--G stars, the MK luminosity type depends on the microturbulent velocity at least as much as on the surface gravity, which implies a substantial uncertainty in luminosities derived from classification--dispersion spectra. Gerald Newsom presented the partially--completed reclassification project by Philip Keenan in which, following on earlier work with Cecilia Barnbaum, he considered the relationship of the red giant clump stars to those on the red giant branch. Ruth Peterson considered spectroscopic luminosity calibrations from the application of model atmospheres to high--resolution spectra and from the Wilson--Bappu relation, and confronted both with the HIPPARCOS parallaxes. Photometric luminosity calibrations for several of the main photometric systems were discussed by Michel Grenon and for the uvby\beta photometry by Carme Jordi and collaborators. Michel considered that the metallicity--dependence of luminosity at a given temperature could be determined accurately, and that unresolved binaries remained as the main source of scatter. Carme allowed for statistical biases to show that the older Crawford calibration yields luminosities which are too faint by about 0.09 mag for the F stars and that there is a luminosity--dependent error for the B stars. Applications of the luminosity calibrations were considered in the final group of papers. The stars of the red giant clump have emerged as potentially important distance indicators for systems within the Local Group, having the advantage that there is an adequate sample within range of accurate parallax measurement for determination of the zero point in luminosity, and this was discussed from a practical point of view by Peter Garnavich who noted the the method gives a smaller modulus for the LMC than most other methods. Leo Girardi gave a theoretical approach and concluded that the absolute magnitude of the red giant clump stars differs systematically from one galaxy to another depending on the different ages and metallicities which predominate. Tim Bedding noted that the oscillation frequencies measured in stars are most useful when other stellar parameters are available and discussed the importance of the HIPPARCOS parallaxes for asteroseismology. Ultracool Dwarf Stars -- Properties and Spectral Classification Hugh R. A. Jones & Iain A. Steele Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK hraj@astro.livjm.ac.uk Background Although astronomers have been searching the skies for brown dwarfs for decades, it is only in the last few years, with more sensitive detectors and new near--infrared all--sky surveys, that these cool objects have popped out from the background. The first reliable detections came in 1995, with the identification of lithium and of methane. Lithium, a light alkali element, is depleted in objects more massive than 65 Jupiter masses, so identification of this line pegs the object as a brown dwarf. Methane on the other hand indicates that the photospheric temperature of the object is less than 1500~K and so by any models for low--mass objects is a brown dwarf. In the years since these exciting discoveries large numbers of ``ultracool dwarfs'' (objects cooler than M dwarfs) have been found. Two new spectral types (L and T) have been proposed for the classification of these objects. Broadly speaking L dwarfs are characterized by the progressive disappearance of the optical TiO and VO bands that dominate late M dwarfs and their replacement by metallic hydrides and neutral alkali metals. The T dwarfs on the other hand have infrared spectra that are dominated by methane. It is important to note that there is no astrophysical significance attached to the particular letters. In particular it should be stressed that lithium--detection is not core to the L spectral class nor does L define an object as being a brown dwarf. The Meeting This meeting was held under the auspices of IAU commissions 29 and 45 was held on 2000 August 12 at the XXIVth IAU General Assembly in Manchester, UK. It was attended by over 70 delegates from a broad range of stellar disciplines and was convened in order to discuss the current status of research in the field of ultracool dwarfs, with special reference to the question of spectral classification. The first session of the day was chaired by James Liebert (Steward Observatory) and was concerned with the question of theoretical model atmospheres of ultracool dwarfs. In his presentation Tsuji (University of Tokyo) showed his new hybrid models where the observed colours and spectra of both L and T dwarfs can be reasonably well reproduced by a unified set of models. In these the dust effects that dominate the spectra of L dwarfs and appear to be absent from T dwarfs can be explained if dust forms only deep in the photosphere, with the upper layers dominated by volatile molecules. Talks by both Burrows (Steward Observatory) and Pavlenko (Main Astronomical Observatory of Ukrainian Academy of Sciences) stressed the importance of the alkali metal strengths. In particular they noted that the strength of the line wings were a dominant effect in the spectra, meaning that the optical colours of ultracool dwarfs could be either red or blue (!). Burrows emphasised that it is vital to investigate improved treatments of atomic and molecular line broadening. Pavlenko described investigations using various models which indicate that it is necessary to introduce a power law opacity into the synthetic spectra to reproduce the overall shape of the observed spectra. This allows for a hotter synthetic temperature scale more in line with more empirical investigations. Pavlenko also presented synthetic spectra showing where potential signatures of deuterium in the lines of deuterated water HDO might be found. Geballe (Gemini Observatory) presented spectra identifying weak methane features in L5 and L7 dwarf spectra and showing that any contamination from the Earth's atmosphere would produce much broader bands that observed. As with lithium in L dwarfs these spectra caution against the idea that only T dwarfs contain methane. He also presented 1 -- 2.5 mu spectra of objects from mid--L to T showing a spectral sequence with CH4 increasing as CO decreased (H2O increasing in parallel with the methane bands). The second session was chaired by Virginia Trimble (University of Maryland/ University of California, Irvine) and considered the observed properties of ultracool dwarfs. Noll (Space Telescope Science Institute) described how a series of model 3--4 mu spectra of late L dwarfs had been constructed using a line list containing over 30,000 H2O lines and 100,000 CH4 lines. This allowed the identification of the weak methane features in the L5 and L7 dwarf spectra presented by Geballe (Gemini Observatory) and the ruling out of other candidate absorbers such as HDO, H2S and HCl. Bailer--Jones (Max--Planck--Institut fuer Astronomie, Heidelberg) described a program of photometric monitoring of 17 late M and L dwarfs both in the field and in the Pleiades and sigma Ori clusters. Evidence for small ( < 5\%) variations was found in a number of the targets. The majority of the variations found were non--periodic. Gizis (California Institute of Technology) presented the results of a study of chromospheric activity in ultracool dwarfs. The frequency of H alpha emission peaks at M7, and then decreases for cooler M and L dwarfs. The kinematics of the active ultracool objects were consistent with an old disk stellar population, while the inactive objects were more typical of a younger population. This suggests that contrary to the usual age--activity relationship, low activity can be an indicator of youth (and hence substellar mass) in ultracool dwarfs. On the other hand lithium detection is found to correlate well with kinematics (v_tan) and supporting the idea that it should be more prevalent at younger ages. Schneider (University of Arizona) described an imaging survey of 85 young, nearby stars using the coronagraph of the HST NICMOS Camera to search for low mass companions. A number of candidates had been found, which were being followed up astrometrically and spectroscopically with the HST STIS camera. Steele (Liverpool John Moores University) described the results of a programme of ``optical'' IZ photometry of L dwarfs, which showed that the colour was a good indicator of spectral type all through the M and L dwarf regime, and is therefore an efficient method of searching for ultracool objects without the expense of wide--field infrared surveys. The final session of the day was chaired by Mike Bessell (Australian National University) and was concerned with the issue of spectral classification. Stephens (New Mexico State University) showed that infrared spectral typing (as opposed to the harder to collect optical spectra) is consistent with those inferred from optical spectra. Observations were made at three wavelengths ( K , L_s and L' ) of a sample of L and T dwarfs. The L' wavelength is of particular interest as it is not affected by methane. Hence the K-L' colour varies between ~ 1.0 and ~1.8 between L0 and the L/T transition objects. In contrast the K-L_s colour varies between ~ 0.1 and ~ 0.6 for L dwarfs before the effect of methane in the L_s spectra reduces this value to 0.2 for the L/T transition objects. Kirkpatrick (California Institute of Technology) described his optical classification system for L dwarfs which is based on the strengths of lines and bands in the region 6300--10000 \AA . Objects of similar types were grouped together to give nine natural groups ranging from L0 to L8. The classification is therefore based solely on optical spectra morphology rather than any physical interpretation of the spectra. He commented that the lack of optical flux for T dwarfs means that this method of spectral classification is not realistic for lower temperature spectral types. He also indicated that the current 2MASS mass function in the ultracool dwarf regime has form dN/dM=M^1 +/-0.25. Rebolo (Instito Astrofisica de Canarias), substituting for Martin (University of Hawaii) described their work on the spectroscopy of substellar objects in the Pleiades and sigma Ori. Some of the sigma Ori objects could have masses below the deuterium burning limit of 13 M_J . This finding is similar to a number of other recent works showing that `free--floating' brown dwarfs are produced below the deuterium--burning limit. The observed spectra are compared with field objects to search for gravity dependent features, and were classified using an alternative classification scheme to that of Kirkpatrick, based on a physical interpretation of the spectra via comparison with model atmospheres. The final presentation was given by Burgasser (California Institute of Technology) who described a spectral typing scheme for T dwarfs based on overall spectral morphology. The observed spectra were dominated by H2 , H2O and CH4 in the near--infrared and FeH, H2O and widely broadened K I and Na I doublets in the optical. The meeting was closed with a general discussion of the issues raised, including the questions of new mnemonics for the O to T spectral sequence, spectral typing beyond T, the sharpness of the L/T dwarf transition and the importance of the ``missing'' late L objects being found by SLOAN. There was also some debate about the usefulness of the deuterium burning limit as a possible dividing point between star and planet formation, however, there seemed to be little supporting observational evidence. The proceedings of the meeting will be edited by Jones \& Steele and be published by Springer--Verlag in their Lecture Notes in Physics Series. Abstracts The Energy Distributions of 111 Late Type Stars V. Burnashev ^1 and S. Guziy ^2 Crimean Astrophysical Observatory, Crimea, Ukraine Nikolaev State University, Nikolaev, UKraine Energy distributions for the spectra of 111 late--type stars have been obtained in the spectral range 320-- 790 nm with a resolution near 3 nm. The observations were carried out by means of the stellar scanning spectrophotometer, mounted on the 80--cm telescope at Crimean Astrophysical Observatory. The absolute calibration is based on the energy distribution of Vega, published by Hayes. Accepted by Izv. Crimskoy Astrophys. Observat. For preprints, contact burnashev@crao.crimea.ua, gss@aok.mk.ua Searching for Solar Analog Candidates Knyazeva L.N. \& Kharitonov A.V. Fessenkov Astrophysical Institute, Almaty,Kazakhstan kniaz@afi.academ.alma-ata.su Our search for solar analogs is based on the calculated color indices of the Sun in the Str\"omgren uvby system (cf. Knyazeva \& Kharitonov 2000), namely b-y =0.404 , m_1 =0.217 and c_1 =0.373 . We have selected from the uvby catalogue of Hauck \& Mermilliod (1997) all stars having values of b-y within the limits from 0.398 to 0.410. This range is based on the b-y index for the Sun and taking into account the observational errors of this index. On this basis 250 stars were selected. All known variable and double stars were excluded from the review. From this list were selected stars having values of m_1 and c_1 close to the Sun. This reduced the list to only 13 stars. This sample of stars and their photometric data are given in Table 1. The star HD 44594 has values b-y , m_1 and c_1 closest to those of the sun. It has already been included in lists of solar analogs. The spectral types were taken from the HIPPARCOS catalog. We present this list of stars in order to draw the attention of observers to them. Most of these stars are in the southern hemisphere and they are inaccessible for observations from our observatory. We are continuing the search of possibilities for the determination of parameters of these stars. This work was presented in the symposium ``Spectrophotometric and photometric catalogues. Standard stars and solar analogues'' (Saint Petersburg, June 5-9, 2000). Table 1: Candidate Solar Analogs HD & V & b-y & m_1 & c_1 & Sp Type 6517 & 8.15 & 0.407 & 0.215 & 0.374 & - 9175 & 7.80 & 0.407 & 0.210 & 0.373 & G5IV 15064 & 6.18 & 0.405 & 0.217 & 0.378 & G2V 18993 & 8.23 & 0.404 & 0.227 & 0.384 & G0V 44594 & 6.60 & 0.408 & 0.214 & 0.370 & G4V 45289 & 6.67 & 0.409 & 0.213 & 0.373 & G5V 45701 & 6.46 & 0.406 & 0.224 & 0.374 & G3III-IV 79985 & 7.5 & 0.405 & 0.217 & 0.380 & G1V 80332 & 7.0 & 0.405 & 0.211 & 0.367 & G3III-IV 111513 & 7.35 & 0.406 & 0.211 & 0.364 & G1V 158783 & 6.8 & 0.407 & 0.210 & 0.378 & G5IV 159222 & 6.56 & 0.406 & 0.216 & 0.364 & G5V 184525 & 7.9 & 0.402 & 0.217 & 0.360 & G0V References Knyazeva L.N., Kharitonov A.V., 2000, A.Zh. (in press) Hauck B., Mermilliod M., 1990, AAS, 86, 107 Homogeneous Photometry for Star Clusters and Resolved Galaxies. II. Photometric Standard Stars Peter B. Stetson Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, British Columbia V8X 4M6, Canada Stars appearing in CCD images obtained over 224 nights during the course of 69 observing runs have been calibrated to the Johnson/Kron--Cousins \it BVRI\/ photometric system defined by the equatorial standards of Landolt (1992, AJ, 104, 340). More than 15,000 stars suitable for use as photometric standards have been identified, where ``suitable'' means that the star has been observed five or more times during photometric conditions and has a standard error of the mean magnitude less than 0.02\mag\ in at least two of the four bandpasses, and shows no significant evidence of intrinsic variability. Many of these stars are in the same fields as Landolt's equatorial standards or Graham's (1982, PASP, 94, 244) southern E--region standards, but are considerably fainter. This enhances the value of those fields for the calibration of photometry obtained with large telescopes. Other standards have been defined in fields containing popular objects of astrophysical interest, such as star clusters and famous galaxies, extending Landolt--system calibrators to declinations far from the equator and to stars of sub--Solar chemical abundances. I intend to continue to improve and enlarge this set of photometric standard stars as more observing runs are reduced. The full current database of photometric indices is being made freely available via a site on the World--Wide Web, or by direct request to the author. Although the contents of the database will evolve in detail, at any given time it should represent the largest sample of precise \it BVRI\/ broad--band photometric standards available anywhere. Accepted by:\, Publications of the Astronomical Society of the Pacific For preprints, contact\, Peter.Stetson@nrc.ca Digital Spectroscopy of O3--O5 and ON/OC Supergiants in Cygnus Nolan R. Walborn ^1 and Ian D. Howarth ^2 1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 2. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK High signal--to--noise, optical digital classification spectrograms of three northern very early--O supergiants and four late--O supergiants with CNO anomalies are illustrated and discussed. Several of these exceptional objects either are the prototypes of their classes, originally discovered photographically, or are unique representatives of them in the Northern Hemisphere. The full blue--violet and yellow--red spectrum of the extreme ON supergiant BD+36 4063, discovered by Mathys with limited wavelength coverage, is shown for the first time. Extensive line identifications are provided, and the high quality of these data reveals numerous new absorption and emission features corresponding either to the high ionization in the case of the very early objects, or to the chemical abundance anomalies in the later ones. These data provide standards for digital classification of related objects in the north, and guidance for subsequent astrophysical analyses with higher spectral resolution. Accepted by PASP, November 2000 issue Preprints from walborn@stsci.edu Longer Contributions Radial Velocities of IAU Standard Stars C. D. Scarfe Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6, Canada scarfe@uvic.ca Abstract As part of an ongoing international campaign, over 2000 radial--velocity observations of IAU standard stars have been obtained with the DAO radial--velocity scanner (RVS). In addition, over 100 new velocities from photographic plates have been added to those published ten years ago. The standard deviation of the RVS velocities is about three times larger than that of the photographic data. The RVS velocities were obtained with a variety of masks, but zero--point adjustments have been made empirically between them and between the RVS and the plates. An absolute zero--point has been provided by observations of bright asteroids. Comparison between the DAO data and large compilations published recently, by groups at the Center for Astrophysics and at the Geneva Observatory, reveals excellent agreement. In particular, a previously troublesome colour--dependent discrepancy between the Geneva observations and others has been eliminated, by adjustments made recently by the Geneva group, to an extent greater than even they had anticipated. The long task of revising the IAU standard system and providing a list of objects with radial velocities known absolutely to better than 100 m/s , and constant at the same level, now seems to be nearly complete. IAU Commission 30 (Radial Velocities) has a Working Group on Standard Stars, one of whose goals is to revise the list provided over 40 years ago by Pearce (1957), and extended over 25 years ago by Heard and Fehrenbach (1974). The purpose of such a list is to permit the stability of instruments used for radial--velocity observations to be monitored, and to facilitate comparisons between measurements made with such instruments. However the precision with which the radial velocities of the standard stars themselves were determined, and the level at which they were known to be constant, was several tenths of a kilometre per second, and advances since those days in the precision of radial--velocity measurements lead us to require standards with velocities known to better than 100 m s ^ -1 and constant to the same level. To achieve that level of accuracy is the objective of the Working Group. I have of necessity taken an interest in standard stars, since many of the binary and multiple stars that are my primary interest require observations over many years, during which the instrument must be checked for stability. I have therefore regularly observed IAU standard stars with the coud\'e mosaic spectrograph of the DAO 1.2--m telescope, both photographically and with the radial--velocity spectrometer (Fletcher et al. 1982), amassing about 300 photographic and over 2000 spectrometer (RVS) observations. A report on the majority of the photographic data was published ten years ago (Scarfe, Batten and Fletcher 1990). Comparison with other published data revealed a systematic difference between the DAO data and those obtained by Mayor and Maurice (1985) with the CORAVEL spectrometer (Baranne, Mayor and Poncet 1979), which increased toward later spectral types from nearly zero for stars like the sun. A similar trend was also found by the group at the Center for Astrophysics (Latham 1993), between their data and those from CORAVEL, as a function of B - V colour index, instead of spectral type. But careful comparison revealed no such colour dependence between CfA and DAO RVS data. More recently the CORAVEL group have developed the ELODIE spectrometer (Baranne 1999), and used it to determine corrections to the CORAVEL velocities, a new list of which has been published by Udry et al. (1999). The CfA results have also now been published (Stefanik, Latham and Torres 1999). The DAO RVS uses masks based on the spectra of Procyon (F--mask) and Arcturus (K--mask). It also underwent substantial modification in 1985 (McClure et al. 1985), including replacement of both masks. Since observations have been made with all the available masks, it has been necessary to intercompare results in order to place them on the same system. No difference between the radial velocity scales of any pair of masks has been found over a range of at least pm 100 km s ^ -1 , but each has been found to have its own zero point. Empirical corrections have been determined to place the observations made with each mask onto the zero point determined for photographic data by Scarfe et al. (1990). The mean velocity for each star from all the RVS data has been determined, as has a new mean for the velocities determined photographically. The photographic data have a root--mean--square standard deviation of 150 m s ^ -1 for one observation, while that of the RVS data is just over three times larger. Thus the weight of a single RVS observation is about one tenth that of a photographic observation. No ``night corrections'' or ``run corrections'' have been used. However, observations of the bright asteroids Ceres, Pallas and Vesta have been obtained with the RVS, and used, along with the photographic ones of Scarfe (1985), to determine an absolute zero--point for the DAO data. Within an uncertainty of 50 m s ^ -1 the zero--point of the data of Scarfe et al. (1990) is in fact zero. Various differences between the DAO photographic, DAO RVS, CORAVEL and CfA data are plotted against B - V in Figures 1 through 6. Only very small trends are apparent in any of those diagrams, although some zero--point differences remain. Udry et al. (1999) noted that the ELODIE corrections removed about half of the colour--dependent difference between the CORAVEL results and those from CfA, and encouraged other groups to seek the origin of the remaining discrepancy in their own data. It appears that this is unnecessary, especially for the DAO data, for which the discrepancy has been reduced to little more than 10\% of its former size (Scarfe et al. 1990). Indeed it has almost wholly disappeared. We are now at last in a position to be able to combine all the data to provide a list of standard stars with velocities of the precision and constancy required by the Working Group. References Baranne, A. 1999, in IAU Coll. No. 170, Precise Stellar Radial Velocities, ed. J.B. Hearnshaw and C.D. Scarfe, San Francisco: Astron. Soc. Pacific (ASP Conf. Ser. 185), 1 Baranne, A., Mayor, M. and Poncet, J.L. 1979, Vistas in Astron. 23, 279 Fletcher, J.M., Harris, H.C., McClure, R.D. and Scarfe, C.D. 1982, PASP 94, 1017 Heard, J.F. and Fehrenbach, Ch. 1974, Trans. IAU 15B, 148 Latham, D.W. 1993, private communication Mayor, M. and Maurice, E. 1985, in IAU Coll. No. 88, Stellar Radial Velocities, ed. A.G.D. Philip and D.W. Latham, Schenectady: L. Davis Press, 299 McClure, R.D., Fletcher, J.M., Grundmann, W.A. and Richardson, E.H. 1985, in IAU Coll. No. 88, Stellar Radial Velocities, ed. A.G.D. Philip and D.W. Latham, Schenectady: L. Davis Press, 49 Pearce. J.A. 1957, Trans. IAU 9, 441 Scarfe, C.D. 1985, in Calibration of Fundamental Stellar Quantities (IAU Symposium 111), ed. D.S. Hayes, L.E. Pasinetti and A.G.D. Philip, Dordrecht: Reidel, 583 Scarfe, C.D., Batten, A.H. and Fletcher, J.M. 1990, Pub. DAO 18, 21 Stefanik, R.P., Latham, D.W. and Torres, G. 1999, in IAU Coll. No. 170, Precise Stellar Radial Velocities, ed. J.B. Hearnshaw and C.D. Scarfe, San Francisco: Astron. Soc. Pacific (ASP Conf. Ser. 185), 354 Udry, S., Mayor, M., Maurice, E., Andersen, J., Imbert, M., Lindgren, H., Mermilliod, J.-C., Nordstr\"om, B. and Pr\'evot, L. 1999, in IAU Coll. No. 170, Precise Stellar Radial Velocities, ed. J.B. Hearnshaw and C.D. Scarfe, San Francisco: Astron. Soc. Pacific (ASP Conf. Ser. 185), 383 Contributions to the next Newsletter , due out in March 2001, will be welcomed at any time by grayro@appstate.edu. WHEN SUBMITTING AN ABSTRACT, PLEASE USE THE FOLLOWING TEMPLATE IF POSSIBLE: \begin{center}{\Large\bf{ Title }}\\{\bf{ A. Author$^1$ and B. Author$^2$ }}\\{\footnotesize $^1$ Institute One and Address \\ $^2$ Institute Two and Address }\end{center} \smallskip{ TEXT OF ABSTRACT }\\{\bf Accepted by} JOURNAL \\{\it For preprints, contact} YOUR ELECTRONIC ADDRESS