Spectral types based upon photoelectric measurements of the strong TiO band near 7100 Å and having an internal accuracy of one-tenth of a subclass are presented for 26 dwarf stars in the range K4 to M6. For the calibration of the TiO index into spectral type, the MK scale for giants established by Wing and Keenan was adopted. Accordingly the types differ systematically from those previously published on any of the systems used for dwarfs, being closest to Joy's. The advantages of the MK giant scale are discussed, and it is suggested that the stars classified here be adopted as standards for a revised system of MK classification for dwarfs.

The relation between TiO band strength and near-infrared color temperature for dwarfs differs significantly from the giant relation. The coolest dwarfs observed were Wolf 359 and Proxima Centauri; although Wolf 359 is both cooler and less luminous than Proxima, they have nearly identical TiO band strengths.

A method of distinguishing between T Tauri-like stars and reddened early type field stars by the application of UBVRI photometry is described, and the results for T Tauri-like variables in NGC 2264 are presented. The plates have been measured using the new measuring machine GALAXY. (V–R) colours, which are less affected by spectral peculiarities, are used to determine infrared and ultraviolet excesses. The range of variability in UBVRI colours of these varables has also been studied.

The theoretical treatment of the blanketing effect and the first photometric results had shown that the separation of stars of different metal content should be better in the RGU system than in the UBV system. A three color photometry of the globular cluster M5 is undertaken to show the position of these stars in the RGU two-color diagram, to derive the conversion formulae between the two photometric systems for these stars and to use the results for the classification of population II field stars in statistical investigations of the galactic halo.

The Strömgren four-color system has been used to classify blue horizontal-branch stars in globular clusters and in the general field. A relation between δ log g (log gmain sequence–log gstar) and δc1 (c1observed–c1main sequence) has been determined which gives log g to within ±0.2 for stars with log g's between 4.4 and 2.0. Newell (1970) has determined a relation between (B–V)0 and θe. Thus the gravities and effective temperatures of blue horizontal-branch stars can be determined from photometric measures alone. Five globular clusters have been studied at the present time. The BHB stars in the globular cluster M3 and M13 have lower surface gravities than BHB stars in the other clusters studied. Iben and Rood (1970) have recently suggested that the BHB stars of M3 may have lost more mass than BHB stars in more metal poor clusters.

uvby photometric observations have been used in conjunction with slit spectra to classify 90 stars which were noted as peculiar by Slettebak and Brundage in a recent objective prism survey of the South Galactic Pole region. In this paper, we review the photometric classification criteria and identify in the Slettebak-Brundage list, 8 subdwarf O stars, 10 subdwarf B stars, 10 horizontal branch stars, 1 white dwarf star and 26 late subdwarf stars. Three stars with outstanding peculiarities are SB (Slettebak-Brundage) 58 which is a helium subdwarf O star, SB 319 (CD–38°245), a late type star with extremely weak metal lines and SB 845 (BD–13°6465), an A type star with a very small Balmer discontinuity.

Six G and K type stars, chosen among Fehrenbach's stars, in the direction of the Large Magellanic Cloud, were recognized as metal deficient galactic stars, on ground of multicolour photometry (UBV system and Lick six-color system). Data concerning these stars are given in Tables I and II. The stars are plotted in a U – B/B - V, and in a U – G/G – I diagram.

Three more of Fehrenbach's stars also appear in the Tables and Figures. They are: HD 30 229 and HD 268 957 – Thackeray's extreme and moderate subdwarfs – and HD 270 011, already recognized by Fehrenbach et al. as an extremely deficient galactic giant. This last star falls close to HD 122 563 in the U – G/G – I diagram. The I-Colour of HD 30 229 is probably contaminated by nearby cooler stars.

Spectrophotometric data of early type stars (spectral intensity distributions from 3100 to 6000 Å and equivalent widths of Hβ, Hγ and Hδ) have been analysed, looking for the best parameters for a two dimensional spectral classification. It was found that the best correlation with MK classification is given by the equivalent width of Hβ and the Balmer discontinuity.

The classification scheme is well defined for stars from B0 to A1 of luminosity classes V to III. No stars of luminosity class II were observed. Luminosity class I is clearly separated from the less luminous stars, but the number of supergiants observed is too small to give a clear separation of spectral types.

Low dispersion (slit 60 Å wide) spectrophotometric observations of late type stars have been made. The sample of stars observed cover from K0 to M8 and luminosity classes V to I.

A selection of these stars including each luminosity class and spectral type is being analyzed. The observed intensity distributions have been corrected for atmospheric extinction and have been normalized to a common maximum intensity. The resulting instrumental intensity distributions are being studied for the best parameters for spectral classification.

The information used by scientists belongs to three basic types: (1) data, (2) procedures (techniques or description of instruments) and (3) theories and ideas. In what follows we shall consider only the first type of information, namely data. We will call ‘data’ all information related to or derived from observable quantities, like radial velocities, spectral types, color indices, etc.

For two years we have undertaken the collection of photoelectric data in view of their utilization by computer techniques. At present we are preparing a fine for each photometric system with the measurements published. As a second step, we shall form another file, alike for each system, with homogeneous measurements. This file will be obtained with weighed means of the published measurements. For that we need to compare each published list with a standard list before attributing the weights.

After that, we shall form a file indicating in which system a star is measured.

This work is undertaken in connection with the Data Center of Strasbourg and the group on spectroscopic and photometric data of the Commission 45.

The concept of a general stellar data bank is not a new idea, but the desirability of this project at the present time has been emphasized by a number of astronomers (Bidelman, Jaschek, Cayrel, Hauck and others) and work is proceeding both in the United States and elsewhere. The status of my own activities in this direction is as follows:

The general stellar data file now at the Warner and Swasey Observatory is continually being updated and much more of the astronomical literature is being systematically searched and the resulting data and references entered into the file. However this project is still largely unfunded and progress is far slower than desirable. In particular the file is still not available in machine-readable form, though several of the newer large data catalogues, such as the Warner and Swasey southern OB-star survey of Stephenson and Sanduleak, will be entered into the file in IBM card-form rather the entire file will be converted to punched cards.

Five thousand sq deg of the Southern sky of intermediate to high galactic latitude have been surveyed with deep objective prism plates, taken with a UV-transparent prism. The plates reach on the average the 13th photographic magnitude and have been searched for the following types of objects: (1) high luminosity stars, (2) planetary nebulae, (3) metal weak late-type giants, (4) Me stars, (5) carbon stars, (6) early-type subdwarfs, (7) peculiar objects. Catalogues containing a total of over 3200 objects of these types have been compiled and will soon be published in Publ. Dpto. Astron. Univ. de Chile.

Of particular interest are the metal-weak late-type giants, which are believed to be members of the galactic halo population. Slit spectra were obtained for a number of these stars and radial velocities derived. In each case the object was found to be a high velocity star. In view of the large number of such objects found in the survey, a method of determining relative radial velocities from pairs of objective prism plates was developed. The method, which is described in detail in the following paper, was tested successfully on several plate pairs, confirming the high velocities for the metal weak stars and showing that the method could be used for an exhaustive search for high velocity stars.

A simple method by which radial velocities of stars may be determined from Schmidt telescope objective prism plates is described, and the results from the initial application of the method are given.

The stars observed are mainly from the Catalogue by Fehrenbach and Duflot. Some other stars – overexposed on the objective-prism plates, faint blue stars in H ii regions, stars with overlapping objective-prism spectra – have been added.

The photoelectric UBV photometry was done with the 1-m telescope at La Silla. The UBV filters have always been those recommended by Johnson. Normally 3 measurements or more on different nights have been made for each star. For a single observation of a program star the internal standard deviations are

The spectra have been taken with a Cassegrain spectrograph mounted on the 1.52-m telescope at La Silla. The dispersion is 73 Å mm−1, the spectral range 3250-5000 Å, and the limiting resolution 1.3 Å.

As a result of our observations, we present 409 stars as members of the LMC, 42 as possible members and 132 as galactic foreground stars (19 of these having high radial velocity). Remarkable features regarding velocities, spectra, magnitudes and colors are noted and commented.

All stars down to B = 11.5 have been observed spectrographically as well as photometrically. This is also the case for the majority of the high-velocity stars down to B = 12.0. For fainter objects the photometry is quite representative, whereas the spectroscopy is more scarce. The limiting magnitude is B = 14.0.

As radial velocities were used as membership criterion, our data do not suffer from any spectral type selection effects.

It was easy to apply the MK criteria to our dispersion using the Yerkes atlas and the Bidelman list of supergiants. A continuous series of supergiant standards in the LMC has been established from 06 to G2. Comparison with Radcliffe data and with recent results of Divan gives a dispersion in spectral type of less than one tenth of a spectral class. Also the luminosity classification shows good agreement.

In the classification several difficulties were met:

(1) The LMC stars are very luminous objects. In the Galaxy we do not have many corresponding stars. This is especially so for later spectral types.

(2) With the dispersion used, the differences between IaO and la are not very pronounced, especially not for F-G type stars.

(3) Many of the LMC supergiants are P Cygni stars. They show very sharp, often asymmetric line profiles with a sharp rise to the long wavelength side. This might cause erroneous classification, and also affect radial velocities.

(4) The presence of an extended atmosphere, causing dilution effects, can give spurious spectral classification.

We have found 8 A type high-velocity stars. The UBV results confirm their classification. 11 G-K type stars have been found to be high-velocity stars, among which are two subdwarfs earlier discussed by Fehrenbach and Thackeray. The number of late type high-velocity stars is quite high.

Full accounts have been given in Astron. Astrophys. Suppl.6 (1972), 249.

A series of finding lists of A stars in regions at high galactic latitudes has been published in the last few years. Strömgren four-color and Hβ measures have been made of stars in five of the regions, allowing the interstellar absorption in each to be calculated. The two most important regions are the North Galactic Pole and the South Galactic Pole where color excesses of EB_V=0.00 and EB_V=0.02 were found respectively. An area in front of the Large Magellanic Cloud has a color excess of EB_V=0.04.

In this paper, I describe briefly the instrument and the reduction system we have used for obtaining ultraviolet magnitudes and present some information concerning the sky areas and types of stars we have observed. I shall also comment on our use of catalogs in machine-accessible form and make suggestions concerning the most useful identifications to be assigned to observed objects, particularly those in the southern hemisphere.